Hybrid interference alignment for mixed macro-FEMTO base station downlink

A method, an apparatus, and a computer program product for wireless communication are provided. The apparatus is a first BS. The apparatus determines a first channel between a second BS and a first UE served by a third BS, determines a second channel between the first base station and the first UE, and determines a first direction vector to be used by the second base station for sending a data transmission. The apparatus transmits a set of resource blocks to a second UE served by the first base station with a second direction vector determined based on the first channel, the second channel, and the first direction vector to be used by the second base station.

BACKGROUND

The present disclosure relates generally to communication systems, and more particularly, to hybrid interference alignment for mixed macro-femto base station downlink.

SUMMARY

In an aspect of the disclosure, a method, a computer program product, and an apparatus are provided. The apparatus is a first base station. The apparatus determines a first channel between a second base station and a first user equipment served by a third base station. The apparatus determines a second channel between the first base station and the first UE. The apparatus determines a first direction vector to be used by the second base station for sending a data transmission. The apparatus transmits a set of resource blocks to a second UE served by the first base station with a second direction vector determined based on the first channel, the second channel, and the first direction vector to be used by the second base station.

DETAILED DESCRIPTION

The E-UTRAN includes the evolved Node B (eNB)106and other eNBs108. The eNB106provides user and control planes protocol terminations toward the UE102. The eNB106may be connected to the other eNBs108via a backhaul (e.g., an X2 interface). The eNB106may also be referred to as a base station (BS), a Node B, an access point, a base transceiver station, a radio base station, a radio transceiver, a transceiver function, a basic service set (BSS), an extended service set (ESS), or some other suitable terminology. The eNB106provides an access point to the EPC110for a UE102. Examples of UEs102include a cellular phone, a smart phone, a session initiation protocol (SIP) phone, a laptop, a personal digital assistant (PDA), a satellite radio, a global positioning system, a multimedia device, a video device, a digital audio player (e.g., MP3 player), a camera, a game console, a tablet, or any other similar functioning device. The UE102may also be referred to by those skilled in the art as a mobile station, a subscriber station, a mobile unit, a subscriber unit, a wireless unit, a remote unit, a mobile device, a wireless device, a wireless communications device, a remote device, a mobile subscriber station, an access terminal, a mobile terminal, a wireless terminal, a remote terminal, a handset, a user agent, a mobile client, a client, or some other suitable terminology.

The eNB106is connected to the EPC110. The EPC110includes a Mobility Management Entity (MME)112, other MMEs114, a Serving Gateway116, a Multimedia Broadcast Multicast Service (MBMS) Gateway124, a Broadcast Multicast Service Center (BM-SC)126, and a Packet Data Network (PDN) Gateway118. The MME112is the control node that processes the signaling between the UE102and the EPC110. Generally, the MME112provides bearer and connection management. All user IP packets are transferred through the Serving Gateway116, which itself is connected to the PDN Gateway118. The PDN Gateway118provides UE IP address allocation as well as other functions. The PDN Gateway118is connected to the Operator's IP Services122. The Operator's IP Services122may include the Internet, an intranet, an IP Multimedia Subsystem (IMS), and a PS Streaming Service (PSS). The BM-SC126may provide functions for MBMS user service provisioning and delivery. The BM-SC126may serve as an entry point for content provider MBMS transmission, may be used to authorize and initiate MBMS Bearer Services within a PLMN, and may be used to schedule and deliver MBMS transmissions. The MBMS Gateway124may be used to distribute MBMS traffic to the eNBs (e.g.,106,108) belonging to an MBSFN area broadcasting a particular service, and may be responsible for session management (start/stop) and for collecting eMBMS related charging information.

FIG. 2is a diagram illustrating an example of an access network200in an LTE network architecture. In this example, the access network200is divided into a number of cellular regions (cells)202. One or more lower power class eNBs208may have cellular regions210that overlap with one or more of the cells202. The lower power class eNB208may be a femto cell (e.g., home eNB (HeNB)), pico cell, micro cell, or remote radio head (RRH). The macro eNBs204are each assigned to a respective cell202and are configured to provide an access point to the EPC110for all the UEs206in the cells202. There is no centralized controller in this example of an access network200, but a centralized controller may be used in alternative configurations. The eNBs204are responsible for all radio related functions including radio bearer control, admission control, mobility control, scheduling, security, and connectivity to the serving gateway116.

