In this work, a new time diversity scheme is proposed to achieve time diversity in flat fading channels without affecting the data transmission rate. The conventional time diversity system reduces the transmission rate of the modulated symbols by a factor equal to the time diversity order. However, in the proposed time diversity system, any required time diversity order is achieved without reducing the transmission rate of the modulated symbols. In the proposed system, a diversity encoder maps vectors of N modulated symbols to vectors of N diversity symbols. By transmitting the diversity symbols, each modulated symbol is transmitted N times through N successive periods. Therefore, a time diversity with order N is achieved without affecting the modulated symbols rate since the transmission rate is N symbols per N channel uses. In the receiver, the outputs of a matched filter during the diversity period are stored in a buffer of length N. After filling the buffer, its contents are multiplied with the conjugate of the fading matrix. Multi-symbol detector removes interferences among the modulated symbols in the decision vector. It applies the algorithm of the diversity decoder and combines the corresponding received symbols to estimate the modulated symbols. The noise samples in the decision vector of the multi-symbol detector are uncorrelated. Maximum likelihood and linear decorrelator detectors are used as multi-symbol detectors. The performance of the proposed system is the same as the performance of the N channels diversity system with maximal ratio combiner receiver. |
