Blind and semi-blind channel estimation under space-time coded transmissions

Linear space-time block codes (STBC) have proven to be efficient in performance improvement of wireless MIMO communication systems. Their successful decoding, however, requires reliable channel knowledge at receivers. We present several novel blind and semi-blind channel acquisition techniques for a variety of MIMO systems that employ STBC. Beginning with flat fading channels in the context of orthogonal STBC (O-STBC), we formulate the blind channel estimation problem in terms of solvability conditions of a matrix equation. Utilizing the code orthogonality property, we obtain a set of identifiability conditions in terms of system parameters that guarantee a unique channel estimate up to a complex scalar ambiguity. For uniquely identifiable channels, we provide a simple, yet effective, sub-space based channel estimation algorithm.; Subsequently, the blind scheme is extended to the broader class of STBC that do not satisfy the code orthogonal design condition. A new comprehensive set of identification conditions that are mostly verifiable in terms of the known code parameters as well as antenna configuration are derived. Furthermore, for channels that are not uniquely identifiable, residual vector ambiguities resulting from the blind estimate are characterized. In order to resolve these ambiguities, hence securing a full and unequivocal channel estimate, a short training stage supplements the blind algorithm.; Since many wireless systems may exhibit non-negligible channel delay spread, the acquisition of frequency-selective channels is then considered in the context of Time-Reversal STBC (TR-STBC). Motivated by the similarities between TR-STBC and the ordinary STBC, the problem of identifying frequency-selective channels is formulated in accordance with the framework dedicated to frequency-flat channels. Consequently, the identification results as well as the blind estimation procedures developed for flat channels are systematically generalized to frequency-selective channels.; Beyond full channel acquisition for coherent detections purposes, our works are expanded to include incoherent MIMO systems employing Differential Space-Time Codes (DSTC). While the detection of DSTC's overcomes the need for channel knowledge, it consequently suffers a penalty of 3 dB loss compared to coherent detection. To mitigate this performance loss, a semi-coherent receiver that takes advantage of partial channel information is alternatively proposed. The partial channel information estimated with the help of a completely blind procedure can provide detection gains in the semi-coherent DSTC receivers that we proposed.