Systems and Methods for Enhancing Efficient Uplink MIMO Performance and Implementation for O-RAN-Based Radio Access Networks

Abstract

A system and method of operating an Open Radio Access Network (O-RAN, in which O-RAN the system includes: a baseband unit (BBU) having an O-RAN centralized unit (O-CU) and an O-RAN distributed unit (O-DU); an O-RAN radio unit (O-RU) remote from the BBU; and a fronthaul interface between the O-RU and the BBU. A functional split of O-RAN functions respectively assigned to O-RU and O-DU for the fronthaul interface between the BBU and the O-RU is different for downlink (DL) and uplink (UL) so that at least one of i) demodulation reference signal (DM-RS)-based channel estimation is performed by the O-DU in the DL and by the O-RU in the UL, ii) equalization is performed by the O-DU in the DL and by the O-RU in the UL, and iii) demodulation is performed by the O-DU in the DL and by the O-RU in the UL.

Claims

1. An Open Radio Access Network (O-RAN) system, comprising: a baseband unit (BBU) having an O-RAN centralized unit (O-CU) and an O-RAN distributed unit (O-DU); an O-RAN radio unit (O-RU) remote from the BBU; and a fronthaul interface between the O-RU and the BBU; wherein a functional split of O-RAN functions respectively assigned to O-RU and O-DU for the fronthaul interface between the BBU and the O-RU is different for downlink (DL) and uplink (UL), and wherein the system is configured such that at least one of i) demodulation reference signal (DM-RS)-based channel estimation is performed by the O-DU in the DL and by the O-RU in the UL, ii) equalization is performed by the O-DU in the DL and by the O-RU in the UL, and iii) demodulation is performed by the O-DU in the DL and by the O-RU in the UL.

2. The system according to claim 1, wherein the system is configured such that the O-DU transfers DM-RS information to the O-RU, the DM-RS information including DM-RS configuration parameters of the scheduled or paired UEs/layers are received by the O-RU, and the O-RU generates a DM-RS sequence using the DM-RS configuration parameters received from O-DU.

3. The system according to claim 2, wherein the system is configured such that the O-RU estimates the UL channels of the UE(s) and/or layer(s) transmitted at a current slot n using the DM-RS information.

4. The system according to claim 2, wherein the system is configured such that the O-DU indicates a combining/digital beamforming matrix calculation method to the O-RU and the O-RU calculates the combining/digital beamforming matrix.

5. The system according to claim 4, wherein system is configured such that the O-RU applies the calculated combining/digital beamforming matrix to a received signal and transfers the calculated combining/digital beamforming matrix to the O-DU.

6. The system according to claim 4,wherein system is configured such that O-DU performs a L1/L2 processing on the resulting signal.

7. The system according to claim 1, wherein system is configured such that i) a demodulation reference signal (DM-RS)-based channel estimation is performed by the O-DU in the DL and by the O-RU in the UL, and ii) an equalization is performed by the O-DU in the DL and by the O-RU in the UL.

8. The system according to claim 7, wherein system is configured such that the O-DU transfers DM-RS information to the O-RU, the DM-RS information including DM-RS configuration parameters of the scheduled or paired UEs/layers are received by the O-RU, and the O-RU generates a DM-RS sequence using the DM-RS configuration parameters received from O-DU.

9. The system according to claim 8, wherein system is configured such that the O-RU estimates the UL channels of the UE(s) and/or layer(s) transmitted at a current slot n using the DM-RS information.

10. The system according to claim 9,wherein system is configured such that the O-RU equalizes the UL channels of the one or more UEs, the one or more layers, or both transmitted at a current slot n.

11. The system according to claim 10,wherein system is configured such that the O-RU calculates a supplementary demodulation information and transfers the supplementary demodulation information along with an equalized signal stream to the O-DU.

12. The system according to claim 11, wherein system is configured such that the O-DU performs a demodulation on a signal of slot n transferred from the O-RU and a L1/L2 processing on the demodulated signal.

13. The system according to claim 1, wherein system is configured such that i) a demodulation reference signal (DM-RS)-based channel estimation is performed by the O-DU in the DL and by the O-RU in the UL, ii) an equalization is performed by the O-DU in the DL and by the O-RU in the UL, and iii) demodulation is performed by the O-DU in the DL and by the O-RU in the UL.

14. The system according to claim 13, wherein system is configured such that the O-DU transfer DM-RS information to the O-RU, the DM-RS information including DM-RS configuration parameters of the scheduled or paired UEs/layers are received by the O-RU, and the O-RU generates a DM-RS sequence using the DM-RS configuration parameters received from O-DU.

15. The system according to claim 14, wherein system is configured such that the O-RU estimates the UL channels of the UE(s) and/or layer(s) transmitted at a current slot n using the DM-RS information.

16. The system according to claim 15,wherein system is configured such that the O-RU equalizes the UL channels of the one or more UEs, the one or more layers, or both, transmitted at a current slot n.

17. The system according to claim 16,wherein system is configured such that, prior to a slot n, the DU transfers modulation information to the RU and the O-RU performs demodulation on an equalized signal.

18. The system according to claim 1, wherein system is configured such that i) a demodulation reference signal (DM-RS)-based channel estimation is performed by the O-DU in the DL and by the O-RU in the UL, ii) an equalization is performed by the O-DU in the DL and by the O-RU in the UL, and iii) demodulation is performed by the O-DU in the DL and by the O-RU in the UL.

19. A method of operating an Open Radio Access Network (O-RAN) system, comprising: providing a baseband unit (BBU) having an O-RAN centralized unit (O-CU) and an O-RAN distributed unit (O-DU); providing an O-RAN radio unit (O-RU) remote from the BBU; and providing a fronthaul interface between the O-RU and the BBU; wherein a functional split of O-RAN functions respectively assigned to O-RU and O-DU for the fronthaul interface between the BBU and the O-RU is different for downlink (DL) and uplink (UL), and wherein at least one of i) demodulation reference signal (DM-RS)-based channel estimation is performed by the O-DU in the DL and by the O-RU in the UL, ii) equalization is performed by the O-DU in the DL and by the O-RU in the UL, and iii) demodulation is performed by the O-DU in the DL and by the O-RU in the UL.

20. The method according to claim 19, wherein: i) the demodulation reference signal (DM-RS)-based channel estimation is performed by the O-DU in the DL and by the O-RU in the UL, and ii) the equalization is performed by the O-DU in the DL and by the O-RU in the UL.

21. The method according to claim 19, wherein i) the demodulation reference signal (DM-RS)-based channel estimation is performed by the O-DU in the DL and by the O-RU in the UL, ii) the equalization is performed by the O-DU in the DL and by the O-RU in the UL, and iii) demodulation is performed by the O-DU in the DL and by the O-RU in the UL.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0101] FIG. 1A illustrates the UL functional split in O-RAN split 7-2x for Cat A O-RU.

[0102] FIG. 1B illustrates the processing blocks of UL processing in ORAN split 7-2x for Cat A O-RU.

[0103] FIG. 2A illustrates the UL functional split in 0-RAN split 7-2x for Cat B O-RU.

[0104] FIG. 2B illustrates the processing blocks of UL processing in ORAN split 7-2x for Cat B O-RU.

[0105] FIG. 3A illustrates an embodiment of a UL functional split of an O-RU Cat C1.

[0106] FIG. 3B illustrates an embodiment of a UL functional split of an O-RU Cat C2.

[0107] FIG. 3C illustrates an embodiment of a UL functional split of an O-RU Cat C3.

[0108] FIG. 4A is a flowchart of UL Split in O-RAN with Cat C1 O-RU.

[0109] FIG. 4B is a flowchart of UL Split in O-RAN with Cat C1 O-RU.

[0110] FIG. 4C is a flowchart of UL Split in O-RAN with Cat C1 O-RU.

[0111] FIG. 4D is a flowchart of UL Split in O-RAN with Cat C1 O-RU.

[0112] FIG. 5A illustrates an exemplary implementation of a signaling mechanism according to Embodiment 1 to enable O-RU Cat C1 a signaling mechanism.

[0113] FIG. 5B illustrates an exemplary implementation of a signaling mechanism according to Embodiment 1 to enable O-RU Cat C1 a signaling mechanism,

[0114] FIG. 5C illustrates an exemplary implementation of a signaling mechanism according to Embodiment 1 to enable O-RU Cat C1 a signaling mechanism.

[0115] FIG. 5D illustrates an exemplary implementation of a signaling mechanism according to Embodiment 1 to enable O-RU Cat C1 a signaling mechanism.

[0116] FIG. 5E illustrates an exemplary implementation of a signaling mechanism according to Embodiment 1 to enable O-RU Cat C1 a signaling mechanism.

[0117] FIG. 5F illustrates an exemplary implementation of a signaling mechanism according to Embodiment 1 to enable O-RU Cat C1 a signaling mechanism.

[0118] FIG. 5G illustrates an exemplary implementation of a signaling mechanism according to Embodiment 1 to enable O-RU Cat C1 a signaling mechanism.

[0119] FIG. 5H illustrates an exemplary implementation of a signaling mechanism according to Embodiment 1 to enable O-RU Cat C1 a signaling mechanism.

[0120] FIG. 6A is a flowchart of UL Split in O-RAN with Cat C2 O-RU.

[0121] FIG. 6B is a flowchart of UL Split in O-RAN with Cat C2 O-RU.

[0122] FIG. 6C is a flowchart of UL Split in O-RAN with Cat C2 O-RU.

[0123] FIG. 7A illustrates an exemplary implementation of a signaling mechanism according to Embodiment 2 to enable O-RU Cat C2 a signaling mechanism.

[0124] FIG. 7B illustrates an exemplary implementation of a signaling mechanism according to Embodiment 2 to enable O-RU Cat C2 a signaling mechanism.

[0125] FIG. 7C illustrates an exemplary implementation of a signaling mechanism according to Embodiment 2 to enable O-RU Cat C2 a signaling mechanism.

[0126] FIG. 8A is a flowchart of UL Split in O-RAN with Cat C3 O-RU.

[0127] FIG. 8B is a flowchart of UL Split in O-RAN with Cat C3 O-RU.

[0128] FIG. 8C is a flowchart of UL Split in O-RAN with Cat C3 O-RU.

[0129] FIG. 9A illustrates an exemplary implementation of a signaling mechanism according to Embodiment 3 to enable O-RU Cat C3 a signaling mechanism.

[0130] FIG. 9B illustrates an exemplary implementation of a signaling mechanism according to Embodiment 3 to enable O-RU Cat C3 a signaling mechanism.

[0131] FIG. 9C illustrates an exemplary implementation of a signaling mechanism according to Embodiment 3 to enable O-RU Cat C3 a signaling mechanism.

[0132] FIG. 10A shows an exemplary 5G NR DM-RS structure.

[0133] FIG. 10B shows an exemplary 5G NR DM-RS structure.

[0134] FIG. 10C shows an exemplary 5G NR DM-RS structure.

[0135] FIG. 10D shows an exemplary 5G NR DM-RS structure.

[0136] FIG. 10E shows an exemplary 5G NR DM-RS structure.

[0137] FIG. 11A shows a channel estimation technique that can be applied at the O-RU.

[0138] FIG. 11B shows a channel estimation technique that can be applied at the O-RU.

[0139] FIG. 11C shows a channel estimation technique that can be applied at the O-RU.

[0140] FIG. 11D shows a channel estimation technique that can be applied at the O-RU.

[0141] FIG. 11E is a flowchart showing channel estimation techniques that can be applied at the O-RU described with respect ot FIGS. 11A-11D.

DETAILED DESCRIPTION OF THE IMPLEMENTATIONS

[0142] Implementations as described herein provide methods to enable an efficient mMIMO system for O-RAN based RANs.

[0143] FIGS. 3A, 3B, and 3C illustrate innovative embodiments of UL functional splits O-RU categories. Three different O-RU categories, namely, O-RU Cat C1, C2, and C3, are as follows: [0144] O-RU Cat C1 (FIG. 3A): 0-RU performs a first level of DM-RS channel estimation on PUSCH/PUCCH and uses the result of this channel estimation to calculate the combining/digital beamforming matrix, and after performing precoding/digital beamforming on the received signal, transfers the resulting signal to O-DU for the rest of processing. [0145] O-RU Cat C2 (FIG. 3B): O-RU performs both DM-RS channel estimation and equalization on PUSCH/PUCCH and transfers the equalized signal stream(s) along with the supplementary demodulation information to O-DU for the rest of the processing. [0146] O-RU Cat C3 (FIG. 3C): O-RU performs DM-RS channel estimation, equalization, and demodulation on PUSCH/PUCCH and transfers the resulting demodulated signal to O-DU for the rest of the processing.

[0147] In order to mitigate the issues of UL 7-2x, an asymmetrical functional split between DL and UL is proposed. The DL processing follows the O-RAN split 7-2x (either Cat A or Cat B) to balance the tradeoff between O-RU complexity and fronthaul throughput, where the UL processing follows a new split architecture. Three different UL functional splits corresponding to three different innovative O-RU categories are summarized in Table 1.

