Specifications

Assigning this value as S, one can also express what signal-to-noise ratio (SNR) can be expected in

relation to noise figure (NF) and transformed to the receiver input

SNR = S -(10.log(kT)+10.log(B

)+NF) [dB]. (2.1)

In (2.1), k is the Boltzmann’s constant, T is the absolute temperature in Kelvin and B

is the receiver

noise bandwidth of e.g. 25 kHz.

3.2.1. Maximum usable data sensitivity

In this section, the results of maximum usable data sensitivity measurement (Figure 3.4) for the complete

narrowband radio transceiver are presented. All the results are given for 25 kHz channel separation.

Firstly, let us focus on operational modes with exponential modulations, Figure 3.4. It can be seen that

the emf sensitivity limit of +3 dBμV (-110 dBm @ 50 Ω) is fulfilled with margin for both modulations

(2CPFSK, 4CPFSK) when running at the symbol rate of 10.4 kBaud. When higher symbol rates are

selected, these modulations loss their power efficiency rapidly and for the selected symbol rate of

17.3 kBaud, the sensitivities lower down to the values of −107 dBm @ BER=10

-2

and

−102 dBm @ BER=10

-2

for 2CPFSK and 4CPFSK respectively. This discrepancy is caused mainly

due to the fact that there is a significantly lower frequency deviation used at the higher symbol rates.

The decrease in power efficiency with increasing spectrum efficiency is not linear as for the typical linear

modulations. Although possible, this example documents that the increase in spectrum efficiency of

exponential modulation techniques cannot be considered for efficient use of assigned bandwidth.

Fig. 3.4: Maximum usable sensitivity measurement results for different settings of exponential

modulations.

The second set of measurement results, presented in Figure 3.5, documents the power efficiency

analysis of operational modes based on the linear modulation techniques. It can be seen that when

using the linear π/4-DQPSK, the radio receiver can still reach the data sensitivity limit even for

17.3 kBaud with a 2 dB margin. Even from this comparison it is evident that the π/4-DQPSK mode of

operation outperforms the 4-CPFSK at higher spectrum efficiencies. Further increase in spectrum effi-

ciency can be reached by higher order constellations such as D8PSK and 16DEQAM and the radio

receiver can still maintain practically applicable sensitivities of −107 dBm @ BER=10

-2

and

−105 dBm @ BER=10

-2

respectively.

Data speed and Modulations