Patent Publication Number: US-8543867-B2

Title: Transmission of acknowledgement and negative acknowledgement in a wireless communication system

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to communication systems. More specifically, the present disclosure relates to the transmission of acknowledgement and negative acknowledgement (ACK/NACK) in a wireless communication system. 
     BACKGROUND 
     Communication systems have become an important means by which many people worldwide have come to communicate. In particular, wireless communication systems have become practically ubiquitous in modern society. Many wireless communication systems include a multitude of wireless communication devices and base stations. 
     A wireless communication device, such as a cellular phone, may be used for voice and/or data communication over a wireless communication system. A base station is a fixed station (e.g., a wireless communication station that is installed at a fixed location) that communicates with wireless communication devices. 
     Wireless communication systems typically use one or more antennas to communicate over the air. For instance, wireless communication devices and base stations typically communicate by sending Radio Frequency (RF) signals to each other. The nature of wireless communication systems often causes difficulties in receiving and decoding signals. For example, noise from a number of sources may be added to a communication signal. The communication signal may also be subject to effects such as Doppler shift and free space attenuation. The noise and other effects may cause a received signal to be incorrectly decoded. Wireless communication systems often convey information about whether signals were correctly received and/or incorrectly received. As can be seen from this discussion, improved systems and methods that improve the efficiency of reporting correctly received and/or incorrectly received signals may be beneficial. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating one configuration of a wireless communication system wherein systems and methods for transmission of ACK/NACK in a wireless communication system may be implemented; 
         FIG. 2  is a block diagram illustrating more detail of one configuration of a wireless communication system wherein systems and methods for transmission of ACK/NACK in a wireless communication system may be implemented; 
         FIG. 3  is a block diagram illustrating an example of several possible configurations of systems and methods for transmission of acknowledgement and negative acknowledgement in a wireless communication system; 
         FIG. 4  is a flow diagram illustrating one configuration of a method for transmission of ACK/NACK in a wireless communication system; 
         FIG. 5  is a flow diagram illustrating a more specific configuration of a method for transmission of ACK/NACK in a wireless communication system; 
         FIG. 6  is a flow diagram illustrating another more specific configuration of a method for transmission of ACK/NACK in a wireless communication system; 
         FIG. 7  is a flow diagram illustrating yet another more specific configuration of a method for transmission of ACK/NACK in a wireless communication system; 
         FIG. 8  is a block diagram illustrating three examples of ACK/NACK source coding or compression; 
         FIG. 9  is a block diagram illustrating one configuration of a communication device in which systems and methods for transmission of ACK/NACK in a wireless communication system may be implemented; 
         FIG. 10  is a block diagram illustrating several possible configurations of a wireless communication device and a base station in which systems and methods for transmission of ACK/NACK in a wireless communication system may be implemented; 
         FIG. 11  is a block diagram illustrating more detail on one configuration of an ACK/NACK source coding module; 
         FIG. 12  is a block diagram illustrating more detail on one configuration of an ACK/NACK balancing module; 
         FIG. 13  illustrates various components that may be utilized in a wireless communication device; and 
         FIG. 14  illustrates various components that may be utilized in a base station. 
     
    
    
