WO2009157859A2

WO2009157859A2 - Error control in multi-carrier wireless systems

Info

Publication number: WO2009157859A2
Application number: PCT/SE2009/050776
Authority: WO
Inventors: Johan Torsner; Stefan Parkvall; Pål FRENGER; Michael Meyer; Henning Wiemann
Original assignee: Telefonaktiebolaget L M Ericsson (Publ)
Priority date: 2008-06-26
Filing date: 2009-06-18
Publication date: 2009-12-30
Also published as: AR072381A1; WO2009157859A3

Abstract

Methods and apparatus for signaling scheduling information in a multi-carrier wireless communications system (700), as well as corresponding methods and apparatus for processing such signaling information, are disclosed. An exemplary method comprises scheduling (610) first and second transport blocks for simultaneous transmission during a first transmission interval on first and second component carriers, and transmitting (620) a common re-transmission process identifier for the first transmission interval. The method further comprises scheduling (640) at least one of the first and second transport blocks for re-transmission during a second transmission interval, along with a third transport block, and transmitting (660) second scheduling information for the second transmission interval, the second scheduling information comprising the same common re-transmission process identifier.

Description

ERROR CONTROL IN M U LT! -CAR RI E R WIRELESS SYSTEMS

TECHNICAL FIELD

The present invention relates generally to wireless communications systems, and more particularly to the signaling of scheduling information in a multi-carrier wireless communications system utilizing re-transmissions for error control.

BACKGROUND

Over the last few decades, a wide variety of both wired and wireless telecommunication systems have been developed. Wireless telecommunication systems in particular have evolved through the so-called second generation (2G) systems into the third generation (3G) systems currently being deployed. Specifications for some 3G systems were developed by the 3rd Generation Partnership Project (3GPP); information regarding these may be found on the Internet at www.3gpp.org. Continuing development of advanced wireless systems has produced techniques enabling even higher data transfer speeds. To this end, for example, so-called High-Speed Downlink Packet Access (HSDPA) technology has recently been developed. HSDPA delivers packet data to a plurality of mobile terminals over a shared downlink channel at high peak data rates, and provides a smooth evolutionary path for 3G networks to support higher data transfer speeds.

In addition to fast packet scheduling and adaptive modulation and coding technologies discussed above, HSDPA further utilizes fast re-transmissions for error control. In particular, HSDPA utilizes an error control method known as Hybrid Automatic Repeat Request, or HARQ. HARQ uses the concept of "incremental redundancy", where re-transmissions contain different coding of the user data relative to the original transmission. When a corrupted packet is received, the user device saves it, sends a "NACK" message to trigger a re-transmission of the packet, and combines the saved packet with subsequent re-transmissions to formulate an error- free packet as quickly and efficiently as possible. Even if the retransmitted packet(s) is itself corrupted, the combining of information from two or more corrupted transmissions can often yield an error-free version of the originally transmitted packet.

In fact, HARQ is a variation of Automatic Repeat-reQuest (ARQ) error control, which is a well-known error control method for data transmission in which the receiver detects transmission errors in a message and automatically requests a re-transmission from the transmitter. HARQ gives better performance than ordinary ARQ, particularly over wireless channels, at the cost of increased implementation complexity. The simplest version of HARQ, Type I HARQ, simply combines Forward Error Correction (FEC) and ARQ by encoding the data block plus error-detection information - such as Cyclic Redundancy Check (CRC) - with an error-correction code (such as Reed-Solomon code or Turbo code) prior to transmission. When the coded data block is received, the receiver first decodes the error-correction code. If the channel quality is good enough, all transmission errors should be correctable, and the receiver can obtain the correct data block. If the channel quality is poor and not all transmission errors can be corrected, the receiver will detect this situation using the error-detection code. In this case, the received coded data block is discarded and a re-transmission is requested by the receiver, similar to ARQ. In more advanced methods, incorrectly received coded data blocks are stored at the receiver rather than discarded, and when the retransmitted coded data block is received, the information from both coded data blocks are combined. When the transmitted and retransmitted blocks are coded identically, so-called Chase combining may be used to benefit from time diversity. To further improve performance, incremental redundancy HARQ has also been proposed. In this scheme, re-transmissions of a given block are coded differently from the original transmission, thus giving better performance after combining since the block is effectively coded across two or more transmissions. HSDPA in particular utilizes incremental redundancy HARQ, wherein the data block is first coded with a punctured Turbo code. During each re-transmission the coded block is punctured differently, so that different coded bits are sent each time.

ARQ schemes in general may be utilized in stop-and-wait mode (after transmitting a first packet, the next packet is not transmitted until the first packet is successfully decoded), or in selective repeat mode, in which the transmitter continues transmitting successive packets, selectively re-transmitting corrupted packets identified by the receiver by a sequence number. A stop-and-wait system is simpler to implement, but waiting for the receiver's acknowledgement reduces efficiency. Thus, in practice multiple stop-and-wait HARQ processes are often performed in parallel so that while one HARQ process is waiting for an acknowledgement one or more other processes can use the channel to send additional packets.

The first versions of HSDPA address up to 8 HARQ processes, numbered 0 through 7. This number is specified to ensure that continuous transmissions to one user may be supported. When a packet has been transmitted from the Node B, the mobile terminal will respond (on the HS-DPCCH) with an ACK (acknowledge) or NACK (not-ACK) indication, depending on whether the packet decoded correctly or not. Because of the inherent delay in processing and signaling, several simultaneous HARQ processes are required. The Node B transmitter thus is able to transmit several new packets before an ACK or NACK is received from a previous packet. HSDPA as specified in 3GPP release 7 and forward is designed to achieve improved data rates of up to 28.8 Mbps. This is accomplished by introducing advanced multi-antenna techniques, i.e., Multiple-Input Multiple-Output (MIMO) technology. In particular, spatial multiplexing is employed to divide the data into two transmission streams, often called data substreams. These substreams are transmitted with multiple transmit antennas, using the same frequencies and the same channelization codes. Given uncorrelated propagation channels, receivers employing multiple receive antennas and using advanced detection techniques such as successive interference cancellation are able to distinguish between and decode the multiplexed data substreams. With the addition of MIMO to HSDPA, the number of required HARQ processes increases, e.g. from 8 to 16 (0-15) processes. If the processes are independently numbered for each data substream and signaled to the receiving mobile terminals, the signaling load on the HS-SCCH will increase significantly. Instead of a 3-bit HARQ process number for identifying eight processes, a 4-bit HARQ process number is needed to distinguish between up to 16 processes. In a dual stream case, as currently under development for HSDPA systems, the signaling overhead would thus increase from three to eight bits (two streams at four bits/stream). Because signaling on HS-SCCH is relatively expensive, i.e., signaling bits are scarce, this increase in overhead is undesirable. Solutions to this problem are disclosed in International Patent Application Publication WO 2008/054313 A1 , titled "HARQ in Spatial Multiplexing MIMO System."

