• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.2 s.332
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• pp.39-48
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• 2005

An HMIPv6 provides micro mobility management using MAP for decreasing handover delay and network load in a mobile IP networks. An HMIPv6 uses distance based algorithm for MAP selection when a mobile host enters a new network domain. However, since every mobile hosts select a farthest router as a MAP, a handover delay and packet loss will be increased. A new MAP selection scheme is herein proposed to solve the problems caused by the distance based MAP selection algorithm by using secondary MAP. We executed the performance evaluation by simulation about handover delay and packet loss of an HMIPv6 and our proposed scheme. The simulation results show that the performance of our proposed scheme is better than that of HMIPv6.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.2 no.1
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• pp.45-51
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• 1998

In the realization of a high speed digital transmission over several tens kbps in mobile communications, it follow delay distortion on a count of transmission path variation by multipath interference waves. Therefore it is inevitably necessary to establish the techniques overcoming the frequency selective fading. In this paper, a feedback running RLS algorithm which is improved the RLS algorithm using exponential weighting factor, is proposed for the control algorithm of DFE and by the computer simulation method, and the performance characteristics of DFE is analyzed for the one-ray and two-ray waves model under the random Gaussian noise. The computer simulation results of proposed RLS algorithm for the $\pi$/4QPSK signal with one symbol time delayed interference signal of S/I = 20［dB］, under the S/N = 10［dB］ with $\lambda$= 0.9 showed excellent following characteristics and equalization characteristics.

• Journal of KIISE:Information Networking
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• v.31 no.6
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• pp.620-632
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• 2004

IP is not suitable for mobile nodes by network-based routing because mobile nodes are dynamically change their network attachment point. Mobile-IP is an IETF standard providing continuous access to the Internet for mobile nodes, but it has the triangle routing problem. Also it has a performance degradation problem by massive packet loss during layer 3 handoff of mobile nodes. Especially, two IETF multicast support schemes for Mobile-IP do not guarantee the quality of realtime multimedia services because they have several problems such as long routing path, packet duplication(hi-directional tunneling) and massive packet loss(remote subscription). In this paper, we propose a lossless remote subscription scheme that guarantees the quality of realtime multimedia services over Mobile-IP. From the result of simulation, we verified that the proposed scheme in this paper can reduce the delay time of remote subscription by the effect of the low latency handoff scheme that is extended to apply to the multicast group management and it requires only 0.58% buffer spaces of the previously proposed lossless remote subscription scheme.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.3
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• pp.560-572
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• 1994

This paper describes a design of RAKE receiver for the cellular CDMA mobile communication system on the multipath fading channel. To measure impulse response on the multipath fading environment. partial correlation properties of short PN code that transmitted at a cell site through the pilot channel was used. We used 12 despread paths for compensating about 10 s multipath spread and proposed the compensation algorithm. For processing of digital converted input signal, we proposed full digitalized logics and its validity was verified by computer and timing simulation.

• Journal of IKEEE
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• v.22 no.3
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• pp.854-857
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• 2018

It becomes important to analyze the effects of electromagnetic wave on human body, as various wireless equipments are widely used in daily life. SAR (specific absorption rate) is a parameter of the effects of electromagnetic wave on human body. However, it considers only human tissues, and it is difficult to evaluate the effects of electromagnetic wave when metal artifacts are inserted such as dental implants. This paper introduces a method to simulate SAR, and gets its simulated results. Simulated SAR of human head model with dental implants in 30 GHz 5th generation mobile communications (5G) frequency band is $2.50{\times}10^{-3}W/kg$ in maximum and $8.58{\times}10^{-7}W/kg$ in average. These values are absolutely below 1.6 W/kg Korean domestic SAR limit.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.10
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• pp.2634-2644
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• 1996

