• 제어로봇시스템학회:학술대회논문집
• /
• 1997.10a
• /
• pp.211-214
• /
• 1997

This paper applies fuzzy self-tuning PID controller in DS/CDMA cellular system. Power control is essential in DS/CDMA to compensate for the differing received powers due to both the slowly varying long-term and fast varying short-term fading processes and co-channel interference. The controller proposed is adaptable for the variations of the system dynamics and especially for the variable time delay which exists in mobile radio systems. Accordingly the results is the smaller power control error, that is, the smaller average transmitting power of mobile compared with the conventional control schemes. Because interferences to the other mobiles are reduced, the capacity of CDMA can be increased.

• Proceedings of the IEEK Conference
• /
• 2004.06a
• /
• pp.55-58
• /
• 2004

This this paper, we propose vertical Bell laboratories layered space time (V-BLAST) system based on variable rate Low-Density Parity Check (LDPC) codes to improve performance of receiver when QR decomposition interference suppression combined with interference cancellation is used over independent Rayleigh fading channel. The different rate LDPC codes can be made by puncturing some rows of a given parity check matrix. This allows to implement a single encoder and decoder for different rate LDPC codes. The performance can be improved by assigning stronger LDPC codes in lower layer than upper layer because the poor SNR of first detected data streams makes error propagation. Keeping the same overall code rates, the V-BLAST system with different rate LDPC codes has the better performance (in terms of Bit Error Rate) than with constant rate LDPC code in fast fading channel.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.16 no.2
• /
• pp.137-144
• /
• 1991

A new demodulation scheeme for differentially encoded GMSK signal is introduced and described. In the proposed differential detection method, the signal is sampled at the center of the time slot, at which the effect of the intersymbol interference is relatively smaller than the edge of the time slot. The proposed differential detector takes this adbantate. The error rate performance of the differential detector has been numerically calculated in the fast fading encountered in the land mobile radio channels. A comparison of performance with the differential detector for MSK signal is given. Finally the possibility of improving performance employing nonredudant error correction is studied.

• ETRI Journal
• /
• v.20 no.1
• /
• pp.16-27
• /
• 1998

In this paper, we consider the acquisition performance of an IS-95 reverse link access channel slot as a function of system design parameters such as postdetection integration length and the number of access channel message block repetitons. The uncertainty region of the reverse link spreading codes compared to that of forward link is very small, since the uncertainty region of the reverse link is determined by a cell radius. Thus, the parallel acquisiton technique in the reverse link is more efficient than a serial acquisition technique in terms of implementation and of acquisition time. The parallel acquisition is achieved by a bank of N parallel I/Q noncoherent correlator are analyzed for band-limited noise and the Rayleigh fast fading channel. The detection probability is derived for multiple correct code-phase offsets and multipath fading. The probability of no message error is derived when rake combining, access channel message block combining, and Viterbi decoding are applied. Numerical results provide the acquisition performance for system design parameters such as postdetection integration length and number of access channel message block repetitions in case of a random access on a mobile station.

• Proceedings of the IEEK Conference
• /
• 2000.07b
• /
• pp.982-985
• /
• 2000

This paper presents channel estimation of an asynchronous W-CDMA reverse link using the interpolation and moving average algorithm in frequency-selective Rayleigh fading channel. The proposed algorithm is an interpolated decision-directed (IDD) block-wise moving average (BWMA) algorithm. The IDD-BWMA algorithm performs two- stage processes. The first stage performs data decision to make a virtual pilot channel by using linear interpolation channel estimation scheme. Then, the second stage performs the channel estimation of the “block-wise moving average” type by using a virtual pilot channel obtained in the first stage. By using Monte-Carlo computer simulations, we show that the proposed channel estimator is superior to other estimation schemes such as the WMSA(K=1) and DD-RAKE at higher Doppler frequencies, especially.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.25 no.10A
• /
• pp.1486-1491
• /
• 2000

A Multicarrier system required a lower speed paralled-type of signal processing in contrast to a fast serial processing in a single carrier CDMA system. For the analysis we evaluate MC-CDMA system performance with that of a single-carrier CDMA system and a multi-carrier CDMA system based on the various jamming conditions. Also we studied to the capacity level against the threat environment through the performance comparison in commercial CDMA system and Limiting repeater system. as a result we found that M-CDMA system has a robustness to narrowband interference and multipath environments like as a Rayleigh fading.

• Journal of the Korean Institute of Telematics and Electronics
• /
• v.24 no.3
• /
• pp.370-375
• /
• 1987

In this study, the Rayleigh fast fading simualtors encountered in channel modelling of mobile radio have been implemented and evaluated. Two models used for the fading environment were frequency composition of phase modulated signals and shaping spectrum of noise sources with filters. The spectrum chosen for our purpose is appropriate to an omnidirectional antenna. From results of the experiment with various parameters, we have obtained satisfying results which are closely agreed to theoretical values.

• Journal of Advanced Information Technology and Convergence
• /
• v.6 no.1
• /
• pp.45-57
• /
• 2016

This paper proposes an adaptive channel estimation scheme for OFDM-based IEEE 802.11ad wireless local area network (WLAN). The standard supports two types of information of OFDM packets for estimating the communication channels, which are the channel estimation field (CEF) of preamble and pilot subcarriers. The CEF-based channel estimation provides better BER (bit error rate) performance at slow fading channel state, whereas the pilot-based channel estimation is good at fast fading channel state. Hence, a combined channel estimation method is introduced to improve the performance. The prediction of the channel state to select the proper channel estimation method is required. In this work, an adaptive channel estimation scheme is also proposed to improve the performance of channel estimation (CE). Basing on a channel quality indicator (CQI), the proper channel estimation method corresponding to the channel type is decided.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.48 no.4
• /
• pp.53-60
• /
• 2011

In order to augment the robustness of OFDM system to Rayleigh multipath fading, there exist two smart antenna algorithms, namely, Pre-FFT smart antenna and Post-FFT smart antenna. After the mathematical modeling of both smart antenna algorithms, computer simulations have been carried to compare and analyze the performance of generalized eigen problem based Pre-FFT algorithm and the performance of Wiener solution based Post-FFT algorithm. It has been shown that the Post-FFT smart antenna far outperforms the Pre-FFT smart antenna due to the computational complexities. Especially it is so when the multipath signal arrives at beyond the guard interval and a rich co-channel interferer is introduced. Performance of a subcarrier clustering method proposed to lessen the computing load has been compared to that of a typical Wiener solution based Post-FFT smart antenna. Performance comparison between MRC(Maximum Ratio Combining) diversity based Post-FFT algorithm and typical Post-FFT algorithm has also been carried.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.30 no.2A
• /
• pp.51-60
• /
• 2005

In this paper, we propose an enhanced SIR measurement algorithm for WCDMA mobile station modem. The proposed algorithm minimizes processing delay by applying velocity estimation-based channel estimator with IIR filter and reduces measured SIR offset by compensating attenuated signal power by using pilot channel(CPICH) in fading channel environment. To improve stability of SIR measurement, we also adopt an IIR filter which can properly reflect variation of fading channel in signal and interference power measurement. We prove that the proposed algorithm outperforms conventional SIR measurement algorithm in mean and jitter of measured SIR. Computer simulation shows that performance results using the proposed algorithm have improvement of approximately 8dB for measured mean and 2dB for measured jitter in the wireless mobile channel, especially in fast mobile speed environment.