• The Journal of the Korea Contents Association
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• v.12 no.9
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• pp.16-26
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• 2012

A path generation method considering the tendencies of users is required because users has the preferred routes through the properties such as time, distance, and congest. The existing method must input the additional information about user's tendency to generate path considering moving tendencies. However, mobile device have the inconvenient interface. Therefore users are reluctant to input additional information for path generation. In this paper, we propose the path generation method considering the tendencies of users without additional input of users tendencies. To show the superiority of the proposed method, we compared it with shortest distance or time path through performance evaluation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.7B
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• pp.706-718
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• 2002

In bluetooth system, there are two kinds of interference. One is the frequency static interference, for example 802.11 direct sequence, the interferer uses fixed frequency band. Another is frequency dynamic interference, for example other piconets or 802.11 frequency hopping, the interferer uses dynamic frequency channel and cant be estimated. In this paper we introduce a novel solution of hybrid method of Listen-Before-Talk (LBT) and Adaptive Frequency Hopping (AFH) to address the coexistence of bluetooth and Direct Sequence of wireless local area network (WLAN). Before any bluetooth packet transmission, in the turn around time of the current slot, both the sender and receiver sense the channel whether there is any transmission going on or not. If the channel is busy, packet transmission is withdrawn until another chance. This is the LBT in Bluetooth. Because of asymmetry sense ability of WLAN and bluetooth, AFH is introduced to combat the left front-edge packet collisions. In monitor period of AFH, LBT is performed to label the channels with static interference. Then, all the labeled noisy channels are not used in the followed bluetooth frequency hopping. In this way, both the frequency dynamic and frequency static interference are effectively mitigated. We evaluate the solution through packet collision analysis and a detail realistic simulation with IP traffic. It turns out that the hybrid method can combat both the frequency dynamic and frequency static interference. The packet collision analysis shows it almost doubles the maximal system aggregate throughput. The realistic simulation shows it has the least packet loss.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.9B
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• pp.785-791
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• 2006

A CF-Poll frame which contains the channel reservation time can be piggybacked in QoS-Data frame to increase the channel efficiency in HCCA. However, if any QSTA in the network uses the low physical transmission rate, the QoS-Data frame which includes the CF-Poll frame must be transmitted by the minimum transmission rate. Therefore, it can cause the decrease of the channel efficiency and the increase of the frame transmission delay for other traffic streams when any QSTA has the low physical transmission rate. In this paper, we define this phenomenon as the piggyback problem at the low physical transmission rate and evaluate the effect of this problem. In the simulation results, when a CF-Poll piggyback is used, the delay is increased about 25% if any QSTA has the low physical transmission rate, while the delay is decreased about 7.8% if all QSTA has the high physical transmission rate. We also found that the gain of the CF-Poll piggyback mechanism is achieved when all QSTA has higher physical transmission rate than 24 or 36Mbps.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.1B
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• pp.86-97
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• 2009

RTLS is a system for automatically locating and tracking people and objects. The TDOA-based RTLS determines the location of the tag by calculating the time differences of a signal received from the tag. In TDOA-based RTLS, time synchronization is essential to calculate the time difference between readers. This paper presents a precision time synchronization method for TDOA-based RTLS over IEEE 802.15.4. In order to achieve precision time synchronization in IEEE 802.15.4 radio, we analyzed the error factors of delay and jitter. We also deal with the implementation of hardware assisted time stamping and the Kalman filtering method to minimize the error factors. In addition, this paper described the experiments and performance evaluation of the proposed precision time synchronization method in IEEE 802.15.4 radio. The results show that the nodes in a network can maintain their clocks to within 10 nanoseconds offset from the reference clock.

• Journal of Digital Contents Society
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• v.6 no.3
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• pp.137-142
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• 2005

CDMA scheme has received a great deal of attenttion as a multiple-access method for future mobile networks. Its main advantage: are higher radio capacity and the capacity of flexible data tranmission. And CDMA scheme is a key technology in the proposals submitted to the ITU on next generation multimedia system with integrated services, namely real-time voice services and non real-time data services. In this paper, capacity evaluation of multiple-input multiple-output(MIMO) Multi-Carrier(MC)/CDMA system is considered to mitigate multiple access interference, partial-band interference and enhance system channel capacity in wireless channel. Recently, to increase the spectrum efficiency and the link reliability, MIMO-MC/CDMA scheme is devised to exploit multi-path in a scattering wireless channel. In particular, the channel capacity of MIMO-MC/CDMA system is evaluated according to Eb/No. Mc, p and B. From the results, in order to inappropriate spacing and the signals are frequency overlapped by partial band interference, the channel capacity of MIMO-MC/CDMA system becomes substantially smaller.