Two different low rate speech coders using one of four types of lattice vector quantizers(LVQ's) with fairly low complexity were investigated for an application to mobile communications. More specifically, two-stage vector quantizer-lattic vector quantizer(VQ-LVQ) systems and vector differenctial pulse code modulation(VDPCM)systems with lattice vector quantizers simulated to encode the line spectrum frequencies of various sentences at the rate 22 to 39 bits per 20 msec frame. The simulation results showed that the VDPCM system with the lattice VQ can save up to 10 bits/fram compared to the quantization scheme used in QCELP system. For the VQ-LVQ system, the spherical quasi-uniform LVQ below 36 bits/frame outperformed the other 3 types of LVQ's and the pyramidal quasi-uniform LVQ at 37 bits/frame outperformed the other 3 types of LVQ's with the spectral distortion 0.97.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.5A
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• pp.284-293
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• 2003

Location service is usually provided by the GPS method using satellites. In the next generation mobile communication systems which use smart antennas, location service can be accomplished using direction of arrival (DOA) estimation techniques. In this paper, we propose a DOA estimation technique for the location service of the next generation mobile communication systems and investigate the validity of the proposed technique through computer simulation. First, DOA estimation problems of distributed sources are considered using vortical and horizontal array processors which are orthogonal to each other. The DOA of the elevation angle is estimated by the vertical array processor and then that of the azimuth angle is estimated by the horizontal array processor. Finally, the procedures of the location service for specific signal sources using three smart antennas are exhibited by computer simulation to show that the proposed DOA estimation technique can be used for the location service in the next generation mobile communication systems.

• Journal of Institute of Control, Robotics and Systems
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• v.22 no.2
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• pp.104-109
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• 2016

In this paper, a localization method for multiple robots based on Bayesian inference is proposed when multiple robots adopting multi-RAT (Radio Access Technology) communications exist in cognitive radio networks. Multiple robots are separately defined by primary and secondary users as in conventional mobile communications system. In addition, the heterogeneous spectrum environment is considered in this paper. To improve the performance of localization for multiple robots, a realistic multiple primary user distribution is explained by using the probabilistic graphical model, and then we introduce the Gibbs sampler strategy based on Bayesian inference. In addition, the secondary user selection minimizing the value of GDOP (Geometric Dilution of Precision) is also proposed in order to overcome the limitations of localization accuracy with Gibbs sampling. Via the simulation results, we can show that the proposed localization method based on GDOP enhances the accuracy of localization for multiple robots. Furthermore, it can also be verified from the simulation results that localization performance is significantly improved with increasing number of observation samples when the GDOP is considered.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.16 no.11
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• pp.2411-2417
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• 2012

Globally, the emergence of smart phones vitalized the ecosystem of mobile data service industry. Consequentially, mobile data traffic has been explosively growing and the speed of growth will be more steep. New spectrum will be required in order to properly accommodate the explosively growing mobile data traffic. However, it will be difficult to acquire a sufficient guard band between different frequency bands because the range of frequency which is suitable for wireless communications is limited. Thus, the performance degradation caused by inter-band interference will be one of challenging problems in the next generation mobile communication systems. In this paper, we analyze the performance degradation caused by inter-band interference by computer simulations in various environments. Our results show that the impact of the inter-band interference is more critical when own signal is poor or its own interference from neighboring cells is low.

• Journal of Korea Multimedia Society
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• v.7 no.5
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• pp.737-743
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• 2004

In this paper, we propose the call control scheme that can improve the capacity of the wireless system for the non-uniform traffic load distribution and the multiple types of services in multiple cells CDMA system. The number of mobile stations that can be served simultaneously in a base station is limited by the amount of total interference received in CDMA system. Further, the average number of mobile stations in each cell may not be uniformly distributed. Considering this factors, the call admission control scheme using the effective bandwidth concept is adapted in this paper. Thus, the bandwidth for a new call can be varied dynamically for reducing the blocking rate of new calls and the dropping rate of handoff calls. The suggested call control scheme is experimented through a simulation by dynamically assigning the bandwidth to new and handoff calls. The simulation results show that the proposed call control scheme can accommodate more mobile stations than the other methods in multiple cells environment.