• KSII Transactions on Internet and Information Systems (TIIS)
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• v.16 no.8
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• pp.2666-2687
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• 2022

As a new alternative communication scheme in 5G, unmanned aerial vehicle (UAV) is used as a relay in the remote base station (BS) for assistant communication. In order to ameliorate the quality of the backhaul link, a UAV backhaul transmission scheme based on improved Nash equilibrium (NE) strategy is proposed. First, the capacity of air-to-ground (A2G) channel by the link preprocess is maximized. Then, the maximum utility function of each UAV is used as the basis of obtaining NE point according to the backhaul channel and the backhaul congestion. Finally, the improved NE strategy is applied in multiple iterations until maximum utility functions of all the UAVs are reached, and the UAVs which are rejected by air-to-air (A2A) link during the process would participate in the source recovery process to construct a multi-hop backhaul network. Simulation results show that average effective backhaul rate, minimum effective backhaul rate increases by 10%, 28.5% respectively in ideal A2G channel, and 11.8%, 42.3% respectively in fading channel, comparing to pure NE strategy. And the average number of iterations is decreased by 5%.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.3A
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• pp.290-296
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• 2007

We propose new routing scheme, Cooperative Diversity-based Routing (CDR) which utilizes the cooperative space diversity for power saving and performance enhancement of wireless ad-hoc networks. The improved performance is compared with Multi-hop Relay Routing (NRR) by analytical methods. When the required outage probability is $1\times10^{-3}$ at the destination node in ad-hoc networks with 7 nodes, we noticed that each node can save power consumption by 15.5 dB in average, by using our proposed CDR compared to MRR.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.7 no.8
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• pp.1638-1643
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• 2003

A shay has designing on the structure of new radio repeater for maritime safety communications system with economical and practical useful, that purpose be capable to exceedingly minimum the accident of small ship in sea, that is system. As Receive the urgency frequency from the SSB transceiver in a small fishery that transmit to convert VHF transceiver frequency. Otherwise, the VHF transmitter frequency is converting to the SSB receiver frequency. It has modeling of the hi­directional relay system, that is proposing the methode m the capability to mutual urgency communication between a SSB transceiver ship and VHF transceiver ship by new maritime safety communications system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.5A
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• pp.511-520
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• 2011

In this paper, we introduce a multiuser (MU) scheduling method for multiuser amplify-and-forward relay systems, which selects both the transmission mode, i.e., either one- or two-hop transmission, and the desired user via two steps. A closed-form expression for the average achievable rate of the proposed scheduling is derived under two transmission modes with MU scheduling, and its asymptotic solution is also analyzed in the limit of large number of mobile stations. Based on the analysis, we perform our two-step scheduling algorithm: the transmission mode selection followed by the user selection that needs partial feedback for instantaneous signal-to-noise ratios (SNRs) to the base station. We also analyze the average SNR condition such that the MU diversity gain is fully exploited. In addition, it is examined how to further reduce a quantity of feedback under certain conditions. The proposed algorithm shows the comparable achievable rate to that of the optimal one using full feedback information, while its required feedback overhead is reduced below half of the optimal one.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.4
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• pp.31-37
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• 2008

Conventional cooperative communications can attain gain of spatial diversity and path loss reduction because destination node independently received same signal from source node and relay node located between source node and destination node. However, these techniques bring about decreased spectral efficiency with relay node and increased complexity of receiver by using maximal ratio combining (MRC). This paper has proposed cooperative ARQ protocol that can improve the above problems and can get the better performance. This method can increase the spectral efficiency than conventional cooperative communication because if the received signal from source node is satisfied by the destination preferentially, the destination transmits ACK message to both relay node and source node and then recovers the received signal. In addition, if ARQ message indicates NACK relay node operates selective retransmission and we can increase reliability of system compared with that of general ARQ protocol in which source node retransmits data. In the proposed protocol, the selective retransmission and ARQ message are to be determined by comparing log-likelihood ratio (LLR) computation of received signal from source node with predetermined threshold values. Therefore, this protocol don't waste redundant bandwidth with CRC code and can reduce complexity of receiver without MRC. We verified spectral efficiency and BER performance for the proposed protocol through Monte-Carlo simulation over Rayleigh fading plus AWGN.

