Licensed, professional two-way radio is on the verge of making the biggest leap forward since the

invention of the transistor — the move from analog to digital. Digital radio offers many advantages

over analog, including improved voice quality at greater range, better privacy, sophisticated call-control

features, the ability to easily integrate with data systems, and more.

 

We’re now at the beginning of what will quickly become a large-scale migration to digital radio in

professional applications. At the same time, regulatory pressures combined with real-world operating

needs are driving radio manufacturers and users to communicate more information in a given slice of

RF spectrum — in other words, to increase “spectral efficiency.” Channels that historically carried a

single call at a time are now being divided so they can carry two.

 

Two technologies exist to enable this “splitting” of channels, allowing multiple access on a single

channel. Frequency-Division Multiple Access (FDMA) splits the channel frequency into two smaller

sub-channels that can carry separate calls side-by-side. Time-Division Multiple Access (TDMA)

preserves the full channel width, but divides it into alternating time slots that can each carry an

individual call. Both technologies are already being used in North America to accomplish the FCC

mandated split of 25 kHz channels into 12.5 kHz channels, and they’re both being used worldwide

to accomplish similar increases in spectral efficiency whether currently mandated or not.

 

In the coming years, new regulations will almost certainly require improvements in the effective

capacity of 12.5 kHz channels: it is only a matter of time before the ability to carry two voice paths in

a single 12.5 kHz channel — also known as 6.25 kHz equivalent efficiency — becomes a requirement.

But because the technology exists today to accomplish this goal, there’s no need for professional

radio users to wait for the regulations to catch up with benefits that are immediately available. Even

in the absence of a mandate, professional users can double the capacity of their existing licensed

channels by adopting digital technologies that enable 6.25 kHz equivalent efficiency. With potential

benefits including increased capacity, lower equipment costs, data integration, added features, and

more, now is a compelling time for analog radio users to make the switch to digital systems that offer

6.25 kHz equivalency.

 

This white paper examines the two leading digital modulation technologies that are capable of

achieving this doubling of spectral efficiency: 6.25 kHz FDMA and two-slot 12.5 kHz TDMA.

Businesses looking to migrate to the most efficient professional digital systems to achieve

greater capacity and performance will need to choose one or the other — FDMA and TDMA

are not interoperable.

 

Two-slot 12.5 kHz TDMA-based systems, providing 6.25 kHz equivalency is the right choice for most

mobile professionals. Professional radio standards based on TDMA technology are already widely

used around the world, and future requirements for even greater spectral efficiency are almost certain

to be based on TDMA as well. Today and tomorrow, TDMA technology provides advantages of

feature flexibility, lower equipment costs, longer battery life, future-readiness, and the proven ability

to increase spectral efficiency without risking increased congestion or radio channel interference.