     DETAILED DESCRIPTION 
     The 3rd Generation Partnership Project, also referred to as “3GPP,” is a collaboration agreement that aims to define globally applicable technical specifications and technical reports for third and fourth generation wireless communication systems. The 3GPP may define specifications for the next generation mobile networks, systems, and devices. 
     3GPP Long Term Evolution (LTE) is the name given to a project to improve the Universal Mobile Telecommunications System (UMTS) mobile phone or device standard to cope with future requirements. In one aspect, UMTS has been modified to provide support and specification for the Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN). 
     At least some aspects of the systems and methods disclosed herein may be described in relation to the 3GPP LTE and LTE-Advanced standards (Release-8 and Release-10). However, the scope of the present disclosure should not be limited in this regard. At least some aspects of the systems and methods disclosed herein may be utilized in other types of wireless communication systems. 
     A wireless communication device may be an electronic device used to communicate voice and/or data to a base station, which in turn may communicate with a network of devices (e.g., public switched telephone network (PSTN), the Internet, etc.). In describing systems and methods herein, a wireless communication device may alternatively be referred to as a mobile station, a user equipment (UE), an access terminal, a subscriber station, a mobile terminal, a remote station, a user terminal, a terminal, a subscriber unit, a mobile device, etc. A wireless communication device may be a cellular phone, a smart phone, a personal digital assistant (PDA), a laptop computer, a netbook, an e-reader, a wireless modem, etc. In 3GPP specifications, a wireless communication device is typically referred to as a user equipment (UE). However, as the scope of the present disclosure should not be limited to the 3GPP standards, the terms “UE” and “wireless communication device” may be used interchangeably herein to mean the more general term “wireless communication device.” 
     In 3GPP specifications, a base station is typically referred to as a Node B, an evolved Node B (eNB), a home enhanced or evolved Node B (HeNB), or some other similar terminology. As the scope of the disclosure should not be limited to 3GPP standards, the terms “base station,” “Node B,” “eNB,” and “HeNB” may be used interchangeably herein to mean the more general term “base station.” Furthermore, the term “base station” may be used to denote an access point. An access point may be an electronic device that provides access to a network (e.g., Local Area Network (LAN), the Internet, etc.) for wireless communication devices. The term “communication device” may be used to denote both a wireless communication device and/or a base station. 
     A communication device configured for compression and transmission of Acknowledgement and Negative Acknowledgement (ACK/NACK) is disclosed. The communication device includes a processor and instructions stored in memory. The communication device determines one or more thresholds based on a size of one or more code words and generates a compressed ACK/NACK sequence. The compressed ACK/NACK sequence identifies one or more correctly received code words and one or more incorrectly received code words if the number of incorrectly received code words is less than the threshold. The compressed ACK/NACK sequence indicates that all of the one or more code words were incorrectly received if the number of incorrectly received code words is greater than the threshold. 
     The communication device may receive a signal including one or more code words. The communication device may transmit the compressed ACK/NACK sequence. The compressed ACK/NACK sequence may identify one or more correctly received code words and one or more incorrectly received code words if the number of incorrectly received code words is equal to the threshold. The compressed ACK/NACK sequence may indicate each incorrectly received code word and at least one correctly received code word as an incorrectly received code word if the number of incorrectly received code words is equal to the threshold. 
     The communication device may also partition an uncoded ACK/NACK sequence and generate a compressed ACK/NACK sequence for each partition. Each partition may use one of the one or more thresholds. Stronger code or unequal error protection may be applied to one or more ACK/NACK bits corresponding to one or more designated code words. The one or more designated code words may carry more sensitive information than other code words. The one or more designated code words may be larger than other code words. 
     The communication device may also communicate threshold information with at least one other communication device. The communication device may format the compressed ACK/NACK sequence such that an ACK/NACK bit is sent only at times corresponding to bit transitions. The status of only one code word may be reported for two or more code words by the communication device if a spectral correlation between channels corresponding to the two or more code words is greater than a spectral threshold. The status of only one code word may be reported for two or more code words by the communication device if a spatial correlation between channels corresponding to the two or more code words is greater than a spatial threshold. 
     The communication device may also channel code the compressed ACK/NACK sequence. The communication device may be a wireless communication device or a base station. 
     A communication device configured for balancing and transmission of Acknowledgement and Negative Acknowledgement (ACK/NACK) is also disclosed. The communication device includes a processor and instructions stored in memory. The communication device receives an ACK/NACK sequence, balances the ACK/NACK sequence and transmits the ACK/NACK sequence. 
     The ACK/NACK sequence may be balanced using a scrambling sequence that is specific to the communication device. The scrambling sequence may be a static scrambling sequence, a semi-dynamic scrambling sequence or a dynamic scrambling sequence. 
     The ACK/NACK sequence may be balanced using Gray coding. The Gray coding may be based on an algorithm or a look-up table. The ACK/NACK sequence may be balanced using distribution shaping using a non-linear transformation. The distribution shaping may be based on an algorithm or a look-up table. The ACK/NACK sequence may be a compressed ACK/NACK sequence. The communication device may also channel code the ACK/NACK sequence. 
     A method for compression and transmission of Acknowledgement and Negative Acknowledgement (ACK/NACK) is also disclosed. The method includes determining one or more thresholds based on a size of one or more code words and generating a compressed ACK/NACK sequence on a communication device. The compressed ACK/NACK sequence identifies one or more correctly received code words and one or more incorrectly received code words if the number of incorrectly received code words is less than the threshold. The compressed ACK/NACK sequence indicates that all of the one or more code words were incorrectly received if the number of incorrectly received code words is greater than the threshold. 
     A method for balancing and transmission of Acknowledgement and Negative Acknowledgement (ACK/NACK) is also disclosed. The method includes receiving an ACK/NACK sequence by a communication device, balancing the ACK/NACK sequence and transmitting the ACK/NACK sequence from the communication device. 
     A non-transitory tangible computer-readable medium for compression and transmission of Acknowledgement and Negative Acknowledgement (ACK/NACK) is disclosed. The computer-readable medium includes executable instructions for determining one or more thresholds based on a size of one or more code words and generating a compressed ACK/NACK sequence. The compressed ACK/NACK sequence identifies one or more correctly received code words and one or more incorrectly received code words if the number of incorrectly received code words is less than the threshold. The compressed ACK/NACK sequence indicates that all of the one or more code words were incorrectly received if the number of incorrectly received code words is greater than the threshold. 
     A non-transitory tangible computer-readable medium for balancing and transmission of Acknowledgement and Negative Acknowledgement (ACK/NACK) is also disclosed. The computer readable medium includes executable instructions for receiving an ACK/NACK sequence, balancing the ACK/NACK sequence and transmitting the ACK/NACK sequence. 
     In Release-10 of the 3GPP standard (e.g., LTE-Advanced) for cellular wireless communication, several channels (e.g., five) known as carrier components may be provisioned for transmission of information for both the uplink (e.g., signals from a wireless communication device to a base station) and downlink (e.g., signals from a base station to a wireless communication device). In addition, a number of spatial channels (e.g., two) may be available on each carrier component by using multiple antennas at a transmitter and a receiver. Therefore, multiple code words may be transmitted simultaneously. In one configuration, a maximum of ten code words (i.e., five channels×two code words per channel) can be transmitted simultaneously. For example, five times more code words may be transmitted according to Release-10 compared to Release-8. 
     Upon reception of the code words, the receiver may inform the transmitter regarding the successful or unsuccessful reception of each of the code words. This is typically accomplished by transmitting a one bit Acknowledgement/Negative Acknowledgement (ACK/NACK) for every received code word. If the code word is received successfully (e.g., correctly), an Acknowledgement (ACK) is transmitted (e.g., with the bit set to 1). Otherwise, a Negative Acknowledgement (NACK) is transmitted (e.g., with the bit set to 0). Thus, one bit per code word may be needed if each code word is acknowledged separately. For example, if ten code words are sent at a time, ten bits of ACK/NACK may be needed to separately acknowledge each code word. These ACK/NACK bits may be sent, for example, on a control channel or shared channel between communication devices (e.g., wireless communication device, base station, etc.). The systems and methods disclosed herein may provide a reduction in the number of transmitted ACK/NACK bits, which may be beneficial in a wireless communication system as control channel bandwidth may be a limited resource. 
     In wireless communication systems, the probability of a code word error may be set (e.g., designed to perform) at a particular operating point, given certain specified channel conditions. For example, the operating point of the LTE and LTE-Advanced standards is set such that the probability of a code word error may be 10% under mostly benign to moderately severe channel conditions in order for voice services to perform with a quality of service that does not appear uncomfortably distorted to typical human hearing. That is, 10% of the time, a receiver sends a Negative Acknowledgement (e.g., with the ACK/NACK bit set to 0) and 90% of the time a receiver sends an Acknowledgement (e.g., with the ACK/NACK bit set to 1). Therefore, an ACK/NACK sequence corresponding to several code words (e.g., ten bits corresponding to ten code words in the example above) sent from the receiver may have an imbalanced distribution of 1&#39;s and 0&#39;s. That is, there are more 1&#39;s in the sequence than 0&#39;s. When channel coding is used for such a sequence, the imbalance may cause a degraded performance in the channel code. The systems and methods disclosed herein may further provide techniques (e.g., a scrambling sequence specific to a communication device, Gray coding, etc.) to make an ACK/NACK bit stream more balanced. 
     It should be noted that as used herein, the general term “ACK/NACK sequence” may refer to an uncoded ACK/NACK sequence, compressed (or lossy-coded) ACK/NACK sequence, unbalanced ACK/NACK sequence, balanced ACK/NACK sequence, balanced compressed ACK/NACK sequence, a channel coded ACK/NACK sequence, or an ACK/NACK sequence in various stages of compression or balancing, for example. The term “channel coded ACK/NACK sequence” may be refer to an ACK/NACK sequence that has been channel coded, including uncoded, compressed, unbalanced, balanced and balanced compressed ACK/NACK sequences. 
     Various configurations are now described with reference to the Figures, where like reference numbers may indicate functionally similar elements. The systems and methods as generally described and illustrated in the Figures herein could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of several configurations, as represented in the Figures, is not intended to limit scope, as claimed, but is merely representative of the systems and methods. 
       FIG. 1  is a block diagram illustrating one configuration of a wireless communication system wherein systems and methods for transmission of ACK/NACK in a wireless communication system may be implemented. One or more wireless communication devices  102  may communicate with a base station  112 . Examples of wireless communication devices include cellular phones, smart phones, e-readers, laptop computers, netbooks, etc. Examples of a base station include a cellular phone tower, an access point, etc. The wireless communication device  102  and the base station  112  may communicate, for example, by sending and receiving data and control signals to and from each other. In one configuration, the wireless communication device  102  includes one or more antennas  108  and the base station  112  includes one or more antennas  110 . 
     The one or more wireless communication devices  102  may receive code words from the base station  112 . A code word may be a binary representation of data (e.g., voice, control and/or other data). When a wireless communication device  102  successfully (e.g., correctly) receives a code word from the base station  112 , for example, the wireless communication device  102  may generate an ACK corresponding to that code word (e.g., a bit set to 1). However, when the wireless communication device  102  unsuccessfully (e.g., incorrectly) receives a code word (e.g., the code word was lost or damaged), the wireless communication device  102  may generate a NACK corresponding to that code word (e.g., a bit set to 0). A sequence of ACKs and NACKs may be formed by putting the ACK/NACK bits of all of the code words in sequence. This series of ACK/NACK bits may be referred to as an uncoded ACK/NACK sequence. 
     The one or more wireless communication devices  102  may include an ACK/NACK source coding module  104  and/or an ACK/NACK balancing module  106 . The ACK/NACK source coding module  104  may be a hardware and/or software module used to code an uncoded ACK/NACK sequence (e.g., sequence of ACK/NACK bits). The ACK/NACK source coding module  104  may compress the uncoded ACK/NACK sequence into a compressed or lossy-coded ACK/NACK sequence. The compressed or lossy-coded ACK/NACK sequence may be shorter (e.g., require fewer bits) than the uncoded ACK/NACK sequence. The compression performed by the ACK/NACK source coding module may also reduce the severity of an unbalance in the uncoded ACK/NACK sequence. 
     The balancing module  106  may be a hardware and/or software module used to balance an ACK/NACK sequence. For example, the balancing module  106  may balance an uncoded ACK/NACK sequence such that the number of 1&#39;s and 0&#39;s in the sequence are closer to equal. Alternatively, the compressed ACK/NACK sequence (generated by the ACK/NACK source coding module  104 ) may optionally be balanced by the ACK/NACK balancing module  106 . For example, the ACK/NACK balancing module  106  may modify the compressed ACK/NACK sequence such that it has a more even distribution of 1&#39;s and 0&#39;s. That is, the ACK/NACK balancing module  106  may modify the compressed ACK/NACK sequence so that the number of 1&#39;s and the number of 0&#39;s in the sequence are closer to equal. The ACK/NACK balancing module  106  may thus generate a balanced ACK/NACK sequence or a balanced compressed ACK/NACK sequence. 
     It should be noted that the ACK/NACK source coding module  104  and the ACK/NACK balancing module  106  may be used independently or in combination. As discussed above, a compressed ACK/NACK sequence (generated by the ACK/NACK source coding module  104 ) may be optionally balanced by the ACK/NACK balancing module  106  in one configuration. In another configuration, however, the compressed ACK/NACK sequence may not be balanced. Furthermore, an uncoded ACK/NACK sequence may be balanced by the ACK/NACK balancing module  106  without any source coding or compression. Thus, a communication device may include one of an ACK/NACK source coding module  104 , an ACK/NACK balancing module  106  or both  104 ,  106 . Furthermore, a communication device may utilize one of an ACK/NACK source coding module  104 , an ACK/NACK balancing module  106  or both  104 ,  106  at one time. 
     The ACK/NACK sequence may be transmitted. For example, the wireless communication device  102  may generate a balanced compressed ACK/NACK sequence (based on one or more received code words) and send it to the base station  112 . The base station  112  may use an ACK/NACK balancing decoding module  185  in order to decode or interpret a balanced ACK/NACK sequence or balanced compressed ACK/NACK sequence. In other words, the base station  112  may decode the balanced ACK/NACK sequence or balanced compressed ACK/NACK sequence to remove the balancing and thus obtain an ACK/NACK sequence (e.g., uncoded ACK/NACK sequence, compressed ACK/NACK sequence, etc.). 
     The base station  112  may also use an ACK/NACK source decoding module  183  to interpret, decode or “decompress” a compressed ACK/NACK sequence and thus obtain an ACK/NACK sequence. Because the compression performed is lossy compression, the ACK/NACK source decoding module  183  may recover the original ACK/NACK sequence for some cases. In other cases, the source decoding module  183  may recover a representation that is not the original ACK/NACK sequence but that indicates at least the incorrectly received code words in addition to some code words that were possibly received correctly. The base station  112  may then retransmit code words that the ACK/NACK sequence indicates were received incorrectly. 
     As illustrated in  FIG. 1 , an ACK/NACK source coding module  114  and/or an ACK/NACK balancing module  116  may be included on the base station  112 . In other words, an ACK/NACK source coding module  104 ,  114  and an ACK/NACK balancing module  106 ,  116  may be implemented on one or more wireless communication devices  102  and/or on the base station  112 . Additionally or alternatively, the wireless communication device  102  may include an ACK/NACK balancing decoding module  181  and/or an ACK/NACK source decoding module  179 . In other words, an ACK/NACK balancing decoding module  181 ,  185  and an ACK/NACK source decoding module  179 ,  183  may be implemented on one or more wireless communication devices  102  and/or on the base station  112 . In one configuration, some or all aspects of ACK/NACK source decoding  179 ,  183  and/or ACK/NACK balancing decoding  181 ,  185  may occur as part of channel decoding. For example, a channel decoder on a communication device  102 ,  112  receiving an ACK/NACK sequence may perform Gray decoding, distribution de-shaping and/or descrambling. 
       FIG. 2  is a block diagram illustrating more detail of one configuration of a wireless communication system wherein systems and methods for transmission of ACK/NACK in a wireless communication system may be implemented. One or more wireless communication devices  202  may communicate with a base station  212  using one or more antennas  208 . The base station  212  may also communicate with the one or more wireless communication devices  202  using one or more antennas  210 . 
     The wireless communication device  202  and the base station  212  may communicate with each other using channels and/or component carriers. For example, a wireless communication device  202  uses an uplink control channel  218  to send control information to the base station  212 . One example of an uplink control channel is a Physical Uplink Control Channel (PUCCH) pursuant to 3GPP specifications. In one configuration, the uplink control channel  218  is assigned to one particular wireless communication device  202 . In other words, each wireless communication device  202  may use a separate uplink control channel  218  for sending control information to the base station  212 . 
     An uplink shared channel  222  may also be used in common by one or more wireless communication devices  202 . The uplink shared channel  222  may be used to send ACK/NACK bits or sequences (e.g., ACK/NACK message C  220   c ), control or other information to the base station  212  from one or more wireless communication devices  202 . One example of an uplink shared channel  222  is a Physical Uplink Shared Channel (PUSCH) pursuant to 3GPP specifications. The base station  212  may use a downlink control channel  224  to send control information to one or more wireless communication devices  202 . One example of a downlink control channel  224  is a Physical Downlink Control Channel (PDCCH) pursuant to 3GPP specifications. 
