Specifications

Tab. 3.1: Measurement results of the transmitter parameters for selected modes of operation.
Spectrum
plotη
TX
P
IN
Occupied
Bandwidth
@ 99.9%
ACI
Lower UpperP
out
Modul.
Parameter
Symbol
Rate
Modulation
Format
[-][%][W][kHz][dBc][dBc][dBm][-][kBaud][-]
Fig. 3.1293519.8-61-6240
h=0.6,
α=0.2810.4
2CPFSK
Fig. 3.1293516.6-61-6240
h=0.2,
α=0.2817.3
Fig. 3.2293519.6-60-6140
h=0.3,
α=0.2810.4
4CPFSK
Fig. 3.2293517.2-60-6140
h=0.1,
α=0.2817.3
Fig. 3.31422.822.0-62-6135α=0.417.3π/4-DQPSK
-1422.822.0-61-6135α=0.417.3D8PSK
Fig. 3.31020.422.0-60.5-60.535α=0.417.316-DEQAM
Measurement uncertainty ±2 dB
The measurement values of achievable output power P
out
, amount of adjacent channel interference
ACI and overall transmitter power efficiency η
TX
are collectively given for all the modulation formats in
Table 3.1. It can be seen that the ACI limit (-60 dBc) is maintained for all of these settings; however,
there are two penalties in case of linear modulation schemes that typically have to be paid for higher
spectrum efficiency. Firstly, it is the lower output power level achievable. For this specific transmitter
architecture it is in particular 35 dBm @ π/4-DQPSK, D8PSK and 33 dBm @ 16-DEQAM. Secondly,
it is the lower value of the overall transmitter power efficiency reached. Comparing to exponential modes
of system operation the efficiency of linear operational modes has decreased to 14% and 10%. Despite
this negative trend, the achieved values of output power exceeding 3 W, and 2 W respectively, are
considered practically applicable for next generation of narrowband LMR devices and as it will be shown
in the next section they enable the system to use its occupied bandwidth with even higher communic-
ation efficiency.
3.2. Narrowband radio receiver
The most important parameters which describe the quality of narrowband radio receiver are maximum
usable (data) sensitivity, co-channel rejection, adjacent channel selectivity, desensitization and inter-
modulation response rejection. Besides the maximum usable sensitivity, all other receiver parameters
can be classified as the measures of the receiver degradation parameters used to analyze the degrad-
ation of its performance due to the presence of unwanted (interfering) signals. Although there is a
strong relation between all of these parameters, in this paper the attention is given only to the first of
them, to the maximum usable sensitivity in particular.
According to [1], the maximum usable data sensitivity is the minimum level of the signal (emf) at the
receiver input, produced by a carrier at the nominal frequency of the receiver, modulated with a normal
test signal, which will, without interference, produce, after demodulation, a data signal with a specified
bit-error-ratio (BER) of 10
-2
or a specified successful message ratio (SMR) of 80%.
The maximum usable sensitivity shall not exceed an electromotive force of 3.0 dBμV under normal
test conditions.
25© RACOM s.r.o. – RipEX Application notes
Data speed and Modulations