Biorthogonal pulse shape modulation for IR-UWB systems over fading channels

In this paper we propose a novel M-ary biorthogonal pulse shape modulation scheme for an Impulse radio ultra wideband (IR-UWB) system transmitting over lognormal fading channels. Our proposed modulation scheme enables different transmission rates for a fixed number of orthogonal pulses M/2, while the symbol period T_s is constant. In our transmission scheme information bits are mapped into N pulses (N symbols), using M/2 orthogonal pulses and their negates. The N generated pulses are superimposed to form one pulse that will be transmitted over the channel. The transmission rate provided by this scheme is N(log₂ M/N)/T_s and is maximized at N = M/4 (i.e., one bit per orthogonal pulse). We consider maximum ratio combing (MRC)-RAKE receiver to demodulate N symbols. For the proposed scheme we derive a closed-form expression for symbol error probability and an upper bound on symbol error rate, using Wilkinsonpsilas method. Given the same channel delay spread, our scheme provides a better error performance and higher throughput than that of pulse position modulation (PPM) scheme.