3GPP is also continuing work on its family of so-called "Long Term Evolution" (LTE) technologies. In particular LTE release-8 has recently been standardized, supporting bandwidths up to 20 MHz. In order to meet the upcoming IMT-Advanced requirements, however, even greater throughput is required, so 3GPP has initiated work on so-called LTE- Advanced standards. One aspect of LTE-Advanced is the support of bandwidths larger than 20 MHz. However, one important requirement on LTE-Advanced is to assure backward compatibility with LTE Rel-8, to include spectrum compatibility. This implies that an LTE- Advanced carrier, which may be wider than 20 MHz, should appear as a number of distinct LTE carriers to an LTE Rel-8 terminal. Each such carrier can be referred to as a "component carrier."

It can be expected that for early LTE-Advanced deployments there will be a relatively small number of LTE-Advanced-capable terminals operating in the field, compared to many LTE legacy terminals. Therefore, it is necessary to assure an efficient use of a wide carrier for legacy terminals as well as for the newer LTE-Advanced terminals. Thus, it is desirable that it be possible to implement the use of multiple component carriers so that legacy terminals can be scheduled in all parts of the wideband LTE-Advanced carrier, i.e., in each component carrier. The straightforward way to obtain this would be by means of carrier aggregation. Carrier aggregation implies that an LTE-Advanced terminal can receive multiple component carriers, where the component carriers have, or at least the possibility to have, the same structure as a Rel-8 carrier. An example of carrier aggregation is illustrated in Figure 1 , where a 10-MHz component carrier, a 20-MHz component carrier, and a 5-MHz component carrier are aggregated, with an aggregate bandwidth of 35 MHz. As each of the component carriers can be backwards compatible with release-7 LTE, legacy release-7 mobile terminals may be scheduled on any of the component carriers. At the same time, an Advanced-LTE mobile terminal may exploit the entire aggregated bandwidth.

Release 8 specifications for LTE systems specify HARQ techniques similar to those described above for HSDPA systems. The introduction of carrier aggregation in multi-carrier wireless communication systems creates new problems with respect to the use of these error control techniques.

SUMMARY

The present invention provides methods and apparatus for signaling scheduling information in a multi-carrier wireless communications system, as well as corresponding methods and apparatus for processing such signaling information. The inventive techniques described herein facilitate efficient signaling of re-transmission process information, such as may be employed in a hybrid automatic repeat-request (HARQ) error control system.

Several of the various error control techniques disclosed herein provide for dynamic and flexible scheduling of re-transmissions in multi-carrier systems. In several embodiments of the invention, a transport block may be re-transmitted in a given transmission interval, on one component carrier, along with another transport block, on a different component carrier, that carries new data. In some embodiments, the re-transmitted transport block may be transmitted on a different component carrier than that used for the original transmission (or earlier retransmission) of the re-transmitted transport block. These methods generally employ a common re-transmission process identifier, applying to two or more component carriers of the multi- carrier system, to reduce signaling overhead.

An exemplary method for signaling scheduling information, such as might be implemented at an LTE evolved Node B (eNB) utilizing aggregated component carriers, thus comprises scheduling first and second transport blocks for simultaneous transmission during a first transmission interval on first and second component carriers, respectively. The exemplary method further comprises assigning a common re-transmission process identifier to the first transmission interval and transmitting first scheduling information for the first transmission interval, the first scheduling information including the common re-transmission process identifier. The method further comprises scheduling one of the first and second transport blocks for re-transmission during a second transmission interval, e.g., in response to a NACK, along with a third transport block, and transmitting second scheduling information for the second transmission interval, the second scheduling information comprising the same re-transmission process identifier. In various embodiments, the common re-transmission process identifier may be used along with explicit or implicit mapping data to determine whether the re-transmitted transport block is transmitted on the same component carrier used for the original transmission or earlier re-transmission. A corresponding method for processing scheduling information in multi-carrier wireless communication system, such as might be implemented in a 3GPP-compliant mobile terminal, comprises receiving first scheduling information for a first transmission interval, the first scheduling information indicating that first and second transport blocks are scheduled for simultaneous transmission to the mobile terminal during the first transmission interval on first and second component carriers, respectively, and comprising a common re-transmission process identifier for the first and second component carriers. The method further comprises receiving second scheduling information for a second transmission interval, the second scheduling information indicating that third and fourth transport blocks are scheduled for simultaneous transmission to the mobile terminal during the second transmission interval transmission interval on the first and second component carriers, respectively, wherein the second scheduling information comprises the same common re-transmission process identifier as the first scheduling information. Finally, the method comprises mapping the first and second transport blocks to first and second re-transmission sub-processes corresponding to the common re-transmission process identifier, determining that only one of the third and fourth transport blocks is a re-transmission, and matching the re-transmitted transport block to one of the first and second re-transmission sub-processes, based at least in part on the correspondence between the third and fourth transport blocks and the first and second component carriers.

Arrangements in a network node in a wireless communication system (such as an LTE base station) are also disclosed, including controllers configured to carry out one or more of the techniques for signaling scheduling information disclosed herein. Similarly, mobile terminals, including mobile controllers configured to process received scheduling information according to various embodiments of the invention, are also disclosed. The present invention may, of course, be carried out in other ways than those specifically set forth herein without departing from essential characteristics of the invention. Upon reading the following description and viewing the attached drawings, the skilled practitioner will recognize that the described embodiments are illustrative and not restrictive, and that all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 illustrates the aggregation of component carriers in a multi-carrier wireless communication system.

Figure 2A illustrates the use of independent HARQ processes with each of several component carriers.

Figure 2B illustrates the use of the same HARQ processes with all of several component carriers.

Figure 3 illustrates the re-transmission of a NACKed transport block on a different component carrier than that used for the NACKed transmission.

Figure 4 illustrates the use of sub-process identifiers in a multi-carrier HARQ process. Figure 5 illustrates the application of spatial multiplexing to HARQ processes in a multi- carrier wireless system.

Figure 6 illustrates an exemplary method for signaling scheduling information in a multi- carrier wireless communications system.

Figure 7 illustrates one embodiment of a multi-carrier wireless communications system. Figure 8 illustrates an exemplary method for processing scheduling information in a mobile terminal operating in a multi-carrier wireless system.

DETAILED DESCRIPTION

The present invention will be described below with reference to the figures. Although the following description is primarily addressed to the application of the inventive techniques to an Advanced-LTE system, those skilled in the art will appreciate that the methods and devices described herein may also be applied in other multi-carrier wireless communications systems, including other systems that may or may not employ the OFDM technology used in LTE.

LTE uses hybrid-ARQ, or HARQ, to accommodate and correct receiver errors in the downlink. Thus, after receiving downlink data in a particular subframe, the receiving mobile terminal attempts to decode it and reports to the base station whether the decoding was successful or not, by sending an ACK (successful) or NACK (unsuccessful). In the event of an unsuccessful decoding attempt, the base station can retransmit the erroneous data.

Downlink transmissions are dynamically scheduled, in that the base station transmits control information in each subframe, the control information identifying those terminals that are scheduled to receive data on that subframe and indicating which particular time-frequency resources are assigned to each mobile terminal in the current downlink subframe. This control signaling is typically transmitted in the first 1 , 2 or 3 OFDM symbols in each subframe.

A mobile terminal will thus continuously (or periodically) monitor the control channel - if it detects a downlink assignment addressed to it, the mobile terminal will decode the data and generate feedback in response to the transmission in the form of an ACK or a NACK, depending on whether the data was decoded correctly or not.

