“From the hardware aspect, being an open architecture, modular design is similar to the design of a PC — mainly a board, and a driver for the board,” notes Phil Lai, JTRS program manager for ITT Corp. in Wayne, Ind. “The key is to reuse whatever we develop depending on the needs, and tailor it to suit the customer’s requirement. That is the basic principle behind the SDR and JTRS. It will take a little time to get this effort perfected to the current state of the PC industry, which has been doing things this way for more than a decade. So we are trying to move that concept from the commercial world into the military world.”
Once ITT engineers finish the JTRS design, manufacturing and repair become very easy, Lai says. As a modular approach, anything that becomes defective later on can be easily replaced at a relatively low cost.
The basic application of JTRS is to understand any signal for which it has a downloadable waveform and act as a relay/interpreter between otherwise incompatible systems. This model also holds true for PCs.
“If an e-mail comes into your computer with an attachment, you just click on it — you don’t care what the format is, so long as you have the software to read it,” MacLaird says. “If you have eight or ten waveforms stored in a radio and a waveform comes across the air, you don’t care which it is in order to receive it.”
The JTRS also acts like a computer in its capacity for rapid, in-the-field upgrading of JTRS software and hardware. JTRS will use software signal processing to handle all kinds of signals instead of dedicated, single-purpose hardware. Many standard communications functions are available off-the-shelf as software libraries that can be compiled into field programmable gate array tool to deal with whatever signal comes along.
“Because you have different processors that need to talk to each other, it is a difficult problem to solve at the subsystem design level, but all of that is transparent to the user. If a board goes out, you simply swap it out — all our new systems are hotswap. So it is simple for them, despite the work it takes at our end to design it,” Uhm says.
“On the technology front, the evolution in processors and things like switched fabric interconnects have come a long way very recently to make the actual implementation of an SDR possible and to make it smaller and more portable. But the technology certainly exists today to support the requirements of JTRS. But there are still a lot of factors preventing SDR from worldwide deployment. Many of those are political or regulatory.”
Software-defined radio is just beginning to hit its strideU.S. military and industry experts are developing the Joint Tactical Radio System (JTRS) as an architectural definition for a software-defined radio. Versions of software-defined radios already are in use by the U.S. military. In simple terms, JTRS will be an advanced version of these software-driven devices.
By definition, users can quickly reprogram a software-defined radio to transmit and receive on any frequency within a wide range using virtually any transmission format. Functions that hardware normally handles, such as generating a transmitted signal and tuning and detecting a received signal, come under control of software and high-speed signal processors.
The software-defined radio is designed to be quickly and easily reprogrammed, and operates over a broad range of frequencies, bandwidths, and transmission standards. That means one device, properly programmed, could operate in all the various military, emergency services, cellular, PCS, and other wireless modes used in the United States and worldwide.
Software controls the radio’s technical characteristics such as operating frequencies and output power. This design approach also may enable these radios to improve spectrum efficiency and spectrum sharing. By monitoring the spectrum for use by other parties, for example, a software-defined radio could locate and transmit on an available open frequency, and in the process provide greater flexibility in using the full spectrum.
Several manufacturers are producing software-defined radios for a variety of applications. Harris Corp. in Rochester, N.Y., for example, has built a family of software defined digital radios, under the Falcon II label. These radios cover different frequency bands. The AN/PRC-117F Multiband/Multimission Radio, currently in use by all the U.S. military services, is a 30-to-512 MHz-band radio that incorporates several different software-defined waveforms, such as SINCGARS, HaveQuick, and old Type 1 encryption modes.
Cooperative research in the U.S., Japan, South Korea, Germany, and the United Kingdom is rapidly advancing the technology, according to the Software Defined Radio Forum (SDRF), a global non-profit organization comprising about 100 suppliers, manufacturers, end users, regulatory agencies, and universities. This, SRDF officials say, will enable:
- end-users to realize “true” choices with “pay as you go” features, device independence, and a single piece of scalable hardware that is at once compatible at a global scale;
- network operators to differentiate their service offerings without supporting many different handhelds and to move to adjacent markets as well as offer new, tiered services to increase their revenue mix;
- infrastructure suppliers to lower cost and insure themselves against price-erosions through concentrated efforts on a common hardware platform and reduced component counts;
- applications developers to enhance value without concern to hardware types; and
- terminal providers to add features, patches and capabilities to devices for broader market participation.
Software-defined radios and their potential for homeland securitySept. 11th demonstrated that domestic security has some of the same problems of communications interoperability as the U.S. military and its allies do. Domestic security also may share the same solution as the military.
Officials of the U.S. Department of Defense (DOD) created the Joint Tactical Radio System (JTRS) program to provide a single software-defined radio (SDR) that could stand as the universal translator for all other incompatible military communications systems. Those working on JTRS and other software-defined radios say they believe the same technology could apply to civil and private emergency services requirements as part of the Homeland Defense effort.
