Coordinated multi-point transmission using interference feedback

The present application claims priority to U.S. Patent Application No. 61/410,740, titled “Advanced Wireless Communication Systems And Techniques,” filed Nov. 5, 2010, the entire specification of which is hereby incorporated by reference in its entirety for all purposes, except for those sections, if any, that are inconsistent with this specification.

Embodiments of the present disclosure relate generally to wireless communication systems, and more particularly, to methods and apparatuses for coordinated multi-point transmission using interference feedback.

A mobile station in a closed-loop multi input and/or multi output (MIMO) system generally transmits channel feedback information (e.g., a channel state information, a channel quality indicator, etc.) to an enhanced Node B (eNB) with which the mobile station is communicating over a wireless channel. The channel feedback information is generally used to employ beamforming at the eNB, to compensate for the current channel conditions.

Embodiments of the present disclosure will be described by way of exemplary embodiments, but not limitations, illustrated in the accompanying drawings in which like references denote similar elements, and in which:

FIG. 1 schematically illustrates a communication system, in accordance with various embodiments of the present disclosure.

FIG. 2 schematically illustrates an exemplary eNB receiving feedback information from a plurality of user equipments, in accordance with various embodiments of the present disclosure.

FIG. 3 schematically illustrates an exemplary user equipment included in the communication system of FIG. 1 in more detail, in accordance with various embodiments of the present disclosure.

FIG. 4 schematically illustrates an exemplary eNB included in the communication system of FIG. 1 in more detail, in accordance with various embodiments of the present disclosure.

FIG. 5 schematically illustrates transmission of channel feedback information and interference feedback information from a user equipment to an eNB, in accordance with various embodiments of the present disclosure.

FIG. 6 illustrates an exemplary method for operating the user equipment of FIGS. 1 and 3 , in accordance with various embodiments of the present disclosure.

FIG. 7 illustrates an exemplary method for operating the eNB of FIGS. 1 and 4 , in accordance with various embodiments of the present disclosure.

FIG. 8 illustrates an example system capable of implementing a communication device, in accordance with various embodiments of the present disclosure.

Illustrative embodiments of the present disclosure include, but are not limited to, methods and apparatuses for coordinated multi-point transmission in a wireless communication network using interference feedback.

Various aspects of the illustrative embodiments will be described using terms commonly employed by those skilled in the art to convey the substance of their work to others skilled in the art. However, it will be apparent to those skilled in the art that alternate embodiments may be practiced with only some of the described aspects. For purposes of explanation, specific numbers, materials, and configurations are set forth in order to provide a thorough understanding of the illustrative embodiments. However, it will be apparent to one skilled in the art that alternate embodiments may be practiced without the specific details. In other instances, well-known features are omitted or simplified in order not to obscure the illustrative embodiments.

Further, various operations will be described as multiple discrete operations, in turn, in a manner that is most helpful in understanding the illustrative embodiments; however, the order of description should not be construed as to imply that these operations are necessarily order dependent. In particular, these operations need not be performed in the order of presentation.

The phrase “in some embodiments” is used repeatedly. The phrase generally does not refer to the same embodiments; however, it may. The terms “comprising,” “having,” and “including” are synonymous, unless the context dictates otherwise. The phrase “A and/or B” means (A), (B), or (A and B). The phrase “A/B” means (A), (B), or (A and B), similar to the phrase “A and/or B”. The phrase “at least one of A, B and C” means (A), (B), (C), (A and B), (A and C), (B and C) or (A, B and C). The phrase “(A) B” means (B) or (A and B), that is, A is optional.

Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a wide variety of alternate and/or equivalent implementations may be substituted for the specific embodiments shown and described, without departing from the scope of the embodiments of the present disclosure. This application is intended to cover any adaptations or variations of the embodiments discussed herein. Therefore, it is manifestly intended that the embodiments of the present disclosure be limited only by the claims and the equivalents thereof.

As used herein, the term “module” may refer to, be part of, or include an Application Specific Integrated Circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and/or memory (shared, dedicated, or group) that execute one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality.

Embodiments of the present disclosure may be used in wireless access networks that employ orthogonal frequency division multiple access (OFDMA) communications as used by multicarrier transmission schemes presented in, e.g., the Institute of Electrical and Electronics Engineers (IEEE) 802.16-2009, approved May 13, 2009, along with any amendments, updates, and/or revisions (e.g., 802.16m, which is presently at predraft stage), 3rd Generation Partnership Project (3GPP) long-term evolution (LTE) project, advanced LTE project, ultra mobile broadband (UMB) project (also referred to as “3GPP2”), Worldwide Interoperability for Microwave Access (WiMAX), etc. In other embodiments, communications may be compatible with additional/alternative communication standards and/or specifications.

