Abstract
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.
Highlights
In terms of some communication scenarios, the channel states may not be constantly known or estimated by the transmitter due to the time-varying nature of wireless channels
We see that the performance of EC-rateless coding (RC) can match well with that of direct polar code designed for that signal-to-noise ratio (SNR) and outperform Incremental freezing (IF)-RC obviously
In this paper, two types of rateless coding schemes of polar codes are separately explored for the sake of rate-seamless transmission in unknown channels
Summary
In terms of some communication scenarios, the channel states may not be constantly known or estimated by the transmitter due to the time-varying nature of wireless channels. To achieve the goal of efficient transmission, some flexible coding and modulation techniques have been proposed, such as adaptive coding and modulation (ACM). ACM only has a cluster of limited choices of rate combination schemes so that the alternative rates used to adapt to the changing channel states are discrete; on the other hand, the best combination of modulation and coding schemes selected by the transmitter is usually determined by the estimated channel quality, but it may be challenging to attain accurate estimation in time-varying channels. To achieve a rate-seamless transmission and avoid the channel estimation requirement, rateless coding (RC) can serve as a flexible technique for the situation where the real-time parameters of communication channels are unknown to the transmitter. Different from the rate-fixed codes, rateless codes are regarded as a family of codes with
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