Maximum Allowable Power Research Articles

A Novel MAC Scheme for Multichannel Cognitive Radio Ad Hoc Networks

This paper proposes a novel medium access control (MAC) scheme for multichannel cognitive radio (CR) ad hoc networks, which achieves high throughput of CR system while protecting primary users (PUs) effectively. In designing the MAC scheme, we consider that the PU signal may cover only a part of the network and the nodes can have the different sensing result for the same PU even on the same channel. By allowing the nodes to use the channel on which the PU exists as long as their transmissions do not disturb the PU, the proposed MAC scheme fully utilizes the spectrum access opportunity. To mitigate the hidden PU problem inherent to multichannel CR networks where the PU signal is detectable only to some nodes, the proposed MAC scheme adjusts the sensing priorities of channels at each node with the PU detection information of other nodes and also limits the transmission power of a CR node to the maximum allowable power for guaranteeing the quality of service requirement of PU. The performance of the proposed MAC scheme is evaluated by using simulation. The simulation results show that the CR system with the proposed MAC accomplishes good performance in throughput and packet delay, while protecting PUs properly.

Highly linear transmission and EVM improvement of vector modulation signals for radio-over-f iber applications

The principle of error vector magnitude (EVM) against modulator nonlinearity for vector modulation signal (VMS) transmission in radio-over-fiber (RoF) systems is theoretically and experimentally investigated. A highly linear modulation scheme is proposed and demonstrated using a single-drive dual parallel Mach–Zehnder modulator (MZM). This method improves EVM performance and enlarges the linear input dynamic range of the VMS transmission. An index of maximum allowable input power difference (MAIPD) that reflects the difference of upper input power limits between these two schemes is measured. An EVM limitation of 5% MAIPD has 5 dB. Both 16- and 64-QAM results indicate that the proposed scheme supports VMS transmission better than the MZM one.

Joint mitigation of laser phase noise and fiber nonlinearity for polarization-multiplexed QPSK and 16-QAM coherent transmission systems

We propose the use of pilot-aided (PA) transmission, enabled by single-sideband-subcarrier modulation of both quadratures in the DSP-domain, in single-carrier systems to mitigate jointly laser phase noise and fiber nonlinearity. In addition to tolerance against laser phase noise, we show that the proposed scheme also improves the nonlinear tolerance of both polarization-division-multiplexed (PDM) QPSK and 16-QAM coherent transmission systems by increasing the maximum allowable launch power by 1 dB and 1.5 dB, respectively. The improved nonlinear performance of both systems also manifests itself as an increase in the maximum reach by 720 km and 480 km, respectively. Finally, when digital-to-analog converters (DACs) with lower bit resolutions are used at the transmitter, PA transmission is shown to preserve the same performance improvement over the non-PA case.

Numerical Thermal Analysis of a Wireless Cortical Implant with Two-Body Packaging

This article presents the numerical analysis of temperature elevation in the head due to the operation of a wireless cortical implant. The thermal analyses are done by using a finite-difference time-domain simulation tool and a high-resolution 3-D head phantom with 22 different tissues. The effects of the power dissipation level, size, location, and packaging of the implant on the temperature distribution in the head are investigated by using a generic silicon chip. Furthermore, the distribution of the power consumption in the implant by using multiple integrated circuits is discussed. In order not to exceed the safety precaution limit of 1°C, maximum allowable power dissipation in a chip of size 2 × 2 × 0.5 mm3 is found to be 5.3 mW, whereas it is 9.3 mW for an implant with two chips of the same size separated by 10 mm. Additionally, the thermal analysis of a wireless cortical implant is also done by using a two-body cortical implant prototype. Maximum allowable power consumption for the two-body implant is found as 35 mW, whereas the unibody implant can only dissipate 17.5 mW without exceeding the safety precaution limit. By using the two-body implant, the maximum allowable power consumption in the implant can be increased or the temperature elevation in the tissues can be decreased.

