• Proceedings of the IEEK Conference
• /
• 2005.11a
• /
• pp.73-76
• /
• 2005

Preamble based synchronization result in performance degradation due to the high time variation in the power delay profile of the channel in fast varying channel. Since most of the timing metric that exploit the preamble is not based on theoretical back ground, it is not easy to find out the reason. In this paper, the behavior of the timing metric in the multipath fading channel is explained.

• Proceedings of the IEEK Conference
• /
• 2001.09a
• /
• pp.959-962
• /
• 2001

Turbo codes of long block sizes have been known to show very good performance in an AWGN channel and the turbo code has been strongly recommended as error correction code for IMT-2000 in 3GPP(3rd Generation Partnership Project). Recently, turbo codes of short block sizes suitable for real time communication systems have attracted a lot of attention. Thus, in this paper we consider the turbo code of 1/3 code rate and short frame size of 192 bits in ITU-R channel model. We analyzed the performance of W-CDMA systems of 10MHz bandwidths employing RAKE receiver with not only MRC diversity but also turbo code.

• Journal of electromagnetic engineering and science
• /
• v.12 no.1
• /
• pp.77-84
• /
• 2012

This paper introduces our development of a MIMO-OTA system with simplified configuration. The key element of our proposal is the adoption of an antenna branch-controlled configuration for generating multipath delayed waves. The signal processing is carried out on IF band signal with an FPGA in a fading-emulator-type MIMO-OTA measurement system. The proposed scheme is largely different from available system configurations for the fading simulator method of constructing the OTA test environment. We describe the principle of the proposed scheme, channel model incorporated in the system, basic configuration of the developed system, and its performance.

• Proceedings of the Acoustical Society of Korea Conference
• /
• 1998.06c
• /
• pp.357-360
• /
• 1998

DS/CDMA system rejected narrow-band interference and additional White Gaussian noise which are occured at multipath, intentional jammer and multiuser to share same bandwidth in mobile communication systems. Because of having not sufficiently obtained processing gain which is related to system performance, they were not effectively suppressed. In this paper, an matched filter channel model using backpropagation neural network based on complex multilayer perceptron is presented for suppressing interference of narrow-band of direct sequence spread spectrum receiver in DS/CDMA mobile communication systems. Recursive least square backpropagation algorithm with backpropagation error is used for fast convergence and better performance in matched filter receiver scheme. According to signal noise ratio and transmission power ratio, computer simulation results show that bit error ratio of matched filter using backpropagation neural network improved than that of RAKE receiver of direct sequence spread spectrum considering of con-channel and narrow-band interference.

• Journal of Communications and Networks
• /
• v.5 no.2
• /
• pp.150-156
• /
• 2003

In this paper, an uplink MC-CDMA system incorporating multiuser detection and smart antennas has been considered. The performance of asynchronous as well as synchronous system is studied over a correlated Rayleigh multipath slow fading channel. A simplified array-processing algorithm suitable for slow fading situation is investigated to overcome the heavy computational complexity associated with Eigen solutions. The effect of variable data rate in the system performance is considered and effectiveness of antenna array to handle high data rate is discussed. A brief investigation on the system performance degradation due to correlated channel is also carried out. Based on the extensive simulation carried out, the performance of the asynchronous uplink system is found dramatically improved with antenna array and multiuser detection. Asynchronicity and channel correlation are found to affect the system performance significantly. The investigated simpli- fied algorithm produces similar results as Eigen solutions in slow fading situation with much reduced complexity.

• Journal of Communications and Networks
• /
• v.12 no.4
• /
• pp.317-329
• /
• 2010

In recent years, many sparse estimation methods, also known as compressed sensing, have been developed. However, most of these methods presume that the measurement matrix is completely known. We develop a new blind maximum likelihood method-the expectation-sparse-maximization (ESpaM) algorithm-for models where the measurement matrix is the product of one unknown and one known matrix. This method is a variant of the expectation-maximization algorithm to deal with the resulting problem that the maximization step is no longer unique. The ESpaM algorithm is justified theoretically. We present as well numerical results for two concrete examples of blind channel identification in digital communications, a doubly-selective channel model and linear time invariant sparse channel model.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.18 no.5
• /
• pp.721-729
• /
• 1993

A new channel simulation method for the urban mobile radio communication is proposed based on the Aulin's mathematical model which is suitable for urban areas. The proposed method maintains advantage of Jakes Method which is readily implemented in hardware and simulated well various channel states, and solves the problem that measured power spectrum generated by Jakes method does not agree with practical power spectrum. It has been shown by simulation; that good agreements between measured values generated by the proposed method and theoretical values for autocorrelation, LCR, ADF and power spectrum are obtained and that method can easily produce several independent fading signals.

• Journal of the Korean Institute of Telematics and Electronics A
• /
• v.32A no.9
• /
• pp.1177-1183
• /
• 1995

This paper proposes a new modulation scheme of $\pi$/4-DQPSK with stepped phase for a frequency selective fading channel. In the proposed modulation scheme, the phase of transmitted signal is shifted in the mid of a symbol duration in order to reduce the effect of multipath delay spread. It reduces the irreducible error of $\pi$/4-DQPSK over a frequency selective fading channel. It is shown that $\pi$/4-DQPSK with stepped phase achieves smaller average bit error probability than regular $\pi$/4- DQPSK by simulation. The former achieves much smaller average bit error probability than the latter for small TEX>${\tau}/T_{s}$.

• Journal of the Korea Computer Industry Society
• /
• v.7 no.1
• /
• pp.39-46
• /
• 2006

Multipath diversity reception is applied to the compensation of the distortion of channel, which occurs in transmission of data at rapid speed. DS/BPSK systems are composed of the equipment with reception structure combined with a compensation algorithm to diversity branch. The efficiency of the system is evaluated from the point of view of average bit error rate according to SNR. In order to remove intersymbol interference, this algorithm is applied to time-invariant channel at every diversity branch with the number of L. As a result, the average bit error rate is saturated by $10^{-2}$ at the conventional compensation algorithm.

• Proceedings of the Korea Institute of Convergence Signal Processing
• /
• 2001.06a
• /
• pp.41-44
• /
• 2001

In the wide variety of radio propagation channel models, frequency selective fading which from multipath waves and diversity noises, electric and electronic devices ...etc in our environment, change characteristics of the sub channels in the wide bandwidth. so orthogonality among the OFDM subcarriers would be distorted and ICI(Inter Channel Interference), ISI(Inter Symbol Interference) be generated. This paper investigate BER characteristics of the OFDM System using Subband Grouping Method which adopted different channel modulation for each subband.