This letter proposes a quadratic optimization decoding (QOD) for space-time block decoding in time-selective Rayleigh fading channels. When channels are fast fading, the simple decoding exploiting the orthogonal structure of the codes can not be used to achieve a proper error performance. In an effort to mitigate the severe performance degradation, in this letter least square decoding and QOD are considered for decoding. Simulation results show that the QOD shows a significant performance improvement compared to the least square and the conventional schemes.

In this letter, we address the performance evaluation of a space-time block coded (STBC) orthogonal frequency and code division multiplexing (OFCDM) system encountered with time-variant channels. For the performance evaluation, the average bit error rate (BER) impairment due to imperfect channel information is investigated taking into account the effect of time-varying channels. Derived results show that the loss of orthogonality due to the time variation of the channel incurs the channel estimation error, which causes performance degradation.

In this letter, a simple peak-to-average power ratio (PAPR) reduction scheme by using a cyclic-shifted sequence mapping is addressed in OFDM-CDMA systems. The PAPR reduction approach is very simple because of no additional complexity and no side information. Also, this simple approach can be easily combined with a modified selective mapping (SLM) approach, which outperforms the original SLM approach at the expense of one additional side information, guaranteeing approximately same transmitter complexity.

This letter derives and computes the detection probability for timing synchronization in an orthogonal frequency division multiplexing (OFDM) system encountered with a multipath Rayleigh fading channel. OFDM timing synchronization using constant amplitude zero auto-correlation (CAZAC) training symbols and correlation techniques is adopted. With this provision, we focus on the numerical analysis for OFDM timing synchronization scheme employing a preadvancement technique to reduce the inter-symbol interference (ISI). For measuring system performance, the sync detection performance derived in the considered system is presented in a multipath Rayleigh fading channel.

This letter addresses the edge effect on a windowed discrete Fourier transform (WDFT)-based channel estimator for orthogonal frequency division multiplexing (OFDM) systems with virtual carriers in non-sample spaced channels and derives a sufficient condition to reduce the edge effect. Moreover, a modified WDFT-based channel estimator with multi-step linear prediction as an edge effect reduction technique is proposed. Simulation results show that it offers around 5 dB signal-to-noise ratio (SNR) gain over the conventional WDFT-based channel estimator at bit error rate (BER) of 10-3.

In this paper, we propose a new digital duplexing scheme, called synchronous digital duplexing (SDD), which can increase data efficiency and flexibility of resource by transmitting uplink signal and downlink signal simultaneously in wireless communication. In order to transmit uplink and downlink signals simultaneously, the proposed SDD obtains mutual information among subscriber stations (SSs) with a mutual ranging symbol. This information is used for selection of transmission time, decision on cyclic suffix (CS) insertion, determination of CS length, and re-establishment of FFT starting point.

This letter investigates an effect of diversity techniques on the performance of OFDM-CDMA based broadband wireless access networks and evaluates the maximum achievable diversity gain for a two-path Rayleigh fading environment. Simulation results show that the OFDM-CDMA system applying a space-time-frequency diversity with a full-rate full diversity code can give the diversity of D=4 and D=8 for both multi-user cases of maximum user and half user capacities, respectively.

In this paper, an interference cancellation (IC) scheme for a multirate VPG DS/CDMA system is evaluated in a multipath fading mobile channel and is designed to accommodate the multimedia sources of varying data-rate requirements. In the this scheme, the strongest user with high-rate transmission will benefit from the multiple access interference (MAI) reduction of the weaker users, which yields more clean estimates in the next cancellation stage. From the numerical results, the proposed scheme outperforms the conventional SIC scheme under the condition of the approximately identical decoding delay at the cost of the hardware burden.