• Journal of Broadcast Engineering
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• v.21 no.4
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• pp.552-561
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• 2016

In OFDM system, frequency-domain sub-carriers of a symbol generally consist of data sub-carriers and scattered pilot sub-carriers and in the receiver, channel is estimated through time-axis interpolating pilot sub-carriers of several OFDM symbols. However, time-axis interpolation fails to keep track of rapid channel variation caused by fast moving receiver. Although symbol by symbol channel estimation without time-axis interpolation enables fast estimation, the performance is severely degraded for a long delay spread channel in a single frequency networks (SFNs) because of insufficient pilot sub-carriers. In this paper, a channel estimation scheme for OFDM receiver in a fast mobile SFN channel is proposed. The proposed scheme is applied to DVB-T receiver to improve the Doppler mobile performance in SFN channel.

• Journal of Communications and Networks
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• v.16 no.5
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• pp.523-533
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• 2014

Orthogonal frequency division multiple access (OFDMA) is a promising technique, which can provide high downlink capacity for the future wireless systems. The total capacity of OFDMA can be maximized by adaptively assigning subchannels to the user with the best gain for that subchannel, with power subsequently distributed by water-filling. In this paper, we propose the use of composite differential evolution (CoDE) algorithm to allocate the subchannels. The CoDE algorithm is population-based where a set of potential solutions evolves to approach a near-optimal solution for the problem under study. CoDE uses three trial vector generation strategies and three control parameter settings. It randomly combines them to generate trial vectors. In CoDE, three trial vectors are generated for each target vector unlike other differential evolution (DE) techniques where only a single trial vector is generated. Then the best one enters the next generation if it is better than its target vector. It is shown that the proposed method obtains higher sum capacities as compared to that obtained by previous works, with comparable computational complexity.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.1
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• pp.102-122
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• 2017

Nanotechnology has provided a set of tools that the engineers can use to design and manufacture integrated nano devices, which are capable of performing sensing, computing, data storing and actuation. One of the main hurdles for nano devices has been the amount of power that it can generate for transmission of data. In this paper, we proposed cooperative nano communication in the Terahertz (THz) Gap frequency band to increase the range of transmission. Outage probability (OP) performances for the proposed cooperative nano communication networks in the THz band (0.1 - 10THz) have been evaluated for the following scenarios; A) A single decode-and-forward (DF) relay over independent identically distributed (i.i.d.) Rayleigh fading channels, B) DF multi-relay network with best relay selection (BRS) over i.i.d. Rayleigh fading channels, and C) DF multi-relay network with multiple hops with BRS over i.i.d. Rayleigh fading channels. The results show that the transmission distance can be improved significantly by employing DF relays. Also, it is shown that by increasing the number of hops in a relay the OP performance is marginally degraded. The analytical results have been verified by Monte-Carlo simulation.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.10
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• pp.5035-5057
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• 2019

Advancements in nanotechnology and novel nano materials in the past decade have provided a set of tools that can be used to design and manufacture integrated nano devices, which are capable of performing sensing, computing, data storing and actuation. In this paper, we have proposed cooperative nano communication using Power Switching Relay (PSR) Wireless Power Transfer (WPT) protocol and Time Switching Relay (TSR) WPT protocol over independent identically distributed (i.i.d.) Rayleigh fading channels in the Terahertz (THz) Gap frequency band to increase the range of transmission. Outage Probability (OP) performances for the proposed cooperative nano communication networks have been evaluated for the following scenarios: A) A single decode-and-forward (DF) relay for PSR protocol and TSR protocol, B) DF multi-relay network with best relay selection (BRS) for PSR protocol and TSR protocol, and C) DF multi-relay network with multiple DF hops with BRS for PSR protocol and TSR protocol. The results have shown that the transmission distance can be improved significantly by employing DF relays with WPT. They have also shown that by increasing the number of hops in a relay the OP performance is only marginally degraded. The analytical results have been verified by Monte-Carlo simulations.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.59 no.11
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• pp.2032-2037
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• 2010

This paper describes a design of dual band amplifier using left handed (LHJ) transmission line, which is a part of composite right/left handed (CRLH) transmission line. It is well known that CRLH transmission lines show dual band frequency response. At first, two single-band amplifiers for frequency f1 and f2 are designed, and their matching networks at both amplifiers are synthesized into the dual band matching network by adopting CRLH structure. As an example for proving the validity of the proposed design, a dual band amplifier operating at 1800MHz and 2300MHz is designed, fabricated and measured. The simulation and measurement show that the proposed amplifier operates well at the desired dual bands with the gain of 13.65dB and 19dB at 1850MHz and 2360MHz, respectively, and a good matching performances. In addition, a quite good agreement between the simulation and measurement is observed.