FIG. 1 schematically illustrates a communication system 100 , in accordance with various embodiments of the present disclosure. In various embodiments, the communication system 100 includes a plurality of eNBs, e.g., eNB 10 a , eNB 10 b and eNB 10 c . Although only three eNBs are illustrated in FIG. 1 , the communication system may include any other number of eNBs. FIG. 1 also illustrates a cell, e.g., an approximate geographical area, covered by a corresponding eNB. For example, eNB 10 a covers cell 12 a , eNB 10 b covers cell 12 b , and eNB 10 c covers cell 12 c . Although individual cells are illustrated to be approximately hexagonal in shape and similar in size, in various other embodiments, the cells can be of any shape and/or size, and/or may overlap.

In various embodiments, an eNB may be communicatively coupled to another eNB through a backhaul channel. For example, the eNB 10 a and the eNB 10 b may be communicatively coupled through a backhaul channel 30 a , the eNB 10 b and the eNB 10 c may be communicatively coupled through a backhaul channel 30 b , and the eNB 10 c and the eNB 10 a may be communicatively coupled through a backhaul channel 30 c . In an embodiment, a backhaul channel (or a part of the backhaul channel) may be established using a wired link and/or a wireless link.

In various embodiments, the communication system 100 may include a plurality of user equipments (UEs), e.g., UE 20 a , . . . , 20 e , disposed throughout the cells 12 a , . . . , 12 c . The UEs (e.g., UE 20 a ) may be, for example, a mobile station, a cellular or mobile phone, or any other appropriate consumer electronic device capable of wirelessly communicating with an eNB over a wireless communication channel using any appropriate wireless transmission protocol. The eNBs (e.g., eNB 10 a ) may be, for example, any appropriate type of evolved Node B and/or any other appropriate type of base station configured to wirelessly communicate with one or more UEs over a wireless communication channel using any appropriate wireless transmission protocol.

Each UE may communicate with a proximally disposed eNB over a wireless communication channel. For example, the UE 20 a is disposed within the cell 12 a , and accordingly, communicates with the eNB 10 a over a wireless communication channel (illustrated by solid line between the UE 20 a and the eNB 10 a ). In various embodiments, an UE may also receive interference from one or more neighboring eNBs. For example, as illustrated in FIG. 1 , the UE 20 a receives interference signal from the eNB 10 b (illustrated by broken line between the UE 20 a and the eNB 10 b ), while the UE 20 a communicates with the eNB 10 a over the wireless communication channel. Similarly, the UE 20 b may be disposed within the cell 12 b , and accordingly, may communicate with the eNB 10 b over another wireless communication channel (illustrated by solid line between the UE 20 b and the eNB 10 b ). Furthermore, the UE 20 b may receive interference signal from the eNB 10 c (illustrated by broken line between the UE 20 b and the eNB 10 c ), while the UE 20 b communicates with the eNB 10 b over the another wireless communication channel.

FIG. 1 only illustrates the UE 20 a and the UE 20 b communicating with the corresponding eNBs, and receiving interference signals from other eNBs. Although not illustrated in FIG. 1 , other UEs (e.g., UE 20 c , . . . , 20 e ) may also communicate over a corresponding wireless communication channel with a corresponding eNB, and possibly receive interference signals from one or more other eNBs.

In various embodiments, one or more of the eNBs and/or the UEs may be MIMO devices. In various embodiments, the communication system 100 may be a closed-loop system that employs beamforming to increase a signal to noise ratio (SNR) of signals transmitted by individual eNBs to the corresponding UEs. In various embodiments, an eNB (e.g., eNB 10 a ) may transmit one or more data streams to a UE (e.g., UE 20 a ), which may be appropriately weighted onto one or more antennas prior to transmission by the eNB 10 a . The term beamforming or precoding is used herein to describe the application of beamforming or precoding coefficients or weights to frequency-domain signals in the data stream(s), prior to transmission of the data stream(s) by an eNB. In various embodiments, the beamforming or precoding coefficients or weights may be determined from a precoding matrix, as will be discussed in more detail herein later.

