WO2018000430A1

WO2018000430A1 - Resource multiplexing and allocation schemes for uplink beam reference signal in massive mimo system

Info

Publication number: WO2018000430A1
Application number: PCT/CN2016/088185
Authority: WO
Inventors: Yi Zhang; Deshan Miao; Yuantao Zhang
Original assignee: Nokia Technologies Oy; Nokia Technologies (Beijing) Co., Ltd.
Priority date: 2016-07-01
Filing date: 2016-07-01
Publication date: 2018-01-04

Abstract

An embodiment of the invention provides a method including receiving, by a base station, capability information for at least one user equipment; determining a number and resource locations of candidate resource units in a cell specific resource set for the at least one user equipment based at least on the capability information; selecting one of the candidate resource units in the cell specific resource set and allocating resources corresponding to the selected resource unit for transmission of an uplink beam reference signal (U-BRS); and transmitting, to the at least one user equipment, an indication indicating at least one of: the selected resource unit and one of a plurality of regions in the cell specific resource set corresponding to the selected resource unit.

Description

RESOURCE MULTIPLEXING AND ALLOCATION SCHEMES FOR UPLINK BEAM REFERENCE SIGNAL IN MASSIVE MIMO SYSTEM

TECHNICAL FIELD

This invention relates generally to wireless systems and， more specifically， relates to massive MIMO wireless systems.

BACKGROUND

This section is intended to provide a background or context to the invention disclosed below. The description herein may include concepts that could be pursued， but are not necessarily ones that have been previously conceived， implemented or described. Therefore， unless otherwise explicitly indicated herein， what is described in this section is not prior art to the description in this application and is not admitted to be prior art by inclusion in this section. Abbreviations that may be found in the specification and/or the drawing figures are defined below， after the main part of the detailed description section.

Typically， LTE systems allow for multiple beams to be transmitted at the base station’s side with an active antenna system (AAS) . Based on beamformed downlink reference signal， e.g. beamformed CSI-RS， a UE can make beam-specific measurement and feed back to the network the UE’s preferred beam index. At the UE’s side， a small number of antennas are used which are subject to size restriction. Therefore， uplink beamforming techniques have generally not been considered in LTE systems. For uplink， Sounding Reference Signals (SRS) are used for obtaining uplink channel state information and maintaining uplink synchronization. The SRS is transmitted in the last OFDM symbol in one subframe， including periodic and aperiodic SRS. The time frequency resources for SRS transmission are configured by high layer signalling. For different users， SRS can be multiplexed by cyclic shifting with CDM and comb with FDM.

Future wireless systems， including 5^th Generation (5G) mobile wireless networks， will be characterized by a greater number of antennas， finer beamforming， and higher antenna gain. These future systems intend to use radio spectrum in higher frequency bands on the order of GHz or more. One current area of discussion for future wireless systems is beamforming at the user equipment (UE) . Uplink beamforming has great potential to improve the link budget in future wireless systems which use higher frequency bands (e.g. 6GHz or higher) .

The following references provide some relevant background information： [1 ]

LTE -The UMTS Long Term Evolution： From Theory to Practice. Ed. Stefania Sesia， Issam Toufik and Matthew Baker. 2nd. John Wiley &Sons Ltd.， 2011. Chapters 11， 29； [2] J. Nsenga， et. al.， “Joint transmit and receive analog beamforming in 60GHz MIMO multipath channels” ， in IEEE Proc. ICC， Jun. 2009； [3] Ahmed Alkhateeb， et. al.， ” Channel estimation and hybrid precoding for millimeter wave cellular system” ， in IEEE Journal of Selected Topics in Signal Processing， vol. 8， no. 5， pp. 831-846， Oct. 2014； and [4] 3GPP TS 36.213 v13.1.1 (2016-03) E-UTRA Physical layer procedures， section 5.

BRIEF SUMMARY

This section is intended to include examples and is not intended to be limiting.

In accordance with one aspect， a method includes： receiving， by a base station， capability information for at least one user equipment； determining a number and resource locations of candidate resource units in a cell specific resource set for the at least one user equipment based at least on the capability information； selecting one of the candidate resource units in the cell specific resource set and allocating resources corresponding to the selected resource unit for transmission of an uplink beam reference signal (U-BRS) ； and transmitting， to the at least one user equipment， an indication indicating at least one of： the selected resource unit and one of a plurality of regions in the cell specific resource set corresponding to the selected resource unit.

According to another aspect， an apparatus includes： at least one processor； and at least one non-transitory memory including computer program code， the at least one memory and the computer program code configured to， with the at least one processor， cause the apparatus at least to： in response to reception of capability information for at least one user equipment； determine， by the apparatus， a number and resource locations of candidate resource units in a cell specific resource set for the at least one user equipment based at least on the capability information； select one of the candidate resource units in the cell specific resource set and allocate resources corresponding to the selected resource unit for transmission of an uplink beam reference signal (U-BRS) ； and transmit， to the at least one user equipment， an indication indicating at least one of： the selected resource unit and one of a plurality of regions in the cell specific resource set corresponding to the selected resource unit.

According to another aspect， a method includes transmitting capability information of a user equipment to a base station； receiving a candidate beam number and a cell specific resource set in response to transmitting the capability information； deriving a number and resource locations of candidate resource units in a cell specific resource set based at least on the capability information； receiving， from the base station， an indication indicating at least one of： a resource unit selected from the candidate resource units， and one of a plurality of regions in the cell specific resource set corresponding to a resource unit selected from the candidate resource units， and determining， based on the indication， resources for transmitting an uplink beam reference signal (U-BRS) ， wherein the resources correspond to the selected resource unit.

Further aspects include computer program comprising program code for executing the methods describe above.

