• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.9
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• pp.4502-4517
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• 2019

Tone Injection (TI) scheme significantly reduces the peak-to-average power ratio (PAPR) of Multicarrier Modulation (MCM). However, the computational complexity of the TI scheme rises exponentially with the extra freedom constellation number. Therefore, a novel immune evolutionary mechanism-based TI scheme is proposed in this paper to reduce the computational complexity. By restraining undesirable degeneracy during the processing, this IEM scheme can dramatically increase the population fitness. Monte Carlo results show that proposed IEM-based TI scheme can achieve a significant PAPR and BER improvement with a low complexity.

• ETRI Journal
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• v.44 no.6
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• pp.955-965
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• 2022

A low Earth orbit (LEO) satellite constellation could be used to provide network coverage for the entire globe. This study considers multi-beam frequency reuse in LEO satellite systems. In such a system, the channel is time-varying due to the fast movement of the satellite. This study proposes an efficient power and bandwidth allocation method that employs two linear machine learning algorithms and take channel conditions and traffic demand (TD) as input. With the aid of a simple linear system, the proposed scheme allows for the optimum allocation of resources under dynamic channel and TD conditions. Additionally, efficient projection schemes are added to the proposed method so that the provided capacity is best approximated to TD when TD exceeds the maximum allowable system capacity. The simulation results show that the proposed method outperforms existing methods.

• The KIPS Transactions:PartC
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• v.14C no.7
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• pp.597-602
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• 2007

In conventional cooperative communication data rate is 1/2 than non cooperative protocols. In this paper, we propose a full data rate DF (Decode and Forward) cooperative transmission scheme. Proposed scheme is based on time division multiplexing (TDM) channel access. When DF protocol has full data rate, it can not obtain diversity gain under the pairwise error probability (PEP) view point. If it increases time slot to obtain diversity gain, then data rate is reduced. The proposed algorithm uses orthogonal frequency and constellation rotation to obtain both full data rate and diversity order 2. Moreover, performance is analyzed according to distance and optimized components that affect the system performance by using computer simulation. The simulation results revealed that the cooperation can save the network power up to 7dB over direct transmission and 5dB over multi-hop transmission at BER of $10^{-2}$. Besides, it can improve date rate of system compared with the conventional DF protocol.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.1C
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• pp.98-104
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• 2009

Tone injection scheme has been known as one of PAPR(Peak to Average Power Ratio) reduction methods deployable to multi-carrier system like OFDM(Orthogonal Frequency Division Multiplexing). The basic idea in tone injection scheme is to enforce the constellation size larger so that each of original constellation points is mapped into the preassigned distinct points. Along the accomplishment of tone injection, it needs great amount of computations to search out not only an appropriate frequency but a phase. Although there is no loss of transmission rate is expected because of no need to send the overhead, the tone injection scheme has not been preferable due to its enormous computations. To alleviate the amount of complexity, this paper proposes the GA(Genetic Algorithm) based tone injection scheme such that its complexity is reduced comparing with that of the conventional method. The simulation results show that the proposed GA based tone injection scheme approaches the PAPR performance associated with the conventional exhaustive search method at the expense of low computations.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.18 no.6
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• pp.113-119
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• 2018

This paper relates the AM-NM-MMA algorithm which possible to adaptive equalization performance improvement using the adaptive modulus instead of fixed modulus in the NM-MMA algorithm. The NM-MMA emerged for the tradeoff the MMA and SE-MMA algorithm characteristics, the MMA provides the less residual values in the steady state and have a slow convergence rate, the SE-MMA provides the fast convergence rate and increae the risidual values in the steady state. But the fixed modulus can not give the zero residual values in the perfect equalization state and eqaulization performance were degrade, the adaptive modulus was applied in order to reducing the residual values, and its improved performance were confirmed by simulation. For this, the equalizer output constellation, residual isi, MD, MSE, SER were used for performance index. As a result of computer simulation, the AM-NM-MMA has more good performance in equalizer output signal constellation, residual isi, MD, MSE than the NM-MMA, but not in SER performance.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.7C
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• pp.644-651
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• 2007

