Abstract:
A method and technique are provided for efficiently acknowledging transmitted information in a system that employs variable rate data transmission, and skips data block sequence numbers depending on the transmission rate used. An RBB field in an ACK/NACK message includes a starting sequence number, an indication of a sequence number step, and a bitmap. The starting sequence number indicates a first block in a series or sequence of transmitted blocks that are being acknowledged via the ACK/NACK message. The sequence number step indicates a minimum difference between sequence numbers of blocks in the sequence. Where the sequence is ordered, the sequence number step is a difference between the sequence numbers of adjacent or consecutive blocks in the series. The bitmap is configured so that each bit in the bitmap represents an acknowledgment of one of blocks in the series. The RBB field can also include multiple starting sequence numbers, and both a sequence number step and a length for each starting sequence number. Each set of starting sequence number, sequence number step and length indicates a subseries or subsequence of the series of transmitted blocks that is being acknowledged via the ACK/NACK message. The starting sequence number indicates a sequence number of a first block in the subsequence, the length indicates how many blocks are in the subsequence, and the sequence number step indicates a difference between sequence numbers of adjacent blocks in the subsequence.

Description:
FIELD OF THE INVENTION 
     The present application claims priority under 35 U.S.C. §119 to U.S. Provisional Patent Application No. 60/110,444, filed Nov. 27, 1998. 
     The present invention generally relates to error handling in the field of communication systems and, more particularly, to error handling using both automatic repeat request (ARQ) and variable rate transmission techniques in digital communication systems. 
     BACKGROUND INFORMATION 
     Variable rate transmission in a radio communication system can be achieved using several methods. For example, in a CDMA (Code Division Multiple Access) system the information transmission rate changes as a function of the spreading factor used for transmissions. In a TDMA (Time Division Multiple Access) system, variable rate transmission is generally achieved by using different numbers of time slots. In a TDMA system the data transmission rate also varies as a function of the modulation and coding scheme used for mapping data bits to channel bits/symbols. 
     EDGE Enhanced Data Rates for Global Evolution) is an example of a system that uses different modulation and coding schemes, in addition to a variable number of time slots, to achieve different transmission rates of user data. The different modulation and coding schemes used in the EDGE system, MCS- 1  through MCS- 6 , have various payload sizes, differing for example in increments of 25 octets as shown in FIG.  1 . FIG. 2 summarizes the different block sizes, code rates, and payload sizes for the different modulation and coding schemes MCS- 1  through MCS- 6 . As indicated in FIG. 2, the modulation schemes can include PSK (Phase Shift Keying) and GMSK (Gaussian Minimum Shift Keying). 
     A block numbering scheme depending upon a payload in a block is disclosed in co-pending U.S. patent application Ser. No. 09/120,163, entitled “Method and Apparatus for Minimizing Overhead in a Communication System”, which is hereby incorporated by reference. The basic principle of the numbering scheme is illustrated in FIG.  3 . 
     As shown in FIG. 3, the block sequence numbers (SNs) can be integer multiples of an identification number of a currently used modulation and coding scheme, or can be separated by a step equal in magnitude to the identification number. For example, as shown in FIG. 3, where the current modulation and coding scheme is MCS- 6 , blocks in a sequence can be assigned sequence numbers  6 ,  12  and  18 . The round trip time (RTT) shown in FIG. 3 refers to an amount of time that elapses between when one or more blocks are sent, and when acknowledgment for them is received. As shown in FIG. 3, the payload size of a block for a current modulation and coding scheme can be defined as a number of octets that is equal to a product of the identification number of the current modulation and coding scheme and a block size increment between modulation and coding schemes. For example, the block payload size of the MCS- 6  modulation and coding scheme can be defined as (6)(25) octets=150 octets large. 