BRIEF DESCRIPTION OF THE DRAWINGS

In the attached Drawing Figures：

FIG. 1 is a block diagram of one possible and non-limiting exemplary system in which the exemplary embodiments may be practiced；

FIGS. 2A-2F are examples of U-BRS transmissions corresponding to resource unit patterns for UEs with different candidate beam numbers and TXRU numbers according to exemplary embodiments；

FIG. 3 illustrates example candidate resource units in resource sets according to exemplary embodiments；

FIG. 4 illustrates an example of multiplexing for three user equipments using the candidate resource unit patterns of FIG. 3 according to exemplary embodiments；

FIGS. 5A-5B illustrate an example of a partial explicit resource allocation scheme using Dynamic Region Indication (DRI) signaling according to exemplary embodiments； and

FIGS. 6 and 7 are logic flow diagrams for resource multiplexing and allocation for uplink beam reference signal in m-MIMO， and illustrate the operation of an exemplary method， a result of execution of computer program instructions embodied on a computer readable memory， functions performed by logic implemented in hardware， and/or interconnected means for performing functions in accordance with exemplary embodiments.

DETAILED DESCRIPTION OF THE DRAWINGS

The word “exemplary” is used herein to mean “serving as an example， instance， or illustration. ” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments. All of the embodiments described in this Detailed Description are exemplary embodiments provided to enable persons skilled in the art to make or use the invention and not to limit the scope of the invention which is defined by the claims.

The exemplary embodiments herein describe techniques for resource multiplexing and allocation schemes for Uplink Beam Reference Signal (U-BRS) in an m-MIMO System. Additional description of these techniques is presented after a system into which the exemplary embodiments may be used is described.

Turning to FIG. 1， this figure shows a block diagram of one possible and non-limiting exemplary system in which the exemplary embodiments may be practiced. In FIG. 1， a user equipment (UE) 110 is in wireless communication with a wireless network 100. A UE is a wireless， typically mobile device that can access a wireless network. The UE 110 includes one or more processors 120， one or more memories 125， and one or more transceivers 130 interconnected through one or more buses 127. Each of the one or more transceivers 130 includes a receiver， Rx， 132 and a transmitter， Tx， 133. The one or more buses 127 may be address， data， or control buses， and may include any interconnection mechanism， such as a series of lines on a motherboard or integrated circuit， fiber optics or other optical communication equipment， and the like. The one or more transceivers 130 are connected to one or more antennas 128. The one or more memories 125 include computer program code 123. The UE 110 includes a U-BRS Configuration Module， comprising one of or both parts 140-1 and/or 140-2， which may be implemented in a number of ways. The U-BRS Configuration Module may be implemented in hardware as U-BRS Configuration Module 140-1， such as being implemented as part of the one or more processors 120. The U-BRS Configuration Module 140-1 may be implemented also as an integrated circuit or through other hardware such as a programmable gate array. In another example， the U-BRS Configuration Module may be implemented as U-BRS Configuration Module 140-2， which is implemented as computer program code 123 and is executed by the one or more processors 120. For instance， the one or more memories 125 and the computer program code 123 may be configured to， with the one or more processors 120， cause the user equipment 110 to perform one or more of the operations as described herein. The UE 110 communicates with eNB 170 via a wireless link 111.

The eNB (evolved NodeB) 170 is a base station (e.g.， for LTE， long term evolution) that provides access by wireless devices such as the UE 110 to the wireless network 100. The eNB 170 includes one or more processors 152， one or more memories 155， one or more network interfaces (N/W I/F (s) ) 161， and one or more transceivers 160 interconnected through one or more buses 157. Each of the one or more transceivers 160 includes a receiver， Rx， 162 and a transmitter， Tx， 163. The one or more transceivers 160 are connected to one or more antennas 158. The one or more memories 155 include computer program code 153. The eNB 170 includes a U-BRS Configuration Module， comprising one of or both parts 150-1 and/or 150-2， which may be implemented in a number of ways. The U-BRS Configuration Module may be implemented in hardware as U-BRS Configuration Module 150-1， such as being implemented as part of the one or more processors 152. The U-BRS Configuration Module 150-1 may be implemented also as an integrated circuit or through other hardware such as a programmable gate array. In another example， the U-BRS Configuration Module may be implemented as U-BRS Configuration Module 150-2， which is implemented as computer program code 153 and is executed by the one or more processors 152. For instance， the one or more memories 155 and the computer program code 153 are configured to， with the one or more processors 152， cause the eNB 170 to perform one or more of the operations as described herein. The one or more network interfaces 161 communicate over a network such as via the links 176 and 131. Two or more eNBs 170 communicate using， e.g.， link 176. The link 176 may be wired or wireless or both and may implement， e.g.， an X2 interface.

The one or more buses 157 may be address， data， or control buses， and may include any interconnection mechanism， such as a series of lines on a motherboard or integrated circuit， fiber optics or other optical communication equipment， wireless channels， and the like. For example， the one or more transceivers 160 may be implemented as a remote radio head (RRH) 195， with the other elements of the eNB 170 being physically in a different location from the RRH， and the one or more buses 157 could be implemented in part as fiber optic cable to connect the other elements of the eNB 170 to the RRH 195.

The wireless network 100 may include a network control element (NCE) 190 that may include MME (Mobility Management Entity) /SGW (Serving Gateway) functionality， and which provides connectivity with a further network， such as a telephone network and/or a data communications network (e.g.， the Internet) . The eNB 170 is coupled via a link 131 to the NCE 190. The link 131 maybe implemented as， e.g.， an S1 interface. The NCE 190 includes one or more processors 175， one or more memories 171， and one or more network interfaces (N/W I/F (s) ) 180， interconnected through one or more buses 185. The one or more memories 171 include computer program code 173. The one or more memories 171 and the computer program code 173 are configured to， with the one or more processors 175， cause the NCE 190 to perform one or more operations.

