A comparative study on outage probabilities of decode-and-forward and lossy-forward relay techniques

The primary objective of this paper is to make a performance comparison in terms of outage probability between decode-and-forward with joint decoding (DF-JD) and lossy-forward (LF) techniques. With DF-JD, only if the relay's received information sequence can be decoded with an arbitrarily low error probability, it is forwarded to the destination. On the contrary, with LF, the relay node always forwards decoded information sequence to the destination even if a decoding error is detected. Interleaving is used at relay and joint decoding is utilized at the destination to exploit the source-relay correlation for both techniques. The outage probability of conventional DF system with maximum ratio combining (DF-MRC) performed at the destination is also presented. Asymmetric statistical properties of the fading variations for each link are taken into account. It is shown that regardless of the presence of line-of-sight component, the outage probability with LF relay system is significantly smaller than that with DF-JD and DF-MRC relay systems. The impact of the per-link spectrum efficiency, representing the modulation multiplicity and channel coding rate, on outage probability is also investigated. It is found that, given that the specified per-link spectrum efficiency is satisfied, LF relay system always achieves lower outage performance than that with DF-JD and DF-MRC systems. The accuracy of the analytical results are verified by a series of Monte Carlo simulations.