• Journal of electromagnetic engineering and science
• /
• v.6 no.4
• /
• pp.209-216
• /
• 2006

This paper investigates a distinct set of complex unitary matrices for QPSK differential space time coding. After properly selecting the initial transmission matrix and unitary matrices we find that the different combinations of them could lead different BER performance over slow/fast Rayleigh fading channels and antennas correlated channels. The numerical results show that the proper selection of the initial transmission matrix and the set of unitary matrices can efficiently improve the bit error rate performance, especially for the antennas correlated fading channel. The computer simulations are evaluated over slow and fast Rayleigh fading channels.

• ETRI Journal
• /
• v.33 no.6
• /
• pp.961-964
• /
• 2011

The cognitive ultra-wideband (UWB) network detects interfering narrowband systems and adapts its configuration accordingly. An inherently adaptive and flexible candidate for cognitive UWB transmission is the wavelet packet multicarrier modulation (WPMCM). In this letter, we use an enhanced forward consecutive mean excision thresholding algorithm to tackle the noise uncertainty in the wavelet-based sensing of WPMCM systems, and mathematical analysis is performed for primary user channel fading. As a benchmark, we compare the proposed system with a conventional fast Fourier transformation-based system, and performance investigation proves significant improvements when primary and secondary links are subjected to multipath fading and noise.

• 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 Korean Institute of Communication Sciences Conference
• /
• 1983.10a
• /
• pp.88-92
• /
• 1983

The performance of noncoherent fast frequency-hopped spread spectrum multiple access communication systems with square-law combining over fading channel is presented. The expression for the probalility of error as a performance measure is derived by means of momenting function of the dedecision variables, and the cross-covariance of the fading process the ambiguty function of the transmitted signals.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.7 no.4
• /
• pp.310-319
• /
• 1996

The existing coders used in the fading channels are designed under the assumption that the ideal interleaver, which removes the fading correlation of the channel, is used. With the non-ideal interleaver of finite size, however, the performance of the coded modulation system degrades rapidly when the fading is very slow. A new method which achieves interleaving effects by switching the transmitter antennas is suggested to improve the performance even in the slow fading. The performance of the new system is analyzed. The results show significant performance improvement in the slow fading and at least no deterioration in the fast fading over the existing systems.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.5 no.6
• /
• pp.1066-1072
• /
• 2001

ALOHA Multi-Carrier DS-CDMA systems in the multipath Rayleigh fading channel. The throughput of two systems are compared according to the length of a packet in the fast Rayleigh and the slow Rayleigh multipath fading. As a result, we have known that Multi-Carrier DS-CDMA system has less capacity than wideband DS-CDMA system in the same bandwidth, but throughput of Multi-Carrier DS-CDMA system is higher than that of wideband DS-CDMA system. And in Multi-Carrier DS-CDMA systems, higher throughput can be obtained through shortening the length of packet in the fast Rayleigh fading, and it is efficient to control the length of a packet adequately or increase the system capacity of Multi-Carrier DS-CDMA system in the slow Rayleigh fading.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.30 no.8A
• /
• pp.664-670
• /
• 2005

OFDM is a very attractive technique for achieving high-bit-rate data transmission and high spectrum efficiency in fading environment. However, the reliable detection of an OFDM signal in time-varying multipath fading channels is a challenging problem. Accordingly, various channel estimation methods have been proposed for performance improvement. But, conventional pilot patterns for channel estimation in OFDM systems have not robust characteristics relating to various mobile speed. To solve this drawback in conventional patterns, we propose the pilot patterns modified from conventional patterns to have a good error performance in time-varying fading channel. Simulation results show that the performance of the proposed pilot patterns is better than conventional patterns in fast time-varying channel.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.13 no.5
• /
• pp.2400-2413
• /
• 2019

Doubly-selective (DS) fading channel is often occurred in many orthogonal frequency division multiplexing (OFDM) communication systems, such as high-speed rail communication systems and underwater acoustic (UWA) wireless networks. It is challenging to provide an accurate and fast estimation over the doubly-selective channel, due to the strong Doppler shift. This paper addresses the doubly selective channel estimation problem based on complex exponential basis expansion model (CE-BEM) in OFDM systems from the perspective of distributed compressive sensing (DCS). We propose a novel DCS-based improved sparsity adaptive matching pursuit (DCS-IMSAMP) algorithm. The advantage of the proposed algorithm is that it can exploit the joint channel sparsity information using dynamic threshold, variable step size and tailoring mechanism. Simulation results show that the proposed algorithm achieves 5dB performance gain with faster operation speed, in comparison with traditional DCS-based sparsity adaptive matching pursuit (DCS-SAMP) algorithm.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.33 no.12C
• /
• pp.1006-1013
• /
• 2008

CZZ (Concatenated Zigzag) Code is a class of fast encodable LDPC codes. In the case that LDPC codes including CZZ codes have short length, short cycles seriously affect the code performance. In this paper, we construct CZZ codes using various degree-2 polynomial interleavers which eliminate cycles of length 4 and through simulation, compare the performance of these CZZ codes and turbo codes in many different fading channels. Especially, quasi-static fading channel, block fading channel, uncorrelated fading channel, and correlated fading channel are considered. Since CZZ codes show similar performance as turbo codes, they can be used in the next generation wireless communication systems.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
• /
• 2003.11a
• /
• pp.589-593
• /
• 2003

Narrowband and wideband characterizations of radio propagation channels in tunnel environments are investigated by using ray tracing techniques. For a rectangular straight tunnel and a rectangular curved tunnel, received power is simulated when the receiver moves away from the transmitter. The fast fading statistics of the narrowband propagation are analyzed in terms of cumulative distribution function, level crossing rate and average fade duration. The tunnel wideband radio propagation channel is characterized in terms of mean excess delay and rms delay spread.