FIG. 2 schematically illustrates the eNB 10 b receiving feedback information from a plurality of UEs, in accordance with various embodiments of the present disclosure. As previously discussed, the UE 20 a may communicate with the eNB 10 a over a wireless communication channel and may also receive interference from the interfering eNB 10 b . In various embodiments, the UE 20 a may generate interference feedback information 210 a based on receiving interference signals from the eNB 10 b , as will be discussed in more detail herein later. In various embodiments, the UE 20 a may also generate channel feedback information 220 a based on receiving signals from the eNB 10 a , as will be discussed in more detail herein later. The UE 20 a may transmit the interference feedback information 210 a and the channel feedback information 220 a to the eNB 10 a over the wireless communication channel. The eNB 10 a may re-transmit the interference feedback information 210 a to the eNB 10 b over the backhaul channel 30 a . Although FIG. 2 illustrates the eNB 10 a re-transmitting the interference feedback information 210 a (e.g., which the eNB 10 a receives from the UE 20 a ) to the eNB 10 b , in various embodiments, the eNB 10 a may process the interference feedback information 210 a before re-transmitting the interference feedback information 210 a to the eNB 10 b . Accordingly, although illustrated using a single label in FIG. 2 , in various embodiments, (i) the interference feedback information 210 a received by the eNB 10 a from the UE 20 a and (ii) the interference feedback information 210 a re-transmitted by the eNB 10 a to the eNB 10 b may be different (e.g., based on any processing performed on the interference feedback information 210 a by the eNB 10 a ), as will be readily understood by those skilled in the art based on the teachings of this disclosure. In various embodiments, the UE 20 b may generate channel feedback information 220 b based on receiving signals from the eNB 10 b , and may transmit the channel feedback information 220 b to the eNB 10 b.

Although not illustrated in FIG. 2 , the UE 20 b may, for example, transmit interference feedback information to another eNB (e.g., eNB 10 c ) via the eNB 10 b . Similarly, although not illustrated in FIG. 2 , the eNB 10 b may receive interference feedback information from one or more other UEs (e.g., from UEs that receive interference signals from the eNB 10 b ) and also receive channel feedback information from one or more other UEs (e.g., UE 20 c , which is in communication with the eNB 10 b ).

In various embodiments, the eNB 10 b may receive the channel feedback information 220 b and the interference feedback information 210 a , and determine a precoding matrix (e.g., which may be used to weight data streams onto antennas prior to transmission by the eNB 10 b ) that reduces interference between the eNB 10 b and UE 20 a and increases signal strength of the signal received by the UE 20 b , as will be discussed in more detail herein later.

FIG. 3 schematically illustrates the UE 20 a included in the communication system 100 of FIG. 1 in more detail, in accordance with various embodiments of the present disclosure. In various embodiments, one or more other UEs included in the communication system 100 of FIG. 1 may have a similar configuration as the UE 20 a of FIG. 3 .

In various embodiments, the UE 20 a may include one or more receive antennas, e.g., receive antennas 334 a and 334 b , configured to receive signals transmitted from one or more eNBs (e.g., from eNB 10 a ). In FIG. 3 , two receive antennas are illustrated, although in various other embodiments, any other suitable number of receive antennas may be included in the UE 20 a . In various embodiments, the UE 20 a may include at least as many receive antennas as a number of data stream(s) being transmitted by the eNB 10 a , although the scope of the present disclosure may not be limited in this respect. The UE 10 a may also include one or more transmit antennas (e.g., transmit antenna 336 ) to transmit, among other information, interference feedback information 210 a and channel feedback information 220 a . In some embodiments, one or more antennas of the UE 20 a may be alternatively used as receive or transmit antennas.

In various embodiments, the UE 20 a may include a UE receiver module 310 a configured to receive signals that are received by the receive antennas 334 and/or 334 b . The UE receiver module 310 a may pre-process the received signals before one or more other components of the UE 20 a processes the signals.

In various embodiments, the UE 20 a may also include a UE channel estimation module 314 a . The UE channel estimation module 314 a may be configured to estimate a wireless communication channel between the UE 20 a and the eNB 10 a , based on the receive antennas 334 a and/or 334 b receiving wireless signals from the eNB 10 a over the wireless communication channel between the UE 20 a and the eNB 10 a . For example, the UE channel estimation module 314 a may estimate a channel matrix H_ 10 a _ 20 a that represents the wireless communication channel between the UE 20 a and the eNB 10 a.

The UE channel estimation module 314 a may also be configured to estimate an interference channel between the UE 20 a and the eNB 10 b , based on the receive antennas 334 a and/or 334 b receiving interference signals from the eNB 10 b over the wireless communication channel between the UE 20 a and the eNB 10 b . For example, the UE channel estimation module 314 a may estimate an interference channel matrix G_ 10 b _ 20 a that represents the interference channel between the UE 20 a and the eNB 10 b . In various embodiments, if the UE 20 a receives interference from more than one eNB (i.e., receives interference from an eNB other than the eNB 10 b ), the UE channel estimation module 314 a may estimate more than one interference channel matrix.

In various embodiments, the UE 20 a may also include a UE feedback determination module 318 a , which is configured to receive the channel matrix H_ 10 a _ 20 a and the interference channel matrix G_ 10 b _ 20 a (and/or receive some other representation, e.g., indices, associated with these matrices) from the UE channel estimation module 314 a . In various embodiments, the UE feedback determination module 318 a may be configured to generate the interference feedback information 210 a and the channel feedback information 220 a of FIG. 2 .