• Journal of Communications and Networks
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• v.10 no.2
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• pp.213-220
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• 2008

This paper analyzes a broadcasting technique for wireless multi-hop sensor networks that uses a form of cooperative diversity called opportunistic large arrays (OLAs). We propose a method for autonomous scheduling of the nodes, which limits the nodes that relay and saves as much as 32% of the transmit energy compared to other broadcast approaches, without requiring global positioning system (GPS), individual node addressing, or inter-node interaction. This energy-saving is a result of cross-layer interaction, in the sense that the medium access control (MAC) and routing functions are partially executed in the physical (PHY) layer. Our proposed method is called OLA with a transmission threshold (OLA-T), where a node compares its received power to a threshold to decide if it should forward. We also investigate OLA with variable threshold (OLA-VT), which optimizes the thresholds as a function of level. OLA-T and OLA-VT are compared with OLA broadcasting without a transmission threshold, each in their minimum energy configuration, using an analytical method under the orthogonal and continuum assumptions. The trade-off between the number of OLA levels (or hops) required to achieve successful network broadcast and transmission energy saved is investigated. The results based on the analytical assumptions are confirmed with Monte Carlo simulations.

• Journal of Communications and Networks
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• v.15 no.5
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• pp.457-463
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• 2013

In recent days, cooperative diversity and communication security become important research issues for wireless communications. In this paper, to achieve low probability of interception (LPI) and high throughput in the cooperative single-carrier frequency division multiple access (SC-FDMA) system, a new physical layer transmission scheme is proposed, where a new encryption algorithm is applied and adaptive modulation is further considered based on channel state information (CSI). By doing so, neither relay node nor eavesdropper can intercept the information signals transmitted from user terminal (UT). Simulation results show above new physical layer transmission scheme brings in high transmission safety and secrecy rate. Furthermore, by applying adaptive modulation and coding (AMC) technique according to CSI, transmission throughput can be increased significantly. Additionally, low peak-to-average power ratio (PAPR) characteristic can still be remained due to the uniform distribution of random coefficients used for encryption algorithm.

• 제어로봇시스템학회:학술대회논문집
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• 1999.10a
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• pp.37-40
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• 1999

ETRI has successfully completed and delivered to KARI the KOMPSAT Mission Control System. This system was designed to work in the conventional TT&C modulation scheme with the pre-assigned frequencies. As a way to accelerate in catching up with future TT&C technology evolutions, a preliminary study needs to be carried out to prepare for the development of a spread spectrum applicable to TT&C. A brief study was carried out to review some points to be considered in designing and implementing spread spectrum schemes to the ground TT&C system intended for a LEO spacecraft. Also a simulation and link design revisit was performed to see the operational and technical benefits with the KOMPSAT TT&C parameters. An experiment concept is proposed to test as many functions at a time once the prototype is developed. In this configuration, a ground-model TT&C transponder is connected via LAN to the ETRI-developed KOMPSAT S/W simulator and linked to the KOMPSAT TM/TC processing s/w via spread spectrum signals through a GEO satellite bent-pipe link. A satellite data relay link simulation could be carried out in this configuration.

• Journal of the Korea Institute of Military Science and Technology
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• v.20 no.3
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• pp.431-440
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• 2017

HF communications are used as a last means of long distance communications without any relay node in NLOS (Non Line-Of-Sight) environment. Conventional analog voice communication in the HF band is vulnerable to security as well as severe background noise. To overcome these shortcoming, digital voice was introduced into HF radios in the early 1980s. In this paper, we analyze avaliable digital voice communication ground wave range of HF radios that applied MELPe CODEC and MIL-STD-188-110B physical layer standard using GRWAVE program. And we evaluate usefulness of digital voice communication in HF band.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.5
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• pp.2009-2028
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• 2018

Considering a dual-hop energy-harvesting (EH) relaying system, this paper advocates novel relaying protocols based on adaptive time power switching-based relaying (AR) architecture for amplify-and-forward (AF) mode. We introduce novel system model relaying network with impacts of co-channel interference (CCI) and derive analytical expressions for the average harvested energy, outage probability, and the optimal throughput of the information transmission link, taking into account the effect of CCI from neighbor cellular users. In particular, we consider such neighbor users procedure CCI both on the relay and destination nodes. Theoretical results show that, in comparison with the conventional solutions, the proposed model can achieve optimal throughput efficiency for sufficiently small threshold SNR with condition of reasonable controlling time switching fractions and power splitting fractions in concerned AR protocol. We also explore impacts of transmission distances in each hop, transmission rate, the other key parameters of AR to throughput performance for different channel models. Simulation results are presented to corroborate the proposed methodology.