Title of Invention: METHOD AND APPARATUS FOR CODING OF HARQ-ACK TRANSMISSION IN TDD SYSTEMS WITH DOWNLINK CARRIER AGGREGATION Abstract: Methods and apparatus are provided for a User Equipment (UE) configured with multiple cells in a DownLink (DL) of a Time Division Duplex (TDD) communication system to determine the coding method for acknowledgement information bits as a function of their number, to apply bundling to the acknowledgement information bits when their number exceeds a first predetermined value, and to partition the acknowledgement information bits, possibly together with other control information bits, into two separate codewords when their total number exceeds a second predetermined value. Detailed Description: PRIORITY This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Application No. 61/409,662 which was filed in the United States Patent and Trademark Office on Nov. 3, 2010, U.S. Provisional Application No. 61/410,162 which was filed in the United States Patent and Trademark Office on Nov. 4, 2010, U.S. Provisional Application No. 61/410,642 which was filed in the United States Patent and Trademark Office on Nov. 5, 2010, U.S. Provisional Application No. 61/411,209 which was filed in the United States Patent and Trademark Office on Nov. 8, 2010, and U.S. Provisional Application No. 61/512,614 which was filed in the United States Patent and Trademark Office on Jul. 28, 2011, the disclosures of which are incorporated herein by reference. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to wireless communication systems and, more particularly, to the transmission of acknowledgement information in an uplink of a communication system. 2. Description of the Art A communication system includes a DownLink (DL) that conveys transmission signals from a Base Station (BS), or NodeB, to User Equipments (UEs), and includes an UpLink (UL) that conveys transmission signals from UEs to the NodeB. A UE, which is also commonly referred to as a terminal or a mobile station, may be fixed or mobile and may be, for example, a wireless device, a cellular phone, or a personal computer device. A NodeB is generally a fixed station and may also be referred to as an access point or some other equivalent terminology. The UL conveys transmissions of data signals carrying information content, transmissions of control signals providing control information associated with the transmission of data signals in the DL, and transmissions of Reference Signals (RSs), which are commonly referred to as pilot signals. The DL also conveys transmissions of data signals, control signals, and RSs. UL data signals are conveyed through a Physical Uplink Shared CHannel (PUSCH) and DL data signals are conveyed through a Physical Downlink Shared CHannel (PDSCH). In the absence of a PUSCH transmission, a UE conveys UL Control Information (UCI) through a Physical Uplink Control CHannel (PUCCH). However, when it has a PUSCH transmission, a UE may convey UCI together with data through the PUSCH. DL control signals may be broadcast or may be sent in a UE-specific nature. Accordingly, UE-specific control channels can be used, among other purposes, to provide UEs with Scheduling Assignments (SAs) for PDSCH reception (DL SAs) or PUSCH transmission (UL SAs). The SAs are transmitted from the NodeB to respective UEs using DL Control Information (DCI) formats through respective Physical DL Control CHannels (PDCCHs). The NodeB may configure a UE through higher layer signaling, such as, for example, Radio Resource Control (RRC) signaling, a PDSCH and a PUSCH Transmission Mode (TM), and other parameters relating to reception of DL signals or transmission of UL signals. The PDSCH TM or PUSCH TM is respectively associated with a DL SA or a UL SA, and defines whether a respective PDSCH or PUSCH conveys one data Transport Block (TB) or two data TBs. PDSCH or PUSCH transmissions are either scheduled to a UE by the NodeB through higher layer signaling or through physical layer signaling (through, for example, the PDCCH) using a respective DL SA or UL SA, or correspond to non-adaptive retransmissions for a given Hybrid Automatic Repeat reQuest (HARQ) process. Scheduling by higher layer signaling is referred to as Semi-Persistent Scheduling (SPS). Scheduling by PDCCH is referred to as dynamic. A PDCCH may also be used to release SPS PDSCH. If a UE misses (i.e., fails to detect) a PDCCH, it also misses the associated PDSCH or PUSCH. This event is referred to as DTX (Discontinuous Transmission). The UCI includes ACKnowledgment (ACK) information associated with a HARQ process (HARQ-ACK). HARQ-ACK information may consist of multiple bits corresponding to positive acknowledgments (ACKs) for TBs a UE correctly received, or corresponding to Negative ACKnowledgements (NACKs) for TBs the UE incorrectly received. When a UE does not receive a TB, it may transmit DTX (tri-state HARQ-ACK information) or it may transmit a NACK that represents both the absence and the incorrect reception of a TB (in a combined NACK/DTX state). In Time Division Duplex (TDD) systems, DL and UL transmissions occur in different Transmission Time Intervals (TTIs) which are referred to as subframes. For example, in a frame comprising of 10 subframes, some subframes may be used for DL transmissions and other subframes may be used for UL transmissions. FIG. 1 is a diagram illustrating a frame structure for a TDD system. Referring to FIG. 1, a 10 millisecond (ms) frame consists of two identical half-frames. Each 5 ms half-frame 110 is divided into eight slots 120 and three special fields. The three special fields include a DL ParT Symbol (DwPTS) 130, a Guard Period (GP) 140, and an UL ParT Symbol (UpPTS) 150. The length of DwPTS+GP+UpPTS is equal to one subframe (1 ms) 160. The DwPTS may be used for the transmission of synchronization signals from the NodeB, while the UpPTS may be used for the transmission random access signals from UEs. The GP facilitates the transition between DL and UL transmissions by absorbing transient interference. The