Maximum Allowable Power Research Articles

Combined Gas-Fluid Buoyancy System for Improved Attitude and Maneuverability Control for Application in Underwater Gliders

Since it was first published the conception of underwater glider by H. Stommel (1989), many designs have been proposed based on the variable buoyancy-gliding principle for application in underwater vehicles. Underwater gliders take advantage of the differential buoyancy of a body submerged in a fluid, the Archimedes principle, for converting part of this buoyancy force in surge velocity. For doing that, gliders need surfaces conveniently oriented for obtaining a resulting velocity in the desired surge direction. This hydrodynamic forward movement is obtained during the vehicle sinking and emerging paths, which is the most characteristic constraint of underwater gliders: the need of conducting a saw-tooth navigation pattern. The differential positive-negative buoyancy effect is based on a small increase of the vehicle volume. This increase is obtained by pumping some amount of liquid-fluid in external bladders, which makes the net buoyancy of the vehicle changing from negative (sinking) to positive (climb). However, bladders as buoyancy elements have limitations in the maximum allowable displacement volume and power requirements. Low value of differential buoyancy of ± (0.25 to ±0.45) provides low values of usable force limiting the dynamic capacity of the vehicle. As a result, speeds of around 0.50 m/s are claimed to be reachable by commercial gliders, although 0.15-0.30 m/s are the most frequent horizontal resultant speed obtained. This paper proposes a different concept on this buoyancy- based propulsion technique by considering the combination of compressed gas and liquid fluid. As an example of application, they are presented first results from the field conducted with the underwater glider Alba-14 HGL. The system proposed is based on a hybrid buoyancy gas/liquid device using oil and compressed air which is expected to be an interesting solution when increased speed and maneuverability may be required. Although the maximum range of the vehicle will be affected due to restrictions in the maximum capacity of compressed gas available and for the need of counting with an associated ballast- compensating system, this concept can provide additional booster ability for dealing with high environmental energetic areas in the ocean. Further works include additional field test of the Alba-14 HGL for testing extended long term operations as well as the validation of each of the individual subsystem proposed.

Hot Wall Epitaxy(HWE)법에 의한 MnAl2S4단결정 박막 성장과 광전도 특성

수평 전기로에서 <TEX>$MnAl_2S_4$</TEX> 다결정을 합성하여 HWE(Hot Wall Epitaxy)방법으로 <TEX>$MnAl_2S_4$</TEX> 단결정 박막을 반절연성 GaAs(100)기판에 성장시켰다. <TEX>$MnAl_2S_4$</TEX> 단결정 박막의 성장 조건은 증발원의 온도 <TEX>$630^{\circ}C$</TEX>, 기판의 온도 <TEX>$410^{\circ}C$</TEX>였고 성장 속도는 <TEX>$0.5{\mu}m/hr$</TEX>였다. 이때 <TEX>$MnAl_2S_4$</TEX> 단결정 박막의 결정성의 조사에서 이중결정 X-선 요동곡선(DCRC)의 반폭치(FWHM)도 132 arcsec로 가장 작아 최적 성장 조건임을 알 수 있었다. <TEX>$MnAl_2S_4$</TEX>/SI(Semi-Insulated) GaAs(100) 단결정 박막의 광흡수를 293 K에서 10 K까지 측정하였다. 광흡수 스펙트럼으로부터 band gap <TEX>$E_g(T)$</TEX>는 Varshni 공식에 따라 계산한 결과 <TEX>$E_g(T)=3.7920eV-(5.2729{\times}10^{-4}eV/K)T^2/(T+786K)$</TEX>였다. <TEX>$MnAl_2S_4$</TEX> 단결정 박막의 응용소자인 photocell로 사용할 수 있는 pc/dc 값이 가장 큰 광전도셀은 S 증기분위기에서 열처리한 셀로 <TEX>$1.10{\times}10^7$</TEX>이었으며, 광전도 셀의 감도(sensitivity)도 S 증기분위기에서 열처리한 셀이 0.93로 가장 좋았다. 또한 최대 허용소비전력(MAPD)값도 S 증기분위기에서 열처리한 셀이 316 mW로 가장 좋았으며, S 증기분위기에서 열처리한 셀의 응답시간은 오름시간 14.8 ms, 내림시간 12.1 ms로 가장 빠르게 나타나, <TEX>$MnAl_2S_4$</TEX> 단결정 박막을 S 분위기에서 <TEX>$290^{\circ}C$</TEX>로 30분 열처리한 photocell이 상용화가 가능할 것으로 여겨진다. A stoichiometric mixture of evaporating materials for <TEX>$MnAl_2S_4$</TEX> single crystal thin films was prepared from horizontal electric furnace. To obtain the single crystal thin films, <TEX>$MnAl_2S_4$</TEX> mixed crystal was deposited on thoroughly etched semi-insulating GaAs(100) substrate by the Hot Wall Epitaxy (HWE) system. The source and substrate temperatures were <TEX>$630^{\circ}C$</TEX> and <TEX>$410^{\circ}C$</TEX>, respectively. The crystalline structure of the single crystal thin films was investigated by the photoluminescence and double crystal X-ray diffraction (DCXD). The temperature dependence of the energy band gap of the <TEX>$MnAl_2S_4$</TEX> obtained from the absorption spectra was well described by the Varshni's relation, <TEX>$E_g(T)=3.7920eV-5.2729{\times}10^{-4}eV/K)T^2/(T+786 K)$</TEX>. In order to explore the applicability as a photoconductive cell, we measured the sensitivity (<TEX>${\gamma}$</TEX>), the ratio of photocurrent to dark current (pc/dc), maximum allowable power dissipation (MAPD) and response time. The results indicated that the photoconductive characteristic were the best for the samples annealed in S vapour compare with in Mn, Al, air and vacuum vapour. Then we obtained the sensitivity of 0.93, the value of pc/dc of <TEX>$1.10{\times}10^7$</TEX>, the MAPD of 316 mW, and the rise and decay time of 14.8 ms and 12.1 ms, respectively.

