• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.5
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• pp.1230-1239
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• 1996

This paper analyzes matched-filter acquistion performance of a direct-sequence spread-specturm multiple-access system in a Rayleigh fading channel. For an application of multiple access system, multiple access interference is considered in the performance analysis. A signal flow graph technique is used to derive mean acquisition time in terms of detection and false alarm probabilities. As aresult of performance analysis, it is shown that mean acquisition time increases as fading rate becomes faster andthe numbre of users increases, and it decreases as a matched-filter length becomes logner. The variation of parameter values hs much influence on acquisition performance as SNR/chip becomes smaller.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.8
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• pp.804-810
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• 2002

The code division multiple access(CDMA) system capacity is limited by the amount of interference of the system. To reduce the unnecessary interference, this paper proposes optimized cell identification codes for site selection diversity transmission(SSDT) power control in wideband code division multiple access system of third generation partnership project(3GPP). The main objective of SSDT power control is to transmit on the downlink from the primary cell, and thus reducing the interference caused by the multiple transmission. In order to select a primary cell, each cell is assigned a temporary identification(ID) and user equipment(UE) periodically informs a primary cell ID to the connecting cells during soft handover. The non-primary cells selected by UE do not transmit the dedicated physical data channel(DPDCH) to reduce the interference. A major issue with the SSDT technology is the impact of uplink symbol errors on its performance. These errors can corrupt the primary ID code and this may lead to wrong decoding in the base station receivers. The proposed SSDT cell ID codes are designed to minimize the problem and to be easily decoded using simple fast Hadamard transformation(FHT) decoder.

• ETRI Journal
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• v.25 no.5
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• pp.418-421
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• 2003

We propose an unbiased signal-to-interference ratio (SIR) estimator for the high speed downlink packet access (HSDPA) system. The proposed SIR estimator solves the problem of underestimation present in conventional SIR estimators and is suitable for channel quality measurement in the adaptive modulation and coding scheme of HSDPA, which requires accurate SIR estimation for optimum adaptive modulation and coding selection. Our analysis and simulation results demonstrate the improved estimation performance of the proposed SIR estimator.

• Journal of Internet Computing and Services
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• v.12 no.1
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• pp.27-38
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• 2011

In this paper, we propose a multiple access scheme using MHP(Modified Hermite Polynomial) pulse and ternary code for high-data and low-data rate for Out-body WBAN(Wireless Body Area Network). To satisfy the requirement of WBAN system, UWB-IR has been considered as a promising candidate for Out-body WBAN. The proposed multiple access scheme, using orthogonal MHP pulse and ternary code sets, reduces multi-user interference and distinguishes user signal from multi-user signals. We propose two algorithms for synchronous and asynchronous WBAN system. The symbol is constructed by MHP pulses and time hopping duration to reduce multi-user interference in the synchronous WBAN system. The symbol also is constructed by ternary code to avoid collision between pulse trains in the asynchronous WBAN system. The results of the proposed multiple access scheme show a clear improvement of BER.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2006.05a
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• pp.410-414
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• 2006

In the present, Orthogonal Frequency Division Multiple Access (OFDMA) that wireless access scheme for high speed data transmission is noticed in mobile communication market and OFDMA/TDD scheme will be used combining Time Division Duplex (TDD) scheme based on OFDMA. The Base Station's receiver synchronizes the symbol timing to anyone user's symbol and the other user's symbols have some Symbol Timing Offset (STO). Linear phase shift is occurred by each user's STO in an OFDMA symbol and the Multiple Access Interference (MAI) caused by the summation of each user's linear phase shift degrades the performance of ranging code detection. In this paper, we analyze the ranging code detection performance for each users STO in OFDMA/TDD system. Simulation results show that the more users access and mobile speed increase, the more ranging code detection performance degrades.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.5
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• pp.901-911
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• 1994

