2-3
6.25 kHz FDMA Technology
8
Other methods were also considered, including ACSB
and the proposed APCO Project 25 Phase II CQPSK.
However, both required a more expensive linear
amplifier in the transmitter and neither is compatible
with existing analogue FM hardware.
Instead, 4LFSK modulation was selected using
FDMA for transmission. This method has a number of
advantages:
•better communication range
•simpler design
•easy to maintain and service
•lower cost for business and industry customers
•compatible with existing FM radio hardware
Icom’s first radio with this technology is the
F3061/F4061. To enable backwards compatibility, the
radio is both analogue and digital and also works in
25 kHz and 12.5 kHz channel bandwidths.
This new digital protocol, NXDN™ (Next Generation
Digital Narrowband) has been registered as a
trademark by Icom Inc. and Kenwood Corporation.
IDAS (Icom Digital Advanced System) is the system
based on this NXDN™ technology.
The product range is steadily expanding , from
handheld transceivers to mobile transceivers to
repeaters. All products are/will be available for VHF
and UHF bands.
Background
As existing spectrum becomes increasingly scarce,
the demand for more options grows. The FCC
essentially created additional spectrum by adding
hundreds of new licenses with 6.25 kHz bandwidth.
To take advantage of this opportunity, Icom and
Kenwood entered into a joint agreement to develop
6.25 kHz technology. This technology is a new digital
communications protocol that provides quality voice
and data, and is designed as a non-proprietary
protocol. It accomplishes this by using 4LFSK (4-
Level Frequency Shift Keying) and FDMA (Frequency
Division Multiple Access).
History
This technology was developed in response to an
FCC revision of the rules concerning transmitters in
the 150MHz to 174MHz and 421MHz to 512MHz
range. To receive FCC certification after January 1
st
2005, transmitters must have proved compliant as a
multi-mode device. This requirement could be
achieved by using 6.25 kHz channel bandwidth. In
addition to the FCC requirement, Europe and Japan
are also moving toward 6.25 kHz technologies.
Because some in the industry believed that this
requirement could not be met by 2005, the FCC
suspended this requirement. (A new deadline of
January 1
st
2011 has been set.)
Icom, however, went ahead to meet this requirement.
It was impossible to do using analogue technology, so
it became necessary to develop a new digital protocol.
6.25kHz Digital mode ready
The IC-FR5100/FR6100 series are 6.25kHz digital mode ready*, the IC-FR5100/FR6100
series provides 6.25kHz digital narrow mode communication, and increases efficiency of
channel allocation and use of spectrum.
