• KSII Transactions on Internet and Information Systems (TIIS)
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• 제17권1호
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• pp.185-201
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• 2023

Grant-free random access (GFRA) can reduce the access delay and signaling cost, and satisfy the short transmission packet and strict delay constraints requirement in internet of things (IoT). IoT is a major trend in the future, which is characterized by the variety of applications and devices. However, most existing studies on GFRA only consider a single type of device and omit the effect of access delay. In this paper, we study GFRA in multicell massive multipleinput multiple-output (MIMO) systems where different types of devices with various configurations and requirements co-exist. By introducing the backoff mechanism, each device is randomly activated according to the backoff parameter, and active devices randomly select an orthogonal pilot sequence from a predefined pilot pool. An analytical approximation of the average spectral efficiency for each type of device is derived. Based on it, we obtain the optimal backoff parameter for each type of devices under their delay constraints. It is found that the optimal backoff parameters are closely related to the device number and delay constraint. In general, devices that have larger quantity should have more backoff time before they are allowed to access. However, as the delay constraint become stricter, the required backoff time reduces gradually, and the device with larger quantity may have less backoff time than that with smaller quantity when its delay constraint is extremely strict. When the pilot length is short, the effect of delay constraints mentioned above works more obviously.

• 한국정보통신학회:학술대회논문집
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• 한국정보통신학회 2016년도 춘계학술대회
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• pp.693-695
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• 2016

무작위와 체계적인 것에 의한 지터를 제어하는 지연고정 루프가 소개 되었다. AC는 연속적인 지연단의 지연 시간을 평균화 하고 모든 지연 단의 지연시간을 동일하게 한다. 지연위상고정을 기반으로한 0.18um CMOS공정으로 제작된 클럭 발생기의 측정결과는 13.4ps rms 지터 크기를 보였다.

• Structural Engineering and Mechanics
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• 제31권5호
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• pp.621-624
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• 2009

The time delay in active and semi-active controls is an important research subject. Many researches on the time-delay control for deterministic systems have been made (Hu and Wang 2002, Yang et al. 1990, Abdel-Mooty and Roorda 1991, Pu 1998, Cai and Huang 2002), while the study on that for stochastic systems is very limited. The effects of the time delay on the control of nonlinear systems under Gaussian white noise excitations have been studied by Bilello et al. (2002). The controlled linear systems with deterministic and random time delay subjected to Gaussian white noise excitations have been treated by Grigoriu (1997). Recently, a stochastic averaging method for quasi-integrable Hamiltonian systems with time delay has been proposed (Liu and Zhu 2007). In the present paper, a stochastic optimal time-delay control method for stochastically excited nonlinear structural systems is proposed based on the stochastic averaging method for quasi Hamiltonian systems with time delay and the stochastic dynamical programming principle. An example of stochastically excited and controlled hysteretic column is given to illustrate the proposed control method.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2000년도 제15차 학술회의논문집
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• pp.433-433
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• 2000

In this paper, we propose a development of internet teleoperation method applying QoS model, which has the real time control capability and the time-delay predicting capability, The QoS model gives a constant bandwidth to a specified application and makes the dynamically irregular time-delay to be predictable and fined so that it can have real-time capability.

• Journal of Applied and Pure Mathematics
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• 제4권3_4호
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• pp.107-122
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• 2022

This manuscript aims to investigate the existence, uniqueness, and stability of non-local random impulsive neutral stochastic differential time delay equations (NRINSDEs) with Poisson jumps. First, we prove the existence of mild solutions to this equation using the Banach fixed point theorem. Next, we demonstrate the stability via continuous dependence initial value. Our study extends the work of Wang, and Wu [16] where the time delay is addressed by the prescribed phase space 𝓑 (defined in Section 3). To illustrate the theory, we also provide an example of our methods. Using our results, one could investigate the controllability of random impulsive neutral stochastic differential equations with finite/infinite states. Moreover, one could extend this study to analyze the controllability of fractional-order of NRINSDEs with Poisson jumps as well.

