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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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Journal of the Institute of Electronics and Information Engineers
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The Institute of Electronics Engineers of Korea
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Volume & Issues
Volume 49, Issue 12 - Dec 2012
Volume 49, Issue 11 - Nov 2012
Volume 49, Issue 10 - Oct 2012
Volume 49, Issue 9 - Sep 2012
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Performance Evaluation of LDPC-LDPC Product Code for next Magnetic Recording Channel
Park, Donghyuk ; Lee, Jaejin ;
Journal of the Institute of Electronics and Information Engineers, volume 49, issue 11, 2012, Pages 3~8
DOI : 10.5573/ieek.2012.49.11.003
Two-dimensional product code has been studied for correcting burst errors on the storage systems. An RS-LDPC product code consists of an RS code in horizontal direction and an LDPC code in vertical direction. First, we detect the position of burst errors by using RS code, then LDPC code corrects the errors by using the burst error positions. In storage system, long burst errors are occurred by various reason. So, we need a strong code for correcting the long burst errors. RS-LDPC product code is good for long burst errors. However, as the storage density grows the length of the burst errors will be longer. Thus, we propose an LDPC-LDPC product code, it is strong for correcting the very long burst errors. Also, the proposed LDPC-LDPC product code performs better than RS-LDPC product code when the random errors are occurred, because a row direction LDPC code performs better than row direction RS code.
Delay Improvement from Network Coding in Networks with High Coefficient of Variation of Transfer Time
Lee, Goo Yeon ; Lee, Yong ;
Journal of the Institute of Electronics and Information Engineers, volume 49, issue 11, 2012, Pages 9~16
DOI : 10.5573/ieek.2012.49.11.009
In this paper, we focus on end-to-end transfer delay improvement by using network coding and propose a scheme where a message is divided into several packets which are network coded generating additional redundancy with the results that the number of transmitted packets increases. In networks with high coefficient of variation of transfer time, increased number of packets could reduce the transfer time of the message to a destination. For the proposed scheme, we investigate the optimum number of divided packets and redundancy considering transfer delay reduction and additional transmission cost caused by using network coding under the restriction of maximum transmission packet size. From the results of the investigation, we see that the proposed scheme is effective in networks having high variability of transfer time and would be very useful and practical especially for the case that expedited deliveries of messages are needed.
Signal Interference of Neighboring Wi-Fi Networks on Data Throughput
Zhang, Jie ; Lee, Goo Yeon ; Kim, Hwa Jong ;
Journal of the Institute of Electronics and Information Engineers, volume 49, issue 11, 2012, Pages 17~23
DOI : 10.5573/ieek.2012.49.11.017
Products of Wi-Fi devices in recent years offer higher throughput and have longer signal coverage which also bring unnecessary signal interference to neighboring wireless networks, and result in decrease of network throughput. Signal interference is an inevitable problem because of the broadcast nature of wireless transmissions. However it could be optimized by reducing signal coverage of wireless devices. On the other hand, smaller signal coverage also means lower transmission power and lower data throughput. Therefore, in this paper, we analyze the relationship among signal strength, coverage, interference and network throughput by simulation on various network topology.
Performance of Energy Efficient Optical Ethernet Systems with a Dynamic Lane Control Scheme
Seo, Insoo ; Yang, Choong-Reol ; Yoon, Chongho ;
Journal of the Institute of Electronics and Information Engineers, volume 49, issue 11, 2012, Pages 24~35
DOI : 10.5573/ieek.2012.49.11.024
In this paper, we propose a dynamic lane control scheme with a traffic predictor module and a rate controller for reconciling with commercial optical PHY modules in energy efficient optical Ethernet systems. The commercial high speed optical Ethernet system capable of 40/100Gbps employs 4 or 10 multiple optical transceivers over WDM or multiple optical links. Each of the transceivers is always turned on even if the link is idle. To save energy, we propose the dynamic lane control scheme. It allows that several links may be entirely turned off in a low traffic load and frames are handled on the remaining active links. To preserve the byte order even if the number of active links may be changed, we propose a rate controller to be sat on the reconciliation sublayer. The main role of the controller is to insert null byte streams into the xGMII of inactive lanes. For the PHY module, the null input streams corresponding to inactive lanes will be disregarded on inactive PMDs. It is very handy to implement the rate controller module with MAC in FPGA without any modification of commercial PHYs. It is very crucial to determine the number of active links based on the fluctuated traffic load, we provide a simple traffic predictor based on both the current transmission buffer size and the past one with different weighting factors for adapting to the traffic load fluctuation. Using the OMNET++ simulation framework, we provide several performance results in terms of the energy consumption.
