Rateless Coding Schemes Using Polar Codes: Truly “No” Rates?

In this paper, aiming to achieve rate adaptation for the rateless coding (RC) schemes of polar codes, we explore their throughput efficiency and optimize a series of rates that are set in two types of RC schemes. First, the RC scheme with incremental freezing (IF-RC) decoding is analyzed from the perspective of rate matching. Then, a new RC scheme based on extending codes and copying information bits (termed EC-RC) is developed in detail. Moreover, to overcome the drawback of an undefined rate sequence in RC transmission, rate optimization strategies are separately proposed for both IF-RC and EC-RC by maximizing throughput efficiency with dynamic programming. Closed-form expressions of throughput for these two RC methods are derived as a consequence. The optimization procedure can be realized in practice with low complexity. Finally, the numerical results and analyses demonstrate that rate adaptation of polar-coded RC can be achieved along with maximum throughput by our proposed strategies over both AWGN channels and Rayleigh fading channels. The two optimized RC schemes provide higher throughput efficiency than other existing rateless codes.