Synthesizing Low Autocorrelation and Low PAPR OFDM Sequences Under Spectral Constraints Through Convex Optimization and GS Algorithm

Sequences with low autocorrelation (AC) and low peak to average power ratio (PAPR) are desired in many communication or signal processing applications. This work investigates the synthesis of OFDM sequences with the desired low AC and low PAPR under spectral constraints. The spectral constraints limit the maximum allowable power on each subcarrier to avoid interference on particular reserved bands and undesirable DC-offset. The first part of this work discusses the design of sequences with periodic AC property under spectral constraints. Specifically, we present a convex optimization method for synthesizing OFDM sequences with minimized peak sidelobe level (PSL) or weighted sum of sidelobe levels (WSSL) of the periodic AC function within specified time lags. The design objective to be minimized can also be a certain convex function of the sequence AC sidelobes. Furthermore, we present methods based on Gerchberg-Saxton (GS) algorithm to decrease the PAPR of the sequences, while maintaining the optimized AC characteristic. The second part of this work investigates the aperiodic AC under spectral constraints. In this case, the optimal sequence design problem is nonconvex. By relaxing the nonconvex problem to a convex problem, we provide lower bounds for PSL and WSSL of the aperiodic AC function. Based on the optimal solution for the relaxed convex problem, we present an efficient algorithm to find sequences with low PAPR and near-optimal aperiodic AC property while the spectral constraints are satisfied.

Solving Multi-Objective Voltage Stability Constrained Power Transfer Capability Problem using Evolutionary Computation

Competitive market forces and the ever-growing load demand are two of the key issues that cause power systems to operate closer to their system stability boundaries. Open access has since introduced competition and therefore promotes inter-regional electrical power trades. However, the economic flows of electrical energy between interconnected regions are usually constrained by system physical limits, e.g. transmission lines capacity and generation active/reactive power capability etc. As such, there is a limitation to the capacity of electrical power that regions can export or import. This maximum allowable electrical power transfer is normally referred to as Total Transfer Capability (TTC). It is critical to understand that TTC does not necessarily represent a safe and reliable amount of inter-regional power transfer as one or more operational limits are usually binding when quantifying TTC. Hence, it is of interest that power system stability issues are being considered during power transfer capability assessment in order to provide a more appropriate and secure power transfer level.The aim of this paper is to formulate an Optimal Power Flow (OPF) algorithm, which is capable of evaluating inter-area power transfer capability considering mathematically-complex voltage collapse margins. Through a multi-objective optimization setup, the proposed OPF-based approach can reveal the nonlinear relationships, i.e. the pareto-optimal front, between transfer capability and voltage stability margins. The feasibility of this approach has been intensively tested on a 3-machine 9-bus and the IEEE 118-bus systems.

Efficient Two-Stage Discrete Bit-Loading Algorithms for OFDM Systems

Aiming at minimizing the transmit power of orthogonal frequency-division multiplexing (OFDM) systems subject to the target data rate, the target bit error rate (BER), the maximum allowable power per subcarrier, and the maximum allowable size of constellations, we present a couple of new discrete bit-loading algorithms, named efficient bit filling (EBF) and efficient bit removal (EBR), which are based on our new idea of group-by-group bit filling. Both EBF and EBR perform bit loading in two stages and are able to converge to the optimal bit-allocation profile. In the first stage, an intermediate bit-allocation profile, which is tightly close to the final bit-allocation profile, is obtained by using our proposed group-by-group bit filling (for EBF) or group-by-group bit removal (for EBR). In the second stage, the well-known greedy bit filling (for EBF) or greedy bit removal (for EBR) is performed for the remaining bits (usually of a small size). Analytical and numerical results reveal that the proposed algorithms converge to the optimal bit allocation with much lower computational complexities than existing optimal algorithms. It is also shown that the proposed algorithms outperform typical suboptimal algorithms in power efficiency with relatively higher computational complexities.

Evaluation of Effects on Power System by Installing the Static Var Compensator

This paper provides the methods for enhancing the stability with normal or emergency operating conditions in real power systems and copes with the unbalance of demand of reactive power due to the loss of facility, such as 765kV transmission line. In this paper, we focused on the maximum allowable transmission power(hereafter, MAXTP) in the metropolitan area. In order to increase the MAXTP, the application of reactive power compensators, SVC, and Shunt compensator and reactor, is analyzed as an enhancing method of stability and MAXTP. Particularly, the f-V analysis was performed for the postulated contingency, in order to evaluate the effects on SVC. Conclusively, the stability of power systems could be enhanced and the MAXTP is increased effectively with Dongseoul SVC which has the capacity 200MVAr.

