A novel selective-relaying protocol for cooperative IR-UWB communications with PPM

In this paper, we propose a novel cooperation strategy for Impulse-Radio Ultra-Wideband (IR-UWB) communication systems with binary Pulse Position Modulation (PPM). Unlike Decode-and-Forward (DF) strategies where a group of PPM symbols, or at least one PPM symbol, is decoded and forwarded to the receiver, the proposed scheme inspects the PPM slots in a sequential manner. In particular, only the UWB pulses that are received at the relay with a sufficient level of fidelity are retransmitted in subsequent PPM slots. This technique limits cooperation to only one symbol duration while avoiding any form of joint decoding at the relay and destination nodes. The proposed scheme corresponds to a selective-relaying protocol where the relay imposes a certain level of selectivity on the symbols to be retransmitted. The error performance of the proposed scheme is evaluated theoretically. Based on this performance analysis, we derived an optimal pulse selection strategy at the relay.