The large number of occupied frequencies worldwide has pushed developers to create smarter tactical radios—ones capable of detecting interference and switching frequencies to open bands.
Cognitive radio is the software-defined radio (SDR) enhancement that, according to many, is the future of military radios. Cognitive radios are smart radios that can detect occupied bandwidth; they make decisions about where to transmit, at which frequencies, and with what modulation scheme. Such cognitive radios are agile in terms of frequency, power, and modulation to adjust to the available spectrum, interference, location, and other conditions. They can also change their characteristics to optimize the connection, as well as to guard radio security (see “Cognitive Radio: Talking Points,” below). What follows are examples of recent technology advancements in this direction.
The development of a highly mobile tactical communications system can test the limits of current wireless network technologies. Such a system must have rapid deployability, scalability, flexibility, reliability, interoperability, transportability, and survivability in the presence of intentional and unintentional jamming. Cognitive radio technology plays a major role in meeting those needs. In fact, the US Army has begun testing a unique tactical cellular telephone system called xMax at its Fort Bliss site, located near El Paso, TX.
A product of Florida-based developer xG Technology , xMax is a carrier-class cognitive radio system in the unlicensed 900-MHz Industrial-Scientific-Medical (ISM) band (902 to 928 MHz). While carriers like AT&T and Verizon paid billions for 20 MHz of spectrum in the most recent 700-MHz auction, xG uses the free and available 26 MHz of spectrum in the ISM band. Industrial users might caution that the openly used bandwidth is just as congested (or worse) than the 2.4-GHz band as far as interference. While it is certainly true that a wide range of services, telemetry, remote control, and video surveillance occupy the band, cognitive radio makes this spectrum suitable for voice and data calls.
Cognitive radio can be thought of as a system that listens to the band in use to determine where the potential interference is then switches to a frequency that is unoccupied. The xG handsets actually scan a band 33 times per second looking for interference and identifying the clear spots where a good link can be formed. It then notifies the base station, causing the link frequency to change as needed to keep a clean connection.
The xMax system adheres to the Federal Communications Commission’s (FCC’s) Part 15 rules for the 902-to-928-MHz spectrum. Radios can have as much as 1 W transmit power, and that applies to the base stations, as well. Figure 1 and Figure 2 show a xMax handset and basestation, respectively. The system divides the spectrum into 18 1.44-MHz channels and uses robust binary-phase-shift-keying (BPSK) modulation. The system also employs time-division-multiple-access (TDMA) access, and each channel has the capability to handle as many as 12 voice calls. Data rate capability to 1.5 Mb/s is also planned for each channel.
As for real-world systems, xG has one major carrier-grade network already in full operation in Ft. Lauderdale, FL. A second—the one being tested at Fort Bliss—was deployed this past February. It is now being evaluated by the soldiers in garrison (the living and working areas of the base) while they finalize training in preparation for the Network Integration Evaluation taking place this summer. Evaluation of the system will continue as xMax is redeployed to the White Sands Missile Range in New Mexico.
“The added deployment and testing in the garrison setting will further demonstrate how xMax is able to support robust communications across the Army’s entire operational continuum,” says John Coleman, Colonel, USMC (Ret.) and CEO of xG. “This provides an additional venue that will help inform the Army community about how the system’s all-IP, cognitive radio, and dynamic spectrum access (DSA) characteristics can effectively meet their need for a cost-efficient enterprise wireless solution that can fulfill both garrison and tactical cellular requirements.”
Development of the Joint Tactical Radio System (JTRS) represents a major Department of Defense (DoD) program, with the goal of developing a complete line of SDR radios for voice, data, and video that can be used to form ad hoc networks on the battlefield. The program has been around since the late 1990s and has had its ups and downs. Overall, however, great progress has been made. The whole basis of JTRS is the Software Communications Architecture (SCA), an open-architecture platform standard that defines how the hardware and software work together.
One of the primary objectives is to develop software that is fully transferrable between different hardware platforms, making all military radios multifunctional and interoperable. The latest version, designated SCA 2.2.2, was recently made available, further improving the programmer’s ability to make the software more flexible and scalable. Called SCA Next, the software helps make programs smaller and require less testing. SCA does not, unfortunately, have specific provisions for cognitive features. However, over the past few years, DARPA has been testing cognitive enhancements to SCA like Dynamic Spectrum Access, which will hopefully be available in the coming next generation of JTRS radios.
