HK1188897B - Synchronous tdm-based communication in dominant interference scenarios - Google Patents

Description

TDM-based synchronous communication in dominant interference scenarios

The present application is a divisional application of an application having an application number of 200980127042.9 filed on 10/07/2009 entitled "synchronous communication based on TDM in a significant interference situation".

This application claims priority from U.S. provisional application No.61/080,025, entitled "enablingcumulans IN THE PRESENCE OF dominantterferer", filed on 11.7.2008, which is assigned to the assignee OF the present application and is incorporated herein by reference.

Technical Field

The present disclosure relates generally to communication, and more specifically to techniques for supporting communication in a wireless communication network.

Background

Wireless communication networks are widely deployed to provide various communication services such as: voice, video, packet data, messaging, broadcast, etc. These wireless networks may be multiple-access networks capable of supporting multiple users by sharing the available network resources. Examples of such multiple access networks include: code Division Multiple Access (CDMA) networks, Time Division Multiple Access (TDMA) networks, Frequency Division Multiple Access (FDMA) networks, Orthogonal FDMA (OFDMA) networks, and single-carrier FDMA (SC-FDMA) networks.

A wireless communication network may include several base stations, which may support communication for several User Equipment (UEs). A UE may communicate with a base station via the downlink and uplink. The downlink (or forward link) refers to the communication link from the base stations to the UEs, and the uplink (or reverse link) refers to the communication link from the UEs to the base stations.

A base station may transmit data and control information to a UE on the downlink and/or may receive data and control information from a UE on the uplink. On the downlink, transmissions from a base station may observe interference caused by transmissions from neighboring base stations. On the uplink, transmissions from a UE may cause interference to transmissions communicated by other UEs to neighboring base stations. Interference can reduce performance on both the downlink and uplink.

Disclosure of Invention

Techniques to support communication in a dominant interference scenario and to support operation of a relay in a heterogeneous network are described. Heterogeneous networks may include base stations with different transmit power levels. In a dominant interference scenario, the UE may communicate with the first base station and may observe and/or cause high interference from/to the second base station. The first base station and the second base station may be of different types and/or may have different transmit power levels.

In an aspect, communication in a dominant interference scenario may be supported by reserving subframes for weaker base stations observing high interference from strong interfering base stations. An eNB may be classified as a "weak" eNB or a "strong" eNB based on the eNB received power at the UE (rather than based on the eNB's transmit power level). Then, in the presence of a strong interfering base station, the UE may communicate with the weaker base station in the reserved subframes.

In another aspect, interference caused by reference signals in a heterogeneous network may be reduced. A first station (e.g., a base station) in a heterogeneous network that causes or observes high interference from a second station (e.g., a UE or another base station) may be identified. In one design, interference caused by a first reference signal from a first station may be reduced by canceling the interference at a second station (e.g., a UE). In another design, interference with the first reference signal may be reduced by avoiding collision with the first reference signal by using different resources for the second station (e.g., another base station) to transmit the second reference signal.

In yet another aspect, the relay station may be operated to achieve good performance. The relay station may determine subframes in which the relay station listens to the macro base station and may transmit in a multicast/broadcast single frequency network (MBSFN) mode in these subframes. The relay station may also determine subframes in which the relay station transmits to the UE and may transmit in a normal mode in these subframes. A relay station in MBSFN mode may transmit reference signals in fewer symbol periods in a subframe than in normal mode. The relay station may also transmit fewer Time Division Multiplexed (TDM) control symbols in a subframe in the MBSFN mode than in the normal mode.

In yet another aspect, the first station may transmit more TDM control symbols than the dominant interferer to improve reception of the TDM control symbols by the UE. A first station (e.g., a pico base station, a relay station, etc.) may identify a strong interfering station for the first station. The first station may determine a first number of TDM control symbols being transmitted in a subframe by a strong interfering station. The first station may transmit a second (e.g., maximum) number of TDM control symbols in the subframe, where the second number of TDM control symbols is greater than the first number of TDM control symbols.

Various aspects and features of the disclosure are described in further detail below.

Drawings

Fig. 1 illustrates a wireless communication network.

Fig. 2 shows an exemplary frame structure.

Fig. 3 shows two exemplary conventional subframe formats.

Fig. 4 shows two exemplary MBSFN subframe formats.

Fig. 5 shows an exemplary transmission timeline for different base stations.

Fig. 6 and 7 illustrate a process and apparatus, respectively, for reducing interference in a wireless communication network.

Fig. 8 and 9 illustrate a procedure and an apparatus for operating a relay station, respectively.

Fig. 10 and 11 illustrate a procedure and an apparatus for transmitting control information in a wireless communication network, respectively.

Fig. 12 shows a block diagram of a base station or relay station and a UE.

Detailed Description

The techniques described herein may be used for various wireless communication networks, such as: CDMA, TDMA, FDMA, OFDMA, SC-FDMA and other networks. The terms "network" and "system" are often used interchangeably. A CDMA network may implement a radio technology such as Universal Terrestrial Radio Access (UTRA), CDMA2000, etc. UTRA includes wideband CDMA (W-CDMA) and other variants of CDMA. cdma2000 covers IS-2000, IS-95 and IS-856 standards. TDMA networks may implement wireless technologies such as global system for mobile communications (GSM). OFDMA systems may be used such as evolved UTRA (E-UTRA), Ultra Mobile Broadband (UMB), IEEE802.11 (Wi-Fi), IEEE802.16 (WiMAX), IEEE802.20, Flash-OFDMAnd so on. UTRA and E-UTRA are part of the Universal Mobile Telecommunications System (UMTS). 3GPP Long Term Evolution (LTE) and LTE-advanced (LTE-A) are new versions of UMTS that use E-UTRA. UTRA, E-UTRA, UMTS, LTE-A and GSM are described in documents from an organization named "third Generation partnership project" (3 GPP)The above-mentioned processes are described. cdma2000 and UMB are described in documents from an organization named "third generation partnership project 2" (3 GPP 2). The techniques described herein may be used for the wireless networks and wireless technologies mentioned above as well as other wireless networks and wireless technologies. For clarity, certain aspects of the technology are described below with respect to LTE, and LTE terminology is used in much of the description below.

