• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.3
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• pp.1311-1324
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• 2019

In the traditional cellular network communication, the cellular user and the base station exchange information through the uplink channel and downlink channel. Meanwhile, device-to-device (D2D) users access the cellular network by reusing the channel resources of the cellular users. However, when cellular user channel conditions are poor, not only D2D user cannot reuse its channel resources to access the network, but also cellular user's communication needs cannot be met. To solve this problem, we introduced a novelty D2D communication mechanism in the downlink, which D2D transmitter users as half-duplex (HD) relays to assist the downlink transmission of cellular users with reusing corresponding spectrum. The optimization goal of the system is to make the cellular users in the bad channel state meet the minimum transmission rate requirement and at the same time maximize the throughput of the D2D users. In addition, i for the purpose of improving the efficiency of relay transmission, we use two-antenna architecture of D2D relay to enable receive and transmit signals at the same time. Then we optimized power of base station and D2D relay separately with consideration of backhaul interference caused by two-antenna architectures. The simulation results show that the proposed HD relay strategyis superior to existing HD and full-duplex (FD) models in the aspects of system throughput and power efficiency.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.25 no.12
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• pp.1258-1268
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• 2014

In this paper, we propose and design IBFD system based on DCR. And then, we analyze effect of DC offset by self-interference in the proposed system. Also, we evaluate BER performance of the proposed system according to DC offset. As a result of the simulation, we can confirm that when the self-interference is not completely cancelled by the RF cancellation, linearity of desired signal and self-interference is distorted by DC offset. Also, in the proposed system using m-QAM modulation, DC offsets of multi-level are caused by self-interference with m-QAM modulation. As a result, constellations of desired signal and self-interference are greatly distorted. In contrast, in the proposed system using m-PSK modulation, DC offset of single level is caused by self-interference with m-PSK modulation. In this condition, we confirm that distortion of constellations of desired signal and self-interference is less than when using m-QAM modulation. That is, we can confirm that m-PSK modulation is effective than m-QAM modulation in DCR based IBFD system. Also, we can confirm that it is important to cancel self-interference as much as possible in RF-stage.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.10
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• pp.769-778
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• 2017

In this paper, a self-interference signal cancellation(SIC) circult for In-band Full-Duplex has been developed and tested in RF/analog region. By use of this SIC circuit, a FM two-way radio has been developed working at FRS(Family Radio Service) band. The two-way radio device is transmitting the FM modulated signal and demodulating the wanted FM signal at the same time. A circulator is used to enable a single antenna to transmit and receive simuultaenously. The receiver circuit needs to cancel out the self-interference signal due to the transmit signal. A vector modulator(VM) is used to control the phase and magnitude of the esitmated signal. And in-phase and quadrature correlators are used to figure out the optimal coefficients of the VM to remove the self-interference signal according to the change of channel environment. In this work, SA58646 has been used as the FM transceiver, and the system is tested with a frequency of 465 MHz and a bandwidth of 12.5 kHz FM signal. The output power is 17.2 dBm at the antenna port, and the self intererence signal level is measured -49.2 dBm at the receiver end. Therefore the SIC level is measured by 66.4 dB.

• ETRI Journal
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• v.35 no.5
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• pp.919-922
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• 2013

A MIMO multi-way relay channel with full data exchange in which K users exchange messages with each other via the help of a single relay is considered. For the case in which each link is quasi-static Rayleigh fading and the relay is full-duplex, the fundamental diversity-multiplexing tradeoff (DMT) is investigated, and we show that a compress-and-forward relay protocol can achieve the optimal DMT.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39A no.2
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• pp.100-108
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• 2014

In this paper, we design SSD(simultaneous single band duplex) system using RF(radio frequency) cancellation and digital cancellation. we analyze characteristic of residual self-interference after RF Cancellation signal when error of phase shifter occur in RF cancellation. When phase shifter error of $0^{\circ}$, $0.5^{\circ}$, $1^{\circ}$ and $2^{\circ}$ occur in RF cancellation, residual self-interference signal power after RF cancellation is bigger than desired signal power of distant station. So, it is impossible to receive transmit data of distant station. but we confirm that it is possible to receive transmit data of distant station by digital cancellation with frame structure. Also, in digital cancellation with frame structure, if residual self-interference signal after RF cancellation is too large then LMS algorithm requires more time to estimate self-interference channel. That is, performance degradation occurs because self-interference channel estimation has not completed in estimation frame.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.9
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• pp.810-816
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• 2013