A good example of a current JTRS radio is Thales Communications’ AN/PRC-148 JTRS Enhanced Multiband (JEM) Inter/Intra Team Radio [Fig. 3(a)]. According to Thales’ Vice-President of Advanced Programs, Lewis Johnston, the AN/PRC-148 JEM covers all HF, VHF, and UHF military frequencies from 30 to 512 MHz. It uses a frequency step size of 5 or 6.25 kHz with enough memory for 256 preset channels.
The transmit output power can be selected from 0.1 to 5.0 W. The receive sensitivity is -119 dBm with frequency modulation (FM). A wide range of modes and waveforms are available, including secure and unsecure amplitude modulation (AM) and FM, HAVEQUICK I AND II, MIL-STD-188-241-1/2 (SINCGARS), MIL-STD-188-181B, MIL-STD-188-181C, MIL-STD-188-182B, MIL-STD-188-183B (SATCOM-IW), ANDVT, and Project 25. Other waveforms are downloadable. Figure 3(b) shows the radio in use.
The AN/PRC-148 JEM also has fully programmable cryptography that supports the requirements of the National Security Agency’s (NSA’s) crypto-modernization program and is certified by NSA to protect the confidentiality of voice and data up through the Top Secret level. Also available are a wide range of accessories for various dismounted, fixed or vehicular use including 20- and 50-W power amplifiers, antennas, and remote control with Global Positioning System (GPS) receivers. Now all the AN/PRC-148 JEM needs is that cognitive download.
Military SDRs can pose a challenge to test with their wide frequency ranges and support for multiple waveforms and protocols. Furthermore, most of the newer SDRs are very highly integrated with few actual serviceable parts. Anti-tamper implementations also make access and testing difficult. Most field testing of handheld and vehicle radios today is of the “go” or “no-go” type. However, specific tests such as cable and antenna checks can be accomplished.
One company committed to testing tactical radios is Aeroflex. The firm recently announced their model 7200 Configurable Automated Test Set (CATS) to speed and simplify the testing of tactical radios (Fig. 4). This instrument is an example of a synthetic instrument (SI) using Aeroflex’s Common Platform architecture. In its basic form, it can test almost any military radio of the SDR design. The US Marine Corps recently placed a significant order for 7200s as part of their Ground Radio Maintenance Automatic Test Systems (GRMATS) program. The 7200 is fully compatible with the Software Communications Architecture (SCA) used by the JTRS. There is no cognitive radio testing capability, as of yet. The 7200 has been future-proofed with its bus structure that lets it add new processing power and software as it becomes available. Other similar testers in the Aeroflex line are the 7100 for LTE testing and the 7300 for most avionics systems.
Cognitive Radio: Talking Points
Synopsis: Cognitive radios are related to software-defined radios—transceivers that use digital signal processing (DSP) for radio functions like filtering, mixing, and demodulation/modulation. SDR transceivers are programmable to be multi-band, multi-mode devices with the flexibility to change features and characteristics as required by the communications need. Cognitive radios provide higher-level intelligence for the SDR, making it a radio that can sense its environment (location, spectrum, etc.); be aware of its internal conditions; learn by listening; and make decisions based on programmed objectives about when, where, and how to transmit and receive. Cognitive radio uses artificial intelligence (AI) techniques to make SDRs smart and adaptive.
Background: Cognitive radio dates back to around 1998. The name is credited to Joseph Mitola, III of the MITRE Corp., who developed the concept for the Defense Advanced Research Projects Agency (DARPA).
Concept: The receivers monitor a wide range of spectrum reading the traffic, noise, interference, and open areas. It then provides information for decisions regarding frequency, modulation, pro-tocol, network availability, and other characteristics for transmission and issues commands to the related SDR. Cognitive radios draw on location information from GPS, internal or external data bases, and preprogrammed policies and directions that allow the radio to adapt to the situation. A cognitive radio also learns from its experiences and can plan for future operations.
Requirements: Cognitive radio requires an SDR that is programmable, frequency agile, and capable of handling required waveforms (modulation/demodulation; related processing) and protocols.
Key References: Wireless Innovation Forum; Cognitive Radio Technology, 2nd edition, Bruce A. Fette, Academic Press/Elsevier, 2009.