Tuesday, 09 November 2004
By Ravi Murty
Overview: Creating Highly Adaptable Radios
Just how many communication devices does a typical user own? A single user could easily own half a dozen: cell phone, cordless phone, wireless Internet gadget, pager, GPS tracker, and scanner. Then there are car phones, wireless intercoms, ham radios, Citizens Band radios, family radios, and more. For every one of these devices, the device design must be separately licensed through the Federal Communications Commission (FCC). And each device is limited to communications on a specific frequency band.
The communications industry is now looking for a way to create radios that can handle multiple frequency bands, understand multiple transmission protocols, be reconfigured on the fly, and be easily upgraded—all in a single device design. With advances in CMOS (complementary metal-oxide semiconductor) technology, programmable digital-signal processors, analog-to-digital converters, high-speed data transfer, and many other technologies, this type of full-featured wireless networking is moving from the possible, into the truly practical.
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Software-defined radios, or SDRs, are radios that use either a general-purpose processor or programmable silicon, as well as hardware modules (such as antennas and radio-frequency front ends) to create a generic hardware base. On top of the generic hardware is a flexible software architecture. The software allows for multiple protocols, fast upgrades, and even complete reconfigurations of a radio's features and functions via a simple download.
Software radios have three main advantages over traditional, single-protocol, hard-wired radios:
- SDRs are lower-cost solutions. Functionality that used to be hard-wired into the radio can now be provided via software.
- SDRs are easy to upgrade. Upgrades can be downloaded from the Internet, an intranet, or even via radio transmission.
- SDRs allow for quick evolution of end-user equipment, communication and network infrastructures, and industry standards.
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Today, we're already moving toward reconfigurable architectures for both computing and communications devices. What the industry needs now are multifunction devices that can replace the plethora of cell phones, pagers, and other radio devices that exist today. SDR is the technology that can make that a practical reality.
Today's Radios: Fixed Hardware Solutions
Radio communication is based on modifying the amplitude and/or frequency of a carrier wave. In today's radios, a hardware modulator circuit is used to convert voice or data information into radio frequency (RF) signals. A hardware demodulator circuit converts the RF signal back to voice or data. Hard-wired radios include circuitry that performs waveform modulation and demodulation, filtering, error correction and interleaving, and so on.
Today's radios are fixed, hardware solutions. For example, radio designers currently assume a particular type of frequency modulation, and build the appropriate circuit for that type of modulation. During use, the radio receiver selects only the specified signal type, and filters out all other signals. Such radios are not flexible, nor are they easy to upgrade, since each physical design must be separately licensed by the FCC. If parts are swapped to create different feature sets or configurations, each configuration must be separately licensed. This places a significant burden on radio manufacturers.
What is needed is a generic, programmable hardware base that would allow software to enable various features, depending on the radio environments in which users move.
Issues with Today's Radios
There are many issues with today's radio communications besides the lack of hardware flexibility. Some of the most basic challenges include:
- The need for an immediate, cost-effective solution that doesn't require agencies to buy new radios.
- The need for radios that are energy efficient and that conserve battery power.
- The need for units to be portable, lightweight, and small.
One of the most serious issues at this time is the lack of compatibility between different types of devices and different communications and network infrastructures. Currently, radios use proprietary software to manage their communications trunking system. This means that, for instance, a Motorola* radio will work only in the trunking system managed by Motorola proprietary software. If one public safety agency uses Motorola devices, and an outside agency uses devices built by a different manufacturer, it's unlikely they will be able to communicate via radio.
Especially in different countries, incompatible wireless network technologies make it difficult to deploy global roaming facilities at all, let alone effectively. For example, the frequency range allowed for cell phone communications in one country may overlap the frequency range regulated for emergency services in another country. Thus, a cell phone licensed for the first country might not be allowed to be used in or even near the borders of the second country.
Another challenge is trying to keep up with evolving link-layer communication (transmission) protocol standards, such as 2.5G, 3G, and 4G. The legacy handsets currently in the market cannot be easily upgraded to new features and/or services. Most aren't even compatible with the new standards.
Problems with upgrades are not limited to evolving communications protocols. Public safety agencies often upgrade their radios with new or reorganized "talk groups." A talk group is a computer-assigned digital word that allows a specific group of people to talk together, even though thousands of users may be sharing only 10 actual frequencies. Today, talk-group upgrades are done by physically handling the radio and, using an encryption key, by downloading the new set of talk-group definitions into each radio unit. The problem is that some handheld units in the field may not be upgraded at the same time as others, or may even be accidentally left out of the upgrade. This means that some police, firefighters, Haz-Mat teams, and so on may be unable to communicate effectively with other officers during incidents that may become dangerous or even deadly.