Fig. 1 shows a wireless communication network 100, which may be an LTE network or some other wireless network. Wireless network 100 may include several evolved node bs (enbs) 110, 112, 114, and 116, as well as other network entities. An eNB may be a station that communicates with UEs and may also be referred to as a base station, a node B, an access point, etc. Each eNB may provide communication coverage for a particular geographic area. In 3GPP, the term "cell" can refer to a coverage area of an eNB and/or eNB subsystem serving the coverage area, depending on the context.

An eNB may provide communication coverage for a macro cell, pico cell, femto cell, and/or other types of cells. A macro cell may cover a relatively large geographic area (e.g., several kilometers in radius) and may allow unrestricted access by UEs with service subscriptions. A pico cell may cover a relatively small geographic area and may allow unrestricted access by UEs with service subscriptions. A femto cell may cover a relatively small geographic area (e.g., a residence) and may allow unrestricted access by UEs having an association with the femto cell (e.g., UEs in a Closed Subscriber Group (CSG), UEs of users in the residence, etc.). The eNB for the macro cell may be referred to as a macro eNB. An eNB for a pico cell may be referred to as a pico eNB. An eNB for a femto cell may be referred to as a femto eNB or a home eNB. In the example shown in fig. 1, eNB110 may be a macro eNB for macro cell 102, eNB112 may be a pico eNB for pico cell 104, and enbs 114 and 116 may be femto enbs for femtocells 106 and 108, respectively. An eNB may support one or more (e.g., 3) cells.

Wireless network 100 may also include relay stations. A relay station is a station that receives a transmission of data and/or other information from an upstream station (e.g., an eNB or UE) and sends a transmission of data and/or other information to a downstream station (e.g., a UE or eNB). A relay station may also be a station that relays transmissions of other UEs. In the example shown in fig. 1, relay 118 may communicate with macro eNB110 and UE128 to facilitate communication between eNB110 and UE 128. A relay station may also be referred to as a relay eNB, relay, etc.

Wireless network 100 may be a heterogeneous network including different types of enbs (e.g., macro enbs, pico enbs, femto enbs, relays, etc.). These different types of enbs may have different transmit power levels, different coverage areas, and different impact on interference in wireless network 100. For example, macro enbs may have a high transmit power level (e.g., 20 watts), while pico enbs, femto enbs, and relays may have a lower transmit power level (e.g., 1 watt).

Wireless network 100 may support synchronous operation. For synchronous operation, the enbs may have similar frame timing, and transmissions from different enbs may be approximately aligned in time. The synchronization operation may support certain transmission features as described below.

Network controller 130 may be coupled to a set of enbs and may provide coordination and control for these enbs. The network controller 130 may communicate with the enbs via a backhaul (backhaul). The enbs may also communicate with each other, e.g., directly or indirectly via a wireless or wired backhaul.

UEs 122, 124, and 128 may be dispersed throughout wireless network 100, and each UE may be fixed or mobile. A UE may also be referred to as a terminal, mobile station, subscriber unit, station, etc. A UE may be a cellular telephone, a Personal Digital Assistant (PDA), a wireless modem, a wireless communication device, a handheld device, a laptop computer, a cordless telephone, a Wireless Local Loop (WLL) station, or the like. The UE can communicate with macro enbs, pico enbs, femto enbs, relays, and the like. In fig. 1, a solid line with double arrows indicates the desired transmission between the UE and the serving eNB, which is the eNB designated to serve the UE on the downlink and/or uplink. The dashed line with double arrows indicates interfering transmissions between the UE and the eNB.

LTE uses Orthogonal Frequency Division Multiplexing (OFDM) on the downlink and single carrier frequency division multiplexing (SC-FDM) on the uplink. OFDM and SC-FDM partition the system bandwidth into multiple (K) orthogonal subcarriers, which are also commonly referred to as tones (tones), bins (bins), and so on. Each subcarrier may be modulated with data. In general, modulation symbols are sent in the frequency domain using OFDM and in the time domain using SC-FDM. The spacing between adjacent subcarriers may be fixed, and the total number of subcarriers (K) may depend on the system bandwidth. For example, K may be 128, 256, 512, 1024 or 2048 for system bandwidth of 1.25, 2.5, 5, 10 or 20 megahertz (MHz), respectively. The system bandwidth may also be divided into sub-bands. For example, a sub-band may cover 1.08MHz, and there may be 1, 2, 4, 8, or 16 sub-bands for a system bandwidth of 1.25, 2.5, 5, 10, or 20MHz, respectively.

Fig. 2 shows a frame structure used in LTE. The transmission timeline for the downlink may be partitioned into units of radio frames. Each radio frame may have a predetermined duration (e.g., 10 milliseconds (ms)) and may be divided into 10 subframes with indices of 0-9. Each subframe may include two slots. Each radio frame may thus include 20 slots with indices of 0-19. Each slot may include L symbol periods, e.g., L =7 symbol periods for a normal cyclic prefix (as shown in fig. 2) or L =6 symbol periods for an extended cyclic prefix. Indexes of 0-2L-1 can be allocated to 2L symbol periods in each subframe.

The available time-frequency resources may be divided into resource blocks. Each resource block may cover N subcarriers (e.g., 12 subcarriers) in one slot and may include several resource units. Each resource element may cover one subcarrier in one symbol period and may be used to transmit one modulation symbol, which may be real-valued or complex-valued. The eNB transmits one OFDM symbol in each symbol period. Each OFDM symbol may include a modulation symbol for transmission on a subcarrier and a zero symbol with a signal value of zero on the remaining subcarriers.

In LTE, an eNB may transmit Primary Synchronization Signals (PSS) and Secondary Synchronization Signals (SSS) at the center 1.08MHz of the system bandwidth for each cell in the eNB. As shown in fig. 2, the primary and secondary synchronization signals may be transmitted in symbol periods 6 and 5, respectively, in each of subframes 0 and 5 of each radio frame with a normal cyclic prefix. The synchronization signal may be used by the UE for cell search and acquisition. The eNB may send a Physical Broadcast Channel (PBCH) in symbol periods 0-3 of slot 1 of subframe 0 in a particular radio frame. The PBCH may carry specific system information.

