• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.4
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• pp.737-747
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• 1997

performance of the cellular CDMA overlay system is analyzed which shares the same band with existing microwave narrowband system to enhance the spectral efficiency. To suppress the interfreence from narrowband system, we used a linear predicition filter that adopts the adaptive least mean square algorithm. Alalyzing the performance in the Personal Communication Services channel, characterized as a multipath Rician fadng channels, we considered the power control to solve the near-far problem, and-off and multipath diversity. We also considered interleaving and channel coding to improve BER performance of the CDMA system.

• Journal of Communications and Networks
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• v.6 no.2
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• pp.112-122
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• 2004

A nonlinear spectral-line method utilizing the fourth absolute moment of the receiver discrete Fourier transform output is proposed as a non-data-aided fine carrier frequency synchronization algorithm for OFDM receivers. A simple modification of the algorithm resulting in low implementation complexity is also developed. Analytic expressions are derived for the steady-state frequency error variances of the algorithms and verified to be very accurate via computer simulations over AWGN and frequency selective multipath channels. Numerical results show that the proposed algorithms provide reliable and excellent steady-state performance, especially with PSK modulation. Also, the proposed algorithms are insensitive to symbol timing offsets, only requiring a coarse symbol timing recovery.

• Journal of Information Processing Systems
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• v.13 no.1
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• pp.141-151
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• 2017

Effective identification of wireless channel in different scenarios or regions can solve the problems of multipath interference in process of wireless communication. In this paper, different characteristics of wireless channel are extracted based on the arrival time and received signal strength, such as the number of multipath, time delay and delay spread, to establish the feature vector set of wireless channel which is used to train backpropagation (BP) neural network to identify different wireless channels. Experimental results show that the proposed algorithm can accurately identify different wireless channels, and the accuracy can reach 97.59%.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.6
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• pp.78-85
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• 2009

In time-varying multipath fading channels, orthogonal frequency division multiple access (OFDMA) uplink systems suffer severe performance degradation caused by inter-channel interference (ICI). In this paper, we propose a hybrid interference cancellation (HIC) for suppressing the degradation effect of ICI. The proposed HIC can achieve both exact interference cancellation and low detection complexity through efficient combination of parallel detection and serial cancellation. Simulation results show that, as the effect of Doppler increases, the proposed HIC achieves bit error rate (BER) performance enhancement in compared with severe performance degradation of conventional OFDMA receivers. In addition, both the computational complexity and total detection time are reduced.

• 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.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.38 no.3
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• pp.1-8
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• 2001

In the DS/CDMA mobile communication systems, the parallel interference canceller is used in order to reduce the multiple access interference and the multipath fading. It is needed the accurate interference estimate in the multistage parallel cancellation. In this paper, the adaptive cancellation method and the new tentative decision device arc proposed and the performance is analyzed. The adaptive cancellation method uses the normalized least mean square(NLMS) algorithm to calculate the weight adaptively, and new tentative decision device uses the hyperbolic tangent decision with null zone. Computer simulation shows that the proposed scheme has the improved performance and the number of user is increased 48% compared with the conventional receiver.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.1C
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• pp.102-108
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• 2006

In this paper, we propose an interference cancellation(IC) scheme using a partial Rake(PRAKE) combining in ultra-wideband(UWB) multipath fading channels. In this IC scheme, differently from the conventional transmitter model, which employs a guard interval between each frame, the guard interval is employed between each slot for estimating the multiple access interference(MAI). The UWB systems using the proposed IC scheme have little performance degradation without regard to the number of user, while the conventional UWB systems have a significant performance degradation according to the number of user. In order to reduce the receiver complexity, the PRAKE combining of post-canceled signal and the partial user IC scheme are also proposed.

• 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.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.6A
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• pp.631-639
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• 2004

In this paper, we presented a new interference suppression method based on code grouping and groupwise decorrelation for multirate DS-CDMA downlink. The code grouping is accomplished according to the correlation property between the mother code and the child codes in OVSF code tree. Using groupwise decorrelation, the proposed receiver has relatively low computational complexity and does not require any information about interference users, such as code, data, and amplitude. From the simulation results in multipath channels, the proposed receiver is to provide significant performance enhancement.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.12A
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• pp.1161-1167
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• 2005

In this Paper, a concept of virtual smart antenna (SA) is introduced for orthogonal Sequency division multiplexing (OFDM)-based cellular systems with a frequency reuse factor equal to 1. The OFDM-based cellular system is robust to multipath channels but has a disadvantage that the intercell interference (ICI) caused by adjacent base stations is large at the edge of a cell. In this paper, after deriving the symbol timing offset estimation scheme for the OFDM signal received from multiple base stations in a quasi-static fading channel, the ICI cancellation method based on virtual smart antenna is proposed using the steering vector formed by the symbol timing offset of the desired signal and interference signals.