CONTROLLER, ACCESS NODE AND AGGREGATION NODE IN A RADIO COMMUNICATION NETWORK

Abstract

The present invention relates to a controller, an access node, an aggregation node and methods thereof in a radio communication network. The controller comprises: a processor configured to select a plurality of spreading codes that are non-orthogonal or short orthogonal, and a transmitter coupled with the processor. The transmitter is configured to notify at least one of an access node or an aggregation node of the plurality of spreading codes.

Claims

1. A controller in a radio communication network, the controller comprising: a processor configured to select a plurality of spreading codes that are non-orthogonal or short orthogonal, and a transmitter coupled with the processor, wherein the transmitter is configured to notify at least one of an access node or an aggregation node of the plurality of spreading codes.

2. The controller of claim 1, wherein the processor is configured to select the plurality of spreading codes based on a channel quality between the access node and the aggregation node.

3. The controller of claim 2, wherein the transmitter is further configured to request a measurement of the channel quality.

4. The controller of claim 2, wherein the processor is configured to select the plurality of spreading codes based on the channel quality by using a channel quality search look-up-table for the plurality of spreading codes, and wherein the look-up-table comprises a mapping from a range of channel quality values to a plurality of spreading codes, and wherein the controller further comprises a receiver configured to receive a channel quality value.

5. An access node in a radio communication network, comprising: at least one first receive antenna configured to receive a plurality of physical signals from one or more user nodes; a processor coupled with the at least one first receive antenna, wherein the processor is configured to: spread the plurality of physical signals with a plurality of spreading codes, wherein the plurality of spreading codes are non-orthogonal or short orthogonal; and compose the plurality of spread signals to generate a first composite signal; and at least one first transmit antenna coupled with the processor, wherein the at least one first transmit antenna is configured to transmit the first composite signal to an aggregation node.

6. The access node of claim 5, wherein the processor is further configured to select the plurality of spreading codes.

7. The access node of claim 5, wherein the access node further comprises a receiver configured to receive the plurality of spreading codes from a controller.

8. The access node of claim 5, further comprising: at least one second receive antenna configured to receive a second composite signal from the aggregation node, wherein the processor is further configured to despread and decompose the second composite signal using the plurality of spreading codes to obtain a plurality of despread signals; a multi-user detector configured to obtain a plurality of estimated signals from the plurality of despread signals; and a plurality of second transmit antennas configured to transmit the plurality of estimated signals to the one or more user nodes.

9. An aggregation node in a radio communication network, comprising: a receive antenna configured to receive a first composite signal from an access node, and a processor coupled with the receive antenna, wherein the processor is configured to despread and decompose the first composite signal using a plurality of spreading codes to obtain a plurality of despread signals, wherein the plurality of spreading codes are non-orthogonal or short orthogonal.

10. The aggregation node of claim 9, wherein the processor is further configured to select the plurality of spreading codes.

11. The aggregation node of claim 9, wherein the aggregation node further comprises a receiver configured to receive the plurality of spreading codes from a controller.

12. The aggregation node of claim 9, wherein the processor is configured to use a multi-user detection scheme to obtain a plurality of estimated signals from the plurality of despread signals.

13. The aggregation node of claim 9, wherein the processor is further configured to: spread a plurality of baseband signals with the plurality of spreading codes; and compose the plurality of spread signals to generate a second composite signal; and wherein the aggregation node further comprises a transmit antenna configured to transmit the second composite signal to the access node.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0077] To illustrate the technical features of embodiments of the present invention more clearly, the accompanying drawings provided for describing the embodiments are introduced briefly in the following. The accompanying drawings in the following description are merely some embodiments of the present invention, but modifications on these embodiments are possible without departing from the scope of the present invention as defined in the claims.

