CN103004160B - Select wave beam group and the device of beam subset, method and computer program product in a communications system - Google Patents

Abstract

Disclose a kind of apparatus and method for selecting wave beam group and beam subset in a communications system.The method includes: measure the channel condition information (CSI) (920) about the downlink from base station；Broadband properties according to CSI identifies the selected wave beam group (930) from wave beam group set；In selected wave beam group, selected beam subset (940) is identified according at least one subband.Wherein, the characteristic of wave beam group set depends on that the number of the wave beam in transmission rank, and selected beam subset is equal to transmission rank.The method farther includes: generates with this form of dicode and identifies selected wave beam group and the encoder feedback information (950) of the selected beam subset for each subband, transmits encoder feedback information to base station.Also disclose a kind of computer program, including being configured so that device realizes the program code of above operation.

Description

Apparatus, method and computer program product for selecting a beam group and a beam subset in a communication system

RELATED APPLICATIONS

The present invention claims priority from PCT application PCT/CN2010/073411 (attorney docket No. EIE100124PCT) entitled "apparatus and method for selecting a group of beams and a sub-station of beams communication system", filed on SIPO at 6/1/2010, the entire contents of which are incorporated herein by reference.

Technical Field

The present invention relates generally to communication systems, and in particular, to an apparatus, method and system for selecting a beam group and a beam subset in a communication system.

Background

The long term evolution ("LTE") (also referred to as 3GPP LTE) of the third generation partnership project ("3 GPP") refers to research and development involving 3GPP LTE release 8 and beyond, which is the name commonly used in the industry to describe ongoing efforts directed at identifying technologies and capabilities that may improve systems such as universal mobile telecommunications system ("UMTS"). The label "LTE-a" is commonly used in the industry to refer to further developments in LTE. The goals of this broad-based project include improving communication efficiency, reducing costs, improving services, using new spectrum resources, and achieving better integration with other open standards.

An evolved universal terrestrial radio access network ("E-UTRAN") in 3GPP includes base stations that provide user plane (including packet data aggregation protocol/radio link control/medium access control/physical ("PDCP/RLC/MAC/PHY") sublayers) and control plane (including radio resource control ("RRC") sublayer) protocol terminations towards wireless communication devices such as cellular telephones. A wireless communication device or terminal is commonly referred to as user equipment (also referred to as "UE"). A base station is an entity of a communication network commonly referred to as NodeB or NB. In particular, in E-UTRAN, an "evolved" base station is called an eNodeB or eNB. For details on the overall architecture of E-UTRAN, see 3GPP technical Specification ("TS") 36.300v8.7.0(2008-12), incorporated herein by reference. For details of radio resource control management, see 3gpp ts25.331v.9.1.0(2009-12) and 3gpp ts36.331v.9.1.0(2009-12), incorporated herein by reference.

As wireless communication systems, such as cellular telephone, satellite and microwave communication systems, become widely deployed and continue to attract a growing number of users, there is a pressing need for large and variable numbers of communication devices that accommodate the transmission of larger and larger amounts of data within fixed spectrum allocations and wired transmission power. The increased amount of data is a result of wireless communication devices transmitting video information and surfing the internet as well as performing ordinary voice communications. To address these continuing needs, a subject of current general interest in 3GPP is the efficient use of spatially multiplexed cellular transmissions. Efficient use of spatially multiplexed transmissions may support transmission of higher data rates at hertz ("Hz") per bandwidth at limited transmit power levels, thereby enabling a wireless communication device to transmit larger amounts of data in shorter periods of time, or equivalently, to accommodate substantially simultaneous operation of larger amounts of wireless communication devices.

To meet peak spectral efficiency requirements (up to 30 bits/Hz), support for up to 8 transmit ("Tx") antennas in the downlink ("DL") will be standardized in 3gpp lte release 10, enabling up to 8 spatial layers to be utilized for downlink spatial multiplexing transmission. We now agree 8-transmit both downlink multiple-input/multiple-output ("MIMO") and enhanced multi-user multiple-input/multiple-output ("MU-MIMO") as part of a release 10 work item related to enhanced downlink MIMO transmission. Such a process would enable higher data rates to be transmitted at limited transmitter power levels per bandwidth hertz.

However, the process of enabling a wireless communication device to communicate channel state and other related information back to a base station so that the base station can efficiently perform spatially multiplexed transmissions in the downlink introduces a number of challenges. One of the problems is how to address the increased degrees of freedom and communication channel dimensions associated with downlink antenna beamforming (also referred to as transmit precoding) without channel state information reporting burdening the uplink communication channel for the wireless communication device. Another problem is to achieve improved single user multiple input/multiple output ("SU-MIMO") performance with a large azimuth extension in the wireless communication channel at the transmit antenna array. It is generally believed that under current configurations, coverage for wireless communication devices located at beam intersections in the antenna beam space may be poor.

In view of the ever-increasing deployment of communication systems, such as cellular communication systems, and these unresolved issues, it would be beneficial to employ an improved codebook format to enable a wireless communication device to efficiently determine and communicate channel states and antenna beam characteristics to a base station, which avoids the drawbacks of current communication systems.

Disclosure of Invention

These and other problems are generally solved or circumvented, and technical advantages are generally achieved, by embodiments of the present invention, which include an apparatus, method, and system for selecting a beam group and a beam subset in a communication system. In one embodiment, an apparatus includes a processor and a memory including computer program code. The memory and the computer program code are configured to, with the processor, cause the apparatus to measure channel state information regarding a downlink from a base station and identify a selected beam group from a set of beam groups according to a broadband property of the channel state information. The characteristics of the set of beam groups depend on the transmission rank. The memory and the computer program code are further configured to, with the processor, cause the apparatus to identify a selected subset of beams in the selected beam group according to the at least one subband. The number of beams in the selected subset of beams is equal to the transmission rank.

The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures or processes for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.

Drawings

For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following detailed description taken in conjunction with the accompanying drawings, in which:

FIGS. 1 and 2 illustrate system level diagrams of embodiments of a communication system that provides an environment for application of the principles of the present invention, the communication system including a base station and a wireless communication device;

FIGS. 3 and 4 illustrate system level diagrams of embodiments of communication systems, including wireless communication systems, that provide an environment for application of the principles of the present invention;

FIG. 5 illustrates a system level diagram of an embodiment of a communication unit of a communication system for application of the principles of the present invention;

6A, 6B, 7A, and 7B illustrate graphical representations of embodiments for forming beam groups in accordance with the principles of the present invention;

FIG. 8 illustrates a graphical representation of an embodiment of a beam group according to the principles of the present invention; and

fig. 9 illustrates a flow chart of an embodiment of a method of operating a communication system in accordance with the principles of the present invention.

Detailed Description

The making and using of the presently preferred embodiments are discussed in detail below. It should be appreciated, however, that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use the invention, and do not limit the scope of the invention. In light of the foregoing, the present invention will be described with reference to exemplary embodiments in the specific context of apparatus, methods and systems for determining channel states and antenna beam characteristics in a communication system and communicating the channel states and antenna beam characteristics from a wireless communication device, such as a user equipment, to a base station. The apparatus, methods and systems are applicable to, but not limited to, any communication system including existing and future 3GPP technologies (i.e., UMTS, LTE and future variations thereof, such as fourth generation ("4G") communication systems).

Turning now to fig. 1, illustrated is a system level diagram of an embodiment of a communication system including a base station 115 and wireless communication devices (e.g., user equipment) 135, 140, 145 that provides an environment for application of the principles of the present invention. The base station 115 is coupled to a public switched telephone network (not shown). The base station 115 is configured with multiple antennas for transmitting and receiving signals in multiple sectors, including a first sector 120, a second sector 125, and a third sector 130, each of which typically spans 120 degrees. Although fig. 1 illustrates one wireless communication device (e.g., wireless communication device 140) in each sector (e.g., first sector 120), a sector (e.g., first sector 120) may typically contain multiple wireless communication devices. In alternative embodiments, the base station 115 may be formed of only one sector (e.g., the first sector 120), and a plurality of base stations may be constructed to transmit according to a cooperative (co-operative) multiple input/multiple output ("C-MIMO") operation or the like.

The sectors (e.g., first sector 120) are formed by focusing and phasing the radiated signals from the base station antenna, and a separate antenna may be employed per sector (e.g., first sector 120). The multiple sectors 120, 125, 130 may increase the number of subscriber stations (e.g., wireless communication devices 135, 140, 145) capable of communicating simultaneously with the base station 115 without increasing the utilized bandwidth by reducing interference from focusing and phasing the base station antennas. Although the wireless communication devices 135, 140, 145 are part of a primary communication system, the wireless communication devices 135, 140, 145 and other devices such as machines (not shown) may be part of a secondary communication system to participate in, but are not limited to, device-to-device and machine-to-machine communication or other communication.

Turning now to fig. 2, illustrated is a system level diagram of an embodiment of a communication system including a base station 210 and wireless communication devices (e.g., user equipment) 260, 270 that provide an environment for application of the principles of the present invention. The communication system includes a base station 210 coupled to a core telecommunications network, such as a public switched telephone network ("PSTN") 230, by a communication path or link 220 (e.g., by a fiber optic communication path). The base station 210 is coupled by wireless communication paths or links 240, 250 to wireless communication devices 260, 270, respectively, within its cellular region 290.

