Abstract:
Disclosed are an apparatus and a method for transmitting data using a CTC (Convolutional Turbo Code) encoder in a mobile communication system. The data transmission method according to the present invention includes: a first encoding step of encoding input data bits inputted through two input terminals of the CTC encoder and outputting first encoding bits; a step of interleaving the input data bits by using four CTC interleaver parameters (P0, P1, P2, and P3) corresponding to the sizes of the input data bits; a second encoding step of encoding the interleaved data bits and outputting second encoding bits; and a step of selectively transmitting the input data bits, the first encoding bits, and the second encoding bits to a receiving side in accordance with a predetermined coding rate, wherein the sizes of the input data bits are one of M-number of predefined data bit sizes, and P0 of the CTC interleaver parameters corresponding to the sizes of the input data bits is a relative prime number to N which is ½ of a data block size, P1 is a natural number which is a multiple of 2, P2 is a natural number which is a multiple of 4, and P3 is a natural number which is a multiple of 2 if P1 mod4=2 and a natural number which is a multiple of 4 if P1mod4=0.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to an apparatus and method for transmitting data, and more particularly, to an apparatus and method for a transmitting end to transmit data using a Convolutional Turbo Code (CTC) encoder in a mobile communication system. 
         [0003]    2. Discussion of the Related Art 
         [0004]    In a wireless communication system, portions of transmission data may sometimes be lost at once due to fading. If consecutive data bits are lost at once, this error cannot be recovered from even when a very excellent error correction code is used. 
         [0005]    In a wireless communication system, the transmitting end transmits an encoded transmission data sequence after changing the order of the transmission data bits according to a specific pattern using a channel interleaving method rather than transmitting the data bits in an order in which the data bits are input. That is, a burst error that frequently occurs in a radio link can be changed to a random error using channel interleaving. 
         [0006]    When error bits are sparsely present among encoded transmission data, the error bits may be corrected using an error correction code such as a convolutional code, a turbo code, or a Low Density Parity Check (LDPC) code. 
         [0007]    Basically, turbo coding, which is a channel coding technology, is a scheme which connects convolutional codes through parallel concatenation. The Convolutional Turbo Code (CTC) is one of the channel codes used in mobile Internet services. 
         [0008]    As is well known, a next-generation mobile communication system requires reliable transmission of multimedia data at a high speed and requires robust channel coding and an efficient modulation scheme in order to increase reliability of high-speed data transmission. Various coding schemes having specifications enabling high-speed data communication such as convolutional coding or turbo coding have been suggested and introduced in many countries. Such channel coding schemes exhibit better performance depending on an interleaver size or a corresponding data block size. Thus, intensive studies have been carried out on an interleaver that greatly affects turbo code performance. 
         [0009]    CTC may support two data block size sets in the case of channel coding in a conventional Institute of Electrical and Electronics Engineers (IEEE) 802.16e system. One of the two data block size sets includes data block sizes of 48, 72, 96, 144, 192, 216, 240, 288, 360, 384, 432, and 480 and the other includes data block sizes of 48, 96, 144, 192, 288, 384, 480, 960, 1920, 2880, 3840, and 4800. However, even when the two data block size sets are combined, data block sizes at great intervals therebetween may be selected from the combined range of 48 to 4800. 
         [0010]    Table 1 shows each data block size and values of corresponding CTC interleaver parameters P 0 , P 1 , P 2 , and P 3  in the conventional IEEE 802.16e system. 
         [0000]    
       
         
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 index 
                 N EP   
                 P 0   
                 P 1   
                 P 2   
                 P 3   
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 1 
                 48 
                 5 
                 0 
                 0 
                 0 
               
               
                   
                 2 
                 72 
                 11 
                 18 
                 0 
                 18 
               
               
                   
                 3 
                 96 
                 13 
                 24 
                 0 
                 24 
               
               
                   
                 4 
                 144 
                 11 
                 6 
                 0 
                 6 
               
               
                   
                 5 
                 192 
                 7 
                 48 
                 24 
                 72 
               
               
                   
                 6 
                 240 
                 13 
                 60 
                 0 
                 60 
               
               
                   
                 7 
                 288 
                 17 
                 74 
                 72 
                 2 
               
               
                   
                 8 
                 360 
                 11 
                 90 
                 0 
                 90 
               
               
                   
                 9 
                 384 
                 11 
                 96 
                 48 
                 144 
               
               
                   
                 10 
                 432 
                 13 
                 108 
                 0 
                 108 
               
               
                   
                 11 
                 480 
                 13 
                 120 
                 60 
                 180 
               
               
                   
                 12 
                 960 
                 53 
                 62 
                 12 
                 2 
               
               
                   
                 13 
                 1920 
                 43 
                 64 
                 300 
                 824 
               
               
                   
                 14 
                 2880 
                 43 
                 720 
                 360 
                 540 
               
               
                   
                 15 
                 3840 
                 31 
                 8 
                 24 
                 16 
               
               
                   
                 16 
                 4800 
                 53 
                 66 
                 24 
                 2 
               
               
                   
                   
               
             
          
         
       
