• Journal of the Korea Institute of Information and Communication Engineering
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• v.13 no.1
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• pp.53-59
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• 2009

As a special type of Wireless Ad Hoc Networks, Wireless Mesh Networks (WMNs) have become the comer stone of research issues. Due to the limited operational environment of WMNs, an efficient connected dominating set (CDS) construction scheme is an important concern since it has been found extremely useful in broadcasting, routing and virtual backbone construction. In this paper, we propose a distributed Bandwidth-Interference aware CDS construction scheme to improve the network performance via two parameters such as node's number of neighbor and link bandwidth. Our CDS construction scheme selects the node that has more neighbors and enough bandwidth to support more end-devices in order to enhance overall network throughput and reliability. We confirm through simulations and show that our scheme constructs the CDS with the small subset of DS and the link that has better bandwidth.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.12 no.6
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• pp.117-125
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• 2012

Recently, there has been a fast paradigm shift in the automotive market from the traditional machine-oriented technology into the technology for vehicle informatics and electronics. In particular, telematics market is accelerating the development of technologies for vehicle informatics through the close cooperation between the vehicle makers and mobile communication companies. However, there may be the degradation of the quality of service by the interference since the telematics uses the wireless communication infrastructure for the base station-to-vehicle communication and the vehicle-to-vehicle communication. This paper presents an analysis device to easily analyze the interference by the wireless communication in the vehicle wireless network environment. Using the analysis results by the presented device, this paper shows that the link quality can be improved through the simulation and the experiment in real environment both.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.8
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• pp.1532-1541
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• 2015

D2D(Device-to-Device) communication is a promising technology to improve the system capacity and spectral efficiency. By sharing the same radio resources with cellular user equipments, D2D communications can significantly enhance the overall spectral efficiency. However, it may cause interference between D2D link and cellular link. So, careful resource allocation and interference coordination between them are very important and need to be properly handled. This paper proposes a radio resource allocation scheme that decreases interference through the use of area grouping and D2D pair grouping. Simulations results are provided to verify the performance improvement of the proposed scheme in terms of the number of assigned resource blocks and computational complexity.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.6A
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• pp.558-567
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• 2011

In this paper, we propose a partial full duplex relay scheme for 3GPP (3rd Generation Partnership Project) LTE (Long Term Evolution)-Advanced system using a Type 1 relay. The Type 1 relay as inband relay is prohibited to transmit and receive simultaneously because of self-interference. Therefore, the Type 1 relay cannot receive synchronization signals which are transmitted to eNB. To overcoming this problem, we propose the partial full duplex relay scheme which transmits to R-UE (Relay-User Equipment) and receives from eNB (evolved NodeB) simultaneously when eNB and the Type 1 relay transmit subframes which have synchronization signals. Additionally, for solving self-interference, the Type 1 relay transmitter and receiver antennas are sufficiently sufficiently isolated and self-interference cancellation is applied for the self-interference signal from the relay transmitter. Thus, the partial full duplex relay scheme can receive synchronization signals from eNB and solve the problems of conventional solutions and we propose the partial channel estimation scheme for partial full duplex relay scheme using SCI. By extensive computer simulation, we verify that the partial full duplex relay scheme is attractive and suitable for the Type 1 relay system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.6C
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• pp.495-505
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• 2010

In this paper, the effect of Near-Far Problem (NFP) among distributed nodes in OFDMA-based Wireless Mesh Networks (WMNs) is analyzed by investigating statistical characteristics of Time Difference of Arrival (TDoA) and Desired-to-Undesired power Ratio (DUR). In order to overcome the effects of Inter-Symbol Interference (ISI), Inter-Carrier Interference (ICI), and Inter Link Interference (ILI), caused by TDoA in WMNs, we derive effective SINR for each subcarrier, and then, propose the optimal starting point of FFT window which can minimize BER for each subcarrier. In addition, we propose a subcarrier-based Zero Forcing - 2 Dimensional Ordered Successive Interference Cancellation (ZF-2DOSIC) technique for signal detection in WMNs with TDoA. It is verified by simulation that the effective SINR and uncoded BER performances of the proposed signal detection technique for OFDMA-based WMNs are significantly improved, compared with those of conventional technique.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.7
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• pp.24-35
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• 2018