UWB Propagation Measurements in Body Area Network Scenarios
Lee, Joon-Yong ; Kim, ChangKyeong ; Ha, Dong-Woo ;
Journal of the Institute of Electronics and Information Engineers, volume 49, issue 11, 2012, Pages 36~43
DOI : 10.5573/ieek.2012.49.11.036
Ultra-wideband propagation measurement results for body area network scenarios are presented. We assumed several different scenarios for around-body and on-body propagations, and for each scenario, we conducted both time domain and frequency domain measurements in an anechoic chamber. For the around-body case, we investigated the effects of human body parts blocking line-of-sight, which could be accounted for by diffraction. On-body measurement results indicate a more complicated propagation mechanism exists in on-body propagation than in around-body propagation and antenna characteristics are affected.
Multi-View Image Deblurring for 3D Shape Reconstruction
Choi, Ho Yeol ; Park, In Kyu ;
Journal of the Institute of Electronics and Information Engineers, volume 49, issue 11, 2012, Pages 47~55
DOI : 10.5573/ieek.2012.49.11.047
In this paper, we propose a method to reconstruct accurate 3D shape object by using multi-view images which are disturbed by motion blur. In multi-view deblurring, more precise PSF estimation can be done by using the geometric relationship between multi-view images. The proposed method first estimates initial 2D PSFs from individual input images. Then 3D PSF candidates are projected on the input images one by one to find the best one which are mostly consistent with the initial 2D PSFs. 3D PSF consists with direction and density and it represents the 3D trajectory of object motion. 야to restore 3D shape by using multi-view images computes the similarity map and estimates the position of 3D point. The estimated 3D PSF is again projected to input images and they replaces the intial 2D PSFs which are finally used in image deblurring. Experimental result shows that the quality of image deblurring and 3D reconstruction improves significantly compared with the result when the input images are independently deblurred.
Adaptive Unsharp Masking using Bilateral Filter
Kim, Hak Gu ; Lee, Dong Bok ; Song, Byung Cheol ;
Journal of the Institute of Electronics and Information Engineers, volume 49, issue 11, 2012, Pages 56~63
DOI : 10.5573/ieek.2012.49.11.056
In this paper, adaptive unsharp masking using bilateral filter, edge-preserving smoothing filter is proposed to reduce the overshoot and jagging artifact in sharpening images. Previous image enhancement methods including unsharp masking(UM) can emphasize high-frequency details strongly, but often cause several artifacts such as overshooting, noise, jagging and so on. Proposed image enhancement method preserves edges well because of using bilateral filter and sensitively controls a weight according to edge's directions. Therefore, it enhances sharpness and effectively reduces overshoot and jagging artifacts. Simulation results comparing output of previous AUM with proposed method show that proposed algorithm makes images properly enhanced, and we know that overshoot and jagging artifacts are many reduced.
Fast Detection of Video Copy Using Spatio-Temporal Group Feature
Jeong, Jae Hyup ; Lee, Jun Woo ; Kang, Jong Wook ; Jeong, Dong Seok ;
Journal of the Institute of Electronics and Information Engineers, volume 49, issue 11, 2012, Pages 64~73
DOI : 10.5573/ieek.2012.49.11.064
In this paper, we propose a method to search for identical videos. The proposed method is spatio-temporal group feature fingerprinting. Frame of video is extracted from fixed rate method and is partitioned into vertical group and horizontal group. Descriptor is made of each group feature that is extracted from binary fingerprinting. Next, use descriptor of original video to build a two type of fingerprinting database and matching with query video. To efficient and effective video copy detection, method have high robustness, independence, matching speed. In proposed method, group feature have high robustness and independence in variable modification of video. Building a original fingerprinting database is able to fast matching with query video. The proposed method shows performance improvement in variable modifications in comparison to the existing methods. Especially, very singular performance in speed improvement is great advantage of this paper.