     
         [0011]    Since a CTC encoder can only support data block sizes corresponding to the preset data block size sets, there is a need to use padding bits when an information block size is not included in the data block size sets. The number of padding bits is equal to the difference between the information block size and the smallest data block size in the set greater than the information block size. Thus, if granularity, which corresponds to the difference between two adjacent data block sizes in a data block size set, is increased in the data block size set, padding overhead is also increased. 
         [0012]    The IEEE 802.16e system has great padding overhead since the CTC data block sizes have a great interval of granularity. Thus, although there is a need to define new CTC data block sizes, CTC data block sizes having better granularity have not yet been suggested in the IEEE 802.16m system. 
       SUMMARY OF THE INVENTION 
       [0013]    Accordingly, an object of the present invention is to provide a method for a transmitting end to transmit data using a Convolutional Turbo Code (CTC) encoder in a mobile communication system. 
         [0014]    Another object of the present invention is to provide an apparatus for a transmitting end to transmit data using a Convolutional Turbo Code (CTC) encoder in a mobile communication system. 
         [0015]    Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
         [0016]    To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, a method for a transmitting data using a Convolutional Turbo Code (CTC) encoder in a mobile communication system includes providing first encoded bits by encoding input data bits inputted to two input ports of the CTC encoder, interleaving the input data bits using 4 CTC interleaver parameters (P 0 , P 1 , P 2 , and P 3 ) corresponding to a size of the input data bits, providing second encoded bits by encoding the interleaved input data bits, and selectively transmitting the input data bits, the first encoded bits, and the second encoded bits according to a predefined code rate, wherein the size of the input data bits is one of M predetermined data bit sizes, and wherein P 0  is relative prime number with N which is ½ of the size of the input data bits, P 1  is a multiple of 2 among natural numbers, P 2  is a multiple of 4 among the natural numbers, and wherein P 3  is a multiple of 2 among the natural numbers when (P 1  modulo 4)=2, and P 3  is a multiple of 4 among the natural numbers when (P 1  modulo 4)=0. 
         [0017]    In another aspect of the present invention, an apparatus for transmitting data using a Convolutional Turbo Code (CTC) encoder in a mobile communication system includes a first encoder for providing first encoded bits by encoding input data bits inputted to two input ports of the CTC encoder, a CTC interleaver for interleaving the input data bits using 4 CTC interleaver parameters (P 0 , P 1 , P 2 , and P 3 ) corresponding to a size of the input data bits, a second encoder for providing second encoded bits by encoding the interleaved input data bits, and a transmission module for selectively transmitting the input data bits, the first encoded bits, and the second encoded bits according to a predefined code rate, wherein the size of the input data bits is one of M predetermined data bit sizes, and wherein P 0  is relative prime number with N which is ½ of the size of the input data bits, P 1  is a multiple of 2 among natural numbers, P 2  is a multiple of 4 among the natural numbers, and wherein P 3  is a multiple of 2 among the natural numbers when (P1 modulo 4)=2, and P 3  is a multiple of 4 among the natural numbers when (P 1  modulo 4)=0. 
         [0018]    It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings: 
           [0020]      FIG. 1  illustrates simulation results of padding overhead according to CTC data block sizes suggested in Table 1. 
           [0021]      FIG. 2  illustrates a preferred embodiment of a CTC encoder according to the present invention. 
           [0022]      FIGS. 3 and 4  illustrate comparison between BLER performance of a CTC interleaver using data block sizes and CTC interleaver parameters suggested in the present invention and BLER performance of the conventional IEEE 802.16e CTC interleaver for each mother code rate. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0023]    Reference will now be made in detail to the preferred embodiments of the present invention with reference to the accompanying drawings. The detailed description, which will be given below with reference to the accompanying drawings, is intended to explain exemplary embodiments of the present invention, rather than to show the only embodiments that can be implemented according to the invention. The following detailed description includes specific details in order to provide a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without such specific details. For example, although the following description will be given with reference to specific terms, the present invention is not necessarily limited to the specific terms and other terms may also be used to indicate the same meanings The same reference numbers will be used throughout this specification to refer to the same or like parts. 
         [0024]    The expression “a portion includes a specific component” used throughout this specification indicates that the portion may also include other components, rather than including the specific component alone, unless explicitly stated otherwise. 
         [0025]    Technologies described below can be used in various communication systems, which may provide various communication services such as voice and packet data services. The communication system technologies can be used in downlink or uplink. In the description of the present invention, the term “Base Station (BS)” may be replaced with another term such as “fixed station”, “Node B”, “eNode B (eNB)”, “access point”, or “ABS”. The “Mobile Station (MS)” may also be replaced with another term such as “User Equipment (UE)”, “Subscriber Station (SS)”, “Mobile Subscriber Station (MSS)”, “AMS”, or “mobile terminal”. 
         [0026]    The term “transmitting end” refers to a node that transmits data or audio services and “receiving end” refers to a node that receives data or audio services. Thus, in uplink, the MS may be a transmitting end and the BS may be a receiving end. Similarly, in downlink, the MS may be a receiving end and the BS may be a transmitting end. 
         [0027]    A Personal Digital Assistant (PDA), a cellular phone, a Personal Communication Service (PCS) phone, a Global System for Mobile (GSM) phone, a Wideband CDMA (WCDMA) phone, or a Mobile Broadband System (MBS) phone may be used as the MS in the present invention. 
         [0028]    The embodiments of the present invention can be supported by standard documents of at least one of the Institute of Electrical and Electronics Engineers (IEEE) 802 system, the 3GPP system, the 3rd Generation Partnership Project Long Term Evolution (3GPP LTE) system, and the 3GPP2 system which are wireless access systems. That is, steps or portions that are not described in the embodiments of the present invention for the sake of clearly describing the spirit of the present invention can be supported by the standard documents. For all terms used in this disclosure, reference can be made to the standard documents. Especially, the embodiments of the present invention can be supported by P802.16-2004, P802.16e-2005, or P802.16Rev2 which are standard documents of the IEEE 802.16 system. 
         [0029]    Specific terms used in the following description are provided for better understanding of the present invention and can be replaced with other terms without departing from the spirit of the present invention. 
         [0030]    CTC data block size requirements in the IEEE 802.16m system are described as follows. First, data block sizes of the IEEE 802.16m system not only need to support data block sizes of the conventional IEEE 802.16e system but also need to be byte-aligned. The data block size is not a multiple of 7 to support a tail-biting encoding structure of CTC. It is preferable that the data block size set be designed to have better granularity to reduce padding overhead. In addition, the CTC data block size of the conventional IEEE 802.16e system needs to be supported by CTC of the IEEE 802.16m system. Each data block size needs to be increased to improve CTC performance and CTC interleaver parameters need to be optimized to achieve better CTC performance than in the IEEE 802.16e system. Rules of the CTC data block size together with granularity are described below. 
         [0031]    1. Granularity for the data block sizes is increased taking into consideration padding overhead. First, it is preferable that a boundary data block size be defined so as to increase the granularity value. It is also preferable that granularity be defined taking into consideration the same padding parts of the boundary data block sizes. 
         [0032]    2. It is preferable that the granularity value of the data block size is a multiple of 8 and byte-aligned. 
         [0033]    3. As an exception to these rules, the granularity value may be twice as high as the desired granularity value in order to avoid data block sizes which are multiples of 7. 
         [0034]    The CTC data block size rules are described below in more detail. 
         [0035]    The boundary data block size used may be expressed as a power of 2 taking into consideration the minimum granularity value of 8. The boundary data block size may be 512, 1024, or 2048. The maximum padding bit portion may be fixed to 1.5625% of the entire boundary data block size. 
         [0036]    For example, let us consider “40” and “48” as adjacent data block sizes. Here, the smaller data block size is 40 and the larger data block size is 48. A granularity value G may be defined by measuring the smaller data block size N EP  among the two adjacent data block sizes. For example, G may be 8 when 40≦N EP ≦512. On the other hand, G may be 16 when 512≦N EP ≦1024, 32 when 1024≦N EP ≦2048, and 64 when 2048≦N EP . 
         [0037]    The greater data block size N EP+ among the two adjacent data block sizes may be defined as follows. 
         [0038]    For example, N EP+ =N EP +G when (N EP +G)%7≠0, otherwise N EP+ =N EP +2G. 
         [0039]    Here, %7 represents a modulo-7 operation. 
         [0040]    According to these rules, the CTC data block size in the IEEE 802.16m system may be defined as shown in Table 1. 
         [0000]    
       
         
               
               
               
             
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Index 
                 N EP   
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 1 
                 40 
               
               
                   
                 2 
                 48 
               
               
                   
                 3 
                 64 
               
               
                   
                 4 
                 72 
               
               
                   
                 5 
                 80 
               
               
                   
                 6 
                 88 
               
               
                   
                 7 
                 96 
               
               
                   
                 8 
                 104 
               
               
                   
                 9 
                 120 
               
               
                   
                 10 
                 128 
               
               
                   
                 11 
                 136 
               
               
                   
                 12 
                 144 
               
               
                   
                 13 
                 152 
               
               
                   
                 14 
                 160 
               
               
                   
                 15 
                 176 
               
               
                   
                 16 
                 184 
               
               
                   
                 17 
                 192 
               
               
                   
                 18 
                 200 
               
               
                   
                 19 
                 208 
               
               
                   
                 20 
                 216 
               
               
                   
                 21 
                 232 
               
               
                   
                 22 
                 240 
               
               
                   
                 23 
                 248 
               
               
                   
                 24 
                 256 
               
               
                   
                 25 
                 264 
               
               
                   
                 26 
                 272 
               
               
                   
                 27 
                 288 
               
               
                   
                 28 
                 296 
               
               
                   
                 29 
                 304 
               
               
                   
                 30 
                 312 
               
               
                   
                 31 
                 320 
               
               
                   
                 32 
                 328 
               
               
                   
                 33 
                 344 
               
               
                   
                 34 
                 352 
               
               
                   
                 35 
                 360 
               
               
                   
                 36 
                 368 
               
               
                   
                 37 
                 376 
               
               
                   
                 38 
                 384 
               
               
                   
                 39 
                 400 
               
               
                   
                 40 
                 408 
               
               
                   
                 41 
                 416 
               
               
                   
                 42 
                 424 
               
               
                   
                 43 
                 432 
               
               
                   
                 44 
                 440 
               
               
                   
                 45 
                 456 
               
               
                   
                 46 
                 464 
               
               
                   
                 47 
                 472 
               
               
                   
                 48 
                 480 
               
               
                   
                 49 
                 488 
               
               
                   
                 50 
                 496 
               
               
                   
                 51 
                 512 
               
               
                   
                 52 
                 528 
               
               
                   
                 53 
                 544 
               
               
                   
                 54 
                 576 
               
               
                   
                 55 
                 592 
               
               
                   
                 56 
                 608 
               
               
                   
                 57 
                 624 
               
               
                   
                 58 
                 640 
               
               
                   
                 59 
                 656 
               
               
                   
                 60 
                 688 
               
               
                   
                 61 
                 704 
               
               
                   
                 62 
                 720 
               
               
                   
                 63 
                 736 
               
               
                   
                 64 
                 752 
               
               
                   
                 65 
                 768 
               
               
                   
                 66 
                 800 
               
               
                   
                 67 
                 816 
               
               
                   
                 68 
                 832 
               
               
                   
                 69 
                 848 
               
               
                   
                 70 
                 864 
               
               
                   
                 71 
                 880 
               
               
                   
                 72 
                 912 
               
               
                   
                 73 
                 928 
               
               
                   
                 74 
                 944 
               
               
                   
                 75 
                 960 
               
               
                   
                 76 
                 976 
               
               
                   
                 77 
                 992 
               
               
                   
                 78 
                 1024 
               
               
                   
                 79 
                 1056 
               
               
                   
                 80 
                 1088 
               
               
                   
                 81 
                 1152 
               
               
                   
                 82 
                 1184 
               
               
                   
                 83 
                 1216 
               
               
                   
                 84 
                 1248 
               
               
                   
                 85 
                 1280 
               
               
                   
                 86 
                 1312 
               
               
                   
                 87 
                 1376 
               
               
                   
                 88 
                 1408 
               
               
                   
                 89 
                 1440 
               
               
                   
                 90 
                 1472 
               
               
                   
                 91 
                 1504 
               
               
                   
                 92 
                 1536 
               
               
                   
                 93 
                 1600 
               
               
                   
                 94 
                 1632 
               
               
                   
                 95 
                 1664 
               
               
                   
                 96 
                 1696 
               
               
                   
                 97 
                 1728 
               
               
                   
                 98 
                 1760 
               
               
                   
                 99 
                 1824 
               
               
                   
                 100 
                 1856 
               
               
                   
                 101 
                 1888 
               
               
                   
                 102 
                 1920 
               
               
                   
                 103 
                 1952 
               
               
                   
                 104 
                 1984 
               
               
                   
                 105 
                 2048 
               
               
                   
                 106 
                 2112 
               
               
                   
                 107 
                 2176 
               
               
                   
                 108 
                 2304 
               
               
                   
                 109 
                 2368 
               
               
                   
                 110 
                 2432 
               
               
                   
                 111 
                 2496 
               
               
                   
                 112 
                 2560 
               
               
                   
                 113 
                 2624 
               
               
                   
                 114 
                 2752 
               
               
                   
                 115 
                 2816 
               
               
                   
