WO2014190547A1

WO2014190547A1 - Dynamic vertical sectorization

Info

Publication number: WO2014190547A1
Application number: PCT/CN2013/076567
Authority: WO
Inventors: Peng Cheng; Chao Wei; Neng Wang; Jilei Hou
Original assignee: Qualcomm Incorporated
Priority date: 2013-05-31
Filing date: 2013-05-31
Publication date: 2014-12-04

Abstract

Vertical sectorization is discussed in which several vertical sectors are dynamically formed based on user equipment (UE) feedback in the elevation domain. For example UEs with similar feedback in the elevation domain may be grouped to form a cluster for which a base station will form a cluster-specific vertical beam. Feedback may be implemented using open-loop schemes, where UEs feedback an index of the best beams observed, or close-loop schemes, where UEs feedback an elevation metric, such as an elevation rank indicator, precoding matrix indicator (PMI), or channel eigen vector. In such aspects, vertical sectors are only formed when necessary and less interference may result between vertical sectors if carefully designing orthogonal sector beams. Moreover, lower overhead and better speed/density performance may be achieved compared against UE-specific elevation beamforming.

Description

DYNAMIC VERTICAL SECTORIZATION

BACKGROUND

Field

[0001] Aspects of the present disclosure relate generally to wireless communication systems, and more particularly, to provide for dynamic vertical sectorization.

Background

[0002] Wireless communication networks are widely deployed to provide various communication services such as voice, video, packet data, messaging, broadcast, and the like. These wireless networks may be multiple-access networks capable of supporting multiple users by sharing the available network resources. Such networks, which are usually multiple access networks, support communications for multiple users by sharing the available network resources. One example of such a network is the Universal Terrestrial Radio Access Network (UTRAN). The UTRAN is the radio access network (RAN) defined as a part of the Universal Mobile Telecommunications System (UMTS), a third generation (3G) mobile phone technology supported by the 3rd Generation Partnership Project (3GPP). Examples of multiple-access network formats include Code Division Multiple Access (CDMA) networks, Time Division Multiple Access (TDMA) networks, Frequency Division Multiple Access (FDMA) networks, Orthogonal FDMA (OFDMA) networks, and Single-Carrier FDMA (SC-FDMA) networks.

[0003] A wireless communication network may include a number of base stations or node Bs that can support communication for a number of user equipments (UEs). A UE may communicate with a base station via downlink and uplink. The downlink (or forward link) refers to the communication link from the base station to the UE, and the uplink (or reverse link) refers to the communication link from the UE to the base station.

[0004] A base station may transmit data and control information on the downlink to a

UE and/or may receive data and control information on the uplink from the UE. On the downlink, a transmission from the base station may encounter interference due to transmissions from neighbor base stations or from other wireless radio frequency (RF) transmitters. On the uplink, a transmission from the UE may encounter interference from uplink transmissions of other UEs communicating with the neighbor base stations or from other wireless RF transmitters. This interference may degrade performance on both the downlink and uplink. [0005] As the demand for mobile broadband access continues to increase, the possibilities of interference and congested networks grows with more UEs accessing the long-range wireless communication networks and more short-range wireless systems being deployed in communities. Research and development continue to advance the UMTS technologies not only to meet the growing demand for mobile broadband access, but to advance and enhance the user experience with mobile communications.

SUMMARY

[0006] In one aspect of the disclosure, a method of wireless communication includes receiving, at a base station, feedback from a plurality of UEs, determining, by the base station, a correlation among the plurality of UEs, configuring, by the base station, one or more UE clusters based on the correlation, wherein each of the one or more UE clusters includes two or more UEs of the plurality having correlation within a predetermined threshold, dynamically configuring, by the base station, a vertical sector for each UE cluster of the one or more UE clusters, and forming, by the base station, an elevation beam corresponding to the vertical sector for each UE cluster of the one or more UE clusters.

[0007] In an additional aspect of the disclosure, an apparatus configured for wireless communication includes means for receiving, at a base station, feedback from a plurality of UEs, means for determining, by the base station, a correlation among the plurality of UEs, means for configuring, by the base station, one or more UE clusters based on the correlation, wherein each of the one or more UE clusters includes two or more UEs of the plurality having correlation within a predetermined threshold, means for dynamically configuring, by the base station, a vertical sector for each UE cluster of the one or more UE clusters, and means for forming, by the base station, an elevation beam corresponding to the vertical sector for each UE cluster of the one or more UE clusters.

[0008] In an additional aspect of the disclosure, a computer program product has a computer-readable medium having program code recorded thereon. This program code includes code to receive, at a base station, feedback from a plurality of UEs, code to determine, by the base station, a correlation among the plurality of UEs, code to configure, by the base station, one or more UE clusters based on the correlation, wherein each of the one or more UE clusters includes two or more UEs of the plurality having correlation within a predetermined threshold, code to dynamically configure, by the base station, a vertical sector for each UE cluster of the one or more UE clusters, and code to form, by the base station, an elevation beam corresponding to the vertical sector for each UE cluster of the one or more UE clusters.

[0009] In an additional aspect of the disclosure, an apparatus includes at least one processor and a memory coupled to the processor. The processor is configured to receive, at a base station, feedback from a plurality of UEs, to determine, by the base station, a correlation among the plurality of UEs, to configure, by the base station, one or more UE clusters based on the correlation, wherein each of the one or more UE clusters includes two or more UEs of the plurality having correlation within a predetermined threshold, to dynamically configure, by the base station, a vertical sector for each UE cluster of the one or more UE clusters, and to form, by the base station, an elevation beam corresponding to the vertical sector for each UE cluster of the one or more UE clusters.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 is a block diagram illustrating an example of a mobile communication system.

[0011] FIG. 2 is a block diagram illustrating a design of a base station/eNB and a UE configured according to one aspect of the present disclosure.

[0012] FIG. 3 is a diagram illustrating an 8x8 antenna array.