     When blocks of data are to be retransmitted at a rate that is lower than a rate at which the blocks of data were initially transmitted, the initially transmitted data can be resegmented into different size blocks, or different blocks having different payload sizes, and the different size blocks can be renumbered accordingly. For example, as shown in FIG. 3, block  12  of the MCS- 6  scheme, containing a payload of 150 octets, can be resegmented into two blocks  9  and  12  each containing a payload of 75 octets, and then retransmitted in accordance with the MCS- 3  scheme. 
     This procedure can be repeated as necessary or appropriate. If, for example, as shown in FIG. 3, the retransmitted block  9  is not correctly received, then it can be resegmented into three blocks  7 ,  8  and  9  each containing a payload of 25 octets in accordance with the MCS- 1  scheme, and resent as the new blocks  7 ,  8  and  9 . 
     Using the technique illustrated in FIG. 3, data can be retransmitted using a modulation and coding scheme that is appropriate at the time of retransmission. For example, the data can be retransmitted using a modulation and coding scheme that is optimal, and/or better at the time of the retransmission than the scheme used for the initial or previous transmission of the data. 
     Multiple blocks of data can also be resegmented into a fewer number of blocks for retransmission. For example, as shown in FIG. 4, where two blocks  4  and  6  of the scheme MCS- 2  are corrupted and need to be retransmitted, and at the time of retransmission the scheme MCS- 4  is optimal or otherwise appropriate, the two blocks  4  and  6  of the MCS- 2  scheme can be combined to form the single block  6  of the scheme MCS- 4  and retransmitted accordingly. The payload of the MCS- 4  scheme block  6  can be formed by concatenating the payloads of the blocks  4  and  6  of the MCS- 2  scheme. Note that when the optimal initial coding scheme is changed from MCS- 2  to MCS- 4  and the two blocks are combined, the resulting concatenated block is identified with the sequence number  6  of the second block. Alternatively, when a series of blocks are combined, the resulting combined block can be identified with the sequence number of any appropriate block in the series. For example, the combined block can be identified with the sequence number of the first block in the series, or the sequence number of the middle block, and so forth. 
     As shown in FIG. 5, ACK/NACK (positive acknowledgment/negative acknowledgment) messages can include a Received Block Bitmap (RBB) field format  506  having a Start Sequence Number (SSN)  502  followed by a bitmap  504 . The bitmap  504  contains an acknowledgment for each possible sequence number in a sequence of data blocks starting with a block whose SN has the same value as that of the SSN  502 . Thus, when this technique is used, a receiver must positively or negatively acknowledge all sequence numbers represented in an RBB field having the format  506 , regardless of whether all of the sequence numbers are actually used to transmit data blocks. 
     FIG. 6 shows an RBB field  606  having the format  506 . A single bit in the bitmap  506  can be used to acknowledge a block. Block sequence numbers of blocks acknowledged in the bitmap  506  correspond to bits in the bitmap  506  in a left-to-right, top-to-bottom order. The bitmap  506  includes a bit for each possible sequence number between the beginning and ending block sequence numbers of an ordered sequence of blocks. In other words, bits in the bitmap represent or acknowledge blocks having sequence numbers that are separated by a minimum step, regardless of whether the step in a particular ordered sequence of blocks is greater than the minimum step. Thus, both used and unused SNs are represented or acknowledged in the bitmap  506 . 