In operation of the communication system illustrated in fig. 2, the base station 210 communicates with each of the wireless communication devices 260, 270 over the control and data communication resources allocated by the base station 210 on communication paths 240, 250, respectively. In frequency division duplex ("FDD") and/or time division duplex ("TDD") communication modes, the control and data communication resources may include frequency and time slot communication resources. While the wireless communication devices 260, 270 are part of a primary communication system, the wireless communication devices 260, 270 and other devices such as machines (not shown) may be part of a secondary communication system to participate in, but are not limited to, device-to-device and machine-to-machine communication or other communications.

Turning now to fig. 3, illustrated is a system level diagram of an embodiment of a communication system, including a wireless communication system, that provides an environment for application of the principles of the present invention. The wireless communication system may be configured to provide evolved UMTS terrestrial radio Access network ("E-UTRAN") universal mobile telecommunications services. A mobile management entity/system architecture evolution gateway ("MME/sae gw", one of which is indicated at 310) provides control functionality for E-UTRAN node bs (indicated as "eNB", "evolved node B", also referred to as "base station", one of which is indicated at 320) via S1 communication links (some of which are indicated as "S1 link"). The base stations 320 communicate via X2 communication links (some of which are indicated by "X2 links"). The various communication links are typically fiber optic, microwave, or other high frequency metallic communication paths, such as coaxial links, or a combination thereof.

The base station 320 communicates with wireless communication devices, such as user equipment ("UE", some of which are indicated at 330), which are typically mobile transceivers carried by users. Thus, the communication links (indicated with "Uu" communication links, some of which are indicated with "Uu links") coupling the base stations 320 to the user equipment 330 are air links employing wireless communication signals such as, for example, orthogonal frequency division multiplexing ("OFDM") signals. While the wireless communication device 330 is part of the primary communication system, the user device 330 and other devices such as machines (not shown) may be part of the secondary communication system to participate in, but are not limited to, device-to-device and machine-to-machine communication or other communication.

Turning now to fig. 4, illustrated is a system level diagram of an embodiment of a communication system, including a wireless communication system, that provides an environment for application of the principles of the present invention. The wireless communication system provides an E-UTRAN architecture including base stations (one of which is indicated at 410) providing E-UTRAN user plane (packet data aggregation protocol/radio link control/medium access control/physical) and control plane (radio resource control) protocol terminations towards wireless communication devices such as user equipment 420 and other devices such as machines 425 (e.g., appliances, televisions, meters, etc.). The base stations 410 are interconnected with an X2 interface or communication link (indicated with "X2"). The base station 410 is also connected via an S1 interface or communication link (indicated with "S1") to an evolved packet core ("EPC") that includes a mobile management entity/system architecture evolution gateway ("MME/sae gw," one of which is indicated with 430). The S1 interface supports a multi-entity relationship between the mobility management entity/system architecture evolution gateway 430 and the base station 410. For applications supporting inter-public land mobile handover, inter-eNB active mode mobility is supported by a mobility management entity/system architecture evolution gateway 430 relocation via the S1 interface.

The base station 410 may host functions such as radio resource management. For example, the base station 410 may perform various functions such as internet protocol ("IP") header compression and encryption of user data streams, transcoding of user data streams, radio bearer control, radio admission control, connection mobility control, dynamic allocation of communication resources to user equipment in uplink and downlink, selection of a mobility management entity at the time of user equipment attachment, routing of user plane data towards the user plane entity, scheduling and transmission of paging messages (sourced from the mobility management entity), scheduling and transmission of broadcast information (sourced from the mobility management entity or operations and maintenance), and measurement and reporting configuration for mobility and scheduling. The mobility management entity/system architecture evolution gateway 430 may host various functions such as distribution of paging messages to the base stations 410, security control, termination of U-plane packets for paging reasons, handover of U-plane for support of user equipment mobility, idle state mobility control, and system architecture evolution bearer control. The user equipment 420 and the machine 425 receive the allocation of the information block groups from the base station 410.

Further, some of the base stations 410 are coupled home base stations 440 (devices) that are coupled to devices such as user equipment 450 and/or machines (not shown) for the secondary communication system. The base station 410 may allocate secondary communication system resources directly to the user equipment 420 and the machine 425 or to the home base station 440 for communication (e.g., local communication) within the secondary communication system. For a better understanding of the home base station (indicated with "HeNB"), see 3gpp ts32.871v.9.1.0(2010-03) incorporated herein by reference. While the user equipment 420, machine 425 are part of the primary communication system, the user equipment 420, machine 425 and home base station 440 (communicating with other user equipment 450 and machines (not shown)) may be part of a secondary communication system to participate, but are not limited to, device-to-device and machine-to-machine communication or other communications.

Turning now to fig. 5, illustrated is a system level diagram of an embodiment of a communication unit 510 of a communication system for application of the principles of the present invention. The communication unit or device 510 may represent, but is not limited to, a base station, a wireless communication device (e.g., subscriber station, terminal, mobile station, user equipment, machine), a network control unit, a communication node, and so forth. The communication unit 510 includes at least a processor 520, a memory 550 that stores programs and data of a temporary or more permanent nature, an antenna 560, and a radio frequency transceiver 570 coupled to the antenna 560 and the processor 520 for bidirectional wireless communication. The communication unit 510 may provide point-to-point and/or point-to-multipoint communication services.

The communication unit 510, such as a base station in a cellular network, may be coupled to a communication network element, such as a network control unit 580 of a public switched telecommunications network ("PSTN"). The network control unit 580 may in turn be formed by a processor, memory and other electronic components (not shown). The network control unit 580 typically provides access to a telecommunications network such as the PSTN. Access may be provided using fiber optic, coaxial, twisted pair, microwave communication, or similar links coupled to appropriate link termination units. The communication unit 510, formed as a wireless communication device, is typically a self-contained device to be carried by an end user.

The processor 520 in the communication unit 510, which may be implemented with one or more processing devices, performs functions associated with its operation, including, but not limited to, precoding of antenna gain/phase parameters (precoder 521), encoding and decoding of individual bits forming a communication message (encoder/decoder 523), formatting of information, and overall control of the communication unit (controller 525), including procedures related to management of communication resources (resource manager 528). Exemplary functions related to management of communication resources include, but are not limited to, hardware installation, traffic management, performance data analysis, end user and device tracking, configuration management, end user management, management of wireless communication devices, charging management, subscription, security, billing, and the like. For example, according to the memory 550, the resource manager 528 is configured to allocate primary and secondary communication resources (e.g., time and frequency communication resources) to communicate voice communications and data to/from the communication unit 510, and thus format messages including the communication resources in the primary and secondary communication systems.

The execution of all or part of specific functions or procedures related to the management of communication resources may be performed in a device separate from and/or coupled to the communication unit 510 and the results of such functions or procedures communicated to the communication unit 510 in relation to the execution. The processor 520 of the communication unit 510 may be of any type suitable to the local application environment, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors ("DSPs"), field programmable gate arrays ("FPGAs"), application specific integrated circuits ("ASICs"), and processors based on a multi-core processor architecture, as non-limiting examples.

The transceiver 570 of the communication unit 510 modulates information onto a carrier waveform for transmission by the communication unit 510 via the antenna 560 to another communication unit. The transceiver 570 demodulates information received via the antenna 560 for further processing by other communication units. The transceiver 570 is capable of supporting duplex operation of the communication unit 510.

As described above, the memory 550 of the communication unit 510 may be one or more memories and of any type suitable to the local application environment and may be implemented using any suitable volatile or non-volatile data storage technology, such as semiconductor-based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. The programs stored in memory 550 may include program instructions or computer program code that, when executed by an associated processor, enable communication unit 510 to perform the tasks described herein. Of course, the memory 550 may form a data buffer for data transmitted to or from the communication unit 510. Exemplary embodiments of the systems, subsystems and modules described herein may be implemented, at least in part, by computer software executable by processors of, for example, a wireless communication device and a base station, or by hardware, or a combination thereof. As will become more apparent, the systems, subsystems, and modules may be implemented in the communication unit 510 as illustrated and described herein.

The discussion in 3GPP has recently focused on codebook design for 8 base station transmit antennas and associated transmit precoding, which is not present in the new LTE release 10 standard. In the ran1no.59 conference, it has been agreed to extend the release 8 implicit feedback framework to LTE release 10. This is based on a modular (or multi-granular) design, combining two feedback components from separate codebooks representing different characteristics of channel state information. One feedback component is directed to a wideband communication channel property (also referred to as a wideband property) and/or a long-term communication channel property (also referred to as a long-term property), while the other is directed to a frequency selective communication channel property (also referred to as a frequency selective property) and/or a short-term communication channel property (also referred to as a short-term property). An example of a long-term property is the directional structure of the optimal transmit beam. For example, the location of the user equipment does not change rapidly and, therefore, its azimuth direction may be substantially fixed. Thus, the directional structure of the transmit beam can be represented by long-term properties that happen to be of a broadband nature, especially when there is strong spatial correlation at the transmit antenna array, which is very likely to be observed under the assumption of closely spaced antenna elements (e.g., spaced by half a wavelength). An example of a short-term attribute is rapid amplitude and phase fluctuations in the communication path through the air. Such rapid fluctuations may be represented by short-term properties that typically have frequency selective properties (i.e., vary according to frequency sub-band).

This communication channel feedback structure is also referred to herein as a dual codebook structure. Although the missing LTE release 10 standard specification relates to one of the 8-layer transmissions in a base station with an 8 transmit antenna configuration, the principles of the double codebook structure can be generalized to any number of transmit antennas. As described herein, a new codebook design and structure for dual codebook-based channel state information ("CSI") feedback in support of downlink SU-/MU-MIMO operation is described for applications not limited to LTE Release 10 and beyond.

