• Journal of electromagnetic engineering and science
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• v.6 no.2
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• pp.103-109
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• 2006

This paper suggests an efficient and comprehensive algorithm of the protection ratio derivation and illustrates some calculated results applicable to the initial planning of frequency coordination in the fixed wireless access networks. The net filter discrimination associated with Tx spectrum mask and overall Rx filter characteristic has been also examined to show the effect of the adjacent channel interference. The calculations for co-channel and adjacent channel protection ratios are performed for the current microwave frequency band of 6.7 GHz including Tx spectrum mask and Rx filter response. According to results, fade margin and co-channel protection ratio reveal 41.4 and 75.2 dB, respectively, for 64-QAM and 60 km at BER $10^{-6}$. It is shown that the net filter discrimination with 40 MHz channel bandwidth provides 28.9 dB at the first adjacent channel, which yields 46.3 dB of adjacent channel protection ratio. In addition, the protection ratio of 38 GHz radio relay system is also reviewed for millimeter wave band applications. The proposed method gives some advantages of an easy and systematic extension for protection ratio calculation and is also applied to frequency coordination in fixed millimeter wave networks.

• Journal of electromagnetic engineering and science
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• v.7 no.2
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• pp.83-90
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• 2007

In this paper, the formulation of the protection ratio based upon a composite fade margin and availability is newly presented for the detailed planning of frequency coordination in the microwave relay system network, and computed results for co-channel and adjacent channel protection ratios are illustrated over an actual system with 6.2 GHz. It is shown that the protection ratio to assure a quality of service can be expressed in terms of the composite fade margin, noise-to-interference ratio, net filter discrimination, and system parameters. In addition, the net filter discrimination, depending upon the transmitter spectrum mask and the overall receiver filter characteristic, has been examined to investigate the effect of the adjacent channel protection ratio caused by the adjacent channel interference. Regarding simulated results for 6.2 GHz, 60 km, 64-QAM, and N/I=6 dB at the bit error rate of $10^{-6}$, composite fade margin and co-channel protection ratio yield 25.14 and 50.3 dB, respectively. Also, the net filter discrimination of 26.5 dB and the adjacent channel protection ratio of 23.8 dB are obtained at the first adjacent channel of 30 MHz. The proposed method provides some merits in view of a comprehensive and practical application with more detailed and various system parameters needed to access the criteria for making the proper frequency coordination.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.7 no.4
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• pp.288-299
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• 1996

The co-channel digital radio-relay system improves effectively the use of radio frequency allocations by transmitting signals separately on both orthogonal allocations, and thereby not only the total transmission capacity of frequency band but also its bandwidth effciency are almost doubled, compared tothe interleaved digital radio-relay system. Therefore, the study on the development and application of the con-channel scheme is of importance, for the efficient use of limited frequency bnad. In this paper, we derived the eqations for calculating fade margin as a function of path length as well as error performance in terms of the outage probability for co-channel digital radio-relay system below 10GHz. And, simulation was given to demonstrate how to apply those equations to the real situation.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.49 no.8
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• pp.46-51
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• 2012

In this paper, we investigate the power allocation for cognitive relay networks. Cognitive relay networks offer not only increasing spectral efficiency by spectrum sharing but also extending the coverage through the use of relays. For spectrum sharing, conventional works have assumed that secondary users know perfect channel information between the secondary and primary users. However, this channel information may be outdated at the secondary user because of the time-varying properties or feedback latency from the primary user. This causes the violation for interference constraint, and the secondary user cannot share the spectrum of the primary after all. To overcome this problem, we propose the power allocation scheme for the secondary user under the allowable primary user's outage probability constraint. Since the proposed power allocation scheme does not use the instantaneous channel information, the secondary users have lower feedback burden. In addition, the proposed scheme is also robust to the outdated channel environment.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.6A
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• pp.558-567
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• 2011

