WO2013158017A2 - Retransmission handling for dual-stream mimo - Google Patents

Description

RETRANSMISSION HANDLING FOR DUAL-STREAM MIMO

RELATED APPLICATIONS

This application claims the benefit of and priority to U.S. Provisional Application Serial No. 61/635,546, filed 19 April 2012. The entire contents of said U.S. Provisional Application are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates generally to wireless communication systems that support Multiple-Input Multiple-Output (MFMO) transmission techniques, and more particularly relates to the handling of retransmissions in such systems.

BACKGROUND

The 3 -Generation Partnership Project (3 GPP) is continuing to improve support for highspeed uplink data in Universal Mobile Telecommunications System (UMTS) networks. High- Speed Uplink Packet Access (HSUPA) was first standardized in Release 6 of the 3 GPP specifications. As of Release 7 of the 3GPP specifications, higher data rates via HSUPA were enabled by the support of 16-QAM (Quadrature Amplitude Modulation). Work continues to increase HSUPA data rates even higher, through the improved support of higher-order modulation and by the introduction of multiple-input multiple-output (MFMO) transmissions, more specifically through the support of 64QAM over dual-stream uplink transmission.

To introduce HSUPA MIMO with 64QAM, procedures for handling retransmissions and Hybrid Automatic Repeat Request (HARQ) signaling must be standardized.

HARQ processing in HSUPA exploits the fact that the received signal for a given data packet contains useful information even if the packet was decoded incorrectly. This information can be utilized by HARQ processing with soft combining. In HARQ with soft combining, received signal information for the erroneously received packet is stored in a buffer memory and later combined with one or more retransmissions, to obtain a single combined packet that is more reliable than its constituents. If decoding of a received packet fails, which can be determined via the use of a cyclic redundancy check (CRC), a retransmission is requested. A single bit is signaled from the NodeB to the UE to indicate successful decoding (ACK) or to request a retransmission (NACK).

Uplink Hybrid ARQ functionality is built on a synchronous, non-adaptive operation. Uplink retransmissions follow a deterministic pattern and occur a predefined time after the initial transmission. This means that the UE and the NodeB both know which HARQ process is targeted at any given transmission time interval (TTI). Retransmissions usually take place either six or eight subframes after the prior transmission attempt for the same HARQ process. The exact timing depends on the number of HARQ processes that are configured.

Non-adaptive HARQ operation implies that the transport format and the redundancy version to be used for each of the retransmissions are known from the time of the original transmission. Retransmitted bits (the coding of which is controlled via the redundancy version) consist of either the same bits as in the prior transmission or a new set of bits based on the same set of information bits, depending on whether Chase-Combining or Incremental Redundancy soft combining is used. Uplink HARQ information (i.e., the Retransmission Sequence Number, or RSN) is transmitted on the E-DCH Dedicated Physical Control Channel (E-DPCCH), and downlink HARQ information (i.e., ACK/NACK) is transmitted from the NodeB to the UE on the E-DCH Hybrid Indicator Channel (E-HICH).

When HSUPA for MIMO is introduced, the HARQ and retransmission procedures described above are complicated by the number of possible transmission scenarios that exist for dual-stream MIMO transmission. To support dual-stream uplink transmission, these procedures must account for the fact that one or several layers may be transmitted during any given transmission time interval, and that one, several, or none of these layers may be successfully received.

Retransmission procedures and HARQ signaling for several of these transmission scenarios have already been agreed, but open cases still exist. One of the remaining questions is whether it should be possible (i.e., permitted by the standard) to use rank-1 transmission (i.e., a one-layer transmission) to re-submit an originally rank-2 transmission if the data for only one of the streams needs to be retransmitted, i.e., if a previous rank-2 transmission resulted in the receipt of a HARQ acknowledgement (ACK) for one stream and a HARQ negative

acknowledgement (NACK) for the other. If it is agreed that rank-1 transmissions may be used in such cases (or in some of these cases), then a mechanism is needed for indicating to the base station (a "NodeB," in 3GPP terminology) which stream is being re-submitted. In fact, what is needed is a mechanism that ensures that both the user terminal ("user equipment," or "UE," in 3GPP terminology) and the NodeB know which HARQ process is used, so that the correct soft combining buffer is used.

In essence, some form of HARQ process identification is needed in these situations. Note that a similar problem arose in the downlink when 2x2 MIMO was introduced in Release 7 of the 3GPP specifications. One possible approach is to add an explicit process identifier to retransmissions in these situations. However, adding an explicit HARQ identity to the existing HARQ process numbers would require changes to the uplink (UL) and downlink (DL) control channel structures, the E-DCH Dedicated Physical Control Channel (E-DPCCH) and the E-DCH Hybrid Indicator Channel (E-HICH), which is undesirable.

SUMMARY

Hybrid Automatic Repeat Request (HARQ) and retransmission procedures need to be developed for certain special cases that can occur when multi-stream transmission is supported in a wireless system, such as the High-Speed Uplink Packet Access (HSUPA) systems standardized by the 3 -Generation Partnership Project (3GPP). One example of such a special case is when the secondary stream of an original rank-2 transmission needs to be retransmitted, but only one stream can be transmitted, because the preferred (or permitted) transmission rank has changed to rank-1. Several different alternatives for the retransmission handling can be envisioned.

In the detailed description that follows, techniques for allowing stream switches due to retransmissions without adding an explicit HARQ identity are described. More particularly, the techniques described below provide a mechanism that allows retransmissions to switch stream (e.g., retransmit original stream2 data on stream 1) without any need to introduce a HARQ identity number and hence without the need to change the control channel structures.

Embodiments of the disclosed techniques included methods suitable for implementation by wireless transceivers, e.g., in mobile terminals and/or radio base stations. An example method begins with the simultaneous sending of first and second data packets, in respective first and second MIMO streams of a rank-2 transmission. In some embodiments the first stream is a primary stream, transmitted according to a primary precoding vector, the second stream is a secondary stream, transmitted according to a secondary precoding vector, and the retransmission of the second data packet uses the primary precoding vector. In other embodiments and/or instances, the opposite mapping of first and second streams to the secondary and primary streams may be applicable.

The example method continues with the transmission of corresponding control data for each of the first and second streams, using first and second associated control channels, respectively. The first and second associated control channels are distinguishable by their respective mappings to the transmitted signal. For example, in some embodiments the first and second associated control channels are I/Q multiplexed, with the first and second associated control channels mapped to an in-phase branch and a quadrature branch of the transmitted signal, respectively.

The method continues with the receiving of HARQ data indicating that the first data packet (carried by the first stream) was successfully decoded, while the second data packet (carried by the second stream) was not. In response, the wireless transceiver retransmits the second data packet in a single stream of a rank-1 MIMO transmission, and transmits corresponding control data for the single stream using the second associated control channel.