Interference alignment schemes have been developed to mitigate interference. Interference alignment schemes include deterministic interference alignment schemes and opportunistic interference alignment schemes. The conditions for deterministic interference alignment schemes can be difficult to solve. The conditions for opportunistic interference alignment schemes can be less difficult to solve by a base station by taking advantage of many UEs being served by the base station. However, the gain from opportunistic interference alignment schemes can be poor if all of the base stations do not have many UEs. An important scenario is that of a plurality of neighboring femto base stations within the coverage area of a macro base station. Typically, femto base stations have one UE, while macro base stations have many UEs. There is currently a need for a hybrid interference alignment scheme that includes deterministic and opportunistic components that can provide good interference mitigation for the femto/macro base station scenario.

FIG. 7is a first diagram700for illustrating exemplary methods. As shown inFIG. 7, a macro base station BS1is serving UE11, UE12, and UE13, a femto base station BS2is serving UE2, a femto base station BS3is serving UE3, and a femto base station BS4is serving UE4. The BS1applies an opportunistic interference alignment scheme to select one of the UEs UE11, UE12, or UE13that will benefit the most from the scheme in a particular subframe/slot, and applies a pseudo-random and orthogonal direction vector v1(t) to data before or when transmitting the data S1to the selected UE in the particular subframe/slot. As shown inFIG. 7, the BS1selects the UE13for the data transmission. The direction vector v1(t) has M dimensions greater than or equal to two. The M dimensions may be antenna dimensions (MIMO) and/or frequency dimensions (e.g., resource blocks in OFDM). Each dimension may modify modulated data symbols in amplitude and/or phase.

The BS2applies a deterministic interference alignment scheme and determines an orthogonal direction vector v2(t), applies the direction vector v2(t) to data, and transmits the data S2to the UE2in the particular subframe/slot. The direction vector v2(t) has M dimensions greater than or equal to two. The M dimensions may be antenna dimensions (MIMO) and/or frequency dimensions (e.g., resource blocks in OFDM). Each dimension may modify modulated data symbols in amplitude and/or phase. The direction vector v2(t) is determined as follows:
v2(t)∝v1(t)H1,3(H2,3)−1,  (1)
where H1,3is the channel between BS1and UE3and H2,3is the channel between BS2and UE3. Similarly, the BS3applies a deterministic interference alignment scheme and determines an orthogonal direction vector v3(t), applies the direction vector v3(t) to data, and transmits the data S3to the UE3in the particular subframe/slot. The direction vector v3(t) has M dimensions greater than or equal to two. The M dimensions may be antenna dimensions (MIMO) and/or frequency dimensions (e.g., resource blocks in OFDM). Each dimension may modify modulated data symbols in amplitude and/or phase. The direction vector v3(t) is determined as follows:
v3(t)∝v1(t)H1,2(H3,2)−1,  (2)
where H1,2is the channel between BS1and UE2and H3,2is the channel between BS3and UE2.

InFIG. 7, the transmitted direction vectors are represented as vi(t) and the received direction vectors are represented as v′i(t). While a received direction vector is labeled v′i(t) for i=1, 2, and 3 for each of the UEs inFIG. 7, the received direction vector v′i(t) for i=1, 2, and 3 for each of the UEs may differ in amplitude and/or phase due to the channel between the transmitting base station and the UE. As such, for example, while the received direction vector v′1(t) at the UE2and the received direction vector v′1(t) at the UE3are labeled the same, the direction vectors v′1(t) for each of the UE2and UE3are different as shown by the different phase directions of the arrows inFIG. 7.

