• The Journal of the Acoustical Society of Korea
• /
• v.37 no.6
• /
• pp.483-488
• /
• 2018

Far field input utterance is one of the major causes of performance degradation of speaker verification systems. In this study, we used teacher student learning framework to compensate for the performance degradation caused by far field utterances. Teacher student learning refers to training the student deep neural network in possible performance degradation condition using the teacher deep neural network trained without such condition. In this study, we use the teacher network trained with near distance utterances to train the student network with far distance utterances. However, through experiments, it was found that performance of near distance utterances were deteriorated. To avoid such phenomenon, we proposed techniques that use trained teacher network as initialization of student network and training the student network using both near and far field utterances. Experiments were conducted using deep neural networks that input raw waveforms of 4-channel utterances recorded in both near and far distance. Results show the equal error rate of near and far-field utterances respectively, 2.55 % / 2.8 % without teacher student learning, 9.75 % / 1.8 % for conventional teacher student learning, and 2.5 % / 2.7 % with proposed techniques.

• Journal of the Institute of Convergence Signal Processing
• /
• v.2 no.3
• /
• pp.45-49
• /
• 2001

Wideband code division multiple access (WCDMA) is the most widely adopted third generation air interface. The physical layer of the air interface is the main discussion topic during standardization processes. This paper aims to investigate the performance of uplink WCDMA over many conceivable transmission scenarios in realistic operating conditions. The focus of the study is placed on the performance under frequency selective fading channel conditions with multiple access interference (MAI) in mixed services environments. For the investigation, a simulator has been developed and it encompasses a variety of WCDMA air interface features. The results show that the performance is greatly affected by MAI and is further aggravated with the presence of frequency selective fading, thereby necessitating a suitable compensation measure.

• Journal of the Institute of Electronics and Information Engineers
• /
• v.49 no.9
• /
• pp.43-48
• /
• 2012

This paper presents an iterative single-frequency continuous-wave signal-based I/Q regeneration method for improving image-rejection performance of multi-port junction-based direct receivers (MPDRs). This paper analyzes I/Q regeneration in MPDRs as I/Q mismatch compensation for direct conversion receivers. Based on the analysis, this paper evaluates the accuracy of I/Q regeneration in terms of the image-rejection ratio (IRR). The proposed method improves the IRR performance more than 20 dB compared to existing I/Q regeneration methods. Simulation results show that MPDRs using the proposed method can achieve an IRR of more than 70 dB, and that the bit error rate performances are almost the same as those of conventional coherent demodulators, even in fading channels.

• Journal of Advanced Navigation Technology
• /
• v.19 no.6
• /
• pp.595-600
• /
• 2015

The implementation possibility of the flexible optical network configuration using the non-midway optical phase conjugator (OPC) in the dispersion-managed (DM) optical link for wavelength division multiplexed (WDM) transmission is demonstrated in this paper. It is confirmed that the implementation possibility of flexible link configuration is more increased, as number of fiber spans is more bigger and the residual dispersion per span (RDPS) is more large. It is also confirmed that the non-midway OPC link, in which RDPS of the latter half transmission section (after OPC) is decided by the averaged RDPS of the former half transmission section (before OPC), has more advantage for the flexible network configuration.

• Journal of Satellite, Information and Communications
• /
• v.1 no.2
• /
• pp.89-94
• /
• 2006

ODFM(Orthogonal Frequency Division Multiplexing) technique is suitable for high speed data transfer both in wired/wireless channels, and is actively studied recently. Among them, WiBro based on IEEE 802.16 uses ODFM as its core technology, and is currently trying to expand market through commercialization. Therefore, if it's used for high speed moving object(KTX, airplane..etc) in near future, there is a possibility of ICI(inter-carrier interference) to occur due to DFS(Doppler Frequency Shift), a critical weak point of ODFM System. This study suggests 3 compensation techniques for Doppler effects in ODFM system operating through satellite, and confirms improved performance through constellation and BER curve.

• Proceedings of the Korea Contents Association Conference
• /
• 2006.05a
• /
• pp.132-135
• /
• 2006

Recently, multimedia data service using mobile terminal has been increased according to the development of wireless network technology which can be used in an indoor or outdoor environment. However, the wireless network shares the channel and it has a high error rate because of characteristics of transmission media. Therefore, it has a lot of problems for guaranteeing QoS(Quality of Services) in various requirements. This paper suggests a CSD-WRR(Channel State Dependent-WRR) method for compensating the service rate considering the transmission deadline. Simulation results show that the suggested method outperforms the conventional WRR in the view of the deadline miss rate and fairness.

• Journal of Satellite, Information and Communications
• /
• v.8 no.3
• /
• pp.25-31
• /
• 2013

In this paper, a new interleaving method for spatially-multiplexed multi-input-multi-output (SM-MIMO) scheme in an integrated mobile satellite and terrestrial system is proposed. In the proposed scheme, the transmitted bits for satellite path are interleaved in an innovative way to make sure that bits multiplied with different channel gains will be located alternatively in one received codeword after demapping, in order to compensate the performance degradation due to high-correlation of the satellite path. In addition, the interleaver can be implemented in a computationally efficient way and with the minimum time delay.

• Journal of the Institute of Electronics Engineers of Korea SC
• /
• v.46 no.1
• /
• pp.63-67
• /
• 2009

Current mismatch in a charge pump causes degradation in spectral purity of the phase locked loops(PLLs), such as reference spurs. The current mismatch can be reduced by increasing the output resistance of the charge pump, as in a cascoded output stage. However as the supply voltage is lowered, it is hard to stack transistors. In this paper, a new method for reducing the current mismatch is proposed. The proposed method is based on a feed-forward compensation for the channel length modulation effect of the output stage. The new method has been demonstrated through simulations on typical $0.18{\mu}m$ CMOS circuits.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.7 no.3
• /
• pp.201-210
• /
• 1996

In this paper, we analyzed performance of a symbol timing recovery scheme for 16QAM Radio system. As a symbol timing recovery scheme, both maximum amplitude method(MAM) and wave difference method(WDM) are analyzed employing a pulse shaping filter, such as raised cosine filter(RCF) and nonlinear filter(NLF). Simulation result shows that the jitter performance of MAM or WDM using NLF is better than that using square root RCF. In order to estimate and compensate for the Rayleigh fading PSAM(Pilot Symbol Assisted Modulation) and space diversity are also employed. Consequently, BER performance of about $10^{-4}$ is obtained for $E_b/N_o$= 20 dB.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.4 no.2
• /
• pp.407-416
• /
• 2000

Adaptive digital filtering and noise cancelling technique using a tree structured filter bank are presented to reduce a undesirable aliasing due to the decimation of filtered output and improve the performance in terms of mean-square error and the convergence speed using a aliasing canceller. A signal is split into two subband by analysis filter bank and decimated by decimator and reconstructed by interpolation technique and synthesis filter bank. A variable step-size LMS algorithm is used to improve the convergence speed in case of existing the measurement noise in desired input of filter. It is shown by computer simulation that the proposed subband structure in this paper is superior to conventional subband filter structure in terms of mean-square error and convergence speed.