     For example, as shown in FIG. 6, when the RBB field  606  is used to indicate the acknowledgment status of a 12-block sequence that is configured in accordance with the MCS- 3  scheme (so that the SNs of the blocks in the 12-block sequence are separated by a step of 3), every third bit in the bitmap  506  indicates the acknowledgment status of a block in a 12-block sequence. As shown in FIG. 6, the sequence starts (as indicated by the SSN  602 ) with data block  15 , and includes blocks having SNs of 15, 18, 21, 24, 27, 30, 33, 36, 39, 42, 45 and 48. As shown in FIG. 6, blocks having SNs of 15, 18, 30 and 39 are each represented by three bits having a zero value, indicating that the blocks having SNs of 15, 18, 30 and 39 are negatively acknowledged (NACKed) and need to be retransmitted. However, unused SNs of 16, 17, 19, 20, 22, 23, 26, 26, 28, 29, 31, 32, 34, 35, 37, 38, 40, 41, 43, 44, 46, 47, 49 and 50 are also acknowledged. Thus, a total of (3)(12)=36 bits in the bitmap  604  are required to indicate the acknowledgment status of a 12-block sequence configured in accordance with the MCS- 3  scheme. Other schemes can require even more bits in the bitmap. For example, if a 12-block sequence were configured in accordance with the MCS- 6  scheme, a total of (6)(12)=72 bits would be required in the bitmap to acknowledge the 12-block sequence. 
     In summary, the RBB format shown in FIG. 5 is poorly suited for positively and negatively acknowledging transmitted blocks in a system that uses variable rate data transmission, and skips block sequence numbers depending on the rate used. For example, in situations where the MCS- 6  scheme is used and N blocks in a consecutive sequence bear the sequence numbers {6, 12, 18, . . . 6*N}, the RBB format would require a separate acknowledgment for each of sequence numbers {1, 2, 3, 4, 5, . . . 6*N}, even though only the sequence numbers {6, 12, 18, . . . 6*N} need to be considered. Thus, the RBB format requires unnecessarily large overheads when used in a system that employs variable rate data transmission and skips block sequence numbers depending on the rate used. 
     Accordingly, a need exists for an efficient, low-overhead method and technique for positively and negatively acknowledging transmitted blocks in a system that employs variable rate data transmission and skips block sequence numbers depending on the rate used. 
     SUMMARY OF THE INVENTION 
     In accordance with various exemplary embodiments of the invention, a method and technique are provided for efficiently acknowledging transmitted information in a system that employs variable rate data transmission, and skips data block sequence numbers depending on the transmission rate used. In accordance with exemplary embodiments of the invention, the ACK/NACK overhead in a variable rate communication system is reduced by providing an RBB format that is more compact and which can therefore be transmitted and evaluated in less time. This conserves time and computing resources, and allows data to be retransmitted with less delay. In other words, exemplary embodiments of the invention reduce an amount of time between a first transmission of data and a subsequent retransmission of the data. 
     In accordance with exemplary embodiments of the invention, in a system that employs variable rate data transmission and skips block sequence numbers depending on the data transmission rate used, the skipped block sequence numbers are not acknowledged, thus reducing RBB field sizes in ACK/NACK messages used in the system. 
     In accordance with an exemplary embodiment of the invention, an RBB field in an ACK/NACK message includes a starting sequence number, an indication of a sequence number step, and a bitmap. The starting sequence number indicates a first block in a series of transmitted blocks that are being acknowledged via the ACK/NACK message. The sequence number step is a minimum difference between sequence numbers of blocks in the series. Where the series is ordered, the sequence number step is a difference between the sequence numbers of adjacent or consecutive blocks in the series. The bitmap can be configured so that each bit in the bitmap represents an acknowledgment of one of the blocks in the series. 
     In accordance with another exemplary embodiment of the invention, the RBB field in the ACK/NACK message includes multiple starting sequence numbers, and both a sequence number step and a length for each starting sequence number. Each set of starting sequence number, sequence number step and length indicates a subseries or subsequence of the series of transmitted blocks that is being acknowledged via the ACK/NACK message. The starting sequence number indicates a sequence number of a first block in the subsequence, the length indicates how many blocks are in the subsequence, and the sequence number step indicates a difference between sequence numbers of adjacent blocks in the subsequence. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description of preferred embodiments, when read in conjunction with the accompanying drawings wherein like elements have been designated with like reference numerals and wherein: 
     FIG. 1 shows various payload sizes of different modulation and coding schemes used in the EDGE system. 