number of DL and UL subframes per frame can be different, and multiple DL subframes may be associated with a single UL subframe. In associating multiple DL subframes with a single UL subframe, a number OQ-ACK of HARQ-ACK information bits generated in response to PDSCH receptions (data TBs) in multiple DL subframes needs to be transmitted in a single UL subframe. This number of DL subframes Nbundle is referred to as bundling window. A first method in which a UE conveys HARQ-ACK information in a single UL subframe, in response to PDSCH receptions in multiple DL subframes, involves HARQ-ACK bundling. In HARQ-ACK bundling the UE transmits an ACK only if it correctly receives all data TBs and transmits a NACK in all other cases. Therefore, HARQ-ACK bundling results in unnecessary retransmissions and reduced DL throughput, since the NACK is transmitted even when a UE incorrectly receives only one data TB and correctly receives all other data TBs. Another method in which a UE conveys up to 4 bits of HARQ-ACK information in a single UL subframe, in response to receptions of data TBs in multiple DL subframes, involves HARQ-ACK multiplexing, which is based on PUCCH resource selection. An additional method in which a UE conveys multiple HARQ-ACK information bits in a single UL subframe, in response to receptions of multiple data TBs in multiple DL subframes, involves joint coding of the HARQ-ACK information bits using, for example, a block code such as a Reed-Mueller (RM) code. If a PDSCH conveys one TB, the respective HARQ-ACK information consists of one bit which is encoded as a binary ‘1’ (ACK value) if the TB is correctly received, and is encoded as a binary ‘0’ (NACK value) if the TB is incorrectly received. If a PDSCH conveys two TBs, in accordance with the Single-User Multiple Input Multiple Output (SU-MIMO) transmission method with a rank higher than one, the HARQ-ACK information consists of two bits [o0ACK o1ACK], with o0ACK for the first TB and o1ACK for the second TB. However, if a UE applies bundling in the spatial-domain for the 2 HARQ-ACK bits associated with the reception of the 2 TBs when a SU-MIMO PDSCH has a rank larger than one, the UE feedback consists of only one HARQ-ACK bit that has the binary value 0 (NACK value) when at least one TB is incorrectly received, or the binary value 1 (ACK value) when both TBs are correctly received. As the PDSCH TM determines a number of conveyed TBs (one or two), it also determines a respective number of HARQ-ACK bits (if spatial-domain bundling is not applied). FIG. 2 is a diagram illustrating a PUCCH structure in one subframe slot for transmitting multiple HARQ-ACK information bits using a Discrete Fourier Transform Spread Orthogonal Frequency Division Multiplexing (DFT-S-OFDM) transmission method. Referring to FIG. 2, after encoding and modulation, using for example, a RM block code and Quadrature Phase Shift Keying (QPSK), respectively, a set of same HARQ-ACK bits 210 is multiplied at multiplier 220 with elements of an Orthogonal Covering Code (OCC) 230, and is subsequently DFT precoded at DFT precoder 240. For example, for 5 symbols per slot carrying HARQ-ACK bits, the OCC has length of 5 {OCC(0), OCC(1), OCC(2), OCC(3), OCC(4)}, and can be {1, 1, 1, 1, 1}, {1, exp(j2π/5), exp(j4π/5), exp(j6π/5), exp(j8π/5)}, {1, exp(j4π/5), exp(j8π/5), exp(j2π/5), exp(j6π/5)}, {1, exp(j6π/5), exp(j2π/5), exp(j8π/5), exp(j4π/5)}, or {1, exp(j8π/5), exp(j6π/5), exp(j4π/5), exp(j2π/5)}. The output of the DFT precoder 240 is passed through an Inverse Fast Fourier Transform (IFFT) unit 250 and it is then mapped to a DFT-S-OFDM symbol 260. Since the previous operations are linear, their relative order may be inter-changed. Because a PUCCH transmission is assumed to be in one PRB, which consists of NscRB=12 REs, there are 24 encoded HARQ-ACK bits transmitted in each slot (12 HARQ-ACK QPSK symbols) and a (32,OHARQ-ACK) RM code is punctured into a (24, OHARQ-ACK) RM code. The same or different HARQ-ACK bits may be transmitted in the second slot of a subframe. In addition to HARQ-ACK signals, RS are transmitted in each slot to enable coherent demodulation of HARQ-ACK signals. Each RS is constructed from a length-12 Zadoff-Chu (ZC) sequence 270, which is passed through an IFFT unit 280 and mapped to another DFT-S-OFDM symbol 290. The PUCCH structure in FIG. 2 can support reliable reception for only a limited number of HARQ-ACK information bits, which is also referred to as a HARQ-ACK payload, without incurring a large coding rate as it can only support 24 encoded HARQ-ACK bits. The use of a dual RM code can allow for support of larger HARQ-ACK payloads. For example, a single RM code can be used for HARQ-ACK payloads up to 10 bits, and a dual RM code can be used for HARQ-ACK payloads between 11 and 20 bits. With a dual RM code, the mapping to successive elements of the DFT can alternate between elements from the output of a first RM code and elements from the output of a second RM code in a sequential manner. For HARQ-ACK payloads of more than 20 bits, convolutional coding can be used. FIG. 3 is a diagram illustrating a transmitter block diagram for transmitting HARQ-ACK information encoded using a single RM code. Referring to FIG. 3, HARQ-ACK information bits 305 are encoded and modulated by an encoder and modulator 310, and then multiplied with an element of an OCC 325 for the respective DFT-S-OFDM symbol at multiplier 320. The output of the multiplier 320 is then DFT precoded by DFT precoder 330. After DFT precoding, sub-carrier mapping is performed by a sub-carrier mapper 340, which is under control of a controller 350. Thereafter, the IFFT is performed by an IFFT unit 360, a CP is added by at CP inserter 370, and the signal is filtered for time windowing by filter 380, thereby generating a transmitted signal 390. Additional transmitter circuitry, such as, for example, a digital-to-analog converter, analog filters, amplifiers, and transmitter antennas may also be included in the transmitter block diagram of FIG. 3. FIG. 