• Journal of Communications and Networks
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• v.18 no.3
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• pp.429-438
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• 2016

In this paper, we investigate an interference mitigation scheme by antenna selection in device-to-device (D2D) communication underlaying downlink cellular networks. We first present the closed-form expression of the system achievable rate and its asymptotic behaviors at high signal-to-noise ratio (SNR) and the large antenna number scenarios. It is shown that the high SNR approximation increases with more antennas and higher ratio between the transmit SNR at the base station (BS) and the D2D transmitter. In addition, a tight approximation is derived for the rate and we reveal two thresholds for both the distance of the D2D link and the transmit SNR at the BS above which the underlaid D2D communication will degrade the system rate. We then particularize on the small cell setting where all users are closely located. In the small cell scenario, we show that the relationship between the distance of the D2D transmitting link and that of the D2D interfering link to the cellular user determines whether the D2D communication can enhance the system achievable rate. Numerical results are provided to verify these results.

• International Journal of Contents
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• v.14 no.2
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• pp.1-6
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• 2018

In a wireless mobile communication system, a pilot signal has been considered to be a necessary signal for estimating a changing channel between a base station and a terminal. All mobile communication systems developed so far have a specification for transmitting pilot signals. However, although the pilot signal transmission is easy to estimate the channel,(Ed: unclear wording: it is easy to use the pilot signal transmission to estimate the channel?) it should be minimized because it uses radio resources for data transmission. In this paper, we propose a pilotless channel estimation scheme (PCE) by introducing the clustering method of unsupervised learning used in our deep learning into channel estimation.(Ed: highlight- unclear) The PCE estimates the channel using only the data symbols without using the pilot signal at all. Also, to apply PCE to a real system, we evaluated the performance of PCE based on the resource block (RB), which is a resource allocation unit used in LTE. According to the results of this study, the PCE always provides a better mean square error (MSE) performance than the least square estimator using pilots, although it does not use the pilot signal at all. The MSE performance of the PCE is affected by the number of data symbols used and the frequency selectivity of the channel. In this paper, we provide simulation results considering various effects(Ed: unclear, clarify).

• Journal of Information Processing Systems
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• v.15 no.4
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• pp.833-852
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• 2019

In real time applications, due to their effective cost and small size, wireless networks play an important role in receiving particular data and transmitting it to a base station for analysis, a process that can be easily deployed. Due to various internal and external factors, networks can change dynamically, which impacts the localisation of nodes, delays, routing mechanisms, geographical coverage, cross-layer design, the quality of links, fault detection, and quality of service, among others. Conventional methods were programmed, for static networks which made it difficult for networks to respond dynamically. Here, machine learning strategies can be applied for dynamic networks effecting self-learning and developing tools to react quickly and efficiently, with less human intervention and reprogramming. In this paper, we present a wireless networks survey based on different machine learning algorithms and network lifetime parameters, and include the advantages and drawbacks of such a system. Furthermore, we present learning algorithms and techniques for congestion, synchronisation, energy harvesting, and for scheduling mobile sinks. Finally, we present a statistical evaluation of the survey, the motive for choosing specific techniques to deal with wireless network problems, and a brief discussion on the challenges inherent in this area of research.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.9
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• pp.4390-4407
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• 2019

The paucity of pilot signals in Massive MIMO system is a vital issue. To accommodate substantial number of users, pilot signals are reused. This leads to interference, resulting in pilot contamination and degrades channel estimation at the Base Station (BS). Hence, mitigation of pilot contamination is exigency in Massive MIMO system. The proposed Time Shifted Pilot Signal Transmission with Pilot signal Hopping (TSPTPH), addresses the pilot contamination issue by transmitting pilot signals in non-overlapping time interval with hopping of pilot signals in each transmission slot. Hopping is carried by switching user to new a pilot signal in each transmission slot, resulting in random change of interfering users. This contributes to the change in channel coefficient, which leads to improved channel estimation at the BS and therefore enhances the efficiency of Massive MIMO system. In this system, Uplink Signal Power to Interference plus Noise Power Ratio (SINR) and data-rate are calculated for pilot signal reuse factor 1 and 3, by estimating the channel with Least Square estimation. The proposed system also reduces the uplink Signal power for data transmission of each User Equipment for normalized spectral efficiency with rising number of antennas at the BS and thus improves battery life.

