• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.9C
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• pp.589-595
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• 2011

This paper proposes an improved multi-stage timing offset estimation scheme for orthogonal frequency division multiplexing (OFDM) systems in multipath fading channel environment. The conventional multi-stage timing offset estimation scheme is very sensitive to the random multipath components. By exploiting the sample standard deviation of the cross-correlation values, the proposed scheme achieves a robustness to the random multipath components. Simulation results demonstrate that the proposed scheme has a higher correct estimation probability and has a better mean square error (MSE) performance than the conventional scheme in multipath fading channels.

• The Journal of the Acoustical Society of Korea
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• v.24 no.3E
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• pp.99-108
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• 2005

To investigate the equalizer performance in underwater acoustic communication m the presence of intersymbol interference (ISI) due to multipath, computer simulations are carried out in discrete multipath shallow water channels for three different horizontal ranges. For the purpose of computation simplicity, least mean square (LMS) algorithm is adopted both in linear equalizer and nonlinear equalizer, decision feedback equalizer (DFE) to cancel out ISI effects. Binary phase shift keying (BPSK) signals have been transmitted with high data rate of 2000bps through the use of equalization technique. The results demonstrate that equalization is an efficient way to achieve high transmission data rate in the shallow water channel.

• Proceedings of the IEEK Conference
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• 2005.11a
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• pp.141-146
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• 2005

In this paper, we propose to extend the TSS-LS (Two-Step Search scheme with Linear search based Second step) scheme which was already proposed by the authors for coherent UWB (Ultra Wide Band) systems, to rapid and reliable acquisition of noncoherent UWB systems in multipath channels. The proposed noncoherent TSS-LS employing simple energy window banks utilizes two different thresholds and search windows to achieve fast acquisition. Furthermore, the linear search is adopted for the second step in the proposed scheme to correctly find the starting point in the range of effective delay spread of the multipath channels, and to obtain reliable BER (Bit Error Rate) performance of the noncoherent UWB systems. Simulation results show that the proposed TSS-LS can achieve significant reduction of the required mean acquisition time as compared to general search schemes. In addition, the proposed scheme achieves quite good BER performance, which is favorably comparable to the case of ideal perfect timing.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.10B
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• pp.1714-1721
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• 2000

In the mobile communication using DS-CDMA systems the problem of multiple user interference which reduce the performance is generated by multiple user access. In this paper to solve this problem we proposed the direct decision blind adaptive receiver with knowledge of only the desired user's spreading sequence. Simulation result present that the total user's power has equal gain The gain of signal to interference ratio for the proposed blind DD-LMS receiver has about 6[dB] than conventional receiver at additive white Gaussian noise and large gain at multipath channels. And when interference user's power has more large gain than desired user's power the gain of SIR for the proposed receiver has large value. And simulation result of bit error rate present that DD-LMS receiver has higher performance than LCCMA receiver. Thus the proposed blind DD-LMS receiver has robustness against interference of high power user and multipath channels.

• Proceedings of the KIEE Conference
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• 1998.07g
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• pp.2467-2469
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• 1998

We examine the performance of high-speed non-directed infrared links using pulse-position modulation (PPM) with trellis-coded modulation (TCM) to mitigate the effects of multipath-induced intersymbol interference(ISI) on such links. Using the measured characteristics of multipath indoor infrared channels, we calculate BER curves and ISI power penalties for maximum-likelihood sequence detection of 8-PPM links using rate-2/3 trellis codes operation at 10 and 30Mb/s. Our results indicate that the suggested decoder of PPM with TCM is a very promising decoder on high-speed non-directed infrared channels.

• 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 Communications and Networks
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• v.7 no.3
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• pp.278-283
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• 2005

This paper proposes a blind channel estimation scheme for long code direct sequence code division multiple access (DS­CDMA) systems with multipath fading channels. This scheme combines the advantages of Toeplitz displacement and correlation matching methods to achieve improved performance. The basic idea is to remove the effects of noise and interferences with Toeplitz displacement operation and then estimate the multi path channel parameters with the correlation matching method. Simulation results are presented to show that the proposed scheme provides better MSE performance and robustness against the near-far problem.

• Proceedings of the IEEK Conference
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• 2000.07b
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• pp.765-768
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• 2000

In this paper, we analyze the channel estimation method by using Reference symbols for burst OFDM transmission systems. We set some parameters (the number of Reference symbols, the pilot spacing in Reference symbols, the update constant of equalizer coefficients) to evaluate their performance in the fixed multipath fading channel as like indoor environment.

• The Journal of the Convergence on Culture Technology
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• v.3 no.4
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• pp.191-198
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• 2017

In this paper, we compare the transmission performance of Code Division Multiple Access (CDMA) and Orthogonal Frequency Division Multiplexing (OFDM) under long duration multipath channel environments. This paper generates underwater channels through Bellhop based on the underwater environmental data of the west sea. BER performance of CDMA and OFDM are analyzed through various underwater channels based on the channels. Computer simulations result show that CDMA has better performance than OFDM when multipath delay time of underwater channel is shorter than spreading factor (SF). However, OFDM has better BER performance than CDMA as multi-path delay time increases.