• Journal of Communications and Networks
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• v.6 no.1
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• pp.9-18
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• 2004

Self-encoded multiple access (SEMA) is a unique realization of random spread spectrum. As the term implies, the spreading code is obtained from the random digital information source instead of the traditional pseudo noise (PN) code generators. The time-varying random codes can provide additional security in wireless communications. Multi-rate transmissions or multi-level grade of services are also easily implementable in SEMA. In this paper, we analyze the performance of SEMA in additive white Gaussian noise (AWGN) channels and Rayleigh fading channels. Differential encoding eliminates the BER effect of error propagations due to receiver detection errors. The performance of SEMA approaches the random spread spectrum discussed in literature at high signal to noise ratios. For performance improvement, we employ multiuser detection and Turbo coding. We consider a downlink synchronous system such as base station to mobile communication though the analysis can be extended to uplink communications.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.10B
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• pp.2004-2010
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• 1999

This paper presents the blind multiuser detector using the constant modulus algorithm(CMA) to solve the near-far problem in DS-CDMA systems. The convergence property of the detector is compared with the conventional MOE(minimum output energy) detector by means of SIR(signal-to-interference ratio). The MOE detector needs both the spreading code of the users and the timing information, while proposed methods needs only information about the spreading code of users Simulation results show that the CMA-based detector is superior to the conventional blind MOE multiuser detector. For this, the BER performance was tested using different values of SNR and near-far ratio. The SIR is also investigated for different number of users in AWGN and Rayleigh fading channels. We have observed that the proposed blind multiuser detector performs better than conventional MOE multiuser detector.

• Journal of The Institute of Information and Telecommunication Facilities Engineering
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• v.2 no.3
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• pp.17-23
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• 2003

Turbo decoding in combination with detection strategy for Multi Access Interference (MAI) cancellation has been shown to be very effective for MC-CDMA system in Rayleigh multi-path fading environment. This paper reports new simulation results on the efficacy of joint decoding and detection for MC-CDMA in nonlinear and fading channel.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.10
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• pp.4738-4758
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• 2017

Resource allocation plays a crucial role in multiuser multiple input multiple output orthogonal frequency division multiplexing (MIMO-OFDM) systems to improve overall system performance. While previously proposed resource allocation algorithms are mainly designed from the point of view of the information-theoretic, we formulate the resource allocation problem as an average bit error rate (BER) minimization problem subject to a total power constraint when considering employing realistic MIMO detection techniques. Subsequently, we derive the optimal subcarrier and power allocation algorithms for three types of well-known MIMO detectors, including the maximum likelihood (ML) detector, linear detectors, and successive interference cancellation (SIC) detectors. To reduce the complexity, we also propose a two-step suboptimal algorithm that separates subcarrier and power allocation for each detector. We also analyze the diversity gain of the proposed suboptimal algorithms for various MIMO detectors. Simulation results confirm that the proposed suboptimal algorithm for each detector can achieve a comparable performance with the optimal allocation with a much lower complexity. Moreover, it is shown that the suboptimal algorithms perform better than the conventional algorithms that are known in the literature.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2000.10a
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• pp.235-238
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• 2000

In this paper the MUD(Multi-User Detection) schemes and turbo codes are utilized in DS-CDMA mobile communication systems. Theses schemes effectively mitigate the effects of MAI(Multiple Access Interference) and Rayleigh fading. Using Monte Carlo simulation, the performance of the proposed schemes is analyzed for various channel conditions.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.1
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• pp.49-56
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• 2006

In this paper, to overcome the effect of nonlinear power amplifier, CE-CPSK(Constant Envelope Continuous Phase Shift Keying)modulation method which has the constant envelope and continuous phase characteristics is proposed. The code acquisition performances of the CE-CPSK modulated system and BPSK system are analyzed. And the performance is evaluated in terms of mean acquisition time and detection probability with the output backoff of the amplifier in multiuser environment. Results performed in a channel having a high degree of AM nonlinearity(AM-to-AM conversion), have shown that the CE-CPSK signal, when passed through class C-nonlinear Amplifier, has a spectrum with greatly reduced sidelobes compared to the conventional BPSK signal. The code acquisition performance of a CE-CPSK modulation system is better than that of BPSK system with nonlinear amplified multiuser environments.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.7B
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• pp.928-936
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• 2001