As an example, the UE feedback determination module 318 a may be configured to determine an interference feedback matrix v_ 10 _ 20 a that is associated with the interference channel between the eNB 10 b and the UE 20 a , based at least in part on the interference channel matrix G_ 10 b _ 20 a . In various embodiments, the interference feedback matrix v_ 10 b _ 20 a may comprise one or more eigenvectors associated with the interference channel (e.g., one or more eigenvectors of the interference channel matrix G_ 10 b _ 20 a ) between the eNB 10 b and the UE 20 a . In various embodiments, the UE feedback determination module 318 a may also determine an interference feedback matrix index that is associated with the interference feedback matrix v_ 10 _ 20 a . In an example, the UE feedback determination module 318 a may determine the interference feedback matrix index from the interference feedback matrix v_ 10 _ 20 a (e.g., using a predetermined codebook stored in the UE 20 a , although any other appropriate method may be used to determine the interference feedback matrix index from the interference feedback matrix v_ 10 _ 20 a ). In various embodiments, the interference feedback matrix index may be an interference precoding matrix index associated with the interference channel between the eNB 10 b and the UE 20 a . In various embodiments, the interference feedback information 210 a may comprise the interference feedback matrix and/or the interference feedback matrix index generated by the UE feedback determination module 318 a.

In various embodiments, the UE feedback determination module 318 a may also determine a channel quality indicator (CQI), and the interference feedback information 210 a and/or the channel feedback information 220 a may also comprise the determined CQI. Determination of the CQI, by the UE feedback determination module 318 a , will be discussed in more detail herein later.

In various embodiments, the interference feedback information 210 a may comprise any other appropriate feedback information. For example, the UE feedback determination module 318 a may determine (e.g., based at least in part on the interference channel matrix G_ 10 b _ 20 a ) a preferred interference rank indicator, and the interference feedback information 210 a may also comprise the preferred interference rank indicator. In various embodiments, the preferred interference rank indicator may include a recommended number of spatial layers (or data streams) that may be transmitted by the interfering eNB 10 b , in order to improve a performance of the UE 20 a (e.g., reduce interference signal experienced by the UE 20 a ).

The UE feedback determination module 318 a may also determine various parameters that are to be included in the channel feedback information 220 a . For example, based on the channel matrix H_ 10 a _ 20 a , the UE feedback determination module 318 a may determine a channel feedback matrix v_ 10 a _ 20 a associated with the wireless communication channel between the UE 20 a and the eNB 10 a , and also determine a corresponding channel feedback matrix index. In various embodiments, the channel feedback matrix may be a matrix of eigenvectors of the channel between the eNB 10 a and the UE 20 a (e.g., one or more eigenvectors of the channel matrix H_ 10 a _ 20 a ). In various embodiments, the channel feedback matrix index may be a precoding matrix index associated with the channel between the eNB 10 a and the UE 20 a . The channel feedback information 220 a may comprise the channel feedback matrix v_ 10 a _ 20 a , the associated channel feedback matrix index, and/or any other information associated with the wireless communication channel between the UE 20 a and the eNB 10 a . For example, the channel feedback information 220 a may also comprise a rank indicator, a modulation and coding scheme (MCS), and/or any other appropriate information.

In various embodiments, the UE 20 a may also include a UE transmitter module 322 a , which may transmit, via the transmit antenna 336 , the channel feedback information 220 a and the interference feedback information 210 a to the eNB 10 a over the wireless communication channel between the UE 20 a and the eNB 10 a.

FIG. 4 schematically illustrates the eNB 10 b included in the communication system 100 of FIG. 1 in more detail, in accordance with various embodiments of the present disclosure. In various embodiments, one or more other eNBs included in the communication system 100 of FIG. 1 may have a similar configuration as the eNB 10 b of FIG. 4 .

In various embodiments, the eNB 10 b may comprise a plurality of transmit antennas 408 a , 408 b , 408 c and 408 d , to transmit a weighted data stream (e.g., weighted by a corresponding precoding matrix). In FIG. 4 , four transmit antennas are illustrated, although in various other embodiments, any other suitable number of transmit antennas may be included in the eNB 10 b . In various embodiments, the eNB 10 b may include at least as many transmit antennas as the number of data stream(s) being transmitted by eNB 10 b , although the scope of the present disclosure may not be limited in this respect.

The eNB 10 b may also include one or more receive antennas (e.g., receive antenna 440 ) that, in various embodiments, may receive, among other information, interference feedback information 210 a from the UE 20 a via the eNB 10 a . In some embodiments, one or more antennas of the eNB 10 b may be alternatively used as receive or transmit antennas.

