• KSII Transactions on Internet and Information Systems (TIIS)
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• v.4 no.4
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• pp.509-528
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• 2010

The random access systems, with retransmission diversity (RD) employment, over large random spreading code division multiple access (CDMA) channel subject to fading is investigated, under the assumption of infinite number of users and infinite spreading gain with their ratio converging to a constant. The low bound of the signal to interference and noise ratio (SINR) is shown to converge almost surely to a constant. The throughput, spectrum efficiency and energy efficiency in the dominating systems are obtained. The analytical results are confirmed by simulations. We find that in high traffic loads the throughput with fading is higher than that without. When the energy efficiency increases, the spectrum efficiency tends to two contrary values due to SNR increases or decreases. For the ordinary stable systems, the stability region is shown to shrink as the traffic increases and enlarge with RD employment.

• Journal of IKEEE
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• v.15 no.3
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• pp.198-204
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• 2011

In this letter, another analytical approach for the opportunistic amplify-and-forward (OAF) relay systems is proposed over Rayleigh fading channels. Based on set-operation at the selected relay node, its selection probability as the best relay is derived and then, the probability density function (PDF) of the received instantaneous signal-to-noise ratio (SNR) is expressed as a more tractable form in which the number of summations and the length of each summation are specified. Then, the average error rate, outage probability, and average channel capacity are obtained as approximated closed-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 OAF schemes can outperform the other non-selective schemes on the average error rate, outage probability, and average channel capacity.

• Journal of Communications and Networks
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• v.8 no.3
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• pp.290-296
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• 2006

In this paper, a generalized blind adaptive algorithm is introduced for multi-user detection of direct sequence code division multiple access (OS-COMA) wireless communication systems. The main property of the proposed algorithm is its ability to resolve the multipath fading channel resulting in inter symbol interference (ISI) as well as multiple access interference (MAI). Other remarkable properties are its low complexity and mitigation to the near-far problem as well as its insensitivity to asynchronous transmission. The proposed system is based on the minimization of the output energy and convergence to the minimum mean square error (MMSE) detector. It is blind in the sense that it needs no knowledge of the other users' signatures, only the intended user signature and timing are required. Furthermore, the convergence of the minimum output energy (MOE) detector to the MMSE detector is analytically proven in case of M-ary PSK. Depicted results show that the performance of the generalized system dominates those previously considered. Further improvements are obtained when multiple input multiple output (MIMO) technique is employed.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.13 no.6
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• pp.93-99
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• 2013

The proposed protocol is to get better performance compared to the existing method, also it can save the node number. There is needed a lot of secondary user for cooperative spectrum detection in Rayleigh fading channel. In this proposal, we suggest the new cooperative spectrum detector which can choose one secondary user with high power, while other SUs can be used as relays.

• Journal of Advanced Navigation Technology
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• v.8 no.1
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• pp.1-9
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• 2004

In this paper, we have studied the reliable scheme for transmission of digital watermarking-inserted image data through wireless channel. Multimedia data and watermarking data are degraded because of the high BER (Bit Error Rate) and the effect of fading in wireless channel. We adapt the error correction scheme for mitigating the degradation in watermarking data. We have evaluated the error performance of watermarking data modulated by OFDM/16QAM and sent through Rician fading channel. The simulation results show that when error correcting scheme is used the watermarking data can be detected without severe error even though watermarking-inserted image data is suffered from severe damage.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.5 no.1
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• pp.3-12
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• 1994

We have proposed the optimum threshold detection(OTD) technique of 16 QAM signal in the Rician fading channel and analyzed its error performance with and without the selective combining(SC) diversity technique. And we compared the error performance of OTD with that of conventional threshold detection(CTD). Having the SC diveresity reception, optimum threshold detection(OTD) technique proposed in this paper provides the performance improvement of 1.8~3.2 [dB] in CNR for fading depth K values ranging from 5 to 30 over CTD when the error rate is $10_5$. From the result of numerical analysis, we know that the proposed OTD technique is superior to CTD technique in the Rician fading channel and adoption of the SC diversity technique with the proposed OTD can be considered as a good countermeasure for the Rician fading.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.35S no.6
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• pp.9-18
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• 1998