As shown inFIG. 7, the UE13receives the data transmission S1with the applied direction vector v1(t) from the BS1. The data transmission S1is modified by the channel H1,13between the BS1and the UE13and is received with a direction vector v′1(t) due to the channel H1,13. The UE13also receives the interfering data transmission S2from the BS2and the interfering data transmission S3from the BS3. The interfering data transmission S2is modified by the channel H2,13between the BS2and the UE13and is received with a direction vector v′2(t) due to the channel H2,13. The interfering data transmission S3is modified by the channel H3,13between the BS3and the UE13and is received with a direction vector v′3(t) due to the channel H3,13. The received direction vectors v′2(t) and v′3(t) are shown aligning (i.e., proportional) or nearly aligning (i.e., nearly proportional), as the BS1previously selected the UE13for the data transmission because of the opportunistic interference alignment.

The UE2receives the data transmission S2with the applied direction vector v2(t) from the BS2. The data transmission S2is modified by the channel H2,2between the BS2and the UE2and is received with a direction vector v′2(t) due to the channel H2,2. The UE2also receives the interfering data transmission S1from the BS1and the interfering data transmission S3from the BS3. The interfering data transmission S1is modified by the channel H1,2between the BS1and the UE2and is received with a direction vector v′1(t) due to the channel H1,2. The interfering data transmission S3is modified by the channel H3,2between the BS3and the UE2and is received with a direction vector v′3(t) due to the channel H3,2. The received direction vectors v′1(t) and v′3(t) align (i.e., proportional) or nearly align (i.e., nearly proportional) due to the application of the direction vector v3(t) by the BS3.

The UE3receives the data transmission S3with the applied direction vector v3(t) from the BS3. The data transmission S3is modified by the channel H3,3between the BS3and the UE3and is received with a direction vector v′3(t) due to the channel H3,3. The UE3also receives the interfering data transmission S1from the BS1and the interfering data transmission S2from the BS2. The interfering data transmission S1is modified by the channel H1,3between the BS1and the UE3and is received with a direction vector v′1(t) due to the channel H1,3. The interfering data transmission S2is modified by the channel H2,3between the BS2and the UE3and is received with a direction vector v′2(t) due to the channel H2,3. The received direction vectors v′1(t) and v′2(t) align (i.e., proportional) or nearly align (i.e., nearly proportional) due to the application of the direction vector v2(t) by the BS2.

When the interfering signals are received with direction vectors that align or nearly align, the UE can more easily cancel the interfering signals from the signal received from the serving base station. Generally, a femto base station BSidetermines a direction vector vi(t) to apply to transmitted data as follows:
vi(t)∝v1(t)Ai,  (3)
where v1(t) is the pseudo-random and orthogonal direction vector applied by the macro base station and Aiis a rotation matrix computed by the femto base station BSi. The rotation matrix Aimay be determined based on channels between the macro base station and a UE served by a neighboring femto base station and between itself and the UE served by the neighboring femto base station. In the example provided inFIG. 7, the BS2determines the rotation matrix A2as A2=H1,3(H2,3)−1and the BS3determines the rotation matrix A3as A3=H1,2(H3,2)−1.

FIG. 8is a second diagram800for illustrating exemplary methods. As shown inFIG. 8, each of the base stations BS1, BS2, BS3may synchronously change the direction vectors each subframe/slot. The director vectors used by the macro base station BS1may be predetermined and known a priori by the macro base station BS1and each of the femto base stations BS2and BS3. The direction vector v1(t) may be based on different pseudo-random sequences or seeds and may hop around to different values. The direction vector v1(t) may be dependent on an identifier of the BS1, subcarriers of the utilized resource blocks, or a corresponding subframe and/or system frame number. When the direction vector v1(t) depends on the subframe and/or on a system frame number, the direction vector v1(t) may be said to be time-varying. As discussed supra, the femto base stations BS2and BS3determine the direction vectors v2(t) and v3(t), respectively, to apply to data for transmission. As such, the femto base stations BS2and BS3determine their direction vectors v2(t) and v3(t), respectively, based on v1(t).