• Journal of Information Processing Systems
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• v.17 no.1
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• pp.63-74
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• 2021

According to the double-phase cluster-head election method (DCE), the final cluster heads (CHs) sometimes are located at the edge of cluster. They have a long distance from the base station (BS). Sensor data is directly transmitted to BS by CHs. This makes some nodes consume much energy for transmitting data and die earlier. To address this problem, energy efficient multi-hop cluster-head election strategy (EEMCE) is proposed in this paper. To avoid taking these nodes far from BS as CH, this strategy first introduces the distance from the sensor nodes to the BS into the tentative CH election. Subsequently, in the same cluster, the energy of tentative CH is compared with those of other nodes, and then the node that has more energy than the tentative CH and being nearest the tentative CH are taken as the final CH. Lastly, if the CH is located at the periphery of the network, the multi-hop method will be employed to reduce the energy that is consumed by CHs. The simulation results suggest that the proposed method exhibits higher energy efficiency, longer stability period and better scalability than other protocols.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.2 no.4
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• pp.545-551
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• 1998

The Radio communication by existing SSB, VHF, etc. in a coast station and a base station for military affairs is still used to a very important the device of information delivery or transmitting and receiving by the remote controller to using to the exclusive cable for a equipment established at a long distance. When a number of consumer to connected and operated by a number of transceiver is essential for a circuit controller of ICS, in KOREA, is devoted by import to considerable quantity because of to be delayed development of this field. This Paper has been realized to optimal algorithm and designing of a circuit connection controller by multi-processor to pre-stage for the development of ICS. The H/W is composed able to remote control to circuit connector with the several slave processor and a processor for master, and this has taken possible through without any obstacle to communication circuits of a control signal by FSK system. The S/W make possible monitoring for communication condition of other circuits by means of a serial communication system by the multi-processing. This paper has been studied for connecting to a circuits wished to rapidly and precisely by the full application to a interrupt technique. A technique to control by remote to a number of transceiver is a way increasing to application for a frequency resource of the limited MF/SF, VHF and the existing radio communication technique. According to, this paper will achieve to be the reduction of energy & equipment and multiplicity of information delivery in the general communication and disposal to rapid and exact for the important communication as distress, urgency and safety on the sea.

• The Transactions of the Korea Information Processing Society
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• v.5 no.11
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• pp.2763-2775
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• 1998

In mobile computing environments, to efficiently use the narrow bandwidth of wireless networks a mobile host caches the data that are frequently accessed. But, because the cached data can be inconsistent with the data n a server due to the host mobility and the disconnection from a server, the usefullness of cached data may be losted. The traditional methods emphasize on the cache consistency and assume that broadcasting times are synchronized at all mobile supprot stations. In this paper, we propose a strategy to maintain cache consistency, which resolves the problems that be caused by the migration of mobile host. The proposed strategy has asynchronous broadcasting time and reduces the communication overhead caused by the synchronization. Also, by preventing the unnecessary messages transmitting from the mobile support station to a mobile host, this strategy can reduce the communication cost and use the narrow bandwidth of wireless networks efficiently.

• The Transactions of the Korea Information Processing Society
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• v.5 no.11
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• pp.2943-2953
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• 1998

As communication networks become very fast, the scope of applications is varied and applications using multi-party communications in which more than one communication station participate, have been increased. In this paper, multicast servers are designed and implemented by two different schemes (centralized multicast server scheme and distributed multicast server scheme). Both scheme contain three operation for joining/leaving of a node, operation for transmitting the name of the group and messages to the server, and operation for a node to read messages and clear shared memory. Based on their implementations, two multicast server schemes are compared in terms of complexity, extendibility, efficiency and real-time aspects. As a result, the average transfer time of the distributed multicast server scheme is shorter than that of the centralized multicast server scheme. Finally, we designed the multi-party real-time communication method to guarantee QoS in multicast.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.39 no.9
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• pp.28-34
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• 2002

In this paper, a new type predistorter using a low frequency intermodulation signals terms of harmonic generator is proposed. A vector modulator, in which fundamental signal is modulated with low frequency intermodulation signals derived from harmonic generator, generates predistorted third and fifth IM components. Using predistorted signals, intermodulation distortion signals of power amplifier suppressed. The suggested predistorter has been manufactured to operate in Korean PCS base-station transmitting band (1840~1870MHz). The test results show that the third IMD signal level is reduced more than 20dB and the fifth IMD signal is reduced about 10dB for CW two-tone signals. The predistorter improves the Adjacent Channel Power Ratio (ACPR) more than 10dB for CDMA (IS-95) signals.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.9
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• pp.924-931
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• 2002

In this paper, a new λ/4 bias transmission line that is added dumbbell-shaped defected ground structure(DGS) on ground plane of the conventional λ/4 bias transmission line is proposed. This DGS λ/4 bias transmission line maintains high characteristic impedance, but physical width is wider and length is shorter than that of the conventional bias line. If the proposed bias line is attached on signal transmission line, this bias line can reduces the $3^{rd}$ harmonic signal as well as the$2^{nd}$ harmonic signal. With harmonic reduction characteristics, efficiency and linearity of amplifier are improved. The proposed bias line is adopted in power amplifier on IMT-2000 base-station transmitting band. This paper presents several simulations and experimental results of DGS to show validity of the proposed power amplifier using the new λ/4 bias transmission line. Experimental results represent that the $3^{rd}$ harmonic signal is reduced about 26.5 dB and efficiency is improved about 9.1 % and IMD3 is improved 4.5 dB than the conventional structure.