Iterative decoder-aided equalization of STANAG 4539 high data rate waveforms

The area of digital communications has undergone a significant transformation in the last ten years due largely to the discovery of turbo codes. The "turbo" concept can be applied to more than just forward error-correction (FEC) schemes. For example, waveforms developed for the high frequency (HF) band typically place an interleaver between the FEC scheme and the transmitted symbols. The purpose of this interleaver is to decorrelate the errors caused by slow fading multipath channels encountered on HF. If no interleaver were used, most FEC schemes would become ineffective (e.g. convolutional codes). The "turbo" concept can be applied to HF waveforms which employ an interleaver by iteratively exchanging soft information between the equalizer and the FEC decoder. This paper investigates the possible performance improvements of applying this technique to a family of high data rate HF waveforms defined in NATO STANAG 4539. Different data rates and interleaver sizes are simulated on a variety of channels to determine the benefits. Instead of standard bit error rate performance curves, block error rate curves are provided since most modern day applications send groups of bits (packets) and expect each group to be received error free. Following this, latency and computational complexity are discussed to assess the feasibility and benefits of applying this technique to improve on-air performance of HF systems.