Energy-Efficient Technologies for the Dismounted Soldier (1997) / Chapter Skim
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5 Communications, Computers, Displays, and Sensors
5 Communications, Computers, Displays, and Sensors
Pages 65-111
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From page 65... ...
clearly indicate that most of the energy dissipated in the Land Warrior system will be associated with the radios and computers to be carried by soldiers and, therefore, that the electronics associated with communications and computing functions afford the greatest opportunities for energy savings. The challenge for future Land Warrior systems and successor systems will be to reduce electrical energy consumption while increasing performance to meet projected increases in communications bandwidth, data file sizes, and computational performance.
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From page 66... ...
TRENDS IN DESIGNING COMMERCIAL PORTABLE EQUIPMENT Suppliers of portable consumer electronics face conflicting demands of increasing performance while decreasing power drain) in order to provide longer battery life.
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From page 67... ...
arid 5-2 is that, because power drain tends to track complexity, the power requirements of semiconductor products have also increased exponentially. The thousandfold increase in complexity over the past 25 years has driven circuit complexity to the point that power Main has become a major problem facing the electronics industry.
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From page 68... ...
Thus, two major factors besides complexity influence power drain: the operating frequency of the logic and the speed-power characteristics of the semiconductor process.
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From page 69... ...
The frequently unrecognized implication of this trend has been an exponential increase in the inherent energy consumption of very-large-scare integrated (VESI) circuits.
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From page 70... ...
heat dissipation and cooling problems for high-performance chips and systems; and reliability problems associated with elevated operating temperatures of semiconductors. Until recently, the electronics industry has not paid much attention to power drain and its associated problems.
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From page 71... ...
The recent improvements in microprocessors and general purpose programmable DSPs are being driven by a number of design and implementation changes: . First and foremost, power drain is being treated as a key design parameter.
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From page 72... ...
. INTEL PENTIUM SnMlps MOT INTEL LP040 MOT ~ ~ AT&T / INTEL HOBBIT · ARM 700 80386SL / -(i_lPS 3V~33MIPS 3V 25MHz 3V / ~ ~ · - ^ / ARM 600 / 25MIPS 5V ~_ III IA~I ~ MOT SH7032 ~ MPC821 ~_ NEC V810 SLOPE = 1 0 x in 2.5 years MOT ~ MPC821 CPU 1989 1990 1991 1992 1993 1994 Year of introduction FIGURE 5-6 Power drain characteristics of recent microprocessors.
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From page 73... ...
· · ~ · 1 1 · ~ ~ 1 1 · ~ 1 1 · ~1 ~ 1, reduction in logic power Could ideally ne acnlevecl By lowering the Supply voltage from5.0Vto O.9V. In practice, it is difficult to implement high-performance logic functions that operate at I V today, but substantial power drain reductions have been achieved by moving from 5.0 V to 3.3 V for portable computer systems and cellular phones (a factor of 2.3)
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From page 74... ...
Manufacturers of portable equipment, at the product level, are using many of the techniques used by component-level designers, as well as several systemoriented methodologies that significantly reduce power drain. These techniques include: System supply voltages are being lowered, and the operating voltage of major subsystems is being selected to optimize both the energy efficiency and the performance of the element.
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From page 75... ...
The single chip environment readily accommodates the implementation of architectural level changes with the greatest potential impact on power drain. The single chip environment eliminates the large interconnect capacitances associated with multichip systems.
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From page 76... ...
products, such as cellular telephones, camcorders, and portable computing devices. At the component level, the power drains of microprocessors and DSPs have been reduced by a factor of 100 over the past five years, and further improvements of at least a factor of five are anticipated as new low voltage semiconductor processes move into production.
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From page 77... ...
The resulting network would be able to collect and distribute tactical information and thereby increase situational awareness at all levels. Power Objectives The soldier radio will be a small, lightweight, low power voice and data radio that uses standard Army signaling protocol.
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From page 78... ...
Transmitter Energy Consumption Transmitters account for most of the energy consumed by radios. For a radio to be energy efficient, practically all of the energy consumption should occur in the final amplifier stage, and the antenna should be matched to the output to minimize energy losses at the antenna interface.
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From page 79... ...
Only modest improvements in the power requirements of commercial PC-based systems have been made. Power drain has been reduced in some PC-based systems similar to the Land Warrior computer, however, and additional energy savings can be achieved without sacrificing performance.
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From page 80... ...