                 116 
                 2880 
               
               
                   
                 117 
                 2944 
               
               
                   
                 118 
                 3008 
               
               
                   
                 119 
                 3072 
               
               
                   
                 120 
                 3200 
               
               
                   
                 121 
                 3264 
               
               
                   
                 122 
                 3328 
               
               
                   
                 123 
                 3392 
               
               
                   
                 124 
                 3456 
               
               
                   
                 125 
                 3520 
               
               
                   
                 126 
                 3648 
               
               
                   
                 127 
                 3712 
               
               
                   
                 128 
                 3776 
               
               
                   
                 129 
                 3840 
               
               
                   
                 130 
                 3904 
               
               
                   
                 131 
                 3968 
               
               
                   
                 132 
                 4096 
               
               
                   
                 133 
                 4160 
               
               
                   
                 134 
                 4224 
               
               
                   
                 135 
                 4288 
               
               
                   
                 136 
                 4352 
               
               
                   
                 137 
                 4416 
               
               
                   
                 138 
                 4544 
               
               
                   
                 139 
                 4608 
               
               
                   
                 140 
                 4672 
               
               
                   
                 141 
                 4736 
               
               
                   
                 142 
                 4800 
               
               
                   
                   
               
             
          
         
       
     
         [0041]      FIG. 1  illustrates simulation results of padding overhead according to CTC data block sizes suggested in Table 1. 
         [0042]    Specifically,  FIG. 1  illustrates results of comparison between padding overhead according to CTC data block sizes of the conventional IEEE 802.16e and padding overhead according to the CTC data block sizes suggested in the present invention. As can be seen from  FIG. 1 , the CTC data block sizes suggested in the present invention have excellent granularity and significantly reduce padding overhead, compared to the CTC data block sizes of the conventional IEEE 802.16e system. 
         [0043]      FIG. 2  illustrates a preferred embodiment of a data transmission apparatus that transmits data using a Convolutional Turbo Code (CTC) encoder according to the present invention. 
         [0044]    As shown in  FIG. 2 , the data transmission apparatus according to the present invention includes a constituent encoder  210 , a CTC interleaver  220 , and a transmission module (not shown). 
         [0045]    When data bits (A, B) for coding are alternately input to the CTC encoder, the CTC encoder encodes the data bits (A, B) using a Dual Binary Circular Recursive Systematic Convolutional (CRSC) code. Data bits may be input to the CTC encoder on an N EP -bit basis (N EP =2×N bits) or on a N-bit-pair basis. Here, N EP  indicates the CTC data block size (or CTC bit size). 
         [0046]    The CTC encoder may perform encoding in two steps. In the first step, a switch provided in the CTC encoder is located to position  1  so that data bits (A, B) for coding is input to the constituent encoder  210  after an initialization process is performed through a circular operation. In the second step, the switch provided in the CTC encoder is switched to position  2  so that data bits (A, B) interleaved by the CTC interleaver  220  is input to the constituent encoder  210  after an initialization process is performed through a circular operation. 
         [0047]    The CTC encoder may receive a signal from the outside or from an upper layer and may acquire N EP  information having an encodable block size. Here, N EP =2×N, where N is the actual interleaver size and N is CTC data block size/2. 
         [0048]    Data bits (A,B) is alternately input to the constituent encoder  210  receive for encoding. Specifically, the Most Significant Bit (MSB) of a data bit sequence may be input as the data bit A and a next bit may be input as the data bit B. This procedure may be repeated for the entire bit sequence. Here, the MSB of a value is a binary number that most significantly affects the magnitude of the value in a bit-based operation. That is, the MSB is the leftmost bit in a bit sequence representing the value. 
         [0049]    The constituent encoder  210  may encode data bits (A, B) received through two input ports. Here, the constituent encoder  210  may perform encoding in two steps. The constituent encoder  210  may include a first encoder C 1  that encodes data bits (A, B) received through the two input ports and a second encoder C 2  that encodes data bits (A, B) received through the two input ports after being interleaved by the CTC interleaver  220 . How data bits are interleaved through the CTC interleaver  220  is described below in more detail. 
         [0050]    The CTC interleaver  220  may interleave data bits (A, B) received through the two input ports. The CTC interleaver  220  may receive the MSB of a data bit sequence as the data bit A and then receive a next bit thereof as the data bit B. This procedure may be repeated for the entire bit sequence input to the CTC interleaver  220 . 
         [0051]    The CTC interleaver  220  randomizes a data bit sequence inputted in units of a predetermined size to be used for improving codeword distance properties. 
         [0052]    The CTC encoder may sequentially output data bits (A, B) inputted through the two input ports and data bit values encoded through the constituent encoder  210 . For example, the output bits may be “ABY1Y2W1W2” in the case of code rate ⅓. The output bits may be “ABY1Y2” through removal of “W 1 ” and “W 2 ” in the case of code rate ⅓. Here, the output data bits (A, B) correspond to a systematic part and the data bits (Y 1 , W 1 ) or (Y 2 , W 2 ) output through the constituent encoder  210  corresponding to a parity part. The size of data bits output at the parity part may vary depending on code rate. 
         [0053]    The transmission module (not shown) may selectively transmit data bits received through the two input ports, first encoded bits output from the first encoder C 1 , and second encoded bits output from the second encoder C 2 . 
         [0054]    The operation of the CTC interleaver  220  is briefly described as follows. 
         [0055]    The CTC interleaver  220  performs interleaving in two steps according to CTC interleaver parameters P 0 , P 1 , P 2 , and P 3 . 
         [0056]    In the first step, the CTC interleaver  220  performs bit pair swapping of the data bits (A, B) to be coded            
         [0000]      220  swaps the positions of each pair of bits such that if (j mod2 =0) let (B,A)=(A,B) for j=0, 1, 2, . . . , N−1. For example, let the input sequence be u 0 =[(A 0 , B 0 ),(A 1 , B 1 ), (A 2 , B 2 ), . . . , (A N−1 , B N−1 )]. The CTC interleaver  220  performs bit pair swapping on each even symbol in the first step. That is, when u 1  is the bit-pair-swapped sequence, u 1 =[(A 0 , B 0 ),(B 1 , A 1 ), (A 2 , B 2 ), . . . , (B N−1 , A N−1 )]=([u 1 (0), u 1 (1), u 1 (2), . . . , u 1 (N−1)]. 
         [0057]    In the second step, the CTC interleaver  220  generates an interleaving address for swapped bit pair. The CTC interleaver  220  generates an interleaving address P(j) for a jth bit pair, completing the interleaving process. Here, P(j) may provide the address of the u 1  sequence. That is, u 2  (j)=u 1 (P(j)). As a result, u 2 =[(B p(0) , A p(0) , (A p(1) , B p(1) ), (B p(2) , A p(2)), . . . , (A   p(N−1 , B p(N−1) )]. This sequence u 2  may be input to the second encoder. 
         [0058]    The above process may be expressed as follows. 
         [0059]    For j=0, 1, 2, . . . , N−1, 
         [0060]    switch (j mod 4): 
         [0061]    case 0: P(j)=(P 0 ·j+1) mod N: 
         [0062]    case 1: P(j)=(P 0 ·j+1+N/2+P 1 ) mod N: 
         [0063]    case 2: P(j)=(P 0 ·j+1+P 2 ) mod N: 
         [0064]    case 3: P(j)=(P 0 ·j+1+N/2+P 3 ) mod N: 
         [0065]    As described above, the CTC interleaver  220  may perform interleaving by swapping a pair of bits of each even symbol in the first step and generating an interleaving address on the j th  bit pair according to the above expression in the second step. The generated address may be associated with a data block index and the CTC interleaver  220  may perform interleaving using the associated data block index and 4 corresponding CTC interleaver parameters. 
         [0066]    A method for optimizing the CTC interleaver  220  in the IEEE 802.16m system is described below. The CTC interleaver  220  may be designed and optimized according to the CTC data block sizes according to the present invention. 
         [0067]    The CTC interleaver structure in the IEEE 802.16m system may be reused. The CTC interleaver  220  knows CTC interleaver parameters (P 0 , P 1 , P 2 , and P 3 ) corresponding to each data block size. The method may be performed using the 4 CTC interleaver parameters and the data block size in the following manner (Here, N is data block size/2). 
         [0068]    The CTC interleaver may be designed and optimized taking into consideration the two steps of interleaving described above. The method for optimally designing CTC interleaver parameters may include the following steps. 
         [0069]    In the first step, a spatial distance is calculated using a parameter test set. The following parameter test set may be considered, taking into account the CTC interleaver structure. That is, four parameters P 0 , P 1 , P 2 , and P 3  preferably have the following characteristics. 
         [0070]    First, P 0  is relatively prime to N. 
         [0071]    P 1  is a natural number, which is a multiple of 2, such that P 1 =0, 2, 4, . . . , N−2. 
         [0072]    P 2  is a natural number, which is a multiple of 4, such that P 2 =0, 4, 8, . . . , N−4. 
         [0073]    P 3  is a natural number, which is a multiple of 2, such that P 3 =0, 2, 4, . . . , N−2 when P 1 % 4=2 and is a natural number, which is a multiple of 4, such that P 3 =0, 4, 8, . . . , N−4 when P 1 % 4=0. 
         [0074]    Here, %4 represents a modulo-4 operation. 
         [0075]    The spatial distance may be defined as in the following Expression 1. 
         [0076]    [Expression 1] 
         [0000]        S ( j   1   j   2 )= f ( j   1   ,j   2 )+ f (Π( j   1 ),Π( j   2 ))  (1)
 
