WO2010055368A1

WO2010055368A1 - Selective decode and forward for mimo relay

Info

Publication number: WO2010055368A1
Application number: PCT/IB2008/054786
Authority: WO
Inventors: Haifeng Wang; Zhenhong Li; Gang Wu; Wei Ni; Wei Zou
Original assignee: Nokia Corporation; Nokia, Inc.
Priority date: 2008-11-14
Filing date: 2008-11-14
Publication date: 2010-05-20

Abstract

From a received n-stream multiple-input/multiple output signal, data is correctly decoded from k streams of the signal and data is incorrectly decoded from m streams of the signal, wherein n≥2, 1≤k<n and 1≤m<n. The correctly decoded data from the k streams is encoded and forwarded on transmit antennas TAs or resource blocks RBs corresponding to at least some the k streams and also on corresponding to at least some of the m streams. In one embodiment, the correctly decoded k stream data is space-time coded onto all TAs/RBs that correspond to the k streams and among at least some of the TAs/RBs that correspond to the m streams. In another embodiment, a first portion of the correctly decoded k stream data is forwarded on TAs/RBs corresponding to the k streams and a second portion of the correctly decoded data is forwarded on TAs/RBs corresponding to the m streams.

Description

SELECTIVE DECODE AND FORWARD FOR MIMO RELAY

TECHNICAL FIELD:

[0001] The exemplary and non-limiting embodiments of this invention relate generally to wireless communication systems, methods, devices and computer programs and, and, more specifically, relate to decoding and forwarding techniques to relay a radio frequency signal between a source and a destination (e.g., such as for relay systems targeted for use in IMT-A).

BACKGROUND:

[0002] This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.

[0003] The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows:

ACK acknowledgement

BS base station

CRC cyclic redundancy check

DF decoding and forwarding

HARQ hybrid automatic repeat request

IMT-A international mobile telecommunications-advanced

MIMO multiple input/multiple output

NACK not acknowledge/negative acknowledgement

QRD-M QR (orthogonal and right triangle) decomposition & M-algorithm

RB resource block

RS relay station

SCM spatial channel model

SDF selective DF

SD sphere decoding

SIC successive interference cancellation

SNR signal to noise ratio

UE user equipment

[0004] Relay technology is utilized to increase coverage extension and system throughput performance. Relays may relay traffic bi-directionally or only in a single direction. [0005] Forwarding is used to guarantee the reliable data transmission in relay. One of the main forwarding methods is decoding and forwarding, in which the data received at a relay is decoded and retransmitted after re-encoding. One drawback of DF is error propagation when the relay has not correctly decoded the data it received. Selective decoding and forwarding (SDF) is proposed in IEEE 802.16j to overcome the drawback [specifically, see IEEE P802.16J/D6 PART 16: AlR INTERFACE FOR FIXED AND MOBILE BROADBAND WIRELESS ACCESS SYSTEMS MULTIHOP RELAY SPECIFICATION]. In SDF, a cyclic redundancy check (CRC) is calculated after decoding. If the CRC results are correct, the relay will forward the data to the destination. If the CRC fails, the relay will not forward the data, but ask for re-transmission from the source.

[0006] Assume a straightforward extension of the SDF technique detailed in 802.16j for a MIMO case, where at least one party to the communication uses multiple antennas. It is well established that the conditions of the multiple different antennas will not be the same. If multiple streams (sometimes termed as multi-codeword) are used, the received data may be decoded correctly at some streams, but not correctly at the other streams due to the different channel conditions. The straightforward extension of SDF detailed at 802.16j is to forward the data on the streams that were correctly decoded, and to forward null or dummy packets on the streams that were not correctly decoded. The processing of the different streams are independent.

[0007] One publication concerning a SDF extension to MIMO may be seen in a paper by lnsoo Hwang, Yungsoo Kim and James (Sungiin) Kim, entitled ANALYSIS OF A MIMO RELAY SYSTEM WITH HARQ (Signal Processing, IEEE 7th Workshop on Advances in Wireless Communications, 2006 SPAWC '06). This paper is seen to focus mainly on a cooperation relay, in which there exists a direct link between the BS/source and the remote UE/destination.

[0008] It is noted that this is not an exhaustive scenario; it is not uncommon for there to be no direct link between the BS and the remote UE, whereby the BS can only connect to the remote UEs through the RS. Specific examples include a network in which the RS is used to provide coverage in a building 'shadow' that blocks a direct link between the BS and a UE within that 'shadow', or where the RS is used to extend coverage beyond an edge of a cell where a direct link from the BS cannot reach.

[0009] Selective forwarding is also discussed in a paper by J.N. Laneman, D. N. C Tse and G.W. Wornell entitled: COOPERATIVE DIVERSITY IN WIRELESS NETWORKS: EFFICIENT PROTOCOLS AND OUTAGE BEHAVIOR (IEEE Transactions on Information Theory 2004, 50(12): 3062 - 3080). In this paper, there is a selection between a direct BS-UE link and a link through a cooperation relay for a single antenna scenario. This paper is not seen to address a MIMO relay.

SUMMARY:

[0010] The foregoing and other problems are overcome, and other advantages are realized, by the use of the exemplary embodiments of this invention.

[0011] In a first aspect thereof, the exemplary embodiments of this invention provide a method that includes determining that from a received n-stream multiple-input/multiple output signal, data is correctly decoded from k streams of the signal and data is incorrectly decoded from m streams of the signal (wherein n≥Z, 1≤k<n and 1<m<n;, and each of n, m and k are integers), and encoding and forwarding the data that was correctly decoded from the k streams on transmit antennas or resource blocks corresponding to at least some the k streams and also on transmit antennas or resource blocks corresponding to at least some of the m streams.

