HK1173281B - Apparatus and method for providing harq feedback in a multi-carrier wireless communication system - Google Patents

Description

Apparatus and method for providing HARQ feedback in a multi-carrier wireless communication system

Cross Reference to Related Applications

The present application claims priority from U.S. patent application No.61/248,666 entitled "HS-DPCCHACK/NACK CODE BOOK DESIGN FOR 4C-HSDPA" filed on 5.10.2009, the entire contents of which are expressly incorporated herein by reference.

Technical Field

Some aspects of the present disclosure generally relate to wireless communication systems, and more particularly, to providing feedback information in a multi-carrier wireless communication system.

Background

Wireless communication networks are widely deployed to provide various communication services such as telephony, video, data, messaging, broadcast, and so on. These networks, typically multiple-access networks, support communication for multiple users by sharing the available network resources. An example of such a network is the UMTS Terrestrial Radio Access Network (UTRAN). UTRAN, which is a Radio Access Network (RAN) defined as part of the Universal Mobile Telecommunications System (UMTS), is a third generation (3G) mobile telephony technology supported by the third generation partnership project (3 GPP). UMTS, as a successor to global system for mobile communications (GSM) technology, currently supports various air interface standards, such as wideband-code division multiple access (W-CDMA), time division-code division multiple access (TD-CDMA), and time division-synchronous code division multiple access (TD-SCDMA). UMTS also supports enhanced 3G data communications protocols, such as high speed packet access (HSDPA), which provides higher data transfer speeds and greater capacity to associated UMTS networks.

With the ever-increasing demand for mobile broadband access, research and development continue to improve UMTS technology not only to meet the increasing demand for mobile broadband access, but also to improve and enhance the user experience with mobile communications.

Disclosure of Invention

The method and apparatus of the present invention provides hybrid automatic repeat request (HARQ) feedback corresponding to the status of multiple downlink carriers with or without MIMO configuration. Here, for at least some configurations, the downlink carriers are grouped into groups of one or two carriers for selection of HARQ feedback symbols such that a codebook of HARQ feedback symbols previously implemented in conventional HSDPA or DC-HSDPA systems may be used. That is, after encoding a data stream, an uplink channel is modulated using HARQ feedback symbols selected from a plurality of codebooks configured for groups of one or two downlink carriers. Modulation and channelization may be accomplished using dual channelization codes or a single channelization code that reduces the spreading factor to insert two symbols into a single slot.

In one aspect of the disclosure, a method of wireless communication is provided, comprising: downlink signaling is received on a plurality of downlink carriers and hybrid automatic repeat request (HARQ) feedback corresponding to each of the plurality of carriers is determined. A first HARQ feedback symbol is selected for encoding HARQ feedback corresponding to a first subset of the plurality of carriers. Here, the first subset includes at least two of the plurality of carriers. Selecting a second HARQ feedback symbol for encoding HARQ feedback corresponding to a second subset of the plurality of carriers. Here, the second subset includes at least one of the plurality of carriers. The first and second HARQ feedback symbols are transmitted on the uplink.

In another aspect of the disclosure, a method of wireless communication is provided, comprising: the method includes providing a first feedback symbol corresponding to a decoding status of information received on a plurality of downlink carriers and providing a second feedback symbol corresponding to a decoding status of information received on at least one downlink carrier.

In yet another aspect of the disclosure, an apparatus of wireless communication is provided that includes a receiver to receive downlink signaling on a plurality of downlink carriers. The apparatus includes a processor configured to: determining hybrid automatic repeat request (HARQ) feedback corresponding to each of the plurality of carriers; selecting a first HARQ feedback symbol for encoding HARQ feedback corresponding to a first subset of the plurality of carriers, wherein the first subset includes at least two of the plurality of carriers; and selecting a second HARQ feedback symbol for encoding HARQ feedback corresponding to a second subset of the plurality of carriers, wherein the second subset includes at least one of the plurality of carriers. The apparatus also includes a transmitter that transmits the first and second HARQ feedback symbols on an uplink.

In yet another aspect of the present disclosure, an apparatus of wireless communication is provided, comprising: the apparatus generally includes means for receiving downlink signaling on a plurality of downlink carriers, and means for determining hybrid automatic repeat request (HARQ) feedback corresponding to each of the plurality of carriers. In addition, the apparatus includes: means for selecting a first HARQ feedback symbol to encode HARQ feedback corresponding to a first subset of the plurality of carriers, wherein the first subset includes at least two of the plurality of carriers; and means for selecting a second HARQ feedback symbol to encode HARQ feedback corresponding to a second subset of the plurality of carriers, wherein the second subset includes at least one of the plurality of carriers; and means for transmitting the first and second HARQ feedback symbols on an uplink.

In yet another aspect of the disclosure, an apparatus for wireless communication is provided, comprising: the apparatus includes means for providing a first feedback symbol corresponding to a decoding status of information received on a plurality of downlink carriers, and means for providing a second feedback symbol corresponding to a decoding status of information received on at least one downlink carrier.

In yet another aspect of the disclosure, a computer program product is provided. The computer program product includes a computer-readable medium having code for causing a computer to: receiving downlink signaling on a plurality of downlink carriers; determining hybrid automatic repeat request (HARQ) feedback corresponding to each of the plurality of carriers; selecting a first HARQ feedback symbol for encoding HARQ feedback corresponding to a first subset of the plurality of carriers, where the first subset includes at least two of the plurality of carriers; selecting a second HARQ feedback symbol for encoding HARQ feedback corresponding to a second subset of the plurality of carriers, where the second subset includes at least one of the plurality of carriers; the first and second HARQ feedback symbols are transmitted on an uplink.

In yet another aspect of the disclosure, an apparatus for wireless communication is provided that includes at least one processor and a memory coupled to the at least one processor. Here, the at least one processor is configured to: receiving downlink signaling on a plurality of downlink carriers; determining hybrid automatic repeat request (HARQ) feedback corresponding to each of the plurality of carriers; selecting a first HARQ feedback symbol for encoding HARQ feedback corresponding to a first subset of the plurality of carriers, wherein the first subset includes at least two of the plurality of carriers; selecting a second HARQ feedback symbol for encoding HARQ feedback corresponding to a second subset of the plurality of carriers, wherein the second subset includes at least one of the plurality of carriers; and transmitting the first and second HARQ feedback symbols on an uplink.

These and other aspects of the invention will be more fully understood after reviewing the following detailed description.