The wireless network 100 may implement network virtualization， which is the process of combining hardware and software network resources and network functionality into a single， software-based administrative entity， a virtual network. Network virtualization involves platform virtualization， often combined with resource virtualization. Network virtualization is categorized as either external， combining many networks， or parts of networks， into a virtual unit， or internal， providing network-like functionality to software containers on a single system. Note that the virtualized entities that result from the network virtualization are still implemented， at some level， using hardware such as processors 152 or 175 and memories 155 and 171， and also such virtualized entities create technical effects.

The computer readable memories 125， 155， and 171 may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology， such as semiconductor based memory devices， flash memory， magnetic memory devices and systems， optical memory devices and systems， fixed memory and removable memory. The computer readable memories 125， 155， and 171 may be means for performing storage functions. The processors 120， 152， and 175 may be of any type suitable to the local technical environment， and may include one or more of general purpose computers， special purpose computers， microprocessors， digital signal processors (DSPs) and processors based on a multi-core processor architecture， as non-limiting examples. The processors 120， 152， and 175 may be means for performing functions， such as controlling the UE 110， eNB 170， and other functions as described herein.

In general， the various embodiments of the user equipment 110 can include， but are not limited to， cellular telephones such as smart phones， tablets， personal digital assistants (PDAs) having wireless communication capabilities， portable computers having wireless communication capabilities， image capture devices such as digital cameras having wireless communication capabilities， gaming devices having wireless communication capabilities， music storage and playback appliances having wireless communication capabilities， Internet appliances permitting wireless Internet access and browsing， tablets with wireless communication capabilities， as well as portable units or terminals that incorporate combinations of such functions.

Having thus introduced one suitable but non-limiting technical context for the practice of the exemplary embodiments of this invention， the exemplary embodiments will now be described with greater specificity.

Future wireless systems， such as 5G wireless systems for example， introduce an Uplink Beam Reference Signal (U-BRS) . U-BRS allows for accurate and instant measurements by an eNB for UL beam selection. Beamformed U-BRS will be transmitted on the resources that are either predefined or indicated by the eNB. The resources may be located in multiple OFDM symbols to support multiple beam measurements with beam switching. The U-BRS resources for different UEs are multiplexed for uplink transmission. However， different UEs may require different amount of resources and different resource unit patterns for at least the following reasons： the number of candidate analog beams are configurable； there are different number of TXRU in user equipments； and there are different requirements of user equipments for link budget.

1. Configurable candidate analog beam number

Analog beams are generated by TXRU， and not by digital precoding for example. For high frequency bands， hybrid beamforming is used and provides a good tradeoff between performance and realization complexity. Hybrid beamforming includes both analog and digital beamforming. For example， there can be 8/4/2/1 analog beams for 4TXRU. More analog beams means more accurate beaming in the analog domain. However， it will cost more complexity for beam selection/tracking/management. If there are fewer users in a cell， finer analog beams can be used to achieve better performance. In general， a larger number of analog beams may generate finer beams and achieve larger beamforming gain. However， the larger number of analog beams also brings problems relating to robustness， high measurement latency， etc. The number of candidate analog beams at UE’s side can be determined based on performance/delay requirements， UE hardware capability and application scenario. When the number of candidate beams is configurable， the amount of U-BRS resources may be different for UEs with a different number ofuplink beams.

2. Number of TXRUs

In a real system， it is difficult to make beam switching from a specific TXRU occur within one OFDM symbol on account of realization issues. Analog beamforming is made with assumption of wideband. Thus， the maximum scanned beam number in one OFDM symbol is limited by TXRU number. When the TXRU number is different for UEs with variable hardware capability， the U-BRS resource unit pattern for UEs is different.

3. Link Budget Requirements

For power limited or coverage limited UEs， enhanced technology is required， such as repetition. In this case， multiple resources， in frequency or time domain， are required for U-BRS transmission. Thus， the U-BRS resource unit pattern can be different for UEs with special link budget requirements.

Referring now to FIGS. 2A-2F， these figure show examples of U-BRS transmissions corresponding to resource unit patterns for UEs with different candidate beam numbers and TXRU numbers according to exemplary embodiments. FIGS. 2A-2C illustrate examples of U-BRS transmissions for UEs having 4 transceiver unit (TRXUs) with 16， 8， and 4 candidate beams， respectively. FIGS. 2D-2F illustrates examples of U-BRS transmissions for UEs having 2 TRXUs for 8， 4， and 2 candidate beams， respectively. In these examples， the resource elements within 4PRB and 4 OFDM symbols are used for U-BRS transmission. These examples are not limiting， and UEs with a different number of TXRU or a different number of resources may also be used.

It can be seen from FIGS. 2A-2F that additional resources are required for U-BRS transmissions when a UE has more candidate beams. To account for UEs having different resource requirements， the network (e.g. the eNB) can flexibly configure a common resource set for U-BRS transmission for multiplexed UEs. It also can be seen that two UEs may have different resource unit patterns for U-BRS transmission even when the two UEs have an equal number of candidate beams. For example， the resource patterns shown in FIG. 2B and FIG. 2D each correspond to a UE having 8 candidate beams， however， a different pattern is used based on the number of TXRUs of the user equipment.

To reduce the measurement delay， multiple beams may be scanned in one OFDM symbol by multiple TXRUs. In FIGS. 2A-C four beams are scanned in one OFDM symbol for UEs having four TXRUs， and in FIGS. 2D-2F two beams are scanned in one OFDM symbol for UEs with two TXRUs. For multiple beam scanning in one OFDM symbol， the FDM scheme in PRB level may be used， or alternatively， a CDM scheme with orthogonal cover code (OCC) in the PRB level may be used. If repetition is used to meet the requirement of link budget for some UEs， the resource allocation pattern can be repetition in frequency or time domain based on the basic resource unit pattern.

