Fast Fading Channel Estimation by Kalman Filtering and CIR Support Tracking

Structured estimation of channel impulse response (CIR) is considered in orthogonal frequency division multiplexing (OFDM) systems for which the channel exhibits a sparse time-domain response. In particular, fast fading channels encountered in mobile wireless communications are envisaged. Such channels are characterized by time varying frequency selective response. This contribution exploits the much slower variation of propagation time delays, compared to propagation gains, to enhance CIR estimation. To this end, we propose a scheme that disjointly and successively tracks the delay-subspace, by Kalman filtering, then tracks the CIR structure. Contrarily to former subspace based channel response tracking, the channel order is unknown. The channel sparsity in the time-domain is accounted for by incorporating an adaptive CIR support tracking. This adaptive procedure combines the last and current OFDM blocks recovered CIR structures. To fine tune the CIR support, enhanced threshold-based CIR structure detection is applied on the recovered CIR estimate over its detected support. Finally, a structured LS estimation is processed. The proposed scheme outperforms sparsity-unaware Kalman tracking algorithm. It achieves similar performance than the best benchmark which is based on perfect CIR structure knowledge.