4 is a diagram illustrating a receiver block diagram for receiving HARQ-ACK information encoded using a single RM code. Referring to FIG. 4, after receiving a Radio-Frequency (RF) analog signal and converting it to a digital signal 410, the digital signal 410 is filtered for time windowing at a filter 420, and a CP is removed at a CP remover 430. Subsequently, the NodeB receiver applies an FFT at an FFT unit 440, performs sub-carrier demapping at a sub-carrier demapper 450, which is under the control of a controller 455, and applies an Inverse DFT (IDFT) at an IDFT unit 460. The output of the IDFT unit 460 is then multiplied with an OCC element 475 for the respective DFT-S-OFDM symbol a multiplier 470. An adder 480 sums the outputs for the DFT-S-OFDM symbols conveying HARQ-ACK signals over each slot, and a demodulator and decoder 490 demodulates and decodes the summed HARQ-ACK signals over both subframe slots to obtain HARQ-ACK information bits 495. Well known receiver functionalities such as, for example, channel estimation, demodulation, and decoding may also be included in the receiver block diagram of FIG. 4. FIG. 5 is a diagram illustrating a transmitter block diagram for transmitting HARQ-ACK information encoded using a dual RM code. Referring to FIG. 5, the payload of OHARQ-ACK HARQ-ACK bits 505 is first segmented into two parts of OHARQ ACK1=┌OHARQ ACK/2┐ bits and OHARQ-ACK2=└OHARQ ACK/2] bits at segmentation block 510. The segmented parts are subsequently individually encoded with a (32, OHARQ-ACK1) RM code and a (32, OHARQ-ACK2), respectively, and each of the 32 coded bits are then punctured to 24 coded bits which are then QPSK modulated to obtain 12 QPSK coded symbols, at coding and modulation blocks 520 and 525, respectively. The first 6 for each of the 12 QPSK coded symbols are combined, for example, by interlacing, at a block 530 and are then multiplied with an element of the OCC 545 for the respective DFT-S-OFDM symbol at a multiplier 540 for transmission in a first slot of a subframe. The same processing applies to the last 6 of the 12 QPSK coded symbols, which are transmitted in a second slot of the subframe. After DFT precoding at a DFT precoder 550, the REs of the assigned PUCCH PRB are selected at a sub-carrier mapper 565, which is under the control of a controller 560. The IFFT is performed at an IFFT block 570 and finally the CP and filtering are applied to a transmitted signal 580. Additional transmitter circuitry, such as, for example, a digital-to-analog converter, analog filters, amplifiers, and transmitter antennas may be included in the transmitter block diagram of FIG. 5. FIG. 6 is a diagram illustrating a receiver block diagram for receiving HARQ-ACK information encoded using a dual RM code. After an antenna receives the RF analog signal and after further processing units (such as filters, amplifiers, frequency down-converters, and analog-to-digital converters), a digital signal 610 is filtered and the CP is removed. Subsequently, the NodeB receiver applies an FFT at an FFT block 620, selects REs used by the UE transmitter at a sub-carrier demapper 630, which is under the control of a controller 635. The NodeB receiver applies an IDFT at an IDFT block 640, multiplies with an OCC element 655 for the respective DFT-S-OFDM symbol at a multiplier 650, sums the outputs for the DFT-S-OFDM symbols over each slot at a summing block 660, collects the QPSK symbols from both subframe slots at a collection block 670, splits (de-interlaces) the 24 QPSK symbols in the original pairs of 12 QPSK symbols in a split block 675, and demodulates and decodes each of the two pairs of 12 QPSK symbols at demodulation and decoding blocks 680 and 685, respectively, to obtain transmitted HARQ-ACK bits 690. Well known receiver functionalities, such as, for example, channel estimation, demodulation, and decoding, may also be included in the receiver block diagram of FIG. 6. Using the maximum HARQ-ACK payload in a PUCCH does not create additional resource overhead. A UE may transmit a NACK or a DTX (in case of tri-state HARQ-ACK information) for the TBs it did not receive. However, the NodeB already knows the DL cells with no DL SA or PDSCH transmission to the UE, and can use the knowledge that the UE transmits a NACK for each of those DL cells (a-priori information) to improve the HARQ-ACK reception reliability. This is possible because a linear block code and QPSK are assumed to be used for the encoding and modulation of the HARQ-ACK bits, respectively, and the NodeB can consider, as candidate HARQ-ACK codewords, only those having NACK (binary ‘0’) at the predetermined locations corresponding to cells without DL SA transmissions to the UE. Due to the implementation of the decoding process, the use of the a-priori information would be impractical or impossible if a convolutional code or a turbo code was used for encoding the HARQ-ACK information bits. Therefore, the coding rate for the transmission of HARQ-ACK information in a PUCCH depends on the number of HARQ-ACK information bits the NodeB does not know in advance. For HARQ-ACK transmission in a PUSCH, a UE determines a respective number of coded symbols Q′ as shown in Equation (1) below. Q ′ = min ( ⌈ O HARQ - ACK · β offset PUSCH Q m · R ⌉ , 4 · M sc PUSCH ) ( 1 ) In Equation (1), βoffsetPUSCH is informed to the UE through higher layer signaling, Qm is the number of data modulation bits (Qm=2, 4, 6 for QPSK, QAM16, QAM64, respectively), R is the data code rate of the initial PUSCH transmission for the same TB, MscPUSCH is the PUSCH transmission BW in the current sub-frame, and ┌ ┐ is the “ceiling” function which rounds a number to its next integer. The code rate R is defined as R = ( ∑ r = 0 C CB - 1  K r ) ( Q m · M sc PUSCH - initial · N symb PUSCH - initial ) where CCB is the total number of code blocks and Kr is the number of bits for code block number r. The maximum number of HARQ-ACK REs is limited to the REs of 4 DFT-S-OFDM symbols (4·MscPUSCH). The value of Qm·R determines the