Reduction of HARQ memory in low mobility LTE systems

Hybrid ARQ (HARQ) combines Automatic Repeat Request (ARQ) and Forward Error Correction (FEC) to exploit information from erroneous packets after retransmissions. Due to its superior reliability, HARQ became a crucial component of several important 3G and 4G systems such as Long Term Evolution (LTE) and LTE-Advanced. Although the performance advantage is very attractive, implementing HARQ is challenging with emerging high throughput communication systems. Knowing that LTE and LTE-A systems would provide Gbps or hundreds of Mbps, a straightforward implementation would require around 10 Mbit memory for a HARQ buffer. With cost and power-limited wireless terminals, the available memory size to support HARQ requires an efficient implementation. In this paper we propose a novel method to exploit the time coherence of the wireless channel in order to reduce the memory storage for HARQ. This method has been evaluated with a full LTE MIMO simulation chain. Compared to state-of-the-art solutions, we show a promising memory compression factor close to 4, whereas performance degradation is marginal.

I. Introduction

Hybrid ARQ (HARQ) is a transmission technique that combines Automatic Repeat Request (ARQ) and Forward Error Correction (FEC). Due to its error correcting power and high reliability it is currently one of the key features for cellular standards such as LTE and LTE-Advanced.