A Novel Modulation Diversity Assisted Ultrawideband Communication System

In this paper, a novel modulation diversity assisted (MDA) ultrawideband (UWB) communication system is proposed. Pulse position modulation and pulse amplitude modulation are applied to successive transmitted pulses alternately. The resulting modulation diversity helps to overcome channel estimation difficulties in typical UWB channels and permits low complexity receiver design. If every two consecutive pulses are grouped together, some connections with a transmitted reference (TR) system are demonstrated. But significant advantages of the proposed system are observed in smooth spectrum and increased data rate. Utilizing statistical properties of the modulated signals and inherent diversity, different receivers are designed for such a system. A conceptual receiver performs symbol detection using neighboring received signal to construct the template, while an advanced receiver uses a block of received signals to obtain a better template. The advanced receiver may continue to improve the template as ongoing detected symbols are available. A maximum likelihood estimator is also derived as a performance benchmark. The conceptual receiver shows slightly better performance than a conventional TR receiver while the advanced receiver shows comparable performance of the receiver using a maximum likelihood template estimator. Performance of the advanced receiver is studied both analytically and numerically. In a case of severe multipath channel distortion that results in interference between received signals from consecutive transmitted pulses, a corresponding template estimator and different receivers are also presented with detection performance numerically studied.