Joint multipath-Doppler diversity in mobile wireless communications

Abstract

Abstract-We introduce a new approach for achieving diversity in spread-spectrum communications over fast-fading multipath channels. The RAKE receiver used in existing systems suffers from significant performance degradation due to the rapid channel variations encountered under fast fading. We show that the Doppler spread induced by temporal channel variations in fact provides another means for diversity that can be further exploited to combat fading. We develop the concept of Doppler diversity and propose a framework that exploits joint multipathDoppler diversity in an optimal fashion. Performance analysis shows that even the relatively small Doppler spreads encountered in practice can be leveraged into significant diversity gains via our approach. The framework is applicable in several mobile wireless multiple access systems and can provide substantial performance improvement over existing systems.

Capacity of sparse wideband channels with partial channel feedback

“…Let D denote the number of non-zero channel coefficients that reflects the (dominant) statistically independent DoF in the channel and also signifies the delay-Doppler diversity afforded by the channel [22]. We decompose D as D = D T D W where D T denotes the Doppler/time diversity and D W denotes the frequency/delay diversity.…”

“…We use a virtual representation [22], [23] of the physical model in (2) that captures the channel characteristics in terms of resolvable paths and greatly facilitates system analysis from a communication-theoretic perspective. The virtual representation uniformly samples the multipath in delay and Doppler at a resolution commensurate with signaling bandwidth W and signaling duration T , respectively.…”

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

“…Temporal channel variations, in fact, provide another form of diversity-Doppler diversity-that can be exploited in conjunction with multipath to attain joint multipath-Doppler diversity [6]- [8]. The concept of joint multipath-Doppler diversity is based on a canonical channel representation [6]- [8] that decomposes the channel into a series of independent flat fading channels corresponding to different (orthogonal) multipath-Doppler-shifted signal components.…”

“…The concept of joint multipath-Doppler diversity is based on a canonical channel representation [6]- [8] that decomposes the channel into a series of independent flat fading channels corresponding to different (orthogonal) multipath-Doppler-shifted signal components. Diversity reception is achieved by a generalization of the RAKE receiver that performs joint multipath-Doppler processing.…”

“…The level of diversity is directly proportional to time-bandwidth product of the signaling waveform-multipath diversity is proportional to the bandwidth and Doppler diversity is proportional to the signaling duration. Thus, maximal exploitation of channel diversity dictates that spread-spectrum frequency-selective signaling should be complemented by maximally spreading the transmitted signal in time, as well to make the channel time-selective [6]- [8].…”