MAC Protocol for Opportunistic Cognitive Radio Networks with Soft Guarantees

Cognitive radio (CR) is the key enabling technology for an efficient dynamic spectrum access. It aims at exploiting an underutilized licensed spectrum by enabling opportunistic communications for unlicensed users. In this work, we first develop a distributed cognitive radio MAC (COMAC) protocol that enables unlicensed users to dynamically utilize the spectrum while limiting the interference on primary (PR) users. The main novelty in COMAC lies in not assuming a predefined CR-to-PR power mask and not requiring active coordination with PR users. COMAC provides a statistical performance guarantee for PR users by limiting the fraction of the time during which the PR users' reception is negatively affected by CR transmissions. To provide such a guarantee, we develop probabilistic models for the PR-to-PR and the PR-to-CR interference under a Rayleigh fading channel model. From these models, we derive closed-form expressions for the mean and variance of interference. Empirical results show that the distribution of the interference is approximately lognormal. Based on the developed interference models, we derive a closed-form expression for the maximum allowable power for a CR transmission. We extend the min-hop routing to exploit the available channel information for improving the perceived throughput. Our simulation results indicate that COMAC satisfies its target soft guarantees under different traffic loads and arbitrary user deployment scenarios. Results also show that exploiting the available channel information for the routing decisions can improve the end-to-end throughput of the CR network (CRN).

Determining the Maximum Allowable Power Bus Voltage to Ensure Compliance With a Given Radiated Emissions Specification

It is generally understood that excessive power bus noise voltage on a printed circuit board will result in unacceptable radiated emissions levels, but how much noise is too much? In this paper, an analysis based on a lossy cavity model is performed to determine the maximum possible radiated field corresponding to a given power bus noise voltage. A closed-form expression relating the maximum power bus noise voltage to the radiation peaks is then derived. This expression is solved in reverse to determine the minimum power bus voltage that is necessary to generate a radiated field above a specified limit. When troubleshooting a radiated emissions problem, this expression can be applied to measured values of power bus noise voltage to determine whether radiation directly from the power bus is potentially the emissions source.

Polarization Dependence of Linear In-Band Crosstalk in Multipoint-to-Point Networks

This letter studies the influence of random polarization on in-band crosstalk caused by residual output power in high split long reach wavelength/time-division-multiplexing passive optical networks. Based on a statistical description of polarization, statistics of network performance are deduced, and it is shown that a significant reduction in requirements for the maximum allowable interburst residual output power is obtained if the bit-error rate (BER) is allowed to fall short of the required BER for a few seconds per annum.

Optimal profile of input contacts of the attenuator plate on the basis of distributed resistive structures

Calculations and experimental results prove that the greatest values of the potential gradients and dissipated power are observed in the neighborhood of the input contact which reduces the level of the maximum allowable dissipated power. Below the methodology is suggested which allows determining the optimal profile of the input contacts and providing greater than double increase in the power dissipated by the plate.

Energy Consumption in Digital Optical ICs With Plasmon Waveguide Interconnects

Limits on energy consumption in digital optical integrated circuits (ICs) using conventional and plasmon waveguide interconnects are presented. The maximum allowable on-chip power density imposes a lower limit on the spacing between devices and together with clock skew imposes an upper limit on the clock frequency. Optical ICs with low-loss plasmon waveguide interconnects may become viable if plasmon waveguide losses in the range 0.1-0.01 dB/m can be achieved.

Limits on Fixed Broadband Devices for Interference-Free Operation in the DTV Spectrum

This paper examines the limits that must be imposed on single and multiple fixed cognitive broadband devices (BDs) transmitting simultaneously on multiple unused TV channels in order to avoid interference with the reception of licensed TV channels. Single and multiple fixed BDs are assumed to radiate 4W peak power relative to an isotropic source and transmit within 10 meters of the nearest digital television (DTV) set antenna. The power and separation limits are shown to depend on whether BDs are licensed, on whether mandated minimum front-end performance specifications for DTV sets are in place, and on the definition of an ldquounused channel.rdquo Short and long-term general conclusions are drawn regarding the maximum allowable directional power and regarding taboo channels for interference-free coexistence with DTV sets. It is shown that unlicensed BDs would result in the least efficient use of the available DTV spectrum because the ldquoworst caserdquo interference limits must be imposed in an unlicensed environment. The most efficient utilization of the DTV spectrum would be achieved if BDs were licensed and then allowed to migrate, together with DTV channels, into two blocks of contiguous channels, one for DTV and one for BDs.

Optimization of X-ray target parameters for a high-brightness microfocus X-ray tube

Parameters of a transmission-type X-ray target have been optimized for a microfocus X-ray tube with an emphasis on maximizing the intensity of X-rays generated from the target while reducing the X-ray focal spot size. Monte Carlo simulation code MCNPX was used for the calculation of X-ray intensity generated from the X-ray tube. The calculation shows that the target thickness plays a dominant role in the enhancement of X-ray intensity. The optimum thickness to get maximum X-ray intensity for a given beam current was derived from the calculation for a broad range of electron energies from 30 keV to 150 keV. In addition, stability of a transmission-type target against localized thermal loading, which is attributed to the electron beam impinging on a micron-sized target region, was also investigated by the calculation of the temperature distribution within the target. From the analysis, we present the maximum allowable electron-beam power loading for a stable operation of the transmission-type target at different incident electron beam energies.