In some embodiments, the rank-2 and rank-1 MIMO transmissions are E-DCH Dedicated Physical Data Channel (E-DPDCH) transmissions in a High-Speed Uplink Packet Access (HSUPA) system and the first and second associated control channels is an E-DCH Dedicated Physical Control Channel (E-DPCCH) or a Secondary E-DCH Dedicated Physical Control Channel (S-E-DPCCH).

Another example method corresponds to the method summarized above, but is carried out by a wireless transceiver receiving a multi-stream transmission. This example method thus begins with the simultaneous receiving of first and second data packets, in respective first and second MIMO streams of a rank-2 transmission. The method continues with the receiving of corresponding control data for each of the first and second streams, using first and second associated control channels, respectively. Again, the first and second associated control channels are distinguishable by their respective mappings to the transmitted signal. The method continues, in response to a successful decoding of the first data packet and an unsuccessful decoding of the second data packet, with the transmission of HARQ data indicating that the first data packet (carried by the first stream) was successfully decoded, while the second data packet (carried by the second stream) was not. The wireless transceiver then receives a retransmission of the second data packet in a single stream of a rank-1 MIMO transmission. The wireless transceiver also determines that corresponding control data for the single stream has been sent using the second associated control channel. Because the second associated control channel was used, the wireless transceiver knows that the retransmitted data packet corresponds to the data packet originally transmitted on the second stream of the earlier rank-2 transmission. The wireless transceiver then maps the retransmitted data packet to a HARQ buffer associated with the second data packet.

Another example method, also implemented by a wireless transceiver that receives a multi-stream MIMO transmission, begins with receiving a rank-2 MIMO transmission, the rank- 2 MIMO transmission comprising a first data packet transmitted via a first stream and a second data packet transmitted via a second stream. In response to a successful decoding of the first data packet and an unsuccessful decoding of the second data packet, the wireless transceiver transmits an ACK on a first indicator channel and transmits a NACK on a second indicator channel. The first and second indicator channels correspond to the first and second streams, respectively. In some embodiments, the first and second indicator channels are encoded using first and second signature sequences, respectively, or first and second orthogonal variable spreading factor (OVSF) codes, respectively. The wireless transceiver subsequently receives a retransmitted data packet in a single stream of a rank-1 MIMO transmission. After determining that the retransmitted data packet corresponds to the second data packet, the wireless transceiver transmits an ACK or NACK corresponding to the retransmitted data packet. This ACK or NACK is transmitted using the second indicator channel, because the retransmitted packet corresponds to a packet that was originally transmitted on the second stream.

Still another example method corresponds to the method summarized immediately above, but is implemented by a wireless transceiver that is transmitting the MIMO transmissions. This example method begins with transmitting a rank-2 MIMO transmission that comprises a first data packet transmitted via a first stream and a second data packet transmitted via a second stream. The wireless transceiver subsequently receives an ACK on a first indicator channel and receives a NACK on a second indicator channel. The first and second indicator channels correspond to the first and second streams, respectively. Again, in some embodiments, the first and second indicator channels are encoded using first and second signature sequences, respectively, or first and second orthogonal variable spreading factor (OVSF) codes,

respectively. In response to the NACK, the wireless transceiver then retransmits the second data packet in a single stream of a rank-1 MIMO transmission. The wireless transceiver subsequently receives an ACK or NACK corresponding to the retransmitted data packet. This ACK or NACK is received over the second indicator channel, because the retransmitted packet corresponds to a packet that was originally transmitted on the second stream.

Other embodiments of the presently disclosed techniques include apparatus

corresponding to the methods described above, including wireless transceiver apparatus adapted to carry out one or more of the methods summarized above, and variants thereof. Of course, the techniques, systems, and apparatus described herein are not limited to the above features and advantages. Indeed, those skilled in the art will recognize additional features and advantages upon reading the following detailed description, and upon viewing the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates precoding of two streams of data for multiple-input multiple-output (MFMO) transmission.

Figure 2 is a table illustrating several ACK/NACK scenarios for dual-stream

transmissions.

Figure 3 is a signal flow diagram illustrating an example technique for retransmission handling.

Figure 4 is a process flow diagram illustrating an example method for retransmission handling. Figure 5 is a process flow diagram illustrating another example method for retransmission handling.

Figure 6 is a process flow diagram illustrating another example method for

retransmission handling.

Figure 7 is a process flow diagram illustrating still another example method for retransmission handling.

Figure 8 is a block diagram illustrating components of an example wireless transceiver.

DETAILED DESCRIPTION

In the discussion that follows, specific details of particular embodiments of the presently disclosed techniques and apparatus are set forth for purposes of explanation and not limitation. It will be appreciated by those skilled in the art that other embodiments may be employed apart from these specific details. Furthermore, in some instances detailed descriptions of well-known methods, nodes, interfaces, circuits, and devices are omitted so as not to obscure the description with unnecessary detail. Those skilled in the art will appreciate that the functions described may be implemented in one or in several nodes. Some or all of the functions described may be implemented using hardware circuitry, such as analog and/or discrete logic gates interconnected to perform a specialized function, ASICs, PLAs, etc. Likewise, some or all of the functions may be implemented using software programs and data in conjunction with one or more digital microprocessors or general purpose computers. Where nodes that communicate using the air interface are described, it will be appreciated that those nodes also have suitable radio

communications circuitry. Moreover, the technology can additionally be considered to be embodied entirely within any form of computer-readable memory, including non-transitory embodiments such as solid-state memory, magnetic disk, or optical disk containing an appropriate set of computer instructions that would cause a processor to carry out the techniques described herein.

Hardware implementations may include or encompass, without limitation, digital signal processor (DSP) hardware, a reduced instruction set processor, hardware (e.g., digital or analog) circuitry including but not limited to application specific integrated circuit(s) (ASIC) and/or field programmable gate array(s) (FPGA(s)), and (where appropriate) state machines capable of performing such functions.

In terms of computer implementation, a computer is generally understood to comprise one or more processors or one or more controllers, and the terms computer, processor, and controller may be employed interchangeably. When provided by a computer, processor, or controller, the functions may be provided by a single dedicated computer or processor or controller, by a single shared computer or processor or controller, or by a plurality of individual computers or processors or controllers, some of which may be shared or distributed. Moreover, the term "processor" or "controller" also refers to other hardware capable of performing such functions and/or executing software, such as the example hardware recited above.

References throughout the specification to "one embodiment" or "an embodiment" mean that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the present invention. Thus, the appearance of the phrases "in one embodiment" or "in an embodiment" in various places throughout the specification are not necessarily all referring to the same embodiment. Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.

