In this paper we present and analyze link adaptation schemes that maximize the average throughput for two-hop relay network with single and multiple source terminals. The relay terminals are constrained by half-duplex assumption and a limit on the maximum total transmit power. We present two practical link adaptation schemes, asymmetric rate transmission (ART) for single-source and layered space-time ART (LST-ART) for multiple-source scenario. ART adapts the modulation modes and the transmission duration in the two hops separately such that the throughput is maximized. For ease of implementation the transmission duration of the hops are selected from a predefined look-up table (LUT). LST-ART allows for simultaneous transmission from the source terminals to the relay and from the relay to the destination through spatial multiplexing (SM) and it also adapts the transmission duration for each hop based on the combined data rate than can be achieved in that hop. Analytical expressions are derived for average spectral efficiency for both single and multiple source scenarios. From the performance analysis, ART is shown to offer higher throughput compared to that of symmetric rate transmission with fixed hop duration by a gap of 2dB between their achievable spectral efficiency.
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