         [0077]    Here, f(u,v)=min [|u-v|,k-|u-v|] and f(j 1 , j 2 ) denotes a distance before interleaving, f(Π(j 1 ),Π(j 2 )) denotes a distance after interleaving. The spatial distance can be calculated for all index combinations (j 1 , j 2 ). In addition, S min  denotes the minimum spatial distance of the CTC interleaver among spatial distances of the index combinations. 
         [0078]    Specifically, a parameter P 0 , which is relatively prime number to N, is selected in the following manner. 
         [0079]    Preferably, P 0  is an integer which is among relative prime numbers with N. However, for some data block sizes. 
         [0080]    S min  may be sorted by magnitude. CTC interleaving patterns may be generated using all combinations (P 1 , P 2 , P 3 )={(0,0,0), . . . , (2, 0, 0), (2, 0, 2, or 4), . . . , (N−2, N−4, N−2, or N−4) together with P 0 . S min  may be calculated for each combination of (P 1 , P 2 , P 3 ). After minimum spatial distances S min  are calculated respectively for all parameter combinations, the top 5 parameter combinations may be extracted from among parameter combinations having the minimum spatial distances when the parameter combinations are sorted in decreasing order of the minimum spatial distance. The 5 parameter combinations having the minimum spatial distances sorted and extracted in this manner may be used in the second step of the method of designing and optimizing CTC interleaver parameters. 
         [0081]    In the second step, a Return To Zero (RTZ) spatial distance may be calculated using the extracted parameter combinations. The RTZ sequence may be represented as follows taking into consideration CTC encoder generation polynomial equations. 
         [0000]    
       
         
               
               
               
               
             
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 idx1 − idx2 = 1 
                 Weight = 6 
                 13 
               
               
                   
                 idx1 − idx2 = 2 
                 Weight = 7 
                 201 
               
               
                   
                 idx1 − idx2 = 3 
                 Weight = 9 
                 2003 
               
               
                   
                 idx1 − idx2 = 4 
                 Weight = 9 
                 30002 
               
               
                   
                 idx1 − idx2 = 5 
                 Weight = 11 
                 100002 
               
               
                   
                 idx1 − idx2 = 6 
                 Weight = 10 
                 3000001 
               
               
                   
                 idx1 − idx2 = 7 
                 Weight = 12 
                 10000001 
               
               
                   
                 idx1 − idx2 = 7 
                 Weight = 14 
                 20000002 
               
               
                   
                 idx1 − idx2 = 7 
                 Weight = 12 
                 30000003 
               
               
                   
                 idx1 − idx2 = 8 
                 Weight = 14 
                 100000003 
               
               
                   
                 idx1 − idx2 = 9 
                 Weight = 15 
                 2000000001 
               
               
                   
                 idx1 − idx2 = 10 
                 Weight = 17 
                 20000000003 
               
               
                   
                 idx1 − idx2 = 11 
                 Weight = 17 
                 300000000002 
               
               
                   
                 idx1 − idx2 = 12 
                 Weight = 19 
                 1000000000002 
               
               
                   
                 idx1 − idx2 = 13 
                 Weight = 18 
                 30000000000001 
               
               
                   
                 idx1 − idx2 = 14 
                 Weight = 20 
                 100000000000001 
               
               
                   
                 idx1 − idx2 = 14 
                 Weight = 22 
                 200000000000002 
               
               
                   
                 idx1 − idx2 = 14 
                 Weight = 20 
                 300000000000003 
               
             
          
           
               
                   
                 . 
               
               
                   
                 . 
               
               
                   
                 . 
               
               
                   
                   
               
             
          
         
       
     
         [0082]    When the result of interleaving of an input RTZ sequence by applying bit pair swapping to the input RTZ sequence in the first step of the interleaving procedure is also an RTZ sequence, a spatial distance may be calculated for the RTZ sequence. Here, S RTZ,min  is the minimum spatial distance of the RTZ sequence. 
         [0083]    After minimum spatial distances S RTZ,min  are calculated respectively for the each parameter combinations extracted in the first step, the calculated five minimum spatial distances S RTZ,min  may sorted in decreasing order. Parameter combinations having the 5 minimum RTZ spatial distances obtained in this manner may be used in the third step of the method of designing and optimizing CTC interleaver parameters. 
         [0084]    In the third step, the minimum distance is calculated using an Error IMpulse (EIM) method. 
         [0085]    The CTC encoder may perform the EIM method using 2-bit data input to the CTC encoder. In order to calculate the minimum distance d min  using interleaving patterns generated using the parameter combinations, each of the first and second encoders may perform the EIM method twice using the input bits A and B through its the first and second encoders. Thus, the minimum distance of code may be checked using the EIM method. Max-Log-MAP decoding having 64 repetitions may be used for the EIM method. This may be represented by the following algorithm. 
         [0000]    
       
         
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
               
             
           
               
                   
                   
               
             
             
               
                   
                 set A min  = d 1  + 0.5 
               
               
                   
                  for i=1 to n do 
               
             
          
           
               
                   
                 A = d 0  −0.5; 
               
               
                   
                 set[{{circumflex over ( x )} = x}= TRUE 
               
               
                   
                 while [{{circumflex over ( x )} = x}= TRUE] and 
               
               
                   
                 {A≦ A min  −1.0} 
               
             
          
           
               
                   
                 do 
               
             
          
           
               
                   
                 A= A+1.0 ; 
               
               
                   
                 y= {−1,•••, −1, −1+ A, −1, −1,••• 
               
               
                   
                 , −1} 
               
             
          
           
               
                   
                 Where −1+A is in position i; 
               
             
          
           
               
                   
                 ML decoding of y {circumflex over ( x )} ; 
               
               
                   
                 if ({circumflex over ( x )} ≠ x) then [{{circumflex over ( x )} = x}= FALSE]; 
               
             
          
           
               
                   
                  end while 
               
             
          
           
               
                   
                 A min  = A 
               
             
          
           
               
                   
                 end for 
               
             
          
           
               
                 d min  is the integer part of A min   
               
               
                   
               
             
          
         
       
     
         [0086]    After minimum distances d min  are calculated respectively for the each parameter combinations obtained in the second step, the top three minimum distances d min  may be obtained when the calculated minimum distances d min  are sorted in decreasing order. Parameter combinations having the three minimum distances d min  obtained in this manner may be used in the last step, namely, the fourth step, of the method of designing and optimizing CTC interleaver parameters. Here, the minimum distance may represent a measure of performance since performance generally increases as the minimum distance increases. 
         [0087]    In the fourth step, performance is estimated using mother code rates of ½ and ⅓. A BLock Error Rate (BLER) may be estimated after the motor code rate is set to ½ and ⅓ for the parameter combinations extracted in the third step. Parameter combinations which exhibit highest performance for all the code rates ½ and ⅓ may be selected after performance is estimated for each data block size. 
         [0088]    The present invention suggests the following data block sizes and the following CTC interleaver parameters corresponding to the data block sizes according to the present invention described above. Some CTC interleaver parameters of the following Table 3 are changed from those of the Table 2. 
         [0000]    
       
         
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 Index 
                 N EP   
                 P 0   
                 P 1   
                 P 2   
                 P 3   
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 1 
                 48 
                 5 
                 0 
                 0 
                 0 
               
               
                   
                 2 
                 64 
                 11 
                 12 
                 0 
                 12 
               
               
                   
                 3 
                 72 
                 11 
                 18 
                 0 
                 18 
               
               
                   
                 4 
                 80 
                 7 
                 4 
                 32 
                 36 
               
               
                   
                 5 
                 88 
                 13 
                 36 
                 36 
                 32 
               
               
                   
                 6 
                 96 
                 13 
                 24 
                 0 
                 24 
               
               
                   
                 7 
                 104 
                 7 
                 4 
                 8 
                 48 
               
               
                   
                 8 
                 120 
                 11 
                 30 
                 0 
                 34 
               
               
                   
                 9 
                 128 
                 13 
                 46 
                 44 
                 30 
               
               
                   
                 10 
                 136 
                 13 
                 58 
                 4 
                 58 
               
               
                   
                 11 
                 144 
                 11 
                 6 
                 0 
                 6 
               
               
                   
                 12 
                 152 
                 11 
                 38 
                 12 
                 74 
               
               
                   
                 13 
                 160 
                 13 
                 68 
                 76 
                 64 
               
               
                   
                 14 
                 176 
                 17 
                 52 
                 68 
                 32 
               
               
                   
                 15 
                 184 
                 13 
                 2 
                 0 
                 2 
               
               
                   
                 16 
                 192 
                 7 
                 58 
                 48 
                 10 
               
               
                   
                 17 
                 200 
                 11 
                 76 
                 0 
                 24 
               
               
                   
                 18 
                 208 
                 11 
                 10 
                 32 
                 42 
               
               
                   
                 19 
                 216 
                 11 
                 54 
                 56 
                 2 
               
