All-digital PPM impulse radio for multiple-access through frequency-selective multipath

Impulse radio (IR) is an ultra-wideband system with attractive features for baseband asynchronous multiple access (MA), multimedia services, and tactical wireless communications. 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 introduce a novel continuous-time PPM-IRMA model, deduce a low-complexity approximate one, and derive its discrete-time equivalent model. Relying on a time-division-duplex access protocol and orthogonal user codes, we design composite linear/non-linear receivers for the downlink. The linear step eliminates MUI deterministically and accounts for frequency-selective multipath while a maximum likelihood (ML) receiver achieves symbol detection.