From the perspective of the network (e.g. an eNB) ， one cell-specific resource set is used for a U-BRS transmission. To guarantee the measurement accuracy of U-BRS， it is typically not desirable to have U-BRS and uplink data from the same or different UEs on the same time frequency resource. The UE performs rate matching for uplink data transmission resources based on this cell-specific resource set. Embodiments herein account for the different amount of resources and resource unit patterns for different UEs by providing optimized U-BRS multiplexing schemes.

Referring now to FIG. 3， this figure illustrates different example candidate resource unit patterns for U-BRS transmission in an example resource set. Each candidate resource unit pattern comprises candidate resource units. A candidate resource unit is the basic unit for the multiplexing and allocation schemes described herein. A candidate resource unit is determined based on UE specific parameters， such as candidate beam number， TXRU number or repetition number. The number and location of candidate resource units for a particular UE can be derived based on the configured resource set and resource unit pattern. In the non-limiting examples shown in FIG. 3， the different candidate resource unit patterns are shown with respect to a resource set having resource elements in 4 PRBs with 4 OFDM symbols. The number and location of the resource candidate units for candidate resource unit patterns 300-316 are outlined in bold and numbered in FIG. 3. In particular， FIG. 3 shows the following candidate resource unit patterns：

· For UEs supporting 4 TXRUs， there are 2 candidate resource units if 8 candidate beams are configured as shown by resource unit pattern 302； and 4 candidate resource units if 4 candidate beams are configured as shown by resource unit pattern 304；

· For UEs supporting 2 TXRUs， there are 2， 4， and 8 candidate resource units if 8， 4， and 2 candidate beams are configured， respectively， as shown by

resource unit patterns

306， 308， and 310； and

· For UEs supporting 1 TXRU， there are 4， 8， and 16 candidate resource units if 4， 2， 1 candidate beams are configured， respectively， as shown by

resource unit patterns

312， 314， 316.

It can be seen that different candidate resource unit patterns are provided for UEs having a different number of TXRUs but the same number of candidate beams. For example， candidate

resource unit patterns

302 and 306， each have the same number of candidate resource units (i.e. 2) ， but the location of the candidate resource units are different.

Referring also to FIG. 4， an example is provided showing how multiplexing efficiency can be improved with suitable selection of candidate resource units. In FIG. 4， UE1 has 4 TXRUs and 8 candidate beams and UE2 and UE3 each have 2 TXRUs and 4 candidate beams. Accordingly， the candidate resource unit pattern 302 is selected for UE1 and the candidate resource unit pattern 308 is selected for UE2 and UE3. The three UEs are multiplexed by using resource unit 1 (from resource unit pattern 302) and

resource units

3， 4 from resource unit pattern 308. This results in an optimized resource set 402 for U-BRS transmissions.

According to exemplary embodiments， implicit and explicit resource allocation schemes are provided that exploit the flexibility of candidate resource units to reduce collision of resource allocation and equalize interference between multiplexed users. In particular， implicit resource allocation may be used to randomize U-BRS resource selection and reduce collisions， and downlink dynamic signaling may be used to adjust resource allocation and to further improve multiplexing efficiency.

Implicit U-BRS Resource Allocation Scheme

An implicit U-BRS resource allocation scheme may be used with periodic transmission of U-BRS， for example. For an implicit U-BRS resource allocation scheme， a resource unit is randomly selected from all the candidate resource units. Randomly selecting the resource unit reduces the collision probability of U-BSR transmission between different UEs. The resource unit may be randomly selected using different randomization methods， such as by using a modulo operation for example. More specifically， the resource unit can be selected by modulo operation between one UE specific parameter， e.g. UE-ID (C-RNTI) ， and the number of candidate resource units， i.e. n_i ＝ n _C-RNTI mod m_candidate. If inter-cell interference is also considered for randomization and equalization， the cell-ID may be included in modulo operation. For example， n_i ＝ (n _C-RNTI + n_Cell-ID) mod m_candidate. Both the UE and BS may have knowledge of the same information of UE’s UE-ID， the candidate resource unit number， and the resource unit selection principle， and therefore there is no ambiguity of the U-BRS resource allocation between the UE and eNB side. This scheme requires no additional signaling； however， it does not guarantee elimination of collisions for the resource allocation.

Partial Explicit U-BRS Resource Allocation Scheme

In some embodiments， a partial explicit U-BRS resource allocation scheme may be used with aperiodic transmission of U-BRS. Due to battery energy consumption， it is generally undesirable to transmit U-BRS frequently. Thus， UEs may be triggered for the U-BRS transmission for beam selection/tracking. Triggering UEs allows for dynamic change of UEs with U-BRS transmission even in one subframe. Thus， the resource unit allocation may be dynamically adjusted according to actual multiplexed UEs. Additionally， the above random resource allocation scheme can only eliminate the collision with a probability. Exemplary embodiments provide an improved scheme to further eliminate the collision probability and improve multiplexing efficiency with importing the dynamic signaling to adjust the selected resource unit.

According to exemplary embodiments a dynamic region indication (DRI) is used to balance the signaling overhead and multiplexing efficiency. For example， if signaling is used to directly indicate the selected resource unit for UEs with a large number of candidate resource units then the signaling overhead may be quite large. Exemplary embodiments use a DRI indication， which may comprise 1 or 2 bits for example. In detail， for UEs with a small number of candidate resource units， DRI can indicate a specific selected resource unit for the U-BRS； whereas for UEs with large number of candidate resource units the DRI can indicate a region corresponding to the selected resource unit. The UE may determine the resource unit in the region of the selected resource units based on the randomization scheme described above， e.g. a modulo operation scheme.