[0012] In a second aspect thereof, the exemplary embodiments of this invention provide a computer readable memory storing a program executable by a processor to perform actions which include determining that from a received n-stream multiple-input/multiple output signal, data is correctly decoded from k streams of the signal and data is incorrectly decoded from m streams of the signal (wherein n≥2, 1 ≤/«n and 1≤m<n), and encoding and forwarding the data that was correctly decoded from the k streams on transmit antennas or resource blocks corresponding to at least some the k streams and also on transmit antennas or resource blocks corresponding to at least some of the m streams.

[0013] In a third aspect thereof, the exemplary embodiments of this invention provide an apparatus that includes at least a processor and an encoder. The processor is configured to determine, from a received n-stream multiple-input/multiple output signal, that data is correctly decoded from k streams of the signal and that data is incorrectly decoded from m streams of the signal, wherein n≥2, 1≤k<n and i≤m<n. The encoder is configured to encode and forward the data that was correctly decoded from the k streams on transmit antennas or resource blocks corresponding to at least some the k streams and also on transmit antennas or resource blocks corresponding to at least some of the m streams.

BRIEF DESCRIPTION OF THE DRAWINGS:

[0014] Fig. 1 shows a simplified block diagram of various electronic devices that are suitable for use in practicing the exemplary embodiments of this invention.

[0015] Fig. 2 presents the flow chart of an extension of IEEE 802.16j SDF in a MIMO relay.

[0016] Fig. 3 is a signaling diagram showing the approach of Fig. 2 if centralized scheduling is used.

[0017] Fig. 4 is a signaling diagram showing the approach of Fig. 2 if distributed scheduling is used.

[0018] Fig. 5 is a process flow diagram showing decode and forward techniques according to exemplary embodiments of this invention.

[0019] Fig. 6 is an exemplary signaling diagram showing particular details of the approach of Fig. 5 for the case where centralized scheduling is used.

[0020] Fig. 7 is an exemplary signaling diagram showing particular details of the approach of Fig. 5 for the case where distributed scheduling is used.

[0021] Fig. 8 is a graph showing simulation results of throughput performance at SNR2=SNR1-4dB and comparing various decode and forward approaches detailed herein, where (SNR1 : BS->RS; SNR2:RS->UE).

[0022] Fig. 9 is similar to Fig. 8 but for SNR2=SNR1 +4dB.

[00231 Figure 10 shows a more detailed block diagram than Fig. 1 of a relay embodied as one exemplary user equipment.

[0024] Figure 11 is a logic flow diagram that illustrates the operation of a method, and a result of execution of computer program instructions embodied on a computer readable memory, in accordance with exemplary embodiments of this invention. DETAILED DESCRIPTION:

[0025] Figure 1 is a high level schematic diagram showing three devices in a network. A source device 10 sends a transmission over a k"¹ stream 41 and an m^th stream (for a total of n=2 shown) to a relay station RS 20 which decodes and forwards them over corresponding /c"¹ streams 51 and m^th streams 52 to a destination device 30. The streams may be considered data transmitted from/received on specific antennas, or as the data carried on specific resource blocks. It is understood that either or both of the source 10 and destination 30 devices may themselves also be RSs which decode and forward the streams shown for which they transmit and receive, respectively. It is further understood that either or both of the source device 10 and the destination device 30 may be network access nodes (e.g., base transceiver station, node B, e-node B, WLAN access point, etc.). The RS 20 may be a fixed or a mobile (e.g., train mounted) relay that forms part of a hierarchical wireless network (e.g., cellular such as E-UTRAN) and operates under control of an associated network access node, or it may be a mobile terminal/user equipment that is used as a RS by the network on a case by case basis when needed. In other embodiments, the RS 20 is a node within a mesh or ad-hoc network in which there is no centralized scheduling of radio resources for the streams 41 , 42, 51 , 52 as there is a hierarchical network.

[0026] Each of the devices 10, 20, 30 shown in Fig. 1 are depicted identically and so only particulars of the RS 20 are detailed, but it is noted that similarly depicted elements of the source 10 and destination 30 are similar to those detailed for the relay device 20.

[0027] The RS 20 includes a controller, such as a computer or a data processor (DP) 2OA, a computer-readable memory medium embodied as a memory (MEM) 2OB that stores a program of computer instructions (PROG) 2OC, and a suitable radio frequency (RF) transceiver 2OD for wireless communications with the source 10 and destination 30 via one or more antennas 20E, 2OE'. A decoder 2OF decodes the signals received from the source 10 on the various streams 41 , 42 and performs an error check (e.g., a cyclic redundancy check of the data) to assure the decoding was properly done. The properly decoded data is then re-encoded at an encoder 2OG and transmitted on the streams 51 , 52 to the destination 30. In various embodiments the decoder 2OF and encoder 20G may be a part of the transceiver front end, or may be a part of the DP 10A. Further options are detailed below with reference to Fig. 10, which shows more detail of one particular embodiment of the RS.

[0028] At least one of the PROGs 2OC stored on the MEM 2OB is assumed to include program instructions that, when executed by the associated DP 2OA, enable the RS 20 to operate in accordance with the exemplary embodiments of this invention, as will be discussed below in greater detail.

