Subject: [NEXTEL-1] Software Defined Radio: The interoperability solution?

From: [email-masked]
Date: Tue, 16 Dec 2003 01:59:51 -0500

Software Defined Radio: The interoperability solution?

By John Powell

November 1, 2003

With local and state public safety first responder agencies spread across 10
discreet RF bands, lack of interoperability is the significant problem most
often quoted in after-action reports from major public safety incidents.
Most citizens do not realize that their police and fire officers cannot
communicate directly with each other by radio, a well-publicized obstacle
faced by the New York City fire and police departments during the terrorist
attacks at the World Trade Center on September 11, 2001

While there has been much discussion about this problem in council chambers
and statehouses across the country, and significant legislation proposed
inside the Beltway, money to improve interoperability is only now starting
to trickle into public safety budgets. Software Defined Radio promises
perhaps the best long-term interoperability solution, providing the field
officer with a belt-worn subscriber unit offering the ability to communicate
in real-time with whomever he or she needs communication within limits
established by agency managers. However, the technology still faces
significant technical challenges as it grows from its infancy at the
Department of Defense and from within commercial development enterprises.

Local, state and federal public safety agencies operate mission critical
voice systems in ten discreet bands, ranging from 30 MHz to 869 MHz, and
employing a number of different air-interface protocols. These bands are
based upon the historical assignment of higher frequencies as the need for
additional public safety spectrum was identified, and as technology provided
cost effective equipment for the higher bands. In reality, this is not a bad
situation because each of the various bands offers propagation
characteristics that, when properly applied, support particular public
safety user communities. For example, the lower bands work well for wide
area rural systems with low population densities, while the higher
frequencies with their improved building penetration characteristics are
more appropriate for urban environments.

Three key interop categories
However, operational requirements highlighted by the horrific events of
September 11 are driving agencies to demand dramatically improved
interoperability between users. Interoperability is divided into three
categories, with each having specific characteristics:

Day-to-day interoperability represents perhaps 95 percent or more of all
interoperability use. It is the communications that takes place between
officers from adjacent agencies, or with overlapping jurisdictions (such as
city and county police) who back each other up on incidents. In the fire
service it is the concept of automatic aid where the closest unit responds
regardless of jurisdiction. In general, the communications links required
for day-to-day interoperability are in-place, cover a specific geographic
area, and are regularly used.

Task force interoperability supports planned events, though they could range
over a wide geographic area. A narcotics surveillance is a one example of
such use, and intercommunications between units of a fire strike team
enroute to the wildfires in Southern California is another. Special events
such as county fairs and political conventions also use task force
interoperability. The links for task force interoperability are preplanned
ahead of the event, and only exist during the event.

Mutual aid interoperability represents the least used, but most demanding of
the three categories. It is the often overwhelming response to major
disasters such as earthquakes, fires and hurricanes where there can be no
detailed preplanning for the event and communications links are established
as the event unfolds and responders arrive at the scene. Fortunately,
overall response strategies are usually in place, defining the general
nature of the communications that will be needed.

It is within these three categories that technology must be applied. The
solutions being implemented today, primarily cross-band links, are not
spectrum efficient, nor do they provide needed coverage in many situations.
Patch systems require one RF path in each band for each conversation path to
be linked, channels that must be taken from the available inventory of one
of the participating agencies in each band. Coverage is limited to that area
that is covered by the overlapping RF footprint of all of the involved
channels. Couple these limitations with the operational requirements to set
up and monitor each of the patch links, along with the limitations of the
patch technology itself (delays in channel keying, inability to detect
 "busy" talkgroups on trunking systems, and the lack of support for
end-to-end encryption) and the usability of these systems can quickly reduce
their benefit to interoperability.

Radio-to-radio needed
The real need for a public safety officer when responding to any of these
situations is to carry a radio on the belt that offers the ability to reach
whomever she or he needs to communicate with in real time. That need must be
supported radio-to-radio without the use of infrastructure for on-scene use
at many incidents.