Referring now to FIGS. 5A and 5B， these figures provide an example of a partial explicit allocation scheme where two DRI bits are used to indicate resources for transmission of U-BRS. In the example shown in FIG. 5A， a candidate resource unit pattern 502 corresponds to a user equipment， UE1 having 2 TXRUs and four uplink beams. The candidate resource unit pattern 502 is determined based on the TXRUs and the number of uplink beams， and accordingly has four candidate resource units. A selected resource unit from among the candidate resource units for UE1 is indicated to UE1 based on two DRI bits as shown at 504. In this example， the selected resource unit is indicated to UE1 as follows： candidate resource unit 1 is indicated when the two bits are set as ‘00’ ； candidate resource unit 2 is indicated when the two bits are set as ‘01’ ； candidate resource unit 3 is indicated when the two bits are set as ‘10’ ； and candidate resource unit 4 is indicated when the two bits are set as ‘11’ . Those skilled in the art will appreciate that two bit DRI signaling may be used to indicate a selected resource unit for candidate resource unit patterns having fewer than four candidate resource units.

Referring now to FIG. 5B， a second resource unit pattern 506 having 8 candidate resource units corresponds to a second user equipment UE2. A selected resource unit from among the 8 candidate resource units cannot be directly indicated to UE2 using the two bit DRI. Instead， the two-bit DRI signaling firstly indicates a region of candidate resource units and then a candidate resource unit is selected， e.g.， using a modulo operation from among candidate resource units within the indicated region. In this example， a four regions are shown (Region 1， Region 2， Region 3， Region 4) ， and the DRI bit signally indicates that Region 1 the selected resource unit for the U-BRS transmission is in Region 1. At 508， a modulo operation is performed to determine the resource unit to be used for the transmission.

The number of regions may be related to dynamic signaling size. For example， there may be 2/3/4 regions. According to some embodiments， the location of regions is implicitly determined by a predefined rule， e.g.， the predefined rule may be specified in a relevant standard. In particular， each region may have similar size. The total resources may be arranged firstly in frequency domain， then in time domain， i.e. OFDM symbol. Then， the resources are divided nearly uniformly for each group. In other embodiments， the group results can be signaled via RRC， e.g.， the resource unit index in each group is indicated by RRC signaling. In these embodiments， the grouping scheme may be flexibly decided by the eNB.

Table 1 below provides one example of the DRI bits that may be used to indicate the four regions shown in FIG. 5B. In some embodiments， 1-bit dynamic signaling is used， and therefore only the first two lines of Table 1 are applicable.

Table 1： Example values for U-BRS Dynamic Region Indication Bits

In these examples， U-BRS transmission is implicitly triggered， which means that when UE receives DRI signaling， the UE will transmit U-BRS in the allocated resource unit. Otherwise， the UE will not transmit U-BRS. In other examples， triggering signaling can be explicitly designed together with resource allocation signaling.

Table 2 below gives another example of the DRI bits that may be used where one state is used for indication of no U-BRS transmission (e.g. ‘00’ as shown in example Table 2) and other states are used for dynamic region indication. Thus according to Table 2， the DRI signaling may be used for dynamic region indication and triggering.

Table 2： Example values for U-BRS Dynamic Region Indication Bits

According to an exemplary embodiment， From the perspective of the eNB， eNB sends signaling to indicate the U-BRS transmit resource. In particular， the eNB obtains the TXRU numbers of each of a plurality of UEs through capability reporting signaling from the UEs. The eNB configures the candidate beam number for each of the UEs. Next， the eNB configures a cell specific resource set for U-BRS transmission. The resource set can be configured by high layer signaling or may be predefined. The predefined resource can locate at be located at center several PRBs with multiple OFDM symbols. The eNB may determine the size of a resource set based on measurement accuracy， delay requirement， etc. The size of resource set is related to the candidate beam number， TXRU number and repetition number of UEs in the cell. Next， the eNB determines a resource unit pattern for each of the UEs and derives the number and location of candidate resource units. The resource unit pattern may be implicitly selected from the prefixed pattern by specification or determined by eNB. The resource unit pattern may be determined based on candidate beam number， TXRU number and repetition number. In some exemplary embodiments， the candidate resource unit in the configured resource set can be sorted firstly in frequency domain and then in time domain. The eNB then determines the U-BRS transmission resource and sends dynamic signaling to indicate the selected resource unit， or the region of the selected resource unit if partial explicit resource allocation scheme is used. If the dynamic signaling is not used， then the eNB determines the U-BRS transmission resource according to the implicit allocation scheme and receives the U-BRS at the determined resources. The eNB then receives the U-BRS and makes a related measurement. This measurement may be related to the U-BRS function， for example， beam tracking/selection/management. In this case， the related measurement can be an RSRP measurement. It may include information for the signal strength for the measured beam. The eNB may manage the related beam by the RSRP measurement result.

In another exemplary embodiment， an apparatus， such as a UE for example， derives a U-BRS transmission resource and transmits a U-BRS. For example， the UE may report the TXRU number by capability signaling. This capability signaling is reported when the UE attaches/connects to a eNB. Its function is similar to， e.g.， “UE Tx antenna port” in LTE system which is in digital domain. The capability signaling includes basic information when UE attaches/connects to the network. The capability signaling is not periodic and is transmitted by RRC signaling by UE-EUTRA-Capability. The UE receives the configured candidate beam number and cell specific resource set for transmission of the U-BRS. In some embodiments， the repetition number may also be indicated by dynamic signaling or high layer signaling if repetition technique is used to improve coverage. The UE derives the resource unit pattern and candidate resource units corresponding to the resource unit pattern and candidate resource units configured by the eNB. The UE then receives dynamic region indication signaling and determines the U-BRS transmission resource. For implicit resource allocation scheme， the candidate resource unit is selected by modulo operation between UE-ID， e.g. C-RNTI， and the number of candidate resource units. For partial explicit resource allocation scheme， the candidate resource unit is selected based on the dynamic region indication signaling and modulo operation between UE-ID， e.g. C-RNTI， and number of candidate resource unit in the indicated region. The UE transmits U-BRS for uplink beam for measurement by the eNB.

