A Hybrid UWB Modulation Design Compatible for Both Coherent and Transmit-Reference Receivers

TR Image
BER versus SNR curves of coherent H-IR receiver versus theoretical performance in an AWGN channel.

In a pulsed UWB system, either coherent receivers or transmit-reference (TR) receivers can be used to demodulate the signals. For coherent receivers, which are typically based on a Rake Structure, the large number of resolvable multipaths is a major challenge for channel estimation and receiver complexity. TR receivers can effectively collect energy from all the received multipath components with much smaller complexity, but show reduced performance. Current modulation formats are tuned to either coherent or TR receivers, but cannot interoperate with both of them. In this paper, we propose an innovative modulation scheme that enables the useage of TR and coherent recievers in the same wireless network. The modulation allows demodulation by TR receivers, while at the same time enabling a coherent receiver to fully exploit all available signal energy, and actually to perform slightly better (by 1.8 dB) than a coherent receiver working with conventional BPSK modulation; this additional gain can be interpreted as a coding gain of a trellis-coded modulation scheme. The scheme thus allows the network designers to trade off performance vs. complexity in the receivers, while allowing a uniform signaling (modulation) scheme for all transmitters.