3gpp LTE downlink MIMO operation is one of several work items under consideration of LTE release 10. Two new improvements to LTE release 8/9 of downlink MIMO are being considered. One improvement resides in optimization of MU-MIMO operation that benefits from a new reference symbol ("RS") design package employing precoded user equipment specific reference symbols (referred to as UE-RS, or "dedicated reference symbols" DM-RS "in 3GPP organizations) and periodic channel state information reference symbols (" CSI-RS "). A second improvement is to extend the downlink transmission operation to 8-layer downlink SU-MIMO.

These improvements serve as support for an enhanced user equipment feedback mode following the implicit feedback principle from LTE release 8. Accurate channel state information feedback plays an important role for reliable, interference-free (or substantially interference-free) communication, in particular for MU-MIMO. Furthermore, the signaling aspect and codebook size are important when considering extensions for 8 transmit SU/MU-MIMO operation due to the increased degrees of freedom and communication channel dimensions therein.

Similar to LTE release 8, the user equipment feedback design of LTE release 10 builds on the implicit feedback principle (channel quality indicator/precoding matrix indicator/rank indicator) but with the following differences: that is, a dual codebook format is used instead of a single codebook format. However, a single codebook feedback can still be seen as a special case of setting one of the codebook entries as an identity matrix. The decision on the release 10 design is traced back to the 3GPP working group ran1no.59, where the precoder for a subband consisting of two matrices belonging to different codebooks is described in the slide show represented in 3GPP document R1-101683 entitled "wayforfordrel-10 feedbackframe" which is incorporated herein by reference. One codebook is directed to wideband communication channel properties and/or long term properties, and the matrix is therefore denoted here as "W₁". The other codebook is directed to frequency selectivity and/or short term properties, and hence the matrix is denoted here as "W₂". The resulting precoder for each subband may be, for example, constructed as a matrix multiplication of two matrices.

In the recent 3gpp ran1 conference, a way to exploit long/short term properties and several codebook design proposals have been proposed. Several key design aspects are included in these proposals: the feedback concept is conceived to operate with cross-polarized ("XP") and uniform linear array ("ULA") array type base station antenna settings, and therefore, the codebook must be designed and optimized accordingly. The long-term and short-term attributes may be sampled at the same or different time periods and reported accordingly (at the same or different times). While taking into account a relatively fixed total feedback rate budget (i.e., a fixed total number of bits in a given time interval), one can attempt to find the best balance of putting feedback bits between codebooks that are characterized by long-term and short-term properties. The final precoder is the output of an operation (e.g., matrix multiplication) between the long-term precoder and the short-term precoder.

In such a product, a wideband/long-term precoder matrix W₁And a short-term precoder matrix W₂May further distinguish the concept. If the wideband/long-term properties are processed after the communication channel (i.e. the channel matrix "H" is right-multiplied by H x W)₁) Then the main antenna beam can be seen as steered towards the user equipment signal space, and further fine tuning (refinement) can enhance the co-phasing (transmission rank-1) or orthogonality (transmission rank > 1) between the beams/precoders at subband level. This can be viewed as W₁*W₂And (4) matrix multiplication operation. On the other hand, the matrix W can be aimed at₁Creating a larger beam space that can be multiplied by the left-hand matrix W₂Is fine-tuned. The final precoder matrix W is W₂*W₁The output of the matrix multiplication. It can be argued that the two ways of forming the product of the two codebooks are almost the same. The main difference is how to define the matrix W₂And W₁Beam and fine tuning. The common property (denoxinator) is the use of an (oversampled) discrete fourier transform ("DFT") vector or matrix-pair matrix W₁And (4) constructing.

From a complexity point of view, the matrix W is selected at the user equipment of the communication channel₂And W₁Is also important and this may affect the performance of the scheme itself. For example, in a wide bandLong-term and short-term precoder (matrix W)₂And W₁) Under the assumption of an exhaustive search of all possible combinations of (a), one feedback proposal can perform optimally, but degrade under more practical and less complex precoder selections. When considering up to 8 spatial layers (or streams), the dual codebook concept is attractive mainly for lower transmission ranks, i.e. transmission ranks 1-2 and possibly also transmission ranks 3-4, while higher transmission ranks may rely on only a single feedback component (e.g. a matrix W of size Nt times R)₂Where Nt and R are the number of transmit antennas and the transmission rank, respectively, at the base station), while the other components are theoretically set to an identity matrix (e.g., a matrix W of size Nt times Nt)₁＝I)。

As with the points described above, the dual codebook concept can be reduced to the definition of beams and vectors or precoders that the beam selection/combination is part of the two codebooks. Because of the matrix W₁The construction of (a) can employ an oversampled discrete fourier transform matrix/vector, the design effectively building on some form of the well-known beam grid concept, where the user equipment effectively selects one beam (one column of the discrete fourier transform matrix) that provides the best transmission performance.

The release 10feedback concept should support SU-MIMO and MU-MIMO, where SU-MIMO is typical and provides most of the performance gain for less correlated cases with high azimuth (angle) spread of the communication channel, and MU-MIMO is typical and provides most of the performance gain for highly correlated cases with small azimuth spread. In the case of higher azimuth extension and SU-MIMO operation, as in conventional beam grids, selecting only one beam (or multiple beams in case of transmission rank > 1) for the entire frequency band is usually not sufficient to achieve good communication performance, since frequency selective precoding and beam selection at subband level are best known to perform in this case. On the other hand, for very low azimuth extension and MU-MIMO operation, the beam-grid is known to perform well, since in this case wideband and frequency selective precoding achieve very close to the same performance, and wideband precoding is more attractive due to much lower associated channel state information feedback overhead. As described herein, the conventional beam-grid concept is improved such that low azimuth extension scenarios are still well supported, while the performance of SU-/MU-MIMO operation is improved in scenarios with high azimuth extension.

The main codebook structure was introduced during the rand1 no.61 conference of montreal, canada, 5 months 10-14, 2010. However, some concepts are even older. A codebook structure is described in document R1-102630 of 3gpp tsg-RANWG1#61 entitled "refementsoffeedbackandcodebooksdesin" (montreal, canada, 10-14, 2010), which is incorporated herein by reference.

In a first proposal for codebook structure, the precoder matrix W is processed mainly in a wideband sense₁Compressing the communication channels in the spatial dimension such that the resulting equivalent communication channel matrix H W₁Having a lower dimension than the physical transmission communication channel matrix H (e.g., having a size Nr times Nt, where Nt and Nr are the number of transmit and receive antennas, respectively). Through a matrix W₂Further combining (co-phasing) or orthogonalization between the two remaining dimensions (or beams) (for cross-polarized antennas) is handled, which is applicable to the frequency selective approach at the sub-band level. Precoder matrix W₁Is a block diagonal matrix in which each block comprises a column of an oversampled discrete fourier transform matrix. Two matrices W₂And W₁May allow for support of cross-polarized and uniform linear array antenna configurations using the same codebook. This is done by pairing matrices W₁Using 4 bits and applying a matrix W₂Implemented using two bits. In the case of four-antenna transmission (e.g., corresponding to four transmit uniform linear array configurations or to each block of four co-polarized transmit antenna elements assuming a cross-polarized 8-transmit antenna configuration), for the matrix W₁Essentially converted into oversampled coefficients for four discrete fourier transform matrices. For matricesW₂While the concept also addresses the operation of transmission rank 1-2 in release 10, the entry in the codebook of (1) includes the 2 transmit antenna codebooks of release 8. At W₁After the matrix structure has been adapted to the communication channel, the precoder matrix W₂Aims at handling cross-polarization combinations (co-phasing and orthogonalization) and also provides support for uniform linear array operation, all based on W₂The operation of the matrix is done in a frequency selective manner at the sub-band level.

Additionally/alternatively, some user equipment feedback reporting modes (e.g., on the physical uplink control channel ("PUCCH")) can be designed under the constraint of very low associated feedback overhead. In the latter case, it makes sense, for example, to consider performing W in a broadband manner₂And W₁Both matrix selection and reporting. The main difference compared to conventional beam grids is that the feedback is based on a dual codebook format or structure, where the format is used to provide beam grid-like operation for uniform linear arrays and cross-polarized type arrays with the same feedback. The problem with this scheme is exactly that mentioned in the foregoing (i.e. it does not support improved SU-MIMO performance when the azimuth extension is high).

In a second proposal, the precoder matrix W₁A set of column vectors is selected from the oversampled discrete fourier transform matrix. For the case of cross-polarized antennas, four antenna beams are created according to the polarization, while 8 beams are used for a uniform linear array. For the matrix W₁The signaling uses 1 bit, the codebook divides the codeword (beam) space into two non-overlapping parts, and one of them is selected for further use via the precoder matrix W₂Fine tuning or appropriate beam adjustment at the subband level. Note that in one bit selection space, the beams are predefined for further processing; thus, in the case of 8 transmit antennas, there is one W₁8 beams defined by a matrix, matrix W₁Is 8 × 16 under the heading "8 txcookdiesign" (montreal, canada, 2010)Months 5, 10-14) in 3gpp tsg-RANWG1#61 document R1-102823, which is incorporated herein by reference.

Also note that the main difference from the previous proposal is that the matrix W is utilized₁The communication channels are compressed in the spatial dimension. Allowing the use of the matrix W₂Further processing of the larger space (i.e., with full communication channel dimensions) at the sub-band level may be seen as an advantage of one of the concepts, particularly in the case of SU-MIMO transmission with larger azimuth extension and higher transmission rank. Signaling precoder matrix W by four bits₂And the associated codebook includes a combiner and a beam selector.