3 GPP has released a technical report describing the findings of extensive studies regarding the potential benefits and possible solutions for extending HSUPA to support 64QAM for MIMO transmissions. This report, 3 GPP TR 25.871, vl 1.0.0 (2011-09), available at www.3gpp.org, describes the findings of these studies. After completing this study, 3GPP agreed to adopt a structure for uplink MIMO that uses two independent transport blocks, with no interleaving across streams. It was further agreed that there is one ACK/NACK per transport block, which effectively doubles the number of HARQ processes. Also, it was proposed to use the E-HICH (E-DCH Hybrid-Indicator Channel) to convey two HARQ-ACKs in the downlink, in response to two-stream uplink transmissions, by assigning two distinct signatures to each MIMO-capable UE. (As noted above, E-HICH is a downlink control channel carrying ACKs and NACKs corresponding to uplink transport blocks previously received by the NodeB.) Hence, one signature is used to convey the HARQ-ACK for stream one, while another signature is used to convey the HARQ-ACK for stream two. Accordingly, a UE that supports dual-stream HSUPA transmissions must maintain both primary and secondary HARQ processes for rank-2 transmission, thus it will be appreciated that there are two distinct HARQ processes associated with each TTI for MIMO transmission.

3GPP also agreed to introduce an additional uplink data control channel associated with the secondary stream, i.e., a channel referred to as a Secondary E-DCH Dedicated Physical Control Channel (S-E-DPCCH). This S-E-DPCCH, which augments the existing E-DPCCH, is only transmitted during rank-2 transmissions, and carries information related to the secondary data stream (S-E-DPDCH), including a 2-bit Retransmission Sequence Number (RSN) and a 7- bit E-DCH Transport Format Combination Indicator.

Uplink MFMO in HSUPA uses a pre-coded channel structure, meaning that the primary stream is pre-coded with a primary pre-coding vector and the secondary stream is pre-coded using a secondary precoding vector. Single stream (rank-1) transmissions using the primary stream are pre-coded using the primary precoding vector, whereas dual stream (rank2) transmissions use both the primary and the secondary pre-coding vectors. Figure 1 illustrates the layer mapping of first and second data streams (si and s2) to pre-coded layers that are simultaneously transmitted by both antennas. Stream 1 data is mapped to antennas 1 and 2 by applying a primary pre-coding vector (wl and w2), while stream 2 is mapped to antennas 1 and 2 with a secondary precoding vector (w3 and w4). Accordingly, antenna 1 transmits wl sl + w3 s2, while antenna 2 transmits w2 sl + w4-s2. Assuming the channel conditions are sufficient to support a rank-2 transmission and that the precoding vectors are properly selected, the receiving NodeB is able to separate the streams and recover the data packet corresponding to each stream.

Encoded user data as carried by the primary stream is denoted E-DPDCH (E-DCH Dedicated Physical Data Channel), which has an associated control channel E-DPCCH (E-DCH Dedicated Physical Control Channel). The data on the secondary stream is denoted S-E- DPDCH, which has an associated control channel S-E-DPCCH. The E-DPCCH and S-E- DPCCH are used to transmit control channel data associated with the E-DPDCH and S-E-

DPDCH, respectively. The NodeB can distinguish between the E-DPCCH and the S-E-DPCCH by their respective mappings to the underlying structure of the uplink signal, which differ in a predictable manner. It is currently anticipated that the E-DPCCH and S-E-DPCCH,

corresponding to the primary and secondary streams, respectively, are I/Q multiplexed, with the E-DPCCH mapped to the I-branch of the signal and the S-E-DPCCH (when present) mapped to the Q-branch. The actual details of the mappings of the E-DPCCH and S-E-DPCCH to the uplink signal may ultimately differ, however; the relevant issue for the present techniques is that the NodeB is able to distinguish between an E-DPCCH and an S-E-DPCCH, even if only one is transmitted at a particular time.

Note that both of the associated control channels (E-DPCCH and S-E-DPCCH) are transmitted from the primary stream, i.e., using the primary pre-coding vector. The primary stream has, in general, a better signal quality than the secondary stream, since it utilizes the stronger eigenmode of the channel. In addition, the primary stream has a more predictable signal quality, since it is power controlled.

With the introduction of uplink MIMO, several questions related to retransmission handling need to be considered. 3 GPP has identified a number of cases, and has agreed to solutions for some of these cases. However, solutions for several cases were not agreed upon during initial meetings, and were left for further study. Figure 2 shows a summary of the identified cases and those that were agreed upon or left open for further study. Those cases left open for further study are indicated by "FFS" in the illustrated table. Generally speaking, the open cases involve situations where a first transmission was a rank-2 transmission and only one of the two transmitted transport blocks was successfully received. Solutions for these open cases are needed.

One possible approach is to use rank-2 for the retransmission, despite that the preferred rank has changed to rank-1, and retransmit the secondary stream on the same stream as before. With this approach, new data could be sent on the primary stream. Instead of new data on the primary stream, one could also consider transmitting the old ACKed primary stream data, dummy data, or even another instance of the secondary stream data. Another alternative is to retransmit the NACK'ed data on the primary stream, using rank-1. In this case, the UE would need to inform the NodeB that it is transmitting data on the primary stream that was sent originally on the secondary stream, so that the NodeB knows which HARQ buffer to use for soft combining.

In the discussion that follows, techniques for allowing stream switches due to

retransmissions without adding an explicit HARQ identity is described. More particularly, the techniques described below provide a mechanism that allows retransmissions to switch stream (e.g., retransmit original stream 2 data on stream 1) without the need to introduce a HARQ identity number and hence without the need to change the control channel structures.

A key feature of several embodiments of the presently disclosed techniques is that a UE is adapted to signal which stream from an earlier rank-2 transmission is being retransmitted via the presence of a particular associated E-DPCCH (E-DPCCH or S-E-DPCCH).

As noted above, the techniques described herein provide a mechanism that allows retransmissions to switch stream (e.g., retransmit original stream 2 data on stream 1) without the need to introduce a HARQ identity number and hence without the need to change the control channel structures. In several embodiments of these techniques, the stream from an earlier rank- 2 transmission that is retransmitted in a rank-1 retransmission is implicitly signaled to the NodeB via the associated control channel E-DPCCH (E-DPCCH or S-E-DPCCH) that is transmitted along with the retransmission. Thus, if data originally transmitted on the primary stream is being retransmitted, then the E-DPCCH is used with the retransmission. If data originally transmitted on the secondary stream is being re-transmitted, then the S-E-DPCCH is used as the control channel, instead. In essence, primary HARQ processes are coupled to the E-DPCCH, while all secondary HARQ processes are coupled to the S-E-DPCCH. Of course, the opposite association might be used, provided that both ends of the link understand the association.

