Novel decoding methods of constant weight coding for molecular communications

Abstract

Molecular communications via diffusion (MCvD) is a popular research area thanks to its potential applications, mostly in nano communications. Despite many recent publications on MCvD, the studies on error correction/channel coding for molecular communications are limited. Low weight channel codes have been proposed in the literature due to their energy efficiency and ISI mitigation. We add the constant weight condition on top of being low weight for MCvD channel codes, since the information of all codewords having the same weight can be utilized at the receiver. Moreover, encoding simplicity of Constant Low Weight Codes (CLWC) compared to the conventional coding schemes makes them appealing for MCvD, considering nanodevice limitations. This paper focuses on the decoding strategies for CLWC at the receiver side. Threshold and sorting-based decoders for molecular communications are reviewed and two different novel decoding mechanisms for CLWC are proposed. Iterative sorting decoder is a decision-feedback heuristic method that iteratively calculates the ISI from a better estimation at each step. The second proposed method is the super trellis decoder, which is a maximum likely sequence estimator. Outer states in the trellis denote the number of total weights in a sequence, whereas inner states represent the memory of the ISI channel. Both proposed methods increase the communication quality significantly by lowering transmission error probabilities. Simulation comparisons with existing methods show performance superiority of the proposed algorithms. Depending on the capability of the receiver and the availability of the channel state information, both methods are viable to be used with CLWC.