Time-selective signaling and reception for communication over multipath fading channels

Abstract

Abstract-The mobile wireless channel affords inherent diversity to combat the effects of fading. Existing code-division multiple-access systems, by virtue of spread-spectrum signaling and RAKE reception, exploit only part of the channel diversity via multipath combination. Moreover, their performance degrades under fast fading commonly encountered in mobile scenarios. In this paper, we develop new signaling and reception techniques that maximally exploit channel diversity via joint multipath-Doppler processing. Our approach is based on a canonical representation of the wireless channel, which leads to a time-frequency generalization of the RAKE receiver for diversity processing. Our signaling scheme facilitates joint multipath-Doppler diversity by spreading the symbol waveform beyond the intersymbol duration to make the channel time-selective. A variety of detection schemes are developed to account for the intersymbol interference (ISI) due to overlapping symbols. However, our results indicate that the effects of ISI are virtually negligible due to the excellent correlation properties of the pseudorandom codes. Performance analysis also shows that relatively small Doppler spreads can yield significant diversity gains. The inherently higher level of diversity achieved by time-selective signaling brings the fading channel closer to an additive white Gaussian noise channel, thereby facilitating the use of powerful existing coding techniques for Gaussian channels.

Time-scale domain characterization of non-WSSUS wideband channels

“…It is evident that diversity performance improves monotonically with increasing number of i.i.d [32]. In fact as the number of i.i.d ℵ approaches infinity, the performance of coherent diversity reception converges to the performance over a nonfading AWGN channel [33][34][35][36][37]. In practice, diversity is physically implemented in a variety of ways such as time diversity, frequency diversity, joint time-frequency diversity, delay diversity, Doppler diversity, scale diversity, joint delay-Doppler diversity, and joint delay-scale diversity.…”

Decentralized multiuser detection for time-varying multipath channels

“…Our framework for designing a range of progressively complex (powerful) receivers by incorporating secondary coordinates serves as a useful approach for striking a judicious practical tradeoff between complexity and performance. Furthermore, while our examples focused on slow fading scenarios, the notion of Doppler diversity with appropriate signaling [13], [23] may also be leveraged in fast-fading scenarios to further enhance system performance.…”

“…To facilitate analysis, we first derive alternate expressions for the optimum solution. Let denote the signal-free component of the canonical coordinates (22) The correlation matrix of is of the form (23) 8 Note that SINR is really a function of all h 's. However, for sufficiently effective MAI suppression, the residual MAI can be lumped to Gaussain noise [20].…”

Canonical space-time processing for wireless communications

“…The parsimonious nature of the proposed canonical coordinate representation simplifies a number of problems in mobile wireless communication. In the case of time-only processing, the representation has been exploited for diversity processing, interference suppression, and timing acquisition [5], [17], [9], [18]. In a multiuser context, the canonical representation provides a natural framework for tailoring receiver complexity to a desired level of performance.…”