This approach is applicable for rank-1 retransmissions of data that was originally transmitted via a rank-2 transmission. During rank-2 transmissions (whether original or retransmissions), the approach is not directly applicable. One particular instance when the basic technique described above is useful is Case 5 in Figure 2. Here, an initial transmission has occurred in Rank 2 and stream 1 is successfully decoded (signaled by an ACK). However, the stream 2 decoding has failed (signaled by a NACK). According to the approach described above, the initial transmission includes two streams, with the E-DPCCH associated with the primary stream data and the S-E-DPCCH associated with the secondary stream data. The NodeB decodes the primary stream successfully, while the decoding of the secondary stream fails. Hence, the NodeB signals an ACK on E- HICH1 and a NACK on E-HICH2. For the retransmission the UE then uses rank-1 and retransmits the failed packet (which originally was sent on stream 2) on the only (primary) stream of the rank-1 transmission, using S-E-DPCCH as the associated control channel.

The NodeB then detects only one E-DPCCH, namely the S-E-DPCCH. The NodeB thus knows that it is a rank-1 transmission, which generally means that the data will come on the primary stream (but see below). Because the NodeB detects the S-E-DPCCH, however, it knows that the data originally was transmitted on the secondary stream, meaning that it knows which soft buffer to use for decoding the data. The NodeB then transmits an acknowledgment. By default, a rank-1 transmission is acknowledged using E-HICH1. As described next, it is also possible to associate the E-HICH used to acknowledge a retransmission with the stream originally used to transmit the data. In this case, as detailed below, the acknowledgement of the re-transmission would take place on the E-HICH2, which is associated with S-E-DPCCH.

Thus, a similar approach can be applied to the downlink signaling information, e.g., by coupling the E-DPCCH to an associated E-HICH. For example, E-DPCCH can be coupled to a primary E-HICH, which uses a signature 1 or OVSF code 1, while S-E-DPCCH is coupled to a secondary E-HICH, which uses a signature 2 or OVSF code 2. (Note that the terminology for these hybrid indicator channels has not been standardized as of this writing. Possibilities include designating the primary and second E-HICH channels as E-HICH1 and E-HICH2, respectively, or E-HICH and S-E-HICH.)

For example, assume that data is originally transmitted on the secondary stream of an uplink rank-2 transmission, but is not successfully received by the NodeB, which sends a NACK in response. (See Case 5 in Figure 2.) As described above, the data is retransmitted in a rank-1 transmission, but in association with the S-E-DPCCH. The NodeB determines from this that the retransmitted data corresponds to the data originally transmitted on the secondary stream. In some embodiments, the NodeB may be adapted to send the subsequent ACK/NACK via the secondary E-HICH, even though the re-transmission was a rank-1 transmission. This approach may be useful in resolving certain ambiguities, but is not essential to all of the embodiments described herein. In a variant of the techniques described above, both E-DPCCHs, i.e., E-DPCCH and S-E- DPCCH are transmitted whenever an original rank-2 transmission is being retransmitted with rank-1 (i.e., when only stream 1 or only stream 2 is retransmitted). As a baseline, the same approach as described earlier is used, where one of the E-DPCCHs is associated with each original stream. In this embodiment, however, additional information can be included in the other E-DPCCH, i.e., the one not associated with the retransmitted data. This can be done, for example, by using special values for the currently existing E-TFCI, RSN or happy bit

parameters. This information can be used by the NodeB to avoid certain signaling or detection error cases, for example.

In the embodiments described so far, retransmissions are always sent on the primary stream, which uses the primary pre-coding vector, but the associated data control channel (E- DPCCH or S-E-DPCCH) can vary, depending on which control channel was used during the original transmission. In another variation, retransmissions of a data packet are always sent on the same stream that was used for that packet in the original transmission. Thus, for example, if the original rank-2 transmission used the secondary pre-coding vector for the NACKed packet, then the retransmission of that packet also uses the secondary precoding vector, even though only one stream is transmitted (i.e., a rank-1 transmission) to carry the retransmitted packet. In this variation, it is still the case that E-DPCCH indicates that data (E-DPDCH) is carried on the primary stream and S-E-DPCCH indicates that data (S-E-DPDCH) is carried on the secondary stream, which helps the decoding process in the NodeB. The difference here is that during a rank-1 retransmission, S-E-DPDCH & S-E-DPCCH might both be transmitted. During a normal rank-1 transmission (i.e., not a retransmission), E-DPCCH & E-DPDCH are transmitted, and never S-E-DPDCH & S-E-DPCCH.

Figure 3 below is a flow chart illustrating an example scheme for retransmission according to one or more embodiments of the techniques described above. The illustrated process shows an example of HARQ process handling when decoding of the secondary stream of a dual-stream HSUPA transmission fails and a rank-2 to rank-1 change is signaled.

As shown at 310, the illustrated flow begins with the NodeB signaling to the UE that rank-2 transmission may be used. This signal is shown for clarity - it may be the case that the rank was signaled previously and is already known to the UE.

As shown at 320, the UE transmits first and second packets, "Packet A-l" and "Packet A- 2," on first and second streams, respectively. These initial packets correspond to primary and secondary HARQ processes. The NodeB detects both E-DPCCH and S-E-DPCCH, indicating a rank-2 transmission. In the illustrated flow, it is assumed that decoding of the primary HARQ process (corresponding to stream 1) succeeds, while decoding of the secondary HARQ process (corresponding to stream 2) fails. Accordingly, an ACK is transmitted on E-HICH1 and a NACK is transmitted on E-HICH2, as shown at 330.

Subsequently to the dual-stream transmission of Packet A-l and Packet A-2, the NodeB signals a change to Rank 1, as shown at 340. Accordingly, retransmission of the failed packet, Packet A-2, must be carried out as a rank- 1 retransmission. This is shown at 350. Here, only the secondary HARQ process is transmitted, since rank 1 has been signaled and only the decoding of stream 2 failed in the initial transmission.

The NodeB detects only S-E-DPCCH, in this case, indicating that only the secondary HARQ process from the previous trank-2 transmission has been retransmitted, using rank 1. In the illustrated process, it is assumed that decoding of the retransmitted secondary HARQ process succeeds, after the soft values demodulated from the retransmitted packet are soft combined with buffered data from the initial transmission. Accordingly, an ACK is transmitted, using E-HICH2 (indicating the secondary HARQ process), as shown at 360. As shown at 370, the UE continues by sending new data, using rank-1 transmission.