               
                   
                 20 
                 232 
                 11 
                 70 
                 60 
                 58 
               
               
                   
                 21 
                 240 
                 13 
                 60 
                 0 
                 60 
               
               
                   
                 22 
                 248 
                 13 
                 6 
                 84 
                 46 
               
               
                   
                 23 
                 256 
                 11 
                 64 
                 8 
                 8 
               
               
                   
                 24 
                 264 
                 13 
                 72 
                 68 
                 8 
               
               
                   
                 25 
                 272 
                 13 
                 82 
                 44 
                 38 
               
               
                   
                 26 
                 288 
                 17 
                 74 
                 72 
                 2 
               
               
                   
                 27 
                 296 
                 13 
                 0 
                 84 
                 64 
               
               
                   
                 28 
                 304 
                 13 
                 130 
                 112 
                 46 
               
               
                   
                 29 
                 312 
                 11 
                 32 
                 124 
                 108 
               
               
                   
                 30 
                 320 
                 17 
                 84 
                 108 
                 132 
               
               
                   
                 31 
                 328 
                 17 
                 148 
                 160 
                 76 
               
               
                   
                 32 
                 344 
                 17 
                 160 
                 116 
                 52 
               
               
                   
                 33 
                 352 
                 17 
                 106 
                 56 
                 50 
               
               
                   
                 34 
                 360 
                 17 
                 40 
                 132 
                 128 
               
               
                   
                 35 
                 368 
                 19 
                 88 
                 0 
                 172 
               
               
                   
                 36 
                 376 
                 13 
                 110 
                 92 
                 14 
               
               
                   
                 37 
                 384 
                 11 
                 96 
                 48 
                 144 
               
               
                   
                 38 
                 400 
                 19 
                 142 
                 0 
                 142 
               
               
                   
                 39 
                 408 
                 23 
                 42 
                 20 
                 46 
               
               
                   
                 40 
                 416 
                 17 
                 102 
                 132 
                 178 
               
               
                   
                 41 
                 424 
                 17 
                 138 
                 56 
                 18 
               
               
                   
                 42 
                 432 
                 17 
                 126 
                 92 
                 74 
               
               
                   
                 43 
                 440 
                 19 
                 48 
                 20 
                 144 
               
               
                   
                 44 
                 456 
                 17 
                 184 
                 0 
                 48 
               
               
                   
                 45 
                 464 
                 17 
                 62 
                 52 
                 114 
               
               
                   
                 46 
                 472 
                 19 
                 40 
                 104 
                 28 
               
               
                   
                 47 
                 480 
                 13 
                 120 
                 60 
                 180 
               
               
                   
                 48 
                 488 
                 17 
                 140 
                 92 
                 220 
               
               
                   
                 49 
                 496 
                 17 
                 194 
                 0 
                 58 
               
               
                   
                 50 
                 512 
                 19 
                 64 
                 52 
                 124 
               
               
                   
                 51 
                 528 
                 17 
                 36 
                 196 
                 100 
               
               
                   
                 52 
                 544 
                 19 
                 222 
                 248 
                 134 
               
               
                   
                 53 
                 576 
                 23 
                 76 
                 220 
                 92 
               
               
                   
                 54 
                 592 
                 23 
                 96 
                 172 
                 36 
               
               
                   
                 55 
                 608 
                 23 
                 288 
                 244 
                 140 
               
               
                   
                 56 
                 624 
                 23 
                 286 
                 220 
                 70 
               
               
                   
                 57 
                 640 
                 23 
                 84 
                 296 
                 236 
               
               
                   
                 58 
                 656 
                 23 
                 24 
                 300 
                 52 
               
               
                   
                 59 
                 688 
                 19 
                 320 
                 4 
                 324 
               
               
                   
                 60 
                 704 
                 19 
                 52 
                 76 
                 256 
               
               
                   
                 61 
                 720 
                 23 
                 130 
                 156 
                 238 
               
               
                   
                 62 
                 736 
                 29 
                 126 
                 208 
                 270 
               
               
                   
                 63 
                 752 
                 23 
                 26 
                 24 
                 230 
               
               
                   
                 64 
                 768 
                 29 
                 252 
                 0 
                 8 
               
               
                   
                 65 
                 800 
                 23 
                 150 
                 216 
                 150 
               
               
                   
                 66 
                 816 
                 29 
                 342 
                 132 
                 42 
               
               
                   
                 67 
                 832 
                 23 
                 354 
                 164 
                 198 
               
               
                   
                 68 
                 848 
                 29 
                 234 
                 388 
                 82 
               
               
                   
                 69 
                 864 
                 29 
                 216 
                 272 
                 180 
               
               
                   
                 70 
                 880 
                 29 
                 410 
                 328 
                 218 
               
               
                   
                 71 
                 912 
                 29 
                 14 
                 264 
                 94 
               
               
                   
                 72 
                 928 
                 23 
                 446 
                 392 
                 186 
               
               
                   
                 73 
                 944 
                 23 
                 356 
                 68 
                 332 
               
               
                   
                 74 
                 960 
                 23 
                 186 
                 61 
                 10 
               
               
                   
                 75 
                 976 
                 31 
                 134 
                 124 
                 366 
               
               
                   
                 76 
                 992 
                 29 
                 358 
                 480 
                 362 
               
               
                   
                 77 
                 1024 
                 29 
                 320 
                 236 
                 324 
               
               
                   
                 78 
                 1056 
                 31 
                 86 
                 380 
                 250 
               
               
                   
                 79 
                 1088 
                 31 
                 432 
                 216 
                 524 
               
               
                   
                 80 
                 1152 
                 31 
                 534 
                 372 
                 246 
               
               
                   
                 81 
                 1184 
                 31 
                 2 
                 568 
                 94 
               
               
                   
                 82 
                 1216 
                 31 
                 368 
                 584 
                 524 
               
               
                   
                 83 
                 1248 
                 31 
                 88 
                 404 
                 608 
               
               
                   
                 84 
                 1280 
                 29 
                 152 
                 8 
                 24 
               
               
                   
                 85 
                 1312 
                 31 
                 214 
                 160 
                 506 
               
               
                   
                 86 
                 1376 
                 31 
                 218 
                 20 
                 670 
               
               
                   
                 87 
                 1408 
                 29 
                 474 
                 584 
                 118 
               
               
                   
                 88 
                 1440 
                 41 
                 288 
                 556 
                 672 
               
               
                   
                 89 
                 1472 
                 29 
                 164 
                 424 
                 76 
               
               
                   
                 90 
                 1504 
                 31 
                 254 
                 416 
                 474 
               
               
                   
                 91 
                 1536 
                 31 
                 34 
                 564 
                 710 
               
               
                   
                 92 
                 1600 
                 31 
                 454 
                 216 
                 234 
               
               
                   
                 93 
                 1632 
                 29 
                 334 
                 564 
                 66 
               
               
                   
                 94 
                 1664 
                 31 
                 156 
                 568 
                 56 
               
               
                   
                 95 
                 1696 
                 37 
                 722 
                 136 
                 698 
               
               
                   
                 96 
                 1728 
                 31 
                 176 
                 152 
                 516 
               
               
                   
                 97 
                 1760 
                 23 
                 646 
                 484 
                 850 
               
               
                   
                 98 
                 1824 
                 41 
                 774 
                 548 
                 898 
               
               
                   
                 99 
                 1856 
                 47 
                 576 
                 212 
                 728 
               
               
                   
                 100 
                 1888 
                 39 
                 342 
                 596 
                 798 
               
               
                   
                 101 
                 1920 
                 43 
                 318 
                 556 
                 778 
               
               
                   
                 102 
                 1952 
                 35 
                 94 
                 144 
                 686 
               
               
                   
                 103 
                 1984 
                 43 
                 84 
                 488 
                 92 
               
               
                   
                 104 
                 2048 
                 31 
                 2 
                 332 
                 622 
               
               
                   
                 105 
                 2112 
                 43 
                 96 
                 720 
                 980 
               
               
                   
                 106 
                 2176 
                 37 
                 428 
                 976 
                 28 
               
               
                   
                 107 
                 2304 
                 41 
                 16 
                 484 
                 888 
               
               
                   
                 108 
                 2368 
                 47 
                 228 
                 440 
                 724 
               
               
                   
                 109 
                 2432 
                 43 
                 452 
                 888 
                 96 
               
               
                   
                 110 
                 2496 
                 43 
                 0 
                 208 
                 528 
               
               
                   
                 111 
                 2560 
                 53 
                 264 
                 488 
                 824 
               
               
                   
                 112 
                 2624 
                 47 
                 378 
                 1092 
                 1250 
               
               
                   
                 113 
                 2752 
                 37 
                 430 
                 880 
                 970 
               
               
                   
                 114 
                 2816 
                 31 
                 624 
                 704 
                 400 
               
               
                   
                 115 
                 2880 
                 53 
                 184 
                 996 
                 1336 
               
               
                   
                 116 
                 2944 
                 41 
                 338 
                 660 
                 646 
               
               
                   
                 117 
                 3008 
                 43 
                 916 
                 1136 
                 912 
               
               
                   
                 118 
                 3072 
                 53 
                 184 
                 824 
                 1368 
               
               
                   
