Wireless communication method, base station, and user equipment using a physical random access channel

Abstract

A wireless communication method includes transmitting, from a base station (BS), multiple downlink (DL) signals. The wireless communication method further includes receiving, with a user equipment (UE), two or more DL signals of the multiple DL signals, and notifying, with the BS, the UE of a number of the two or more DL signals. The two or more DL signals are associated with a Physical Random Access Channel (PRACH) resource.

Claims

1. A wireless communication method comprising: transmitting, from a base station (BS), multiple downlink (DL) signals; receiving, with a user equipment (UE), two or more DL signals of the multiple DL signals; notifying, with the BS, the UE of a number of the two or more DL signals assigned to a group; and controlling, with the UE, transmission of a Physical Random Access Channel (PRACH) based on the number of the two or more DL signals of the group, wherein the two or more DL signals are associated with a resource of the PRACH for the group, and wherein the multiple DL signals are Synchronization Signals (SSs).

2. The wireless communication method according to claim 1, further comprising: notifying, with the BS, the UE of a PRACH resource configuration.

3. The wireless communication method according to claim 2, wherein the PRACH resource configuration includes at least one of starting timing, a frequency offset, duration, a PRACH format, a PRACH sequence, and a PRACH sequence set in each of the DL signal groups.

4. The wireless communication method according to claim 3, wherein parameters of the starting timing, the frequency offset, the duration, the PRACH format, the PRACH sequence, and the PRACH sequence set are common values in each of the DL signal groups.

5. The wireless communication method according to claim 1, wherein the multiple DL signals are Broadcast Channels (BCHs) or Demodulation Reference Signals (DM-RSs).

6. The wireless communication method according to claim 1, wherein the number indicates a cardinality of the two or more DL signals.

7. A base station (BS) comprising: a transmitter that transmits, to a user equipment (UE): multiple downlink (DL) signals that comprise two or more DL signals; and a number of the two or more DL signals assigned to a group; and a processor that allocates the two or more DL signals to a Physical Random Access Channel (PRACH) resource for the group, wherein the processor controls a reception of the PRACH transmitted based on the number of the two or more DL signals from the UE for the group, and wherein the multiple DL signals are Synchronization Signals (SSs).

8. The BS according to claim 7, wherein the number indicates a cardinality of the two or more DL signals.

9. A user equipment (UE) comprising: a receiver that receives, from a base station (BS): two or more downlink (DL) signals; and a number of the two or more DL signals assigned to a group; and a processor that controls transmission of a Physical Random Access Channel (PRACH) based on the number of the two or more DL signals of the group, wherein the two or more DL signals are associated with a resource of the PRACH for the group, wherein the two or more DL signals are included in multiple DL signals transmitted from the BS, and wherein the multiple DL signals are Synchronization Signals (SSs).

10. The UE according to claim 9, wherein the number indicates a cardinality of the two or more DL signals.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1A and 1B are diagrams showing PSS/SSS frame structure type 1 (FDD mode) and type 2 (TDD mode), respectively, according to conventional LTE standard.

(2) FIG. 2 is a diagram showing Massive MIMO systems on mmWave bands, according to conventional LTE standard.

(3) FIGS. 3A and 3B are diagrams showing analog beamforming implementation Hybrid beamforming implementation, respectively, according to conventional LTE standard.

(4) FIG. 4 is a diagram showing a configuration of a wireless communication system according to one or more embodiments of the present invention.

(5) FIGS. 5A and 5B are diagrams showing association between DL signal groups and PRACH resources according to one or more embodiments of the present invention.

(6) FIGS. 6A-6C are diagrams showing comparison examples between a method according to one or more embodiments of the present invention and conventional methods.

(7) FIG. 7 is a diagram showing parameters indicated in MIB according to conventional LTE standard.

(8) FIG. 8 is a table diagram showing a DL signal group index associated with a DL SS sequence according to one or more embodiments of the present invention.

(9) FIG. 9 is a diagram showing various PRACH transmission modes according to one or more embodiments of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

(10) Embodiments of the present invention will be described in detail below, with reference to the drawings. In embodiments of the invention, numerous specific details are set forth in order to provide a more thorough understanding of the invention. However, it will be apparent to one of ordinary skill in the art that the invention may be practiced without these specific details. In other instances, well-known features have not been described in detail to avoid obscuring the invention.