In various embodiments, the backhaul channel 30 a (or a part of the backhaul channel 30 a ) may be a wired link (e.g., a copper wire link, an optical fiber link, or any appropriate type of wired link), and the eNB 10 b may receive the interference feedback information 210 a over a wired link (e.g., instead of receiving using the receive antenna 440 ). In various other embodiments, the backhaul channel 30 a (or a part of the backhaul channel 30 a ) may be a wireless link in a frequency band that, for example, is different from a frequency band used for communication between a UE (e.g., the UE 20 a ) and an eNB (e.g., the eNB 10 a ). In some of these embodiments, the frequency band used for the backhaul channel 30 a may be arranged in a millimeter-wave band using frequencies substantially close to 60 GHz, although the scope of the disclosure is not limited in this respect. In these embodiments, the backhaul link 30 a may be referred to as an out-of-band wireless backhaul link. In various other embodiments, any other suitable frequency bands may also be used for the backhaul channel 30 a . For example, in various other embodiments, the backhaul channel 30 a may be a wireless link in a frequency band that is substantially similar to the frequency band used for communication between a UE (e.g., the UE 20 a ) and an eNB (e.g., the eNB 10 a ). In these embodiments, the backhaul link 30 a may be referred to as an in-band wireless backhaul link.

The eNB 10 b (e.g., the receive antenna 440 ) may also receive channel feedback information 220 b from the UE 20 b , wherein the channel feedback information 220 b may include feedback information about the wireless communication channel between the UE 20 b and the eNB 10 b.

The eNB 10 b may also include an eNB receiver module 440 b configured to receive signals that are received by the receive antennas 408 a , . . . , 408 d . In various embodiments and although not illustrated in FIG. 4 , the receive antennas 408 a , . . . , 408 d may be a part of the eNB receiver module 440 b . The eNB receiver module 440 b may pre-process the received signals before one or more other components of the eNB 10 b processes the signals. In various embodiments, the eNB receiver module 440 b may receive the interference feedback information 210 a and the channel feedback information 220 b.

The eNB 10 b may also include an eNB precoding matrix module 444 b . In various embodiments, the eNB precoding matrix module 444 b may receive interference feedback information from one or more UEs that receive interference signals from the eNB 10 b . For example, as illustrated in FIG. 2 , the eNB precoding matrix module 444 b may receive the interference feedback information 210 a from the UE 20 a . Furthermore, the eNB precoding matrix module 444 b may receive channel feedback information from one or more UEs that communicate with the eNB 10 b over one or more corresponding wireless communication channels. For example, the eNB precoding matrix module 444 b may receive the channel feedback information 220 b from the UE 20 b.

Based on the received interference feedback information 210 a and the channel feedback information 220 b , the eNB precoding matrix module 444 b may determine a precoding matrix PM_b. As an example, the received interference feedback information 210 a and the channel feedback information 220 b may include the interference feedback matrix v_ 10 _ 20 a and the channel feedback matrix v_ 10 _ 20 b , respectively (or include indices associated with the respective matrix). In various embodiments, the eNB precoding matrix module 444 b may determine the precoding matrix PM_b as:

PM — b=V (( V H ) V ) −1   ,Equation (1)

where the matrix V H represents the Hermitian matrix of the matrix V (i.e., the matrix V H is a complex conjugate of the matrix V), and the matrix V=[(v_ 10 _ 20 b ) (v_ 10 _ 20 a )]. That is, the matrix V may be a concatenation of the interference feedback matrix v_ 10 _ 20 b and the channel feedback matrix v_ 10 _ 20 a.

In various embodiments, the precoding matrix PM_b may be portioned as

PM — b=[w 1 w 2],  Equation (2)

where w 1 includes precoding weights corresponding to transmission of signals from the eNB 10 b to the UE 20 b , and whereas w 2 includes precoding weights corresponding to transmission of signals from the eNB 10 b to the UE 20 a . That is, the precoding matrix PM_b may be a concatenation of the matrices w 1 and w 2 .

In various embodiments, a number of columns in the matrix w 1 may be equal to a number of data streams transmitted by the eNB 10 b . In various embodiments, the number of data streams transmitted by the eNB 10 b may be pre-configured, or may be adaptively determined based on, for example, the preferred interference rank indicator transmitted by the UE 20 a to the eNB 10 b as a part of the interference feedback information 210 a.

As the eNB 10 b intends to transmit signals to UE 20 b (but not to UE 20 a ), the eNB precoding matrix module 444 b may determine a truncated precoding matrix PM_b_t such that

PM — b — t=[w 1].  Equation (3)

That is, in the truncated precoding matrix PM_b_t, the component of the precoding matrix PM_b (i.e., w 2 ) associated with the interference channel between the eNB 10 b and the UE 20 a is truncated.

In various embodiments, the eNB 10 b also includes an eNB transmitter module 448 b configured to transmit (e.g., via the transmit antenna 440 ) one or more data streams (e.g., to the UE 20 b ), which may be appropriately weighted (e.g., in the eNB precoding matrix module 444 b ) by the truncated precoding matrix PM_b_t prior to transmission by the eNB 10 b.