Especially in the SU-MIMO case described above, due to the fact that the matrix W₁The freedom to select multiple beams per subband resulting from the main segmentation of the operation can be seen as an advantage. However, because of the matrix W₁The defined beam space is very large resulting in a matrix W₁This flexibility brings its own drawbacks, since it cannot be used alone well. In addition, due to the use of the matrix W₁The two spaces created result in poor coverage for user equipment located at the intersection of the spaces.

In a third proposal, the signal is passed through a matrix W₁Multiple beams are supported per subband. Second precoder matrix W₂Redefining W by left multiplication₁(i.e., W)₂*W₁) Thereby performing the rotation of the initial beam. The first codebook (i.e., the AND matrix W)₁Associated codebook) also contains combiners along the primary beam and has a large size of 32 beams in total, while the second codebook (i.e., the sum W of W and W) is used for combining the primary beams with the secondary beams₂Associated codebooks) may have only 2-3 bits, including several rotation matrices. In fact, there are only two interpolar combiners available for cross-polarized operation, which can be seen as a drawback. For matrix W₁Codebook subset restriction of (a) is also possible. In 3GPPTSG-RANWG1#61 titled "Viewson the feedbackFramework for Rel.10" (Montreal, Canada, 5.2010, 10-14) document R1-10302A codebook structure is described in 6, which is incorporated herein by reference.

A summary of the mainly proposed concepts is illustrated below in table 1:

TABLE I

Consider for matrix W₁And W₂The same time of reporting (which affects the utilization of the physical uplink shared channel ("PUSCH")) and the same time of reporting with the matrix W₂With 6 PRB granularity and 10 millisecond ("ms") period for the reported 50 physical resource blocks ("PRBs"), table 2 below illustrates the feedback rate of the main proposed concept.

TABLE II

As described herein, a codebook structure is described that provides improved support for scenarios with low spatial correlation/high azimuth extension, where improved frequency selective feedback is required for good performance. The codebook format or structure also provides improved support for higher transmission ranks, particularly for the case of uniform linear arrays.

As previously described, the codebook structure is based on similar beam groups as in the second proposal (i.e., the first part of the feedback signal performs beam group selection and the second part of the feedback signal performs beam selection from the selected beam group). The first part of the feedback applies to the whole band or wideband properties, while the second part of the feedback is subband-specific. MakingThe second part of the feedback can also be applied in a broadband manner for special cases. In this particular case, it should be appreciated that there is a single sub-band for channel state information feedback, where the width is equal to the wideband system bandwidth. To support beam group selection with dual codebook formats or structures and beam selection from the selected beam group, there is a precoder matrix W containing e.g. discrete fourier transform based sub-matrices₁And a precoder matrix W comprising column selection vectors and phase shifts₂Such that the actual beams in the beam group are determined by a matrix multiplication of the form:

W＝W₁*W₂。

as described herein, the beam groups may overlap. Overlapping beam groups are intended to cover situations with higher azimuth extension, where the enhanced broadband/long-term transmission direction is at the "edge" or in other words at the boundary of two beam groups. In such a case, there is no beam group overlap, and a portion of the azimuthal spread may not be captured with precoding because it falls into an adjacent beam group. Overlapping generally refers to the total angular domain (or angular domains) spanned by the beam sets being overlapping. The angular domain may refer to the angular range from the direction of maximum array gain for the first beam to the direction of maximum array gain for the last beam in the beam group, or equivalently, the largest possible angular range in terms of the direction of maximum array gain between any two beams within the beam group. One special case of such overlapping of beam groups is that the beam groups partly contain the same beam. In this case, different matrices W may be partially constructed from the same column vector₁。

Secondly, the number of beam groups and/or the beam group size (number of beams in the group) and/or the total angular domain of the beam groups (angular range spanned by the beam groups) depends on the transmission rank. Typically 8 transmit antenna arrays have antennas that are physically very closely spaced. Because higher transmission ranks employ fairly uncorrelated communication channels, the communication channel azimuth spread must be large to support higher rank transmissions. In the case of a dual codebook format or structure, such high azimuth spread can be properly captured if the beam group size and total angular field are large enough so that it covers a large range of azimuth angles. Therefore, for higher transmission ranks, the beam set size and the total angular domain should be made larger. Thus, the two aspects presented may be combined. Overlapping beam groups are constructed, where the size, number, and angular domain of the overlapping beam groups may vary depending on the transmission rank.

As introduced herein in the exemplary embodiments, this description is provided in terms of a beam group selected from a set of beam groups and a subset selection of beams from the selected beam group, and possibly overlapping beam groups. This can be equally translated in terms of matrix/vector descriptions and codebook formats or structures. Set of beam groups specific to transmission rank is converted into or associated with a transmission rank in a codebook-targeted wideband and/or long-term property W₁A set of matrices. The number of beam groups within a set of beam groups depends on the transmission rank referring to the W in the set of matrices associated with a given rank₁The number of matrices depends on the rank itself. Beams within a given beam group are converted to W associated with the beam group₁A particular column vector within the matrix or, equivalently, the resulting precoder matrix W ═ W₁*W₂The particular column of (a). Thus, the number of beams within a beam group is converted to the number of columns within the associated precoder. The overlap of beam groups within a set of beam groups may be described as having other precoders associated with other beam groups within the set of beam groups (e.g., other ws)₁Matrix or matrices) associated with the beam group of a subset of the column vectors found in the matrix (e.g., W)₁A matrix). Selecting a subset of beams from the selected beam group, for example, translates from a matrix (e.g., W) associated with the selected beam group₁Matrix) of a column selection vector/matrix (e.g., W)₂A matrix). Moreover, beam co-phasing or orthogonalization on a subband level may be handled with other vector or matrix precoder components (e.g., in addition to column selection)Outside of the elements, W₂Including a phase shifter).

Thus, user equipment feedback is employed, wherein the user equipment first measures channel state information and then selects beam groups from a set of beam groups according to the wideband or long-term channel state information, wherein the size of each beam group (i.e. the number of beams in each beam group of the set of beam groups) and/or the number of beam groups (i.e. the number of beam groups in the set of beam groups) and/or the total angular domain spanned by each beam group (i.e. the total angular domain spanned from the direction of maximum array gain of the first beam to the direction of maximum array gain of the last beam in each beam group of the set of beam groups) depends on the transmission rank and/or wherein different beam groups overlap. In other words, the characteristic of the set of beam groups comprises at least one of: the number of beams in each beam group of the set of beam groups, the number of beam groups in the set of beam groups, and a total angular domain spanned in each beam group of the set of beam groups from a direction of maximum array gain for a first beam to a direction of maximum array gain for a last beam. For each subband, the user equipment selects a subset of beams in the selected beam group, wherein the size of the subset is equal to the transmission rank. Further, the selected subset of beams may include beams that are orthogonal to each other. The user equipment encodes the feedback information into a matrix W₁And W₂To transmit on an uplink communication channel, and transmitting the dual codebook format to a base station.

The base station receives the feedback transmitted on the uplink communication channel, decodes the feedback information, and converts it into a dual codebook or precoder format or structure (i.e., into the matrix W)₁And W₂). The base station is based on the matrix W, e.g. by matrix multiplication₁And W₂The final precoder (i.e., antenna weights) to be used for transmission to the user equipment is calculated per frequency subband:

W＝W₁*W₂。

when transmitting data to the user equipment, the base station antenna-weights the scheduled subbands according to the weights in the matrix W.

To calculate the feedback to the base station, the user equipment first measures the channel state information. In the case of an LTE-based communication system, the measurement may be made using a reference signal, e.g., CSI-RS in the case of 8 transmit antennas or CSI-RS in the case of 4 transmit antennas (or less). Then, the user equipment obtains channel state information for the entire system bandwidth.

Once the user equipment has obtained the channel state information, the feedback may be computed (i.e., the user equipment determines the beam groups and selects the beams for each subband). In case of a dual codebook format or structure, the user equipment selects the wideband/long-term precoder matrix W₁And in the selected precoder matrix W₁Under the condition (3), selecting a precoder matrix W for each subband₂. In one aspect, a matrix W is utilized₁To select a beam group and precoder matrix W₁And W₂The final beams (precoders) are formed together within each beam group. Then, matrix multiplication is employed to construct the final precoder:

W＝W₁*W₂。

turning now to fig. 6A and 6B, a graphical representation of an embodiment of forming a beam group in accordance with the principles of the present invention is illustrated. It should be understood that the azimuth gain characteristic of a particular transmit beam is not flat and is precisely limited in the angular domain as represented in the figures. In fig. 6A, 4 beam groups are illustrated for the case of transmission rank 1-2, each beam group comprising, for example, 4 beams. As shown in fig. 6B for transmission rank 3-4, there are two beam groups, but with a larger beam group angle (azimuth) field, each group comprising, for example, 8 beams. The size of the beam groups and/or the number of beam groups and/or the total angular domain spanned by the beam groups depends on the transmission rank. The precoder matrix W used to support this format or structure is presented below₁、W₂Exemplary codebook entries of (1).

Turning now to fig. 7A and 7B, a graphical representation of an embodiment of forming a beam group in accordance with the principles of the present invention is illustrated. In the illustrated embodiment, the beam groups overlap. Note that the number, size, and angular domain spanned by each beam group is dependent on the transmission rank. Exemplary codebook entries for such formats or structures are set forth below.