Drawings

FIG. 1 is a diagram illustrating an example hardware implementation of an apparatus using a processing system;

FIG. 2 is a block diagram conceptually illustrating an example of a telecommunications system;

fig. 3 is a block diagram conceptually illustrating a frame structure of an uplink high speed dedicated physical control channel (HS-DPCCH);

figure 4 is a block diagram conceptually illustrating three exemplary channelization schemes for encoding HARQ feedback to HS-DPCCH;

figure 5 is a block diagram conceptually illustrating three exemplary slots for carrying HARQ feedback in the HS-DPCCH;

fig. 6A and 6B are simplified schematic diagrams of a UE and a node B communicating according to exemplary aspects of the disclosure;

FIG. 7 is a pair of flow diagrams illustrating an exemplary process in accordance with aspects of the present disclosure;

fig. 8 is a block diagram conceptually illustrating an example of a node B communicating with a UE in a telecommunication system.

Detailed Description

The detailed description set forth below in connection with the appended drawings is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of various concepts. It will be apparent, however, to one skilled in the art that these concepts may be practiced without these specific details. In some instances, well-known structures and components are shown in block diagram form in order to avoid obscuring such concepts.

Fig. 1 is an example of a hardware implementation showing an apparatus 100 using a processing system 114. In this example, the processing system 114 may be implemented using a bus structure, represented generally by the bus 102. The bus 102 may include any number of interconnecting buses and bridges based on the specific application of the processing system 114 and the overall design constraints. The bus 102 couples various circuits together, including one or more processors, represented generally by the processor 104, and computer-readable media, represented generally by the computer-readable medium 106. The bus 102 may also connect various other circuits such as timing sources, peripherals, voltage regulators, and power management circuits, which are well known in the art, and therefore, will not be described any further. Bus interface 108 provides an interface between bus 102 and transceiver 110. The transceiver 110 provides a means for communicating with various other apparatus over a transmission medium. Depending on the nature of the device, a user interface 112 (e.g., keypad, display, speaker, microphone, and joystick) may also be provided.

The processor 104 is responsible for managing the bus 102 and conventional processing, including the execution of software stored in the computer-readable medium 106. The software, when executed by the processor 104, may cause the processing system 114 to perform the various functions described below for any particular apparatus. The computer-readable medium 106 may also be used for storing data that is manipulated by the processor 104 when executing software.

The various concepts presented throughout this disclosure may be implemented in a variety of telecommunications systems, network architectures, and communication standards. By way of example, and not limitation, the aspects of the disclosure illustrated in fig. 2 are presented with reference to a UMTS system 200 using a W-CDMA air interface. The UMTS network comprises three interoperating domains: a Core Network (CN)204, a UMTS Terrestrial Radio Access Network (UTRAN)202, and User Equipment (UE) 210. In this example, the UTRAN 202 provides various wireless services including telephony, video, data, messaging, broadcast, and/or other services. The UTRAN 202 may include a plurality of Radio Network Subsystems (RNSs) (e.g., RNSs 207), each controlled by a respective Radio Network Controller (RNC) (e.g., RNC 206). Here, the UTRAN 202 may include any number of RNCs 206 and RNSs 207 in addition to the RNCs 206 and RNSs 207 shown here. In addition to this, the RNC 206 is a device responsible for allocating, reconfiguring, and releasing radio resources in the RNS 207. The RNC 206 may be interconnected with other RNCs (not shown) in the UTRAN 202 using any suitable transport network through various types of interfaces such as a direct physical connection, a virtual network, and so on.

Communication between the UE 210 and the node B208 may be considered to include a Physical (PHY) layer and a Medium Access Control (MAC) layer. In addition, communication between the UE 210 and the RNC 206 via the respective node B208 may be considered to include a Radio Resource Control (RRC) layer. In this specification, the PHY layer may be regarded as layer 1; the MAC layer can be considered layer 2; the RRC layer may be considered as layer 3. The information below is made use of terminology introduced in the Radio Resource Control (RRC) protocol specification (3GPP TS 25.331v9.1.0), which is incorporated herein by reference.

The geographic area covered by the SRNS 207 may be divided into a plurality of cells with a wireless transceiver apparatus serving each cell. In UMTS applications, the radio transceiver apparatus is commonly referred to as a node B, but may also be referred to by those skilled in the art as a Base Station (BS), a Base Transceiver Station (BTS), a radio base station, a radio transceiver, a transceiver function, a basic service set (BSs), an Extended Service Set (ESS), an Access Point (AP), or other suitable terminology. For clarity, three node bs 208 are shown in each SRNS 207; however, the SRNSs 207 may include any number of wireless node bs. The node bs 208 provide wireless access points to the Core Network (CN)204 for any number of mobile devices. Examples of mobile devices include cellular phones, smart phones, Session Initiation Protocol (SIP) phones, laptops, notebooks, netbooks, smartbooks, Personal Digital Assistants (PDAs), satellite radios, Global Positioning System (GPS) devices, multimedia devices, video devices, digital audio players (e.g., MP3 players), cameras, game consoles, or any other similar functioning devices. In UMTS applications, a mobile device is commonly referred to as User Equipment (UE), but may also be referred to by those skilled in the art as a Mobile Station (MS), a subscriber station, a mobile unit, a subscriber unit, a wireless unit, a remote unit, a mobile device, a wireless communications device, a remote device, a mobile subscriber station, an Access Terminal (AT), a mobile terminal, a wireless terminal, a remote terminal, a handset, a terminal, a user agent, a mobile client, a client, or some other suitable terminology. In the UMTS system, the UE 210 may further include a Universal Subscriber Identity Module (USIM)211, which contains subscriber subscription information to the network. For purposes of illustration, one UE 210 is shown in communication with multiple node bs 208. The Downlink (DL) (also known as the forward link) refers to the communication link from the node B208 to the UE 210, and the Uplink (UL) (also known as the reverse link) refers to the communication link from the UE 210 to the node B208.

The core network 204 interfaces with one or more access networks, such as the UTRAN 202. As shown, the core network 204 is a GSM core network. However, as those skilled in the art will recognize, the various concepts presented throughout this disclosure may be implemented in a RAN or other suitable access network to provide UEs with access to a variety of core networks other than GSM networks.

