1. Field of the Invention
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.
2. Discussion of the Related Art
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.
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.
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.
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.
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.
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.
Table 1 shows each data block size and values of corresponding CTC interleaver parameters P0, P1, P2, and P3 in the conventional IEEE 802.16e system.
TABLE 1indexNEPP0P1P2P31485000272111801839613240244144116065192748247262401360060728817747228360119009093841196481441043213108010811480131206018012960536212213192043643008241428804372036054015384031824161648005366242
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.
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.