Biological channel modeling and implantable UWB antenna design for neural recording systems.

Ultrawideband (UWB) short-range communication systems have proved to be valuable in medical technology, particularly for implanted devices, due to their low-power consumption, low cost, small size, and high data rates. Neural activity monitoring in the brain requires high data rate (800kb/s per neural sensor), and we target a system supporting a large number of sensors, in particular, aggregate transmission above 430 Mb/s (∼512 sensors). Knowledge of channel behavior is required to determine the maximum allowable power to 1) respect ANSI guidelines for avoiding tissue damage, and 2) respect FCC guidelines on unlicensed transmissions. We utilize a realistic model of the biological channel to inform the design of antennas for the implanted transmitter and the external receiver under these requirements. Antennas placement is examined under two scenarios having contrasting power constraints. Performance of the system within the biological tissues is examined via simulation and experiment. Our miniaturized antennas, 12 mm ×12 mm, need worst-case receiver sensitivities of -38 and -30.5 dBm for the first and second scenarios, respectively. These sensitivities allow us to successfully detect signals transmitted through tissues in the 3.1-10.6-GHz UWB band.

On the Performance of Adaptive Packetized Wireless Communication Links Under Jamming

We employ a game theoretic approach to formulate communication between two nodes over a wireless link in the presence of an adversary. We define a constrained, two-player, zero-sum game between a transmitter/receiver pair with adaptive transmission parameters and an adversary with average and maximum power constraints. In this model, the transmitter's goal is to maximize the achievable expected performance of the communication link, defined by a utility function, while the jammer's goal is to minimize the same utility function. Inspired by capacity/rate as a performance measure, we define a general utility function and a payoff matrix which may be applied to a variety of jamming problems. We show the existence of a threshold such that if the jammer's average power exceeds this threshold, the expected payoff of the transmitter at Nash Equilibrium (NE) is the same as the case when the jammer uses its maximum allowable power all the time. We provide analytical and numerical results for transmitter and jammer optimal strategies and a closed form expression for the expected value of the game at the NE. As a special case, we investigate the maximum achievable transmission rate of a rate-adaptive, packetized, wireless AWGN communication link under different jamming scenarios and show that randomization can significantly assist a smart jammer with limited average power.

Possible Design of Long-Life Small Prismatic HTGR for Passive Decay Heat Removal

In the past decade, greater emphasis has been placed in nuclear reactor design on passive systems for the removal of decay heat. This study focuses on the passive safety feature of decay heat removal in modular high-temperature gas-cooled reactors (HTGRs). The availability of this feature depends largely on reactor dimensions, power, and initial core temperature. It is assumed that the initial temperatures of fuel, graphite matrix, and coolant are the same, and so are represented by the initial core temperature, which is uniformly distributed throughout the core. However, little is known in general about the relationships among the parameters mentioned above or on the ability of the core to passively reject decay heat. To obtain a general understanding of the relationship of those parameters in HTGRs, analyses were performed, estimating the effects of initial core and soil temperatures and of the presence of structural materials on the maximum core temperature, allowable power, and size. Appropriate sizes were evaluated for reactors with given powers having various maximum power densities and operating at different initial core temperatures. Criticality and burnup analyses for the proposed reactors were performed, and it was found that all reactors with 20 wt% of uranium enrichment can be critical for over 16 years of operation.