For U-BRS， it may be transmitted by a Zadoff Chu sequence in a selected resource unit. Then， multiple UEs can be multiplexed by configuring different cyclic shift for transmit sequences. The interference between UEs is not large with assumption of time-frequency synchronization. Thus， the CDM scheme， e.g. different cyclic shift values for different UEs， can be used together with proposed resource allocation schemes to eliminate collision of resource allocation.

FIG. 6 is a logic flow diagram for a resource multiplexing and allocation scheme for U-BRS in a m-MIMO system. This figure further illustrates the operation of an exemplary method， a result of execution of computer program instructions embodied on a computer readable memory， functions performed by logic implemented in hardware， and/or interconnected means for performing functions in accordance with exemplary embodiments. For instance， the U-BRS Configuration module 150-1 and/or 150-2 may include multiples ones of the blocks in FIG. 6， where each included block is an interconnected means for performing the function in the block. The blocks in FIG. 6 are assumed to be performed by a base station such as eNB 170， e.g.， under control of the U-BRS Configuration Module 150-1 and/or 150-2 at least in part.

In one example embodiment， a method may include receiving， by a base station， capability information for at least one user equipment as indicated by block 600； determining a number and resource locations of candidate resource units in a cell specific resource set for the at least one user equipment based at least on the capability information as indicated by block 602； selecting one of the candidate resource units in the cell specific resource set and allocating resources corresponding to the selected resource unit for transmission of an uplink beam reference signal (U-BRS) by block 604； transmitting， to the at least one user equipment， an indication indicating at least one of： the selected resource unit and one of a plurality of regions in the cell specific resource set corresponding to the selected resource unit as indicated by block 606.

The selecting one of the candidate resource units may include： selecting the candidate resource unit based on a modulo operation between an identity of the at least one user equipment and the number of candidate resource units. The selecting one of the candidate resource units may be based on at least a modulo operation between an identity of the at least one user equipment and a number of candidate resource units in the region corresponding to the selected resource unit in the cell specific resource set. Each of the plurality of regions may include at least two candidate resource units. The cell specific resource set may be at least one of： a predefined cell specific resource set comprising at least one physical resource block with a plurality of orthogonal frequency division multiplexing (OFDM) symbols； and configured by the base station， wherein a size of the resource set may be based on at least one of： measurement accuracy and a delay requirement. The number and resource locations of the candidate resource units may be based on at least a number of transceiver units of the at least one user equipment and a number of uplink candidate beams configured for the at least one user equipment. The number and resource locations of the candidate resource units may be based on a repetition number in response to the at least one user equipment requiring repetition to meet a link budget requirement. The method may further include measuring the uplink candidate beams of the at least user equipment in response to receiving the U-BRS on the selected resource unit. The indication may trigger the user equipment to transmit the U-BRS on the determined resources. The indication may indicate at least whether the at least one user equipment is to transmit the U-BRS. The indication may be two bits. The capability information may include at least the number of transceivers units of the at least one user equipment.

In one example embodiment， an apparatus may include at least one processor； and at least one non-transitory memory including computer program code， the at least one memory and the computer program code configured to， with the at least one processor， cause the apparatus at least to in response to reception of capability information for at least one user equipment； determine， by the apparatus， a number and resource locations of candidate resource units in a cell specific resource set for the at least one user equipment based at least on the capability information； select one of the candidate resource units in the cell specific resource set and allocate resources corresponding to the selected resource unit for transmission of an uplink beam reference signal (U-BRS) ； and transmit， to the at least one user equipment， an indication indicating at least one of： the selected resource unit and one of a plurality of regions in the cell specific resource set corresponding to the selected resource unit.

The selection of one of the candidate resource units may include selection of the candidate resource unit based on a modulo operation between an identity of the at least one user equipment and the number of candidate resource units. The selection of one of the candidate resource units may be based on at least a modulo operation between an identity of the at least one user equipment and a number of candidate resource units in the region corresponding to the selected resource unit in the cell specific resource set. Each of the plurality of regions comprises at least two candidate resource units. The cell specific resource set may be at least one of： a predefined cell specific resource set comprising at least one physical resource block with a plurality of orthogonal frequency division multiplexing (OFDM) symbols； and configured by the base station， wherein a size of the resource set may be based on at least one of： measurement accuracy and a delay requirement. The number and resource locations of the candidate resource units may be based on at least a number of transceiver units of the at least one user equipment and a number of uplink candidate beams configured for the at least one user equipment. The at least one non-transitory memory including computer program code， the at least one memory and the computer program code may be configured to， with the at least one processor， cause the apparatus at least to： measure the uplink candidate beams of the at least user equipment in response to reception of the U-BRS on the selected resource unit. The indication may indicate at least whether the at least one user equipment is to transmit the U-BRS. The indication is two bits.

FIG. 7 is a logic flow diagram for a resource multiplexing and allocation scheme for U-BRS in a m-MIMO system. This figure further illustrates the operation of an exemplary method， a result of execution of computer program instructions embodied on a computer readable memory， functions performed by logic implemented in hardware， and/or interconnected means for performing functions in accordance with exemplary embodiments. For instance， the U-BRS Configuration Module 140-1 and/or 140-2 may include multiples ones of the blocks in FIG. 7， where each included block is an interconnected means for performing the function in the block. The blocks in FIG. 7 are assumed to be performed by the UE 110， e.g.， under control of the U-BRS Configuration Module 140-1 and/or 140-2 at least in part.

