Data reception wih interference cancellation in a relay communication network

Description of equivalent WO 2010047727 A2

DATA RECEPTION WIH INTERFERENCE CANCELLATION IN A RELAY COMMUNICATION

NETWORK

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is related to concurrently filed and commonly owned U.S. Patent Application No. 12/257,265, entitled "METHOD AND APARATUS FOR COMMUNICATING IN A RELAY COMMUNICATION NETWORK," and assigned Attorney Docket No. 071863; the disclosure of which is hereby incorporated by reference herein.

BACKGROUND

I. Field

[0002] The present disclosure relates generally to communication, and more specifically to techniques for transmitting and receiving data in a wireless communication network.

II. Background

[0003] A wireless communication network may include a number of stations that can transmit and receive data. The coverage of a given station may be smaller than a desired coverage area. The small coverage may be due to various reasons such as low maximum transmit power, spectral mask constraints, high frequency spectrum, etc. [0004] A large number of stations may be used to cover a given geographic area. These stations should be able to communicate with one other over the air since interconnecting many stations via a backhaul network may be expensive. The stations may be operated as unplanned repeaters that can "amplify and forward" transmissions. However, the unplanned repeaters may result in positive feedback loops and may also amplify noise. The stations may also be operated as incremental redundancy (IR) stations that can "decode and forward" transmissions in an uncoordinated manner. However, the IR stations may require carrier sensing and/or route planning in order to minimize collisions and manage interference. The IR stations may thus be highly inefficient if there is a large number of stations. Techniques for effectively transmitting and receiving data over a large geographic area are desirable.

SUMMARY

[0005] Techniques for transmitting and receiving data in a relay communication network are described herein. In one design, stations in the relay network may be grouped into multiple depths. Packets may be transmitted in a pipelined manner in the relay network to obtain broad coverage. Stations at progressively higher depth may send transmissions of a packet in successive frames, and stations at each depth may send the same transmission at the same time.

[0006] In an aspect, a station may receive data with interference cancellation in the relay network. The station may obtain a received signal comprising (i) at least one transmission of a first packet from at least one first station at a first depth and (ii) at least one transmission of a second packet from at least one second station at a second depth. In one design, the at least one first station may comprise at least one downstream station, and the at least one second station may comprise at least one upstream station. In another design, the first and second stations may comprise upstream stations at different depths. For both designs, the station may estimate and cancel interference due to the at least one transmission of the first packet from the received signal to obtain an interference canceled signal. The station may then process the interference canceled signal for the second packet, as described below.

[0007] In another aspect, a station may transmit data using boot-up packets in the relay network. The station may send transmissions of packets, with each packet being transmitted in a pipeline by stations at different depths in successive frames. The station may periodically send transmissions of boot-up packets to initialize the pipeline and allow interference cancellation to start. When the station sends a transmission of a boot-up packet, stations at higher depths may be silent and send no transmissions. [0008] Various aspects and features of the disclosure are described in further detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG. 1 shows a relay communication network.

[0010] FIG. 2 shows a transmission scheme for the relay network. [0011] FIG. 3 shows packet decoding with interference cancellation. [0012] FIG. 4 shows packet decoding using transmissions from stations at different depths.

[0013] FIG. 5 shows a transmission scheme with periodic boot-up packets. [0014] FIG. 6 shows a transmission scheme for half-duplex stations. [0015] FIG. 7 shows packet transmissions by three stations.

[0016] FIGS. 8 and 9 show a process and an apparatus, respectively, for receiving data with interference cancellation in the relay network.

[0017] FIGS. 10 and 11 show a process and an apparatus, respectively, for receiving data with interference cancellation for downstream stations.

[0018] FIGS. 12 and 13 show a process and an apparatus, respectively, for receiving data with interference cancellation for upstream stations.

[0019] FIGS. 14 and 15 show a process and an apparatus, respectively, for sending data with boot-up packets. [0020] FIG. 16 shows a block diagram of two stations in the relay network.

DETAILED DESCRIPTION

[0021] The techniques described herein may be used for a relay communication network having any number of stations. The terms "network" and "system" are often used interchangeably. The relay network may utilize Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), Orthogonal FDMA (OFDMA), Single-Carrier FDMA (SC-FDMA), etc. The relay network may also implement a radio technology such as (i) Universal Terrestrial Radio Access (UTRA) or cdma2000 for CDMA, (ii) Global System for Mobile Communications (GSM) for TDMA, (iii) Evolved UTRA (E-UTRA), Long Term Evolution (LTE), Ultra Mobile Broadband (UMB), or Flash-OFDM® for OFDMA, (iv) IEEE 802.11 or Hiperlan for wireless local area network (WLAN), (v) IEEE 802.16 for wireless metropolitan area network (WMAN), etc. The techniques may also be used with other multiple access schemes and/or other radio technologies. The techniques may be used for communication networks supporting unicast transmission to specific stations, multicast transmission to groups of stations, and/or broadcast transmission to all stations. [0022] FIG. 1 shows a relay communication network 100, which may also be referred to as a peer-to-peer network, a broadcast network, a distributed broadcast network, a mesh network, etc. Relay network 100 may include any number of stations 110, which may also be referred to as nodes. A station may be a base station, a terminal, etc. A base station may be a fixed station that communicates with the terminals and may also be referred to as an access point, a Node B, an evolved Node B (eNB), etc. A terminal may be stationary or mobile and may also be referred to as an access terminal, a mobile station, a user equipment, a subscriber unit, a station, etc. A terminal may be a cellular phone, a personal digital assistant (PDA), a wireless modem, a wireless communication device, a handheld device, a laptop computer, a cordless phone, a wireless local loop (WLL) station, etc. A terminal may communicate with a base station and/or peer-to-peer with other terminals.

