• Journal of electromagnetic engineering and science
• /
• v.1 no.2
• /
• pp.113-119
• /
• 2001

Conventional channel estimation methods for orthogonal frequency division multiplexing (OFDM) system don't show the good characteristics in terms of fast fading channels. To solve this drawback in conventional methods, we propose the channel estimation method fur OFDM, assisted pilot for improvement and convergence in mobile system (APIM), which has a good performance and computational complexity in consideration of other methods. APIM uses the more developed concept of conventional methods and a block frame structure within a whole channel. This concept prevents overall performance from diverging or showing a poor one. The simulation results demonstrate the APIM outperforms pilot symbol assisted modulation (PSAM) and extended symbol aided estimation (ESAE) in terms of mean square error (MSE) and bit error rate (BER) performance under all Rayleigh fading environment. Considering the simulation performance and computational complexity, we can see APIM shows better characteristics than conventional methods for OFDM and has not any error floor even in a fast Rayleigh fading environment.

• Journal of Broadcast Engineering
• /
• v.10 no.1 s.26
• /
• pp.4-13
• /
• 2005

An equalization algorithm is proposed to guarantee a stable performance in fast fading channels for digital television (DTV) systems from the advanced television system committee (ATSC) standard. In channels with high Doppler shifts, the conventional equalization algorithm shows severe performance degradation. Although the conventional equalizer compensates poor channel conditions to some degree, long filter taps required to overcome long delay profiles are not suitable for fast fading channels. The Proposed sparse equalization algorithm is robust to the multipaths with long delay Profiles as well as fast fading by utilizing channel estimation and equalizer initialization. It can compensate fast fading channels with high Doppler shifts using a filter tap selection technique as well as variable step-sizes. Under the ATSC test channels, the proposed algorithm is analyzed and compared with the conventional equalizer. Although the proposed algorithm uses small number of filter taps compared to the conventional equalizer, it is stable and has the advantages of fast convergence and channel tracking.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.41 no.8
• /
• pp.1-7
• /
• 2004

The effect of the sub-optimal beam-forming and the fading channel correlation on the closed loop transmit antenna diversity(CTD) system is investigated in frequency flat Rayleigh fading channels. The fast channel fading prevents the perfect channel estimation at a mobile station, hence the imperfect weight is applied to the antenna branch of transmitter. The weight causes sub-optimalbeam-forming and aggravates the performance of CTD system. The fading correlation or a wireless channel also is one of the factors decreasing the diversity gain. A bit error rate expression for the CTD system is analytically derived as a function of the channel estimation error, the channel correlation coefficient the feedback delay, and fading index. It is shown that the channel estimation error gives more severe effect to the system performance than the channel correlation.

• Journal of information and communication convergence engineering
• /
• v.4 no.4
• /
• pp.131-135
• /
• 2006

In this paper, we discusses that the theoretical analysis is made for the performance of FS MC-CDMA by the aid of the Nakagami fading channels and the block error probabilities of the FS MC-CDMA in Nakagami fading channel are presented. The channel fading speed, slow or fast, is considered in evaluating block error probabilities. The effectiveness of diversity combining in improving block error performance is examined.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2004.05b
• /
• pp.399-403
• /
• 2004

In this paper, we have analyzed the TCP throughput of Portable Internet system in 2.3GHz wireless environment with considering user's mobility speed. As the Portable Internet uses large cells compared to wireless LAM and supports user's nobility, we have adapted different wireless channel model to derive the TCP throughput of the system. We have assumed wireless channel is Rayleigh fading channel and the channel is modeled as two-state Markov model with which user's nobility speed can be considered by varying transition matrix of the model. from the simulation results, we have known that higher TCP throughput under the slow fading than under the fast fading. Because the TCP throughput is closely related to the sender's congestion control, the more congestion control is done by the sender, the lower TCP throughput we have. The more congestion control is caused in the sender under the fast fading than the slow fading so the lower TCP throughput is resulted in the fast fading environment.

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

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.9 no.8
• /
• pp.3068-3078
• /
• 2015

Although the massive MIMO system supports a high throughput, it requires a lot of channel information for channel compensation. For the reduction of overhead, the massive MIMO system generally uses TDD as duplexing scheme. Therefore, the massive MIMO system is sensitive to rapidly changing fast fading in according to time. For the improvement of reduced SINR by fast fading, the adaptive power control is proposed. Unlike the conventional scheme, the proposed scheme considers mobility of device for adaptive power control. The simulation of the proposed scheme is performed with consideration for mobility of device. The result of the simulation shows that the proposed scheme improves SINR. Since SINR is decreased in according to the number of device in the network by unit of cell, each base station can accommodate more devices by the proposed scheme. Also, because the massive MIMO system with high SINR can use high order modulation scheme, it can support higher throughput.

• Journal of Communications and Networks
• /
• v.6 no.1
• /
• pp.1-8
• /
• 2004

In this paper, we investigate the properties and performance of space-time bit-interleaved coded modulation (STBICM) systems in fast Rayleigh fading channels. We first show that ST-BICM with QPSK signaling in fast fading channels possesses the uniform distance property, which makes performance analysis tractable. We also derive the probability distribution of the squared Euclidean distance between space-time symbols assuming uniform bit-interleaving. Based on the distribution, we show that the diversity order for each codeword pair becomes maximized as the frame length becomes sufficiently long. This maximum diversity order property implies that the bit-interleaver transforms an ST-BICM system over transmit diversity channels into an equivalent coded BPSK system over independent fading channels. We analyze the performance of ST-BICM in fast fading channels by deriving an FER upper bound. The derived bound turns out very accurate, requiring only the distance spectrum of the binary channel codes of ST-BICM. Numerical results demonstrate that the bound is tight enough to render an accurate estimate of performance of ST-BICM systems.

• The Journal of the Acoustical Society of Korea
• /
• v.6 no.1
• /
• pp.5-14
• /
• 1987

In this paper, the transmission characteristics of a frequency-hopped spread spectrum communication system operating in the presence of both time and frequency-selective fading channel is presented. The receiver is a binary noncoherent matched-filter FFH-SS system with square-law combiner. The probability of error to the variations of the parameters such as signal-to-noise ratio, selectivity of a channel, and power ratio is derived with the use of diversity concept without considering the data rate. The analysis of the data for probability of error shoves that the performance of FFH-SS system in time-selective fading channel is better than in frequency-selective fading channel.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.8 no.5
• /
• pp.1010-1019
• /
• 2004

In this paper, we represent Nakagami-m fading channel as finite-State Markov Channel (FSMC) and analyze the performance of wireless communication system with varying the fading channel condition. In FSMC model, the received signal's SNR is divided into finite intervals and these intervals are formed into Markov chain states. Each state is modeled by a BSC and the transition probability is dependent upon the physical characterization of the channel. The steady state probability and average symbol error rate of each state and transition probability are derived by numerical analysis and FSMC model is formed with these values. We found that various fading channels can be represented with FSMC by changing state transition index. In fast fading environment in which state transition index is large, the channel can be viewed as i.i.d. channel and on the contrary, in slow fading channel where state transition index is small, the channel can be represented by simple FSMC model in which transitions occur between just adjacent states. And we applied the proposed FSMC model to analyze the coding gain of random error correcting code on various fading channels via computer simulation.