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Design and Analysis on Macro Diversity Scheme for Broadcast Services in Mobile Cellular Systems

Recently, broadcast services are introduced in cellular networks and macro diversity is an effective way to combat fading. In this paper, we propose a kind of distributed space-time block codes (STBCs) for macro diversity which is constructed from the total antennas of multiple cooperating base stations, and all the antennas form an equivalent multiple input multiple output (MIMO) system. This code is termed High-Dimension-Full-Rate-Quasi-Orthogonal STBC (HDFR-QOSTBC) which can be characterized as: (1) It can be applied with any number of transmit antennas especially when the number of transmit antennas is large; (2) The code is with full transmit rate of one; (3) The Maximum Likelihood (ML) decoding complexity of this code is controllable and limited to Nt/2-symbol-decodable for total Nt transmit antennas. Then, we completely analyze the structure of the equivalent channel for the kind of codes and reveal a property that the eigenvectors of the equivalent channel are constant and independent from the channel realization, and this characteristic can be exploited for a new transmission structure with single-symbol linear decoder. Furthermore, we analyze different macro diversity schemes and give a performance comparison. The simulation results show that the proposed scheme is practical for the broadcast systems with significant performance improvement comparing with soft-combination and cyclic delay diversity (CDD) methods.