Pilot-symbol-aided (PSA) channel estimation for OFDM wireless access systems enables the periodic estimation of channel frequency response by generating reference data from the received OFDM signals. The accuracy of this channel estimation can be improved through the average over a certain time period in each subcarrier-channel. However, the accuracy of the channel estimates by the average degrades as the Doppler shift is large due to a decrease in the average section size according to the Doppler shift for the tracking of the time-varying channel. This paper proposes a novel PSA channel estimation method to mitigate the influence of the noises and interferences. This method detects the channel estimates affected by the noises and interferences, and then removes them before the arithmetic or harmonic averaging to avoid propagating the influence of the noises and interferences. This paper also evaluated the proposed channel estimation method by clipping log-likelihood ratio (LLR) data to inspect the influence of the channel estimation on the LLR calculation by computer simulation.

We have been investigating an orthogonal frequency division multiple access (OFDMA) based cellular system that is called "dynamic parameter controlled orthogonal frequency and time division multiple access (DPC-OF/TDMA)" for the development of beyond third generation (B3G) mobile communication systems. Moreover, we have already proposed a time alignment control (TAC) to compensate propagation delays that induce a multiple-access interference (MAI) in the uplink OFDMA. However, that TAC includes a large amount of computations. This means that it is quite difficult for the OFDMA systems to implement TAC into volume-limited hardware devices such as field programmable gate array (FPGA). Thus, we propose a new complexity-reduced TAC (CRTAC) in this paper. CRTAC can be implemented into such devices easily. In this paper, we show some computer simulation results, and then evaluate the error rate performances of DPC-OF/TDMA employing CRTAC. Moreover, we also show the benefit of the reasonable level of the implementation complexity made by CRTAC.

This paper proposes a simple timing synchronization method in order to design a timing synchronization circuit with low-complex and low-volume digital signal processing (DSP) for orthogonal frequency division multiplexing (OFDM) packet transmission systems. The proposed method utilizes the subtraction process for acquirement of a timing metric of fast Fourier transform (FFT) window, whereas the conventional methods utilize the multiplication process. This paper adopts the proposed method to a standardized OFDM format, IEEE 802.11a, and elucidates that the proposed one shows good transmission performance as well as the conventional one in fast time-variant multi-path Rayleigh fading channels by computer simulation.

The Start-frame-delimiter (SFD) is crucial in packet-based communications system since it indicates the end of preamble and the start of a frame. In 802.15 smart utility network system, the function of SFD is extended. Two different SFDs are used for achieving frame synchronization and at the same time, to differentiate coded and uncoded packets. This paper proposes a systematic method for the selection of SFD pair for FSK based systems. The design method is adopted by 802.15.4g Task Group with the backward compatibility to IEEE 802.15.4d systems taken into account. Four selection criteria are specified and discussed to determine the pair of sequences providing least packet error detection rate with the consideration of eliminating the adjacent channel image signal commonly occurred in the low IF receiver. The probability of false alarm and miss detection is analyzed to verify the effectiveness of the proposed selection method. The simulation results confirm that error frame detection rate of 1e-3 can be achieved with selected SFD sequences. The proposed method for selection of SFD pairs ensures a robust packet header and thus better payload protection. The SFD design approach is applicable to other packet-based wireless communication FSK systems with the support of more than one SFD sequence.

IEEE 802.15.3c has been standardized for wireless personal area networks (WPANs) to realize high-speed wireless communications with 1 Gbps throughput. In this paper we introduce a 802.15.3c WPAN prototype. The introduced 802.15.3c WPAN prototype applies the enhanced MAC functions of data separation on hybrid multiple access, long frame size, aggregation, block acknowledgment, and timing operation, which can realize Gbps throughput in IEEE 802.15.3c. Moreover, the experiment performance studies on the prototype show that around 1.6 Gbps throughput can be successfully achieved and video streaming applications can be accommodated. Also, our studies provide the useful information of MAC capacity for developing the 802.15.3c devices.