As previously discussed, the matrix w 1 may be associated with the direction of the channel between the eNB 10 b and UE 20 b , and the matrix w 2 may be associated with the direction of the interference channel between the eNB 10 b and UE 20 a . Furthermore, the vectors in the matrices w 1 and w 2 may be unitary and orthogonal to each other (as the vectors in the matrices w 1 and w 2 are a part of the precoding matrix PM_b). Accordingly, signals transmitted by the eNB 10 b to the UE 20 b , subsequent to being weighted by the truncated precoding matrix PM_b_t, may create relatively reduced interference at the UE 20 a.

Referring again to FIG. 3 , as previously discussed, the UE feedback determination module 318 a may also determine a CQI. While determining the CQI, the UE 20 a may be aware (e.g., based on transmitting the interference feedback information 210 a ) that the eNB 10 b is determining the truncated precoding matrix PM_b_t based on the interference feedback matrix v_ 10 _ 20 a . In various embodiments, the UE 20 a may use this information to determine the CQI. For example, the signal model used for determining the CQI at the UE 20 a may be:

r =[( H — 10 a — 20 a )( v — 10 a — 20 a ) x ]+[( G _ 10 b — 20 a )( v — 10 — 20 a ⊥ ) y]+n,   Equation (4)

where H_ 10 a _ 20 a is the channel matrix that represents the wireless communication channel between the UE 20 a and the eNB 10 a , G_ 10 b _ 20 a is the interference channel matrix that represents the interference channel between the UE 20 a and the eNB 10 b , x is the signal transmitted by the eNB 10 a (e.g., before applying any precoding weights), y is the signal transmitted by the eNB 10 b (e.g., before applying any precoding weights), n is additive noise plus interference from other eNBs (e.g., eNBs which are not involved in cooperative transmission of signals using the interference feedback information), and r is the signal received at the UE 20 a . Furthermore, v_ 10 _ 20 a ⊥ may be a vector, or a set of unitary vectors orthogonal to v_ 10 b _ 20 a.

In various embodiments, based on the above discussed signal model, the UE 20 a may estimate a signal to noise ratio (SINR) of the signals for a k th data stream as follows:

SINR_ ⁢ 20 ⁢ a_k = 1 [ H e H ⁡ ( G e ⁢ G e H + R nn ) - 1 ⁢ H e + I ] k , k - 1 - 1 , Equation ⁢ ⁢ ( 5 )

where R nn =E(n H n) may be a covariance matrix for additive noise plus interference n, matrix H e =[(H_ 10 a _ 20 a )(v_ 10 a 200 ], matrix G e =[(G_ 10 b _ 20 a )(v_ 10 b _ 20 a ⊥ )], matrix H e H may be a Hermitian matrix of the matrix H e , and matrix G e H may be a Hermitian matrix of the matrix G e . As previously discussed, v_ 10 _ 20 a ⊥ may be a vector, or a set of unitary vectors orthogonal to v_ 10 b _ 20 a . In various embodiments, if multiple alternatives exists for the vector v_ 10 _ 20 a ⊥ (e.g., if multiple set of unitary vectors are orthogonal to v_ 10 b _ 20 a ), the UE 20 a may select one of the alternatives for v_ 10 _ 20 a ⊥ that increases (e.g., nearly maximizes) the SINR_ 20 a _k.

In various embodiments, it may be assumed that the interference from the eNB 10 b to the UE 20 a is substantially cancelled as a result of forming the precoding matrix PM_b (and the associated truncated precoding matrix PM_b_t) using the interference feedback information 210 a . In some of these embodiments, the UE feedback determination module 318 a may further simplify the determination of the SINR_ 20 a _k of Equation 5 using a simplified signal model (e.g., instead of the signal model of Equation 4). For example, the signal model used for determining the CQI at the UE 20 a may be:

r =[( H — 10 a — 20 a )( v — 10 a — 20 a ) x]+n.   Equation (4a)

That is, in the simplified signal model of Equation 4a, the term [(G_ 10 b _ 20 a )(v_ 10 _ 20 a ⊥ )y] is ignored (as the interference from the eNB 10 b to the UE 20 a is substantially cancelled). In various embodiments, the corresponding SINR_ 20 a _k may be determined as:

SINR_ ⁢ 20 ⁢ a_k = 1 [ H e H ⁡ ( R nn ) - 1 ⁢ H e + I ] k , k - 1 - 1. Equation ⁢ ⁢ ( 5 ⁢ a )

That is, in Equation 5a, the term associated with the Ge matrix is ignored (as the interference from the eNB 10 b to the UE 20 a is substantially cancelled).