In multiple antenna systems, vertical Bell Labs Layered Space-Time (V-BLAST) systems enable very high throughput by nulling and cancelling at each layer detection. In this paper, we propose a V-BLAST system which combines with signal space diversity technique. The benefit of the signal space diversity is that we can obtain an additional gain without extra bandwidth and power expansion by applying inphase/quadrature interleaving and the constellation rotation. Through simulation results, it is shown that the performance of the proposed system is less than 0.5dB away from the ideal upper bound.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.2
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• pp.211-215
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• 2006

In this paper, design and applications of a generalized, versatile and customizable IF signal generator that can model the modernized GPS and Galileo signal is given. It generates IF sampled data that can be directly used by a software receiver. Entire constellation of satellites which is independent of satellite-user geometry is easily determined using a real or simulated ephemeris data. Since the IF center frequency, sampling frequency and quantization bit number are user location dependent parameters, their effects are also considered in IF signal generator. The generalized IF signal generator will be very well suited for the development phase of a software receiver due to its versatility. The full access to the sampling frequency, front-end filter definition and ADC parameters also offers a great opportunity for cost-effective analysis of tracking loops and error mitigation techniques at the receiver level. Interference sources can be easily added to the generator to simulate specific environments. This software IF signal generator can also be used to feed a multi-frequency multi-system software receiver for the prototyping of a combined GPS/Galileo receiver. The test result using the generated signals and a real software receiver shows the effectiveness of the implemented IF signal generator.

• Journal of Positioning, Navigation, and Timing
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• v.12 no.1
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• pp.75-81
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• 2023

In this study, we design an optimized Graphics Processing Unit (GPU)-based GNSS signal processing technique with the goal of designing and implementing a GNSS Software Defined Receiver (SDR) that can operate in real time all-in-view mode under multi-constellation and multi-frequency signal environment. In the proposed structure the correlators of the existing GNSS SDR are processed by the GPU. We designed a memory structure and processing method that can minimize memory access bottlenecks and optimize the GPU memory resource distribution. The designed GNSS SDR can select and operate only the desired GNSS or desired satellite signals by user input. Also, parameters such as the number of quantization bits, sampling rate, and number of signal tracking arms can be selected. The computing capability of the designed GPU-based GNSS SDR was evaluated and it was confirmed that up to 2400 channels can be processed in real time. As a result, the GPU-based GNSS SDR has sufficient performance to operate in real-time all-in-view mode. In future studies, it will be used for more diverse GNSS signal processing and will be applied to multipath effect analysis using more tracking arms.

• Journal of Positioning, Navigation, and Timing
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• v.13 no.3
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• pp.341-353
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• 2024

This paper presents the design results of a Multi-band Global Positioning System (GPS)/Korean Positioning System (KPS) Real-Time Kinematics (RTK) precise positioning simulator and evaluate its functionalities. The designed simulator consists of a trajectory generation module, a Radio Frequency (RF) signal generation module, a RF signal reception module, a coarse positioning module, a precise positioning module, and an error statistics reporting module. Simulations in realistic scenarios confirm that the proposed baseband simulator works appropriately. The developed simulator can adjust the type, number, band, and Pseudo Random Noise (PRN) code type of the satellite constellation in various ways, and the practical positioning performance can be tested. It can also reflect the channel influence at the actual RF stage and the influence during the initial synchronization and tracking process. Considering such advantages, the proposed simulator would be useful in future researches and developments related to KPS.

• Journal of the Korean Institute of Telematics and Electronics C
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• v.35C no.1
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• pp.42-54
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• 1998

For decreasing intersymbol interference (ISI) due to band-limited channels in digitalcommunication, the uses of equalization techniques are necessary. Among the useful adaptive equalization techniques, because of their ease of implementation and nonlinear capabilites, the neural networks have been used as an alternative for effectively dealing with the channel distortion. In this paepr, a complex-valued multilayer percepron is proposed as a nonlinear adaptive equalizer. After the important properties that a suitable complex-valued activation function must possess are discussed, a new complex-valued activation function is developed for the proposed schemes to deal with M-ary QAM signals of any constellation sizes. It has been further proven that by the nonlinear transformation of the proposed function, the correlation coefficient between the real and imaginary parts of input data decreases when they are jointly Gaussian random variables. Lastly, the effectiveness of the proposed scheme is demonstrated by simulations. The proposed scheme provides, compared with the linear equalizer using the least mean squares (LMS) algorith, an interesting improvement concerning Bit Error Rate (BER) when channel distortions are nonlinear.