• KSII Transactions on Internet and Information Systems (TIIS)
• /
• 제7권6호
• /
• pp.1379-1397
• /
• 2013

We consider a system where a licensed radio spectrum is shared by multiple primary users(PUs) and secondary users(SUs). As the spectrum of interest is licensed to primary network, power and channel allocation must be carried out within the cognitive radio network so that no excessive interference is caused to PUs. For this system, we study the joint beamforming and power allocation problem via game theory in this paper. The problem is formulated as a non-cooperative beamforming and power allocation game, subject to the interference constraints of PUs as well as the peak transmission power constraints of SUs. We design a joint beamforming and power allocation algorithm for maximizing the total throughput of SUs, which is implemented by alternating iteration of minimum mean square error based decision feedback beamforming and a best response based iterative power allocation algorithm. Simulation results show that the algorithm has better performance than an existing algorithm and can converge to a locally optimal sum utility.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• 제12권4호
• /
• pp.1655-1673
• /
• 2018

Mobile computing environment is subject to the constraints of bounded network bandwidth, frequently encountered disconnections, insufficient battery power, and system asymmetry. To meet these constraints and to gain high scalability, data broadcasting has been proposed on data transmission techniques. However, updates made to the database in any broadcast cycle are deferred to the next cycle in order to appear to mobile clients with lower data currency. The main goal of this paper is to enhance the transaction performance processing and database currency. The main approach involves decomposing the main broadcast cycle into a number of sub-cycles, where data items are broadcasted as they were originally sequenced in the main cycle while appearing in the most current versions. A concurrency control method AOCCRBSC is proposed to cope well with the cycle decomposition. The proposed method exploits predeclaration and adapts the AOCCRB method by customizing prefetching, back-off, and partial backward and forward validation techniques. As a result, more than one of the conflicting transactions is allowed to commit at the server in the same broadcast cycle which empowers the processing of both update and read-only transactions and improves data currency.

• Journal of Electrical Engineering and Technology
• /
• 제4권3호
• /
• pp.353-359
• /
• 2009

This paper proposes a novel technique for calculating the security costs that properly includes ramping constraints in the operation of a deregulated power system. The ramping process is modeled by a piecewise linear function with certain assumptions. During this process, a ramping cost is incurred if the permissible limits are exceeded. The optimal production costs of the power producers are calculated with the ramping cost included, considering a time horizon with N-1 contingency cases using contingency constrained optimal power flow (CCOPF), which is solved by the primal-dual interior point method (PDIPM). A contingency analysis is also performed taking into account the severity index of transmission line outages and its sensitivity analysis. The results from an illustrative case study based on the IEEE 30-bus system are analyzed. One attractive feature of the proposed approach is that an optimal solution is more realistic than the conventional approach because it satisfies physical constraints, such as the ramping constraint.

• Journal of information and communication convergence engineering
• /
• 제15권2호
• /
• pp.79-84
• /
• 2017

In a cognitive radio network (CRN), cognitive radio users (CUs) should be powered by a small battery for their operations. The operations of the CU often include spectrum sensing and data transmission. The spectrum sensing process may help the CU avoid a collision with the primary user (PU) and may save the energy that is wasted in transmitting data when the PU is present. However, in a time-slotted manner, the sensing process consumes energy and reduces the time for transmitting data, which degrades the achieved throughput of the CRN. Subsequently, the sensing process does not always offer an advantage in regards to throughput to the CRN. In this paper, we propose a scheme to find an optimal policy (i.e., perform spectrum sensing before transmitting data or transmit data without the sensing process) for maximizing the achieved throughput of the CRN. In the proposed scheme, the data collection period is considered as the main factor effecting on the optimal policy. Simulation results show the advantages of the optimal policy.

• 한국정보처리학회논문지
• /
• 제7권2S호
• /
• pp.649-655
• /
• 2000

Real-time application programs have constraints which need to be met between media-data. These constraints represents the delay time ad quality of service between media-data to be presented. In order to efficiently describe the delay time and quality of service, a new synchronization mechanism is needed. Proposed paper is a dynamic synchronization that minimized the effects of adaptive transmission delay time. That is, the method meets the requirements of synchronization between media-dat by handling dynamically the adaptive waiting time resulted from variations of delay time. In addition, the mechanism has interval adjustment using maximum delay jitter time. This paper decreases the data loss resulted from variation of delay time and from loss time of media-data by means of applying delay jitter in order to deal with synchronization interval adjustment. Plus, the mechanism adaptively manages the waiting time of smoothing buffer, which leads to minimize the gap from the variation of delay time. The proposed paper is suitable to the system which requires the guarantee of high quality of service and mechanism improves quality of services such as decrease of loss rate, increase of playout rate.