The methods described above can be applicable whenever a retransmission is performed in rank-1, where the retransmitted data was originally transmitted as part of a rank-2

transmission. It does not necessarily have to be the case that the primary stream was ACKed and the secondary stream was NACKed, as in case 5 from Table 1. It can, for example, be the other way around, i.e., that the primary stream was NACKed and the secondary stream was ACKed, as in case 7 of Table 1. Another possibility is that the NodeB successfully decodes both streams and sends two ACKs, but the UE fails to detect or misinterprets the second E-HICH message. In either of these cases, however, the E-DPCCH would be used for the retransmission of the NACKed packet, and not the S-E-DPCCH, as in the previous example. In the appended claims and in the description that follows, the words "first" and "second" are used at various times to refer to streams, packets, and/or associated control channels. As used herein, the words "first" and "second" do not necessarily imply an order, and do not necessarily indicate the "primary" or "secondary" stream.

One concept underlying several of the embodiments described above is that the data control channel (E-DPCCH or S-E-DPCCH) used for uplink HSUPA rank-1 retransmissions gives an indication of which HARQ process is associated with the retransmitted data. This enables the NodeB to know which HARQ buffer is targeted. With this approach, there is no need to change existing uplink and downlink control channel structures. The several

embodiments described above are variants based on this same concept, and provide a few different alternatives for whether and how control channels are coupled with/associated to streams/precoder vectors. Some of the described embodiments also allow the possibility of conveying additional information via a (redundant) control channel.

Figure 4 is a process flow diagram illustrating an example method for retransmission handling, as implemented in a wireless transceiver. In some embodiments, the wireless transceiver is a mobile terminal, e.g., a 3GPP UE, and the rank-2 and rank-1 MIMO

transmissions are uplink transmissions to a radio base station, such as a UMTS NodeB.

The process begins, as shown at block 410, with the simultaneous sending of first and second data packets, in respective first and second MIMO streams of a rank-2 transmission. Note that the first and second streams do not necessarily correspond to the "primary" and "secondary" MIMO streams, as the latter terms are used in 3GPP documentation. In some instances and/or embodiments, the first and second streams are, in fact, the primary and secondary streams, respectively, while in others, the first and second streams may instead correspond to respective secondary and primary streams. Accordingly, in some embodiments the first stream is a primary stream, transmitted according to a primary precoding vector, the second stream is a secondary stream, transmitted according to a secondary precoding vector, and the retransmission of the second data packet uses the primary precoding vector. In other embodiments and/or instances, the opposite mapping of first and second streams to the secondary and primary streams may be applicable.

As shown at block 420, the illustrated method continues with the transmission of corresponding control data for each of the first and second streams, using first and second associated control channels, respectively. The first and second associated control channels are distinguishable by their respective mappings to the transmitted signal. For example, in some embodiments the first and second associated control channels are I/Q multiplexed, with the first and second associated control channels mapped to an in-phase branch and a quadrature branch of the transmitted signal, respectively.

Note that in some embodiments, the rank-2 and rank-1 MFMO transmissions are E-DCH Dedicated Physical Data Channel (E-DPDCH) transmissions in a High-Speed Uplink Packet Access (HSUPA) system and the first and second associated control channels is an E-DCH Dedicated Physical Control Channel (E-DPCCH) or a Secondary E-DCH Dedicated Physical Control Channel (S-E-DPCCH). However, it will be appreciated that the illustrated method is not limited to this particular context.

As seen at block 430, the method continues with the receiving of HARQ data indicating that the first data packet (carried by the first stream) was successfully decoded, while the second data packet (carried by the second stream) was not. In response, the wireless transceiver retransmits the second data packet in a single stream of a rank-1 MFMO transmission, as shown at block 440, and transmits corresponding control data for the single stream using the second associated control channel, as seen at block 450.

In some embodiments, the receiving HARQ data comprises an ACK received on a first indicator channel and a NACK on a second indicator channel, where the first and second indicator channels correspond to the first and second streams, respectively. In some of these embodiments, the method further comprises receiving an ACK or NACK corresponding to the retransmission, where the ACK or NACK is received on the second indicator channel (because the retransmission corresponded to data originally sent on the second stream). In some embodiments, the first and second indicator channels are decoded using first and second signature sequences, respectively, or first and second orthogonal variable spreading factor (OVSF) codes, respectively.

In some embodiments, the first associated control channel is also transmitted along with the rank-1 retransmission, even though the retransmission was for data originally sent in the second stream. In these embodiments, the first associated control channel may be used to carry additional control data placed in one or more data fields of the first associated control channel, such as the fields normally used for a happy bit, and/or the RSN, etc.

Figure 5 is another process flow diagram illustrating another example method for retransmission handling, as implemented in a wireless transceiver. This method corresponds to the method illustrated in Figure 4, but is implemented at the receiving end of the dual-stream transmission. Accordingly, in some embodiments of the method illustrated in Figure 5, the wireless transceiver is a radio base station, such as a UMTS NodeB, receiving uplink

transmissions from a mobile terminal.

The process begins, as shown at block 510, with the simultaneous receiving of first and second data packets, in respective first and second MIMO streams of a rank-2 transmission. Again, it should be noted that the first and second streams do not necessarily correspond to the "primary" and "secondary" MIMO streams, as the latter terms are used in 3GPP documentation. In some instances and/or embodiments, the first and second streams are, in fact, the primary and secondary streams, respectively, while in others, the first and second streams may instead correspond to respective secondary and primary streams. Accordingly, in some embodiments the first stream is a primary stream, transmitted according to a primary precoding vector, the second stream is a secondary stream, transmitted according to a secondary precoding vector, and the retransmission of the second data packet uses the primary precoding vector. In other

embodiments and/or instances, the opposite mapping of first and second streams to the secondary and primary streams may be applicable. As shown at block 520, the illustrated method continues with the receiving of corresponding control data for each of the first and second streams, using first and second associated control channels, respectively. Again, the first and second associated control channels are distinguishable by their respective mappings to the transmitted signal. For example, in some embodiments the first and second associated control channels are I/Q multiplexed, with the first and second associated control channels mapped to an in-phase branch and a quadrature branch of the transmitted signal, respectively. As was the case with Figure 4, the rank-2 and rank-1 MFMO transmissions in some embodiments are E-DCH Dedicated Physical Data Channel (E-DPDCH) transmissions in a High-Speed Uplink Packet Access (HSUPA) system and the first and second associated control channels are an E-DCH Dedicated Physical Control Channel (E-DPCCH) and a Secondary E-DCH Dedicated Physical Control Channel (S-E-DPCCH), respectively. Again, however, it will be appreciated that the illustrated method is not limited to this particular context.