     FIG. 2 shows different block sizes, code rates, and payload sizes for the different modulation and coding schemes used in the EDGE system. 
     FIG. 3 illustrates a block numbering system that is based on the payload sizes of different blocks, and shows how data can be resegmented into more blocks for retransmission. 
     FIG. 4 illustrates how data can be resegmented into fewer blocks for retransmission. 
     FIG. 5 shows a received block bitmap (RBB) format of an RBB field in a positive acknowledgment/negative acknowledgment (ACK/NACK) message, that is known in the prior art. 
     FIG. 6 shows a specific example of an RBB field in an ACK/NACK message, that has the format shown in FIG.  5 . 
     FIG. 7 shows an RBB format of an RBB field in an ACK/NACK message, in accordance with an exemplary embodiment of the invention. 
     FIG. 8 shows a specific example of an RBB field in an ACK/NACK message, that has the format shown in FIG.  7 . 
     FIG. 9 shows an RBB format of an RBB field in an ACK/NACK message, in accordance with an exemplary embodiment of the invention. 
     FIG. 10 shows a specific example of an RBB field in an ACK/NACK message, that has the format shown in FIG.  9 . 
     FIG. 11A shows an RBB format of an RBB field in an ACK/NACK message, in accordance with an exemplary embodiment of the invention. 
     FIG. 11B shows a specific example of an RBB field in accordance with the RBB format shown in FIG.  11 A. 
     FIG. 12 shows an RBB format of an RBB field in an ACK/NACK message, in accordance with an exemplary embodiment of the invention. 
     FIG. 13 shows an RBB format of an RBB field in an ACK/NACK message, in accordance with an exemplary embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In accordance with exemplary embodiments of the invention, a single ACK/NACK message is used to positively or negatively acknowledge a plurality of received blocks. 
     In accordance with a first exemplary embodiment of the invention, a single sequence number step (SNS) is employed. The SNS defines a difference between adjacent sequence numbers in an ordered sequence of block sequence numbers. This concept is illustrated, for example, in FIG.  7 . As shown in FIG. 7, an RBB format  700  includes an SSN field  702 , an SNS field  704 , and a bitmap field  706 . The SNS can be, for example, an increment or a decrement, depending on whether the values in the ordered sequence increase or decrease. 
     FIG. 8 shows an RBB field  800  having the format  700 . The SSN  802  is 15, the SNS  804  is 3, and the bits in the bitmap  806  indicate which of the blocks have been successfully received, and which have not. For example, the bitmap  806  can be configured so that the sequence ascends from left to right and from top to bottom across the bitmap  806 , and so that “0” indicates NACK and “1” indicates ACK. Given this configuration, the bitmap  806  indicates that blocks having SNs of 15, 18, 30 and 39 are negatively acknowledged and should therefore be retransmitted, and blocks having SNs of 21, 24, 27, 33, 36, 42, 45 and 48 are positively acknowledged. 
     When three bits are used to represent the SNS  804 , only (3+12)=15 bits total (3 for the SNS  804  and 12 for the bit map  806 ) are necessary to positively or negatively acknowledge each block in a sequence of 12 blocks having SNs of 15, 18, 21, 24, 27, 30, 33, 36, 39, 42, 45 and 48. In contrast, 34 bits are necessary in the bit map  604  to acknowledge each block in the sequence {15, 18, 21, . . . 48}. This reduction in the number of bits necessary to positively or negatively acknowledge each block in a sequence of blocks reduces overhead and increases efficiency. 
     Although an example of an SNS having 3 bits is described above, those skilled in the art will recognize that any appropriate number of bits can be chosen to represent the SNS. 
     As an alternative to explicitly acknowledging the first block in the sequence, as shown for example in FIGS. 7 and 8, the SSN  702  can negatively acknowledge the corresponding block implicitly. For example, where the MCS- 3  sequence (15, 18, 21, . . . 45, 48) is to be acknowledged, the first entry in the bitmap  806  would correspond to the block having the SN=18, not SN=15. Of course, the SSN  702  could alternatively be understood to positively acknowledge the corresponding block implicitly. 