[0013] FIG. 4 is a diagram illustrating a wireless network area having two eNBs that provide conventional vertical sectorization coverage.

[0014] FIGs. 5A and 5B are block diagrams illustrating a wireless coverage area serviced by an eNB.

[0015] FIG. 6 is a functional block diagram illustrating example blocks executed to implement one aspect of the present disclosure.

[0016] FIG. 7 is a transmission timeline illustrating a dynamic vertical sectorization procedure configured according to one aspect of the present disclosure.

[0017] FIG. 8 is a block diagram illustrating a coverage area of an eNB configured according to one aspect of the present disclosure.

[0018] FIG. 9A is a functional block diagram illustrating example blocks executed to implement an open-loop elevation feedback scheme according to one aspect of the present disclosure. [0019] FIG. 9B is a diagram illustrating an eNB configured for an open-loop elevation feedback mechanism according to the aspect of the present disclosure disclosed in FIG. 9A.

[0020] FIG. 10 is a functional block diagram illustrating example blocks executed to implement a closed-loop elevation feedback scheme according to one aspect of the present disclosure.

DETAILED DESCRIPTION

[0021] The detailed description set forth below, in connection with the appended drawings, is intended as a description of various configurations and is not intended to limit the scope of the disclosure. Rather, the detailed description includes specific details for the purpose of providing a thorough understanding of the inventive subject matter. It will be apparent to those skilled in the art that these specific details are not required in every case and that, in some instances, well-known structures and components are shown in block diagram form for clarity of presentation.

[0022] The techniques described herein may be used for various wireless communication networks such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA and other networks. The terms "network" and "system" are often used interchangeably. A CDMA network may implement a radio technology, such as Universal Terrestrial Radio Access (UTRA), Telecommunications Industry Association's (TIA's) CDMA2000®, and the like. The UTRA technology includes Wideband CDMA (WCDMA) and other variants of CDMA. The CDMA2000® technology includes the IS-2000, IS-95 and IS-856 standards from the Electronics Industry Alliance (EIA) and TIA. A TDMA network may implement a radio technology, such as Global System for Mobile Communications (GSM). An OFDMA network may implement a radio technology, such as Evolved UTRA (E- UTRA), Ultra Mobile Broadband (UMB), IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Flash-OFDMA, and the like. The UTRA and E-UTRA technologies are part of Universal Mobile Telecommunication System (UMTS). 3GPP Long Term Evolution (LTE) and LTE-Advanced (LTE-A) are newer releases of the UMTS that use E-UTRA. UTRA, E-UTRA, UMTS, LTE, LTE-A and GSM are described in documents from an organization called the "3rd Generation Partnership Project" (3GPP). CDMA2000® and UMB are described in documents from an organization called the "3rd Generation Partnership Project 2" (3GPP2). The techniques described herein may be used for the wireless networks and radio access technologies mentioned above, as well as other wireless networks and radio access technologies. For clarity, certain aspects of the techniques are described below for LTE or LTE-A (together referred to in the alternative as "LTE/- A") and use such LTE/-A terminology in much of the description below.

[0023] FIG. 1 shows a wireless network 100 for communication, which may be an LTE-

A network. The wireless network 100 includes a number of evolved node Bs (eNBs) 110 and other network entities. An eNB may be a station that communicates with the UEs and may also be referred to as a base station, a node B, an access point, and the like. Each eNB 110 may provide communication coverage for a particular geographic area. In 3GPP, the term "cell" can refer to this particular geographic coverage area of an eNB and/or an eNB subsystem serving the coverage area, depending on the context in which the term is used.

[0024] An eNB may provide communication coverage for a macro cell, a pico cell, a femto cell, and/or other types of cell. A macro cell generally covers a relatively large geographic area (e.g., several kilometers in radius) and may allow unrestricted access by UEs with service subscriptions with the network provider. A pico cell would generally cover a relatively smaller geographic area and may allow unrestricted access by UEs with service subscriptions with the network provider. A femto cell would also generally cover a relatively small geographic area (e.g., a home) and, in addition to unrestricted access, may also provide restricted access by UEs having an association with the femto cell (e.g., UEs in a closed subscriber group (CSG), UEs for users in the home, and the like). An eNB for a macro cell may be referred to as a macro eNB. An eNB for a pico cell may be referred to as a pico eNB. And, an eNB for a femto cell may be referred to as a femto eNB or a home eNB. In the example shown in FIG. 1, the eNBs 110a, 110b and 110c are macro eNBs for the macro cells 102a, 102b and 102c, respectively. The eNB 11 Ox is a pico eNB for a pico cell 102x. And, the eNBs HOy and HOz are femto eNBs for the femto cells 102y and 102z, respectively. An eNB may support one or multiple (e.g., two, three, four, and the like) cells.

[0025] The wireless network 100 also includes relay stations. A relay station is a station that receives a transmission of data and/or other information from an upstream station (e.g., an eNB, a UE, or the like) and sends a transmission of the data and/or other information to a downstream station (e.g., another UE, another eNB, or the like). A relay station may also be a UE that relays transmissions for other UEs. In the example shown in FIG. 1, a relay station 11 Or may communicate with the eNB 110a and a UE 120r, in which the relay station 1 lOr acts as a relay between the two network elements (the eNB 110a and the UE 120r) in order to facilitate communication between them. A relay station may also be referred to as a relay eNB, a relay, and the like.

[0026] The wireless network 100 may support synchronous or asynchronous operation.

For synchronous operation, the eNBs may have similar frame timing, and transmissions from different eNBs may be approximately aligned in time. For asynchronous operation, the eNBs may have different frame timing, and transmissions from different eNBs may not be aligned in time.