As shown in fig. 2, the eNB may transmit a Physical Control Format Indicator Channel (PCFICH) in the first symbol period of each subframe. The PCFICH may convey the number of symbol periods (M) used for the control channel in a subframe, where M may be equal to 1, 2, or 3, and may vary from subframe to subframe. For narrower system bandwidths (e.g., having less than 10 resource blocks), M may also be equal to 4. The eNB may send a Physical HARQ Indicator Channel (PHICH) and a Physical Downlink Control Channel (PDCCH) in the first M symbol periods (not shown in fig. 2) of each subframe. The PHICH may carry information for supporting hybrid automatic repeat request (HARQ). The PDCCH may carry information on resource allocation for the UE and control information for a downlink channel. The first M OFDM symbols of a subframe may also be referred to as TDM control symbols. The TDM control symbols may be OFDM symbols carrying control information. The eNB may transmit a Physical Downlink Shared Channel (PDSCH) in the remaining symbol periods of each subframe. The PDSCH may carry data for a UE scheduled for data transmission on the downlink. Various signals and Channels in LTE are described in 3GPP TS36.211, publicly available, entitled "Evolved Universal radio Access (E-UTRA); Physical Channels and Modulation".

LTE supports the transmission of unicast information to a specific UE. LTE also supports the transmission of broadcast information to all UEs and multicast information to a group of UEs. Multicast/broadcast transmissions may also be referred to as MBSFN transmissions. The subframe for transmitting unicast information may be referred to as a regular subframe. Subframes used to transmit multicast and/or broadcast information may be referred to as MBSFN subframes.

Fig. 3 illustrates two exemplary conventional subframe formats 310 and 320 that may be used to send unicast information on the downlink to a particular UE. For a common cyclic prefix in LTE, a left time slot comprises 7 symbol periods 0-6, and a right time slot comprises 7 symbol periods 7-13.

Subframe format 310 may be used by an eNB equipped with two antennas. The reference signal for a particular cell may be transmitted in symbol periods 0, 4, 7, and 11 and may be used by the UE for channel estimation. The reference signal is a signal known a priori by the transmitter and the receiver and may also be referred to as a pilot. The reference signal for a particular cell is a cell-specific reference signal, e.g., generated using one or more symbol sequences determined based on a cell Identification (ID). For simplicity, the reference signal for a particular cell may be referred to simply as the reference signal. In fig. 3, for a given resource unit with a tag Ri, a reference symbol may be transmitted on that resource unit from antenna i, and no symbols may be transmitted on that resource unit from other antennas. Subframe format 320 may be used by an eNB equipped with four antennas. The reference signals may be transmitted in symbol periods 0, 1, 4, 7, 8, and 11.

In the example shown in fig. 3, 3 TDM control symbols are transmitted in a regular subframe of M = 3. The PCFICH may be transmitted in symbol period 0, and the PDCCH and PHICH may be transmitted in symbol periods 0-2. The PDSCH may be transmitted in the remaining symbol periods 3-13 of the subframe.

Fig. 4 shows two exemplary MBSFN subframe formats 410 and 420, which may be used to send broadcast/multicast information to UEs on the downlink. Subframe format 410 may be used by an eNB equipped with two antennas. The reference signal may be transmitted in symbol period 0. For the example shown in fig. 4, M =1, and one TDM control symbol may be transmitted in the MBSFN subframe. Subframe format 420 may be used by an eNB equipped with four antennas. The reference signal may be transmitted in symbol periods 0 and 1. For the example shown in fig. 4, M =2, and two TDM control symbols may be transmitted in an MBSFN subframe.

In general, the PCFICH may be transmitted in symbol period 0 of the MBSFN subframe, and the PDCCH and PHICH may be transmitted in symbol periods 0 to M-1. The broadcast/multicast information may be transmitted in symbol periods M-13 of the MBSFN subframe. Alternatively, no transmission may be sent in symbol periods M-13.

Fig. 3 and 4 show some subframe formats that may be used for the downlink. Other subframe formats may also be used, e.g., for more than 2 antennas at the eNB.

An eNB or relay may operate in a normal mode, an MBSFN mode, and/or other modes of operation. The eNB or relay may switch modes on a subframe-by-subframe basis or at a lower rate. In the normal mode, the eNB or relay may transmit using a normal subframe format, e.g., as shown in fig. 3. The regular patterns may be associated with particular characteristics, such as: a configurable number of TDM control symbols, reference signals are transmitted from each antenna in two or more symbol periods of a subframe, and so on. In MBSFN mode, the eNB or relay may transmit using MBSFN subframe format, e.g., as shown in fig. 4. MBSFN modes may be associated with specific characteristics, such as: a minimum number of TDM control symbols, reference signals transmitted from each antenna in one symbol period of a subframe, and so on. For example, as shown in fig. 3 and 4, the eNB or the relay may transmit the control information and the reference signal in fewer symbol periods in the MBSFN mode than in the conventional mode. The eNB or relay may also transmit fewer TDM control symbols in MBSFN mode than in normal mode. As described below, therefore, in certain operating scenarios, MBSFN mode may be desirable.

The UE may be in coverage of multiple enbs. One of these enbs may be selected to serve the UE. The serving eNB may be selected based on various criteria, such as: received power, path loss, signal-to-noise ratio (SNR), etc.

The UE may operate in a dominant interference scenario, where the UE may observe high interference from one or more interfering enbs. A dominant interference situation may arise from a restricted association. For example, in fig. 1, UE124 may be close to femto eNB114 and may have high received power for eNB 114. However, UE124 may not be able to access femto eNB114 due to restricted association and thus may connect to macro eNB110 (as shown in fig. 1) or femto eNB116 (not shown in fig. 1) with lower received power as well. UE124 may then observe high interference from femto eNB114 on the downlink and may also cause high interference to eNB114 on the uplink.

A dominant interference situation may also arise due to range extension, in which case the UE connects to an eNB with lower path loss and possibly lower SNR among all enbs detected by the UE. For example, in fig. 1, UE122 may detect macro eNB110 and pico eNB112 and have a lower received power for pico eNB112 than macro eNB 110. However, if UE122 has a lower pathloss for pico eNB112 than macro eNB110, UE122 may desire to connect to pico eNB 112. This may result in less interference to the wireless network for a given data rate of the UE 122.

