Joint delay-Doppler diversity for wireless mobile communications
Abstract
Due to the limited resolution of time delay in direct-sequence spread-spectrum system, the RAKE receiver suffers performance degradation if multipath components are unresolvable in time delay. In future broadband mobile communications, this degradation will be exacerbated for the RAKE receiver due to the existence of the Doppler effect. In this study, we utilize the Doppler effect to obtain another diversity in conjunction with multipath diversity. By employing a coherent pulse train in a direct-sequence spread-spectrum system, propagation paths can be resolved jointly in delay and Doppler, and thus a greater number of resolvable paths are available for coherently combining to improve system performance. Furthermore, the resultant receiver structure is a two-dimensional delay-Doppler extension of the RAKE receiver that achieves the diversity exploited in both delay and Doppler. In addition to multipath fading, multiuser interference is one of the major factors limiting the performance of wireless multiuser systems. When the joint delay-Doppler RAKE receiver is applied to a mobile CDMA system, significant multiuser interference, known as the near-far problem, will impair the system performance. To suppress multiuser interference and estimate the channel parameters for the multiuser receivers, a subspace-based approach incorporated with the joint-delay Doppler channel estimation can be applied to resolve the propagation paths of the desired users in both delay and Doppler. Finally, several types of multiuser receivers are presented for multiuser suppression in multipath fading channel. One multiuser receiver, the joint delay-Doppler MMSE receiver, is developed to obtain the gain exploited in delay and Doppler.
Degree
Ph.D.
Advisors
Bell, Purdue University.
Subject Area
Electrical engineering
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