[0027] The UEs 120 are dispersed throughout the wireless network 100, and each UE may be stationary or mobile. A UE may also be referred to as a terminal, a mobile station, a subscriber unit, a station, or the like. A UE may be a cellular phone, a personal digital assistant (PDA), a wireless modem, a wireless communication device, a handheld device, a tablet computer, a laptop computer, a cordless phone, a wireless local loop (WLL) station, or the like. A UE may be able to communicate with macro eNBs, pico eNBs, femto eNBs, relays, and the like. In FIG. 1, a solid line with double arrows indicates desired transmissions between a UE and a serving eNB, which is an eNB designated to serve the UE on the downlink and/or uplink. A dashed line with double arrows indicates interfering transmissions between a UE and an eNB.

[0028] LTE/-A utilizes orthogonal frequency division multiplexing (OFDM) on the downlink and single-carrier frequency division multiplexing (SC-FDM) on the uplink. OFDM and SC-FDM partition the system bandwidth into multiple (K) orthogonal subcarriers, which are also commonly referred to as tones, bins, or the like. Each subcarrier may be modulated with data. In general, modulation symbols are sent in the frequency domain with OFDM and in the time domain with SC-FDM. The spacing between adjacent subcarriers may be fixed, and the total number of subcarriers (K) may be dependent on the system bandwidth. For example, K may be equal to 72, 180, 300, 600, 900, and 1200 for a corresponding system bandwidth of 1.4, 3, 5, 10, 15, or 20 megahertz (MHz), respectively. The system bandwidth may also be partitioned into sub- bands. For example, a sub-band may cover 1.08 MHz, and there may be 1, 2, 4, 8 or 16 sub-bands for a corresponding system bandwidth of 1.4, 3, 5, 10, 15, or 20MHz, respectively. [0029] The wireless network 100 uses the diverse set of eNBs 110 (i.e., macro eNBs, pico eNBs, femto eNBs, and relays) to improve the spectral efficiency of the system per unit area. Because the wireless network 100 uses such different eNBs for its spectral coverage, it may also be referred to as a heterogeneous network. The macro eNBs 110a- c are usually carefully planned and placed by the provider of the wireless network 100. The macro eNBs 1 lOa-c generally transmit at high power levels (e.g., 5 W - 40 W). The pico eNB 1 lOx and the relay station 1 lOr, which generally transmit at substantially lower power levels (e.g., 100 mW - 2 W), may be deployed in a relatively unplanned manner to eliminate coverage holes in the coverage area provided by the macro eNBs 1 lOa-c and improve capacity in the hot spots. The femto eNBs 1 lOy-z, which are typically deployed independently from the wireless network 100 may, nonetheless, be incorporated into the coverage area of the wireless network 100 either as a potential access point to the wireless network 100, if authorized by their administrator(s), or at least as an active and aware eNB that may communicate with the other eNBs 110 of the wireless network 100 to perform resource coordination and coordination of interference management. The femto eNBs 110y-z typically also transmit at substantially lower power levels (e.g., 100 mW - 2 W) than the macro eNBs 1 lOa-c.

[0030] FIG. 2 shows a block diagram of a design of a base station/eNB 110 and a UE

120, which may be one of the base stations/eNBs and one of the UEs in FIG. 1. For a restricted association scenario, the eNB 110 may be the macro eNB 110c in FIG. 1, and the UE 120 may be the UE 120y. The eNB 110 may also be a base station of some other type. The eNB 110 may be equipped with antennas 234a through 234t, and the UE 120 may be equipped with antennas 252a through 252r.

[0031] At the eNB 110, a transmit processor 220 may receive data from a data source

212 and control information from a controller/processor 240. The control information may be for the PBCH, PCFICH, PHICH, PDCCH, etc. The data may be for the PDSCH, etc. The transmit processor 220 may process (e.g., encode and symbol map) the data and control information to obtain data symbols and control symbols, respectively. The transmit processor 220 may also generate reference symbols, e.g., for the PSS, SSS, and cell-specific reference signal. A transmit (TX) multiple-input multiple-output (MIMO) processor 230 may perform spatial processing (e.g., precoding) on the data symbols, the control symbols, and/or the reference symbols, if applicable, and may provide output symbol streams to the modulators (MODs) 232a through 232t. Each modulator 232 may process a respective output symbol stream (e.g., for OFDM, etc.) to obtain an output sample stream. Each modulator 232 may further process (e.g., convert to analog, amplify, filter, and upconvert) the output sample stream to obtain a downlink signal. Downlink signals from modulators 232a through 232t may be transmitted via the antennas 234a through 234t, respectively.

[0032] At the UE 120, the antennas 252a through 252r may receive the downlink signals from the eNB 110 and may provide received signals to the demodulators (DEMODs) 254a through 254r, respectively. Each demodulator 254 may condition (e.g., filter, amplify, downconvert, and digitize) a respective received signal to obtain input samples. Each demodulator 254 may further process the input samples (e.g., for OFDM, etc.) to obtain received symbols. A MIMO detector 256 may obtain received symbols from all the demodulators 254a through 254r, perform MIMO detection on the received symbols if applicable, and provide detected symbols. A receive processor 258 may process (e.g., demodulate, deinterleave, and decode) the detected symbols, provide decoded data for the UE 120 to a data sink 260, and provide decoded control information to a controller/processor 280.

[0033] On the uplink, at the UE 120, a transmit processor 264 may receive and process data (e.g., for the PUSCH) from a data source 262 and control information (e.g., for the PUCCH) from the controller/processor 280. The transmit processor 264 may also generate reference symbols for a reference signal. The symbols from the transmit processor 264 may be precoded by a TX MIMO processor 266 if applicable, further processed by the demodulators 254a through 254r (e.g., for SC-FDM, etc.), and transmitted to the eNB 110. At the eNB 110, the uplink signals from the UE 120 may be received by the antennas 234, processed by the modulators 232, detected by a MIMO detector 236 if applicable, and further processed by a receive processor 238 to obtain decoded data and control information sent by the UE 120. The processor 238 may provide the decoded data to a data sink 239 and the decoded control information to the controller/processor 240.

