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Hybrid systems for LMR

Written by Stephenie Slahor

Needs grow for public safety, but the budget doesn’t always keep up with those needs. A network that integrates multiple technologies and frequency bands for land mobile radios (LMR) might solve some of the problem. Building such a “hybrid” was the topic of discussion for John Facella, Director and Market Manager, Public Safety, M/A-COM Wireless Systems Business Unit.

A composite system of two or more different air interfaces and one or two or more frequency bands, all using a common backbone network, would solve the problem of meeting public safety needs in both urban and rural areas in capacity and coverage, Facella said. Because public safety serves the missions of law enforcement, emergency medical services, fire fighting and transportation, there are different networks needed for support of such a broad application. Also, many present systems are aging, Facella said, so there is a need to migrate to newer systems.

The re-banding to 800 MHz is occurring, but it is not proving to be an easy task. There may have to be a parallel network and an upgrade to something else. If a system is voice only, it won’t have the capacity to do such things as having survey cameras at busy intersections or neighborhoods, data sharing or video. P25 is in Phase 1 now, and Phase 2 is coming with additional capacity, new air interfaces and applications. There will likely be a need for a regional system of rural, suburban and urban users, and perhaps a combination dispatch center.

Most hybrid networks have a common IP backbone and switches, Facella explained. Users can share switch and routing equipment, so there is no need for duplication of equipment. One manager or administrator can run the system. It might include fleet mapping and talk groups as well.

It’s important to have a “scalable” system as changes mandate, he said, one that can grow as towns incorporate into cities, and as rural areas develop or not. Reducing the total ownership cost is also a factor. Acquisition is one cost, but it doesn’t project what the long term costs will be. Facella said there needs to be a total cost picture that includes not only purchase, but also maintenance and upgrade.

In the past, narrowband voice-over console/switches/backbone were the “system,” and were probably proprietary. Then high-speed or wideband data use emerged, usually with a separate base station, management and another “silo” to maintain. Broadband data, especially 700 MHz data above 1 million bps, offers fast communications with different transmitters and modulations.

Going to hybrid LMR is a start, and can begin with IP WAN with routers to route packets around the system, mission critical for each agency. Add geographically redundant network switching center computers (at least two), and each could operate for the other, and could also operate in different locations for backup capacity in case one is inoperative, Facella said. Add administration communication network management and subscriber management, then a radio system of P25 Phase 1.

Legacy LMR should be converted from analog to digital, with Network First gateways. A broadband would help allow the flexibility needed to show public safety entities video of an incident at its start, to its end. There could also be such additions as a local EDACS system, Open Sky system, Phase 2 of Project 25, voice-over IP telephone interconnection and ISSI to other P25 systems. Then software defined radios could round out the system. It’s busy, Facella said, but one network does it all.

Other additions could include a management switching system link to mission critical voice, emergency services, LMR data in an LMR network, 3G mission critical data, WEB client applications, broadband backhaul, cell network with PTT over cell, and 3 and 4G data. As data speeds go up, more information can be sent. But there is a price paid in coverage, Facella said. There will be shorter distance. You will need the bandwidth to send the information for silent dispatch, NCIC lookups, mug shots, field reports, maps, floor plans, Web access, streaming video and desktop applications.

Add metropolitan-area high-speed or wideband data for increased speed and capacity, then hot spot broadband for backhaul in select areas such as boat or bike patrol. In other words, make your system a “hybrid” by designing exactly what you need, combining different systems, Facella said.

Scalability in any setting can start small and grow into a larger system, but Facella said it can only be done right with an IP-based backbone. The system may be able to blend sites, for example, using the same towers and filling in with extra “site-friendly” poles, etc., that use existing poles or infrastructure.

Facella described the State of Nevada’s EDACS trunking, involving linkage among Nevada Power, Sierra Pacific, the Nevada Department of Transportation, Washoe County and Reno in the “Nevada Shared Radio System.” Everything will be able to link with hybrid systems, assisting more than 10,000 users in a 10,000-square-mile area, and with 95% of the roads covered in the system.

Facella also cited the example of New York State with a mixed technologies and bands system, using 700 and 800 MHz, and VHF, all P25. Cross band repeaters allow 700/800 MHz portable radios to talk to each other and to the base center. Because VHF is not good in urban areas, and 700/800 MHz would have too many sites, the hybrid model worked best.

He said key sharing needs an interoperability encryption key to talk. Hybrid networks can be built now with common IP backbone, switches, and management systems to combine multiple bands, air interfaces, VoIP phones, interoperability, data and cellular. According to Facella, it can be scalable and future ready.

Stephenie Slahor, Ph.D., J.D., writes in the fields of law enforcement and security. She can be reached at drss12@msn.com.

Published in Public Safety IT, Jan/Feb 2010

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