• 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.

• Journal of the Korea Society of Computer and Information
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• v.20 no.2
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• pp.89-97
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• 2015

In this paper, we propose a handoff method supporting LBS (Location Based Services) Information in mobile clouding environment. In mobile clouding computing, handoff delay and re-authentication is occurred. A mobile node needs re-authentication procedure from cloud server whenever it arrives new AP. But Using of location information of node enables to reduce delay time due to re-authentication. To reduce re-authentication delay time, proposed method stores location information of APs on WiFi based location server to complement. GPS-based technology which can't receive satellite signal in indoor and then node collects location information of AP at handoff time. And also enables to process LBS without increasing handoff delay by splitting the process of handoff from process of requesting location information. For analysis of proposed method, We analyze handoff delay and location information process time and have compared previous handoff method in cloud environment. We confirmed that proposed method shows lower delay time without increasing LBS process time than previous method because node receives location information from location information server when handoff is occurred.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38B no.1
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• pp.87-96
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• 2013

Influence propagation is an important research issue in social networks. Influence propagation means that the status or the disposition of nodes get changed by new idea, information and gossip propagated by other nodes. Influenced nodes also make other nodes influenced across the network. The influence propagation problem based on 'word of mouth' referral is to find most influential nodes set in networks to maximize influence. In this paper, we study the influence measuring and finding most influential nodes set in Delay-Tolerant Networks. It is difficult to measure exact influential power in Delay-Tolerant networks where network topology is not stable due to the nodal mobility. In this paper, we propose a distributed scheme that each node constructs $k$-clique community structure and estimates local influential power in Delay-Tolerant Networks. Simulation results show that the influential nodes information estimated by proposed scheme is in agreement with a global view of influential nodes information.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.16 no.2
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• pp.69-76
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• 2023

A high-quality audio/voice codec using the MDCT/IMDCT process can perfectly restore the current frame through an overlap-add process with the previous frame. In the overlap-add process, an algorithm delay equal to the frame length occurs. In this paper, we propose a MDCT/IMDCT process that reduces algorithm delay by using a variable phase shift in MDCT/IMDCT process. In this paper, a low-delay audio/speech codec was proposed by applying the low delay MDCT/IMDCT algorithm to the ITU-T standard codec G.729.1 codec. The algorithm delay in the MDCT/IMDCT process can be reduced from 20 ms to 1.25 ms. The performance of the decoded output signal of the audio/speech codec to which low-delay MDCT/IMDCT is applied is evaluated through the PESQ test, which is an objective quality test method. Despite of the reduction in transmission delay, it was confirmed that there is no difference in sound quality from the conventional method.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37A no.10
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• pp.895-902
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• 2012

In this paper, we propose a novel equalizer to compensate for the group delay including AM/PM nonlinear distortion characteristics by the nonlinear power amplifier (PA). The group delay characteristic is a nonlinear non-constant time delay that appears differently depending on each frequency component. The phase distortion by AM/PM characteristics arising from the power amplifier is a major factor to increase group delay. By the group delay distortion, the signal in the constellation expands and is rotated. Considering the problem mentioned above, the nonlinear time delay that appears differently depending on each frequency component is classified as a static group delay and AM/PM characteristic of PA, the different phase transitions depending on the size of input signal as a dynamic group delay. Static group delay estimates and compensate for phase distortions in the frequency domain with type-based method and dynamic group delay compensates for phase rotation in the time domain. We confirmed that the group delay compensation techniques were enough to compensate the group delay characteristics including AM/PM characteristics of the power amplifier.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.15 no.2
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• pp.98-111
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• 1990

In this paper a queneing model for the D channel access protocal recommeded by CCITT is developed, and delays of the signalling and packet messages are analyzed using the model, Behaviors of packet and signalling messages in the D-channel access system are also investigated. The analytical results have been verified by simulation.

• Korean Journal of Optics and Photonics
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• v.16 no.6
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• pp.547-552
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• 2005

We have fabricated and characterized optical delay lines for optical coherence tomography, which is composed of cylindrical PZT(piezoelectric transducer) and single mode optical fiber. The polarization mode dispersion from the optical delay lines was compensated by the polarization controllers. By applying the duplex optical delay line, we minimized the thermal drift due to optical delay lines and obtained the scan range of 2 times that of a single optical delay line. The OCT system showed resolution of $18.6\pm0.5{\mu}m$, scanning range of 1.68mm, and scanning speed of 360.4mm/s.

• Journal of Korea Society of Digital Industry and Information Management
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• v.6 no.1
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• pp.83-90
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• 2010

DTNs (Delay Tolerant Networks) refer to the networks that can support data transmission in the extreme networking situations such as continuous delay and no connectivity between ends. DTMNs (Delay Tolerant Networks) are a specific range of DTNs, and its chief considerations in the process of message delivery in the routing protocol are the transmission delay, improvement of reliability, and reduction of network loading. This article proposes a new LCN (Largest Common Neighbor) routing algorism to improve Spray and Wait routing protocol that prevents the generation of unnecessary packets in a network by letting mobile nodes limit the number of copies of their messages to all nodes to L. Since higher L is distributed to nodes with directivity to the destination node and the maximum number of common neighbor nodes among the mobile nodes based on the directivity information of each node and the maximum number of common neighbor nodes, more efficient node transmission can be realized. In order to verify this proposed algorism, DTN simulator was designed by using ONE simulator. According to the result of this simulation, the suggested algorism can reduce average delay and unnecessary message generation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.5A
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• pp.355-362
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• 2009

In real-time communication services, delay constraints are among the most important QoS (Quality of Service) factors. In particular, it is difficult to guarantee the delay requirement over wireless channels, since they exhibit dynamic time-varying behavior and even severe burst-errors during periods of deep fading. Channel throughput may be increased, but at the cost of the additional delays when ARQ (Automatic Repeat Request) schemes are used. For real-time communication services, it is very essential to predict data deliverability. This paper derives the delay distribution and the successful delivery probability within a given delay budget using a priori channel model and a posteriori information from the perspective of queueing theory. The Gilbert-Elliot burst-noise channel is employed as an a Priori channel model, where a two-state Markov-modulated Bernoulli process $(MMBP_2)$ is used. for a posteriori information, the channel parameters, the queue-length and the initial channel state are assumed to be given. The numerical derivation is verified and analyzed via Monte Carlo simulations. This numerical derivation is then applied to a rate control scheme for real-time video transmission, where an optimal encoding rate is determined based on the future channel capacity and the distortion of the reconstructed pictures.

• Journal of the Korean Mathematical Society
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• v.46 no.4
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• pp.713-731
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• 2009

In this paper, a three-dimensional eco-epidemiological model with delay is considered. The stability of the two equilibria, the existence of Hopf bifurcation and the permanence are investigated. It is found that Hopf bifurcation occurs when the delay ${\tau}$ passes though a sequence of critical values. The estimation of the length of delay to preserve stability has also been calculated. Numerical simulation with a hypothetical set of data has been done to support the analytical findings.