WO2012125931A1

WO2012125931A1 - Methods for providing precoding and feedback and base station

Info

Publication number: WO2012125931A1
Application number: PCT/US2012/029453
Authority: WO
Inventors: Yingxue K. Li; Hongsan Sheng; Guodong Zhang; Robert L. Olesen; Enoch LU; I-Tai Lu
Original assignee: Interdigital Patent Holdings, Inc.
Priority date: 2011-03-16
Filing date: 2012-03-16
Publication date: 2012-09-20
Also published as: TW201242293A

Abstract

Beamforming, precoding, and feedback systems and methods are provided. For example, user equipment (UE) estimates an effective channel using a predetermined channel independent matrix or beamforming. Such an effective channel estimate along with other feedback information including a channel quality indicator (CQI) and a precoding matrix indicator (PMI) is fed back to an eNB. The eNB may precode data and may provide channel estimation at the eNB using a double codebook or double precoder. For example, the eNB may precode data based on the feedback information (e.g. using a channel dependent precoder) and the eNB may precode the data based on the channel independent matrix (e.g. using a channel independent precoder) that may be channel independent and/or preset (e.g. known to both eNB and UE), and may change each TTI. Such precoding along with scaling factors approximated from the PMI or CQI feedback may be used to enable the eNB to estimate a channel based covariance matrix and design the channel dependent precoder.

Description

METHODS FOR PROVIDING PRECODING AND FEEDBACK AND BASE STATION

CROSS-REFERENCE

[0001] This application claims benefit under 35 U.S.C. §.119(e) of provisional U.S. Patent Application Nos, 61/453,292, 61/480,039, and 61/480,738, the disclosures of which are incorporated herein by reference.

BACKGROUND

[0002] Typically, wireless communication systems transmit and receive signals within a designated electromagnetic frequency spectrum. Unfortunately, the capacity of such a designated electromagnetic frequency spectrum tends to be limited. Additionally, the demand for wireless communication systems continues to increase and expand. As such, a number of wireless communication techniques have been developed to improve spectral efficiency including multiple-input multiple- output (MIMO) techniques such as single user MIMO (SU)-MIMO, multiple user MIMO (MU)-lVHlViO, enhanced 8U/MU-MIMO (E-MIMO), and the like (e.g. through preceding) that may be used to support base stations or eNBs with multiple antennas and user equipment (UEs) or wireless transmit/receive units (WTRUs) with one or more antennas on the same frequency, time, and/or code channel. For example, base stations or eNBs usually send or transmit data, signals such as sounding signals, and the like, and/or receive channel state information (CSI) that may be fed back from the UEs and/or WTRUs. Typically, the base station or eNB then makes a scheduling decision and derives a preceding matrix for transmissions at the base station or eNB using, for example, such CSI that may be fed back. Unfortunately, such CSI tends to be increase overhead in a wireless communication system. Additionally, such CSI tends to be quantized (e.g. include quantization errors) that may cause inaccuracy in the CSI and, as such, results in cross interference between co-scheduled users operating UEs and/or WTRUs. Such inaccuracy and cross-interference, in turn, limits the performance (e.g. especially in the high signal to noise ratio (SNR) region where inter-user interference may be a dominant factor) of the wireless communication system and tends to becomes more severe as the number of eNB antennas increases.

SUMMARY

[0003] Orthogonal frequency division multiplexing (OFDM) downlink transmission using semi- opportunistic beamforming techniques may be disclosed. According to an embodiment, a method that may be performed at a base station may include forming channel-independent beams according to a pre-determined pattern. The method may also include performing precoding based on channel state information from user equipment,

[0004] According to another embodiment, a method that may be performed at a UE may include estimating channel state information (CSI) based on unprecoded cell- specific reference symbols to generate an unprecoded channel matrix. The method may also include generating an effective channel using the matrix and a channel independent precoding matrix. Further, the method may include performing channel quantization using a predefined codebook and broadcasting feedback information including the effective channel estimate, a. channel quality indicator (CQI), and/or a precoding matrix indicator (PMI).

[0005] The Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, not is it intended to be used to limit the scope of the claimed subject matter. Furthermore, the claimed, subject matter is not limited, to any limitations that solve any or all disadvantages noted in any part of this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] A. more detailed understanding may be had from the following description, given by way of example in conjunction with the accompanying drawings. [0007] FIG. 1A depicts a system diagram of an example communications system in which one or more disclosed embodiments may be implemented.

[0008] FIG. IB depicts a system diagram of an example wireless transmit/receive unit (WTRU) that may be used within the communications system illustrated in FIG. 1A.

[0009] FIG. 1C depicts a system diagram of an example radio access network and an example core network that may be used within the communications system illustrated in FIG. 1A.

[0010] FIG. ID depicts a system diagram of an example RAN and core network according to an embodiment.

[0011] FIG. IE depicts a system diagram of an example RAN and core network according to an embodiment.

[0012] FIG. 2 depicts a block diagram of an example embodiment of user equipment (UE) processing.

[0013] FIG. 3 depicts a block diagram of an example embodiment of an eNB that may be in communication with a UE such as the UE show⁷n in FIG, 2.

[0014] FIGs. 4a and 4b depict diagrams of an example embodiment of wideband based and subband based channel independent preceding respectively.

[0015] FIG. 5 depicts a block diagram of an example embodiment of UE processing in accordance with another embodiment.

[0016] FIG. 6 depicts a block diagram of an example embodiment of an eNB that may be in communication with a UE such as the UE shown in FIG. 5.

[0017] FIGs. 7 and 8 depict charts of an example embodiment of a performance associated with a 10-percentile and 50-percentile UE respectively.

DETAILED DESCRIPTION

[0018] Systems, methods, and/or techniques for supporting multi-user multiple-input multiple output (MU-MIMO) preceding in, for example, a communication system such as an orthogonal frequency division multiplexing (OFDM) systems may be provided. For example, systems, methods and/or techniques for implementing channel dependent and channel independent preceding (e.g. double codebook preceding) in such a communication system may be provided.

[0019] FIG. 1A depicts a diagram of an example communications system 100 in which one or more disclosed embodiments may be implemented. The communications system 100 may be a multiple access system that provides content, such as voice, data, video, messaging, broadcast, etc., to multiple wireless users. The communications system 100 may enable multiple wireless users to access such content through the sharing of system resources, including wireless bandwidth. For example, the communications systems 100 may employ one or more channel access methods, such as code division multiple access (CDMA), time division multiple access (TDM A), frequency division multiple access (FDMA), orthogonal FDMA (OFDM A), single-carrier FDMA (SC-FDMA), and the like.

[0020] As shown in FIG. 1A, the communications system 100 may include wireless transmit/receive units (WTRUs) 102a, 102b, 102c, 102d, a radio access network (RAN) 104, a core network 106, a public switched telephone network (PSTN) 108, the Internet 110, and other networks 112, though it will be appreciated that the disclosed embodiments contemplate any number of WTRUs, base stations, networks, and/or network elements. Each of the WTRUs 102a, 102b, 102c, 102d may be any type of device configured to operate and/or communicate in a wireless environment. By way of example, the WTRUs 102a, 102b, 102c, 102d may be configured to transmit and/or receive wireless signals and may include user equipment (UE), a. mobile station, a. fixed or mobile subscriber unit, a pager, a cellular telephone, a personal digital assistant (PDA), a smartphone, a laptop, a netbook, a personal computer, a wireless sensor, consumer electromcs. and the like.

[0021] The communications systems 100 may also include a base station 114a and a base station 114b. Each of the base stations 114a, 114b may be any type of device configured to wirelessly interface with at least one of the WTRUs 102a, 102b, 102c, 102d to facilitate access to one or more communication networks, such as the core network 106, the Internet 110, and/or the networks 112. By way of example, the base stations 114a, 114b may be a base transceiver station (BTS), a Node-B, an eNode B, a Home Node B, a Home eNode B, a site controller, an access point (AP), a wireless router, and the like. While the base stations 114a, 114b are each depicted as a single element, it will be appreciated that the base stations 114a, 114b may include any number of interconnected base stations and/or network elements.

[0022] The base station 114a may be part of the RAN 104, which may also include other base stations and/or network elements (not shown), such as a base station controller (BSC), a radio network controller (RNC), relay nodes, etc. The base station 114a and/or the base station 114b may be configured to transmit and/or receive wireless signals within a particular geographic region, which may be referred to as a cell (not shown). The cell may further be divided into cell sectors. For example, the cell associated with the base station 114a may be divided into three sectors. Thus, in one embodiment, the base station 114a may include three transceivers, i.e., one for each sector of the cell, in another embodiment, the base station 114a may employ multiple-input multiple output (MIMO) technology and, therefore, may utilize multiple transceivers for each sector of the cell.

[0023] The base stations 114a, 114b may communicate with one or more of the WTRUs 102a, 102b, 102c, 102d over an air interface 116, which, may be any suitable wireless communication link (e.g., radio frequency (RF), microwave, infrared (IR), ultraviolet (LJV), visible light, etc.). The air interface 116 may be established using any suitable radio access technology (RAT).

[0024] More specifically, as noted above, the communications system 100 may be a multiple access system and may employ one or more channel access schemes, such as CDMA. TDMA, FDMA, OF DMA, SC-FDMA, and the like. For example, the base station 114a in the RAN 104 and the WTRUs 102a. 102b. 102c may implement a radio technology such as Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access (UTRA), which may establish the air interface 116 using wideband CDMA (WCDMA). WCDMA may include communication protocols such as High-Speed Packet Access (HSPA) and/or Evolved. HSPA (HSPA+). HSPA may include High-Speed Downlink Packet Access (HSDPA) and/or High-Speed Uplink Packet Access (HSUPA). [0025] In another embodiment, the base station 114a and the WTRUs 102a, 102b, 102c may implement a radio technology such as Evolved UMTS Terrestrial Radio Access (E-UTRA), which may establish the air interface 116 using Long Term Evolution (LTE) and/or LTE- Advanced (LTE-A).

[0026] In other embodiments, the base station 114a and the WTRUs 102a, 102b, 102c may implement radio technologies such as IEEE 802.16 (i.e., Worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000, CDMA2000 IX, CDMA2000 EV-DO, Interim Standard 2000 (18-2000), interim Standard 95 (IS-95), Interim Standard 856 (IS-856), Global System for Mobile communications (GSM), Enhanced. Data rates for GSM! Evolution (EDGE), GSM EDGE (GERAN). and the like.

