Extraordinary growth is evident in capabilities for ''untethered" communications, the union of wireless and mobile technologies. An example is cellular telephones, which were virtually unheard of in 1980 and are now used by almost 200 million subscribers worldwide. The subscriber base for wireless communications services is growing 15 times faster than the subscriber base for wired services; by 2010 wireless and wired systems are expected to serve equal numbers of users. The vigorous public demand for wireless services is fueling intense industrial and government activity, including research and development (R&D) aimed at improving the quality and reducing costs of wireless technology, design of innovative systems and services, and implementation of new technical standards and policies. This dynamic environment is producing diverse wireless technologies and standards, in stark contrast to other areas of communications marked by a convergence toward uniformity. All this activity will bring the reality of the next century close to the vision of "anytime, anywhere" communications.
Historically, U.S. national defense needs have stimulated many advances in wireless communications technologies, and the Department of Defense (DOD) has been among the first users. Today, however, some DOD systems lag the state of the art. Whereas the commercial sector has greater incentives than ever before to push the technology envelopeat a cost driven down by a growing mass marketsome military wireless equipment is based on 1970s and 1980s technology. The adequacy of the current defense communications infrastructure was called into question
during the Gulf War, when voice and data systems failed to keep up with rapidly moving front-line troops. Only 10 percent of soldiers currently have voice communications capabilities, and only satellites, certain aircraft, and "smart" missiles carry sensors for still imagery or video.
Changes in military operations are stimulating DOD interest in untethered systems. U.S. military personnel now need to be prepared to move quickly throughout the world to respond to rapidly evolving regional conflicts and carry out a variety of noncombat roles, such as peacekeeping and humanitarian response. Just as past hardware advances (e.g., aircraft carriers, long-range jet aircraft) shaped the military conflicts of yesteryear, information technology is now shaping plans for the nation's future defense. Plans are being made for a digitized battlefield in which sensors are widely distributed, and rapidly deployable, multimedia wireless systems extend from front-line soldiers all the way to the Pentagon and the North Atlantic Treaty Organization (NATO). Advanced command, control, communications, computing, and intelligence (C4I) systems will make it possible to monitor an adversary on a computer screen, target specific threats, and neutralize them with the press of a button.
The DOD is taking a dual approach to meeting its future communications needs by funding selected R&D and demonstration projects, focusing primarily on components, while also relying increasingly on commercial off-the-shelf (COTS) technologies. In the Gulf War, for example, the military obtained satellite-transmitted positioning data using commercial receivers, which were rapidly fielded to meet an urgent military need. On the other hand, for some military applications, commercial products do not meet stringent requirements for security, interoperability, and other capabilities. And yet, with defense budgets flat or declining, the DOD can no longer rely solely on military suppliers to provide defense-unique solutions. The military needs to find a way to ride the wave of commercial technology advances while maintaining technical capabilities that exceed those of any potential adversary.
This report, the result of a one-year study by the Computer Science and Telecommunications Board (CSTB) of the National Research Council, recommends strategies and R&D to help the DOD field state-of-the-art, cost-effective untethered communications systems that meet military needs. The report concentrates on wireless technologies that use the radio frequency (RF) part of the electromagnetic spectrum. The study was funded by the Defense Advanced Research Projects Agency (DARPA) to address the following questions:
Answers to those questions are outlined in this summary, which contains two major sections. The first section presents the report's five conclusions and summarizes the supporting facts and analysis contained in Chapters 1 through 3 of the report. The conclusions represent the expert judgments of the 15 members of the CSTB's Committee on the Evolution of Untethered Communications. The second section presents the committee's 12 recommendations, which are based on the conclusions and the supporting facts and analysis. The recommendations, which are directed to DOD and DARPA, are discussed in detail in Chapter 4. It should be noted that although the report focuses on military needs, it also contains a wealth of information about commercial technology developments as well as a primer on the many technical challenges involved in designing wireless systems. The report therefore should also interest a wider, civilian audience.