TABLE-US-00001 A summary of possible options for DL and ULfunctional splits DL UL Brief Description Cat A Cat C1 O-RU performs “DM-RS based Channel Estimation” in the UL. Cat A Cat C2 O-RU performs “DM-RS based Channel Estimation” and “Equalization” in the UL. Cat A Cat C3 O-RU performs “DM-RS based Channel Estimation”, “Equalization”, and “Demodulation” in the UL. Cat B Cat C1 O-RU performs “DM-RS based Channel Estimation” in the UL. Cat B Cat C2 O-RU performs “DM-RS based Channel Estimation” and “Equalization” in the UL. Cat B Cat C3 O-RU performs “DM-RS based Channel Estimation”, “Equalization”, and “Demodulation” in the UL.

[0148] The following describes detailed processing steps for UL functional splits with O-RU Cat C1, O-RU Cat C2, O-RU Cat C3.

Embodiment 1: Processing Steps for UL Functional Split With O-RU Cat C1

[0149] Embodiment 1 describes the processing steps for UL functional split with O-RU Cat C1, in which O-RU performs a “DM-RS based Channel Estimation” in the UL. FIGS. 4A, 4B, 4C, and 4D are flowcharts of UL Split in O-RAN with Cat C1 O-RU.

[0150] As shown in FIGS. 4A, 4B, 4C and 4D, in this embodiment, O-RU performs the following steps to process the received signal:

[0151] As shown in FIG. 4A, at 1-1), prior to slot n, O-DU transfers “DM-RS information” to O-RU so that O-RU can obtain the DM-RS signal and perform channel estimation. Some options for the “DM-RS information” are as follows:

[0152] Option 1-1-A: “DM-RS configuration parameters” of the scheduled or paired UEs/layers. O-RU generates the “DM-RS sequence” using the “DM-RS configuration parameters” received from O-DU. The “DM-RS configuration parameters” are summarized in Table 4. Also, the details of the “DM-RS sequence” generation and mapping using the “DM-RS configuration parameters” are provided below under section Embodiment 6: 5G NR DM-RS.

[0153] Option 1-1-B: “DM-RS sequence” of the scheduled or paired UEs/layers.

[0154] As shown in FIG. 4A, at 1-2 (Optional) Prior to slot n, O-DU transfers the “DM-RS channel estimation method information” to O-RU to indicate the “channel estimation method” and possibly “details of the indicated channel estimation method”. Exemplary channel estimation methods are listed below: [0155] Least-squares (LS) channel estimation [0156] Minimum mean-squared error (MMSE) channel estimation [0157] Discrete Fourier transform (DFT) based channel estimation [0158] Discrete cosine transform (DCT) based channel estimation

[0159] The above channel estimation methods are described in more detail in Embodiment 7: Channel Estimation. The “details of the indicated channel estimation method” depends on the indicated channel estimation method and may include any of the following: [0160] RMS delay spread of the channel (τ.sub.RMS) [0161] Maximum Doppler spread of the channel (Δf.sub.max) [0162] Initial SINR estimation (SINR.sub.0) [0163] MMSE matrix elements [0164] Channel Estimation granularity in the frequency domain [0165] Window type [0166] Window size

[0167] Indication of the “channel estimation method” and/or “details of the indicated channel estimation method” can be done based on one of the following options:

[0168] Option 1-2-A: O-DU indicates the “channel estimation method” to the O-RU using a particular bitfield in the signaling from O-DU to O-RU. O-RU determines the channel estimation details, including parameters and processing steps based on its own implementation. An example of a mapping between the bitfield content and corresponding channel estimation methods is provided in Table 5.

[0169] Option 1-2-B: O-DU indicates “channel estimation method” and “details of the indicated channel estimation method” to the O-RU using particular bitfields in the signaling from O-DU to O-RU. O-RU uses a table, such as Table 5, to find the channel estimation method and uses other look-up tables, such as Table 6 to Table 9, to obtain the channel estimation details using these indications from O-DU. A summary of channel estimation methods and their corresponding look-up table(s) is provided in Table 10.

[0170] Option 1-2-C: O-DU provides “partial channel estimation details” to O-RU, using which O-RU calculates full channel estimation details. In this option, the “DM-RS channel estimation method information” includes the channel estimation method and its partial details as listed in Table 11 to Table 14. O-RU calculates the channel estimation details, such as MMSE matrix, CE granularity in the frequency-domain, and window size, based on the channel estimation method and its received details from O-DU. The details of these channel estimation calculations can be found in Embodiment 7: Channel Estimation.

[0171] Option 1-2-D: O-DU provides “full channel estimation details” to O-RU. In this option, the “DM-RS channel estimation method information” includes the channel estimation method and its full details as listed in Table 15. O-DU transfers the channel estimation details by either indicating bits in a bitfield for a particular parameter or directly transferring IQ/integer values of relevant parameters to O-RU.

[0172] As shown in FIG. 4B, at 1-3 (Optional) O-DU transfers “combining/digital beamforming matrix enhancement information” to O-RU prior to slot n. This information improves the quality of the combining/digital beamforming matrix when it is calculated by the O-RU. Some options for the “combining/digital beamforming matrix enhancement information” are as follows:

[0173] Option 1-3-A: “Combining/digital beamforming matrix enhancement information” includes SRS channel estimates of the scheduled or paired UEs/layers. Later in Step 1-6, O-RU combines SRS and DM-RS channel estimates using weighting coefficients. Options for the weighting coefficients of Option 1-3-A:

[0174] Option 1-3-A-1: O-RU either uses pre-configured weighting coefficients or determines the weighting coefficients based on other parameters.

[0175] Option 1-3-A-2: O-DU provides the weighting coefficients to 0-RU as part of “combining/digital beamforming matrix enhancement information”.

[0176] Option 1-3-B: “Combining/digital beamforming matrix enhancement information” includes preliminary combining/digital beamforming matrix elements corresponding to the scheduled or paired UEs/layers. This preliminary combining/digital beamforming matrix is calculated at O-DU prior to slot n using SRS channel estimates. Later in Step 1-6, O-RU combines its own calculated combining/digital beamforming matrix elements with the preliminary combining/digital beamforming matrix using weighting coefficients. Options for the weighting coefficients of Option 1-3-B:

[0177] Option 1-3-B-1: O-RU either uses pre-configured weighting coefficients or determines the weighting coefficients based on other parameters.

[0178] Option 1-3-B-2: O-DU provides the weighting coefficients to O-RU as part of “combining/digital beamforming matrix enhancement information”.

[0179] As shown in FIG. 4B, at 1-4 O-RU estimates the UL channels of the UE(s) and/or layer(s) transmitted at the current slot n using the “DM-RS information” obtained in Step 1-1. Depending on whether the optional Step 1-2 is executed, one of the following options are taken by O-RU regarding the channel estimation method and its details:

[0180] Option 1-4-A: (Step 1-2 is not executed): O-RU uses a pre-configured channel estimation method and its details.

[0181] Option 1-4-B: (Step 1-2 is executed): O-RU uses “DM-RS channel estimation method information” provided by O-DU to obtain the channel estimation method and its details.

[0182] As shown in FIG. 4C, at 1-5 (Optional) O-DU indicates “combining/digital beamforming matrix calculation method” to O-RU. Some examples for the combining/digital beamforming matrix calculation method are as follows: [0183] Conjugate combining [0184] Zero forcing [0185] MMSE [0186] MMSE-IRC [0187] Null-space dimension increase based [0188] DFT-compression

[0189] An example of a mapping between the bitfield contents and corresponding combining/digital beamforming matrix calculation methods is provided in Table 16.

[0190] As shown in FIG. 4C, at 1-6 O-RU calculates the “combining/digital beamforming matrix” either based on the calculation method provided by O-DU in Step 1-5 (if Step 1-5 is executed) or based on a pre-configured method (if Step 1-5 is not executed). Depending on whether the optional Step 1-3 is executed, one of the following options are taken by O-RU:

[0191] Option 1-6-A (Step 1-3 is not executed): O-RU calculates the “combining/digital beamforming matrix” based on the estimated DM-RS channel(s).

[0192] Option 1-6-B (Step 1-3 with Option 1-3-A is executed): O-RU combines SRS channel estimates provided by O-DU with its own estimated DM-RS channel estimates using weighting coefficients. O-RU calculates the “combining/digital beamforming matrix” based on the combined DM-RS and SRS channel estimates.

[0193] Option 1-6-C (Step 1-3 with Option 1-3-B is executed): O-RU calculates the “combining/digital beamforming matrix” based on the estimated DM-RS channel(s), and using weighting coefficients, combines it with the SRS-based preliminary combining/digital beamforming matrix received from O-DU.

[0194] As shown in FIG. 4D, at 1-7, O-RU applies the calculated “combining/digital beamforming matrix” to the received signal in slot n and transfers the resulting signal to O-DU through the fronthaul link.

[0195] As shown in FIG. 4D, at 1-8, O-DU performs DM-RS channel estimation on the signal of slot n transferred from O-RU and subsequently performs UL MIMO processing by equalizing the channel using the estimated channel (with optional inter-cell interference rejection). Afterward, O-DU performs the rest of L1/L2 processing on the resulting signal.

[0196] FIGS. 5A, 5B, 5C, 5D, 5E, 5F, 5G, and 5H illustrate different variations of Embodiment 1 to enable O-RU Cat C1 through different signaling mechanisms.

[0197] Depending on the type of information provided by O-DU to O-RU, different implementations are described, as illustrated in FIGS. 5A to 5H and summarized in table 2

TABLE-US-00002 Implementations from embodiment 1 Embodiment # Executed steps from Embodiment 1 Block diagram 1-A (1-1), (1-4), (1-6), (1-7), (1-8) FIG. 5A 1-B (1-1), (1-4), (1-5), (1-6), (1-7), (1-8) FIG. 5B 1-C (1-1), (1-2), (1-4), (1-6), (1-7), (1-8) FIG. 5C 1-D (1-1), (1-2), (1-4), (1-5), (1-6), (1-7), (1-8) FIG. 5D 1-E (1-1), (1-3), (1-4), (1-6), (1-7), (1-8) FIG. 5E 1-F (1-1), (1-3), (1-4), (1-5), (1-6), (1-7), (1-8) FIG. 5F 1-G (1-1), (1-2), (1-3), (1-4), (1-6), (1-7), (1-8) FIG. 5G 1-H (1-1), (1-2), (1-3), (1-4), (1-5), (1-6), (1-7), (1-8) FIG. 5H

Embodiment 2: Processing Steps for UL Functional Split With O-RU Cat C2

[0198] Embodiment 2 describes the processing steps for UL functional split with O-RU Cat C2, in which O-RU performs the “DM-RS based Channel Estimation” and “Equalization” in the UL. FIGS. 6A, 6B, and 6C present a flowchart of UL Split in O-RAN with Cat C2 O-RU.

[0199] As shown in FIGS. 6A, 6B, and 6C, in this embodiment, O-RU performs the following steps to process the received signal:

[0200] As shown in FIG. 6A, at 2-1 (Mandatory) Prior to slot n, O-DU transfers “DM-RS information” to O-RU so that O-RU can obtain the DM-RS signal and perform channel estimation. Some options for the “DM-RS information” are as follows:

[0201] Option 2-1-A: “DM-RS configuration parameters” of the scheduled or paired UEs/layers. O-RU generates the “DM-RS sequence” using the “DM-RS configuration parameters” received from O-DU. These “DM-RS configuration parameters” are summarized in Table 4. Also, the details of the “DM-RS sequence” generation and mapping using the “DM-RS configuration parameters” are provided in Embodiment 6: 5G NR DM-RS.

[0202] Option 2-1-B: “DM-RS sequence” of the scheduled or paired UEs/layers.

[0203] As shown in FIG. 6A, at 2-2 (Optional) prior to slot n, O-DU transfers the “DM-RS channel estimation method information” to O-RU to indicate the “channel estimation method” and possibly “details of the indicated channel estimation method”. Exemplary channel estimation methods are listed below: [0204] Least-squares (LS) channel estimation [0205] Minimum mean-squared error (MMSE) channel estimation [0206] Discrete Fourier transform (DFT) based channel estimation [0207] Discrete cosine transform (DCT) based channel estimation

[0208] The details of the above channel estimation methods are described in Embodiment 7: Channel Estimation below. The “details of the indicated channel estimation method” depends on the indicated channel estimation method and may include any of the following: [0209] RMS delay spread of the channel (τ.sub.RMS) [0210] Maximum Doppler spread of the channel (Δf.sub.max) [0211] Initial SINR estimation (SINR.sub.0) [0212] MMSE matrix elements [0213] Channel Estimation granularity in the frequency domain [0214] Window type [0215] Window size

[0216] Indication of the “channel estimation method” and/or “details of the indicated channel estimation method” can be done based on one of the following options:

[0217] Option 2-2-A: O-DU indicates the “channel estimation method” to the O-RU using a particular bitfield in the signaling from O-DU to O-RU. O-RU determines the channel estimation details, including parameters and processing steps based on its own implementation. An example of a mapping between the bitfield content and corresponding channel estimation methods is provided in Table 5.

[0218] Option 2-2-B: O-DU indicates “channel estimation method” and “details of the indicated channel estimation method” to the O-RU using particular bitfields in the signaling from O-DU to O-RU. O-RU uses a table, such as Table 5, to find the channel estimation method and uses other look-up tables, such as Table 6 to Table 9, to obtain the channel estimation details using these indications from O-DU. A summary of channel estimation methods and their corresponding look-up table(s) is provided in Table 10.