Spectral Efficiency (SE) of the data transmission in the PUSCH and, given MscPUSCH, it can be directly derived from the Modulation and Coding Scheme (MCS) used for the data transmission. In TDD systems, as a UE needs to send HARQ-ACK information corresponding to potential TB receptions over multiple DL subframes in a bundling window, a DL Assignment Index (DAI) Information Element (IE), VDAIDL, is included in the DL SAs to inform the UE of the number of DL SAs transmitted to it by the NodeB. Since the NodeB cannot predict whether there will be a DL SA for a UE in future DL subframes, the VDAIDL is a relative counter which is incremented in each DL SA transmitted to the UE and starts from the beginning after the last DL subframe in the bundling window. If the UE fails to detect the last DL SA, it cannot become aware of this event while if the UE fails to detect a DL SA other than the last one, it can become aware of this event if it receives another DL SA in a subsequent DL subframe of the same bundling window. FIG. 7 is a diagram illustrating a setting for a DL DAI IE over 4 DL subframes of a bundling window. Referring to FIG. 7, in a DL subframe 0 710, the NodeB transmits a DL SA to a UE and sets the DL DAI IE value to VDAIDL=0. In a DL subframe 1 720, the NodeB transmits a DL SA to the UE and sets the DL DAI IE value to VDAIDL=1. In a DL subframe 2 730, the NodeB does not transmit a DL SA to the UE and does not increment the DL DAI IE value. In a DL subframe 3 740, the NodeB transmits a DL SA to the UE and sets the DL DAI IE value to VDAIDL=2. If a UE has data transmission in a UL subframe where it is expected to also transmit HARQ-ACK information, then both data and HARQ-ACK may be transmitted in a PUSCH. In order to avoid error cases where the UE has missed the last DL SA and ensure the same understanding between the NodeB and the UE of the number of HARQ-ACK bits in the PUSCH, a DAI IE is also included in the UL SA (UL DAI IE) scheduling the PUSCH to indicate the number of HARQ-ACK bits the UE should include. For the setup in FIG. 7 where Nbundle=4, the UL DAI IE can be represented by 2 bits with respective values of VDAIUL=0 or 4, 1, 2, 3. If the UE receives a DL SA in the bundling window, then the UL DAI IE bits of “00” map to a UL DAI IE value of VDAIUL=4 instead of VDAIUL=0. In order to support high data rates in a communication system, Carrier Aggregation (CA) of multiple cells is considered to provide higher operating BandWidths (BWs). For example, to support communication over 60 MHz, CA of three 20 MHz cells can be used. FIG. 8 is a diagram illustrating the principle of CA. Referring to FIG. 8, an operating DL BW of 60 MHz 810 is constructed by the aggregation of 3 cells, DL CC 1 821, DL CC 2 822, and DL CC 3 823, each having a DL BW of 20 MHz. Similarly, an operating UL BW of 60 MHz 830 is constructed by the aggregation of 3 cells, UL CC 1 841, UL CC 2 842, and UL CC 3 843, each having an UL BW of 20 MHz. For simplicity, in FIG. 8, each cell is assumed to have a unique DL and UL pair (symmetric CA), but it is also possible for more than one DL to be mapped to a single UL and the reverse (asymmetric CA). This mapping is typically UE-specific and the NodeB can configure a set of C cells to a UE, using for example Radio Resource Control (RRC) signaling, and activate a subset of A cells (A≦C) for PDSCH reception in a subframe, using for example Medium Access Control (MAC) signaling (a UE may not monitor inactive cells for communication with the NodeB). If a PDSCH activating or deactivating configured cells is missed, then the UE and the NodeB may have a misunderstanding of the active cells. Moreover, in order to maintain the communication, one cell with a DL/UL pair needs to remain always activated and it is referred to as the primary cell. The PUCCH transmissions from a UE are assumed to be only in its primary cell (Pcell) and HARQ-ACK information is conveyed only in a single PUSCH. FIG. 9 is a diagram illustrating the parallelization of the DL DAI design in FIG. 7 to multiple DL cells. Referring to FIG. 9, a NodeB transmits to a UE DL SAs in 3 DL subframes in Cell 0 910 and sets the DL DAI IE values according to the number of DL SAs transmitted to the UE only for PDSCH receptions in Cell 0. In a similar manner, the NodeB transmits to the UE DL SAs in 2 DL subframes in Cell 1 920 and 2 DL subframes in Cell 2 930 and sets the DL DAI IE values according to the number of DL SAs transmitted to the UE only for PDSCH receptions in Cell 1 and Cell 2, respectively. A fundamental condition for proper communication of the HARQ-ACK information is for a UE and a NodeB to have a same understanding of the HARQ-ACK payload. This includes the same understanding about the ordering of HARQ-ACK information bits across cells and subframes in a transmitted HARQ-ACK codeword and of the coding method used to transmit the HARQ-ACK payload (single RM or dual RM code). The actual HARQ-ACK payload also needs to be limited as desired reliability requirements are difficult to achieve otherwise. Additionally, the required resources in a PUSCH for transmitting large HARQ-ACK payloads can become excessive and lead to unacceptable overhead or an inability to reliably receive the HARQ-ACK payload. For this reason, the HARQ-ACK payload needs to be compressed and spatial-domain bundling is considered as the first choice, possibly followed by bundling across DL subframes (time-domain bundling) or across cells (cell-domain bundling). SUMMARY OF THE INVENTION The present invention has been made to address at least the above problems and/or disadvantages and to provide at least the advantages described below. Accordingly an aspect of the present invention provides methods and apparatus for a UE operating in a TDD communication system and configured with multiple DL cells to determine the coding method for acknowledgement information bits as a function of their number. In accordance with an aspect of the present invention, a method is provided for a UE to encode acknowledgement