• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.4
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• pp.1884-1903
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• 2019

Device-to-Device (D2D) communications can provide proximity based services in the future 5G cellular networks. It allows short range communication in a limited area with the advantages of power saving, high data rate and traffic offloading. However, D2D communications may reuse the licensed channels with cellular communications and potentially result in critical interferences to nearby devices. To control the interference and improve network throughput in overlaid D2D cellular networks, a novel channel assignment approach is proposed in this paper. First, we characterize the performance of devices by using Poisson point process model. Then, we convert the throughput maximization problem into an optimal spectrum allocation problem with signal to interference plus noise ratio constraints and solve it, i.e., assigning appropriate fractions of channels to cellular communications and D2D communications. In order to mitigate the interferences between D2D devices, a cluster-based multi-channel assignment algorithm is proposed. The algorithm first cluster D2D communications into clusters to reduce the problem scale. After that, a multi-channel assignment algorithm is proposed to mitigate critical interferences among nearby devices for each D2D cluster individually. The simulation analysis conforms that the proposed algorithm can greatly increase system throughput.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.9
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• pp.2967-2981
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• 2014

Device-to-Device (D2D) communication is a technology component for long-term evolution-advanced (LTE-A). In D2D communication, users in close proximity to each other can communicate directly without going through a base station; such direct communication can improve spectral efficiency. Although D2D communication brings improvement in spectral efficiency, it also causes interference to the cellular network as a result of spectrum sharing. In particularly, D2D communication can generate interference for each D2D pair when the common wireless medium in a co-located limited area is accessed. Even though the interference management for between the D2D pair and cellular networks has been proposed, the interference reducing methods have still not been fully studied for the D2D pairs. In this paper, we investigate the problem of D2D pair coexistence in which interference is considered between D2D pairs. Using a signal to interference model for a target D2D pair, we provide an analysis of the aggregated throughput of a dense D2D network. For a target D2D pair, we assume that the desired signal and interference signals obey multipath fading and shadow fading. Through analysis, we demonstrate the effect of cluster size such as the number of D2D pairs and the size of the considered area on the network performance. The analytical results are compared with computer simulations. Our work can be used for a rough guideline for controlling the system throughput in a dense D2D network environment.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.4
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• pp.453-461
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• 2011

In order to use more efficiently limited frequency resources at the broadcasting band and to eliminate blanket area of the terrestrial broadcasting and to improve broadcasting quality. The importance of repeaters has increasing continuously. However, in case of T-DMB digital on channel repeater in OFDM systems, some of the signal radiated feedback again at the receiver antenna. So it generates feedback signal interference in repeater system. Also phase noise increases ICI(Inter Carrier Interference). It affects seriously the frequency domain equalizer. In this paper, we remove the feedback signal interference by LMS with correlation. Also we propose an effective equalizer algorithm that can remove ICI caused by phase noise and the power amplifier's back-off. In this simulation results, this system is satisfied the performance of BER=$10^{-4}$ at less than SNR=14 dB after compensation of phase noise.

• Journal of Communications and Networks
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• v.13 no.4
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• pp.360-366
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• 2011

In this paper, we investigate the problem of power allocation in a heterogeneous network that is composed of a pair of cognitive users (CUs) and an infrastructure-based primary network. Since CUs have only limited effective spectrum-sensing ability and primary users (PUs) are not active all the time in all locations and licensed bands, we set up a new multi-area model to characterize the heterogeneous network. A novel combined interference-avoidance policy corresponding to different PU-appearance situations is introduced to protect the primary network from unacceptable disturbance and to increase the spectrum secondary-reuse efficiency. We use dual decomposition to transform the original power allocation problem into a two-layer optimization problem. We propose a low-complexity joint power-optimizing method to maximize the transmission rate between CUs, taking into account both the individual power-transmission constraints and the combined interference power constraint of the PUs. Numerical results show that for various values of the system parameters, the proposed joint optimization method with combined PU protection is significantly better than the opportunistic spectrum access mode and other heuristic approaches.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.11A
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• pp.861-869
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• 2011

In this paper, we propose coordinated scheduling and beamforming based on limited feedback to overcome the effects of inter-cell interference in multi-cell environment. The goal of this study is to improve a performance of cell-edge area significantly affected by the inter-cell interference and also to guarantee a performance of the entire system. Existing coordinated scheduling and beamforming based on the perfect channel state information generates an overhead for the channel state information feedback and exchange at the users and base stations, respectively. In this study, first we propose a novel codebook to obtain a null space of an interference channel efficiently which can be used to reduce the inter-cell interference. Using the proposed codebook, we propose coordinated scheduling and beamforming to improve the performance of cell-edge area and the entire system. Through the proportional fair scheduling, the performance of the proposed technique is shown as improvement of channel capacity for users located cell-edge area and entire system.

