• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.12
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• pp.2800-2804
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• 2015

Recently, device-to-device (D2D) direct communication is attracting much interest and many researches have been conducted. In this paper, we investigated an algorithm to support the D2D direct communication in cellular mobile communication networks. We investigated the optimal D2D scheduling algorithm which can achieve the maximal sum-rate in cellular uplink frequency. We also proposed a simple scheduling algorithm which can considerably reduce the computational complexity, compared to the optimal scheme. Finally, we analyzed the performance of the proposed scheme based on computer simulations.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.1
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• pp.203-228
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• 2012

It is expected that device-to-device (D2D) communication is allowed to underlay future cellular networks such as IMT-Advanced for spectrum efficiency. This article studies the mechanisms of D2D communication and interference avoidance when the D2D subsystem reuses uplink resources and downlink spectrums with a cellular system, respectively. We firstly propose an effective scheme to establish and maintain D2D communication. Moreover, a novel method to deal with the resource allocation and interference avoidance issues by utilizing the network peculiarity of a hybrid network to share the uplink resource is proposed. Most research focuses on reusing the uplink spectrums, but how to share the downlink frequency bands is seldom addressed. To share the downlink spectrums and avoid the interference to the primary cellular devices, a labeled time slots based mechanism is proposed. Implementation details are described in a real cellular system and simulation results prove that satisfying performance can be achieved by using the proposed mechanisms.

• Proceedings of the Korea Information Processing Society Conference
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• 2014.04a
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• pp.206-209
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• 2014

Control message exchange is major job for cognitive radio to exist and use spectrum opportunistically. For this control message exchange they need a common control channel (CCC). Once this channel is affected by a primary user, communication stops until new CCC is setup. This takes substantial time and if they could not get free channel, this halt continues for long time. To prevent such cease of communication, we propose a combination of two networks, namely WLAN and UWB, to let the communication continue. In our proposed idea if the CCC of a certain CR in WLAN is affected, the CR changes its network from WLAN to UWB and keeps the communication because UWB cannot be affected by PU. In the proposed idea every cognitive radio has two transceivers; one for the overlay network (WLAN) and another UWB network. If a primary user is detected in the spectrum of a cognitive radio, it continues exchanging control messages under the UWB network and in parallel negotiates for a new CCC using the WLAN network. This idea solves the communication interruption until new CCC is setup.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.4
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• pp.1941-1960
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• 2019

Unmanned aerial vehicles (UAVs), acting as mobile base stations (BSs), can be deployed in the typical fifth-generation mobile communications (5G) scenarios for the purpose of substantially enhancing the radio coverage. Meanwhile, UAV aided underlay device-to-device (D2D) communication mode can be activated for further improving the capacity of the 5G networks. However, this UAV aided D2D communication system is more vulnerable to eavesdropping attacks, resulting in security risks. In this paper, the D2D receivers work in full-duplex (FD) mode, which improves the security of the network by enabling these legitimate users to receive their useful information and transmit jamming signal to the eavesdropper simultaneously (with the same frequency band). The security communication under the UAV coverage is evaluated, showing that the system's (security) capacity can be substantially improved by taking advantage of the flexible radio coverage of UAVs. Furthermore, the closed-form expressions for the coverage probabilities are derived, showing that the cellular users (CUs)' secure coverage probability in downlink transmission is mainly impacted by the following three factors: its communication area, the relative position with UAV, and its eavesdroppers. In addition, it is observed that the D2D users or DUs' secure coverage probability is relevant to state of the UAV. The system's secure capacity can be substantially improved by adaptively changing the UAV's position as well as coverage.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2013.11a
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• pp.34-35
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• 2013

기존 연구에서 무선 인지 네트워크의 성능 분석에 관한 연구는 많았지만 무선 인지 네트워크에 차량 통신을 접목시킨 무선 인지 차량 네트워크의 성능 분석에 관한 연구는 많지 않았다. 또한 최근 실질적인 채널환경을 고려하기 위해 불완전한 채널정보를 가잔 시스템에서의 성능 분석에 대한 연구가 많이 진행되고 있는데 무선 인지 차량 네트워크에서의 연구는 아직 진행되지 않았다. 본 논문에서는 불완전한 채널정보가 존재하는 인지 차량 네트워크의 성능 분석을 한다. 본 논문에서는 언더레이 (underlay) 무선 인지 네트워크를 가정하고 차량간 통신이 일어나는 2차 사용자 네트워크의 채널들을 double Rayleigh fading으로 모델링한다. 성능 분석의 지표로 불능 확률을 사용하고 컴퓨터 모의실험을 통해 분석된 불능확률 값이 상관계수가 변화함에 따라 어떠한 변화가 있는지 확인하였다.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2012.11a
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• pp.69-70
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• 2012

