Wavelet-based separating kernels for array processing of cellular DS/CDMA signals in fast fading

Abstract

We propose new detectors for direct-sequence code-division multiple-access (CDMA) signals that outperform known approaches in rapidly fading multipath channels. Multipath compensation in CDMA systems is a problem of significant complexity especially when rapidly fading is afflicting the radio frequency channel. In this work, we depart from typical approaches in search of new kernels that can more accurately characterize the time-varying nature of the estimation problem and focus on a multiresolution representation of the fading processes. The unknown channel time variations are in fact decomposed using optimal unconditional bases in the family of the orthonormal wavelets. We show that it is possible to represent the channel in a reduced-order dimensional space by matching the scattering function of the multipath channel to its decomposition and obtain an approach that is effective in fast fading environments, such as those practically found in macrocell wireless communication applications. We apply this representation to the development of a practical multiscale filter that achieves multiuser separation minimizing a time-averaged squared error. The technique is studied by means of computer simulations and hardware experiments that employ a currently deployed base-station system.

Time-varying FIR equalization for doubly selective channels

“…3. We estimate for as (12) Since the doubly selective channel was described by the BEM, it is also convenient to design the TV FIR equalizer using the BEM. This approach will allow us to turn a complicated equalizer design problem into an equivalent simpler equalizer design problem, containing only the BEM coefficients of both the doubly selective channel and the TV FIR equalizer or, as we explain next, it will allow us to convert a complicated TV 1-D deconvolution problem into an equivalent simpler TIV 2-D deconvolution problem.…”

Orthogonal wavelet division multiplexing for wideband time-varying channels

“…Receivers for single-scaled wavelet-based pulses for wideband MSML channels are presented in [1,2], and a similar waveform is adopted in spread-spectrum systems [5] over wideband channels modeled by wavelet transforms; while [6] considers equalizers for block transmissions in wideband MSML channels. In order to achieve better realistic channel matching, single-scaled rational wavelet modulation was designed in [7].…”

Block transmission over multi-scale multi-lag wireless channels

“…Approximation by a bank of multiple narrowband time-varying channels [8] can be considered as well, wherein each sub-channel is modeled by a multi-Doppler shift, multi-lag model. Finally, in [9], [10], [11], the channel itself is modeled by wavelet (packet) transforms. Although approached from a different viewpoint, these models can somehow be related to the existing scale-lag canonical models.…”