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Pseudo-orthogonal space-time block coded OFDM system (POSTBC-OFDM) has recently been proposed as a novel scheme for the frequency-selective channel scenario. However, a general assumption underlying the use of space-time codes is that the channel should be quasi-static, which is violated from the nature of high mobility environment. Additionally, large Doppler spread causing rapidly time-varying channels could destroy the orthogonality among neighboring subcarriers and lead to intercarrier-interference (ICI). This paper studies the extension of the POSTBC-OFDM scheme to the rapidly time-varying channel case by adopting sectorized antenna reception technique which could reduce Doppler spread and the channels time-variance by restricting the incident angle of imping waves to a finite range. Simulation results show that this proposed system is not only suitable for high mobility condition, but also can get a better tradeoff among performance, code rate and complexity of receiver.

In this paper, capacity of the MIMO-OFDM systems using both space diversity and polarization diversity is analyzed. Based on a multi-path channel model defined by IEEE 802.16d indoor channel standard, an MIMO-OFDM system with two transmit antennas and two receive antennas is investigated. In both the transmitter and the receiver, the space diversity and the polarization diversity are simultaneously considered. For comparison, the capacity of a system only with spatial diversity is also examined.

In this paper, a new Rake receiver of the Ultra-wide band (UWB) system with multiple receive antennas is proposed. To economize the system resource, an antenna selection scheme is used. For each selected antenna, the maximal ratio RAKE combination is applied to the multi-path signals. The outputs corresponding to all selected antennas are then combined according to the minimum mean square error (MMSE) criterion. Furthermore, we designed a MMSE equalizer in the time-domain to effectively eliminate the inter-symbol interference. The joint utilization of the antenna selection, RAKE and equalization schemes in the receiver gives the presented system superior performance compared with the existing UWB receivers. Simulation examples based on IEEE 802.15.3a channel model are given.

In this paper, performance of beams-based transmit diversity in a multi-path fading channel is investigated. At the transmitter, Alamouti' s coding signals is transmitted by two independent transmitting beams. Since the received signals at each receive antenna encompasses all the multi-path components from every transmitting beam, a technique is proposed to combine the space-time block coding signals and implement space-time decoding. Simulations are conducted to show the effectiveness of the proposed approach.

Applying smart antennas to an OFDMA system is investigated. A simple resource allocation scheme for array-antenna based OFDMA systems is proposed. The resource allocation algorithm is applied to the pilot data when no beam is formed and channel estimation in frequency-domain is implemented. After piloting, a beam is formed for each user to enhance the performance of the system. Simulations based on the SUI channel model according to the standard of IEEE 802.16e WMAN are carried out to examine the performance of the proposed approach.

This paper presents a space-time coded VBLAST scheme for OFDM communication based on IEEE 802.16d protocol. At the transmitter, the data stream is partitioned into several groups and each group is STBC encoded and OFDM modulated independently. At the receiver, conventional VBLAST detection techniques can be employed. The SUI channel model which is recommended by the IEEE 802.16d working group is used in the simulations to compare performance of the STBC coded VBLAST scheme with that of the classic VBLAST for IEEE 802.16 d-based OFDM systems at the same spectrum efficiency.

In this paper, a simple and efficient post-fast-Fourier-transform (FFT) beamforming scheme for OFDM systems is proposed. The carriers are uniformly divided into several groups in the proposed scheme. For each group, only one beamforming weight is calculated by using the pilot-based channel estimate in the frequency-domain. The remaining weights are linearly interpolated by using the pilot-based weighs. Compared to the existing techniques, the proposed approach exhibits computational simplicity with efficient performance

In this paper, a simple method for space-frequency channel estimation in an orthogonal frequency division multiplexing (OFDM) system with an antenna array is proposed. The space-frequency channel impulse response is estimated in the frequency domain. The estimated channel is further used to implement joint space-frequency channel equalization in the uplink and the beamforming in the downlink. Compared with the existing systems where independent beamforming and channel equalization in frequency domain are conducted, the proposed method can significantly reduce the complexity of the system without loss of performance. Simulations are conducted to show the effectiveness of the proposed approach.

A Laplace power azimuth spectrum distribution model is applied to the analysis of the performance of a beamformer in CDMA communication systems. The effects of angle spread on beamforming in both the uplink and the downlink are investigated. Compared to a single-antenna-based system, the array processing gains of a mobile communication system with a smart antennas array are derived. Numerical results for a uniform linear array and a uniform circular array, respectively, are provided.