Both the base station and the user equipment are aware of codebooks constructed using these principles. The user equipment may select a codebook entry using, for example, the following exemplary matrix selection scheme. First, the user equipment calculates a wideband communication channel spatial covariance matrix R:

R＝E{H^HH}，

where E is the desired operator, and the superscript operator "H" represents the Hermitian operator (i.e., the conjugation and transposing of the corresponding matrix). Again, (non-superscript) H denotes the communication channel matrix. The user equipment then selects the matrix W using, for example, but not limited to, one of the following ways₁。

In an exemplary method, the user equipment passes through the matrix W₁And W₂Is scanned (searched) to form all matrix combinations,

W＝W₁*W₂

the search may be for the matrix W₂Is done over a wide bandwidth (i.e., over the entire system bandwidth) to limit computational complexity. The user equipment then finds a precoder matrix W that reduces (e.g., minimizes) the chord, the frinity-schlieren, or the projected double norm distance of the relative V, where matrix S,

R＝USV^H

is the singular value decomposition of the matrix R. The matrices U and V are custom unitary matrices associated with converting the matrix R to the diagonal matrix S. Precoder matrix W₁Is selected as the one corresponding to the enhanced (e.g., optimal) W.

In another exemplary method, the user equipment passes through a pair matrix W₁And W₂Is scanned (e.g., in a wideband sense) to form all combinations of matrices.

W＝W₁*W₂。

Then, the user equipment finds the precoder matrix W that enhances (e.g., maximizes) the capability (e.g., maximizes the following expression):

$\det (I+\frac{1}{{\mathrm{\σ}}^2}{W}^H\mathrm{RW}).$

precoder matrix W₁Is selected as the one corresponding to the enhanced (e.g., optimal) W.

To reduce the complexity of the above-mentioned methods, combining

W＝W₁*W₂

May be sampled such that, for example, only one beam from each beam group is selected as representative of the beam group, and the selection is done based on a subset of the matrix W, with the enhancement selected (e.g., maximized) $\det (I+\frac{1}{{\mathrm{\σ}}^2}{W_1}^H{\mathrm{RW}}_1)$ Matrix W of₁。

The second option is to select an enhanced (e.g., maximized) trace (W)₁ ^HRW₁) Matrix W of₁. Once the wideband/long-term precoder matrix W is selected₁Is in the matrix W₁E.g., by finding a precoder matrix W that enhances (e.g., maximizes) throughput over a given subband₂To select precoder matrix W per frequency subband₂。

Once the user equipment determines the beam group and determines the beam selection within the beam group per subband, the user equipment encodes the selection for transmission on the uplink communication channel. Matrix W₁And W₂Both are encoded as indices in a codebook known to both the base station and the user equipment. The user equipment transmits the selected matrix W to the base station₁And the selected matrix W₂Index (e.g., dual codebook format). In the case of an LTE-based communication system, the uplink communication channel used for feedback transmission may be a physical uplink control channel ("PUCCH") or PUSCH. In case of PUCCH, at least two alternative signaling solutions are considered.

In one signaling solution, the matrix W₁May be encoded in a first PUCCH report together with a transmission rank indicator, and the matrix W₂May be encoded in another PUCCH report along with a channel quality indicator ("CQI"). In another signaling solution, the transmission rank indicator is transmitted separately in a first PUCCH report and the matrix W is transmitted in another PUCCH report₁Index and matrix W of₂The index of (c), and the CQI. In an exemplary embodiment, the same frequency reports may be used for the matrix W₁Data of and for the matrix W₂Or may be used for the matrix W₁Is reported for the matrix W at a higher frequency₂The data of (1). In case of PUSCH, it can be in one PUAll information including the transmission rank indicator, the two codebook indices (e.g., dual codebook format), and the CQI is transmitted in the SCH report. In contrast to PUCCH, transmission of PUSCH feedback reports is typically triggered by the base station, which occurs periodically according to some semi-static configuration.

The base station obtains the final precoder matrix according to the result of the matrix multiplication,

W＝W₁*W₂。

neither of the codebook matrices is self-contained, and it is advantageous to receive both matrices in one report. However, due to the matrix W₁Using the wideband/long-term properties of the communication channel, the pairing of the matrix W can therefore be done with a lower time periodicity₁While the matrix W may be sent with a higher time periodicity₂And (6) fine adjustment. Assume matrix W₁Such decoupling signaling may be employed over time, quite stable and error-free transmission has been performed.

An exemplary codebook design for a beam group depending on transmission rank in case of transmission rank 1-4 operation is now described. In this exemplary design, there are 4 beam groups in the case of transmission ranks 1 and 2, and two beam groups across the larger beam space in the case of transmission ranks 3 and 4. The 4 beam groups in case of transmission ranks 1 and 2 are described as follows with a block diagonal matrix based on a discrete fourier transform.

$W_1^{\left(\mathrm{1,2}\right)}\left(0\right)=\frac{1}{2}\left[\begin{array}{cccccccc}1& 1& 1& 1& 0& 0& 0& 0\\ 1& e^{i\frac{\mathrm{\π}}{8}}& e^{i\frac{\mathrm{\π}}{4}}& e^{i\frac{3\mathrm{\π}}{8}}& 0& 0& 0& 0\\ 1& e^{i\frac{\mathrm{\π}}{4}}& i& e^{i\frac{3\mathrm{\π}}{4}}& 0& 0& 0& 0\\ 1& e^{i\frac{3\mathrm{\π}}{8}}& e^{i\frac{3\mathrm{\π}}{4}}& e^{i\frac{9\mathrm{\π}}{8}}& 0& 0& 0& 0\\ 0& 0& 0& 0& 1& 1& 1& 1\\ 0& 0& 0& 0& 1& e^{i\frac{\mathrm{\π}}{8}}& e^{i\frac{\mathrm{\π}}{4}}& e^{i\frac{3\mathrm{\π}}{8}}\\ 0& 0& 0& 0& 1& e^{i\frac{\mathrm{\π}}{4}}& i& e^{i\frac{3\mathrm{\π}}{4}}\\ 0& 0& 0& 0& 1& e^{i\frac{3\mathrm{\π}}{8}}& e^{i\frac{3\mathrm{\π}}{4}}& e^{i\frac{9\mathrm{\π}}{8}}\end{array}\right]$

$W_1^{\left(\mathrm{1,2}\right)}\left(1\right)=\frac{1}{2}\left[\begin{array}{cccccccc}1& 1& 1& 1& 0& 0& 0& 0\\ i& e^{i\frac{5\mathrm{\π}}{8}}& e^{i\frac{3\mathrm{\π}}{4}}& e^{i\frac{7\mathrm{\π}}{8}}& 0& 0& 0& 0\\ -1& e^{i\frac{5\mathrm{\π}}{4}}& -i& e^{i\frac{7\mathrm{\π}}{4}}& 0& 0& 0& 0\\ -i& e^{i\frac{15\mathrm{\π}}{8}}& e^{i\frac{\mathrm{\π}}{4}}& e^{i\frac{5\mathrm{\π}}{8}}& 0& 0& 0& 0\\ 0& 0& 0& 0& 1& 1& 1& 1\\ 0& 0& 0& 0& i& e^{i\frac{5\mathrm{\π}}{8}}& e^{i\frac{3\mathrm{\π}}{4}}& e^{i\frac{7\mathrm{\π}}{8}}\\ 0& 0& 0& 0& -1& e^{i\frac{5\mathrm{\π}}{4}}& -i& e^{i\frac{7\mathrm{\π}}{4}}\\ 0& 0& 0& 0& -i& e^{i\frac{15\mathrm{\π}}{8}}& e^{i\frac{\mathrm{\π}}{4}}& e^{i\frac{5\mathrm{\π}}{8}}\end{array}\right]$

$W_1^{\left(\mathrm{1,2}\right)}\left(2\right)=\frac{1}{2}\left[\begin{array}{cccccccc}1& 1& 1& 1& 0& 0& 0& 0\\ -1& e^{i\frac{9\mathrm{\π}}{8}}& e^{i\frac{5\mathrm{\π}}{4}}& e^{i\frac{11\mathrm{\π}}{8}}& 0& 0& 0& 0\\ 1& e^{i\frac{\mathrm{\π}}{4}}& i& e^{i\frac{3\mathrm{\π}}{4}}& 0& 0& 0& 0\\ -1& e^{i\frac{11\mathrm{\π}}{8}}& e^{i\frac{7\mathrm{\π}}{4}}& e^{i\frac{\mathrm{\π}}{8}}& 0& 0& 0& 0\\ 0& 0& 0& 0& 1& 1& 1& 1\\ 0& 0& 0& 0& -1& e^{i\frac{9\mathrm{\π}}{8}}& e^{i\frac{5\mathrm{\π}}{4}}& e^{i\frac{11\mathrm{\π}}{8}}\\ 0& 0& 0& 0& 1& e^{i\frac{\mathrm{\π}}{4}}& i& e^{i\frac{3\mathrm{\π}}{4}}\\ 0& 0& 0& 0& -1& e^{i\frac{11\mathrm{\π}}{8}}& e^{i\frac{7\mathrm{\π}}{4}}& e^{i\frac{\mathrm{\π}}{8}}\end{array}\right]$