In various embodiments, the UE feedback determination module 318 a may determine the SINR_ 20 a _k (e.g., using Equation (5) and/or Equation (5a)), and also determine a CQI from the determined SINR_ 20 a _k. In various embodiments, the UE transmitter module 322 a may transmit the determined CQI to the eNB 10 a as a part of the interference feedback information 210 a and/or the channel feedback information 220 a.

In various embodiments, the eNB 10 b may receive the CQI from the UE 20 a as a part of the interference feedback information 210 a , and use the CQI to determine the precoding matrix PM_b. For example, the CQI may be used to fine tune the precoding matrix PM_b generated using Equation 1. In various embodiments, characterized in that a single spatial stream is transmitted from the eNB 10 a to the UE 20 a , the precoding matrix PM_b may be determined (e.g., instead of, or in addition to, determining using Equation (1)) as:

PM_b = V ⁡ ( ( V H ) ⁢ V + [ ρ 1 - 1 0 0 ρ 2 - 1 ] ) - 1 , Equation ⁢ ⁢ ( 6 )

where V H and V matrices have been previously discussed with respect to Equation 1, ρ 1 is equal to the SINR_ 20 a _k of Equation 5, and

ρ 2 = SINR_ ⁢ 20 ⁢ a_k SINR_ ⁢ 20 ⁢ a_k ′ - 1 ,

for the case of k=1. The SINR_ 20 a _k′ corresponds to a SINR of the k th data stream, where k=1, at UE 20 a that is determined without taking into account the interference feedback information 210 a that is fed back from the UE 20 a to the eNB 10 b (i.e., without taking into account the v_ 10 _ 20 a ⊥ ). For example, the SINR_ 20 a _k′ may be determined from Equation 5, after replacing the matrix H e with the matrix H_ 10 a _ 20 a , and after replacing the matrix G e with the matrix G_ 10 b _ 20 a . In various embodiments, the UE 20 a may transmit the SINR_ 20 a _k′ (and/or an associated CQI) to the eNB 10 a and eNB 10 b , e.g., to facilitate determination of the Equation 6. In various embodiments, Equation (6) may be used to adjust the precoding matrix PM_b to account for a relative power difference in signals received by the UE 20 a from the eNB 10 a and 10 b.

In various embodiments, the eNB 10 b may receive a CQI from the UE 20 b as a part of the channel feedback information 220 b . The eNB 10 b may determine one or more of a modulation and coding scheme (MCS), a transmission rank, and the precoding matrix PM_b, associated with signal transmission by the eNB 10 b , based at least in part on the CQI received from the UE 20 b.

FIG. 5 schematically illustrates transmission of the channel feedback information 220 a and the interference feedback information 210 a from the UE 20 a to the eNB 10 a , in accordance with various embodiments of the present disclosure. As illustrated in FIG. 5 , in various embodiments, the interference feedback information 210 a may be interleaved in between the channel feedback information 220 a . Thus, the channel feedback information 220 a and the interference feedback information 210 a may be time multiplexed while being transmitted from the UE 20 a to the eNB 10 a . In various embodiments, the UE 20 a may transmit the channel feedback information 220 a more frequently compared to transmitting the interference feedback information 210 a to the eNB 10 a , as illustrated in FIG. 5 , although the scope of the present disclosure may not be limited in this respect.

FIG. 6 illustrates an exemplary method 600 for operating the UE 20 a of FIGS. 1 and 3 , in accordance with various embodiments of the present disclosure. Referring to FIGS. 1-3 and 6 , the method 600 includes, at 604 , wirelessly receiving, by the UE 20 a , interference signal from the eNB 10 b while the UE 20 a is communicating with the eNB 10 a over a wireless communication channel. At 608 , the UE 20 a generates the interference feedback information 210 a , associated with an interference channel between the eNB 10 b and the UE 20 a , based at least in part on receiving the interference signal from the eNB 10 b . The UE 20 a also generates the channel feedback information 220 a , associated with the wireless communication channel between the eNB 10 a and the UE 20 a , based at least in part on communicating with the eNB 10 a . At 612 , the UE 20 a transmits the interference feedback information 210 s to the eNB 10 b via the eNB 10 a , and the channel feedback information 220 a to the eNB 10 a . In various embodiments, the UE 20 a transmits the interference feedback information 210 a to the eNB 10 b to facilitate a determination of a precoding matrix, by the eNB 10 b , that reduces the interference signal.

FIG. 7 illustrates an exemplary method 700 for operating the eNB 10 b of FIGS. 1 and 4 , in accordance with various embodiments of the present disclosure. Referring to FIGS. 1-2 , 4 and 6 , the method 700 includes, at 704 , receiving, by the eNB 10 b , the interference feedback information 210 a from the UE 20 a through the eNB 10 a . Furthermore, at 704 , the eNB 10 b also receives, from the UE 20 b , the channel feedback information 220 b . At 708 , the eNB 10 b determines (e.g., using Equations 1 and/or 6) the precoding matrix PM_b based at least in part on the interference feedback information 210 a and the channel feedback information 220 b . At 712 , the eNB 10 b determines the truncated precoding matrix PM_b_t using, e.g., Equations 2 and 3. At 716 , the eNB 10 b transmits signals to UE 20 b subsequent to weighting the signals by the truncated precoding matrix PM_b_t.