[0029] That is, the exemplary embodiments of this invention may be implemented at least in part by computer software executable by the DP 2OA of the RS 20 and/or by the DP of the source 10 and/or destination 30 (particularly when they also act as RS), or by hardware, or by a combination of software and hardware (and firmware).

[0030] Below are detailed exemplary embodiments of this invention for implementing SDF in a relay system. This is seen to be quite different from the straightforward extension of 802.16j for the MIMO case, the proof being that it achieves a higher throughput. The straightforward extension of 802.16j SDF, which is assumed for Fig. 2 and detailed below, does not make use of the spatial characteristic and therefore cannot achieve the higher throughput. Higher throughput is but one technical advantage of these teachings.

[0031] As noted above, there may be two different types of networks in which the relay might be operating, one using centralized radio resource scheduling and one using distributed scheduling. Examples of the former include traditional hierarchical cellular systems (GSM, UTRAN, E-UTRAN). Examples of the latter are more varied, and include WLAN style networks where different devices may contend for radio resources (e.g., ad hoc or mesh networks, and device-to-device communications using radio resources that the devices find opportunistically when not in current use by a co-located hierarchical network). Within the broader teachings presented herein there are two distinct SDF schemes for MIMO relay, corresponding to whether the environment in which the relaying occurs employs centralized or distributed scheduling. The most pronounced advantages gained by these teachings are seen to be under the situation where the CRC detection results at the RS 20, for the signal it receives and intends to forward, have errors at some streams but are correctly decoded at other streams. Referring back to Fig. 1 , consider that the data that the RS 20 receives on the kth stream(s) 41 is correctly decoded and the data the RS 20 receives on the mth stream(s) 42 is incorrectly decoded. For the kth stream 41 which has the decoding error (CRC failure), the packet will not be forwarded by the RS 20 but instead the RS 20 will send a NACK back to the source 10 asking for re-transmission. MIMO re-construction in the RS 20 will be used among all the transmit antennas 2OE, 2OE' or resource blocks to forward the correct packets to the next RS/destination 30 according to the type of system it is operating: centralized scheduling or distributed scheduling.

[0032] For the centralized scheduling situation, where the radio resource (time /frequency resource) has been pre-allocated for the forwarding by the RS 20, space time coding (STC) is adopted in the RS's MIMO re-construction. The k received correct streams 41 will be space-time encoded among all the transmit antennas or RBs that correspond to the k correctly decoded streams 41 and to the m incorrectly decoded streams 42. In this manner transmit diversity gain can be achieved in the RS. The transmit antennas (e.g., 2OE') or RBs (e.g., stream 52) allocated to the wrong streams are used to transmit the STC version of the k correctly decoded streams 41.

[0033] For the distributed scheduling situation, multi-stream MlMO is adopted in the RS's MIMO re-construction. This means that part of the k correctly decoded streams 41 will be forwarded directly (e.g., on antenna 2OE or RBs 51 ); and the other part of the k correct streams 41 will be forwarded at other transmit antennas or RBs which correspond in the RS 20 to the wrongly decoded streams (e.g., on antenna 2OE' or RBs 52). The remaining radio resources will be allocated to other new packets, which are unrelated to the received n-stream MIMO signal received on streams 41 and 42 of Fig. 1 (e.g, they may be other signals for relay, new transmissions from the RS 20 as source, etc.).

[0034] Stated generically for both scenarios, when it is determined that from a received /7-stream multiple-input/multiple output signal, data is correctly decoded on k streams and data is incorrectly decoded on m streams, wherein n≥2, λ≤k<n and 1 ≤m<n; then the data that was correctly decoded from the k streams is encoded and forwarded on antennas or resource blocks corresponding to at least some the k streams and also on antennas or resource blocks corresponding to at least some of the m streams.

[0035] There are three cases after CRC detection for multi-streams: all streams are correct; some but not all streams are correct; and all streams are wrong. These possible cases and the corresponding forwarding methods are shown in the table below.

[0036] Table 1 : The possible forwarding cases in MIMO relay

10037] Case I and case III are not separately considered by these teachings as the RS 20 can simply use the above forwarding rules for those scenarios, which are seen to be conventional. Case Il presents a clear distinction over straightforward extensions of 802.16j. Before detailing further specifics how these teachings deal with case Il above, let us first assume how a direct extension of IEEE 802.16j might look, to more clearly illuminate the distinctions therebetween.

[0038] This straightforward extension into MIMO is shown in the flow chart at Fig. 2. For simplicity of explanation, assume the source is the BS. The assumption of MlMO RS include that it is a dual hop relay (one RS between source and destination); that the BS uses MIMO mode (multi-stream/multi-codeword MIMO), the multi-stream MIMO can occupy one or multiple resource blocks (RBs), each stream/codeword has one CRC, and there are multiple transmit and receive antennas in both the BS and the relay link.

[0039] Fig. 2 then presents a straightforward extension of 802.16j SDF as follows. At 202 the received packets in relay node go through MIMO detection firstly. The detection algorithm can be SD, QRD-M, SIC (as shown this would be pre-processing SlC), etc. At 204 decoding is used to improve the detection performance, and at 206 the CRC is detected after decoding. If the CRC detection is correct, then at 208 perform the encoding and modulation to re-generate the received packets at 210 which are sent to the destination/UE and at 212 an ACK is sent to the source BS for the correctly decoded and forwarded data if distributed scheduling is used. If instead the CRC detection at block 206 is not correct, then at 214 the RS sends null/dummy packets to the destination/UE if centralized scheduling is used, or alternatively the RS sends new/different packets to the destination/UE if distributed scheduling is used (where the new packets are not the same underlying data as the received packets which are to be decoded and forwarded). Then at 216 the RS sends a NACK to the source/BS to ask for re-transmission.