$W_1^{\left(\mathrm{1,2}\right)}\left(3\right)=\frac{1}{2}\left[\begin{array}{cccccccc}1& 1& 1& 1& 0& 0& 0& 0\\ -i& e^{i\frac{13\mathrm{\π}}{8}}& e^{i\frac{7\mathrm{\π}}{4}}& e^{i\frac{15\mathrm{\π}}{8}}& 0& 0& 0& 0\\ -1& e^{i\frac{5\mathrm{\π}}{4}}& -i& e^{i\frac{7\mathrm{\π}}{4}}& 0& 0& 0& 0\\ i& e^{i\frac{7\mathrm{\π}}{8}}& e^{i\frac{5\mathrm{\π}}{4}}& e^{i\frac{13\mathrm{\π}}{8}}& 0& 0& 0& 0\\ 0& 0& 0& 0& 1& 1& 1& 1\\ 0& 0& 0& 0& -i& e^{i\frac{13\mathrm{\π}}{8}}& e^{i\frac{7\mathrm{\π}}{4}}& e^{i\frac{15\mathrm{\π}}{8}}\\ 0& 0& 0& 0& -1& e^{i\frac{5\mathrm{\π}}{4}}& -i& e^{i\frac{7\mathrm{\π}}{4}}\\ 0& 0& 0& 0& i& e^{i\frac{7\mathrm{\π}}{8}}& e^{i\frac{5\mathrm{\π}}{4}}& e^{i\frac{13\mathrm{\π}}{8}}\end{array}\right]$

Two beam groups for the case of transmission rank 3-4 may be described as follows:

$W_1^{\left(\mathrm{3,4}\right)}\left(n\right)=\frac{1}{2}\·\left[\begin{array}{cc}X\left(n\right)& 0\\ 0& X\left(n\right)\end{array}\right],n=\mathrm{0,1}$

wherein,

$X\left(n\right)=\left[\begin{array}{cccc}1& 0& 0& 0\\ 0& {(-1)}^n& 0& 0\\ 0& 0& 1& 0\\ 0& 0& 0& {(-1)}^n\end{array}\right]\left[\begin{array}{ccccc}1& 1& 1& ...& 1\\ 1& e^{j\frac{\mathrm{\π}}{8}}& e^{j\left(2\right)\frac{\mathrm{\π}}{8}}& ...& e^{j\left(7\right)\frac{\mathrm{\π}}{8}}\\ 1& e^{j\left(2\right)\frac{\mathrm{\π}}{8}}& e^{j\left(2\right)\left(2\right)\frac{\mathrm{\π}}{8}}& ...& e^{j\left(7\right)\left(2\right)\frac{\mathrm{\π}}{8}}\\ 1& e^{j\left(3\right)\frac{\mathrm{\π}}{8}}& e^{j\left(2\right)\left(3\right)\frac{\mathrm{\π}}{8}}& ...& e^{j\left(7\right)\left(3\right)\frac{\mathrm{\π}}{8}}\end{array}\right]$

corresponding W₂The vector/matrix includes the beam selection vector multiplied by the complex number to shift the phase of the vector. Only those for transmission rank-1 are listed in table 3, while the design of transmission rank 2-4 is similarly followed by appropriate phase shifting of the transmission rank 2-4 beam selection vectors. In Table III below, e_iA 4 × 1 vector representing the selection of the ith beam, e.g.,

e₂＝[0100]^T。

TABLE III

Now described forExemplary codebook designs for overlapping beam groups for transmission rank 1-2 operation. In this exemplary design, there are 8 beam groups that partially overlap. By setting some columns in two adjacent matrices to be the same so that the overlap is at W₁Visible in the matrix.

$W_1^{\left(\mathrm{1,2}\right)}\left(0\right)=\frac{1}{2}\left[\begin{array}{cccccccc}1& 1& 1& 1& 0& 0& 0& 0\\ 1& e^{i\frac{\mathrm{\π}}{8}}& e^{i\frac{\mathrm{\π}}{4}}& e^{i\frac{3\mathrm{\π}}{8}}& 0& 0& 0& 0\\ 1& e^{i\frac{\mathrm{\π}}{4}}& i& e^{i\frac{3\mathrm{\π}}{4}}& 0& 0& 0& 0\\ 1& e^{i\frac{3\mathrm{\π}}{8}}& e^{i\frac{3\mathrm{\π}}{4}}& e^{i\frac{9\mathrm{\π}}{8}}& 0& 0& 0& 0\\ 0& 0& 0& 0& 1& 1& 1& 1\\ 0& 0& 0& 0& 1& e^{i\frac{\mathrm{\π}}{8}}& e^{i\frac{\mathrm{\π}}{4}}& e^{i\frac{3\mathrm{\π}}{8}}\\ 0& 0& 0& 0& 1& e^{i\frac{\mathrm{\π}}{4}}& i& e^{i\frac{3\mathrm{\π}}{4}}\\ 0& 0& 0& 0& 1& e^{i\frac{3\mathrm{\π}}{8}}& e^{i\frac{3\mathrm{\π}}{4}}& e^{i\frac{9\mathrm{\π}}{8}}\end{array}\right]$

$W_1^{\left(\mathrm{1,2}\right)}\left(1\right)=\frac{1}{2}\left[\begin{array}{cccccccc}1& 1& 1& 1& 0& 0& 0& 0\\ e^{i\frac{\mathrm{\π}}{4}}& e^{i\frac{3\mathrm{\π}}{8}}& i& e^{i\frac{5\mathrm{\π}}{8}}& 0& 0& 0& 0\\ i& e^{i\frac{3\mathrm{\π}}{4}}& -1& e^{i\frac{5\mathrm{\π}}{4}}& 0& 0& 0& 0\\ e^{i\frac{3\mathrm{\π}}{4}}& e^{i\frac{9\mathrm{\π}}{8}}& -i& e^{i\frac{15\mathrm{\π}}{8}}& 0& 0& 0& 0\\ 0& 0& 0& 0& 1& 1& 1& 1\\ 0& 0& 0& 0& e^{i\frac{\mathrm{\π}}{4}}& e^{i\frac{3\mathrm{\π}}{8}}& i& e^{i\frac{5\mathrm{\π}}{8}}\\ 0& 0& 0& 0& i& e^{i\frac{3\mathrm{\π}}{4}}& -1& e^{i\frac{5\mathrm{\π}}{4}}\\ 0& 0& 0& 0& e^{i\frac{3\mathrm{\π}}{4}}& e^{i\frac{9\mathrm{\π}}{8}}& -i& e^{i\frac{15\mathrm{\π}}{8}}\end{array}\right]$

$W_1^{\left(\mathrm{1,2}\right)}\left(2\right)=\frac{1}{2}\left[\begin{array}{cccccccc}1& 1& 1& 1& 0& 0& 0& 0\\ i& e^{i\frac{5\mathrm{\π}}{8}}& e^{i\frac{3\mathrm{\π}}{4}}& e^{i\frac{7\mathrm{\π}}{8}}& 0& 0& 0& 0\\ -1& e^{i\frac{5\mathrm{\π}}{4}}& -i& e^{i\frac{7\mathrm{\π}}{4}}& 0& 0& 0& 0\\ -i& e^{i\frac{15\mathrm{\π}}{8}}& e^{i\frac{\mathrm{\π}}{4}}& e^{i\frac{5\mathrm{\π}}{8}}& 0& 0& 0& 0\\ 0& 0& 0& 0& 1& 1& 1& 1\\ 0& 0& 0& 0& i& e^{i\frac{5\mathrm{\π}}{8}}& e^{i\frac{3\mathrm{\π}}{4}}& e^{i\frac{7\mathrm{\π}}{8}}\\ 0& 0& 0& 0& -1& e^{i\frac{5\mathrm{\π}}{4}}& -i& e^{i\frac{7\mathrm{\π}}{4}}\\ 0& 0& 0& 0& -i& e^{i\frac{15\mathrm{\π}}{8}}& e^{i\frac{\mathrm{\π}}{4}}& e^{i\frac{5\mathrm{\π}}{8}}\end{array}\right]$

$W_1^{\left(\mathrm{1,2}\right)}\left(3\right)=\frac{1}{2}\left[\begin{array}{cccccccc}1& 1& 1& 1& 0& 0& 0& 0\\ e^{i\frac{3\mathrm{\π}}{4}}& e^{i\frac{7\mathrm{\π}}{8}}& -1& e^{i\frac{9\mathrm{\π}}{8}}& 0& 0& 0& 0\\ -i& e^{i\frac{7\mathrm{\π}}{4}}& 1& e^{i\frac{\mathrm{\π}}{4}}& 0& 0& 0& 0\\ e^{i\frac{\mathrm{\π}}{4}}& e^{i\frac{5\mathrm{\π}}{8}}& -1& e^{i\frac{11\mathrm{\π}}{8}}& 0& 0& 0& 0\\ 0& 0& 0& 0& 1& 1& 1& 1\\ 0& 0& 0& 0& e^{i\frac{3\mathrm{\π}}{4}}& e^{i\frac{7\mathrm{\π}}{8}}& -1& e^{i\frac{9\mathrm{\π}}{8}}\\ 0& 0& 0& 0& -i& e^{i\frac{7\mathrm{\π}}{4}}& 1& e^{i\frac{\mathrm{\π}}{4}}\\ 0& 0& 0& 0& e^{i\frac{\mathrm{\π}}{4}}& e^{i\frac{5\mathrm{\π}}{8}}& -1& e^{i\frac{11\mathrm{\π}}{8}}\end{array}\right]$