• 한국군사과학기술학회지
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• 제14권4호
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• pp.684-693
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• 2011

Measurement time delay in the transfer alignment is very important. It has been well known that the time delay degrades the alignment performance and makes some navigation errors on the transfer alignment of slave INS(SINS). Therefore there are many schemes to eliminate that time delay but the compensation technique through the estimation by Kalman filter through modeling the time delay as a random constant is generally used. In the case of change over measurement time delay or the large measurement time delay, estimation performance in the existing compensation technique is degraded because model of time delay is not correct any more. In this paper, we propose the method to keep the time delay almost constant even though in the abnormal communication state and very small through feedback compensation using double buffer. Double buffer consists of two moving window to temporarily store measurements from master INS and slave INS in real time.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 심포지엄 논문집 정보 및 제어부문
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• pp.340-342
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• 2007

When a system is teleoperated in the indoor environment through the wireless LAN, the communication time delay that is due to the inherent characteristic and surrounding environment is random and unbounded. The time delay has a significant effect on the stability and performance of the teleoperating system. In this paper, we present the method that is the image compression, measuring time delay and switching control-mode corresponding to time delay automatically, to improve stability and performance, and the simple experiment is conducted to demonstrate the feasibility

• 한국정보통신학회논문지
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• 제21권7호
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• pp.1261-1266
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• 2017

지연 시간 전압 분산 변환기 (DVVC) 및 평균 회로 (AC)가 있는 지터 억제 지연 고정 루프 (DLL) 기반 클록 발생기를 제안하였다. 제안한 클록 발생기는 지연고정루프에서 무작위로 발생하는 지터와 회로의 구조에 의해 발생하는 지터를 억제하도록 하였다. 지연 시간 전압 분산 변환기는 각 지연단의 지연 차이를 감지하고 출력 전압을 생성한다. 평균회로는 두개의 연속되는 지연 시간 전압 분산 변환기의 출력 전압을 평균화 한다. 지연 시간 전압 분산 변환기 및 평균 회로는 연속적인 지연단의 지연 시간을 평균화하고 모든 지연단의 지연 시간을 동일하게 만든다. 또한 루프필터 출력 전압의 변동을 줄이기 위해 부궤환 기능으로 효과적인 작동을 하는 스위치가 있는 커패시터가 도입되었다. One-poly six-metal $0.18{\mu}m$ CMOS 공정으로 제작 된 DLL 기반 클록 발생기의 측정 결과는 13.4 ps rms 지터특성을 보여준다.

• 한국정보처리학회논문지
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• 제7권2호
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• pp.536-541
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• 2000

터보코드는 인터리버의 크기가 클수록 반복 복호횟수가 많을수록 복호 성능은 우수하지만 시스템이 복잡해져 한 개의 정보비트를 복호할 때 많은 시간지연을 발생시켜 실시간 통신에는 부적합하다는 단점이 있다. 따라서 본 논문에서는 터보코드 부$\cdot$복호기에 사용되는 인터리버의 크기를 감소시켜 한 개의 정보비트를 복호할 때 소요되는 시간지연을 줄이는 새로운 세미 랜덤(Semi-Random) 인터리버 알고리즘을 제안하였다. 세미 랜덤 인터리버 알고리즘은 입력 데이터 길이의 1/2 크기만큼 인터리버를 구성하고, 인터리버 내에 쓸때는 블록 인터리버처럼 행으로 쓰고, 읽을 때는 랜덤하게 읽음과 동시에 다음 데이터가 그 주소 번지에 위치하게 된다. 따라서 기존의 블록, 대각, 랜덤 인터리버와 알고리즘의 복잡도를 비교할 시 그 복잡도를 1/2로 감소시킬 수 있게 된다.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2006년도 International Symposium on GPS/GNSS Vol.2
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• pp.223-228
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• 2006

The main purpose of this paper is to describe the code tracking performance of a non-coherent digital delay lock loop (DLL) or coherent DLL while tracking GNSS signal in the presence of signal masking. The masking effect is usually caused by buildings that obscure the signal in either a periodic or random manner. In some cases, ideal masking is used to remove random or periodic interference. Three types of the masked signal are considered - no masking, periodic masking, and random masking of the signal input to the receiver. The mean time to lose lock (MTLL) of the code tracking loop are evaluated, and some numerical result and simulation results are reported. Finally, the steadystate tracking errors on the performance of the tracking loop in interference environment are also presented.