In a Release 8 LTE system, the HARQ protocol uses several concurrently operating HARQ processes, where each HARQ process is essentially a pointer to a logical buffer in the receiver. When a re-transmission is performed for a given higher layer protocol data unit (PDU), the re-transmission is associated with the same HARQ process. The receiver knows from the HARQ process identifier (more generally a "re-transmission process identifier") that the retransmission should be combined with the original transmission. When the transmitter has received an ACK for the transmitted data corresponding to a given HARQ process, it can start sending new data using that HARQ process. The transmitter indicates that new data is present in a given transmission with a "New Data Indicator" signaled on the L1/L2 control channel.

A stop-and-wait protocol is used for each HARQ process, but since transmissions can be ongoing in multiple, staggered, HARQ processes maintained simultaneously, a continuous transmission is possible. The number of HARQ processes needed to achieve a continuous transmission depends on, among other things, the processing requirements in the base station (in LTE, an evolved Node B, or "eNB") and the user equipment (UE). For LTE, around eight retransmission processes are needed in a frequency-division duplexing (FDD) configuration.

One possibility for maintaining HARQ processes in a wireless system that uses carrier aggregation is to perform coding and HARQ re-transmissions per component carrier, i.e., using completely independent HARQ processes. This is illustrated in Figure 2A, where a scheduling entity 20 schedules data for a given mobile terminal for simultaneous transmission on three component carriers 10, 12, and 14. In the existing LTE structure, this would correspond to having a transport block (or two transport blocks in case of spatial multiplexing) per component carrier. In the system pictured in Figure 2A, a separate set of HARQ processes are maintained for each separate component carrier, so that a separate and distinct HARQ entity 22 corresponds to each of several separate layer-1 (L1 ) processing units 24, each of which in turn is tied to one of the component carriers 10, 12, and 14. The advantage of this structure is its simplicity, in that the implementation of multi-carrier processing simply requires duplication of the current LTE structures.

A different approach is illustrated in Figure 2B, in which a single HARQ entity 22 services all three of the L1 processing units 24. With this approach, a given transport block (the output of the HARQ entity) may have parts scheduled for any or several of the three component carriers 10, 12, and 14, and is managed within a single set of HARQ processes and corresponding re-transmission process identifiers. Because a single transport block can be mapped to one, two, or several of the component carriers, this approach is clearly more complex than that of Figure 2A, even though only a single HARQ entity is needed. As noted above, the structure Figure 2A uses multiple independent HARQ entities 22.

Of course, for the operation of HARQ in general, acknowledgements informing the transmitter of whether the reception of a transport block was successful or not are required. Perhaps the most straightforward way of implementing this is for the mobile terminal receiving data on two or more component carriers to transmit multiple acknowledgement messages, i.e., one per component carrier, but other possibilities are possible. (Those skilled in the art will appreciate that in the case of dual-stream spatial multiplexing, as in the first release of LTE, a single acknowledgement message may require two bits, as there are two transport blocks on a single component carrier in this case. In the absence of spatial multiplexing, however, an acknowledgement message may be a single bit, as there is only a single transport block per component carrier.)

Given the general structure illustrated in Figure 2A, a separate transport block may be transmitted on each component carrier. If the HARQ protocol currently used in LTE is not modified, then a separate HARQ process per component carrier is needed. To maintain continuous transmissions, accounting for feedback time, eight processes are needed for each carrier. If, for example, four component carriers are used, then 32 HARQ processes are needed instead of the eight used in LTE release 8. In order for these processes to be uniquely numbered, five bits are needed to encode the HARQ process identifier per component carrier; one of these process identifiers must be transmitted on a given subframe for each of the component carriers scheduled for a given mobile terminal. Thus, if a solution is adopted where the control information for all component carriers is transmitted on a single control channel, then a total of 20 bits per subframe is needed to transmit the re-transmission process identifiers, given four component carriers, instead of the three bits used in LTE release 8. This implies a significant increase in the HARQ related control information.

A related, but distinct, problem arises in wireless systems using spatial multiplexing. A solution for reducing re-transmission process identifier signaling in spatial multiplexing systems has been described in WO 2008/054313. In particular, an approach is described in which HARQ process pairs are used to reduce the amount of HARQ-related signaling, where the second HARQ process identifier may be derived from the process of the first HARQ process using a predefined rule. With this approach, when spatial multiplexing is used the control channel does not explicitly indicate the HARQ process for both transport blocks. Instead, only a single HARQ process is explicitly signaled and the HARQ process identifier of the second HARQ process identifier is derived from that of the first HARQ process by a predefined rule. When a re-transmission is made, it is possible that the channel conditions have changed such that only a single transport block can be transmitted in a subframe (i.e., only one MIMO layer is possible). In this event, the control channel indicates whether the mapping of the retransmitted transport block to the MIMO layer has changed. However, this approach is restricted to two transport blocks per subframe, corresponding to the two MIMO substreams, and cannot directly be applied for carrier aggregation. Furthermore, because spatial multiplexing may be used along with carrier aggregation, more comprehensive approaches to error control processing in multi-carrier wireless systems are needed. An advantage of the system generally illustrated in Figure 2A is its flexibility. If, as discussed above, five bits per component carrier are used to identify the independent HARQ sub-processes (for a total of 20 bits), then re-transmissions may be freely scheduled on any component carrier without regard to which component carrier carried the original transmission (or prior re-transmission). This can be seen in Figure 3, which illustrates a simplified transmission scenario involving just two component carriers. Various transport blocks 110, associated with re-transmission process identifiers RP-1 , RP-2, etc., are transmitted using first and second component carriers. Thus, during a first transmission interval 115, transport blocks 110 associated with RP-1 and RP-8 are transmitted. To signal this scheduling, five retransmission process identifier bits (assuming up to four component carriers are available, with each requiring up to eight concurrent processes to maintain continuity) are sent on the control channel for each of the data substreams.

In the example illustrated by Figure 3, the transport block 110 associated with process identifier RP-1 is not decoded correctly. Thus, a NACK 120 is sent to the Node B, indicating that this transport block 110 should be re-transmitted. At a later transmission interval 125, the incorrectly decoded transport block 1 10 is rescheduled and the re-transmission 130 is performed over the second component carrier, despite the fact that the transport block was originally transmitted on the first component carrier. However, because independent process identifier information is sent for each component carrier in the control channel data corresponding to interval 125, the receiver is able to correctly match the re-transmitted transport block 1 10 to the original failed transmission. Data from the re-transmission may be combined with the originally received data to improve the probability that the re-transmitted transport block 1 10 is decoded correctly, using incremental redundancy.

Although five bits per component carrier are required for maximum flexibility (given the preceding assumptions), fewer may be used if certain scheduling restrictions are accepted. For instance, in each of several HARQ processing approaches discussed in more detail below, a common re-transmission process identifier is used in each transmission interval. Additional information is used to identify a unique sub-process, associated with that common process identifier, for each scheduled component carrier.