$W_1^{\left(\mathrm{1,2}\right)}\left(4\right)=\frac{1}{2}\left[\begin{array}{cccccccc}1& 1& 1& 1& 0& 0& 0& 0\\ -1& e^{i\frac{9\mathrm{\π}}{8}}& e^{i\frac{5\mathrm{\π}}{4}}& e^{i\frac{11\mathrm{\π}}{8}}& 0& 0& 0& 0\\ 1& e^{i\frac{\mathrm{\π}}{4}}& i& e^{i\frac{3\mathrm{\π}}{4}}& 0& 0& 0& 0\\ -1& e^{i\frac{11\mathrm{\π}}{8}}& e^{i\frac{7\mathrm{\π}}{4}}& e^{i\frac{\mathrm{\π}}{8}}& 0& 0& 0& 0\\ 0& 0& 0& 0& 1& 1& 1& 1\\ 0& 0& 0& 0& -1& e^{i\frac{9\mathrm{\π}}{8}}& e^{i\frac{5\mathrm{\π}}{4}}& e^{i\frac{11\mathrm{\π}}{8}}\\ 0& 0& 0& 0& 1& e^{i\frac{\mathrm{\π}}{4}}& i& e^{i\frac{3\mathrm{\π}}{4}}\\ 0& 0& 0& 0& -1& e^{i\frac{11\mathrm{\π}}{8}}& e^{i\frac{7\mathrm{\π}}{4}}& e^{i\frac{\mathrm{\π}}{8}}\end{array}\right]$

$W_1^{\left(\mathrm{1,2}\right)}\left(5\right)=\frac{1}{2}\left[\begin{array}{cccccccc}1& 1& 1& 1& 0& 0& 0& 0\\ e^{i\frac{5\mathrm{\π}}{4}}& e^{i\frac{11\mathrm{\π}}{8}}& -i& e^{i\frac{13\mathrm{\π}}{8}}& 0& 0& 0& 0\\ i& e^{i\frac{3\mathrm{\π}}{4}}& -1& e^{i\frac{5\mathrm{\π}}{4}}& 0& 0& 0& 0\\ e^{i\frac{7\mathrm{\π}}{4}}& e^{i\frac{\mathrm{\π}}{8}}& i& e^{i\frac{7\mathrm{\π}}{8}}& 0& 0& 0& 0\\ 0& 0& 0& 0& 1& 1& 1& 1\\ 0& 0& 0& 0& e^{i\frac{5\mathrm{\π}}{4}}& e^{i\frac{11\mathrm{\π}}{8}}& -i& e^{i\frac{13\mathrm{\π}}{8}}\\ 0& 0& 0& 0& i& e^{i\frac{3\mathrm{\π}}{4}}& -1& e^{i\frac{5\mathrm{\π}}{4}}\\ 0& 0& 0& 0& e^{i\frac{7\mathrm{\π}}{4}}& e^{i\frac{\mathrm{\π}}{8}}& i& e^{i\frac{7\mathrm{\π}}{8}}\end{array}\right]$

$W_1^{\left(\mathrm{1,2}\right)}\left(6\right)=\frac{1}{2}\left[\begin{array}{cccccccc}1& 1& 1& 1& 0& 0& 0& 0\\ -i& e^{i\frac{13\mathrm{\π}}{8}}& e^{i\frac{7\mathrm{\π}}{4}}& e^{i\frac{15\mathrm{\π}}{8}}& 0& 0& 0& 0\\ -1& e^{i\frac{5\mathrm{\π}}{4}}& -i& e^{i\frac{7\mathrm{\π}}{4}}& 0& 0& 0& 0\\ i& e^{i\frac{7\mathrm{\π}}{8}}& e^{i\frac{5\mathrm{\π}}{4}}& e^{i\frac{13\mathrm{\π}}{8}}& 0& 0& 0& 0\\ 0& 0& 0& 0& 1& 1& 1& 1\\ 0& 0& 0& 0& -i& e^{i\frac{13\mathrm{\π}}{8}}& e^{i\frac{7\mathrm{\π}}{4}}& e^{i\frac{15\mathrm{\π}}{8}}\\ 0& 0& 0& 0& -1& e^{i\frac{5\mathrm{\π}}{4}}& -i& e^{i\frac{7\mathrm{\π}}{4}}\\ 0& 0& 0& 0& i& e^{i\frac{7\mathrm{\π}}{8}}& e^{i\frac{5\mathrm{\π}}{4}}& e^{i\frac{13\mathrm{\π}}{8}}\end{array}\right]$

$W_1^{\left(\mathrm{1,2}\right)}\left(7\right)=\frac{1}{2}\left[\begin{array}{cccccccc}1& 1& 1& 1& 0& 0& 0& 0\\ e^{i\frac{7\mathrm{\π}}{4}}& e^{i\frac{15\mathrm{\π}}{8}}& 1& e^{i\frac{\mathrm{\π}}{8}}& 0& 0& 0& 0\\ -i& e^{i\frac{7\mathrm{\π}}{4}}& 1& e^{i\frac{\mathrm{\π}}{4}}& 0& 0& 0& 0\\ e^{i\frac{5\mathrm{\π}}{4}}& e^{i\frac{13\mathrm{\π}}{8}}& 1& e^{i\frac{3\mathrm{\π}}{8}}& 0& 0& 0& 0\\ 0& 0& 0& 0& 1& 1& 1& 1\\ 0& 0& 0& 0& e^{i\frac{7\mathrm{\π}}{4}}& e^{i\frac{15\mathrm{\π}}{8}}& 1& e^{i\frac{\mathrm{\π}}{8}}\\ 0& 0& 0& 0& -i& e^{i\frac{7\mathrm{\π}}{4}}& 1& e^{i\frac{\mathrm{\π}}{4}}\\ 0& 0& 0& 0& e^{i\frac{5\mathrm{\π}}{4}}& e^{i\frac{13\mathrm{\π}}{8}}& 1& e^{i\frac{3\mathrm{\π}}{8}}\end{array}\right]$

Corresponding W₂The vectors/matrices are similar to those in the first exemplary codebook design (i.e., these matrices include beam selection column vectors).

Thus, improved support for higher azimuth extension scenarios may be achieved in case of a beam-type feedback grid. When there is less spatial correlation in the communication channel (i.e., when there is a higher azimuthal spread), the entire signal space can be better captured in a frequency selective manner. The benefits of the beam grid for MU-MIMO in highly correlated cases are also retained.

Turning to fig. 8, a graphical representation of an embodiment of a beam group for the case of transmission rank 1-2 is illustrated in accordance with the principles of the present invention. The first beam group (indicated as beam group 1) includes 4 beams, with the first beam 810 having a maximum gain of 6 decibels ("dB") in the azimuth direction of zero degrees and the 4 th beam 820 having a maximum gain of 6 decibels ("dB") in the azimuth direction of-22 degrees. The second beam group (indicated as beam group 2) includes 4 beams, with the first beam 830 having a maximum gain of 6 decibels ("dB") in the azimuth direction of 18 degrees and the 4 th beam having a maximum gain of 6 decibels ("dB") in the azimuth direction of-4 degrees. An angular range 850 from the direction of the maximum array gain of the first beam 810 in the first beam group to the direction of the maximum array gain of the fourth beam (last beam) 820 is 22 degrees, and overlaps in an angular domain with an angular range 860 from the direction of the maximum array gain of the first beam 830 in the second beam group (adjacent beam group) to the direction of the maximum array gain of the fourth beam (last beam) 840.

Turning now to fig. 9, a flow diagram of an embodiment of a method of operating a communication system in accordance with the principles of the present invention is illustrated. After a start step or module 910, elements of the communication system (e.g., user equipment and/or base stations therein) measure channel state information for the downlink from the base station in a step or module 920. In step or module 930, a beam group selected from a set of beam groups is identified according to a wideband property of the channel state information, wherein a characteristic of the set of beam groups depends on the transmission rank. The characteristic of the set of beam groups may be a number of beams in each beam group of the set of beam groups, a number of beam groups in the set of beam groups, and/or a total angular domain spanned in each beam group of the set of beam groups from a direction of maximum array gain for a first beam to a direction of maximum array gain for a last beam. In step or module 940, the selected subset of beams is identified in the selected beam group according to at least one subband, wherein the number of beams in the selected subset of beams is equal to the transmission rank.

In step or module 950, the coded feedback information is generated in a dual codebook format to identify the selected beam group and the selected subset of beams for each subband. The dual codebook format is constructed as a first matrix representing the selected beam group and a second matrix representing the selected beam subset for each subband. The first matrix may be formed using a set of columns obtained from an oversampled discrete fourier transform matrix. Thus, an angular range from the direction of maximum array gain of the first beam to the direction of maximum array gain of the last beam in the selected beam group may overlap in the angular domain with an angular range from the direction of maximum array gain of the first beam to the direction of maximum array gain of the last beam in the adjacent beam group. The selected beam set may be used to drive 8 transmit antennas of the base station. From the coded feedback information, a precoder is formed in step or module 960 using a dual codebook format (e.g., in a base station) to transmit signals in the communication system. The method ends at step or block 970.

Accordingly, an apparatus, method, and system for selecting a beam group and a beam subset in a communication system are presented herein. In one embodiment, an apparatus (e.g., implemented in user equipment) includes a processor and a memory including computer program code. The memory and the computer program code are configured to, with the processor, cause the apparatus to measure channel state information about a downlink from a base station and identify a beam group selected from a set of beam groups according to a wideband property of the channel state information. The characteristics of the set of beam groups depend on the transmission rank. The memory and the computer program code are further configured to, with the processor, cause the apparatus to identify a selected subset of beams of the selected set of beams according to the at least one subband. The number of beams in the selected beam subset is equal to the transmission rank.

