Performance of RS coded M-ary modulation with and without symbol overlapping

In this paper, we present analytical bit error probability results for M-ary modulation concatenated with Reed Solomon (RS) codes. The analysis of bit error probability is nontrivial as the number of bits per symbol for the RS codes may not be an integer multiple of the number of bits per symbol for a modulation symbol. We propose a Markov chain technique which allows analytical evaluation of the bit error probability for such cases. The performance of RS coding with coherent biorthogonal, coherent/non-coherent orthogonal modulation over an additive white Gaussian noise (AWGN) channel is evaluated. Simulation of the bit error probability of RS code concatenated with a Nordstrom Robinson (NR) code as an inner code is performed and compared with the case of biorthogonal modulation. From the results, we notice that a stronger inner code gives better bit error probability. In addition, the throughput of the coded system with biorthogonal modulation over an AWGN channel is discussed. For a Rayleigh flat fading and block fading channel, we analyze the bit error probability of RS codes concatenated with biorthogonal modulation. From the result, we notice that a stronger outer code gives a better bit error probability for the case of Rayleigh flat fading channel.     

An Intelligent Product Recommendation Model to Reflect the Recent Purchasing Patterns of Customers

Mobile Networks and Applications - This study suggests a new product recommendation model to reflect the recent purchasing patterns of customers. There are many methods to measure the similarity...     

Covalent 0D–2D Heterostructuring of Co9S8–MoS2 for Enhanced Hydrogen Evolution in All pH Electrolytes

Ultrasmall Co₉S₈ nanoparticles are introduced on the basal plane of MoS₂ to fabricate a covalent 0D–2D heterostructure that enhances the hydrogen evolution reaction (HER) activity of electrochemical water splitting. In the heterostructure, separate phases of Co₉S₈ and MoS₂ are formed, but they are connected by Co–S–Mo type covalent bonds. The charge redistribution from Co to Mo occurring at the interface enhances the electron‐doped characteristics of MoS₂ to generate electron‐rich Mo atoms. Besides, reductive annealing during the synthesis forms S defects that activates adjacent Mo atoms for further enhanced HER activity as elucidated by the density functional theory (DFT) calculation. Eventually, the covalent Co₉S₈–MoS₂ heterostructure shows amplified HER activity as well as stability in all pH electrolytes. The synergistic effect is pronounced when the heterostructure is coupled with a porous Ni foam (NF) support to form Co₉S₈–MoS₂/NF that displays superior performance to those of the state‐of‐the‐art non‐noble metal electrocatalysts, and even outperforms a commercial Pt/C catalyst in a practically meaningful, high current density region in alkaline (>170 mA cm^?2) and neutral (>60 mA cm^?2) media. The high HER performance and stability of Co₉S₈–MoS₂ heterostructure make it a promising pH universal alternative to expensive Pt‐based electrocatalysts for practical water electrolyzers.     

Efficient traffic prediction scheme for real-time VBR MPEG videotransmission over high-speed networks

The efficient transportation of real-time variable bit rate (VBR) video traffic in high-speed networks is currently an active area of research. The capability to predict VBR video traffic can significantly improve the effectiveness of numerous management tasks, including dynamic bandwidth allocation and congestion control. This paper proposes an adaptive traffic prediction method for VBR MPEG videos, a major multimedia application. Rapid traffic variations due to scene changes are analyzed, then a prediction scheme using the identification of scene changes related to I and P frames is presented. For predicting multiplexed MPEG traffic, a prediction interval is derived that represents a highly correlated traffic sequence. In addition, to reduce the prediction error, a less fluctuating signal instead of the original multiplexed traffic is used as the input for the predictor. Simulation results show that the proposed method is able to predict the original traffic more accurately than the conventional LMS method     

CW operation and threshold characteristics of all-monolithic InAlGaAs 1.55-/spl mu/m VCSELs grown by MOCVD

We demonstrate an all-monolithic metal-organic chemical vapor epitaxy (MOCVD)-grown 1.55-/spl mu/m vertical-cavity surface-emitting laser operating continuous wave up to 35/spl deg/C. The structure is based on the InAlGaAs-InP material system grown by a single step of MOCVD. Wet oxidation of a strained In/sub 0.4/Al/sub 0.6/As layer is used for the current confinement. The threshold current, threshold voltage and the external quantum efficiency at room temperature are about 1.6 mA, 2.3 V, and 5.4%, respectively.     