Synchronous serial I/O 0.2 0.15 0.0 0 0.00 TOTAL 18.4 14.8 1.48 - 8.27 Table 5-2 lists the estimated power requirement for the major computer subsystems. The data reflect a 90 percent duty cycle factor for the computer because the Land Warrior architecture uses the computer as a central processing hub for other elements of the system, including the radio a configuration that precludes the use of conventional power management techniques because the computer must continually monitor the radio for incoming messages.
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From page 81... ...
Two other metrics, energy consumption and physical size, are also becoming important as computers become more mobile. Table 5-3 summarizes the current range of values for these eight metrics for three classes of computer systems: high-performance workstations, laptop computers, and personal digital assistants (PDAs)
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From page 82... ...
millions of bytes 4,000 400 millions of pixels 1 millions of 100 bits/second meters 1/kW flog x m 0.307 0.115 10 0.0338 100 10,000 125 1,000 200 6,000 boundaries of various attributes can be considered to be increasing with time as depicted in Figure 5- ~ 3, where each metric is plotted on a logarithmic scale. Technological advances have created three successive computer classes with each succeeding class exhibiting functionalities identical to its predecessor.
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From page 83... ...
General-purpose computing architectures achieve their general-purpose attributes at the expense of system complexity and energy consumption. Appendix E describes the evolution of wearable speech-operated computers from generalpurpose laptop computers.
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From page 84... ...
Although microprocessors targeted for PC applications show little improvement in energy consumption, processors designed for embedded systems, such as the ARM_ processor (see Figure 5-6) , are continuing to reduce the power drain per MTPS.
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From page 85... ...
Computing System Partitioning for Low Power The multimedia terminal will be connected through a wireless link to the squad leader. This arrangement minimizes power requirements at the system level by partitioning computational tasks among the portable soldier terminal and other remote computing resources on the network.
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From page 86... ...
The multimedia terminal project confirms that the power requirements of the Land Warrior system could be reduced by moving away from a design concept based on generaT-purpose computing and toward a concept based on customized embedded subsystems. User Interfaces The user's interface to the computer greatly affects energy consumption.
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From page 87... ...
87 Human interface design is one of the most challenging problems facing Land Warrior designers. As computing devices move from the desktop to more mobile environments, many conventions of human interfacing developed primarily for office environments must be re-evaluated for effectiveness.
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From page 88... ...
For example, the keyboard with an alphanumeric display using textual information is representative of time-sharing systems of the early 1970s. The keyboard and mouse, graphical output, and iconic desktop are representative of personal computers of the early 198Os.
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From page 89... ...
lit is clear from Table 5-6 that user interface technology influences energy consumption. Although the size, weight, and volume of electronics watt continue to shrink, mechanical interface devices have a minimum "footprint." These devices will have to be oversized for ease of use for soldiers wearing gloves or other TABLE 5-6 Computational Requirements to Support Various User Interfaces Interface Type Required Performance (MIPS)
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From page 90... ...
Desired features include minimal energy consumption, high quality images for night operations, and situational awareness. Optimal situational awareness requires: wide field of view from imager (e.g., 60 degree field of view, which requires a minimum resolution of 2,048 x 2,048 pixels for a 20 mrn display [Crawford, 19961)
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From page 91... ...
The head-up display and the weapon-mounted display, on the other hand, are expected to be in use at least 50 percent of the mission duration in many scenarios. Therefore, the need to reduce energy consumption in the near term is more urgent.
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From page 92... ...
Until recently, this would have been a major problem, but the losses associated with DC-DC power conversion can be minimized through clever circuit designs (Chandrakasan et al., 1994~. Thus, the combination of AMEL display technology and high-efficiency DC-DC converters have reduced the energy consumption from 1.4 Wh to a respectable 0.32 Wh of energy dissipation in the nighttime display and 0.20 Wh in the daytime display.
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From page 93... ...
With an anticipated duty cycle of 5 percent or less, the handheld display can readily achieve reductions in energy consumption through the addition of power management circuitry. Careful design of the interface and drive electronics should also significantly reduce the drain on the batteries.
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From page 94... ...
In fact, one would expect the power requirements for a virtual retinal display to be dominated by its drive electronics and the scanning mechanism. The former could be minimized through the application of standard ULPE design and power management techniques, and the latter could be accomplished either by acousto-optic deflection of the optical output or by using microelectromechanical parts, whichever proves to be more reliable and efficient.
