Yi Gong

Space-frequency-time coded OFDM for broadband wireless communications

In this paper, we propose and analyze an efficient space-frequency-time coded OFDM technique for high-speed transmission over wireless links. Joint use of space-time trellis coding and space-time block coding is considered. It is shown that the maximum achievable diversity order increases linearly not only with the number of transmit and receive antennas but also with the number of multiple paths provided that a proper joint coding scheme is employed. Because of the orthogonality of space-time block codes, space-time trellis codes with low trellis complexity can be used to efficiently achieve the full diversity provided by the fading channel. This is in contrast to traditional space-frequency coded OFDM systems, where we need to design space-time trellis codes with very high trellis complexity to exploit the maximum achievable diversity of the fading channel. Numerical results are provided to demonstrate the significant performance improvement achieved by the proposed space-frequency-time coded OFDM technique.

Performance evaluation and analysis of space-time coding in unequalized multipath fading links

This paper investigates the use of space-time (ST) coding for high-speed data transmission, as well as studies the effect of time delay spread on such scheme over unequalized fading channels. Using a random variable decomposition technique, we present an analytical model and obtain an approximate bound of the pairwise-error probability for ST coded systems over multipath and time-dispersive fading channels. It is shown that the presence of multipath does not reduce the diversity gain provided by the original design criteria, which is adopted to construct specific ST codes in quasi-static flat fading, but the coding gain diminishes due to the effect of multipath fading.

Concatenated space-time block coding with trellis coded modulation in fading channels

Trellis coded modulation (TCM) is a bandwidth efficient transmission scheme that can achieve high coding gain by integrating coding and modulation. This paper presents an analytical expression for the error event probability of concatenated space-time block coding with TCM which reveals some dominant factors affecting the system performance over slow fading channels when perfect interleavers are used. This leads to establishing the design criteria for constructing the optimal trellis codes of such a concatenated system over slow flat fading channels. Through simulation, significant performance improvement is shown to be obtained by concatenating the interleaved streams of these codes with space-time block codes over fading channels. Simulation results also demonstrate that these trellis codes have better error performance than traditional codes designed for single-antenna Gaussian or fading channels. Performance results over quasi-static fading channels without interleaving are also compared in this paper. Furthermore, it is shown that concatenated space-time block coding with TCM (with/without interleaving) outperforms space-time trellis codes under the same spectral efficiency, trellis complexity, and signal constellation.

An efficient space-frequency coded wideband OFDM system for wireless communications

A space-frequency coded OFDM system for high-speed transmission over wireless links is proposed. The analytical expression for the error event probability of such space-frequency coded OFDM system is derived in slow, spatial and frequency selective fading channels. The design criteria of TCM codes for the proposed system are then developed and discussed. It is shown that the proposed space-frequency coded OFDM with low trellis complexity can efficiently exploit the available diversity resources of the fading channel, while in conventional space-frequency coded OFDM systems, space-time trellis codes with very high trellis complexity are required to make full use of the diversity resources. Simulation results show that at a FER of 10/sup -2/, the proposed scheme outperforms the traditional space-frequency coded OFDM by 2-4 dB at an equal trellis complexity and spectral efficiency.

Low rank channel estimation for space-time coded wideband OFDM systems

To provide high-speed data transmission for the next generation wireless communication systems employing multiple transmit antennas, a space-time coded orthogonal frequency division multiplexing (OFDM) system has previously been proposed as a promising and efficient approach with both transmit diversity and high coding gains. In this paper, we study the channel estimation for spacetime coded OFDM using least squares (LS) and minimum mean-squared error (MMSE) criteria. In particular, the MSE bounds are given for the temporal channel estimations. By assuming that the channel frequency response is quasi-static over two consecutive OFDM symbols, a low rank Wiener filter based channel estimator is proposed. This significantly reduces the computation complexity while retaining accurate frequency domain channel estimation. Numerical results are provided to demonstrate the performance of the low-rank frequency-domain channel estimation for space-time coded OFDM systems.

Analysis and design of trellis coded modulation with transmit diversity for wireless communications

Trellis coded modulation (TCM) is a bandwidth efficient transmission scheme that can achieve high coding gain by integrating coding and modulation. This paper presents an analytical expression for the error event probability of TCM with transmit diversity (Realized by space-time block coding) which reveals some dominant factors affecting the system performance over slow fading channels when perfect interleavers are used. This leads to establishing the design criteria for constructing optimal trellis codes for use with space-time block coding over flat fading channels. These results also apply to fast fading channels where the maximum Doppler spread normalized by the symbol rate is of the order of 10/sup -2/. Through simulation, significant performance improvement is shown to be achieved by concatenating the interleaved streams of these codes with space-time block codes over fading channels. Simulation results also demonstrate that these outer codes have better error performance than codes of the same number of states designed for Gaussian or fading channels without the use of transmit diversity.

Performance of space-time trellis coding over Nakagami fading channels

Space-time trellis codes have previously been proposed as an efficient method to provide both transmit diversity and coding gains for high-data-rate wireless communications. In this paper, we study the use of space-time trellis coding over Nakagami fading channels. The performance analysis and evaluation of space-time trellis coding over slow Nakagami fading channels are presented. By assuming that all diversity branch fadings and noise are statistically independent, an upper bound of the pairwise error probability of space-time coding in Nakagami fading is obtained. In particular, the analysis shows that the design criteria of space-time trellis codes for Rayleigh fading still hold when used over both independent and correlated Nakagami fading channels. Simulation results are provided for space-time trellis coding over independent and correlated Nakagami fading channels with various fading parameters and correlation coefficients.

Performance evaluation and analysis of space-time coding for high data rate wireless personal communications

The third generation wireless personal and mobile communication systems are required to support both high-quality and high data-rate services. However, high-speed transmission over wireless communication links is severely restricted by the wireless environment limitations such as intersymbol interference, propagation fading, additive noise and co-channel interference. This paper investigates the use of space-time coding for high-speed data transmission, as well as, study the effect of time delay spread on such scheme in multipath fading channels. Using a random variable decomposition technique, we also present an analytical model and obtain an approximate bound of the pair-wise error probability for space-time coded systems over multipath and time-dispersive fading channels. It is shown that the presence of multipath does not reduce the diversity gain provided by the original design criteria which is adopted to construct specific space-time codes in quasi-static flat fading, but the coding gain decreases due to the effect of multiple paths.