A scalable family of unitary and differential space-time codes for UWB communications

In this paper, we consider the problem of differential space-time (ST) block coding in the context of impulse-radio ultra-wideband (IR-UWB) communications with two transmit antennas and Pulse Position Modulation (PPM). We propose a novel family of codes where the information is encoded differentially through the number of transmitted pulses, the positions of these pulses and the locations of the non-idle symbol durations within each ST block. In order to maintain a low complexity of the UWB transmitter, unipolar transmissions are ensured by avoiding all forms of amplitude-domain encoding. The proposed scheme provides a full scalability capability where depending on the value taken by the scale parameter Θ, different levels of compromise between data rates and error rates (along with the decoding complexity) can be achieved. Finally, the proposed scheme lends itself to optimal detection with cross-correlation receivers that can be implemented in the analog domain in the absence of all forms of channel state information at the transmitter and receiver sides.