                 119 
                 3200 
                 43 
                 1382 
                 632 
                 1086 
               
               
                   
                 120 
                 3264 
                 49 
                 142 
                 828 
                 1354 
               
               
                   
                 121 
                 3328 
                 37 
                 258 
                 28 
                 1522 
               
               
                   
                 122 
                 3392 
                 51 
                 460 
                 56 
                 1608 
               
               
                   
                 123 
                 3456 
                 43 
                 170 
                 920 
                 1518 
               
               
                   
                 124 
                 3520 
                 57 
                 776 
                 1232 
                 1012 
               
               
                   
                 125 
                 3648 
                 49 
                 132 
                 720 
                 276 
               
               
                   
                 126 
                 3712 
                 41 
                 1328 
                 772 
                 1036 
               
               
                   
                 127 
                 3776 
                 53 
                 772 
                 256 
                 408 
               
               
                   
                 128 
                 3840 
                 53 
                 92 
                 1124 
                 476 
               
               
                   
                 129 
                 3904 
                 51 
                 664 
                 200 
                 64 
               
               
                   
                 130 
                 3968 
                 57 
                 1296 
                 760 
                 1360 
               
               
                   
                 131 
                 4096 
                 55 
                 148 
                 808 
                 308 
               
               
                   
                 132 
                 4160 
                 79 
                 214 
                 308 
                 262 
               
               
                   
                 133 
                 4224 
                 59 
                 14 
                 668 
                 1474 
               
               
                   
                 134 
                 4288 
                 57 
                 662 
                 1516 
                 42 
               
               
                   
                 135 
                 4352 
                 59 
                 2052 
                 712 
                 1804 
               
               
                   
                 136 
                 4416 
                 59 
                 1342 
                 1968 
                 1562 
               
               
                   
                 137 
                 4544 
                 65 
                 1380 
                 1068 
                 1036 
               
               
                   
                 138 
                 4608 
                 67 
                 954 
                 1140 
                 1566 
               
               
                   
                 139 
                 4672 
                 67 
                 410 
                 1020 
                 114 
               
               
                   
                 140 
                 4736 
                 59 
                 2 
                 956 
                 458 
               
               
                   
                 141 
                 4800 
                 53 
                 66 
                 24 
                 2 
               
               
                   
                   
               
             
          
         
       
     
         [0089]    Compared to Table 2, in the case of index 16, the data block size (or bit size) is 192 and the CTC interleaver parameters P 0 , P 1 , P 2 , and P 3  are changed to 7, 58, 48, and 10. In the case of index 34, the data block size is 360 and the CTC interleaver parameters P 0 , P 1 , P 2 , and P 3  are changed to 17, 40, 132, and 128, respectively. In the case of index 42, the data block size is 432 and the CTC interleaver parameters P 0 , P 1 , P 3 , and P 4  are changed to 17, 126, 92, and 74, respectively. In the case of index 74, the data block size is 960 and the CTC interleaver parameters P 0 , P 1 , P 2 , and P 3  are changed to 23, 186, 61, and 10, respectively. In the case of index 101, the data block size is 1920 and the CTC interleaver parameters P 0 , P 1 , P 2 , and P 3  are changed to 43, 318, 556, and 778, respectively. In the case of index 115, the data block size is 2880 and the CTC interleaver parameters P 0 , P 1 , P 2 , and P 3  are changed to 53, 184, 996, and 1336, respectively. In the case of index 128, the data block size is 3840 and the CTC interleaver parameters P 0 , P 1 , P 2 , and P 3  are changed to 53, 92, 1124, and 476, respectively. The changed portions of Table 3 are shown in the following Table 4. 
         [0090]    That is, Table 4 illustrates information of some data block sizes whose CTC interleaver parameters have been changed from those of Table 3. 
         [0000]    
       
         
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 4 
               
               
                   
                   
               
               
                   
                 Index 
                 N EP   
                 P 0   
                 P 1   
                 P 2   
                 P 3   
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 16 
                 192 
                 7 
                 58 
                 48 
                 10 
               
               
                   
                 34 
                 360 
                 17 
                 40 
                 132 
                 128 
               
               
                   
                 42 
                 432 
                 17 
                 126 
                 92 
                 74 
               
               
                   
                 74 
                 960 
                 23 
                 186 
                 61 
                 10 
               
               
                   
                 101 
                 1920 
                 43 
                 318 
                 556 
                 778 
               
               
                   
                 115 
                 2880 
                 53 
                 184 
                 996 
                 1336 
               
               
                   
                 128 
                 3840 
                 53 
                 92 
                 1124 
                 476 
               
               
                   
                   
               
             
          
         
       
     
         [0091]    As shown in Table 4, new CTC interleaver parameters are provided for the data block sizes 192, 360, 432, 960, 1920, 2880, and 3840 in order to improve performance. The remaining CTC interleaver parameters may be identical to those of the IEEE 802.16e system to achieve downward compatibility (i.e., to support the legacy system). 
         [0092]    The following Table 5 is created by removing 34 data block sizes and corresponding CTC interleaver parameters from those of Table 3 and adding 42 new data block sizes and corresponding CTC interleaver parameters. 
         [0000]    
       
         
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 5 
               
               
                   
                   
               
               
                   
                 Index 
                 N EP   
                 P 0   
                 P 1   
                 P 2   
                 P 3   
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 1 
                 48 
                 5 
                 0 
                 0 
                 0 
               
               
                   
                 2 
                 64 
                 11 
                 12 
                 0 
                 12 
               
               
                   
                 3 
                 72 
                 11 
                 18 
                 0 
                 18 
               
               
                   
                 4 
                 80 
                 7 
                 4 
                 32 
                 36 
               
               
                   
                 5 
                 88 
                 13 
                 36 
                 36 
                 32 
               
               
                   
                 6 
                 96 
                 13 
                 24 
                 0 
                 24 
               
               
                   
                 7 
                 104 
                 7 
                 4 
                 8 
                 48 
               
               
                   
                 8 
                 120 
                 11 
                 30 
                 0 
                 34 
               
               
                   
                 9 
                 128 
                 13 
                 46 
                 44 
                 30 
               
               
                   
                 10 
                 136 
                 13 
                 58 
                 4 
                 58 
               
               
                   
                 11 
                 144 
                 11 
                 6 
                 0 
                 6 
               
               
                   
                 12 
                 152 
                 11 
                 38 
                 12 
                 74 
               
               
                   
                 13 
                 160 
                 13 
                 68 
                 76 
                 64 
               
               
                   
                 14 
                 176 
                 17 
                 52 
                 68 
                 32 
               
               
                   
                 15 
                 184 
                 13 
                 2 
                 0 
                 2 
               
               
                   
                 16 
                 192 
                 7 
                 58 
                 48 
                 10 
               
               
                   
                 17 
                 200 
                 11 
                 76 
                 0 
                 24 
               
               
                   
                 18 
                 208 
                 11 
                 10 
                 32 
                 42 
               
               
                   
                 19 
                 216 
                 11 
                 54 
                 56 
                 2 
               
               
                   
                 20 
                 232 
                 11 
                 70 
                 60 
                 58 
               
               
                   
                 21 
                 240 
                 13 
                 60 
                 0 
                 60 
               
               
                   
                 22 
                 248 
                 13 
                 6 
                 84 
                 46 
               
               
                   
                 23 
                 256 
                 11 
                 64 
                 8 
                 8 
               
               
                   
                 24 
                 264 
                 13 
                 72 
                 68 
                 8 
               
               
                   
                 25 
                 272 
                 13 
                 82 
                 44 
                 38 
               
               
                   
                 26 
                 288 
                 17 
                 74 
                 72 
                 2 
               
               
                   
                 27 
                 296 
                 13 
                 0 
                 84 
                 64 
               
               
                   
                 28 
                 304 
                 13 
                 130 
                 112 
                 46 
               
               
                   
                 29 
                 312 
                 11 
                 32 
                 124 
                 108 
               
               
                   
                 30 
                 320 
                 17 
                 84 
                 108 
                 132 
               
               
                   
                 31 
                 328 
                 17 
                 148 
                 160 
                 76 
               
               
                   
                 32 
                 344 
                 17 
                 160 
                 116 
                 52 
               
               
                   
                 33 
                 352 
                 17 
                 106 
                 56 
                 50 
               
               
                   
                 34 
                 360 
                 17 
                 40 
                 132 
                 128 
               
               
                   
                 35 
                 368 
                 19 
                 88 
                 0 
                 172 
               
               
                   
                 36 
                 376 
                 13 
                 110 
                 92 
                 14 
               
               
                   
                 37 
                 384 
                 11 
                 96 
                 48 
                 144 
               
               
                   
                 38 
                 400 
                 19 
                 142 
                 0 
                 142 
               
               
                   
                 39 
                 416 
                 17 
                 102 
                 132 
                 178 
               
               
                   
                 40 
                 432 
                 17 
                 126 
                 92 
                 74 
               
               
                   
                 41 
                 440 
                 19 
                 48 
                 20 
                 144 
               
               
                   
                 42 
                 456 
                 17 
                 184 
                 0 
                 48 
               
               
                   
                 43 
                 472 
                 19 
                 40 
                 104 
                 28 
               
               
                   
                 44 
                 480 
                 13 
                 120 
                 60 
                 180 
               