In an aspect, communication in a dominant interference scenario may be supported by reserving subframes for weaker enbs observing high interference from strong interfering enbs. Then, in the presence of a strong interfering eNB, the UE may communicate with the weaker eNB in the reserved subframes. An eNB may be classified as a "weak" eNB or a "strong" eNB based on the received power of the eNB at the UE (rather than based on the transmit power level of the eNB). Furthermore, different enbs may transmit their synchronization signals so that interference from dominant interferers may be avoided.

In one design, the enbs and relays may be arranged in different groups. Each group may include enbs and/or relays that are not significantly interferers to each other. For example, one group may include macro enbs, another group may include pico enbs and relays, and one or more groups may include femto enbs. The relay station may have a similar transmit power level as the pico eNB and thus may be grouped with the pico eNB. If multiple femto enbs are dominant interferers to each other, they may be grouped into multiple groups. By having each group include enbs that are not significantly interferers to each other, failure scenarios may be avoided and the benefits of range extension achieved.

In one design, different eNB groups may be associated with different subframe offsets. The timing of the enbs in the different groups may be offset from each other by an integer number of subframes. For example, when a macro eNB in a first group transmits subframe 0, a pico eNB in a second group may transmit subframe 1, a femto eNB in a third group may transmit subframe 2, and so on. Using subframe offsets may allow enbs and relays in different groups to transmit their synchronization signals so that UEs may detect these signals.

Fig. 5 shows an exemplary transmission timeline for 4 sets of enbs and relays. The first group may include macro eNB110, which has subframe 0 at time T₀And starting. The second group may include pico eNB112 and relay 118, which have subframe 0 at time T₀The next subframe begins. The third group may include femto eNB114 having subframe 0 at time T₀The next two subframes begin. The fourth group may include femto eNB116 having subframe 0 at time T₀The next three subframes begin. In general, any number of groups may be formed, and each group may include any number of enbs and/or relays.

In one design, a strong interfering eNB may reserve or clear some subframes for a weaker eNB to allow the weaker eNB to communicate with its UEs. The interfering eNB may transmit in the reserved subframes as few as possible to reduce interference to the weaker eNB. In one design, the interfering eNB may configure the reserved subframes as MBSFN subframes. For example, as shown in fig. 4, the interfering eNB may transmit the PCFICH of M =1 and the reference signal only in the first symbol period of each reserved subframe, and may not transmit in the remaining symbol periods of the subframe. In another design, the interfering eNB may operate in 1-Tx mode with one transmit antenna or 2-Tx mode with two transmit antennas. For example, as shown in fig. 3, the interfering eNB may transmit the PCFICH and the reference signal of M =1 in each reserved subframe. In yet another design, the interfering eNB may transmit reference signals in reserved subframes, but may avoid transmitting PCFICH to reduce interference to the weaker eNB. For the foregoing design, the interfering eNB may avoid sending other control channels (e.g., PHICH and PDCCH) and data in each reserved subframe. In yet another design, the interfering eNB may not transmit in each reserved subframe to avoid any interference to the weaker eNB. The interfering eNB may also transmit in the reserved subframes in other manners. The interfering eNB may transmit the minimum number of modulation symbols required by the LTE standard in each reserved subframe.

In the example shown in fig. 5, macro eNB110 reserves subframes 1 and 6 for pico eNB112 and transmits one TDM control symbol of M =1 for PCFICH in each reserved subframe. Femto eNB114 (femto eNB a) reserves subframes 3 and 8 for macro eNB110, reserves subframes 4 and 9 for pico eNB112, and reserves subframe 1 for femto eNB116 (femto eNB B). Femto eNB114 transmits one TDM control symbol of M =1 for PCFICH in each reserved subframe. Femto eNB116 reserves subframes 2 and 7 for macro eNB110, reserves subframes 3 and 8 for pico eNB112, and reserves subframe 9 for femto eNB 114. Femto eNB116 transmits one TDM control symbol of M =1 for PCFICH in each reserved subframe. As shown in fig. 5, subframes reserved by femto enbs 114 and 116 for macro eNB110 are time aligned and allow the macro eNB to transmit in its subframes 0 and 5 with little interference from the femto enbs. The subframes reserved by macro eNB110 and femto enbs 114 and 116 for pico eNB112 are time aligned and allow the pico eNB to transmit in its subframes 0 and 5 with little interference from the macro and femto enbs.

Referring back to fig. 2, each eNB may transmit its synchronization signal in subframes 0 and 5, and may also transmit PBCH in subframe 0. The UE may search for synchronization signals when detecting enbs and may receive a PBCH from each detected eNB to communicate with the eNB. To allow the UE to detect the weaker eNB, the strong interfering eNB may reserve or clear subframes used by the weaker eNB to transmit the synchronization signals and PBCH. The clear-up operation may be performed for all subframes or only for some subframes used by the weaker eNB to transmit the synchronization signals and PBCH. The clearing operation should be performed such that the UE can detect the weaker eNB in a reasonable time.

Referring to the example shown in fig. 5, subframes 0 and 5 of macro eNB110 are cleared by femto enbs 114 and 116 to avoid interference with the synchronization signals and PBCH from the macro eNB. Subframes 0 and 5 of pico eNB112 are cleared by macro eNB110 and femto enbs 114 and 116 to avoid interference with the synchronization signals and PBCH from the pico eNB. Subframe 0 of femto eNB114 is cleared by femto eNB116, and subframe 0 of femto eNB116 is cleared by femto eNB 114.

In one design, the eNB may communicate via a backhaul to negotiate reservation/clearance of subframes. In another design, a UE desiring to communicate with a weaker eNB may request the interfering eNB to reserve some subframes for the weaker eNB. In yet another design, a designated network entity may decide to reserve subframes for the eNB, e.g., based on data requests sent by the UE to a different eNB and/or reports from the eNB. For all designs, subframes may be reserved based on various criteria, such as: the loading of the enbs, the number of neighboring enbs, the number of UEs within each eNB coverage, pilot measurement reports from the UEs, etc. For example, a macro eNB may reserve subframes to allow multiple pico enbs and/or femto enbs to communicate with their UEs, which may provide cell division gain.

