• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.10
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• pp.1986-1993
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• 2015

We investigate the optimal resource and power allocation for device-to-device (D2D) communications in a multicell environment. When D2D links reuse the cellular radio resources, each D2D user will interfere with a cellular link and other D2D links, in its own cell as well as in adjacent cells. Under such situation, we propose a coordinated resource allocation scheme that can handle the intercell interferences as well as the intracell interference. For a given resource allocation, we also formulate a power optimization problem and present an algorithm for finding the optimal solution. The resource and power allocation algorithms are designed to maximize the achievable rate of the D2D link, while limiting the generated interference to the cellular link. The performance of the proposed algorithms is evaluated through simulations in a multicell environment. Numerical results are presented to verify the coordination gain in the resource and power allocation.

• Journal of Communications and Networks
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• v.14 no.1
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• pp.51-62
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• 2012

The exponential growth in wireless services has resulted in an overly crowded spectrum. The current state of spectrum allocation indicates that most usable frequencies have already been occupied. This makes one pessimistic about the feasibility of integrating emerging wireless services such as large-scale sensor networks into the existing communication infrastructure. Cognitive radio is an emerging dynamic spectrum access technology that can be used for flexibly and efficiently achieving open spectrum sharing. Cognitive radio is an intelligent wireless communication system that is aware of its radio environment and that is capable of adapting its operation to statistical variations of the radio frequency. In ad hoc cognitive radio networks, a common control channel (CCC) is usually used for supporting transmission coordination and spectrum-related information exchange. Determining a CCC in distributed networks is a challenging research issue because the spectrum availability at each ad hoc node is quite different and dynamic due to the interference between and coexistence of primary users. In this paper, we propose a novel CCC selection protocol that is implemented in a distributed way according to the appearance patterns of primary systems and connectivity among nodes. The proposed protocol minimizes the possibility of CCC disruption by primary user activities and maximizes node connectivity when the control channel is set up. It also facilitates adaptive recovery of the control channel when the primary user is detected on that channel.

• Journal of electromagnetic engineering and science
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• v.9 no.1
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• pp.17-24
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• 2009

In recent years, OFDMA(orthogonal frequency division multiple access) and SC-FDMA(Single Carrier Frequency Division Multiple Access) have been widely studied for the uplink of a mobile communication system. In this paper, PAPR(Peak-to-Average Power Ratio) and BER(Bit Error Rate) performance of the OFDMA and SC-FDMA systems are studied in relation to the uplink of a mobile communication system. Three kinds of sub-carrier allocation methods in the OFDMA system and 2 kinds of sub-carrier allocation methods in SC-FDMA system are suggested to compare and improve system performance. Simulation results show that in the OFDMA system, the first sub-band allocation method has better PAPR reduction performance than the other methods. In the SC-FDMA system, the distributed allocation method offers similar P APR, compared with the sub-band allocation method. P APR can be further reduced by adding a spectrum shaping filter with an appropriate roll of factor. Furthermore, it is found that on average, SC-FDMA can reduce the PAPR by more than 5 dB compared to OFDMA, when the total sub-carrier number is 1,024 and the sub-carrier number allocated to each user changes trom 8 to 512. Because of the frequency diversity and low PAPR characteristics, SC-FDMA system of the distributed sub-carrier allocation method can achieve better BER performance than the OFDMA system.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.3
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• pp.924-944
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• 2014

This paper investigates the power allocation and outage performance of MIMO full-duplex relaying (MFDR), based on orthogonal space-time block codes (OSTBC), in cognitive radio systems. OSTBC transmission is used as a simple means to achieve multi-antenna diversity gain. Cognitive MFDR systems not only have the advantage of increasing spectral efficiency through spectrum sharing, but they can also extend coverage through the use of relays. In cognitive MFDR systems, the primary user experiences interference from the secondary source and relay simultaneously, owing to full duplexing. It is therefore necessary to optimize the transmission powers at the secondary source and relay. In this paper, we propose an optimal power allocation (OPA) scheme based on minimizing the outage probability in cognitive MFDR systems. We also analyse the outage probability of the secondary user in noise-limited and interference-limited environments in Nakagami-m fading channels. Simulation results show that the proposed schemes achieve performance improvements in terms of reducing outage probability.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.7
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• pp.1777-1791
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• 2012

This paper considers a downlink cognitive radio (CR) network where one secondary user (SU) and one primary user (PU) share the same base station (BS). The spectrum of interest is divided into a set of independent, orthogonal subchannels. The communication of the PU is of high priority and the quality of service (QoS) is guaranteed by the minimum rate constraint. On the other hand, the communication of the SU is of low priority and the SU opportunistically accesses the subchannels that were previously discarded by the PU during power allocation. The BS assigns fractions ?? and 1 ?? of the total available transmit power to the PU and the SU respectively. Two power allocation schemes with opportunistic subchannel access are proposed, in which the optimal values of ??'s are also obtained. The objective of one scheme is to maximize the rate of the SU, and the objective of the other scheme is to maximize the sum rate of the SU and the PU, both under the PU minimum rate constraint and the total transmit power constraint. Extensive simulation results are obtained to verify the effectiveness of the proposed schemes.

