• Journal of Satellite, Information and Communications
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• v.12 no.1
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• pp.1-5
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• 2017

In this paper, multiuser detector (MUD) based on radial basis function (RBF) is proposed and simulated for a multicode direct sequence/code division multiple access (DS/CDMA) system in a multipath fading channel. The performance of RBF-based MUD is compared with that of many suboptimal multiuser detectors in terms of bit error probability. From the simulation results, it is confirmed that the RBF-based MUD outperforms decorrelating detector, and achieves near-optimum performance under various environments. The results in this paper can be applied to design of MUD for a multicode DS/CDMA system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.3B
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• pp.188-195
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• 2002

In this paper, we consider efficient multiuser receiver structures using Hopfield neural network algorithm focused to construct a synchronous multi-rate code division multiple access (CDMA) system. Although the optimum receiver for multiuser detection can be realized attaining the best BER performance, it is too complex for practical implementation. Therefore, we propose near-optimal receivers of relatively low computationally complex multiuser detection structures for realizing multi-rate CDMA system and their performances are compared with conventional matched filter and other prominent multi-rate multiuser detectors, Computer simulations show that the Hopfield neural network based multiuser receiver achieves substantially better BER performance in Rayleigh fading environments.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.2A
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• pp.96-101
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• 2003

This paper is on the user equipment (UE) side time tracker design and implementation of the wideband code division multiple access (WCDMA) system. The time tracker is constructed as a second order closed loop including time error detector (TED), loop filter (LP), numerically controlled oscillator (NCO), and sample selector (SS). Through the simulation, we found the gain of the TED as a function of the CPICH power contribution to the total transmission power of the base station. Also we derived the transfer function of the loop and the BER versus DPCH power relationships where timing offsets and loop noise bandwidths are used as parameters. In the curve, we can conclude that there are appropriate loop noise bandwidths according to the given environments for the better performance.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.9A
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• pp.1368-1376
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• 2000

This paper describes the codesign method for IS-95 based CDMA(Code Division Multiple Access). By codesign we mean to design hardware and software simultaneously. Codesign lead to reduction in design time, cost and power consumption. When we partition a system into hardware and software, some modules with longer processing time and larger power consumption are implemented using hardware and the remaining part is implemented using software. In proposed design, we design the synchronous accumulator of CDMA searcher in hardware and the other part in software, The hardware part is designed using VHDL, while software part is designed using GC(Generic C). We simulated and verified the system using COSSAP in SYNOPSYSTM. Experimentation showed the maximum 48.5% speed reduction compared with the design using software only.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2008.05a
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• pp.121-124
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• 2008

In this paper, we will design a 800MHz broadband antenna after a problem of the narrow bandwidth is improved. This multiple band antenna unifies the CDMA(Code Division Multiple Access), GSM(Global System for Mobile telecommunication) and TRS(Trunked Radio System) band in the UHF bandwidth, and then it is possible at the shore base station or repeater as the commercial use. It used the duplex resonance effect It had the L-shaped feeding structure which adds the V-slot. And it improved profit using stack structure. It was measured that the frequency bandwidth of the designed antenna which is planed $792{\sim}1040MHz$ with 248MHz(33%). And the antenna gain is 9.4dBi, 3dB beam width $60^{\circ}$ in radiation pattern.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.5
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• pp.755-764
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• 2001

In this paper, we propose maximum likelihood (ML) decision feedback channel estimation (DFCE) for M-ary orthogonal modulation in direct sequence/code division multiple access (DS/CDMA) systems. The proposed DFCE uses the maximum combiner output in a RAKE receiver as decision feedback information, enabling M-ary orthogonal signals to be demodulated coherently and a RAKE receiver to use a em maximal ration combining (MRC) scheme. However, the performance of the proposed DFCE in the multiuser environment is severely degraded due to multiple access interference (MAI). To overcome this problem, a multistage parallel interference cancellation (PIC) scheme is combined with the proposed DFCE for multiuser environments. Accurate knowledge of the channel coefficient estimated by the proposed DFCE is used to regenerate the signal of each user for the multistage PIC scheme. According to the results of our simulations, the performance of coherent demodulation using the proposed system is significantly improved in comparison with conventional noncoherent demodulation.

• Proceedings of the IEEK Conference
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• 2000.07a
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• pp.497-500
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• 2000

In this paper, we compare the bit-error-rate performance of the fast-frequency-hopped spread-spectrum multiple-access (FFH/SSMA) and direct-sequence code-division multiple access (DS/CDMA) systems in a Rician fading channel. Each system has a same data rate, bandwidth and transmits over a Rician fading channel. The results illustrate tradoffs in performance between the FFH/SSMA and DS/CDMA systems as a function of the parameters such as average signal to noise ratio and processing gain. The performance of the FFH/SSMA system is shown to be less sensitive to the change of fading environments, while the change of processing gain and average signal to noise ratio gives considerable affect to the FFH/SSMA system compared with the DS/CDMA system. Without respect to the change of system parameters, for most of Rician fading channels (except non-fading channel), FFH/SSMA system gives better performance than DS/CDMA system in BBR < 10$\^$-3/.

• Information and Communications Magazine
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• v.19 no.7
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• pp.40-55
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• 2002

The advent of Third Generation (3G) communication systems, with their ability to process real-time multimedia applications and their large bandwidths, will greatly enhance mobile Internet access. Not only does Wideband Code Division Multiple Access (WCDMA) and cdma2000 radio technology offer an advantageous density for voice in terms of spectral efficiency, it also supports higher rates and offers differentiated levels of duality of Service (QoS) for data applications. The early introduction of packet and multimedia technologies will be a key element in realizing a quick and successful return on the operator's investments in Universal Mobile Telecommunications System (UMTS) and cdma2000.

• Journal of Communications and Networks
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• v.7 no.3
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• pp.258-262
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• 2005

An adaptive beamforming system based on code filtering and differential correlation approaches is proposed. The differential correlation method was originally proposed for time delay estimation of direct sequence code division multiple access (DS-CDMA) systems under near-far ratio conditions and the code filtering correlation algorithm, on the other hand, was proposed for array response estimation in DS-CDMA systems under perfect power control. In this paper, by combining differential correlation concept with the code filtering beamforming technology, an accurate estimate of the beam forming weights and an enhanced performance of DS-CDMA systems under sever near-far ratio conditions is achieved. The system performance in terms of beam pattern and bit-error-rate (HER) shows that the proposed adaptive beamformer outperforms the conventional code filtering correlation technique.

• 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.