Humidity Sustained Wearable Pouch‐Type Triboelectric Nanogenerator for Harvesting Mechanical Energy from Human Activities

Triboelectric nanogenerators (TENGs) are gaining much research interest recently owing to their facile and cost‐effective device structure. However, the effect of relative humidity (in moisture atmosphere) on the output performance still needs to be resolved. Herein, a pouch‐type TENG is proposed to significantly reduce the effect of relative humidity on its electrical output and a stable performance is also attained in a humid environment. In this regard, a dielectric and dielectric materials‐based TENG (DD‐TENG) is first developed using nanoarchitecture polydimethylsiloxane (NA‐PDMS) and multiwalled carbon nanotube/nylon composite layers as a triboelectric material with the negative and positive tendencies, respectively. The NA‐PDMS and nylon composite layers play a key role in increasing the surface contact area and surface charge density between the dielectric/triboelectric materials as well as the output performance of DD‐TENG. However, the DD‐TENG device exhibits a stable and high output performance with the effective output power density of ≈25.35 W m^?2. Additionally, the performance of the pouch‐type DD‐TENG device is not almost affected even though the relative humidity is increased from 35 to 81%, while it is dramatically decreased for the nonpouch‐type device. Finally, the pouch‐type DD‐TENG is employed as a wearable device to effectively harvest the mechanical energy from daily human activities.     

Joint spectrum sensing and resource allocation optimization using genetic algorithm for frequency hopping–based cognitive radio networks

In cognitive radio (CR) networks, secondary users should effectively use unused licensed spectrums, unless they cause any harmful interference to the primary users. Therefore, spectrum sensing and channel resource allocation are the 2 main functionalities of CR networks, which play important roles in the performance of a CR system. To maximize the CR system utility, we propose a joint out‐of‐band spectrum sensing and operating channel allocation scheme based on genetic algorithm for frequency hopping–based CR networks. In this paper, to effectively sense the primary signal on hopping channels at each hopping slot time, a set of member nodes sense the next hopping channel, which is called out‐of‐band sensing. To achieve collision‐free cooperative sensing reporting, the next channel detection notification mechanism is presented. Using genetic algorithm, the optimum sensing and data transmission schedules are derived. It selects a sensing node set that participate the spectrum sensing for the next expected hopping channel during the current channel hopping time and another set of nodes that take opportunity for transmitting data on the current hopping channel. The optimum channel allocation is performed in accordance with each node's individual traffic demand. Simulation results show that the proposed scheme can achieve reliable spectrum sensing and efficient channel allocation.     

Timeout Period Analysis to Detect Black Hole Attack in Multihop Wireless Ad Hoc Networks

A novel approach is proposed to estimate the timeout period used in wireless ad hoc networks in order to detect misbehaving nodes that make black hole attacks. Timeout period is an acceptable time frame for a node to forward a packet and is used to judge if the node is behaving properly. To avoid misjudgment and false alarms, the accuracy of the estimate of the timeout period is very important. Our method is based on the IEEE 802.11 MAC protocol and Dynamic Source Routing protocol. The main contribution of this paper is proposing a queuing analysis to calculate the mean and maximum delay per hop implementing the 95-percentile of medium access waiting time. In addition, a new technique is introduced that can be applied to determine the mean number of hops in flooding-based ad hoc networks, taking into account edge effects. For each proposed model, analytical results are compared with results obtained from simulations and the validity of the models is confirmed by observing the close relationship between the results.     