     One or more carrier components  226  may be used to transmit data between the one or more wireless communication devices  202  and the base station  212 . Carrier components  226  may be communication channels that are separated in the frequency domain. In one configuration, several carrier components  226  comprise a data channel that is used to send and/or receive voice and other data. For example, voice data and other data may be represented as code words  228  carried on the carrier components  226 . Each carrier component  226  may also be used to transmit separate code words using multiple antenna  208 ,  210  techniques. For example, multiple spatial channels may be formed by using multiple antennas  208 ,  210 . In this way, multiple code words  228  may be sent on each carrier component  226  using different spatial channels. For example, code word A  228   a  is sent on carrier component A  226   a  using spatial channel A, code word B  228   b  is sent on carrier component A  226   a  using spatial channel B, code word C  228   c  is sent on carrier component B  226   b  using spatial channel A and code word D  228   d  is sent on carrier component B  226   b  using spatial channel B. 
     The wireless communication device  202  may include an ACK/NACK source coding module  204  and/or an ACK/NACK balancing module  206 . The wireless communication device  202  may receive one or more code words  228  sent from the base station  212  on one or more carrier components  226 . The wireless communication device  202  may generate an uncoded ACK/NACK sequence indicating which of the one or more code words  228  was/were successfully (e.g., correctly) and/or unsuccessfully (e.g., incorrectly) received. The ACK/NACK source coding module  204  may use the uncoded ACK/NACK sequence to generate a compressed (e.g., lossy-coded) ACK/NACK sequence, a balanced ACK/NACK sequence (which may be balanced by the ACK/NACK balancing module  206 ) or a balanced compressed ACK/NACK sequence, for example. In one configuration, the compressed and/or balanced ACK/NACK sequence is channel coded and sent to the base station  212  as ACK/NACK message A  220   a  using the uplink control channel  218 . The base station  212  may use an ACK/NACK balancing decoding module  285  to remove balancing from the ACK/NACK sequence (e.g., that was received as part of ACK/NACK message A  220   a ). The base station  212  may also use an ACK/NACK source decoding module  283  to decode or decompress the compressed ACK/NACK sequence to obtain a decompressed ACK/NACK sequence. The base station  212  may retransmit any code words  228  that the ACK/NACK sequence indicates were incorrectly received. Thus, the base station  212  may retransmit any code words  228  that ACK/NACK message A  220   a  indicates were unsuccessfully received by the wireless communication device  202 . 
     The base station  212  may alternatively or additionally include an ACK/NACK source coding module  214  and/or an ACK/NACK balancing module  216 . These modules  214 ,  216  may function similarly to those  204 ,  206  described above in connection with the wireless communication device  202 . However, ACK/NACK message B  220   b  may be generated based on code words that were successfully (e.g., correctly) or unsuccessfully (e.g., incorrectly) received by the base station  212  from the wireless communication device  202 . ACK/NACK message B  220   b  may be sent using the downlink control channel  224 . The wireless communication device  202  may retransmit those unsuccessfully (e.g., incorrectly) received code words (i.e., by the base station  212 ) as indicated by ACK/NACK message B  220   b.    
     The wireless communication device  202  may alternatively or additionally include an ACK/NACK source decoding module  279  and/or an ACK/NACK balancing decoding module  281 . These modules  279 ,  281  may function similarly to those  283 ,  285  described above in connection with the base station  212 . However, the ACK/NACK balancing decoding module  281  and/or the ACK/NACK source decoding module  279  may be used to interpret or decode a balanced and/or compressed ACK/NACK sequence sent from the base station  212  (e.g., in ACK/NACK message B  220   b ). 
     A more specific example of the configuration illustrated in  FIG. 2  is given hereafter. In the downlink channel(s) specified in 3GPP Release-10 (e.g., LTE-Advanced), five carrier components  226  (i.e., five communication channels that are separated in the frequency domain) can be used for transmission of data to the wireless communication device (e.g., User Equipment (UE))  202 . In addition, two separate code words (e.g., code words  228   a - b ,  228   c - d , etc.) may be transmitted concurrently (at approximately the same time) on each carrier component (e.g., carrier component A  226   a , carrier component B  226   b , etc.)  226  using multiple antenna  208 ,  210  techniques. Thus, a total of ten code words  228  may be concurrently transmitted to the wireless communication device (e.g., UE)  202 . 
     One ACK/NACK bit is associated with each code word  228 , which indicates whether the code word  228  was received correctly or incorrectly. For example, if a code word  228  is received correctly (i.e., successfully), the value of the corresponding ACK/NACK bit is 1, otherwise it is set to 0. All of the bits corresponding to the ten transmitted code words  228  create a sequence of ACK/NACK bits, referred to as an uncoded ACK/NACK sequence. As discussed above, the uncoded ACK/NACK sequence may be compressed to generate a lossy-coded ACK/NACK sequence. ACK/NACK source coding  204  techniques that may reduce the length of the uncoded ACK/NACK sequence are described in greater detail below. 
     An ACK/NACK sequence may be channel coded prior to transmission. Some examples of channel coding include a repetition code, which can be achieved by simply repeating the ACK/NACK sequence or spreading the ACK/NACK sequence using spreading codes (or sequences) used in Code Division Multiple Access (CDMA) schemes. More complex channel coding schemes such as Reed-Muller codes may be used to channel code the ACK/NACK sequence. The resultant bit stream may be referred to as a channel-coded ACK/NACK sequence. That is, an ACK/NACK sequence may be channel coded to produce an ACK/NACK message  220  (e.g., ACK/NACK message A  220   a ) for transmission. 
     The adaptive coding and modulation scheme in LTE and LTE-Advanced are designed such that the code word  228  error rate may be around 10%. That is, about 10% of the time a code word  228  is received erroneously and the other 90% of the time the code word is received correctly. As a result, in an ACK/NACK sequence there may be more 1&#39;s (i.e., corresponding to correctly received code words  228 ) than 0&#39;s. The imbalance in the ACK/NACK sequence degrades the performance of the channel-coded ACK/NACK sequence. Thus, the ACK/NACK balancing module  206  may be used in order to balance the ACK/NACK sequence (e.g., in terms of number of 0&#39;s and 1&#39;s). For example, the ACK/NACK balancing module  206  may use a scrambler sequence, a Gray code and/or a non-linear mapping to balance the ACK/NACK sequence. 
       FIG. 3  is a block diagram illustrating an example of several possible configurations of systems and methods for transmission of acknowledgement and negative acknowledgement in a wireless communication system. In this example, ten code words  1428   a - j  are received by a receiver/decoder module  1452 . It should be noted that the systems and methods disclosed herein are not limited to ten code words  1428   a - j , but may utilize any number of code words  228 . The receiver/decoder module  1452  and/or a code word loss detection module  1450  may generate ACK/NACK bits  1487   a - j  based on whether the code words  1428   a - j  were received or decoded correctly. In this example, the receiver/decoder module  1452  and/or a code word loss detection module  1450  detect that code word A  1428   a  and code word C  1428   c  were received incorrectly, while the remainder of the code words  1428   b ,  1428   d - j  were received correctly. The receiver/decoder module  1452  and/or a code word loss detection module  1450  generates ACK/NACK A  1487   a  as 0, ACK/NACK C  1487   c  as 0, and the remainder of the ACK/NACK bits  1487   b ,  1487   d - j  as 1&#39;s. In this example, the ten ACK/NACK bits  1487   a - j  are combined to form an uncoded ACK/NACK sequence  1448  of 0101111111. In this case, the uncoded ACK/NACK sequence  1448  of 0101111111 may be “unbalanced” since it has many more 1&#39;s than 0&#39;s. 
       FIG. 3  illustrates several paths that may be taken by an ACK/NACK sequence. Two of the several paths illustrated in  FIG. 3  are given for clarity. On one path, the uncoded ACK/NACK sequence  1448  may be sent to a transmitter for transmission. On another path, the uncoded ACK/NACK sequence  1448  may be channel coded using a channel coding module  1474  and sent using a transmitter. 
     Several possible configurations of the systems and methods are described as follows. In one configuration, the uncoded ACK/NACK sequence  1448  (which may also be unbalanced) may be balanced by the balancing module  1406 . This balanced ACK/NACK sequence  1489  may be sent to the transmitter to be transmitted with a repetition code. This repetition code may simply be where two or more copies of the balanced ACK/NACK sequence  1489  are transmitted by occupying different communication device (e.g., wireless communication device  102 , base station  112 ) resources. Examples of communication device resources include time resources, frequency resources and spatial or antenna resources. 
     In another configuration, the balanced ACK/NACK sequence  1489  may be input into a channel coding module  1474 . The channel coding module  1474  may channel code an ACK/NACK sequence to produce a channel coded ACK/NACK sequence  1491  in preparation for transmission. One example of a channel code that may be used is a Reed-Muller code. Because the balanced ACK/NACK sequence  1489  may be more balanced than the uncoded ACK/NACK sequence  1448 , the performance of the channel coding may be increased. That is, the channel coding performance may be increased due to a more balanced use of the code in comparison to the case where the uncoded unbalanced ACK/NACK sequence  1448  is channel coded  1474  without balancing  1406 . 
     In another configuration, the uncoded ACK/NACK sequence  1448  may be source coded or compressed using an ACK/NACK source coding/compression module  1404 . The ACK/NACK source coding/compression module  104  may use the uncoded ACK/NACK sequence  1448  to produce a compressed ACK/NACK sequence  1470 . The compressed ACK/NACK sequence  1470  may be input into the balancing module  1406 . In this case, a balanced (lossy) compressed ACK/NACK sequence  1472  may be generated. In some configurations, the ACK/NACK sequence compression  1404  and balancing  1406  may be lumped together. The balanced compressed ACK/NACK sequence  1472  may be sent to the transmitter without channel coding  1474 . Alternatively, the balanced compressed ACK/NACK sequence  1472  may be channel coded using the channel coding module  1474  and sent to a transmitter. 
     In another configuration, the compressed ACK/NACK sequence  1470  may be input into the channel coding module  1474  without balancing. That is, the output of the lossy compression module  1404  may be encoded by the channel coding module  1474  and sent to a transmitter. 
     In another configuration, the compressed ACK/NACK sequence  1470  is sent to the transmitter. In this case, coding schemes such as repetition coding schemes may be used. In a repetition coding scheme, two or more copies of the same compressed ACK/NACK sequence  1470  may be transmitted using two or more different communication device resources (e.g., time, frequency or space/antenna). For example, two copies of an ACK/NACK sequence may be transmitted at two different times, on different frequencies or using different spatial channels. 
       FIG. 4  is a flow diagram illustrating one configuration of a method  300  for transmission of ACK/NACK in a wireless communication system. The communication device may receive  302  one or more code words. For example, a wireless communication device  102  may receive  302  a signal (e.g., containing one or more code words  228 ) from a base station  112 . The communication device may decode  304  the signal to produce one or more code words. 
     The communication device may determine  306  whether each of the one or more code words  228  was received successfully. For example, the communication device may utilize an error detection code to determine  306  which of the one or more code words  228  was/were successfully and/or unsuccessfully received. For example, a Cyclic Redundancy Check (CRC) may be used to determine  306  which code words  228  were correctly or incorrectly received. Other approaches known in the art may be used to determine  306  correct/incorrect reception of code words  228 . The communication device may generate  308  an uncoded ACK/NACK sequence based on whether each of the one or more code words  228  was received successfully. In one configuration, the communication device generates an ACK/NACK bit corresponding to each code word  228 . If a code word  228  was successfully received, its  228  corresponding ACK/NACK bit is set to 1. Otherwise (if the code word  228  was unsuccessfully received), its  228  corresponding ACK/NACK bit is set to 0. The uncoded ACK/NACK sequence may comprise a group of ACK/NACK bits. 
     The communication device may source code  310  the uncoded ACK/NACK sequence to produce a compressed ACK/NACK sequence. The source coding  310  disclosed herein may be a lossy source-coding. Hence, the uncoded ACK/NACK sequence may be source coded  310  by the communication device to produce a compressed (e.g., lossy source-coded) ACK/NACK sequence. More detail regarding lossy source coding  310  is given below, particularly in connection with  FIGS. 5 ,  6 ,  7 ,  8 ,  9  and  11 . The communication device may balance  312  the compressed ACK/NACK sequence  1470  to produce a balanced compressed ACK/NACK sequence  1472 . Alternatively, the communication device may balance the uncoded ACK/NACK sequence  1448  to produce a balanced ACK/NACK sequence  1489 . More detail regarding ACK/NACK balancing  312  is given below, particularly in connection with  FIG. 12 . 
     The communication device may channel code  314  the ACK/NACK sequence (e.g., uncoded ACK/NACK sequence  1448 , balanced ACK/NACK sequence  1489 , compressed ACK/NACK sequence  1470  or balanced compressed ACK/NACK sequence  1472 ) to produce a channel-coded ACK/NACK sequence  1491 . The channel-coded ACK/NACK sequence  1491  may be transmitted  316  by the communication device. The channel-coded ACK/NACK sequence  1491  may be received and decoded by another communication device, which may retransmit one or more unsuccessfully received code words  228  as indicated by the ACK/NACK sequence. As discussed above, the channel coded ACK/NACK sequence  1491  (e.g., ACK/NACK message  220 ) may be transmitted on a control channel  218 ,  224 . The method  300  illustrated in  FIG. 4  may be repeated for additional received signals and/or code words  228 . 
       FIG. 5  is a flow diagram illustrating one more specific configuration of a method  400  for transmission of ACK/NACK in a wireless communication system. The communication device may determine  402  whether each of a number (e.g., N) of code words  228  was successfully (e.g., correctly) received. For example, the communication device may use an error detecting code to detect whether each of the code words  228  was successfully received or not. The communication device may generate  404  an uncoded ACK/NACK sequence  1448  based on whether each of the code words  228  was successfully received. As described above, a group of bits each corresponding to a code word  228  may indicate which of the code words  228  was successfully received or unsuccessfully received. 
     The communication device may determine  406  a threshold (e.g., K) based on the size of the code words  228 . Alternatively, the communication device may determine  406  the threshold based on data received from another communication device. For example, a wireless communication device  102  may receive one or more code words  228  and determine  406  the threshold based on the size of those code words  228 . Alternatively, the base station  112  may send data to the wireless communication device  102  (e.g., a threshold) that the wireless communication device  102  may use to determine  406  a threshold. 
     The communication device may then determine  408  whether the number of code words  228  unsuccessfully (e.g., incorrectly) received is greater than the threshold. For example, the communication device may use the uncoded ACK/NACK sequence to determine the number of code words  228  that were unsuccessfully received and compare it to the threshold. 
     If the number of unsuccessfully (e.g., incorrectly) received code words  228  is greater than the threshold, the communication device may generate  410  a compressed (e.g., lossy-coded) ACK/NACK sequence  1470  indicating that all of the code words  228  corresponding to the uncoded ACK/NACK sequence were unsuccessfully received. That is, the compressed ACK/NACK sequence  1470  may indicate that all of the code words  228  corresponding to the uncoded ACK/NACK sequence  1448  may need to be retransmitted. 
     If the number of unsuccessfully received code words  228  is not greater than the threshold (i.e., less than or equal to the threshold), the communication device may generate  412  a compressed (e.g., lossy-coded) ACK/NACK sequence  1470  indicating each code word  228  that was successfully received and each code word  228  that was unsuccessfully received. That is, if the number of unsuccessfully received code words  228  is less than or equal to the threshold, the compressed ACK/NACK sequence  1470  will indicate which of the code words  228  (i.e., corresponding to the uncoded ACK/NACK sequence) were unsuccessfully received and may need to be retransmitted. The method  400  illustrated in  FIG. 4  may be repeated for additional received code words  228 . 
     One example of the compression or coding technique described in connection to  FIG. 5  is given hereafter. Assume that ten code words  228  are transmitted on downlink component carriers  226  from a base station  112  to a wireless communication device  102 . At the receiver (e.g., the wireless communication device  102 ), one ACK/NACK bit  1487  is generated for each received code word  228 . The communication device determines  402  whether each code word  228  was received correctly. If a code word  228  is received correctly (i.e., successfully), the value of the corresponding ACK/NACK  1487  bit is 1, otherwise it is 0 (e.g., for an unsuccessfully received code word). All of the ten ACK/NACK  1487  bits are combined to create a sequence (e.g., S) of ACK/NACK bits. Hence, an uncoded ACK/NACK sequence  1448  is generated  404 . 
     In other ACK/NACK schemes, the uncoded ACK/NACK sequence  1448  may be sent back to the transmitter (e.g., the base station  112 ) to inform it about the status of the received code words  228  at the receiver (e.g., the wireless communication device  102 ). If a code word  228  was not received correctly, the transmitter (e.g., the base station  112 ) resends the corresponding code word  228 . 
     However, the length of the uncoded ACK/NACK sequence (S) is the same as the number of code words  228 . Instead of sending the uncoded ACK/NACK sequence (S)  1448 , a compressed ACK/NACK sequence (e.g., S′)  1470  may be transmitted, having a length smaller than the uncoded ACK/NACK sequence (S)  1448 . That is, lossy source coding may be applied to the uncoded ACK/NACK sequence (S)  1448 . For example, instead of sending the uncoded ACK/NACK sequence  1448  with a length of ten, a shorter ACK/NACK sequence (e.g., with a length of six or seven) may be transmitted. By sending the shorter compressed ACK/NACK sequence (S′)  1470 , not all of the combinations of bits in the uncoded ACK/NACK sequence (S) can be covered and incomplete information about the status of the code words  228  may be received (e.g., by the transmitting communication device). This is why the source coding technique disclosed herein may be described as “lossy-coding.” However, by designing a proper length for the compressed ACK/NACK sequence (S′), system overhead may be reduced and higher performance achieved. 
     In lossy ACK/NACK source coding, a threshold (K) is determined  406 . More detail on determining  406  the threshold (K) is given below. For purposes of this example, assume that K=2. Once the threshold (K) is determined  406 , the communication device determines  408  if more than K code words were unsuccessfully (e.g., incorrectly) received. If more than K code words  228  are in error (i.e., their corresponding uncoded ACK/NACK bits are 0) at the receiver (e.g., the wireless communication device  102 ), an ACK/NACK message  220  is sent back to the transmitter (e.g., the base station  112 ) requesting retransmission of all of the code words  228 . That is, the ACK/NACK message  220  may include a compressed ACK/NACK sequence  1470  indicating that all of the code words  228  were unsuccessfully received (e.g., as generated  410  by the communication device). 
     Using this approach, multiple combinations of ACK/NACK bits in the uncoded ACK/NACK sequence (S)  1448  may be represented with a single sequence in the compressed ACK/NACK sequence (S′)  1470 . Thus, the uncoded ACK/NACK sequence (S)  1448  may be “compressed,” where the compressed ACK/NACK sequence (S′)  1470  has a shorter length in bits compared to the uncoded ACK/NACK sequence (S)  1448 . In the example with ten code words where K=2, there is 1 combination of bits in the uncoded ACK/NACK sequence (S)  1448  indicating that all of the code words  228  were successfully received (e.g., 1111111111). This is illustrated in Equation (1): 
                     (         10           0         )     =   1           (   1   )               
There are also ten combinations of bits in the uncoded ACK/NACK sequence (S)  1448  indicating that one code word was unsuccessfully received (e.g., 0111111111, 1011111111, 1101111111, 1110111111, 1111011111, 1111101111, 1111110111, 1111111011, 1111111101 and 1111111110). This is illustrated in Equation (2):
 