information bits for transmission to a base station in a TDD communication system. The acknowledgement information bits are generated for each of a plurality of TTIs and for each of a plurality of cells configured for the UE. One acknowledgement information bit is generated for each cell configured with a Transmission Mode (TM) that conveys one data TB. Two acknowledgement information bits are generated for each cell configured with a TM conveying two data TBs. The acknowledgement information bits corresponding to the plurality of TTIs for each of the plurality of cells are arranged in a first codeword in an order of ascending cell index values. The first codeword is encoded, when a total number of acknowledgement information bits is less than or equal to a predetermined value. Successive acknowledgement information bits from the first codeword are placed into a second codeword and a third codeword, in an alternating manner, and the second codeword and the third codeword are encoded, when the total number of acknowledgement information bits is greater than the predetermined value. In accordance with another aspect of the present invention, a method is provided for a UE to transmit acknowledgement information bits to a base station in a TDD communication system. The acknowledgement information bits are generated for each of a plurality of TTIs and for each of a plurality of cells configured for the UE. One acknowledgement information bit is generated for each cell configured with a TM that conveys one data TB. Two acknowledgement information bits are generated for each cell configured with a TM conveying two data TBs. The UE is configured to apply spatial-domain bundling for the acknowledgement information bits over a subset of the plurality of cells through higher layer signaling. A total number of acknowledgement information bits are transmitted in accordance with the spatial-domain bundling, a number of the plurality of TTIs, a number of the plurality of cells, and a number of the subset of the plurality of cells. In accordance with an additional aspect of the present invention, a UE apparatus is provided for transmitting acknowledgement information bits. The UE apparatus communicates with a base station in a TDD system. The apparatus includes a receiver for receiving data Transport Blocks (TBs) over at least one of a plurality of configured cells and over at least one of a plurality of Transmission Time Intervals (TTIs), for generating the acknowledgement information bits for each of a subset of the plurality of TTIs and for each of the plurality of configured cells, wherein one acknowledgement information bit is generated for each cell configured with a Transmission Mode (TM) that conveys one data TB, and wherein two acknowledgement information bits are generated for each cell configured with a TM that conveys two data TBs, and for arranging, in a first codeword, the acknowledgement information bits corresponding to the subset of the plurality of TTIs for each of the plurality of cells in an order of ascending cell index values. The apparatus also includes an encoder for encoding the first codeword when a total number of the acknowledgement information bits is less than or equal to a predetermined value, and for placing successive acknowledgement information bits from the first codeword into a second codeword and a third codeword, in an alternating manner, and encoding the second codeword and the third codeword when the total number of the acknowledgement information bits is greater than the predetermined value. The apparatus further includes a transmitter for transmitting the encoded acknowledgement information bits of the first codeword or the encoded acknowledgement information bits of second codeword and the third codeword. In accordance with a further aspect of the present invention, a UE apparatus is provided for transmitting acknowledgement information bits. The UE apparatus communicates with a base station in a TDD system. The apparatus includes a receiver for receiving data TBs over at least one of a plurality of configured cells and over at least one of a plurality of TTIs, for generating the acknowledgement information bits for each of a subset of the plurality of TTIs and for each of the plurality of configured cells, wherein one acknowledgement information bit is generated for each cell configured with a TM that conveys one data TB, and wherein two acknowledgement information bits are generated for each cell configured with a TM that conveys two data TBs, and for applying spatial-domain bundling for the acknowledgement information bits over a subset of the plurality of cells through higher layer signaling. The apparatus also includes a transmitter for transmitting a total number of acknowledgement information bits in accordance with the spatial-domain bundling, a number of the plurality of TTIs, a number of the plurality of cells, and a number of the subset of the plurality of cells. BRIEF DESCRIPTION OF THE DRAWINGS The above and other aspects, features, and advantages of the present invention will be more apparent from the following detailed description when taken in conjunction with the accompanying drawings, in which: FIG. 1 is a diagram illustrating a frame structure for a TDD system; FIG. 2 is a diagram illustrating a conventional PUCCH structure in one subframe slot for transmitting multiple HARQ-ACK information bits using a DFT-S-OFDM transmission method. FIG. 3 is a block diagram illustrating a transmitter for transmitting HARQ-ACK information encoded using a single RM code; FIG. 4 is a block diagram illustrating a receiver for receiving HARQ-ACK information encoded using a single RM code; FIG. 5 is a block diagram illustrating a transmitter for transmitting HARQ-ACK information encoded using a dual RM code; FIG. 6 is a block diagram illustrating a receiver for receiving HARQ-ACK information encoded using a dual RM code; FIG. 7 is a diagram illustrating a setting for a DL DAI IE over 4 DL subframes of a bundling window; FIG. 