An LTE implementation of a novel strategy for the Gaussian half-duplex relay channel

This paper presents a practical implementation of a novel three-message transmission strategy for the Gaussian half-duplex relay channel based on Turbo code superposition encoding and interference-aware successive interference cancellation. The impact of finite block-length and discrete input constellations on the Block Error Rate (BLER) performance is evaluated through extensive simulations on an LTE simulation test bench and compared to the theoretical performance of asymptotically large block-length Gaussian codes. For the practically relevant BLER value of 10^-2 and by varying the direct source-destination link strength, the maximum spectral efficiency gap between theory and the presented implementation is found to be of 0.458 bits/dim when the strength of the source-destination and relay-destination links is the same and of 0.681 bits/dim when the relay-destination link is 5 dB stronger than the source-destination link. These values indicate that practical implementations of high-performing HD relay techniques for future Heterogeneous Network deployments are within reach. A comparison with a baseline strategy without direct source-destination transmission, as currently proposed in the LTE standard for relay scenarios, shows superior performances of the proposed scheme. In particular, the rate gain is of a factor of 2 when the strength of the source-destination and relay-destination links is the same and of a factor of 1.2 when the relay-destination link is 5 dB stronger than the source-destination link, thereby highlighting the critical importance of physical-layer cooperation in broadband wireless systems.