A large gap remains between public expectations for mobile communications and the available technology. Voracious consumer demand is stimulating many advances in wireless communications technology, particularly cellular and cordless telephones. As of 1997 there were more than 50 million cellular subscribers in the United States. The portfolio of wireless services now available in the commercial marketplace includes a wide range of telephony, paging, and data applications delivered over a variety of service offerings, ranging from land-based mobile radio to cellular and satellite communications. Each service offers a unique combination of coverage region, bandwidth (i.e., capacity), subscriber equipment features, and connectivity.
In the aggregate, commercial wireless capabilities are considerable. Yet many technical challenges remain. Wireless systems, especially those serving mobile users, are extremely complex. A network needs to be capable of rerouting information seamlessly and efficiently as users move, and sophisticated digital signal processors (DSPs) and antennas are needed to minimize interference, distortion, jamming, and interception without undue power burdens on portable devices. The cost of wireless voice systems remains high compared to that of wired networks, and transmission quality and security could be improved. Specialized wireless data networks
have not taken off as yet, perhaps because they are not powerful enough or because two-way mass market applications have yet to emerge.
For a worldwide operator, the management and coordination of diverse systems are complicated by the absence of any trend toward convergence toward a single standard in wireless communications. One digital wireless technology, global system for mobile communications (GSM), is deployed throughout Europe and in more than 100 countries worldwide, whereas the Japanese use their own technology, the personal handyphone system (PHS), and the United States supports three competing technologies: GSM, a time-division system (IS-136), and a code-division system (IS-95). The diversity of technologies in the United States is a result of spectrum regulation policies, which require only that systems not interfere with one another. These policies leave interoperability and other system properties such as quality and efficiency to be settled in the marketplace.
Over the next 10 years or so, market forces will fill the gap between public expectations and the available technology by developing new technologies for commercial wireless communications. Fueled by the success of cellular communications and projections of ever-expanding markets for wireless services, U.S. and foreign industries are performing extensive R&D to overcome remaining technical challenges in wireless systems. For example, efforts are under way to enable portable devices to communicate at the high bit rates needed for advanced information services. In addition, to foster economies of scale in R&D and manufacturing in a world of diverse and changing technical standards, considerable effort is dedicated to advancing the technology of software radios. These radios, by downloading different types of operating software, can serve as single platforms that transmit signals conforming to a variety of standards.
The European Union, which supports cooperative research leading to development of precompetitive technologies, has a vision of the future extending beyond 2002, when universal mobile telecommunication services are scheduled to be deployed. That vision and various industry road maps suggest that, by early in the twenty-first century, commercial wireless communications will achieve the "anytime, anywhere" paradigm.
This optimism does not extend to prospects for fully interoperable wireless communications systems anytime soon. In the United States, wireless communications research is performed by individual companies in the context of their own product plans, and coordination occurs primarily in standards-setting organizations (e.g., Telecommunications Industry Association, Internet Engineering Task Force). Moreover, in the past there was a proliferation of proprietary rather than open network interfaces. The trends toward open systems and digital components will make
it easier to build customized systems, but the capabilities of commercial services will continue to depend on consumer demand as well as trade-offs between technology availability and costs.
The military has much to gain from positioning itself to use COTS communications equipment to the greatest extent possible. The civilian and military sectors have a long history of interaction in the design and deployment of wireless technology, such as mobile radios and satellite systems. Commercial wireless technologies are now more attractive than ever in terms of their performance, quality, and cost. By acquiring commercial equipment when it meets military needs, the DOD can field state-of-the-art equipment while also lowering its costs by benefiting from the economies of scale achievable in mass-market manufacturing. For example, software radios for military applications can be built using many COTS components, such as analog-to-digital converters, DSPs, RF amplifiers, displays, batteries, and data-storage devices.