8 is a diagram illustrating the principle of CA; FIG. 9 is a diagram illustrating a parallelization of the DL DAI IE design in FIG. 7 to multiple DL cells; FIG. 10 is a diagram illustrating the application of HARQ-ACK spatial-domain bundling across cells and subframes, according to an embodiment of the present invention; FIG. 11 is a diagram illustrating the application of HARQ-ACK spatial-domain bundling in a PUSCH associated with a UL SA conveying an UL DAI IE, according to an embodiment of the present invention; FIG. 12 is a diagram illustrating the application of HARQ-ACK spatial-domain bundling followed by time-domain bundling that is prioritized for cells without spatial-domain bundling, according to an embodiment of the present invention; FIG. 13 is a diagram illustrating the application of different HARQ-ACK bundling in a PUSCH relative to a PUCCH, according to an embodiment of the present invention; FIG. 14 is a diagram illustrating a first splitting of HARQ-ACK information bits and of other UL control information bits, if any, for coding with 2 RM codes, according to an embodiment of the present invention; and FIG. 15 is a diagram illustrating a second splitting of HARQ-ACK information bits and of other UL control information bits, if any, for coding with 2 RM codes, according to an embodiment of the present invention. DETAILED DESCRIPTION OF EMBODIMENTS OF THE PRESENT INVENTION Embodiments of the present invention are described in detail with reference to the accompanying drawings. The same or similar components may be designated by the same or similar reference numerals although they are illustrated in different drawings. Detailed descriptions of constructions or processes known in the art may be omitted to avoid obscuring the subject matter of the present invention. Additionally, although the embodiments of the present invention are described below with reference to DFT-spread OFDM transmission, they also are applicable to all Frequency Division Multiplexing (FDM) transmissions in general, and to Single-Carrier Frequency Division Multiple Access (SC-FDMA) and OFDM in particular. A UE is assumed to generate HARQ-ACK information in response to each TB associated with a DL SA. However, a UE may also deterministically generate HARQ-ACK information associated with each SPS TB the NodeB transmits to the UE at predetermined DL subframes without transmitting a respective DL SA. A UE is understood to include HARQ-ACK information due to SPS PDSCH, when it exists, with the one it generates in response to DL SAs and its placement can be, for example, in the beginning of the HARQ-ACK codeword. A UE is assumed to generate a HARQ-ACK information bit corresponding to each DL SA. The embodiments of the present invention relate the configured cells to a UE but may also directly apply if the activated cells are instead considered. The embodiments of the present invention consider aspects for the determination of the coding method for HARQ-ACK information bits in a PUCCH or in a PUSCH as a function of the HARQ-ACK payload, and for the partitioning of the HARQ-ACK information bits in a dual RM code. It is assumed that a single RM code is used if the HARQ-ACK payload is less than or equal to S1 bits, and that a dual RM code is used if the HARQ-ACK payload is greater than S1 bits but less than or equal to S2 bits. If the HARQ-ACK payload is greater than S2 bits, selective or full spatial-domain bundling applies to reduce the HARQ-ACK payload to S2 bits or below S2 bits, respectively. If, after full spatial-domain bundling, the HARQ-ACK payload continues to exceed S2 bits, time-domain bundling or cell-domain bundling are additionally performed until the HARQ-ACK payload becomes less than or equal to S2 bits. For a UE with C configured cells, NDAIDL(c) denotes a number of DL SAs the UE determines as being transmitted from a NodeB based on DL DAI IEs in DL SAs the UE detects in a bundling window of Nbundle subframes, and Qadd(c) denotes a number of additional DL SAs the UE may not be able to determine from the DL DAI IE in the DL SAs it detects (for example, Qadd(c)=0 if the UE detects a DL SA in the last DL subframe of the bundling window in cell c and Qadd(c)=1 otherwise). TBmax(c) denotes the maximum number of TBs a UE may receive in a subframe in cell c according to the configured PDSCH TM, the HARQ-ACK payload without spatial-domain bundling in a PUCCH or in a PUSCH not associated with an UL SA can be determined without misunderstanding between the NodeB and the UE as shown in Equation (2) below. O HARQ - ACK = ∑ c = 0 C - 1  ( N DAI DL  ( c ) + Q add  ( c ) ) · TB max  ( c ) . ( 2 ) Depending on the DL DAI design, the HARQ-ACK payload may be determined differently than in Equation (2), but the exact determination is not material to embodiments of the present invention and Equation (2) only serves as an example. For example, an alternative approach to compute the HARQ-ACK payload is OHARQ-ACK=Nbundle·(C+C2), where C2 is a number of cells for which the UE is configured a TM enabling the reception of 2 TBs per subframe. Based on the value of OHARQ-ACK, the coding method for a HARQ-ACK transmission in a PUCCH is determined as follows: a) If 2≦OHARQ-ACK≦S1, single RM code is used without spatial-domain bundling a. As DL CA implies the existence of at least C=2 cells, the minimum value for OHARQ-ACK is obtained for NDAIDL(c)=1, Qadd(c)=0 and TBmax(c)=1. b. Although a different coding method can be used for the transmission of OHARQ-ACK=2 bits in the PUSCH, for simplicity the single RM code is assumed. b) If S1<OHARQ-ACK≦S2, dual RM code is used without spatial-domain bundling. c) If S2<OHARQ-ACK, dual RM code is used with spatial-domain bundling and possible time-domain or cell-domain bundling. The first aspect of embodiments of the present invention focuses on the case that S2<OHARQ-ACK and considers the selection of a single RM code or a dual RM code and the application of bundling in various domains. Assuming that a UE is assigned for each cell a unique