The core network 204 includes a Circuit Switched (CS) domain and a Packet Switched (PS) domain. Some of the circuit-switched elements are a mobile services switching centre (MSC), a Visitor Location Register (VLR) and a gateway MSC. The packet-switched element includes a Serving GPRS Support Node (SGSN) and a Gateway GPRS Support Node (GGSN). Some network elements, such as EIR, HLR, VLR and AuC, may be shared by both the circuit switched domain and the packet switched domain. In the illustrated example, the core network 204 utilizes the MSC212 and the GMSC 214 to support circuit-switched services. In some applications, the GMSC 214 may be referred to as a Media Gateway (MGW). One or more RNCs, such as RNC 206, may be connected to MSC 212. MSC212 is a device that controls call setup, call routing, and UE mobility functions. MSC212 also includes a Visitor Location Register (VLR) that contains subscriber-related information about the UE during the coverage area of MSC 212. The GMSC 214 provides a gateway through the MSC212 for the UE to access the circuit-switched network 216. The GMSC 214 includes a Home Location Register (HLR)215 that contains subscriber data, e.g., data reflecting the details of the services to which a particular subscriber has subscribed. The HLR is also associated with an authentication center (AuC) containing subscriber-specific authentication data. When a call is received for a particular UE, the GMSC 214 queries the HLR 215 to determine the UE's location and forwards the call to the particular MSC serving that location.

The core network 204 also supports packet data services using a Serving GPRS Support Node (SGSN)218 and a Gateway GPRS Support Node (GGSN) 220. GPRS (standing for general packet radio service) is designed to: packet data services are provided at higher speeds than are available for standard circuit switched data services. The GGSN 220 provides a connection to the packet network 222 for the UTRAN 202. Packet network 222 may be the internet, a private data network, or some other suitable packet network. The primary function of the GGSN 220 is to provide the UE 210 with packet network connectivity. Data packets may be communicated between the GGSN 220 and the UE 210 via the SGSN 218, which may perform primarily the same functions in the packet domain as the MSC212 performs in the circuit switched domain.

The UMTS air interface is a spread spectrum direct sequence code division multiple access (DS-CDMA) system. Spread spectrum DS-CDMA spreads user data by multiplying it by a pseudo-random sequence of bits called chips. The W-CDMA air interface for UMTS is based on this direct sequence spread spectrum technique and also requires Frequency Division Duplexing (FDD). FDD uses different carrier frequencies for Uplink (UL) and Downlink (DL) between node B208 and UE 210. Another air interface for UMTS that employs DS-CDMA and uses time division duplexing is the TD-SCDMA air interface. Those skilled in the art will appreciate that the various examples described herein, while referring to a WCDMA air interface, the underlying principles may be equally applicable to a TD-SCDMA air interface.

The HSPA configuration employed in this example includes a series of enhancements to the 3G/WCDMA air interface, resulting in greater throughput and reduced latency. In other modifications to previous releases, HSPA employs hybrid automatic repeat request (HARQ), shared channel transmission, and adaptive modulation and coding. Standards defining HSPA include HSDPA (high speed downlink packet access) and HSUPA (high speed uplink packet access).

HSDPA employs a high speed downlink shared channel (HS-DSCH) as its transport channel. The HS-DSCH is implemented by three physical channels: a high speed physical downlink shared channel (HS-PDSCH), a high speed shared control channel (HS-SCCH), and a high speed dedicated physical control channel (HS-DPCCH).

In these physical channels, the HS-DPCCH can carry uplink feedback signaling related to downlink HS-DSCH transmission and HS-SCCH order. For example, fig. 3 illustrates an HS-DPCCH frame structure according to an exemplary aspect of the present disclosure. The feedback signaling may include a hybrid ARQ acknowledgement (HARQ-ACK)302 and a Channel Quality Indication (CQI)304, and a Precoding Control Indication (PCI)306 if the UE is configured in MIMO mode. Each subframe (e.g., 2ms (3 × 2560 chips) in length) may include 3 slots 308A, 308B, and 308C, each slot 308 having a length of 2560 chips. The HARQ-ACK 302 may be carried in the first slot 308A of the HS-DPCCH subframe. The CQI 304, and (if the UE is configured in MIMO mode) the PCI 306, may be carried in the second slot 308B and/or the third slot 308C of the HS-DPCCH subframe.

In a typical direct sequence code division multiple access (DS-CDMA) system, such as HSPA, data signals on both the uplink and downlink are combined with respective spreading codes having a particular chip rate, respectively, so that simultaneous multiple transmissions are separated from each other and independent data signals can be recovered. For example, on a given downlink carrier, a data stream intended for a given user may be spread using an appropriate spreading code. At the receiving end of the signal, the signal is descrambled and the data stream is recovered by applying an appropriate spreading code. By using multiple spreading codes, multiple codes can be assigned to each user so that multiple services can be transmitted simultaneously. Similarly, in the uplink, multiple streams may be transmitted from the UE on the same channel using multiple channelization codes.

In one aspect of the disclosure, proper selection of a channelization code enables encoding of additional information in a data stream. For example, two forms of channelization codes may be employed on HSDPA links: one for Precoding Control Indication (PCI) and Channel Quality Indication (CQI) and the other for harq ack/NACK (acknowledgement/negative acknowledgement) or DTX (discontinuous transmission) indication.

In particular, the channelization codes corresponding to the HARQ feedback may encode the HARQ ACK/NACK/DTX status for each transport block on each carrier on the downlink with an appropriate number of bits. In a conventional W-CDMA system, 10 code bits are used for HARQ feedback, using a channelization code with a Spreading Factor (SF) of 256 chips/symbol.

Systems employing HSDPA may implement multiple carriers (3GPP uses the term "cell" to refer to a carrier), e.g. 4C-HSDPA stands for 4 carrier system or, more generally, MC-HSDPA stands for multi-cell, where multiple HS-DSCH channels on different carriers may be employed. That is, the UE may be scheduled in the serving HS-DSCH cell and one or more secondary serving HS-DSCH cells on parallel HS-DSCH transport channels from the same node B. Of course, those skilled in the art will appreciate that any one of the multiple carriers may be configured to act as either a serving HS-DSCH cell or a secondary serving HS-DSCH cell for a particular UE. Here, both the data rate and the system capacity are improved as compared with a system using only a single carrier for downlink.

For MC-HSDPA systems, HARQ ACK/NACK feedback signaling may be sent separately for each downlink channel or sent together as a composite HARQ ACK/NACK corresponding to two or more downlink channels. For systems that encode the HARQ ACK/NACK with the selected channelization code, as described above, if the HARQ ACK/NACK is sent separately for each downlink carrier, the UE may employ a plurality of channelization codes. When multiple channelization codes are employed, each channelization code may be adapted to provide HARQ ACK/NACK for one corresponding downlink carrier.

However, the DC-HSDPA system may implement one or more channelization codes that may provide composite HARQ ACK/NACK information as feedback corresponding to multiple downlink carriers. Here, the channelization code may be selected from a codebook, where each code symbol corresponds to a composite harq ACK/NACK, that is, an ACK/NACK corresponds to each of a plurality of downlink carriers at a time.

