无线微传感器中英文对照外文翻译文献.docx

1、无线微传感器中英文对照外文翻译文献无线微传感器中英文对照外文翻译文献(文档含英文原文和中文翻译)A Simple Energy Model for Wireless Microsensor TransceiversAbstract This paper describes the modelling of shortrange transceivers for microsensor applications. A simple energy model is derived and used to analyze the transceiver battery life. This mode

2、l takes into account energy dissipation during the start-up, receive, and transmit modes. It shows that there is a significant fixed cost in the transceiver energy consumption and this fixed cost can be driven down by increasing the data rate of the transceiver.I. IntroductionWireless microsensor ne

3、tworks can provide short-range connectivity with significant fault tolerances. These systems find usage in diverse areas such as environmental monitoring, industrial process automation, and field surveillance. As an example, Table I shows a detailed specification for a sensor system used in a factor

4、y machine monitoring environment.The major characteristics of a microsensor system are high sensor density, short range transmissions, and low data rate. Depending on the application, there can also be stringent BER and latency requirements. Due to the large density and the random distributed nature

5、 of these networks, battery replacement is a difficult task. In fact,a primary issue that prevents these networks to be used in many application areas is the short battery life. Therefore, maximizing the battery life time of the sensor nodes is important. Figure 1 shows the peak current consumption

6、limit when a 950mAh battery is used as the energy source. As seen in the figure, battery life can vary by orders of magnitude depending on the duty cycle of each operation. To allow for higher maximum peak current, it is desirable to have the sensor remain in the off-state for as long as possible.Ho

7、wever, the latency requirement of the system dictates how often the sensor needs to be active. For the industrial sensor application described above, the sensor needs to operate every 5ms to satisfy the latency requirement.Assuming that the sensor operates for 100s every 5ms,the duty cycle is 2%. To

8、 achieve a one-year battery life, the peak current consumption must be kept under 5.4mA, which translates to approximately 10mW at 2V supply.This is a difficult target to achieve for sensors that communicate at giga-Hertz carrier frequencies. There has been active research in microsensor networks ov

9、er the past years. Gupta 1 and Grossglauser 2 established information theoretic bounds on the capacity of ad-hoc networks. Chang 3 and Heinzelman 4 suggested algorithms to increase overall network life-time by spreading work loads evenly among all sensors. Much of the work in this area, especially t

10、hose that deal with energy consumption of sensor networks, require an energy model 5. This paper develops a realistic energy model based on the power consumption of a state of the art Bluetoothtransceiver 6. This model provides insights into how to minimize the power consumption of sensor networks a

11、nd can be easily incorporated into work that studies energy limited wireless sensor networks. The outline of this paper is as follows. Section II derives the transceiver model. Section III applies this model to analyzing the battery life time of the Bluetooth transceiver.Section IV investigates the

12、dependencies in the model and shows how to modify the design of the Bluetooth transceiver to improve the battery life. Section V shows the battery life improvement realized by applying the results in Section IV. Section VI summarizes the paper.II. Microsensor Transceiver ModellingThis section derive

13、s a simple energy model for low power microsensors. Figure 2 shows the model of the sensor node.It includes a sensor/DSP unit for data processing, D/A and A/D for digital-to-analog and analog-to-digital conversion, and a wireless transceiver for data communication. The sensor/DSP, D/A, and A/D opera

14、te at low frequency and consume less than 1mW. This is over an order of magnitude less than the power consumption of the transceiver. Therefore, the energy model ignores the contributions from these components. The transceiver has three modes of operation: start-up, receive, and transmit. Each mode

15、will be described and modelled.A. Start-up ModeWhen the transceiver is first turned on, it takes some time for the frequency synthesizer and the VCO to lock to the carrier frequency. The start-up energy can be modelled as follows:where P LO is the power consumption of the synthesizer and the VCO. Th

16、e term t start is the required settling time. RF building blocks including PA, LNA, and mixer have negligible start-up time and therefore can remain in the off-state during the start-up mode. B. Receive Mode The active components of the receiver includes the low noise amplifier (LNA), mixer, frequen

17、cy synthesizer, VCO, intermediate-frequency (IF) amplifier (amp), and demodulator (Demod). The receiver energy consumption can be modelled as follows:where P RX includes the power consumption of the LNA,mixer, IF amplifier, and demodulator. The receiver power consumption is dictated by the carrier f