Cell_Index value, HARQ-ACK spatial-domain bundling corresponding to the last DL subframe in the bundling window is performed first starting from the cell with the largest (or smallest) Cell_Index, considering only cells with configured TM enabling the reception of 2 TBs, and continuing first across the cell-domain and subsequently across the time-domain in an iterative fashion. Spatial-domain bundling in the primary cell, if the UE is configured a TM enabling reception of 2 TBs in the primary cell, may be performed last regardless of the respective Cell_Index. The reason for first performing spatial-domain bundling across the cell-domain is to minimize or avoid penalizing some cells more than other cells. The reason for first performing spatial-domain bundling for the last subframe of the bundling window is because it is the one more likely to not convey actual HARQ-ACK information bits (as a UE cannot identify whether it failed to detect a DL SA in the last subframe) and therefore the impact of information loss due to bundling can be minimized. FIG. 10 is a diagram illustrating the application of HARQ-ACK spatial-domain bundling across cells and subframes, according to an embodiment of the present invention. Referring to FIG. 10, the Cell_Index of each cell is represented by a respective number. In a Cell 0 1010, a Cell 2 1030, and a Cell 3 1040, a UE is configured a TM enabling reception of 2 TBs per DL subframe, and for NDAIDL(c)=3 DL subframes (Qadd(c)=1), it generates 8 HARQ-ACK bits, 1015, 1035, and 1045, for each of these cells, respectively. The order of the HARQ-ACK bits is the same as the order of the DL subframes they correspond to. In a Cell 1 1020, the UE is configured a TM enabling reception of 1 TB per DL subframe and it generates 4 HARQ-ACK bits, 1025. Therefore, the total number of HARQ-ACK bits is 28. Assuming that S2=20, spatial-domain bundling of 8 HARQ-ACK pairs is needed and it begins from the last subframe in the bundling window of Nbundle=4 subframes (DL subframe 3) and from the cell with the largest Cell_Index (or the smallest Cell_Index) and continues sequentially in decreasing (or increasing) Cell_Index order, for cells having configured a TM enabling transmission of 2 TBs, until the cell with the smallest Cell_Index, if needed. Therefore, spatial-domain bundling is performed for the HARQ-ACK bits corresponding to DL subframes 3, 2, and 1 of Cell 3, for the HARQ-ACK bits corresponding to DL subframes 3, 2, and 1 of Cell 2, and for DL subframes 3 and 2 of Cell 0, resulting in bundle HARQ-ACK bits 1050, 1060 and 1070, respectively The primary cell may be considered last for spatial-domain bundling. This is because scheduling may occur more often in the primary cell than in other cells, and therefore it is more likely that spatial-domain bundling in the primary cell will apply to actual HARQ-ACK bits instead of preferably applying to HARQ-ACK bits not associated with actual DL SAs. The latter HARQ-ACK bits are generated to achieve the predetermined HARQ-ACK codeword size of OHARQ-ACK bits and do not carry any information (they are filler bits set to a NACK value that the NodeB decoder knows in advance as they correspond to DL SAs the NodeB did not transmit). Moreover, the primary cell may convey data with higher priority than the data in the remaining cells and it may be desirable to not compress the HARQ-ACK information through spatial-domain bundling. An alternative approach for performing spatial-domain bundling is for the NodeB to configure a UE through RRC signaling the order of the cells for which the UE should perform spatial-domain bundling. Therefore, the Cell_Index can be viewed as being replaced by the NodeB configured order for a set of configured cells for which the UE should perform spatial-domain bundling. Additionally, the NodeB may also configure, to a UE, the starting subframe for spatial-domain bundling. If a UE receives an UL SA for PUSCH transmission in a same UL subframe as the expected HARQ-ACK signal transmission, and the HARQ-ACK information is included in the PUSCH, the HARQ-ACK payload is determined as set forth below in Equation (3). OHARQ-ACK=VDAIUL·(C+C2) (3) Equation (3) assumes that VDAIUL indicates the cell with the largest number of DL SAs and that HARQ-ACK bits are generated for all cells assuming the transmission of VDAIU LDL SAs in each cell regardless of the actual number of DL SAs in each cell. The UE can use a NACK value for HARQ-ACK information bits in a cell that do not correspond to a received TB or DL SA (filler bits in order to transmit a total of OHARQ ACK bits as in Equation (3)). If the HARQ-ACK payload determined with Equation (2) is smaller than the one determined with Equation (3), the former one may be considered regardless of the UL DAI IE value. For VDAIUL=3 and Nbundle=4, the HARQ-ACK payload in a PUSCH for C=4 and C2=3, is reduced from O HARQ - ACK = ∑ c = 0 C - 1  ( N DAI DL  ( c ) + Q add  ( c ) ) · TB max  ( c ) = 28 bits (or from OHARQ-ACK=Nbundle·(C+C2)=28 bits) to OHARQ-ACK=VDAIUL·(C+C2)=21 bits. Consequently, assuming that S2=20, spatial-domain bundling for only 1 HARQ-ACK pair is needed. FIG. 11 is a diagram illustrating the application of HARQ-ACK spatial-domain bundling in a PUSCH associated with a UL SA conveying an UL DAI IE, according to an embodiment of the present invention. Referring to FIG. 11, the Cell_Index of each cell is represented by a respective number. In a Cell 0 1110, a Cell 2 1130, and a Cell 3 1140, a UE is configured a TM enabling reception of 2 TBs per DL subframe, and for VDAIUL=3, it generates 6 HARQ-ACK bits, 1115, 1135, and 1145, for each of these cells, respectively. The order of the HARQ-ACK bits is the same as the order of the DL subframes they correspond to. In a Cell 1 1120, the UE is configured a TM enabling reception of 1 TB per DL subframe, and for VDAIUL=3, it generates 3 HARQ-ACK bits, 1125. Therefore, the total number of HARQ-ACK bits is 21. As spatial-domain bundling of HARQ-ACK bits begins from the last subframe in the