[0078] FIG. 1 is a block diagram illustrating a controller in accordance with an embodiment of the present invention,

[0079] FIG. 2a is a block diagram illustrating an access node in accordance with an embodiment of the present invention,

[0080] FIG. 2b is a block diagram illustrating a further access node in accordance with an embodiment of the present invention,

[0081] FIG. 3 is a block diagram illustrating an aggregation node in accordance with an embodiment of the present invention,

[0082] FIG. 4 is a block diagram illustrating a radio communication network in accordance with an embodiment of the present invention,

[0083] FIG. 5 is a flow chart of a method for a radio communication network in accordance with an embodiment of the present invention, wherein the method is preferably implemented in a controller,

[0084] FIG. 6 is a flow chart of a method for a radio communication network in accordance with an embodiment of the present invention, wherein the method is preferably implemented in an access node,

[0085] FIG. 7 is a flow chart of a method for a radio communication network in accordance with an embodiment of the present invention, wherein the method is preferably implemented in an aggregation node,

[0086] FIG. 8 is a flow chart of a method for a radio communication network in accordance with an embodiment of the present invention,

[0087] FIG. 9 is a schematic illustration of a system for calculating precoders using upload beacons from N user nodes,

[0088] FIG. 10 is a schematic illustration of a system comprising an access node and aggregation node in accordance with embodiments of the present invention,

[0089] FIG. 11 is a diagram illustrating the performance of beamforming with the systems shown in FIGS. 9 and 10, and

[0090] FIG. 12 is a further diagram illustrating the performance of beamforming with the systems shown in FIGS. 9 and 10.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0091] FIG. 1 is a block diagram illustrating a controller 100 in accordance with an embodiment of the present invention. The controller 100 comprises a processor 110 and a transmitter 120. The processor 110 is configured to select a plurality of spreading codes which are non-orthogonal or short orthogonal. In a possible embodiment the processor 110 is configured to use a look-up table 114, indicated with dashed lines in FIG. 1, to select the plurality of spreading codes. FIG. 1 shows that the look-up table is part of the controller 100, however, in other embodiments the look-up table could also be external to the controller, e.g. in the cloud.

[0092] In a possible embodiment the controller 100 further comprises a receiver 112, indicated with dashed lines in FIG. 1, for receiving a channel quality value. For example, the channel quality value could be measured by an access node and/or aggregation node and be transmitted to the receiver 112 of the controller 100.

[0093] FIG. 2a is a block diagram illustrating an access node 200a in accordance with an embodiment of the present invention. The access node 200a comprises a plurality of first receive antennas 210, 212, 214. FIG. 2a shows three first receive antennas 210, 212, 214, but it is understood that in other embodiments of the invention, the access node 200a could comprise a different number of first receive antennas. The first receive antennas 210, 212, 214 are configured to receive a plurality of physical signals from one or more user nodes (not shown in FIG. 2a). The access node 200a further comprises a processor 220 which is configured to spread the plurality of physical signals with a plurality of spreading codes and compose the plurality of spread signals to generate a first composite signal.

[0094] The access node 200a further comprises at least one first transmission antenna 230 configured to transmit the first composite signal to an aggregation node.

[0095] In a possible embodiment, the access node 200a further comprises a receiver 240, shown with dashed lines in FIG. 2a, configured to receive the plurality of spreading codes from a controller. In other embodiments, the access node 200a does not comprise such a receiver, but the processor 220 is configured to select the plurality of spreading codes.

[0096] FIG. 2b is a block diagram illustrating a further access node 200b in accordance with a further embodiment of the present invention. Compared to the access node 200a shown in FIG. 2a, the access node 200b of FIG. 2b further comprises a plurality of second receive antennas 270, 272, 274 and a second transmit antenna 240. The second receive antenna 240 is configured to receive a second composite signal from the aggregation node. The processor 220 is configured to despread and decompose the second composite signal using the plurality of spreading codes to obtain a plurality of despread signals.

[0097] In a possible embodiment of the invention, the same physical antenna acts as first transmit antenna 230 and second receive antenna 240 and/or the same plurality of physical antennas act as first receive antennas 210, 212, 214 and second transmit antennas 270, 272, 274.

