• ETRI Journal
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• v.30 no.3
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• pp.355-364
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• 2008

Multiple-input multiple-output (MIMO) systems can provide significant increments in capacity; however, the capacity of MIMO systems degrades severely when spatial correlation among multipath channels is present. This paper demonstrates that the influence of shadowing on the channel capacity is more substantial than that of multipath fading; therefore, the shadowing effect is actually the dominant impairment. To overcome the composite fading effects, we propose combining macroscopic selection diversity (MSD) schemes with MIMO technology. To analyze the system performance, the capacity outage expression of MIMO-based MSD (MSD-MIMO) systems using a characteristic function is applied. The analytic results show that there are significant improvements when MSD schemes are applied, even for the two-base-station diversity case. It is also observed that the effect of spatial correlation due to multipath fading is almost negligible when multiple base stations cooperatively participate in the mobile communication topology.

• Journal of Integrative Natural Science
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• v.13 no.2
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• pp.69-75
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• 2020

Multiple Input Multiple Output (MIMO) is one of the important wireless communication technologies. This paper proposes MIMO system capacity enhancement by using convolution of periodic circulating vector signals. This signal represents statistical dependencies between transmission signal with discrete noise and receiver signal with the linear shifting of MIMO channel capacity by positive extents. We examine the channel capacity, outage probability and SNR of MIMO receiver by adding log determinant signal with validated in terms of numerical simulation.

• Journal of Communications and Networks
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• v.11 no.4
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• pp.384-389
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• 2009

Optical wireless communication (OWC) systems are rapidly gaining popularity as effective means of transferring data at high rates over short distances. OWC facilitates rapidly deployable, lightweight, high-capacity communication without licensing fees and tariffs. Nevertheless, the performance of this new technology depends strongly on the atmospheric conditions and the characteristics of the link. In this work, we study the influence of these parameters on both the average (ergodic) capacity and the outage capacity of an OWC system over moderate to strong turbulence channels modeled by gamma-gamma distribution. Moreover, we compare the results that we obtain estimating the average and outage capacities.

• International Journal of Reliability and Applications
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• v.4 no.1
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• pp.13-26
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• 2003

This paper presents a comparative study of a few commonly used maintenance scheduling methods for small utilities that consists solely of thermal generating plants. Two deterministic methods and a stochastic method are examined. The deterministic methods employ the leveling of reserve capacity criterion, of which one uses a heuristic rule to level the deterministic equivalent load obtained by using the product of the unit capacity and its corresponding forced outage rate. The stochastic method simulates the leveling of risk criterion by using the peak load carry capacity of available units. The results indicate that for the size and type of the maintenance scheduling problem described In this study, the stochastic method does not produce a schedule which is significantly better than the deterministic methods.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.9
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• pp.947-955
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• 2002

In this paper, we derive an outage probability for the Erlang capacity and the link margin respectively, calculate them with the same parameters and outage probability, and then analyze a capacity and cell coverage in city, suburban, and open area. So, the Erlang capacity is more real than in a cell, and the cell coverage can be calculated with high reliability by the margin. When the $E_b/N_o$ decreases from 7 dB to 5 dB within the outage probability of 5 %, it is observed that the capacity is increased from 18 Erlang to 31 Erlang with the same margin of 2.8 dB, then the coverage is increased to 0.4 km, 1 km, and 2.5 km in city, suburban, and open area respectively. Also if the outage probability is decreased from 5 % to 2 % in case of $E_b/N_o$ of 5 dB, the result shows a very reliable link with additional increment of 0.88 dB in the margin and a high QoS (quality of service) within decrement of 0.15 km, 0.5 km, and 1.5 km for the same areas with decrement of 3 Erlang from 31 Erlang.