As seen at block 530, the illustrated method continues, in response to a successful decoding of the first data packet and an unsuccessful decoding of the second data packet, with the transmission of HARQ data indicating that the first data packet (carried by the first stream) was successfully decoded, while the second data packet (carried by the second stream) was not. The wireless transceiver then receives a retransmission of the second data packet in a single stream of a rank-1 MIMO transmission, as shown at block 540. As seen at block 550, the wireless transceiver also determines that corresponding control data for the single stream has been sent using the second associated control channel. Because the second associated control channel was used, the wireless transceiver knows that the retransmitted data packet corresponds to the data packet originally transmitted on the second stream of the earlier rank-2 transmission. The wireless transceiver then maps the retransmitted data packet to a HARQ buffer associated with the second data packet, as shown at block 560. The retransmitted data may be soft combined with the earlier received data, in some embodiments.

In some embodiments, the transmitted HARQ data comprises an ACK transmitted on a first indicator channel and a NACK transmitted on a second indicator channel, where the first and second indicator channels correspond to the first and second streams, respectively. In some of these embodiments, the method further comprises transmitting an ACK or NACK

corresponding to the retransmission, where the ACK or NACK is transmitted on the second indicator channel (because the retransmission corresponded to data originally sent on the second stream). This is not shown in Figure 5, but is discussed in further detail in connection with the description of Figure 6, below. In some embodiments, the first and second indicator channels are encoded using first and second signature sequences, respectively, or first and second orthogonal variable spreading factor (OVSF) codes, respectively. In some embodiments, the first associated control channel is also received along with the rank-1 retransmission, even though the retransmission was for data originally sent in the second stream. (This is not shown in Figure 5.) In these embodiments, the base station may obtain additional control data placed in one or more data fields of the first associated control channel, such as the fields normally used for a happy bit, and/or the RSN, etc.

As was noted above, in some embodiments the retransmitted packet is acknowledged using an indicator channel that is associated with the stream that the packet was originally transmitted on. It should be appreciated that this particular technique may be implemented separately from the techniques shown in Figures 4 and 5, in some cases.

Accordingly, Figure 6 illustrates another example for MTMO retransmission handling, as implemented in a wireless transceiver that is receiving the MIMO transmissions. The illustrated method may be implemented in conjunction with the method shown in Figure 5, in some embodiments, or separately, in others.

As shown at block 610, the method begins with receiving a rank-2 MFMO transmission, comprising a first data packet transmitted via a first stream and a second data packet transmitted via a second stream. In response to a successful decoding of the first data packet and an unsuccessful decoding of the second data packet, the wireless transceiver transmits an ACK on a first indicator channel and transmits a NACK on a second indicator channel, as shown at block 620. The first and second indicator channels correspond to the first and second streams, respectively. In some embodiments, the first and second indicator channels are encoded using first and second signature sequences, respectively, or first and second orthogonal variable spreading factor (OVSF) codes, respectively.

As shown at block 630, the wireless transceiver subsequently receives a retransmitted data packet in a single stream of a rank-1 MFMO transmission. After determining that the retransmitted data packet corresponds to the second data packet, as shown at block 640, the wireless transceiver transmits an ACK or NACK corresponding to the retransmitted data packet, as shown at block 650. This ACK or NACK is transmitted using the second indicator channel, because the retransmitted packet corresponds to a packet that was originally transmitted on the second stream.

Figure 7 illustrates a corresponding process flow for MIMO retransmission handling, as implemented in a wireless transceiver that is transmitting the MIMO transmissions. The illustrated method may be implemented in conjunction with the method shown in Figure 4, in some embodiments, or separately, in others.

As shown at block 710, the method begins with transmitting a rank-2 MFMO

transmission, comprising a first data packet transmitted via a first stream and a second data packet transmitted via a second stream. As shown at block 720, the wireless transceiver subsequently receives an ACK on a first indicator channel and receives a NACK on a second indicator channel. The first and second indicator channels correspond to the first and second streams, respectively. Again, in some embodiments, the first and second indicator channels are encoded using first and second signature sequences, respectively, or first and second orthogonal variable spreading factor (OVSF) codes, respectively.

As shown at block 730, the wireless transceiver then retransmits the second data packet in a single stream of a rank-1 MIMO transmission. The wireless transceiver subsequently receives an ACK or NACK corresponding to the retransmitted data packet, as shown at block 740. This ACK or NACK is received over the second indicator channel, because the

retransmitted packet corresponds to a packet that was originally transmitted on the second stream.

Other embodiments of the presently disclosed techniques include apparatus

corresponding to the methods described above, including wireless transceiver apparatus adapted to carry out one or more of the methods illustrated in Figures 4, 5, 6, and 7, and variants thereof.

More particularly, several of the techniques described above can be implemented in connection with a wireless transceiver in a radio access terminal, such as a mobile station (UE) generally configured to operate in wireless networks according to 3 GPP specifications for HSUPA. A radio access terminal, which communicates wirelessly with fixed base stations in the wireless network, can also be called a system, subscriber unit, subscriber station, mobile station, mobile, remote station, remote terminal, mobile device, user terminal, terminal, wireless communication device, user agent, user device, or user equipment (UE). An access terminal can be a cellular telephone, a cordless telephone, a Session Initiation Protocol (SIP) phone, a wireless local loop (WLL) station, a personal digital assistant (PDA), a handheld device having wireless connection capability, computing device, or other processing device connected to a wireless modem.

Similarly, several of the techniques described above are implemented in connection with a wireless base station, such as a NodeB configured to support 3 GPP specifications for HSUPA. In general, a base station communicates with access terminals and is referred to in various contexts as an access point, Node B, Evolved Node B (eNodeB or eNB) or some other terminology. Although the various base stations discussed herein are generally described and illustrated as though each base station is a single physical entity, those skilled in the art will recognize that various physical configurations are possible, including those in which the functional aspects discussed here are split between two physically separated units. Thus, the term "base station" is used herein to refer to a collection of functional elements (one of which is a radio transceiver that communicates wirelessly with one or more mobile stations), which may or may not be implemented as a single physical unit.

Figure 8 is a block diagram of a wireless transceiver apparatus 800, illustrating a few of the components relevant to the present techniques, as realized in either a mobile station or a base station. Accordingly, the apparatus pictured in Figure 8 can correspond to either end of a communication link, such as the link between a Node B and a UE.

The pictured apparatus includes radio circuitry 820 and baseband & control processing circuit 810. Radio circuitry 820 includes receiver (RX) circuits 830 and transmitter (TX) circuits 825, which each use known radio processing and signal processing components and techniques, typically according to a particular telecommunications standard such as the 3 GPP standard for WCDMA and/or HSUPA. In various embodiments, either or both of RX circuits 830 and TX circuits 825 are adapted for MIMO operation, using antennas 828 and 833. Because the various details and engineering trade-offs associated with the design and implementation of such circuitry are well known and are unnecessary to a full understanding of the invention, additional details of the radio 820 are not shown here.