[0098] The access node 200b further comprises a multi-user detector 260 configured to obtain a plurality of estimated signals from the plurality of despread signals. The plurality of second transmit antennas 270, 272, 274 is configured to transmit the plurality of estimated signals to the user nodes.

[0099] FIG. 2b shows that the multi-user detector 260 is separate from the processor 220, however, in other embodiments, the processor 260 can be configured to implement a multi-user detection scheme, so that no multi-user detector 260 external to the processor 220 is required.

[0100] In another embodiment of the invention, the access node 200b comprises a receiver 240, indicated with dashed lines in FIG. 2b. The receiver 240 can be configured to receive the plurality of spreading codes from a controller.

[0101] FIG. 3 is a block diagram illustrating an aggregation node 300 in accordance with an embodiment of the present invention. The aggregation node 300 comprises a receive antenna 310 and a processor 320.

[0102] Optionally, the aggregation node 300 also comprises a receiver 330, indicated with dashed lines in FIG. 3, wherein the receiver 330 is configured to receive the plurality of spreading codes from a controller.

[0103] FIG. 4 is a block diagram illustrating a radio communication network 400 in accordance with an embodiment of the present invention. The radio communication network 400 comprises a controller 100, an aggregation node 300, and an access node 200.

[0104] Within one communication network, the information is transferred from information source node to the information reception node. Very often the transferring is achieved wirelessly through one or multiple radio communication links. The radio links have different properties due to the different frequency bands used. Preferably, the millimetre wave band is used for the link between the access node 200 and the aggregation node 300.

[0105] Preferably, the radio communication network 400 is configured to establish a radio communication link 402, indicated in FIG. 4 as a dashed line, between the access node 200 and the aggregation node 300, wherein a quality of the radio communication link 402 can be measured e.g. at the aggregation node 300 and/or the access node 200.

[0106] Optionally, the controller 100 is connected to the aggregation node 300 through a wired link 404, indicated in FIG. 4 as a dashed line. In other embodiments of the invention, the controller can be configured to notify the aggregation node of the plurality of spreading codes through a radio link (not shown in FIG. 4).

[0107] FIG. 5 is a flow chart of a method for a radio communication network in accordance with an embodiment of the present invention, wherein the method is preferably implemented in a controller of the radio communication network.

[0108] The method comprises a first step 510 of selecting a plurality of spreading codes which are non-orthogonal or short orthogonal.

[0109] In a second step 520, at least one of an access node and an aggregation node is notified of the plurality of spreading codes.

[0110] The method of FIG. 5 can preferably be implemented in a controller of a radio communication network. However, the method of FIG. 5 can also be implemented in other entities, e.g. in other nodes of a radio communication network. Current communication networks often comprise multiple nodes of different types. The terminology node includes, but is not limited to a user terminal device, a base station, a relay station, or any other type of device capable of operating in a wireless or wire-line environment. When referred to herein, the terminology node includes but is not limited to a base station, a Node-B or eNode-B, an access node, a base station controller, an aggregation point or any other type of interfacing device in a communication environment.

[0111] FIG. 6 is a flow chart of a method for a radio communication network in accordance with an embodiment of the present invention. The method comprises a first step 610 of receiving a plurality of signals from one or more user nodes using a plurality of receive antennas. In a second step 620, the plurality of signals is spread with a plurality of spreading codes. In a third step 630, the plurality of spread signals are composed to generate a composite signal. In a fourth step 640, the composite signal is transmitted to an aggregation node.

[0112] The method of FIG. 6 can preferably be implemented in an access node of a radio communication network. However, the method of FIG. 6 can also be implemented in other entities, e.g. in other nodes of the radio communication network.

[0113] FIG. 7 is a flow chart of a method for a radio communication network in accordance with an embodiment of the present invention. The method comprises a first step 710 of receiving a composite signal from an access node. In a second step 720, the composite signal is despread and decomposed using a plurality of spreading codes to obtain a plurality of despread signals.

[0114] The method of FIG. 7 can preferably be implemented in an aggregation node of a radio communication network. However, the method of FIG. 7 can also be implemented in other entities, e.g. in other nodes of the radio communication network.

