Ultra wide bandwidth spread spectrum impulse radio for wireless multi-access communications
by Nejib Benmedhedi Boubaker
Ph.D. Electrical and Electronic Engineering
x, 109 leaves : ill. ; 30 cm
Ultra-wideband (UWB) is a wireless transmission technology that allows high data rate with low power consumption for short distances. UWB technology has recently gone through some revolutionary changes, including the legalization of the technology in the US for communication systems. To become truly ubiquitous, UWB research has to address several challenges such as multipath, multi-access and narrow-band interferences....[ Read more ]
Ultra-wideband (UWB) is a wireless transmission technology that allows high data rate with low power consumption for short distances. UWB technology has recently gone through some revolutionary changes, including the legalization of the technology in the US for communication systems. To become truly ubiquitous, UWB research has to address several challenges such as multipath, multi-access and narrow-band interferences.
Traditionnally, time hopping spread spectrum with pulse position modulation is the multi-access scheme of choice for UWB. To better access UWB potency, we analytically investigate the performance of asynchronous time-hopping ultra-wideband (TH-UWB) multiple access spread spectrum in a UWB realistic multipath channel and in the presence of narrowband interference (NBI). In particular, an interference suppression receiver for TH-UWB wireless systems is proposed. It consists of selecting the first strongest multipath components using an appropriate Rake receiver with the path diversity combining being based on the minimum mean square error criterion. Results reveal that the proposed receiver can almost completely eliminate the effect of NBI.
Much of the research has focused on employing time hopping spread spectrum with impulse radio using pulse position modulated signals under perfect power control conditions. Direct-sequence (DS) spread spectrum technique is a well known and powerful multi-access technique. In our work, we analyse the performance of DS ultra wideband multiple access systems em-ploying antipodal signaling and compare it with time-hopping under perfect and imperfect power control conditions. To alleviate the effect of imperfect power control on UWB systems and take advantage of the dense multipath channel, we further propose a multiuser receiver, which employs a partial Rake receiver, followed by a successive interference cancellation tech-nique with optimal ordering. Numerical results will demonstrate that significant performance improvements would result when the proposed architecture is employed.
In order to completely avoid any frequence band characterized by a strong narrow-band interference, we propose prolate spheroidal wave functions (PSWF) as an orthogonal set of pulses that meet the Federal Communications Commission (FCC) requirements and has a constant pulse width regardless of the pulse order. The designed pulse shape is optimum in the sense of minimizing the out of band energy and is very practical for the implementation of UWB multiband soft spectrum adaptation.
Using PSWF pulses to improve the UWB transmission power efficiency while meeting the FCC transmission requirements, a biorthogonal pulse shape modulation (BPSM) is proposed. The system performance and channel capacity are investigated in a realistic indoor UWB mul-tipath channel. Results reveal that the proposed UWB receiver based on BPSM holds a great promise for practical implementation both from the performance and complexity perspectives.
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