Each eNB may transmit its reference signal on a set of subcarriers determined based on its cell ID. In one design, the cell ID spaces of a strong interfering eNB (e.g., a macro eNB) and a weaker eNB (e.g., a pico eNB) may be defined such that the reference signals of these enbs are transmitted on different subcarriers without collision. Some enbs (such as femto enbs and relays) may be self-configuring. These enbs may select their cell IDs such that their reference signals do not collide with the reference signals of strong neighboring enbs.

The UE may communicate with the weaker eNB in the reserved subframes and may observe high interference caused by the PCFICH, reference signals, and other transmissions that may be from a strong interfering eNB. In one design, the UE may discard each TDM control symbol with high interference from the interfering eNB and may process the remaining TDM control symbols. In another design, the UE may discard symbols received on subcarriers with high interference and may process the remaining received symbols. The UE may also process the received symbols and TDM control symbols in other manners.

The UE may obtain a channel estimate for the weaker eNB based on the reference signal transmitted by the weaker eNB. The reference signal of the weaker eNB may be transmitted on different subcarriers and may not overlap with the reference signal of the strong interfering eNB. In this case, the UE may obtain a channel estimate for the weaker eNB based on the reference signals from the eNB. The UE may employ interference cancellation for channel estimation if the reference signal of the weaker eNB collides with the reference signal of the interfering eNB. The UE may estimate interference caused by the reference signal from the interfering eNB based on the known reference symbols transmitted by the interfering eNB and the known subcarriers used to transmit the reference signal. The UE may subtract the estimated interference from the received signal at the UE to cancel the interference generated by the interfering eNB, and may then obtain a channel estimate for the weaker eNB based on the interference-canceled signal. The UE may also perform interference cancellation for control channels from interfering enbs (e.g., PCFICH) colliding with reference signals from weaker enbs. The UE may decode each such control channel from the interfering eNB, estimate the interference caused by each decoded control channel, subtract the estimated interference from the received signal, and obtain a channel estimate for the weaker eNB after subtracting the estimated interference. In general, the UE may perform interference cancellation on any decodable transmission from the interfering eNB to improve channel estimation performance. The UE may decode control channels (such as PBCH, PHICH, and PDCCH) and data channels (e.g., PDSCH) from the weaker eNB based on the channel estimates.

The weaker eNB may send control information and data to the UE in subframes reserved by the interfering eNB. For example, as shown in fig. 4, the interfering eNB may transmit only the first TDM control symbol in a subframe. In this case, the UE may observe high interference only on the first TDM control symbol and may observe no interference from the interfering eNB on the remaining TDM control symbols of the subframe.

The weaker eNB may send control information in a manner that facilitates reliable reception by the UE in the presence of the interfering eNB. In one design, a weaker eNB may send 3 TDM control symbols in a reserved subframe by setting M for PCFICH to M = 3. In another design, the weaker eNB may send a predetermined number of TDM control symbols in the reserved subframe. For both designs, the UE may know the number of TDM control symbols being sent by the weaker eNB. The UE will not need to decode the PCFICH sent by the weaker eNB in the first TDM control symbol, which will observe high interference from the interfering eNB.

The weaker eNB may send 3 PHICH transmissions in 3 TDM control symbols, one PHICH transmission in each TDM control symbol. The UE may decode the PHICH based on the two PHICH transmissions sent in the second and third TDM control symbols, which will not observe interference from the interfering eNB. The UE may also decode the PHICH based on a portion of the PHICH transmission sent on subcarriers not used by the interfering eNB in the first TDM control symbol.

The weaker eNB may also send the PDCCH in 3 TDM control symbols. The weaker eNB may send the PDCCH to the UE so that adverse effects due to interference from the interfering eNB may be reduced. For example, a weaker eNB may send PDCCH in TDM control symbols where there is no interference from the interfering eNB, PCFICH on subcarriers not used by the interfering eNB, and so on.

The weaker eNB may be aware of the interference caused by the interfering eNB and may send control information to reduce the adverse effects of the interference. In one design, a weaker eNB may adjust the transmit power of PHICH, PDCCH, and/or other control channels to achieve the desired performance. The power adjustment may account for loss of part of the control information due to high interference induced corruption (pure) from the interfering eNB.

Knowing that some of the first TDM control symbols may be lost or corrupted (corrupted) by high interference from the interfering eNB, the UE may decode the control channel (e.g., PHICH and PDCCH) from the weaker eNB. In one design, the UE may discard received symbols with high interference from the interfering eNB and may decode the remaining received symbols. During decoding, the discarded symbols may be replaced with erasures (erasures) and given neutral weights. In another design, the UE may perform decoding on the control channel using interference cancellation. The UE may estimate interference in the TDM control symbols due to the interfering eNB, remove the estimated interference from the received symbols, and decode the control channel using the interference-canceled received symbols.

The UE may decode the data channel (e.g., PDSCH) from the weaker eNB, possibly with knowledge that some modulation symbols may be corrupted by high interference from the interfering eNB. In one design, the UE may discard received symbols with high interference from the interfering eNB and may decode the remaining received symbols to recover data transmitted by the weaker eNB. In another design, the UE may decode the data channel using interference cancellation.

The UE may also decode control and data channels from the weaker eNB based on other techniques to improve performance in the presence of high interference from the interfering eNB. For example, the UE may detect and/or decode by considering high interference to particular received symbols.

The techniques described herein may be used to support the operation of a relay station, such as relay station 118. In the downlink direction, relay 118 may receive data and control information from macro eNB110 and may retransmit the data and control information to UE 128. In the uplink direction, relay 118 may receive data and control information from UE128 and may retransmit the data and control information to macro eNB 110. Relay 118 may appear as a UE to macro eNB110 and as an eNB to UE 128. The link between macro eNB110 and relay 118 may be referred to as a backhaul link, and the link between relay 118 and UE128 may be referred to as a relay link.