[0027] The base station 114b in FIG, lA may be a wireless router, Home Node B, Home eNode B, or access point, for example, and may utilize any suitable RAT for facilitating wireless connectivity in a localized area, such as a place of business, a home, a vehicle, a campus, and the like. In one embodiment, the base station 114b and the WTRUs 102c, 102d may implement a radio technology such as IEEE 802.11 to establish a wireless local area network (WLAN), In another embodiment, the base station 114b and the WTRUs 102c, 102d may implement a radio technology such as IEEE] 802.15 to establish a wireless personal area network (WPAN). In yet another embodiment, the base station 114b and the WTRUs 102c, 102d may utilize a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE, LTE-A, etc.) to establish a picocell or femtocell. As shown in FIG. lA, the base station 114b may have a direct connection to the Internet 110. Thus, the base station 114b may not be required to access the Internet 110 via the core network 106.

[0028] The RAN 104 may be in communication with the core network 106, which may be any type of network configured to provide voice, data, applications, and/or voice over internet protocol (VoIP) services to one or more of the WTRUs 102a, 102b, 102c, 102d. For example, the core network 106 may provide call control, billing services, mobile location-based services, pre-paid calling, Internet connectivity, video distribution, etc., and/or perform high-level security functions, such as user authentication. Although not shown in FIG. 1A, it will be appreciated that the RAN 104 and/or the core network 106 may be in direct or indirect communication with other RANs that employ the same RAT as the RAN 104 or a different RAT. For example, in addition to being connected to the RAN 104. which may be utilizing an E-UTRA radio technology, the core network 106 may also be in communication with another RAN (not shown) employing a GSM radio technology.

[0029] The core network 106 may also serve as a gateway for the WTRUs 102a, 102b, 102c, 102d to access the PSTN 108, the Internet 110, and/or other networks 112. The PSTN 108 may include circuit-switched, telephone networks that provide plain old telephone service (POTS). The Internet 110 may include a global system of interconnected computer networks and devices that use common communication protocols, such as the transmission control protocol (TCP), user datagram protocol (UDP) and the internet protocol (IP) in the TCP/IP internet protocol suite. The networks 112 may include wired or wireless communications networks owned and/or operated by other service providers. For example, the networks 112 may include another core network connected to one or more RANs, which may employ the same RAT as the RAN 104 or a different RAT.

[0030] Some or all of the WTRUs 102a, 102b, 102c, 102d in the communications system 100 may include multi-mode capabilities, i.e.. the WTRUs 102a, 102b, 102c, 102d may include multiple transceivers for communicating with different wireless networks over different wireless links. For example, the WTRU 102c shown in FIG. 1A may be configured to communicate with the base station 114a, which may employ a cellular-based radio technology, and with the base station 114b, which may employ an IEEE 802 radio technology.

[0031] FIG . IB depicts a system diagram of an example WTRU 102. As shown in FIG . IB, the WTRU 102 may include a processor 118, a transceiver 120, a transmit/receive element 122, a speaker/microphone 124, a keypad 126, a display/touchpad 128, non-removable memory 106, removable memory 132, a power source 134, a global positioning system (GPS) chipset 136, and other peripherals

i 138. It will be appreciated that the WTRU 102 may include any sub -combination of the foregoing elements while remaining consistent with an embodiment.

[0032] The processor 118 may be a general purpose processor, a special purpose processor, a conventional processor, a digital signal processor (DSP), a plurality of microprocessors, one or more microprocessors in association with a DSP core, a controller, a microcontroller, Application Specific Integrated Circuits (ASICs), Field Programmable Gate Array (FPGAs) circuits, any other type of integrated circuit (IC), a state machine, and the like. The processor 118 may perform signal coding, data processing, power control, input/output processing, and/or any other functionality that enables the WTRU 102 to operate in a wireless environment. The processor 118 may be coupled to the transceiver 120, which may be coupled to the transmit/receive element 122. While FIG, IB depicts the processor 118 and the transceiver 120 as separate components, it will be appreciated that the processor 118 and the transceiver 120 may be integrated together in an electronic package or chip.

[0033] The transmit/receive element 122 may be configured to transmit signals to, or receive signals from, a base station (e.g., the base station 114a) over the air interface 116. For example, in one embodiment, the transmit/receive element 122 may be an antenna configured to transmit and/or receive RF signals. In another embodiment, the transmit/receive element 122 may be an emitter/detector configured to transmit and/or receive IR, UV, or visible light signals, for example. In yet another embodiment, the transmit/receive element 122 may be configured to transmit and receive both RF and light signals. It will be appreciated that the transmit/receive element 122 may be configured to transmit and/or receive any combination of wireless signals.

[0034] In addition, although the transmit/receive element 122 is depicted in FIG, IB as a single element, the WTRU 102 may include any number of transmit/receive elements 122. More specifically, the WTRU 102 may employ MIMO technology. Thus, in one embodiment, the WTRU 102 may include two or more transmit/receive elements 122 (e.g., multiple antennas) for transmitting and receiving wireless signals over the air interface 116. [0035] The transceiver 120 may be configured to modulate the signals that are to be transmitted by the transmit/receive element 122 and to demodulate the signals that are received by the transmit/receive element 122. As noted above, the WTRU 102 may have multi-mode capabilities. Thus, the transceiver 120 may include multiple transceivers for enabling the WTRU 102 to communicate via multiple RATs, such as UTRA and IEEE 802.11, for example.

[0036] The processor 118 of the WTRU 102 may be coupled to, and may receive user input data from, the speaker/microphone 124, the keypad 126, and/or the display/touchpad 128 (e.g., a liquid crystal display (LCD) display unit or organic light- emitting diode (OLED) display unit). The processor 118 may also output user data to the speaker/microphone 124, the keypad 126, and/or the display/touchpad 128. In addition, the processor 118 may access information from, and store data in, any type of suitable memory, such as the non-removable memory 106 and/or the removable memory 132. The non-removable memory 106 may include random- access memory (RAM), read-only memory (ROM), a hard disk, or any other type of memory storage device. The removable memory 132 may include a subscriber identity module (SIM) card, a memory stick, a secure digital (SD) memory card, and the like. In other embodiments, the processor 118 may access information from, and store data in, memory that is not physically located on the WTRU 102, such as on a server or a home computer (not shown) .

[0037] The processor 118 may receive power from the power source 134, and may be configured to distribute and/or control the power to the other components in the WTRU 102. The power source 134 may be any suitable device for powering the WTRU 102. For example, the power source 134 may include one or more dry cell batteries (e.g., nickel-cadmium (NiCd), nickel-zinc (NiZn), nickel metal hydride (NiMH), lithium-ion (Li-ion), etc.), solar cells, fuel cells, and the like.

[0038] The processor 118 may also be coupled to the GPS chipset 136, which may be configured to provide location information (e.g., longitude and latitude) regarding the current location of the WTRU 102. In addition to, or in lieu of, the information from the GPS chipset 136, the WTRU 102 may receive location information over the air interface 116 from a base station (e.g., base stations 114a, 114b) and/or determine its location based on the timing of the signals being received from two or more nearby base stations. It will be appreciated that the WTRU 102 may acquire location information by way of any suitable location-determination method while remaining consistent with an embodiment.

[0039] The processor 118 may further be coupled to other peripherals 138, which may include one or more software and/or hardware modules that provide additional features, functionality and/or wired or wireless connectivity. For example, the peripherals 138 may include an accelerometer, an e-compass, a satellite transceiver, a digital camera (for photographs or video), a universal serial bus (USB) port, a vibration device, a television transceiver, a hands tree headset, a Bluetooth® module, a frequency modulated (FM) radio unit, a digital music player, a media player, a video game player module, an internet browser, and the like.

[0040] FIG. 1C depicts a system diagram of the RAN 104 and the core network 106 according to an embodiment. As noted above, the RAN 104 may employ a UTRA radio technology to communicate with the WTRUs 102a, 102b, 102c over the air interface 116. The RAN 104 may also be in communication with the core network 106, As shown in FIG. IC, the RAN 104 may include Node-Bs 140a, 140b, 140c, which may each, include one or more transceivers for communicating with the WTRUs 102a, 102b, 102c over the air interface 1.16. The Node-Bs 140a, 140b, 140c may each be associated, with a particular cell (not shown) within the RAN 104. The RAN 104 may also include RNCs 142a, 142b. It will be appreciated that the RAN 104 may include any number of Node-Bs and RNCs while remaining consistent with an embodiment.

[0041] As shown in FIG. IC, the Node-Bs 140a, 140b may be in communication with the RNC 142a. Additionally, the Node-B 140c may be in communication with the RNCl42b. The Node-Bs 140a, 140b, 140c may communicate with the respective RNCs 142a, 142b via an Iub interface. The RNCs 142a, 142b may be in communication with one another via an lur interface. Each, of the RNCs 142a, 142b may be configured to control the respective Node-Bs 140a, 140b, 140c to which it is connected. In addition, each of the RNCs 142a, 142b may be configured to carry out or support other functionality, such as outer loop power control, load control, admission control, packet scheduling, handover control, macrodiversity, security functions, data encryption, and the like.

[0042] The core network 108 shown in FIG. 1C may include a media gateway (MGW) 144, a mobile switching center (MSG) 146, a serving GPRS support node (SGSN) 148. and/or a gateway GPRS support node (GGSN) 150. While each of the foregoing elements are depicted as part of the core network 106, it will be appreciated that any one of these elements may be owned and/or operated by an entity other than the core network operator.

[0043] The RNC 142a in the RAN 104 may be connected to the MSG 146 in the core network 106 via an iuCS interface. The MSG 146 may be connected to the MGW 144. The MSG 146 and the MGW 144 may provide the WTRUs 102a, 102b, 102c with access to circuit- switched networks, such as the PSTN 108, to facilitate communications between the WTRUs 102a, 102b, 102c and traditional land-line communications devices.

