Link Level Performance Assessment of Reliability-Based HARQ Schemes in LTE

This paper discusses two approaches of adapting the size of Hybrid-ARQ (HARQ) retransmissions in a 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) uplink system. One goal of communication systems is to achieve a reliable transmission with a minimum utilization of the channel. In case of a decoding error of the first transmission LTE adapts the coderate by using Incremental Redundancy (IR). We focus on the adaptation of the retransmission size in terms of physical resources by using information 1) of the channel, namely the signal-to-noise ratio (SNR) or 2) reliability information coming from the decoder output, namely the bit error probability (BEP). Both approaches will be compared to the HARQ system used in LTE uplink in terms of throughput performance measurements in a link-level simulation chain including a single bit feedback and a 2 bit multilevel ACK/NAK.