(11) FIG. 4 is a wireless communications system 1 according to one or more embodiments of the present invention. The wireless communication system 1 includes user equipments (UEs) 10 (UEs 10#1-#3) and a base station (BS) 20. The wireless communication system 1 may be a New Radio (NR) system. The wireless communication system 1 is not limited to the specific configurations described herein and may be any type of wireless communication system such as an LTE/LTE-Advanced (LTE-A) system.

(12) The BS 20 may communicate uplink (UL) and downlink (DL) signals with the UE 10 in a cell of the BS 20. The DL and UL signals may include control information and user data. The BS 20 may communicate DL and UL signals with the core network 30 through backhaul links 31. The BS 20 may be a gNodeB (gNB). The BS 20 may be referred to as a TRP. For example, when the wireless communications system 1 is a LTE system, the BS may be an evolved NodeB (eNB). As show in FIG. 4, the BS 20 may transmit multiple DL signals using multiple beams to the UE 10. In other words, the BS 20 may transmit multiple DL signals with beam sweeping.

(13) The BS 20 includes antennas, a communication interface to communicate with an adjacent BS 20 (for example, X2 interface), a communication interface to communicate with the core network (for example, S1 interface), and a Central Processing Unit (CPU) such as a processor or a circuit to process transmitted and received signals with the UE 10. Operations of the BS 20 may be implemented by the processor processing or executing data and programs stored in a memory. However, the BS 20 is not limited to the hardware configuration set forth above and may be realized by other appropriate hardware configurations as understood by those of ordinary skill in the art. Numerous gNBs 20 may be disposed so as to cover a broader service area of the wireless communication system 1.

(14) The UE 10 may communicate DL and UL signals that include control information and user data with the BS 20 using Multi Input Multi Output (MIMO) technologies. The UE 10 may be a mobile station, a smartphone, a cellular phone, a tablet, a mobile router, or information processing apparatus having a radio communication function such as a wearable device.

(15) The UE 10 includes a CPU such as a processor, a RAM (Random Access Memory), a flash memory, and a radio communication device to transmit/receive radio signals to/from the BS 20 and the UE 10. For example, operations of the UE 10 described below may be implemented by the CPU processing or executing data and programs stored in a memory. However, the UE 10 is not limited to the hardware configuration set forth above and may be configured with, e.g., a circuit to achieve the processing described below.

(16) One or more embodiments of the present invention configure the UL PRACH resources for a group of Tx beams (or a group of DL signals), where each group of Tx beams share the same Tx analog beamforming. The Rx analog beamforming to receive the UL PRACH on the allocated PRACH resources should be same as the Tx analog beamforming of the DL signal group. In other words, it is the partial association between the Tx beam sweeping of DL signal transmission and Rx beam sweeping of PRACH reception to match the Tx/Rx analog beamforming only. In one or more embodiments of the present invention, the DL signal may be a SS, a Broadcast Channel (BCH), and a Demodulation Reference Signal (DM-RS).

(17) The Tx beam sweeping has to switch every narrow beam generated by analog/digital beamforming in different time slots due to the Tx power limitation and to avoid inter-beam interference. On the other hand, the Rx beam sweeping is different, where the analog beamforming is switched in a Time Division Multiplexing (TDM) mode but multiple digital beamformings/digital filterings could be processed in parallel within each analog beamforming period.

(18) The beam sweeping of DL SS transmission is illustrated as in FIG. 5, where each SS beam is sent at different time slot respectively. The Tx beams divided into several DL signal groups according to the Tx analog beamforming. The UL PRACH resources are configured per DL signal group. Assuming the same Tx/Rx analog beamforming, the PRACH resources for the DL signal group using the Tx analog beamforming should be received by the same Rx analog beamforming at the BS side. The association between a Tx DL signal group and the PRACH resources for the same Rx analog beamforming may be pre-defined or informed to UE through broadcast system information (MIB/SIB). Within the period per Rx analog beamforming, the parallel Rx digital beamforming/digital filtering processing could be transparent to UE. According to hybrid Rx analog/digital beamforming, the best Rx beam detected by BS will be same as the best Tx beam selected by UE.