[0023] In relay network 100, a station may be a source station, a relay station, or a destination station. A source station is a station that originates a transmission of data. A relay station is a station that receives a transmission from one or more upstream stations and resends the transmission to one or more downstream stations. A destination station is a station that receives a transmission from one or more other stations and does not resend the transmission. An upstream station is a station from which a transmission is received, and a downstream station is a station to which a transmission is sent. [0024] In one design, the stations in the relay network may be grouped based on depth. Depth may also be referred to as tier, level, etc. The grouping may be done in a distributed and ad-hoc manner, without the need for pre-planning. Source stations are at the lowest depth 0 and are referred to as depth-0 stations or nodes. Stations that can correctly decode transmissions from source stations are at depth 1 and are referred to as depth- 1 stations. In general, stations that can correctly decode transmissions from depth-d stations are at depth d+1 and are referred to as depth-(d+l) stations, for d ≥ 0 . In the example shown in FIG. 1, station A is a source/depth-0 station, stations B, E, F and G are depth- 1 stations, and stations C, D, H, I and J are depth-2 stations. In general, the relay network may include depths 0 through D, with depth 0 being the lowest depth, depth D being the highest depth, and D being an integer value.

[0025] In an aspect, the relay network may support transmission of packets in a pipelined manner. A packet may be transmitted by stations at different depths in successive time intervals. Furthermore, all stations at the same depth may transmit the packet at the same time. [0026] FIG. 2 shows a design of a transmission scheme 200 for the relay network. The transmission timeline may be partitioned into units of frames. A frame is a unit of time and may have a predetermined time duration, e.g., 1 millisecond (ms), etc. A frame may also be referred to as a time interval, a transmission time interval, a slot, a subframe, etc. In the example shown in FIG. 2, station A is a source/depth-0 station, station B is a depth- 1 station within range of station A, and station C is a depth-2 station within range of station B.

[0027] In frame t, station A transmits packet 0, which is received and decoded by station B. In frame t+1, station A transmits packet 1, which is received and decoded by station B. Station B also transmits packet 0, which is received and decoded by station C. In frame t+2, station A transmits packet 2, which is received and decoded by station B. Station B also transmits packet 1, which is received and decoded by station C. Station C also transmits packet 0 to downstream stations at the next higher depth. [0028] Packet transmission may occur in similar manner in each subsequent frame. In each frame, a station at depth d may receive and decode a packet from upstream stations at depth d-1 and may transmit a prior decoded packet to downstream stations at depth d+1 (if any).

[0029] As shown in FIG. 2, a given packet is transmitted by stations at progressively higher depths in consecutive frames. For example, packet 0 is transmitted by station A in frame t, then transmitted by station B in frame t+1, and then transmitted by station C in frame t+2. Station A at the lowest depth 0 may transmit a new packet in each frame. Station B at the next higher depth 1 may receive a packet from station A in each frame and may also transmit the packet received in the prior frame (if any) to station C at the next higher depth 2. In each frame, each station may receive a packet from upstream stations and may transmit a prior received packet to downstream stations.

[0030] In one design, all stations at a given depth d may send transmissions having the same waveform. The terms "transmission" and "signal" may be used interchangeably. Depth-d stations may send their transmissions in the same frame. A station at the next higher depth d+1 may receive transmissions from one or more depth- d stations. Since the transmissions have the same waveform, the depth-(d+l) station may treat the transmissions from different depth-d stations in the same manner as transmissions received via different propagation paths in a multipath channel. The depth-(d+l) station may process the transmissions received from all depth-d stations to recover a packet sent by the depth-d stations. The coverage achieved by the relay network may be equal to that of a single frequency network (SFN) with all upstream stations transmitting the same waveform.

[0031] A station may generate a transmission of a packet using orthogonal frequency division multiplexing (OFDM), single-carrier frequency division multiplexing (SC-FDM), or some other modulation technique. An OFDM symbol may be generated by (i) performing a K-point inverse fast Fourier transform (IFFT) on K symbols mapped to K subcarriers to obtain a useful portion containing K time-domain samples and (ii) copying the last C samples and appending these C samples to the front of the useful portion to obtain an OFDM symbol containing K + C samples. An SC- FDM symbol may be generated by (i) performing an M-point discrete Fourier transform (DFT) on M time-domain symbols to obtain M frequency-domain symbols, (ii) mapping the frequency-domain symbols and zero symbols to the K subcarriers, (iii) performing a K-point IFFT on the K mapped symbols to obtain a useful portion containing K time- domain samples, and (iv) appending a cyclic prefix of C samples to the front of the useful portion to obtain an SC-FDM symbol containing K + C samples. For both OFDM and SC-FDM, a receiving station may obtain a received OFDM or SC-FDM symbol containing transmissions from one or more stations and can effectively handle multipath by simply discarding the cyclic prefix. Other multiplexing schemes besides OFDM and SC-FDM may also be used by the relay network.