Moreover, the memory and computer program code are further configured to, with the processor, cause the apparatus to generate encoded feedback information in a dual codebook format, the encoded feedback information identifying the selected beam group and the selected subset of beams for each subband, and transmit the encoded feedback information to the base station. The dual codebook format includes a first matrix representing the selected beam group and a second matrix representing the selected subset of beams for each subband. A set of columns obtained from the oversampled discrete fourier transform matrix is used to form a first matrix. Moreover, the characteristic of the set of beam groups includes at least one of: the number of beams in each beam group of the set of beam groups, the number of beam groups in the set of beam groups, and a total angular domain spanned from a direction of maximum array gain for a first beam to a direction of maximum array gain for a last beam in each beam group of the set of beam groups. Further, the selected beam group may overlap with an adjacent beam group in the total angular domain (or angular domain). For example, an angular range from a direction of maximum array gain of a first beam in the selected beam group to a direction of maximum array gain of a last beam may overlap in an angular domain with an angular range from the direction of maximum array gain of the first beam in an adjacent beam group to the direction of maximum array gain of the last beam. Also, the selected beam group may be characterized by 8 transmit antennas.

In another embodiment, an apparatus (e.g., implemented in a base station) includes a processor and a memory including computer program code. The memory and the computer program code are configured to, with the processor, cause the apparatus to receive from a user equipment encoded feedback information having a dual codebook format, the encoded feedback information identifying a selected beam group and a selected subset of beams for at least one subband. The selected beam group represents one of a set of beam groups that coincides with a wideband property of channel state information measured by the user equipment, and the characteristic of the set of beam groups is based on a transmission rank. Furthermore, the selected subset of beams is selected among the selected set of beams according to at least one subband, and the number of beams in the selected subset of beams is equal to the transmission rank. The memory and the computer program code are further configured to, with the processor, cause the apparatus to use dual codeThe format forms a precoder for transmitting signals to user equipment. Although the apparatus, methods, and systems described herein have been described with respect to a cellular-based communication system, the apparatus and methods are equally applicable to other types of communication systems, such as WiMaxA communication system.

Programs or code segments that constitute various embodiments of the present invention may be stored in a computer readable medium or transmitted by a computer data signal embodied in a carrier wave, or a signal modulated by a carrier, over a transmission medium. For example, a computer program product comprising program code stored in a computer readable medium may form various embodiments of the present invention. "computer-readable media" may include any medium that can store or transfer information. Examples of computer-readable media include circuits, semiconductor memory devices, read-only memory ("ROM"), flash memory, erasable ROM ("EPROM"), floppy disks, compact disks ("CD") -ROMs, optical disks, hard disks, fiber optic media, radio frequency ("RF") links, and so forth. The computer data signal may include any signal that can propagate over a transmission medium such as electronic communication network communication channels, optical fibers, air, electromagnetic links, RF links, etc. The code segments may be downloaded via a computer network such as the internet, an intranet, etc.

As described above, the exemplary embodiments provide a method and corresponding apparatus including various modules providing functionality for performing the method steps. A module may be implemented as hardware (implemented in one or more chips, including integrated circuits such as application specific integrated circuits), or as software or firmware for execution by a computer processor. In particular, in the case of firmware or software, the exemplary embodiments can be provided as a computer program product including a computer readable storage structure embodying computer program code (i.e., the software or firmware) thereon for execution by the computer processor.

Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. For example, many of the features and functions described above may be implemented in software, hardware, or firmware, or a combination thereof. Moreover, many of the features, functions, and steps of operating the same may be reordered, omitted, added, etc., and still fall within the broad scope of the present invention.

Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.

Claims (22)

1. An apparatus for communication, comprising:

an apparatus for measuring channel state information on a downlink from a base station,

means for identifying a selected beam group from a set of beam groups according to a broadband property of the channel state information, wherein a characteristic of the set of beam groups depends on a transmission rank, an

Means for identifying a selected subset of beams in the selected beam group according to at least one subband, wherein the number of beams in the selected subset of beams is equal to the transmission rank.

2. The apparatus of claim 1, further comprising means for performing at least the following:

generating coded feedback information in a dual codebook format, the coded feedback information identifying the selected beam group and the selected subset of beams for each subband, an

Transmitting the encoded feedback information to the base station.

3. The apparatus of claim 2, wherein the dual codebook format comprises a first matrix representing the selected beam group and a second matrix representing the selected beam subset for each subband.

4. The apparatus of claim 3, wherein the first matrix is formed using a set of columns obtained from an oversampled Discrete Fourier Transform (DFT) matrix.

5. The apparatus of claim 1, wherein the characteristics of the set of beam groups comprise at least one of: a number of beams in each beam group of the set of beam groups, a number of beam groups in the set of beam groups, and a total angular domain spanned in each beam group of the set of beam groups from a direction of maximum array gain for a first beam to a direction of maximum array gain for a last beam.

6. The apparatus of any of claims 1-5, wherein an angular range from a direction of maximum array gain for a first beam to a direction of maximum array gain for a last beam in the selected beam group overlaps in an angular domain with an angular range from a direction of maximum array gain for a first beam to a direction of maximum array gain for a last beam in an adjacent beam group.

7. A method for communication, comprising:

measuring channel state information on a downlink from a base station;

identifying a selected beam group from a set of beam groups according to a wideband property of the channel state information, wherein a characteristic of the set of beam groups depends on a transmission rank; and

identifying a selected subset of beams in the selected beam group according to at least one subband, wherein a number of beams in the selected subset of beams is equal to the transmission rank.

8. The method of claim 7, further comprising:

generating coded feedback information in a dual codebook format, the coded feedback information identifying the selected beam group and the selected subset of beams for each subband; and

transmitting the encoded feedback information to the base station.

9. The method of claim 8, wherein the dual codebook format includes a first matrix representing the selected beam group and a second matrix representing the selected beam subset for each subband.

10. The method of claim 8, wherein the characteristics of the set of beam groups include at least one of: a number of beams in each beam group of the set of beam groups, a number of beam groups in the set of beam groups, and a total angular domain spanned in each beam group of the set of beam groups from a direction of maximum array gain for a first beam to a direction of maximum array gain for a last beam.

11. The method according to any of claims 7-10, wherein an angular range from a direction of maximum array gain of a first beam to a direction of maximum array gain of a last beam in the selected beam group overlaps in an angular domain with an angular range from a direction of maximum array gain of a first beam to a direction of maximum array gain of a last beam in an adjacent beam group.

12. An apparatus for communication, comprising:

a device for a user to receive from a user equipment encoded feedback information having a dual codebook format, the encoded feedback information identifying a selected beam group and a selected subset of beams for at least one subband, wherein the selected beam group represents one of a set of beam groups that is consistent with a wideband property of channel state information measured by the user equipment and a characteristic of the set of beam groups is based on a transmission rank, and wherein the selected subset of beams is selected in the selected beam group according to the at least one subband and a number of beams in the selected subset of beams is equal to the transmission rank; and

means for forming a precoder for transmitting a signal to the user equipment using the dual codebook format.

13. The apparatus of claim 12, wherein the dual codebook format comprises a first matrix representing the selected beam group and a second matrix representing the selected beam subset for each subband.

14. The apparatus of claim 13, wherein the first matrix is formed using a set of columns obtained from an oversampled Discrete Fourier Transform (DFT) matrix.

15. The apparatus of claim 12, wherein the characteristics of the set of beam groups comprise at least one of: a number of beams in each beam group of the set of beam groups, a number of beam groups in the set of beam groups, and a total angular domain spanned in each beam group of the set of beam groups from a direction of maximum array gain for a first beam to a direction of maximum array gain for a last beam.

16. The apparatus of claim 12, wherein an angular range from a direction of maximum array gain for a first beam to a direction of maximum array gain for a last beam in the selected beam group overlaps in an angular domain with an angular range from a direction of maximum array gain for a first beam to a direction of maximum array gain for a last beam in an adjacent beam group.

17. The apparatus of any of claims 12-16, wherein the selected beam group is characterized by 8 transmit antennas.

18. A method for communication, comprising:

receiving encoded feedback information from a user equipment having a dual codebook format, the encoded feedback information identifying a selected beam group and a selected subset of beams for at least one subband, wherein the selected beam group represents one of a set of beam groups that is consistent with a wideband property of channel state information measured by the user equipment and a characteristic of the set of beam groups is based on a transmission rank, and wherein the selected subset of beams is selected in the selected beam group according to the at least one subband and a number of beams in the selected subset of beams is equal to the transmission rank; and

forming a precoder for transmitting a signal to the user equipment using the dual codebook format.

19. The method of claim 18, wherein the dual codebook format includes a first matrix representing the selected beam group and a second matrix representing the selected beam subset for each subband.

20. The method of claim 19, wherein the first matrix is formed using a set of columns obtained from an oversampled Discrete Fourier Transform (DFT) matrix.

21. The method of claim 18, wherein the characteristics of the set of beam groups include at least one of: a number of beams in each beam group of the set of beam groups, a number of beam groups in the set of beam groups, and a total angular domain spanned in each beam group of the set of beam groups from a direction of maximum array gain for a first beam to a direction of maximum array gain for a last beam.

22. The method of any of claims 18-21, wherein an angular range from a direction of maximum array gain for a first beam to a direction of maximum array gain for a last beam in the selected beam group overlaps in an angular domain with an angular range from a direction of maximum array gain for a first beam to a direction of maximum array gain for a last beam in an adjacent beam group.