Soft Iterative Decoding Algorithms for Rateless Codes in Satellite Systems

Abstract

The satellite system is one of the most efficient means for broadcasting due to its wide service coverage as well as the fact that it can provide high data rate services by using high frequency bands. However, there are a number of problems in the satellite system, such as a long round trip delay (RTD) and heterogeneity of the channel conditions of the earth stations. Even though utilizing adaptive coding and modulation (ACM) is almost mandatory for the satellite systems using high frequency bands due to the serious rain fading, the long RTD makes it difficult to quickly respond to channel quality information, resulting in a decrease in the efficiency of ACM. A high heterogeneity of earth stations caused by a wide service coverage also makes it difficult to apply a uniform transmission mode, and thus satellite systems require receiver-dependent transmission modes. A rateless code can be an effective means to compensate for these disadvantages of satellite systems compared to terrestrial wireless systems. This paper presents soft iterative decoding algorithms for efficient application of rateless codes in satellite systems and demonstrates that rateless codes can be effectively used for hybrid automatic repeat request schemes.

Physical layer rateless codes for the SATCOM on‐the‐move system with blockage

“…To show the robustness of rateless codes on the channel with blockages, we compare the performance of raptor codes and some HARQ schemes. The type‐I and type‐II HARQ schemes 22 are considered here. In type‐I HARQ, the same codeword is retransmitted whenever NACK is received and the optimized rate‐1/2 irregular LDPC codes with σ = 0.977 in Chung 25 is taken.…”

“…Then, the parts of the generated parity blocks of LT codes are transmitted at the following transmissions if the previous decoding is unsuccessful. The joint iterative decoding algorithm 22 is also applied to improve performance. It can be seen that the above type‐II HARQ scheme is almost the same to SR coding, only that its outer code‐rate is not as high as that of conventional SR codes ( normally , ≥ 0.95) and several retransmissions of parity symbols may be required.…”

“…The resulting codes are essentially the so‐called SR codes, 11 which are further combined with hybrid automatic repeat request (HARQ) schemes. They also provide a cross‐layer coding scheme, 22 where the encoding order of LDPC codes and SLT codes are exchanged. Physical layer LT codes are employed to combat the blockage of SOTM systems, 23 where the bit‐error‐rate (BER) performance of LT codes and LDPC codes are compared by computer simulations.…”

Design of Improved BP Decoders and Corresponding LT Code Degree Distribution for AWGN Channels

“…However, it is only useful for RA rateless codes. A parallel soft iterative decoding algorithm was proposed for satellite systems [9]. Similar to the study in [7], it is only effective when combining LDPC codes with LT codes in the physical layer.…”