A Test Time Theorem and its Applications

Power dissipated during test is a constraint when it comes to test time reduction. In this work, we show that for a given test the minimum test application time is achieved when the total energy is dissipated evenly at the rate of the maximum allowable power for the device under test. This result, the test time theorem, leads to two alternatives for reducing test time. In the first alternative, we scale the supply voltage down to reduce power, which in turn allows us to increase the clock frequency, of course within the limit imposed by the critical path. Thus, optimum voltage and frequency can be found to minimize the test time of a fixed frequency synchronous test. In the other alternative, which also benefits from the reduced voltage, the clock period is dynamically varied so that each cycle dissipates the maximum allowable power. This test, termed aperiodic clock test, according to the theorem achieves the lower bound on test time. An illustrative example of an ISCAS'89 benchmark circuit shows a test time reductionof 71 %.

Coupling of a Lumped Parameter and a Finite Difference Model for Estimation of a Reactivity-Induced Transient in a PWR with Annular Fuel Rods

This paper develops a finite difference and a semianalytical model to evaluate the thermal behavior of fuel rods during a hypothetical reactivity-induced transient (absorber rod ejection) in a pressurized water reactor (PWR). The calculations are carried out for two different reactor core designs, namely, for a typical PWR core with typical fuel rods and for a modified PWR core containing annular fuel rods. The overall dimensions of the core internals and fuel assemblies are unchanged, and the total number of fuel assemblies is the same in both designs. The finite difference code was verified on the results provided by the semianalytical model. In the calculations, two point models were used (neutron kinetics to compute the fission power of the reactor; power balance of coolant in the active core region). The point models were coupled to the one-dimensional, finite difference heat conductivity model to calculate the radial temperature profile in the solid and the annular cylindrical pellets (UO2). The latter are the constituent part of annular fuel rods cooled both on their external and internal surfaces. The fuel, cladding, and fluid temperatures were evaluated for the annular and the solid fuel design in the hot spot, where the maximum allowable power rating of rods is 2.5 times higher than the average one. It was assumed that before the transient, (a) the reactor with annular fuel runs continuously at higher nominal power (150%) and at higher nominal coolant flow rate (150%) at the core inlet than the reference reactor with solid fuel (100%) and (b) the modified and the reference reactors have the same coolant temperature at the core inlet and the same temperature rise of coolant along their core. These conditions correspond to a 150% power uprate of the reference reactor. The coupled models require limited computational resources only. The calculated results showed that during the transient, in the annular fuel pellet, the temperatures peaked at considerably lower values, even at 150% power, than in the solid pellets at 100% power. These evaluations show that in the case of the reactivity-induced transient analyzed, the annular fuel cooled from both sides has a better safety performance than the solid fuel cooled only on its external surface.

Temperature elevation profile inside the rat brain induced by a laser beam

The thermal effect may be a desired outcome or a concerning side effect in laser-tissue interactions. Research in this area is particularly motivated by recent advances in laser applications in diagnosis and treatment of neurological disorders. Temperature as a side effect also limits the maximum power of optical transfer and harvesting of energy in implantable neural prostheses. The main objective was to investigate the thermal effect of a near-infrared laser beam directly aimed at the brain cortex. A small, custom-made thermal probe was inserted into the rat brain to make direct measurements of temperature elevations induced by a free-air circular laser beam. The time dependence and the spatial distribution of the temperature increases were studied and the maximum allowable optical power was determined to be 2.27 W/cm2 for a corresponding temperature increase of 0.5°C near the cortical surface. The results can be extrapolated for other temperature elevations, where the margin to reach potentially damaging temperatures is more relaxed, by taking advantage of linearity. It is concluded that the thermal effect depends on several factors such as the thermal properties of the neural tissue and of its surrounding structures, the optical properties of the particular neural tissue, and the laser beam size and shape. Because so many parameters play a role, the thermal effect should be investigated for each specific application separately using realistic in vivo models.