                     (         10           1         )     =   10           (   2   )               
Furthermore, there are 45 combinations of bits in the uncoded ACK/NACK sequence (S)  1448  indicating that two code words  228  were unsuccessfully received (e.g., 0011111111, 0101111111, 0110111111, etc.). This is illustrated in Equation (3):
 
                     (         10           2         )     =   45           (   3   )               
According to the lossy-coding or compression herein, there is only one case where there are more than two unsuccessfully (e.g., incorrectly) received code words. Thus, by sending an ACK/NACK message  220  indicating that all code words  228  were unsuccessfully received when more than two code words are unsuccessfully received, the number of combinations is reduced from 10 2 =1024 (e.g., assuming 10 bits in the uncoded ACK/NACK sequence S) to (1+10+45+1)=57, which are needed to be represented by the compressed ACK/NACK sequence (S′). In order to represent the 57 cases, the length of the compressed ACK/NACK sequence (S′)  1470  needs to be Log 2 (57)=5.8 bits. With the constraint of accepting only an integer number for the length of the compressed ACK/NACK sequence (S′)  1470 , the length of the compressed ACK/NACK sequence (S′)  1470  would be six bits in this example.
 
     By using the compressed ACK/NACK sequence (S′)  1470  when the number of unsuccessfully received code words  228  is greater than the threshold (K) (e.g., where K=2 in the example), all of the code words  228  are retransmitted even though some of them may have been successfully received. The retransmission of the successfully received code words  228  may be considered overhead caused by compressing the uncoded ACK/NACK sequence  1448 . By sending fewer bits on the uplink (e.g., the uplink control channel  218 ), control information and non-data transmissions (e.g., “overhead”) are reduced. However, additional overhead is added by retransmitting successfully received code words  228 . Thus, several factors may be used to determine  406  the threshold (K): the length of code words (i.e., in bits), code word error rate and the amount of overhead reduction (e.g., the difference between the length of the compressed ACK/NACK sequence (S′) and the uncoded ACK/NACK sequence (S)). 
     The threshold (K) may be determined  406  by selecting a threshold (K) when the overhead reduction (e.g., the number of bits saved in the transmission of the compressed ACK/NACK  1470  instead of the uncoded ACK/NACK  1448  on the uplink control channel  218 ) is greater than or equal to the number of additional overhead bits caused by the retransmission of successfully received code words (e.g., on one or more carrier components  226 ). Thus, the threshold (K) may be determined  406  based on the size of the code words  228 . In one configuration, the reduction of overhead (e.g., in the uplink control channel  218 ) may be valued more than the added overhead (e.g., in the downlink carrier components  226 ). In this case, a weighted tradeoff between the overhead reduction (e.g., in the uplink control channel  218 ) and the overhead addition (e.g., in the downlink carrier components  226 ) may be used to determine the threshold. 
     Determination of a threshold (K) may be implemented in several ways. For example, a threshold (K) may be set and fixed for a desirable amount of compression. In this case, the compression on a control channel  218 ,  224  may be highly valued and the overhead may be considered “tolerable.” The threshold (K) may also be computed dynamically or semi-dynamically. For dynamic computation, the threshold (K) may be computed repeatedly by a communication device (e.g., wireless communication device  102 , base station  112 , etc.). Alternatively, the threshold (K) may be computed semi-dynamically (e.g., by a communication device) where a computed threshold value (K) may be used for a period of time and then updated periodically. As yet another alternative, the threshold (K) may be determined through the use of a look-up table on a communication device (e.g., wireless communication device  102 , base station  112 , etc.). 
     One example of how a threshold (K) may be computed follows. One way for computing the threshold (K) is by considering the tradeoff between the savings in the uplink transmission and the overhead in the downlink transmission. The savings in the uplink is caused by compression (e.g., in ACK/NACK message  220  size on the uplink control channel  218  or uplink shared channel  222 ). For instance, ACK/NACK message  220  size is reduced by sending fewer bits than ten (e.g., 6, 7, 8, etc.). The overhead in the downlink is caused by the retransmission of correctly received (or decoded) code words  228  on downlink carrier components  226 . For example, if there are more than K errors (assume K=3), then all code words  228  are NACKed. For the sake of example, assume that four code words  228  out of ten transmitted code words  228  are in error or received incorrectly. By sending NACKs for all code words  228 , the transmitter retransmits all ten code words  228  once again, including the six code words that were successfully decoded in the first transmission. This extra transmission of the correctly received code words  228  is considered downlink overhead. Note that the amount of savings in the uplink and downlink overhead varies with the threshold (K). 
     The value of the threshold (K) may be determined, for example, when Equation (4) is satisfied.
 
Savings in Uplink=α−(Downlink Overhead)  (4)
 
In Equation (4), α is a real number factor between 0 and 1 that can control the importance of load reduction on a control channel  218  versus overhead addition on the downlink carrier components  226 . The downlink overhead may be computed for a 10 bit ACK/NACK sequence as illustrated by Equation (5).
 
                     Overhead   ⁢           ⁢     (   K   )       =       ∑     i   =     K   +   1       10     ⁢       Pr   ⁡     (       #   ⁢   error     =   i     )       ·     (       ∑     correctly_received   ⁢   _code   ⁢   _words       ⁢     code_word   ⁢   _size       )                 (   5   )               
The number of compressed bits (ANBits) may be computed, for example, as illustrated in Equation (6).
 
                     ANBits   ⁡     (   K   )       =     [       Log   2     ⁡     [         ∑     i   =   0     K     ⁢     (         10           i         )       +   1     ]       ]             (   6   )               
Therefore, the amount of savings by compression may be computed, for example, as illustrated in Equation (7).
 
Savings( K )=10− AN Bits( K )  (7)
 
Listing (1) illustrates a procedure (in pseudo-code) for determining the threshold (K).
 
     
       
         
           
               
             
               
                   
               
               
                 Listing (1) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                   
                 flag = ‘false’ 
               
               
                   
                 K = 1 
               
               
                   
                 while (flag is ‘false’) 
               
               
                   
                   compute Overhead(K) 
               
               
                   
                   compute Savings(K) 
               
               
                   
                   if (Savings(K) ≧ α · Overhead(K)) 
               
               
                   
                     then store K and set flag = ‘true’ 
               
               
                   
                   K = K + 1 
               
               
                   
                 return to while 
               
               
                   
               
            
           
         
       
     
