• Journal of the Korean Institute of Telematics and Electronics A
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• v.33A no.6
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• pp.11-22
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• 1996

We address an issue of channel sharing among users by using a random assignment-transmitter-based (RA-T) spread-spectrum transmission scheme which permits the contention mode only in the transmission of a header while avoiding collision during the data packet transmission. Once the header being successfully received, the data packet is ready for reception by switching to one of programmable matched-filters. But the receoption may be blocked due to limited number of matched-filters so that this effect is taken into account in our analysis. For realistic analysis, we integrate detection performance at the physical level with channel activity at the link level through a markov chain model. We also consider an acknowledgement scheme to notify whether the header is correctly detcted and the data packet can be processed continuously, which aims at reducing the interference caused unwanted data transmission. It is shown that receiver complexity can be greatly reduced by choosing a proper number of RA codes at the cost of only a little throughput degradation.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.12 no.2
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• pp.181-188
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• 2012

In this paper, the measurement data is analyzed and channel parameters are derived through MIMO Channel measurements at 781MHz considering outdoor multi-path environment. 781MHz frequency band currently operates the DTV system. However, it will be allocated new mobile communication frequency band. The channel characteristics at 781MHz seem to be similar existing mobile communication system at 900MHz but a study on channel characteristics of signal transfer process is necessary because there is incomplete study in mobile networks at 781MHz. To avoid interference with Korean DTV broadcasting, we measured channel characteristics in city/suburban areas of Jeju island by channel sounder and $4{\times}4$ antenna of the ETRI(Korea Electronics and Telecommunications Research Institute). Path Loss, Delay Spread, Angular Spread and K-factor were derived based on measured data.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.5
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• pp.438-444
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• 2016

In this paper, A real-time channel module which can apply the wireless propagation channel was developed using USRP and Lab-VIEW. When the proposed channel module is used in conjunction with the implemented HW(hardware) simulators for cognitive radio and frequency interference analysis and so on, it can increase the reliability about wireless propagation environments. In addition, the proposed module overcomes the limit of existing HW simulator that data transfer rate is limitative in communication system through the design of the inner parts. Along with this, it is possible to apply channel parameters necessary to estimate the easier communication performance. Also, this has the advantage that it can be flexibly applied in implementing the communication channel with the upcoming new scenarios. The proposed module can estimate the communication performance via constellation and BER using the implemented module.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.42 no.4
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• pp.819-830
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• 2017

An FM radio based PCL system is a passive radar technique for detecting the multiple moving targets from FM radio signals and tracking the trajectories of the targets by calculating the cross-correlation function of direct-path signal and target echo signals. However, the interference signals are received from a surveillance channel, which is designed to receive the target echo signals. Because of this problem, the target echo signals are masked by the strong interference signals and this makes it difficult to detect the true targets from the cross-correlation function. Adaptive filters are known as effective methods for suppressing the interference signals but there is a problem to present their accurate performances in the PCL system because many literatures used the cross-correlation function and the ratio of input and output power as a measure of the performance analysis. In this paper, a performance analysis method is proposed to evaluate the performance of interference cancellation algorithms. By using the property that each component of the filter weight vector is adjusted to suppress the specific interference signal, a performance measure of the interference signal suppression is defined by a function of adaptive filter weights. Based on the proposed method, we compare the performance of the adaptive filters used in the PCL system. Simulation results show that the proposed method can be very effective for evaluating the performance of interference cancellation algorithms.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.5
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• pp.501-509
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• 2010

In this paper, the interference avoidance performance of the RFID reader with the compressive receiver was analyzed. In the environment of the multiple dense readers operating, the recognition rates of the conventional RFID reader and the proposed RFID reader with the compressive receiver were measured and compared. The recognition rate of the proposed reader was improved more than 2.7 times compared to the conventional reader. Especially, in the environment of two proposed RFID readers operating simultaneously, little degradation of the recognition rate was observed.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.8C
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• pp.655-662
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• 2012

In this work, we propose an airborne cognitive radio system that searches a new spectrum band to avoid a communication interruption due to the interference from many radar signals. We develop a method of fast spectrum sensing based on an effective frequency by recognizing the interfering radar as well as geographical information. This effective frequency is calculated by the free-space path loss between a base station and a fighter with the speed parameter. From our analysis, it is verified that the maximum frequency searching time is reduced by half by using our method.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.16 no.9
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• pp.3172-3193
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• 2022

