• Journal of Communications and Networks
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• v.8 no.1
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• pp.38-48
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• 2006

A synchronous multicarrier (MC) code-division multiple access (CDMA) system using inverse fast Fourier transform (IFFT) and fast Fourier transform (FFT) for the downlink mobile communication system operating in a frequency selective Rayleigh fading channel is analyzed. Both carrier frequency offset and timing offset are considered in the analysis. Bit error rate performance of the system with both equal gain combining and maximum ratio combining are obtained. The performance is compared to that of the conventional system using correlation receiver. It is shown that when subcarrier number is large, the system using IFFT/FFT has nearly the same performance as the conventional one, while when the sub carrier number is small, the system using IFFT/FFT will suffer slightly worse performance in the presence of carrier frequency offset.

• Proceedings of the IEEK Conference
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• 2002.07b
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• pp.1086-1089
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• 2002

In this paper, an adaptive packet acquisition performance of a CDMA/TDD packet radio system is analyzed and simulated in a frequency-selective Rayleigh fading channel. The frequency-selective fading process is assumed to be WSSUS model which is typical for a satellite and a mobile radio communications. The performance is evaluated in terms of packet error probability. In this adaptive packet acquisition scheme, an auxiliary training sequence is placed within data packet to estimate time-varying channel state. From the simulation results, it is confirmed that the proposed acquisition scheme significantly improves packet error performance compared to the conventional fixed acquisition scheme, especially, for the case of low Doppler frequency. The analysis in this paper can be applied to the design of a CDMA/TDD packet radio system.

• ETRI Journal
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• v.26 no.5
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• pp.405-412
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• 2004

MC-CDMA, a multicarrier (MC) modulation scheme based on code division multiple access (CDMA), is the most likely candidate for the next generation of mobile radio communications. The rate compatible punctured turbo (RCPT) coded hybrid automatic repeat request (HARQ) has been found to give improved throughput performance in a direct sequence (DS) CDMA system. However, the extent to which the RCPT HARQ improves the throughput performance of an MC-CDMA system has not been fully understood. In this paper, we apply the RCPT HARQ to MC-CDMA and evaluate by computer simulations its performance in a frequency selective Rayleigh fading channel. We found that the performance of RCPT HARQ MC-CDMA is almost insensitive to channel characteristics. The performance can be drastically improved with receive diversity combined with space-time transmit diversity. In addition, the comparison of RCPT HARQ MC-CDMA, orthogonal frequency division multiplexing, and DS-CDMA shows that under similar conditions the throughput of MC-CDMA is the best in a frequency selective fading channel.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.7A
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• pp.628-638
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• 2005

The analysis of maximum diversity order and coding gain for multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems over time-and frequency-selective (or doubly-selective) channels is addressed in this paper. A novel channel time-space correlation function is developed given the spatially correlated doubly-selective Rayleigh fading channel model. Based on this channel-model assumption, the upper-bound of pairwise error probability (PEP) for MIMO-OFDM systems is derived under the maximum likelihood (ML) detection. For a certain space-frequency code, we quantify the maximum diversity order and deduce the expression of coding gain. In this wort the impact of channel time selectivity is especially studied and a new definition of time diversity is illustrated correspondingly

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.11B
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• pp.1522-1533
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• 2001

In this paper, we handle the estimation method of the received $E_{b}l1_{o}$ for forward closed-loop power control in cdma2000 systems. The estimation of MS-received $E_{b}l1_{o}$ utilizes the symbols related to the forward power control subchannel transmission. The estimation of the received bit energy and noise variance is analyzed for the frequency-selective Rayleigh fading channel. In order to improve SIR (signal-to-interference), the estimation of the received bit energy is made by the coherent combining of the rake-fingers and received I/Q symbols. And, in this paper, we evaluate the performance of forward closed-loop power control according to the mobile speed and the power adjustment step size in terms of the bit error rate (BER) and power control error. Simulation results present the optimal power adjustment step sizes according to the mobile speeds.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.7A
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• pp.557-567
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• 2005

We evaluate the BER performance of OFDMA system for Wibro services in frequency selective Rayleigh fading channel, considering the carrier frequency offset and the nonlinear high power amplifier. In the uplink OFDMA, nonlinear amplifier and frequency offset introduce larger BER degradation than in the downlink. We explain the reason and obtain the required output back-off of the nonlinear amplifier and value of frequency offset for good BER performance.

• Journal of Communications and Networks
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• v.6 no.3
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• pp.203-208
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• 2004

A combined precoding and turbo decoding strategy for multi-path frequency-selective fading channels is presented. The precoder and multi-path fading channel are jointly modeled as a finite-state probabilistic channel to provide the multi-stage turbo decoder with its statistics information. Both a priori and a posteriori probabilities are used in the metric computation to improve the system performance. Structures of the combined turbo-encoder, interleaver, and precoder in the transmitter and two-stage turbo decoder in the receiver are described. Performance of the proposed scheme in fixed, Rician and Rayleigh multi-path fading channels are evaluated by simulation. The results indicate that the combined precoding and two-stage turbo decoding strategy provides a considerable performance improvement while maintaining the same inner structure of a conventional turbo decoder.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.35S no.2
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• pp.22-30
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• 1998

In this paper, we analyze CDMA systems using M-orthogonal spreading codes. We assume that each user one set of M-orthogonal spreading codes allocated randomaly. The effect of multiple access interference from the reference and adjacent cells is considered slowly frequency selective rayleigh fading channels. and the adjacent cells interference is considered toanalyze the system performance. We calculate bit error rate and the maximum number of users whoe can communicate simulaneously within a cell by suing Rake receiver. By comparing CDMA systemwhich transmits 1 bit/spreding code, our system shows bit error rate decreases as M increases under the same bandwidth and infromation rate.

• Proceedings of the IEEK Conference
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• 2000.07b
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• pp.982-985
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• 2000

This paper presents channel estimation of an asynchronous W-CDMA reverse link using the interpolation and moving average algorithm in frequency-selective Rayleigh fading channel. The proposed algorithm is an interpolated decision-directed (IDD) block-wise moving average (BWMA) algorithm. The IDD-BWMA algorithm performs two- stage processes. The first stage performs data decision to make a virtual pilot channel by using linear interpolation channel estimation scheme. Then, the second stage performs the channel estimation of the “block-wise moving average” type by using a virtual pilot channel obtained in the first stage. By using Monte-Carlo computer simulations, we show that the proposed channel estimator is superior to other estimation schemes such as the WMSA(K=1) and DD-RAKE at higher Doppler frequencies, especially.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.7B
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• pp.1351-1360
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• 1999

In frequency selective channels, conventional PN code acquisition schemes are not ideal candidates. This is because they are primarily designed for the AWGN channel. In this paper, a direct-sequence spread-spectrum(DSSS) PN code acquisition system based on digital matched filtering (DMF) with automatic threshold control(ATC) algorithm is presented and analyzed with regards to probability of detection and probability of false alarm. These two important probabilities, the probability of detection ($P_D$) and the probability of false alarm ($P_{FA}$) are derived and analyzed in considering Doppler shift, sampling rate, mean acquisition time, and PN chip rate in frequency selective Rayleigh fading channel when using serial-search method as detection technique. From computer simulation results of a DMF acquisition system model, it is shown that the performance of the acquisition system using ATC algorithm is better than that of constant threshold system.