This chapter presents wideband time-varying channel models and their application towards improving wireless communication performance. It investigates two types of wideband channels: the wideband delay-scale channel that causes multipath and Doppler scaling on the transmitted signal and the wideband dispersive channel that causes nonlinear dispersive changes on the transmitted signal. For the wideband delay-scale channel, the conditions under which Doppler changes in the signal cannot be approximated as Doppler shifts are provided. The corresponding channel representation is based on the wideband spreading function. It is demonstrated that the Doppler scale parameter of this representation can be sampled geometrically using the Mellin transform, and for each discrete scale, the multipath parameter can be uniformly sampled. It is furthermore demonstrated that the delay-scale framework can be used to improve wideband channel communication performance due to its inherent multipath-scale diversity, which is captured by the discrete time-scale model. This is achieved by using a wavelet signaling scheme to dyadically decompose the channel into independent subchannels. The adoption of wavelet signaling also facilitates the efficient implementation of a wideband time-scale rake receiver using wavelet transform techniques. The wideband dispersive channel generalizes the narrowband channel characterization. This generalization framework provides an important foundation to exploit dispersive characteristics and improve system performance.
|Original language||English (US)|
|Title of host publication||Wireless Communications Over Rapidly Time-Varying Channels|
|Number of pages||42|
|State||Published - Dec 1 2011|
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