FIG. 9is a third diagram900for illustrating exemplary methods.FIG. 9specifically illustrates the phase rotation of a modulated data symbol. As discussed supra, the BS1, BS2, and BS3apply direction vectors to modulated data symbols before transmitting (frequency dimensions) the modulated data symbols or when transmitting (antenna dimensions) the modulated data symbols. The direction vectors modify an amplitude and/or a phase of the modulated data symbols. Assume that the number of dimensions is two (i.e., M=2). Accordingly, with respect to the femto base station BS2, v2(t)=[v2,1(t) v2,2(t)], where v2,1(t)=A1ejθ1and v2,2(t)=A2ejθ2. Assume also that the direction vector v2(t) modifies the modulated data symbols in phase only (i.e., A1=1 and A2=1). Further, assume the femto base station BS2modulates the data using QPSK. The diagram900illustrates possible QPSK values. As shown in the diagram950, if the BS2applies a phase rotation to the QPSK value 11, the BS2may rotate a phase of the modulated symbol by θ. The value θ is a function of a phase applied by the macro base station BS1(as discussed in relation to equations (1) and (3)). In a frequency dimension configuration, the BS2duplicates the data by mapping the same data to both a first set of resource blocks/elements and a second set of resource blocks/elements. The BS2applies a first phase rotation θ1to modulated data symbols in the first set of resource blocks/elements and a second phase rotation θ2to modulated data symbols in the second set of resource blocks/elements. In an antenna dimension configuration, the BS2duplicates the modulated data symbols not through a mapping of modulated data symbols onto resource blocks/elements, but through the transmission of the same modulated data symbols through a plurality of transmit antennas. A first set of transmit antennas applies a first phase rotation θ1to the modulated data symbols and a second set of transmit antennas applies a second phase rotation θ2to the modulated data symbols.

FIG. 10Ais a fourth diagram1000for illustrating exemplary methods. When applying frequency dimensions, the base stations BS1, BS2, and BS3map the same modulated data symbols to both a first set of resource blocks/elements and to a second set of resource blocks/elements. ForFIG. 10A, assume that the base stations BS1, BS2, and BS3map the same modulated data symbols to different sets of resource blocks (i.e., the granularity is resource blocks and not resource elements). Accordingly, a base station may map the same modulated data symbols to a first set of resource blocks1002and to a second set of resource blocks1004. The base station applies the direction vector v(t) to the modulated data symbols in the first set of resource blocks1002and the second set of resource blocks1004, which results in the modulated data symbols in the first set of resource blocks and the second set of resource blocks being modified in amplitude and/or phase as shown by the arrows1012,1014.

FIG. 10Bis a fifth diagram1050for illustrating exemplary methods. When applying antenna dimensions, the base stations BS1, BS2, and BS3map modulated data symbols to a set of resource blocks/elements and transmit the same set of resource blocks/elements using a different set of transmit antennas to apply the direction vector v(t) on the modulated data symbols. Accordingly, a base station may map modulated data symbols to a set of resource blocks1052and transmit the set of resource blocks1052through different transmit antennas so as to modify an amplitude and/or a phase of the modulated data symbols as shown by the arrows1062,1072.

FIG. 11is a flow chart1100of a first method of wireless communication. The method may be performed by a base station, such as the femto base station BS2or the femto base station BS3. As shown inFIG. 11, in step1102a first BS determines a first channel between a second BS and a first UE served by a third BS. In step1104, the first BS determines a second channel between the first BS and the first UE. In step1108, the first BS determines a first direction vector to be used by the second BS for sending a data transmission. In step1112, the first BS transmits a set of resource blocks (using frequency dimensions and/or antenna dimensions) to a second UE served by the first BS with a second direction vector determined based on the first channel, the second channel, and the first direction vector to be used by the second BS. In step1106, the first BS may receive information indicating direction vectors to be used in sequence by the second BS. The information indicating direction vectors may include information indicating the first direction vector determined in step1108. In step1110, the first BS may determine the second direction vector such that a product of the second channel and the second direction vector approximately aligns with (i.e., is proportional to) a product of the first channel and the first direction vector.