[0219] Option 2-2-C: O-DU provides “partial channel estimation details” to O-RU, using which O-RU calculates full channel estimation details. In this option, the “DM-RS channel estimation method information” includes the channel estimation method and its partial details as listed in Table 11 to Table 14. O-RU calculates the channel estimation details, such as MMSE matrix, CE granularity in the frequency-domain, and window size, based on the channel estimation method and its received details from O-DU. The details of these channel estimation calculations can be found in Embodiment 7: Channel Estimation.

[0220] Option 2-2-D: O-DU provides “full channel estimation details” to O-RU. In this option, the “DM-RS channel estimation method information” includes the channel estimation method and its full details as listed in Table 15. O-DU transfers the channel estimation details by either indicating bits in a bitfield for a particular parameter or directly transferring IQ/integer values of relevant parameters to O-RU.

[0221] As shown in FIG. 6B, at 2-3 O-RU estimates the UL channels of the UE(s) and/or layer(s) transmitted at the current slot n using the “DM-RS information” obtained in Step 2-1. Depending on whether the optional Step 2-2 is executed, one of the following options are taken by O-RU regarding the channel estimation method and its details:

[0222] Option 2-3-A: (Step 2-2 is not executed): O-RU uses a pre-configured channel estimation method and its details.

[0223] Option 2-3-B: (Step 1-2 is executed): O-RU uses “DM-RS channel estimation method information” provided by O-DU to obtain the channel estimation method and its details.

[0224] As shown in FIG. 6B, at 2-4 (Optional) prior to slot n, O-DU transfers the “channel equalization information” to O-RU to indicate the “channel equalization method” and possibly further details of the channel equalization procedure through the “additional channel equalization information”. Exemplary channel equalization methods are listed below: [0225] ZF [0226] MMSE [0227] MMSE-IRC

[0228] The details of the channel equalization are described in Embodiment 8: Channel Equalization below. The “additional channel equalization information” of the demodulation procedure during the log-likelihood ratio (LLR) calculation can be provided in several ways. Based on the indicated “additional channel equalization information”, which may be a part of the “channel equalization information”, the supplementary demodulation information is calculated. Exemplary “additional channel equalization information” options are listed below: [0229] Equalization Gain and Post-processed Noise plus Interference Power [0230] Post-processed Noise plus Interference Power divided by Equalization Gain [0231] Equalization Gain divided by Post-processed Noise plus Interference Power [0232] Equalization Gain [0233] Post-processed Noise plus Interference Power [0234] Channel Estimates and Estimated DM-RS Noise plus Interference Power

[0235] Indication of the “channel equalization method” and “additional channel equalization information” can be done based on selecting one or both of the following options below:

[0236] Option 2-4-A: O-DU indicates the “channel equalization method” to the O-RU using a particular bitfield in the signaling from O-DU to O-RU. An example of a mapping between the bitfield content and corresponding channel equalization methods is provided in Table 17.

[0237] Option 2-4-B: O-DU indicates “additional channel equalization information” to the O-RU using particular bitfields in the signaling from O-DU to O-RU. Examples of mapping between the bitfield content and corresponding “additional channel equalization information”, which determines the “supplementary demodulation information” calculation method, are provided in Table 18 and Table 19.

[0238] As shown in FIG. 6B, at 2-5 (Mandatory) O-RU equalizes the UL channels of the UE(s) and/or layer(s) transmitted at the current slot n. Depending on whether the optional Step 2-4-A is executed, one of the following options are taken by O-RU regarding the “channel equalization method information”:

[0239] Option 2-5-A: (Step 2-4-A is not executed): O-RU uses a pre-configured channel equalization method and its details.

[0240] Option 2-5-B: (Step 2-4-A is executed): O-RU uses “channel equalization method information” provided by O-DU to obtain the channel equalization method and its details.

[0241] As shown in FIG. 6C, at 2-6 O-RU calculates the “supplementary demodulation information” and transfers it along with the equalized signal stream(s) to O-DU through the fronthaul link. Depending on whether the optional 2-4-B is executed, one of the following options are taken by O-RU regarding the “additional channel equalization information”:

[0242] Option 2-6-A: (Step 2-4-B is not executed): O-RU uses a pre-configured “supplementary demodulation information” calculation method.

[0243] Option 2-6-B: (Step 2-4-B is executed): O-RU uses the “supplementary demodulation information” calculation method provided by O-DU.

[0244] As shown in FIG. 6C, at 2-7 O-DU performs demodulation on the signal of slot n transferred from O-RU and subsequently performs the rest of L1/L2 processing on the resulting signal.

[0245] FIGS. 7A, 7B, and 7C illustrate different variations of Embodiment 2 to enable O-RU Cat C2 through different signaling mechanisms, as summarized Table 2.

TABLE-US-00003 Summary of selected embodiments from embodiment 2 Embodiment # Executed steps from Embodiment 2 Block diagram 2-A (2-1), (2-3), (2-5), (2-6), (2-7) FIG. 7A 2-B (2-1), (2-2), (2-3), (2-5), (2-6), (2-7) FIG. 7B 2-C (2-1), (2-2), (2-3), (2-4), (2-5), (2-6), (2-7) FIG. 7C

Embodiment 3: Processing Steps for UL Functional Split With O-RU Cat C3

[0246] Embodiment 3 describes the processing steps for UL functional split with O-RU Cat C3, in which O-RU performs the “DM-RS based Channel Estimation”, “Equalization”, and “Demodulation” in the UL. FIGS. 8A, 8B, and 8C are a flowchart of UL Split in O-RAN with Cat C3 O-RU.

[0247] In this embodiment, O-RU performs the following steps to process the received signal:

[0248] As shown in FIG. 8A, at 3-1, prior to slot n, O-DU transfers “DM-RS information” to O-RU so that O-RU can obtain the DM-RS signal and perform channel estimation. Some options for the “DM-RS information” are as follows:

[0249] Option 3-1-A: “DM-RS configuration parameters” of the scheduled or paired UEs/layers. O-RU generates the “DM-RS sequence” using the “DM-RS configuration parameters” received from O-DU. These “DM-RS configuration parameters” are summarized in Table 4. Also, the details of the “DM-RS sequence” generation and mapping using the “DM-RS configuration parameters” are provided in Embodiment 6: 5G NR DM-RS.

[0250] Option 3-1-B: “DM-RS sequence” of the scheduled or paired UEs/layers.

[0251] As shown in FIG. 8A, at 3-2 (Optional) Prior to slot n, O-DU transfers the “DM-RS channel estimation method information” to O-RU to indicate the “channel estimation method” and possibly “details of the indicated channel estimation method”. Exemplary channel estimation methods are listed below: [0252] Least-squares (LS) channel estimation [0253] Minimum mean-squared error (MMSE) channel estimation [0254] Discrete Fourier transform (DFT) based channel estimation [0255] Discrete cosine transform (DCT) based channel estimation

[0256] The details of the above channel estimation methods are described in Embodiment 7: Channel Estimation. The “details of the indicated channel estimation method” depends on the indicated channel estimation method and may include any of the following: [0257] RMS delay spread of the channel (τ.sub.RMS) [0258] Maximum Doppler spread of the channel (Δƒ.sub.max) [0259] Initial SINR estimation (SINR.sub.0) [0260] MMSE matrix elements [0261] Channel Estimation granularity in the frequency domain [0262] Window type [0263] Window size

[0264] Indication of the “channel estimation method” and/or “details of the indicated channel estimation method” can be done based on one of the following options:

[0265] Option 3-2-A: O-DU indicates the “channel estimation method” to the O-RU using a particular bitfield in the signaling from O-DU to O-RU. O-RU determines the channel estimation details, including parameters and processing steps based on its own implementation. An example of a mapping between the bitfield content and corresponding channel estimation methods is provided in Table 5.

[0266] Option 3-2-B: O-DU indicates “channel estimation method” and “details of the indicated channel estimation method” to the O-RU using particular bitfields in the signaling from O-DU to O-RU. O-RU uses a table, such as Table 5, to find the channel estimation method and uses other look-up tables, such as Table 6 to Table 9, to obtain the channel estimation details using these indications from O-DU. A summary of channel estimation methods and their corresponding look-up table(s) is provided in Table 10.

[0267] Option 3-2-C: O-DU provides “partial channel estimation details” to O-RU, using which O-RU calculates full channel estimation details. In this option, the “DM-RS channel estimation method information” includes the channel estimation method and its partial details as listed in Table 11 to Table 14. O-RU calculates the channel estimation details, such as MMSE matrix, CE granularity in the frequency-domain, and window size, based on the channel estimation method and its received details from O-DU. The details of these channel estimation calculations can be found in Embodiment 7: Channel Estimation.

[0268] Option 3-2-D: O-DU provides “full channel estimation details” to O-RU. In this option, the “DM-RS channel estimation method information” includes the channel estimation method and its full details as listed in Table 15. O-DU transfers the channel estimation details by either indicating bits in a bitfield for a particular parameter or directly transferring IQ/integer values of relevant parameters to O-RU.

[0269] As shown in FIG. 8B, at 3-3 (Mandatory) O-RU estimates the UL channels of the UE(s) and/or layer(s) transmitted at the current slot n using the “DM-RS information” obtained in Step 3-1. Depending on whether the optional Step 3-2 is executed, one of the following options are taken by O-RU regarding the channel estimation method and its details:

[0270] Option 3-3-A: (Step 3-2 is not executed): O-RU uses a pre-configured channel estimation method and its details.

[0271] Option 3-3-B: (Step 3-2 is executed): O-RU uses “DM-RS channel estimation method information” provided by O-DU to obtain the channel estimation method and its details.

[0272] As shown in FIG. 8B, at 3-4 (Optional) Prior to slot n, O-DU transfers the “channel equalization method information” to O-RU to indicate the type and, possibly, further details of the channel equalization method to be adopted by O-RU. In the following, “channel equalization method” may refer to any of the following example channel equalization techniques: [0273] ZF [0274] MMSE [0275] MMSE-IRC An example of a mapping between the bitfield contents and the corresponding channel equalization method is provided in Table 17.

[0276] As shown in FIG. 8B, at 3-5 (Mandatory) O-RU equalizes the UL channels of the UE(s) and/or layer(s) transmitted at the current slot n. Depending on whether the optional Step 3-4 is executed, one of the following options are taken by O-RU regarding the “channel equalization method information”:

[0277] Option 3-5-A: (Step 3-4 is not executed): O-RU uses a pre-configured channel equalization method and its details.

[0278] Option 3-5-B: (Step 3-4 is executed): O-RU uses “channel equalization method information” provided by O-DU to obtain the channel equalization method and its details.

[0279] As shown in FIG. 8C, at 3-6 (Mandatory) Prior to slot n, O-DU transfers “modulation information” to O-RU. Afterward, O-RU performs demodulation on the equalized signal in Step 3-5 during slot n and transfers the resulting signal to O-DU through the fronthaul link.

[0280] As shown in FIG. 8C, at 3-7 (Mandatory) O-DU performs descrambling on the signal of slot n transferred from O-RU and subsequently performs the rest of L1/L2 processing on the resulting signal.

[0281] FIGS. 9A, 9B, and 9C illustrate different variations of Embodiment 3 to enable O-RU Cat C3 through different signaling mechanisms, as shown in Table 4.

TABLE-US-00004 Summary of selected embodiments from embodiment 3 Embodiment # Executed steps from Embodiment 2 Block diagram 3-A (3-1), (3-3), (3-5), (3-6), (3-7) FIG. 9A 3-B (3-1), (3-2), (3-3), (3-5), (3-6), (3-7) FIG. 9B 3-C (3-1), (3-2), (3-3), (3-4), (3-5), (3-6), (3-7) FIG. 9C

Embodiment 4: Example Tables for the Signaling Mechanisms that Enables Asymmetrical Functional Splits

[0282] FIGS. 10A, 10B, 10C, 10D, and 10E clarify the 5G NR DM-RS structures with examples for a better understanding. Example Tables 5-20 show exemplary parameters for the signaling mechanisms that enables asymmetrical functional splits as shown in FIGS. 10A, 10B, 10C, 10D, and 10E.