HSPA + (or evolved HSPA) is an evolution of the HSPA standard that includes Multiple Input Multiple Output (MIMO) and 64-QAM, enabling increased throughput and higher performance. That is, in one aspect of the disclosure, the node B208 and/or the UE 210 (see fig. 2) may have multiple antennas supporting MIMO technology. The use of MIMO techniques enables the node B208 to exploit the spatial domain to support spatial multiplexing, beamforming, and transmit diversity.

MIMO is a term commonly used to refer to multiple antenna techniques, i.e., multiple transmit antennas (multiple inputs to a channel) and multiple receive antennas (multiple outputs from a channel). MIMO systems generally enhance data transmission performance, allow diversity gain to reduce multipath fading and improve transmission quality, and spatial multiplexing gain to improve data throughput.

Spatial multiplexing may be used to transmit different data streams simultaneously on the same frequency. These data streams may be sent to a single UE 210 to increase the data rate, or to multiple UEs 210 to increase the overall system capacity. This is achieved by: each data stream is spatially precoded and each spatially precoded stream is then transmitted over a different transmit antenna on the downlink. These spatially precoded streams arrive at the UEs 210 with different spatial signatures (spatial signatures) that enable each UE 210 to recover one or more data streams destined for that UE 210. On the uplink, each UE 210 transmits a spatially precoded data stream, which enables the node B208 to identify the source of each spatially precoded data stream.

Spatial multiplexing is typically used when channel conditions are good. Beamforming may be used to focus the transmit energy in one or more directions when channel conditions are not good. This may be achieved by spatially precoding data for transmission via multiple antennas. In order to obtain good coverage at the cell edge, single stream beamforming transmission can be used in combination with transmit diversity.

In summary, for a MIMO system using n transmit antennas, n transport blocks may be transmitted simultaneously on the same carrier using the same channelization code. It should be noted that the different transport blocks sent on the n transmit antennas may have the same or different modulation and coding schemes from each other.

Single Input Multiple Output (SIMO), on the other hand, generally refers to a system that uses a single transmit antenna (a single input to a channel) and multiple receive antennas (multiple outputs from a channel). Thus, in the SIMO system, a single transport block is transmitted on a corresponding carrier. Using this term, a single-input single-output system (SISO) refers to a system that uses a single transmit antenna and a single receive antenna.

HARQ-ACK feedback can become very cumbersome when MIMO may be implemented across one or more of the multiple carriers. That is, the number of ACK/NACK hypotheses that the UE may use in response to different scheduling scenarios, including SIMO and MIMO transmissions from the node B, may become very large. For purposes of illustration, table 1 lists HARQ-ACK assumptions for a 3C-HSDPA node B, which schedules SIMO transmissions on two carriers and schedules MIMO transmissions (including two transport blocks) on the third carrier (S/M). On each of the two SIMO carriers, the HARQ feedback may be an ACK, NACK, or an indication that no signal was received on that carrier (referred to as discontinuous transmission, DTX). On a MIMO carrier, the HARQ feedback may be an ACK for one or both of the two transport blocks (depending on what is received), an ACK for one transport block and a NACK for the other transport block, or a DTX (if neither transport block is received). For this relatively simple system, where only one of the three carriers is a MIMO carrier, there are 44 HARQ hypotheses to cover all possible feedback, and no traditional PRE/POST indication is included, which adds two more hypotheses.

TABLE 1

In addition, the codebook used to encode the HARQ feedback may be even larger than the number of HARQ hypotheses for a given system. That is, in the example above with two SIMO carriers and one MIMO carrier (abbreviated S/M), the UE should have not only response preparation for S/M transmissions, but also response preparation for S/S transmissions, since the UE can receive only one of the transport blocks scheduled on the MIMO channel without receiving an indication that the channel is indeed a MIMO channel. For the example of an S/S/M system, the ACK/NACK/DTX codebook size includes 62 unique codewords (excluding PRE/POST).

As can be seen from this expression, the number of HARQ hypotheses increases rapidly as the number of carriers increases, and as more carriers may configure MIMO. In a 4C-HSDPA system with MIMO configured on all four carriers, a codebook with 2320 unique codewords is required (excluding PRE/POST).

Theoretically, the optimal solution for providing HARQ feedback in MC-HSDPA systems would be: a single codebook is established and the ACK/NACK feedback is encoded for all carriers together. That is, according to exemplary aspects of the present disclosure, a single channelization code may be used on the HS-DPCCH, with a legacy spreading factor SF of 256, where a new codebook is designed for encoding HARQ feedback for each of the multiple carriers.

However, the code rate corresponding to sending a 4C-HSDPA codeword on a single channelization code is essentially one. That is, although there are typically 10 symbols per ACK/NACK slot, more than 10 bits are required, e.g., 2320 unique codewords required for MIMO-enabled 4C-HSDPA systems.

According to an aspect of the present disclosure, it is feasible from a practical point of view to encode the feedback of groups of two carriers together at a time. That is, previous releases to the 3GPP specifications have spent a significant amount of time and expense to generate an effective codebook for up to two carrier systems (i.e., DC-HSDPA). In this way, existing codebooks already implemented in UE hardware may be reused to provide HARQ feedback in HSDPA systems with more than two carriers and MIMO.

In one aspect of the disclosure, HARQ feedback may be provided using a plurality of channelization codes, where each channelization code is adapted to provide HARQ feedback for a group of one or two carriers. For example, in a 3C-HSDPA or 4C-HSDPA system, dual channelization codes may be used, where each channelization code provides HARQ feedback for a group of one or two downlink carriers.

In another aspect of the present disclosure, a single channelization code may be used, wherein the spreading factor is reduced below the conventional SF-256. Thus, when the spreading factor is less than 256, the number of symbols per ACK/NACK slot may increase to more than 10, and thus, a codebook sufficient to encode HARQ feedback for 4C-HSDPA + MIMO is possible. In a further aspect, the spreading factor is set to SF-128. In this way, the number of symbols that the ACK/NACK slot can carry is doubled to 20, thus allowing two HARQ-ACK codewords to be inserted into the ACK/NACK slot. Here, each of the two HARQ-ACK codewords may correspond to a composite ACK/NACK for a group of one or two downlink carriers in a manner similar to the case using dual channelization codes described above.

In yet another aspect of the disclosure, the above aspects may be combined, for example, designing a new codebook that uses a single channelization code and legacy SF 256 for one or more configurations (e.g., in one example, a 3-carrier configuration as S/S), while using other aspects for other configurations (e.g., using spreading factors reduced to SF 128 for 3-carrier or 4-carrier configurations in all configurations except S/S). Of course, other combinations of the above aspects may be combined within the scope of the disclosure.