[0115] FIG. 8 is a flow chart of a further method in accordance with an embodiment of the present invention. The method is implemented for communication between fronthaul nodes, which act as access nodes, and aggregation fronthaul nodes, which act as aggregation nodes.

[0116] In a first step 810, it is determined whether there is a need for spectral multiplexing among fronthaul nodes. If there is a need, the method continues in step 820, where a fronthaul controller requests a measurement of a signal-to-noise ratio of a fronthaul link.

[0117] In step 830, a measurement unit, associated with the aggregation fronthaul node or located in the cloud, makes the measurement. In response to this request, in step 840, the measurement unit sends the measurement results to the fronthaul controller.

[0118] In step 850, the fronthaul controller compares the measurement with a threshold value or a mapping table to select the to-be-used spreading codes.

[0119] In step 860, the fronthaul controller sends the selected spreading codes to one or more fronthaul nodes and the aggregation node fronthaul node. In step 870, the fronthaul nodes and the aggregation fronthaul nodes use the sent spreading codes in their fronthaul link transmission.

[0120] FIG. 9 is a schematic of the basic approach for calculating precoders using upload beacons from N user nodes. FIG. 9 shows the processing steps for a first user node 902a, and an n-th user node 902b.

[0121] The user nodes 902a, 902b send a beacon signal, which is polluted with additive noise (indicated with reference number 904) and then received at an antenna array 906, which comprises M antennas, thus yielding M antenna outputs which are processed at an OFDM demodulator 908 to yield N.sub.c subcarrier signals for each of the M antennas. Subsequently, a channel estimator 910 obtains channel estimates .sub.1 to .sub.N. The precoders are obtained from a Zero-Forcing (ZF) solution using the channel estimates. The channel estimates .sub.m(f.sub.n) .sup.N1 can be obtained using the method illustrated in FIG. 10.

[0122] The antenna outputs can be processed on a central node (such as in CRAN) via a fronthaul connection or the precoder calculation can be done at remote radio units.

[0123] FIG. 10 is a block diagram of a system 1000 comprising an access node 1010 and an aggregation node 1030 that are connected via a fronthaul radio link 1020.

[0124] The access node 1010 comprises an antenna array 1012 with M antennas. The antenna array outputs M antenna output signals, including a first antenna output signal 1013a up to an M-th antenna output signal 1013b. The M antenna output signals are encoded using a spreading unit 1014, which employs M spreading codes. Thus, M coded output signals are obtained, including a first coded output signal 1015a up to an M-th coded output signal 1015b. The coded output signals 1015a, 1015 are summed by a summing unit 1016 to obtain a compressed signal 1018, which is composite signal. The compressed signal 1018 is transmitted over the fronthaul radio link 1020 to the aggregation node 1030.

[0125] The aggregation node 1030 comprises a Despreading and OFDM Demodulator unit 1032, which can be implemented by a processor (not shown in FIG. 10) configured to despread and demodulate the received compressed signal. The Despreading and OFDM Demodulator unit 1032 yields M despread signals, corresponding to the M output signals. Since non-orthogonal or short spreading codes were used, each of the M despread signals can comprise interference from the other signals.

[0126] Each of the M despread signals 1033a, 1033b comprises Nc subcarrier signals, which can also be affected by the interference.

[0127] A multi-user detection unit 1034 is used to remove interference and provide estimated antenna signals 1035a, 1035b.

[0128] The channel can be estimated once the symbols at each subcarrier and for all of the antennas are obtained. This last part can be identical to the procedure illustrated in FIG. 9.

[0129] Next, the performance of the Zero-forcing beamformer is given in terms of array output SINR. The weight vectors are found from channel estimates obtained according to the scheme illustrated in FIG. 9 (no coding) and with the scheme illustrated in FIG. 10 (with coding).