The relay 118 is generally unable to transmit and receive simultaneously on the same frequency channel or bandwidth. In the downlink direction, relay 118 may designate some subframes as backhaul downlink subframes in which relay 118 will listen to macro eNB110 and some subframes as relay downlink subframes in which relay 118 will transmit to UEs. In the uplink direction, relay 118 may designate some subframes as relay uplink subframes in which relay 118 will listen for UEs and some subframes as backhaul uplink subframes in which relay 118 will transmit to macro eNB 110. In the example shown in fig. 5, in the downlink direction, relay 118 may transmit to its UEs in subframes 0 and 5, which subframes 0 and 5 may be cleared by macro eNB110, and may listen to macro eNB110 in subframes 1, 2, 3, 4, and 9. The subframes in the uplink direction are not shown in fig. 5.

In a range expansion scenario, macro eNB110 may be a strong interfering eNB for UEs communicating with relay 118 and new UEs that may be served by relay 118. For relay downlink subframes in which relay 118 transmits to UEs, the timing of relay 118 may be shifted from the timing of macro eNB110 by an integer number of subframes (e.g., by one subframe in fig. 5). Macro eNB110 may clear some subframes (e.g., subframes 1 and 6 in fig. 5) for relay 118. Relay station 118 may transmit its synchronization signals and PBCH in relay downlink subframes that coincide with subframes reserved by macro eNB 110. The UE may detect the synchronization signal from relay 118. The UE may know the symbols corrupted (by the macro eNB 110) and may utilize this information to decode the control channel from the relay 118 as described above.

For backhaul downlink subframes, relay 118 may only desire to listen to macro eNB110 and not to send anything to its UEs in these subframes. However, since relay 118 is an eNB for its UEs, relay 118 may be expected to transmit certain signals to its UEs in the backhaul downlink subframes. In one design, relay 118 may operate in MBSFN mode for backhaul downlink subframes. In MBSFN mode, relay 118 may transmit only in the first symbol period of the backhaul downlink subframe and may listen to macro eNB110 in the remaining symbol periods of the subframe. In the example shown in fig. 5, relay 118 transmits only in the first symbol periods of subframes 1, 2, 3, 4, and 9, in which relay 118 listens to macro eNB 110.

In one design, macro eNB110 may set PCFICH to a predetermined value (e.g., M = 3) in subframes in which macro eNB110 transmits to relay 118 (e.g., subframes 0 and 5 of macro eNB110 in fig. 5). Relay station 118 may know the predetermined value of PCFICH from macro eNB110 and may skip the operation of decoding PCFICH. Relay station 118 may transmit the PCFICH to its UEs in the first symbol period and may skip decoding of the PCFICH transmitted by macro eNB110 in the same symbol period. Macro eNB110 may send three PHICH transmissions, one in each TDM control symbol. Relay station 118 may decode the PHICH from macro eNB110 based on the PHICH transmission in the second and third TDM control symbols. Macro eNB110 may also transmit PDCCH such that all or most of the PDCCH transmissions to relay station 118 are transmitted in the second and third TDM control symbols. Relay station 118 may decode the PDCCH based on a portion of the PDCCH transmission received in the second and third TDM control symbols. The macro eNB110 may boost transmit power (e.g., PHICH and/or PDCCH) for the control channel of the relay 118 to improve reception of the control channel by the relay 118 based on the portions sent in the second and third TDM control symbols. Macro eNB110 may also skip transmitting control information to relay 118 in the first TDM control symbol. Macro eNB110 may send data to relay 118 in symbol periods 3-13. Relay 118 may recover the data in a conventional manner.

Relay 118 may not be able to receive reference signals from macro eNB110 in symbol period 0. Relay 118 may obtain a channel estimate for macro eNB110 based on reference signals received by relay 118 from macro eNB 110. In scheduling relay 118, macro eNB110 may utilize information regarding which subframes relay 118 is likely to have better channel estimates for. For example, relay 118 may listen to macro eNB110 in two consecutive subframes. In this case, the channel estimate for the first subframe may be worse than the channel estimate for the second subframe because the channel estimate for the first subframe may be extrapolated, while the channel estimate for the second subframe may be interpolated and may have more reference symbols in its vicinity. Macro eNB110 may then transmit the data to relay 118 in a second subframe, if possible.

In subframes 0 and 5, which carry synchronization signals, relay 118 may not be able to operate in MBSFN mode. In one design, even though subframes 0 and 5 of relay 118 are designated as backhaul downlink subframes, relay 118 may skip listening to macro eNB110 in these subframes and may instead transmit to its UEs. In another design, even though subframes 0 and 5 are designated as relay downlink subframes, relay 118 may skip transmitting to its UEs in subframes 0 and 5 and may instead listen to macro eNB 110. Relay 118 may also perform a combination of the two and may transmit to its UEs in some of subframes 0 and 5 and may listen to macro eNB110 in other of subframes 0 and 5.

In the uplink direction, relay 118 may operate in a UE-like manner in a backhaul uplink subframe in which relay 118 transmits data and control information to macro eNB 110. Relay 118 may operate in a manner similar to an eNB in a relay uplink subframe in which relay 118 listens for data and control information from UE 128. A scheduler at macro eNB110 and/or a scheduler at relay 118 may ensure that the uplink of relay 118 and the uplink of UEs served by relay 118 are properly scheduled.

Fig. 6 shows a design of a process 600 for reducing interference in a wireless communication network. Process 600 may be performed by a UE, a base station/eNB, a relay, or some other entity. A first station in a heterogeneous network that causes high interference to or observes high interference from a second station may be identified (block 612). The heterogeneous network may include base stations of at least two different transmit power levels and/or different association types. The interference to the first reference signal may be reduced by canceling the interference caused by the first reference signal from the first station at the second station or by selecting a different resource by the second station to transmit the second reference signal to avoid collision with the first reference signal (block 614).

In one design, the first station may be a base station or a relay station and the second station may be a UE. For block 614, interference due to the first reference signal may be cancelled at the UE. In one design, interference due to the first reference signal may be estimated and subtracted from a received signal at the UE to obtain an interference canceled signal. The interference canceled signal may then be processed to obtain a channel estimate for a base station or relay station communicating with the UE. The interference-canceled signal may also be processed to obtain data and/or control information sent by the base station or the relay station to the UE.