[0032] In an aspect, a relay station may decode transmissions received from upstream stations with interference cancellation (IC) for downstream stations. Transmissions sent by the downstream stations may act as interference to the transmissions from the upstream stations and may degrade received signal quality at the relay station. The relay station has knowledge of the transmissions sent by the downstream stations and can thus estimate and cancel the interference due to these transmissions.

[0033] FIG. 3 shows a design of packet decoding with interference cancellation for downstream stations. In this example, packet 0 is transmitted by station A in frame t, decoded by station B and retransmitted in frame t+1, and decoded by station C and retransmitted in frame t+2. The next packet 1 is transmitted by station A in frame t+1, decoded by station B and retransmitted in frame t+2, and decoded by station C and retransmitted in frame t+3. [0034] The next packet 2 is transmitted by station A in frame t+2. Station B receives packet 2 from station A as well as packet 0 from station C in frame t+2. Station B may estimate the interference due to packet 0 transmitted by station C. Station B may then subtract the estimated interference from its received signal to obtain an interference canceled signal. Station B may then process the interference canceled signal to recover packet 2 transmitted by station A in frame t+2. Station B may decode each subsequent packet transmitted by station A with interference cancellation for a packet transmitted by station C.

[0035] Interference cancellation for a given packet X may be performed in various manners. In one design, a depth-d station may generate a transmission of packet X after correctly decoding the packet. The depth-d station may also estimate the channel response for one or more depth-(d+l) stations based on pilots received from the depth- (d+1) stations. The depth-d station may then pass the transmission of packet X through the estimated channel response to obtain the estimated interference for the depth-(d+l) stations. The depth-d station may then subtract the estimated interference from the received signal.

[0036] In another aspect, a station at depth d may use transmissions from upstream stations at different depths to recover a packet. The depth-d station may receive transmissions of the packet from stations at depths 0 through d-1 in d consecutive frames. The depth-d station may collect information for the packet in each frame based on a received signal for that frame. The depth-d station may then perform decoding based on all collected information for the packet, which may improve decoding performance.

[0037] In one design, the collected information may be given in the form of log likelihood ratios (LLRs) for code bits of the packet. An LLR for a given code bit may be defined as a ratio of the probability of the code bit being '1 ' to the probability of the code bit being '0'. LLRs may be computed in a manner known in the art based on available information such as a received signal, a channel estimate, an interference estimate, etc. In general, the quality of the LLRs improves with less noise and interference, which may improve decoding performance.

[0038] FIG. 4 shows a design of packet decoding using transmissions from upstream stations at different depths. In this example, in frame t, station A sends a transmission of packet 0, which is received and decoded by station B. Station C also receives the transmission of packet 0 from station A and computes LLRs for packet 0 based on its received signal. Station C may attempt to decode the LLRs to recover packet 0 or may simply store these LLRs.

[0039] In frame t+1, station A sends a transmission of packet 1, and station B sends a transmission of packet 0. Station C receives the transmission of packet 1 from station A as well as the transmission of packet 0 from station B. Station C computes LLRs for packet 0 based on its received signal. Station C then decodes the LLRs obtained in frames t and t+1 to recover packet 0. Station C may also compute LLRs for packet 1 based on its received signal and may store these LLRs (not shown in FIG. 4). Station C may compute and decode LLRs for subsequent packets in similar manner. [0040] FIG. 4 also shows a design of LLR computation with interference cancellation. Station C receives the transmission of packet 1 from station A as well as the transmission of packet 0 from station B in frame t+1. These transmissions interfere with one another at station C. Station C may decode the LLRs obtained in frames t and t+1 to recover packet 0. In one design, station C may then estimate the interference due to the transmission of packet 0 from station B in frame t+1, e.g., by generating the transmission of packet 0 after correctly decoding the packet and passing the transmission through the estimated channel response for station B to obtain the estimated interference. Station C may then subtract the estimated interference from its received signal in frame t+1 to obtain an interference canceled signal. Station C may then compute the LLRs for packet 1 based on the interference canceled signal (instead of the received signal) in frame t+1.

