Kiseon Kim

Multicast Scheduling and Resource Allocation Algorithms for OFDMA-Based Systems: A Survey

Multicasting is emerging as an enabling technology for multimedia transmissions over wireless networks to support several groups of users with flexible quality of service (QoS) requirements. Although multicast has huge potential to push the limits of next generation communication systems; it is however one of the most challenging issues currently being addressed. In this survey, we explain multicast group formation and various forms of group rate determination approaches. We also provide a systematic review of recent channel-aware multicast scheduling and resource allocation (MSRA) techniques proposed for downlink multicast services in OFDMA based systems. We study these enabling algorithms, evaluate their core characteristics, limitations and classify them using multidimensional matrix. We cohesively review the algorithms in terms of their throughput maximization, fairness considerations, performance complexities, multi-antenna support, optimality and simplifying assumptions. We discuss existing standards employing multicasting and further highlight some potential research opportunities in multicast systems.

Localization with a mobile beacon based on geometric constraints in wireless sensor networks

The location information of sensor nodes is needed for location-based services and network management in wireless sensor networks. Among the many kinds of localization schemes researched to find the location of sensor nodes, a few some schemes presume the use of mobile beacons because using mobile beacons has many potentialities. In particular, a localization scheme with mobile beacons, such as proposed by Ssu et al. [5], has fine-grained accuracy, scalability, and power efficiency even without distance or angle information. To improve the localization accuracy encountered in Ssus scheme, this paper proposes a localization scheme that estimates the location of a sensor node from a possible area where the sensor node is supposed to be, by using geometric constraints. Through simulation results, the proposed scheme is shown to provide higher localization accuracy and reduce the power consumption of sensor nodes by decreasing the communication overhead between sensor nodes and a mobile beacon in comparison to Ssus scheme.

HydroCast: Pressure Routing for Underwater Sensor Networks

A Sensor Equipped Aquatic (SEA) swarm is a sensor cloud that drifts with water currents and enables 4-D (space and time) monitoring of local underwater events such as contaminants, marine life, and intruders. The swarm is escorted on the surface by drifting sonobuoys that collect data from the underwater sensors via acoustic modems and report it in real time via radio to a monitoring center. The goal of this study is to design an efficient anycast routing algorithm for reliable underwater sensor event reporting to any surface sonobuoy. Major challenges are the ocean current and limited resources (bandwidth and energy). In this paper, these challenges are addressed, and HydroCast, which is a hydraulic-pressure-based anycast routing protocol that exploits the measured pressure levels to route data to the surface sonobuoys, is proposed. This paper makes the following contributions: a novel opportunistic routing mechanism to select the subset of forwarders that maximizes the greedy progress yet limits cochannel interference and an efficient underwater dead end recovery method that outperforms the recently proposed approaches. The proposed routing protocols are validated through extensive simulations.

Effect of third-order intermodulation on radio-over-fiber systems by a dual-electrode Mach-Zehnder modulator with ODSB and OSSB signals

Third-order intermodulation (IM3) is a very important issue as a degradation factor of system performance in the range of high input signal power. In this paper, the effect of IM3 from a dual-electrode Mach-Zehnder modulator (DEMZM) and a photodetector (PD) is analyzed for optical single-sideband (OSSB) and optical double-sideband (ODSB) signals incorporating fiber dispersion. In addition, the optimum input signal power and the signal-to-noise-and-distortion ratio (SNDR) for the two cases are also investigated to optimize the performance of the entire system. In the case of OSSB signals, the fundamental components are robust against fiber dispersion, whereas their IM3 components are still sensitive to fiber dispersion. Subsequently, the SNDR for OSSB signals fluctuated to within 6 dB in the relatively high input power range due to fiber dispersion. In the case of ODSB signals, both powers of the fundamental and IM3 components are attenuated. However, the power attenuation of IM3 due to fiber dispersion is significantly faster than that of the fundamental. Thus, the SNDR for ODSB signals is improved as fiber dispersion increases until the power of IM3 is greater than that of the additive noise level.

