An ASIC fast decoder of rate compatible modulation and its application in wireless communication system

Abstract

Rate Compatible Modulation (RCM) is a new rate adaptation scheme in wireless communication system, which can achieve very high spectrum efficiency both in additive white Gaussian noise (AWGN) channel and fading channel. But the high decoding complexity of RCM hinders its application in practical communication systems. This paper introduces an Application Specific Integrated Circuit (ASIC) based fast decoder of RCM to implement belief propagation (BP) algorithm in logarithm domain. Though BP algorithm has natural parallel characteristic, a partial-parallel full-pipelined architecture is designed to achieve a tradeoff between hardware resource and processing speed. In order to reduce the computing complexity and improve the throughput of the decoder, we adopt some reduced algorithms, such as piecewise function approximation, lookup tables, fixed-point computing and etc. We build a communication system to test our ASIC decoder in AWGN channel and IEEE 802.11a fading channel. The original RCM is a rateless code modulation scheme, which can get high spectral efficiency, but is not feasible in some communication systems (such as deep space communications system) for too long transmission delay. In this paper we propose a non-rateless RCM scheme and implement it both in AWGN channel and fading channel. Through testing we confirm that the performance of our proposed scheme is very close to the original rateless scheme, but can greatly reduce transmission time.