• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.8 no.4
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• pp.25-33
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• 2008

The performance of power constrained cooperative multi-relay system with/without opportunistic transmission is considered in Rayleigh fading. The three power allocation methods are considered to maximize the system performance when the total network power is limited. It is analyzed that the opportunistic power allocation strategy has the best performance enhancement compared to the other power allocation strategies. The opportunistic relays increases with the total network power, which induce the higher diversity order of the opportunistic cooperative diversity, consequently improves the end-to-end outage probability.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.9 no.6
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• pp.1-8
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• 2009

Though the wireless ad-hoc network which is recently highly focused is power limited network, one of the main research topic is power saving. We propose a optimal power allocation strategy and derive the optimal power of the opportunistic transmission relays for minimum outage probability of the power limited network. It is shown that the proposed optimal power allocation has always better performance than that of the equal power allocation.

• The Journal of the Acoustical Society of Korea
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• v.25 no.8
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• pp.356-361
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• 2006

We present the performance of differential space-time block decoders. which does not require the channel state information. We suggest the structure of the multiple blocks differential space time decoders. which does not require the channel state information, and analyze the Performances. In quasi-static flat fading channels. the Performance of multiple blocks differential detection (MD-STC) outperforms that of 2 blocks(D-STC) by 1.5dB. But in the time-selective fading channels due to Doppler frequency $(f_d)$, the performance of MD-STC degrades as the vehicular speed is greater than 200km/hr in 802.16e systems, where the data transmission rate is 144kbps.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.3
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• pp.731-736
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• 1996

In this paper, we propose a modified Type-II HARQ system having adaptive power to channel and analyze its performance in terms of throughput and reliability. Its performance is also compared with Typd-I and Type-II HARQ ystems and is verified using computer simulations over AWGN and frequenyc-nonselective, slowly Rayleigh fading channels.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.4 s.346
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• pp.39-43
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• 2006

In this contribution, the achievable performance of orthogonal multicarrier DS-CDMA systems employing synchronous uplink transmissions is investigated. The bit error ratio (BER) performance is analyzed under dispersive Rayleigh multipath fading conditions as a function of the number of users.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.10A
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• pp.1462-1470
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• 1999

In this paper, the performance of packet radio networks using the ALOHA protocol in Rayleigh fading channels is analyzed in terms of the capture probability and the throughput. We consider capture effect in order to increase the probability of the channel access and to include cellular environment we assume that the traffic is a truncated bell-shaped distribution. The packet proposed in this paper consists of a competition part and a data part to decrease the probability of collision in the channel access. In the competition part, DS system with common spreading code is used and in the data, hybrid DS/FH system is used. We consider the linear correlation receiver and the hard-limiting correlation receiver as the receiver model. BPSK modulation is also employed. Because hybrid DS/FH systems are not sensitive to variation of the interference power, as we choose a proper chip number N and a frequency hopping number q, we can obtain a steady system performance even though the variation of interference power is severe fading channels such as Rayleigh fading.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.8
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• pp.1804-1810
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• 2013

In this paper, we study the opportunistic cooperation scheme that improves the outage performance through the efficient selection between a cooperative mode and a non-cooperative mode. Especially, in decode-and-forward relaying systems, we analyze the outage performance for the opportunistic cooperation using partial relay selection, where closed-form expressions of exact and asymptotic outage probabilities are derived assuming independent and identically distributed Rayleigh fading channels. In the numerical results, we verify the derived expressions, and investigate the outage performances for various target data rates and different numbers of relays. Also, we compare the outage performances of the conventional cooperation scheme and the opportunistic cooperation scheme.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.3C
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• pp.314-319
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• 2010

The chirp spread spectrum (CSS) technique that spreads the data signal over a wider frequency band via chirp signal for transmission has attracted much attention in the field of wireless communications due to capability to resist multipath fading signals. However, there has been little mathematical analysis for the performance of CSS-based communication systems in the multipath fading environments. In this paper, we study the influence of the multipath channel on the direct modulation (DM) scheme with M-ary phase shift keying (MPSK). When a chirp signal is transmitted on the Rayleigh fading channel and affected by additive white Gaussian noise (AWGN), we derive the theoretical performance. From numerical results, it is confirmed that the analytic symbol error rate (SER) agrees closely with the empirical SER.

• Journal of the Institute of Electronics Engineers of Korea TE
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• v.37 no.2
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• pp.54-61
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• 2000

This paper presents the performance evaluation of channel estimation algorithm using RLS algorithm lot W-CDMA reverse link over Rayleigh fading channels. By obtaining BER(Bit Error Rate) performance through computer simulations, the RLS(Recursive Least Square) algorithm is compared with the existing WMSA(Weighted Averaging)(K=1,3) and constant gain algorithm. The channel structure, modulation and pilot patterns are applied to the ARIB (Association of Radio Industries and Business) and 3GPP (3rd Generation Partnership Project) ITU-R proposal for the IMT-2000. The BER performance of RLS algorithm with linear interpolation is similar to that of WMSA(K=1) and slightly superior to that of constant gain algorithm at low Doppler frequencies. Also, RLS algorithm performance is better than that of the WMSA(K=1,3) and constant gain algorithms about 4dB at BER=2.0$\times$$10^{-2}$ and Doppler frequencies $F_D$=320Hz. With increasing Doppler frequency, therefore, the BER performance of RLS algorithm with linear interpolation is superior to WMSA(K=L.3) and constant rain algorithms.

• The Journal of the Acoustical Society of Korea
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• v.13 no.1
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• pp.63-70
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• 1994

In this paper, we Investigate the $Q^2PSK$ modulation and demodulation system and analyze the BER performance of the receiver system under 2-way Rayleigh fading and Gaussian noisy channel environment. The TDL equalizer with the adaptive LMS algorithm is used to improve the receiver performance since the received signal is distorted through that channel and the recovered carrier from the noncoherent demodulation has much phase deviation error. From the results of computer simulation, It is shown that at 12dB SNR, the reception performance is improved by $83.7\%$ in the fading case, $89.3\%$ in the carrier phase error case and $60.4\%$ in the case of the fading and carrier phase error.