“There is an effort being mounted for a JTRS approach within the U.S. to unify the communications for emergency services. That apparently has gotten some initial approval,” says Rodger Hosking, vice president of software radio maker Pentek Inc. in Upper Saddle River, N.J.
“In many cases, the concept may be the same, but the implementation would be done at a different level,” Hosking says. “Municipalities might not have quite the specs of a military radio system, but they do see value in the concept of a capable and configurable front-end tunable over a wide range of frequencies, digitizing those, and bringing them down to a computer platform that can be configured for everything from cell phones to fire, police, ambulance, and all other signals that might arise in an emergency.
“So it does cross over, even to commercial wireless,” Hosking says. “There is no longer a great disparity in the level of complexity between government and commercial communications systems. That has put considerable demand on the signal-processing capabilities of both civilian handsets and base stations that rivals or exceeds that of military systems. A municipal radio capability where 911 calls could go directly to a municipal radio and not have to rely on a traditional service provider, such as Verizon or Sprint, is part of what this initiative should be doing.”
The JTRS concept also may apply to the war on terrorism outside the United States by non-military agencies, such intelligence experts who monitor cell phone activity in areas where U.S. officials suspect terrorist activities.
“The question is, what are the tactical needs of our forces around the world and what do we need to do at home in terms of homeland security — and how do those mesh,” Hosking says. “The only way to do that is to make those systems adaptable and configurable so they can identify the signals they need to deal with and then use software to modify the system to talk to those systems. All that is very DSP [digital signal processing] intensive and more and more of it is being done in configurable logic as opposed to dedicated logic.
“Another thing we’ve been hearing about is the 911 system itself, in terms of the ability to do direction finding with regard to cell phones,” Hosking continues. “We’ve been talking to customers for several years who have been chasing that, trying to triangulate signals from the towers. That also could be of vital interest in a national emergency, being able to locate the source of emergency calls.”
The solution for bringing together the vast variety of standards in both the civil and military communications worlds — in the U.S. and overseas — lies at the heart of JTRS and other advanced software-defined radios. They key is the software radio’s common platform and software, augmented by specialized algorithms.
For widespread application, that would require identifying all of the necessary waveforms and creating an available library, then determining the size of memory required for individual radios — especially handhelds — in order to handle multiple waveforms. Less memory would be required if the unit was able to detect and identify a new signal, then download the required waveform on the fly.
This approach, however, will not come to pass overnight. “An actual physical JTRS radio is some years away,” admits Kevin Kane, director of business development for U.S. ground forces at the Harris RF Communications Division in Rochester, N.Y. If a software radio were in production today as originally conceived, “you would be able to use it as a retransmission site for multiple agencies [in a terrorist attack response mode,” Kane says.
Federal officials have identified a waveform for the federal over-the-air interoperability standard, called APCO-25, to deal with several different civilian law-enforcement agency and emergency services radios on the federal, state, and local levels. JTRS, however, “is not currently planned to include that. Once JTRS reaches more mature technical levels, there’s no reason it could not be incorporated into the system,” Kane says.
Applications such as homeland defense would require encryption keys to prevent signal interdiction or spoofing, even for units with the necessary waveform. Operators could exchange encryption keys on secure links, as necessary, and change them periodically, depending on the level of security required.
“You also could set up groups of JTRS radios that only could communicate with each other and not outside that group, creating a cell of users, perhaps only one member of which could communicate outside that cell for enhanced security,” Hosking adds.
Yet there is a dark flip side to the security that software-defined radios offer to military and domestic security applications, warns Manuel Uhm, senior manager for strategic marketing at software radio designer Spectrum Signal Processing in Burnaby, British Columbia. “The flexibility of SDR also would make it easier for terrorists to have secured communications,” he says. “Right now, the technology isn’t there for them to have the portability they probably want.”
Still, the versatility of the software-defined radio may raise problems with allies, as well. “Old hardware radios could only support a very defined bandwidth you were authorized to use, but an SDR can access any bandwidth in the spectrum, which makes things difficult for governments to regulate,” Uhm says. “Even allies like the United Kingdom will not be thrilled with U.S. forces coming in with SDRs that are free of restraints,” he warns. “Encryption is a key element of SDR — to how you ensure it will operate within the parameters governments want them to operate in. In essence, you are trying to limit the capabilities of an SDR.”
Cost is also a factor — ironically, probably more so for civil emergency services agencies than for well-funded terrorist organizations such as al-Qaida. While software-defined radio technology is available to the commercial buyers, its cost has not low enough to attract commercial customers.
In simple terms, despite its advantages, it is not yet cost-effective compared to existing fixed-function radios. That may be another spur-to-the-hub concept for emergency services — one or more software-defined radios on the infrastructure side, communicating with existing radios, with handsets coming along later.
But that approach also may speed along eventual commercial availability, Uhm notes: “When you talk about emergency services, it gets much closer to the commercial requirement, where you have price sensitivity, but also a very large market. That would drive economies of scale and make SDRs much more affordable across a broader spectrum of users.”
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