18、requency and the noise and linearity requirements. Once these parameters are determined, to the first order the power consumption can be approximated as a constant, for data rates up to 10s of Mb/s. In other words, the power consumption is dominated by the RF building blocks that operate at the carr

19、ier frequency. The IF demodulator power varies with data rate, but it can be made small by choosing a low IF.C. Transmit ModeThe transmitter includes the modulator (Mod), frequency synthesizer and VCO (shared with the receiver), and power amplifier (PA). The data modulates the VCO and produces a FSK

20、 signal at the desired data rate and carrier frequency. A simple transmitter energy model is shown in Equation (3). The modulator consumes very little energy and therefore can be neglected.P LO can be approximated as a constant. P PA depends on additional factors and needs to be modelled more carefu

21、lly as follows:where is the PA efficiency, r is the data rate, d is the transmission distance, and n is the path loss exponent. PA is a factor that depends on E b /N O , noise factor F of the receiver, link margin L mar , wavelength of the carrier frequency , and the transmit/receive antenna gains G

22、 T ,G R :From Equations (3) and (4), the transmitter power consumption can be written as a constant term plus a variable term. The energy model thus becomesIII. Bluetooth TransceiverHere we demonstrate how the above model can be used to calculate the battery life time of a Bluetooth transceiver 6. T

23、his is one of the lowest power Bluetooth transceivers reported in literature. The energy consumption of the transceiver depends on how it operates. Assuming a 100-bit packet is received and a 100-bit packet is transmitted every 5ms, Figure 3 showsthe transceiver activity within one cycle of operatio

24、n.The transceiver takes 120s to start up. Operating at 1Mb/s, the receiver takes 100s to receive the packet. The transceiver then switches to the transmit mode and transmits a same-length packet at the same rate. A 10s interval, t switch , between the receive and the transmit mode is allowed to swit

25、ch channel or to absorb any transient behavior. Therefore, the energy dissipated in one cycle of operation is simplyBoth the average power consumption and the duty cycle can be found From Figure 3. Knowing that the transceiver operates at 2V, the life time for a 950mAh battery is calculated to be ap

26、proximately 2-months.IV. Energy OptimizationThe microsensor system described in Section I requires a battery life of one year or better. Although the Bluetooth transceiver described in the last section falls short of this requirement, it serves as a starting point for making improvements. This secti

27、on examines E op in detail and suggests ways to increase the battery life by considering both circuit and system improvements.A. Start-up Energy The start-up energy can be a significant part of the total energy consumption, especially when the transceiver is used to send short packets in burst mode.

28、 For the Bluetooth transceiver, E start accounts for 20% of E op .The start-up energy becomes negligible if the following condition is held true:For the receive/transmit scheme shown in Figure 3, the right hand-side of Equation (8)is evaluated to be approximately 450s. To keep E start an order of ma

29、gnitude below E op , it is desirable to have a start-up time of less than 45s. Cho has demonstrated a 5.8GHz frequency synthesizer im-plementation with a start-up time under 20s 7.B. Power AmplifierThe PA power consumption is given bywhere is the power efficiency and P out is the RF output power. P

30、out can be determined by link-budget analysis. For a Bluetooth transceiver, the required P out is 1mW 8.This enables a maximum transmission distance of 10 meters, which is adequate for microsensor applications. Note that P out is small as compared to P LO . The Bluetooth transceiver discussed in Sec

31、tion II has a maximum RF output power of 1.6mW and a PA power consumption of 10mW, so the efficiency is at 16%. At frequencies around 2GHz, the PA efficiency can vary from 10% 9 to 70% 10 depending on linearity, circuit topology, and technology. Since FSK signal has a constant envelope, nonlinear PA

32、s can be used so that better efficiency can be achieved. As will be shown in the next section, PA efficiency has a significant impact on the battery life.C. Data RateAssuming a packet of length L pkt is transmitted at dat rate r, then the transmit time isThe transmitter energy consumption can be re-written asEquation (12) shows that the contribution of the fixed cost P LO can be reduced by increasing the data rate. The energy per bit, E bit , is defined as E op divided by the total number of bits received and sent during one cycle of ope