The communication devices (e.g., the eNBs 10 a , 10 b , etc. and/or the user equipments 20 a , 20 b , etc.) described herein may be implemented into a system using any suitable hardware and/or software to configure as desired. FIG. 8 illustrates, for one embodiment, an example system 800 comprising one or more processor(s) 804 , system control logic 808 coupled to at least one of the processor(s) 804 , system memory 812 coupled to system control logic 808 , non-volatile memory (NVM)/storage 816 (e.g., which may be a non-transitory storage medium) coupled to system control logic 808 , and one or more communications interface(s) 820 coupled to system control logic 808 .

System control logic 808 for one embodiment may include any suitable interface controllers to provide for any suitable interface to at least one of the processor(s) 804 and/or to any suitable device or component in communication with system control logic 808 .

System control logic 808 for one embodiment may include one or more memory controller(s) to provide an interface to system memory 812 (e.g., which may be a non-transitory storage medium). System memory 812 may be used to load and store data and/or instructions, for example, for system 800 . System memory 812 for one embodiment may include any suitable volatile memory, such as suitable dynamic random access memory (DRAM), for example.

System control logic 808 for one embodiment may include one or more input/output (I/O) controller(s) to provide an interface to NVM/storage 816 and communications interface(s) 820 .

NVM/storage 816 may be used to store data and/or instructions, for example. NVM/storage 816 may include any suitable non-volatile memory, such as flash memory, for example, and/or may include any suitable non-volatile storage device(s), such as one or more hard disk drive(s) (HDD(s)), one or more compact disc (CD) drive(s), and/or one or more digital versatile disc (DVD) drive(s) for example.

The NVM/storage 816 may include a storage resource physically part of a device on which the system 800 is installed or it may be accessible by, but not necessarily a part of, the device. For example, the NVM/storage 816 may be accessed over a network via the communications interface(s) 820 .

System memory 812 and NVM/storage 816 may include, in particular, temporal and persistent copies, respectively, of logic 824 .

In various embodiments, the system 800 may be a part of the UE 20 a , and the logic 824 may include instructions that when executed by at least one of the processor(s) 804 result in the system 800 generating the interference feedback information 210 a and/or the channel feedback information 220 a , and transmitting these information to the eNB 10 b and/or 10 a , e.g., as discussed with respect to the method 600 of FIG. 6 .

In various other embodiments, the system 800 may be a part of the eNB 10 b , and the logic 824 may include instructions that when executed by at least one of the processor(s) 804 result in the system 800 receiving the interference feedback information 210 a and the channel feedback information 220 b , determining the precoding matrix PM_b, determining the truncated precoding matrix PM_b_t, and/or transmitting signals to UE 20 b subsequent to weighting the signals by the truncated precoding matrix PM_b_t, e.g., as discussed with respect to the method 700 of FIG. 7 .

Communications interface(s) 820 may provide an interface for system 800 to communicate over one or more network(s) and/or with any other suitable device. Communications interface(s) 820 may include any suitable hardware and/or firmware. Communications interface(s) 820 for one embodiment may include, for example, a network adapter, a wireless network adapter, a telephone modem, and/or a wireless modem. For wireless communications, communications interface(s) 820 for one embodiment may use one or more antennae.

For one embodiment, at least one of the processor(s) 804 may be packaged together with logic for one or more controller(s) of system control logic 808 . For one embodiment, at least one of the processor(s) 804 may be packaged together with logic for one or more controllers of system control logic 808 to form a System in Package (SiP). For one embodiment, at least one of the processor(s) 804 may be integrated on the same die with logic for one or more controller(s) of system control logic 808 . For one embodiment, at least one of the processor(s) 804 may be integrated on the same die with logic for one or more controller(s) of system control logic 808 to form a System on Chip (SoC).

In various embodiments, system 800 may have more or less components, and/or different architectures.

Although certain example methods, apparatus, and articles of manufacture have been described herein, the scope of coverage of the present disclosure is not limited thereto. On the contrary, the present disclosure covers all methods, apparatus, and articles of manufacture fairly falling within the scope of the appended claims either literally or under the doctrine of equivalents. For example, although the above discloses example systems including, among other components, software or firmware executed on hardware, it should be noted that such systems are merely illustrative and should not be considered as limiting. In particular, it is contemplated that any or all of the disclosed hardware, software, and/or firmware components could be embodied exclusively in hardware, exclusively in software, exclusively in firmware or in some combination of hardware, software, and/or firmware.