[0034] The controllers/processors 240 and 280 may direct the operation at the eNB 110 and the UE 120, respectively. The controller/processor 240 and/or other processors and modules at the eNB 110 may perform or direct the execution of various processes for the techniques described herein. The controllers/processor 280 and/or other processors and modules at the UE 120 may also perform or direct the execution of the functional blocks illustrated in FIGS. 6, 9A, and 10, and/or other processes for the techniques described herein. The memories 242 and 282 may store data and program codes for the eNB 110 and the UE 120, respectively. A scheduler 244 may schedule UEs for data transmission on the downlink and/or uplink.

[0035] In order to increase system capacity, three-dimensional (3D)-MIMO technology has been considered, in which an eNB uses a two-dimensional (2D) antenna array with a large number of antennas. With this type of configuration, small intra-cell interference would be expected with a high beamforming gain. 3D-MIMO and elevation beamforming are currently study items for 3GPP LTE Rel-12 technologies.

[0036] Beamforming has typically been implemented using only horizontal directioning.

However, with the increase in smart antenna technologies, elevation beamforming now allows for vertical directioning in the beamforming process. Elevation beamforming currently supports up to 8 antenna ports. FIG. 3 is a diagram illustrating an 8x8 antenna array 30. Antenna array 30 includes 8 rows and 8 columns of antenna elements, each separated from an adjacent antenna element by a distance of λ/2, where λ is the wavelength of the signal from the antenna elements. Antenna array 30 includes azimuth elements in direction 300 and elevation elements in direction 301 that may be used in both horizontal and elevation beamforming. In various implementations of antenna array 30, each such antenna element may include an individual transceiver and power amplifier.

[0037] Elevation beamforming currently employs vertical sectorization in which the beams are formed at fixed elevations over the coverage area. FIG. 4 is a diagram illustrating a wireless network area 40 having eNB-A 400 and eNB-B 401 provide conventional vertical sectorization coverage. For example, eNB-A 400 is configured with beam L 406 and beam H 407 in a vertical sectorization of the coverage area of eNB-

A 400. Similarly, eNB-B 401 is configured with beam L 408 and beam H 409, in a vertical sectorization of the coverage area of eNB-B 401. Some of the problems with such conventional vertical sectorization, such as the provision of beams L 406 and 408 and beams H 407 and 409, are in the fixed elevation beam, which causes loss degree of freedom (DOF) in the elevation domain, and the loss of flexibility. Beams H 407 and

409 are intended for coverage of UEs at the cell edge, such as UEs 403 and 404, while beams L 406 and 408 are intended for coverage of UEs at the cell interior, such as UEs

402 and 405. However, if UEs 403 and 404 were not present and additional UEs were located in the cell interior, cell capacity would be limited because eNB-A 400 and eNB- B 401 would maintain beams H 407 and 409, even though no UEs were located within the cell edges. In such cases, the beam will be wasted. Moreover, without flexibility in elevation such conventional vertical sectorization may not be feasible for a scenario with UEs located at different elevations.

[0038] FIG. 5A is a block diagram illustrating a wireless coverage area 50 serviced by eNB 500. eNB 500 employs vertical sectorization with beams 501 and 502 providing elevation coverage of vertical sector 1 503 and vertical sector 2 504. As indicated, with the fixed vertical sectors, vertical sectors 1 502 and 2 504, beams will be wasted when few UEs occupy the defined vertical sectors. For example, vertical sector 1 502 is illustrated in which UEs 505-510 are located. However, only UE 511 is located in vertical sector 2 504, yet eNB 500 will expend system resources in maintaining beam

501 for coverage of only UE 511 within vertical sector 504. Even though many more UEs are located within vertical sector 1 503, eNB 500 will not be able to expand beam

502 to increase the capacity of vertical sector 1 503.

[0039] FIG. 5B is a block diagram illustrating a wireless coverage area 51 serviced by eNB 512. eNB 512 employs vertical sectorization with beams 513 and 514 providing elevation coverage of vertical sector 1 515 and vertical sector 2 516. Fixed vertical sectors also limits the flexibility to cover UEs having elevation differences. For example, buildings 517 and 518 are located within vertical sector 1 515, while building 519 is located within vertical sector 2 516. However, each of buildings 517 and 518 are multistory. Thus, UEs located within buildings 517 and 518 have elevation differences. Beam 513, providing coverage to vertical sector 2 516 will not be capable of providing service to the UEs at a different elevation in buildings 517 and 518. Accordingly, the fixed vertical sectorization would likely be infeasible for such locations.

[0040] Various aspects of the present disclosure are directed to perform elevation beamforming by dynamically forming several vertical sectors based on UE feedback in the elevation domain. For example, UEs with similar feedback in the elevation domain may be grouped to form a cluster. The serving base station may then form a cluster- specific vertical beam for these UEs. These vertical sectors may be changed dynamically after a certain period. Since a UE changing elevation is a slow statistical property, the designed period for changing the vertical sectors may be defined as a longer period.

71367969.1 10

0414US.P1 Moreover, as UEs move from one location to another, they may join other vertical clusters when their elevation domain feedback associates with a particular cluster.

[0041] FIG. 6 is a functional block diagram illustrating example blocks executed to implement one aspect of the present disclosure. At block 600, a base station configured according to an aspect receives feedback from multiple UEs within its coverage area. The base station, in an open-loop scheme, may form multiple orthogonal elevation beams for the UEs to analyze and compile the feedback on by designating a particular index of the preferred beam. Alternatively, in a closed-loop scheme, the feedback received by the base station may be a metric obtained or calculated by the UEs such as a precoding matrix indicator (PMI), channel eigenvector, or the like.

[0042] At block 601, the base station determines a correlation in the elevation domain among the UEs using the feedback. The correlation provides for an ability of the base station to group the UEs into logic clusters that would benefit from an elevation beam formed based on the feedback. Depending on whether the base station operates using an open-loop or closed-loop scheme, the correlation may be analyzing the distribution of preferred beam indices reported by the UEs or may be determining the correlation between the various feedback metrics in order to determine the logical grouping of UEs. As such, as block 602, the base station configures one or more UE clusters based on the correlation, where each cluster of includes a set of UEs that have a similar correlation or, which are correlated within a predetermined threshold.