[0044] The RNC 142a in the RAN 104 may also be connected to the SGSN 148 in the core network 106 via an IuPS interface. The SGSN 148 may be connected to the GGSN 150. The SGSN 148 and the GGSN 150 may provide the WTRUs 102a, 102b, 102c with access to packet-switched networks, such as the internet 110, to facilitate communications between and the WTRUs 102a, 102b, 102c and IP-enabled devices.

[0045] As noted above, the core network 106 may also be connected to the networks 112, which may include other wired or wireless networks that are owned and/or operated by other service providers.

[0046] FIG. ID depicts a system diagram of the RAN 104 and. the core network 106 according to an embodiment. As noted, above, the RAN 104 may employ an E-UTRA radio technology to communicate with the WTRUs 102a, 102b, 102c over the air interface 116. The RAN 104 may also be in communication with the core network 106.

[0047] The RAN 104 may include eNode-Bs 140a, 140b, 140c, though it will be appreciated that the RAN 104 may include any number of eNode-Bs while remaining consistent with an embodiment. The eNode-Bs 140a, 140b, 140c may each include one or more transceivers for communicating with the WTRUs 102a, 102b, 102c over the air interface 116. In one embodiment, the eNode-Bs 140a, 140b, 140c may implement MIMO technology. Thus, the eNode-B 140a, for example, may use multiple antennas to transmit wireless signals to, and receive wireless signals from, the WTRU 102a.

[0048] Each of the eNode-Bs 140a, 140b, 140c may be associated with a particular cell (not shown) and may be configured to handle radio resource management decisions, handover decisions, scheduling of users in the uplink and/or downlink, and the like. As shown in FIG. 1C, the eNode-Bs 140a, 140b, 140c may communicate with one another over an X2 interface.

[0049] The core network 106 shown in FIG. IC may include a mobility management gateway (MME) 142, a serving gateway 144, and a packet data network (PDN) gateway 146, While each of the foregoing elements are depicted as part of the core network 106, it should be appreciated that any one of these elements may be owned and/or operated by an entity other than the core network operator.

[0050] The MME 142 may be connected to each of the eNode-Bs 142a, 142b, 142c in the RAN 104 via. an Si interface and may serve as a control node. For example, the MME 142 may be responsible for authenticating users of the WTRUs 102a, 102b, 102c, bearer activation/deactivation, selecting a particular serving gateway during an initial attach of the WTRUs 102a, 102b, 102c, and the like. The MME 142 may also provide a control plane function for switching between the RAN 104 and other RANs (not shown) that employ other radio technologies, such as GSM or WCDMA.

[0051] The serving gateway 144 may be connected to each of the eNode Bs 140a, 140b, 140c in the RAN 104 via the Si interface. The serving gateway 144 may generally route and forward user data packets to/from the WTRUs 102a, 102b, 102c. The serving gateway 144 may also perform other functions, such as anchoring user planes during inter-eNode B handovers, triggering paging when downlink data is available for the WTRUs 102a, 102b, 102c, managing and storing contexts of the WTRUs 102a, 102b, 102c, and the like. [0052] The serving gateway 144 may also be connected to the PDN gateway 146. which may provide the WTRUs 102a, 102b, 102c with access to packet- switched networks, such as the Internet 110, to facilitate communications between the WTRUs 102a, 102b, 102c and IP-enabled devices.

[0053] The core network. 106 may facilitate communications with other networks. For example, the core network 106 may provide the WTRUs 102a, 102b, 102c with access to circuit- switched networks, such as the PSTN 108, to facilitate communications between the WTRUs 102a, 102b, 102c and traditional land-line communications devices. For example, the core network 106 may include, or may communicate with, an IP gateway (e.g., an IP multimedia subsystem (IMS) server) that serves as an interface between the core network 106 and the PSTN 108. In addition, the core network 106 may provide the WTRUs 102a, 102b, 102c with access to the networks 112, which may include other wired or wireless networks that axe owned and/or operated by other service providers.

[0054] FIG. IE depicts a system diagram of the RAN 104 and the core network 106 according to an embodiment. The RAN 104 may be an access service network (ASN) that employs IEEE 802.16 radio technology to communicate with the WTRUs 102a, 102b, 102c over the air interface 116. As will be further discussed below, the communication links between the different functional entities of the WTRUs 102a, 102b, 102c, the RAN 104. and the core network 106 may be defined as reference points.

[0055] As shown in FIG. IE, the RAN 104 may include base stations 140a, 140b, 140c, and an ASN gateway 142, though, it will be appreciated, that the RAN 104 may include any number of base stations and ASN gateways while remaining consistent with an embodiment. The base stations 140a, 140b, 140c may each be associated with a particular cell (not shown) in the RAN 104 and may each include one or more transceivers for communicating with the WTRUs 102a, 102b, 102c over the air interface 116. In one embodiment, the base stations 140a, 140b, 140c may implement MIMO technology. Thus, the base station 140a, for example, may use multiple antennas to transmit wireless signals to, and receive wireless signals from, the WTRU 102a. The base stations 140a, 140b, 140c may also provide mobility management functions, such as handoff triggering, tunnel establishment, radio resource management, traffic classification, quality of service (QoS) policy enforcement, and the like. The ASN gateway 142 may serve as a traffic aggregation point and may be responsible for paging, caching of subscriber profiles, routing to the core network 106, and the like.

[0056] The air interface 116 between the WTRUs 102a, 102b, 102c and the RAN 104 may be defined as an Rl reference point that implements the IEEE 802.16 specification. In addition, each of the WTRUs 102a, 102b, 102c may establish a logical interface (not shown) with the core network 106. The logical interface between the WTRUs 102a, 102b, 102c and the core network 106 may be defined as an R2 reference point, which may be used for authentication, authorization, IP host configuration management, and/or mobility management,

[0057] The communication link between each of the base stations 140a, 140b, 140c may be defined as an R8 reference point that includes protocols for facilitating WTRU handovers and the transfer of data between base stations. The communication link between the base stations 140a, 140b, 140c and the ASN gateway 215 may be defined as an R6 reference point. The R6 reference point may include protocols for facilitating mobility management based on mobility events associated with each of the WTRUs 102a, 102b, 100c.

[0058] As shown in FIG. IE, the RAN 104 may be connected to the core network 106. The communication link between the RAN 104 and the core network 106 may defined as an R3 reference point that includes protocols for facilitating data transfer and mobility management capabilities, for example. The core network 106 may include a mobile IP home agent (MIP-HA) 144, an authentication, authorization, accounting (AAA) server 146, and a gateway 148. While each of the foregoing elements are depicted as part of the core network 106, it will be appreciated that any one of these elements may be owned and/or operated by an entity other than the core network operator.

[0059] The MIP-HA. may be responsible for IP address management, and may enable the WTRUs 102a, 102b, 102c to roam between different ASNs and/or different core networks. The MIP-HA 144 may provide the WTRUs 102a, 102b, 102c with access to packet- switched networks, such as the Internet 110, to facilitate communications between the WTRUs 102a, 102b, 102c and IP-enabled devices. The AAA server 146 may be responsible for user authentication and for supporting user services. The gateway 148 may facilitate interworking with other networks. For example, the gateway 148 may provide the WTRUs 102a, 102b, 102c with access to circuit- switched networks, such as the PSTN 108, to facilitate communications between the WTRUs 102a, 102b, 102c and traditional land-line communications devices. In addition, the gateway 148 may provide the WTRUs 102a, 102b, 102c with access to the networks 112, which may include other wired or wireless networks that are owned and/or operated by other service providers.

[0060] Although not shown in FIG. IE, it should be appreciated that the RAN 104 may be connected to other ASNs and the core network 106 may be connected to other core networks. The communication link between the RAN 104 the other ASNs may be defined as an R4 reference point, which may include protocols for coordinating the mobility of the WTRUs 102a, 102b, 102c between the RAN 104 and the other ASNs. The communication link between the core network 106 and the other core networks may be defined as an R5 reference, which may include protocols for facilitating interworking between home core networks and visited core networks.

[0061] In a communication systems or network such, as communication system 100 where base stations or components may be equipped with multiple antennas (and e.g. when correlation between base station antennas may be high), multiple users on the same frequency, time, and/or code channel may be supported to improve spectral efficiency. As described above, MU-MIMO through precoding may be implemented, and used. According to an example embodiment, there may be two classes of precoding for MU-MIMO. In a first class (e.g. that may be referred to as opportunistic beamforming), base stations or eNBs may form random beams without channel state information (CSI) feedback from receivers or UEs. Each receiver or UE may then determine and calculate a channel qualify indicator (CQI) associated with a beam (e.g. the best beam) and the index to best beam, and may feedback such CQI (and index). Based on the feedback, base stations or eNBs may schedule one or more users or UE or WTRUs to receive data according to certain criterion or criteria. In a second class, receivers or UEs may feedback CSI. Base stations or eNBs may then make scheduling decisions, and derive proper precoding matrix for the transmission based on the CSI that may be fed back. In an opportunistic beamforming or first class, although multiple users may be served by the network, one user may be served on a particular time or frequency slot regardless of the number of antennas at a particular base station or eNB. As such, the spectral efficiency may be limited.

[0062] When CSI feedback may be used (e.g. in the second class), the inaccuracy of such CSI feedback may cause cross interference between co-scheduled users or UEs thereby limiting the system performance (e.g. especially in a high SNE. region where inter-user interference is may be dominant factor or where the number of base station or UE antennas may increases),

[0063] Thus, in an embodiment, precoding and/or feedback systems, methods, and/or techniques may be provided to improve spectrum usage efficiency, improve system performance, reduce inaccuracy of feedback and/or the results of such inaccuracies, and the like as described herein. Such precoding and/or feedback systems, methods, and/or techniques may be separated into two stages and, as such, may invoke a double codebook. In a first stage, a base station or eNB may form or establish channel independent beams or precoders (e.g. simultaneously) according to or based on a pre-determined pattern (e.g. as shown in FIG. 4 where predetermined values of the V matrices may be across time and frequency space) and may use or apply such channel independent beams or precoders to data or information that may be precoded using channel dependent beams or precoders as described, for example, below. According to an example embodiment, the number of simultaneously formed beams may be less than number of transmit antenna so that the dimension of the resulting effective channel between basestation and UE is reduced. In a second stage, the base station or eNB may perform precoding (e.g. channel dependent precoding) based on channel state information (CSI) that may be fed back from a UE or WTRU. The CSI feedback may be based on the effective channel that may include the effect of the first stage beamforming or precoding (e.g. opportunistic beamforming) at the UE or WTRU. According to an example embedment, the dimension of the effective channel may reduced compared to the original channel using such methods or techniques such that the CSI feedback overhead may be reduced without diminishing the feedback accuracy or the same overhead, may be used improving the feedback accuracy.