               
                   
                 45 
                 496 
                 17 
                 194 
                 0 
                 58 
               
               
                   
                 46 
                 512 
                 19 
                 64 
                 52 
                 124 
               
               
                   
                 47 
                 528 
                 17 
                 36 
                 196 
                 100 
               
               
                   
                 48 
                 544 
                 19 
                 222 
                 248 
                 134 
               
               
                   
                 49 
                 552 
                 13 
                 198 
                 180 
                 190 
               
               
                   
                 50 
                 568 
                 19 
                 102 
                 140 
                 226 
               
               
                   
                 51 
                 584 
                 21 
                 74 
                 20 
                 214 
               
               
                   
                 52 
                 600 
                 31 
                 12 
                 272 
                 28 
               
               
                   
                 53 
                 608 
                 23 
                 288 
                 244 
                 140 
               
               
                   
                 54 
                 624 
                 23 
                 286 
                 220 
                 70 
               
               
                   
                 55 
                 640 
                 23 
                 84 
                 296 
                 236 
               
               
                   
                 56 
                 656 
                 23 
                 24 
                 300 
                 52 
               
               
                   
                 57 
                 664 
                 23 
                 272 
                 220 
                 60 
               
               
                   
                 58 
                 680 
                 19 
                 48 
                 240 
                 144 
               
               
                   
                 59 
                 696 
                 31 
                 252 
                 216 
                 48 
               
               
                   
                 60 
                 712 
                 25 
                 214 
                 180 
                 286 
               
               
                   
                 61 
                 720 
                 23 
                 130 
                 156 
                 238 
               
               
                   
                 62 
                 736 
                 29 
                 126 
                 208 
                 270 
               
               
                   
                 63 
                 752 
                 23 
                 26 
                 24 
                 230 
               
               
                   
                 64 
                 768 
                 29 
                 252 
                 0 
                 8 
               
               
                   
                 65 
                 776 
                 29 
                 100 
                 196 
                 140 
               
               
                   
                 66 
                 800 
                 23 
                 150 
                 216 
                 150 
               
               
                   
                 67 
                 824 
                 29 
                 130 
                 332 
                 42 
               
               
                   
                 68 
                 848 
                 29 
                 234 
                 388 
                 82 
               
               
                   
                 69 
                 872 
                 29 
                 408 
                 300 
                 316 
               
               
                   
                 70 
                 888 
                 25 
                 414 
                 84 
                 414 
               
               
                   
                 71 
                 912 
                 29 
                 14 
                 264 
                 94 
               
               
                   
                 72 
                 936 
                 25 
                 272 
                 168 
                 400 
               
               
                   
                 73 
                 960 
                 53 
                 62 
                 12 
                 2 
               
               
                   
                 74 
                 984 
                 31 
                 142 
                 40 
                 342 
               
               
                   
                 75 
                 1000 
                 29 
                 290 
                 148 
                 446 
               
               
                   
                 76 
                 1024 
                 29 
                 320 
                 236 
                 324 
               
               
                   
                 77 
                 1048 
                 27 
                 424 
                 212 
                 416 
               
               
                   
                 78 
                 1072 
                 35 
                 290 
                 228 
                 390 
               
               
                   
                 79 
                 1096 
                 23 
                 178 
                 392 
                 430 
               
               
                   
                 80 
                 1112 
                 33 
                 38 
                 244 
                 550 
               
               
                   
                 81 
                 1136 
                 37 
                 170 
                 276 
                 134 
               
               
                   
                 82 
                 1160 
                 31 
                 314 
                 348 
                 222 
               
               
                   
                 83 
                 1184 
                 31 
                 2 
                 568 
                 94 
               
               
                   
                 84 
                 1216 
                 31 
                 368 
                 584 
                 524 
               
               
                   
                 85 
                 1248 
                 31 
                 88 
                 404 
                 608 
               
               
                   
                 86 
                 1280 
                 29 
                 152 
                 8 
                 24 
               
               
                   
                 87 
                 1312 
                 31 
                 214 
                 160 
                 506 
               
               
                   
                 88 
                 1336 
                 39 
                 2 
                 168 
                 646 
               
               
                   
                 89 
                 1368 
                 29 
                 570 
                 348 
                 574 
               
               
                   
                 90 
                 1392 
                 31 
                 218 
                 484 
                 446 
               
               
                   
                 91 
                 1424 
                 31 
                 676 
                 124 
                 184 
               
               
                   
                 92 
                 1448 
                 33 
                 254 
                 372 
                 158 
               
               
                   
                 93 
                 1480 
                 31 
                 32 
                 716 
                 736 
               
               
                   
                 94 
                 1504 
                 31 
                 254 
                 416 
                 474 
               
               
                   
                 95 
                 1536 
                 31 
                 34 
                 564 
                 710 
               
               
                   
                 96 
                 1560 
                 29 
                 300 
                 248 
                 568 
               
               
                   
                 97 
                 1600 
                 31 
                 454 
                 216 
                 234 
               
               
                   
                 98 
                 1640 
                 33 
                 164 
                 432 
                 748 
               
               
                   
                 99 
                 1672 
                 35 
                 164 
                 368 
                 700 
               
               
                   
                 100 
                 1712 
                 41 
                 4 
                 848 
                 332 
               
               
                   
                 101 
                 1752 
                 31 
                 314 
                 656 
                 666 
               
               
                   
                 102 
                 1784 
                 33 
                 886 
                 888 
                 518 
               
               
                   
                 103 
                 1824 
                 41 
                 774 
                 548 
                 898 
               
               
                   
                 104 
                 1864 
                 33 
                 504 
                 444 
                 664 
               
               
                   
                 105 
                 1896 
                 35 
                 936 
                 940 
                 832 
               
               
                   
                 106 
                 1920 
                 43 
                 318 
                 556 
                 778 
               
               
                   
                 107 
                 1952 
                 35 
                 94 
                 144 
                 686 
               
               
                   
                 108 
                 2000 
                 37 
                 290 
                 692 
                 638 
               
               
                   
                 109 
                 2048 
                 31 
                 2 
                 332 
                 622 
               
               
                   
                 110 
                 2096 
                 39 
                 400 
                 688 
                 68 
               
               
                   
                 111 
                 2144 
                 29 
                 298 
                 252 
                 610 
               
               
                   
                 112 
                 2192 
                 39 
                 1074 
                 148 
                 710 
               
               
                   
                 113 
                 2232 
                 29 
                 240 
                 496 
                 1100 
               
               
                   
                 114 
                 2280 
                 41 
                 474 
                 376 
                 814 
               
               
                   
                 115 
                 2328 
                 41 
                 254 
                 884 
                 1054 
               
               
                   
                 116 
                 2368 
                 47 
                 228 
                 440 
                 724 
               
               
                   
                 117 
                 2432 
                 43 
                 452 
                 888 
                 96 
               
               
                   
                 118 
                 2496 
                 43 
                 0 
                 208 
                 528 
               
               
                   
                 119 
                 2560 
                 53 
                 264 
                 488 
                 824 
               
               
                   
                 120 
                 2624 
                 47 
                 378 
                 1092 
                 1250 
               
               
                   
                 121 
                 2752 
                 37 
                 430 
                 880 
                 970 
               
               
                   
                 122 
                 2816 
                 31 
                 624 
                 704 
                 400 
               
               
                   
                 123 
                 2880 
                 43 
                 720 
                 360 
                 540 
               
               
                   
                 124 
                 2944 
                 41 
                 338 
                 660 
                 646 
               
               
                   
                 125 
                 3008 
                 43 
                 916 
                 1136 
                 912 
               
               
                   
                 126 
                 3072 
                 53 
                 184 
                 824 
                 1368 
               
               
                   
                 127 
                 3200 
                 43 
                 1382 
                 632 
                 1086 
               
               
                   
                 128 
                 3264 
                 49 
                 142 
                 828 
                 1354 
               
               
                   
                 129 
                 3328 
                 37 
                 258 
                 28 
                 1522 
               
               
                   
                 130 
                 3392 
                 51 
                 460 
                 56 
                 1608 
               
               
                   
                 131 
                 3456 
                 43 
                 170 
                 920 
                 1518 
               
               
                   
                 132 
                 3520 
                 57 
                 776 
                 1232 
                 1012 
               
               
                   
                 133 
                 3648 
                 49 
                 132 
                 720 
                 276 
               
               
                   
                 134 
                 3712 
                 41 
                 1328 
                 772 
                 1036 
               
               
                   
                 135 
                 3776 
                 53 
                 772 
                 256 
                 408 
               
               
                   
                 136 
                 3840 
                 53 
                 92 
                 1124 
                 476 
               
               
                   
                 137 
                 3904 
                 51 
                 664 
                 200 
                 64 
               
               
                   
                 138 
                 3968 
                 57 
                 1296 
                 760 
                 1360 
               
               
                   
                 139 
                 4096 
                 55 
                 148 
                 808 
                 308 
               
               
                   
                 140 
                 4160 
                 79 
                 214 
                 308 
                 262 
               
               
                   
                 141 
                 4224 
                 59 
                 14 
                 668 
                 1474 
               
               
                   
                 142 
                 4288 
                 57 
                 662 
                 1516 
                 42 
               
               
                   