With this general approach, the signaling overhead required to identify the HARQ processes can be reduced, while retaining some flexibility in scheduling re-transmissions. This is generally illustrated in Figure 4. At a first time interval 415, transport blocks 1 10 are transmitted on the first and second component carriers, and are each associated with a common re-transmission process identifier RP-1. (This is quite different than the case in Figure 3, where the re-transmission process identifiers for the first and second component carriers are unrelated.) However, each transport block also has a sub-process identifier A or B. With this approach, transmissions in a given subframe are limited to sub-processes that are associated with a single, common re-transmission process identifier. However, retransmission of a given transport block is not necessarily limited to the same component carrier on which it was originally transmitted. This is seen at transmission interval 425, in which transport blocks 410 having the common process identifier RP-1 are again transmitted. However, the sub-process identifiers A and B in transmission interval 425 are mapped differently to the component carriers than they were in the earlier transmission interval 415. Thus, re-transmission 430, carried on the second component carrier, could be a re-transmission of the transport block 410 originally carried on the first component carrier.

The situation gets somewhat more complex if MIMO techniques are used in conjunction with multi-carrier technology. This is illustrated in Figure 5. Each of the illustrated first and second component carriers is capable, under favorable channel conditions, of carrying two spatially multiplexed substreams, designated substreams A and B in the figure. For maximum flexibility, it is preferred that the re-transmission of a given transport block may be scheduled for any available substream of any component carrier, without regard to which component carrier or substream carried the earlier transmission. Indeed, in some instances a particular substream that was used for an original transmission may not be available when a re-transmission becomes necessary, due to changing channel conditions. This is shown in Figure 5, where the unavailability of Substream B on Component Carrier 2 is indicated by an "X".

Of course, retaining the maximum possibility flexibility for scheduling re-transmissions requires more signaling bits to identify the HARQ processes than may be desirable. The techniques disclosed herein, in which a common process identifier is associated with all of the HARQ processes for a given transmission time interval, may be applied to multi-carrier systems with or without MIMO, to reduce this signaling. Thus, for example, referring once again to Figure 5, a re-transmission 530, corresponding to a common re-transmission process identifier RP-1 , may be transmitted on a different component carrier, as well as on a different substream, than those used for the original transmission of that transport block 510. Those skilled in the art will appreciate in particular that the techniques disclosed herein may be combined with the techniques disclosed in WO 2008/054313. In particular, the "disambiguation data" discussed in WO 2008/054313 may be used in combination with the common re-transmission process identifier and other techniques discussed herein to resolve the potential ambiguity that arises when re-transmitted transport blocks may be scheduled on either substream of a component carrier.

In the following detailed discussion it is assumed that the feedback delay and processing requirements of the wireless system are such that N_PR0C HARQ processes are needed to achieve continuous transmission when data is transmitted on a single carrier. The value N_PROC = 8 is used in some of the specific examples that follow, to illustrate the potential gains from the approaches described herein. This value corresponds to LTE FDD, in release 8. However, those skilled in the art will appreciate that other values may apply to other wireless systems or to future releases of LTE.

In several embodiments of the present invention, when data is transmitted on each of several component carriers, the data scheduled on each component carrier is transmitted in its own HARQ process. However, the flexibility of the HARQ protocol is restricted, such that the HARQ processes in a sub frame have a dependency and cannot be selected without constraint. In return for these constraints, the signaling needed to indicate the HARQ processes is reduced. Several alternative approaches exist, as described below. In systems employing a first solution, the L1/L2 control channel carrying scheduling information for the component carriers contains a common HARQ process number, K , which can range from zero to N_PR0C - 1 (i.e., K G [0,l, ...,N_PROC - I] ), as well as an additional parameter M for each component carrier, ranging from zero to one less than the number of carriers (i.e., M G [0,l,...,N_CARRIERS - I] ). The parameter M for each component carrier indicates, for HARQ purposes, the identity of that component carrier. The HARQ process number for a component carrier associated with a given value for parameter M is derived from the single HARQ process number K and the component carrier-specific value of M by a predefined rule. An example of such a rule is:

HARQ _ID_M = (K + N_PROC *M) . (1 ) Assuming (for the sake of this example only) that the wireless system supports a maximum of four component carriers, then three bits are required to encode the common HARQ process number K , while 4 * 2 = 8 bits are required to encode the parameter M for each of the four carriers. Thus, a total of eleven bits are needed with this approach, compared to the twenty bits that would be needed if each HARQ process were identified explicitly and independently in the HARQ protocol. With this solution, it is still possible to retransmit the data for only one or a few of the component carriers, which may become necessary if the channel conditions changed or if the data on only one or a few of the component carriers has been acknowledged. Further, the retransmitted transport block may be transmitted simultaneously with a new transport block on a different component carrier. Also, the data transmitted on one component carrier may be retransmitted on another component carrier if needed, allowing a great deal of flexibility in scheduling re-transmissions. This is controlled by selecting a suitable M for each component carrier in the re-transmission.

In a second, related solution, the L1/L2 control channel is configured to include a single, common HARQ process number K , just as in the previous solution, as well as an indication of which component carriers have been scheduled. This indication may take the form of a bitmap generated expressly for the purposes of supporting HARQ processing, or may be implicitly encoded within the resource allocation. If a bitmap is used, and if four component carriers are assumed as in the previous example, then three bits are needed to encode the common HARQ re-transmission process identifier, while four bits are needed to encode the bitmap. Thus, a total of seven bits are needed to encode, rather than the twenty bits required for an approach employing distinct, completely independent HARQ entities for each of the four component carriers. In this case, however, the reduced number of signaling bits comes with a cost, as the HARQ protocol is operated on each component carrier separately, and any re-transmission of data needs to be done on the same component carrier used for the prior transmission or retransmission.

In a variant of this solution, the HARQ processing circuit is configured to derive, from the resource allocation itself, information indicating which component carriers are currently scheduled to carry data for the mobile terminal. In this case it is not necessary to have the bitmap included on the control channel. This variant comes with the same restrictions regarding re-transmissions as previously discussed. However, in this solution, as in the previous two, one or more new transmissions and one or more re-transmissions may be transmitted in the same sub frame, on different component carriers, provided that separate new data indicators and/or redundancy versions are indicated for each component carrier. In yet another related approach, the L1/L2 control channel again contains a single, common HARQ process number K per subframe. The unique HARQ process identifier for each component carrier is derived from K and a number identifying the component carrier as the first approach described above. However, in this variant, a component carrier number M is not explicitly signaled. Instead, the control channel number is derived from the detected control channels according to a predefined rule known to the mobile terminal. An example of such a rule is that the data in the n-th detected control channel uses a HARQ process having an identifier calculated according to:

HARQ _ ID(n) = (K + N_PR0C * n) . (2)

This approach is quite similar to the first solution described above, except that the index n , which maps the common process identifier to a unique process identifier for each of the separate component carriers, is not explicitly signaled. Thus, the control channel overhead is smaller. However, in some embodiments this approach may result in a somewhat increased sensitivity to errors, in some circumstances. For example, if the control channel for one of the component carriers is not detected, the mobile terminal may make an incorrect determination of the mapping of the index n to one or more component carriers. In this case, the received data will be associated with the wrong HARQ process, potentially leading to data loss or long delays.

