6 System Feature Overview
April 2011 68007024085
By comparison, analog radios operate on the concept of Frequency Division Multiple Access
(FDMA). In FDMA, each transmitting radio transmits continuously on a designated channel, and
the receiving radio receives the relevant transmission by tuning to the desired carrier frequency.
TDMA thereby offers a straightforward method for achieving 6.25 kHz equivalency in 12.5 kHz
repeater channels – a major benefit for users of increasingly crowded licensed bands. Instead of
dividing channels into smaller slices of decreased bandwidth – which is what would be required to
increase spectrum efficiency with FDMA methods, TDMA uses the full 12.5 kHz channel
bandwidth, but increases efficiency by dividing it into two alternating time slots. Additionally, this
method preserves the well-known radio frequency (RF) performance characteristics of the 12.5
kHz signal. From the perspective of RF physics – that is, actual transmitted power and radiated
emissions – the 12.5 kHz signal of two-slot TDMA occupies the channel, propagates, and
performs essentially in the same way as today’s 12.5 kHz analog signals. With the added
advantages of digital technology, TDMA-based radios can work within a single repeater channel to
provide roughly twice the traffic capacity, while offering RF coverage performance equivalent to, or
better than, today’s analog radio.
Figure 2-2 Comparison between Today’s Analog and MOTOTRBO
Time
12.5kHz Analog
- 1 voice for each 12.5kHz channel
- A single repeater for each channel
12.5kHz TDMA
- Divides existing channel into two timeslots
- Delivers twice the capacity through repeater
- Performance is same or better than 12.5kHz FDM
- Single repeater does work of two repeaters
- Reduces need for combining equipment
- Enables 40% increase in radio battery life
Regulatory
emissions
mask
Slot 1
Slot 1
Slot 1
Slot 2
Slot 2
Slot 2
Frequency
12.5KHz channel
Frequency
12.5KHz channel
Today’s Analog
MOTOTRBO
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