Prabodh Varshney

Channel estimation and signal detection for multi-carrier CDMA systems with pulse-shaping filter

We consider the problem of digital communication in a fading environment using the multi-carrier CDMA technology. By incorporating the effect of the pulse-shaping filter in the channel estimation and signal detection modules, we develop new estimator and detector structures which significantly outperform the commonly used time-domain equalizers and matched filter detector. Our simulation results demonstrate the elimination of some of the error floors which one would experience if usual time-domain techniques were used to cancel the effect of non-ideal pulse-shaping filter.

Linear MMSE chip equalization and parallel interference cancellation as applied to 1xEV-DV

1xEV-DV is a 3G CDMA standard, capable of achieving data rates up to 3 Mbps. This standard employs high-order modulation (up to 16-QAM) which makes the detection at the receiver difficult, due to the multipath distortion. In this paper, we investigated the linear minimum mean square error (LMMSE) chip equalizer, as well as the parallel interference canceller (PIC), and their hybrid approaches, as applied to the 1xEV-DV downlink receiver. The results showed that the hybrid receivers perform excellently in all scenarios tested, and outperform previous art LMMSE and PIC receivers.

Partially coherent constellations for multi-carrier systems

For wireless communication systems in high mobility environments, the usual assumption of perfect channel state information at the receiver is not very realistic. In the presence of channel estimation errors, the conventional PSK or QAM constellations, which are designed based on maximizing the minimum Euclidean distance between constellation points, are no longer optimal. Multi-carrier systems, which are the main focus of this work, are no exception to this fact. In this work, we first characterize the estimation variance of a pilot-based channel estimator for multi-carrier systems. Then, based on a previously derived KL-based criterion, we design new constellations for the ITU vehicular A channel at different SNR regions. The proposed constellations show significant performance improvement over the conventional QAM constellations. We show that the error floor due to the residual channel taps can be reduced by as much as one order of magnitude, if the proposed constellations are used in a multi-carrier system.

Performance comparison between MC-CDMA and 1xEV-DV

This paper presents performance comparison between a cellular system implemented according to the IxEV-DV standard, and a MC-CDMA system with similar parameters. The downlink peak data rate of the IxEV-DV system is 3.0912 Mbps. The proposed MC-CDMA system can provide the same data rates with significantly better performance. The MC-CDMA in this paper is comparable to the IxEV-DV system in the sense that same channel coding, modulation and slot structure as defined for IxEV-DV system are used.