Another problem that today's police, fire, and other government agencies have is with the number of talk groups available on the 10 or so communication channels assigned to public safety. A single officer may be using a radio programmed with over 200 talk groups, and still not have the specific talk group he or she needs. Even if officers do have the right talk groups programmed into their radios, they might not be able to find the one currently being used by another agency—or even another group of local officers, especially when the action is fast and furious.
A recent scenario occurred in which a K9 police officer from one town was helping officers from another city track a bank robber. During the incident, the city officers switched to a different talk group. The K9 officer's radio was programmed for her town's services, and didn't have the talk group to which the other officers switched. In this case, the K9 officer was forced to communicate through dispatch—a clumsy, awkward, and potentially dangerous solution—instead of directly with the other officers. With SDR technology, that K9 officer could have quickly downloaded the new talk group so she could participate in resolving the tracking incident safely and more effectively.
Finally, there is already a huge strain on existing bandwidth and infrastructures from the growing number of mobile and wireless devices. With more and more users requiring access to different types of spectrum, this problem can only grow worse. Today's hardwired radios cannot resolve these issues. However, solutions can be found in software.
Software-Defined Radios Offer New Options
So, what is a software-defined radio? It's a radio with a generic hardware base of analog CMOS circuitry, under a flexible software architecture. SDRs can include software modal radios, reconfigurable radios, software-based radios (SoftRadios), and SDRs based on digital signal processing technology. Although SDR concepts have been around for a while, practical designs are only now becoming possible due to advances in many technologies, including:
- CMOS
- Silicon Germanium (SiGe)
- Field-programmable gate arrays (FPGAs)
- Powerful, cost-effective programmable digital signal processors (DSPs)
- Adaptive computing machines (ACMs), which handle multiple protocols by adjusting themselves to the algorithm or mathematical equation being executed
- High-performance analog-to-digital converters (ADCs)
- Ultra-fast data-transfer interfaces
These advances are now allowing manufacturers to design radios with programmable silicon—radios that can be upgraded via software, possibly even over the air.
In an SDR, generic hardware provides the programmable silicon (or general-purpose processor) and other parts needed to transmit and receive radio signals on any appropriate frequencies. This means that one basic device could have the ability to transmit and receive signals in multiple frequency bands, using multiple link-layer protocols. For example, a single radio might be able to transmit and receive on frequencies currently regulated for cell phone communications, digital downloads (such as e-mail), and even marine communications, such as those used to receive permission to enter or leave the locks on a well-traveled river.
Hardware modules for an SDR include antennas, analog front ends (which convert radio frequency, or RF, signals into intermediate signals), and matching digital baseband modules. It's possible that some or all of the hardware parts could be precertified by the FCC for use in radios with modular designs. A modular approach and generic hardware base will significantly reduce the burden on manufacturers who want to enable different feature sets for different radio environments.
With a generic hardware base, radio functions that have traditionally been handled by hardware can now be defined in software. These functions include:
- Signal generation
- Waveform modulation and demodulation
- Baseband and digital signal processing functions
- Use of intermediate frequencies (such as for frequency hopping)
- Use of multiple link-layer protocols
- Security and encryption
Advantages of SDR
SDRs have several advantages over today's hard-wired radios. The most obvious advantage is flexibility. SDRs can be reprogrammed and/or reconfigured on the fly. Users could initially configure their radios by downloading a personalized package of software features. Upgrades and reconfigurations could be done via another, simple Internet access, and downloads could even be received over the air.
The ease with which units can be reconfigured may offer a significant benefit to public service industries. For example, to prepare for emergencies such as flooding, volcano eruptions, train wrecks, and tornados, government organizations keep a stock of extra radios on hand, usually sitting in closets in chargers. That can be problematic, because batteries can burn out in chargers. During an emergency when the units are handed out to extra, incoming personnel, it's usually not known if a unit will actually work, or for how long.
SDRs offer a solution to this problem by allowing an incoming agency, such as the National Transportation Safety Board (NTSB), to quickly upgrade their radios with the frequency information and protocols being used by the on-site agency. Instead of using local, possibly burned-out units, the incoming agency can, with the proper security and encryption keys, adapt their own equipment to help manage the incident.
SDRs can also be configured to handle multiple communications protocols. This is the concept of an "agile" radio. An agile SDR could handle 802.11a, 802.11b, and CDMA (code division multiple access) protocols, all from a single design implementation. This means that one end-user radio device could act as a cell phone, then switch to performing as a cordless phone. It could then act as a wireless Internet device to download e-mail, then accept GPS (global positioning system) signals, and even act as a garage-door opener when the user gets home.
Finally, because of their modularity and flexible software architecture, SDRs will be an effective low-cost solution for both manufacturers and end users.