                 143 
                 4352 
                 59 
                 2052 
                 712 
                 1804 
               
               
                   
                 144 
                 4416 
                 59 
                 1342 
                 1968 
                 1562 
               
               
                   
                 145 
                 4544 
                 65 
                 1380 
                 1068 
                 1036 
               
               
                   
                 146 
                 4608 
                 67 
                 954 
                 1140 
                 1566 
               
               
                   
                 147 
                 4672 
                 67 
                 410 
                 1020 
                 114 
               
               
                   
                 148 
                 4736 
                 59 
                 2 
                 956 
                 458 
               
               
                   
                 149 
                 4800 
                 53 
                 66 
                 24 
                 2 
               
               
                   
                   
               
             
          
         
       
     
         [0093]    As shown in Table 5, the 42 newly added data block sizes are 552, 568, 584, 600, 664, 680, 696, 712, 776, 824, 872, 888, 936, 984, 1000, 1048, 1072, 1096, 1112, 1136, 1160, 1336, 1368, 1392, 1424, 1448, 1480, 1560, 1640, 1672, 1712, 1752, 1784, 1864, 1896, 2000, 2096, 2144, 2192, 2232, 2280, and 2328. 
         [0094]    Table 6 shows 39 data block sizes, which are preferable for use in interleaving among data block sizes shown in Table 5, and CTC interleaver parameters values corresponding to the 39 data block sizes. 
         [0000]    
       
         
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 6 
               
               
                   
                   
               
               
                   
                 Index 
                 N EP   
                 P 0   
                 P 1   
                 P 2   
                 P 3   
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 1 
                 48 
                 5 
                 0 
                 0 
                 0 
               
               
                   
                 2 
                 64 
                 11 
                 12 
                 0 
                 12 
               
               
                   
                 3 
                 72 
                 11 
                 18 
                 0 
                 18 
               
               
                   
                 4 
                 80 
                 7 
                 4 
                 32 
                 36 
               
               
                   
                 5 
                 88 
                 13 
                 36 
                 36 
                 32 
               
               
                   
                 6 
                 96 
                 13 
                 24 
                 0 
                 24 
               
               
                   
                 7 
                 104 
                 7 
                 4 
                 8 
                 48 
               
               
                   
                 8 
                 120 
                 11 
                 30 
                 0 
                 34 
               
               
                   
                 9 
                 136 
                 13 
                 58 
                 4 
                 58 
               
               
                   
                 10 
                 152 
                 11 
                 38 
                 12 
                 74 
               
               
                   
                 11 
                 176 
                 17 
                 52 
                 68 
                 32 
               
               
                   
                 12 
                 200 
                 11 
                 76 
                 0 
                 24 
               
               
                   
                 13 
                 216 
                 11 
                 54 
                 56 
                 2 
               
               
                   
                 14 
                 248 
                 13 
                 6 
                 84 
                 46 
               
               
                   
                 15 
                 288 
                 17 
                 74 
                 72 
                 2 
               
               
                   
                 16 
                 320 
                 17 
                 84 
                 108 
                 132 
               
               
                   
                 17 
                 352 
                 17 
                 106 
                 56 
                 50 
               
               
                   
                 18 
                 400 
                 19 
                 142 
                 0 
                 142 
               
               
                   
                 19 
                 456 
                 17 
                 184 
                 0 
                 48 
               
               
                   
                 20 
                 512 
                 19 
                 64 
                 52 
                 124 
               
               
                   
                 21 
                 568 
                 19 
                 102 
                 140 
                 226 
               
               
                   
                 22 
                 640 
                 23 
                 84 
                 296 
                 236 
               
               
                   
                 23 
                 720 
                 23 
                 130 
                 156 
                 238 
               
               
                   
                 24 
                 800 
                 23 
                 150 
                 216 
                 150 
               
               
                   
                 25 
                 912 
                 29 
                 14 
                 264 
                 94 
               
               
                   
                 26 
                 1024 
                 29 
                 320 
                 236 
                 324 
               
               
                   
                 27 
                 1160 
                 31 
                 314 
                 348 
                 222 
               
               
                   
                 28 
                 1312 
                 31 
                 214 
                 160 
                 506 
               
               
                   
                 29 
                 1448 
                 33 
                 254 
                 372 
                 158 
               
               
                   
                 30 
                 1640 
                 33 
                 164 
                 432 
                 748 
               
               
                   
                 31 
                 1864 
                 33 
                 504 
                 444 
                 664 
               
               
                   
                 32 
                 2096 
                 39 
                 400 
                 688 
                 68 
               
               
                   
                 33 
                 2328 
                 41 
                 254 
                 884 
                 1054 
               
               
                   
                 34 
                 2624 
                 47 
                 378 
                 1092 
                 1250 
               
               
                   
                 35 
                 2944 
                 41 
                 338 
                 660 
                 646 
               
               
                   
                 36 
                 3328 
                 37 
                 258 
                 28 
                 1522 
               
               
                   
                 37 
                 3776 
                 53 
                 772 
                 256 
                 408 
               
               
                   
                 38 
                 4224 
                 59 
                 14 
                 668 
                 1474 
               
               
                   
                 39 
                 4800 
                 53 
                 66 
                 24 
                 2 
               
               
                   
                   
               
             
          
         
       
     
         [0095]    The CTC interleaver parameter tables may be expressed according to data block sizes as described above with reference to Tables 2 to 6 according to the CTC interleaver design and optimization procedure according to the present invention. 
         [0096]      FIGS. 3 and 4  illustrate comparison between BLER performance of a CTC interleaver using data block sizes and CTC interleaver parameters suggested in the present invention and BLER performance of the conventional IEEE 802.16e CTC interleaver for each mother code rate. 
         [0097]    Specifically,  FIGS. 3 and 4  illustrate comparison between a Signal to Noise Ratio (SNR) required for the data block size when mother code rate is ½ and ⅓ and when BLER is 10%, 1%, and 0.1%. Performance increases as the data block size increases since the SNR decreases as the data block size increases as shown in  FIGS. 3 and 4 . This indicates that the performance of the CTC interleaver according to the present invention is better than the CTC interleaver of the conventional IEEE 802.16m system using small data block sizes. 
         [0098]    The apparatus and method for transmitting data using the CTC interleaver have been described above. An apparatus and method for receiving data using the CTC interleaver corresponding to the transmission apparatus and method are described below with reference to the above description. 
         [0099]    The apparatus for receiving data using the CTC interleaver may include a first decoder that decodes received values of data bits input through two input terminals and outputs a Log Likelihood Ratio (LLR) of first decoded bits, a CTC interleaver that interleaves received values of the input data bits using 4 CTC interleaver parameters P 0 , P 1 , P 2 , and P 3  corresponding to the size of the input data bits, and a second decoder that decodes the received value of the interleaved data bits and outputs a Log Likelihood Ratio (LLR) of second decoded bits. The functions and processes of the interleaver of the CTC decoder are identical to those of the interleaver of the CTC encoder. Thus, a detailed description of the interleaver of the CTC decoder is omitted herein. 
         [0100]    The above embodiments are provided by combining components and features of the present invention in specific forms. The components or features of the present invention should be considered optional unless explicitly stated otherwise. The components or features may be implemented without being combined with other components or features. The embodiments of the present invention may also be provided by combining some of the components and/or features. The order of the operations described above in the embodiments of the present invention may be changed. Some components or features of one embodiment may be included in another embodiment or may be replaced with corresponding components or features of another embodiment. It will be apparent that claims which are not explicitly dependent on each other can be combined to provide an embodiment or new claims can be added through amendment after this application is filed. 
         [0101]    The embodiments of the present invention can be implemented by hardware, firmware, software, or any combination thereof. In the case where the present invention is implemented by hardware, an embodiment of the present invention may be implemented by one or more Application Specific Integrated Circuits (ASICs), Digital Signal Processors (DSPs), Digital Signal Processing Devices (DSPDs), Programmable Logic Devices (PLDs), Field Programmable Gate Arrays (FPGAs), processors, controllers, microcontrollers, microprocessors, or the like. 
         [0102]    In the case where the present invention is implemented by firmware or software, the embodiments of the present invention may be implemented in the form of modules, processes, functions, or the like which perform the features or operations described above. Software code can be stored in a memory unit so as to be executed by a processor. The memory unit may be located inside or outside the processor and can communicate data with the processor through a variety of known means. 
         [0103]    As is apparent from the above description, an apparatus and method for a transmitting end to transmit data using a Convolutional Turbo Code (CTC) encoder in a mobile communication system according to the present invention have a variety of advantages. 
         [0104]    For example, it is possible to significantly reduce padding overhead by applying additional input data bit sizes suggested in the present invention. 
         [0105]    The reduction of the padding overhead also enables more efficient data transmission. 
         [0106]    The apparatus and method for transmitting data using a CTC interleaver according to the present invention can be used industrially. 
         [0107]    Those skilled in the art will appreciate that the present invention may be embodied in other specific forms than those set forth herein without departing from the spirit and essential characteristics of the present invention. The above description is therefore to be construed in all aspects as illustrative and not restrictive. The scope of the invention should be determined by reasonable interpretation of the appended claims and all changes coming within the equivalency range of the invention are intended to be embraced in the scope of the invention.