     It should be noted that the assumption of a transmission of ten code words  228  used in the examples herein is based on a scenario in accordance with the 3GPP Release-10 standard (i.e., LTE-Advanced). In this scenario, five carrier components  226  (e.g., five transmission bands each with up to a 20 megahertz (MHz) bandwidth) are provisioned for a downlink. Furthermore, two code words  228  are transmitted in each carrier component  226  using multiple antenna  108 ,  110  techniques. It should also be noted that the systems and methods disclosed herein are not limited to the numbers presented in this example and may be generalized to an arbitrary number of transmitted code words  228 . 
       FIG. 6  is a flow diagram illustrating another configuration of a method  500  for transmission of ACK/NACK in a wireless communication system. The communication device may determine  502  whether each of a number (N) of code words  228  was successfully received. The communication device may generate  504  an uncoded ACK/NACK sequence  1448  based on which of the number (N) of code words  228  was/were successfully or unsuccessfully received. 
     The communication device may partition  506  the uncoded ACK/NACK sequence  1448  into a number (P) of partitions. More specifically, compressing or lossy-coding the uncoded ACK/NACK sequence (S)  1448  may not be limited to compressing or encoding the whole uncoded ACK/NACK sequence (S)  1448 . The algorithm may be applied to any subset of the uncoded ACK/NACK sequence (S)  1448 . That is, the uncoded ACK/NACK sequence (S)  1448  may be partitioned  506 . Compression or lossy ACK/NACK source coding may be applied to each partition with a different threshold (K p ) assigned to each partition. That is, the communication device may determine  508  a threshold (K p ) for each of the number (P) of partitions. This determination  508  may be based on the size of the code words  228  and/or partitions in a similar fashion to the determination  406  described above in connection with  FIG. 5 . 
     Each partition threshold (K p ) may be determined  508  based on data local to the communication device or based on data received from another communication device. For example, a communication device may use a locally determined code word  228  size (e.g., partition size), error rate and/or overhead reduction (e.g., for partitions) to determine  508  each partition threshold (K p ). Alternatively, the communication device may receive this data or one or more partition thresholds (K p ) from another communication device (e.g., a wireless communication device  102  may receive it from a base station  112 ). The communication device may determine  508  its partition thresholds (K p ) based on the received data or partition thresholds (K p ). 
     The communication device may determine  510  whether the number of unsuccessfully received code words  228  is greater than the partition threshold (K p ) for each partition. If the number of unsuccessfully (e.g., incorrectly) received code words  228  is greater than the partition threshold (K p ) for a particular partition, the communication device may generate  512  a compressed ACK/NACK sequence (S p ′)  1470  indicating that all of the code words  228  were unsuccessfully received (and may need to be retransmitted) for that partition. If the number of unsuccessfully received code words  228  is not greater than the partition threshold (K p ) for a particular partition, the communication device may generate  514  a compressed ACK/NACK sequence (S p ′)  1470  indicating each code word  228  that was successfully (e.g., correctly) received and each code  228  word that was unsuccessfully received for that partition. It should also be noted that the method  500  illustrated in  FIG. 6  may be repeated for additional received code words  228 . 
       FIG. 7  is a flow diagram illustrating another configuration of a method  600  for transmission of ACK/NACK in a wireless communication system. A communication device may determine  602  whether each of a number (N) code words  228  was successfully (e.g., correctly) received. The communication device may generate  604  an uncoded ACK/NACK sequence  1448  based on which of the code words  228  was/were successfully or unsuccessfully (e.g., incorrectly) received. The communication device may also determine  606  a threshold (K) based on the size of the code words  228 . 
     The communication device may determine  608  whether the number of unsuccessfully received code words  228  is greater than the threshold (K). If the number of unsuccessfully received code words  228  is greater than the threshold (K), the communication device may generate  610  a compressed ACK/NACK sequence  1470  indicating that all of the code words  228  were unsuccessfully (e.g., incorrectly) received (e.g., requesting a retransmission of all of the code words  228  corresponding to the uncoded ACK/NACK sequence  1448 ). If the number of unsuccessfully received code words  228  is not greater than the threshold (K), the communication device may determine  612  whether the number of unsuccessfully received code words  228  is equal to the threshold (K). If the number of unsuccessfully received code words  228  is not equal to the threshold (e.g., it is less than the threshold (K)), the communication device may generate  616  a compressed ACK/NACK sequence  1470  indicating each code word  228  that was successfully received and each code word  228  that was unsuccessfully received. 
     If the number of unsuccessfully received code words  228  is equal to the threshold (K), the communication device may generate  614  a compressed ACK/NACK sequence  1470  where multiple cases of a number (e.g., K) of unsuccessfully received code words  228  are represented with a single ACK/NACK sequence indicating a greater number (e.g., K+J) of unsuccessfully received code words  228 . This approach is described in greater detail using an example below. It should also be noted that the method  600  illustrated in  FIG. 7  may be repeated for additional received code words  228 . 
     According to the earlier example discussed in connection with  FIG. 5  (i.e., with a threshold of two (K=2)), the cases where two code words  228  were unsuccessfully received 
             (       e   .   g   .     ,       (         10           2         )     =   45       )         
contributed the largest number of cases. That is, in the above example (e.g., with a threshold of two (K=2)), 45 combinations out of a total 57 combinations were allocated for covering cases in which two code words  228  were unsuccessfully received.
 
     For a threshold of three (e.g., K=3), the total number of combinations is 177 (e.g., 1+10+45+120+1=177) out of which 120 cases are for 3 unsuccessfully received code words  228 . In order to add more compression, one or more additional code word  228  retransmissions may be allowed. For example, consider a case in which four NACKs are reported (e.g., in an uncoded ACK/NACK sequence): S=0000111111. This sequence may represent the following combinations in which three code words  228  are in error: S 1 =0001111111, S 2 =0010111111, S 3 =0100111111 and S 4 =1000111111. There is one extra NACK in S=0000111111 compared to each of the cases with three errors shown S 1-4 . If four combinations (S 1-4 ) are represented by a single sequence (S), then the total number of combinations with three errors can be reduced from 120 cases to 120/4=30 cases. Thus, the total number of combinations may be reduced from 177 cases (e.g., 1+10+45+120+1=177) needing eight bits for representation to 87 cases (e.g., 1+10+45+30+1=87) needing seven bits for representation. In this example, one bit is saved by compressing the uncoded ACK/NACK sequence at the price of one extra retransmission when there are three errors (e.g., with K=3). 
     Although the example was given for ease in explanation, the systems and methods disclosed herein are not limited to representing three-error sequences with four-error sequences. That is, this approach can be generalized to cases in which sequences with K NACKs are represented by sequences with K+J NACKs (e.g., where the uncoded ACK/NACK sequence has a number of (K+J) “0” bits with the remainder being “1” bits). 
       FIG. 8  is a block diagram illustrating three examples of ACK/NACK source coding or compression. As discussed above, a communication device (e.g., a wireless communication device  102 , base station  112 , etc.) may obtain one or more code words  228  from a received signal. In the first example illustrated in  FIG. 8 , ten code words  730   a  are obtained. A code word loss detection module  732   a  determines  402  which of the ten code words  730   a  were successfully or unsuccessfully received. 
     In this example, the code word loss detection module  732   a  detects one unsuccessfully received code word  734   a . The communication device generates  404  a ten bit uncoded ACK/NACK sequence  736   a . In this example, the ten bit uncoded ACK/NACK sequence S=1011111111  738   a . Assume that an ACK/NACK source coding module  704   a  has determined  406  a threshold K=2  740   a . The ACK/NACK source coding module  704   a  determines  408  that the number of unsuccessfully received code words  228  is not greater than the threshold K=2  740   a  (i.e., 1≦2). The ACK/NACK source coding module  704   a  then generates  412  a six bit compressed ACK/NACK sequence  744   a  indicating that the second code word of the ten code words  730   a  was unsuccessfully received. The six bit compressed ACK/NACK sequence  744   a  also indicates that the first code word and the third through tenth code words were successfully received. For the ten bit uncoded ACK/NACK sequence S=1011111111  738   a , one example of a six bit compressed ACK/NACK sequence S′=000010  744   a . More examples of possible ten bit uncoded ACK/NACK sequences  736  and corresponding six bit compressed ACK/NACK sequences  744  are illustrated below in Table (1) (e.g., where K=2). 
     
       
         
           
               
               
               
             
               
                 TABLE (1) 
               
               
                   
               
               
                   
                   
                 Compressed 
               
               
                   
                   
                 ACK/NACK 
               
               
                 Uncoded ACK/NACK Sequence 
                 Index 
                 Sequence 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
            
               
                 No Errors 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 000000 
               
            
           
           
               
            
               
                 1 Error 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 2 
                 000001 
               
               
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 3 
                 000010 
               
               
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 4 
                 000011 
               
               
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 5 
                 000100 
               
               
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 6 
                 000101 
               
               
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 7 
                 000110 
               
               
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                 8 
                 000111 
               
               
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 9 
                 001000 
               
               
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 10 
                 001001 
               
               
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 11 
                 001010 
               
            
           
           
               
            
               
                 2 Errors 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 0 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 12 
                 001011 
               
               
                 0 
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 13 
                 001100 
               
               
                 0 
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 14 
                 001101 
               
               
                 0 
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 15 
                 001110 
               
               
                 0 
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 16 
                 001111 
               
               
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                 17 
                 010000 
               
               
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 18 
                 010001 
               
               
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 19 
                 010010 
               
               
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 20 
                 010011 
               
               
                 1 
                 0 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 21 
                 010100 
               
               
                 1 
                 0 
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 22 
                 010101 
               
               
                 1 
                 0 
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 23 
                 010110 
               
               
                 1 
                 0 
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 24 
                 010111 
               
               
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                 25 
                 011000 
               
               
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 26 
                 011001 
               
               
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 27 
                 011010 
               
               
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 28 
                 011011 
               
               
                 1 
                 1 
                 0 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 29 
                 011100 
               
               
                 1 
                 1 
                 0 
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 30 
                 011101 
               
               
                 1 
                 1 
                 0 
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 31 
                 011110 
               
               
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                 32 
                 011111 
               
               
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 33 
                 100000 
               
               
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 34 
                 100001 
               
               
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 35 
                 100010 
               
               
                 1 
                 1 
                 1 
                 0 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 36 
                 100011 
               
               
                 1 
                 1 
                 1 
                 0 
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 37 
                 100100 
               
               
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                 38 
                 100101 
               
               
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 39 
                 001100 
               
               
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 40 
                 100111 
               
               
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 41 
                 101000 
               
               
                 1 
                 1 
                 1 
                 1 
                 0 
                 0 
                 1 
                 1 
                 1 
                 1 
                 42 
                 101001 
               
               
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 0 
                 1 
                 1 
                 1 
                 43 
                 101010 
               
               
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 0 
                 1 
                 1 
                 44 
                 101011 
               
               
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                 0 
                 1 
                 45 
                 101100 
               
               
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 0 
                 46 
                 101101 
               
               
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 0 
                 1 
                 1 
                 1 
                 47 
                 101110 
               
               
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 0 
                 1 
                 1 
                 48 
                 101111 
               
               
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 0 
                 1 
                 49 
                 110000 
               
               
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                 0 
                 50 
                 110001 
               
               
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 0 
                 1 
                 1 
                 51 
                 110010 
               
               
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 0 
                 1 
                 52 
                 110011 
               
               
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 0 
                 53 
                 110100 
               
               
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 0 
                 1 
                 54 
                 110101 
               
               
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 0 
                 55 
                 110110 
               
               
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 0 
                 56 
                 110111 
               
            
           
           
               
            
               
                 More Than 2 Errors 
               
            
           
           
               
               
               
            
               
                   
                 57 
                 111111 
               
               
                   
               
            
           
         
       
     
     Ten code words  730   b  are also obtained in the second example illustrated in  FIG. 8 . In this example, the code word loss detection module  732   b  detects (e.g., determines  402 ) three unsuccessfully received code words  734   b . The communication device generates  404  a ten bit uncoded ACK/NACK sequence  736   b . In this example, the uncoded ACK/NACK sequence S=0001111111  738   b . Assume again that the ACK/NACK source coding module  704   b  has determined  406  a threshold K=2  740   b . The ACK/NACK source coding module  704   b  determines  408  that the number of unsuccessfully (e.g., incorrectly) received code words  734   b  is greater than the threshold  740   b  (i.e., 3&gt;2). The ACK/NACK source coding module  704   b  generates  410  a six bit compressed ACK/NACK sequence  744   b  indicating that all of the ten code words  730   b  were unsuccessfully received. This may also indicate that all ten code words  730   b  need to be retransmitted. In this second example, the six bit compressed ACK/NACK sequence  744   b  may be 111111 as illustrated in Table (1) above. 
     The third example given in  FIG. 8  also illustrates that ten code words  730   c  are obtained by the communication device. The code word loss detection module  732   c  determines  602  that three code words were unsuccessfully received  734   c . The communication device generates  604  a ten bit uncoded ACK/NACK sequence  736   c  S=0001111111  738   c . In this example, the ACK/NACK source coding module  704   c  has determined  606  a threshold K=3  740   c . Furthermore, the ACK/NACK source coding module  704   c  uses additional compression, using cases of K+1 unsuccessfully received code words  228  to represent cases with K unsuccessfully received code words (e.g., K=3)  742 . The ACK/NACK source coding module  704   c  determines  612  that the number of unsuccessfully received code words is equal to the threshold  740   c  (i.e., 3=3). In this example, the ACK/NACK coding module generates  614  a seven bit compressed ACK/NACK sequence  744   c  indicating that four specific code words  228  were unsuccessfully received, which may also indicate that they  228  need to be retransmitted. For the ten bit uncoded ACK/NACK sequence S=0001111111  738   c , one example of a seven bit compressed ACK/NACK sequence S′=0111000  744   c . In this case, S′ may be interpreted as 0000111111, with one extra NACK reported (e.g., the fourth code word  228 ). Additional examples of seven bit compressed ACK/NACK sequences (abbreviated as “Comp. A/N Seq.” for convenience) corresponding to ten bit uncoded ACK/NACK sequences are illustrated in Table (2) below. 
     