Fig. 4 illustrates three schemes for implementing HARQ feedback in accordance with various aspects of the disclosure. Block a represents the conventional case of using a single channelization code with spreading factor SF-256; block B represents the case where a single channelization code is used reduced to a spreading factor of SF-128; block C represents the case where dual channelization codes are used, with a spreading factor SF of 256 for each channelization code.

In each case shown in fig. 4, k bits of information are input to an encoder 402, which encoder 402 may encode the information, e.g., using various forward error correction schemes or any other suitable encoding scheme known to those skilled in the art. In block a, an encoder 402A is configured to encode k bits of input information to obtain an output of n/2 bits of encoded information. Then, as in the conventional system, n/2 bits are combined with a single channelization code, with spreading factor SF of 256. As described above, a codebook from which channelization codes are selected for appropriate HARQ feedback according to a HARQ scenario may be implemented in such a way as to sufficiently optimize the characteristics of uplink transmissions.

In blocks B and C, the encoder 402B or 402C is configured to encode the input information of k bits to obtain an output of n-bit encoded information. Here, the encoders 402B and 402C are substantially the same encoders. In block B, the HARQ feedback may be encoded onto the channel using a single channelization code, where the single channelization code uses a spreading factor reduced to less than 256, e.g., SF-128. In block C, after dividing the n-bit coded information into two paths that may be sent to two uplink carriers, the HARQ feedback may be coded onto the channel using dual channelization codes with spreading factor SF-256. As described in further detail below, the channelization processes for encoding HARQ feedback in blocks B and C are very similar, both allowing grouping into groups of two downlink carriers, allowing the use of codebooks previously designed for conventional single carrier or DC-HSDPA systems. That is, in block B, HARQ feedback for a first set of downlink carriers may be placed into a first portion (e.g., half a slot) of a slot and HARQ feedback for a second set of downlink carriers may be placed into a second portion (e.g., half a slot) of the slot using a single channelization code and spreading factor reduced to SF-128. And in block C, HARQ feedback for the first set of downlink carriers and HARQ feedback for the second set of downlink carriers may be placed into the same time slot using dual channelization codes, but separated according to code division multiplexing using dual channelization codes. For example, the dual channelization codes may be substantially orthogonal to each other and thus may be decomposed at the receiver.

Fig. 5 shows the HARQ-ACK slot 302 as shown in fig. 3 in more detail. In fig. 5, a frame a, a frame B, and a frame C show a time slot of a single channelization code with SF of 256, a time slot of a single channelization code with SF of 128, and a time slot of a dual channelization code with SF of 256, respectively. That is, blocks a to C in fig. 5 correspond to blocks a to C in fig. 4. Returning to fig. 5, the slot 302A in block a includes a field 302A1, which may include a single channelization code symbol in field 302A 1. Here, as described above, a codebook configured to provide HARQ feedback for all downlink carriers may be used such that a single channelization code symbol will be sufficient to provide feedback for all corresponding downlink carriers. In block B, the slot 302B includes two consecutive fields 302B1 and 302B 2. A respective channelization code symbol may be inserted in each of the two fields 302B1 and 302B 2. Here, as described above, the spreading factor may be reduced to, for example, SF 128. Thus, channelization code symbols of the same length as in the conventional case can be used in half a slot instead of the entire slot. That is, a smaller spreading factor SF compresses the information in time. When the spreading factor SF is reduced to half, the same information part that was previously transmitted in one time slot can now be transmitted in half a time slot. Thus, reducing the spreading factor SF to half and grouping the downlink carriers into groups of two carriers allows to provide HARQ feedback in a three-carrier system or a four-carrier system using two pre-existing codebooks designed for two-carrier systems, using a corresponding code in each half slot.

As a simple example, if a four-carrier 4C-HSDPA system is configured such that the first two carriers are configured for SIMO and the second two carriers are configured for MIMO (i.e., S/M), two of the carriers may be grouped into a first group (S/S) and the other two carriers may be grouped into a second group (M/M). Here, the 3GPP standard previously defined in release 8 for DC-HSDPA includes a suitable codebook that provides HARQ feedback for two carriers configured as S/S. The codebook may thus be used to provide channelization code symbols in the first half 302B1 of the time slot 302B. Similarly, the 3GPP standard previously defined in release 9 for DC-HSDPA + MIMO includes a suitable codebook that provides HARQ feedback for two carriers configured as M/M. The codebook may thus be used to provide channelization code symbols in the second half 302B2 of the slot 302B. Of course, these codebook instances reused from previous 3GPP standards are merely exemplary in nature, and in particular implementations other codebooks from different pre-existing standards, other standards, or even new codebooks for encoding HARQ feedback for two downlink carriers may be used.

Block C illustrates a method of using dual channelization codes with spreading factor SF of 256. Here, the spreading factor is the same as that described in block a, such that channelization code symbols occupy the entire time slot 302C. However, dual channelization codes are used so that as described above in relation to block B, the four downlink carriers in a 4C-HSDPA system may be grouped into two groups of two carriers each, the channelization codes providing code division multiplexing of HARQ feedback for each of the two groups (two downlink carriers per group).

In systems with an odd number of downlink carriers for which feedback needs to be provided (e.g., 3C-HSDPA systems), each of the three methods shown in fig. 5 may be used, except that one of the groups of downlink carriers will include only one downlink carrier. For example, in a three carrier system (i.e., S/M) configured for SISO on the first two downlink carriers and MIMO on the third downlink carrier, the first group may include the first two carriers (S/S) and the second group may include the third carrier (M). Thus, the HARQ feedback of the first set may use the channelization codebook defined in release 8DC-HSDPA, while the HARQ feedback of the second set may use the channelization codebook defined in release 7 DL-MIMO. Of course, as noted above, these pre-existing codebooks in previous versions of the 3GPP standards are given merely as illustrative examples, and any other suitable codebooks may be used by aspects of the present disclosure.

In further embodiments, HARQ feedback for any number of downlink carriers may be provided by using any number of codebooks that encode HARQ feedback for a corresponding number of groups (two downlink carriers per group) together.