[0040] The other streams are processed similarly as stream 1 , as seen at Fig. 2. In this straightforward extension of 802.16j into MIMO, it is seen that the processing of the different streams are independent from one another.

[0041] Fig. 3 illustrates in a signaling diagram the same straightforward extension of 802.16j for the centralized scheduling scenario, and Fig. 4 illustrates the same for the distributed scheduling scenario. Data_str_1_1 represents the k streams 41 of Fig. 1 that are decoded correctly; Data_str_2_1 represents the m streams 42 of Fig. 1 that are decoded incorrectly; and Data_str_1_2 represents new data packets unrelated to the other two data streams (which is decoded correctly in these diagrams).

[0042] For the Fig. 3 centralized scheduling scenario, it is seen that Data_str_1_1 is correctly decoded and forwarded on the corresponding antenna or resource block 302, which in Fig. 1 would be antenna 12E or stream 51. Since Data_str_2_1 was not correctly decoded, a null or dummy packet is sent on the antenna or resource block corresponding to the failed decoding 304, which in Fig. 1 would be antenna 12E' or stream 52. The null packet is set because the resources are already scheduled prior to the time the RS knows the decoding of Data_str_2_1 is failed. The next burst from the BS to the RS carries the new data on Data_str_1_2 and a re-transmission of the data that failed the decoding on Data_str_2_1. The RS combines the original and re-transmission of Data_str_2_1 for better accuracy, and sends Data_str_1_2 and the combined Data_str_2_1 on corresponding antennas or resource blocks corresponding to the streams on which they were received. In each case there is a one-to-one correspondence between the stream on which data was received and the antenna/RB on which it is forwarded, and so detect failure on one stream has no effect on what is sent on other streams not corresponding to the failed stream. Fig. 4 shows the distributed scheduling, which differs from Fig. 3 in that instead of the null/dummy packet, the RB is released and the RS sends new data on it, shown as Data_str_2_2. Just as with Fig. 3, in each case there is a one-to-one correspondence between the stream on which correctly decoded data was received and the antenna/RB on which it is forwarded. [0043] Fig. 5 illustrates a flow diagram similar in structure to Fig. 2, but showing processing at the RS according to exemplary embodiments of these teachings. At block 502 the received signal in the RS 20 goes through MIMO detection at block 502. The detection algorithm can be SD, QRD-M, SIC (as shown this would be pre-processing SIC), etc. Then at block 504 decoding on each stream is used to improve the detection performance. At block 506 the CRC or other error detection code is detected after decoding.

[0044] If the CRC detections at block 506 are correct at all streams, this is case I from the table above: at block 508 perform the encoding and modulation to re-generate at block 510 the received packets which are sent to the destination/UE, and at block 512 send an ACK for those packets back to the source/BS to confirm the transmission at all streams.

[0045] If the CRC detections at block 506 are incorrect at all streams, this is case III from the table above: at block 514 send null/dummy packets to the destination/UE if centralized scheduling is used or send the new packets to the destination/UE if distributed scheduling is used (where the new packets are different from the received packets), and at block 516 send a NACK to the source/BS to ask for re-transmission at all streams.

[0046] Case Il of the above table follows the center portion of Fig. 5. If the CRC detection at block 506 is correct at some streams (e.g., k of the n streams) and incorrect at other of the streams (e.g., m of the n streams), then at block 518 the RS encodes and modulates according to the correct streams. This means that at block 520 the RS adopts multi-stream MIMO in its MIMO re-construction if distributed scheduling is used; or adopts STC in its MIMO re-construction if centralized scheduling is used. Then at block 522 the RS 20 sends the MIMO re-constructed packets to the destination/UE 30 at multiple transmit antennas or RBs. Then at block 524 the RS 20 sends to the source/BS 10 an ACK to confirm the transmission at the correct streams, and sends a NACK to the source/BS 10 to ask for re-transmission at the wrong streams.

[0047] Fig. 6 illustrates in a signaling diagram the centralized scheduling approach from Fig. 5, and Fig. 7 illustrates the in a signaling diagram the distributed scheduling approach from Fig. 5. Like Figs 3-4, Data_str_1_1 represents the k streams 41 of Fig. 1 that are decoded correctly; Data_str_2_1 represents the m streams 42 of Fig. 1 that are decoded incorrectly; and Data_str_1_2 represents new data packets unrelated to the other two data streams (which is decoded correctly in these diagrams). Consider for this example n=2 streams, in which the kth stream is decoded correctly in the RS 20 and the mth stream fails the CRC.

[0048] The centralized scenario at Fig. 6 begins with the source/BS 10 scheduling the resource blocks (RB) for all the streams and hops before it sends its transmission. The source/BS 10 transmits Data_str1_1 at stream 1 (602 of Fig 6, the kth stream, #41 at Fig. 1) and 607 Data_str2_1 at stream 2 (604 of Fig. 6, the mth stream, #42 at Fig. 1) in the first hop. The RS 20 receives the data from the source/BS 10, and detects and decodes it. The CRC is detected after the decoding. Assuming that stream 1 succeeds 602' by the CRC detection, and stream 2 fails 604', the RS 20 stores the Data_str2_1 for the combination 606 in the future.