[0064] As such, the systems, methods, and/or techniques disclosed herein may provide the benefit of, for example, both opportunistic beamforming (e.g. channel independent beamforming or preceding) and CSI feedback based preceding (e.g. channel dependent beamforming or preceding). According to an. example embodiment, the impact of the channel independent preceding or beamforming may be two-fold. First, the channel independent preceding or beamforming may artificially introduce a time and/or frequency varying channel that may be explored by a scheduler or scheduling component to approach the performance of closed loop preceding. Secondly, the channel independent preceding or beamforming may reduce the dimension of the channel matrix to be quantized, resulting in smaller quantization error. The CSI feedback may also enable an eNB to perform channel dependent precoding such as zero forcing to minimize inter-user interference. With the reduced quantization error, the inter-user interference can be reduced even further. As such, according to example embodiments, the systems, methods, and techniques disclosed herein may provide improved performance under practical circumstances.

[0065] FIG. 2 illustrates a block diagram of an example embodiment of user equipment (UE) signal processing including precoding or beamforming and/or feedback. As shown in FIG. 2, a UE or WTRU such as the WTRUs 102a-d may include one or more antennas (e.g. antenna 122). According to one embodiment, the UE or WTRU may receive one or more signals (e.g. at 201) that may include data or information such as precoding information and/or channel state information, reference symbols, and the like via the one or more antennas (e.g. antenna 122). After receiving the one or more signals, the signals may be pre-processed via a front end processing unit. For example, the UE or WTRU such as the WTRU 102a-d may include a front end processing unit such as a front end processing unit 205. According to one embodiment, the front end processing unit (e.g. 205) may receive the one or more signals (e.g. from the antennas such as 122 at 201) and may perform one or more pre-processing methods or procedures such Radio Frequency (RF) processing including low noise amplification, filtering, down-conversion, and the like. Fast Fourier Transformation (FFT), demapping or decoding including data and/or reference symbol demapping, and the like.

[0066] After a front end processing unit (e.g. 205) may process the one or more signals, the processed signals may be provided to and received, for example, in parallel to a Channel State information (CSI) channel estimation component such as a CSI channel estimation component 210 (e.g. at 211) that may estimate feedback information and an effective channel as described below and a data demodulation component such as a data demodulation component 215 (e.g. at 221) to demodulate data or signals using suitable techniques or methods. As such, in an example embodiment, the one or more signals may be provided to two parallel branches (e.g. a first branch associated with CSI channel estimation and a second branch associated with data demodulation) of processing in a UE or WTRU such as the WTRU 102a-d after front end processing (e.g. by a front end processing unit 205).

[0067] According to one embodiment (e.g. in the first branch), a CSI estimation component such as a CSI channel estimation component 210 may determine (or estimate) a channel based on cell-specific reference symbols (CRS) (e.g. unprecoded CRS or Channel State Information Reference Symbols (CSI-RS)), An estimated, unprecoded channel matrix may then be generated or calculated (e.g. by the CSI channel estimation component 210) based on the estimated channel and/or the unprecoded cell- specific reference symbols such as CRS and/or CSI-RS.

[0068] The UE may then use a pre- determined precoding matrix that may be channel independent (e.g. a channel independent precoding matrix) and the unprecoded channel matrix to construct an effective channel via a channel construction component such as a channel construction component 220. For example, a channel construction component (e.g. 220) may receive the unprecoded channel matrix and the channel independent precoding matrix (e.g. at 231) and may construct an effective channel (e.g. at 261) based on the unprecoded channel matrix and the channel independent preceding matrix that may be received. According to an embodiment, the effective channel may be calculated or constructed as the product of the unprecoded channel matrix, and the channel independent preceding matrix. For example, an effective channel or effective channel estimate Heff may be expressed or defined as:

where the unprecoded channel matrix estimate may be Hi, and the channel independent precoding matrix may be V, which may be described in more detail herein. The channel matrix estimate H₁ and/or the channel independent precoding matrix Vmay be a function of time and/or frame or subframe number. Additionally, in one embodiment, Vmay be a tall matrix where the number of rows may be greater than number of columns such that the effective channel estimate may have a reduced dimension when compared to the original channel matrix Hi.

[0069] After constructing the effective channel, the effective channel may be quantized using a predefined codebook via a quantization component such as a quantization component 225 and fed back (i.e. transmitted) to an eNB such as a serving eNB or other component of a communication system such as the communication system 100 (e.g. at 251). For example, a quantization component (e.g. 225) may receive (e.g. at 251) the estimated or constructed effective channel such as Heff and may quantize the received effective channel.

[0070] In quantizing the effective channel or effective channel estimate, various approaches such as PMI feedback techniques may be used. For example, if the feedback may be rank-1, a dominant singular vector of the effective channel or the effective channel estimate may be calculated by the UE or WTRU such as the WTRUs 102a-d and a precoding matrix from a predefined codebook may be selected by the UE or WTRU such as the WTRUs 102a-d such that an inner product between the precoding matrix and the dominant singular vector may be maximized. As described above, the effective channel estimate may have reduced dimensions (e.g. I⁷ may be a tall matrix where the number of rows may be greater than number of columns) . As such, the mismatch between the channel feedback and actual channel may be reduced under the same feedback overhead.

[0071] According to an example embodiment, a channel quality indicator (CQI) may also be provided, fed back, broadcast, or transmitted (e.g. at 251). For example, along with the effective channel or effective channel estimate, the UE or WTRU such as the WTRUs 102a-d may also feedback or transmit (e.g. at 251) a channel quality indicator (CQI) to an eNB to assist the eNB in scheduling and link adaptation. According to additional embodiments, demodulation and/or precoding information may also be provided., fed back, broadcast, or transmitted (e.g. at 251).

[0072] FIG. 3 illustrates a block diagram of a component such as an eNB (e.g. 140a-c) of a network that may be in communication with a UE or WTRU such as the UE shown in FIG. 2. The component or eNB may receive (e.g. at 301) the feedback such as an effective channel or effective channel estimate, CQI, and/or PMI. Based on the feedback received (e.g. at 301) from the UE (or UEs) within the network and/or information such as traffic load, quality of service (QoS)

information, and the like associated with the UE (or each UE in the in the network such as the communication network 100), the component such as the eNB (e.g. 300) may make a scheduling decision, may determine and apply a channel dependent precoder (e.g. to be used in, for example, the next transmission or subsequent transmission time interval (TTI)), may determine and apply a channel independent precoder, and/or may generate and transmit Channel State Information (CSI) and/or reference symbols indicative of CSI such as CSI reference symbols (CSI-RS) that may be used, for example, for the next transmission or subsequent TTI.

[0073] For example, as shown in FIG. 3, data or feedback (e.g. feedback information) from a UE (or one or more UEs such as UEi to UEk that may be included in a network such as the communication system 100) may be received by a. controller such as a controller 305 (e.g. at 301). The controller (e.g. 305) may provide data or feedback and/or demodulation information such as demodulation reference symbols (DM-RS) for one or more UEs to a scheduling component such as a scheduling component 310 and a channel dependent preceding component such as a channel dependent precoding component 315 such that the scheduling component (e.g. 310) may receive the data or feedback and/or DM-RS (e.g. at 311), may schedule one or UEs (e.g. make scheduling decisions), and/or may provide such scheduling to other components in the UE and the channel dependent precoding component (e.g. 315) may receive (e.g. at 321) data or feedback and/or DM-RS associated with one or more UEs, information associated with the scheduling, and/or additional information, may determine a precoding technique or scheme, and/or may precede such data or feedback and/or information as described herein.

[0074] In one embodiment, scheduling and precoding decisions at the component or eNB may be made jointly or at the same time by the scheduling component (e.g. 310) and the channel dependent preceding component (e.g. 315) to, for example, achieve a particular performance (e.g. an optimum performance).

[0075] According to other embodiments, separate scheduling and precoding decisions may be made to reduce complexity or an iterative technique may be used for scheduling and precoding decisions.

[0076] For example, in one embodiment, the scheduling component (e.g. 310) may receive (e.g. at 311) data or feedback information, DM-RS, and/or additional information and may make a scheduling decision based on such information. Independent of (e.g. separate from) such a scheduling determination, the channel dependent precoding component (e.g. 315) may receive (e.g. at 321) the data or feedback information, DM-RS, and/or additional information and may determine a channel depending precoding technique or scheme (e.g. a precoding decision) that may be used, based on such information.

[0077] According to another embodiment, the scheduling component (e.g. 310) may receive (e.g. at 311) the data, feedback information, DM-RS, and/or additional information and may make a scheduling decision based on such information. The scheduling component (e.g. 310) may then provide scheduling information or information associated with scheduling decision to the channel dependent precoding component (e.g. 315) such that the channel dependent precoding component (e.g. 315) may receive (e.g. at 331) the scheduling information. [0078] The channel dependent precoding component (e.g. 315) may also receive (e.g. at 321) the data, feedback information. DM-RS, and/or additional information and may determine or select a channel dependent preceding technique or scheme (e.g. a precoding decision) that may be used based on such data, feedback information, DM-RS, scheduling, and/or additional information such that the channel dependent preceding component (e.g. 315) may precode the data or feedback, DM-RS, scheduling, and/or additional information using the determined or selected precoding technique or scheme. For example, the channel dependent precoding component (e.g. 315) may precode data, DM-RS, or information based on the feedback information such as the effective channel or effective channel estimate, the CQI, and the like that may be fed back and received (e.g. at 301). According to one embodiment, a channel dependent precoding matrix Wthat may be based on the feedback information may be used to precode the data, DM-RS, or information as described herein.