       
         
           
               
               
               
             
               
                 TABLE (2) 
               
               
                   
               
               
                   
                   
                 Comp. 
               
               
                 Uncoded ACK/NACK 
                   
                 A/N 
               
               
                 Sequence 
                   
                 Seq. 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                 No Errors 
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                   
                 1 
                 0000000 
               
            
           
           
               
               
            
               
                 1 Error 
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                   
                 2 
                 0000001 
               
               
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                   
                 3 
                 0000010 
               
               
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                   
                 4 
                 0000011 
               
               
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                   
                 5 
                 0000100 
               
               
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                   
                 6 
                 0000101 
               
               
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                   
                 7 
                 0000110 
               
               
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                   
                 8 
                 0000111 
               
               
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                   
                 9 
                 0001000 
               
               
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                   
                 10 
                 0001001 
               
               
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                   
                 11 
                 0001010 
               
            
           
           
               
               
            
               
                 2 Errors 
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 0 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                   
                 12 
                 0001011 
               
               
                 0 
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                   
                 13 
                 0001100 
               
               
                 0 
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                   
                 14 
                 0001101 
               
               
                 0 
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                   
                 15 
                 0001110 
               
               
                 0 
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                   
                 16 
                 0001111 
               
               
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                   
                 17 
                 0010000 
               
               
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                   
                 18 
                 0010001 
               
               
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                   
                 19 
                 0010010 
               
               
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                   
                 20 
                 0010011 
               
               
                 1 
                 0 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                   
                 21 
                 0010100 
               
               
                 1 
                 0 
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                   
                 22 
                 0010101 
               
               
                 1 
                 0 
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                   
                 23 
                 0010110 
               
               
                 1 
                 0 
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                   
                 24 
                 0010111 
               
               
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                   
                 25 
                 0011000 
               
               
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                   
                 26 
                 0011001 
               
               
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                   
                 27 
                 0011010 
               
               
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                   
                 28 
                 0011011 
               
               
                 1 
                 1 
                 0 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                   
                 29 
                 0011100 
               
               
                 1 
                 1 
                 0 
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                   
                 30 
                 0011101 
               
               
                 1 
                 1 
                 0 
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                   
                 31 
                 0011110 
               
               
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                   
                 32 
                 0011111 
               
               
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                   
                 33 
                 0100000 
               
               
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                   
                 34 
                 0100001 
               
               
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                   
                 35 
                 0100010 
               
               
                 1 
                 1 
                 1 
                 0 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                   
                 36 
                 0100011 
               
               
                 1 
                 1 
                 1 
                 0 
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                   
                 37 
                 0100100 
               
               
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                   
                 38 
                 0100101 
               
               
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                   
                 39 
                 1001100 
               
               
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                   
                 40 
                 0100111 
               
               
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                   
                 41 
                 0101000 
               
               
                 1 
                 1 
                 1 
                 1 
                 0 
                 0 
                 1 
                 1 
                 1 
                 1 
                   
                 42 
                 0101001 
               
               
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 0 
                 1 
                 1 
                 1 
                   
                 43 
                 0101010 
               
               
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 0 
                 1 
                 1 
                   
                 44 
                 0101011 
               
               
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                 0 
                 1 
                   
                 45 
                 0101100 
               
               
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 0 
                   
                 46 
                 0101101 
               
               
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 0 
                 1 
                 1 
                 1 
                   
                 47 
                 0101110 
               
               
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 0 
                 1 
                 1 
                   
                 48 
                 0101111 
               
               
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 0 
                 1 
                   
                 49 
                 0110000 
               
               
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                 0 
                   
                 50 
                 0110001 
               
               
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 0 
                 1 
                 1 
                   
                 51 
                 0110010 
               
               
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 0 
                 1 
                   
                 52 
                 0110011 
               
               
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 0 
                   
                 53 
                 0110100 
               
               
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 0 
                 1 
                   
                 54 
                 0110101 
               
               
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 0 
                   
                 55 
                 0110110 
               
               
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 0 
                   
                 56 
                 0110111 
               
            
           
           
               
               
               
            
               
                   
                 Representative 4-Error 
                   
               
               
                 3 Errors 
                 Sequence 
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 0 
                 0 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 0 
                 0 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 57 
                 0111000 
               
               
                 0 
                 0 
                 1 
                 0 
                 1 
                 1 
                 1 
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                 0 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 1 
                 1 
                 1 
                 1 
                 0 
                 0 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 0 
                 0 
                 0 
                 1 
                 1 
                 100 
                 1100011 
               
               
                 1 
                 1 
                 1 
                 1 
                 0 
                 0 
                 1 
                 0 
                 1 
                 1 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 1 
                 1 
                 1 
                 1 
                 0 
                 0 
                 1 
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 0 
                 1 
                 1 
                 0 
                 0 
                 101 
                 1100100 
               
               
                 1 
                 1 
                 1 
                 1 
                 0 
                 0 
                 1 
                 1 
                 1 
                 0 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 0 
                 102 
                 1100101 
               
               
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 0 
                 1 
                 1 
                 0 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 0 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 0 
                 0 
                 0 
                 103 
                 1100110 
               
               
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 1 
                 0 
                 1 
                 0 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 0 
                 1 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 0 
                 1 
                 0 
                 0 
                 104 
                 1100111 
               
               
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 0 
                 1 
                 1 
                 0 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 0 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 0 
                 0 
                 0 
                 105 
                 1101000 
               
               
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 0 
                 0 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 0 
                 0 
                 0 
                 106 
                 1101001 
               
               
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 0 
                 1 
                 0 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
            
           
           
               
               
               
               
            
               
                 4 Or More Errors 
                   
                   
                   
               
               
                 All Sequences With 4 Or 
                   
                 107 
                 1111111 
               
               
                 More Errors 
               
               
                   
               
            
           
         
       
     
