NTC-HARQ: Network–Turbo-Coding Based HARQ Protocol for Wireless Broadcasting System

Abstract

Wireless broadcasting systems employ multiple retransmissions to guarantee the correct reception of each packet. The traditional hybrid automatic retransmission request (HARQ) protocol retransmits one packet per slot. Hence, a large amount of retransmissions is required to correctly receive all the packets, which leads to low spectrum efficiency. In this paper, we propose a Network-coding-and-distributed-Turbo-Coding-based type-III HARQ (NTC-HARQ) protocol, including an xoring Network Coding Combined (XNCC) retransmission strategy at the access node (AN) and a joint network-turbo decoding (JNTD) strategy at the user equipment (UE). Specifically, to reduce the overall number of retransmissions, lost packets of different UEs are network coding (NC) combined at the AN by utilizing the XNCC strategy. The soft information of the lost packet at each UE can be recovered from the received network-coded retransmission packet by using the proposed xoring soft network decoder. The recovered soft information of the UE's lost packet is combined with the local undecodable soft information of the same packet to form a distributed turbo code. A Chase-combining-based distributed turbo decoder is proposed to perform turbo decoding, which introduces coding gain and improves packet-error-rate (PER) performance. Theoretical analyses and simulation results show that the average-number-of-transmission performance of the proposed NTC-HARQ protocol outperforms that of the XNCC-based type-I HARQ protocol, the traditional NC-based HARQ protocol, and the JNTD-based protocol.