For example, referring toFIG. 7, the BS2determines a first channel H1,3between the BS1and the UE3served by the BS3. The BS2determines a second channel H2,3between the BS2and the UE3. The BS2determines a first direction vector v1(t) to be used by the BS1for sending a data transmission. The BS2transmits a set of resource blocks to a UE2served by the BS2with a second direction vector v2(t) determined based on the first channel H1,3, the second channel H2,3, and the first direction vector v1(t) to be used by the BS1. As discussed in relation toFIG. 8, the BS2may receive information indicating direction vectors v1(t) to be used in sequence by the BS1. As discussed in relation to Eq. (1), the BS2may determine the second direction vector v2(t) such that a product of the second channel H2,3and the second direction vector v2(t) approximately aligns with (i.e., is proportional to) a product of the first channel H1,3and the first direction vector v1(t).

The first BS may receive information indicating the first channel from the second base station. The first BS may receive information indicating the first channel from the third base station. The first BS may transmit a pilot signal to the second UE, and receive information indicating the second channel from the third base station, the second channel being based on the transmitted pilot signal. The first BS may transmit a pilot signal to the second UE, and receive information indicating the second channel from the second base station, the second channel being based on the transmitted pilot signal. The first BS may receive an uplink pilot signal from the first UE. The second channel may be determined based on the received uplink signal.

For example, referring toFIG. 7, the BS2may receive information indicating the first channel H1,3from the BS1. The BS1may receive information indicating the first channel H1,3from the BS3and provide the received information to the BS2. In TDD systems, the BS1may receive an uplink pilot signal from the UE3, determine an uplink channel H3,1based on the received uplink pilot signal, and provide the uplink channel H3,1to the BS2. The BS2may then assume that the channel H1,3=H3,1. The BS2may receive information indicating the first channel H1,3from the BS3. The BS2may transmit a pilot signal to the UE2, the UE3may receive the pilot signal, the UE3may send information indicating the second channel H2,3to the BS3, and the BS2may receive information indicating the second channel H2,3from the BS3. As such, the second channel H2,3is based on the transmitted pilot signal. The BS2may transmit a pilot signal to the UE2, the UE3may receive the pilot signal, the UE3may determine the second channel H2,3based on the received pilot signal and send information indicating the second channel H2,3to either the BS1or the BS3, the BS3may send information indicating the second channel H2,3to the BS1if the BS3receives the information indicating the second channel H2,3from the UE3, and the BS2may receive information indicating the second channel H2,3from the BS1. As such, the second channel H2,3is based on the transmitted pilot signal. In TDD systems, the BS2may receive an uplink pilot signal from the UE3. The BS2may determine the uplink channel H3,2based on the received uplink pilot signal and assume the second channel H2,3=H3,2.

Referring again toFIG. 7, the UE3receives a first interfering signal S2from the BS2and a second interfering signal S1from the BS1. The second interfering signal S1is associated with a first direction vector v1(t). The first interfering signal S2is associated with a second direction vector v2(t) determined based on a first channel H1,3between the BS1and the UE3, on a second channel H2,3between the BS2and the UE3, and on the first direction vector v1(t). A product of the second channel H2,3and the second direction vector v2(t) approximately aligning with (i.e., is proportional to) a product of the first channel H1,3and the first direction vector v1(t). The UE3receives a data transmission S3from the BS3serving the UE3. The UE3cancels, at least partially, the first interfering signal S2and the second interfering signal S1from the data transmission S3in order to decode the data transmission S3. The UE3may receive a pilot signal from the BS1, and determine the first channel H1,3based on the received pilot signal. The UE3may transmit first channel information indicating the first channel H1,3to the BS1. The BS1may then provide the first channel information to the BS2. The UE3may transmit first channel information indicating the first channel H1,3to the BS3. The BS3may then provide the first channel information directly to the BS2or directly to the BS1, which then provides the received first channel information to the BS2. In TDD systems, the UE3may transmit an uplink pilot signal to the BS3, the BS1may receive the uplink pilot signal, the BS1may determine the channel H3,1based on the received uplink pilot signal, the BS1may provide the determined channel H3,1to the BS2, and the BS2may determine the first channel H1,3based on the uplink pilot signal by assuming H1,3=H3,1. The UE3may receive a pilot signal from the BS2, and determine the second channel H2,3based on the pilot signal. The UE3may transmit second channel information indicating the second channel H2,3to the BS1, which then provides the received second channel information to the BS2. The UE3may transmit second channel information indicating the second channel H2,3to the BS3, which may then provide the second channel information directly to the BS2or directly to the BS1, which then provides the received second channel information to the BS2. In TDD systems, the UE3may transmit an uplink signal to the BS3, the BS2may receive the uplink signal, the BS2may determine the channel H3,2, and the BS2may determine the second channel H2,3based on the uplink signal by assuming H2,3=H3,2.