In wireless communications environments, a link adaptation technique that selects the proper rate from among several transmission rates is adopted to cope with variations in channel status. In block coded modulation, the frame time and/or the block length can be adjusted to the channel status. A smaller frame time can cause inter-frame interference (IFI), however, a larger frame time can reduce the data rate. Therefore, frame time is the design factor decided by a tradeoff between performance and the data rate. This paper presents a method to determine the frame time based on the processing gain for the channel model, CM1~CM4, recommended by IEEE 802.15a. Also, a link adaptation technique for block coded modulation is proposed for efficient communications by varying the frame time and the block length. Through simulation, link adaptation can be carried out with a step size of 2~5 nsec in a frame time range of 14~ 50 nsec for channel models CM1~CM4.

• The KIPS Transactions:PartC
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• v.9C no.3
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• pp.439-444
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• 2002

In this paper, we present both the link budget analysis according to system parameters and the cell coverage according to transmitter power and modulation scheme of digital MMDS among the wireless CATV system methods which is bated on the wireless internet service. Also, in this paper, we present C/I and number of subscriber according to splitting cell. In this paper, the cell coverage of which obtain the results according to both transmitter power from 0dBW to -9dBW and modulation scheme of QPSK, 16QAM and 64QAM based on link budget was analysis for system parameter of digital MMDS was able to provide from maximum 134km to minimum 4.3km. Also, in this paper, the number of subscriber of which obtain the results according to polarization wave, frequency of frequency reuse and C/I in 4. 6 and 8 sectors was able to provide from maximum 5,200DSI to minimum 1,300DSI.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.4A
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• pp.371-376
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• 2008

In this paper, we explain the unified inter-cell interference avoidance and cancellation in OFDM mobile cellular systems. Interference avoidance is used for cell-interior or two-cell-edge users, and interference cancellation is applied to three-cell-edge users. The performance of the unified scheme is evaluated by simplified system simulation. Link simulation results are used in the interpretation of system simulation output. We compare three schemes which are "no interference management," "only interference avoidance," "both avoidance and cancellation." Primary performance measures are the data rate of the 5th percentile user and the mean data rate. Simulation results show that interference management schemes greatly improve the cell edge performance, but slightly reduce the mean data rate. Use of both avoidance and cancelaltion is better than that of only avoidance in terms of the cell edge throughput and the mean data rate.

• Journal of Communications and Networks
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• v.14 no.1
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• pp.1-9
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• 2012

We consider a receiving node, located at the origin, and a Poisson point process (PPP) that models the locations of the desired transmitter as well as the interferers. Interference is known to be non-Gaussian in this scenario. The capacity bounds for additive non-Gaussian channels depend not only on the power of interference (i.e., up to second order statistics) but also on its entropy power which is influenced by higher order statistics as well. Therefore, a complete statistical characterization of interference is required to obtain the capacity bounds. While the statistics of sum of signal and interference is known in closed form, the statistics of interference highly depends on the location of the desired transmitter. In this paper, we show that there is a tradeoff between entropy power of interference on the one hand and signal and interference power on the other hand which have conflicting effects on the channel capacity. We obtain closed form results for the cumulants of the interference, when the desired transmitter node is an arbitrary neighbor of the receiver. We show that to find the cumulants, joint statistics of distances in the PPP will be required which we obtain in closed form. Using the cumulants, we approximate the interference entropy power and obtain bounds on the capacity of the channel between an arbitrary transmitter and the receiver. Our results provide insight and shed light on the capacity of links in a Poisson network. In particular, we show that, in a Poisson network, the closest hop is not necessarily the highest capacity link.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.11
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• pp.1639-1644
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• 2016

In this paper, we consider the performance improvement that can be obtained with interference alignment (IA) technique applied to 802.11ac based multi-BSS WiFi service. To this end, we developed a system simulator consisting of a link-level PHY simulator, based on 802.11ac specification, and multi-BSS proportional-fair scheduler. Specifically, assuming perfect channel side information and synchronization of signals from multiple APs, we used a SLNR based interference alignment algorithm proposed in [13] and compared its performance with that of multiuser beamforming based time-sharing system. The performance was evaluated in terms of average throughput per BSS and 5% worst user throughput. The results show that 70 to 100% throughput gain can be obtained in this ideal scenario.