The previous approach may also be used in a system where there is only a single control channel containing information about several component carriers. In this case, the sub- process for a component carrier would instead be tied to, i.e., derived from, the control information related to that component carrier, within the single control channel. For example, the order in which control channel information for the various scheduled component carriers is mapped to the single control channel structure may be used to indicate the correspondence between re-transmission sub-processes and the component carriers. In other words, the order of the component carrier information may implicitly signal the value of the index n for each component carrier; this index n may be used to uniquely identify the sub-process given a common process identifier, such as according to Equation (2) above.

Those skilled in the art will appreciate that each of the approaches described above reduce the signaling overhead in the L1/L2 control channels, through the use of a common retransmission process identifier. In return for this reduced signaling load, each of these approaches sacrifices, to some degree, flexibility in scheduling the re-transmission of incorrectly received transport blocks.

Although the discussion herein generally assumes that the HARQ process is applied to a downlink communication (i.e., for transport blocks transmitted to a mobile terminal from a base station), those skilled in the art will appreciate that the techniques described herein may be applied to HARQ processing in either direction. That is, the techniques described herein may be applied as well to HARQ processing used to provide error control for transport blocks sent from user equipment to the radio base station. Similarly, those skilled in the art will appreciate that the inventive techniques described herein are not limited to LTE systems, but are equally applicable to any wireless communication system or standard employing multi-carrier transmission, and where multiple acknowledgement processes run simultaneously on each of the component carriers. With the previous discussion of various approaches to HARQ processing in mind, Figure 6 illustrates an exemplary method for signaling scheduling information to a mobile terminal in a multi-carrier wireless system. The process begins, as illustrated at block 610, with the scheduling of first and second transport blocks for simultaneous transmission in a first transmission interval on first and second component carriers, respectively. Of course, more than two component carriers may be used in some systems, in which case an additional transport block may be scheduled in any additional component carrier. Further, although the process of Figure 6 suggests a "beginning," at block 610, and "end," at block 660, those skilled in the art will appreciate that the illustrated process may represent but one cycle in a repetitive process, in some embodiments of the invention. Indeed, several instances of the process illustrated in Figure 6 may be implemented concurrently, in some embodiments of the invention, e.g., in an overlapping fashion to account for processing delays and feedback delays in the wireless system and devices.

In any event, the illustrated process continues, as shown at block 620, with the transmission of scheduling information for the first transmission interval. This scheduling information includes a common re-transmission process identifier that is effectively assigned to that transmission interval, and that therefore corresponds to both of the first and second transport blocks scheduled for that interval. In some embodiments, the common retransmission process identifier may comprise a 3-bit datum, supporting 8 unique process identifiers. The scheduling information corresponding to the first transmission interval is sent to the receiver over the downlink control channel (which is transmitted during the first 1 , 2, or 3 OFDM symbols in an LTE system). As will be discussed further below, in some embodiments this scheduling information may include explicit sub-process mapping data relating a distinct retransmission sub-process to each of the first and second component carriers for the first transmission interval, although this relation may be derived in other ways in other embodiments.

As shown at block 630, a NACK is received for the first transport block sent during the first interval. (The terms "first" and "second," and similar terms, are generally used herein simply to distinguish one instance of an item from another, rather than to indicate an order, unless the context clearly indicates otherwise. Here, the "first" transport block simply refers to an arbitrary one of the transport blocks scheduled in the first transmission time interval.) Those skilled in the art will appreciate that this NACK may be received several transmission time intervals after the first interval, due to signal propagation and processing delays. In response to the NACK, the eNB must re-schedule the NACKed transport block (or blocks) for a subsequent interval. As shown at block 640, the first transport block is scheduled for re-transmission for a second transmission interval. Under some circumstances, the NACKed transport block may simply be scheduled for the same component carrier as was used for the original transmission. However, in other circumstances it may be desirable to switch component carriers for the retransmission of the NACKed transport block. Thus, in some embodiments, the first transport block may scheduled for re-transmission on the second component carrier, i.e., a component carrier other than the one originally used, for the second transmission interval.

Because a common re-transmission process identifier applies to all of the component carriers used in a particular transmission time interval, other transport blocks transmitted in the same interval as the re-transmission of the first transport block share the same common retransmission process identifier. However, other transport blocks transmitted in that interval need not be re-transmissions. Thus, as shown in block 650, a third transport block is also scheduled for transmission in the second transmission interval, on a different component carrier from the re-transmission of the first transport block. Second scheduling information is then transmitted for the second interval, the scheduling information including the same common retransmission process identifier as used in the first transmission. The fact that the third transport block carries new data can be signaled with a component-carrier-specific "new data indicator" flag, for example.

The flexibility to schedule a re-transmission on a different component carrier from that used for an original transmission may be enabled by several of the techniques described earlier. Of course, in some embodiments of the invention, the common re-transmission process identifier may be used in a HARQ process in which re-transmissions are restricted to the same component carrier as the original transmission, thus obviating the need for additional signaling information to map specific sub-processes to the scheduled component carriers. In some of these embodiments, mapping data may be sent, in addition to the common re-transmission process identifier, that simply identifies which of the available component carriers is currently scheduled. If a "new data indicator" or other mechanism is used to identify which, if any, component carriers are carrying new data, rather than re-transmissions, then new data and retransmissions can be mixed in the same transmission interval.

In some embodiments of the invention, as suggested above, the re-transmission process described in Figure 6 is extended to cover the use of spatial multiplexing. In some of these embodiments, two transport blocks may be scheduled on each of two or more component carriers, with a transport block scheduled on each of first and second spatially multiplexed substreams. (Those skilled in the art will appreciate, of course, that one component carrier may carry two substreams while another carries only one, at any given time; at other times all or none of the component carriers may support spatial multiplexing.) In these embodiments, a re- transmission of a given transport block may be scheduled for a different substream than used for the original transmission. This may be necessary, for example, if the channel conditions have changed so that a second substream is not available in a second transmission interval, or if the channel conditions necessitate a change in the modulation and coding scheme used in one or both substreams. The common re-transmission process identifier may be coupled, in these embodiments, with first and second disambiguation data transmitted during the first and second transmission intervals, respectively. The first and second disambiguation data, which may be as simple as a single bit associated with each carrier, jointly indicates whether the retransmitted block is scheduled for a different substream than that used for the original transmission. This can be done, for example, by simply setting the bit to an arbitrary state (e.g., "0") for the original transmission, and then inverting the bit (to "1") for the re-transmission interval if and only if the re-transmission in that interval is on a different substream from the original transmission. In some embodiments, a re-transmission may be restricted to the same component carrier (or, alternatively, may be restricted to the same component carrier if it changes substreams). In others, the re-transmission may be on a different substream as well as on a different component carrier. In the latter case, the disambiguation data for the first and second transmission intervals jointly indicates that the re-transmission is on a different substream and a different component carrier than used for the original transmission (or earlier re-transmission).

In some embodiments, the common re-transmission process identifier, which corresponds to all of the component carriers, is accompanied by sub-process mapping data, which relates a distinct re-transmission sub-process to each of the first and second component carriers for the respective transmission interval. In this way, sub-processes can be mapped arbitrarily to component carriers, even while the sub-processes share a common retransmission process identifier. As discussed earlier, the length of the sub-process mapping data will generally depend on the number of supported component carriers. For four component carriers, only two bits are needed per component carrier, to provide each component carrier with a "sub-process" identifier to supplement the common re-transmission process identifier. The mapping of a particular sub-process identifier to a particular component carrier may change from one transmission interval to the next, or may remain the same.