[0043] At block 603, the base station dynamically configures a vertical sector for each of the UE clusters based on the resulting correlation among the UEs in the elevation domain. When the base station determines that the feedback of a number of UEs are correlated together and have been configured as a UE cluster, it may define and configure a vertical sector that will service each of the correlated UEs in that UE cluster. The base station will dynamically configure such a vertical sector for each such UE cluster formed by UEs with a certain similar correlation. At block 604, the base station forms an elevation beam corresponding to the vertical sector for each such UE cluster configured. The base station will generate the appropriate beam weighting in order to form the beam that will serve the dynamic vertical sector for each UE cluster.

[0044] The various aspects of the present disclosure also allow a compatible eNB to reserve some beams for UE-specific elevation beamforming. For any given coverage area, it may be a tradeoff between cluster-specific beams and UE-specific beams. The UE-specific beams may provide stronger communications for an individual UE, while the cluster-specific beams may provide a marked increase in system capacity. As noted, the various mechanisms for such cluster-specific beam forming may be implemented using open-loop or closed-loop schemes.

[0045] FIG. 7 is a transmission timeline 70 illustrating a dynamic vertical sectorization procedure configured according to one aspect of the present disclosure. In the various aspects a periodical super-frame may be defined consisting of tens of frames. Super- frame 700 is illustrated on transmission timeline 70 including X number of frames. At the first subframe, n, the base station sends CSI-RS transmissions 701. Each UE measures its channel in CSI-RS and provides feedback in the elevation domain back to the base station. The scheme used by the base station and UEs may be either open-loop or closed-loop. In an open-loop mode, the UEs feedback the index of the best of the orthogonal elevation beams. In a closed-loop mode, the UEs feedback a metric, such as the rank-1 PMI/channel eigen vector or the like. The base station collects the channel information feedback in the elevation domain from UEs and forms dynamic vertical sectors 702 for a cluster of UEs based on a correlation of the open-loop/closed-loop feedback. UE-specific beamforming 703 may still be applicable for UEs that do not fit within the correlated cluster of UEs. The formed vertical sectors will then not change during the end of super- frame 700 at n + X.

[0046] It should be noted that the overhead that would be used to transmit CSI-RS for elevation feedback is very low. Accordingly, the illustrated aspects of the present disclosure would not substantially increase the overhead or processing requirements of the base station or UEs.

[0047] FIG. 8 is a block diagram illustrating a coverage area 80 of an eNB 800 configured according to one aspect of the present disclosure. eNB 800 is configured for dynamic vertical sectorization and begins the sectorization process by transmitting CSI- RS for elevation feedback from the UEs located within coverage area 80. Multiple UEs are located within coverage area 80, including UE 806, UEs on various floors of building 807, and UEs in building 809. The UEs within coverage area 80 each provide feedback to eNB 800 in the elevation domain. eNB 800 correlates the feedback to dynamically determine vertical sectors. Building 807 includes UEs on the third floor 807-A and the first floor 807-B. The correlation of the elevation feedback for the UEs in building 807 cause eNB 800 to configure a vertical sector 802 for the cluster of UEs on the third floor 807-A and a vertical sector 803 for the cluster of UEs on the first floor 807-B. eNB 800 also finds a correlation between multiple UEs outdoors in coverage area 80 and defines a UE cluster 808 and a vertical sector 804 associated with UE cluster 808. The correlation of the elevation feedback for the UEs in building 809 cause eNB 800 to configure a vertical sector 805 for the cluster of UEs on the third floor 809-A of building 809. Finally, the elevation feedback received from UE 806 does not correlate to any of the other UEs located within coverage area 80. Accordingly, eNB 800 determines to configure a UE-specific elevation beam 801 to serve UE 806. This distribution of UEs and the resulting dynamic vertical sectorization implemented by eNB 800 may remain in place for tens of frames. Moreover, as any UE in any vertical sector moves into another vertical sector, it may become a part of that particular cluster of UEs. For example, if one of the UEs on the third floor 807-A of building 807 moves to the first floor 807-B, it will leave the cluster of UEs for which vertical sector 802 was configured and join the cluster of UEs on the first floor 807-B for which vertical sector 803 was configured. Accordingly, by dynamically configuring vertical sectors based on feedback from the UEs in the elevation domain, eNB 800 may more flexibly handle UEs having varying elevations without wasting system capacity through fixed vertical sectors.

[0048] The elevation feedback mechanisms may be implemented in the various aspects of the present disclosure using an open-loop scheme, a closed-loop scheme, or some combination or variation of both. FIG. 9A is a functional block diagram illustrating example blocks executed to implement an open-loop elevation feedback scheme according to one aspect of the present disclosure. FIG. 9B is a diagram illustrating an eNB 900 configured for an open-loop elevation feedback mechanism according to the aspect of the present disclosure disclosed in FIG. 9A. At block 90, eNB 900 uses a common CSI-RS resource to form multiple orthogonal elevation beams, elevation beam 1 901 through elevation beam K 904, on a time and frequency multiplexing method.

[0049] At block 91, eNB 900 receives feedback from each of the UEs, UEs 907-910.

Each of UEs 907-910 feeds back the index of one of elevation beams 901-904 that is its best beam in the elevation domain. For example, UE 907 may feedback index K of elevation beam 904, while UE 908 may feedback index 2 of elevation beam 902, as the indices for the best beams, respectively.

[0050] At block 92, eNB 900 analyzes the distribution of preferred beam indices of UEs

907-910. A determination is made, at block 93, whether any of the UEs report the same or similar best beam indices. If UEs report a neighboring beam then those UEs may also be grouped with a unified beam. For example, UEs 908 and 910 each feedback index 2 of elevation beam 902 as the best beam, while UE 909 feeds back the index 1 of the neighboring elevation beam 901. Accordingly, eNB 900 configures a unified beam 905 for a vertical sector to serve the cluster of UEs, UEs 908-910.