bundling window (DL subframe 3) and from the cell with the largest Cell_Index, it is only performed for the HARQ-ACK bits corresponding to DL subframe 3 of Cell 3, resulting in bundle HARQ-ACK bits 1150. If spatial-domain bundling is not sufficient to reduce the HARQ-ACK payload at or below S2 bits, time-domain bundling and/or cell-domain bundling are additionally applied. Assuming that time-domain bundling is performed first (although the reverse may also apply), as spatial-domain bundling already compresses the HARQ-ACK information for 2 TBs into 1 HARQ-ACK bit, time-domain bundling is prioritized in cells where spatial-domain bundling is not performed (that is, in cells where the configured TM enables the reception by the UE of only 1 TB). Otherwise, if time-domain bundling is performed on cells for which spatial-domain bundling is also performed, the HARQ-ACK information for 4 TBs would be further compressed into 1 HARQ-ACK which is not desirable, as it increases the loss in system throughput due to the compressed HARQ-ACK information. FIG. 12 is a diagram illustrating the application of HARQ-ACK spatial-domain bundling followed by time-domain bundling that is prioritized for cells without spatial-domain bundling, according to an embodiment of the present invention. Referring to FIG. 12, the order of cells for spatial-domain bundling is not material as spatial-domain bundling is performed over all cells it is applicable, a Cell 0 1210, a Cell 2 1230, a Cell 3 1240, and a Cell 4 1250 and, for a bundling window size of Nbundle=4 DL subframes, the respective 8 HARQ-ACK bits, 1215, 1235, 1245, and 1255, are compressed into respective 4 HARQ-ACK bits, 1218, 1238, 1248, and 1258. As the total number of Q=24 HARQ-ACK bits after spatial-domain bundling is above S2=20, time-domain bundling for a Cell 1 1220, and a Cell 5 1260 follows. The bundling size in the time-domain in each applicable cell is determined from the required reduction in HARQ-ACK bits as ┌(Q−S2)·Nbundle/C1┐ (or, for the last cell where time-domain bundling is performed, as └(Q−S2)·Nbundle/C1┘), where └ ┘ is the “floor” function which rounds a number to its lower integer and C1 is the number of cells having configured TM enabling the reception of only 1 TB. Then, the original 4 HARQ-ACK bits, 1225 and 1265, are compressed into respective 2 HARQ-ACK bits, 1228 and 1268. The order of the cells for the application of time-domain bundling can be based on the respective “Cell_Index”, or can be configured for each UE by the NodeB and time-domain bundling on the primary cell may be performed last. For HARQ-ACK transmission in a PUCCH, the required resources for a maximum payload already exist, such as, for example, for the transmission of 10 bits in FIG. 3 or the transmission of 20 bits in FIG. 5, and further reduction of the HARQ-ACK payload below the maximum will not result in overhead reduction. This is not the case for the HARQ-ACK transmission in the PUSCH, where the required resources increase as the HARQ-ACK payload increases (for example, as indicated in Equation (1)). For very large HARQ-ACK payloads, such as, for example, 10 bits or above, the overhead introduced by HARQ-ACK multiplexing in a PUSCH can be substantial and affect the data reception reliability, particularly if it is not associated with an UL SA (as, for example, for an SPS transmission or a non-adaptive HARQ retransmission where the maximum possible HARQ-ACK payload may be assumed). Moreover, the maximum resources that can be allocated to HARQ-ACK multiplexing in a PUSCH may not be sufficient to ensure a desired HARQ-ACK reception reliability. The second aspect of embodiments of the present invention addresses the issue by considering that additional bundling can be applied to a HARQ-ACK transmission in a PUSCH relative to one in a PUCCH in order to achieve a smaller HARQ-ACK payload in a PUSCH. For example, the HARQ-ACK payload in a PUCCH may be allowed to be up to S2 bits while the HARQ-ACK payload in a PUSCH may be allowed to be up to S0 bits with S0<S2 (for example, S0=S1). The process for the additional HARQ-ACK bundling in a PUSCH can follow the same principles as previously described in FIG. 10 and FIG. 12, where it is first performed in the spatial-domain and, if additional bundling is needed to achieve the maximum allowed HARQ-ACK payload, it continues in the time-domain (or in the cell-domain). Unlike HARQ-ACK transmission in a PUCCH, where the application or not of HARQ-ACK bundling is default according to the maximum HARQ-ACK payload that can be supported by a respective PUCCH structure (that is, according to the values of S1 and S2), the application of HARQ-ACK bundling in a PUSCH may further depend on the parameters of the PUSCH transmission, such as its size and/or the MCS for the data transmission, and S0 is then a function of these parameters. In a first approach, the value of S0 can be predetermined, for example, to be equal to S1. Then, although HARQ-ACK bundling in a PUCCH applies until the HARQ-ACK payload is compressed to S2 bits and a dual RM code is used, additional HARQ-ACK bundling can apply for HARQ-ACK transmission in a PUSCH until the HARQ-ACK payload is compressed to S1 bits and single RM code is always used. In a second approach, the value of S0 is dynamically computed depending on the PUSCH transmission parameters. One such parameter is the MCS of the data transmission. For example, S0=S1 if the MCS is below a predetermined threshold MCSthr while S0=S2 otherwise. This is motivated by the fact that the MCS of the data transmission, or equivalently the spectral efficiency of the data transmission, determines the PUSCH resources required for HARQ-ACK multiplexing in the PUSCH, for example as indicated in Equation (1). Then, in order to avoid a substantial HARQ-ACK overhead particularly for PUSCH transmissions with relatively low data spectral efficiency, a larger amount of HARQ-ACK bundling can apply for MCS below MCSthr in order to improve
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