• Journal of the Institute of Convergence Signal Processing
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• v.12 no.3
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• pp.188-193
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• 2011

In this letter, we have derived another exact performance analysis for the OADF(opportunistic adaptive decode-and-forward) relay systems over Rayleigh fading channels. Based on error-events at relay nodes, the received instantaneous SNR(signal-to-noise ratio) is presented and its PDF(probability density function) is expressed as a more tractable form in which the number of summations and the length of each summation are specified. Then, exact average error rate, outage probability, and average channel capacity are obtained as general forms. Simulation results are finally presented to validate that the proposed analytical expressions can be a unified frame work covering all Rayleigh fading channel conditions. Furthermore, it is confirmed that OADF schemes can outperform the other schemes on the average error rate, outage probability, and average channel capacity.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39B no.11
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• pp.803-809
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• 2014

In this paper, we investigate physical layer security in a cooperative cognitive radio networks (CRN) with a relay selection in the presence of a primary user and an eavesdropper. To protect the CRN from wiretapping by the eavesdropper, we propose employing an opportunistic relay selection scheme and multiple antennas at the destination that work based on the availability of channel state information at the receivers. Under these configurations, we derive an exact closed-form expression for the secrecy outage probability of the CRN, and also derive an asymptotic probability. Numerical results will be presented to verify the analysis.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.9
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• pp.3016-3033
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• 2014

The downlink performance of distributed antenna systems (DAS) with antennas selection is investigated in Rayleigh fading multicell environment, and the corresponding system capacity and bit error rate (BER) analysis are presented. Based on the moment generating function, the probability density function (PDF) and cumulative distribution function (CDF) of the effective signal to interference plus noise ratio (SINR) of the system are first derived, respectively. Then, with the available CDF and PDF, the accurate closed-form expressions of average channel capacity and average BER are further derived for exact performance evaluation. To simplify the expression, a simple closed-form approximate expression of average channel capacity is obtained by means of Taylor series expansion, with the performance results close to the accurate expression. Besides, the system outage capacity is analyzed, and an accurate closed-form expression of outage capacity probability is derived. These theoretical expressions can provide good performance evaluation for DAS downlink. It can be shown by simulation that the theoretical analysis and simulation are consistent, and DAS with antenna selection outperforms that with conventional blanket transmission. Moreover, the system performance can be effectively improved as the number of receive antennas increases.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.2
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• pp.229-234
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• 2012

This paper presents channel measurements for wireless body area network(WBAN) and provides performance evaluation from the measurement. We measured the radio propagation in 2.45 GHz ISM band in an anechoic chamber according to various human movements and the position of transmit antennas. Two transmit antennas are mounted on different positions of human body for the purpose of comparing the diversity gain and correlation between the channels in $2{\times}1$ multiple-input single-output(MISO) systems. The experimental results show that the outage capacity is closely related with the correlation coefficient between channels in transmit diversity system.

• Journal of Communications and Networks
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• v.10 no.4
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• pp.371-383
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• 2008

Application of network coding in wireless two-way relay channels (TWRC) has received much attention recently because its ability to improve throughput significantly. In traditional designs, network coding operates at upper layers above (including) the link layer and it requires the input packets to be correctly decoded. However, this requirement may limit the performance and application of network coding due to the unavoidable fading and noise in wireless networks. In this paper, we propose a new wireless network coding scheme for TWRC, which is referred to as soft network coding (SoftNC), where the relay nodes applies symbol-by-symbol soft decisions on the received signals from the two end nodes to come up with the network coded information to be forwarded. We do not assume further channel coding on top of SoftNC at the relay node (channel coding is assumed at the end nodes). According to measures of the soft information adopted, two kinds of SoftNC are proposed: amplify-and-forward SoftNC (AF-SoftNC) and soft-bit-forward SoftNC (SBF-SoftNC). We analyze the both the ergodic capacity and the outage capacity of the two SoftNC schemes. Specifically, analytical form approximations of the ergodic capacity and the outage capacity of the two schemes are given and validated. Numerical simulation shows that our SoftNC schemes can outperform the traditional network coding based two-way relay protocol, where channel decoding and re-encoding are used at the relay node. Notable is the fact that performance improvement is achieved using only simple symbol-level operations at the relay node.