Fig. 6A is a simplified schematic diagram illustrating a UE 602 in communication with a node B604. Here, the node B604 transmits downlink signaling 606 on multiple downlink carriers and the UE transmits HARQ feedback 608 on one or more uplink carriers. For example, downlink signaling 606 may include four downlink carriers in a 4C-HSDPA system and HARQ feedback 608 may be provided on one uplink carrier. In other aspects of the disclosure, each of the downlink signaling 606 and HARQ feedback 608 may be provided on any suitable number of carriers. Fig. 6B is a block diagram illustrating certain details of the UE 602. In the illustrated example, the UE 602 includes a processor 610 for performing functions such as: HARQ feedback corresponding to each of a plurality of downlink carriers received in downlink signaling 606 is determined. The processor 610 is in communication with the transmitter 620, the receiver 630, and the memory 640. Receiver 630 may include one or more receive antennas 631 and 632 for receiving downlink signaling 606, and transmitter 620 may include one or more transmit antennas 621 and 622 for transmitting HARQ feedback 608 on the uplink. Memory 640 may include any suitable form of data structure, such as a first codebook 641 and a second codebook 642, for storing HARQ feedback symbols, e.g., HARQ ACK, NACK, DTX, or PRE/POST, corresponding to the decoding status of information received on multiple downlink carriers. That is, symbols stored in a codebook (such as the first codebook 641) may encode HARQ feedback for a subset of the plurality of downlink carriers. Here, the subset may include any number of downlink carriers, including one downlink carrier up to all downlink carriers. In one exemplary aspect of the present disclosure, the first codebook 641 may include HARQ feedback symbols for encoding HARQ feedback corresponding to two downlink carriers, and the second codebook 642 may include HARQ feedback symbols for encoding HARQ feedback corresponding to a third downlink carrier. Of course, more than two codebooks may be stored in the memory 640, each of which may be configured to store encoded HARQ feedback symbols corresponding to HARQ feedback for substantially any number of downlink carriers.

In another exemplary aspect of the present disclosure, one of the codebooks stored in the memory comprises: HARQ feedback symbols corresponding to HARQ feedback for three downlink carriers (S/S/S) configured for SIMO transmission. In this aspect, when the UE 602 is configured for communication over three SIMO downlink channels (S/S), a single codebook may encode HARQ feedback for all three carriers; when the UE 602 is configured for communication over any other structure (i.e., three carriers with at least one carrier configured for MIMO, or four carriers with zero or more carriers configured for MIMO), then a codebook storing HARQ feedback symbols encoding HARQ feedback for a subset of one or two carriers may be accessed. That is, the change for legacy systems that require a reduction in spreading factor or use dual channelization codes may be larger than that required for cases such as S/S (where the size of the codebook is relatively small). A special exception may therefore be made in this case, whereby HARQ feedback for all downlink carriers are coded together into a single codebook, similar to the conventional case, where the feedback may be provided using a single channelization code with spreading factor SF of 256.

Fig. 7 is a flow diagram illustrating exemplary processes 700 and 750 of wireless communication in which HARQ feedback corresponding to states of a plurality of downlink carriers are grouped into two or more groups, and at least one of the two or more groups includes two of the downlink carriers, according to an aspect of the disclosure. In block 702 of process 700, downlink signaling is received over a plurality of downlink carriers. For example, downlink signaling may be received on three or four downlink carriers in a 3C-HSDPA or 4C-HSDPA system, respectively, in accordance with two exemplary aspects of the present disclosure. In block 704, HARQ feedback corresponding to each of a plurality of downlink carriers is determined. For example, processor 610 in fig. 6B may determine that: whether the encoded information on the transport block on the corresponding downlink carrier is decoded correctly or whether any other content is received at all. In block 706, based on the HARQ feedback determined in block 704, a first HARQ feedback symbol is selected for encoding HARQ feedback corresponding to a first subset of the plurality of carriers, wherein the first subset includes at least two carriers of the plurality of carriers. Similarly, in block 710, a second HARQ feedback symbol is selected for encoding HARQ feedback corresponding to a second subset of the plurality of carriers, wherein the second subset includes at least one carrier of the plurality of carriers. In an exemplary aspect of the disclosure, the second subset may include two downlink carriers in a 4C-HSDPA system, or one carrier in a 3C-HSDPA system. In block 712, the first HARQ feedback symbol and the second HARQ feedback symbol are transmitted on the uplink. In certain aspects of the present disclosure, HARQ feedback symbols corresponding to the first subset are encoded by modulating respective slots in one or both uplink channels, as shown in fig. 4 and 5 and described above.

In block 714 of process 750, a first feedback symbol is provided that corresponds to a decoding status (e.g., HARQ feedback) for information received on a plurality of downlink carriers. In block 716, a second feedback symbol is provided, which is relative to a decoding status of information received on the at least one downlink carrier. For example, for a 4C-HSDPA system, the first feedback symbol may include HARQ feedback for the first and second downlink carriers, and the second feedback symbol may include HARQ feedback for the third and fourth downlink carriers. For a 3C-HSDPA system, the second symbol may include HARQ feedback for only the third downlink carrier.

Fig. 8 is a block diagram of a node B810 and a UE850 in communication, where node B810 may be node B208 in fig. 2 and UE850 may be UE 210 in fig. 2. In downlink communications, a transmit processor 820 may receive data from a data source 812 and control signals from a controller/processor 840. Transmit processor 820 provides various signal processing functions for data and control signals as well as reference signals (e.g., pilot signals). For example, transmit processor 820 may provide: a Cyclic Redundancy Check (CRC) code for error detection; encoding and interleaving to facilitate Forward Error Correction (FEC); mapping to signal constellations based on various modulation schemes (e.g., binary phase-shift keying (BPSK), quadrature phase-shift keying (QPSK), M-ary phase-shift keying (M-PSK), M-quadrature amplitude modulation (M-QAM), etc.); spreading with an Orthogonal Variable Spreading Factor (OVSF); and multiplying with the scrambling code to produce a series of symbols. Controller/processor 840 may utilize the channel estimates from channel processor 844 to determine the coding, modulation, spreading, and/or scrambling schemes to use for transmit processor 820. These channel estimates may be derived from reference signals transmitted by the UE850 or from feedback from the UE 850. The symbols generated by the transmit processor 820 are provided to a transmit frame processor 830 to create a frame structure. The transmit frame processor 830 creates the frame structure by multiplexing the symbols with information from the controller/processor 840, resulting in a series of frames. The frames are then provided to a transmitter 832, which transmitter 832 provides various signal conditioning functions including amplification, filtering, and modulation of the frames onto a carrier wave for downlink transmission over the wireless medium via an antenna 834. Antenna 834 may comprise one or more antennas, e.g., comprising beam steering bi-directional adaptive antenna arrays or other similar beam technologies.