• Smart Structures and Systems
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• v.18 no.3
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• pp.449-470
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• 2016

Energy harvesting is an emerging technique that extracts energy from surrounding environments to power low-power devices. For example, it can potentially provide sustainable energy for wireless sensing networks (WSNs) or structural control systems in civil engineering applications. This paper presents a comprehensive study on harvesting energy from earthquake-induced structural vibrations, which is typically of low frequency, to power WSNs. A macroscale pendulum-type electromagnetic harvester (MPEH) is proposed, analyzed and experimentally validated. The presented predictive model describes output power dependence with mass, efficiency and the power spectral density of base acceleration, providing a simple tool to estimate harvested energy. A series of shaking table tests in which a single-storey steel frame model equipped with a MPEH has been carried out under earthquake excitations. Three types of energy harvesting circuits, namely, a resistor circuit, a standard energy harvesting circuit (SEHC) and a voltage-mode controlled buck-boost converter were used for comparative study. In ideal cases, i.e., resistor circuit cases, the maximum electric energy of 8.72 J was harvested with the efficiency of 35.3%. In practical cases, the maximum electric energy of 4.67 J was extracted via the buck-boost converter under the same conditions. The predictive model on output power and harvested energy has been validated by the test data.

• ETRI Journal
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• v.43 no.3
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• pp.389-399
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• 2021

In this paper, we propose one-bit feedback-based distributed beamforming (DBF) techniques for simultaneous wireless information and power transfer in interference channels where the information transfer and power transfer networks coexist in the same frequency spectrum band. In a power transfer network, multiple distributed energy transmission nodes transmit their energy signals to a single energy receiving node capable of harvesting wireless radio frequency energy. Here, by considering the Internet-of-Things sensor network, the energy harvesting/information decoding receivers (ERx/IRx) can report their status (which may include the received signal strength, interference, and channel state information) through one-bit feedback channels. To maximize the amount of energy transferred to the ERx and simultaneously minimize the interference to the IRx, we developed a DBF technique based on one-bit feedback from the ERx/IRx without sharing the information among distributed transmit nodes. Finally, the proposed DBF algorithm in the interference channel is verified through the simulations and also implemented in real time by using GNU radio and universal software radio peripheral.

• Journal of The Korean Astronomical Society
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• v.55 no.6
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• pp.207-213
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• 2022

The Seoul Radio Astronomy Observatory (SRAO) operates a 6.1-meter radio telescope on the Gwanak campus of Seoul National University. We present the efforts to reform SRAO to a Very Long Baseline Interferometry (VLBI) station, motivated by recent achievements by millimeter interferometer networks such as Event Horizon Telescope, East Asia VLBI Network, and Korean VLBI Network (KVN). For this goal, we installed a receiver that had been used in the Combined Array for Research in Millimeter-wave Astronomy and a digital backend, including an H-maser clock. The existing hardware and software were also revised, which had been dedicated only to single-dish operations. After several years of preparations and test observations in 1 and 3-millimeter bands, a fringe was successfully detected toward 3C 84 in 86 GHz in June 2022 for a baseline between SRAO and KVN Ulsan station separated by 300 km. Thanks to the dual frequency operation of the receiver, the VLBI observations will soon be extended to the 1 mm band and verify the frequency phase referencing technique between 1 and 3-millimeter bands.

• Journal of Communications and Networks
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• v.5 no.4
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• pp.303-308
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• 2003

We present a statistical model for the path loss of ultrawideband (UWB) channels in indoor environments. In contrast to our previously reported measurements, the data reported here are for a bandwidth of 6GHz rather than 1.25GHz; they encompass commercial buildings in addition to single-family homes (20 of each); and local spatial averaging is included. As before, the center frequency is 5.0GHz. Separate models are given for commercial and residential environments and, within each category, for lineof sight (LOS) and non-line-of-sight (NLS) paths. All four models have the same mathematical structure, differing only in their numerical parameters. The two new models (LOS and NLS) for residences closely match those derived from the previous measurements, thus affirming the stability of our path loss modeling. We find, also, that the path loss statistics for the two categories of buildings are quite similar.

• Journal of Communications and Networks
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• v.8 no.2
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• pp.144-150
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• 2006

A serious problem with traditional 'command & control' spectrum management techniques is that they do not easily accommodate new technologies and new services. This paper describes the necessary principles of flexible-use spectrum rights which may allow a wide variety of spectrum uses in a single general-purpose band. Based on the electrospace description of the radio spectrum, these principles allow general aggregation or division of licensed electrospace regions via secondary markets, providing rules for how regulatory limits change under aggregation or division. These flexible-use principles limit transmitter behaviors that tend to create a more difficult operating environment for receivers, while making receivers responsible for handling any remaining interference. The author shows how flexible-use principles could provide a basis for real-world flexible-use frequency bands.