TABLE-US-00005 DM-RS configuration parameters Purpose Parameter Brief Description Value Range Waveform Selection TransformPrecoding Enable/disable transform precoding {0,1} DMRS Sequence Generation [00009]$N_{ID}^{n_{SCID}}$ DMRS Scrambling Identity (for CP-OFDM) {0,1, ..., 65535} n.sub.SCID DMRS Scrambling Initialization {0,1} [00010]$N_{symb}^{slot}$ Number of OFDM Symbols in a Slot {12,14} [00011]$n_{s,f}^u$ Slot Number in a Radio Frame {0, ..., 159} I Symbol Number within a Slot {0,1, ...,13} [00012]$n_{ID}^{RS}$ DM-RS Scrambling Identity (for DFT-s-OFDM) {0,1, ..., 65535} dmrsGH Group Hopping {0,1} dmrsSH Sequence Hopping {0,1} DMRS Configuration dmrs- Type DMRS Configuration Type {1,2} maxLength Single Symbol or Double Symbol {1,2} dmrs- TypeA- Position DMRS Start Pos for Type A {pos2,pos3} dmrs- AdditionalPosition Additional DMRS Position {0,1,2,3} p̃ Antenna Port Index {0,1, ...,11}

TABLE-US-00006 An example look-up table for the channel estimation methods Bitfield Channel estimation method 00 LS 01 MMSE 10 DFT based 11 DCT based

TABLE-US-00007 An example look-up table for MMSE channel estimation matrix elements. Bitfield MMSE matrix 000 ∅.sub.1 001 ∅.sub.2 010 ∅.sub.3 011 ∅.sub.4 100 ∅.sub.5 101 ∅.sub.6 110 ∅.sub.7 111 ∅.sub.8

TABLE-US-00008 An example look-up table for the channel estimation granularity in the frequency domain. Bitfield CE Granularity in the Frequency Domain [RBs] 00 N.sub.1 01 N.sub.2 10 N.sub.3 11 N.sub.4

TABLE-US-00009 An example look-up table for window type Bitfield Window type 00 Type 1 01 Type 2 10 Type 3 11 Type 4

TABLE-US-00010 An example look-up table for window size Bitfield Window size 00 Window size 1 01 Window size 2 10 Window size 3 11 Window size 4

TABLE-US-00011 Summary of relevant look-up tables for channel estimation Channel estimation method Relevant look-up table(s) LS Table 5, Table 7 MMSE Table 5, Table 6, Table 7 DFT based Table 5, Table 7, Table 8, Table 9 DCT based Table 5, Table 7, Table 8, Table 9

TABLE-US-00012 A summary of channel estimation methods and their corresponding details for option 1-2-C (Example-1) Channel estimation method CE Granularity in the Frequency Domain (Integer Values for #RBs) SINR.sub.0 (IQ Values) τ.sub.RMS (IQ Values) Δƒ.sub.max (IQ Values) Window type (Indicator for a row in a table) Window size (Integer Values) LS ü - - - - - MMSE ü ü ü ü - - DFT based ü - - - ü ü DCT based ü - - - ü ü

TABLE-US-00013 A summary of channel estimation methods and their corresponding details for option 1-2-C (Example-2) Channel estimation method SINR.sub.0 (IQ Values) τ.sub.RMS (IQ Values) Δƒ.sub.max (IQ Values) Window type (Indicator for a row in a table) Window size (Integer Values) LS - ü - - - MMSE ü ü ü - - DFT based - ü - ü ü DCT based - ü - ü ü

TABLE-US-00014 A summary of channel estimation methods and their corresponding details for option 1-2-C (Example-3) Channel estimation method SINR.sub.0 (IQ Values) τ.sub.RMS (IQ Values) Δƒ.sub.max (IQ Values) LS - ü - MMSE ü ü ü DFT based - ü - DCT based - ü -

TABLE-US-00015 A summary of channel estimation methods and their corresponding details for option 1-2-C (Example-4) Channel estimation method τ.sub.RMS (IQ Values) Δƒ.sub.max (IQ Values) LS ü - MMSE ü ü DFT based ü - DCT based ü -

TABLE-US-00016 A summary of channel estimation methods and their corresponding details for option 1-2-D Channel estimation method CE Granularity in the Frequency Domain (Integer Values for #RBs) MMSE matrix (IQ Values) Window type (Indicator for a row in a table) Window size (Integer Values) LS ü - - - MMSE ü ü - - DFT based ü - ü ü DCT based ü - ü ü

TABLE-US-00017 An example look-up table for the combining/digital beamforming matrix calculation methods Bitfield Combining/digital beamforming matrix calculation method 000 Conjugate combining 001 Zero forcing 010 MMSE 011 MMSE-IRC 100 Null-space dimension increase based 101 DFT-compression

TABLE-US-00018 An example look-up table for the channel equalization methods Bitfield Channel equalization method 00 Zero forcing 01 MMSE 10 MMSE-IRC

TABLE-US-00019 An example look-up table for the additional channel equalization information Bitfield Supplementary Demodulation Information Calculation Method 000 Equalization Gain and Post-processed Noise plus Interference Power 001 Post-processed Noise plus Interference Power divided by Equalization Gain 010 Equalization Gain divided by Post-processed Noise plus Interference Power 011 Equalization Gain 100 Post-processed Noise plus Interference Power 101 Channel Estimates and Estimated DM-RS Noise plus Interference Power

TABLE-US-00020 Another example look-up table for the additional channel equalization information Bitfield Supplementary Demodulation Information Calculation Method 00 Equalization Gain and Post-processed Noise plus Interference Power 01 Post-processed Noise plus Interference Power divided by Equalization Gain 10 Equalization Gain 11 Post-processed Noise plus Interference Power

Embodiment 5: C-Plane and M-Plane Messages for the UL functional splits with O-RU Cat C1, O-RU Cat C2, O-RU Cat C3:

M-plane Embodiments for the O-RU to Report Its Capabilities About the Supported O-RU Categories

[0283] In one embodiment, the O-RU exposes its ability to support category C1, category C2, or category C3 to the SMO or the O-RU controller in the O-RAN module-cap.yang. One example of the RU-supported-category leaf under the RU-capabilities structure in the O-RAN-module-cap.yang can be shown as follows:

TABLE-US-00021 grouping ru-capabilities { description “Structure representing set of capabilities.”; leaf ru-supported-category { type enumeration { enum CAT_A {  description   “Informs that precoding is not supported in O-RU”; enum CAT_B {  description   “Informs that precoding is supported in O-RU”; enum CAT_A_C1 {  description   “Informs that precoding is not supported in O-RU for DL and DM-RS based channel estimation is supported in the O-RU for UL”; } enum CAT_A_C2 {  description   “Informs that precoding is not supported in O-RU for DL and DM-RS based channel estimation and equalization are supported in the O-RU for UL ”; } enum CAT_A_C3 {  description   “Informs that precoding is not supported in O-RU for DL and DM-RS based channel estimation, equalization, and demodulation are supported in the O-RU for UL”; } enum CAT_B_C1 {  description   “Informs that precoding is supported in O-RU for DL and DM-RS based channel estimation is supported in the O-RU for UL ”; } enum CAT_B_C2 {  description   “Informs that precoding is supported in O-RU for DL and DM-RS based channel estimation and equalization are supported in the O-RU for UL ”; } enum CAT_B_C3 {  description   “Informs that precoding is supported in O-RU for DL and DM-RS based channel estimation, equalization, and demodulation are supported in the O-RU for UL ”; } } description “Informs about which category O-RU supports”; }

M-Plane Embodiments to Cover DM-RS Based Channel Estimation Features Support at the O-RU

[0284] The O-RU exposes its ability to support DM-RS-based channel estimation locally and the dependent features by supporting of the feature DMRS-BASED-CHANNEL-ESTIMATION-SUPPORTED in o-ran-module-cap.yang module.

TABLE-US-00022 feature DMRS-BASED-CHANNEL-ESTIMATION-SUPPORTED { description “This is used to indicate O-RU’s support for demodulation reference signal (DMRS)-based channel estimation.”; }

[0285] If feature DMRS-BASED-CHANNEL-ESTIMATION-SUPPORTED is true, the O-RU reports its support for the following dependent features: [0286] dmrs-based-channel-estimation-configuration-type [0287] static-dmrs-based-channel-estimation-configuration-type [0288] dynamic-dmrs-based-channel-estimation-configuration-type [0289] dmrs-generation-method [0290] dmrs-local-generation [0291] dmrs-sequence-reception [0292] dmrs-channel-estimation-technique [0293] Is-channel-estimation [0294] mmse-channel-estimation [0295] dft-channel-estimation [0296] dct-channel-estimation [0297] dmrs-channel-estimation-fh-method [0298] static-channel-estimation-type-only-indication-method [0299] static-full-id-based-channel-estimation-method [0300] real-time-channel-estimation-method [0301] partial-real-time-channel-estimation-method [0302] combining-digital-bf-matrix-enhancement-information [0303] srs-channel-estimates [0304] weighting-coefficients-local-generation [0305] weighting-coefficients-reception [0306] preliminary-combining-digital-bf-matrix [0307] weighting-coefficients-local-generation [0308] weighting-coefficients-reception [0309] combining-matrix-calculation-method [0310] conjugate-combining [0311] zero-forcing [0312] dft-compression [0313] null-space-dimension-increase-based [0314] mmse-irc-based

M-plane Embodiments to Cover DM-RS Based Channel Estimation Features Support at the O-RU

[0315] One example implementation in the o-ran-module-cap.yang can be described as follows.

TABLE-US-00023 grouping dmrs-based-channel-estimation-features { description “O-RU’s capabilities related to supported DMRS-based channel estimation”; - container dmrs-based-channel-estimation-configuration-type {    description    “O-RU’s capabilities related to DMRS-based channel estimation configuration type. ”;        o leaf static-dmrs-based-channel-estimation-configuration-type {             type boolean;             description             “O-RU supports static configurations, via M-plane, for the DMRS-based    channel estimation parameters.”;             }        o leaf dynamic- dmrs-based-channel-estimation-configuration-type{             type boolean;             description             “O-RU supports real-time configurations, via C-plane, for the DMRS-    based channel estimation parameters.”;    } } - container dmrs-generation-method {    description    “O-RU’s capabilities related to DMRS signal generation. O-DU transfers DM-RS information to O-RU so that O-RU can obtain DM-RS signal and perform channel estimation”;        o leaf dmrs-local-generation {             type boolean;             description             “O-RU supports reception of the DM-RS configuration parameters of    the scheduled or paired UEs/layers. O-RU supports local generation of the DM-    RS sequence using the DM-RS configuration parameters received from O-DU.    ”;             }        o leaf dmrs-sequence-reception {             type boolean;             description             “O-RU supports DMRS sequence reception from O-DU.”;    } } - container dmrs-channel-estimation-technique {    description    “O-RU’s capabilities related to supported channel estimation techniques”;        o leaf ls-channel-estimation {             type boolean;             description             “Least-squares (LS) channel estimation ”;             }        o leaf mmse-channel-estimation {             type boolean;             description             “Minimum mean-squared error (MMSE) channel estimation ”;             }        o leaf dft-channel-estimation {             type boolean;             description             “Discrete Fourier transform (DFT) based channel estimation ”;             }        o leaf dct-channel-estimation {             type boolean;             description    }“Discrete cosine transform (DCT) based channel estimation ”; - container dmrs-channel-estimation-fh-method {    description    “O-RU’s capabilities related to supported fronthaul indication methods of channel estimation parameters”;        o leaf static-channel-estimation-type-only-indication-method {             type boolean;             description             “Static channel estimation indication method refers to the case where    the O-DU only indicates channel estimation type/method to the O-RU. O-RU    determines the channel estimation details, including coefficients and    processing steps based on its own implementation”;             }        o leaf static-full-id-based-channel-estimation-method {             type boolean;             description             “static ID-based channel estimation method refers to the case where    the O-DU indicates the channel estimation type/method as well as other    channel estimation parameters needed at the O-RU. O-RU uses look-up tables    to obtain the channel estimation details”;             }        o leaf real-time-channel-estimation-method {             type boolean;             description             “real-time-channel-estimation-method refers to the case where the O-    DU provides full channel estimation details to O-RU in real-time”;             }        o leaf partial-real-time-channel-estimation-method {             type boolean;             description             “Partial-real-time-channel-estimation-method refers to the case where    the O-DU provides partial channel estimation parameters to O-RU, using    which O-RU calculates full channel estimation details. In this option, the    channel estimation method information includes the channel estimation    method and other parameters. O-RU calculates the channel estimation details,    such as MMSE matrix, CE granularity in the frequency-domain, and window    size, based on the channel estimation method and its received details from O-    DU.”;    } } - container combining-digital-bf-matrix-enhancement-information {    description    “O-RU’s capabilities related to supporting of utilizing combining/digital beamforming matrix enhancement information, which improves the quality of the combining/digital beamforming matrix.”;        o container srs-channel-estimates {    description    “O-RU supports combining/digital beamforming matrix enhancement    information which includes SRS channel estimates of the scheduled or paired    UEs/layers. The O-RU combines SRS and DM-RS channel estimates using    weighting coefficients. Two options exist for the weighting coefficients:”;                 ■ leaf weighting-coefficients-local-generation {             type boolean;             description             “O-RU supports either using pre-configured weighting coefficients or             determining the weighting coefficients based on other parameters.”;              }                 ■ leaf weighting-coefficients-reception {             type boolean;             description             “O-RU supports reception of the weighting coefficients from the O-DU.”;        o container preliminary-combining-digital-bf-matrix {    description    “O-RU supports combining/digital beamforming matrix enhancement    information which includes preliminary combining/digital beamforming    matrix elements corresponding to the scheduled or paired UEs/layers. This    preliminary combining/digital beamforming matrix is calculated at O-DU    prior to slot n using SRS channel estimates. Later, the O-RU combines its own    calculated combining/digital beamforming matrix elements with the    preliminary combining/digital beamforming matrix using weighting    coefficients. Two options exist for the weighting coefficients.”;                 ■ leaf weighting-coefficients-local-generation {             type boolean;             description             “O-RU supports local generation of the weighting coefficients”;              }                 ■ leaf weighting-coefficients-reception {             type boolean;             description             “O-RU supports reception of the weighting coefficients from the O-DU”;  } } } - container combining-matrix-calculation-method {    description    “O-RU capabilities related to combining/digital beamforming matrix calculation method.”;        o leaf conjugate-combining {             type boolean;             description             “O-RU’s support for Conjugate combining method.”;             }        o leaf zero-forcing {             type boolean;             description             “O-RU’s support for Zero-forcing combining method”;             }        o leaf dft-compression {             type boolean;             description             “O-RU’s support for Discrete Fourier transform compression based    combining method. ”;             }        o leaf null-space-dimension-increase-based {             type boolean;             description             “O-RU’s support for Null-space dimension increase based combining    calculation method.”;             }        o leaf mmse-irc-based {             type boolean;             description             “O-RU’s support for Minimum mean square error - Interference    rejection combining (MMSE-IRC) based combining calculation method.”; } } }