     As an alternative to including an SSN field, it can be understood that the SSN is always 0 (zero). In this case, the SSN field  702  in the RBB format  700  can be omitted. 
     In accordance with a second exemplary embodiment of the invention, blocks in a sequence of blocks that has different sequence number steps can be positively or negatively acknowledged using the same RBB field. In other words, a single RBB field can be used to acknowledge all blocks in a sequence, where the sequence includes subsequences of blocks and different subsequences can have different sequence number steps. 
     In accordance with the second embodiment of the invention, FIG. 9 shows an exemplary RBB field format  900  for representing a sequence of blocks, where the sequence can include subsequences of blocks that can each have a different sequence number step. 
     As shown in FIG. 9, the RBB field format  900  also includes a step flags field  902 . Each bit in the step flags field  902  represents a different possible sequence number step, and functions as a flag for that step. The step flags field  902  can be configured so that when a bit in the step flags field  902  is “1”, the corresponding flag is set, and when the bit is “0”, the corresponding flag is not set. 
     Each subsequence of blocks in the sequence is defined using a pair  904  of a starting sequence number (SSN) of a first block in the subsequence, a number of blocks L in the subsequence, and one of the flags in the step flags field  902 . For example, the RBB field format can be configured so that a first set flag in the step flags field  902  corresponds to a first pair  904 , a second set flag in the step flags field  902  corresponds to a second pair  904 , and so forth. The “first” set flag can be, for example, the first flag encountered when moving from left to right across the field  902  that is set. The “first” pair  904  can be, for example, the first pair  904  encountered when moving from top to bottom through a sequence of pairs  904  in the RBB field  900 . For example, the first pair  904  can be the pair  904  including the SSN field  906  and the length field  908  as shown in FIG.  9 . 
     Thus, the first set flag indicates the sequence number step for the subsequence of blocks corresponding to the first pair  904  and the first set flag. Likewise, the second set flag indicates the sequence number step for the subsequence of blocks corresponding to the second pair  904 , and so forth. 
     The SSN fields  906  and  910  of the pairs  904  can contain different SSNs from different subsequences, and the length fields  908  and  912  can each contain a number indicating a length of a corresponding subsequence. The length of the subsequence can be, for example, a number of blocks in the subsequence. All of the blocks in the subsequences are acknowledged using bits in the bitmap  914 . 
     FIG. 10 shows an exemplary RBB field  1000  having the format  900 . As shown in FIG. 10, the step flags field  902  indicates which sequence number steps are present in a sequence of blocks represented by the field  1000 . The step flags field  902  represents steps in ascending value from left to right. For example, the flags corresponding to the steps or step values  1 ,  3  and  6  are set equal to “1”, indicating that the sequence contains subsequences having the steps  1 ,  3  and  6 . Pairs  1004  correspond to the steps present in the sequence, and are ordered in the field  1000  from top to bottom in descending step value. 
     For example, the uppermost pair  1004  of an SSN  1006  and an L  1008  corresponds to the step having a value of 6. The value 24 of the SSN  1006  indicates that the first block in the subsequence has an SN of 24. The value 12 of the length L  1008  indicates that the subsequence is 12 blocks long. Thus, the step  6  and the SSN  1006  and the L  1008  of the uppermost pair  1004 , together represent or define a subsequence of blocks having SNs of 24, 30, 36, 42, 48, 54, 60, 66, 72, 78, 84 and 90. 
     Similarly, the pair  1004  of an SSN  1010 =93, an L  1012 =7 and the step  3  represent a subsequence of blocks having SNs of 93, 96, 99, 102, 105, 108 and 111. 