[0130] In the following, we consider a multi-user single-input-multiple-output (MU-SIMO) scenario with M users and a receive antenna array composed of N elements. Each user transmits an OFDM symbol of duration T.sub.s=3.2 s. Each OFDM symbol is comprised of N.sub.c=640 subcarriers with a subcarrier spacing of F.sub.s=312.5 kHz. The overall bandwidth is thus 200 MHz. For channel estimation, the symbols modulating the subcarriers are taken from a Gold sequence of size 1280, and the modulation scheme is QPSK.

[0131] We consider an LOS Urban Micro-Cell environment where the distance between the Tx and Rx is at most 40 meters. The signal received at the antenna array at subcarrier f.sub.n is written as

y(f.sub.n)=H(f.sub.n)x(f.sub.n)+n(f.sub.n),

where f.sub.n=1 . . . N.sub.c. Moreover, the dimensions of the above quantities are y(f.sub.n) .sup.N1 H(f.sub.n) .sup.NM, and x(f.sub.n) .sup.M1. The channel of the mth user is given by the mth-column of matrix H(f.sub.n), and it is denoted by h.sub.m(f.sub.n) .sup.N1. Vector n(f.sub.n) .sup.N1 denotes the Additive White Gaussian Noise (AWGN) and it is taken from N(0, .sub.n.sup.2).

[0132] The array output SINR for the mth user is given by:

[00001]${\mathrm{SINR}}_m=1/N_c.Math.\underset{f_n=1}{\overset{N_c}{.Math.}}.Math.\frac{{.Math.{w\left(f_n\right)}_m^H.Math.h_m\left(f_n\right).Math.}^2}{{w\left(f_n\right)}_m^H.Math.R_{i+n}.Math.{w\left(f_n\right)}_m}$

where w(f.sub.n).sub.m .sup.N1 denotes the beamformer weights (precoders) to the mth-user and R.sub.i+n .sup.N1 denotes the interference-plus-noise covariance matrix:

[00002]$R_{i+n}=\underset{\underset{jm}{j=1}}{\overset{M}{.Math.}}.Math.h_j\left(f_n\right).Math.{h_j\left(f_n\right)}^H+{}_n^2.Math.I.$

The precoders are obtained from a Zero-Forcing (ZF) solution using channel estimates. The channel estimate .sub.m(f.sub.n) .sup.N1 is obtained by least-squares estimation (LSE) using either y(f.sub.n), or the compression method proposed next.

[0133] The proposed solution makes use of multi-carrier direct-sequence spread-spectrum (MC-DSSS) techniques for multiple-access in wireless communications and multiuser detection.

[0134] Let y.sub.n(t) be the signal at the output of the nth antenna element and c.sub.n(t) the corresponding spreading sequence. The proposed solution consists in code-multiplexing the output of the antenna array with a low-rate code such that the code-multiplexed signal has a smaller bandwidth than transmitting {y.sub.n(t)}n=1.sup.N in disjoint frequency bands. In particular, the code-multiplexed data is given as follows:

[00003]$z\left(t\right)=\underset{n=1}{\overset{N}{.Math.}}.Math.y_n\left(t\right).Math.c_n\left(t\right).$

The spreading sequence is given by c.sub.n(t)=.sub.l.sup.L=1 c.sub.n.sup.l p.sub.T.sub.c(tlT.sub.c), where T.sub.c denotes the chip-period. The chip-period is related to the OFDM symbol duration by T.sub.c=T.sub.s/L, where L denotes the code-length. Moreover, {c.sub.n.sup.l}.sub.l=1.sup.L denote the chips of the antenna specific spreading sequence and p.sub.T.sub.c(t) denotes the rectangular pulse of period T.sub.c. This type of multiple access scheme is referred to as multi-carrier direct-sequence spread-spectrum technique.