Baseband & control processing circuit 810 includes a central processing unit (CPU) 1940, which may comprise one or more microprocessors or microcontrollers as well as other digital hardware, which may in turn include digital signal processors (DSPs), special-purpose digital logic, and the like. Any of the microprocessor s), microcontroller(s) and DSP(s) may be configured to execute program code, which is stored in the program storage portion 860 of memory 850. Also stored in memory 850 are radio parameters, other program data, and user data, all of which are stored in data storage portion 855 of memory 850. Again, because the various details and engineering tradeoffs associated with the design of baseband processing circuitry for mobile devices and wireless base stations are well known and are unnecessary to a full understanding of the invention, additional details are not shown here

The program code stored in the program storage portion 860 of memory 850, which may comprise one or several types of memory such as read-only memory (ROM), random-access memory, cache memory, flash memory devices, optical storage devices, etc., includes program instructions for executing one or more telecommunications and/or data communications protocols, as well as instructions for carrying out one or more of the techniques described herein, in several embodiments. The radio parameters stored in data storage 855 include various predetermined configuration parameters as well as parameters determined from system

measurements, such as channel measurements, and may include, for example, precoding vectors for use in transmitting data, signatures or OVSF codes used to encode and/or decode the associated control channels discussed above, etc. Accordingly, in various embodiments of the invention, processing circuits, such as the baseband & control processing circuits 810 of Figure 8, are configured to carry out one or more of the techniques described above for retransmission handling. In some cases, these processing circuits are configured with appropriate program code, stored in one or more suitable memory devices, to implement one or more of the techniques described herein. Of course, it will be appreciated that not all of the steps of these techniques are necessarily performed in a single microprocessor or even in a single module.

Examples of several embodiments of the present invention have been described in detail above, with reference to the attached illustrations of specific embodiments. Because it is not possible, of course, to describe every conceivable combination of components or techniques, those skilled in the art will appreciate that the present techniques can be implemented in other ways than those specifically set forth herein, without departing from essential characteristics of the inventive techniques described herein. The present embodiments are thus to be considered in all respects as illustrative and not restrictive.

With these and other variations and extensions in mind, those skilled in the art will appreciate that the foregoing description and the accompanying drawings represent non-limiting examples of the systems and apparatus taught herein for handling retransmissions in a system that supports MIMO transmissions. As such, the present invention is not limited by the foregoing description and accompanying drawings. Instead, the present invention is limited only by the following claims and their legal equivalents.

Claims

CLAIMS What is claimed is:

1. A method, in a wireless transceiver, for Multiple-Input Multiple-Output, MIMO,

retransmission handling, the method comprising:

in a rank-2 MEVIO transmission, simultaneously transmitting (410) a first data packet via a first stream and a second data packet via a second stream;

transmitting (420) corresponding control data for each of the first and second streams using first and second associated control channels, respectively, wherein the first and second associated control channels are distinguishable by their respective mappings to the transmitted signal;

receiving (430) Hybrid Automatic Repeat Request, HARQ, data indicating that the first data packet was successfully decoded and that the second data packet was not; retransmitting (440) the second data packet in a single stream of a rank-1 MEVIO

transmission; and

transmitting (450) corresponding control data for the single stream using the second associated control channel.

2. The method of claim 1, wherein the wireless transceiver is a mobile terminal and the rank-2 and rank-1 MEVIO transmissions are uplink transmissions to a radio base station.

3. The method of claim 2, wherein the rank-2 and rank-1 MEVIO transmissions are E-DCH Dedicated Physical Data Channel, E-DPDCH, transmissions in a High-Speed Uplink Packet Access, HSUPA, system and wherein each of the first and second associated control channels is an E-DCH Dedicated Physical Control Channel, E-DPCCH, or a Secondary E-DCH Dedicated Physical Control Channel, S-E-DPCCH.

4. The method of any of claims 1-3, wherein the first and second associated control channels are I/Q multiplexed, with the first and second associated control channels mapped to an in-phase branch and a quadrature branch of the transmitted signal, respectively.

5. The method of any of claims 1 to 4, further comprising placing additional control data in one or more data fields of the first associated control channel and also transmitting the first associated control channel in association with the rank-1 MEVIO transmission.

6. The method of any of claims 1 to 5, wherein the first stream is a primary stream, transmitted according to a primary precoding vector, and the second stream is a secondary stream, transmitted according to a secondary precoding vector, and wherein the retransmission of the second data packet uses the primary precoding vector.

7. The method of any of claims 1-6, wherein receiving HARQ data indicating that the first data packet was successfully decoded and that the second data packet was not comprises receiving an ACK on a first indicator channel and receiving a NACK on a second indicator channel, wherein the first and second indicator channels correspond to the first and second streams, respectively, the method further comprising receiving an ACK or NACK corresponding to the retransmission, wherein said ACK or NACK is received on the second indicator channel.

8. The method of claim 7, wherein the first and second indicator channels are decoded using first and second signature sequences, respectively, or first and second orthogonal variable spreading factor, OVSF, codes, respectively.

9. A method, in a wireless transceiver, for Multiple-Input Multiple-Output, MIMO,

retransmission handling, the method comprising:

receiving (510) a rank-2 MIMO transmission, the rank-2 MIMO transmission comprising a first data packet transmitted via a first stream and a second data packet transmitted via a second stream;

receiving (520) corresponding control data for each of the first and second streams using first and second associated control channels, respectively, wherein the first and second associated control channels are distinguishable by their respective mappings to the received signal;

in response to a successful decoding of the first data packet and an unsuccessful decoding of the second data packet, transmitting (530) HARQ data indicating that the first data packet was successfully decoded and that the second data packet was not; subsequently receiving (540) a retransmitted data packet in a single stream of a rank-1 MIMO transmission;

determining (550) that control data for the single stream was received via the second associated control channel; and

mapping (560) the retransmitted data packet to a HARQ buffer associated with the

second packet, received in the second stream of the rank-2 MIMO transmission.

10. The method of claim 9, wherein the wireless transceiver is a radio base station and the rank- 2 and rank-1 MTMO transmissions are uplink transmissions to the radio base station from a mobile station.

11. The method of claim 9 or 10, wherein the first and second associated control channels are I/Q multiplexed, with the first and second associated control channels mapped to an in-phase branch and a quadrature branch of the received signal, respectively.

12. The method of any of claims 9 to 11, further comprising receiving the first associated control channel in association with the rank-1 MTMO transmission and obtaining additional control data from one or more data fields of the first associated control channel.