A review on application of technology systems, standards and interfaces for agriculture and food sector

Application of technology systems is seen in many sectors including agriculture and food. Traditionally, agricultural industry has been solely dependent on human labor with limited application of mechanical equipment and machines. The applications of advanced technology such as embedded computing, robotics, wireless technology, GPS/GIS (Geographical Positioning System/Geographical Information System) and DBMS (Database Management System) software are seen to be recent developments. This paper reviews the applications of technology systems in agriculture and food. Because knowledge on standardization and interfacing plays a key role in using the technology systems in any application domain, this paper aims to highlight the important attributes of such an emerging research area. In particular, the paper describes soil sampling methods and technology applications; field and yield mapping with GPS and GIS; harvesters and future research in robotic-based harvesters; food processing and packaging technology such as traceability and status of RFID networking research; application of sensor network; data management and execution systems; and the automation and control standards such as fieldbus systems and OMAC guidelines.

Robust minimax detection of a weak signal in noise with a bounded variance and density value at the center of symmetry

In practical communication environments, it is frequently observed that the underlying noise distribution is not Gaussian and may vary in a wide range from short-tailed to heavy-tailed forms. To describe partially known noise distribution densities, a distribution class characterized by the upper-bounds upon a noise variance and a density dispersion in the central part is used. The results on the minimax variance estimation in the Huber sense are applied to the problem of asymptotically minimax detection of a weak signal. The least favorable density minimizing Fisher information over this class is called the Weber-Hermite density and it has the Gaussian and Laplace densities as limiting cases. The subsequent minimax detector has the following form: i) with relatively small variances, it is the minimum L2-norm distance rule; ii) with relatively large variances, it is the L1 -norm distance rule; iii) it is a compromise between these extremes with relatively moderate variances. It is shown that the proposed minimax detector is robust and close to Hubers for heavy-tailed distributions and more efficient than Hubers for short-tailed ones both in asymptotics and on finite samples

A new fusion formula and its application to continuous-time linear systems with multisensor environment

The problem of fusion of local estimates is considered. An optimal mean-square linear combination (fusion formula) of an arbitrary number of local vector estimates is derived. The derived result holds for all dynamic systems with measurements. In particular, for scalar uncorrelated local estimates, the fusion formula represents the well-known result in statistics. The fusion formula is applied to fusion of local Kalman estimates in multisensor filtering problem. Examples demonstrate high accuracy of the proposed fusion formula.

On Secure Spectrum Sensing in Cognitive Radio Networks Using Emitters Electromagnetic Signature

As Cognitive Radio Network (CRN) emerges as an extremely promising next generation wireless technology that can ease the apparent spectrum scarcity and support novel wireless applications; they will become bigger targets for hackers. Moreover, they will also be exposed to diverse security threats especially at the physical layer (PHY) spectrum sensing module. Hence, security consideration is central in its development. Starting with overview of on-going research efforts in CR-based network security, this paper describes a PHY attacker model that exploits the adaptability and flexibility of CRN. In thwarting this attack, we propose a waveform pattern recognition scheme to identify emitters and detect camouflaging attackers by using the Electromagnetic Signature (EMS) of the transceiver. On the performance of the technique, our simulation results show that our approach is effective for spectrum monitoring, mitigating denial-of-service threats and facilitating spectral efficiency.

Erlang capacity of multiaccess systems with service-based access selection

In this letter, we provide the lower and upper bounds of Erlang capacity of multiaccess systems supporting several different radio access technologies in the multiservice scenario, by considering two extreme operation methods; separate and common operation. In a numerical example with GSM/EDGE-like and WCDMA-like subsystems, it is shown that the common operation method can provide up to 60% Erlang capacity improvement over the separate operation method when using a near optimum so-called service-based user assignment scheme, with the combined effects of the assignment and the trunking gains. Even in the worst-case, the common operation method still can provide about 15% capacity improvement over the separate operation method, which mainly comes from the trunking gain.

Approximation of SNR degradation due to carrier frequency offset for OFDM in shadowed multipath channels

We derive an approximate expression for signal-to-noise ratio (SNR) degradation of orthogonal frequency division multiplexing due to carrier frequency offset over a shadowed multipath channel, to explicitly show the effects of system and channel parameters on the degradation of the received SNR. The results show that, for small frequency offset, the SNR degradation is proportional to the square of the frequency offset and the square of the number of subcarriers. It is also shown that, if E/sub s//N/sub 0/ is reasonably large, the SNR degradation becomes insensitive to E/sub s//N/sub 0/, which is contrary to the case of the additive white Gaussian noise channel.