At UE850, a receiver 854 receives the downlink transmission through an antenna 852 and processes the transmission to recover the information modulated onto the carrier. The information recovered by the receiver 854 is provided to a receive frame processor 860, which receive frame processor 860 parses each frame, provides information from the frames to a channel processor 894, and provides data, control, and reference signals to a receive processor 870. The receive processor 870 then performs the inverse of the processing performed by the transmit processor 820 in the node B810. More specifically, the receive processor 870 descrambles and despreads the symbols, and then determines the most likely signal constellation points transmitted by the node B810 based on the modulation scheme. These soft decisions may be based on channel estimates computed by the channel processor 894. These soft decisions are then decoded and deinterleaved to recover the data, control and reference signals. The CRC code is then checked to determine whether the frames were successfully decoded. The data carried by the successfully decoded frames will then be provided to a data sink 872, which data sink 872 represents applications and/or various user interfaces (e.g., displays) running in the UE 850. Control signals carried by successfully decoded frames are provided to a controller/processor 890. The controller/processor 890 may also support retransmission requests for frames using an Acknowledgement (ACK) and/or Negative Acknowledgement (NACK) protocol when frames are not successfully decoded by the receive processor 870.

In the uplink, data from a data source 878 and control signals from the controller/processor 890 are provided to the transmit processor 880. The data source 878 may represent applications running in the UE850 and various user interfaces (e.g., a keyboard). Similar to the functionality described in connection with the downlink transmission by node B810, transmit processor 880 provides various signal processing functions including CRC codes, coding and interleaving to facilitate FEC, mapping to signal constellations, spreading with OVSFs, and scrambling to produce a series of symbols. The appropriate coding, modulation, spreading, and/or scrambling schemes may be selected using channel estimates derived by the channel processor 894 from a reference signal transmitted by the node B810 or from feedback contained in a midamble transmitted by the node B810. The symbols generated by the transmit processor 880 are provided to a transmit frame processor 882 to create a frame structure. The transmit frame processor 882 creates this frame structure by multiplexing the symbols with information from the controller/processor 890, resulting in a series of frames. The frames are then provided to a transmitter 856, which provides various signal conditioning functions including amplification, filtering, and modulation of the frames onto a carrier for uplink transmission over the wireless medium via antenna 852.

The uplink transmissions are processed at node B810 in a manner similar to that described in connection with the receiver function at UE 850. A receiver 835 receives the uplink transmission through antenna 834 and processes the transmission to recover the information modulated onto the carrier. The information recovered by the receiver 835 is provided to a receive frame processor 836, which receives frame processor 836 parses each frame, provides information from the frame to a channel processor 844, and provides data, control, and reference signals to the receive processor 838. The receive processor 838 performs the inverse of the processing performed by the transmit processor 880 in the UE 850. The data and control signals carried by the successfully decoded frames may then be provided to a data sink 839 and a controller/processor, respectively. Controller/processor 840 may also support retransmission requests for some frames using an Acknowledgement (ACK) and/or Negative Acknowledgement (NACK) protocol if the receiving processor fails to successfully decode the frames.

Controllers/processors 840 and 890 may also be used to direct the operation at node B810 and UE850, respectively. For example, controller/processors 840 and 890 may provide various functions including timing, peripheral interfaces, voltage regulation, power control, and other control functions. The computer readable media of memories 842 and 892 may store data and software for the node B and the UE850, respectively. A scheduler/processor 846 at node B810 may be used to allocate resources to the UE and to schedule downlink and/or uplink transmissions for the UE.

In one configuration, the apparatus 850 for wireless communication includes means for receiving downlink signaling on a plurality of downlink carriers and means for transmitting first and second HARQ feedback on an uplink. In one aspect, the aforementioned means may be the receiver 854, the receive frame processor 860, and the receive processor 870; and a transmitter 856, a transmit frame processor 882, and a transmit processor 880. In addition, the apparatus 850 according to this configuration includes: means for determining hybrid automatic repeat request (HARQ) feedback corresponding to each of a plurality of carriers; means for selecting a first HARQ feedback symbol for encoding HARQ feedback corresponding to a first subset of a plurality of carriers, wherein the first subset includes at least two carriers of the plurality of carriers; and means for selecting a second HARQ feedback symbol for encoding HARQ feedback corresponding to a second subset of the plurality of carriers, wherein the second subset includes at least one carrier of the plurality of carriers. In one aspect, the aforementioned means may be the channel processor 894 and/or the controller/processor 890. In another aspect, the aforementioned means may be a module or any apparatus configured to perform the functions presented by the aforementioned means.

In another configuration, the means for wireless communication 850 comprises: the apparatus generally includes means for providing a first feedback symbol corresponding to a decoding status (e.g., HARQ feedback) of information received on a plurality of downlink carriers, and means for providing a second feedback symbol corresponding to a decoding status of information received on at least one downlink carrier. In one aspect, the aforementioned means may be the controller/processor 890, the channel processor 894, the transmit processor 880, the transmit frame processor 882, and/or the transmitter 856. In another aspect, the aforementioned means may be a module or any apparatus configured to perform the functions presented by the aforementioned means.

Several aspects of a telecommunications system have been presented with reference to a W-CDMA system. Those skilled in the art will readily appreciate that the various aspects described throughout this disclosure may be extended to other telecommunications systems, network architectures, and communication standards. That is, the modulation and multiple access schemes used by the access network in accordance with various aspects of the present disclosure may differ depending on the particular communication standard deployed. For example, the criteria may include evolution data optimized (EV-DO) or Ultra Mobile Broadband (UMB). EV-DO and UMB are air interface standards promulgated by the third generation partnership project 2(3GPP2) as part of the CDMA2000 family of standards and use CDMA to provide broadband internet access to mobile stations. The standard may additionally be Universal Terrestrial Radio Access (UTRA) using wideband-CDMA (W-CDMA) and other CDMA variants such as TD-SCDMA; global system for mobile communications (GSM) using TDMA; and evolved UTRA (E-UTRA), Ultra Mobile Broadband (UMB), IEEE802.11(Wi-Fi), IEEE 802.16(WiMAX), IEEE 802.20, and Flash-OFDM using OFDMA. UTRA, E-UTRA, UMTS, LTE Advanced and GSM are described in documents of the 3GPP organization. CDMA2000 and UMB are described in documents organized by 3GPP 2. The actual wireless communication standard and the multiple access technique used will depend on the particular application and the overall design constraints imposed on the system.

