Exploiting frequency correlation in LTE to reduce HARQ memory

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. Although the performance advantage is very attractive, implementing HARQ is challenging with emerging high throughput communication systems such as LTE and LTE-A. Specifically, a large amount of data needs to be stored whenever there is a retransmission. Knowing that LTE/LTE-A systems would provide Gbps or hundreds of Mbps, a straightforward implementation would require around 14 Mbit memory as HARQ buffer. With cost and power limited wireless terminals, the available memory size to support HARQ is a strict and challenging constraint. Hence, it is essential to find efficient techniques to minimize the memory footprint for storing erroneous packets with marginal or, preferably, no degradation. In the context of LTE systems, we propose a novel method to reduce the memory footprint for HARQ systems. This method has been evaluated with a fully fledged practical LTE simulation chain with MIMO transmissions. Compared to state-of-the-art solutions, we show a promising memory compression factor that is close to 5, whereas communication performance degradation is marginal.