[0079] After the data, for example, received from one or more UEs or WTRUs, demodulation reference signal (DM-RS), and/or any other suitable information may be preceded (e.g. using a channel dependent pecoding matrix W) by the channel dependent precoding component (e.g. 315), the preceded data, information, or DM-RS may then further be precoded by a channel independent precoding component such as a channel independent precoding component 320. For example, a channel independent precoding component (e.g. 320) may receive (e.g. at 341) the channel dependent precoded data, information and/or DM-RS and may further precode the channel dependent precoded data, information, and/or DM- RS using an independent channel precoding (e.g. a precoding not dependent upon feedback, received (e.g. at 301)) as described herein. According to an example embodiment, the channel dependent and channel independent precoding

components (e.g. 315 and 320) may be separate components as shown in FIG. 3. Alternatively, the channel dependent and channel independent components (e.g. 315 and 320) may be combined into a single precoding component that may perform, the functionality of both the channel dependent and channel independent

components described herein. According to an example embodiment, data, DM-RS, and/or other suitable information may be preceded by the channel independent preceding component (e.g. 320) using preceding techniques or schemes without receiving or using feedback information or additional feedback information. For example, the channel independent precoding component (e.g. 320) may precede the data, information, or DM-RS without relying on feedback information or any additional information or feedback. As such, the channel independent component (e.g. 320) may be pre-arranged or arranged in a predetermined manner across time and frequency that may provide additional scheduling gain and the channel independent component (e.g. 320) may also provide additional channel variations (e.g. via time and frequency) and dimensions for scheduling decisions.

[0080] According to one embodiment (e.g. as shown in FIG. 3), the channel independent precoding component (e.g. 320) may receive (e.g. at 341) the data, DM-RS, and/or other suitable information preceded by the channel dependent precoding component (e.g. 315) and may further precede the data, DM-RS, and/or other suitable information using the precoding techniques or schemes included in the channel independent precoding component (e.g. 320) without using or relying on feedback information such as the feedback information received (e.g. at 301) or any additional feedback information. As such, the channel independent precoding component (e.g. 320) may further precede the data, DM-RS, and/or suitable information received from the channel dependent precoding component (e.g. 315) independent of feedback information.

[0081] According to another embodiment, the channel independent precoding component (e.g. 320) may receive the data, DM-RS, and/or other suitable information directly from the scheduling component (e.g. 310) and may precode the data, DM-RS, and/or other suitable information using precoding techniques or schemes included in the channel independent precoding component (e.g. 320) without using or relying on feedback information such as the feedback information received (e.g. at 301) or any additional feedback information. For example, the channel dependent precoding component (e.g. 315) may not be included in the eNB. As such, the channel independent precoding component (e.g. 320) may receive the data, DM-RS, and/or suitable information directly from the scheduling component (e.g. 310) and may precede such data, DM-RS, and/or suitable information independent of feedback information. Additionally, according to one embodiment, the preceding (e.g, the preceding technique or scheme and matrix associated therewith) that may be used by the channel independent precoding component (e.g. 320) may be the same precoding that may be used by a UE or WTRU such as the WTRUs 102a-d when generating channel state feedback as described above. For example, the channel independent precoding component (e.g. 320) may use the same channel independent precoding matrix V as the UE or WTRU such as WTRUs 102a-d may use to generate channel state feedback as described in FIG. 2. As such, channel independent precoding used by a component such as an eNB shown in FIG. 3 and a UE or WTRU such as WTRUs 102a-d may be synchronized.

[0082] Such a synchronization for channel independent precoding at a UE and. for example, an eNB may be achieved by making the channel independent precoder a function of system frame number or subframe number and/or a sub-band index (e.g. when the channel independent precoding may be on a sub-band basis).

[0083] In an example embodiment, a controller such as an eNB controller (e.g, 305) may have already made a selection of a UE or WTRU (e.g.

WTRUsl02a-d) before precoding.

[0084] A.s shown in FIG. 3, a first UE such as UEi and a second UE such as UEa may be scheduled, to a radio resource at a particular frequency and time slot (additional UEs such as UEk may also be scheduled also as shown). As such, an effective channel that may be quantized may be generated and provided by the first and second UEs as described above. For example, a quantized effective channel may be determined, generated or calculated by the UEi and fed

back and a quantized effective channel may be determined, generated, or

calculated by the UE2 and fed back.

[0085] In one embodiment, a component or eNB may implement and perform zero forcing (ZF) precoding using the channel dependent precoding component (e.g. 315) such that the received inter-user interference at the UEs such as UEi and UE2 may be close to zero. To enable such ZF precoding, the eN B may first form a composite channel by stacking effective channels or effective channel estimates associated with co-scheduled UEs such as UEi and UE2. The composite channel based on the effective channels associated the co- scheduled UEs such as UEi and UE2 may be defined as follows:

The precoder (e.g. the channel dependent precoder or preceding matrix) may then be calculated or generated using the ZF criteria or composite channel generated based on the ZF as follows:

where

normalizes the column vector of matrix X.

[0086] In an example embodiment, with, both channel dependent and independent precodmg, the received signals at, for example, the first and second UEs (e.g. UEi and UE2) may be expressed as follows (e.g. ignoring noise):

Where Y may be the combination of the received vectors of both UEi and UE2 andY1 and ¥2 may sub-vectors received by UEi and UE2 respectively, W may be the channel dependent precoder or preceding matrix as described, herein, Vmay be the channel independent precoder or preceding matrix, H_eff may be the effective channel, Di and D2 may be the source vector of UEi and. UE2 respectively, and Hi and H¾ may be unprecoded channel matrices associated with UE-. and UE2 respectively.

[0087] Under ideal conditions (e.g. if there may be no channel estimation errors and if the channel feedback may be ideal, i.e., quantization may zero),

such, that the inter-user interference may be suppressed using the precoding methods and techniques used herein. When channel quantization error may exist, the level of inter-user interference may depend on a magnitude of the quantization error that may typically include largely dominate channel estimation errors in practice due to limitations in feedback. As described above, the proposed precodmg method and techniques described herein may reduce dimensions of the channel matrix to be quantized such that the quantization error and inter-user interference may be reduced.

[0088] According to an example embodiment, the use of channel independent precoding as described herein may reduce a beamforming gain (e.g. an overall beamforming gain) for a given time and/or frequency slot. Additionally, in a communication system or network such as communication system 100 where multiple users may be simultaneously communicating with an eNB, a scheduler such as the scheduling component (e.g. 310) may be provided that may take advantage of multiple users to achieve multiuser gain. For example, a proportional fairness (PF) scheduler may be used in a scheduling component (e.g. 310). The PF scheduler may schedule each UE (e.g. UEi and UE2) to a time and/or frequency slot with a particular channel quality relative to a long term average. As such, for a given user or UE, as long as some of the radio resources (e.g. a time and/or frequency slot) associated with the user or UE achieves good channel quality, the loss of beamforming gain due to channel independent precoding may be minimized by a reasonable scheduler.

[0089] Additionally, in one embodiment, the precoder that may be used in a channel independent precoding component (e.g. 320) or even in the UE may be wideband, such that the precoder may be the same across the whole band.

According to another embodiment, to achieve maximum scheduling flexibility, the precoder used in a channel independent precoding component (e.g. 320) or even in the UE may also be subband based such that the precoder may be the same across a subband but different from subband to subband. in either case, both UE and eNB may have agreement on the type of precoder that may be used therein.

[0090] In another embodiment, the channel dependent precoding and channel independent precoding may be swapped. For example, instead of providing or reporting the feedback and channel dependent precoding matrix or precoder Wto a component or eNB, the UE may provide the channel independent precoding matrix or precoder V such that there may be a preconfigured pattern of a channel dependent precoding matrix or precoder Win each ΤΤΪ (and even each sub-band) that may be known between the UE and the eNB,

[0091] As shown in FIG. 3, a reference symbol component such as a reference symbol component 325 may be provided such that cell- specific reference symbols may be inserted into or combined with the preceded data, DM-RS, and/or other suitable information (e.g. reference symbols may be inserted into the precoded data stream, received from the channel independent precoding component (e.g. 320) and/or the channel dependent precoding component (e.g. 315)) and/or may be used to assist the channel independent precoding (e.g. by the channel independent precoding component (e.g. 320)). For example, the channel independent precoding information, matrix or precoder V and/or data, DM-RS, and/or information precoded thereby may be provided and received (e.g. at 351) by a reference symbol component (e.g. 325) such that reference symbols that may be associated with channel state information and precoding formats used by the precoding components may be generated from such information and/or may be inserted into or combined with the precoded data, DM-RS, and/or other suitable information. In an example

embodiment, one or more frequency subbands may be configured such that cell- specific reference symbols such as CSI-RS within a subband may be generated by the reference symbol component (e.g. 325). The reference symbols and/or the precoded data, DM-RS, and/or other suitable information may then be transmitted via one or more antennas (e.g. at 361). For example, the reference symbols such as CSI-RS that may be associated with the precoding formats and/or the precoded data, DM-RS, and/ any other suitable information may be broadcasted or

transmitted (e.g. at 361) from the component or eNB to one or more UEs or WTRUs such as WTRUs 102a-d of a. communication system such as the communication system 100.

[0092] FIGs. 4a and 4b illustrate diagrams of example embodiments, respectively, of a wideband based channel independent precoding (CIP) that may be implemented herein by the UE and/or eNB (e.g. WTRUs 102a-b and/or base stations or eNBs 140a-c) and subband based channel independent preceding that may be implemented herein by the UE and/or eNB where the index in parenthesis may represent a time domain index and the index, in subscription may represent a subband index. As shown in FIGs. 4a and 4b, when the subband. index may be dropped, the precoding may be and may apply to wideband. For example, V_n(t) and Wn(t) may represent a precoding matrix for CIP and a channel dependent precoding (CDP) respectively on the n-th subband and during the t-th TTI as shown in FIG. 4b and. V(t) may represent precoding matrix for CIP across a whole bandband during the t-th TTI as shown in FIG. 4a.

[0093] According to one embodiment, in subband based channel independent precoding (CIP) (e.g. as shown in FIG. 4b), the bandwidth of CIP subband may be consistent to that of the subband CQI feedback. For example, in a LTE UE feedback, mode 3-1, the CIP subband size may be 6 radio bearers (RBs) for a 10MHz communication system, which may be identical to subband size of CQI feedback that may be provided.