Optical Properties Correction of a Heterogeneous Stereoscopic Camera
Jung, Eun Kyung ; Baek, Seung-Hae ; Park, Soon-Yong ; Jang, Ho-Wook ;
Journal of the Institute of Electronics and Information Engineers, volume 49, issue 11, 2012, Pages 74~85
DOI : 10.5573/ieek.2012.49.11.074
In this paper, we propose a optical property correction technique for a low-cost heterogeneous stereoscopic camera. Three main optical properties of a stereoscopic camera are zoom, focus, and DOF(depth of field). The difference or mis-match of these properties between two stereoscopic videos are the main causes of the visual fatigue to human eyes. The proposed correction technique reduces the difference of the optical properties between the stereoscopic videos and produces high-quality stereoscopic videos. To correct the zoom difference, a LUT(look-up table) is established to match the zoom ratio between the stereoscopic videos. To correct the DOF difference, the magnitude of image edge is measured and the lens iris is changed to control the DOF of the camera. A vertical-type stereoscopic rig is developed for the experiments of the optical property correction. Based on the experimental results, we find that a low-cost heterogeneous stereoscopic camera can be implemented, which can yield low visual fatigue to human eyes.
A New Hardware Design for Generating Digital Holographic Video based on Natural Scene
Lee, Yoon-Hyuk ; Seo, Young-Ho ; Kim, Dong-Wook ;
Journal of the Institute of Electronics and Information Engineers, volume 49, issue 11, 2012, Pages 86~94
DOI : 10.5573/ieek.2012.49.11.086
In this paper we propose a hardware architecture of high-speed CGH (computer generated hologram) generation processor, which particularly reduces the number of memory access times to avoid the bottle-neck in the memory access operation. For this, we use three main schemes. The first is pixel-by-pixel calculation rather than light source-by-source calculation. The second is parallel calculation scheme extracted by modifying the previous recursive calculation scheme. The last one is a fully pipelined calculation scheme and exactly structured timing scheduling by adjusting the hardware. The proposed hardware is structured to calculate a row of a CGH in parallel and each hologram pixel in a row is calculated independently. It consists of input interface, initial parameter calculator, hologram pixel calculators, line buffer, and memory controller. The implemented hardware to calculate a row of a
CGH in parallel uses 168,960 LUTs, 153,944 registers, and 19,212 DSP blocks in an Altera FPGA environment. It can stably operate at 198MHz. Because of the three schemes, the time to access the external memory is reduced to about 1/20,000 of the previous ones at the same calculation speed.
Design of Wireless Underground Sensor System Using Magnetic Field Communication
Kim, Sun-Hee ; Lee, Seungjun ; Hwang, Kyu-Sung ;
Journal of the Institute of Electronics and Information Engineers, volume 49, issue 11, 2012, Pages 97~102
DOI : 10.5573/ieek.2012.49.11.097
Recently, a wireless sensor network system has been receiving great attention for management of underground facilities. However, traditional wireless communication systems using microwaves in several hundred MHz ~ several GHz experience significant performance degradation in the non-uniform underground environment. In this research, in order to make a robust communication for the underground facilities, we propose a wireless underground sensor system based on magnetic field communication. In 3 meters underground environment including rocks, soils, water, etc.,, our proposed sensor network system has proved fully functional and met its performance specification.
Development & Test of A Small-Sized Autonomous Underwater Vehicle "BOTO"
Byun, Seung-Woo ;
Journal of the Institute of Electronics and Information Engineers, volume 49, issue 11, 2012, Pages 103~109
DOI : 10.5573/ieek.2012.49.11.103
Samsung Thales has developed a small-sized autonomous underwater vehicle "BOTO" verified by a mathematical model simulation. The hydrodynamic coefficients and drag force were experimented at circulating water channel for validating cruising performance of the AUV. Based on the mathematical model, we simulated turning radius and way-point tracking on horizontal plane using way-point tracking algorithm. In this paper we introduce the vehicle system and the sea trial test results will be shown.
