• The Journal of Korean Institute of Communications and Information Sciences
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• 제39B권5호
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• pp.251-259
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• 2014

In this paper, we propose Low Energy Service Discovery (LESD) protocol for common discovery mode of IEEE 802.15.8 Peer Aware Communications (PAC). In order to minimize power consumption, Basic Repetition Block (BRB) is defined. Device is able to select operating mode and synchronize other devices through it. Proposed MAC procedure is Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) based on overhearing technique. Even if device has not been received response signal since transmitted request signal, it is able to discover other devices of same group through the overhearing technique. IEEE 802.15.8 PAC has required that performances of common discovery mode are presented about discovered devices during the simulation time, discovery latency and average power consumption. By considering the number of devices per group and channel environment, two scenarios are evaluated through system level simulation and the simulation results of proposed scheme are compared with CSMA/CA in same simulation conditions. As a result, proposed scheme is able to get high energy efficiency of devices as well as increase the number of discovered devices during simulation time when the longer the number of devices is distributed over a limited area.

• Journal of the Korean Institute of Intelligent Systems
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• 제21권1호
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• pp.36-41
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• 2011

Configuration space(C-space) including configuration obstacle(C-obstacle) is one of the most important concepts in mobile robot path planning. Using C-space and C-obstacles, the robot with different shapes and moving mechanisms can be considered as a point in the C-space. And, as a result, the collision-free path for the robot can be easily achieved. To make C-space including C-obstacle, many researchers used circular approximation method for the efficient caluculation time. This method can help us to save our time by approximating the shape of a robot as the minimum sized circle which can cover all the area of robot. But, by using the circle larger than the robot, more space are considered as the part of robot and, as a result, some obstacles which are very near each other may be considered as a combined one obstacle. To solve this problem, multi-level configuration space is proposed by this paper. This multi-level method also use the circular approximation method as the initial step. But, after finding the initial path, it will check how many obstacles are combined. And then, for each combined obstacle, more accurate C-space generation will be continued. To check the efficiency of the proposed algorithm, time for c-space generation are compared with the well-known accurate C-space generation method using various types of robot shape.

• Journal of the Korea Society for Simulation
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• 제20권4호
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• pp.81-89
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• 2011

Underwater wireless network can be useful in various fields such as underwater environment observation, catastrophe prevention, ocean resources exploration, ocean organism research, and vessel sinking exploration. We need to develop an efficient design for Medium Access Control (MAC) protocol to improve multiple data communication in underwater environment. Aloha protocol is one of the basic and simple protocols, but it has disadvantage such as collision occurs oftenly in communication. If there is collision occured in RF communication, problem can be solved by re-sending the data, but using low frequency in underwater, the re-transmission has difficulties due to slow bit-rate. So, Time Division Multiple Access (TDMA) based MAC protocol is going to be used to avoid collisions, but if there is no data to send in existing TDMA, time slot should not be used. Therefore, this paper proposes dynamic TDMA protocol mechanism with reducing the time slots by sending short "I Have No Data" (IHND) message, if there is no data to transmit. Also, this paper presents mathematic analysis model in relation to data throughput, channel efficiency and verifies performance superiority by comparing the existing TDMA protocols.

• The Journal of the Korea institute of electronic communication sciences
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• 제8권10호
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• pp.1491-1497
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• 2013

Radio frequency identification (RFID) is an important and essential components of ubiquitous computing, with the development of wireless communication technologies and mobile computing environment. Recently, RFID becomes the mainstream application that helps fast handling and uniquely identifying the physical objects. It utilizes the electromagnetic energy for data transmission from a tag to a reader in the presence of arbitrary interference and noise. In order to employ the portable mobile RFID reader, a tag-collision problem between two or more adjacent tags should be considered. In this paper, we present the operation of RFID system in which numerous tags are present in the interrogation zone of a single reader at the same time. Since there may exist a number of tagged objects in the narrow area, multiple RFID tags may interfere each other, caused to degrade the data reliability and efficiency of the RFID system. In order to suppress interference signals from multiple neighboring tags, we present an application of Gold code for RFID communication system, which uses spread spectrum technique. In this RFID system, data bits are spreaded in each tags with the unique Gold code and the spreaded data bits are despreaded in the reader with the same Gold code. The performance analysis of the considered RFID anti-collision system is illustrated via computer simulation examples.

