Transmitted Reference Ultra Wideband Transceivers for Multiuser Communication

Abstract : A conventional transmitted reference (TR) modulation scheme is an effective means to combat severe multipath distortion in an ultra wideband (UWB) system, significantly relaxing the equalization requirements at a cost in performance. However, it suffers from multiple access and other interference, and a rate loss of 50%. In this paper we extend TR modulation to the multiuser case, while boosting data transmission to near full rate. To enable multiple access, the proposed multiuser TR (MTR) scheme assigns a pair of frame rate pseudo-random (PN) sequences to each user, modulating the amplitude of each of two consecutive pulses, respectively. Given a user's reference-pulse modulating PN sequence, mean-based estimation is proposed to obtain a clean waveform template, which is appropriate for both pulseamplitude (PAM) or pulse-position modulation (PPM). Along with interference reduction, this method enables arbitrarily small spacing of pulse pairs, leading to near full rate transmission. Using the waveform template and the data-pulse modulating PN sequence, any reference pulse interference is subtracted and data demodulation carried out. Aided by the PN sequences, the proposed estimation and data detection scheme is able to mitigate both inter-pulse and multi-access interference. To further reduce interference a time-hopping code can also be employed. Waveform estimation and bit error rate analysis are provided for the multi-user case, and confirmed with simulations. Substantial detection improvements over conventional TR detectors are observed.

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