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From page 95... ...
Currently, many of these modules require excessive amounts of power, as cart be seen in Table 5-~. One of the by-products of the campaign to TABLE 5-8 Land Warrior Sensor Suite Power Requirements Projected Projected (2015)
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From page 96... ...
This implies a need to be alert for and to develop technologies that are voTtage-compatible with commercial CMOS whenever possible. Additional reductions in energy consumption are possible by introducing power optimizing hardware and software design methodologies.
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From page 97... ...
In general, one can predict the drop in power requirements (assuming everything else remains fixed) by scaling the drive voltage.
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From page 98... ...
MEMS could also be used to implement sensor mechanisms with moving parts, such as micro strutters; microchoppers for the infrared sensors; chemical sensors, such as miniature mass spectrometers ("electronic nosiest; and micromechanical beam writing scanners for the virtual retinal display. MEMS technology may also apply to micro-machined oscillators, filters, diplexers, and switches used in radio communications.
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From page 99... ...
This realization led to a significant shift away from cryogenically cooled detector arrays to temperature controlled bolometers that operate near room temperature. This means that sensor cooling power will only be
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From page 100... ...
If the fabrication problems can be solved, thermocouple junction thin films have the added advantage of generating an internal voltage, which eliminates the need for an external power source. Ultra Low Power Electronics for the Sensor Interface The active pixel sensor (APS)
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From page 101... ...
The resultant imager system-on-a-chip exhibits ultra-low power requirements (more than a 100-fold reduction compared to the state of the art) and extensive miniaturization (more than tenfold reductions in mass and size)
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From page 102... ...
A network of optical collectors might also double as the backbone for an infrared wireless link between the helmet, vest, and weapon to handle data. Power requirements for the wireless communications interfaces needed to link the soldier subsystems are discussed in a later section in this chapter.
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From page 103... ...
If the large infrared sensor arrays and their associated control and analog-to-digital converter electronics can be deployed requiring 50 mW of power using 5 V CMOS technology, the same technology applied to a single system would enable power requirements of less than 5 mW.
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From page 104... ...
Its peak power requirement is 75 mW, and its 5 percent duty cycle implies that the average power required over a mission will be about 4 mW. Laser Rangefinder With diode lasers, it is possible to achieve 65 percent power conversion efficiencies from edge-emitting lasers, although 25 percent is typical of commercial lasers.
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From page 105... ...
Low average power requirements make R&D to reduce energy Toss in the infrared pointers a low priority compared to losses due to other sensors. The optical conversion efficiencies are expected to continue to rise as a result of heavy investment in R&D by telecommunications companies and other companies concerned with users of multimedia and the internet.
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From page 106... ...
Ephemera information takes about one minute to acquire and must be updated about every four hours. Even though these two kinds of data take a long time to acquire the Tow data rate of 50 bits per second still results in a duty cycle of less than one percent the impact on energy consumption is not as important as the problem of phase synchronization.
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From page 107... ...
When factoring in the duty cycle, a GPS receiver estimating a position every 2 seconds will require an average power of ~ mW, which allows a much longer battery life than any of the current designs (Men", 1997~. Table 5-~]
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From page 108... ...
Adopting a wireless interface, however, means using separate batteries for each of the three sensor suite subsystems in the vest, the weapon, and the helmet. Of the three subsystems, the helmet watt require the smallest, lightest battery in order to minimize torque on the head from the weight of sensor electronics.
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From page 109... ...
Once optical wireless links are available at comparable energy consumption levels to those achievable with BodyLAN, one can begin to trade off the advantages of optical and radio frequency links. The chief reason for considering optical interfaces is that they are intrinsically wideband and can thus easily accommodate a more complex sensor suite.
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From page 110... ...
1.3 mW 0.03 mW Peak~ansmit power 375 Am 375 ,um Number of nodes 128 128 FINDINGS Advancing microelectronics technologies hold great promise for reducing the power requirements of systems for the dismounted soldier. Processing capability and device complexity are growing according to Moore's law, i.e., doubling every I S months.
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From page 111... ...
Critical chips within a multimedia terminal combining both computing and radio functions have already been designed to draw 5 mW three orders of magnitude less than existing commercial counterparts. Displays and Sensors Improvements in the drive electronics for both displays and imaging sensors will account for most of the reductions in power requirements for the sensors, the ISM, the THAS, and the hand-held displays.
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