All-digital Impulse Radio Formui/isi-resilient Multi-user Communications over Frequency-selective Multipath Channels

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 continuoustime 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 Multiple Input Multiple Output (MIMO) PPMIRMA scheme, and derive its discrete-time equivalent model. Relying on a time-division-duplex access protocol and orthogonal user codes, we design composite linear and non-linear receivers for the downlink. The linear step eliminates MUI deterministically and accounts for frequency-selective multipath, while a Maximum Likelihood (ML) receiver performs symbol detection.