• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.12A
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• pp.998-1005
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• 2009

In the uplink of OFDMA (Orthogonal Frequency Division Multiple Access) based M-WiMAX(Mobile-Worldwide Interoperability for Microwave Access) system, linear phase shift is caused by signals transmitted from multiuser with different delay time and thus, MAI (Multiple Access Interference) occurs. MAI degrades the performance of ranging code detection and delay time estimation in the uplink. Therefore, in this paper, we propose ranging algorithm, applying SIC (Successive Interference Cancellation) to the conventional ranging algorithm, to minimize MAI and to improve ranging performance. The proposed ranging algorithm is verified through the Monte Carlo simulation, which shows the improved performance of ranging code detection and delay time estimation compared to the conventional algorithms. Through compared with random access of the 3GPP LTE, we can know limit of ranging performance.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.12
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• pp.1252-1263
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• 2009

In this paper, in order to improve a service quality and to broaden the service coverage in the mobile communication system a study on a digital RF repeater employed with an Interference Cancellation System(ICS) is performed. The digital RF repeater employed with an ICS is implemented to remove interference and feedback signals which are disadvantages of a conventional(or general) RF repeater. This thesis presents the design and experiments of the new wireless repeater. The proposed wireless repeater consists of a RF repeater mounted with digital engine. The digital ICS engine consists of a DSP and FPGA. The digital engine and RF circuit are designed into a one-piece. After developing hardware through the digital platform they are also designed and fabricated into a one-piece in order to apply a best performance repeater system. The method of removing interference and feedback signals is an adaptive IF technique employed with a LMS algorithm. The powerful performance and fast convergence speed is obtained by using this method.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.10 no.2
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• pp.7-12
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• 2010

In this paper, we analyze and simulate the performance of a cooperative communication system adopting a maximum likelihood (ML) equalizer. In wireless communication systems, cooperative communication schemes employing several relays can be applied for extending the communication coverage. It is assumed that both relays and user terminals can move. Therefore, coverages of two or more relays can overlap each other. If wanted and interfering signals are transmitted through the same channel and there are one terminal in the overlapped region, its performance is degraded due to interference. Hence, we use a ML equalizer for rejecting the effect of interfering signal and enhancing the communication system performance. The cooperative system performance is evaluated in terms of bit error probability. From the simulation results, it is demonstrated that the ML receiver shows good interference cancellation performance although its complexity is high.

• The Journal of the Korea institute of electronic communication sciences
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• v.13 no.5
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• pp.917-922
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• 2018

In the conventional interchannel interference self-cancellation (ICI-SC) schemes, the length of sampling window is the same as the symbol length of orthogonal frequency division multiplexing (OFDM). Thus, the number of complex operations to compute the interference coefficient of each subchannel is significantly increased. To solve this problem, we present an approximated mathematical model for the coefficients of ICI-SC schemes. Based on the proposed approximation, we analyze mean squared error (MSE) and computational complexity of the ICI-SC schemes with the length of sampling window. As a result, the presented approximation has an error of less than 0.01% on the MSE compared to the original equation. When the number of subchannels is 1024, the number of complex computations for the interference coefficients is reduced by 98% or more. Since the computational complexity can be remarkably reduced without sacrificing the self-cancellation capability, it is considered that the proposed approximation is very useful to develop an algorithm for the ICI-SC scheme.

• Journal of IKEEE
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• v.24 no.4
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• pp.1028-1033
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• 2020

The existing in-band interference reduction method recommends the physical separation distance between wireless devices and interference signals, and the interference can be suppressed through the separation distance. If the in-band interference signals can be reduced in a wireless device, a margin can be given to the physical separation distance. Since there is an effect of extending the receiver dynamic range of receivers, it is highly useful for interference reduction and improvement method. In this paper, the structure of an in-band analog IRM(Interference Reduction Module) is proposed and the design and implementation of the proposed analog IRM are described. To design an analog IRM, the interference reduction performance according to the delay mismatch, phase error and the number of delay lines that affect the performance of the analog IRM was simulated. The proposed analog IRM composed of 16 delay lines was implemented and the implemented IRM has the interference reduction performance of about 10dB for a 5G(NR-FR1-TM-1.1) signal having a 40MHz bandwidth at a center frequency of 3.32GHz. The analog IRM proposed in this paper can be used as an in-band interference canceller.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.9 no.2
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• pp.105-110
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• 2009

The techniques of intelligent interference cancellation are used for achieving the improvement of deterioration, which is arisen to the interoperable terminal(GSM and DVB-H). In this paper, we propose a novel system that improve the DVB-H received performance by using the method of an adaptive interference canceller for GSM900 and DVB-H terminal. The interference for the collocated GSM900 and DVB-H receiver is cancelled by using the adaptive canceller with the low-noise ADC(Analog to Digital Converter) in the RF stage.