[0049] For the second hop of the data, the RS 20 forwards Data_str1_1 at stream 1 (608 of Fig. 6), and forwards the STC version of Data_str1_1 at stream 2 (610 of Fig. 6) on the pre-scheduled resource block. The RS 20 then sends back NACK_str2_1 (612) to the source/BS 10 to ask for retransmission.

[0050] The destination/UE 30 receives the packets from the RS 20 at 608 and 610. If the CRC detection is correct, the UE 30 sends ACK_str1_1 614 to the BS 10 via the RS 20 to show the success of the transmission; if CRC has errors, the UE sends a NACK to the RS 20 to ask for re-transmission (not shown).

[0051] Now, once the source/BS 10 receives ACK_str1_1 (614), it releases the pre-allocated resource and transmits new packets, Data_str1_2 (616) at stream 1. If the BS receives NACK_str2_1 (612), it retransmits Data_str2_1 at stream 2 (618) on the pre-allocated resource block.

[0052] The RS 20 receives the data from source/BS 10 and detects it. Chase combining 606 is adopted in the combination of re-transmission of Data_str2_1 and its previous version. The combination results are decoded and detected by CRC. If the CRC detection is correct, the RS forwards to the destination/UE 30 the Data_str1_2 (618) and Data_str2_1 (618). If the CRC detection has errors, the RS 20 continue to ask for re-transmission.

[0053] The destination/UE 30 receives the packets from the RS 20. If the CRC detection is correct, the destination/UE 30 sends ACK_str1_2 (620) and ACK_str2_1 (622) to the source/BS 10 via the RS 20 to show the success of the transmission. If the CRC has errors, the destination/UE 30 sends a NACK (not shown) to the RS 20 to ask for re-transmission.

[0054] The signaling diagram of Fig. 7 is now detailed for the distributed scheduling scenario, where multi-stream is adopted in the second hop. The distributed scenario at Fig. 7 begins with the source/BS 10 scheduling the resource blocks (RB) for all the streams and the first hops before it sends its transmission. The source/BS 10 transmits Data_str1_1 at stream 1 (702 of Fig 7, the kth stream, #41 at Fig. 1) and 607 Data_str2_1 at stream 2 (704 of Fig. 7, the mth stream, #42 at Fig. 1) in the first hop. The RS 20 receives the data from the source/BS 10, and detects and decodes it. The CRC is detected after the decoding. Assuming that stream 1 succeeds 702' by the CRC detection, and stream 2 fails 704', the RS 20 sends back ACK_str1_1 (708) to the source/BS 10 to show the success of the transmission, stores the Data_str2_1 for the combination 710 in the future, and sends back NACK_str2_1 (708) to the source/BS 10 to ask for retransmission.

[0055] The RS 20 schedules the resource blocks for all the stream s and the second hop before the new packet transmission. The RS 20 forwards half of Data_str1_1 and Data_str2_2 at stream 1 (712), and the other half of Data_str1_1 and Data_str2_2 at stream 2 (714). The half of the data block occupies the half of RB. For the case where n>2, the division of the data among the RBs will depend on how many streams were correctly decoded and how many were incorrectly decoded.

[0056] Then the destination/UE 30 receives the packets from RS 20. If the CRC detection is correct, the destination/UE 30 sends ACK_str1_1(#716, for the 2^nd hop) and ACK_str2_2(#718, also for the 2^nd hop) to the RS 20 to show the success of the transmission; if CRC has errors, the destination/UE 30 sends a NACK (not shown) to the RS 20 to ask for re-transmission.

[0057] If the source/BS 10 receives ACK_str1_1 (706), it releases the pre-allocated resource and transmits Data_str1_2 (720) at stream 1. If the source/BS 10 receives NACK_str2_1 (708), it retransmits Data_str2_1 (722) at stream 2 on the pre-allocated resource block.

[0058] The RS 20 receives this data from the source/BS 10 and detects it. Chase combining 710 is adopted in the combination of re-transmission of Data_str2_1 (722) and its previous version (704). The combination results are decoded and detected by CRC. If the CRC detection is correct, the RS 20 forwards to the destination/UE 30 (at 724, 726) the Data_stιi_2 and Data_str2_1 , and sends back to the source/BS 10 (at 728, 730) ACK_str1_2 and ACK_str2_1. If the CRC detection has errors, the RS 20 continue to ask for re-transmission.

[0059] Finally, the destination/UE 30 receives the packets from the RS 20. If the CRC detection is correct, the destination/UE 30 sends ACK_str1_2(#732, for the 2^nd hop) and ACK_str2__1 (#734, for the 2^nd hop) to the RS 20 to show the success of the transmission. If instead the CRC has errors, the destination/UE 30 sends a NACK (not shown) to the RS 20 to ask for re-transmission.

[0060] Performance of the proposed schemes have been evaluated by simulation, results of which are shown at Figs. 8-9 for throughput performance. The main simulation conditions are summarized as: turbo code (3GPP R7, 1/2), QPSK, 2 transmit and 2 receive antennas, 1.5*10⁴ info bits/frame, 3GPP SCM (Case IV, single path, 3km/h), SIC detection for MIMO, iteration decoding number is 4, Chase combining, and Retransmission number is 1. The benchmarks are the straightforward extension of conventional 802.16j SDF as presented herein to MIMO, in centralized scheduling and distributed scheduling respectively. In the centralized scheduling approach, space-time block coding for two transmit antennas are adopted (see for example V. Tarokh, H. Jafarkhani and A.R. Calderbank: SPACE-TIME BLOCK CODES FROM ORTHOGONAL DESIGNS (IEEE Transactions on Information Theory 1999, 45(5): 1456 - 1469). In the distributed scheduling approach, multi-stream MIMO are adopted.