In this paper, an equalization technique for OFDM(orthogonal frequency division multiplexing) in a time-variant multipath fading environment is described. A loss of subchannel orthogonality due to time-varying multipath fading channels leads to interchannel interference (ICI) which increases the error floor in proportion to Doppler frequency. A simple frequency-domain equalizer which can compensate the effect of ICI caused by time variation of multipath fading channel is proposed by modifying the previous frequency-domain equalization technique with taking into account only the ICI terms significantly affecting the error performance. The effectiveness of the proposed approach is demonstrated via computer simulation by applying it to OFDM systems when the multipath fading channel is slowly time variant.

• Journal of Advanced Navigation Technology
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• v.14 no.1
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• pp.33-40
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• 2010

In this paper, the bit-error-ratio (BER) performances of Digital Radio Mondiale Plus (DRM+) system which stand for the European standard to bring analogue FM radio to digital radio in Band-II(30-170 MHz) are evaluated under multipath fading channel models used in Band-II and the adjacent channel interference (ACI) caused by FM signal. From the simulation results, the DRM+ system shows robust performances under time-varying channel environments even though the speed of a vehicle is equal to 300km/h. And it is shown that the frequency diversity, determined by delay spread of multipath fading channel, increases the coding gain of the DRM+ system with an increase of delay spread. In addition, to guarantee the BER performance of 10-4 for DRM+ system with ACI due to FM signal, the simulation results show that the desired signal-to-ACI power ratio must be more than -30 dB when the carrier frequency distance is 150 kHz.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.37 no.5
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• pp.1-9
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• 2000

In this paper, for the reverse link of a imperfect power controlled DS/CDMA cellular system when a mobile radio channel is a Rayleigh distributed multipath fading channel, A extended DS/CDMA blocking probability formula considering both shadowing and multipath fading is derived. Erlang capacity and equivalent channel number considering shadowing are analyzed and compared with those considering both shadowing and multipath fading, respectively. The DS/CDMA blocking probability is calculated based on the analysis method that obtains Erlang capacity and ICF(interference correction factor) using the median value of $E_{b(i)}$/ $I_{0}$ corresponding to each reverse link user Assuming that the blocking probability set 2%, it is observed that the Erlang capacity is 19.97 Erlang at the data rate $R_{b}$=9.6 kbps and 11.67 Erlang at the data rate $R_{b}$=14.4 kbps and then is less 16% and 19% than the Erlang capacity considering shadowing only, respectively. It is also shown that the effect of multipath fading must not be ignored and then exact Erlang capacity and equivalent channel numbers that the DS/CDMA cellular system can support are provided.d.d.d.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.7
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• pp.2992-3009
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• 2016

The performance of D-MIMO systems is not only affected by multipath fading but also from shadowing fading, as well as path loss. In this paper, we investigate the ergodic capacity of D-MIMO systems operating in non-correlated K fading (Rayleigh/Gamma) channels. With the aid of majorization and Minkowski theory, we derive analytical closed-form expressions of the upper and lower bounds on the ergodic capacity for D-MIMO systems over non-correlated K fading channels, which are quite general and applicable for arbitrary signal-to-noise ratio (SNR) and the number of transceiver antennas. To intuitively reveal the impacts of system and fading parameters on the ergodic capacity, we deduce asymptotic approximations in the high and low SNR regimes. Finally, we pursue the massive MIMO systems analysis for the lower bound and derive closed-form expressions when the number of antennas at BS grows large, and when the number of antennas at transceivers becomes large with a fixed and finite ratio. It is demonstrated that the proposed expressions on the ergodic capacity accurately match with the theoretical analysis.