Performance Analysis of a HARQ Algorithm with Two-Hop Relaying

The relay-assisted Hybrid ARQ (RHARQ) technique is regarded as a mean of further improving the coverage and reliability performance of future wireless networks. Most of the algorithms implementing this approach use the source-destination link, besides the source-relay and relay-destination links, and employ either Chase combining or space-time coding, thus requiring more resource-consuming processing at destination for synchronization and decoding the transmitted data. This paper studies the reliability, spectral efficiency and delay performance of a Repetition Redundancy RHARQ algorithm that does not use the direct source-destination link, thus requiring less processing and simpler synchronization at destination. The analysis is made over block-faded Rayleigh channels using decode&forward relaying and practical modulation and channel code. The results show that the RHARQ algorithm provides smaller block-error rate (BLER) and delay at low signal-to-noise ratios (SNR) and/or ensures a target BLERt at SNRs much smaller than the noncooperative HARQ algorithm that uses only the source-destination link, at the expense of smaller spectral efficiency.