Design of Rateless Polar Accumulate Tornado Codes Using EXIT Chart for UAV Communications

Abstract

This paper proposes Tornado codes based on the concatenation of Polar codes, Luby Transform (LT) codes, and Accumulator, referred to as rateless Polar Accumulate Tornado (PA-Tornado) codes for possible applications to unmanned aerial vehicle (UAV) communications, where the channels are assumed to be highly varying. The accumulator is added after the LT codes to avoid direct connection of LT check-nodes (CND) to the channels. The effectiveness of the proposed PA - Tornado codes is analyzed using Extrinsic Information Transfer (EXIT) chart under the binary erasure channels (BEC) due to its simplicity. We reveal the mechanism of rateless capability of the proposed codes, which is not the case of traditional codes, as well as the significant contribution of the accumulator to bring the MI of LT to close to (1,1) point. With the proposed rateless PA-Tornado codes, the EXIT tunnel, which is originaly closed at <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\epsilon=0.67$</tex> , suddenly open by performing internal iteration of accumulator. We also provide a suitable degree distribution having minimum EXIT chart gap, but practical for UAV communications.