[0041] As shown in FIGS. 2 to 4, packets may be transmitted in a pipelined manner, with each station transmitting a packet only once. A relay station may decode transmissions received from upstream stations with interference cancellation of transmissions sent by downstream stations, as shown in FIG. 3. A station may also perform decoding based on LLRs obtained for upstream stations at one or more depths and may also perform interference cancellation prior to computing LLRs, as shown in FIG. 4. The effectiveness of pipelined transmissions is dependent on correct decoding of packets by each relay station, so that the station can send correct transmissions of packets to downstream stations. The effectiveness of interference cancellation is also dependent on correct decoding of packets by each station, so that the station can estimate and cancel the interference due to the decoded packets. If a given station decodes a packet in error, then the station may send an erroneous transmission of the packet. In this case, downstream stations may not be able to correctly decode the packet. If interference cancellation is relied on for packet decoding, then the pipeline may break once a packet is decoded in error. This is because interference cancellation may be ineffective with the packet decoded in error, and the next packet may also be decoded in error with higher interference due to ineffective interference cancellation. [0042] In an aspect, boot-up packets may be sent periodically to re-initialize the pipeline and limit propagation of errors. A boot-up packet is a packet sent by only the source station in a designated frame, with stations at higher depths not transmitting during the designated frame. A boot-up packet may be sent at the start of each superframe. A superframe may include T frames with indices of 0 through T-I, where T may be any suitable value. In one design, in each superframe, only stations at depth d or higher can transmit packets in frame d, for 0 ≤ d < T . This design may allow downstream stations to correctly decode packets and perform interference cancellation. [0043] FIG. 5 shows a design of a transmission scheme with periodic boot-up packets. In this example, station A is a source station, station B is a depth- 1 station, station C is a depth-2 station, and the highest depth is D = 2 . A superframe includes T = IO frames with indices 0 through 9.

[0044] In frame 0, only station A transmits packet 0, and all other stations at higher depths are silent. Packet 0 is a boot-up packet for the superframe. In frame 1, station A transmits packet 1, station B transmits packet 0, and station C is silent. In frame 2, station A transmits packet 2, station B transmits packet 1, and station C transmits packet 0. Stations A, B and C all transmit packets in each of frames 3 through 6. In frame 7, station A transmits the last packet 7 in the superframe, and stations B and C transmit packets 6 and 5, respectively. In frame 8, station B transmits the last packet 7, and station C transmits packet 6. Station A may be silent (not shown in FIG. 5) or may act as a depth- 1 station and transmit packet 7 (as shown in FIG. 5). In the last frame 9, station C transmits the last packet 7. Stations A and B may be silent (not shown in FIG. 5) or may act as depth-2 stations and transmit packet 7 (as shown in FIG. 5). [0045] Packet transmission in the next superframe occurs in similar manner. In frame 0 of the next superframe, only station A transmits the next packet 8, which is a boot-up packet for this superframe, and all other stations at higher depths are silent. Packet transmission continues in each subsequent frame as described above. [0046] As shown in FIG. 5, the boot-up packets may allow the decoding and interference cancellation pipeline to start properly. Since only source station A transmits packet 0 in the first frame 0 of a superframe, depth- 1 station B can correctly decode packet 0 without interference from other stations. In frame 2, station B may receive interference due to packet 0 from depth-2 station C. Station B may estimate and cancel the interference due to packet 0 from station C prior to decoding packet 2 from source station A. If the interference cancellation is effective, then the received signal quality for packet 2 may be comparable to the received signal quality for packet 0 without any transmission from station C.

[0047] Furthermore, since only source station A transmits packet 0 in the first frame 0, depth-2 station C can compute LLRs for packet 0 without interference from other stations. In frame 1, station C receives both packet 0 from depth- 1 station B and packet 1 from source station A and can compute LLRs for packet 0 with interference from station A. Station C may decode the LLRs obtained in both frames 0 and 1 to recover packet 0. Station C may then estimate the interference due to packet 0 from station B and may subtract the estimated interference from the received signal. Station C may then compute LLRs for packet 1 from station A based on the interference canceled signal. If the interference cancellation is effective, then the received signal quality for packet 1 in frame 1 may be comparable to the received signal quality for packet 0 in frame 0. The decoding and interference cancellation pipeline may thus start successfully with station B not transmitting in frame 0 and station C not transmitting in frames 0 and 1 of each superframe.

[0048] Overhead for the boot-up packets may be dependent on the superframe duration T and the maximum depth D in the relay network. A shorter superframe may reduce packet error propagation whereas a longer superframe may reduce overhead. The maximum depth D may be dependent on the desired coverage. [0049] In the designs described above, interference cancellation may be performed based on full packet decoding. As shown in FIG. 3, a relay station (e.g., station B) may perform interference cancellation for packets transmitted by downstream stations (e.g., station C) based on packets that have been correctly decoded by the relay station. Furthermore, as shown in FIG. 4, a depth-d station (e.g., station C) may perform interference cancellation for packets that have been correctly decoded by that station prior to LLR computation for packets from depth-(d-2) stations (e.g., station A). [0050] In another design, interference cancellation may be performed without decoding packets. Station B or C may use estimates of modulation symbols based on the received symbols or may use the LLRs after a few Turbo iterations. Station B or C may also use other techniques such as spatial nulling to help reduce interference. Most of the interference due to a packet may be correctly cancelled even without decoding the packet.

[0051] A station may support full-duplex or half-duplex operation. For full-duplex operation, the station can simultaneously transmit and receive data at the same time, as shown in FIGS. 3 to 5. For half-duplex operation, the station can only transmit or receive data at any given moment.