[0061] In Fig. 8, SNR1>SNR2 (SNR1 is BS to RS; SNR2 is RS to UE). Specifically, SNR2=SNR1-4dB. The performance of the total system mainly depends on the SNR of the second hop. In low SNR, the throughput performance of the centralized scheduling solution is better than that of the distributed scheduling solution. In high SNR, throughput performance of the distributed scheduling solution is better than that of the centralized scheduling solution. Both of the solutions have better performance than the conventional SDF in centralized scheduling and distributed scheduling respectively. For example, compared to the conventional SDF in centralized scheduling, the centralized scheduling solution has 3dB improvement at 1.6b/s/Hz; compared to the conventional SDF in distributed scheduling, the distributed scheduling solution has 0.5dB improvement at 1.6b/s/Hz.

[0062] In Fig. 9, SNR1<SNR2 (specifically, SNR2=SNR1-4dB). The performance of the total system mainly depends on the SNR of the first hop. In low SNR, the throughput performance of the centralized scheduling solution is better than that of the distributed scheduling solution. In high SNR, throughput performance of the distributed scheduling solution is better than that of the centralized scheduling solution. Both of the solutions have better performance than the conventional SDF in centralized scheduling and distributed scheduling respectively. For example, compared to the conventional SDF in centralized scheduling, the centralized scheduling solution has nearly 3dB improvement at 1.6b/s/Hz; compared to the conventional SDF in distributed scheduling, the distributed scheduling solution has 0.5dB improvement at 1.6b/s/Hz.

[0063] As can be seen from the details provided above, certain embodiments of the invention offer one or more of the following technical advantages:

• forwarding performance is improved by providing diversity gain when some of the streams can be forwarded directly, and the others ask for re-transmission

• especially in centralized scheduling, a large performance improvement can be achieved, and full use of the resources allocated to the wrong streams is made;

• no additional resources are needed, and signaling overhead is same as the conventional SDF presented herein

[0064] It is noted that the STC combining in the destination 30 for the centralized scheduling solution is not seen to greatly increase complexity of the destination's process.

[0065] Further to the high level diagrams of Fig. 1 , reference is now made to Figure 10 for illustrating a more detailed schematic diagram of a RS 20 which may be embodied as a UE/mobile terminal 110. In general, the various UE embodiments of the RS can include, but are not limited to, cellular telephones, personal digital assistants (PDAs) having wireless communication capabilities, portable computers having wireless communication capabilities, gaming devices having wireless communication capabilities, Internet appliances permitting wireless Internet access and browsing, as well as portable units or terminals that incorporate combinations of such functions.

[0066] Note that while Fig. 10 is illustrated as a UE, the relay embodying the invention as detailed herein is not limited to a UE but may also be a relay operating under control of one or multiple networks. A relay station embodying these teachings may be embodied as a multihop relay base station, a micro base station, or an enhanced UE, which is a generalized equipment set providing connectivity to other relay stations or subscriber stations (SSs/UEs). The relay station may be fixed in location (i.e. attached to a building or tower) or, in the case of an access relay station, it may be mobile (i.e. traveling with a transportation vehicle or a mobile terminal). See for example IEEE P802.16J/D6 PART 16 and 3GPP R1-083712 'FURTHER DETAILS AND CONSIDERATIONS OF DIFFERENT TYPES OF RELAYS' for various forms the relay station may take.

[0067] The computer readable MEMs 2OB shown at Fig. 1 may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor based memory devices, flash memory, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. The DPs 2OA may be of any type suitable to the local technical environment, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on a multicore processor architecture, as non-limiting examples.

[0068] At Figure 10 the UE 110 has a graphical display interface 120 and a user interface 122 illustrated as a keypad but understood as also encompassing touch-screen technology at the graphical display interface 120 and voice-recognition technology received at the microphone 124. A power actuator 126 controls the device being turned on and off by the user. The exemplary UE 110 may have a camera 128 which is shown as being forward facing (e.g., for video calls) but may alternatively or additionally be rearward facing (e.g., for capturing images and video for local storage). The camera 128 is controlled by a shutter actuator 130 and optionally by a zoom actuator 130 which may alternatively function as a volume adjustment for the speakers ) 134 when the camera 128 is not in an active mode.

[0069] Within the sectional view of Fig. 10 are seen multiple transmit/receive antennas 136 that are typically used for wireless communication. The antennas 136 may be multi-band for use with other radios in the UE 110. The operable ground plane for the antennas 136 is shown by shading as spanning the entire space enclosed by the UE housing though in some embodiments the ground plane may be limited to a smaller area, such as disposed on a printed wiring board on which the power chip 138 is formed. The power chip 138 controls power amplification on the channels being transmitted and/or across the antennas that transmit simultaneously where spatial diversity is used, and amplifies the received signals. The power chip 138 outputs the amplified received signal to the radio-frequency (RF) chip 140 which demodulates and downconverts the signal for baseband processing. The baseband (BB) chip 142 detects the signal which is then converted to a bit-stream and finally decoded. Similar processing occurs in reverse for signals generated in the apparatus 10 and transmitted from it.

[0070] Signals to and from the camera 128 pass through an image/video processor 144 which encodes and decodes the various image frames. A separate audio processor 146 may also be present controlling signals to and from the speakers 134 and the microphone 124. The graphical display interface 120 is refreshed from a frame memory 148 as controlled by a user interface chip 150 which may process signals to and from the display interface 120 and/or additionally process user inputs from the keypad 122 and elsewhere.

