• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.10A
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• pp.807-815
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• 2003

MultiCode-CDMA (MC-CDMA) system of chip level MPSK incorporating with clipper (MP-CDMA)[l] shows constant envelope signal which can mitigate the performance degradation due to nonlinear transmit amplifier. In this paper, modulation is modified to carry out differential encoded MPSK rather than MPSK. The modified system is called DMP-CDMA. DMP-CDMA using differential detection has advantages on receiver complexity and pilot overhead. However, it is inferior to coherent detection by about 4.0dB due to inherent power inefficiency of noncoherent detection and the error propagation. Multiple symbol differential detection is employed in order to improve DMP-CDMA using differential detection. As the result, the performance of DMP-CDMA system is improved about 3.6dB compared to differential detection.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.1
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• pp.32-42
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• 2015

In this paper, we considered the scenario that one cellular link and muti-D2D links share the same frequency resource which can improve the spectrum efficiency during uplink communication in LTE (Long Term Evolution)-Advanced network. In order to reduce the interference caused to the D2D users, we set DME (Discovery and Management Entity) which can send the area information to eNB(evolved Node B). We proposed a resource allocation scheme by using these assistant devices to reduce the interference that CUE (Cellular User Equipment) causes to DUE Rx (D2D UE Receiver). Basing on the area information, in order to mitigate the interference among the D2D pairs which share the same frequency resource, a power control scheme has been proposed. The simulation results prove that by using the DMEs, the proposed schemes improve the stability of D2D communication and bring the highest performance of the communication system when comparing to the other different schemes.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.10A
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• pp.727-735
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• 2009

To alleviate positioning error using wireless ultra-wideband (UWB) is primary concern, and it has been studied how to reduce the positioning error effectively. Thanks to many repeated transmissions of UWB signals, we can have a variety of selections to point out the most precise positioning result. Towards this, scanning method has been preferred to be used due to its simplicity. This exhaustive method firstly fixes the candidate position, and calculates the sum of distances from observed positions. However, it has tremendous number of computations, and the complexity is more serious if the size of two-dimensional range is the larger. To mitigate the large number of computations, this paper proposes the technique employing genetic algorithm and block windowing. To exploit its superiority, simulations will be conducted to show the reduction of complexity, and the efficiency on positioning capability.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.1A
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• pp.50-57
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• 2009

Tag collection is one of the major functions in RFID systems. In this paper, we propose a multichannel slotted-aloha anticollision protocol to mitigate the tag collision problem and improve tag collection performance in active RFID systems. In the proposed anticollision protocol, while an RFID reader transmits commands to multiple RFID tags via a common channel, it receives multiple tag responses over multiple channels simultaneously. We also implemented an active RFID system supporting the proposed anticollision protocol. In experiments with the implemented reader and 60 tags, the proposed dual-channel slotted-aloha anticollision protocol showed a large improvement in tag collection performance compared with the single-channel slotted-aloha anticollision protocol. With 60 tags, the average time spent on tag collection using the dual-channel anticollision protocol was 600.543 ms, which was 46.3% of the 1289.721 ms required using the single-channel anticollision protocol.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.11A
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• pp.891-897
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• 2009

In the satellite communications, the frequency sharing with other services is important because the service coverage is generally very wide and overlaps with those of other wireless services. This paper introduces a new technique to mitigate interference into the terrestrial stations from the Earth station in the same frequency band by means of band segmentations which are portions of the overall operation frequency band divided by frequency reuse factor. We consider a multi-beam satellite system, where frequency bands are reused in each satellite cell. The terrestrial stations use band segmentations of adjacent satellite cells, and this may decrease the interferences. By this way, the terrestrial and satellite systems can share the same frequency bands efficiently. The simulation is performed at frequency reuse factors, seven and three. The simulation results show that the proposed method can highly reduce the interference level to -168 dBW or -163 dBW depending on the considered frequency reuse factor from -117 dBW at the 90% link availability.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.6A
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• pp.573-587
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• 2007

In this paper, we analyze the adjacent interference between WCDMA and M-WiMAX systems in the 2.6GHz Band under the SISO (Single Input Single Output) configuration. The interference scenarios are characterized into 8 scenarios with different victim and interfering links. Among the 8 scenarios, we find that the most performance loss is observed in the scenarios of victim uplink suffering interference from downlink in both systems. Besides, guard band is applied to mitigate the adjacent interference in all the scenarios. Especially, we reveal that M-WiMAX system is much more sensitive to adjacent interference than WCDMA system due to the lower transmission power. In this paper, we consider the worst interference environment, where interferers always transmit with the maximum power, a loose spectrum mask is adapted, and no additional channel fitters are equipped in both systems.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.6A
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• pp.642-647
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• 2007

HAP(High Altitude Platform) systems have been proposed due to their unique advantages over terrestrial and satellite systems as the alternative wireless communication system to deliver the third generation IMT-2000 wireless services. It has been required to study for the power control in W-CDMA HAP system as well as the terrestrial mobile system in order to mitigate interference and increase the capacity. In this paper, a new power control has been proposed for HAP system considering the interference profile into the DB(distributed balancing) SIR(signal to interference ratio)-based algorithm which has been considered in terrestrial system, and estimated by the outage performance of the proposed DB algorithm is better remarkably than DBPA(distance-based power allocation) which is proposed for HAP system, and it is the same regardless of the antenna maximum gain and its sidelobe characteristics.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39B no.3
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• pp.169-179
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• 2014

For vehicle safety-related services using wireless communications, reliable collection of various driving informations transmitted periodically by neighbor vehicles is the most important. Every host vehicle analyses them to estimate a potential dangerous situation in a very short time and warns drivers to prevent an accident. However tremendous amount of periodic messages can cause the wireless communication in chaos and the services not in safe. In this paper, we propose a time-division broadcasting protocol to mitigate the communication congestion. It utilizes the received information of vehicle velocity and location, i.e. vehicle traffic density on a road to adjust the number of time slots in a given broadcasting period, and transmission power. The simulation results show that message reception ratio is changed to approximately 40% and channel access time also decreased from 10ms to 0.23ms.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.5 s.120
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• pp.465-470
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• 2007

The co-channel interference is a primary factor of loss in multimedia mobile communications. In this paper, we present a performance of the frequency reuse partitioning to refrain the co-channel interference and maximize system performance. First, we analyze the co-channel interference using the frequency reuse partitioning through the statistical modeling. From this results, we decide on the frequency reuse partitioning for the system throughput which is maximized. Finally, analysis and simulation results show that the frequency reuse partitioning based cellular system can mitigate the co-channel interference and maximize the system throughput. The experimental results show that system throughput is maximized from 0.7 to 0.8 according to traffic road. We can maximize the system throughput using the results with cellular system design parameter.

• The Journal of the Korea institute of electronic communication sciences
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• v.9 no.5
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• pp.543-548
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• 2014

Multiple-model based speech recognition framework (MMSR) has been known to be very successful in speech recognition. Since it uses multiple hidden Markov modes (HMMs) that corresponds to various noise types and signal-to-noise ratio (SNR) values, the selected acoustic model can have a close match with the test noisy speech. However, since the number of HMM sets is limited in practical use, the acoustic mismatch still remains as a problem. In this study, we experimentally determined the optimal SNR mapping between the test noisy speech and the HMM set to mitigate the mismatch between them. Improved performance was obtained by employing the SNR mapping instead of using the estimated SNR from the test noisy speech. When we applied the proposed method to the MMSR, the experimental results on the Aurora 2 database show that the relative word error rate reduction of 6.3% and 9.4% was achieved compared to a conventional MMSR and multi-condition training (MTR), respectively.