[0052] In an aspect, data transmission may be supported by having half-duplex stations at different depths transmit in different frames. In one design, stations at even depths (e.g., depth 0, 2, etc.) may transmit packets in even-numbered frames, and stations at odd depths (e.g., depth 1, 3, etc.) may transmit packets in odd-numbered frames. Depth-0 stations do not need to receive data and can thus transmit in both even- numbered and odd-numbered frames, which may improve performance. [0053] FIG. 6 shows a design of a transmission scheme for half-duplex stations. In this example, station A is a source station, station B is a depth- 1 station, and station D may be a depth- 1 or depth-2 station. Stations A, B and D support half-duplex operation. [0054] In frame t, station A transmits packet 0, which is received and decoded by station B. In frame t+1, stations A and B both transmit packet 0, which is received and decoded by station D. In each odd-numbered frame, station A acts as a depth- 1 station and transmits the same packet as station B. In frame t+2, station A transmits packet 1 and station D transmits packet 0. Station B performs interference cancellation for packet 0 and then decodes packet 1. In frame t+3, stations A and B both transmit packet 1, which is received and decoded by station D. In frame t+4, station A transmits packet 2 and station D transmits packet 1. Station B performs interference cancellation for packet 1 and then decodes packet 2. Packet transmission may occur in similar manner in each subsequent frame.

[0055] As shown in FIG. 6, station D may be a depth-2 station that can receive only during odd-numbered frames and may not be able to compute LLRs for packets transmitted by depth-0 station A during even-numbered frames. However, station A may transmit each packet in both an even-numbered frame as well as the following odd- numbered frame. In this case, station D can receive each packet from both stations A and B in the same frame. The decoding performance of station D with half-duplex operation in FIG. 6 may be comparable to the decoding performance of station C with full-duplex operation and interference cancellation in FIG. 4. [0056] In one design, stations at a given depth may be partitioned into two sets. A first set of stations may transmit in first frames and receive in second frames. A second set of stations may transmit in the second frames and receive in the first frames. The first frames may be even-numbered frames, and the second frames may be odd- numbered frames, or vice versa. For example, stations B and D in FIG. 6 may both be depth- 1 stations, with station B belonging in the first set, and station D belonging in the second set. The two sets of stations at the same depth may thus transmit and receive in different frames. This may allow destination stations to receive in both even-numbered and odd-numbered frames, which may improve performance.

[0057] In an aspect, stations at different depths may transmit different pilots, which may allow other stations to determine the depths of these stations. A pilot is known data that is processed in a known manner and may be used by a receiving station for various purposes such as channel estimation, time and/or frequency acquisition, signal strength measurement, station identification, etc. A pilot may also be referred to as a reference signal, a preamble, a training sequence, etc. In one design, code division multiplexing (CDM) may be used for the pilots. The stations at each depth may generate their pilots with a different scrambling code and/or a different orthogonal code assigned to that depth. The stations at different depths may transmit their pilots concurrently, e.g., in the same time and frequency block in order to reduce pilot overhead.

[0058] In another design, frequency division multiplexing (FDM) may be used for the pilots. The stations at different depths may transmit their pilots on different sets of subcarriers, and these pilots may be orthogonal to one another in the frequency domain. In yet another design, time division multiplexing (TDM) may be used for the pilots. The stations at different depths may transmit their pilots in different symbol periods, and these pilots may be orthogonal to one another in the time domain. In general, the pilots for stations at different depths may utilize any one or any combination of multiplexing schemes. The pilots may be transmitted in designated frames, in designated symbol periods of each frame or each designated frame, whenever packets are transmitted, and/or at some other times.

[0059] In another aspect, stations at different depths may transmit different synchronization signals. A synchronization signal may carry pertinent information such as depth information (e.g., the maximum allowed depth in the network), station identifier (ID), system bandwidth, FFT size, frame timing, superframe timing, data rate information, etc. Upon recovering the pertinent information from a synchronization signal, a receiving station may use the synchronization signal in the same manner as a pilot for various purposes described above. A synchronization signal may comprise a pilot and/or other signals, depending on the information to send in the synchronization signal. A station may transmit a synchronization signal and/or a pilot. [0060] A station may derive a channel estimate for stations at a given depth based on the pilots and/or synchronization signals received from these stations. The station may also use part of a data portion transmitted by downstream stations to derive a channel estimate for these stations. The station may also perform iterative channel estimation prior to performing interference cancellation in order to improve performance. The station may also perform iterative channel estimation and interference cancellation in order to improve performance.

[0061] In an aspect, a station may perform auto-configuration and determine its depth without the need for manual configuration. The station may perform auto- configuration when the station is added to or moved within the relay network. The station may perform auto-configuration when the station is powered up, when the station decodes one or more packets in error, etc.

[0062] For auto-configuration, the station may receive pilots and/or synchronization signals from other stations and may determine the depths of the detected stations based on their pilots and/or synchronization signals. The station may attempt to decode packets from detected stations at the lowest depth. If the packet decoding is unsuccessful, then the station may attempt to decode packets from stations at the next higher depth. The station may attempt to decode packets from detected stations at progressively higher depth until the packets can be correctly decoded. The station may then determine its depth as one higher than the depth of the stations from which packets can be correctly decoded. Thus, if the station can correctly decode packets from depth- d stations but not from depth-(d-l) stations, then the station becomes a depth-(d+l) station.

[0063] The relay network described herein may support low power transmissions, higher carrier frequencies, and/or higher data rates. The performance of the relay network may be illustrated by the following example.