[0051] If the index of the preferred beam is not the same for a UE, then, at block 95, eNB 900 will form a UE-specific beam using the reported beam index. For example, UE 907 reported the index K, which does not neighbor any of the elevation beams reported by UEs 908-910. Accordingly, eNB 900 forms a UE-specific beam 906 for UE 907, with some of the beams reserved for such UE-specific elevation beamforming.

[0052] It should be noted that UEs 908-910 in the vertical sector served by unified beam

905 may act in the same manner as if they were in a 2D MIMO system.

[0053] FIG. 10 is a functional block diagram illustrating example blocks executed to implement a closed-loop elevation feedback scheme according to one aspect of the present disclosure. At block 1000, an eNB receives elevation feedback metrics from UEs within a coverage area of the eNB. The elevation feedback metrics may include rank-1 PMI, eigen vectors, and the like.

[0054] At block 1001, the eNB determines correlations for all combinations of pairs of the multiple UEs. For example, the elevation feedback metrics for UEs 1-N are represented as hi,h₂,...,h_N. The eNB determines the correlations according to the following algorithm:

[0056] for j=i:N

[0058] end

[0059] d_j represents the correlation between the elevation feedback metric, hi, and the paired elevation feedback metric, h_j, where i is a first index of UEs from 1-N, and j is the paired index of UEs from i to N. [0060] At block 1002, the eNB compares the value of any correlations with a first predetermined threshold, Ti. The comparison with the first predetermined threshold determines how closely correlated the pair of UEs are. If the correlation is less than the first predetermined threshold, then, at block 1006, the UEs of the pair are deemed not to be candidates for a cluster and the eNB continues comparing the other combinations, at block 1002.

[0061] If the correlation of the pair is equal to or greater than the first predetermined threshold, then the UEs of the pair are designated to be cluster candidates and, at block 1003, counted by the eNB as correlated UEs.

[0062] At block 1004, the eNB compares the number of UEs counted as correlating to each other against a second predetermined threshold. Depending on the design of the network, an operator may designate a certain threshold number of matched UEs that must exist before forming a cluster of UEs for the dynamic vertical sectorization. If the number of correlated UEs does not exceed the second threshold, then, at block 1007, no unified elevation beam is formed for the cluster of UEs.

[0063] Otherwise, if the number of correlated UEs meets or exceeds the second threshold, then, at block 1005, the eNB forms a vertical sector for the cluster of these correlated UEs with a unified elevation beam. Accordingly, the eNB may dynamically form the elevation beam for the cluster of UEs based on the feedback received from the UEs in the elevation domain.

[0064] It should be noted that the beam weight for this vector may be selected as: w(i)=

SVD([hi ... h_n(i₎])*, where the weight, w(i) is the singular value decomposition (SVD) of the conjugate of the correlated UEs elevation metrics. The SVD operates to select the principal eigenvector of the feedback metrics.

[0065] It should further be noted that, in order to mitigate interference between different vertical sectors, block diagonalization (BD) may be applied. Moreover, UE-specific beams may also be formed using zero forcing (ZF) or BD to mitigate the interference to the formed vertical vectors.

[0066] Open-loop and close-loop schemes each offer benefits and detriments to implementation. For example, open-loop feedback schemes require less feedback, and, therefore, are suitable for scenarios with medium UE speed. Open-loop schemes also require less complexity on both the eNB and UE sides. On the contrary, there are a limited number of orthogonal beams. Thus, fewer elevation beams may be used for determining the UE feedback.

[0067] Compared to UE-specific elevation beamforming, dynamic vertical sectorization requires little overhead and the beamforming related signaling may be multicast to the UEs in one cluster, thus, obviating the need to notify UEs one by one. Additionally, the vertical sectors may remain in place for a longer period because the statistical properties in the vertical direction or elevation domain changes slowly over time. In typical operations, UEs usually move in the azimuth domain. Because of the lower overhead and longer vertical sector periods, the various aspects of the present disclosure offer better performance when UEs move at medium speed or move within a dense UE distribution. Accurate channel info cannot be obtained in the scenario of UE medium speed. In dense UE distributions, e.g., airport, a beam may be not narrow enough to separate different UEs.

[0068] Those of skill in the art would understand that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

[0069] The functional blocks and modules in FIGs. 6, 9A, and 10 may comprise processors, electronics devices, hardware devices, electronics components, logical circuits, memories, software codes, firmware codes, etc., or any combination thereof.

[0070] Those of skill would further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the disclosure herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present disclosure. Skilled artisans will also readily recognize that the order or combination of components, methods, or interactions that are described herein are merely examples and that the components, methods, or interactions of the various aspects of the present disclosure may be combined or performed in ways other than those illustrated and described herein.

[0071] The various illustrative logical blocks, modules, and circuits described in connection with the disclosure herein may be implemented or performed with a general- purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general- purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

[0072] The steps of a method or algorithm described in connection with the disclosure herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user terminal. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal.

[0073] In one or more exemplary designs, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. A computer-readable storage medium may be any available media that can be accessed by a general purpose or special purpose computer. By way of example, and not limitation, such computer-readable storage media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code means in the form of instructions or data structures and that can be accessed by a general-purpose or special-purpose computer, or a general- purpose or special-purpose processor. Also, non-transitory connections may properly be included within the definition of computer-readable medium. For example, if the instructions are transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, or digital subscriber line (DSL), then the coaxial cable, fiber optic cable, twisted pair, or DSL are included in the definition of medium. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.

[0074] As used herein, including in the claims, the term "and/or," when used in a list of two or more items, means that any one of the listed items can be employed by itself, or any combination of two or more of the listed items can be employed. For example, if a composition is described as containing components A, B, and/or C, the composition can contain A alone; B alone; C alone; A and B in combination; A and C in combination; B and C in combination; or A, B, and C in combination. Also, as used herein, including in the claims, "or" as used in a list of items prefaced by "at least one of indicates a disjunctive list such that, for example, a list of "at least one of A, B, or C" means A or B or C or AB or AC or BC or ABC (i.e., A and B and C).