In another example embodiment， a method may include： transmitting capability information of a user equipment to a base station as indicated by block 700； receiving a candidate beam number and a cell specific resource set in response to transmitting the capability information as indicated by block 702； deriving a number and resource locations of candidate resource units in a cell specific resource set based at least on the capability information as indicated by block 704； receiving， from the base station， an indication indicating at least one of： a resource unit selected from the candidate resource units， and one of a plurality of regions in the cell specific resource set corresponding to a resource unit selected from the candidate resource units as indicated by block 706； and determining， based on the indication， resources for transmitting an uplink beam reference signal (U-BRS) ， wherein the resources may correspond to the selected resource unit as indicated by block 708.

The determining may include： determining the selected resource unit is based on a modulo operation between an identity of the at least one user equipment and the number of candidate resource units. The determining may include： determining the selected candidate resource unit based on at least a modulo operation between an identity of the at least one user equipment and a number of candidate resource units in the region corresponding to the selected resource unit in the cell specific resource set. Each of the plurality of regions may include at least two candidate resource units. The number and resource locations of the candidate resource units may be based on at least a number of transceiver units of the user equipment and the number of uplink candidate beams configured for the user equipment. The number and resource locations of the candidate resource units may be further based on a repetition number in response to the user equipment requiring repetition to meet a link budget requirement. The method may further include transmitting the U-BRS to the base station on the selected resource unit. The indication may trigger the user equipment to transmit the U-BRS on the determined resources. The indication may indicate at least whether the user equipment is to transmit the U-BRS. The indication may be two bits. The capability information may include at least the number of transceivers units of the at least one user equipment.

In one example embodiment， an apparatus may include at least one processor； and at least one non-transitory memory including computer program code， the at least one memory and the computer program code configured to， with the at least one processor， cause the apparatus at least to： in response to reception of capability information for at least one user equipment； determine， by the apparatus， a number and resource locations of candidate resource units in a cell specific resource set for the at least one user equipment based at least on the capability information； select one of the candidate resource units in the cell specific resource set and allocate resources corresponding to the selected resource unit for transmission of an uplink beam reference signal (U-BRS) ； and transmit， to the at least one user equipment， an indication indicating at least one of： the selected resource unit and one of a plurality of regions in the cell specific resource set corresponding to the selected resource unit.

In another example embodiment， a computer program comprising program code for executing the methods described above. The computer program may be a computer program product comprising a computer-readable medium bearing computer program code embodied therein for use with a computer.

Without in any way limiting the scope， interpretation， or application of the claims appearing below， a technical effect of one or more of the example embodiments disclosed herein is efficient multiplexing and low U-BRS overhead. Another technical effect of one or more of the example embodiments disclosed herein is high measurement accuracy and low interference between candidate beams. Another technical effect of one or more of the example embodiments disclosed herein is low signaling overhead.

Embodiments herein may be implemented in software (executed by one or more processors) ， hardware (e.g.， an application specific integrated circuit) ， or a combination of software and hardware. In an example embodiment， the software (e.g.， application logic， an instruction set) is maintained on any one of various conventional computer-readable media. In the context of this document， a “computer-readable medium” may be any media or means that can contain， store， communicate， propagate or transport the instructions for use by or in connection with an instruction execution system， apparatus， or device， such as a computer， with one example of a computer described and depicted， e.g.， in FIG. 1. A computer-readable medium may comprise a computer-readable storage medium (e.g.， memories 125， 155， 171 or other device) that may be any media or means that can contain， store， and/or transport the instructions for use by or in connection with an instruction execution system， apparatus， or device， such as a computer. A computer-readable storage medium does not comprise propagating signals.

If desired， the different functions discussed herein may be performed in a different order and/or concurrently with each other. Furthermore， if desired， one or more of the above-described functions may be optional or may be combined.

Although various aspects of the invention are set out in the independent claims， other aspects of the invention comprise other combinations of features from the described embodiments and/or the dependent claims with the features of the independent claims， and not solely the combinations explicitly set out in the claims.

It is also noted herein that while the above describes example embodiments of the invention， these descriptions should not be viewed in a limiting sense. Rather， there are several variations and modifications which may be made without departing from the scope of the present invention as defined in the appended claims.

The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows：

eNB (or eNodeB) evolved Node B (e.g.， an LTE base station)

m-MIMO Massive Multiple-Input Multiple Output

BS Base Station

CSI-RS Channel State Information Reference Signal

C-RNTI Cell Radio Network Temporary Identity

CDM Code Division Multiplexing

DCI Dynamic Control Information

DRI Dynamic Region Indication

FDM Frequency Division Multiplexing

I/F interface

LTE long term evolution

MME mobility management entity

NCE network control element

N/W network

PRB Physical Resource Block

RRC Radio resource control

RRH remote radio head

Rx receiver

SGW serving gateway

SRS Sounding Reference Signal

Tx transmitter

TXRU Transceiver Unit

U-BRS Uplink Beam Reference Signal

UE user equipment (e.g.， a wireless， typically mobile device)

Claims

A method comprising：

receiving， by a base station， capability information for at least one user equipment；

determining a number and resource locations of candidate resource units in a cell specific resource set for the at least one user equipment based at least on the capability information；

selecting one of the candidate resource units in the cell specific resource set and allocating resources corresponding to the selected resource unit for transmission of an uplink beam reference signal (U-BRS) ； and

transmitting， to the at least one user equipment， an indication indicating at least one of： the selected resource unit and one of a plurality of regions in the cell specific resource set corresponding to the selected resource unit.
The method of claim 1， wherein selecting one of the candidate resource units comprises：

selecting the candidate resource unit based on a modulo operation between an identity of the at least one user equipment and the number of candidate resource units.
The method of claim 1， wherein selecting one of the candidate resource units is based on at least a modulo operation between an identity of the at least one user equipment and a number of candidate resource units in the region corresponding to the selected resource unit in the cell specific resource set.
The method of claim 3， wherein each of the plurality of regions comprises at least two candidate resource units.
The method of claim 1， wherein the cell specific resource set is at least one of：