본 논문에서는 다중중계기가 존재하는 인지 차량 네트워크의 성능 분석을 한다. 기존 연구에서 무선 인지 네트워크의 성능 분석에 관한 연구는 많았지만 무선 인지 네트워크에 차량 통신을 접목시킨 무선 인지 차량 네트워크의 성능 분석에 관한 연구는 많지 않았다. 본 논문에서는 언더레이(underlay) 무선 인지 네트워크를 가정하고 차량간 통신이 일어나는 2차 사용자 네트워크의 채널들을 cascaded Rayleigh fading으로 모델링 한다. 성능 분석의 지표로 불능 확률을 사용하고 컴퓨터 모의실험을 통해 분석된 불능확률 값과 모의실험을 통해 얻어진 불능확률 값이 거의 일치한다는 것을 보인다.

• Journal of Communications and Networks
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• v.16 no.2
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• pp.110-120
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• 2014

This article proposes a spectrum sharing method which can avoid the mutual interference in both primary and secondary systems. The two systems make them a priority to use two single-dimension orthogonal signals, the real and imaginary pulse amplitude modulation signals, if the primary system is not in outage with this use. A secondary transmitter is selected to be the primary relay and the active secondary source to perform this. This allows a simultaneous spectrum access without any mutual interference. Otherwise, the primary system attempts to use a full two-dimensional signal, the quadrature amplitude modulation signal. If there is no outage with respect to this use, the secondary spectrum access is not allowed. When both of the previous attempts fail, the secondary system is allowed to freely use the spectrum two whole time slots. The analysis and simulation are provided to analyze the outage performance and they validate the considerable improvement of the proposed method as compared to the conventional one.

• Journal of Communications and Networks
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• v.18 no.5
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• pp.744-761
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• 2016

For about the past decade and a half research efforts into cognitive radio networks (CRNs) have increased dramatically. This is because CRN is recognized as a technology that has the potential to squeeze the most out of the existing spectrum and hence virtually increase the effective capacity of a wireless communication system. The resulting increased capacity is still a limited resource and its optimal allocation is a critical requirement in order to realize its full benefits. Allocating these additional resources to the secondary users (SUs) in a CRN is an extremely challenging task and integer programming based optimization tools have to be employed to achieve the goals which include, among several aspects, increasing SUs throughput without interfering with the activities of primary users. The theory of the optimization tools that can be used for resource allocations (RA) in CRN have been well established in the literature; convex programming is one of them, in fact the major one. However when it comes to application and implementation, it is noticed that the practical problems do not fit exactly into the format of well established tools and researchers have to apply approximations of different forms to assist in the process. In this survey paper, the optimization tools that have been applied to RA in CRNs are reviewed. In some instances the limitations of techniques used are pointed out and creative tools developed by researchers to solve the problems are identified. Some ideas of tools to be considered by researchers are suggested, and direction for future research in this area in order to improve on the existing tools are presented.

• Journal of Information Technology Services
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• v.13 no.1
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• pp.125-134
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• 2014

Device discovery for D2D (device-to-device) communication enables a device to discover other devices in order to initiate communication with them. Devices should perform the discovery phase using a small quantity of radio resource in a short time and be able to reduce the load of the base station. Legacy device discovery schemes have focused on discovering as many target devices as possible. However, it is not appropriate for peer-to-peer D2D communication scenario. Further, synchronization problems are an important issue for discovery signal transmission. This paper proposes a discovery method that one requesting device discovers a specific target for communication. Multiple antenna beamforming is employed for the synchronization between the base station and a target device. The proposal can reduce the load of the base station using the information that it already maintains and improve the reliability of the device discovery because two times of synchronizations using beamforming among the base station and devices can make the exact discovery of a target device with mobility possible.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.6
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• pp.2450-2469
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• 2018

In this paper, we develop a spatiotemporal model to analysis of cellular user in underlay D2D communication by using stochastic geometry and queuing theory. Firstly, by exploring stochastic geometry to model the user locations, we derive the probability that the SINR of cellular user in a predefined interval, which constrains the corresponding transmission rate of cellular user. Secondly, in contrast to the previous studies with full traffic models, we employ queueing theory to evaluate the performance parameters of dynamic traffic model and formulate the cellular user transmission mechanism as a M/G/1 queuing model. In the derivation, Embedded Markov chain is introduced to depict the stationary distribution of cellular user queue status. Thirdly, the expressions of performance metrics in terms of mean queue length, mean throughput, mean delay and mean dropping probability are obtained, respectively. Simulation results show the validity and rationality of the theoretical analysis under different channel conditions.