• KSII Transactions on Internet and Information Systems (TIIS)
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• 제7권12호
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• pp.3037-3054
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• 2013

Interference between primary user (PU) and secondary user (SU) transceivers should be mitigated in order to implement underlay spectrum sharing in cognitive radio networks (CRN). Considering this scenario, an improved joint subcarrier and bit allocation scheme for cognitive user with primary users' cooperation (PU Coop) in CRN is proposed. In this scheme, the optimization problem is formulated to minimize the average interference power level at the PU receiver via PU Coop, which guarantees a higher primary signal to interference plus noise ratio (SINR) while maintaining the secondary user total rate constraint. The joint optimal scheme is separated into subcarrier allocation and bit assignment in each subcarrier via arith-metric geo-metric (AM-GM) inequality with asymptotical optimization solution. Moreover, the joint subcarrier and bit optimization scheme, which is evaluated by the available SU subcarriers and the allocated bits, is analyzed in the proposed PU Coop model. The performance of cognitive spectral efficiency and the average interference power level are investigated. Numerical analysis indicates that the SU's spectral efficiency increases significantly compared with the PU non-cooperation scenario. Moreover, the interference power level decreases dramatically for the proposed scheme compared with the traditional Hughes-Hartogs bit allocation scheme.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제16권1호
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• pp.350-364
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• 2022

Traditionally, in multi-user multi-carrier systems, the neighboring subband will be gapped by one subcarrier, which is set as guard band to reduce multiple access interference (MAI) between neighboring subbands. The empty subcarrier for guard band will degrade the spectral efficiency of the whole system. In order to enhance the spectral efficiency of multi-user filter bank multiple carrier (FBMC) systems, a new subband allocation method is introduced, in which the neighboring subband is gapped by half subcarrier instead of one subcarrier. Meanwhile, in order to implement the proposed resource allocation scheme, an optimized FBMC prototype filter is designed to decrease the inter-subband interference to the neighboring subband. The detailed simulations about the comparison between the proposed spectrum assignment and traditional FBMC are given, as well as the performance in the different interference scenarios. The simulation results show that the combination of the proposed spectrum assignment scheme and the optimized filter has better performance compared to the traditional scheme. The proposed scheme can be used in the system which serves massive users to get higher spectrum efficiency.

• 한국멀티미디어학회논문지
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• 제16권5호
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• pp.601-609
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• 2013

One of the most serious factors constraining the next generation cellular mobile consumer communication systems will be the severe co-channel interference experienced at the cell edge. Such a capacity-degrading impairment combined with the limited available spectrum resource makes it essential to develop more spectrally efficient solutions to enhance the system performance and enrich the mobile user's application services. This paper proposes a unique hybrid method of frequency hopping (FH) and subcarrier-reuse-partitioning that can maximize the system capacity by efficiently utilizing the available spectrum while at the same time reduce the co-channel interference effect. The main feature of the proposed method is that it applies an optimal combination of different frequency reuse factors (FRF) and FH-subcarrier allocation patterns into the partitioned cell regions. From the simulation results, it is shown that the proposed method can achieve the optimum number of subcarrier subsets according to the frequency-reuse distance and results in better performance than the fixed FRF methods, for a given partitioning arrangement. The results are presented in the context of both blocking probability and BER performances. It will also be shown how the proposed scheme is well suited to FH-OFDMA based cellular systems aiming at low co-channel interference performance and optimized number of subcarriers.

• 한국통신학회논문지
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• 제36권6A호
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• pp.601-608
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• 2011

기존에 연구된 OFDMA(Orthogonal Frequency Division Multiple Access) 기반 다중 홉 전송망의 부반송파 페어링 방법들은 단순히 채널의 신호대잡음비(SNR)만을 고려한 것이므로, 2차 시스템의 사용으로 인해 1차 사용자에게 미치는 간섭량을 고려해야 하는 무선 인지 환경에는 적합하지 않다. 따라서, 본 논문은 OFDMA 기반의 다중 홉 무선 인지 시스템에서 1차 사용자에게 미치는 간섭을 제거하기 위해 전력제어를 수행할 경우, 감소된 수율을 향상시키기 위한 효과적인 부반송파 할당 방법에 관해 연구를 수행하였다. 간섭 채널 이득만을 고려한 IT(Interference channel gain) 방법과 채널 이득과 간섭 채널 이득의 비를 고려한 CI(Channel SNR over interference channel gain) 방법, 2가지의 부반송파 페어링 방법을 제안했으며, 모의실험을 통해 기존 방법과 성능비교를 수행하였다. 무선 인지 시스템에서 간섭 임계치를 만족시키기 위해 전력 제어가 필요한 경우에는 제안한 CI 방법이 성능이 가장 우수했으며, 기존 방법보다 최대 약 10% 이상의 수율 향상을 거두는 것을 확인하였다.

• 센서학회지
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• 제28권3호
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• pp.191-197
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• 2019

In this study, we propose a dimming control method for a visible light communication (VLC) system, in which the subcarrier on-off keying (OOK) modulation of Manchester code is used for data transmission. In the VLC transmitter, non-return-to-zero (NRZ) code data is transformed to Manchester code, which is OOK modulated with a subcarrier. Manchester code is used for flicker-free lighting; the duty factor is changed for dimming control, and the subcarrier is used for preventing the adjacent noise light interference. In the experiments, the dimming control was carried out from about 8%-92% of the continuous wave (CW) LED light. This configuration is simple and effective in constructing a VLC system for indoor wireless sensor networks with flicker-free illumination and dimming control capability without adjacent noise light interference.

