• 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.15 no.1
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• pp.38-44
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• 2013

This paper proposes a new dynamic spectrum access (DSA) algorithm for cognitive radio networks. Once initialized, this algorithm works without the need of coordination overhead and hence can be used when no control channel is available. Secondary user (SU) lists and predetermined access control are used in this algorithm. We analyze the probability of no SU collision with primary user and the throughput of our proposed algorithm. Extensive simulations show that our algorithm outperforms the existing DSA algorithm in terms of both the aggregate throughput and the traffic distribution fairness. Furthermore, the validity of our analysis is confirmed by simulation results.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.25 no.10
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• pp.983-994
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• 2014

In this paper, we analyze the telecom services and their socio-economic effect of using open spectrum, which is to access sharing spectrum. For this, we suggest a concept and a classification of open spectrum as spectrum access model and make a survey for analyzing the socio-economic effect of spectrum, 2,605 MHz which is candidated for sharing between 2.9~5.925 Hz in Korea. From survey results, we propose Mobile Telecommunications Assist Service and WiFi as the most effective services and Smart Car Service and M2M, IoT, and RFID/USN Service as the effective services to open spectrum.

• Proceedings of the KIEE Conference
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• 1987.07b
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• pp.833-836
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• 1987

The error probability for coherent frequency-hopped spread-spectrum multiple-access communications is computed. We employ PSK as a modulation scheme. The channel capacity is performance measure and the minimum bit signal-to-noise ratio for reliable communications is obtained.

• Information and Communications Magazine
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• v.30 no.1
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• pp.67-76
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• 2012

본고에서는 jamming 이나 은폐 등으로 인하여 통신 채널이 동적으로 변화하는 전장환경에서 dynamic spectrum access(DSA) 기술을 토대로 보다 안정된 통신을 하는 기술을 알아본다. DSA 통신의 핵심기술을 설명하고, 미국의 DARPA에서 수행한 neXt Generation(XG) 프로젝트와 Wireless Network after Next(WNaN) 국방통신 프로젝트를 소개한 후에 결론에서 시사점을 다룬다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.4
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• pp.1489-1503
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• 2018

Spectrum reuse has attracted much concern of researchers and scientists, however, the dynamic spectrum access is challenging, since an individual secondary user usually just has limited sensing abilities. One key insight is that spectrum usage forecasting among secondary users, this inspiration enables users to obtain more informed spectrum opportunities. Therefore, spectrum usage forecasting is vital to cognitive radio networks (CRNs). With this insight, a spectrum usage forecasting model for the occurrence of primary users prediction is derived in this paper. The proposed model is based on auto regressive enhanced primary user emergence reasoning (AR-PUER), which combines linear prediction and primary user emergence reasoning. Historical samples are selected to train the spectrum usage forecasting model in order to capture the current distinction pattern of primary users. The proposed scheme does not require the knowledge of signal or of noise power. To verify the performance of proposed spectrum usage forecasting model, we apply it to the data during the past two months, and then compare it with some other sensing techniques. The simulation results demonstrate that the spectrum usage forecasting model is effective and generates the most accurate prediction of primary users occasion in several cases.

• Journal of IKEEE
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• v.16 no.1
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• pp.51-55
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• 2012

In this paper, we propose to employ a ternary sequence as a cyclic code shift keying (CCSK) modulation sequence. And we simulate the performance in a frequency hopping spread spectrum/time division multiple access (FHSS/TDMA) system with CCSK. Wireless channel is modeled as Rayleigh fading channel. From the simulation results, it is demonstrated that the system adopting the ternary sequence as a CCSK sequence has higher performance than that with a random sequence.

• Journal of Korea Society of Digital Industry and Information Management
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• v.12 no.4
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• pp.81-87
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• 2016

Recently, as the heterogeneous network (HetNet) has been deployed widely to support various kinds of Radio Access Networks(RANs) with a combination of Macro, Pico, and/or Femto cells, research and standardization efforts have been very active regarding the concept of Licensed Shared Access (LSA) for supporting spectrum sharing. In order for a mobile device to efficiently support the spectrum sharing, the mobile device shall be reconfigurable, meaning that its radio application code has to be adaptively changed in accordance with the hopping of desired spectral band. Especially, Working Group 2 (WG2) of Technical Committee (TC) Reconfigurable Radio System (RRS) of European Telecommunications Standards Institute (ETSI) has been a main driving force for developing standard architecture for Multi-mode Mobile Device (MD) that can be applied to the LSA system. In this paper, we introduce the Multi-mode MD architecture for supporting LSA-based spectrum sharing. An implementation of a test-bed of Multi-mode MD is presented in order to verify the feasibility of the standard MD architecture for the purpose of LSA-based spectrum sharing through various experimental tests.

• Journal of Communications and Networks
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• v.16 no.2
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• pp.193-201
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• 2014

In cognitive radio networks, the packet transmissions of the secondary users (SUs) can be interrupted randomly by the primary users (PUs). That is to say, the PU packets have preemptive priority over the SU packets. In order to enhance the quality of service (QoS) for the SUs, we propose a spectrum access strategy with an ${\alpha}$-Retry policy. A buffer is deployed for the SU packets. An interrupted SU packet will return to the buffer with probability ${\alpha}$ for later retrial, or leave the system with probability (1-${\alpha}$). For mathematical analysis, we build a preemptive priority queue and model the spectrum access strategy with an ${\alpha}$-Retry policy as a two-dimensional discrete-time Markov chain (DTMC).We give the transition probability matrix of the Markov chain and obtain the steady-state distribution. Accordingly, we derive the formulas for the blocked rate, the forced dropping rate, the throughput and the average delay of the SU packets. With numerical results, we show the influence of the retrial probability for the strategy proposed in this paper on different performance measures. Finally, based on the trade-off between different performance measures, we construct a cost function and optimize the retrial probabilities with respect to different system parameters by employing an iterative algorithm.

• Journal of Communications and Networks
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• v.15 no.1
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• pp.8-14
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• 2013

For alleviating the low spectrum efficiency problem of orthogonal frequency division multiplexing (OFDM), due to the strong inter-cell-interference (ICI) at cell's edge, we introduce comb-spectrum code division multiple access (CS-CDMA) into broadband OFDM system at downlink channel for enabling the use of entire spectrum for seamless coverage. In addition, we develop a new method, called orthogonal cell code (OCC) scheme, to assist CS-CDMA for nullifying the ICI from contiguous cells. In system operation, each of the conventional cells is divided into an outer cell and an inner cell, and a mobile station (MS) should access to the CS-CDMA when it is in the outer cell and access to OFDM when it is in the inner cell. This study investigates the spectrum efficiency of using CS-CDMA and makes a comparison with that of long term evolution (LTE) in the following cases; (1) under an assumption of perfect channel state information and (2) based on channel estimates at a MS station. The results show the great advantage of utilizing the proposed system.