• International Journal of Internet, Broadcasting and Communication
• /
• v.15 no.1
• /
• pp.1-7
• /
• 2023

TCP is considered a major candidate transport protocol even for constrained IoT networks due to its ability to integrate into the existing network infrastructures. Since TCP implementations such as uIP TCP often allow only a single TCP segment per connection to be unacknowledged at any given time due to resource constraints, the congestion control relies only on RTO management. In our previous work, to address the problem that uIP TCP performs poorly particularly when a radio duty cycling mechanism is enabled and the hidden terminal problem is severe, we proposed a RTO scheme for uIP TCP and validated the performance through Cooja simulation. In this study, we investigate the effect of other factors that were not considered in our previous work. More specifically, the effect of traffic intensity, the degree of the hidden terminal problem, and RDC is investigated by varying the offered load and the transmission range, and the RDC channel check rate. Simulation results imply that we need to further investigate how to improve TCP performance when the radio duty cycling mechanism is used.

• Journal of Internet Technology
• /
• v.20 no.1
• /
• pp.301-313
• /
• 2019

In this paper, we propose a new MAC protocol for Cognitive Radio (CR)-based IoT networks, called MSMA/CA. We extend the standard CSMA/CA, adopted in IEEE 802.11 WLANs, to the CR networks with the minimal modification since it works well in the real world. We resolve the classical hidden/exposed terminal problems by a variant of RTS/CTS mechanism and further, the hidden primary terminal problem by the mutual spectrum sensing at the transmitter and the receiver. We also modify the backoff process of CSMA/CA to incorporate the blocking of secondary transmitters, with the aim of protecting ongoing primary transmissions from aggressive secondary users. We analyze the throughput and delay of our proposed scheme using the Markov chain model on the backoff procedure, and verify its accuracy by simulations. Simulation results demonstrate that our protocol is suitable for IoT networks since the performance is insensitive to the number of users or devices.

• Journal of KIISE:Information Networking
• /
• v.37 no.4
• /
• pp.307-311
• /
• 2010

Most wireless ad hoc networks use sender-centric carrier sensing where a data sender determines the transmission timing through channel assessment. However, sender-centric carrier sensing suffers from both exposed and hidden terminal problems even with physical and virtual carrier sensing. In this paper, we propose a new receiver-centric carrier sense (RCS) technique where a data receiver triggers packet transmission based on local channel assessment. Through both numerical analysis and simulation studies, we show that the proposed RCS achieves up to 20.9% higher throughput than previous receiver-centric approaches.

• The Journal of the Institute of Internet, Broadcasting and Communication
• /
• v.11 no.4
• /
• pp.39-45
• /
• 2011

In this paper, we propose an efficient multichannel MAC protocol with idle nodes assistance to avoid the multi-channel hidden terminal problem in cognitive radio ad hoc network and further to improve the performance of the network. The proposed MAC protocol can be applied to the cognitive radio adhoc network where every node is equipped with the single transceiver and one common control channel exists for control message negotiation. In the proposed protocol, the idle nodes available in the neighbour of communication nodes are utilized because the idle nodes have the information about the channels being utilized in their transmission range. Whenever the nodes are negotiating for the channel, idle nodes can help the transmitting and receiving nodes to select the free data channel for data transfer. With the proposed scheme, we can minimize the hidden terminal problem and decrease the collision between the secondary users when selecting the channel for data transfer. As a result, the performance of the network is increased.

• The Journal of the Institute of Internet, Broadcasting and Communication
• /
• v.14 no.2
• /
• pp.93-100
• /
• 2014

IEEE 802.11 Wireless LAN Medium Access Control(MAC) supports two transmission methods, a DCF basic and a RTS/CTS in contention-based access. Even though the RTS/CTS method has been optionally introduced to solve the hidden terminal problem, it is able to produce better performance in some network environments than the basic transmission method. In this paper, the collision probability of wireless channel is mathematically analyzed and applied to measure network throughput using real transmission parameters so that a reference value between throughputs of two methods is obtained. We also confirmed that control signal rates affect overall network throughput and evaluated network throughputs considering collision probability, number of stations, and contention window size of Backoff between two methods respectively.

• Journal of Information Display
• /
• v.10 no.1
• /
• pp.16-18
• /
• 2009

A three-terminal hybrid-aligned nematic liquid crystal (3T-HAN LC) cell capable of fast turn-off switching is proposed in this paper. By employing the relaxation process initiated by an electric-field pulse, a fast turn-off time of less than 1 ms can be obtained through optically hidden relaxation. A low operating voltage and high transmittance were confirmed through simulations and experiments.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.44 no.8
• /
• pp.33-41
• /
• 2007

The IEEE 802.11 DCF channel access function allows single transmission inside two-hop network in order to avoid collisions and eliminate the hidden and exposed terminal problems. Singular transmission capability causes data frames waiting for the entire roundtrip time in the transmitter neighborhood, and results in increased frame latency and lower network throughput. Real-time and pervasive applications are severely affected for the lower medium utilization; especially with high network traffic. This work proposes a new scheme with the help of Frame Aggregation technique in IEEE802.11n and overcomes the single transmission barrier maintaining the basic DCF functionality. Proposed scheme allows parallel transmissions in non-interfering synchronized slots. Parallel transmissions bypass the conventional physical carrier sense and random Backoff time for several cases and reduce the frame latency and increase the medium utilization and network capacity.

• Journal of Power Electronics
• /
• v.16 no.1
• /
• pp.217-226
• /
• 2016

A new method is proposed based on a hidden Markov model (HMM) to estimate and analyze battery states of health. Battery system health states are defined according to the relationship between internal resistance and lifetime of cells. The source data (terminal voltages and currents) can be obtained from vehicular battery models. A characteristic value extraction method is proposed for HMM. A recognition framework and testing datasets are built to test the estimation rates of different states. Test results show that the estimation rates achieved based on this method are above 90% under single conditions. The method achieves the same results under hybrid conditions. We can also use the HMMs that correspond to hybrid conditions to estimate the states under a single condition. Therefore, this method can achieve the purpose of the study in estimating battery life states. Only voltage and current are used in this method, thereby establishing its simplicity compared with other methods. The batteries can also be tested online, and the method can be used for online prediction.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
• /
• 1999.11a
• /
• pp.256-261
• /
• 1999

Many control techniques have been proposed in order to improve the control performance of discrete-time domain control system. In the position control system using a DC servo motor as control system, the response-characteristic of system is controlled by the I-PD controller. In the I-PD longer if gains of I-PD controller are unsuitable. In this paper, therefore, a expanded I-PD control system is constructed by inserting a pre-compensator at out terminal of I-PD controller. It is implemented by neural network with two hidden layers. From the result of computer simulation in the proposed control algorithm, its usefulness is verified.

• Communications of the Korean Institute of Information Scientists and Engineers
• /
• v.5 no.2
• /
• pp.105-107
• /
• 1987

A storage tube, Tektronix 4010, was added to NOVA 840 system at Korea Advanced Institute of Science in 1974 and efforts were made to develop an interactive graphics system. These include a software library, called TCS(Terminal Control System) [4], algorithms for hidden line and surface eliminations [5. 6], and two single user graphics systems based on different concepts involving graphic languages [2, 11]. A storage tube is a low-cost terminal, which is useful in certain applications, but introduces some problems since partial modification of the screen is not possible without erasing it entirely. Thus it has far reaching effects on the design of an interactive graphics system. The components of an interactive graphics system will be explained in section 2 and their relation ships with the choice of storage tube as the output device will be pointed out.