One would be hard-pressed to name a wireless technology that didn’t have its beginnings in the military world. Some obvious examples are radar systems, satellite communications, and GPS. But defense’s heritage extends to other lesser known wireless technologies as well. Consider ultra-wideband (UWB) systems, which are now being used for commercial wireless personal-area networks (WPANs). This technology was highly prized by the military for its covert nature. How about the third-generation (3G) spread-spectrum technique known as Code Division Multiple Access (CDMA)? This, too, was originally implemented by the military. It was used to lessen detection and prevent enemy "signal jamming."
Going as far back as the 1960s, vocoder technology was used for voice digitization in military voice radios. Now, this technology forms the foundation for all digital cellular communications. Free-space optics (FSO) also reveal wireless technologies’ roots in defense systems. FSO was first used for military communications in the ‘80s. Currently, it’s acting as the final piece in the wireless-broadband connectivity puzzle. The software-defined radio (SDR) may serve as the most recent example of military technology that has found a place in the commercial market. Though this technology is being used chiefly by the military, it has drawn great interest from the wireless commercial sector.
The truth of the matter is that most of today’s wireless technology, as well as the careers of the technical experts that design such systems, began in the military. This evolutionary cycle - from initial development in government-sponsored agencies to viable consumer products - has become the norm rather than the exception. It is a workable and stable model for technology development, as well as a successful way to transfer professional knowledge. Governments have the monetary resources and sustainability to explore ideas, reduce the risks associated with development, and ultimately create new technology. The commercial sector, on the other hand, can improve efficiency, open new markets, and create wealth.
In today’s military environment, what are some of the issues that remain critical to the development and deployment of wireless systems? Not surprisingly, many of them are the same for both commercial and military environments: security, spectrum, interoperability, and product integrity. But in a military scenario, each of these common requirements takes on new meaning.
Communication-system security, for instance, is of paramount importance to both sectors for different reasons. Commercial cellular systems use frequency-hopping technologies to help avoid fading and other signal-degradation problems. Military systems, on the other hand, use frequency hopping to prevent an enemy from jamming their signal on a particular frequency.
The security of transmitted data also is a shared requirement. It is met through the use of strong encryption algorithms. Yet here too, the requirement has additional meaning for the military designer. Byron Tarver, Business Development Manager for General Dynamics Decision Systems (www.gd-decisionsystems.com), puts it this way, "Commercial systems employ encryption to ensure the privacy of communications. But very rarely does compromised information lead to life and death situations \[as in military operations\]."
In addition to the technical challenges of encryption, the logistical requirements must be addressed. Encryption systems have to accommodate different security services and cryptographic algorithms. The flexibility and dynamic nature of software has proven invaluable in satisfying these requirements. Take software-defined radios, which are being developed by the military to handle a variety of different security environments and purposes. One way to implement SDRs in military products is through the use of General Dynamics’ Advanced INFOSEC Machine (AIM). It can completely execute cryptographic algorithms in environments where tight security is essential.
Once sensitive data has been encrypted, it must be modulated before transmission. Studying advanced modulation schemes is an ongoing task for wireless designers. After all, changes in operating frequencies and encoding schemes affect the type of modulation that can be used.
Joel Kirshman, Applied Wave Research’s (AWR’s) Marketing Segment Manager for System Simulation (www.appwave.com), notes that military engineers must be able to predict and analyze the impact of these changes in order to answer such critical questions as the susceptibility of a new signal to jamming and unauthorized interception. Regression analysis and testing are also important to determine whether the new signal rendered the existing RF/microwave link useless.
These issues highlight the importance of having system-simulation tools that are tightly coupled to RF/microwave simulation software. A good system program will provide the designer with an understanding of both the jamming signals and the consequences of using higher-order modulation schemes. Similarly, a quality RF/microwave simulation tool helps the engineers grasp the impairments of the RF link. Applied Wave Research’s Visual System Simulator (VSS) design suite is an example of one such tightly interfaced simulation tool.