• Journal of the Korean Institute of Intelligent Systems
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• v.22 no.5
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• pp.663-668
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• 2012

A TPMS(Tire Pressure Monitoring System) is a wireless communication system designed to monitor the pressure and temperature of pneumatic tires of a vehicle. In order to provide the aid in protecting a driver, this system reports tire pressure information to the driver of the vehicle. Since the wireless communication technique should be employed to transmit the TPMS data from each tire to signal processing unit in the vehicle, it suffers from interference signals from external electrical or electronics equipments. In this paper, we propose the TPMS interference cancellation technique based on GSC(Generalized Sidelobe Canceler), which does not have only the excellent performance like MVDR(Minimum-Variance-Distortionless-Response) but also has the low computational complexity comparing with MVDR. The performance of interference suppression is conformed by computer simulation examples.

• Journal of the Institute of Electronics and Information Engineers
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• v.52 no.11
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• pp.3-11
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• 2015

An advanced receiver which can manage inter-cell interference is required to cope with the explosively increasing mobile data traffic. 3rd Generation Partnership Project (3GPP) has discussed network assisted interference cancellation and suppression (NAICS) to improve signal-to-noise-plus-interference ratio (SINR) and receiver performance by suppression or cancellation of interference signal from inter-cells. In this paper, we propose the advanced receiver based on soft decision to reduce the interference from neighbor cell in LTE-Advanced downlink system. The proposed receiver can suppress and cancel the interference by calculating the unbiased estimation value of interference signal using minimum mean square error (MMSE) or interference rejection combing (IRC) receiver. The interference signal is updated using soft information expressed by log-likelihood ratio (LLR). We perform the system level simulation based on 20MHz bandwidth of 3GPP LTE-Advanced downlink system. Simulation results show that the proposed receiver can improve SINR, throughput, and spectral efficiency of conventional system.

• Journal of the Institute of Electronics and Information Engineers
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• v.52 no.1
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• pp.17-23
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• 2015

In this paper, we propose an efficient joint demodulation and decoding scheme for FTN (Faster than Nyquist) systems. Several previous works have demonstrated that ISI (Inter Symbol Interference) cancellation schemes based on BCJR (Bahl-Cocke-Jelinek-Raviv) algorithm are suitable for FTN systems. Unfortunately, required complexity of the previous ISI cancellation schemes is very high, especially when a multi-level modulation scheme is employed. In this paper, we propose a joint demodulation and decoding scheme for FTN systems with an iteratively decodable channel coding scheme and a multi-level modulation. Compared with the previously proposed schemes, the proposed scheme not only offers reliable performance but also requires relatively low complexity. Also, the proposed scheme can be easily applied to the FTN system with a multi-level modulation with a minor modification.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.11
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• pp.5343-5364
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• 2016

Considering the tradeoff between energy consumption and outage behavior in buffer-aided relay selection, a novel energy-efficient buffer-aided optimal relay selection scheme with power adaptation and Inter-Relay Interference (IRI) cancellation is proposed. In the proposed scheme, energy consumption minimization is the objective with the consideration of relay buffer state, outage probability and relay power control, in order to eliminate IRI. The proposed scheme selects a pair of optimal relays from multiple candidate relays, denoted as optimal receive relay and optimal transmit relay respectively. Source-relay and relay-destination communications can be performed within a time-slot, which performs as Full-Duplex (FD) relaying. Markov chain model is applied to analyze the evolution of relay buffer states. System steady state outage probability and achievable diversity order are derived respectively. In addition, packet transmission delay and power reduction performance are investigated with a specific analysis. Numerical results show that the proposed scheme outperforms other relay selection schemes in terms of outage behavior with power adaptation and IRI cancellation in the same relay number and buffer size scenario. Compared with Buffer State relay selection method, the proposed scheme reduces transmission delay significantly with the same amount of relays. Average transmit power reduction can be implemented to relays with the increasing of relay number and buffer size, which realizes the tradeoff between energy-efficiency, outage behavior and delay performance in green cooperative communications.