Design and Implementation of an Acoustic Modem for Small Underwater Devices Operating at Shallow Water
Jeon, Jun-Ho ; Park, Sung-Joon ;
Journal of the Institute of Electronics and Information Engineers, volume 49, issue 11, 2012, Pages 110~117
DOI : 10.5573/ieek.2012.49.11.110
As the demand for underwater systems providing pollution monitoring, marine ecosystem observation, surveillance monitoring is increased, acoustic modem for short-range underwater communication is spotlighted as one of significant research topics. Typically, in shallow water, it is so hard to analyze acoustic wave which undergoes spreading, absorption, reflection and scattering through transmission that there are limited advanced results. Furthermore, in order for the modem to be loaded in a fixed node or a moving vehicle in shallow water, its size should be small enough. In this paper, we address underwater acoustic channel model and design and implement an efficient micro acoustic modem which is adequate for short-range underwater communication. The developed modem is verified in a lake by varying working range and data rate up to 500 meters and 2 kbps, respectively.
The Smart Electronic Tagging System for Sexual Offenses Prevention Context-Aware Services in Extreme Situations such as Location Unrecognized
Lee, Gil-Yong ; Park, Soo-Hyun ;
Journal of the Institute of Electronics and Information Engineers, volume 49, issue 11, 2012, Pages 118~131
DOI : 10.5573/ieek.2012.49.11.118
The existing electronic tagging system traces the location of a sex offender through communicating with GPS satellites and mobile phone base stations in order to prevent repeated crimes. However, the GPS satellite communication method does not work well in the interiors of downtown buildings or on the subways where it is difficult to receive satellite signals. In such cases, the location can be traced through communication with mobile phone base stations. But the distance between mobile phone base stations is several hundred meters, and as a result the margin of error for location tracing can be maximum of 2km in accuracy reduction. Take for example, if a kindergarten is located on the 2nd floor and a coffee shop and the sex offender are located on the 3rd floor in a 5-story building that is downtown, the existing electronic tagging system cannot trace the location of the sex offender as the GPS satellite communication does not work in the interior of the building and the exact floor that the sex offender is located on cannot be recognized through communication with mobile phone base stations. This occurrence is a big problem for the existing electronic tagging system, which is based on position recognition. Therefore, this study suggests a smart electronic tagging system that can monitor sex offenders by using a Ubiquitous Sensor Network in such extreme situations where position recognition is not possible.
Design of MAC Algorithm Supporting Adaptive Transmission Rate on VANET
Park, Sanghyun ; Kim, Nam-Il ;
Journal of the Institute of Electronics and Information Engineers, volume 49, issue 11, 2012, Pages 132~138
DOI : 10.5573/ieek.2012.49.11.132
VANET(Vehicular Ad-hoc Network), standardization of IEEE 802.11p specification is in process. 802.11 MAC protocol grants all nodes equal opportunity to acquire channel without regard to their bit-rates, making it possible for lower bit-rate nodes to occupy communication channel for a fair amount of time thus keeping the higher bit-rate nodes from acquiring connection channel which downward-equalize the overall network performance. Also with the 802.11p MAC protocol, the probability of collision occurring increases as the number of nodes grow. The proposed algorithm is a new MAC protocol that guarantees nodes with acquired channel a firm priority over other nodes for a fixed amount of time with TXOP concept added to 'packet burst' according to the current transmitting speed. This newly designed algorithm allows the construction of wireless network with enhanced network throughput, decreased probability of collisions as well as providing the means to grant each node a fair chance of acquiring connection according to their channel conditions. The algorithm sets the CW's (Contention Window) width wider than the standard's and modulates the continuous transmitting threshold value depending on channel acquired time, thus improving the overall performance of the network.
Sigma Delta Decimation Filter Design for High Resolution Audio Based on Low Power Techniques
Au, Huynh Hai ; Kim, SoYoung ;
Journal of the Institute of Electronics and Information Engineers, volume 49, issue 11, 2012, Pages 141~148
DOI : 10.5573/ieek.2012.49.11.141
A design of a 32-bit fourth-stage decimation filter decimation filter used in sigma-delta analog-to-digital (A/D) converter is proposed in this work. A four-stage decimation filter with down-sampling factor of 512 and 32-bit output is developed. A multi-stage cascaded integrator-comb (CIC) filter, which reduces the sampling rate by 64, is used in the first stage. Three half-band FIR filters are used after the CIC filter, each of which reduces the sampling rate by two. The pipeline structure is applied in the CIC filter to reduce the power consumption of the CIC. The Canonic Signed Digit (CSD) arithmetic is used to optimize the multiplier structure of the FIR filter. This filter is implemented based on a semi-custom design flow and a 130nm CMOS standard cell library. This decimation filter operates at 98.304 MHz and provides 32-bit output data at an audio frequency of 192 kHz with power consumption of
. In comparison to the previous work, this design shows a higher performance in resolution, operation frequency and decimation factor with lower power consumption and small logic utilization.
