Space-Time Codes for MIMO Systems with Non-Collocated Transmit Antennas

We consider space-time coding methods for cooperative narrowband and wideband downlink transmission from multiple base stations. The communication channels in multi base-station signaling differ from those involving collocated transmit-antenna systems, and, if properly used, can provide improved resistance to shadowing and extended range. One challenge, however, that arises in this context is asynchronous reception of the signal elements. In the narrowband case the proposed designs generate asynchrony robust space-time block codes (STBCs) via transformations of existing orthogonal STBCs. Subject to a maximum allowable relative delay between signals from distinct transmit antennas, the resulting received signal can be equivalently modeled as arising from synchronous STBC transmission with orthogonal or diagonal STBCs, implying that these designs provide full space diversity with low-complexity decoding in asynchronous settings. We also describe three system approaches for wideband transmission with throughput diversity receiver-complexity trade-offs. Common to all these systems are elements such as OFDM- type signaling, bit-interleaved coded modulation, and iterative decoding. The lowest data-rate lowest complexity system employs an inner orthogonal space-time block code with embedded OFDM-type transmission, while the highest data-rate highest complexity scheme does not employ an inner code. The latter group of schemes can also conveniently provide high data rates at the cost of reduced space diversity. All schemes can be readily extended to provide flexible unequal error protection for media transport.