     The pair  1004  of an SSN  1016 =112, and L  1018 =5 and the step  1  represent a subsequence of blocks having SNs of 112, 113, 114, 115 and 116. 
     A bitmap  1014  indicates which blocks in the sequence are positively acknowledged, and which are negatively acknowledged. For example, the bitmap  1014  is configured so that a bit value of “1” indicates that a corresponding block is positively acknowledged, and a bit value of “0” indicates that a corresponding block is negatively acknowledged. The subsequences represented in top to bottom order of the pairs  1004  are represented in left to right and top to bottom order in the bitmap  1014 . In addition, the block SNs within the subsequences are represented in ascending order left to right and top to bottom in the bitmap  1014 . 
     Thus, as can be seen in FIG. 10, the bits in the bitmap  1014  indicate that blocks having the SNs of 24, 48, 54, 66, 84, 93, 96, 108, 112 and 115 are negatively acknowledged and need to be retransmitted. 
     The steps represented in the step flags field  902  and the subsequences represented by the pairs  904  can be ordered in any appropriate fashion. For example, as an alternative to the orders described above, the step flags field  902  can represent steps in descending order from left to right, and the pairs  904  can be arrayed in order of occurrence or correspondence from bottom to top instead of top to bottom. 
     As an alternative to flags, the field  902  can contain actual step values instead of single-bit flags. In this case each step value, together with a corresponding pair  904 , defines a subsequence of blocks. The step values can be ordered in the field  902  so that a first step value in the field  902  corresponds to a first pair  904  and helps define a first subsequence of blocks in a sequence, a second step value in the field  902  corresponds to a second pair  904  and helps define a second subsequence, and so forth. Furthermore, as an alternative to grouping the step values in the field  902 , each of the step values can be located with a corresponding pair SNS and length values. 
     For example, as illustrated in FIG. 11A, an RBB format  1100  in accordance with an embodiment of the invention, includes triples  1104  that each define a subsequence in a sequence of blocks. Each triple includes a sequence number step SNS, a sequence number of a first block in the subsequence (e.g., an SSN), and a length L of the subsequence. The RBB format  1100  can also contain a field  1106  containing a number N that indicates how many subsequences are in the sequence of blocks acknowledged and/or represented. As an alternative to the field  1106 , each triple  1104  can also include a bit field E, to indicate whether the bitmap will immediately follow. Thus, one of the field  1106  and the bit fields E can be omitted. Other appropriate mechanisms can alternatively be provided to indicate a location of the bitmap in the RBB format  1100 . 
     FIG. 11B shows an example RBB field  1102  in accordance with the RBB format  1100 , which contains two triplets  1104 . The first triplet  1104  indicates that the subsequence it defines starts with SN=1, has an SNS=4, and has a length of 4 (i.e., there are 4 sequence numbers or blocks in the subsequence). The bit value E=0 indicates that the first triplet  1104  is not followed by the bitmap. The second triplet indicates that the subsequence it defines starts with SN=14, has an SNS=2, and has a length of 4. The bit value E=1 indicates that the bitmap  1114  does immediately follow the second triplet  1104 , and the bitmap  1114  indicates that blocks having sequence numbers of 1, 8, 14, 16 and 20 need to be retransmitted. 
     As an alternative, the bitmap  1114  can be replaced with a list of sequence numbers that correspond to blocks in the subsequences defined by the triplets  1104 , which need to be retransmitted. If for example this technique were applied to the RBB field shown in FIG. 11B, then the list of sequence numbers would include  1 ,  8 ,  14 ,  16  and  20 . Where the RBB field acknowledges a large number blocks and a percentage of blocks that need to be retransmitted is low, this technique can be more efficient than using the bitmap  1114 . 