Decision-directed, pilot-symbol-aided channel estimation (PSACE) for coded orthogonal frequency division multiplexing (COFDM) systems has structurally unavoidable processing delay owing to the generation of new reference data. In a fast fading environment, the channel condition which varies during the delay induces channel estimation error. This paper proposes a method of reducing this estimation error. In this method, channel equalization is performed for the received signal twice. One is done as pre-equalization with the delayed estimates of channel frequency response in order to update them periodically. At the same moment, the other is done as post-equalization for the received signal that is delayed by the processing delay time, with the same estimates as the pre-equalization. By the proposed method, more accurate channel estimation can be realized without significant output delay. Computer simulations are performed by utilizing the IEEE 802.11a packet structure of 24 Mbit/s. The result shows that the proposed OFDM transmission scheme having the delay time of 20 µs offers 2.5 dB improvement in the required Eb/N0 at PER = 10-2 in the ESTI-BRAN model C Rayleigh fading channel with fd = 500 Hz.

In this paper, throughput and error performance analysis is conducted on the proposed space-time resource management (STRM) scheme to realize a multi-Gbps millimeter-wave wireless personal area network (WPAN) system. The proposed STRM allows multiple peer-to-peer communication links to occupy the same time-division-multiple-access (TDMA) time slot, in contrary to the conventional TDMA system that allocates only one time slot to one communication link. Theoretical analysis is performed to investigate the achievable system throughput in the presence of co-channel interference (CCI) generated by communication links co-sharing the same time slot. To increase accuracy, the analysis results are validated by Monte Carlo simulations. Firstly, it is found that the upper bound of the achievable throughput increases linearly with the number of communication links sharing the same time slot. However, optimum throughput exists corresponding to the CCI present in the system. Secondly, by manipulating a parameter that controls the allowable CCI in the network, the system throughput can be optimized. Lastly, it is also found that in a millimeter-wave band system, a victim system with transmitter-receiver separation of 1-meter can achieve bit error rate (BER) of 10-6 provided that the interferer is at least 6-meters away.

This paper proposes a time alignment control (TAC) for reducing an influence of multiple access interference (MAI) due to propagation delays (PDs) in uplink transmission from multiple mobile stations (MSs) to an access point (AP) for an orthogonal frequency division multiple access (OFDMA) based mobile communication system. In addition, this paper presents our evaluation of the proposed TAC as applied to dynamic parameter control orthogonal frequency and time division multiple access (DPC-OF/TDMA) which has been suggested for use in new generation mobile communication system. This paper also proposes several formats for an activation slot (ACTS) in which the GIs are lengthened in order to avoid the MAI because the TAC cannot be performed yet in an initial registration of the MSs. Computer simulation elucidates that lengthening the GIs of data symbols in the ACTS adequately to compensate a maximum delay improves the transmission performance of the ACTS at the initial registration without PDs compensation. The simulation also elucidates that the proposed TAC is performed to reduce the influence of the MAI effectively and that updating the estimates of the PDs every certain period is needed to compensate the PDs accurately under high-mobility environment.

In one-cell-frequency-reuse Orthogonal Frequency Division Multiple Access based Time Division Multiple Access (OF/TDMA) systems, communication is blocked by interference from adjacent cells. The most promising solution would be an adaptive modulation and coding scheme that is controlled by estimating the signal-to-interference ratio (SIR). However, there has so far been no way to accurately estimate the SIR using the spreading codes for OF/TDMA systems, because of the asynchronous fast Fourier transform (FFT). In this paper, we propose a novel SIR estimation method that uses a spread pulse-wave symbol and carrier interferometry. Moreover, to introduce multi- input multi-output systems, we modify the proposed method by allocating a different spreading code to each cell. Computer simulation confirmed that the SIR is estimated accurately even if the FFT is asynchronous. On cell boundaries, the average estimation errors that are a ratio between accurate and estimated propagation characteristics are less than 2 dB.

An exact expression of error rate is developed for maximal ratio combining (MRC) in an independent but not necessarily identically distributed frequency selective Nakagami fading channel taking into account inter-symbol, co-channel and adjacent channel interferences (ISI, CCI and ACI respectively). The characteristic function (CF) method is adopted. While accurate analysis of MRC performance cannot be seen in frequency selective channel taking ISI (and CCI) into account, such analysis for ACI has not been addressed yet. The general analysis presented in this paper solves a problem of past and present interest, which has so far been studied either approximately or in simulations. The exact method presented also lets us obtain an approximate error rate expression based on Gaussian approximation (GA) of the interferences. It is shown, especially while the channel is lightly faded, has fewer multipath components and a decaying delay profile, the GA may be substantially inaccurate at high signal-to-noise ratio. However, the exact results also reveal an important finding that there is a range of parameters where the simpler GA is reasonably accurate and hence, we don't have to go for more involved exact expression.