[0316] Another example implementation in the o-ran-uplane-conf.yang can be described as follows, where dependent features can be marked as read-write for capabilities reporting and configurations

TABLE-US-00024 grouping dmrs-based-channel-estimation-features { description “Dependent features on DMRS-based channel estimation”; - container dmrs-based-channel-estimation-configuration-type {    description    “DMRS-based channel estimation configuration type.”;        o leaf static-dmrs-based-channel-estimation-configuration-type {             type boolean;             description             “Static configurations, via M-plane, for the DMRS-based channel    estimation parameters.”;             }        o leaf dynamic- dmrs-based-channel-estimation-configuration-type{             type boolean;             description             “Real-time configurations, via C-plane, for the DMRS-based channel    estimation parameters.”;              }     } - container dmrs-generation-method {    description    “DMRS signal generation. O-DU transfers DM-RS information to O-RU so that O-RU can obtain DM-RS signal and perform channel estimation”;        o leaf dmrs-local-generation {             type boolean;             description             “O-RU’s reception of the DM-RS configuration parameters of the    scheduled or paired UEs/layers. O-RU’s local generation of the DM-RS    sequence using the DM-RS configuration parameters received from O-DU. ”;             }        o leaf dmrs-sequence-reception {             type boolean;             description             “O-RU’s DMRS sequence reception from O-DU.”;             }    } - container dmrs-channel-estimation-technique {    description    “Supported channel estimation techniques”;        o leaf Is-channel-estimation {             type boolean;             description             “ Least-squares (LS) channel estimation ”;              }        o leaf mmse-channel-estimation {             type boolean;             description             “Minimum mean-squared error (MMSE) channel estimation ”;             }        o leaf dft-channel-estimation {             type boolean;             description             “Discrete Fourier transform (DFT) based channel estimation ”;             }        o leaf dct-channel-estimation {             type boolean;             description             “Discrete cosine transform (DCT) based channel estimation ”;     } } - container dmrs-channel-estimation-fh-method {    description    “Fronthaul indication methods of channel estimation parameters”;        o leaf static-channel-estimation-type-only-indication-method {             type boolean;             description             “Static channel estimation indication method refers to the case where    the O-DU only indicates channel estimation type/method to the O-RU. O-RU    determines the channel estimation details, including coefficients and    processing steps based on its own implementation”;             }        o leaf static-full-id-based-channel-estimation-method {             type boolean;             description             “static ID-based channel estimation method refers to the case where    the O-DU indicates the channel estimation type/method as well as other    channel estimation parameters needed at the O-RU. O-RU uses look-up tables    to obtain the channel estimation details”;             }        o leaf real-time-channel-estimation-method {             type boolean;             description             “real-time-channel-estimation-method refers to the case where the O-    DU provides full channel estimation details to O-RU in real-time”;             }        o leaf partial-real-time-channel-estimation-method {             type boolean;             description             “Partial-real-time-channel-estimation-method refers to the case where    the O-DU provides partial channel estimation parameters to O-RU, using    which O-RU calculates full channel estimation details. In this option, the    channel estimation method information includes the channel estimation    method and other parameters. O-RU calculates the channel estimation details,    such as MMSE matrix, CE granularity in the frequency-domain, and window    size, based on the channel estimation method and its received details from O-    DU.”;     } } - container combining-digital-bf-matrix-enhancement-information {    description    “O-RU’s utilizing combining/digital beamforming matrix enhancement information, which improves the quality of the combining/digital beamforming matrix.”;        o container srs-channel-estimates {    description    “Combining/digital beamforming matrix enhancement information which    includes SRS channel estimates of the scheduled or paired UEs/layers. The O-    RU combines SRS and DM-RS channel estimates using weighting coefficients.    Two options exist for the weighting coefficients:”;                 ■ leaf weighting-coefficients-local-generation {             type boolean;             description             “O-RU uses pre-configured weighting coefficients or determines the             weighting coefficients based on other parameters.”;              }                 ■ leaf weighting-coefficients-reception {             type boolean;             description             “O-RU’s reception of the weighting coefficients from the O-DU.”;     } }        o container preliminary-combining-digital-bf-matrix {    description    “Combining/digital beamforming matrix enhancement information which    includes preliminary combining/digital beamforming matrix elements    corresponding to the scheduled or paired UEs/layers. This preliminary    combining/digital beamforming matrix is calculated at O-DU prior to slot n    using SRS channel estimates. Later, the O-RU combines its own calculated    combining/digital beamforming matrix elements with the preliminary    combining/digital beamforming matrix using weighting coefficients. Two    options exist for the weighting coefficients.”;                 ■ leaf weighting-coefficients-local-generation {             type boolean;             description             “O-RU’s local generation of the weighting coefficients”;             }                 . leaf weighting-coefficients-reception {             type boolean;             description             “O-RU’s reception of the weighting coefficients from the O-DU”; }}} - container combining-matrix-calculation-method {    description    “O-RU’s combining/digital beamforming matrix calculation method.”;        o leaf conjugate-combining {             type boolean;             description             “Conjugate combining method.”;             }        o leaf zero-forcing {             type boolean;             description             “Zero-forcing combining method”;             }        o leaf dft-compression {             type boolean;             description             “Discrete Fourier transform compression based combining method. ”;             }        o leaf null-space-dimension-increase-based {             type boolean;             description             “Null-space dimension increase based combining calculation method.”;             }        o leaf mmse-irc-based {             type boolean;             description             “Minimum mean square error - Interference rejection combining    (MMSE-IRC) based combining calculation method.”;             } }}

C-plane Embodiment Related to Real-Time DMRS Sequence Generation at the O-RU

DMRS Configuration Parameters

[0317] C-plane Embodiment: If dmrs-local-generation and dynamic-dmrs-based-channel-estimation-configuration-type features are supported by the O-RU and configured by the SMO/O-RU controller, the O-DU appends the UL C-plane message sent in the DL to the O-RU with the following section extension and includes the DM-RS configuration parameters to enable the O-RU to locally generate the DM-RS signal.

[0318] ExtType=21: Section description for DMRS sequence generatio

[0319] This section extension applies to DMRS signal generation. This enables the O-DU to provide the DMRS configuration parameters at the O-RU to generate the DMRS signal locally. This section extension applies to section types 1 and 3.

TABLE-US-00025 Section Extension Type 21 ef extType = 0x15 1 Octet N extLen 1 N+1 TP scramblingInit GH SH configType maxLen pos reserved 1 N+2 scramblingID[15:8] 1 N+3 scramblingID [7:0] 1 N+4 addPos[1:0] antPortInd[3:0] reserved 1 N+5 zero pad to 4-byte boundary 1 N+6 zero pad to 4-byte boundary 1 N+7

TP (transformPrecoding)

[0320] Description: This parameter is used to indicate if Transform precoding is enabled or disabled. The default is that transform precoding is disabled. [0321] Value range: {0b: Disabled; 1b: Enabled}. [0322] Type: binary bit. [0323] Field length: 1 bit. [0324] Default Value: 0

[0325] Description of the remaining fields in the above section extension follows the same definitions in Table 2 above.

M-plane Embodiment Related to Static DMRS Sequence Generation at the O-RU

[0326] M-plane Embodiment for static DMRS sequence generation: If dmrs-local-generation and static-dmrs-based-channel-estimation-configuration-type features are supported by the O-RU and configured by the SMO/O-RU controller, the SMO/O-RU controller statically configures the DM-RS parameters to enable the O-RU to locally generate the DM-RS signal and execute DMRS-based channel estimation.

TABLE-US-00026 list dmrs-based-channel-estimation-configuration { if-feature mcap: DMRS-BASED-CHANNEL-ESTIMATION-SUPPORTED; key dmrs-ce-config-id; description “List of DMRS-based channel estimation configurations. An O-RU shall reject any configuration modification which exceed the maximum permitted configurations supported by the O-RU”; leaf dmrs-ce-config-id { type uint8; description  “Supplementary parameter acting as key in list of DMRS based channel estimation configurations.”; } uses dmrs-based-channel-estimation-configuration; grouping dmrs-based-channel-estimation-configuration { description “Set of parameters related to DMRS-based channel estimation configuration”; list dmrs-sequence-generation { key dmrs-sequence-id; min-elements 1; description  “Provides configuration parameters by the O-RU to generate the DMRS sequence locally to be used for channel estimation.”; leaf dmrs-sequence-id { type uint16;  mandatory true;  description    “Supplementary parameter acting as key for dmrs-sequence list.”; } leaf transform-recoding { type boolean{ }  mandatory true;  description   “This parameter enable or disable transform precoding. True means transform precoding is enabled.”; } leaf dmrs-scrambling-id{ type uint16{ } range 0..65535;  mandatory true;  description } “DMRS scrambling Identity.”; leaf dmrs-scrambling-initialization{ type uint8{   range 0,1; }  mandatory true;  description } “DMRS scrambling initialization”; leaf number-of-ofdm-symbols-in-slot{ type uint8{   range 12, 14; }  mandatory true;  description } “Number of OFDM symbols per slot”; leaf slot-index-in-radio-frame{ type uint8{ } range 0..159;  mandatory true;  description } “DMRS slot index in radio frame”; leaf symbol-index-within-slot{ type uint8{   range 0..13; }  mandatory true;  description } “Symbol index within a slot”; leaf dmrs-group-hopping{ type uint8{   range 0,1; }  mandatory true;  description } “DMRS group hopping”; leaf dmrs-sequence-hopping{ type uint8{   range 0,1; }  mandatory true;  description } “DMRS sequence hopping”; leaf dmrs-configuration-type{ type uint8{   range 1,2; }  mandatory true;  description } “DMRS configuration type”; leaf dmrs-max-length{ type uint8{   range 1,2; }  mandatory true;  description   “DMRS maximum length: Single symbol or double symbol”; } leaf dmrs-typeA-position{ type uint8{   range 2,3; }  mandatory true;  description   “DMRS TypeA position: DMRS start position for Type A. 2 refers to pos2 and 3 refers to pos3”; } leaf additional-dmrs-position{ type uint8{   range 0,1,2,3; }  mandatory true;  description } “Additional DMRS position”;

C-Plane Embodiment Related to O-DU Transmission in Real-Time DMRS Sequence to the O-RU

[0327] C-plane Embodiment: If dmrs-sequence-reception and dynamic-dmrs-based-channel-estimation-configuration-type features are supported by the O-RU and configured by the SMO/O-RU controller, the O-DU appends the UL C-plane message sent in the DL to the O-RU with the following section extension and includes the DM-RS sequence to enable the O-RU to do DMRS-based channel estimation.

TABLE-US-00027 Section Extension Type 22 ef extType = 0x16 1 Octet N extLen 1 N+1 re startRec (4 bits) reserved udCompHdr (not always present) 1 N+2 reserved (not always present) udCompLen (not always present) udCompParam (not always present) iSample (1.sup.st RE in the PRB) 1 N+3 qSample (1.sup.st RE in the PRB) 1 N+4 ... 1 N+5 iSample (12.sup.th RE in the PRB) qSample (12.sup.th RE in the PRB) udCompParam (not always present) iSample (1.sup.st RE in the PRB) qSample (1.sup.st RE in the PRB) ... 1 N+6 iSample (12.sup.th RE in the PRB) 1 N+7 qSample (12.sup.th RE in the PRB)

[0328] ExtType=22: Section description for DMRS sequence transmission

[0329] This section extension applies to DMRS signal transmission. This enables the O-DU to provide the DMRS sequence needed at the O-RU to execute DMRS-based channel estimation. This section extension applies to section types 1 and 3.

Re (Resource Element Indicator)

[0330] Description: This parameter is used to indicate if every RE is used or every other RE is used. The starting RE is defined by startRec [0331] Value range: {0 b=every RE used; 1 b=every other RE used}. [0332] Type: binary bit. [0333] Field length: 1 bit. [0334] Default Value: 0 b (every RE used) startRec (start RE) [0335] Description: This parameter is used to indicate the first RE within a PRB. [0336] Value range: {0 -11}. [0337] Type: uint. [0338] Field length: 4 bits. [0339] Default Value: 0iSample and qSample represent the I and Q samples, respectively of the DMRS signal.

C-Plane Embodiment Related to Real-Time Configuration of the O-RU by the O-DU for the Channel Estimation Method and Parameters

[0340] If dynamic-dmrs-based-channel-estimation-configuration-type and real-time-channel-estimation-method features are supported by the O-RU and configured by the SMO/O-RU controller, the O-DU configures the O-RU in real time with the channel estimation method and needed parameters to enable the O-RU to do channel estimation locally.