[0075] The previous description of the disclosure is provided to enable any person skilled in the art to make or use the disclosure. Various modifications to the disclosure will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other variations without departing from the spirit or scope of the disclosure. Thus, the disclosure is not intended to be limited to the examples and designs described herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

[0076] WHAT IS CLAIMED IS:

Claims

1. A method of wireless communication, comprising:

receiving, at a base station, feedback from a plurality of user equipments (UEs); determining, by the base station, a correlation among the plurality of UEs;

configuring, by the base station, one or more UE clusters based on the correlation, wherein each of the one or more UE clusters includes two or more UEs of the plurality of UEs having correlation within a predetermined threshold;

dynamically configuring, by the base station, a vertical sector for each UE cluster of the one or more UE clusters; and

forming, by the base station, an elevation beam corresponding to the vertical sector for each UE cluster of the one or more UE clusters.

2. The method of claim 1, further including:

transmitting the elevation beam to the two or more UEs in each of the one or more UE clusters.

3. The method of claim 1, further including:

transmitting a channel status information-reference signal to the plurality of UEs.

4. The method of claim 1, further including:

utilizing a two-dimensional antenna array at the base station.

5. The method of claim 1, wherein the feedback includes one or more of: a precoding matrix indicator (PMI);

a channel eigenvector; and

an index of preferred beam.

6. The method of claim 5, wherein one or both of the PMI and the channel eigenvector are received at the base station from one or more of:

a physical uplink control channel; and

a physical uplink shared channel.

7. The method of claim 1 , wherein the determining the correlation among the plurality of UEs includes analyzing a distribution of a preferred beam of each UE of the plurality of UEs and grouping two or more UEs with the at least similar preferred beams to form each of the one or more UE clusters.

8. The method of claim 1 , wherein each elevation beam is orthogonal to the other.

9. The method of claim 1 , wherein the determining the correlation among the plurality of UEs includes calculating a pair correlation for each pair of UEs of the plurality of UEs in the elevation domain.

10. The method of claim 9, wherein values of the pair correlations of all combinations of each pair of UEs are denoted according to the following equation:

; ( h )" h _: : < i, j < N wherein C_; . is a matrix indicating channel similarity between a pair of UE_i and UE_j , z. is one of: a Rank-1 PMI or channel eigenvector of UE_i , h_j is one of: the Rank- 1 PMI or channel eigenvector of UE_j , and N is a total number of the plurality of UEs.

1 1. The method of claim 9, further including:

comparing a value of the pair correlation with a first predetermined threshold, wherein the first predetermined threshold is a minimum value of correlation indicating that the pair of UEs correlate with each other;

calculating a number of UEs that correlate with each other and comparing the number with a second predetermined threshold, wherein the second predetermined threshold is a minimum number of UEs to form each of the one or more UE clusters; and grouping the two or more UEs that correlate with each other to form each of the one or more UE clusters when the number of correlated UEs is at least the same as the second predetermined threshold.

12. The method of claim 11, wherein each UE of the number of UEs are assigned to one UE cluster of the one or more UE clusters.

13. The method of claim 1, wherein each vertical sector has a beamforming weight equal to a principal eigenvector of a composite channel, wherein the composite channel is formed based on the feedback in the elevation domain from the two or more UEs in each of the one or more UE clusters.

14. The method of claim 1, further including:

forming a UE-specific elevation beam based on the feedback in the elevation domain from the UE of the plurality of UEs.

15. The method of claim 14, further including:

mitigating interference between the elevation beam of the vertical sector and the UE-specific elevation beam.

16. The method of claim 15, wherein the mitigating interference includes forming the UE-specific elevation beam with one or both of:

a zero-forcing method; and

a block diagonalization method.

17. The method of claim 1 , wherein the elevation beam remains unchanged during a period of time of a periodic super- frame.

18. The method of claim 1, wherein the configuration of the one or more UE clusters changes when one or more UEs associated with the one or more UE clusters moves in the elevation domain.

19. The method of claim 1 , wherein the elevation beam is transmitted by one or more of:

a time multiplexing method; and

a frequency multiplexing method.

20. An apparatus configured for wireless communication, comprising:

means for receiving, at a base station, feedback from a plurality of user equipments (UEs);

means for determining, by the base station, a correlation among the plurality of

UEs;

means for configuring, by the base station, one or more UE clusters based on the correlation, wherein each of the one or more UE clusters includes two or more UEs of the plurality of UEs having correlation within a predetermined threshold;

means for dynamically configuring, by the base station, a vertical sector for each UE cluster of the one or more UE clusters; and

means for forming, by the base station, an elevation beam corresponding to the vertical sector for each UE cluster of the one or more UE clusters.

21. The apparatus of claim 20, further including:

means for transmitting the elevation beam to the two or more UEs in each of the one or more UE clusters.

22. The apparatus of claim 20, further including:

means for transmitting a channel status information-reference signal to the plurality of UEs.

23. The apparatus of claim 20, further including:

means for utilizing a two-dimensional antenna array at the base station.

24. The apparatus of claim 20, wherein the feedback includes one or more of: a precoding matrix indicator (PMI);

a channel eigenvector; and

an index of preferred beam.

25. The apparatus of claim 24, wherein one or both of the PMI and the channel eigenvector are received at the base station from one or more of: a physical uplink control channel; and

a physical uplink shared channel.

26. The apparatus of claim 20, wherein the means for determining the correlation among the plurality of UEs includes means for analyzing a distribution of a preferred beam of each UE of the plurality of UEs and means for grouping two or more UEs with the at least similar preferred beams to form each of the one or more UE clusters.

27. The apparatus of claim 20, wherein each elevation beam is orthogonal to the other.

28. The apparatus of claim 20, wherein the means for determining the correlation among the plurality of UEs includes means for calculating a pair correlation for each pair of UEs of the plurality of UEs in the elevation domain.

