So what is the main difference between Digital and Analog and also between FDMA and TDMA?
Digital versus Analog Two-Way Radio Communications
The shift to digital radio from analog has increased over the last five years, and this trend shows no sign of abating across the many industries which rely on two-way radio for their operations.
The main difference is in the way signals are transmitted and received. As in digital musical recordings, rather than use electrical signals resembling sound waves in order to deliver audio, digital radio transmits and receives by processing sounds into patterns of numbers.
So how does this translate into benefits for business users? Here are a few of the major ones.
Greater range: Both analog and digital signals diminish as distance increases from a station transmitter. However, digital two-way radio offers improved audio quality at a greater range than analog through better resistance to interference from other signals and avoiding the imperfections of transmission and reception which are typical of analog.
Preserve analog investments: Digital and analog voice can be combined in the same devices, making it easier to transition to digital for those companies who have already made significant investments in analog infrastructure.
Longer battery life: Transmitting analog radio is power-intensive, but new digital technology allows some radios to function about 40 percent longer on a battery charge than a comparable analog system.
Data: Digital two-way radio allows users some of the data functionality enjoyed by cellular users, such as text messaging.
Location services: GPS-enabled radios allow employers to track employee locations and monitor productivity.
Privacy: Digital two-way radio is easier to secure than analog, which suffers from a notable loss in voice quality when scrambled for privacy purposes.
Better spectral efficiency: The RF spectrum is crowded, and FCC regulations are mandating more efficiency and capacity. Digital two-way radio technologies such as Frequency-Division Multiple Access (FDMA) and Time-Division Multiple Access (TMDA) allows single-call channels to be divided, doubling call capacity. An explanation of the differences, and a recommendation as to which to choose follows in the next section.
TDMA or FDMA?
Two different technologies provide increased spectral efficiency: Frequency-Division Multiple Access (FDMA) and Time-Division Multiple Access (TDMA). Each provides the same end result — the ability to hold two calls on a single line — but each achieves this in a different way.
FDMA splits each 12.5 kHz channel into two smaller 6.25 kHz channels which can each carry a call. TDMA divides the channel into time slots capable of carrying one call each while preserving the width of the original 12.5 kHz channel.
So which one should businesses choose? Motorola suggests supporting the latter:
“TDMA fits seamlessly into existing licensed channel structures in UHF and VHF — known performance, no need for rebanding or relicensing, and no risk of new forms of radio channel interference. The choice of TDMA digital technology makes it quick and easy to gain spectrum efficiency and improve your two-way radio communications.”
Furthermore, because the FCC mandates a separate repeater for each frequency, splitting the 12.5 kHz into two 6.25 kHz channels as in FDMA will increases costs compared with TDMA, which achieves the same effect using the original channel.
References: Staleycom Telecommunications Blog: http://www.staleycom.com/blog/digital-versus-analog-two-way-radio-communications/