[0341] ExtType=23: Section description for channel estimation

[0342] This section extension applies to channel estimation at the O-RU. This enables the O-DU to provide the channel estimation technique and relevant configuration parameters needed at the O-RU to locally perform channel estimation. This section extension applies to section types 1 and 3.

TABLE-US-00028 Section Extension Type 23 ef extType = 0x17 1 Octet N extLen 1 N+1 chEstMeth mmseMatrixId chEstGranularity 1 N+2 windowType windowSize reserved 1 N+3

chEstMeth (Channel Estimation Method)

[0343] Description: This parameter is used to indicate the channel estimation method. The default is the LS method.. [0344] Value range: {00 b: LS; 01 b: MMSE; 10 b: DFT based; 11 b: DCT based}. [0345] Type: unsigned integer. [0346] Field length: 2 bits. [0347] Default Value: 00

mmseMatrixId (MMSE Matrix ID)

[0348] Description: This parameter is used to indicate the channel estimation matrix ID. This field is feasible only if the chEstMeth = 00 b (i.e., LS channel estimation). For other channel estimation methods, the O-DU shall set this field to the default value and the O-RU shall ignore this field. [0349] Value range: {000 b: ∅.sub.1 - 111 b: ∅.sub.8}. [0350] Type: unsigned integer. [0351] Field length: 3 bits. [0352] Default Value: 000

chEstGranularity (Channel Estimation Granularity)

[0353] Description: This parameter is used to indicate the channel estimation granularity in the frequency domain. [0354] Value range: {00 b: N.sub.1; 01 b: N.sub.2; 10 b: N.sub.3; 11 b: N.sub.4}. [0355] Type: unsigned integer. [0356] Field length: 2 bits. [0357] Default Value: 00

windowType (Channel Estimation Window Type)

[0358] Description: This parameter is used to indicate the channel estimation window type. This field is feasible only if the chEstMeth = 10 b or 11 b(i.e., DFT or DCT based channel estimation). For other channel estimation methods, the O-DU shall set this field to the default value and the O-RU shall ignore this field. [0359] Value range: {00 b: Type 1; 01 b: Type 2; 10 b: Type 3; 11 b: Type 4}. [0360] Type: unsigned integer. [0361] Field length: 2 bits. [0362] Default Value: 00

windowSize (Channel Estimation Window Size)

[0363] Description: This parameter is used to indicate the channel estimation window size. This field is feasible only if the chEstMeth = 10 b or 11 b(i.e., DFT or DCT based channel estimation). For other channel estimation methods, the O-DU shall set this field to the default value and the O-RU shall ignore this field. [0364] Value range: {00 b: Size 1; 01 b: Size 2; 10 b: Size 3; 11 b: Size 4}. [0365] Type: unsigned integer. [0366] Field length: 2 bits. [0367] Default Value: 00

Embodiment 6: 5G NR DM-RS

[0368] In 5G NR, DM-RS is used for channel estimation as part of coherent demodulation of the physical channels (i.e., PUSCH/PDSCH). It is designed to support various use cases, channel conditions, and deployment scenarios. DM-RS configuration depends on other PHY layer parameters such as the resource allocation type and utilized waveform (i.e., CP-OFDM or DFT-s-OFDM), and these are detailed in the following parts. In order for O-RU to be able to perform DM-RS channel estimation, either DM-RS sequence or DM-RS configuration parameters, which are required to generate DM-RS sequence at O-RU, need to be provided by O-DU to O-RU. This part explains the latter option and lists the parameters with detailed instructions for DM-RS sequence generation, precoding, and mapping. FIGS. 11A, 11B, 11C, 11D, and 11E demonstrate the possible channel estimation techniques that can be applied at the O-RU.

DM-RS Sequence Generation

For CP-OFDM

[0369] A length-31 Gold sequence is used as the DM-RS sequence for CP-OFDM (i.e., when transform precoding is disabled). This pseudo-random sequence, c(n), with a length of M.sub.PN is defined as follows:

[00013]$c\left(n\right)=\left(x_1\left(n+N_C\right)+x_2\left(n+N_C\right)\right)mod2$

[00014]$x_1\left(n+31\right)=\left(x_1\left(n+3\right)+x_1\left(n\right)\right)mod2$

[00015]$x_2\left(n+31\right)=\left(x_2\left(n+3\right)+x_2\left(n+2\right)+x_2\left(n+1\right)+x_2\left(n\right)\right)mod2$

where n = 0,1, ..., M.sub.PN - 1 and N.sub.c is 1600. The first m-sequence, x.sub.1(n), can be initialized with x.sub.1(0) = 1 and x.sub.1(n) = 0 for n = 1,2, ...,30. Also, the second m-sequence, x.sub.2(n) is initialized according to

[00016]$c_{init}={\displaystyle {.Math.}_{i=0}^{30}{x}_2\left(i\right)2^i.}$

[0370] Using the pseudo-random sequence, the DM-RS sequence for CP-OFDM, r(n), can be generated as follows:

[00017]$r\left(n\right)=\frac{1}{\sqrt{2}}\left(1-2.c\left(2n\right)\right)+\text{j}\frac{1}{\sqrt{2}}\left(1-2.c\left(2n+1\right)\right).$

[0371] The initialization of the random sequence is performed as follows:

[00018]$c_{init}=\left(2^{17}\left(N_{symb}^{slot}{n}_{s,f}^{\mu }+l+1\right)\left(2N_{ID}^{n_{SCID}}+1\right)+2N_{ID}^{n_{SCID}}+n_{SCID}\right)mod{2}^{31}$

where I is the OFDM symbol number within the slot and

[00019]$n_{s,f}^{\mu }$

is the slot number within a frame. Furthermore,

[00020]$N_{ID}^{n_{SCID}}$

denotes the DM-RS scrambling identity and n.sub.SCID represents DM-RS scrambling initialization parameter.

For DFT-s-OFDM

[0372] The Zadoff-Chu sequence is used as the DM-RS sequence for DFT-s-OFDM (i.e., when transform precoding is enabled). This low-PAPR sequence,

[00021]$r_{u,v}^{\left(\alpha ,\delta \right)}\left(n\right),$

(n), is defined by a cyclic shift a of a base sequence r̅.sub.u,.sub.v (n) as follows:

[00022]$r_{u,v}^{\left(\alpha ,\delta \right)}\left(n\right)=e^{j\alpha n}{\overline{r}}_{u,v}\left(n\right)$

where

[00023]$n=0,1,\mathrm{...},M_{ZC}-1\text{and}{M}_{ZC}=m{N}_{sc}^{RB}/2^{\delta }$

denotes the length of the sequence. Also,

[00024]$N_{sc}^{RB}$

represents the number of subcarriers in a resource block. Multiple orthogonal sequences can be generated from a base sequence through different values of a and δ. The base sequences, r̅.sub.u,v (n), are divided into groups, where u ∈ {0,1,2, ..., 29} specifies the group number and ν ∈ {0,1} represents the base sequence number within the group.

[0373] The base sequence definition depends on the sequence length as follows: [0374] 1) When M.sub.ZC ≥ 36:

[0375] The length N.sub.ZC is defined as the largest prime number, which is less than the base sequence length M.sub.ZC. [0376] 2) When M.sub.ZC ∈ {6,12,18,24}: where n = 0,1, ...,M.sub.ZC - 1 and the value of φ(n) is provided by Tables 5.2.2.2-1 to 5.2.2.2-4 in TS 38.211. [0377] 3) When M.sub.ZC = 30: where n = 0,1, ..., M.sub.ZC - 1.

[0378] Using the Zadoff-Chu sequence, the DM-RS sequence for DFT-s-OFDM, r(n), can be generated as follows:

[00031]$r\left(n\right)=r_{u,v}^{\left(\alpha ,\delta \right)}\left(n\right)$

where

[00032]$n=0,1,\mathrm{...},\left(M_{sc}^{PUSCH}\right)/2^{\delta }-1.$

The low-PAPR sequence parameters δ is given as 1 and the cyclic shift, α, is set to 0 for a PUSCH transmission. The sequence group number, u, equals to

[00033]$\left(f_{gh}+n_{ID}^{RD}\right)mod30,$

where

[00034]$n_{ID}^{RS}$

denotes the DM-RS scrambling identity. Furthermore, the values of f.sub.gh and the base sequence number, ν, are given as follows: [0379] 1) When neither group nor sequence hopping is enabled: [0380] 2) When group hopping is enabled: and where the pseudo-random sequence, c(i), should be initialized with c.sub.init = [0381] 3) When sequence hopping is enabled: where the pseudo-random sequence, c(i), should be initialized with c.sub.init = .

DM-RS Precoding and Mapping to Physical Resources

[0382] The orthogonality of the DM-RS sequences that are allocated to the different antenna ports is achieved by multiplexing in time, frequency, and code domains. To realize this, the DM-RS sequence is multiplied with the orthogonal cover codes in time and frequency domains (i.e., w.sub.t(k) and w.sub.f(k) respectively). Also, shifts in the frequency domain are included to support more antenna ports. The DM-RS sequence, r(m) is mapped to an intermediate quantity

[00040]${\tilde{a}}_{k,l}^{\left({\tilde{p}}_j,\mu \right)}$

as follows:

[00041]$\begin{array}{c}{\tilde{a}}_{k,l}^{\left({\tilde{p}}_j,\mu \right)}=w_f\left(k^{\prime }\right)w_t\left(l^{\prime }\right)r\left(2n+k^{\prime }\right)\\ k=\left\{\begin{array}{c}4n+2k^{\prime }+\Delta ConfigurationType1\\ 6n+k^{\prime }+\Delta ConfigurationType2\end{array}\right\}\\ k^{\prime }=0,1\\ l=\overline{l}+l^{\prime }\\ n=0,1,.Math.\\ j=0,1,.Math.,v-1\end{array}$

where w.sub.f(k′), w.sub.t(l′), and Δ are defined by Tables 6.4.1.1.3-1 and Tables 6.4.1.1.3-2 in TS .. Also, p̃.sub.j represents the antenna port for transmission layer j. However, DFT-s-OFDM supports only single-layer transmission, and j is equal to 0 when transform-precoding is enabled.

[0383] DM-RS configuration type determines the DM-RS density in the frequency domain, which also impacts the available number of orthogonal sequences. DM-RS configuration Type 1 has a higher density in the frequency domain and provides a more accurate channel estimation. On the other hand, DM-RS configuration Type 2 has a lower density in the frequency domain, and it allows supporting more antenna ports. Type 1 can support up to 8 antenna ports, whereas Type 2 can support up to 12 antenna ports. These are illustrated in FIGS. 10A and 10B, along with the associated mapping and orthogonal cover codes obtained from Tables 6.4.1.1.3-1 and Tables 6.4.1.1.3-2 in TS 38.211.

[0384] The reference point for k depends on the waveform type. For CP-OFDM (i.e., when transform precoding is disabled), k is subcarrier 0 in the common resource block. On the other hand, for DFT-s-OFDM (i.e., when transform precoding is enabled), k is subcarrier 0 of the lowest-numbered RB of the scheduled PUSCH allocation.

[0385] The reference point of l and the position of the first DM-RS symbol (l.sub.o) depends on the PUSCH mapping type and activation of the frequency hopping scheme. For PUSCH Mapping Type A, l is defined relative to the start of the slot if frequency hopping is disabled, and it is defined relative to the start of each hop if frequency hopping is enabled. l.sub.0 is indicated by dmrs — TypeA — Position parameter, and it refers to either the third or fourth OFDM symbol in a slot. On the other hand, for PUSCH Mapping Type B, l is defined relative to the start of the scheduled PUSCH resources if frequency hopping is disabled, and it is defined relative to the start of each hop if frequency hopping is enabled. In this case, l.sub.0 equals to 0; in other words, it refers to the first symbol in the scheduled data symbol duration. Exemplary DM-RS mappings are illustrated in FIGS. 10C and 10D for PUSCH Mapping Type A and PUSCH Mapping Type B accordingly.

[0386] The position(s) of the DM-RS symbols is provided by l̃ parameter and it depends on the PUSCH mapping type, activation of the frequency hopping scheme, and the number of additional DM-RS symbols. Up to 4 DM-RS symbols (i.e., up to 3 additional positions) in a slot are possible for high mobility scenarios. Exemplary DM-RS allocations with additional positions are presented in FIG. 10E. The position(s) of the DM-RS symbols (l̃), the time-domain index (l′), and the supported antenna ports p̃.sub.j are provided by Tables 6.4.1.1.3-3 through 6.4.1.1.3-6 in TS 38.211

[0387] In the following step, the intermediate quantity,

[00042]${\tilde{a}}_{k,l}^{\left({\tilde{p}}_j,\mu \right)}$

, is precoded with W, multiplied with the amplitude scaling factor

[00043]${\beta }_{PUSCH}^{DMRS}$

and mapped to the physical resources as follows:

[00044]$\left[\begin{array}{c}{a}_{k,l}^{\left(0,\mu \right)}\left(m\right)\\ .Math.\\ a_{k,l}^{\left(p_{v-1},\mu \right)}\left(m\right)\end{array}\right]={\beta }_{PUSCH}^{DMRS}W\left[\begin{array}{c}{\tilde{a}}_{k,l}^{\left(0,\mu \right)}\left(m\right)\\ .Math.\\ {\tilde{a}}_{k,l}^{\left({\tilde{p}}_{v-1},\mu \right)}\left(m\right)\end{array}\right]$

where and β.sub.DMRS is given by Table 6.2.2-1 in TS 38.214. The required β.sub.DMRS value is signaled with the number of DM-RS CDM groups without data parameter. Also, W is given by Table 6.3.1.5-1 to Table 6.3.1.5.-7 in TS 38.211. The required precoding matrix is signaled through the TPMI index parameter.

