This paper presents a closed form expression of an exact average bit error rate (BER) for a time-division duplex (TDD) transmit diversity scheme employing maximal ratio combining (MRC) over time selective flat Rayleigh fading channels. In the proposed analysis, the feed back delay which degrades the BER performance is taken into account. The results are generally applicable to an arbitrary modulation scheme, as well as an arbitrary number of transmitting branches. To confirm the validity of the proposed analysis, the theoretical results are compared with the simulated ones.

This paper proposes a 2-dimensional linear propagation prediction (LPP) in maximal ratio combining (MRC) transmitter diversity for orthogonal frequency division multiplexing (OFDM) time division multiple access--time division duplex (TDMA/TDD) systems in order to overcome the degradation of the transmission performance due to the fast fading or the TDD duration. In the proposed scheme, the downlink channel condition of each sub-channel is predicted by interpolating the uplink fading fluctuation with both the amplitude and phase, and the predicted downlink channel condition is used for the weighting factor to employ MRC transmitter diversity. Numerical results obtained by the computer simulation show that the proposed 2-dimensional LPP with the second-order Lagrangeis interpolation predicts the downlink channel condition accurately under the fast fading or the long TDD duration. Moreover, in such a condition, the proposed LPP provides far better performance than the conventional 1-dimensional LPP.

In transmitter diversity, the received signal is the superposition of signals transmitted from transmitter antennas. Thus, the separation of channel characteristics corresponding to each transmitter antennas from these signals is very important. The conventional channel estimation scheme tends to show higher computational complexity for larger channel delay profile. To reduce this computational complexity, significant-tap-catching method has been proposed. However, there is still a burden of complexity for data transmission mode. Reference [14] has shown how to reduce the complexity for data transmission mode in system with constant modulus modulation. However, this method can't reduce the complexity required for multi-level signals such as QAM. In this paper, we propose an efficient channel estimation scheme for OFDM systems with transmitter diversity using space-time trellis coding. The computational complexity of the proposed scheme is independent of channel delay profile. Also, compared with the conventional scheme, the complexity of the proposed scheme is not related to modulation methods including multi-level signals such as QAM. The performance of the proposed scheme is evaluated by computer simulation in various multipath fading environments.

In this letter, a two-dimensional pilot-symbol aided (2-D PSA) channel estimation technique for coherent orthogonal frequency-division multiplexing (OFDM) systems with transmitter diversity is proposed. The 2-D PSA channel estimator and the corresponding orthogonality condition between the sets of pilot symbols are derived under minimum mean-square error (MMSE) criterion for OFDM systems with transmitter diversity. The proposed estimator is shown to be accurate and effective for tracking variations of channels between multiple transmitter antennas and receiver antennas.

Transmitter diversity is a powerful technique to improve the transmission quality of downlink in microcellular mobile communications systems. Under cochannel interference (CCI) at the base station (BS), the transmitter diversity is not necessarily effective, because the desired-plus-interference signal power used as a criterion of downlink branch selection is not always relative to the downlink propagation condition. This paper proposes the theoretical derivation of bit error rate (BER) performance in the transmitter diversity under CCI occurring at BS, as parameters of average SIR at BS, normalized Doppler frequency, and so on. It is confirmed from the correspondence of theoretical results with simulation results that the proposed theoretical approach is applicable to the CCI environments at BS.

In this paper, we propose an efficient channel estimation technique for orthogonal frequency-division multiplexing (OFDM) systems with transmitter diversity. The proposed technique estimates uniquely all channel frequency responses needed in space-time coded OFDM systems using "comb-type" training symbols. The computational complexity of the proposed technique is reduced dramatically, compared with the previous minimum mean-squared error (MMSE) technique, due to the processing made all in the frequency-domain. Also, several other techniques for mitigating random noise effect and tracking channel variation are discussed to further improve the performance of the proposed approach. The performances of the proposed approach are demonstrated by computer simulation for mobile wireless channels.

The paper proposes a transmitter diversity scheme with a desired signal selection for the mobile communication systems in which the severe cochannel interference (CCI) is assumed to occur at the base station. The feature of the proposed scheme is that the criterion of the downlink branch selection is based on the desired signal power estimated by the correlation between the received signal and the unique word at the matched filter. Moreover, the unique word length control method according to the instantaneous SIR is applied to the proposed scheme, taking account of the uplink transmission efficiency. Computer simulation results show that the proposed scheme provides the better performance than the conventional transmitter diversity in the severe CCI environments, and that the unique word length control method applied to the proposed scheme decreases the unique word length without the degradation of the transmission quality, comparing with the fixed unique word length method.