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Impulse radio (IR) is an ultra-wideband system with attractive features for baseband asynchronous multiple-access (MA), multimedia services, tactical wireless communications and networking. Implemented with analog components, the continuous-time IRMA model utilizes pulse-position modulation (PPM) and random time-hopping codes to alleviate multipath effects and suppress multiuser interference (MUI). We develop here a novel all-digital IRMA scheme and its discrete-time equivalent model that relies on pulse-amplitude modulation (PAM) and judiciously designed orthogonal user codes to eliminate MUI deterministically and account for frequency-selective multipath in the downlink. We also design a time-division-duplex access protocol and low-complexity linear multichannel receivers that we compare and test both analytically and by simulation.
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Martret et al. (2002) studied this question.