Interpolated Digital Delta-Sigma Modulator for Audio D/A Converter
Noh, Jinho ; Yoo, Changsik ;
Journal of the Institute of Electronics and Information Engineers, volume 49, issue 11, 2012, Pages 149~156
DOI : 10.5573/ieek.2012.49.11.149
A digital input class-D audio amplifier is presented for digital hearing aid. The class-D audio amplifier is composed of digital and analog circuits. The analog circuit converts a digital input to a analog audio signal (DAC) with noise suppression in the audio band. An interpolated digital delta-sigma modulator is used to convert data types between digital signal processor (DSP) and digital-to-analog converter (DAC). An 16-bit, 25-kbps pulse code modulated (PCM) input is interpolated to 16-bit, 50-kbps by a digital filter. The output signal of interpolation filter is noise-shaped by a third-order digital sigma-delta modulator (SDM). As a result, 1.5-bit, 3.2-Mbps signal is applied to simple digital to analog converter.
A Study of High Precision Position Estimator Using GPS/INS Sensor Fusion
Lee, Jeongwhan ; Kim, Hansil ;
Journal of the Institute of Electronics and Information Engineers, volume 49, issue 11, 2012, Pages 159~166
DOI : 10.5573/ieek.2012.49.11.159
There are several ways such as GPS(Global Positioning System) and INS (Inertial Navigation System) to track the location of moving vehicle. The GPS has the advantages of having non-accumulative error even if it brings about errors. In order to obtain the position information, we need to receive at least 3 satellites information. But, the weak point is that GPS is not useful when the 혠 signal is weak or it is in the incommunicable region such as tunnel. In the case of INS, the information of the position and posture of mobile with several Hz~several hundreds Hz data speed is recorded for velocity, direction. INS shows a very precise navigational performance for a short period, but it has the disadvantage of increasing velocity components because of the accumulated error during integration over time. In this paper, sensor fusion algorithm is applied to both of INS and GPS for the position information to overcome the drawbacks. The proposed system gets an accurate position information from experiment using SVD in a non-accessible GPS terrain.
Design of a Ultrasonic Oil Level Meter Using a FPGA
Cho, Jeong Yeon ; Kang, Moon Ho ;
Journal of the Institute of Electronics and Information Engineers, volume 49, issue 11, 2012, Pages 167~174
DOI : 10.5573/ieek.2012.49.11.167
In this paper a ultrasonic oil level meter for measuring oil levels of vehicle transmissions is designed and its effectiveness is shown by experiments. On a FPGA(Field Programmable Gate Array) project IDE(Integrated Development Environment), all digital circuits for the meter is designed using a FPGA, which enables simplicity and high performance of the meter as well as short developing time. Also, power supplying circuit and analog circuits to process low voltage ultrasonic echo signal are designed and simulated. Under experiments, the designed level meter is verified to provide accuracy to within 1mm.
Grid Noise Removal in Computed Radiography Images Using the Combined Wavelet Packet-Fourier Method
Lee, A Young ; Kim, Dong Youn ;
Journal of the Institute of Electronics and Information Engineers, volume 49, issue 11, 2012, Pages 175~182
DOI : 10.5573/ieek.2012.49.11.175
The scattered radiation always occurs when X-ray strikes the object. To absorb the scattered X-rays, the antiscatter grids are used, however these grids images are superimposed in the projection radiography images. When those images are displayed on the monitor, moir
patterns are overlapped over the images and disturb the anatomical informations. Most of the researches performed to date removed the grid noises by calculating or observing those frequencies in one dimensional frequency domain, two dimensional wavelet transform or Fourier transform. Those methods filtered not only the grid noises but also diagnostic informations. In this paper, we proposed the combined wavelet packet-Fourier method to remove the grid artifact in CR images. For the phantom image, the proposed method achieved from 5.2 to 7.4 dB better than others in SNR and for CR images by rejecting the grid noise bands effectively while leaving the remaining bands unchanged, the loss of images could get minimal results.
