Specifications

Tab. 3.2: Overall performance characteristics of the narrowband radio transceiver for selected
modes of operation.
System
Gain
Available
Output
Power
Data
Sensitivity
@ BER 10
-2
Spectrum
Efficiency
Raw Bit
Rate
Symbol
Rate
Modul.
Param.
Modulation
Format
[dB][dBm][dBm][bit/s/Hz][kbits/s][kBaud][-][-]
15740-1170.4210.4210.42
h=0.6,
α=0.28
2CPFSK
14740-1070.6917.3617.36
h=0.2,
α=0.28
15340-1130.8320.8310.42
h=0.3,
α=0.28
4CPFSK
14240-1021.3934.7217.36
h=0.1,
α=0.28
14735-1121.3934.7217.36α=0.4π/4-DQPSK
14235-1072.0852.0817.36α=0.4D8PSK
13833-1052.7869.4417.36α=0.416-DEQAM
Measurement uncertainty ±2 dB
3.3. Conclusion
As it was shown in this paper, the strict limits of the referenced standard as well as the state of the
technology hindered increasing the communication efficiency with which the narrowband systems have
been using the occupied frequency bandwidth. The key limiting factor that has been identified was the
limit of adjacent channel power attenuation. Lessening the requirement from -70 dBc to -60 dBc in
2007 has opened up the closed door for implementation of linear digital modulation techniques. However,
as it has been shown in later sections, a reasonable use of the exponential modulation can be still be-
neficial for these systems. Based on the results presented, the most important concluding notes can
be seen in the following:
• When the long distance coverage as well as the overall power efficiency are of the primary applic-
ation concern, the use of exponential modulation techniques 2CPFSK and 4CPFSK at relatively
low symbol rates e.g 10.4 kBaud can be the recommended option. In this case, the nonlinear
modulation techniques can make use of higher frequency deviation and increase the system gain
by outstanding values of receiver sensitivities. At the 10 W of output power the system gain of
157 dB and 153 dB for 2CPFSK and 4CPFSK modulation techniques respectively can be expected.
• When higher symbol rates are selected, the exponential modulation techniques lose their power
efficiency (and their main advantage) significantly. Further increase of the exponential modulation
spectrum efficiency from the values currently being used by the narrowband systems (up to 1 bit/s/Hz)
can be therefore considered inefficient.
• From all the modulation formats studied, the π/4-DQPSK can provide the narrowband LMR system
with communication efficiency closest to the optimal communication systems. The proposed solution
based on this modulation technique can reach the spectrum efficiency of up to 1.5 bit/s/Hz. The
data sensitivity limit required by [1] can also by fulfilled with margin of 2-3 dB, resulting in the system
gain of 147 dB.
RipEX Application notes – © RACOM s.r.o.28
Data speed and Modulations