Capacity improvement in CDMA downlink with orthogonal code-hopping multiplexing

Orthogonal code-hopping multiplexing (OCHM) is a statistical multiplexing scheme designed to increase the number of allowable downlink channels in code division multiple access (CDMA) systems. OCHM is expected to compensate for a lack of codewords in future communication systems. In CDMA systems including OCHM, system capacity is limited by the number of codewords and power (or interference), and the maximum system capacity is determined by a stronger limitation between them. Call blockings due to power limitation may occur firstly if downlink channels demand large E/sub b//I/sub 0/ values and a high-channel activity. On the other hand, code limitation may occur prior to power limitation in CDMA. The maximum system capacities determined by both code and power limitations must be known, even in OCHM. However, previous studies on OCHM system capacity focused only on increasing the number of multiplexed users with no consideration of the power limitation. In this paper, the overall system capacity of OCHM considering both code and power limitations was evaluated. For this analysis, the transmission chip energy of base station (BS) and inner/outer-cell interference is mathematically derived in a multicell and multiuser environment. The downlink system capacity for OCHM is larger than for orthogonal code division multiplexing (OCDM) as other cell interference (OCI), mean channel activity, and the required E/sub b//I/sub 0/ value decrease.     

A Video Streaming System for Mobile Phones: Practice and Experience

This paper presents a case of video streaming system for mobile phone which has actually been implemented and deployed for commercial services in CDMA2000 1X cellular phone networks. As the computing environment and the network connection of cellular phones are significantly different from the wired desktop environment, the traditional desktop streaming method is not applicable. Therefore, a new architecture is required to suit the successfully streaming in the mobile phone environment. We have developed a very lightweight video player for use in mobile phone and the related authoring tool for the player. The streaming server has carefully been designed to provide high efficiency, reliability and scalability. Based on a specifically-designed suite of streaming protocol, the server employs an adaptive rate control mechanism which transmits the media packets appropriately into the network according to the change in network bandwidth.Hojung Cha is currently a professor in computer science at Yonsei University, Seoul, Korea. His research interests include multimedia computing system, multimedia communication networks, wireless and mobile communication systems and embedded system software. He received his B.S. and M.S. in computer engineering from Seoul National University, Korea, in 1985 and 1987, respectively. He received his Ph.D. in computer science from the University of Manchester, England, in 1991.Jongmin Lee is a Ph.D. candidiate in computer science at Yonsei University, Seoul, Korea. His research interests include wireless multimedia system, QoS architecture, multimedia communication networks. He received his B.S. and M.S. in computer science from Kwangwoon University in 1999 and 2001, respectively.Jongho Nang is a professor in the Department of Computer Science at Sogang University. He received his B.S. degree from Sogang University, Korea, in 1986 and M.S. and Ph.D. degree from KAIST, in 1988 and in 1992, respectively. His research interests are in the field of multimedia systems, digital video library, and Internet technologies. He is a member of KISS, ACM, and IEEE.Sung-Yong Park is an associate professor in the Department of Computer Science at Sogang University, Seoul, Korea. He received his B.S. degree in computer science from Sogang University, and both the M.S. and Ph.D. degrees in computer science from Syracuse University. From 1987 to 1992, he worked for LG Electronics, Korea, as a research engineer. From 1998 to 1999, he was a research scientist at Telcordia Technologies (formerly Bellcore) where he developed network management software for optical switches. His research interests include high performance distributed computing and systems, operating systems, and multimedia.Jin-Hwan Jeong received the B.S. and M.S. degrees in computer science from Korea University, Seoul, Korea, in 1997, and 1999, respectively. He is currently in Ph.D. course at Korea University. His research interests include video processing for thin devices, multimedia streaming and operating systems.Chuck Yoo received the B.S. degree in electronics engineering from Seoul National University, Seoul, Korea and the M.S. and Ph.D. in computer science in University of Michigan. He worked as a researcher in Sun Microsystems Lab. from 1990 to 1995. He joined the Computer Science and Enginnering Department, Korea University, Seoul, Korea in 1995, where he is currently a professor. His research interests include high performance network, multimedia streaming, and operating systems.Jin-Young Choi received the B.S. degree from Seoul National University, Seoul, Korea, in 1982, the M.S. degree from Drexel University in 1986, and the Ph.D. degree from University of Pennsylvania, in 1993. He is currently a professor of Computer Science and Engineering Department, Korea University, Seoul, Korea. His current research interests are in real-time computing, formal methods, programming languages, process algebras, security, software engineering, and protocol engineering.