Enter Software Defined Radio. As already demonstrated by companies such as
Thales and Vanu, SDR offers the potential of providing a multi-band platform
that supports a number of different public safety waveforms. A waveform is
the "software package" that defines the air interface and protocols
necessary to enable communications using a particular technology. Project 25
Phase I, M/A-COM EDACS and Motorola SmartNet are all examples of waveforms
that could be supported on an SDR platform. Equipping a field officer with a
radio that supported the waveforms of agencies in that geographic area,
along with a common national interoperability waveform, would enable that
officer to have direct interoperability without the need for enabling
infrastructure.

Additionally, SDR offers important other benefits to public safety. The
ability to download software onto an existing platform allows for the
addition of new features to existing waveforms and supports forward
migration to new technologies with new waveforms.

On-the-street reality?
However, SDR is not yet an on-the-street reality. Through a contract with
DoD, Thales has developed its MBITR portable radio that is not yet
type-certified for public safety use. Likewise, Vanu Inc has demonstrated a
multi-mode multi-band radio operating on a Compaq iPAQ platform. This latter
product is a proof-of-concept device, requiring repackaging into a
ruggedized public safety housing, with the proper form factor and supporting
characteristics. Both require added waveforms to be of significant benefit
to the user community, though they have proven the SDR concept is viable.
Vanu is also developing a proof-of-concept base station for use in rural
areas where a single SDR processor will support waveforms for public safety
as well as for commercial cellular voice and for commercial wireless data.

That is not to say that significant technological hurdles have been
overcome. The development of a public safety portable subscriber set is
hindered by a number of technology requirements: battery capacity, antenna
development and physical form factor remain major issues, as does the cost
of the overall product. SDR processors and broadband power amplifiers
require significant power. Public safety users require a battery that will
support a radio for shifts that routinely extend to 12 hours. Today's
multiband antennas are physically too large to carry if they have to support
a very wide range of frequency bands. And all of the hardware, including an
appropriate battery must fit in an easy-to-carry package with an appropriate
form factor that supports ease of use. Finally, the product must be
affordable; while agencies will be willing to pay a premium for the features
provided, all are constrained by today's limited public budgets.

But perhaps the greatest impediment to fielding a useful SDR product will be
the licensing of intellectual property (patents). Each of the major public
safety waveforms, with the exception of analog FM and Project 25 digital,
will require negotiations with those manufacturers that could introduce
major delays.

SDR will make its way into the public safety radio services. As with any new
technology, introduction will be slow and the initial products costly. But
the benefits obtained from the technology will eventually drive demand up
and cost down. Will SDR be the ultimate solution to the interoperability
problem? Only time will tell, but research to date certainly supports that
claim, and significant R&D funds from both private and public sources are
being devoted to the development effort.

John S. Powell is an electrical engineer and a director of the Software
Defined Radio Forum, representing government agencies. Among his many
achievements, Powell served as statewide Police Communications Coordinator
for the University of California system. He is a life-member and
past-president of the Association of Public Safety Communications
Officials-International (APCO). He is a member of the Project 25 Steering
Committee and has been a member of the California Legislature's Joint
Committee on Fire, Police, Emergency and Disaster Services, APCO Law
Enforcement Service Committee. Powell is past-chairman of the
Interoperability Subcommittee of the National Coordination Committee, a
federally chartered advisory committee to the FCC regarding implementing the
700 MHz public safety band and past-chairman of the FCC-chartered State
Interoperability Executive Committee for the State of California, Governor's
Office of Emergency Services. Recently, Powell has been consulting for
several agencies within the U.S. Justice Department, the Department of
Homeland Security, and the Executive Office of the President of the United
States on issues related to public-safety communications interoperability,
development of next-generation public safety broadband equipment and
standards, and Software Defined Radio.

Interoperability:

-- The ability to talk to who you need to talk to when you need to talk
(data and voice, realtime).

-- NOT the ability to talk with everyone all of the time!

 http://iwce-mrt.com/ar/radio_software_defined_radio_2/index.htm

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