[0064] FIG. 7 shows an example of packet transmissions for three stations in the relay network. In this example, station A is a source station, station B is a relay station, and station C is a destination station. Each station transmits at a power level of P, and the thermal noise at each station is No. The channel gain between stations A and B is g, the channel gain between stations B and C is hi, and the channel gain between stations A and C is h₂. The capacity of each link (assuming other links are not active) may be expressed as:

I ² - P

C_AB = IOB 1 + Eq (I)

N_r

<img file="WO2010047727A2_D0001.tif" />

where C_AB is the capacity of the link from station A to station B,

C_BC is the capacity of the link from station B to station C, and C_AC is the capacity of the link from station A to station C.

[0065] An overall data rate R is a data rate at which station A can transmit data to stations B and C. The overall data rate R should be less than C_AB in order for station B to correctly decode packets from station A. The overall data rate R should also be less than the capacity of the links to station C in order for station C to correctly decode packets from stations A and B. [0066] A received signal at station C may be expressed as:

y = h_j • r + h₂ • s + n , Eq (4)

where r is a signal transmitted by station B, s is a signal transmitted by station A, y is the received signal at station C, and n is the noise at station C.

[0067] In frame t, signal s may carry packet 0, and signal r may not be present. Station C may compute LLRs for packet 0 based on the received signal y, which may contain only signal s carrying packet 0 from station A. The amount of received mutual information C_t in frame t may be expressed as: <img file="WO2010047727A2_D0002.tif" />

C_t is equal to the capacity of the link from station A to station C.

[0068] In frame t+1, signal s may carry packet 1, and signal r may carry packet 0. The received signal y may contain signal r carrying packet 0 from station B as well as signal s carrying packet 1 from station A. Station C may compute LLRs for packet 0 in signal r from station B based on the received signal y. However, signal r is interfered by signal s with power of | h₂ | ² • P . The amount of received mutual information Q₊₁ in frame t+1 may be expressed as:

<img file="WO2010047727A2_D0003.tif" />

[0069] As shown in equation (6), the received signal component corresponding to signal s acts as interference and is reflected by the term | h₂ | ² • P added to noise No in the denominator. The total received mutual information Q_otal for packet 0 may be expressed as:

| ²) - P

C_total = C_t + C_t+1 = log 1 + ( ^v I h^"₁ h₂ 1^[ , ^"2 ' ^* . Eq (7)

N₀

[0070] Ctotai is equal to the capacity obtained with both stations A and B transmitting to station C and with ( | \ | ² + | h₂ | ²) - P being the received power at station C. Station C can correctly decode packet 0 if it is sent at a data rate less than

Ctotal-

[0071] After decoding packet 0, station C may cancel the interference due to signal r carrying packet 0 from received signal y to obtain an interference canceled signal. The interference canceled signal may include mostly signal s carrying packet 1 from station A. Station C may then compute LLRs for packet 1 based on the interference canceled signal. The amount of received mutual information, after the interference cancellation, may be as shown in equation (5). Station C may decode packet 1 as well as subsequent packets in similar manner. [0072] The data rate from station A to station B is limited by C_AB- The data rate from stations A and B to station C is limited by C_totai since the total received power at station C is ( | h_j | + | h₂ | ) • P . The overall data rate R may be selected as follows:

R &lt; min [C_AB, C_total] . Eq (8)

The overall data rate R in equation (8) may achieve the capacity of an SFN network with transmitters at stations A and B.

[0073] For simplicity, the overall data rate R has been determined for a simply scenario with three stations A, B and C. The computation of the overall data rate may be extended to a relay network with any number of stations and any number of depths. In general, the data rate supported by a given station may be less than C = IOg (^ P_11x ZN₀) , where P_RX is the total received power at that station from all detectable upstream stations operating in an SFN manner. The overall data rate may be the minimum of the supported data rates for all stations in the relay network. The overall data rate may also be larger than the minimum supported data rate for all stations, in which case a fraction of the stations may be out of coverage. [0074] The transmission schemes shown in FIGS. 2 to 6 may be used for all or a portion of the system bandwidth. The system bandwidth may also be partitioned into multiple subbands, and different data streams may be sent on different subbands. This partitioning of the frequency resources may be beneficial for transmission of unicast data.

[0075] FIG. 8 shows a design of a process 800 for receiving data with interference cancellation in a relay communication network, e.g., a network supporting unicast, multicast and/or broadcast transmissions. Process 800 may be performed by a station, which may be a terminal, base station, etc. The station may obtain a received signal comprising (i) at least one transmission of a first packet from at least one first station at a first depth and (ii) at least one transmission of a second packet from at least one second station at a second depth in the relay network (block 812). The first and second packets may be broadcast by the first and second stations in the relay network. [0076] The station may estimate and cancel interference due to the at least one transmission of the first packet from the received signal to obtain an interference canceled signal (block 814). In one design, the station may estimate interference due to the at least one transmission of the first packet based on a decoded first packet and a channel estimate for the at least one first station. In another design, the station may estimate interference due to the at least one transmission of the first packet based on LLR information for the first packet, without decoding the first packet. For both designs, the station may subtract the estimated interference from the received signal to obtain the interference canceled signal. The station may then process the interference canceled signal for the second packet (block 816).