Potential SDR Issues
Because of its obvious advantages, SDR technology is gaining a lot of momentum. However, there are many issues to be resolved before the technology can be fully accepted for military, commercial, or civilian applications. One of the most basic issues is that the tools and network infrastructure must be in place before SDR products can become effective, reconfigurable and agile devices in a widespread marketplace.
Another obvious issue is the security of downloads. For example, given a script that describes a link-layer protocol, there must be a phase in which the protocol is downloaded to the hardware and run as a configurable protocol. The question is, how is that download secured? Obviously, it must be signed and have digital authorization. Otherwise, downloads might be made to devices that could then broadcast on unauthorized bands. Security issues facing SDR technology include encryption, user identification, device authentication, and others.
A third major challenge facing SDR technology is convincing the FCC to open the radio spectrum. In the past, the FCC has regulated specific radio bands for different types of communications. A radio device is then licensed for use in only a specific frequency range. Intel and other industry leaders would like to see devices licensed for multiple radio spectra, rather than for only one communications band. This would allow manufacturers to make a single device that could broadcast and/or receive at any appropriate frequency. The frequency used for a specific type of communication could then depend on the device or user identification, such as for National Guard, police, fire, Air-Sea Rescue, animal control, border patrol, road construction, clean-water works, and so on.
SDR developers are already starting to address these challenges. The task now is to work toward a secure, practical, immediate use of SDR technology, such as agile radios, while designing for the features—such as cognitive radio—still to come.
Cognitive Radios On the Horizon
The word "cognitive" refers to being aware of and making judgements about something. In the future of SDR technology, a cognitive radio will be able to sense its surroundings and the presence of other signals. Using that information, it will then be able to adapt, without user intervention, to its user's communication needs. Essentially, cognitive radios will be able to create their own adaptable, on-the-fly wireless networks, based on the needs of the user at that moment.
To illustrate, a user might enter an area with several communication hubs. In this environment, a standard radio will choose the nearest hub as its communication base. In contrast, a cognitive radio could choose a hub with a relatively low usage load, even if the distance to that hub is greater than a closer, but more heavily loaded hub. A cognitive radio could also change its frequency modulation language and output energy to communicate better with other SDR radios in the area.
One of the biggest advantages of SDR technology may be giving radios the ability to make use of frequencies that are not currently in use. Right now, at any given time, only a small portion of the radio spectrum is in active use. SDR technology may allow a cognitive radio to determine an unused frequency in what is currently an unlicensed spectrum, and then shift to that frequency for communications. This may make it easier to manage the overall radio spectrum, and even avoid the need for some types of FCC licensing.
One of the most interesting potential applications of a cognitive radio is in a military radio environment. Right now, traditional radios perform signal conversions as close to the antenna as possible. In contrast, SDR technology would let military radios choose arbitrary, intermediate frequency (IF) bandwidth, modulation schemes, and coding schemes. This offers military personnel features that are useful for intelligence gathering and other tasks. An SDR radio could allow military users to frequency "hop" to find secure channels for themselves and their allies.
Industry Directions
Many companies already have commercial products running different SDR radio communication protocols and standards. Companies that are working on SDR solutions include Intel, Morphics Technology, Chameleon, Vanu Inc., and Raytheon, among many others.
There is also significant academic research going on in SDR areas. Researchers are exploring new energy-efficient algorithms, reconfigurable architectures based on ASICs (application-specific integrated circuits), digital signal processing for SDRs, and the use of FPGAs (field-programmable gate arrays) for SDR silicon.
In addition, Intel is working with United States, European, and some Asian regulatory authorities to adapt regulatory guidelines for agile radio technology. 
Summary
Software-defined radios are a rapidly evolving technology that resolves many of the problems seen with today's hardware-based radios and incompatible communications protocols. With programmable silicon and flexible software architecture, SDR is the logical convergence of communications and computing. And, with SDR, upgrades can be as simple as another Internet download, much like running a new or improved version of an application on a computer.
SDR technology is only now becoming commercially viable because of recent advances in CMOS, RF technology, and other areas. SDR products will likely appear first in specialized areas, such as military and public safety applications. SDR devices for general consumers will follow when the tools and infrastructures are developed and economies of scale take effect.
Initial SDR offerings will likely let users enable, reconfigure, and upgrade a single device to support multiple functions and protocols. This will let people use a single device in a variety of ways as they move from one radio environment to another. In the future, SDR will allow radios to perform intelligent networking and other advanced functions. Portable SDR devices could not only create communication links between different radios, but they could establish an infrastructure where none exists. An SDR could even supplement the inadequacies of an existing infrastructure by serving as a base-station.
With both technical and regulatory challenges to address, SDR technology is in a somewhat amorphous childhood. Developers interested in SDR should get involved now in forums and other development groups to help determine the directions this flexible, low-cost technology will take.
http://www.intel.com/update/contents/wi07031.htm | |