a predefined cell specific resource set comprising at least one physical resource block with a plurality of orthogonal frequency division multiplexing (OFDM) symbols； and

configured by the base station， wherein a size of the resource set is based on at least one of： measurement accuracy and a delay requirement.
The method of claim 1， wherein the number and resource locations of the candidate resource units are based on at least a number of transceiver units of the at least one user equipment and a number of uplink candidate beams configured for the at least one user equipment.
The method of claim 6， wherein the number and resource locations of the candidate resource units are further based on a repetition number in response to the at least one user equipment requiring repetition to meet a link budget requirement.
The method of claim 1， further comprising：

measuring the uplink candidate beams of the at least user equipment in response to receiving the U-BRS on the selected resource unit.
The method of claim 1， wherein the indication triggers the user equipment to transmit the U-BRS on the determined resources.
The method of claim 1， wherein the indication indicates at least whether the at least one user equipment is to transmit the U-BRS.
The method of claim 1， wherein the indication is two bits.
The method of claim 1， wherein the capability information comprises at least the number of transceivers units of the at least one user equipment.
An apparatus comprising：

at least one processor； and

at least one non-transitory memory including computer program code， the at least one memory and the computer program code configured to， with the at least one processor， cause the apparatus at least to：

in response to reception of capability information for at least one user equipment； determine， by the apparatus， a number and resource locations of candidate resource units in a cell specific resource set for the at least one user equipment based at least on the capability information；

select one of the candidate resource units in the cell specific resource set and allocate resources corresponding to the selected resource unit for transmission of an uplink beam reference signal (U-BRS) ； and

transmit， to the at least one user equipment， an indication indicating at least one of： the selected resource unit and one of a plurality of regions in the cell specific resource set corresponding to the selected resource unit.
The apparatus of claim 13， wherein the selection of one of the candidate resource units comprises：

selection of the candidate resource unit based on a modulo operation between an identity of the at least one user equipment and the number of candidate resource units.
The apparatus of claim 13， wherein the selection of one of the candidate resource units is based on at least a modulo operation between an identity of the at least one user equipment and a number of candidate resource units in the region corresponding to the selected resource unit in the cell specific resource set.
The apparatus of claim 15， wherein each of the plurality of regions comprises at least two candidate resource units.
The apparatus of claim 13， wherein the cell specific resource set is at least one of：

a predefined cell specific resource set comprising at least one physical resource block with a plurality of orthogonal frequency division multiplexing (OFDM) symbols； and

configured by the base station， wherein a size of the resource set is based on at least one of：measurement accuracy and a delay requirement.
The apparatus of claim 13， wherein the number and resource locations of the candidate resource units are based on at least a number of transceiver units of the at least one user equipment and a number of uplink candidate beams configured for the at least one user equipment.
The apparatus of claim 13， wherein the at least one non-transitory memory including computer program code， the at least one memory and the computer program code are configured to， with the at least one processor， cause the apparatus at least to：

measure the uplink candidate beams of the at least user equipment in response to reception of the U-BRS on the selected resource unit.
The apparatus of claim 13， wherein the indication indicates at least whether the at least one user equipment is to transmit the U-BRS.
The apparatus of claim 13， wherein the indication is two bits.
A method comprising：

transmitting capability information of a user equipment to a base station；

receiving a candidate beam number and a cell specific resource set in response to transmitting the capability information；

deriving a number and resource locations of candidate resource units in a cell specific resource set based at least on the capability information；

receiving， from the base station， an indication indicating at least one of： a resource unit selected from the candidate resource units， and one of a plurality of regions in the cell specific resource set corresponding to a resource unit selected from the candidate resource units， and

determining， based on the indication， resources for transmitting an uplink beam reference signal (U-BRS) ， wherein the resources correspond to the selected resource unit.
The method of claim 22， wherein the determining comprises：

determining the selected resource unit is based on a modulo operation between an identity of the at least one user equipment and the number of candidate resource units.
The method of claim 22， wherein the determining comprises：

determining the selected candidate resource unit based on at least a modulo operation between an identity of the at least one user equipment and a number of candidate resource units in the region corresponding to the selected resource unit in the cell specific resource set.
The method of claim 24， wherein each of the plurality of regions comprises at least two candidate resource units.
The method of claim 22， wherein the number and resource locations of the candidate resource units are based on at least a number of transceiver units of the user equipment and the number ofuplink candidate beams configured for the user equipment.
The method of claim 26， wherein the number and resource locations of the candidate resource units are further based on a repetition number in response to the user equipment requiring repetition to meet a link budget requirement.
The method of claim 22， further comprising transmitting the U-BRS to the base station on the selected resource unit.
The method of claim 22， wherein the indication triggers the user equipment to transmit the U-BRS on the determined resources.
The method of claim 22， wherein the indication indicates at least whether the user equipment is to transmit the U-BRS.
The method of claim 22， wherein the indication is two bits.
The method of claim 22， wherein the capability information comprises at least the number of transceivers units of the at least one user equipment.
An apparatus comprising：

at least one processor； and

at least one non-transitory memory including computer program code， the at least one memory and the computer program code configured to， with the at least one processor， cause the apparatus at least to：

in response to reception of capability information for at least one user equipment； determine， by the apparatus， a number and resource locations of candidate resource units in a cell specific resource set for the at least one user equipment based at least on the capability information；

select one of the candidate resource units in the cell specific resource set and allocate resources corresponding to the selected resource unit for transmission of an uplink beam reference signal (U-BRS) ； and

transmit， to the at least one user equipment， an indication indicating at least one of： the selected resource unit and one of a plurality of regions in the cell specific resource set corresponding to the selected resource unit.
A computer program comprising program code for executing the method according to any of claims 1 to 11 or 22 to 32.
The computer program according to claim 34， wherein the computer program is computer program product comprising a computer-readable medium bearing computer program code embodied therein for use with a computer.