       FIG. 9  is a block diagram illustrating one configuration of a communication device  846  in which systems and methods for transmission of ACK/NACK in a wireless communication system may be implemented. The communication device  846  may include one or more antennas  854 , a receiver/decoder module  852 , a code word loss detection module  850 , an ACK/NACK source coding module  804 , a balancing module  806 , channel encoder module  874  and transmitter module  893 . The receiver/decoder module  852  may be a hardware and/or software module used to receive and decode signals from another communication device. The receiver/decoder module  852  may be coupled to one or more antennas  854  to receive signals. Received signal demodulation and channel decoding are two examples of functions that may be performed by the receiver/decoder module  852 . Furthermore, threshold information  864 , correlation information  866  and balancing information  868  may be output by the receiver/decoder module. The threshold information  864  may include one or more code word sizes  858 , one or more code word error rates  860  and/or a threshold, for example. In one configuration, threshold information (e.g., one or more thresholds (K), code word sizes  858 , code word error rates  860 , etc.) may be determined by the communication device  846  and explicitly communicated (e.g., between a wireless communication device  102  and a base station  112 ) using an uplink control channel  218  (e.g., PUCCH) or uplink shared channel  222  (e.g., PUSCH). The threshold information  864  may indicate the threshold (K) and consequently may be used to determine the number of bits representing the compressed ACK/NACK sequence  870 . Examples of correlation information  866  include temporal correlation information, spectral correlation information and/or spatial correlation information. The balancing information  868  may include, for example, information used for scrambling, Gray coding and/or distribution shaping. 
     The receiver/decoder module  852  may output one or more code words  828  to the code word loss detection module  850 . The communication device  846  may use the codeword loss detection module  850  to generate an uncoded ACK/NACK sequence  848  based on the code words  828 . 
     The ACK/NACK source coding module  804  may be a hardware and/or software module used to generate a compressed ACK/NACK sequence  870 . The ACK/NACK source coding module  804  may use the uncoded ACK/NACK sequence  848 , threshold information  864  and/or correlation information  866 . In particular, the ACK/NACK source coding module  804  may include a threshold determination module  856 . The threshold determination module  856  may use the threshold information  864  to determine a threshold (K). For example, the threshold determination module  856  may use the code word size  858 , the error rate  860  and/or the compression savings  862  to determine the threshold (K). 
     More specifically, the code word size  858  and the error rate  860  may be used to compute a number of “retransmission” overhead bits from retransmitting successfully (e.g., correctly) received code words for one or more threshold values. This number of retransmission overhead bits may be compared to a number of “compression” overhead bits saved  862  by reducing the length of the uncoded ACK/NACK sequence  848  for one or more threshold values. The threshold determination module  856  may select a threshold value where the number of compression overhead bits saved  862  is greater than or equal to the number of retransmission overhead bits saved. As mentioned above, the amount of compression overhead bits saved may be optionally weighted in this comparison, since control channel  218 ,  224  bandwidth may be more valuable than data channel (e.g., carrier component  226 ) bandwidth. In this case, the threshold (K) may be selected when the number of compression overhead bits multiplied by a weighting factor is greater than or equal to the number of retransmission overhead bits. The threshold determination module  856  may also select a threshold (K) that saves the most bandwidth or weighted bandwidth. 
     As discussed above, the threshold information  864  may include a threshold. For example, the communication device  846  (e.g., a wireless communication device  102 ) may receive one or more thresholds determined by another communication device. The receiver/decoder module  852  may send the threshold to the ACK/NACK source coding module  804 . The ACK/NACK source coding module  804  may use the received threshold to determine a threshold. In one configuration, the threshold determination module  856  may simply adopt the received threshold as the threshold to be used in compressing the uncoded ACK/NACK sequence  848 . 
     The ACK/NACK source coding module  804  may optionally use correlation information  866  such as temporal correlation information, spectral correlation information and/or spatial correlation information to further compress the uncoded ACK/NACK sequence  848 . The optional use of correlation information  866  is described in greater detail below in connection with  FIG. 11 . 
     The ACK/NACK source coding module  804  may output a compressed ACK/NACK sequence  870 , which may be used by the balancing module  806 . Alternatively, the ACK/NACK source coding/compression module  804  may not be included in the communication device  846  or bypassed. Thus, an uncoded ACK/NACK sequence  848  may be input into the balancing module  806 . The balancing module  806  may be a hardware and/or software module that uses the uncoded  848  or compressed  870  ACK/NACK sequence to generate a balanced  889  or balanced compressed  872  ACK/NACK sequence. More specifically, the balancing module  806  may modify the uncoded  848  or compressed  870  ACK/NACK sequence such that the number of 1&#39;s is closer to the number of 0&#39;s in the resulting ACK/NACK sequence  889 ,  872 . The balancing module  806  may generate balancing information such as scrambling information, Gray coding information and/or distribution shaping information. Alternatively or in addition, the balancing module  806  may use balancing information  868  (e.g., scrambling information, Gray coding information and/or distribution shaping information) from the receiver/decoder module  852  in generating the balanced  889  and/or balanced compressed  872  ACK/NACK sequence. The balancing module  806  is described in greater detail below in connection with  FIG. 12 . 
     The balancing module  806  may be optional. For example, the communication device  846  may optionally input the uncoded  848  or compressed  870  ACK/NACK sequence into the channel encoder module  874  for channel coding. However, ACK/NACK sequences (e.g., uncoded ACK/NACK sequence  848  or compressed ACK/NACK sequence  870 ) may have an imbalanced distribution of 1&#39;s and 0&#39;s, possibly causing degraded channel code performance. As a result, balancing the ACK/NACK sequences before channel coding may be beneficial to avoid degraded channel code performance. Thus, the uncoded  848 , compressed  870 , balanced  889  or balanced compressed  872  ACK/NACK sequence may be input into the channel encoder module  874 . The channel encoder module  874  may channel code the ACK/NACK sequence  848 ,  870 ,  889 ,  872  to produce a channel coded ACK/NACK sequence  891 . The ACK/NACK sequence  848 ,  870 ,  889 ,  872 ,  891  may be transmitted by the transmitter module  893  using one or more antennas  854 . The ACK/NACK sequence  848 ,  870 ,  889 ,  872 ,  891  may also be modulated by the communication device  846  in preparation for transmission. 
     It should be noted that different code words  828  may carry different amounts or types of information. In particular, some designated code words  828  may carry more sensitive information or may be significantly larger (i.e., in number of bits) than others. One example of more sensitive code words is when the code words are carrying delay-sensitive information. When a particular code word  828  is large or carrying sensitive information, it may be beneficial to assign more priority to the corresponding ACK/NACK bit. Stronger code or unequal error protection may be used for the transmission of those ACK/NACK bits. The stronger code or unequal error protection may be applied in the channel encoder module  874 . One example of unequal error protection follows. Assume that out of ten code words  228 , the first code word  228  and the second code words  228  are large packets where it would be beneficial to not retransmit them unless they are in error. In this case, the corresponding ACK/NACK bits may be separated from the uncoded ACK/NACK sequence  848 , with compression being performed on the remainder of the ACK/NACK sequence. Thus, unequal error protection is applied where the two uncompressed ACK/NACK bits  1487  received higher protection than the compressed ACK/NACK bits. 
       FIG. 10  is a block diagram illustrating several possible configurations of a wireless communication device  902  and a base station  912  in which systems and methods for transmission of ACK/NACK in a wireless communication system may be implemented. A wireless communication device  902  may send and receive information to and from a base station  912  using one or more antennas  908 . Additionally, a base station  912  may send and receive information to and from a wireless communication device  902  using one or more antennas  910 . Several types of information may be generated and/or communicated by the wireless communication device  902  and/or base station  912 . For example, the wireless communication device  902  and/or the base station  912  may generate, receive and/or transmit temporal correlation information  976 ,  992 , spectral correlation information  978 ,  994 , spatial correlation information  980 ,  996 , threshold information  982 ,  998 , scrambling information  984 ,  901 , gray coding information  986 ,  903  and/or distribution shaping information  988 ,  905 . Temporal correlation information  976 ,  992 , spectral correlation information  978 ,  994 , spatial correlation information  980 ,  996  and/or threshold information  982 ,  998  may be used by the ACK/NACK source coding module(s)  904 ,  914  to generate a compressed ACK/NACK sequence  870 . Additionally, this information  976 ,  992 ,  978 ,  994 ,  980 ,  996 ,  982 ,  998  may be used by an ACK/NACK source decoding module  179 ,  183  to interpret, decode or decompress the compressed ACK/NACK sequence  870 . The scrambling information  984 ,  901 , Gray coding information  986 ,  903 , and/or distribution shaping information  988 ,  905  may be used by the ACK/NACK balancing module(s)  990 ,  907  to balance an ACK/NACK sequence (e.g., uncoded  1448 , compressed  1470  ACK/NACK sequence). Additionally, this information  984 ,  901 ,  986 ,  903 ,  988 ,  905  may be used by an ACK/NACK balancing decoding module  181 ,  185  to interpret or decode an ACK/NACK sequence (e.g., balanced  1489  or balanced compressed  1472  ACK/NACK sequence). 
     Depending on the configuration used, one or more of these types of information  976 ,  992 ,  978 ,  994 ,  980 ,  996 ,  982 ,  998 ,  984 ,  901 ,  986 ,  903 ,  988 ,  905  may be used by the wireless communication device  902  and/or base station  912  to compress and/or balance an ACK/NACK sequence. Furthermore, one or more of these types of information  976 ,  992 ,  978 ,  994 ,  980 ,  996 ,  982 ,  998 ,  984 ,  901 ,  986 ,  903 ,  988 ,  905  may be used to interpret (e.g., decode) an ACK/NACK sequence (e.g., compressed  1470 , balanced  1489  and/or balanced compressed  1472  ACK/NACK sequence).  FIG. 10  illustrates that each of these types of information  976 ,  992 ,  978 ,  994 ,  980 ,  996 ,  982 ,  998 ,  984 ,  901 ,  986 ,  903 ,  988 ,  905  may be generated and/or transmitted by either the wireless communication device  902 , the base station  912  or both. All of the types of information  976 ,  992 ,  978 ,  994 ,  980 ,  996 ,  982 ,  998 ,  984 ,  901 ,  986 ,  903 ,  988 ,  905  need not be generated exclusively by either the wireless communication device  902  or the base station  912 . Rather, the wireless communication device  902  and/or the base station  912  may generate and exchange one or more different types of information  976 ,  992 ,  978 ,  994 ,  980 ,  996 ,  982 ,  998 ,  984 ,  901 ,  986 ,  903 ,  988 ,  905  with each other. 
     By way of example and not limitation, one possible configuration is given hereafter. In this example, the wireless communication device  902  generates threshold information  982 . For example, the wireless communication device  902  may determine a code word size  858  (e.g., based on received code words  228  or configuration information), a code word  228  error rate  860  (e.g., using a code word  228  loss detection module  850 ) and/or compression savings  862  (e.g., based on an uncoded ACK/NACK sequence  848  length and possible compressed ACK/NACK sequence lengths). The wireless communication device  902  may use this information to determine a threshold value (K), which it  902  may send to the base station  912  (e.g., using an uplink control channel  218  (e.g., PUCCH) or an uplink shared channel  222  (e.g., PUSCH)) to aid the base station  912  in decoding the compressed ACK/NACK sequence  870 . For example, the threshold value (K) included in the threshold information  982  may be used to determine the number of bits representing the compressed ACK/NACK sequence  870 . Continuing with the example, the base station  912  may generate temporal correlation information  992 , spectral correlation information  994 , spatial correlation information  996 , scrambling information  901 , Gray coding information  903  and/or distribution shaping information  905 , which it  912  may send to the wireless communication device  902 . The wireless communication device  902  may use this received information  992 ,  994 ,  996 ,  901 ,  903 ,  905  to compress and/or balance an ACK/NACK sequence. The wireless communication device  902  may additionally or alternatively use this received information  992 ,  994 ,  996 ,  901 ,  903 ,  905  to interpret a compressed  1470 , balanced  1489  and/or balanced compressed  1472  ACK/NACK sequence received from the base station  912 . 
     In another example, the base station  912  may determine the threshold information  998  (e.g., including a threshold) and consequently the number of bits representing the compressed ACK/NACK sequence  870 . The base station  912  may share (e.g., transmit) this threshold information  998  to the wireless communication device  902  using explicit signaling. The threshold information  998  may be sent to the wireless communication device  902  using a downlink control channel  224  (e.g., PDCCH). 
       FIG. 11  is a block diagram illustrating more detail on one configuration of an ACK/NACK source coding module  1004 . The ACK/NACK source coding module  1004  may receive an uncoded ACK/NACK sequence  1048 . The uncoded ACK/NACK sequence  1048  may be optionally partitioned  1009  as described above in connection with  FIG. 6 . The uncoded and optionally partitioned ACK/NACK sequence  1048  may be input into an initial ACK/NACK source coding module  1011 . The initial ACK/NACK source coding module  1011  may use a threshold (K)  1082  to compress (e.g., lossy-code) the uncoded ACK/NACK sequence  1048  as described above in connection with  FIG. 5 ,  6 , or  7 . The output of the initial ACK/NACK source coding module  1011  may be input into an additional compression module  1013 . The additional compression module  1013  may further compress the output of the initial ACK/NACK source coding module  1011 . 
     The additional compression module  1013  may include a temporal correlation module  1015 , a spectral correlation module  1017  and/or a spatial correlation module  1019 . Temporal correlation information  1076 , spectral correlation information  1078  and/or spatial correlation information  1080  may be received by the additional compression module  1013 . 
     In general, temporal, spectral and spatial correlation among code words  228  or communication channels (e.g., carrier components  226 ) may be exploited in order to further compress the ACK/NACK sequence. For instance, if the transmission scheme (e.g., coding and modulation or communication rate) is not changing from one transmission to another and the corresponding channel is not changing, then it may be assumed that the outcome of the two transmissions are correlated as well. 
     The temporal correlation module  1015  may use temporal correlation information  1076  to further compress the ACK/NACK sequence. More specifically, temporal correlation may be used to send an ACK/NACK bit corresponding to changes (e.g., bit transitions) in the status of received code words. For example, if at time t 1  a received code word  228  (e.g., packet) is in error, a NACK is generated and/or transmitted. If the received signal (e.g., another code word  228 ) is still erroneous at time t 2 , nothing is generated and/or transmitted. If the received signal (e.g., yet another code word  228 ) is successfully received at time t 3 , then an ACK may be generated and/or sent. Thereafter, nothing may be generated and/or sent until another received code word  228  is in error. Thus, since ACKs/NACKs may only be generated and/or transmitted when there is a change between successful and unsuccessful reception (i.e., and vice-versa), the ACK/NACK sequence may be compressed even further. 
     The spectral correlation module  1017  and/or spatial correlation module  1019  may also be used to further compress the ACK/NACK sequence. For example, a spectral correlation threshold and/or a spatial correlation threshold may be determined. The spectral correlation threshold and/or the spatial correlation threshold may be generated by a communication device (e.g., a wireless communication device  102 ) and/or another communication device (e.g., a base station  112 ). The spectral correlation threshold may be sent and/or received as part of the spectral correlation information  1078 . The spatial correlation threshold may similarly be sent and/or received as part of the spatial correlation information  1080 . The spectral correlation threshold and/or the spatial correlation threshold may be explicitly communicated between communication devices (e.g., between a wireless communication devices  102  and a base station  112 ). If one or more of the spectral or spatial correlations between channels (e.g., carrier components  226 , spatial channels) corresponding to two or more code words  228  is greater than the corresponding spectral and/or spatial threshold, only the status (ACK/NACK) of one of the two or more code words  228  may be reported (e.g., included in the compressed ACK/NACK sequence  1070 ). 
       FIG. 12  is a block diagram illustrating more detail on one configuration of an ACK/NACK balancing module  1106 . In terms of the numbers of 1&#39;s and 0&#39;s, ACK/NACK sequences may often be imbalanced as discussed above. This imbalance may degrade the performance of a channel code. 
     For example, in 3GPP LTE and LTE-Advance, the desired code word  228  error rate is typically less than 50%. In most cases, the desired code word  228  error rate is approximately 10%. As a consequence, the ACK/NACK bit corresponding to a received code word  228  takes the value 1 (e.g., for a successfully received code word  228 ) more often than the value 0. Therefore, in the uncoded ACK/NACK sequence (S)  1148  there are often more 1&#39;s than 0&#39;s. In a configuration where a communication device  846  channel encodes the uncoded ACK/NACK sequence (S)  1148 , the input into the channel encoder (e.g., transmitter/encoder module  874 ) is often imbalanced. In other words, some realizations of the uncoded ACK/NACK sequence (S) occur more often than others. For example, an uncoded ACK/NACK sequence (S) having all 1&#39;s may occur much more often than a sequence having all 0&#39;s. That is, for a 10% code word  228  error rate, an uncoded ACK/NACK sequence (S) having all 1&#39;s occurs 0.9 10 ≈0.34 or about 34% of the time. In contrast, an uncoded ACK/NACK sequence (S) having all 0&#39;s occurs almost never or 0.1 10 =10 −10 =0.00000001% of the time. As a result, some of the compressed ACK/NACK code words  228  may be used more often that other code words  228 . 
     The performance of a channel code is typically determined more by the performance of those code words  228  that are used more frequently, instead of the whole code book. In order to prevent this degradation in performance, the ACK/NACK balancing module  1106  may optionally balance the ACK/NACK sequence. That is, the ACK/NACK balancing module  1106  may transform the ACK/NACK sequence such that the number of 1&#39;s and 0&#39;s are roughly equal prior to channel coding. As discussed above, the ACK/NACK balancing module  1106  may operate on either an uncoded ACK/NACK sequence  1148  or a compressed ACK/NACK sequence  1170 . In some cases, balancing may be more beneficial when applied to an uncoded ACK/NACK sequence  1148 , since compression of an ACK/NACK sequence may reduce the severity of the unbalance. However, balancing may be combined with compression. 
     The ACK/NACK balancing module  1106  may use a scrambling module  1121 , a Gray coding module  1129  and/or a distribution shaping module  1135  to balance the ACK/NACK sequence  1148 ,  1170 , thereby producing a balanced  1189  or balanced compressed  1172  ACK/NACK sequence. 
     The scrambling module  1121  may modify the ACK/NACK sequence  1148 ,  1170  as follows. A pseudo-random sequence may be generated by the communication device  846  or generated by and/or received from another communication device. For example, a wireless communication device  102  may generate the pseudo-random sequence, may receive the pseudo-random sequence, or may receive parameters used to determine the pseudo random sequence from a base station  112 . The pseudo-random sequence may be part of the information for scrambling  1184 . The pseudo-random sequence may be used to scramble the ACK/NACK sequence  1148 ,  1170 . 
     In one example, a pseudo-random scrambling sequence is generated by a wireless communication device  102  (e.g., UE) that is also known to a base station  112  (e.g., eNB). The ACK/NACK sequence  1148 ,  1170  may be exclusive or-ed (e.g., xor-ed) bit-by-bit with the scrambling sequence. In this example, a pseudo-random sequence generator (not shown) on the wireless communication device  102  (e.g., UE) can be initialized by a C-RNTI (Cell-Radio Network Temporary Identifier). This value is known at both the wireless communication device  102  (e.g., UE) and the base station (e.g., eNB)  112 . Hence, no extra signaling may be required. However, other values may be used that are not known at either the wireless communication device  102  or the base station  112 . In this case, signaling may be required to negotiate the pseudo-random sequence, the seed or initial values for the random or pseudo-random number generator. 
     As illustrated in  FIG. 12 , the information regarding the scrambling sequence (which may be specific to a particular communication device) may be static  1123 , semi-dynamic (or “semi-static,” for example)  1125  or dynamic  1127 . For example, a specific scrambler sequence may be static  1123  as long as the wireless communication device  102  is registered with the base station  112 . Or, the scrambler sequence may be updated frequently (e.g., dynamic  1127 ) or less frequently (e.g., semi-dynamic  1125 ). In either case, the scrambling information  1184  may need to be signaled to the wireless communication device  102  (e.g., via a PDCCH  224 ). 
     The Gray coding module  1129  may additionally or alternatively be used to balance the ACK/NACK sequence  1148 ,  1170 . For example, a ten bit Gray code may be used for mapping the ACK/NACK sequence  1148 ,  1170  to a better-distributed sequence. The Gray coding module  1129  may use an algorithm  1131  and/or a look-up table  1133  to balance the ACK/NACK sequence  1148 ,  1170 . The Gray coding information  1186  (e.g., configuration and/or parameters) may be negotiated (i.e., generated and/or exchanged) as described above. For example, the Gray coding information  1186  (e.g., an algorithm  1131  or look-up table  1133 ) for encoding and decoding may need to be available at both a wireless communication device  102  and its corresponding base station  112 . One example of a Gray coding scheme is illustrated in Table (3) below. For convenience, only an example of a short Gray code is given. However, longer Gray coding sequences may be used in connection with the systems and methods disclosed herein. For the systems and methods herein, an ACK/NACK sequence may be indexed. The Gray code value may then be determined through the use of a look-up table. 
     