• Journal of the Korea Institute of Military Science and Technology
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• v.14 no.5
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• pp.833-841
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• 2011

In this paper, we propose uncoordinated dynamic frequency(channel) allocation schemes based on cognitive radio in mobile cellular networks(MCNs). Under the assumptions that mobile base stations are equipped with cognitive radio(CR) function and they construct uncoordinated network, the proposed scheme enables the MCNs by suppression of successive channel switching and management of channel allocation in a dynamic and distributed manner. The proposed scheme is composed of two phase processes. In the first phase, highly orthogonal sequences are generated and assigned to mobile base stations. In the second phase, each mobile base station is allocated a channel according to the pre-assigned orthogonal sequences. Simulation results show that the number of successive spectrum switching is reduced significantly compared with the random switching scheme.

• The Journal of the Korea Contents Association
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• v.9 no.7
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• pp.95-101
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• 2009

Cognitive Radios are encouraging solutions to improve the utilization of the radio spectrum In this paper, we propose channel allocation model for cognitive radio and analyse the performance of the model with Petri Nets. We design the model with an assumption that only partial information about current channel allocation information is known to CR users. The model is designed to communicate efficiently avoiding interference with primary and CR users and contains channel reobtaining process of CR users. The dropping rate and throughput of CR users under the various channel utilization of primary users are given as performance index.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.2
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• pp.611-627
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• 2017

For enhancing the coverage of wireless networks and increasing the spectrum efficiency, small cell networks (SCNs) are considered to be one of the most prospective schemes. Most of the existing literature on resource allocation among non-cooperative small cell base stations (SBSs) has widely drawn close attention and there are only a small number of the cooperative ideas in SCNs. Based on the motivation, we further investigate the cooperative approach, which is formulated as a coalition formation game with power control algorithm (CFG-PC). First, we formulate the downlink sub-channel resource allocation problem in an SCN as a coalition formation game. Pareto order and utilitarian order are applied to form coalitions respectively. Second, to achieve more availability and efficiency power assignment, we expand and solve the power control using particle swarm optimization (PSO). Finally, with our proposed algorithm, each SBS can cooperatively work and eventually converge to a stable SBS partition. As far as the transmit rate of per SBS and the system rate are concerned respectively, simulation results indicate that our proposed CFG-PC has a significant advantage, relative to a classical coalition formation algorithm and the non-cooperative case.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.4C
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• pp.232-240
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• 2011

While the water-filling algorithm is an efficient power allocation method that maximizes the ergodic capacity of adaptive MIMO systems, its excessive residual power causes spectrum loss in real systems employing discrete modulation indices. In this paper we propose new power allocation algorithms that improve the spectral efficiency of MIMO systems by efficiently reallocating the residual power of the water-filling algorithm. We apply the proposed algorithms to the adaptive turbo-coded MIMO system to verify their performance through computer simulation in various environments. Simulation results show that the spectral efficiency of the proposed algorithms is better than that of the water-filling algorithm by about 8.9% at SNR of 20dB in Rayleigh fading environments.

• KDI Journal of Economic Policy
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• v.36 no.4
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• pp.1-32
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• 2014

Auction is widely used in allocation and procurement of resources due to its desirable properties: efficiency and revenue maximization. It is well-known, however, that auction may fail to achieve efficiency when allocative externalities exist. Such a result may happen in the auction of the resources that are very scarce, for example, radio spectrum. This is because allocation of the resources has effects on competition of the firms in the aftermarket, and thus a firm that utilizes the resources less efficiently may make a higher bid to lessen competition. This paper shows first that efficient allocation may not be achieved by auction even when the number of bidders is 2, while it is shown in the literature that auction may result in inefficient allocation when the number of bidders is greater than or equal to 3. There exist 2 firms, who make a bid to win the scarce resources that increase the value or decrease the production cost of their own product. After the auction ends, the firms engage in Bertrand competition on the Hotelling line. Inefficient allocation may happen even under the second-price auction rule, and it happens only when the firms are different in the initial value or the initial cost of their products as well as in the value of the auctioned resources. The firm who has been the leader loses a large portion of the market if it fails to win the auction, and thus makes a high bid even when the other firm can use the resources more efficiently. Allocative efficiency Pareto improves when the smaller firm's bid counts more than the leader's bid. This paper suggests a modified rule that the smaller firm wins the auction when its bid multiplied by some constant is greater than the leader's bid. The multiplier can be calculated from the market shares. It is equal to 1 when the two firms are the same, and is increasing in the leader's market share. Allocation is efficient in a strictly larger set of parameters under the modified rule than under the standard second-price auction rule.