Enhancement of the rf characteristics of a soda dummy load by reduction of the skin depth effect

A new soda water dummy load is developed by considering the skin depth effect. Compared with the conventional soda dummy load where the resistive medium is filled both in the inner and outer cylinder, the soda water only exists on the annular volume so as to reduce the skin depth effect at the new design. The length of the soda water column is 97 cm and the input port size of the rf power is 9(3/16) in. The maximum allowable rf power is about 1 MW at the flow rate of 50 m 3/h. In addition, the mechanical effort is also added for sealing the soda water at the top region of dummy load due to the water pressure imbalance on the sealing region. The water pressure distribution of the top region for the conventional and new one are calculated by the commercial software for the fluid dynamics named CFX and a bar type supporter made by a high purity alumina (96%) fix the water leak problem. The cold rf-test using the network analyzer shows that the VSWR is less than 1.15 up to 200 MHz for the new one whereas the VSWR for the conventional one is as high as 1.3 around 200 MHz. The VSWR is less than 1.35 for the temperature variations of the soda water from 35 °C to 45 °C.

Static design of a liquid-salt-cooled pebble bed reactor (LSPBR)

A renewed interest has been raised for liquid-salt-cooled nuclear reactors. The excellent heat transfer properties of liquid-salt coolants provide several benefits, like lower fuel temperatures, higher average coolant temperature, increased core power density and better decay heat removal, and thus higher achievable core power. In order to benefit from the on-line refueling capability of a pebble bed reactor, the liquid salt pebble bed reactor (LSPBR) is proposed. This is a high temperature pebble bed reactor with a fuel design similar to existing HTRs, but using a liquid-salt as coolant. In this paper, the selection criteria for the liquid-salt coolant are described. Based on its neutronic properties, LiF–BeF 2 (flibe) was selected for the LSPBR. Two designs of the LSPBR were considered: a cylindrical core and an annular core with a graphite inner reflector. Coupled neutronic thermal-hydraulic calculations were performed to obtain the steady state power distribution and the corresponding fuel temperature distribution. Calculations were performed to investigate the decay heat removal capability in a protected loss-of-forced cooling accident. The maximum allowable power that can be produced with the LSPBR is hereby determined.

Power dissipation sources and possible control techniques in ultra deep submicron CMOS technologies

As technology scales down into the ultra deep-submicron (UDSM) region, the static power dissipations grow exponentially and become an increasingly dominant component of the total power dissipation in CMOS circuits. With increase in gate leakage current resulting from thinner gate oxides in UDSM and the problems associated with short channel effects, leakage power dissipation is becoming a huge factor challenging a continuous success of CMOS technology in the semiconductor industry. With strict limitations of maximum allowable power (the power being limited more by system level cooling and test constraints than packaging) of 2.8W (in 2005) to 3W (in 2020) for battery (low cost/handheld) operated devices as projected by the International Technology Roadmap for Semiconductors (ITRS) 2005, innovations in leakage control and management are urgently needed. This paper presents an overview of the sources of the power dissipation mechanisms in the UDSM technologies, and the device and circuit techniques to control them.

Power levels and packet lengths in random multiple access with multiple-packet reception capability

This paper extends our earlier results. We assume that the receiver has the capability of capturing multiple packets so long as the signal-to-interference-plus-noise ratio (SINR) of each packet is above a designed threshold T throughout its transmission period. We prove that, compared with a multiple-power-level system, the single-power-level system in which all nodes transmit at the maximum allowable power level achieves optimal throughput, under a condition that T exceeds the value 3.33. Given a minimum throughput requirement, under the same condition on T, the single-power-level system also achieves the maximum average packet capture probability as well as the optimum energy usage efficiency. If the multiple-power-level systems are constrained such that higher power levels always have shorter packet lengths, then the above results hold for T greater than 2.

Automation of clock distribution network design for digital integrated circuits using divide and conquer technique

One of the most carefully engineered components of a digital integrated circuit is the clock distribution network. A clock is unarguably the most important signal and the network used for its distribution contributes to nearly half of the entire power dissipated by the IC. The design of a clock distribution network requires tremendous resources in terms of time and effort to achieve optimized results. This paper discusses the development of a new algorithm with smaller time complexity for automation of the design of clock distribution network that can greatly reduce the time and effort required, at the same time meeting the conditions set for delays and maximum allowable power dissipation.