[0388] The DM-RS sequence can either be sent from O-DU to O-RU or the DM-RS configuration parameters, which are required to re-generate the DM-RS sequence in the O-RU, can be transmitted from O-DU to O-RU.

Embodiment 7: Channel Estimation

[0389] In an OFDM system with N subcarriers, the received signal in the frequency domain can be expressed as follows:

[00045]$Y=XH+Z$

where Y is received signal vector, X is a diagonal matrix where each diagonal element represents a reference signal (such as DM-RS) in subcarrier k, H is the channel vector, and Z is the noise vector.

[0390] FIG. 11 E is flow chart showing 4 exemplary implementations for DM-RS channel estimation techniques, described in more detail with respect to FIGS. 11A-11D. Examples of DM-RS channel estimation techniques that O-RU can use include the following:

Frequency-Domain Channel Estimation Techniques:

1) Least-Squares (LS) Channel Estimation

[0391] FIG. 11A illustrates an LS channel estimation. After extracting the DM-RS symbols of the received signal in the frequency domain, the LS channel estimation can be expressed as follows:

[00046]$H_{LS}\left(k_i,l_j,r_m,t_n\right)=\frac{Y_{RS}\left(k_i,l_j,r_m,t_n\right)}{X_{DMRS}\left(k_i,l_j,r_m,t_n\right)}$

where k.sub.i represents the subcarrier index, l.sub.j represents the symbol index, r.sub.m is the receiver antenna index, and t.sub.n is the DM-RS transmission port index. If the DM-RS belongs to code-division multiplexing (CDM) group of size L with an orthogonal cover code (OCC), the channel estimate can be de-spreaded as follows:

[00047]${{\widehat{H}}^{\prime }}_{LS}\left(DMR{S}_g,r_m,t_n\right)={\displaystyle \underset{i,j=1}{\overset{2}{.Math.}}\frac{H_{LS}\left(k_i,l_j,r_m,t_n\right)c_{ij}\left(t_n\right)}{L}}$

where c.sub.ij(t.sub.n) represents the code in symbol i, subcarrier j, and DM-RS transmission port n. Also, L is the size of the RE group where the 2-length OCC is applied. When single DM-RS is used, L is equal to 2, and when double DM-RS is used, L is equal to 4.

[0392] The channel estimates, Ĥ′.sub.LS(DMRS.sub.g,r.sub.m,t.sub.n), in a given RB can be interpolated in the time and frequency domains to obtain channel estimates over data symbol. Also, these channel estimates can be averaged for an initial channel estimate as follows:

[00048]${{\widehat{H}}^{\prime }}_{LS}\left(n_{RB},n_s,r_m,t_n\right)={\displaystyle \underset{g=1}{\overset{G}{.Math.}}\frac{{{\widehat{H}}^{\prime }}_{LS}\left(DMR{S}_g,r_m,t_n\right)}{G}}$

where n.sub.RB represents the RB index, n.sub.s shows the slot index, DMRS.sub.g denotes the DM-RS RE group index, and G is the total number of DM-RS RE groups in a given RB. Depending on the complexity and channel conditions, the channel estimates belong to multiple RBs can be averaged as well.

2) Minimum Mean-Square Error (MMSE) Channel Estimation

[0393] FIG. 11B illustrates an MMSE channel estimation. Considering, a channel estimate of Ĥ, the MMSE finds a better linear estimate (i.e., WĤ) that minimizes the minimum square error (MSE), which is calculated as E{||H — Ĥ||.sup.2}. Without loss of generality, the LS channel estimate (Ĥ.sub.LS) can be used as an initial estimate, and the MMSE channel estimate can be expressed as follows:

[00049]${\widehat{H}}_{MMSE}=W{\widehat{H}}_{LS}=R_{H{\widehat{H}}_{LS}}{\left(R_{HH}+\frac{{\sigma }_Z^2}{{\sigma }_x^2}I\right)}^{-1}{\widehat{H}}_{LS}$

where

[00050]$\frac{{\sigma }_Z^2}{{\sigma }_x^2}$

denotes the

[00051]$\frac{1}{SNR}$

and R is the cross-correlation matrix. The expression inside the parenthesis (i.e., R.sub.HH +

[00052]$\frac{{\sigma }_Z^2}{{\sigma }_x^2}$

I) is called as the MMSE matrix and can be denoted with Ø. The elements of R.sub.HĤLS and R.sub.HH are given as follows:

[00053]$E\left\{h_{K,l}\widehat{h}{*}_{k\prime ,l\prime }\right\}=E\left\{h_{k,l}h{*}_{k\prime ,l\prime }\right\}=r_f\left(k-k\prime \right)r_t\left(l-l\prime \right)$

[0394] Assuming an exponentially decaying multipath power delay profile, the frequency-domain correlation can be stated as follows:

[00054]$r_f\left(k\right)=\frac{1}{1+j2\pi {\tau }_{RMS}k\Delta f}$

where τ.sub.RMS denotes the RMS delay spread of the channel, and Δf is the subcarrier spacing. Also, assuming a fading channel with Jake’s spectrum, the time-domain correlation can be expressed as follows:

[00055]$r_t\left(l\right)=J_0\left(2\pi f_{D_{max}}l{T}_s\right)$

where f.sub.Dmax is the maximum Doppler spread of the channel, T.sub.s is the OFDM symbol duration, and J.sub.0 is the first kind of the 0.sup.th-order Bessel function. Alternatively, a sinc function can be adapted to represent the frequency and time domain correlations as well, and the elements of R.sub.HĤLS and R.sub.HH can also be formulated as follows:

[00056]$r_f\left(k-k^{\prime }\right)r_t\left(l-l^{\prime }\right)=sinc\left(2{\tau }_{RMS}\Delta f\left(k-k^{\prime }\right)\right)sinc\left(2\pi f_{D_{max}}{T}_s\left(l-l^{\prime }\right)\right)$

[0395] After calculating W, the MMSE channel estimation can be performed as below:

[00057]${{\widehat{H}}^{\prime }}_{MMSE}\left(k,l,r,t\right)=W\left(k,l;k^{\prime },l^{\prime }\right){\widehat{H}}_{LS}\left(k^{\prime },l^{\prime },r,t\right)$

[0396] Considering the DM-RS structure, the MMSE channel estimation in the vicinity of a group of REs, where a 2-length OCC is applied, can be calculated as follows:

[00058]$\begin{array}{l}{{\widehat{H}}^{\prime }}_{MMSE}\left(DMR{S}_g\left(k_i,l_j\right),r_m,t_n\right)=\\ W\left(k_i,l_j;k_{i\prime },l_{j\prime }\right){{\widehat{H}}^{\prime }}_{LS}\left(DMR{S}_g\left(k_{i\prime },l_{j\prime }\right),r_m,t_n\right)\end{array}$

where k.sub.i, and l.sub.j, show the subcarrier and symbol indices of the DM-RS RE group. Also, these channel estimates can be averaged for an initial channel estimate as follows:

[00059]${\widehat{H}}_{MMSE}\left(n_{RB},n_s,r_m,t_n\right)={\displaystyle {.Math.}_{i,j,g=1}^{I,J,G}\frac{{{\widehat{H}}^{\prime }}_{MMSE}\left(DMR{S}_g\left(k_i,l_j\right),r_m,t_n\right)}{I\times J\times G}}$

where n.sub.RB represents the RB index, n.sub.s shows the slot index, I and J represents the total number of subcarriers and symbols that are used in this averaging operation. Depending on the complexity and channel conditions, the channel estimates belong to multiple RBs can be averaged as well.

[0397] Accordingly, the noise power can be estimated as follows:

[00060]$\begin{array}{c}\widehat{Z}\left(k_i,l_j,r_m\right)=Y_{RS}\left(k_i,l_j,r_m\right)-{\displaystyle \underset{n}{.Math.}{X}_{DMRS}\left(k_i,l_j,t_n\right)c_{ij}\left(t_n\right)}\\ {{\widehat{H}}^{\prime }}_{MMSE}\left(DMR{S}_g\left(k_i,l_j\right),r_m,t_n\right)\\ {\widehat{\sigma }}_Z^2=mean\left(\widehat{Z}{\widehat{Z}}^H\right)\end{array}$

where the mean operation is defined over all receiver antennas and DM-RS REs.

Time-Domain Channel Estimation:

1) Discrete Fourier Transform (DFT) Based Channel Estimation

[0398] A DFT-based channel estimation is illustrated in FIG. 11C. The performance of channel estimation (LS or MMSE) can be improved with a DFT-based channel estimation technique by filtering the noise outside the maximum delay of the channel. Considering the complexity of the system, the LS channel estimate (Ĥ.sub.LS) can be used as an initial estimate, and it can be converted to the time domain with an IDFT operation as follows:

[00061]${\widehat{h}}_{LS}^{DFT}\left(n_i,l_j,r_m,t_n\right)=IDFT\left\{{{\widehat{H}}^{\prime }}_{LS}\left(k_i,l_j,r_m,t_n\right)\right\}$

[0399] Afterward, a window (e.g., rectangular) can be applied to filter the noise outside the maximum delay of the channel as follows:

[00062]${\widehat{h}}_{filtered}^{DFT}\left(n_i,l_j,r_m,t_n\right)=\left\{\begin{array}{cc}{\widehat{h}}_{LS}^{DFT}\left(n_i,l_j,r_m,t_n\right)& 0\le n_i\le w\\ 0& otherwise\end{array}\right\}$

where w denotes the window length. To improve the performance further, the channel taps that are below a certain threshold value are set to 0. This threshold value can be calculated by the average energy of the channel taps outside the window. The thresholding operation is performed as follows:

[00063]${\widehat{h}}_{thresholded}^{DFT}\left(n_i,l_j,r_m,t_n\right)=\left\{\begin{array}{cc}{\widehat{h}}_{LS}^{DFT}\left(n_i,l_j,r_m,t_n\right)& P_{n_i}\ge Threshold\\ 0& otherwise\end{array}\right\}$

where P.sub.ni represents the tap power at n.sub.i. Also, the noise power can be estimated (i.e.,

[00064]$\left({\widehat{\sigma }}_Z^2\right)$

by taking the average power of all taps that are set to 0. Following this operation, the time-domain estimate is transformed to the frequency domain by the DFT operation.

[00065]${{\widehat{H}}^{\prime }}_{DFT}\left(k_i,l_j,r_m,t_n\right)=DFT\left\{{\widehat{h}}_{thresholded}^{DFT}\left(n_j,l_j,r_m,t_n\right)\right\}$

[0400] These channel estimates can be averaged for an initial channel estimate as follows:

[00066]${\widehat{H}}_{DFT}\left(n_{RB},n_s,r_m,t_n\right)={\displaystyle .Math.{}_{i,j}^{I,J}\frac{{{\widehat{H}}^{\prime }}_{DFT}\left(k_i,l_j,r_m,t_n\right)}{I\times J}}$

[0401] Depending on the complexity and channel conditions, the channel estimates belong to multiple RBs can be averaged as well.

2) Discrete Cosine Transform (DCT) Based Channel Estimation

[0402] A DCT based channel estimation is illustrated in FIG. 11D.

[0403] The performance of channel estimation (LS or MMSE) can be improved with a DCT-based channel estimation technique by filtering the noise outside the maximum delay of the channel, similar to the DFT-based estimation. However, the DCT-based estimation provides better power concentration and lower aliasing error than the DFT-based interpolation. Considering the complexity of the system, the LS channel estimate (Ĥ.sub.LS) can be used as an initial estimate, and it can be converted to the transform domain with a DCT operation as follows:

[00067]${\widehat{h}}_{LS}^{DCT}\left(n_i,l_j,r_m,t_n\right)=DCT\left\{{{\widehat{H}}^{\prime }}_{LS}\left(k_i,l_j,r_m,t_n\right)\right\}$

[0404] Afterward, a window (e.g., rectangular) can be applied to filter the noise outside the maximum delay of the channel as follows:

[00068]${\widehat{h}}_{filtered}^{DCT}\left(n_i,l_j,r_m,t_n\right)=\left\{{{}^{{\widehat{h}}_{LS}^{DCT}}}_0^{\left(n_i,l_j,r_m,t_n\right)}{}_{otherwise}^{0\le n_j\le w}\right\}$

where w denotes the window length. To improve the performance further, the channel taps that are below a certain threshold value are set to 0. This threshold value can be calculated by the average energy of the channel taps outside the window. The thresholding operation is performed as follows:

[00069]${\widehat{h}}_{thresholded}^{DCT}\left(n_i,l_j,r_m,t_n\right)=\left\{{{}^{{\widehat{h}}_{LS}^{DCT}}}_0^{\left(n_i,l_j,r_m,t_n\right)}{}_{otherwise}^{P_{nj}\ge Threshold}\right\}$

where P.sub.ni represents the tap power at n.sub.i. Following this operation, it is transformed to the frequency domain by the IDCT operation.

