Specifications

Fig. 3.5: Maximum usable sensitivity measurement results. Channel separation 25 kHz.

3.2.2. Efficient use of narrowband radio channel

As it has been written in the Section 1, the radio transceiver in exponential modulation mode can make

use of higher transmitter power. In order to take this fact into account the system gain (SG) or the

maximum allowed path loss (2.2)

SG [dB] = P

out

- S , (2.2)

is usually calculated for the wireless communication systems. Here the P

out

is the available transmitter

power expressed in dBm and S is the measured value of radio receiver sensitivity, also in dBm. It ex-

presses the referential value of the link budget, assuming 0 dBi of antennas gain and together with the

spectrum efficiency given by (2.3) it expresses how effectively the radio device uses its assigned

bandwidth

η [bit/s/Hz] = —— . (2.3)

In (2.3), the R

is the raw bit rate given in [bits/s] and B is the frequency bandwidth assigned to the radio

system, 25 kHz in particular.

All these performance characteristics are collectively given in Table 3.2. It can be seen that even with

the lower available transmitter power, the radio transceiver can reach wider system gain at higher

spectrum efficiencies while running in linear as oppose to the exponential modulation mode. On the

other hand, if the long distance coverage is of the primary application concern, even the 2CPFSK

modulation having spectrum efficiency of 0.4 bit/s/Hz, but the system gain of impressive, 157 dB, can

be a reasonable option.

Data speed and Modulations