Optimum Design Of Polar Codes In Distributed Scenario

Distributed communication network, including distributed antenna system and wireless sensor network, is of great interest in wireless communication field recently. It has wide applications in various communication scenarios. However, as the number of access nodes and the amount of user data increase, the network load increases dramatically. In order to mitigate the network load and efficiently utilize the limited wireless spectrum resources, it is necessary to employ the source coding to compress the data, and use the channel coding to ensure the reliable transmission of information in the network.This paper studies two typical distributed scenarios. The first is the distributed antenna system, which can cost-effectively expand the network coverage and save network energy consumption. It is a development trend of network architecture. The second is the collaborative relay system, which is the basic component of distributed network. It can guarantee the reliable transmission of data and has very important research value.Polar codes, which were proposed by Erdal Arikan, have been proven to achieve the symmetric capacity of any binary-input discrete memoryless channel. They have perfect theoretical analysis, low encoding/decoding complexity and can be applied to a variety of communication scenarios. Therefore, polar codes show a promising prospect in theoretical research and practical applications. Based on Polar codes, this paper studies the data compression and reliable data transmission in distributed scenarios, including the following three aspects:(1) For lossless source coding, it is proved that the multi-level polar source coding can achieve the entropy of arbitrary discrete source.Furthermore, a low-complexity lossless source coding scheme based on polar codes is proposed. For lossy source coding, a low-complexity multi-level based polar coded quantization (PCQ) scheme is proposed.What's more, an efficient upper bound of encoding rate for a given distortion is derived.(2) In order to reduce the transmission data rate of fronthaul link in the distributed antenna systems, this paper proposes an efficient time-domain compression scheme combining linear prediction coding and lossless polar source coding. Firstly, an improved structure of linear prediction coding (LPC) is proposed to remove the in-band redundancy of LTE/LTE-Advanced signal. Secondly, a label sequence is utilized to represent the information indicating the index of large and small amplitude signal. Lastly, a multi-level lossless polar source coding is utilized to compress the small-amplitude signal and the label sequence.Simulation results demonstrate that the proposed compression algorithm can achieve high compression ratio (1/5) with EVM < 2% and outperform the traditional algorithms in terms of compression ratio or EVM. In addition, the proposed scheme is more flexible in bandwidth configurations.(3) For the scenario when the channel between the source node and the relay node is in poor condition, this paper proposes a soft decoded-and-forward (DF) scheme based on a CRC-aided list cancellation decoder (CASCL) and proposes a method to calculate the soft information in CASCL. The proposed scheme solves the error-floor problem caused by the iterative message propagation in the factor graph in belief propagation decoder and soft cancellation decoder. Moreover,this paper proposes a semi-dynamic CASCL decoder to efficiently reduce the complexity of relay node. Simulation results show that the proposed scheme outperforms the soft DF based on low-density parity-check codes and the soft DF with belief propagation or soft cancellation decoder.In addition, a relaying scheme based on Wyner-Ziv polar source coding is proposed and the proposed scheme is proved to achieve the compression-and-forward capacity of half-duplex relay channel when the modulation signals obey the geometrically Gaussian-like distribution.Above all, this paper establishes a theoretical framework of source coding based on multi-level polar codes, solves the problem of date compression in the distributed antenna system and perfects the theory of reliable transmission in half-duplex relay system based on polar codes.