(19) The PRACH resources for each Rx analog beamforming could be configured independently, including the time offset, duration, frequency offset as well as the PRACH format. This is because each Tx/Rx analog beamforming may have various beam coverage, shape, the number of narrow beams generated by digital beamforming, the channel environment as well as the traffic load and user distribution.

(20) According to one or more embodiments of the present invention, the BS 20 may transmit, to the UE 10, multiple DL signals that are divided into DL signal groups and allocate the PRACH resource in each of the DL signal groups. FIGS. 5A and 5B are diagrams showing association between DL signal groups and PRACH resources according to one or more embodiments of the invention. In an example of FIGS. 5A and 5B, the DL signal may be the SS. In one or more embodiments of the present invention, the DL signal group may be referred to as a beam group.

(21) According to one or more embodiments of the present invention, the BS 20 may notify the UE of a configuration of the DL signal groups. The BS 20 may notify the UE 10 of the configuration using at least one of a MIB and a SIB. The configuration indicates at least one of a number of the multiple DL signals, a number of DL signal groups, a number of the multiple DL signals in each of the DL signal groups, and a DL signal group index that identifies each of the DL signal groups. The multiple DL signals are transmitted using different multiple beams, respectively, and the configuration includes at least one of a beam index that identifies each of the multiple beams and the beam index in each of the DL signal groups.

(22) As shown in FIG. 5A, the BS 20 may transmit multiple SSs a1-a4, b1-b4, and c1-c4. The SSs a1-a4 may be divided into a DL signal group a. The SSs b1-b4 may be divided into a DL signal group b. The SSs c1-c4 may be divided into a DL signal group c. Tx analog beams may be applied to the multiple SSs a1-a4, b1-b4, and c1-c4, respectively. Thus, the PRACH resources are allocated for different DL signal group a, b, and c, respectively.

(23) In other words, there are total 12 beams transmitted in TDM mode and every 4 beams are sharing the same analog beamforming, e.g., {a1, a2, a3, a4} are generated by using Tx analog beam a, {b1, b2, b3, b4} are generated by using Tx analog beam b, and {c1, c2, c3, c4} are generated by using Tx analog beam c. {a1, a2, a3, a4} are regarded as the DL signal group a, {b1, b2, b3, b4} are regarded as the DL signal group b, and {c1, c2, c3, c4} are regarded as the DL signal group c. By detecting/comparing the multi-beam DL SS, the UEs who identify DL SS beam in DL signal group a will be allocated PRACH Resource_a, the Rx analog beamforming a is used for the PRACH reception. The PRACH Resource_b is allocated for the UEs that find the best DL SS beam(s) in DL signal group b and the Rx analog beamforming b is used for the PRACH reception. Similarly, the PRACH Resource_c is allocated for the UEs that find the best DL SS beam(s) in DL signal group c and the Rx analog beamforming c is used for the PRACH reception. In addition, the PRACH resources for different DL signal groups could be configured independently, which will be illustrated in the following embodiments.

(24) The above conventional method 1 defines the one-by-one relationship between every Tx beam and Rx beam. The UE has to wait for the timing of target Rx beam (same as the selected Tx beam) to send its PRACH over the allocated PRACH resources. Therefore, the random access procedure for the TDM-based multi-beam transmission/reception takes longer time, especially in case of larger number of Tx/Rx beams.

(25) The above conventional method 2 does not define the association between Tx and Rx beamforming. The common PRACH resources are allocated without the knowledge of Rx beamforming. The UEs transmit their PRACH over the common resources. It may take longer time for receiver to try different Rx beamforming. However, only if the Rx analog beamforming is same as the Tx analog beamforming, PRACH can be detected. When the Rx analog beamforming is different from that of the detected Tx beam, the PRACH transmission power is wasted because there is marginal contribution to the diversity gain.

(26) Comparing with the above conventional methods, one or more embodiments of the present invention may have the following advantages:

(27) flexible network-controlled configuration of the PRACH resources and transmission modes for each UE aligned with that of Rx Analog BF, considering the beam shape, beam coverage, user distribution;

(28) no waste power on the Rx Analog BF different from the detected Tx Analog BF of the UE-detected Beam; and

(29) achieve PRACH detection combining gain over the duration using the Rx Analog BF same as the Tx Analog BF of the UE-detected Beam.