[0077] In one design that is shown in FIG. 3, the at least one first station may comprise at least one downstream station, and the at least one second station may comprise at least one upstream station. The received signal may be obtained by a relay station at a third depth between the first and second depths. The first packet may correspond to packet 0 in frame t+2, and the second packet may correspond to packet 2. In another design that is shown in FIG. 4, the first and second stations may comprise upstream stations at different depths. The received signal may be obtained by a station at a third depth higher than the first and second depths. The first packet may correspond to packet 0 in frame t+1, and the second packet may correspond to packet 1. [0078] FIG. 9 shows a design of an apparatus 900 for receiving data with interference cancellation in a relay communication network. Apparatus 900 includes a module 912 to obtain a received signal comprising at least one transmission of a first packet from at least one first station at a first depth and at least one transmission of a second packet from at least one second station at a second depth in the relay network, a module 914 to estimate and cancel interference due to the at least one transmission of the first packet from the received signal to obtain an interference canceled signal, and a module 916 to process the interference canceled signal for the second packet. [0079] FIG. 10 shows a design of a process 1000 for receiving data with interference cancellation for downstream stations in a relay communication network, which may support unicast, multicast and/or broadcast transmissions. Process 1000 is a specific design of process 800 in FIG. 8 and may be performed by a station, e.g., station B in FIG. 3. The station may obtain a first received signal comprising at least one transmission of a first packet (e.g., packet 0) from at least one upstream station (e.g., station A) in a first frame (e.g., frame t in FIG. 3) (block 1012). The station may process the first received signal to recover the first packet (block 1014). The station may send a transmission of the first packet to at least one downstream station (e.g., station C) in a second frame (e.g., frame t+1 in FIG. 3) (block 1016). [0080] The station may obtain a second received signal comprising at least one transmission of the first packet (e.g., packet 0) from the at least one downstream station and at least one transmission of a second packet (e.g., packet 2) from the at least one upstream station in a third frame (e.g., frame t+2 in FIG. 3) (block 1018). The station may estimate interference due to the at least one transmission of the first packet sent by the at least one downstream station (block 1020). The station may then subtract the estimated interference from the second received signal to obtain an interference canceled signal (block 1022). The station may then process the interference canceled signal to recover the second packet from the at least one upstream station (block 1024). [0081] FIG. 11 shows a design of an apparatus 1100 for receiving data with interference cancellation for downstream stations in a relay communication network. Apparatus 1100 includes a module 1112 to obtain a first received signal comprising at least one transmission of a first packet from at least one upstream station in a first frame, a module 1114 to process the first received signal to recover the first packet, a module 1116 to send a transmission of the first packet to at least one downstream station in a second frame, a module 1118 to obtain a second received signal comprising at least one transmission of the first packet from the at least one downstream station and at least one transmission of a second packet from the at least one upstream station in a third frame, a module 1120 to estimate interference due to the at least one transmission of the first packet sent by the at least one downstream station, a module 1122 to subtract the estimated interference from the second received signal to obtain an interference canceled signal, and a module 1124 to process the interference canceled signal to recover the second packet from the at least one upstream station.

[0082] FIG. 12 shows a design of a process 1200 for receiving data with interference cancellation for upstream stations in a relay communication network, which may support unicast, multicast and/or broadcast transmissions. Process 1200 is another design of process 800 in FIG. 8 and may be performed by a station, e.g., station C in FIG. 4. The station may obtain a received signal comprising (i) at least one transmission of a first packet (e.g., packet 0) from at least one first station (e.g., station B) at a first depth and (ii) at least one transmission of a second packet (e.g., packet 1) from at least one second station (e.g., station A) at a second depth in the relay network (block 1212). The station may process the received signal to recover the first packet (block 1214). The station may then estimate interference due to the at least one transmission of the first packet based on the recovered first packet (block 1216). The station may subtract the estimated interference from the received signal to obtain an interference canceled signal (block 1218). The station may then process the interference canceled signal for the second packet (block 1220).

[0083] In one design, the station may obtain a first received signal comprising at least one transmission of the first packet from the at least one second station in a first frame. The station may obtain the received signal in block 1212 in a second frame. The station may process the two received signals to recover the first packet. In one design, the station may (i) compute first LLRs for the first packet based on the first received signal obtained in the first frame, (ii) compute second LLRs for the first packet based on the received signal obtained in the second frame, and (iii) decode the first and second LLRs to recover the first packet. In one design of block 1220, the station may compute LLRs for the second packet based on the interference canceled signal and may use these LLRs in a subsequent frame to recover the second packet.