Distributed power control for multiuser cognitive radio networks with quality of service and interference temperature constraints

AbstractOne of the most challenging problems in dynamic resource allocation for cognitive radio networks is to adjust transmission power of secondary users (SUs) while quality of service needs of both SUs and primary users (PUs) are guaranteed. Most power control algorithms only consider interference temperature constraint in single user scenario while ignoring the interference from PUs to SUs and minimum signal to interference plus noise ratio (SINR) requirement of SUs. In this paper, a distributed power control algorithm without user cooperation is proposed for multiuser underlay CNRs. Specifically, we focus on maximizing total throughput of SUs subject to both maximum allowable transmission power constraint and SINR constraint, as well as interference temperature constraint. To reduce the burden of information exchange and computational complexity, an average interference constraint is proposed. Parameter range and convergence analysis are given for feasible solutions. The resource allocation is transformed into a convex optimization problem, which is solved by using Lagrange dual method. In computer simulations, the effectiveness of our proposed scheme is shown by comparing with distributed constrained power control algorithm and Nash bargaining power control game algorithm. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Development of a micro-cogeneration laboratory and testing of a natural gas CHP unit based on PEM fuel cells

This work discusses the design and the development of a Laboratory of Micro-Cogeneration (LMC) at Politecnico di Milano. The LMC laboratory is a unique structure devoted to small-scale power generation, with the main goals of testing and improving the performance of systems that produce or utilize electric and thermal (hot and/or cold) power in a very general sense, spanning from combined heat and power (CHP) units to heaters, from absorption chillers to heat pumps, but also able to perform tests on fuel processors and electrolyzers. The laboratory features a supply of natural gas as well as H2 and O2 from a high pressure electrolyzer and of CO, CO2 and N2 from bottles, permitting to carry out experiments with simulated synthesis fuels. The maximum allowable electrical power produced, exported to the grid or to an electronic loadbank, or consumed by the system under test is 100 kW; maximum allowable thermal power is roughly 200 kW with variable temperature water circuits (from chilled water up to a 150 °C at 8 bar superheated water loop). This work outlines also the instruments used for on-line recording of thermodynamic properties, emissions and power, aiming at monitoring and reconstructing mass and energy balances.One of the first experimental campaign has been carried out on a CHP system based on polymer electrolyte membrane fuel cells (PEM), a promising candidate for distributed CHP thanks to low pollutant emissions and good efficiency, rapid startup and flexibility, although affected by a rather complex fuel processing section to provide the appropriate fuel to the PEM. This work presents the experimental analysis of a 20 kW prototype PEM CHP system complete of natural gas processor. The prototype is operated at LMC to characterize the processing section and the thermodynamic performances of the overall system. Despite its non-optimized layout, the unit has shown encouraging total efficiency (76%) and primary energy saving index (6%).

질소희석량 조절에 따른 터빈 운전조건 변화를 고려한 IGCC 용 가스터빈의 성능분석

IGCC 가스터빈과 공기분리기와의 결합이 중요한데 공기분리기로 공급되는 공기를 가스터빈에서 추출하는 정도와 공기분리기에 남는 질소를 연소기로 공급하는 정도가 중요한 운전 파라미터이다. 이러한 파라미터들이 가스터빈의 성능과 운전성에 미치는 영향은 설계조건인 ISO 조건뿐만 아니라 다양한 외기조건에 대해서도 고려되어야 한다. 본 연구에서는 여러 외기조건에서 터빈 블레이드 온도와 생산가능한 출력의 한계를 만족하도록 하는 질소희석량과 터빈입구온도를 예측하였다. 공기 결합도는 0 으로 두었다. 해석결과 질소공급량이 많을수록 출력은 높아지고 블레이드 온도는 낮아졌다. 상온 근처의 특정온도 이하의 외기 조건에서는 가스터빈이 낼 수 있는 최대 출력을 얻을 수 있으나 그 이상에서는 최대 출력을 생산하지 못함을 확인하였다.

13.56 MHz 무선 에너지 전송 시스템의 효율적인 전자파 장해(EMI) 예측 및 분석 방법

The effective way of estimation and analysis of EMI(Electromagnetic Interference) in Wireless Power Transfer System operating at 13.56 MHz is proposed. In this paper methodology of driving magnetic field strength and electric loop current of two antennas which are in free space and on PEC plane using image theory and duality is proposed. Perfect electric conductor(PEC) is planar, infinite in extent, and perfectly conducting plane. And we will refer it as PEC plane. A equivalent circuit model is used to analyze. Using this theoretical analysis, we can derive maximum magnetic field strength of the far-field region numerically using measured data of near-field maximum magnetic field strength. The experimental results using commercial numerical simulation tool are in agreement with the theoretical results. Also, using the derivation of maximum magnetic field strength in the far-field region, we can easily estimate the maximum allowable power dissipation that meets EMI regulations.