• 대한전자공학회논문지TC
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• 제45권2호
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• pp.60-66
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• 2008

본 논문에서는 직교주파수분할다중접속(Orthogonal Frequency Division Multiple Access) 하향링크 시스템에서 부반송파 별 채널 이득(channel gain)이 다름을 이용하여 시스템의 용량을 향상시킬 수 있는 핸드오버 기법을 제안한다. 제안하는 기법에서 핸드오버 중인 사용자는 소스 기지국(source base station)과 타겟 기지국(target base station)에서 할당 받은 부반송파 중 강한 채널이득을 가진 부반송파를 선택해 줌으로써 이득을 얻는다. 부반송파 선택 과정에서 탈락한 부반송파에 대한 정보는 기지국으로 피드백(feedback)되어 사용하지 않도록 하여 시스템 전체의 간섭(interference)량을 줄인다. 제안하는 기법은 핸드오버하고 있는 사용자의 오수신 확률을 22% 줄였으며, 이에 따라 시스템 전체의 전송률이 향상된다.

• International Journal of Contents
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• 제12권1호
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• pp.70-75
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• 2016

In this paper, we considered heterogeneous spectrum sharing system where the number of subcarriers of the primary user (PU) was twice as much as that of the secondary user (SU). In this case, due to non-orthogonality and inter-carrier interference (ICI) from SU to PU, it is difficult to satisfy the interference constraint of PU. In order to mitigate ICI and satisfy the interference constraint, we proposed a new transmission scheme of the SU with power allocation scheme. The proposed scheme will only generate subcarrier-by-subcarrier interference. Therefore, it can easily satisfy the interference constraint of the PR and enhance the capacity of the SU. In addition, we derived the ergodic capacity of the SU. Based on numerical results, we confirmed that the proposed schemes could guarantee SU with a reliable capacity while satisfying the interference constraint of the PU. In addition, the derived capacity well matched the numerical results.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제7권2호
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• pp.288-307
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• 2013

This paper formulates resource allocation for decode-and-forward (DF) relay assisted multi-cell orthogonal frequency division multiple (OFDM) networks as an optimization problem taking into account of inter-cell interference and users fairness. To maximize the transmit rate of system we propose a joint interference coordination, subcarrier and power allocation algorithm. To reduce the complexity, this semi-distributed algorithm divides the primal optimization into three sub-optimization problems, which transforms the mixed binary nonlinear programming problem (BNLP) into standard convex optimization problems. The first layer optimization problem is used to get the optimal subcarrier distribution index. The second is to solve the problem that how to allocate power optimally in a certain subcarrier distribution order. Based on the concept of equivalent channel gain (ECG) we transform the max-min function into standard closed expression. Subsequently, with the aid of dual decomposition, water-filling theorem and iterative power allocation algorithm the optimal solution of the original problem can be got with acceptable complexity. The third sub-problem considers dynamic co-channel interference caused by adjacent cells and redistributes resources to achieve the goal of maximizing system throughput. Finally, simulation results are provided to corroborate the proposed algorithm.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권5호
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• pp.1638-1653
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• 2014

A sequential optimization algorithm (SOA) for resource allocation in a cyclic-prefixed single-carrier cognitive relay system is proposed in this study. Both subcarrier pairing (SP) and power allocation are performed subject to a primary user interference constraint to minimize the mean squared error of frequency-domain equalization at the secondary destination receiver. Under uniform power allocation at the secondary source and optimal power allocation at the secondary relay, the ordered SP is proven to be asymptotically optimal in maximizing the matched filter bound on the signal-to-interference-plus-noise ratio. SOA implements the ordered SP before power allocation optimization by decoupling the ordered SP from the power allocation. Simulation results show that SOA can optimize resource allocation efficiently by significantly reducing complexity.

• 한국정보통신학회:학술대회논문집
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• 한국정보통신학회 2013년도 추계학술대회
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• pp.54-56
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• 2013

직교 주파수 분할 다중 접속 (OFDMA) 방식을 사용하는 중계 시스템에서는 기지국, 중계기, 사용자에게 어떤 주파수를 할당하느냐에 따라 성능이 달라질 수 있다. 본 논문에서는 OFDMA 중계 시스템에서 인접셀 간섭과 네트워크 코딩을 고려하여 주파수를 할당하는 기법을 제안한다. 네트워크 코딩을 사용하는 구간에서는 중계기가 기지국과 사용자에게 네트워크 코딩을 이용하여 동시에 전송할 수 있는 환경을 고려한다. OFDMA 중계 시스템에서 하향 링크와 상향 링크 및 네트워크 코딩으로 동작하는 구간을 나누고, 각 구간별로 기지국, 중계기, 사용자가 이용하는 주파수를 인접셀 간섭을 고려하여 할당해준다. 제안하는 주파수 할당 기법에 대해서 시뮬레이션을 통해 성능 평가를 수행한다.