As mentioned, military and commercial wireless designs have another shared requirement in spectrum. The U.S. military must maintain its portion of this valuable resource while facing an even harsher requirement: spectrum coordination with other countries. Because the U.S. military operates around the world and may be deployed at a moment’s notice, it must contend with the global community’s varying and often conflicting RF standards.
Byron Tarver of GDDS states,"The coordination of spectrum usage is a significant problem, because there are few worldwide agreements in the allocation for spectrum for specific purposes." For proof, he refers to a situation in which a U.S. military deployment may use their existing combat net radios (CNRs). In some countries, those CNRs could actually interfere with taxicab dispatch services.
Interoperability is another important design issue for military and commercial wireless engineers alike. U.S. military communication systems have evolved differently for each service. The Army, for instance, operates at lower frequencies because it must deal with natural ground obstacles, like foliage. Its communication systems therefore use the high-frequency (HF) and very-high-frequency (VHF) spectrums, while implementing frequency-modulation (FM) schemes. Meanwhile, the Air Force prefers the ultra-high-frequency (UHF) band with amplitude-modulation (AM). Its systems typically have a line-of-sight advantage.
When joint operations are required, though, these differences between the Army and Air Force communication systems create a disadvantage. One service may not be able to talk to the other. This is another reason why SDRs are being developed by the military. Byron Tarver of GDDS explains that SDR technology treats each of these different radios as an application in software. It automatically translates between the different communications systems in a process that is often called bridging or cross-banding.
Just as interoperability can create more severe problems for the military, so too can a lack of ruggedness. On the surface, the need for ruggedness seems to be the most glaring difference between military and commercial wireless designs. Conditions in the battle environment are obviously much harsher than the commercial world. Yet commercial products have ruggedness requirements as well.
Andrew Girson is the CEO of InHand Electronics, Inc. (www.inhandelectronics.com), a provider of high-performance/low-power handheld and wireless computing devices. He agrees that even in the commercial sector, ruggedization is a concern. "HP-Compaq now has an optional rugged cover for the iPAQ. Of course, Symbol, Intermec, Itronix, and other vendors of industrial handheld have field-rugged units."
But what about standard military-type design and testing for environmental requirements? For the moment, military technology developers are using the commercial-off-the-shelf(COTS) approach to acquiring wireless technology like PDAs for the battlefield (Fig. 2). With COTS, the military can quickly acquire the latest technology while enjoying the statistical advantage of high production. This helps to ensure high quality and reliability of products.
Actually, many COTS-technology proponents believe that the consumer may be a tougher customer than the military in terms of rejecting inadequate products. If a commercial manufacturer of PDAs produces units that break too easily, consumers will cease to buy their products. The marketplace will quickly "weed out" the weaker products - or so the theory goes.
Of course, the COTS approach to developing military systems is not without its challenges. Who ensures the system-level design and testing of PDAs? According to In Hand’s Andrew Girson, "Because most IC vendors are no longer creating mil-spec components, we are relying on handheld vendors to qualify the entire system from start to finish, including EMI issues."
How can the military verify the worthiness of such designs? There are two traditional approaches to answering this question, points out Steve Tanner, Head of the Naval Air Warfare Center Weapson’s Division’s (NAWCWD) Electromagnetic Environmental Effects (E3) Branch. The choice is either to reverse engineer or analyze the original design and manufacturing specification. The former approach is typically as expensive as designing the same system from scratch. But the latter may not be possible, because commercial designs and testing don’t usually address the harsh conditions in which military systems must operate.
Typically, Steve Tanner observes, the design margin of commercial systems like PDAs is unknown. The design margin is the difference between the strength of a component or device and the actual operating environment. In commercial products, it is cost effective to make the design margin as small as possible. Military products, however, must operate in mission-critical - that is, life or death - and extreme environmental conditions. As a result, the design margin is often significantly higher.
From its military beginnings, wireless systems have evolved into highly complex commercial products. As a result, their design needs also changed. They’re now being used once again in the defense community. Appreciating the different design requirements between the commercial and military segments will help ensure the continued benefit of this valuable interplay.
\[Reprinted with permission from Wireless Systems Design magazine, September 2002\]