In another design, the first and second stations may include (i) a macro base station and a pico base station, respectively, (ii) two femto base stations, or (iii) some other combination of macro, pico, and femto base stations and relay stations. For block 614, a first resource used by the first station to transmit a first reference signal may be determined. A cell ID associated with a second resource used to transmit a second reference signal may be selected such that the second resource is different from the first resource. The first resource may include a first set of subcarriers and the second resource may include a second set of subcarriers, which may be different from the first set of subcarriers. The second reference signal may be transmitted by the second station on the second resource and may then avoid collision with the first reference signal. A primary synchronization signal and a secondary synchronization signal may be generated based on the selected cell ID and transmitted by the second station in designated subframes (e.g., subframes 0 and 5).

Fig. 7 shows a design of an apparatus 700 for reducing interference. The apparatus 700 comprises: a module 712 for identifying a first station in the heterogeneous network that causes high interference to or observes high interference from a second station; and a module 714 for reducing interference to the first reference signal by canceling the interference at the second station due to the first reference signal from the first station, or by selecting a different resource by the second station to transmit the second reference signal to avoid collision with the first reference signal.

Fig. 8 shows a design of a process 800 for operating a relay in a wireless communication network. The relay station may determine subframes in which the relay station listens to the macro base station (block 812). The relay station may transmit in MBSFN mode in those subframes in which the relay station listens to the macro base station (block 814). The relay station may also determine a subframe in which the relay station transmits to the UE (block 816). The relay may transmit in the normal mode in the subframes in which the relay transmits to the UE (block 818).

The relay station may transmit the reference signal in fewer symbol periods in a given subframe in MBSFN mode than in regular mode. In one design, for example, as shown in fig. 4, the relay station may transmit reference signals from each antenna in one symbol period of each subframe in which the relay station listens to the macro base station in MBSFN mode. For example, as shown in fig. 3, the relay station may transmit reference signals from each antenna in multiple symbol periods of each subframe in which the relay station transmits to the UE in the normal mode. In one design, the relay may transmit the reference signal only in the first symbol period or the first two symbol periods of each subframe in which the relay listens to the macro base station in MBSFN mode. The relay station may transmit the reference signal in more symbol periods of each subframe in which the relay station transmits to the UE in the normal mode. The relay station may also transmit reference signals in the MBSFN mode and the normal mode in other manners.

In one design of block 814, the relay station may send a single TDM control symbol and may not send data in every subframe in which the relay station listens to the macro base station. The relay station may receive a maximum number (e.g., 3) of TDM control symbols from the macro base station in each subframe in which the macro base station transmits to the relay station. The relay station may decode at least one control channel (e.g., PHICH and PDCCH) from the macro base station based on the second and third TDM control symbols.

Fig. 9 shows a design of an apparatus 900 for operating a relay station. The apparatus 900 comprises: a module for determining subframes in which the relay station is listening to the macro base station 912; means 914 for transmitting by the relay station in the MBSFN mode in subframes in which the relay station is listening to the macro base station; a module 916 for determining a subframe in which the relay station is transmitting to the UE; and a module 918 for transmitting by the relay station in the normal mode in a subframe in which the relay station is transmitting to the UE.

Fig. 10 shows a design of a process 1000 for transmitting control information in a wireless communication network. Process 1000 may be performed by a first station, which may be a base station/eNB, a relay station, or some other entity. The first station may identify a strong interfering station for the first station (block 1012). The first station may determine a first number of TDM control symbols being transmitted in a subframe by a strong interfering station (block 1014). The first station may transmit a second number of TDM control symbols in the subframe, where the second number of TDM control symbols is greater than the first number of TDM control symbols (block 1016). The second number of TDM control symbols may be a maximum number of TDM control symbols allowed by the first station and may include 3 TDM control symbols.

The first station and the strong interfering station may have different transmit power levels. In one design, the first station may be a pico base station and the interfering station may be a macro base station. In another design, the first station may be a macro base station and the interfering station may be a femto base station, or vice versa. In yet another design, the first station may be a femto base station and the interfering station may be another femto base station. The first station and the strong interfering station may also be some other combination of macro base station, pico base station, femto base station, relay station, etc.

In one design, if a strong interfering station is not present, the first station may transmit a control channel (e.g., PCFICH) indicating the second number of TDM control symbols transmitted in the subframe. The first station may not transmit the control channel if there is a strong interfering station. In this case, a predetermined value may be assumed for the second number of TDM control symbols.

In one design of block 1016, the first station may send a control channel (e.g., PHICH or PDCCH) in a first TDM control symbol at a first transmit power level. The first station may transmit the control channel in at least one additional TDM control symbol at a second transmit power level, which may be higher than the first transmit power level. In another design of block 1016, the first station may send a control channel (e.g., PHICH or PDCCH) in a second number of TDM control symbols on a selected resource element selected to avoid or reduce collision with a reference signal from a strong interfering station. The first station may also transmit the second number of TDM control symbols in other manners to reduce the impact of interference from the strong interfering station.

Fig. 11 shows a design of an apparatus 1100 for transmitting control information. The apparatus 1100 comprises: a module 1112 for identifying a strong interfering station to the first station; means 1114 for determining a first number of TDM control symbols being transmitted by a strong interfering station in a subframe; and a module 1116 for transmitting a second number of TDM control symbols in the subframe by the first station, wherein the second number of TDM control symbols is greater than the first number of TDM control symbols.

The modules in fig. 7, 9 and 11 may include: a processor, an electronic device, a hardware device, an electronic component, a logic circuit, a memory, software code, firmware code, etc., or any combination thereof.

Fig. 12 shows a block diagram of a design of station 110x and UE 120. Station 110x may be a macro base station 110, a pico base station 112, a femto base station 114 or 116, or a relay 118 in fig. 1. UE120 may be any of the UEs in fig. 1. Station 110x may be equipped with T antennas 1234a through 1234T and UE120 may be equipped with R antennas 1252a through 1252R, where typically T ≧ 1 and R ≧ 1.