본 논문은 CDMA 시스템을 근간으로 향후 서비스 될 3세대 이동통신 시스템에 선택적으로 적용될 수 있는 다중 사용자 간섭 제거 기법을 제안한다. 제안 방식은 다단계 간섭 제거기의 각 단계에 직교 다항식의 근사화 기법을 적용하여 제거될 간섭 신호의 양을 결정하고, 이를 상호 보완적으로 제거한다. 사용자 용량의 포화도에 따른 최적해로의 수렴성을 각 방식의 스펙트럼 반경의 분석을 통해 비교하였으며, 제안한 방식이 병렬 간섭 제거 기법(Parallel Interference Cancellation, PIC)을 사용한 방식과 비교하여 2배 이상의 적은 단계를 사용했음에도 거의 같은 정도의 오차 성능을 보였으며, 실험을 통해 비트 오율이 $10^{-5}$을 기준으로 약 30% 정도의 사용자 수용 능력이 증대되었다. 또한 전력 제어의 적용 여부에 대한 시스템의 비트 오율 측면의 성능 비교, 원근 효과의 관점에서 성능을 비교하여 제안된 간섭 제거 기법이 비적응형 가중치를 적용한 병렬 간섭 제거 기법보다 우수함을 보였다.

• Proceedings of the IEEK Conference
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• 2000.09a
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• pp.963-966
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• 2000

현재 상용화된 CDMA (code division multiple access)방식은 사용자가 증가함에 따라 다중 사용자 간섭(multiuser interference)에 의해 통화품질 향상 및 가입자 수용 용량 증대에 한계를 가지고 있다. 이러한 문제를 극복하기 위해 다양한 다중 사용자 간섭 제거 알고리즘이 제안되었다 〔1-5〕. 본 논문에서는 여러 형태의 알고리즘들 가운데, 역상관 successive interference cancellation(SIC) , zero-forcing decision-feedback(ZF-DF) 검파기와 parallel interference cancellation(PIC) 검파기를 하이브리드 형태로 구성하는 방법을 제안하였고. 그에 따른 성능 분석 및 Rayleigh 페이딩 환경에서 컴퓨터 시뮬레이션을 통한 성능비교를 하였다. 컴퓨터 모의시험결과, 본 논문에서 제안한 3가지 하이브리드 검파기 모두 기존 검파기에 비하여 우수한 성능을 보였다.

• Journal of Communications and Networks
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• v.1 no.2
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• pp.118-133
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• 1999

In this paper we compare linear and non-linear inter-ference cancellation for systems employing code division multi-ple access (CDMA) techniques. Specifically, we examine linear and non-linear parallel interference cancellation(also called multi-stage cancellation) in relationship to other multiuser detection al-gorithms. We show the explicit relationship between parallel inter-ference cancellation and the decorrelator (or direct matrix inver-sion). This comparison gives insight into the performance of paral-lel interference cancellation (PIC) and leads to vetter approaches. We also show that non-linear PIC approaches with explicit chan-nel setimation can provide performance improvement over linear PIC, especially when using soft non-linear symbol estimates. The application of interference cancellation to non-linear modulation techniques is also presented along with a discussion on minimum mean-squared error(MMSE) symbol estimation techniques. These are shown to further improve the performance of parallel cancella-tion.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.11C
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• pp.1085-1091
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• 2006

The major goal of this paper is to develop a practically implemental radial basis function (RBF) neural network based multi-user detector (MUD) for direct sequence (DS)-CDMA system. This work is expected to provide an efficient solution for RBF based MUD by quickly setting up the proper number of RBF centers and their locations required in training. The basic idea in this research is to estimate all the possible RBF centers by using supervised ${\kappa-means$ clustering technique, and select the only centers which locate near seemingly decision boundary between centers, and reduce further by grouping the some of centers adjacent each other. Therefore, it reduces the computational burden for finding the proper number of RBF centers and their locations in the existing RBF based MUD, and ultimately, make its implementation practical.