(30) The comparison between a method according to one or more embodiments of the present invention and conventional methods is illustrated in FIGS. 6A-6C. FIG. 6A is a diagram showing a method of transmission of multiple DL signal that are divided into DL signal groups according to one or more embodiments of the present invention. In FIG. 6A, for example, the UEs 10#1 (UE1), 10#2 (UE2), and 10#3 (UE3) may receive the DL signals a1 (beam a1), b2, and c3, respectively.

(31) In accordance with one or more embodiments of the present invention, a class of methods and apparatuses are disclosed, which allow increasing the network spectral efficiency per unit area in dense antenna/antenna-site network deployments. Methods rely on the combined use of appropriately designed pilot codes or reference signals (RS) for use in the uplink by active (scheduled) user terminals, and mechanisms for fast user detection at each antenna-site by the network. The designed uplink pilots can be used for uplink sounding procedure for channel estimation as well as uplink random access procedure.

First Example

(32) In one or more embodiments of a first example of the present invention, how to indicate the configuration of the PRACH resources for multiple DL signal groups may be described. The signaling may include the configuration of DL signal groups for DL signal transmission (SS, BCH, DM-RS, MIB, and SIB) and the PRACH configuration for different DL signal groups.

(33) The configuration of DL signal groups (beam group) may include, the maximum number of DL signals (beams), the maximum number of DL signal groups, the maximum number of DL signals (beams) per DL signal group, the total number of DL signals (beams), the number of DL signal groups, the number of DL signals (beams) per DL signal group, a beam index (beamIndex), a DL signal group index (groupIndex), and a beam index in DL signal group (beamIndex_groupIndx).

(34) The PRACH configuration field for different DL signal groups may include: rootSequenceIndex[groupIndex] prach_ConfigIndex[groupIndex], which include { prach_format[groupIndex] prach_frameIndex[groupIndex] prach_subframeIndex[groupIndex] prach_trasnmissionMode[groupIndex] prach_duration[groupIndex] } zeroCorrelationZoneConfig[groupIndex] prach_FreqOffset[groupIndex]

(35) In LTE, the parameter “prach_ConfigIndex” in SIB2, defined in 3GPP specification TS36.211-Table 5.7.1-2, determines what type of preamble format should be used and at which system frame and subframe UE can transmit PRACH Preamble. The PRACH format defined in 3GPP specification TS36.211-Table 5.7.1-1 defines the length of PRACH sequences. The parameter “prach-FreqOffset” in SIB2 (together with PRACH format type for TDD) informs the UE and other neighbor cells know about which PRB is available for RACH access. In LTE, the parameters indicated in MIB are shown in FIG. 7. For example, parameters of the starting timing, the frequency offset, the duration, the PRACH format, the PRACH sequence, and the PRACH sequence set may be common values in each of the DL signal groups.

(36) Considering backward compatibility, some parameters in the DL signal group configuration may be indicated in the reserved field of MIB and the parameters or partial parameters of DL signal group configuration and PRACH configuration field for different DL signal groups may be included in the SIB2. Also, some parameters, such as maximum number of beams, maximum number of DL signal groups, max number of beams per group, may be pre-defined to save the signaling overhead. In order to save the signaling overhead, some of the parameters may be implicitly indicated. For example, the DL signal group is identified by the beam-group-specific DL reference signal sequence or a set of DL reference signal sequences, as illustrated in FIG. 8.

Example 2

(37) Regarding the UE behavior for random access, it is possible to define one or several transmission modes for PRACH. In one or more embodiments of a second example of the present invention, the network-controlled UL PRACH transmission mode per DL signal group may be indicated in MIB/SIB2, considering the traffic load, user distribution, channel environment, etc. Various PRACH transmission modes are illustrated in FIG. 9. During the PRACH resources allocated for a DL signal group, the PRACH may use short sequence with repetition, long sequence, random/scheduled hopping in different time slots/symbols, random/scheduled hopping in different resource blocks (RBs) or subcarriers.

(38) Although the disclosure has been described with respect to only a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that various other embodiments may be devised without departing from the scope of the present invention. Accordingly, the scope of the invention should be limited only by the attached claims.