[00070]${{\widehat{H}}^{\prime }}_{DCT}\left(k_i,l_j,r_m,t_n\right)=IDCT\left\{{\widehat{h}}_{thresholded}^{DCT}\left(n_i,l_j,r_m,t_n\right)\right\}$

These channel estimates can be averaged for an initial channel estimate as follows:

[00071]${\widehat{H}}_{DCT}\left(n_{RB,}{n}_s,r_m,t_n\right)={\displaystyle {.Math.}_{i,j}^{I,J}\frac{{{\widehat{H}}^{\prime }}_{DCT}\left(k_i,l_j,r_m,t_n\right)}{I\times J}}$

[0405] Depending on the complexity and channel conditions, the channel estimates belong to multiple RBs can be averaged as well, similar to the other channel estimation techniques that are described previously.

Embodiment 8: Channel Equalization

[0406] Examples of channel equalization techniques that O-RU can use include the following:

A. Zero-Forcing (ZF) Equalizer

[0407] In a MIMO OFDM system, the received data symbols in the frequency domain can be expressed as follows:

[00072]$Y_{DS}\left(k,r\right)=X\left(k,t\right)H\left(k,r,t\right)+Z\left(k,r\right)$

[00073]$\begin{array}{l}H\left(k,r,t\right)=\\ \left[\begin{array}{cccc}H\left(k,0,0\right)& H\left(k,0,1\right)& .Math.& H\left(k,0,N_{tx}-1\right)\\ H\left(k,1,0\right)& H\left(k,1,1\right)& .Math.& H\left(k,1,N_{tx}-1\right)\\ .Math.& .Math.& \ddots & .Math.\\ H\left(k,N_{rx}-1,0\right)& H\left(k,N_{rx}-1,1\right)& .Math.& H\left(k,N_{rx}-1,N_{tx}-1\right)\end{array}\right]\end{array}$

where Y.sub.DS represents the frequency domain data symbols, X shows the transmitted signal, H is the estimated channel response, Z is the noise, k denotes the subcarrier index, r shows the receiver antenna index, t represents the DM-RS transmission port index, N.sub.tx is the number of DM-RS transmission ports and N.sub.rx is the number of receiver antennas.

[0408] The MIMO ZF equalization matrix W is calculated as follows:

[00074]$W={\left(H^{H}H\right)}^{-1}{H}^H$

[0409] Correspondingly, the equalized data symbol of a user (Ŷ.sub.DS) can be expressed as follows:

[00075]${\widehat{Y}}_{DS}=W{Y}_{DS}\left(k,r\right)={\left(H^{H}H\right)}^{-1}{H}^H{Y}_{DS}\left(k,r\right)$

B. Minimum Mean-Square Error (MMSE) Equalizer

[0410] Considering the same system model in part a, the MIMO MMSE equalization matrix W is calculated as follows:

[00076]$W={\left(H^{H}H+{\sigma }_Z^2{I}_{N_t}\right)}^{-1}{H}^H$

where

[00077]${\sigma }_Z^2$

represents the estimated noise power. Correspondingly, the equalized data symbol of a user (Ŷ.sub.DS) can be expressed as follows:

[00078]${\widehat{Y}}_{DS}=W{Y}_{DS}\left(k,r\right)={\left(H^{H}H+{\sigma }_Z^2{I}_{N_t}\right)}^{-1}{H}^H{Y}_{DS}\left(k,r\right)$

C. MMSE-Interference Rejection Combiner (MMSE-IRC) Equalizer

[0411] Considering an interference component in the system model that is described in part a, the received data symbols in the frequency domain can be expressed as follows:

[00079]$Y_{DS}\left(k,r\right)=X\left(k,t\right)H\left(k,r,t\right)+Z\left(k,r\right)+Q\left(k,r\right)$

where Q denotes the sum of interference from all interference users. The MIMO MMSE-IRC equalization matrix W is calculated as follows:

[00080]$W=H^H{\left(H{H}^H+R_{nn}\right)}^{-1}$

[00081]$R_{nn}=\frac{1}{N_{DMRS}}{\displaystyle .Math.R_{IpN}}$

[00082]$R_{IpN}=\left(Y_{DS}-H{X}_{DMRS}\right){\left(Y_{DS}-H{X}_{DMRS}\right)}^H$

where R.sub.IpN represents the covariance matrix of interference plus noise and N.sub.DMRS denotes the number of DM-RS subcarriers in an RB. An interpolation operation in the time/frequency domains is required to calculate the covariance matrix in the scheduled subcarriers. Correspondingly, the equalized data symbol of a user (Ŷ.sub.DS) can be expressed as follows:

[00083]${\widehat{Y}}_{DS}=W{Y}_{DS}\left(k,r\right)=H^H{\left(H{H}^H+R_{nn}\right)}^{-1}{Y}_{DS}\left(k,r\right)$

[0412] The demodulation procedure requires “additional channel equalization information” during the log-likelihood ratio (LLR) calculation, and it can be provided in several ways. A universal solution, which is independent of the equalization method, can be providing one of the following options: [0413] a) Equalization Gain and Post-processed Noise plus Interference Power (i.e., after equalization operation) [0414] b) Post-processed Noise plus Interference Power divided by Equalization Gain [0415] c) Equalization Gain divided by Post-processed Noise plus Interference Power

[0416] The equalization gain can be calculated as follows:

[00084]$\gamma =Real\left\{diag\left(WH\right)\right\}$

where y is the equalization gain, W denotes the equalization matrix, and H represents the estimated channel response. The post-processed noise plus interference power refers to the noise plus interference power that is obtained after the equalization procedure. Also, it should be noted that in the case of options (b) and (c), the equalized signal should be normalized by either equalization gain or post-processed noise plus interference power, respectively.

[0417] When the MMSE equalizer is used, only “equalization gain” can be sufficient as the “additional channel equalization information”, whereas only “post-processed noise plus interference power” is required when ZF equalizer is used. Furthermore, these values, which are used during the LLR calculation operation, can be calculated from the channel estimates and estimated DM-RS noise plus interference power as well.

Embodiment 9: Combining/Digital Beamforming Matrix Calculation

[0418] In the following, we provide a brief description of example combining/digital beamforming matrix calculation methods which can be used in any of the embodiments in this disclosure. In all of these me, the UL channel between the UEs and BS is denoted as H, which is a matrix of size N.sub.RX × N.sub.UE where N.sub.RX is the number of RX antennas at BS and N.sub.UE is the number of UEs or layers being simultaneously transmitted over the same resources on the PUSCH slot. It is noted that H is an estimation of the UL channel, for example, based on SRS or DM-RS or a combination thereof or a linearly predicted UL channel based on SRS channel estimation. [0419] a) Conjugate combining: In this method, the combining/digital beamforming matrix is calculated using H.sup.H. [0420] b) Zero forcing: In this method, the combining/digital beamforming matrix is calculated using (H.sup.H H).sup.-1H.sup.H. [0421] c) MMSE: In this method, the combining/digital beamforming matrix can be calculated in two alternative forms: or H.sup.H (HH.sup.H + where is the estimated noise power. [0422] d) MMSE-IRC: In this method, the combining/digital beamforming matrix is calculated using H.sup.H (HH.sup.H + R.sub.nn).sup.-1 where R.sub.nn the covariance matrix of interference plus noise. [0423] e) Null-space dimension increase based: In this method, the singular-value decomposition (SVD) of the channel subspace of the desired UEs and the intra-site interfering UEs, if any, is first calculated, and its null-space is characterized. A sufficient number N of singular vector(s) are selected in the null-space so that N + N.sub.UE = L where L is the total number of streams to be transferred from RU to DU. Then, the combining/digital beamforming matrix is constructed as a vertical concatenation of H.sup.H and the selected singular vectors. [0424] f) DFT compression: In this method, the energy of each row of W × H is calculated and sorted in decreasing order of energy, where W is the two-dimensional Discrete-Fourier Transform (DFT) matrix. Then, the combining/digital beamforming matrix is constructed as the L rows of W which correspond to the first L rows in the sorted list, where L is the total number of streams to be transferred from RU to DU.

Acronyms

[0425] 3GPP: Third generation partnership project [0426] BS: Base Station [0427] CA: Carrier Aggregation [0428] CAPEX: Capital Expenditure [0429] CBRS: Citizens Broadband Radio Services [0430] CC: Component carrier [0431] COTS: Commercial off-the-shelf [0432] CP: cyclic prefix [0433] C-plane: Control plane [0434] C-RAN: cloud radio access network [0435] CU: Central unit [0436] DCI: downlink control indicator [0437] DL: downlink [0438] DU: Distribution unit [0439] eAxC ID: Extended Antenna-Carrier identifier: a data flow for a single antenna (or spatial stream) for a single carrier in a single sector. [0440] eNB: Evolved Node B (applies to LTE) [0441] FDD: Frequency-division duplex [0442] FEC: forward error correction [0443] FH: Fronthaul [0444] FFT: Fast Fourier Transform [0445] gNB: g NodeB (applies to NR) [0446] iFFT: inverse Fast Fourier Transform [0447] HARQ: hybrid automatic repeat request [0448] LTE: long term evolution [0449] LTE-A: LTE Advanced [0450] M-plane: Management plane [0451] MCS: modulation and coding scheme [0452] MIMO: multiple input, multiple output [0453] MMSE-IRC: Minimum mean square error - interference rejection combining [0454] MMSE-MRC: Minimum mean square error - maximum-ratio combining [0455] mmWave: millimeter wave [0456] MNO: Mobile network operator [0457] NR: New radio [0458] OAM: Operation and management [0459] O-DU: O-RAN Distributed Unit [0460] O-RU: O-RAN Radio Unit [0461] O-RAN: Open RAN (Basic O-RAN specifications are prepared by the O-RAN alliance) [0462] OPEX: Operating Expense [0463] PBCH: Physical Broadcast Channel [0464] PCFICH: Physical Control Format Indicator Channel [0465] PDCCH: Physical downlink Control Channel [0466] PDCP: Packet Data Convergence Protocol [0467] PDSCH: physical downlink shared channel [0468] PHICH: Physical Hybrid ARQ Indicator Channel [0469] PHY: physical layer [0470] LPHY: lower physical layer [0471] UPHY: upper physical layer [0472] PUCCH: Physical Uplink Control Channel [0473] PUSCH: Physical Uplink Shared Channel [0474] QAM: quadrature amplitude modulation [0475] QPSK: Quadrature Phase Shift Keying [0476] RACH: random access channel [0477] PRACH: physical random access channel [0478] RF: radio frequency interface [0479] RLC: Radio Link Control [0480] RRC: Radio Resource Control [0481] RRM: Radio resource management [0482] RRU: Remote radio unit [0483] RU: Radio Unit [0484] RS: reference signal [0485] RSSI: received signal strength indicator [0486] RPC: Remote procedure call [0487] SMO: Service Management and Orchestration [0488] S-plane: Synchronization plane [0489] SCell: Secondary cell [0490] SIMO: single input, multiple output [0491] SINR: signal-to-interference-plus-noise ratio [0492] SRS: Sounding reference signal [0493] SSS: Secondary Synchronization Signal [0494] TB: transport block [0495] TTI: Transmission Time Interval [0496] TDD: Time division duplex [0497] U-plane: User plane [0498] UCI: Uplink Control Information [0499] UE: user equipment [0500] UL: uplink [0501] UL DMRS: uplink demodulation reference signal [0502] ULSCH: Uplink Shared Channel [0503] vBBU: Virtualized baseband unit [0504] VNF: Virtual Network Function

Definitions

[0505] Channel: the contiguous frequency range between lower and upper frequency limits.

[0506] C-plane: Control Plane: refers specifically to real-time control between O-DU and O-RU, and should not be confused with the UE’s control plane

[0507] DL: DownLink: data flow towards the radiating antenna (generally on the LLS interface)

[0508] LLS: Lower Layer Split: logical interface between O-DU and O-RU when using a lower layer (intra-PHY based) functional split.

[0509] M-Plane: Management Plane: refers to non-real-time management operations between the O-DU and the O-RU

[0510] O-CU: O-RAN Control Unit - a logical node hosting PDCP, RRC, SDAP and other control functions

[0511] O-DU: O-RAN Distributed Unit: a logical node hosting RLC/MAC/High-PHY layers based on a lower layer functional split.

[0512] O-RU: O-RAN Radio Unit: a logical node hosting Low-PHY layer and RF processing based on a lower layer functional split. This is similar to 3GPP’s “TRP” or “RRH” but more specific in including the Low-PHY layer (FFT/iFFT, PRACH extraction).

[0513] OTA: Over the Air

[0514] S-Plane: Synchronization Plane: refers to traffic between the O-RU or O-DU to a synchronization controller which is generally an IEEE 1588 Grand Master (however, Grand Master functionality may be embedded in the O-DU).

[0515] U-Plane: User Plane: refers to IQ sample data transferred between O-DU and O-RU

[0516] UL: UpLink: data flow away from the radiating antenna (generally on the LLS interface)

References

[0517] ORAN-WG4.MP.0-v06.00: O-RAN Fronthaul Working Group Management Plane Specification, Release 06.00.

[0518] ORAN-WG4.CUS-plane.0-v06.00: O-RAN Fronthaul Working Group Control, User, and Synchronization Plane Specification, Release 06.00.