     In accordance with another embodiment of the invention, an RBB format can include explicit sequence numbers, whose presence acknowledges the corresponding blocks. FIG. 12 shows, for example, an RBB format  1200  that is similar to the RBB format  700 , but also includes a list of explicit sequence number fields  1208 ,  1210  and  1212  which contain sequence numbers SN i , SN j  and SN k . Any appropriate number of explicit sequence number fields can be included, and the RBB format  1200  can optionally include a sequence number quantity (SNQ)  1214  that indicates how may explicit sequence numbers follow the bitmap  706 . The acknowledgment can be understood to be negative, or alternatively to be positive, or can be indicated by an optional bit P/N  1216  whose value indicates whether the acknowledgment is negative or positive. 
     An accordance with another embodiment of the invention, an RBB format can include parameters that explicitly identify a sequence of sequence numbers that are all positively acknowledged or all negatively acknowledged. For example, as shown in FIG. 13, an RBB format  1300  that is similar to the RBB format  700  also includes a set of parameters that defines a sequence of sequence numbers. The set includes, for example, an SSN field  1308  that contains a starting sequence number, an SNS field  1310  that indicates a sequence number step for the sequence or subsequence, and a length field Len  1312  that indicates how many sequence numbers are in the sequence or subsequence. The field Len  1312  can alternatively contain a sequence number of a last block in the sequence. The acknowledgment (positive or negative) for all the blocks in the sequence can be understood, or can be indicated by an optional bit P/N  1314  whose value indicates whether the acknowledgment is negative or positive. 
     The techniques illustrated in FIGS. 12 and 13 can also be implemented with other embodiments of the invention described above, besides the embodiment shown in FIG.  7 . As a further alternative, when the techniques illustrated in FIGS. 12 and 13 are used the bitmap field  706  and the SSN and SNS fields  702  and  704  can be omitted entirely. 
     In accordance with different embodiments of the invention, the order of elements within the RBB field can be varied, and the order of SNs within the RBB field can also be varied. For example, the bits in the field  1002  can alternatively represent steps that descend in value from left to right across the field  1002 . Sequence numbers represented in the bitmaps can descend from left to right, and/or from top to bottom within each subsequence. 
     Where an RBB field applies to a sequence of blocks and includes different steps where each subsequence in the sequence of blocks has a single step, the subsequences can also be represented in the RBB field in different orders. For example, the subsequences can appear (as represented by information such as the pairs  1004 , and/or as represented by corresponding portions in the bitmap of the RBB field) ordered in ascending or descending order by step, or by SSN. Furthermore, instead of a starting sequence number corresponding to the sequence number of a first block in a sequence or subsequence, the sequence number of a final block in the sequence or subsequence can be used. 
     In general, information contained in fields or subfields within exemplary RBB field formats in accordance with various embodiments of the invention, can be ordered in any appropriate way. Information within those fields or subfields can likewise be ordered in any appropriate way. 
     Where, in accordance with exemplary embodiments of the invention, actual values instead of flags are stored within an RBB field, numbers of bits used to represent the values can be chosen appropriately. For example, with respect to an SNS field that stores a starting sequence number of a block in a sequence or subsequence, the size of the SNS field, for example the number of bits used to represent the value stored in the SNS field, can be appropriately selected to be a minimum number that is sufficient to represent a largest SN of a first block in the sequence or subsequence. 
     In accordance with an embodiment of the invention, instead of using “0” to represent a negative acknowledgment and “1” to represent a positive acknowledgment, “0” can be used to represent a positive acknowledgment and “1” can be used to represent a negative acknowledgment. 
     In accordance with an embodiment of the invention, where one or more sequence number steps indicated in the RBB field represent step magnitudes, the RBB field can include a separate indication for each step, or in the alternative can include an indication that applies all of the steps, indicating whether the corresponding step(s) is a decrement or an increment. 
     It will be appreciated by those skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics thereof, and that the invention is not limited to the specific embodiments described herein. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restrictive. The scope of the invention is indicated by the appended claims rather than the foregoing description, and all changes that come within the meaning and range and equivalents thereof are intended to be embraced therein.