A multi-carrier wireless communications system according to some embodiments of the present invention is illustrated in Figure 7. Wireless communications system 700, which may in some embodiments comprise an Advanced-LTE system utilizing both multi-carrier and MIMO technology, comprises a network node 720, such as an LTE base station, communicating with mobile terminal 750, using two or more base station antennas 725 and two or more mobile terminal antennas 755. Network node 720 comprises a transmitter subsystem 730, which is configured to convert baseband information signals and control signals to radio signals for transmission via antennas 720, base-station receiver 740, and controller 745, which is configured to perform fast packet scheduling, among other things. Exemplary mobile terminal 750 comprises a receiver subsystem 760 adapted to receive radio signals transmitted according to the LTE standards (for example), a mobile transmitter section 770, and mobile controller 775. Controller 745 is configured to carry out one or more of the methods described herein, or variants thereof, for signaling scheduling information in a multi-carrier wireless communications system such as wireless communications system 700. In particular, controller 745 may be configured to schedule first and second transport blocks for simultaneous transmission during a first transmission interval on first and second component carriers, respectively, to prepare first scheduling information for the first transmission interval, the first scheduling information comprising a common re-transmission process identifier for the first and second component carriers, and to transmit the first scheduling information to the mobile terminal, via transmitter subsystem 730. Controller 745 may be further configured to schedule the first transport block for re-transmission during a second transmission interval, along with a third transport block scheduled for a different one of the component carriers from the re-transmission. Finally, the controller 745 may be further configured to prepare second scheduling information for the second transmission interval, the second scheduling information comprising the same common re-transmission process identifier, and to transmit the second scheduling information to the mobile terminal, via the transmitter subsystem 730. As described in more detail above, explicit mapping data, disambiguation data, and/or information implicit in scheduling data may be used in some embodiments to determine whether the re-transmission is on the same or a differing component carrier from the original transmission, and/or on a different substream. Thus, in some embodiments, the first and second scheduling data may include sub-process mapping data for each of the first and second component carriers, the values of which relate a distinct retransmission sub-process to each component carrier. In other embodiments, the sub-process mapping is implicit, and may be derived from the first and second scheduling information.

In some embodiments, re-transmission of a transport block via transmitter subsystem 730 is triggered by receipt of a NACK message, which may be received by controller 745 via base-station receiver 740.

In various embodiments, controller 745 may comprise one or more microprocessors, microcontrollers, digital signal processors, or the like, any or all of which may be configured with software and/or firmware comprising program instructions for carrying out some or all of the techniques described herein. Those skilled in the art will appreciate that the functionality of the controller 745 described above may be implemented on a single processor or application- specific integrated circuit (ASIC), or split between two or more processors and/or ASICs, and that some processing may be carried out with special-purpose hardware rather than a programmable device. Similarly, mobile terminal 750 includes a mobile controller 775 configured to carry out methods corresponding to the above-described receiver-based methods for processing scheduling information in a multi-carrier wireless communications system, such as wireless communications system 700. One exemplary receiver-based method is shown in Figure 8. As shown at blocks 810 and 820, controller 775 is configured to receive (via the receiver subsystem 760) first and second transport blocks 1 10 simultaneously transmitted during a first transmission interval on first and second component carriers, after receiving scheduling information for the first transmission interval. The received scheduling information includes a common re-transmission process identifier for the component carriers and may also include sub-process mapping data and/or substream disambiguation data, in some embodiments. In some embodiments, controller 775 is configured to generate a negative acknowledgement (NACK), and to transmit the NACK to base station 720, via transmitter subsystem 770. The NACK indicates that at least one of the first and second transport blocks 110 transmitted during the first transmission interval was received with errors. In any case, controller 775 is configured to map the first and second transport blocks to first and second re-transmission processes that correspond to the common re-transmission process identifier, as shown in block 830. Then, controller 775 subsequently receives second scheduling information for a second transmission interval, as shown at block 840, the second scheduling information including the same common re-transmission process identifier used for the first transmission interval. (Those skilled in the art will appreciate that several transmission intervals, corresponding to different re-transmission process identifiers, may intervene between the first and second transmission intervals discussed here.) As shown at blocks 850 and 860, the controller 775 then receives third and fourth transport blocks, on the first and second component carriers, and determines that one of third and fourth transport blocks received during the second transmission interval is a re-transmission of the NACKed transport block (e.g., via the absence of a new data indicator.) Finally, the controller 775 is configured to match the retransmitted transport block to one of the first and second re-transmission sub-processes, as shown at block 870, based at least in part on the correspondence between the third and fourth transport blocks and the first and second component carriers. In some embodiments, the matching of the re-transmitted transport block to one of the first and second re-transmission sub-processes is based simply on a p re-determined rule restricting scheduling of re-transmitted transport blocks to the same component carrier that carried the original transmissions. In some of these embodiments, the first and second scheduling information may include component carrier mapping data that indicates which of the aggregated component carriers is scheduled for the corresponding transmission interval, in which case mapping the first and second transport blocks to the first and second re- transmission sub-processes is based at least in part on the mapping data. In others of these embodiments, controller 775 may be configured to derive similar mapping data from the first and second scheduling information, rather than receiving explicitly signaled mapping data.

In some embodiments, controller 775 is further configured to receive sub-process mapping data for each of the first and second transmission intervals, wherein the sub-process mapping data relates a distinct re-transmission sub-process to each of the first and second component carriers for the respective transmission interval. Controller 775 may then use the sub-process mapping data to map the first and second transport blocks to the first and second re-transmission sub-processes, and to match the re-transmitted transport block to the correct one of the first and second re-transmission sub-processes. In some of these embodiments, the sub-process mapping data comprises one or more mapping bits for each of the first and second component carriers, such that the one or more mapping bits identify a particular sub-process of a pre-determined group of sub-processes.

In still other embodiments, controller 775 is configured to match the re-transmitted transport block to one of the first and second re-transmission sub-processes by receiving and decoding control channel information for each of the first and second component carriers according to a pre-determined control channel format, and then determining the correspondence of re-transmission sub-processes to the first and second component carriers, for each of the first and second transmission intervals, based on the order of the control channel information for the first and second components within the pre-determined control channel format.

Finally, any of the controllers described above may be further configured to process first scheduling information that further indicates that the first transport block and a fifth transport block are scheduled for first and second spatially multiplexed substreams, respectively, of the first component carrier during the first transmission interval, and to process second scheduling information that further indicates that the first transport block is scheduled for re-transmission on the first component carrier during the second transmission interval. In these embodiments, controller 775 is further configured to receive first and second disambiguation data corresponding to the first and second transmission intervals, respectively, and to use the first and second disambiguation data to determine whether the re-transmission of the first transport block is scheduled for the first or second spatially multiplexed substream of the first component carrier during the second transmission interval.