• Tunnel and Underground Space
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• 제29권6호
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• pp.480-507
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• 2019

This paper aims at optimizing the auxiliary ventilation system in large-opening limestone mines with unducted fans. An extensive CFD and also site study were carried out for optimization at the blind entries. The fan location, operating mode, and layout are the parameters for optimization. Since the jet stream discharged from the auxiliary fan is flowing faster than 15 m/s in most of the cases, the stream collides with floor, sides or roof and even with the jet stream generated from the other fan placed upstream. Then, it is likely to lose a large portion of its inertial force and then its ventilation efficiency drops considerably. Therefore, the optimal fan installation interval is defined in this study as an interval that maximizes the uninterrupted flowing distance of the jet stream, while the cross-sectional installation location can be optimized to minimize the energy loss due to possible collision with the entry sides. Consequently, the optimization of the fan location will improve ventilation efficiency and subsequently the energy cost. A number of different three-dimensional computational domains representing a full-scale underground space were developed for the CFD study. The velocity profiles and the CO concentrations were studied to design and optimize the auxiliary ventilation system without duct and at the same time mine site experiments were carried out for comparison purposes. The ultimate goal is to optimize the auxiliary ventilation system without tubing to provide a reliable, low-cost and efficient solution to maintain the clean and safe work environment in local large-opening underground limestone mines.

• The Journal of Korean Institute of Communications and Information Sciences
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• 제32권2A호
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• pp.143-151
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• 2007

One of the consideration things to design protocol in wireless sensor networks is to maximize lifetime of sensor node as reducing energy consumption. In this paper propose reserve based multichannel CSMA mac protocol for minimizing energy consumption which arise from collision and waiting retransmission at channel access process in mac layer Each sensor node which constitute sensor networks has data channel and control channel. And as sensor node reserve channel for data transmission by using control channel and receipt node allow reservation node to use data channel, sending node can abbreviate try of retransmission after random interval time. Also, When sending node delivers selects option channel in available channels to receipt node, the receipt node decide whether the channel is available to oneself and through the result select transmission channel ultimately. Performance evaluation compare with previous simple multichannel CSMA.

• Journal of Korean Society of Environmental Engineers
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• 제36권3호
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• pp.172-177
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• 2014

Low pressure air flotation (LAF) pilot plant for sludge thickening was installed in Chung Nam N.S. municipal waste water treatment plant to verify its application possibility. Effects of operating conditions such as coagulant dosages and microbubble water ratio on thickening of the mixed sludge were examined. Microbubbles which were generated in the chamber of $1.5kgf/cm^2$ by high speed collision method with foaming agent were used to float sludge. Solid loading of $30kg/m^2/hr$, solid contents in thickened sludge of 60,300 mg/L and SS removal efficiency of 99% were obtained through long period operating LAF in conditions of mixed sludge concentration of 14,400 mg/L, coagulant dosage of 27.6 mg/L, foaming agent addition of 4.0 mg/L and microbubble water injection ratio of 9.7%.

• Journal of the Institute of Electronics Engineers of Korea TC
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• 제43권5호
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• pp.137-146
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• 2006

IP address lookup has become a major bottleneck of packet forwarding and a critical issue for high-speed networking techniques in routers. In this paper, we propose an efficient high-speed IP address lookup scheme using adaptive multiple hashing and prefix grouping. According to our analysis results based on routing data distributions, we grouped prefix lengths and selected the number of hash functions in each group adaptively. As a result, we can reduce collisions caused by hashing. Accordingly, a forwarding table of our scheme has good memory efficiency, and thus is organized with the proper number of memory modules. Also, the proposed scheme has the fast building and searching mechanisms to develop the forwarding table only during a single memory access.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• 제15권11호
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• pp.1108-1115
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• 2004

A new type of a Rotman lens is presented in this paper fur millimeter-wave applications, such as collision avoidance radar. A dielectric slab Rotman lens is proposed to reduce the conductor loss and to create an appropriate farm for favorable implementation at millimeter-wave frequency. The proposed lens consists of a dielectric slab and slot lines whereas the conventional lenses are constructed with parallel conducting plates. The dielectric slab Rotman lens excited in TE$\_$0/ mode shows a high degree of confinement for the fields, low dispersion, and has an appropriate feed structure. A prototype lens has been designed and fabricated with 9 beam ports and 9 array ports together with 9 tapered slot antennas. This lens has been tested in the range from 10 GHz to 15 GHz and the measured beam widths are about 15$^{\circ}$ at 13 GHz. The measurements also show low mutual coupling between beam ports and an efficiency of about 34.6 %. The overall performance is comparable to that of conventional Rotman lenses even though the prototype was tested at lower than desired frequencies in the microwave frequency range due to our limited resources for fabrications and measurements. It is expected that at millimeter-wave frequency the dielectric slab Rotman lens will have lower conductor loss and lower mutual coupling than conventional Rotman lenses.an lenses.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• 제27권3호
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• pp.330-333
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• 2016

In this paper, we propose 77 GHz power amplifier for long range automotive collision avoidance radar using 65 nm CMOS process. The proposed circuit has a 3-stage single power amplifier which includes common source structure and transformer. The measurement results show 18.7 dB maximum voltage gain at 13 GHz 3 dB bandwidth. The measured maximum output power is 10.2 dBm, input $P_{1dB}$ is -12 dBm, output $P_{1dB}$ is 5.7 dBm, and maximum power add efficiency is 7.2 %. The power amplifier consumes 140.4 mW DC power from 1.2 V supply voltage.