[0084] FIG. 13 shows a design of an apparatus 1300 for receiving data with interference cancellation for upstream stations in a relay communication network. Apparatus 1300 includes a module 1312 to obtain a received signal comprising at least one transmission of a first packet from at least one first station at a first depth and at least one transmission of a second packet from at least one second station at a second depth in the relay network, a module 1314 to process the received signal to recover the first packet, a module 1316 to estimate interference due to the at least one transmission of the first packet based on the recovered first packet, a module 1318 to subtract the estimated interference from the received signal to obtain an interference canceled signal, and a module 1320 to process the interference canceled signal for the second packet. [0085] FIG. 14 shows a design of a process 1400 for sending data with boot-up packets in a relay communication network, which may support unicast, multicast and/or broadcast transmissions. Process 1400 may be performed by a station. The station may be at a first depth in the relay network and may send transmissions of packets, with each packet being transmitted in a pipeline by stations at different depths in successive frames (block 1412). The station may periodically send transmissions of boot-up packets to initialize the pipeline, with no transmissions being sent by stations at depths higher than the first depth during the transmissions of the boot-up packets (block 1414). [0086] In one design, the station may send a transmission of a boot-up packet in a designated frame of each superframe comprising multiple frames. The multiple frames in each superframe may be assigned sequentially increasing indices starting with 0. Only stations at depth d or lower may send transmissions of packets in frame d, where d is a frame index. The station may send either transmissions of prior packets (as shown in FIG. 5) or no transmissions of packets in at least one frame at the end of each superframe to clear the pipeline. The number of frames to send no transmissions or transmissions of prior packets may be dependent on the depth of the station and the highest depth in the relay network.

[0087] FIG. 15 shows a design of an apparatus 1500 for sending data with boot-up packets in a relay communication network. Apparatus 1500 includes a module 1512 to send transmissions of packets from a station at a first depth in the relay network, with each packet being transmitted in a pipeline by stations at different depths in successive frames, and a module 1516 to periodically send transmissions of boot-up packets from the station to initialize the pipeline, with no transmissions being sent by stations at depths higher than the first depth during the transmissions of the boot-up packets. [0088] The modules in FIGS. 9, 11, 13 and 15 may comprise processors, electronics devices, hardware devices, electronics components, logical circuits, memories, etc., or any combination thereof.

[0089] FIG. 16 shows a block diagram of a design of two stations HOa and HOb, which may be any two stations in FIG. 1. In this design, station 110a is equipped with U antennas 1634a through 1634u, and station 110b is equipped with V antennas 1652a through 1652v, where in general U &gt; 1 and V &gt; 1 .

[0090] At station 110a, a transmit processor 1620 may receive packets of data from a data source 1612 and control information from a controller/processor 1640. Transmit processor 1620 may process (e.g., encode, interleave, and modulate) the packets and control information and provide data symbols and control symbols, respectively. Transmit processor 1620 may also generate pilot symbols for a pilot and/or a synchronization signal for station 110a. A transmit (TX) multiple-input multiple-output (MIMO) processor 1630 may perform spatial processing (e.g., precoding) on the data symbols, the control symbols, and/or the pilot symbols, if applicable, and may provide U output symbol streams to U modulators (MODs) 1632a through 1632u. Each modulator 1632 may process a respective output symbol stream (e.g., for OFDM, SC- FDM, CDMA, etc.) to obtain an output sample stream. Each modulator 1632 may further process (e.g., convert to analog, amplify, filter, and upconvert) the output sample stream to obtain a radio frequency (RF) signal. U RF signals from modulators 1632a through 1632u may be transmitted via U antennas 1634a through 1634u, respectively. [0091] At station HOb, antennas 1652a through 1652v may receive the RF signals from station 110a and may provide received signals to demodulators (DEMODs) 1654a through 1654v, respectively. Each demodulator 1654 may condition (e.g., filter, amplify, downconvert, and digitize) a respective received signal to obtain received samples. Each demodulator 1654 may further process the received samples (e.g., for OFDM, SC-FDM, CDMA, etc.) to obtain received symbols. A MIMO detector 1656 may obtain received symbols from all V demodulators 1654a through 1654v, perform MIMO detection on the received symbols if applicable, and provide detected symbols. A receive processor 1658 may process (e.g., demodulate, deinterleave, and decode) the detected symbols, provide decoded packets to a data sink 1660, and provide decoded control information to a controller/processor 1680.

[0092] At station HOb, packets of data from a data source 1662 and control information from controller/processor 1680 may be processed by a transmit processor 1664, precoded by a TX MIMO processor 1666 if applicable, further processed by modulators 1654, and transmitted via antennas 1652. At station 110a, the RF signals from station 110b may be received by antennas 1634, processed by demodulators 1632, detected by a MIMO detector 1636 if applicable, and further processed by a receive processor 1638 to recover the packets and control information transmitted by station 110b.

[0093] Controllers/processors 1640 and 1680 may direct the operation at stations 110a and 110b, respectively. Controllers/processors 1640 and 1680 may each perform or direct process 800 in FIG. 8, process 1000 in FIG. 10, process 1200 in FIG. 12, process 1400 in FIG. 14, and/or other processes for the techniques described herein. Memories 1642 and 1682 may store data and program codes for stations 110a and 110b, respectively.

[0094] 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.

[0095] 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.

[0096] The various illustrative logical blocks, modules, and circuits described in connection with the disclosure herein 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. [0097] The steps of a method or algorithm described in connection with the disclosure herein 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 that 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.

[0098] 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 that can be used to carry or store desired program code means in the form of instructions or data structures and that 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 and 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 reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer- readable media.

[0099] 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 described herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

[00100] WHAT IS CLAIMED IS: