• The Journal of the Acoustical Society of Korea
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• v.30 no.2
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• pp.86-91
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• 2011

In the underwater communications, the acoustic channel is in poor communication conditions, such as long propagation delay, narrow bandwidth, and high bit-error rate. For these bad acoustic channels, we propose an efficient automatic repeat request (ARQ) for multi-hop underwater network by using the concepts of concurrent bi-directional transmission, multiple sub-packets, and overhearing data packet instead of the acknowledgement signal. Our results show that the proposed ARQ significantly reduces the transmission latency especially in high BER compared with the existing Stop and Wait ARQ.

• The KIPS Transactions:PartC
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• v.14C no.7
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• pp.571-582
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• 2007

Vehicular ad-hoc networks is temporarily established through inter-vehicle communication without any additional infrastructure aids. It requires a immediate message propagation because it mainly deals with critical traffic information such as traffic accidents. The distance-based broadcast scheme is one of the representative broadcast schemes for vehicular ad-hoc network. In this scheme, a node to disseminate messages is selected based on a distance from a source node. However, a message propagation delay will be increased if the relay nodes are not placed at the border of transmission range of the source node. In particular, when the node density is low, the message propagation delay is getting longer. In this paper, we propose a time-window reservation based relay node selection scheme. A node receiving the alert message from the source node has its time-window and randomly selects its waiting time within the given time-window range. A proportional time period of the given time-window is reserved in order to reduce the message propagation delay. The experimental results show that the proposed scheme has shorter message propagation delay than the distance-based broadcast scheme irrespective of node density in VANET. In particular, when the node density is low, the proposed scheme shows about 26% shorter delay and about 46% better performance in terms of compound metric, which is a function of propagation latency and network traffic.

• The Journal of the Korea institute of electronic communication sciences
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• v.19 no.1
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• pp.1-10
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• 2024

The radio propagation characteristics of the 6, 10, and 17 GHz frequency bands in multiple paths in an indoor lobby environment were analyzed. The line-of-sight (LOS) and non-LOS (NLOS) paths were measured from a distance of 2-16 m (0.5 m intervals) from the transmitting to the receiving antenna positions. For basic transmission losses, three parameters were compared using the floating intercept path loss model corresponding to the path. For a root mean square delay spread, the measurement results were compared for cumulative probabilities of 10, 50, and 90%. Propagation loss and propagation delay occurred in all measured frequencies owing to the existence of pillars and an unusual lobby structure. Thus, a measurement scenario for an indoor lobby environment and the provision of standard measurement data was proposed. The results may facilitate research on the radio propagation characteristics of 5G and millimeter-wave bands in indoor lobby environments with various structures.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.46 no.1
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• pp.63-70
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• 2009

The purpose of this paper is to propose a CSMA/CA protocol to reduce the delay time and increase the throughput of the original CSMA/CA protocol. In underwater environments, the efficiency of the protocol is reduced due to the increase of the propagation delay time, which results in increase of the collision possibility causing lowering of the transmission efficiency Considering this propagation delay, this paper propose to insert the STANDBY frame in a CTS packet in order to avoid the TimeOut status of the CSMA/CA protocol. According to the simulated test results, proposed protocol is increased about 20% throughput than original CSMA/CA protocol. And the more value of propagation per transmission delay 'a' is low, the more throughput of protocol is better.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.8 no.2
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• pp.232-238
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• 2004

In this paper, radio propagation in a subway tunnel is investigated using fan beam antennas, circular polarization antennas and directional antennas at 2.4㎓ and 5.8㎓ band, respectively. The results of narrowband channel measurements show that received power level for NLOS(Non-Line-Of-Sight) path is decreased drastically as compared with LOS(Line-Of-Sight) path. Wideband channel measurements are obtained using a PN sliding correlation method. The parameters of the channel such as mean access delay and RMS delay spread are compared as to different types of directional beam at IEEE 802.11 WLAN(Wireless Local Area Network) band including 2.4㎓ and 5.8㎓ bands, respectively.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.48 no.10
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• pp.1344-1348
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• 1999

This paper proposes concurrent event propagation technique for timing analysis. The technique makes it possible to find several input vectors and sensitizable paths at the same time. The concurrent event propagation technique is based on the event driven simulation and the timing analysis technique with boolean equations. The technique propagates as many events as possible at the same time while preventing propagation of boolean terms which do not sensitize paths. Since events do not propagate through false paths, the longest path which successfully propagates events to one of the primary outputs is one of the longest sensitizable paths. The technique can speed up timing analysis by unifying path sensitization and maximum delay calculation.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2003.11a
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• pp.589-593
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• 2003

Narrowband and wideband characterizations of radio propagation channels in tunnel environments are investigated by using ray tracing techniques. For a rectangular straight tunnel and a rectangular curved tunnel, received power is simulated when the receiver moves away from the transmitter. The fast fading statistics of the narrowband propagation are analyzed in terms of cumulative distribution function, level crossing rate and average fade duration. The tunnel wideband radio propagation channel is characterized in terms of mean excess delay and rms delay spread.

• 전자공학회논문지 IE
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• v.48 no.3
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• pp.1-9
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• 2011

In this paper, we develop an analytical expression for the propagation delay of submicrometer CMOS inverter using the triangle-shaped waveform of output current and two fitting parameters. Our model shows that simulation results are well in accordance with HSPICE results. Maximum simulation errors of total inverter delay and jitter are below 0.6% and 2.8%, respectively. Comparing with previous researches, the new model has better fittering characteristics in the range of low operating voltage. We also have fabricated the inverters with ten chains and estimated inverter delay and jitter characteristics. The results show that the values of delay and jitter in the fabricated samples come close to the values of those in the new model.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.38 no.4
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• pp.266-276
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• 2001

Due to the rapid development of semiconductor technology, the complexity of VLSI circuits has heavily increased. With the increased densities of integrated circuits, several different types of faults can occur Thus, testing such circuits is becoming a sever problem. Delay testing can detect system timing failures caused by delay faults. However, the conventional delay fault coverage in terms of the number of detected faults may not be an effective measure of delay testing because, unlike a stuck-at-faults, the impact of a delay fault is dependent on its delay defect size rather than on its existence. Thus, the effectiveness of delay testing is dependent on the propagation delay of the path to be tested, the delay defect size, and the system clock interval. This paper proposes a new delay defect fault coverage that considers both propagation delay of the path to be tested and additional delay defect size. And the relationship between delay defect fault coverage and defect level is analyzed.

• Proceedings of the IEEK Conference
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• 2002.07c
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• pp.1748-1751
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• 2002

An expression for the average carry propagation delay in a ripple carry adder is obtained which is exact up to terms of the order 0(n$\^$-1/ln n). The case of several adders working in parallel is also considered.