At station 110x, a transmit processor 1220 may receive data from a data source 1212 and control information from a controller/processor 1240. The control information may be for PBCH, PCFICH, PHICH, PDCCH, etc. The data may be for PDSCH, etc. Processor 1220 may process (e.g., encode and symbol map) the data and control information to obtain data symbols and control symbols, respectively. Processor 1220 may also generate reference symbols, e.g., reference signals for PSS, SSS, and for a particular cell. A Transmit (TX) multiple-input multiple-output (MIMO) processor 1230 may perform spatial processing (e.g., precoding) on the data symbols, the control symbols, and/or the reference symbols, if applicable, and may provide T output symbol streams to T Modulators (MODs) 1232 a-1232T. Each modulator 1232 may process a respective output symbol stream (e.g., for OFDM, etc.) to obtain an output sample stream. Each modulator 1232 may further process (e.g., convert to analog, amplify, filter, and upconvert) the output sample stream to obtain a downlink signal. T downlink signals from modulators 1232a through 1232T may be transmitted via T antennas 1234a through 1234T, respectively.

At UE120, antennas 1252a through 1252r may receive the downlink signals from station 110x and may provide received signals to demodulators (DEMODs) 1254a through 1254r, respectively. Each demodulator 1254 may condition (e.g., filter, amplify, downconvert, and digitize) a respective received signal to obtain input samples. Each demodulator 1254 may further process the input samples (e.g., for OFDM, etc.) to obtain received symbols. A MIMO detector 1256 may obtain received symbols from all R demodulators 1254a through 1254R, perform MIMO detection on the received symbols, if applicable, and provide detected symbols. A receive processor 1258 may process (e.g., demodulate, deinterleave, and decode) the detected symbols, provide decoded data for UE120 to a data sink 1260, and provide decoded control information to a controller/processor 1280.

On the uplink, at UE120, a transmit processor 1264 may receive and process data from a data source 1262 (e.g., for the PUSCH), and receive and process control information from a controller/processor 1280 (e.g., for the PUCCH). Processor 1264 may also generate reference symbols for a reference signal. The symbols from transmit processor 1264 may be precoded by a TX MIMO processor 1266, further processed by modulators 1254a through 1254r (e.g., for SC-FDM, etc.), and transmitted to station 110x, if applicable. At station 110x, the uplink signals from UE120 may be received by antennas 1234, processed by demodulators 1232, detected by a MIMO detector 1236 if applicable, and further processed by a receive processor 1238 to obtain the decoded data and control information sent by UE 120. Processor 1238 may provide the decoded data to a data sink 1239 and the decoded control information to controller/processor 1240.

Controllers/processors 1240 and 1280 may control operations at station 110x and UE120, respectively. Processor 1240 and/or other processors and modules located at station 110x may perform or control process 600 in fig. 6, process 800 in fig. 8, process 1000 in fig. 10, and/or other processes for the techniques described herein. Processor 1280 and/or other processors and modules located at UE120 may perform or control process 600 in fig. 6 and/or processes for other techniques described herein. Memories 1242 and 1282 may store data and program codes for station 110x and UE120, respectively. A scheduler 1244 schedules UEs for data transmission on the downlink and/or uplink.

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

Those of skill would further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the disclosure herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present disclosure.

The various illustrative logical blocks, modules, and circuits described in connection with the disclosure may be implemented or performed with a general purpose processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

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

In one or more exemplary designs, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Computer-readable media includes both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A storage media may be any available media that can be accessed by a general purpose or special purpose computer. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to carry or store desired program code means in the form of instructions or data structures and which can be accessed by a general-purpose or special-purpose computer, or a general-purpose or special-purpose processor. Also, any connection is properly termed a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, Digital Subscriber Line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. Disk or disc, as used herein, includes Compact Disc (CD), laser disc, optical disc, Digital Versatile Disc (DVD), floppy disk and blu-ray disc where disks usually reproduce data magnetically, while discs usually reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.

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

Claims (12)

1. A method for wireless communication, comprising:

identifying a strong interfering station that is interfering with the first station;

determining a first number of TDM control symbols being transmitted by the strong interfering station in a downlink subframe; and

transmitting, by the first station, a second number of TDM control symbols in the downlink subframe, the second number of TDM control symbols being greater than the first number of TDM control symbols.

2. The method of claim 1, wherein the strong interfering station and the first station are base stations with different transmit power levels.

3. The method of claim 1, wherein the second number of TDM control symbols comprises: a maximum number of TDM control symbols allowed for the first station.

4. The method of claim 1, wherein the second number of TDM control symbols comprises 3 TDM control symbols.

5. The method of claim 1, further comprising:

if the strong interfering station is not present, transmitting a control channel indicating the second number of TDM control symbols being transmitted in the downlink subframe by the first station, and

and if the strong interference station exists, not transmitting the control channel.

6. The method of claim 1, wherein transmitting the second number of TDM control symbols comprises:

transmitting the control channel in a first TDM control symbol at a first transmit power level, an

Transmitting the control channel in at least one further TDM control symbol at a second transmit power level, the second transmit power level being higher than the first transmit power level.

7. The method of claim 1, wherein transmitting the second number of TDM control symbols comprises: transmitting a control channel in the second number of TDM control symbols on a selected resource element, wherein the resource element is selected to reduce collisions with reference signals from the strong interfering stations.

8. The method of claim 1, wherein the first number of TDM control symbols is transmitted by the strong interfering station at a beginning of the downlink subframe and the second number of TDM control symbols is transmitted by the first station at the beginning of the downlink subframe.

9. An apparatus for wireless communication, comprising:

means for identifying a strong interfering station that is interfering with a first station;

means for determining a first number of TDM control symbols being transmitted by the strong interfering station in a downlink subframe; and

means for transmitting, by the first station, a second number of TDM control symbols in the downlink subframe, the second number of TDM control symbols being greater than the first number of TDM control symbols.

10. The apparatus of claim 9, further comprising:

means for transmitting a control channel indicating the second number of TDM control symbols being transmitted by the first station in the downlink subframe if the strong interfering station is not present, and

means for not transmitting the control channel if the strong interfering station is present.

11. The apparatus of claim 9, wherein the means for transmitting the second number of TDM control symbols comprises:

means for transmitting a control channel in a first TDM control symbol at a first transmit power level, an

Means for transmitting the control channel in at least one additional TDM control symbol at a second transmit power level, the second transmit power level being higher than the first transmit power level.

12. The apparatus of claim 9, wherein the means for transmitting the second number of TDM control symbols comprises: means for transmitting a control channel in the second number of TDM control symbols on a selected resource element, wherein the resource element is selected to reduce collisions with reference signals from the strong interfering stations.