One of the main problems in ultra wide band (UWB) impulse radio (IR) systems is the need to cope efficiently with multiple access interference (MAI). As outlined recently in the literature, this can be achieved by modeling MAI as a Gaussian mixture (GM) random process and deriving the receiver in accordance with a maximum likelihood paradigm. Depending on the chosen context, both rake and chip-matched solutions can be identified. In this paper we compare different solutions, generalize them to a QAM context, and investigate their implementation complexity and robustness to impulsive interference. We also investigate efficient methods to lower the computational demand.

One of the main concerns in ultra wide band (UWB) impulse radio (IR) technology is the presence of severe multiple access interference (MAI). Efficient receivers should therefore be capable of deleting, or at least mitigating, this effect. Based on the observation that MAI has an impulsive structure, we model it as a Gaussian mixture random process, to derive the optimum receiver accordingly. By carefully simplifying parts of the resulting algorithm, we are able to propose a receiver approach which is efficient in mitigating MAI, while having low computational complexity. Its effectiveness is compared to state of the art approaches by simulations in a realistic scenario.

Recently, innovative multicarrier schemes have been proposed that exploit the transmission of chirp-shaped waves e/sup -j2/spl pi/ct2/ by optimally choosing the chirp parameter c on the basis of the channel characteristics and are more robust to time-varying channels than ordinary OFDM schemes. This concept was applied to continuous-time and to discrete-time systems. In the present paper, we aim at developing those ideas using the affine Fourier transform (AFT), which is a very general formulation of chirp transforms. We present a multicarrier modulation based upon the discrete form of the AFT that is therefore inherently discrete and strictly invertible. Moreover, it allows to define a circular prefix concept that is coherent with the chirp nature of the transmission. The system can be efficiently implemented by adding a simple phase-correction block to standard OFDM modulators/demodulators and can effectively combat interchannel interference when the propagation channel is made of few multipath components affected by independent frequency offsets. Our discrete-time multicarrier scheme is an improved version of Martone's approach (as we also show by simulation results), and exhibits analogous characteristics to Barbarossa's continuous-time system.