       
         
           
               
               
               
             
               
                 TABLE (3) 
               
               
                   
               
               
                   
                 Index 
                 Code 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 0 
                 0000 
               
               
                   
                 1 
                 0001 
               
               
                   
                 2 
                 0011 
               
               
                   
                 3 
                 0010 
               
               
                   
                 4 
                 0110 
               
               
                   
                 5 
                 0111 
               
               
                   
                 6 
                 0101 
               
               
                   
                 7 
                 0100 
               
               
                   
                 8 
                 1100 
               
               
                   
                 9 
                 1101 
               
               
                   
                 10 
                 1111 
               
               
                   
                 11 
                 1110 
               
               
                   
                 13 
                 1010 
               
               
                   
                 14 
                 1011 
               
               
                   
                 15 
                 1001 
               
               
                   
                 16 
                 1000 
               
               
                   
               
            
           
         
       
     
     As illustrated in  FIG. 12 , a distribution shaping module  1135  may additionally or alternatively be used by the ACK/NACK balancing module  1106  to change the distribution of 1&#39;s and 0&#39;s of the ACK/NACK sequence  1148 ,  1170 . The distribution shaping module  1135  may use a non-linear transformation to accomplish the balancing. 
     The distribution shaping module  1135  may use an algorithm  1137  and/or a look-up table  1139  to perform the distribution shaping. The algorithm  1137  and/or look-up table  1139  may be part of the distribution shaping information  1188 . For example, the distribution shaping information  1188  may be generated on either a wireless communication device  102  or its corresponding base station  112 . The algorithm  1137  and/or look-up table  1139  may be needed at both and/or communicated between the wireless communication device  102  (e.g., UE) and the base station  112  (e.g., eNB). 
     More detail on one example of distribution shaping follows. As discussed above, an ACK/NACK sequence  1148 ,  1170  may include many more 1&#39;s than 0&#39;s. A non-linear algorithm  1137  or look-up table  1139  may be used by the distribution shaping module  1135  to make the number of 1&#39;s and 0&#39;s closer to equal. One example of a non-linear function or algorithm is a Bernoulli code. The Bernoulli code may be expressed as Bern(δ) code. The term Bern(δ) may refer to a binary code whose bits are distributed as in a Bernoulli distribution with probability δ. In a Bernoulli distribution with probability δ, the probability that the r-th bit in an ACK/NACK sequence  1148 ,  1170  is 0 is δ and the probability that the r-th bit in the ACK/NACK sequence  1148 ,  1170  is 1 is 1−δ. The ACK/NACK sequence  1148 ,  1170  may be encoded using a Bern(½) code. In a Bern(½) code, the probability that each bit is 0 is equal to the probability that each bit is 1 which is equal to ½. Thus, the Bern(δ) code may be used by the distribution shaping module to make the number of 1&#39;s and 0&#39;s closer to equal. 
     As mentioned above, a look-up table  1139  may also be used by the distribution shaping module. For convenience, Table (4) below gives a short example of a lookup table that might be used by the distribution shaping module  1135  to shape the distribution of a seven bit ACK/NACK sequence  1148 ,  1170  into a “more balanced” five bit output. Table (4) also illustrates that compression and balancing may be done in a single mapping. In one example, a ten bit uncoded ACK/NACK sequence illustrated in Table (2) may be mapped directly to a “more balanced” five bit output in Table (4). Larger look-up tables with longer sequences may be used according to the systems and methods disclosed herein. 
     
       
         
           
               
               
               
             
               
                 TABLE (4) 
               
               
                   
               
               
                 Seven Bit 
                   
                   
               
               
                 ACK/NACK 
                   
                 “More Balanced” 
               
               
                 Sequence 
                 Index 
                 Five Bit Output 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 1100001 
                 1 
                 00000 
               
               
                 1100011 
                 2 
                 00011 
               
               
                 1100101 
                 3 
                 00111 
               
               
                 1100111 
                 4 
                 01010 
               
               
                 1101001 
                 5 
                 01100 
               
               
                 1101011 
                 6 
                 01110 
               
               
                 1101101 
                 7 
                 01111 
               
               
                 1101111 
                 8 
                 10011 
               
               
                 1110001 
                 9 
                 10101 
               
               
                 1110011 
                 10 
                 10110 
               
               
                 1110101 
                 11 
                 11000 
               
               
                 1110111 
                 12 
                 11010 
               
               
                 1111001 
                 13 
                 11100 
               
               
                 1111011 
                 14 
                 11101 
               
               
                 1111101 
                 15 
                 11110 
               
               
                 1111111 
                 16 
                 11111 
               
               
                   
               
            
           
         
       
     
     Thus, the ACK/NACK balancing module  1106  may use scrambling  1121 , Gray coding  1129  and/or distribution shaping  1135  in order to generate a balanced  1189  or balanced compressed  1172  ACK/NACK sequence  1172  from an uncoded  1148  or compressed  1170  ACK/NACK sequence. 
       FIG. 13  illustrates various components that may be utilized in a wireless communication device  1202 . The wireless communication device  1202  may be utilized as the wireless communication device  102  in  FIG. 1 . The wireless communication device  1202  includes a processor  1239  that controls operation of the wireless communication device  1202 . The processor  1239  may also be referred to as a CPU. Memory  1251 , which may include both read-only memory (ROM), random access memory (RAM) or any type of device that may store information, provides instructions  1241   a  and data  1243   a  to the processor  1239 . A portion of the memory  1251  may also include non-volatile random access memory (NVRAM). Instructions  1241   b  and data  1243   b  may also reside in the processor  1239 . Instructions  1241   b  loaded into the processor  1239  may also include instructions  1241   a  from memory  1251  that were loaded for execution by the processor  1239 . The instructions  1241   b  may be executed by the processor  1239  to implement the systems and methods disclosed herein. 
     The wireless communication device  1202  may also include a housing that contains a transmitter  1247  and a receiver  1249  to allow transmission and reception of data. The transmitter  1247  and receiver  1249  may be combined into a transceiver  1245 . One or more antenna  1208   a - n  are attached to the housing and electrically coupled to the transceiver  1245 . 
     The various components of the wireless communication device  1202  are coupled together by a bus system  1257  which may include a power bus, a control signal bus, and a status signal bus, in addition to a data bus. However, for the sake of clarity, the various buses are illustrated in  FIG. 13  as the bus system  1257 . The wireless communication device  1202  may also include a digital signal processor (DSP)  1253  for use in processing signals. The wireless communication device  1202  may also include a communications interface  1255  that provides user access to the functions of the wireless communication device  1202 . The wireless communication device  1202  illustrated in  FIG. 13  is a functional block diagram rather than a listing of specific components. 
       FIG. 14  illustrates various components that may be utilized in a base station  1312 . The base station  1312  may be utilized as the base station  112  in  FIG. 1 . The base station  1312  may include components that are similar to the components discussed above in relation to the wireless communication device  1202 , including a processor  1359 , memory  1371  that provides instructions  1361   a  and data  1363   a  to the processor  1359 , instructions  1361   b  and data  1363   b  that may reside in the processor  1359 , a housing that contains a transmitter  1367  and a receiver  1369  (which may be combined into a transceiver  1365 ), one or more antennas  1310   a - n  electrically coupled to the transceiver  1365 , a bus system  1377 , a DSP  1373  for use in processing signals, a communications interface  1375 , and so forth. 
     The term “computer-readable medium” or “processor-readable medium” refers to any available medium that can be accessed by a computer or a processor. The term “computer-readable medium,” as used herein, may denote a computer- and/or processor-readable medium that is non-transitory and tangible. By way of example, and not limitation, a computer-readable medium may comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and that can be accessed by a computer. Additionally, a processor-readable medium may similarly comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and that can be accessed by a processor. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray® disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. 
     Each of the methods disclosed herein comprises one or more steps or actions for achieving the described method. The method steps and/or actions may be interchanged with one another, combined into a single step or incorporated into other ancillary aspects of the communication system without departing from the scope of the claims. For example, channel decoding at the receiver may subsume source compression Gray decoding, distribution de-shaping and/or descrambling functions. In other words, unless a specific order of steps or actions is required for proper operation of the method that is being described, the order and/or use of specific steps and/or actions may be modified without departing from the scope of the claims. 
     It is to be understood that the claims are not limited to the precise configuration and components illustrated above. Various modifications, changes and variations may be made in the arrangement, operation and details of the systems, methods, and apparatus described herein without departing from the scope of the claims.