As with the controller 745, controller 775 may comprise one or more microprocessors, microcontrollers, digital signal processors, or the like, any or all of which may be configured with software and/or firmware comprising program instructions for carrying out some or all of the mobile-based techniques described herein. Those skilled in the art will appreciate that the functionality of the controller 745 described above may be implemented on a single processor or application-specific integrated circuit (ASIC), or split between two or more processors and/or ASICs, and that some processing may be carried out with special-purpose hardware rather than a programmable device.

The present invention may, of course, be carried out in other ways than those specifically set forth herein without departing from essential characteristics of the invention. The present embodiments are to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.

Claims

CLAIMSWhat is claimed is:

1. A method for signaling scheduling information to a mobile terminal (750) in a multi- carrier wireless communications system (700) using two or more aggregated component carriers, the method comprising scheduling (610) first and second transport blocks for simultaneous transmission to the mobile terminal (750) during a first transmission interval on first and second component carriers, respectively; and scheduling (640) the first transport block for re-transmission to the mobile terminal (750) during a second transmission interval, in response to an unsuccessful reception of the first transport block; characterized in that the method further comprises: transmitting (620) first scheduling information to the mobile terminal (750) for the first transmission interval, the first scheduling information comprising a common retransmission process identifier for the first and second component carriers; scheduling (650) a third transport block for simultaneous transmission to the mobile terminal (750) during the second transmission interval, on a different one of the first and second component carriers from the first transport block; and transmitting (660) second scheduling information to the mobile terminal (750) for the second transmission interval, the second scheduling information comprising the common re-transmission process identifier.

2. The method of claim 1 , characterized in that the method further comprises restricting the scheduling of the re-transmission of the first transport block during the second transmission interval to the first component carrier.

3. The method of claim 2, characterized in that the transmitted first and second scheduling information comprise component carrier mapping data indicating which of the two or more aggregated component carriers is scheduled for the corresponding transmission interval.

4. The method of claim 2 or 3, characterized in that the method further comprises: scheduling the first transport block and a fourth transport block for simultaneous transmission on first and second spatially multiplexed substreams, respectively, of the first component carrier during the first transmission interval; scheduling the first transport block for re-transmission on the second spatially multiplexed substream of the first component carrier during the second transmission interval; and transmitting first and second disambiguation data during the first and second transmission intervals, respectively, the first and second disambiguation data jointly indicating that re-transmission of the first transport block is scheduled for the second spatially multiplexed substream of the first component carrier during the second transmission interval.

5. The method of claim 1 , further characterized in that each of the transmitted first and second scheduling information further comprises sub-process mapping data, the sub-process mapping data relating a distinct re-transmission sub-process to each of the first and second component carriers for the respective transmission interval.

6. The method of claim 5, further characterized in that the sub-process mapping data comprises one or more mapping bits for each of the first and second component carriers, the one or more mapping bits identifying a particular sub-process of a pre-determined group of sub- processes.

7. The method of claim 1 , further characterized in that the method further comprises: mapping control channel information for each of the first and second component carriers to a pre-determined control channel format in an order that indicates the correspondence of re-transmission sub-processes to the first and second component carriers, for each of the first and second transmission intervals; and transmitting the mapped control channel information during the first and second transmission intervals.

8. The method of any of claims 5-7, characterized in that the method further comprises: scheduling the first transport block and a fourth transport block for simultaneous transmission on first and second spatially multiplexed substreams, respectively, of the first component carrier during the first transmission interval; scheduling the first transport block for re-transmission on the second spatially multiplexed substream of the second component carrier during the first transmission intervals; and transmitting first and second disambiguation data during the first and second transmission intervals, respectively, the first and second disambiguation data jointly indicating that re-transmission of the first transport block is scheduled for the second spatially multiplexed substream of the second component carrier during the second transmission interval.

9. An arrangement in a network node (720) in a multi-carrier wireless communications system (700) using two or more aggregated component carriers, the arrangement comprising a controller (745) configured to schedule first and second transport blocks for simultaneous transmission to a mobile terminal (750) during a first transmission interval on first and second component carriers, respectively, and to schedule the first transport block for re-transmission to the mobile terminal (750) during a second transmission interval, in response to an unsuccessful reception of the first transport block; characterized in that the controller (745) is further configured to: prepare first scheduling information for the mobile terminal (750) for the first transmission interval and transmit the first scheduling information to the mobile terminal (750) via a transmitter subsystem (730), the first scheduling information comprising a common re-transmission process identifier for the first and second component carriers; schedule a third transport block for simultaneous transmission to the mobile terminal

(750) during the second transmission interval, on a different one of the first and second component carriers from the first transport block; and prepare second scheduling information to the mobile terminal (750) for the second transmission interval and transmit the second scheduling information to the mobile terminal (720) via a transmitter subsystem , the second scheduling information comprising the common re-transmission process identifier.

10. The arrangement of claim 9, characterized in that the controller (745) is further configured to restrict the scheduling of the re-transmission of the first transport block during the second transmission interval to the first component carrier.

11. The arrangement of claim 10, characterized in that the transmitted first and second scheduling information comprise component carrier mapping data indicating which of the two or more aggregated component carriers is scheduled for the corresponding transmission interval.

12. The arrangement of claim 10 or 1 1 , characterized in that the controller (745) is further configured to: schedule the first transport block and a fourth transport block for simultaneous transmission on first and second spatially multiplexed substreams, respectively, of the first component carrier during the first transmission interval; schedule the first transport block for re-transmission on the second spatially multiplexed substream of the first component carrier during the second transmission interval; and transmit first and second disambiguation data during the first and second transmission intervals, respectively, the first and second disambiguation data jointly indicating that re-transmission of the first transport block is scheduled for the second spatially multiplexed substream of the first component carrier during the second transmission interval.

13. The arrangement of claim 9, further characterized in that the re-transmission of the first transport block during the second transmission interval is scheduled for the second component carrier, and in that each of the transmitted first and second scheduling information further comprises sub-process mapping data, the sub-process mapping data relating a distinct retransmission sub-process to each of the first and second component carriers for the respective transmission interval.

14. The arrangement of claim 13, further characterized in that the sub-process mapping data comprises one or more mapping bits for each of the first and second component carriers, the one or more mapping bits identifying a particular sub-process of a pre-determined group of sub- processes.

15. The arrangement of claim 9, further characterized in that the controller (745) is further configured to: map control channel information for each of the first and second component carriers to a pre-determined control channel format in an order that indicates the correspondence of re-transmission sub-processes to the first and second component carriers, for each of the first and second transmission intervals; and transmit the mapped control channel information during the first and second transmission intervals.

16. The arrangement of any of claims 5-7, characterized in that the controller (745) is further configured to: schedule the first transport block and a fourth transport block for simultaneous transmission on first and second spatially multiplexed substreams, respectively, of the first component carrier during the first transmission interval; schedule the first transport block for re-transmission on the second spatially multiplexed substream of the second component carrier during the first transmission intervals; and transmit first and second disambiguation data during the first and second transmission intervals, respectively, via the transmitter subsystem (730), the first and second disambiguation data jointly indicating that re-transmission of the first transport block is scheduled for the second spatially multiplexed substream of the second component carrier during the second transmission interval.