[0071] Certain embodiments of the UE 110 may also include one or more secondary radios such as a wireless local area network radio WLAN 137 and a Bluetooth® radio 139, which may incorporate an antenna on-chip or be coupled to an off-chip antenna. Throughout the apparatus are various memories such as random access memory RAM 143, read only memory ROM 145, and in some embodiments removable memory such as the illustrated memory card 147 on which the various programs 10C are stored. All of these components within the UE 110 are normally powered by a portable power supply such as a battery 149.

[0072] The aforesaid processors 138, 140, 142, 144, 146, 150, if embodied as separate entities in a UE 110 or other type of RS 20, may operate in a slave relationship to the main processor 2OA, which may then be in a master relationship to them. Embodiments of this invention are most relevant to the baseband chip 142 which may or may not access either or both of the RAM 143 and ROM 145, depending on the design of the apparatus operating as the relay.

[0073] It is noted that other embodiments need not be disposed at the baseband chip 142 but may be disposed across various chips and memories as shown or disposed within another processor that combines some of the functions described above for Figure 10. Any or all of these various processors of Fig. 10 access one or more of the various memories, which may be on-chip with the processor or separate therefrom. Similar function-specific components that are directed toward communications over a network broader than a piconet (e.g., components 136, 138, 140, 142-145 and 147) may also be disposed in exemplary embodiments of the source device 10 and/or destination device 30.

[0074] Note that the various chips (e.g., 138,140, 142, etc.) that were described above may be combined into a fewer number than described and, in a most compact case, may all be embodied physically within a single chip.

[0075] Figure 11 is a logic flow diagram that illustrates the operation of a method, and a result of execution of computer program instructions, in accordance with the exemplary embodiments of this invention. In accordance with these exemplary embodiments a method performs, at block 1102, the RS (or one or more components thereof) determines that from a received n-stream multiple-input/multiple output signal, data is correctly decoded on k streams and data is incorrectly decoded on m streams. At block 1104 the RS 20 (or one or more components thereof) encodes and forwards the data that was correctly decoded from the k streams on antennas or resource blocks corresponding to at least some the k streams and also on antennas or resource blocks corresponding to at least some of the m streams.

[0076] Block 1106 gives further detail of block 1104 for the centralized scheduling case detailed above: space-time encode the data that was correctly decoded from the k streams among all the transmit antennas or RBs that correspond to the k streams on which the data was correctly decoded, and among all the transmit antennas or RBs that correspond to the m streams on which the data was incorrectly decoded.

[0077] Block 1108 gives further detail of block 1104 for the distributed scheduling case detailed above: encode and forward a first portion of the data that was correctly decoded from the k streams on antennas or resource blocks corresponding to the k streams on which the data was correctly decoded, and encode and forward a second portion of the data that was correctly decoded from the k streams on antennas or resource blocks corresponding to the m streams on which the data was incorrectly decoded.

[0078] The various blocks shown in Figure 11 may be viewed as method steps, and/or as operations that result from operation of computer program code, and/or as a plurality of coupled logic circuit elements constructed to carry out the associated function(s). [0079] In general, the various exemplary embodiments may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. For example, some aspects may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device, although the invention is not limited thereto. While various aspects of the exemplary embodiments of this invention may be illustrated and described as block diagrams, flow charts, or using some other pictorial representation, it is well understood that these blocks, apparatus, systems, techniques or methods described herein may be implemented in, as nonlimiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

[0080] It should thus be appreciated that at least some aspects of the exemplary embodiments of the inventions may be practiced in various components such as integrated circuit chips and modules, and that the exemplary embodiments of this invention may be realized in an apparatus that is embodied as an integrated circuit. The integrated circuit, or circuits, may comprise circuitry (as well as possibly firmware) for embodying at least one or more of a data processor or data processors, a digital signal processor or processors, baseband circuitry and radio frequency circuitry that are configurable so as to operate in accordance with the exemplary embodiments of this invention.

[0081] Various modifications and adaptations to the foregoing exemplary embodiments of this invention may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings. However, any and all modifications will still fall within the scope of the non-limiting and exemplary embodiments of this invention.

[0082] It should be noted that the terms "connected," "coupled," or any variant thereof, mean any connection or coupling, either direct or indirect, between two or more elements, and may encompass the presence of one or more intermediate elements between two elements that are "connected" or "coupled" together. The coupling or connection between the elements can be physical, logical, or a combination thereof. As employed herein two elements may be considered to be "connected" or "coupled" together by the use of one or more wires, cables and/or printed electrical connections, as well as by the use of electromagnetic energy, such as electromagnetic energy having wavelengths in the radio frequency region, the microwave region and the optical (both visible and invisible) region, as several non-limiting and non-exhaustive examples.

[0083] Furthermore, some of the features of the various non-limiting and exemplary embodiments of this invention may be used to advantage without the corresponding use of other features. As such, the foregoing description should be considered as merely illustrative of the principles, teachings and exemplary embodiments of this invention, and not in limitation thereof.

Claims

CLAIMS:What is claimed is:

1. A method, comprising: determining that from a received n-stream multiple-input/multiple output signal, data is correctly decoded from k streams of the signal and data is incorrectly decoded from m streams of the signal, wherein n≥2, 1≤/c</7 and ϊ≤nrKn; and encoding and forwarding the data that was correctly decoded from the k streams on transmit antennas or resource blocks corresponding to at least some the k streams and also on transmit antennas or resource blocks corresponding to at least some of the m streams.

