gained at enormous energy cost. With continued reductions in scale, from, say, 180 nm to 45 nm, an estimated 18-fold net advantage in efficiency can be expected.

For functions requiring a low number of operations to be executed (one such is the user interface), the energy cost of solutions providing high flexibility will not be a significant component of the overall system power demand. For functions with high processing rates, such as video processing and communications, solutions should be more dedicated to take advantage of the multiple orders-of-magnitude reductions in power that can be achieved. Combining applications that possess both low and high processing demands leads to the most generalized SoC approach, a chip design that provides software programmability where needed for functions that must have full flexibility and more dedicated, power-efficient solutions for high-performance signal processing. It is believed that more than an order of magnitude reduction in the power demand of the digital computation would be achievable in the OFW system if an SoC approach is taken.

On the other hand, it is clear that specification decisions that simply mandate a fully software-based system would result in crippling requirements from an energy-cost perspective, as appears to have happened in the JTRS program. For example, compatibility with multiple waveforms can be achieved by several strategies. Multiple dedicated radios could be placed onto a single chip, and since there is an area advantage similar to the power advantage for each dedicated radio using the SOC approach, a number of radios could easily be implemented in the same area that a software programmable solution would require. For the special case of radio designs, this is consistent with an approach that requires specialization in any case, because of the analog RF circuits that will require optimization if reasonable power levels are to be achieved. The energy efficiency of multiple dedicated radios on a single chip would easily be more than an order of magnitude better than that of a software-programmable solution.

Another development in the commercial arena that provides increased flexibility is use of reconfiguration as opposed to software programmability, such as used in field-programmable gate arrays (FPGAs). Computation is implemented on these chips using an architecture that is essentially the same approach as that used in dedicated SoCs, giving them an inherent advantage over a software processor-based solution. FPGAs are able to exploit the improvements in the underlying technology better than the software processors, so in the future it is likely that for high-performance computation requiring energy efficiency and full flexibility, the approach of choice will be based on reconfiguration.

At present, even though they are not optimized for energy efficiency, commercial FPGAs are still more efficient than software processors. The OFW soldier radio, for example, is being prototyped using FPGAs. An investment by the Army that would develop an energy-efficient, reconfigurable processor could achieve the dual goals of flexibility with reasonable energy efficiency. However, this solution will probably always be more than an order of magnitude less efficient than a more dedicated solution.

If all of the high-performance computation were integrated onto one OFW SoC chip the power demand of these functions could be reduced by more than an order of magnitude. Design of this chip using reconfigurable architectures could achieve these gains without compromising flexibility. In the OFW scenario, this flexibility could include radio and communication processors, Voice over Internet Protocol (VoIP) processing, as well as processing for video compression and decompression. For low-rate human interface processing, a software processor could be integrated onto the chip to provide additional flexibility to meet evolving future requirements. Chapter 6 discusses design concepts for such a Future Warrior system.

FINDINGS

The Army has come a very long way since Energy-Efficient Technologies (NRC, 1997) in understanding the soldier as a system and in taking appropriate actions that result from this understanding. Though in some cases there have been impressive reductions in the power demand of individual items, the reductions are being more than offset by the demands of new and more capable devices as well as the desire to have a highly flexible open architecture. Based on its observations of the overall evolution of the LW and OFW-ATD programs, the committee made six findings, which are discussed next.

Constraints on Reducing Power

For the LW systems the average power has been 20 W and the peaks have been 60 W over all three generations. The energy savings made possible by technology improvements have been traded for improvements in combat effectiveness as well as to allow the use of plug-and-play architecture to support future evolution. While the desire for such flexibility is understood, turning plug-and-play into a basic requirement comes at a high energy cost and will restrict the use of solutions that could reduce power demand by more than an order of magnitude.

Technology Time Horizon

The time horizon for OFW is too close. The LW program needs enough time to develop a SoC solution for the OFW and not be constrained to off-the-shelf component solutions. Increasing the development time horizon would allow the program to build on prior programs by evolving the SoC to meet new needs and requirements, similar to the successful approach taken for commercial cell phone evolution, in which each new generation is an enhancement of the last generation with new capabilities.



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement