Variable-Rate Capacity-Approaching LDPC Codes for HF Communications

Pandya, Nishit and Honary, Bahram (2006) Variable-Rate Capacity-Approaching LDPC Codes for HF Communications. In: The 10th Institution of Engineering and Technology International Conference on Ionospheric Radio Systems & Techniques (IRST 2006). IET Press, London, UK, pp. 123-127. ISBN 0863416594

Abstract

The HF propagation channel involves several interrelated phenomena that results in a highly variable medium, which poses a challenge in designing and implementing effective high speed digital communications systems for HF band. The reliability of HF communication is affected by time-varying propagation conditions of HF channel that demands requirement for coding schemes with adaptive protection capabilities, to combat the ever-changing channel conditions and thus improve the reliability and performance of the channel. The novel idea introduced in this paper, proposes a variable forward error correction scheme using capacity-approaching 'low density parity check' codes that enables the switching between LDPC codes of constant length but variable rates (1/4, 1/2, & 9/10) to provide variable-error protection based on the channel condition at any given time. These codes have been simulated over a Rayleigh fading channel and their capacity approaching performance using the sum-product decoding algorithm is shown.