Doubly selective channel estimation using superimposed training and exponential bases models
EURASIP Journal on Applied Signal Processing
Optimizing training lengths and training intervals in time-varying fading channels
IEEE Transactions on Signal Processing
Channel estimation using time-multiplexed pilots in HSUPA uplink
WCNC'09 Proceedings of the 2009 IEEE conference on Wireless Communications & Networking Conference
On the pilot spacing constraints for continuous time-varying fading channels
IEEE Transactions on Communications
IEEE Transactions on Image Processing
| Hi-index | 35.69 |
Reliable coherent wireless communication requires accurate estimation of the time-varying multipath channel. This paper addresses two issues in the context of direct-sequence code-division multiple access (CDMA) systems: (i) linear minimum-mean-squared-error (MMSE) channel estimation based on a pilot transmission and (ii) impact of channel estimation errors on coherent receiver performance. A simple characterization of the MMSE estimator in terms of a bank of filters is derived. A key channel characteristic controlling system performance is the normalized coherence time, which is approximately the number of symbols over which the channel remains strongly correlated. It is shown that the estimator performance is characterized by an effective signal-to-noise ratio (SNR)-the product of the pilot SNR and the normalized coherence time. A simple uniform averaging estimator is also proposed that is easy to implement and delivers near-optimal performance if properly designed. The receivers analyzed in this paper are based on a time-frequency RAKE structure that exploits joint multipath-Doppler diversity. It is shown that the overall receiver performance is controlled by two competing effects: shorter coherence times lead to degraded channel estimation but improved inherent receiver performance due to Doppler diversity, with opposite effects for longer coherence times. Our results demonstrate that exploiting Doppler diversity can significantly mitigate the error probability floors that plague conventional CDMA receivers under fast fading due to errors in channel estimation