• ETRI Journal
• /
• 제33권2호
• /
• pp.155-162
• /
• 2011

The scalable extension of the H.264/AVC video coding standard (SVC) demonstrates superb adaptability in video communications. Joint source and channel coding (JSCC) has been shown to be very effective for such scalable video consisting of parts of different significance. In this paper, a new JSCC scheme for SVC transmission over packet loss channels is proposed which performs two-dimensional optimization on the quality layers of each frame in a rate-distortion (R-D) sense as well as on the temporal hierarchical structure of frames under dependency constraints. To compute the end-to-end R-D points of a frame, a novel reduced trellis algorithm is developed with a significant reduction of complexity from the existing Viterbi-based algorithm. The R-D points of frames are sorted under the hierarchical dependency constraints and optimal JSCC solution is obtained in terms of the best R-D performance. Experimental results show that our scheme outperforms the existing scheme of [13] with average quality gains of 0.26 dB and 0.22 dB for progressive and non-progressive modes respectively.

• Journal of Electrical Engineering and Technology
• /
• 제12권3호
• /
• pp.1307-1313
• /
• 2017

Sensor networks are composed of provide low powered, inexpensive distributed devices which can be deployed over enormous physical spaces. Coordination between sensor devices is required to achieve a common communication. In low cost, low power and short-range wireless environment, sensor networks cope with significant resource constraints. Security is one of main issues in wireless sensor networks because of potential adversaries. Several security protocols and models have been implemented for communication on computing devices but deployment these models and protocols into the sensor networks is not easy because of the resource constraints mentioned. Memory intensive encryption algorithms as well as high volume of packet transmission cannot be applied to sensor devices due to its low computational speed and memory. Deployment of sensor networks without security mechanism makes sensor nodes vulnerable to potential attacks. Therefore, attackers compromise the network to accept malicious sensor nodes as legitimate nodes. This paper provides the different security models as a metric, which can then be used to make pertinent security decisions for securing wireless sensor network communication.

• Journal of Communications and Networks
• /
• 제13권5호
• /
• pp.472-480
• /
• 2011

In this paper, we investigate two new candidate transmission schemes, non-orthogonal frequency reuse (NOFR) and beam-hopping (BH). They operate in different domains (frequency and time/space, respectively), and we want to know which domain shows overall best performance. We propose a novel formulation of the signal-to-interference plus noise ratio (SINR) which allows us to prove the frequency/time duality of these schemes. Further, we propose two novel capacity optimization approaches assuming per-beam SINR constraints in order to use the satellite resources (e.g., power and bandwidth) more efficiently. Moreover, we develop a general methodology to include technological constraints due to realistic implementations, and obtain the main factors that prevent the two technologies dual of each other in practice, and formulate the technological gap between them. The Shannon capacity (upper bound) and current state-of-the-art coding and modulations are analyzed in order to quantify the gap and to evaluate the performance of the two candidate schemes. Simulation results show significant improvements in terms of power gain, spectral efficiency and traffic matching ratio when comparing with conventional systems, which are designed based on uniform bandwidth and power allocation. The results also show that BH system turns out to show a less complex design and performs better than NOFR system specially for non-real time services.

• 정보처리학회논문지C
• /
• 제9C권6호
• /
• pp.953-960
• /
• 2002

실시간 응용 프로그램은 미디어 데이터간에 만족되어야 할 동기화 제약조건(synchronization constraints)을 가지고 있다. 멀티미디어 데이터의 가변적 전송 시연 시간을 흡수하여 피드백 제어와 재생정책에 의한 동기화 기법을 수행한다. 버퍼의 수위가 정상레벨을 유지하는가에 대한 문제는 재생률과 QoS 서비스에 중요한 영향을 주게 된다. 본 논문에서는 버퍼의 수위를 안정상태고 유지하기 위해 피트백을 위한 필터링함수를 적용하고, 재생시간을 적응적으로 적용하여 미디어의 재생 시 끊어짐이 없는 유연한 재생을 한다. 또한 버퍼의 주 미디어인 오디오 프레임의 버퍼가 상위임계레벨에 수위가 존재 할 경우는 적응적으로 재생시간을 줄이고, 하위임계레벨에 버퍼의 수위가 있을 경우는 점차적으로 재생시간을 늘리는 시스템이다.

• ETRI Journal
• /
• 제44권5호
• /
• pp.733-745
• /
• 2022

In software-defined wireless networking (SDWN), the optimal routing technique is one of the effective solutions to improve its performance. This routing technique is done by many different methods, with the most common using integer linear programming problem (ILP), building optimal routing metrics. These methods often only focus on one routing objective, such as minimizing the packet blocking probability, minimizing end-to-end delay (EED), and maximizing network throughput. It is difficult to consider multiple objectives concurrently in a routing algorithm. In this paper, we investigate the application of machine learning to control routing in the SDWN. An intelligent routing algorithm is then proposed based on the machine learning to improve the network performance. The proposed algorithm can optimize multiple routing objectives. Our idea is to combine supervised learning (SL) and reinforcement learning (RL) methods to discover new routes. The SL is used to predict the performance metrics of the links, including EED quality of transmission (QoT), and packet blocking probability (PBP). The routing is done by the RL method. We use the Q-value in the fundamental equation of the RL to store the PBP, which is used for the aim of route selection. Concurrently, the learning rate coefficient is flexibly changed to determine the constraints of routing during learning. These constraints include QoT and EED. Our performance evaluations based on OMNeT++ have shown that the proposed algorithm has significantly improved the network performance in terms of the QoT, EED, packet delivery ratio, and network throughput compared with other well-known routing algorithms.