Resource management for infrastructure-based two-hop fixed relay systems which are applicable to TDD-FH-OFDMA based cellular systems with sectorization is proposed in this paper. The severe interference problem caused by both inter-sector and inter-cell can be tackled by employing 6-sector directional antennas combined with the resource allocation. The simulation results demonstrate that at the outer-region of the cell, the high data rate service coverage can be extended.

In this paper, we investigate the performance of the orthogonal frequency division multiplexing (OFDM) system based on a configuration of pilot symbol arrangement under a time-varying fading channel and verify it by simulation. A particular channel of concern is modeled by a wide-sense stationary uncorrelated scattering (WSSUS) Rayleigh fading process and furthermore, the inter-carrier interference (ICI) caused by the fading process is assumed to be Gaussian noise. The current analysis focuses on the performance limit of the pilot symbol-assisted channel estimation, in which a minimum mean squared error (MMSE) channel estimator is employed to exploit both time- and frequency-domain correlation simultaneously. In particular, the optimum pilot symbol arrangement was investigated for the time-varying fading channel, which has been rarely addressed with any analytical approach in previous research. Although the proposed channel estimation scheme is subject to the intensive processing complexity in the receiver, it has been shown that the better BER performance can be achieved as compared with that of the differential detection scheme and the error floor can be removed.

The optimal antenna weighting scheme that minimizes the average bit error rate in a closed-loop transmit antenna diversity system is investigated under the assumption that channel state information is provided at both the transmitter and the receiver. A closed-form expression for the optimal transmitter weights is derived with a fixed average transmit power constraint. Also, the effect of limited peak transmit power on the performance of the optimal weighting method is analyzed. Base on this analysis, it is shown that the proposed transmitter weights yield significant performance improvements over the conventional weights on the wide range of practical system parameters.

As a data transmission rate must be increased as required to support the future high-speed wireless communication systems under multipath fading, the conventional DS-CDMA scheme suffers considerably from an intensive processing requirement for the increased spreading rate to combat the inter-chip interference (ICI) and furthermore, from the intersymbol interference (ISI) as the symbol duration becomes less than the channel delay spread. In this paper, a multi-carrier parallel combinatory DS-CDMA (MC-PC-CDMA) scheme is considered as one possible variant access scheme to realize a bandwidth efficient transmission for high transmission rate while maintaining the beneficial features of the DS-CDMA scheme. This scheme combines the parallel combinatory signaling feature of the existing parallel combinatory CDMA (PC-CDMA) scheme with the orthogonal carrier multiplexing feature of multi-carrier modulation so as to improve the bandwidth efficiency and to reduce the self-interference among the parallel spreading sequences of each user, respectively. This particular system configuration also treats the previously proposed multi-carrier DS-CDMA systems as a special case. Our analysis of the bit error rate for the asynchronous CDMA system investigates the performance characteristics of the proposed system on varying design parameters, and shows the performance comparison with other types of multi-carrier DS-CDMA systems.

In this letter, we propose a symbol repetition technique combined with parallel channel encoding for multiband orthogonal frequency division multiplexing systems with ultra wideband channels. It can resolve timing asynchronous cochannel interference from another simultaneously operating piconet. Our simulation results demonstrate that the proposed scheme can effectively reduce the effect of the interference.