APCO-25, FDMA, FHSS ajd TDMA digital radio comparison

There are basically four digital technologies currently available for private radio communications system use. They are
as follows:

APCO-25 (C4FM and CQPSK)

More commonly known as P25, this is the digital standard selected by U.S. Government agencies and presumed by many
to be the platform best suited for all public safety users. The purpose of P25 was and is to provide a common platform
offering the highest level of interoperability while simultaneously addressing the need to move to narrow frequency channel
spacing. On of the best overviews of P25 has been prepared by Aeroflex, a test equipment manufacturer offering equip-
ment for the servicing of P25 equipment. For additional information, click here. Technically, this is known as C4FM,
compatible four-level frequency modulation) in a 12.5 kHz channel or CQPSK, compatible quadrature phase shift keying)
in a 6.25 kHz channel.

FDMA (4 Level FSK)

FDMA is a new commercial digital standard jointly developed by ICOM and Kenwood to provide the ability for a radio to
function in either a digital or analog mode at 25 kHz, 12.5 kHz, or 6.25 kHz. Technically known as Frequency Division
Multiple Access (4 level FSK), it is currently the most flexible and affordable platform available for VHF or UHF systems.
Additional information is available by clicking here.

FHSS (Frequency Hopping Spread Spectrum)

FHSS is the platform used in the Motorola DTR 900 MHz on site radios. FHSS has been around for a long time. A
pioneer developer, Aironet (now a part of Cisco Systems) developed this technology for wireless Access Points and
Bridges in the 2.4 GHz band. This has become a defacto standard for today's Wireless Local Areas Networks (LANS)
as well as cellular phones operating at 900 MHz, 2.4, and the 5 GHz range.

TDMA (Time Division Multiple Access)

TDMA has been around for a long time in the cellular industry although most advanced cellular systems are moving to
GSM or advanced CDMA technology. Variations of TDMA are used in the recently announced MOTOTRBO radios for
UHF was introduced in the first quarter of 2007. VHF models are expected to be announced in the third quarter of 2007.
For additional information on MOTOTRBO, click here.

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