[0094] FIG. 5 illustrates a block diagram of another example embodiment of user equipment (UE) signal processing. As shown in FIG. 5, a UE may first perform channel estimation on the preceded cell specific RS to obtain an estimate of an effective channel such that channel independent precoding at an eNB may be taken into account. The effective channel estimate may then be quantized and fed back to eNB. As described above, the dimension of the effective channel may reduced compared to original unprecoded channel, matrix and the quantization error may be reduced.

[0095] For example, as shown in FIG. 5, a UE or WTRU such as the WTRUs 102a-d may include one or more antennas such as antenna 122 that may receive one or more signals (e.g. at 501) that may include information such as precoding information and/or channel state information, reference symbols (e.g. cell specific reference symbols (RS) or preceded cell specific reference symbols (RS)), and the like via the one or more antennas (e.g. 122). After receiving the one or more signals, the signals may be pre-processed via a front end processing unit (e.g. 505) as described above. The pre-processed signals including the information associated therewith may then be provided and received, for example, (e.g. at 511 and 521) in parallel by a channel estimation component such as a channel estimation component 510 and data demodulation component such as a data demodulation component 515. The channel estimation component (e.g. 510) may perform channel estimation on the cell specific RS or preceded cell specific RS (e.g. cell specific RS that may be inserted into a preceded data stream) to obtain an estimate of an effective channel such that channel independent preceding at an eNB may be taken into account. The effective channel or effective channel estimate may then be provided and received (e.g. at 531) by a channel quantization component such, as a channel quantization component 520 such that the effective channel or effective channel estimate may be quantized by the channel quantization component (e.g. 520) and fed back to an eNB (e.g. at 541).

[0096] FIG. 6 illustrates a block diagram of a component such as an eNB (e.g. 140a-e) of a network that may be in communication with a UE such as the UE shown in FIG. 5. As shown in FIG. 6, cell specific reference symbols (RS) may be inserted into channel dependent preceded data stream, and may then be preceded by the channel independent preceding component along with the data, DM-RS, or other suitable information. As described above, the channel independent precoding can be either wideband based or subband based.

[0097] For example, as described above with respect to FIG. 3, a controller such as a controller 605 may receive (e.g. at 601) feedback from one or more UEs may provide the feedback, data, DM-RS and/or other suitable information to a scheduling component such as a scheduling component 610 and/or a channel dependent precoding component such as a channel dependent precoding component 615 such that the scheduling component (e.g. 610) may receive (e.g. at 611) to make scheduling decisions as described above and the channel dependent precoding component (e.g. 615) may apply a channel dependent precoding matrix or precoders such as W to the data, DM-RS, and/or other suitable information based on the feedback. According to an example embodiment, the channel dependent precoding component (e.g. 615) may also receive (e.g. at 621) information associated with a scheduling decision and may use such information to precode the data, DM-RS, and/or other information as described above. As shown in FIG. 6, the precoded data, DM-RS, and/or information may then be provided to and received by (e.g. at 641) a cell specific reference component such as a cell specific reference component 620 such that the cell specific reference component (e.g. 620) may insert cell specific reference symbols (RS) into the channel dependent precoded data stream that may include the precoded data, DM-RS, and/or information. The cell-specific reference component (e.g. 620) may then provide the precoded data stream with the cell- specific RS to a channel independent precoding component such as a channel independent precoding component 625 such that the channel independent precoding component (e.g. 625) may receive (e.g. at 651) the precoded data stream including the cell specific RS and may apply a channel independent precoding method or technique including a channel independent precoder or precoding matrix such as V to the data stream as described above. The data stream may then be transmitted (e.g. at 661).

[0098] According to an example embodiments, the use of cell- specific RS may provide one or more of the following: for users that may be expected to be scheduled to lower rank transmission (e.g. as part of MU-MIMO), precoded cell specific RS may reduce the number of resource element required to transmit cell specific RS to achieve similar channel estimation quality and/or the number of elements that may be for RS may also potentially reduce inter-cell interference and, thus, may improve the quality of channel estimate. Alternatively, estimation of the effective channel may also be improved when using same number resource element as described above where non-precoded cell specific RS may be used and/or transmitted.

[0099] In one embodiment, when multiple base stations may transmit the same signals, such as coordinate multiple-point (CoMP), the signals may be multiplied with a pre- determined precoding matrix that may be channel

independent to generate an effective channel, or may be assisted with a precoded cell-specific reference symbols. The channel independent precoding matrix may be different from base station to base station, and changeable in time in a predetermined fashion. The multiple base stations may have predetermined frequency offsets to enhance a fast fading environment.

[00100] Additionally, the multiple base stations may use the concept of dirty paper coding (DPC) to generate multiple beams successively. In particular, each base station may generate a first beam for a small number of UEs. The first beams from each of the base stations may be included in a first group. Other beams may then be generated sequentially and may be orthogonal to the first beam using opportunistic multiple beamforming. Some decomposition methods such as Gram- Schmidt orthogonal method may also be used such that the first beam may be allocated optimally and other orthogonal beams may obtain, multiuser diversity with scheduling. According to an example embodiment, the first beam may not suffer from any interference from other beams as the other beams may be generated orthogonally to the first beam. The other beams may also use multiuser diversity to obtain additional gain.

[00101 ] In such embodiments, the UE may feedback a beam index, CQI. and/or quantized CSI to base stations when certain criteria may be met. Such criteria may include a CQI being higher than a predetermined threshold. As such, when a CQI may be higher than a predetermined threshold the UE may feedback a beam index, CQI, and quantized CSI to base stations according to an embodiment,

[00102] For opportunistic beamforming, the UE may also feedback CQI/CSI in an uplink (UL) sounding reference signal (SRS) rather than on a dedicated PUCCH. Alternatively, the UE may feedback such information (e.g. beam index, CQI, and/or quantized CSI) on a dedicated PUCCH.

[00103] As described, above, in an example embodiment. Vmay characterize the long term channel properties, and Wmay characterize the frequency- selective or short term properties of the channel. In such embodiment, the UE may report Vand/or Was described herein by the methods or techniques below.

[00104] Additionally, in an embodiment, the CSI for short term feedback, W, may be reported to the eNB. For example, V may be preset, and channel independent such that V may not be reported to the eNB by the UE but already stored or known by the eNB, In particular, as described above, V may be fixed, may slowly vary with time or sub-frame number, and may known to both the eNB and UE such that V may not need to be reported,

[00105] As such, according to one embodiment, an aperiodic reporting of Wor CQI/PMI/Ri may performed on PUSCH and may be triggered by a scheduling grant. In such an embodiment, suitable methods and procedures for periodic CSI reporting on PUCCH may be used and the methods or procedures for aperiodic reporting are changed or modified.

[00106] in another embodiment, V may be defined by the long term feedback, used for periodic CSI reporting using PUCCH. As such, V may be repoted to an eNB and/or UE.

[00107] Aperiodic reporting modes for UE may be semi- statically configured by higher layers to feed back CQI and PMI and corresponding RI on the same PUSCH using a suitable CSI reporting mode, in this embodiment, the modes 2-0 and 3-0 may be unchanged from methods and/or procedures currently used (e.g. in LTE-A R10).

[00108] In another example method, a preceding matrix indicator for W may be reported by the UE to the eNB. In such an embodiment, the reporting overhead for aperiodic feedback for the reporting modes 1-2, 2-2, and 3-1 that may be defined in Table 1 below may be reduced. For mode 1—2, a wideband CQI with multiple PMI may reported. A precoding matrix may also be selected for each subband from a codebook subset assuming transmission that particular subband. Then, a single wideband CQI value per codeword may be calculated assuming the use of the corresponding selected precoding matrix in each subband and.

transmission on set S subbands where S may be a higher layer configuration. In an embodiment, for transmission mode 9 with 8 CSI-RS ports, a second precoding matrix indicator for W may also be reported for each set S subband.

[00109] According to another example embodiment, for mode 2-2, the UE may perform joint selection, of a set of M (M<S) subbands of size k within the set of S subbands. A single precoding matrix may be defined for Fas described above. For transmission mode 9 with 8 CSI-RS ports suitably configured, the UE may also report a second preceding matrix indicator for W for the set S subbands.

[OOlJGj In yet another embodiment, the UE may report another second preceding matrix indicator for the M selected subbands (e.g. W₂ may be generated or calculated using an equation similar to Eq. 3 such that the second precoding matrix indicator for M selected subbands and not all subbands may be reported) that may be a short term feedback matrix for the M selected subbands.

[00111] For a higher layer configured subband feedback mode 3-1, a single precoding matrix V'as described above may be assumed for transmission on set S subbands. The UE may then report one subband CQI value per codeword far each set S subband. For transmission mode 9 with 8 CSI-RS ports suitably configured, the UE may report a second precoding matrix indicator for W that may correspond to the precoding matrix V.

[00112] in example embodiments, a UE such as the UEs or WTRUs (e.g. WTRUs 102a-d) described, herein may use periodic reporting and may be semi- statically configured by higher layers to periodically feedback different CSI (CQI, PMI. PTI, and/or RI) (e.g. to an eNB (e.g. eNBs 140a-c) as described herein on a PUCCH using the reporting modes given in Table 1 below.

Table 1: CQI and PMI Feedback Types for PUCCH CSI reporting Modes

[00113] Various CQI/PMI and RI reporting types (e.g. that may be used in LTE-A R10) with distinct periods and offsets may also be used and/or provided for the PUCCH CSI reporting modes shown in Table 2 below. For example, a type I report that may support CQI feedback for the UE selected sub-bands; a type la report that may support subband CQI and second PMI feedback; a type 2, type 2b, and/or type 2c report that may support wideband CQI and PMI feedback; a type 2a report that may support wideband PMI feedback; a type 3 report that may support RI feedback; a type 4 report that may support wideband CQI; a type 5 report that may support RI and wideband PMI feedback; and/or a type 6 report that may support RI and PTI feedback may be used and/or provided for the PUCCH CSI reporting modes shown in Table 2 below.

Table 2: PUCCH Format Payload size per PUCCH Reporting Mode and Mode State

[00114] According to one embodiment, to support the methods described herein, a reporting type 7 may be provided, and used. A type 7 report may support RI and a second PMI feedback where the second PMI feedback may correspond to the W matrix for short term feedback. V may either be configured by higher layers as described above, or may be associated with a first PMI determined at the time of the last downlink grant. Table 3 illustrates the type 7 and may be concatenated with the row disclosed therein for reporting a type 7.

