1. Field of the Invention
The present invention relates to a method and an apparatus for signal transmission/reception in a communication system using a Hybrid Automatic Repeat reQuest (HARQ) scheme.
2. Description of the Related Art
Next generation communication systems are developing towards systems capable of providing a high speed large-capacity service to Mobile Stations (MSs). Representative examples of the next generation communication systems include an Institute of Electrical and Electronics Engineers (IEEE) 802.16 communication system, a Mobile Worldwide Interoperability for Microwave Access (WiMAX) communication system, and an IEEE 802.11 communication system. The Mobile WiMAX communication system is a communication system based on the IEEE 802.16 communication system, and the IEEE 802.16 communication system is a communication system using an IEEE 802.16 standard.
In the next generation communication systems, use of Low Density Parity Check (LDPC) codes is taken into consideration to support high speed large-capacity data transmission/reception, because it is possible to achieve parallel implementation of the LDPC codes, which makes it possible to implement a decoder having a throughput higher than other channels codes, such as turbo codes or convolutional codes.
Hereinafter, a conventional parity check matrix for structured LDPC codes will be described with reference to FIG. 1.
FIG. 1 illustrates a conventional parity check matrix for structured LDPC codes.
Referring to FIG. 1, structured LDPC codes may be generated using a parity check matrix having a size of mL×nL. That is, each row of the parity check matrix for structured LDPC codes includes m square matrixes each having a size of  and each column of the parity check matrix for structured LDPC codes includes n square matrixes each having a size of  wherein the square matrix may be a zero matrix or a permutation matrix. As used herein, each row or each column of the permutation matrix includes a weight of one (1), wherein the weight corresponds to the number of elements having a value (e.g. 1) other than zero (0). In FIG. 1, Pm,n refers to a square matrix located at a position at which the mth square matrix row and the nth square matrix column intersect when the parity check matrix includes m square matrix rows and n square matrix columns.
According to the parity check matrix for structured LDPC codes as described above with reference to FIG. 1, it is possible to generate LDPC codes having various lengths by using only one parity check matrix, through a change of the size (i.e. the vale ) of each square matrix in the parity check matrix. Hereinafter, the scheme of changing the size of the square matrix to generate LDPC codes having different lengths will be referred to as a “lifting scheme”.
Meanwhile, in the next generation communication systems, various schemes including a Hybrid Automatic Repeat reQuest (HARQ) scheme and an Adaptive Modulation and Coding (AMC) scheme have been proposed to support high speed large capacity data transmission/reception. To use the HARQ scheme and the AMC scheme, it may be necessary to support various code rates.
However, the structured LDPC codes are disadvantageous in view of the code rates. That is, since the structured LDPC codes are generated by using a parity check matrix having a fixed size, it is relatively difficult to change the length of the structured LDPC codes, in comparison with other channel codes. Therefore, the structured LDPC codes are not flexible in view of the coding rate.