29. The apparatus of claim 28, wherein values of the pair correlations of all combinations of each pair of UEs are denoted according to the following equation:

( ; (li: )" h , : 0 < i, j < N wherein C_; . is a matrix indicating channel similarity between a pair of UE_i and UE_j , is one of: a Rank-1 PMI or channel eigenvector of C/E_:. , A . is one of: the Rank- 1 PMI or channel eigenvector of UE_j , and N is a total number of the plurality of UEs.

30. The apparatus of claim 28, further including:

means for comparing a value of the pair correlation with a first predetermined threshold, wherein the first predetermined threshold is a minimum value of correlation indicating that the pair of UEs correlate with each other;

means for calculating a number of UEs that correlate with each other and means for comparing the number with a second predetermined threshold, wherein the second predetermined threshold is a minimum number of UEs to form each of the one or more UE clusters; and means for grouping the two or more UEs that correlate with each other to form each of the one or more UE clusters when the number of correlated UEs is at least the same as the second predetermined threshold.

31. The apparatus of claim 30, wherein each UE of the number of UEs are assigned to one UE cluster of the one or more UE clusters.

32. The apparatus of claim 20, wherein each vertical sector has a

beamforming weight equal to a principal eigenvector of a composite channel, wherein the composite channel is formed based on the feedback in the elevation domain from the two or more UEs in each of the one or more UE clusters.

33. The apparatus of claim 20, further including:

means for forming a UE-specific elevation beam based on the feedback in the elevation domain from the UE of the plurality of UEs.

34. The apparatus of claim 33, further including:

means for mitigating interference between the elevation beam of the vertical sector and the UE-specific elevation beam.

35. The apparatus of claim 34, wherein the means for mitigating interference includes means for forming the UE-specific elevation beam with one or both of:

a zero-forcing method; and

a block diagonalization method.

36. The apparatus of claim 20, wherein the elevation beam remains unchanged during a period of time of a periodic super- frame.

37. The apparatus of claim 20, wherein the configuration of the one or more UE clusters changes when one or more UEs associated with the one or more UE clusters moves in the elevation domain.

38. The apparatus of claim 20, wherein the elevation beam is transmitted by one or more of:

a time multiplexing method; and

a frequency multiplexing method.

39. A computer program product for wireless communications in a wireless network, comprising:

a computer-readable medium having program code recorded thereon, the program code including:

program code to receive, at a base station, feedback from a plurality of user equipments (UEs);

program code to determine, by the base station, a correlation among the plurality of UEs;

program code to configure, by the base station, one or more UE clusters based on the correlation, wherein each of the one or more UE clusters includes two or more UEs of the plurality of UEs having correlation within a predetermined threshold;

program code to dynamically configure, by the base station, a vertical sector for each UE cluster of the one or more UE clusters; and

program code to form, by the base station, an elevation beam corresponding to the vertical sector for each UE cluster of the one or more UE clusters.

40. The computer program product of claim 39, further including:

program code to transmit the elevation beam to the two or more UEs in each of the one or more UE clusters.

41. The computer program product of claim 39, further including:

program code to transmit a channel status information-reference signal to the plurality of UEs.

42. The computer program product of claim 39, wherein the feedback includes one or more of:

a precoding matrix indicator (PMI); a channel eigenvector; and

an index of preferred beam.

43. The computer program product of claim 39, wherein the program code to determine the correlation among the plurality of UEs includes program code to analyze a distribution of a preferred beam of each UE of the plurality of UEs and program code to group two or more UEs with the at least similar preferred beams to form each of the one or more UE clusters.

44. The computer program product of claim 39, wherein the program code to determine the correlation among the plurality of UEs includes program code to calculate a pair correlation for each pair of UEs of the plurality of UEs in the elevation domain.

45. The computer program product of claim 39, wherein each vertical sector has a beamforming weight equal to a principal eigenvector of a composite channel, wherein the composite channel is formed based on the feedback in the elevation domain from the two or more UEs in each of the one or more UE clusters.

46. The computer program product of claim 39, further including:

program code to form a UE-specific elevation beam based on the feedback in the elevation domain from the UE of the plurality of UEs.

47. An apparatus configured for wireless communication, the apparatus comprising:

at least one processor; and

a memory coupled to the at least one processor,

wherein the at least one processor is configured to:

receive, at a base station, feedback from a plurality of user equipments

(UEs);

determine, by the base station, a correlation among the plurality of UEs; configure, by the base station, one or more UE clusters based on the correlation, wherein each of the one or more UE clusters includes two or more UEs of the plurality of UEs having correlation within a predetermined threshold;

dynamically configure, by the base station, a vertical sector for each UE cluster of the one or more UE clusters; and

form, by the base station, an elevation beam corresponding to the vertical sector for each UE cluster of the one or more UE clusters.

48. The apparatus of claim 47, wherein the at least one processor is further configured to transmit the elevation beam to the two or more UEs in each of the one or more UE clusters.

49. The apparatus of claim 47, wherein the at least one processor is further configured to transmit a channel status information-reference signal to the plurality of UEs.

50. The apparatus of claim 47, wherein the feedback includes one or more of: a precoding matrix indicator (PMI);

a channel eigenvector; and

an index of preferred beam.

51. The apparatus of claim 47, wherein the configuration of the at least one processor to determine the correlation among the plurality of UEs includes configuration of the at least one processor to:

analyze a distribution of a preferred beam of each UE of the plurality of UEs, and group two or more UEs with the at least similar preferred beams to form each of the one or more UE clusters.

52. The apparatus of claim 47, wherein the configuration of the at least one processor to determine the correlation among the plurality of UEs includes configuration of the at least one processor to calculate a pair correlation for each pair of UEs of the plurality of UEs in the elevation domain.

53. The apparatus of claim 47, wherein each vertical sector has a

54. The apparatus of claim 47, wherein the at least one processor is further configured to form a UE-specific elevation beam based on the feedback in the elevation domain from the UE of the plurality of UEs.