FIG. 12is a flow chart1200of a second method of wireless communication. The method may be performed by a base station, such as the femto base station BS2or the femto base station BS3. In step1202, a first BS determines a first proximity to the first UE. In step1204, the first BS determines a second proximity to a third UE served by a fourth base station. In step1206, the first BS determines that the first proximity is less than the second proximity and therefore that the first BS is closer to the first UE than the third UE. In step1208, the first BS determines to transmit the set of resource blocks (using frequency dimensions and/or antenna dimensions) to align interfering signals with each other for the first UE based on the determination that the first proximity is less than the second proximity. If the first BS determines that the second proximity is less than the first proximity, then the first BS may determine instead to transmit the set of resource blocks (using frequency dimensions and/or antenna dimensions) to align interfering signals with each other for the third UE.

For example, referring toFIG. 7, the BS2determines a first proximity to the UE3. In step1204, the BS2determines a second proximity to the UE4served by the BS4. In step1206, the BS2determines that the first proximity is less than the second proximity and therefore that the BS2is closer to the UE3than the UE4. In step1208, the BS2determines to transmit the set of resource blocks (using frequency dimensions and/or antenna dimensions) to align interfering signals with each other for the UE3based on the determination that the first proximity is less than the second proximity. If the BS2determines that the second proximity is less than the first proximity, then the BS2may determine instead to transmit the set of resource blocks (using frequency dimensions and/or antenna dimensions) to align interfering signals with each other for the UE4. If the BS2determines to align interfering signals for the UE3, the BS2uses Eq. (1) to determine the direction vector v2(t). If the BS2determines to align interfering signals for the UE4, the BS2determines v2(t) by the relationship v2(t)∝v1(t)H1,4(H2,4)−1, where H1,4is the channel between the BS1and the UE4and H2,4is the channel between the BS2and the UE4.

FIG. 13is a conceptual data flow diagram1300illustrating the data flow between different modules/means/components in an exemplary apparatus1302. The apparatus may be a base station, such as the femto base station BS2or the femto base station BS3. The apparatus1302, which is a first base station, may include one or more of a receiving module1304, a channel determination module1306, a direction vector determination module1308, a transmission module1310, and a proximity determination module1312. The channel determination module1306is configured to determine a first channel between a second base station and a first UE1360served by a third base station. The channel determination module1306is further configured to determine a second channel between the first base station and the first UE1360. The direction vector determination module1308is configured to determine a first direction vector to be used by the second base station for sending a data transmission. The transmission module1310is configured to transmit a set of resource blocks to a second UE1370served by the first base station with a second direction vector determined based on the first channel, the second channel, and the first direction vector to be used by the second base station. The direction vector determination module1308may be further configured to determine the second direction vector such that a product of the second channel and the second direction vector approximately aligns with a product of the first channel and the first direction vector. The receiving module1304may be configured to receive information indicating the first channel from the second base station. The receiving module1304may be further configured to receive information indicating the first channel from the third base station. The transmission module1310may be configured to transmit a pilot signal to the second UE1370, and the receiving module1304may be configured to receive information indicating the second channel from the third base station. The second channel may be based on the transmitted pilot signal. The transmission module1310may be configured to transmit a pilot signal to the second UE1370, and the receiving module1304may be configured to receive information indicating the second channel from the second base station, the second channel being based on the transmitted pilot signal. The receiving module1304may be configured to receive an uplink pilot signal1365from the first UE1360. The second channel may be determined based on the received uplink signal. The proximity determination module may be configured to determine a first proximity to the first UE1360, to determine a second proximity to a third UE served by a fourth base station, to determine that the first proximity is less than the second proximity, and to determine to transmit the set of resource blocks to align interfering signals with each other for the first UE1360based on the determination that the first proximity is less than the second proximity. The receiving module1304may be configured to receive information indicating direction vectors to be used in sequence by the second base station. The direction vectors include the first direction vector.