• The Journal of the Korea Contents Association
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• v.10 no.12
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• pp.101-108
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• 2010

Many works on energy-efficient cluster event detection schemes have been done considering the energy restriction of sensor networks. The existing cluster event detection schemes transmit only the boundary information of detected cluster event nodes to the base station. However, If the range of the cluster event is widened and the distribution density of sensor nodes is high, the existing cluster event detection schemes need high transmission costs due to the increase of sensor nodes located in the event boundary. In this paper, we propose an energy-efficient cluster event detection scheme using the minimum boundary polygons (MBP) that can compress and summarize the information of event boundary nodes. The proposed scheme represents the boundary information of cluster events using the MBP creation technique in the large scale of sensor network environments. In order to show the superiority of the proposed scheme, we compare it with the existing scheme through the performance evaluation. Simulation results show that our scheme maintains about 92% accuracy and decreases about 80% in energy consumption to detect the cluster event over the existing schemes on average.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.46 no.2
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• pp.36-43
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• 2009

In this paper, we propose a Cooperative Routing using ARQ-based Transmission (CRARQ) in Mobile Ad-hoc Wireless Sensor Networks (MAWSN). The goals of the CRARQ are to improve both the efficiency of transmission and the reliability of transmission together. The main features and contributions of the proposed CRARQ for supporting these goals are as follows. First, CRARQ uses a reactive concept to construct a route from a source to a destination. Second, CRARQ chooses the most stable relay at each hop along the route by mobility-based strategy. Third, cooperative transmission using the ARQ technique which can improve reliability is used at each hop to send data packets from source to destination. Finally, we present a theoretical analysis model for the proposed CRARQ. The performance evaluation of our protocol is implemented via simulation using Optimized Network Engineering Tool (OPNET) and analysis. The results of both simulation and analysis show that CRARQ achieves the improved packet delivery ratio (PDR) and outage probability.

• The KIPS Transactions:PartA
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• v.10A no.2
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• pp.123-130
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• 2003

This paper presents a new striped checkpointing scheme for serverless cluster computers, where the local disks are attached to the cluster nodes collectively form a distributed RAID with a single I/O space. Striping enables parallel I/O on the distributed disks and staggering avoids network bottleneck in the distributed RAID. We demonstrate how to reduce the checkpointing overhead and increase the availability by striping and staggering dynamically for communication intensive applications. Linpack HPC Benchamark and MPI programs are applied to these checkpointing schemes for performance evaluation on the 16-nodes cluster system. Benchmark results prove the benefits of the striped checkpointing scheme compare to the existing schemes, and these results are useful to design the efficient checkpointing scheme for fast rollback recovery from any single node failure in a cluster system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.1B
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• pp.95-105
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• 2010

IEEE 802.15.4 is the one of the protocols for radio communication in a personal area network. Since it aims to provide low cost and low power communication for ubiquitous communication, it requires high level of optimization in implementation. Recently, there have been many studies on the performance evaluation of IEEE 802.15.4 MAC protocol. According to the results of the studies, it is tendency that the transceiver is implemented to SoC type. On the implementation, the specific functions of MAC like CSMA-CA and MAC frame handling is designed to hardwired functions. In this paper, we implemented the protocol with hardwired low MAC (HL-MAC) and its state machine for the optimization from the physical layer and MAC layer. it has the characteristics of the small code size and the enhanced power consumption.

• ETRI Journal
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• v.37 no.3
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• pp.450-459
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• 2015

Small cell networks, as an important evolution path for next-generation cellular networks, have drawn much attention. Different from the traditional base stations (BSs) always-on model, we proposed a BSs on-off model, where a new, simple expression for the probabilities of active BSs in a heterogeneous network is derived. This model is more suitable for application in practical networks. Based on this, we develop an analytical framework for the performance evaluation of small cell networks, adopting stochastic geometry theory. We derive the system coverage probability; average energy efficiency (AEE) and average uplink power consumption (AUPC) for different association strategies; maximum biased received power (MaBRP); and minimum association distance (MiAD). It is analytically shown that MaBRP is beneficial for coverage but will have some loss in energy saving. On the contrary, MiAD is not advocated from the point of coverage but is more energy efficient. The simulation results show that the use of range expansion in MaBRP helps to save energy but that this is not so in MiAD. Furthermore, we can achieve an optimal AEE by establishing an appropriate density of small cells.