• KSII Transactions on Internet and Information Systems (TIIS)
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• v.17 no.1
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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.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2016.05a
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• pp.693-695
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• 2016

A random and systematic jitter suppressed DLL is presented. The AC averages the delay time of successive delay stages and equalizes the delay time of all delay stages. Measurement results of the DLL-based clock generator fabricated in a one-poly six-metal $0.18{\mu}m$ CMOS process shows 13.4-ps rms jitter.

• Structural Engineering and Mechanics
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• v.31 no.5
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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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• 2000.10a
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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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• v.4 no.3_4
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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.

• Journal of the Korea Institute of Military Science and Technology
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• v.14 no.4
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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.

• Proceedings of the KIEE Conference
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• 2007.04a
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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

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.7
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• pp.1261-1266
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• 2017

A random and systematic jitter suppressed delay locked loop (DLL)-based clock generator with a delay-time voltage variance converter (DVVC) and an averaging circuit (AC) is presented. The DVVC senses the delay variance of each delay stage and generates a voltage. The AC averages the output voltages of two consecutive DVVCs to suppress the systematic and random delay variance of each delay stage in the VCDL. The DVVC and AC averages the delay time of successive delay stages and equalizes the delay time of all delay stages. In addition, a capacitor with a switch working effectively as a negative feedback function is introduced to reduce the variation of the loop filter output voltage. Measurement results of the DLL-based clock generator fabricated in a one-poly six-metal $0.18{\mu}m$ CMOS process shows 13.4-ps rms jitter.

• The Transactions of the Korea Information Processing Society
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• v.7 no.2
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• pp.536-541
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• 2000

Turbo code has excellent decoding performance but had limitations for real time communications because of the system complexity and time delay in decoding procedure. To overcome this problem, a new SRI(Semi-Random Interleaver) algorithm which realize the reduction of the interleaver size is proposed for reducing the time delay during the decoding prodedure. SRI compose the interleaver 0.5 size from the input data sequence. In writing the interleaver, data is recorded by row such as block interleaver. But, in reading, data is read by randomly and the text data is located by the just address simultaneously. Therefore, the processing time of with the preexisting method such as block, helical random interleaver.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.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.