• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.12 no.1
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• pp.58-71
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• 2019

This paper proposes architecture of a cognitive radio engine platform and the allowable frequency channel reasoning method that enables acquisition of the allowable channels for the military tactical network environment. The current military tactical wireless communication system is increasing need to secure a supplementary radio frequency to ensure that multiple wireless networks for different military wireless devices coexist, so that tactical wireless communication between the same or different systems can be operated effectively. This paper presents the allowable frequency channel reasoning method based on cognitive radio engine for realizing DSA(Dynamic Spectrum Access) as an optimal available frequency channel. To this end, a case-based allowable frequency channel reasoning method for cognitive radio devices is proposed through modeling of primary user's traffic status and calculation of channel occupancy probability. Also through the simulation of the performance analysis, changing rate of collision probability between the primary users' occupancy channel and the available channel acquisition information that can be used by the cognitive radio device was analysed.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.34S no.4
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• pp.1-11
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• 1997

In this paper, modeling of the communication channel occupancy characteristics at the base station in the wide area radio trunking syste has been performed. Using the results, mathematical analysis for the switching capacity at the network switch has also been done. Specificatlly, we propose a G/M/m queueing model for the single service area modeling, and analyze changes in call blockingprobabilities accoridng to changes in the burstness characteristics of group paging calls. As a result, we have observe dthat the channel occupancy variations become larger as the burstness characteristics become more apparent, to make the call blocking probability higher. Next, based on the single service area analysis, we have anayzed mathematically the average switching capacity required to serve mobile subscribers for a wide area radio trunking sytem, where multiple switching port assignments are required when the people in the same group are distributed over several base stations. Accordingly, we have observed that the average and the variance of switching channel occupancy are closely related to the mobility characteristics of subscribers, and that we need a netowrk switch having bigger capacity as subscribers show wider distribution. Especially, with the call dropping probability within 0.2%, a switch having about 5 to 6 times bigger can be required, compared with the one when the mobility of subscribers is mostly restricte dto a single service area.

• Journal of Communications and Networks
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• v.16 no.1
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• pp.56-66
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• 2014

We propose a novel opportunistic access scheme for cognitive radios in an interweave cognitive system, that considers the channel gain as well as the predicted idle channel probability (primary user occupancy: Busy/idle). In contrast to previous work where a cognitive user vacates a channel only when that channel becomes busy, the proposed scheme requires the cognitive user to switch to the channel with the next highest idle probability if the current channel's gain is below a certain threshold. We derive the threshold values that maximize the long term throughput for various primary user transition probabilities and cognitive user's relative movement.

• Journal of Korean Institute of Industrial Engineers
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• v.25 no.3
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• pp.351-359
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• 1999

We present a new approach to the analysis of mobile cellular communication systems under the environment of mixed platforms adopting a guard channel scheme. We assume general cell residence time distributions according to platform-types. Our system model is based on a heterogeneous M/G/c loss system with customer-dependent guard channels, where heterogeneous customers with different service time distributions have different numbers of their own guard channels. We develop the general formula of steady state probabilities for the heterogeneous M/G/c loss system with customer-dependent guard channels. The mean channel occupancy times of new and handoff calls are rigorously derived under a general setting. Finally, our numerical results show that the blocking probability and the forced termination probability are sensitive to the cell residence time distributions.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.6 no.4
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• pp.544-551
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• 2002

In this paper, BER performance of DS/CDMA-BPSK system is analyzed in mixed lading channel that is consist of Rayleigh fadins Rician fading, and shadowed Rician fading. From the results, we know that proposed mixed fading model is very suitable to describe the different channel situations. and, the occupancy probability and the shadowing depth are very dependent to the system performance. Finally, we know that the Reed-Solomon coded DS/ CDMA-BPSK system is very robust to simultaneous user interference and mixed lading channel.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.47 no.4
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• pp.63-70
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• 2010

In IEEE 802.11e system providing differentiated services, there exist some problems as follows; collision probability increase due to the increase in the number of nodes by employing CSMA/CA transmission mode, transmission speed declining tendency towards the worst of it, which is caused by different transmission mode and decrease of TCP transmission rate as the result of the link occupancy by UDP when TCP shares the link with UDP by the TCP’s flow control characteristic. In this thesis, the initial minimum and maximum CW are set differently according to the number of connected nodes in the network to avoid collisions and TXOP is adjusted according to the channel state, in which ACs with low priority but better channel state will get gradually more chances to transmit leading to optimal channel capacity. Also, by allowing higher priority for ACK frames which control the TCP transmission, the flow control becomes better because that reduces the channel occupancy by UDP flow, and by this, fair transmission is obtained from the result of the more fair transmission and active resource allocation.

• Proceedings of the IEEK Conference
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• summer
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• pp.57-60
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• 2004

Next generation wireless network is evolving toward IP-based network that can various provide multimedia services. A challenge in wireless mobile Internet is support of quality of service over wireless access networks. DiffServ architecture is proposed for evolving wireless mobile Internet. In this paper we propose an algorithm for optimal buffer partitioning which requires the minimal channel capacity to satisfy the QoS requirements of input traffic. We used a partitioned buffer with size B to serve a layered traffic at each DiffServ router. We consider a traffic model with a single source generates traffic having J $(J\geq2)$ quality of service (QoS) classes. QoS in this case is described by loss probability $\varepsilon_j$. for QoS class j. Traffic is admitted or rejected based on the buffer occupancy and its service class. Traffic is generated by heterogeneous Markov-modulated fluid source (MMFS).

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.12 no.1
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• pp.88-97
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• 2013

Most of the traditional spectrum sensing methods consider only the current detected data sets of Primary User (PU). However previous state of PU is a kind of conditional probability that strengthens the reliability of the detector. Therefore, in the cross entropy spectrum sensing method, relationship of the previous and current spectrum sensing is considered to detect PU signal more effectively. But these cross entropy spectrum sensing methods only consider the ideal system. In other words, PU always occupy the channel during the same period. However, PU can occupy the channel either for a longer or a shorter period than the ideal case in the real system. For this reason, the spectrum sensing performance can be varied. In this paper, we propose the method that can maintain the performance of spectrum sensing in the real system and we confirm the results with the help of simulation.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.3 no.4
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• pp.795-804
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• 1999

The increasing number of users of mobile communication systems and the corresponding need for increased system capacity require the use of a modulation scheme which is both power and spectrally efficient. In this paper, we numerically calculate the BER performance of DS/CDMA-BPSK system in different fading channel (Rayleigh, Rician, Shadow Rician). Also, we calculate BER performance and the channel capacity of DS/CDMA-BPSK system which is constant or nearly constant envelopes in 3-state fading channel model. The Shadow Rician fading model described in this paper apply the parameters of the Canadian Mobile Satellite (MSAT). And we assume that the 3-state fading channel model is consist of Rayleigh fading state, Rician fading state, and shadow Rician fading state. This model can be used as a basis for the simulation of the land mobile satellite channel. The dynamic 3-state fading channel model is considered corresponding to different environments and the transitions between these environments. From the numerically calculate results, the DS/CDMA-BPSK system with MUI-20, PG-511 can not achieve the BER performance ($P_b\leq10^{-5}$). And the channel capacity did not meet the system requirement. Also, we know that the BER performance is depend m the occupancy probability of radio channel and the degree of shadow. From the results, we how that during shadowed time intervals it is necessary to use some form of error control coding and receiver diversity in order to support reliable data communication.