13. The method of any of claims 9-12, wherein transmitting HARQ data indicating that the first data packet was successfully decoded and that the second data packet was not comprises transmitting an ACK on a first indicator channel and transmitting a NACK on a second indicator channel, wherein the first and second indicator channels correspond to the first and second streams, respectively, the method further comprising transmitting an ACK or NACK

corresponding to the retransmitted data packet, using the second indicator channel.

14. The method of claim 13, wherein the first and second indicator channels are transmitted using first and second signature sequences, respectively, or first and second orthogonal variable spreading factor, OVSF, codes, respectively.

15. A method, in a wireless transceiver, for Multiple-Input Multiple-Output, MIMO, retransmission handling, the method comprising:

receiving (610) a rank-2 MIMO transmission, the rank-2 MEVIO transmission comprising a first data packet transmitted via a first stream and a second data packet transmitted via a second stream;

in response to a successful decoding of the first data packet and an unsuccessful decoding of the second data packet, transmitting (620) an ACK on a first indicator channel and transmitting a NACK on a second indicator channel, wherein the first and second indicator channels correspond to the first and second streams,

respectively;

subsequently receiving (630) a retransmitted data packet in a single stream of a rank-1 MIMO transmission; determining (640) that the retransmitted data packet corresponds to the second data packet; and

transmitting (650) an ACK or NACK corresponding to the retransmitted data packet, using the second indicator channel.

16. A method, in a wireless transceiver, for Multiple-Input Multiple-Output, MIMO, retransmission handling, the method comprising:

in a rank-2 MIMO transmission, simultaneously transmitting (710) a first data packet via a first stream and a second data packet via a second stream;

receiving (720) an ACK on a first indicator channel and a NACK on a second indicator channel, the first and second indicator channels corresponding to the first and second streams, respectively;

in response to said NACK, retransmitting (730) the second data packet in a single stream of a rank-1 MIMO transmission; and

subsequently receiving (740) an ACK or NACK corresponding to the retransmitted

second data packet, wherein said ACK or NACK is received on the second indicator channel.

17. A wireless transceiver apparatus (800) comprising radio circuitry (820) and a processing circuit (810) adapted to control the radio circuitry (820), characterized in that the processing circuit (810) is further adapted to, using the radio circuitry (820):

in a rank-2 MIMO transmission, simultaneously transmit a first data packet via a first stream and a second data packet via a second stream;

transmit corresponding control data for each of the first and second streams using first and second associated control channels, respectively, wherein the first and second associated control channels are distinguishable by their respective mappings to the transmitted signal;

receive Hybrid Automatic Repeat Request, HARQ, data indicating that the first data packet was successfully decoded and that the second data packet was not;

retransmit the second data packet in a single stream of a rank-1 MIMO transmission; and transmit corresponding control data for the single stream using the second associated control channel.

18. The wireless transceiver apparatus (800) of claim 17, wherein the processing circuit (810) is further adapted to place additional control data in one or more data fields of the first associated control channel and to also transmit the first associated control channel in association with the rank-1 MTMO transmission, using the radio circuitry (820).

19. The wireless transceiver apparatus (800) of claim 17 or 18, wherein the processing circuit (810) is adapted to receive HARQ data indicating that the first data packet was successfully decoded and that the second data packet was not by receiving an ACK on a first indicator channel and receiving a NACK on a second indicator channel, wherein the first and second indicator channels correspond to the first and second streams, respectively, and wherein the processing circuit (810) is further adapted to receive an ACK or NACK corresponding to the retransmission, on the second indicator channel.

20. A wireless transceiver apparatus (800) comprising radio circuitry (820) and a processing circuit (810) adapted to control the radio circuitry (820), characterized in that the processing circuit (810) is further adapted to, using the radio circuitry (820):

receive a rank-2 MTMO transmission, the rank-2 MIMO transmission comprising a first data packet transmitted via a first stream and a second data packet transmitted via a second stream;

receive corresponding control data for each of the first and second streams using first and second associated control channels, respectively, wherein the first and second associated control channels are distinguishable by their respective mappings to the received signal;

in response to a successful decoding of the first data packet and an unsuccessful decoding of the second data packet, transmit HARQ data indicating that the first data packet was successfully decoded and that the second data packet was not; subsequently receive a retransmitted data packet in a single stream of a rank-1 MIMO transmission;

determine that corresponding control data for the single stream was received via the

second associated control channel; and

map the retransmitted data packet to a HARQ buffer associated with the second packet received the second stream of the rank-2 MEVIO transmission.

21. The wireless transceiver apparatus (800) of claim 20, wherein the processing circuit (810) is further adapted to receive the first associated control channel in association with the rank-1 MIMO transmission, using the radio circuitry (820) and to obtain additional control data from one or more data fields of the first associated control channel.

22. The wireless transceiver apparatus (800) of claim 20 or 21, wherein the processing circuit (810) is adapted to transmit HARQ data indicating that the first data packet was successfully decoded and that the second data packet was not by transmitting an ACK on a first indicator channel and transmitting a NACK on a second indicator channel, wherein the first and second indicator channels correspond to the first and second streams, respectively, and wherein the processing circuit (810) is further adapted to transmit an ACK or NACK corresponding to the retransmitted data packet, using the second indicator channel.

23. A wireless transceiver apparatus (800) comprising radio circuitry (820) and a processing circuit (810) adapted to control the radio circuitry (820), characterized in that the processing circuit (810) is further adapted to, using the radio circuitry (820):

receive a rank-2 MTMO transmission, the rank-2 MTMO transmission comprising a first data packet transmitted via a first stream and a second data packet transmitted via a second stream;

in response to a successful decoding of the first data packet and an unsuccessful decoding of the second data packet, transmit an ACK on a first indicator channel and transmit a NACK on a second indicator channel, wherein the first and second indicator channels correspond to the first and second streams, respectively;

subsequently receive a retransmitted data packet in a single stream of a rank-1 MEVIO transmission;

determine that the retransmitted data packet corresponds to the second data packet; and transmit an ACK or NACK corresponding to the retransmitted data packet, using the second indicator channel.

24. A wireless transceiver apparatus (800) comprising radio circuitry (820) and a processing circuit (810) adapted to control the radio circuitry (820), characterized in that the processing circuit (810) is further adapted to, using the radio circuitry (820):

in a rank-2 MEVIO transmission, simultaneously transmit a first data packet via a first stream and a second data packet via a second stream;

receive an ACK on a first indicator channel and a NACK on a second indicator channel, the first and second indicator channels corresponding to the first and second streams, respectively;

in response to said NACK, retransmit the second data packet in a single stream of a rank- 1 MEVIO transmission; and subsequently receive an ACK or NACK corresponding to the retransmitted second data packet, wherein said ACK or NACK is received on the second indicator channel.