Table 3: PUCCH Format Payload size per PUCCH Reporting Mode and Mode State for

Report Type 7

[0ΘΤ15] As described above, the channel dependent precoder and channel independent precoder (e.g. the double codebook approaches described, above) may be used to reduce the feedback overhead and/or the CSI quantization error. Additionally, as described above, the overall feedback of a subband may be the product of two matrices such as V and W. According to an example embodiment, V and W may belong to two separate codebooks where V may characterize the wideband and/or long-term, channel properties and W may characterize the frequency- selective and/or short-term channel properties. Such a double codebook technique (e.g. the use of channel dependent and independent preceding matrices V and W (or precoders)) may allow for a reduction of feedback overhead where V may be fed back less frequently than W and W may be less complex than the single codebook based feedback.

[00116] To further reduce overhead and further enhance such a double codebook approach, in an embodiment, channel state information (CSI) may be obtained at a transmitter (CSIT) such as an eNB rather than at a receiver such as a UE as described above and shown in FIGs. 2-3 and 5-6. The preceding may still be split into two stages and two codebooks may be used as described above. For example, the V may be preset, channel independent, and/or may change each transmit time interval (ΤΤΊ) or after a predetermined number of TTFs. A UE or WTRU may also select a matrix W to increase the capacity. Along with, the preceding matrix index (PMI) for W, the UE may also feedback the channel quality indicator (CQI) for link adaptation purposes. With enough TTIs (e.g. with enough PMIs, enough CQIs, and the described estimation techniques), an eNB may estimate a channel based covariance matrix that may include information based on or associated with the CSIT. The eNB may then use the channel based covariance matrix associated with the CSIT to design and/or derive a precoder component such as a channel dependent precoder component (e.g. 315 or 615) and to design and/or derive a scheduling component (e.g. 310 or 610).

[00117] The dimensions of W may be less than those of the single codebook based feedbacks and V, as described above, may not have to be fed. back. Positive scaling factors may be obtained or approximated from the CQIs. Additionally, a resulting CSIT (e.g. based on the covariance matrix or other suitable format may help mitigate the cross interference between, co-scheduled users and may improve the spectral efficiency.

[00118] The following methods, techniques, and/or equations may be used to calculate and/or generate W and V and/or any other vectors or matrices that may be used to calculate or generate such W and V and/or CSTI. According to example embodiments, the letters identified below may indicate vectors (lower case) or matrices (upper case). A^', A, A^*, tr(A), rank(A), and E(A) may stand for the transpose, complex conjugate, conjugate transpose, trace, rank, and expectation of A.respectively. I may denote the identity matrix with proper dimensions, 0 may denote the zero matrix with proper dimensions. A > 0 may denote that A may be a semi-positive definite matrix. |A | F may denote the Frobenius norm of A. diag(,,.) may denote the diagonal matrix with [...] on its diagonal. If B may be a set, j J3 j may denote the cardinality of B, vecO) and urwecO) may be the matrix vectorization operator and. the inverse matrix vectorization operator respectively.

According to an example embodiment (e.g. to estimate CSIT and/or W and V) a system such as the communication system 100 may include an eNB with t antennas and a UE or WTRU with φ antennas. A resource block (RB) may also be provided, for example, with 12 subcarriers. For the s^th subcarrier of such a RB, k^th TTI may denote the φΧ-l received vector at the UE by the following equation:

where

and may be the <pxt channel, precoder, diagonal power loading matrix, source vector, and noise vector respectively. Both sources and. noises may be zero-mean. As such, the covariance matrices may be

K

I and

According to such an embodiment, the channel may be constant for a RB or a TTI. The singu lar value decomposition (SVD) of H,% = ΩΨU* where rank(H¾) ^~ r, singular values {ψι,.,.,ψτ} may be in descending order, and U = [ui . ..Ui] . Additi nally, the lxi row vector may be defined as follows:

be limited to rank 1 for a particular eNB and UE or WTRU pair, Eq. (1) may be simplified (e.g.,

and n_k ^(s) may be scalars). Additionally, maximum ratio decoders (MRC) may be used whenever there are multiple receive antennas (φ>1).

10012! j In the k^th TTI, UE or WTRU channel estimation.. UE or WTRU feedback, channel estimation at an eNB, and/or data transmission may be performed. In UE or WTRU channel estimation, the UE or WTRU may estimate the channel matrix H¾ (e.g. as described above). The UE or WTRU may then construct the effective channel or effective channel, estimate by multiplying the estimated channel matrix by a preset txτ precoder V._k to generate or calculate feedback. According to one embodiment,

After constructing the effective channel or effective channel estimate, the UE or WTRU may generate (and determine) a PMI and CQI to feedback, in the channel estimation at an eNB, the eNB may use the n most recent PMIs and CQIs to estimate a channel based covariance matrix, g¾^*g,%. The eNB may the use the estimated channel based convariance matrix a precoder F& and a power loading matrix P_K for a RB,

00122] In one embodiment, the UE or WTRU may select and feedback a

PMI and CQI in the k^th TTI. For example, the estimate of H_K by the UE or WTRU may have a predetermined quality (e.g. it may be assumed to be perfect). Additionally, the UE or WTRU feedback may be limited to a predetermined rank (e.g. rank 1) to support MU-MIMO. As such, the codebook {W(l)} from which the UE or WTRU may determines the codeword (and thus PMI) may include unit-norm zxl vectors. The UE or WTRU may also generate or determine a codeword (e.g. Wk) to maximize the received Signal-to- noise ratio (SNR) as follows:

[00123] The CQI may then be calculated as a normalized receive SNR (P.¾ may be an identity matrix) with. Fk = V_kW _k as follows:

[00126] For φ=1, Wk may also be also the solution to the following:

[00127] For a given codeword W(0, the z that may minimize Eq. (9b) may be ir(H/A⁷¾W(l)). As such, z_k . = p_ke^J8" and Eq. (8) may follow.

[00128] For φ>1, more approximation may be used. For example, since W.% may be chosen as shown in Eq. (7a), the Rayleigh-Ritz theorem may result (e.g. roughly) in V.¾W,¾ to be approximately proportional to m. Using V¾^*VA = al, i//i ui^*V,¾ may be approximatel proportional to Wk^* and Eq. (8) may follow as:

[00129] According to an example embodiment, both PMI and /¾ may be fed back to an eNB for channel estimation (e.g. for CSiT estimation). Alternatively, 0k may be approximated from CQI feedback such that no additional feedback may be used.

The CQI for φ-l (and also (<p>l)) may be as follows:

[00130] Channel estimation may also be performed at the eNB. According to one embodiment, due to the processing and feedback of the UE or WTRU, the eNB may be configured to approximate (e.g. at the k^th TTI) the following:

Eq. (11a)

[00131] According to an embodiment, the eNB may not know the channels and the #'s. Here, d may be the feedback delay in number of TTIs. Given that d+n « the coherent time, the eNB may derive or arrive at equations for g_k from Eq. (1 la):

where V

and the like. The eNB may then use one of the following two methods or techniques to estimate gk^*gk from Eq. (lib).

[00132] In a first embodiment, to determine the channels and the θ's or Oi S, the eNB may perform computations to transform such channels and 0's or 9i s into a system of linear equations, As such, Eq, (lib) may be multiplied by its conjugate transpose to yield the following:

Such an operation may remove the unknown phases ft.'s leaving one unknown, gk^'gk. Then, the vecQ of Eq, (12) may be taken to yield the following:

where

Ai may be a τ²χί² matrix with rank τ². bi may be r²xl. Stacking all the equations in Eq. (13a) may yield the following:

[00133] The eNB may use some inverse problem solver to obtain x, an estimate of vec(gk^*gk). Once obtained, the eNB may use unvec(n) or some approximation thereof as an estimate of gk^*gk. For example, if unvec{x) may not Hermitian, the eNB may use that may be a Hermitian

approximation..

[00134] In a second embodiment, to determine the channels and the 0's, the eNB may use a Least Squares calculation. As in the first embodiment, first left multiply Eq. (lib) by its conjugate transpose to obtain Eq. (12). In such an embodiment, however, the following may be calculated:

To calculated or solve Eq. (15), variation may be used. For example, consider where may an arbitrary Hermitian perturbation and s may be a

real scalar, In such an embodiment, Qk+εΑ may be an admissible Q. As such, for every Δ, the following may be applied :

because /XQ/d-al) may have a minimum at £=0, As Eq. (17) may be true for every A, Q/ϊ may satisfy the following:

In such an embodiment, and

(19) may be obtained by taking the vec operation of both sides of

Eq, (18). KM-¹ may exist, then Qk may be defined as follows:

f

Then, the conjugate (e.g. ^*) of Eq, (20) may be taken, for example, to indicate that Eq. (19) may be a Hermitian that may be used..

[00135] If M may be singular, Q,% may still exist and. may be determined. First of all, the eNb may determine that Eq. (19) may consistent (e.g. there exists a solution to Eq, (18) or that an unvec of it may not be Hermitian), As such, a Ω may be determined, such that g(Q) = z. A Hermitian solution may further be determined, to g(X) = z. According to an example embodiment,

and

may follow from ^(Ω) = z. As, for example, any two Hermitian solutions to g(X) = z may yield the same cost function value,

may be a valid choice for Q¾ by the eNB.