The error performance of M-ary differential phase shift keying (MDPSK) through m-distribution fading channel in hybrid direct sequence/slow frequency hopped spread spectrum multiple access (DS/SFH-SSMA) systems has been evaluated, and also the error probability has been evaluate when adopting diversity technique and coding technique. From the results, we know that the error performance more deteriorates as depth of fading becomes deeper. In Rayleigh fading environment (m=1), increasing of the number of frequency hopping (q) reduces the effect of multiple access interference, because it decreases the probability a hit. When q is much larger than the number of user (K), the probability of error in high E/N region is dominated by the multipath interference while the multiple access interference is negligible. In lower E/N region, the probability of error is independent of q because the effect of gaussian noise becomes dominat.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.23 no.11
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• pp.1407-1413
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• 2019

In this paper, we assume that another transmitter can transmit its data signal in the same frequency band in order to maximize the frequency efficiency of non-orthogonal multiple access(NOMA) systems. We also focus on the improvement in fairness performance of receiver's data rates, not the maximization of sum data rate for NOMA systems. Thus, in this paper, we propose a power allocation scheme to enhance the fairness performance of average data rates of receivers considering the NOMA systems in the presence of interference. Assuming Rayleigh fading channels, the average data rates of receivers are defined, and the power allocation coefficients to improve the data-rate fairness are derived by using high signal-to-noise power ratio approximation. In addition, through simulations, it is shown that the proposed power allocation scheme can improve the data-rate fairness in the NOMA system with interference.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.3A
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• pp.362-374
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• 2000

In this paper, trellis coded 16 QAM Multi-Carrior CDMA system is proposed, Using the equivalent signal-to-noise plus interference Power ratio (SNIR) of Multi-Carrier CDMA system in the reverse link, capacity and BER performance of trellis coded 16 QAM Multi-Carrier CDMA system are analyzed taking into account the number of multi-carrier, the number of multiple access user, the number of SC/MRC diversity branch, and Rician fading parameter in multiuser interference and Rician fading channel. And the capacity and the BER performance of trellis coded 16 QAM Multi-Carrier CDMA system using selection combining (SC) and maximal ratio cabining (MRC) diversity are numerically compared. Obtained results show that the capacity of proposed system depends on the number of multi-carrier. ti is found that the trellis coded 16 QAM Multi-Carrier CDMA system with SC/MRC antenna diversity scheme is efficient to combat multipath fading and to increase the maximum number of users in high speed data communication. With the results of analysis. MRC diversity technique provides the performance fro high speed data communications. Finally, we present a numerical approach to derive the capacity and the BER performance and to find the maximum number of multiple access user for Multi-Carrier system in multiuser interference and Rician fading channel.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.3C
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• pp.228-236
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• 2006

A Multicarrier code division multiple access(MC-CDMA) is a scheme that combines multicarrier modulation with CDMA. It offers robustness to frequency selective fading effect and can support higher rate data transmission with higher spectral efficiency. The objective of this article is proposed and analyzed a new asynchronous MC-CDMA system with various kinds of data rates which employs a multiple access interference (MAI) canceller. The proposed multirate MC-CDMA system can be accomplished by changing the number of Parallel branch(P) according to their data rate and hybrid interference canceller(HIC) are used for MAI cancellation. We compare the performance of proposed system in terms of average bit error rate(BER) with that of a single rate MC-CDMA system. The results show the large improvement in performance that can be attained by the cancellation scheme under multipath environments.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.7 no.6
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• pp.1153-1160
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• 2003

In this paper, the performance of the UWB communication systems is analyzed in the presence of the Narrow Band Interference(NBI). UWB communication systems are modeled as using the Pulse Position Modulation(PPM). In this system, a Gaussian monocycle is used as the received pulses. The NBI is considered as a zero-mean random process with a constant spectral power density over its whole bandwidth. We obtain the mathematical expressions for describing the effect of the NBI on the UWB system. And it can be shown that the suppression of the effect of NBI on the UWB systems is available by adjusting the PPM related parameter.