In this paper, we propose a partial full duplex relay scheme for 3GPP (3rd Generation Partnership Project) LTE (Long Term Evolution)-Advanced system using a Type 1 relay. The Type 1 relay as inband relay is prohibited to transmit and receive simultaneously because of self-interference. Therefore, the Type 1 relay cannot receive synchronization signals which are transmitted to eNB. To overcoming this problem, we propose the partial full duplex relay scheme which transmits to R-UE (Relay-User Equipment) and receives from eNB (evolved NodeB) simultaneously when eNB and the Type 1 relay transmit subframes which have synchronization signals. Additionally, for solving self-interference, the Type 1 relay transmitter and receiver antennas are sufficiently sufficiently isolated and self-interference cancellation is applied for the self-interference signal from the relay transmitter. Thus, the partial full duplex relay scheme can receive synchronization signals from eNB and solve the problems of conventional solutions and we propose the partial channel estimation scheme for partial full duplex relay scheme using SCI. By extensive computer simulation, we verify that the partial full duplex relay scheme is attractive and suitable for the Type 1 relay system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.12
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• pp.2317-2323
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• 2015

In this paper, we analyze the performance of dual-hop amplify-and-forward (AF) relaying in cooperative networks with partial relay selection. An AF relay gain considered in this paper includes channel-noise-assisted relay gain. Leveraging a received signal-to-noise ratio (SNR) model, we derive exact closed-form expressions for the probability density function (pdf) and cumulative distribution function (cdf) of the end-to-end SNR. Moreover, an exact closed-form expression of the ergodic capacity for dual-hop AF relaying with channel-noise-assisted relay gain and partial relay selection is investigated. The analytical results shown in this paper are confirmed by Monte-Carlo simulations.

• Journal of Communications and Networks
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• v.16 no.3
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• pp.301-304
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• 2014

This paper proposes accurate interference probability and bit error rate formulas for cognitive relay networks with underlay spectrum sharing and channel estimation error (CEE). Numerous results reveal that the CEE not only degrades the performance of secondary systems (SSs) but also increases interference power caused by SSs to primary systems (PSs), eventually unfavorable to both systems. A solution to further protect PSs from this effect through reducing the power of secondary transmitters is investigated and analyzed.

• ETRI Journal
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• v.34 no.4
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• pp.511-517
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• 2012

The best linear unbiased estimator (BLUE) is most suitable for practical application and can be determined with knowledge of only the first and second moments of the probability density function. Although the BLUE is an existing algorithm, it is still largely unexplored and has not yet been applied to channel estimation in amplify and forward (AF)-based wireless relay networks (WRNs). In this paper, a BLUE-based algorithm is proposed to estimate the overall channel impulse response between the source and destination of AF strategy-based WRNs. Theoretical mean square error (MSE) performance for the BLUE is derived to show the accuracy of the proposed channel estimation algorithm. In addition, the Cram$\acute{e}$r-Rao lower bound (CRLB) is derived to validate the MSE performance. The proposed BLUE channel estimation algorithm approaches the CRLB as the length of the training sequence and number of relays increases. Further, the BLUE performs better than the linear minimum MSE estimator due to the minimum variance characteristic exhibited by the BLUE, which happens to be a function of signal-to-noise ratio.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.48 no.5
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• pp.1-7
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• 2011

In this paper, CDD(Cyclic Delay Diversity)-DF(Decode-and-Forward)-Relay scheme is proposed for MC-CDMA(Multicarrier-Code Division Multiple Access) systems over multipath Rayleigh fading channels. The advantages of general DF schemes come at the expense of the spectral efficiency since the source and all the relays must transmit on orthogonal channels. In order to mitigate this disadvantage of general DF schemes, we have applied CDD techniques to each relays so that all the relays can transmit on single channel. It means that all R-D link channels can be considered as a single channel which is widely delay spread. Namely, it causes the increasing the number of multipath so that the frequency diversity gain can be achieved in MC-CDMA systems. By simulations, we have compared proposed one with general DF scheme. Therefore, it is confirmed that the proposed one can be a possible solution to achieve cooperative diversity gain without a reduction of spectral efficiency.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.4A
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• pp.394-400
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• 2010

Mobile Multi-hop Relaying (MMR) system can provide increased system capacity of wireless access network by coverage extension and enhanced transmission rate within the Base Station (BS) coverage area. The previous researches for the MMR system with a non-transparent mode Relay Station (RS) do not consider channel selection procedure of Mobile Station (MS), co-channel interference and Multi-hop Relay Base Station (MR-BS) coverage and RS coverage ratio in MMR system. In this paper, we investigate the performance of MMR uplink system in multicell environments with various topologies. The performance is presented in terms of call blocking probability, channel utilization, outage probability and system throughput by varying offered load. It is found that, for certain system parameters, the MMR uplink system achieve the maximum system throughput when MR-BS coverage to RS coverage ratio is 7.