[00136] in an example embodiment, the eNB may use Q_k or approximations of Q.¾ as its estimate of

As Q,% may not necessarily be positive semidefmite and of rank 1, the eNB may instead use a determined positive semi- definite approximation of Q,¾; may perform the eigendecomposition

where ξι≥...≥ξί and Ψ^*Ψ= I; and/or may replace the negative eigenvalues by zeros. If Q_k may have at least one positive eigenvalue, the eNB may also use a determined positive semi-definite, correct rank, and an approximation of Q¾ (e.g. that may be the same as the best positive semi-definite approximation except that the largest eigenvalue may be kept),

[00137] in one embodiment, in a TTL the same precoder and power loading matrix may be used across the whole RB. For example, and may be

the unit-norm dominant eigenvector and dominant eigenvalue of the eNB's estimate

the

[00138] According to another embodiment, a single user (SU) transmission mode may also be implemented, in such a SU transmission mode, a. UE or WTRU may get data in the k^th TTL If v may denote the index of the chosen UE or WTRU, the precoder F,% may be a unit-norm column vector, and

The eNB may select the UE or WTRU with the higher β__η. and may set may

be used as rank

may equal 1. Alternatively, the u^th UE or WTRU may be configured to feedback the index corresponding to the unit-norm codeword

that may maximize the capacity for the RB. The UE or WTRU (e.g. the u^th UE or WTRU) may also feedback the CQI with F The eNB may make scheduling decisions (e.g. as described above). For example, the eNB may select the UE or WTRU with, the higher CQI and may sets F

[00139] A. Multi User (MU) Transmission Mode may also be implemented, in such a MU transmission mode, the UE or WTRU may get data in the k^th TTL The eNB may then construct a estimate system channel matrix as folio ws:

Then, the eNB may calculate the zero forcing (ZF) precoder F,% (e.g. the ZF as described above) as follows:

Lastly, the eNB may allocate equal power to be used for each UE or WTRU by setting Pk ~ (PI 2)1. In one embodiment,

since rank(

In another embodiment,,

In yet another embodiment,

Perform anee Examp j e

[00140] An example of performance comparison between the presently disclosed technique and a conventional scheme may be provided in FIGs 7-8. For such a comparison, a simulation may be set up as follows:

[00141] As shown, both schemes may use a 4 bit feedback. Performance of 10-percentile and oO-percentile UE may be shown in FIG. 7 and FIG. 8, respectively.

[00142] In Eq, (1) as described above, a full content of effective channel may quantized and fed back to an eNB (e.g. eNBs 140a-c) described herein. To support a higher number of data streams without losing quantization accuracy, a

UE such as the UEs or WTRUs (e.g. WTRUs 102a-d) may be directed to feedback

CSI corresponding to a subset of the effective channel and may treat the rest of effective channel as interference in a CQI calculation. Additionally, UEs in a system such, as the communication system 100 may be divided into groups. UEs in the same group may feedback the same subset of the effective channel. For example, UEi and UE2 from a group 1 may feedback a PMI corresponding to the first half of column vectors and treat the 2^nd half of column vectors of the effective channel as an interference channel in CQI calculation. Similarly, UE3 and UE4 from a group 2 may feedback a PMI corresponding to the second half of column vectors of the effective channel and may treat the 1^st half of column vectors of the effective channel as an interference channel in CQI calculation.

[00143] if V= [Vi, V2], with V. being the 1^st half of column vectors, and V2 being the 2^nd half of column vectors. The UE₁ and UE2 may feedback H₁ V₁ and H₂V₁ (e.g. via PMI) respectively. Additionally, the UE3 and UE4 may feedback H₃V₂ and H4V2 respectively.

[00144] At an eNB, assuming the UEs (e.g. the four mentioned above) may be scheduled on the same radio resources, the eNB may calculate two separate zero forcing (or its variations) preceding matrices between UEi and UE2 and U E3 and. UE4 such that interference between UEi and UE2 and. LJE3 and UE4 may be suppressed when signals reach the receivers associated with the UEs. The interference between groups (UE1/UE2 and UE3/UE4) may be implicitly handled by the scheduler as the inter-group interference may be counted in CQI calculation, and the scheduler tends to schedule UEs that report high CQI and. low inter-group interference.

[00145] Although the terms beamforming and preceding may be used herein, it may and should be understood that the use of such terms may be used interchangeably and. as such, may not be distinguishable.

[00146] It may and. should be further understood that features and elements are described above may be extended to be used with other techniques and/or methods. For example, according to an embodiment, the methods or techniques disclosed herein may also be extended to open loop mode by disabling a 2^nd preceding phase (e.g. the channel dependent portion). Under such mode, PMI feedback may not be used. Each UE may derive an effective channel by multiplying a channel matrix by a predetermined preceding matrix. The predetermined, preceding matrix may vary in both time and frequency domain. When varying in frequency domain, the CQI report bandwidth and channel independent preceding bandwidth may be aligned. For a single user MIMO (SU-MIMO), the UE may use the effective channel to generate CQI feedback. Open loop may also support multiuser MIMO. Under such mode, each UE may consider and/or use a subset of the effective channel as its own channel and may treat the rest of the effective channel as interference channel in calculating CQI feedback. As such, the UEs in the system may be divided into groups, and UEs within the same group may consider the same subset of effective channel as their own channel. At an eNB, UEs from different group may be co-scheduled by a scheduler or scheduling component. Since the scheduler tends to schedule UEs with high CQI report, inter-user interference may be managed via scheduling.

[00147] Additionally, although features or elements such as the methods or procedures for determining V, and for the UE to report W may have been described with respect to use of 8 antennas at an eNB, It should be understood that the methods or procedures described for 8 CSI-RS ports and/or 8 antennas may also apply to more or less antennas or antenna ports including, for example, four or two antenna ports at an eNB.

[00148] Furthermore, although features and elements are described above in particular combinations, one of ordinary skill in the art will appreciate that each feature or element can be used alone or in any combination with the other features and elements. In addition, the methods described herein may be implemented in a computer program, software, or firmware incorporated in a computer-readable medium for execution by a computer or processor. Examples of computer-readable media include electronic signals (transmitted over wired or wireless connections) and computer-readable storage media. Examples of computer-readable storage media include, but are not limited to, a read only memory (ROM), a random access memory (RAM), a register, cache memory, semiconductor memory devices, magnetic media such as internal hard disks and removable disks, magneto-optical media, and optical media such as CD-ROM disks, and digital versatile disks (DVDs). A processor in association with software may be used to implement a radio freciuency transceiver for use in a WTRU, UE, terminal, base station, RNC, or any host computer.

Claims

What is claimed:

1. A method for providing feedback, the method comprising:

receiving a signal;

estimating a channel from reference information included in the received signal;

generating an unprecoded channel matrix based on the estimated channel and reference information;

constructing an effective channel estimate based on the unprecoded channel matrix and a predetermined channel independent precoding matrix; and

broadcasting feedback information including the effective channel estimate,

2. The method of claim 1, further comprising pre-processing the received signal and estimating the channel state information based on the pre-processed, received signal.

3. The method of claim 2, wherein pre-processing the received signal comprises performing at least one of the following: Radio Frequency (KF) processing Fast Fourier Transformation (FFT); demapping: and decoding.

4. The method of claim 1, further comprising quantizing the effective channel estimation using a predefined codebook, wherein the feedback information includes the quantized, effective channel estimate.

5. The method of claim 1, wherein constructing the effective channel estimate based on the unprecoded channel matrix and the predetermined channel independent precoding matrix comprises multiplying the unprecoded channe matrix by the predetermined channel independent matrix.

6. The method of claim 5, wherein the predetermined channel independent matrix is a tall matrix, and wherein the effective channel estimate has less dimensions than the unprecoded channel matrix when the unprecoded channel matrix is multiplied by the tall matrix associated with the predetermined channel independent matrix.

7. The method of claim 1, wherein broadcasting the effective channel estimate further comprises broadcasting a channel quality indicator (CQI), wherein the CQI is configured to assist scheduling and link adaptation.

8. A method for providing preceding, the method comprising:

receiving data and feedback information;

preceding the data based on the feedback information; preceding the data based on a channel independent beamform; and transmitting the precoded data.

9. The method of claim 8, further comprising scheduling user equipment based on the received feedback information.

10. The method of claim 8, further comprising inserting reference symbols into the precoded. data, wherein the transmitted precoded data includes the reference symbols.

11. The method of claim 8, wherein the feedback information includes an

effective channel estimate, and wherein the effective channel estimate is generated, using the channel independent beamform.

12. The method of claim 8, wherein the data comprises demodulation reference symbols (DM-RS).

13. The method of claim 8, wherein the feedback information comprises one or more preceding matrix indicators (PMIs) and one or more channel quality indicators (CQIs).

14. The method of claim 13, further comprising

estimating a channel covariance matrix based on the received PMIs and CQIs included in the feedback information; and

determining a precoder and a power loading matrix at least in part based on the channel covariance matrix, wherein the precoded is configured to precede the received data using the feedback information.

15. The method of claim 14, wherein a subset n of recent PMIs and CQIs are used to estimate the channel based covariance .matrix.

16. A base station for preceding, the base station comprising:

a processor, wherein the processor is configured to:

receive a data stream, and feedback information;

precede the data stream based on the feedback, information;

precede the data stream based on a channel independent precoder and matrix, wherein at least a portion of the feedback information is generated based on the channel independent precoder and matrix;

insert reference symbols into the precoded data stream; and transmit the precoded. data stream.

17. The base station of claim 16, wherein the processor is further configured to schedule user equipment based on the received feedback information,

18. The base station of claim. 16, wherein the feedback information includes an effective channel estimate, and wherein the effective channel estimate is generated using the channel independent precoder and matrix.

19. The base station of claim 18, wherein, the feedback information comprises a. subset of an effective channel estimate, and wherein a remaining portion of the effective channel estimate is configured to be treated as interference.

20. The base station of claim 18, wherein the feedback information further comprises at least one of the following: one or more precoding matrix indicators (PMIs) and one or more channel quality indicators (CQIs),

21. The base station of claim 20, wherein the feedback information is configured to be received from groups of user equipment (UEs), and wherein the feedback information received from a first group of UEs comprises a first subset of the effective channel estimate and the feedback information received from, a second group of UEs comprises a second subset of the effective channel estimate,

22. The base station of claim 21, wherein the first subset of the effective channel estimate comprises a first PMI corresponding to a first half of column vectors associated with the effective channel estimate, and wherein the second subset of the effective channel estimate comprises a second PMI corresponding to a second half of column vectors associated with the effective channel estimate.

23. The base station of claim 22, wherein the processor is further configured to calculate separate zero forcing precoding matrices between the UEs included the first group of UEs and the UEs included in the second group of UEs such that interference between the UEs included the first group of UEs and interference between the UEs included in the second group is configured to be suppressed when signals from the base station reach the UEs.

24. The base station of claim. 23, wherein the processor is further configured, to handle scheduling of the UEs.

25. The base station of claim 24, wherein the processor is further configured to handle interference between the first group of UEs and the second group of UEs during scheduling of the UEs.