Development of Exercise Analysis System Using Bioelectric Abdominal Signal
Gang, Gyeong Woo ; Min, Chul Hong ; Kim, Tae Seon ;
Journal of the Institute of Electronics and Information Engineers, volume 49, issue 11, 2012, Pages 183~190
DOI : 10.5573/ieek.2012.49.11.183
Conventional physical activity monitoring systems, which use accelerometers, global positioning system (GPS), heartbeats, or body temperature information, showed limited performances due to their own restrictions on measurement environment and measurable activity types. To overcome these limitations, we developed a portable exercise analysis system that can analyze aerobic exercises as well as isotonic exercises. For bioelectric signal acquisition during exercise, waist belt with two body contact electrodes was used. For exercise analysis, the measured signals were firstly divided into two signal groups with different frequency ranges which can represent respiration related signal and muscular motion related signal, respectively. After then, power values, differential of power values, and median frequency values were selected for feature values. Selected features were used as inputs of support vector machine (SVM) to classify the exercise types. For verification of statistical significance, ANOVA and multiple comparison test were performed. The experimental results showed 100% accuracy for classification of aerobic exercise and isotonic resistance exercise. Also, classification of aerobic exercise, isotonic resistance exercise, and hybrid types of exercise revealed 92.7% of accuracy.
A CV.CC Concurrent-Controled LED Converter
Mang, Chung-Yong ; Lee, Won-Seok ;
Journal of the Institute of Electronics and Information Engineers, volume 49, issue 11, 2012, Pages 193~198
DOI : 10.5573/ieek.2012.49.11.193
An LED converter used to operate an LED with high efficiency and long lifespan, activates an LED by keeping voltage and current constant. In spite of voltage drop by LED's overheating and over-voltage by damage of a power line and by circuit problem, most existing LED converters supply unchanged constant voltage and current to the LED. Eventually, LED is out of order because of over-voltage or over-current. To avoid the breakdown of an LED by over-voltage and over-current, we propose a new scheme which deactivate the PWM circuit in the event of over-current generating. The PWM circuit operates below the pre-determined level of current. While the over-voltage is generated in PWM circuit, the feedback circuit makes the PWM circuit stopped and therefore prevents LED from being damaged by over-voltage and over-current.
A Study of Lighting Flxtures Power Supply That Use Current Control
Lee, Byung-Sun ; Kim, Young Sun ;
Journal of the Institute of Electronics and Information Engineers, volume 49, issue 11, 2012, Pages 199~204
DOI : 10.5573/ieek.2012.49.11.199
The study for developments and economics about the energies from the global warming is very active. For the effective saving and the spanning of the life extension about the 19% rates for the illumination system spending power about the whole electric energies, we proposed the new type of the current control method using a mixing system of the frequency modulation together with the pulse width modulation for the half-bridge power instrument. And we proved the excellence and the stability for our suggested system and analyzed the characteristics.
QoS Management Using Variations of RED Parameters
Chun, Sang Hun ;
Journal of the Institute of Electronics and Information Engineers, volume 49, issue 11, 2012, Pages 205~210
DOI : 10.5573/ieek.2012.49.11.205
This paper investigated the performance of QoS management using variations of RED parameters in Differentiated Service. Differentiated Service separates packets from a specific traffic by using QoS parameters such as CIR or PIR. A code point is used to mark each packet which is enqueued into each virtual queue. Different RED parameters are configured for virtual queues according to each code point. As the code point value increases, the RED parameters become harsher. To show QoS Management using variations of RED parameters, this paper used the policy model of time sliding window with 2 color marking (TSW2CM). Simulation results using NS-2 showed that the QoS management of a differentiated service can be obtained from using variations of RED parameters.
Performance Analysis of an OFDM System over an underwater acoustic channel
Kang, Heehoon ; Lee, Youngjong ; Han, Wanok ;
Journal of the Institute of Electronics and Information Engineers, volume 49, issue 11, 2012, Pages 211~216
DOI : 10.5573/ieek.2012.49.11.211
Such as disaster rescue in deep water, undersea exploration and monitering for environmental pollution, many applications require the acoustic communication for high data rate over underwater acoustic channel. As underwater channel is very complex and is time-varying, In this paper, The proposed OFDM system with synchronization errors and multipath delay spread is analyzed for high data rate and reliability and rubust service over UWA channels.