Cognitive radio-simultaneous wireless information and power transfer (CR-SWIPT) has attracted much interest since it can improve both the spectrum and energy efficiency of wireless networks. This paper focuses on the resource sharing between a point-to-point primary system (PRS) and a multiuser multi-antenna cellular cognitive radio system (CRS) containing a large number of cognitive users (CUs). The resource sharing optimization problem is formulated by jointly scheduling CUs and adjusting the transmit power at the cognitive base station (CBS). The effect of accessing CUs' spatial channel correlation on the possible transmit power of the CBS is investigated. Accordingly, we provide a low-complexity suboptimal approach termed the semi-correlated semi-orthogonal user selection (SC-SOUS) algorithm to enhance the spectrum efficiency. In the proposed algorithm, CUs that are highly correlated to the information decoding primary receiver (IPR) and mutually near orthogonal are selected for simultaneous transmission to reduce the interference to the IPR and increase the sum rate of the CRS. We further develop a spatial correlation-based resource sharing (SC-RS) strategy to improve energy sharing performance. CUs nearly orthogonal to the energy harvesting primary receiver (EPR) are chosen as candidates for user selection. Therefore, the EPR can harvest more energy from the CBS so that the energy utilization of the network can improve. Besides, zero-forcing precoding and power control are adopted to eliminate interference within the CRS and meet the transmit power constraints. Simulation results and analysis show that, compared with the existing CU selection methods, the proposed low-complex strategy can enhance both the achievable sum rate of the CRS and the energy sharing capability of the network.

• IEIE Transactions on Smart Processing and Computing
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• v.6 no.3
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• pp.200-209
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• 2017

In this paper, we investigate the tradeoff between security and reliability for a multi-hop protocol in cluster-based underlay cognitive radio networks. In the proposed protocol, a secondary source communicates with a secondary destination via the multi-hop relay method in the presence of a secondary eavesdropper. To enhance system performance under the joint impact of interference constraint required by multiple primary users and hardware impairments, the best relay node is selected at each hop to relay the source data to the destination. Moreover, the destination is equipped with multiple antennas and employs a selection combining (SC) technique to combine the received data. We derive closed-form expressions of the intercept probability (IP) for the eavesdropping links and the outage probability (OP) for the data links over a Rayleigh fading channel. Finally, the correction of our derivations is verified by Monte-Carlo simulations.

• The Journal of the Korea institute of electronic communication sciences
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• v.6 no.2
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• pp.163-170
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• 2011

This study proposed the composition of a new long-code MMSE detector using the pilot channel that demonstrated the most excellent performance under Rayleigh fading in the previous studies. It analyzed and explained how to maintain the stability of the weight vector(introduction to the course of radio waves) in the receiver. In the operation of the receiver system to remove radio interference, the signal vector distortion received in the channel where fading was present achieved good results by compensating for signal errors. When there was distortion, the response characteristics of the received signals were superior to the common matching filter according to the computer simulation. The long-code MMSE receiver proposed in the study was able to prolong the cycle by $16{\times}T_b$ in the fading environment to fulfill the satisfaction.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.10 no.7
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• pp.1010-1021
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• 1999

In this paper, error performance of DS/CDMA GMSK system has been analyzed in a radio channel which is characterized by multi-user interference(MUI) and Nakagami fading. The DS/CDMA GMSK system adopts Maximum Ratio Combining(MRC) diversity and co-channel interference (CCI) to enhance system performance. Using the derived error probability equation, the error performance of DS/CDMA GMSK system has been evaluated and shown in figures to discuss as a function of PN code length(N), number of multi-user(K), number of diversity branch(L), and bit energy per noise power ratio ($E_b/N_0$), fading index(m). The results show that there is a substantial enhancement in performance by employing an MRC diversity or a CCI canceller. Additional improvement can be obtained when the MRC diversity and the CCI canceller are adopted in cascade form. Consequently, we expected that proposed system structure is reliable to the voice communication system in Nakagami fading, multi-user interferences and multipath channel.