Electronic Design

A Failure To Communicate? London Gets The Message

A recent report from the July 7 Review Committee of the London Assembly says the most serious failure during rescue operations following the terrorist bombings in the London subway last year was poor communications between emergency services. Police, fire, and ambulance personnel used different radio systems and couldn't coordinate their response.

London is now upgrading its subway system communications. But it's going to take about two years to complete. The problem continues to be the inability to communicate between equipment built by different manufacturers operating over different frequencies.

Here in the U.S., similar communications concerns stemming from the Sept. 11, 2001 terrorist attacks and Hurricane Katrina sparked the Project 25 (P25) interoperability standard. It addresses the fact that public service radios operate on different frequency bands, such as VHF and UHF.

"The technology side of interoperability has been solved for a number of years", says Craig M.. Jorgensen, co-chair and project director of P25.

"Implementing that technology in a way that satisfies the needs of the various user agencies is another issue".

The P25 interoperability standard for digital two-way wireless communications has been developed for public safety and federal agencies under the auspices of the Association of Public-Safety Communications Officials, with support from the Telecommunications Industry Association (TIA).

P25 enables migration from existing analog systems (including conventional, trunked, and encryption technologies) to narrowband public safety digital P25 systems. At least 46 radio manufacturers have signed on to the P25 intellectual property rights agreement. But even with P25 standards in place, Jorgensen says how users will provide cross-band communications is still up to them.

To get disparate first-response systems to communicate, radios from different systems need to be linked into a switch/programmable interconnect device. If an emergency service with VHF radios arrives at a scene where the home radio system operates at 800 MHz, the VHF and 800-MHz radios both have to be plugged into the switch. When a responder with a VHF radio talks, the VHF radio connected to the switch outputs the audio through the switch, where the 800-MHz radio rebroadcasts the same audio.

DIFFERENT FREQUENCIES
Even though P25 standards apply to all of those frequency bands individually, users still must define how they will provide cross-band communications. The TIA recently adopted the first part of the Inter Sub-system Interface standard, which will let users from one standard system access another standard system in the same frequency band.

Fred Frantz, who heads the Software Defined Radio (SDR) Forum's Public Safety Special Interest Group, says manufacturers of digital trunked radio systems have proprietary protocols that make radios programmed for one system incompatible with other systems. The SDR Forum supports the development and deployment of SDR systems to enable flexible and adaptable architectures by changing software in advanced wireless systems.

The Federal Communications Commission has called for a mobile wireless system that would enable first responders to talk directly to each other in a crisis. But funding, much of which would come from the U.S. Department of Homeland Security, has been slow in coming.

A new report by the SDR Forum notes that most public safety land mobile radio products now being developed use SDR technology to support multiple protocols and multiband, multiservice radios. First responders now can have a single radio configured to operate on any radio system, regardless of band.

Another major step, according to Frantz, would be the ability to license the protocols of proprietary systems so first responders could have radios that operate independently of frequency band and vendor protocols. Both of these areas are under discussion, he says.

What's next? Jorgensen says future generations of the P25 trunked system will enable mobiles in any given band to roam from system to system with either prior authorization or on an emergency basis as defined by the system operator. More information is available from the P25 Technology Interest Group at www.Project25.org.

See associated figure 1 and 2

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