• Journal of the Institute of Convergence Signal Processing
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• v.2 no.3
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• pp.32-38
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• 2001

Multi-carrier data transmission system performance is mostly limited by Inter- symbol-interference that is caused by a dispersive characteristic of the transmission channel. In order to enhance the system performance to meet the service requirements of local access, the channel impulse response shortening method incorporated with a channel frequency response compensation method is proposed. For a fast and efficient implementation of the equalizer proposed, Kalman and LMS algorithms are successively used. To verify the channel equalization performance, a set of computer simulation is performed on a filter bank based multitone system operating in a typical high-speed local area data transmission environment. The results showed us a comparable signal-to-interference improvement over the conventional multitone equalization scheme.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.2B
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• pp.87-96
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• 2012

In this paper, we consider a 2-hop relay system where both the relay and destination nodes suffer from the arbitrary number of co-channel interferers. More specifically, assuming that the relay and access channels as well as interference channels are all subject to Rayleigh fading, we derive an exact closed-form expression for outage probability of the amplify-and-forward (AF) relay system, and furthermore compute its upper and lower bounds. Based on these bounds, we derive the upper and lower bounds on the average bit error rate (BER) of the AF relay system. We also confirm the accuracy of our derivation by investigating the performance gap between the performance bounds under consideration and simulation results.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.1
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• pp.17-27
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• 2005

In this paper, we introduce a Parallel Interference Canceller (PIC) based sorting method to improve performance in the MC-DS/CDMA environment. A conventional PIC estimates and subtracts out all of the MAI (Multiple Access Interference) for each user in parallel. The parallel process ensures the low delay for the detection of all users. Also this scheme requires more stages for having better performance. Since the performance of PIC is strongly related to the correct MAI estimation, we introduce the IC (Interference Cancellation) scheme to estimate the accurate weaker signal group than the desired signal using conventional PIC. The principle of the proposed receiver sorts in descending order by the strength of signal and subtracts the MAI of the strong interferers from the desired signal for the accurate estimate of the weaker signals. Following this, the proposed scheme cancels out the improved weaker interference from the desired signal, using the output of the pre-step. In this result, the proposed system obtains better BER performance than the conventional PIC because the accuracy of the strong signal is improved. However, a disadvantage exists in that the processing time has slightly longer delay than the PIC owing to the power sorting and the MAI estimation process. The system performance evaluates and compares other non-liner It according to the number of sub-carriers in the limited-bandwidth.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.10
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• pp.4844-4864
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• 2017

Interference-aware routing protocol design for underwater wireless sensor networks (UWSNs) is one of the key strategies in reducing packet loss in the highly hostile underwater environment. The reduced interference causes efficient utilization of the limited battery power of the sensor nodes that, in consequence, prolongs the entire network lifetime. In this paper, we propose an energy-efficient interference-aware routing (EEIAR) protocol for UWSNs. A sender node selects the best relay node in its neighborhood with the lowest depth and the least number of neighbors. Combination of the two routing metrics ensures that data packets are forwarded along the least interference paths to reach the final destination. The proposed work is unique in that it does not require the full dimensional localization information of sensor nodes and the network total depth is segmented to identify source, relay and neighbor nodes. Simulation results reveal better performance of the scheme than the counterparts DBR and EEDBR techniques in terms of energy efficiency, packet delivery ratio and end-to-end delay.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.6 no.7
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• pp.1032-1037
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• 2002

In this paper, derived monocycle pulse that application is possible within permission frequency band (3.1 ~ 10.6GHz) that establish in FCC. Also, PPM modulated TH IR system simulator is designed in AWGN environment. It is analyzed monocycle pulse specific property and system performance using simulator. Also, analyzed BER performances of IR system in multiple access interference environment using proposed parameters. According to result, application of possible pulse duration$(t_n)$ is very limited by 0.04~0.0326 ns in permission frequency range that establish in FCC. In the case of same pulse signal power, we could know that system performance changes by $N_s$ regardless of pulse duration. IR system that need high speed transmission more than 50 Mbps in multiple access interference environment could know that very serious performance decrease by multiple access Interference happens.