[0135] Once z(t) is received, the modulating symbols are obtained by first de-spreading and taking a DFT, and then employing a multiuser detection technique. An example with a zero-forcing linear multiuser detection method is given as follows:

[00004]${\tilde{s}}_n\left(n_c\right)=z\left(t\right).Math.c_n\left(t\right).Math.e^{j.Math..Math.2.Math..Math..Math.f_{n_c}.Math.t}$$\hat{s}=R_c^{-1}.Math.\tilde{s},$

where {tilde over (s)}=[{tilde over (s)}.sub.1 . . . {tilde over (s)}.sub.N].sup.T .sup.NN.sup.c.sub.1, {tilde over (s)}.sub.n=[{tilde over (s)}.sub.n(1) . . . {tilde over (s)}.sub.n(N.sub.c)].sup.T, and {tilde over (s)} .sup.NN.sup.c.sup.1. Matrix R.sub.c .sup.NN.sup.c.sup.NN.sup.c denotes the code correlation, and it is a scaled diagonal if

[00005]$c_n\left(t\right).Math.e^{j.Math..Math.2.Math..Math..Math.f_{n_c}.Math.t}$

is orthogonal among different codes and subcarriers. In order to minimize the bandwidth in the fronthaul we employ low-rate codes, leading to a code correlation and a non-diagonal matrix R.sub.c. Decreasing the rate of the code leads to an increase of the condition number of the correlation matrix, and the multiuser detection problem becomes ill-conditioned.

[0136] It is important to note that the employed code-rate scales with the product between the number of antennas and the number of subcarriers. This is because the code-spreading operating introduces inter-carrier interference, and the code needs to ensure orthogonality among different subcarriers. For example, a system with 8 antennas and 640 subcarriers needs a code-length of 5120 (640*8) in order to have an orthogonality between all of the symbols, i.e. the correlation matrix is diagonal. With such a code-length there are no savings in bandwidth compared to using no spreading at all. In fact, using a code-length of size 5120 leads to a bandwidth of 1.8 GHz which is even larger than that of using no spreading (1.6 GHz). Such a result follows by noting that code-spreading a multi-carrier signal results in spreading each of the subcarriers. It then follows that the bandwidth of each subcarrier increases from 312.5 kHz to 1.6 GHz (312. kHz*5120). The overall bandwidth of the code-spread signal is 1.8 GHz since the bandwidth of the multicarrier signal is 200 MHz (1.6 GHz+200 MHz).

[0137] FIG. 11 is a diagram illustrating the performance of Zero-forcing beamforming, in terms of array output SINR, when the processing is done at the RRU or at the CRAN. When the processing is done at the CRAN, the array output signals are code-multiplexed using Walsh-Hadamard and M-Sequence codes. When there is no coding, the bandwidth requirement in the fronthaul is 1.6 GHz while using a code-multiplexed approach the bandwidth requirement is 640 MHz. Hence, the code-multiplexed approach provides a 60% gain in terms of bandwidth. In this numerical result we assume 8 users, and an antenna array of 8 elements.

[0138] FIG. 12 is a diagram illustrating the performance of the Zero-forcing beamforming in terms of array output SINR, when the processing is done at the RRU or at the CRAN. When the processing is done at the CRAN, the array output signals are code-multiplexed using Walsh-Hadamard and M-Sequence codes. When there is no coding, the bandwidth requirement in the fronthaul is 1.6 GHz while using a code-multiplexed approach the bandwidth requirement is 640 MHz. Hence, the code-multiplexed approach provides a 60% gain in terms of bandwidth. In this numerical result we assume 8 users, and an antenna array of 8 elements.

[0139] As can be seen from FIGS. 11 and 12, when the SNR at the fronthaul is high enough, the interference caused by spreading with non-orthogonal codes can be kept low while the impact on the demodulation quality is negligible.

[0140] The reconfiguration of the spreading codes is then based on a measured quality of the fronthaul link. Signalling including the to-be-used spreading code shall be sent from one resource management node, for example a fronthaul controller. In at least one embodiment, the aggregation node can act as such fronthaul controller.

[0141] The foregoing descriptions are only implementation manners of the present invention, the protection of the scope of the present invention is not limited to this. Any variations or replacements can be easily made through person skilled in the art. Therefore, the protection scope of the present invention should be subject to the protection scope of the attached claims.