고출력 LED 패키지에서 칩 배열에 따른 정션온도 변화

It is extremely important that the junction temperature of a high-power, multi-chip LED package be managed so as not to exceed the allowable temperature range (‒40-100 °C) due to the large heat dissipated from the package. In this study, chip configuration was modified in a 4-chip LED package, and the number of chips was changed to 12-chip and 16-chip packages to investigate their effects on the thermal characteristics of the packages. Thermal resistance was estimated using thermal transient analysis, and the ambient temperature of the package was measured by thermo-couple. Ultimately, the junction temperatures of the packages were obtained using these data. The results showed that the maximum allowable input power of the 4-chip package was 3.4 W, which was enlarged up to 5.5 W using 12-chip and 16-chip LED packages. †(Received July 10, 2012)

The parameter sensibility analysis for fishing box tap based on the overall process of elastoplasticity in oil and gas wells

In view that the selections of box tap and thread making parameters are still groundless and lack scientific evidence, which has caused many practical engineering problems, such as long fishing cycle and low success rate, this study establishes a mathematical model such that fish is fished by the box tap based on the theory of large deformation and principle of virtual work. The analysis and evaluation methods of the whole elastoplasticity process for tapping and fishing are proposed as well in accordance with Johnson and Cook’s experimental model and separation criterion in our study. In addition, the effects of such factors (drilling pressure, rotation speed, box tap strength, taper and pitch) on the thread making capacity of the box tap and the new thread strength of fish have been systemically analyzed. In the case study, the paper derives the safety rotation speed range of tapping, the optimal box tap tape and parameter combination of fishing, and the maximum allowable lifting power. The results obtained in our study show that the analyzing model and evaluation methods are quite reasonable and can be generally applied, which will be of great significance for the enhancement of fishing efficiency in future industry.

Spectrum Sharing with Distributed Relay Selection and Clustering

We consider a spectrum-sharing network where n secondary relays are used to increase secondary rate and also mitigate interference on the primary by reducing the required overall secondary emitted power. We propose a distributed relay selection and clustering framework, obtain closed-form expressions for the secondary rate, and show that secondary rate increases proportionally to log n. Remarkably, this is on the same order as the growth rate obtained in the absence of a primary system and its imposed constraints. Our results show that to maximize the rate, the secondary relays must transmit with power proportional to n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> (thus the sum of relay powers is bounded) and also that the secondary source may not operate at its maximum allowable power. The tradeoff between the secondary rate and the interference on the primary is also characterized, showing that the primary interference can be reduced asymptotically to zero as n increases, while still maintaining a secondary rate that grows proportionally to log n. Finally, to address the rate loss due to half-duplex relaying in the secondary, we propose an alternating relay protocol and investigate its performance.

Delta-sigma-based transmitters: Advantages and disadvantages

Power efficiency is one of the most important parameters in designing communication systems, especially battery operated mobile terminals. In a typical transceiver, most of the power is dissipated in the power amplifier (PA) and consequently, it is very important to obtain the maximum efficiency from the PA. A PA operating in Class AB or B is at its maximum efficiency when it is driven by its maximum allowable input power [1]. In practice, the input signal of the PA usually has a varying envelope, and to avoid distortion the PA should not be driven to more than its maximum input saturating power. Unfortunately, this peak power of the input signal happens at very short periods, and most of the time the signal power is around its average power, which is much smaller than its peak power, meaning that, often, the PA works at much lower efficiencies than its maximum efficiency. The power difference is defined as the peak to average power ratio (PAPR) of the signal. For example, for a signal with 12 dB PAPR, a Class B PA would be driven with 12 dB power back-off from its peak input power, and at this power back-off, the efficiency of the PA will degrade from 78.5% to around 20% [1]. Unfortunately, by moving to high throughput modulation schemes, for example, quadrature amplitude modulations (QAMs) such as 16-QAM and 64-QAM mean that more envelope variation is needed to encode the information, and, consequently, lower efficiency is achieved.