2. The method of claim 1 , wherein encoding and forwarding the data comprises space-time encoding the data that was correctly decoded from the k streams among all the transmit antennas or resource blocks that correspond to the k streams on which the data was correctly decoded and among at least some of the transmit antennas or resource blocks that correspond to the m streams on which the data was incorrectly decoded.

3. The method of claim 2, wherein the said at least some of the transmit antennas or resource blocks that correspond to the m streams on which the data was incorrectly decoded comprise all the transmit antennas or resource blocks that correspond to the m streams on which the data was incorrectly decoded.

4. The method of any one of claims 1 , 2 or 3, executed by a relay device that receives the n-stream multiple-input/multiple output signal, and wherein radio resources for forwarding the data are scheduled prior to when the relay device receives the n-stream multiple-input/multiple output signal.

5. The method of claim 1 , wherein encoding and forwarding the data comprises: encoding and forwarding a first portion of the data that was correctly decoded from the k streams on antennas or resource blocks corresponding to the k streams on which the data was correctly decoded; and encoding and forwarding a second portion of the data that was correctly decoded from the k streams on antennas or resource blocks corresponding to the m streams on which the data was incorrectly decoded.

6 The method of claim 5, wherein encoding and forwarding comprises spreading the data that was correctly decoded from the k streams equally among the antennas or resource blocks corresponding to the k streams and among the antennas or resource blocks corresponding to the m streams.

7. The method of any one of claims 1 , 5 or 6, executed by a relay device that receives the n-stream multiple-input/multiple output signal, and wherein radio resources for forwarding the data are not scheduled prior to when the relay device receives the n-stream multiple-input/multiple output signal.

8. A computer readable memory storing a program executable by a processor to perform actions comprising: determining that from a received /7-stream multiple-input/multiple output signal, data is correctly decoded from k streams of the signal and data is incorrectly decoded from m streams of the signal, wherein n≥2, λ≤k<n and 1≤m<n; and encoding and forwarding the data that was correctly decoded from the k streams on transmit antennas or resource blocks corresponding to at least some the k streams and also on transmit antennas or resource blocks corresponding to at least some of the m streams.

9. The computer readable memory of claim 9, wherein encoding and forwarding the data comprises space-time encoding the data that was correctly decoded from the k streams among all the transmit antennas or resource blocks that correspond to the k streams on which the data was correctly decoded and among at least some of the transmit antennas or resource blocks that correspond to the m streams on which the data was incorrectly decoded.

10. The computer readable memory of claim 9, wherein the said at least some of the transmit antennas or resource blocks that correspond to the m streams on which the data was incorrectly decoded comprise all the transmit antennas or resource blocks that correspond to the m streams on which the data was incorrectly decoded.

11. The computer readable memory of claim 8, wherein encoding and forwarding the data comprises: encoding and forwarding a first portion of the data that was correctly decoded from the k streams on antennas or resource blocks corresponding to the k streams on which the data was correctly decoded; and encoding and forwarding a second portion of the data that was correctly decoded from the k streams on antennas or resource blocks corresponding to the m streams on which the data was incorrectly decoded.

12 The computer readable memory of claim 11 , wherein encoding and forwarding comprises spreading the data that was correctly decoded from the k streams equally among the antennas or resource blocks corresponding to the k streams and among the antennas or resource blocks corresponding to the m streams.

13. An apparatus comprising a processor configured to determine, from a received n-stream multiple-input/multiple output signal, that data is correctly decoded from k streams of the signal and that data is incorrectly decoded from m streams of the signal, wherein n≥2, λ ≤k<n and 1<m<n; and an encoder configured to encode and forward the data that was correctly decoded from the k streams on transmit antennas or resource blocks corresponding to at least some the k streams and also on transmit antennas or resource blocks corresponding to at least some of the m streams.

14. The apparatus of claim 13, wherein the encoder is configured to encode and forward the data by space-time encoding the data that was correctly decoded from the k streams among all the transmit antennas or resource blocks that correspond to the k streams on which the data was correctly decoded and among at least some of the transmit antennas or resource blocks that correspond to the m streams on which the data was incorrectly decoded.

15. The apparatus of claim 14, wherein the said at least some of the transmit antennas or resource blocks that correspond to the m streams on which the data was incorrectly decoded comprise all the transmit antennas or resource blocks that correspond to the m streams on which the data was incorrectly decoded.

16. The apparatus of any one of claims 13, 14 or 15, further comprising a receiver configured to receive the /7-stream multiple-input/multiple output signal, and wherein radio resources for forwarding the data are scheduled prior to when the apparatus receives the n-stream multiple-input/multiple output signal.

17. The apparatus of claim 13, wherein the encoder is configured to encode and forward the data by: encoding and forwarding a first portion of the data that was correctly decoded from the k streams on antennas or resource blocks corresponding to the k streams on which the data was correctly decoded; and encoding and forwarding a second portion of the data that was correctly decoded from the k streams on antennas or resource blocks corresponding to the m streams on which the data was incorrectly decoded.

18. The apparatus of claim 17, the encoder is configured to encode and forward the data by spreading the data that was correctly decoded from the k streams equally among the antennas or resource blocks corresponding to the k streams and among the antennas or resource blocks corresponding to the m streams.

19. The apparatus of any one of claims 13, 17 or 18, further comprising a receiver configured to receive the n-stream multiple-input/multiple output signal, and wherein radio resources for forwarding the data are not scheduled prior to when the apparatus receives the n-stream multiple-input/multiple output signal.