17. A method in a mobile terminal (750) for processing scheduling information in a multi- carrier wireless communications system (700) using two or more aggregated component carriers, characterized in that the method comprises: receiving (810) first scheduling information for a first transmission interval, the first scheduling information indicating that first and second transport blocks are scheduled for simultaneous transmission to the mobile terminal (750) during the first transmission interval on first and second component carriers, respectively, wherein the scheduling information comprises a common re-transmission process identifier for the first and second component carriers; receiving (840) second scheduling information for a second transmission interval, the second scheduling information indicating that third and fourth transport blocks are scheduled for simultaneous transmission to the mobile terminal (750) during the second transmission interval transmission interval on the first and second component carriers, respectively, wherein the second scheduling information comprises the same common re-transmission process identifier as the first scheduling information; mapping (830) the first and second transport blocks to first and second re-transmission sub-processes corresponding to the common re-transmission process identifier; and determining (860) that only one of the third and fourth transport blocks is a re- transmission, and matching (870) the re-transmitted transport block to one of the first and second re-transmission sub-processes, based at least in part on the correspondence between the third and fourth transport blocks and the first and second component carriers.

18. The method of claim 17, characterized in that matching (870) the re-transmitted transport block to one of the first and second re-transmission sub-processes is based on a pre- determined rule restricting scheduling of re-transmitted transport blocks to the same component carriers carrying the original transmissions.

19. The method of claim 18, characterized in that the transmitted first and second scheduling information comprise component carrier mapping data indicating which of the two or more aggregated component carriers is scheduled for the corresponding transmission interval, wherein mapping (830) the first and second transport blocks to first and second re-transmission sub-processes corresponding to the common re-transmission process identifier is based at least in part on the mapping data.

20. The method of claim 18, characterized in that the method further comprises deriving mapping data from the transmitted first and second scheduling information, the derived mapping data indicating which of the two or more aggregated component carriers is scheduled for the corresponding transmission interval, wherein mapping (830) the first and second transport blocks to first and second re-transmission sub-processes corresponding to the common retransmission process identifier is based at least in part on the derived mapping data.

21. The method of claim 17, further characterized in that the method further comprises receiving sub-process mapping data for each of the first and second transmission intervals, the sub-process mapping data relating a distinct re-transmission sub-process to each of the first and second component carriers for the respective transmission interval, wherein mapping (830) the first and second transport blocks to first and second re-transmission sub-processes and matching the re-transmitted transport block to one of the first and second re-transmission sub- processes are based on the sub-process mapping data.

22. The method of claim 21 , further characterized in that the sub-process mapping data comprises one or more mapping bits for each of the first and second component carriers, the one or more mapping bits identifying a particular sub-process of a pre-determined group of sub- processes.

23. The method of claim 17, further characterized in that the matching the re-transmitted transport block to one of the first and second re-transmission sub-processes comprises: receiving and decoding control channel information for each of the first and second component carriers according to a pre-determined control channel format; and determining the correspondence of re-transmission sub-processes to the first and second component carriers, for each of the first and second transmission intervals, based on the order of the control channel information for the first and second components within the pre-determined control channel format.

24. The method of any of claims 17-23, characterized in that the first scheduling information further indicates that the first transport block and a fifth transport block are scheduled for first and second spatially multiplexed substreams, respectively, of the first component carrier during the first transmission interval; and in that the second scheduling information further indicates that the first transport block is scheduled for re-transmission on the first component carrier during the second transmission interval; and in that the method further comprises: receiving first and second disambiguation data corresponding to the first and second transmission intervals, respectively; and using the first and second disambiguation data to determine whether the re-transmission of the first transport block is scheduled for the first or second spatially multiplexed substream of the first component carrier during the second transmission interval.

25. An arrangement in a mobile terminal (750), comprising a controller (775) configured to process received scheduling information for operating in a multi-carrier wireless communications system using two or more aggregated component carriers, characterized in that the controller (775) is configured to: receive first scheduling information for a first transmission interval, the first scheduling information indicating that first and second transport blocks are scheduled for simultaneous transmission to the mobile terminal (750) during the first transmission interval on first and second component carriers, respectively, wherein the scheduling information comprises a common re-transmission process identifier for the first and second component carriers; receive second scheduling information for a second transmission interval, the second scheduling information indicating that third and fourth transport blocks are scheduled for simultaneous transmission to the mobile terminal (750) during the second transmission interval transmission interval on the first and second component carriers, respectively, wherein the second scheduling information comprises the same common re-transmission process identifier as the first scheduling information; map the first and second transport blocks to first and second re-transmission sub- processes corresponding to the common re-transmission process identifier; and determine that only one of the third and fourth transport blocks is a re-transmission, and match the re-transmitted transport block to one of the first and second re- transmission sub-processes, based at least in part on the correspondence between the third and fourth transport blocks and the first and second component carriers.

26. The arrangement of claim 25, characterized in that the controller (775) is configured to match the re-transmitted transport block to one of the first and second re-transmission sub- processes using a p re-determined rule restricting scheduling of re-transmitted transport blocks to the same component carriers carrying the original transmissions.

27. The arrangement of claim 26, characterized in that the transmitted first and second scheduling information comprise component carrier mapping data indicating which of the two or more aggregated component carriers is scheduled for the corresponding transmission interval, and wherein the controller (775) is configured to use the mapping data to map the first and second transport blocks to first and second re-transmission sub-processes corresponding to the common re-transmission process identifier.

28. The arrangement of claim 26, characterized in that the controller (775) is further configured to derive mapping data from the transmitted first and second scheduling information, the derived mapping data indicating which of the two or more aggregated component carriers is scheduled for the corresponding transmission interval, and to use the derived mapping data to map the first and second transport blocks to first and second re-transmission sub-processes corresponding to the common re-transmission process identifier.

29. The arrangement of claim 25, further characterized in that the controller (775) is further configured to receive sub-process mapping data for each of the first and second transmission intervals, the sub-process mapping data relating a distinct re-transmission sub-process to each of the first and second component carriers for the respective transmission interval, and to use the sub-process mapping data to map the first and second transport blocks to first and second re-transmission sub-processes and to match the re-transmitted transport block to one of the first and second re-transmission sub-processes.

30. The arrangement of claim 29, further characterized in that the sub-process mapping data comprises one or more mapping bits for each of the first and second component carriers, the one or more mapping bits identifying a particular sub-process of a p re-determined group of sub- processes.

31. The arrangement of claim 25, further characterized in that the controller (775) is configured to match the re-transmitted transport block to one of the first and second retransmission sub-processes by: receiving and decoding control channel information for each of the first and second component carriers according to a pre-determined control channel format; and determining the correspondence of re-transmission sub-processes to the first and second component carriers, for each of the first and second transmission intervals, based on the order of the control channel information for the first and second components within the pre-determined control channel format.

32. The arrangement of any of claims 25-31 , characterized in that the first scheduling information further indicates that the first transport block and a fifth transport block are scheduled for first and second spatially multiplexed substreams, respectively, of the first component carrier during the first transmission interval; and in that the second scheduling information further indicates that the first transport block is scheduled for re-transmission on the first component carrier during the second transmission interval; and in that the controller (775) is further configured to: receive first and second disambiguation data corresponding to the first and second transmission intervals, respectively; and use the first and second disambiguation data to determine whether the re-transmission of the first transport block is scheduled for the first or second spatially multiplexed substream of the first component carrier during the second transmission interval.