Hybrid link adaptation for inter-carrier interference adjustment in orthogonal frequency division multiple access cellular uplink systems

In the uplink of orthogonal frequency division multiple access (OFDMA) systems, rate adaptation may not be exploitable mainly because of severe inter-carrier interference (ICI). In this study, the authors propose a novel hybrid link adaptation that simultaneously uses power adaptation for ICI adjustment and rate adaptation for capacity improvement in the uplink of OFDMA systems. The proposed hybrid link adaptation determines a maximum allowable transmission power according to the channel gain and velocity of each user, enabling all users to have a guaranteed loss of carrier to interference ratio (CIR). Moreover, the proposed hybrid link adaptation adjusts the transmission rate according to CIR of each user, while keeping the maximum allowable transmission power unchanged. The performance of the proposed hybrid link adaptation is analysed in OFDMA cellular uplink systems. Finally, the analytic results are verified by computer simulation.

WWER core pattern enhancement using adaptive improved harmony search

The efficient operation and fuel management of PWRs are of utmost importance. Core performance analysis constitutes an essential phase in core fuel management optimization. Finding an optimum core arrangement for loading of fuel assemblies, FAs, in a nuclear core is a complex problem. In this paper, application of classical harmony search (HS) and adaptive improved harmony search (IHS) in loading pattern (LP) design, for pressurized water reactors, is described. In this analysis, finding the best core pattern, which attains maximum multiplication factor, keff, by considering maximum allowable power picking factors (PPF) is the main objective. Therefore a HS based, LP optimization code is prepared and CITATION code which is a neutronic calculation code, applied to obtain effective multiplication factor, neutron fluxes and power density in desired cores. Using adaptive improved harmony search and neutronic code, generated LP optimization code, could be applicable for PWRs core with many numbers of FAs. In this work, at first step, HS and IHS efficiencies are compared with some other heuristic algorithms in Shekel's Foxholes problem and capability of the adaptive improved harmony search is demonstrated. Results show, efficient application of IHS. At second step, two WWER cases are studied and then IHS proffered improved core patterns with regard to mentioned objective functions.

Numerical assessment of the performance of a scalp‐implantable antenna: Effects of head anatomy and dielectric parameters

We numerically assess the effects of head properties (anatomy and dielectric parameters) on the performance of a scalp-implantable antenna for telemetry in the Medical Implant Communications Service band (402.0-405.0 MHz). Safety issues and performance (resonance, radiation) are analyzed for an experimentally validated implantable antenna (volume of 203.6 mm(3) ), considering five head models (3- and 5-layer spherical, 6-, 10-, and 13-tissue anatomical) and seven scenarios (variations ± 20% in the reference permittivity and conductivity values). Simulations are carried out at 403.5 MHz using the finite-difference time-domain method. Anatomy of the head model around the implantation site is found to mainly affect antenna performance, whereas overall tissue anatomy and dielectric parameters are less significant. Compared to the reference dielectric parameter scenario within the 3-layer spherical head, maximum variations of -19.9%, +3.7%, -55.1%, and -39.2% are computed in the maximum allowable net input power imposed by the IEEE Std C95.1-1999 and Std C95.1-2005 safety guidelines, return loss, and maximum far-field gain, respectively. Compliance with the recent IEEE Std C95.1-2005 is found to be almost insensitive to head properties, in contrast with IEEE Std C95.1-1999. Taking tissue property uncertainties into account is highlighted as crucial for implantable antenna design and performance assessment. Bioelectromagnetics 34:167-179, 2013. © 2012 Wiley Periodicals, Inc.

Distributed power control over multiple channels for ad hoc wireless networks

In this paper, we investigate the deficiency of uncontrolled asymmetrical transmission power over multiple channels in ad hoc environments. We further propose a novel distributed transmission power control protocol called the distributed power level DPL protocol for multi-channel ad hoc networks without requiring clock synchronization. Specifically, different transmission power levels are assigned to different channels, and nodes search for an idle channel on the basis of the received power so that the maximum allowable power of the preferred data channel is larger than or equal to the received power. If the most preferred channel of the least maximum power is busy, the nodes are able to select the next channel and so forth. As a result, interference is reduced over channels because the nodes that require higher transmission power are separated from interfering with the nodes that require lower transmission power. Two transmission power control modes are introduced for DPL: symmetrical and asymmetrical. For the symmetrical DPL protocol mode, nodes transmit at the same power level assigned to the selected channel. On the other hand, for the asymmetrical DPL protocol, nodes are allowed to transmit at a lower or equal power level that is assigned to the selected channel. Extensive ns-2-based simulation results are presented to demonstrate that the proposed protocols can enhance the network throughput compared with the existing uncontrolled asymmetrical transmission power protocol. Copyright © 2012 John Wiley & Sons, Ltd.