FIG. 14is a diagram1400illustrating an example of a hardware implementation for an apparatus1302′ employing a processing system1414. The processing system1414may be implemented with a bus architecture, represented generally by the bus1424. The bus1424may include any number of interconnecting buses and bridges depending on the specific application of the processing system1414and the overall design constraints. The bus1424links together various circuits including one or more processors and/or hardware modules, represented by the processor1404, the modules1304,1306,1308,1310,1312and the computer-readable medium1406. The bus1424may also link various other circuits such as timing sources, peripherals, voltage regulators, and power management circuits, which are well known in the art, and therefore, will not be described any further.

The processing system1414may be coupled to a transceiver1410. The transceiver1410is coupled to one or more antennas1420. The transceiver1410provides a means for communicating with various other apparatus over a transmission medium. The transceiver1410receives a signal from the one or more antennas1420, extracts information from the received signal, and provides the extracted information to the processing system1414, specifically the receiving module1304. In addition, the transceiver1410receives information from the processing system1414, specifically the transmission module1310, and based on the received information, generates a signal to be applied to the one or more antennas1420. The processing system1414includes a processor1404coupled to a computer-readable medium1406. The processor1404is responsible for general processing, including the execution of software stored on the computer-readable medium1406. The software, when executed by the processor1404, causes the processing system1414to perform the various functions described supra for any particular apparatus. The computer-readable medium1406may also be used for storing data that is manipulated by the processor1404when executing software. The processing system further includes at least one of the modules1304,1306,1308,1310, and1312. The modules may be software modules running in the processor1404, resident/stored in the computer readable medium1406, one or more hardware modules coupled to the processor1404, or some combination thereof. The processing system1414may be a component of the eNB610and may include the memory676and/or at least one of the TX processor616, the RX processor670, and the controller/processor675.

In one configuration, the apparatus1302/1302′ for wireless communication is a first base station and includes means for determining a first channel between a second base station and a first UE served by a third base station, means for determining a second channel between the first base station and the first UE, and means for determining a first direction vector to be used by the second base station for sending a data transmission. Apparatus further include means for transmitting a set of resource blocks to a second UE served by the first base station with a second direction vector determined based on the first channel, the second channel, and the first direction vector to be used by the second base station. The apparatus may further include means for determining the second direction vector such that a product of the second channel and the second direction vector approximately aligns with a product of the first channel and the first direction vector. The apparatus may further include means for receiving information indicating the first channel from the second base station. The apparatus may further include means for receiving information indicating the first channel from the third base station. The apparatus may further include means for transmitting a pilot signal to the second UE, and means for receiving information indicating the second channel from the third base station, the second channel being based on the transmitted pilot signal. The apparatus may further include means for transmitting a pilot signal to the second UE, and means for receiving information indicating the second channel from the second base station, the second channel being based on the transmitted pilot signal. The apparatus may further include means for receiving an uplink pilot signal from the first UE. The second channel may be determined based on the received uplink signal. The apparatus may further include means for determining a first proximity to the first UE, means for determining a second proximity to a third UE served by a fourth base station, means for determining that the first proximity is less than the second proximity, and means for determining to transmit the set of resource blocks to align interfering signals with each other for the first UE based on the determination that the first proximity is less than the second proximity. The apparatus may further include means for receiving information indicating direction vectors to be used in sequence by the second base station, the direction vectors including the first direction vector.

The aforementioned means may be one or more of the aforementioned modules of the apparatus1302and/or the processing system1414of the apparatus1302′ configured to perform the functions recited by the aforementioned means. As described supra, the processing system1414may include the TX Processor616, the RX Processor670, and the controller/processor675. As such, in one configuration, the aforementioned means may be the TX Processor616, the RX Processor670, and the controller/processor675configured to perform the functions recited by the aforementioned means.