In this paper, we propose a SSD (simultaneous single-band duplex) system using Digital Cancellation. Also, we propose a method for Digital Cancellation when RF Cancellation is effectively performed. The proposed system has estimation frame for effective self-interference channel estimation in time-domain. The proposed system calculates signal power for selection of optimal coefficient after digital cancellation. Then, the proposed system selects coefficient of minimum signal power. Further, the proposed system uses LDPC code to minimize the effects of remaining self-interference signal. The proposed system shows BER performance of at 20dB by cancelling self-interference and iterating LDPC code. That is, the proposed system shows that the SSD communication is possible in static self-interference channel.

• The Magazine of the IEIE
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• v.43 no.4
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• pp.35-45
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• 2016

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.2
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• pp.711-732
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• 2019

Many unmanned aerial vehicle (UAV) applications have been employed for performing data collection in facilitating tasks such as surveillance and monitoring objectives in remote and dangerous environments. In light of the fact that most of the existing UAV relaying applications operate in conventional half-duplex (HD) mode, a full-duplex (FD) based UAV relay aided wireless network is investigated, in which the UAV relay helps forwarding information from the source (S) node to the destination (D). Since the activated UAV relays are always floating and flying in the air, its channel state information (CSI) as well as channel capacity is a time-variant parameter. Considering decode-and-forward (DF) relaying protocol in UAV relays, the cooperative relaying channel capacity is constrained by the relatively weaker one (i.e. in terms of signal-to-noise ratio (SNR) or signal-to-interference-plus-noise ratio (SINR)) between S-to-relay and relay-to-D links. The channel capacity can be optimized by adaptively optimizing the transmit power of S and/or UAV relay. Furthermore, a hybrid HD/FD mode is enabled in the proposed UAV relays for adaptively optimizing the channel utilization subject to the instantaneous CSI and/or remaining self-interference (SI) levels. Numerical results show that the channel capacity of the proposed UAV relay aided wireless networks can be maximized by adaptively responding to the influence of various real-time factors.

• ETRI Journal
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• v.42 no.1
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• pp.138-149
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• 2020

In this paper, we describe a simultaneously transmitted jamming (ST-jamming) for bi-directional in-band full-duplex (IFD) system to improve information security at the physical layer. By exploiting ST-jamming, each legitimate user transmits data samples and jamming samples together in one orthogonal frequency division multiplexing symbol according to given traffic asymmetry. Regardless of the traffic difference in both directions in IFD communication, eavesdropping of confidential information is prevented in both directions simultaneously without the loss of data rate. We first propose an encoding scheme and the corresponding decoding scheme for ST-jamming to be used by the legitimate users. In addition, we study a transceiver structure of the legitimate users including a baseband modem uniquely designed for the use of ST-jamming. The leakage of confidential information at an eavesdropper is then quantified by studying the mutual information between the confidential transmit signals and the received signals of the eavesdropper. Simulation results show that the proposed ST-jamming significantly reduces the leakage of legitimate information at the eavesdropper.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.17 no.10
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• pp.2732-2749
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• 2023

Device-to-Device (D2D) communication has received increasing attention and been studied extensively thanks to its advantages in improving spectral efficiency and energy efficiency of cellular networks. This paper proposes a novel relay selection algorithm for multi-hop full-duplex D2D communications underlaying cellular networks. By selecting the relay of each hop in a reverse manner, the proposed algorithm reduces the heavy signaling overhead that traditional relay selection algorithms introduce. In addition, the social domain information of mobile terminals is taken into consideration and its influence on the performance of D2D communications studied, which is found significant enough not to be overlooked. Moreover, simulations show that the proposed algorithm, in absence of social relationship information, improves data throughput by around 70% and 7% and energy efficiency by 64% and 6%, compared with two benchmark algorithms, when D2D distance is 260 meters. In a more practical implementation considering social relationship information, although the proposed algorithm naturally achieves less throughput, it substantially increases the energy efficiency than the benchmarks.