In accordance with various aspects of the disclosure, a unit, any portion of a unit, or any combination of units may be implemented using a "processing system" that includes one or more processors. Examples of processors include microprocessors, microcontrollers, Digital Signal Processors (DSPs), Field Programmable Gate Arrays (FPGAs), Programmable Logic Devices (PLDs), state machines, gated logic, discrete hardware circuits, and other suitable hardware configured to implement the functionality described in this disclosure. One or more processors in the processing system may execute software. Software should be construed broadly to mean instructions, instruction sets, code segments, program code, programs, subprograms, software modules, application programs, software applications, software packages, routines, subroutines, objects, executables, threads of execution, procedures, functions, etc. The software may reside on a computer readable medium. The computer readable medium may be a non-transitory computer readable medium. Non-transitory computer-readable media include, by way of example, magnetic storage devices (e.g., hard disks, floppy disks, magnetic strips, etc.), optical disks (e.g., Compact Disks (CDs), Digital Versatile Disks (DVDs)), smart cards, flash memory devices (e.g., cards, sticks, key drives), Random Access Memory (RAM), Read Only Memory (ROM), programmable ROMs (proms), erasable proms (eproms), electrically erasable proms (eeproms), registers, removable disks, and any other medium suitable for storing software and/or instructions that may be accessed and read by a computer. Computer-readable media may also include, by way of example, carrier waves, transmission lines, and any other medium suitable for transmitting software and/or instructions that may be accessed and read by a computer. The computer readable medium may reside in a processing system, a peripheral to the processing system, or distributed across multiple entities including the processing system. The computer readable medium may be embodied in a computer program product. For example, the computer program product may include a computer-readable medium in packaging material. Those skilled in the art will recognize how best to implement the described functionality presented throughout the disclosure, depending upon the particular application and the overall design constraints imposed on the overall system.

It is to be understood that the specific order or hierarchy of steps in the methods disclosed is an illustration of exemplary procedures. It will be appreciated that the specific order or hierarchy of steps in the methods may be rearranged based on design preferences. The accompanying method claims present elements of the various steps in a sample order, and are not intended to be limited to the specific order or hierarchy presented unless specifically indicated herein.

The above description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but is to be accorded the full scope consistent with the language claims, wherein reference to an element in the singular is not intended to mean "one and only one" unless specifically so stated, but rather "one or more. Unless explicitly stated otherwise, the terms "a", "an", and "the" mean "one or more". A phrase referring to "at least one of" a list of items refers to any combination of those items, including a single member. For example, "at least one of a, b, or c" is intended to encompass: a; b; c: a and b; a and c; b and c; and a, b and c. All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Furthermore, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. Furthermore, no element of the claims should be construed in accordance with the provisions of clause 6 of 35u.s.c. 112, unless the element is explicitly recited in the phrase "element for … …" or in a method claim, the element is recited in the phrase "step for … …".

Claims (14)

1. A method of wireless communication, comprising:

receiving downlink signaling on a plurality of downlink carriers;

determining hybrid automatic repeat request (HARQ) feedback corresponding to each of the plurality of downlink carriers;

selecting a first HARQ feedback symbol for encoding HARQ feedback corresponding to a first subset of the plurality of downlink carriers, wherein the first subset includes at least two carriers of the plurality of downlink carriers, wherein the first HARQ feedback symbol is selected from one of a plurality of codebooks that store symbols corresponding to composite values representing decoding statuses of information received on the at least two carriers of the plurality of downlink carriers;

selecting a second HARQ feedback symbol for encoding HARQ feedback corresponding to a second subset of the plurality of downlink carriers, wherein the second subset includes at least one carrier of the plurality of downlink carriers, wherein the second HARQ feedback symbol is selected from one of a plurality of codebooks that store symbols corresponding to composite values representing decoding statuses of information received on the at least one carrier of the plurality of downlink carriers; and

transmitting the first HARQ feedback symbol and the second HARQ feedback symbol on an uplink.

2. The method of claim 1, wherein the transmitting comprises: modulating at least a first portion of a slot of an uplink carrier using the first HARQ feedback symbol.

3. The method of claim 2, wherein the transmitting step further comprises: modulating a second portion of a slot of the uplink carrier other than the first portion of the slot using the second HARQ feedback symbol.

4. The method of claim 3, wherein modulating the first portion of the uplink carrier comprises using a spreading factor of less than 256 chips per bit and modulating the second portion of the uplink carrier comprises using a spreading factor of less than 256 chips per bit.

5. The method of claim 4, wherein the spreading factor is 128.

6. The method of claim 2, wherein modulating at least a first portion of the time slot comprises: modulating an entire time slot of the uplink carrier using the first HARQ feedback symbol; and

the transmitting step further comprises: modulating an entire time slot of the uplink carrier using the second HARQ feedback symbol.

7. The method of claim 6, wherein modulating the slot with the first HARQ feedback symbol comprises using a spreading factor of 256 chips per bit and modulating the slot with the second HARQ feedback symbol comprises using a spreading factor of 256 chips per bit.

8. An apparatus for wireless communication, comprising:

a receiver for receiving downlink signaling on a plurality of downlink carriers;

a processor configured to determine hybrid automatic repeat request (HARQ) feedback corresponding to each of the plurality of downlink carriers, select a first HARQ feedback symbol for encoding HARQ feedback corresponding to a first subset of the plurality of downlink carriers, wherein the first subset includes at least two carriers of the plurality of downlink carriers, wherein the first HARQ feedback symbol is selected from one of a plurality of codebooks that store symbols corresponding to composite values representing decoding statuses of information received on the at least two carriers of the plurality of downlink carriers, and select a second HARQ feedback symbol for encoding HARQ feedback corresponding to a second subset of the plurality of downlink carriers, wherein the second subset includes at least one carrier of the plurality of downlink carriers, wherein the second HARQ feedback symbol is selected from one of a plurality of codebooks that store symbols corresponding to composite values representing decoding statuses of information received on the at least one of the plurality of downlink carriers; and

a transmitter for transmitting the first HARQ feedback symbol and the second HARQ feedback symbol on an uplink.

9. The apparatus of claim 8, wherein the transmitter is configured to: modulating at least a first portion of a slot of an uplink carrier using the first HARQ feedback symbol.

10. The apparatus of claim 9, wherein the transmitter is further configured to: modulating a second portion of a slot of the uplink carrier other than the first portion of the slot using the second HARQ feedback symbol.

11. The apparatus of claim 10, wherein modulating the first portion of the uplink carrier comprises using a spreading factor of less than 256 chips per bit and modulating the second portion of the uplink carrier comprises using a spreading factor of less than 256 chips per bit.

12. The apparatus of claim 11, wherein the spreading factor is 128.

13. The apparatus of claim 9, wherein modulating at least a first portion of the time slot comprises: modulating an entire time slot of the uplink carrier using the first HARQ feedback symbol; and is

The transmitter is further configured to: modulating an entire time slot of the uplink carrier using the second HARQ feedback symbol.

14. An apparatus for wireless communication, comprising means for performing the method of any one of claims 1 to 7.