The insertion of commercial technologies into military systems is not always easy. As an example, asynchronous transfer mode (ATM) offers many attractive features, such as high-speed transmission, fast switching, the capability to assign message priority, and queue management. It could provide the basis for improved situational awareness, enabling the DOD to provide real-time imagery, cryptographic security, and low-cost devices for wide distribution. However, the integration of ATM and Internet protocols into wireless battlefield communications will require sophisticated link protocols. Industry is addressing these issues, but the DOD can ensure that its needs are met only by participating in standards-setting activities to influence technology directions and by testing emerging COTS products in battlefield exercises.
Some military needs for wireless communications technologies will exceed or differ significantly from anticipated commercial developments. For example, the military has unique concerns with respect to network design, security, interoperability, and multimode/multiband systems. Although there is clearly overlap between the capabilities of commercial technologies and the DOD's needs, they also differ in a number of respects (see Table ES-1). For example, commercial R&D on integrated (i.e., multimedia) systems is oriented toward base-station-oriented network architectures, an efficient and reliable design in which mobile users communicate with central access nodes. An alternative is the easily reconfigurable peer-to-peer architecture, in which network elements communicate directly. It is not yet clear which architecture will be the most appropriate in future military settings. Improved modeling and simulation tools, especially for communications traffic and mobility of network
elements, would support realistic analyses of complex military networks and the design of appropriate protocols and optimization algorithms.
Commercial capabilities and military needs also differ with respect to the security of networks, radio links, and hardware. Commercial users
are concerned mainly with privacy and the prevention of unauthorized access to their hardware and data. Some security breaches are tolerated (in fact, analog cellular telephones typically provide no link security). By contrast, the military requires end-to-end encryption to prevent unauthorized access and monitoring of network activity. The military also requires hardware security to prevent an adversary who is opening a device from discerning the hardware or software secrets. Military systems also benefit from antennas and other technologies designed to make signals difficult to detect, jam, or intercept.
Interoperability is another area in which the DOD's needs exceed the interests of the commercial sector. Advanced military wireless systems need to be compatible with the 17 legacy communications networks as well as systems operated by NATO and the United Nations. One means of achieving this objective is the software radio. Now the focus of several military R&D programs, the ideal military software radio is a multimode, multiband unit using many different waveforms over a broad frequency range, whereas commercial versions are likely to offer less flexibility and operate in a single frequency band. To make optimal use of this promising technology, the DOD needs to support specialized R&D focusing on antennas, filters, and adaptive waveforms.
The commercial sector has its own incentives to produce advanced communications devices, components, and subsystems as well as complete systems. To use commercial technologies effectively, the DOD will have to take special measures to promote the development and acquisition of COTS products that can be integrated into systems that meet specialized military requirements. Current commercial R&D and standards activities seek to enable the transmission of many types of information, including data, video, and images, to and from portable wireless devices. Although this work is certain to create new technology, the commercial deployment of the technology is not assured. The availability of the technology in the marketplace will depend on business, social, and government policy factors. Military planners will need to maintain a continuing awareness of the differences between what is possible technically and what is available in the market to meet military needs.
As part of this process, the DOD needs to translate its operational requirements into technical specifications that can be used to determine the suitability of commercial wireless technologies for military applications. New approaches to procurement, as well as technology demonstration and testing rather than development, will help DOD obtain the greatest return on its investments. In addition, by fully understanding the barriers to synergy between the commercial and defense sectors, the DOD can develop processes for accommodating or overcoming these barriers.
For example, the commercial sector tends to add functions to equipment only if economically justified by customer demand; by participating in standards-setting activities the DOD can encourage the design of COTS products that can be more easily modified to meet military needs.
The committee's 12 recommendations are organized from the general to the specific. The first three recommendations identify organizational changes that DOD should make to foster an environment conducive to the absorption of state-of-the-art commercial wireless communications technologies. The other nine recommendations identify research that should be undertaken by DARPA to fill gaps in commercial development efforts and ensure that advanced wireless systems meet military needs. The research recommendations are presented in order of priority, reflecting the committee's view that top-level systems issues are paramount. The remaining recommendations deal with subsystems and components.