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 beneficial 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 application 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  can also by fulfilled with margin of 2-3 dB, resulting in the system gain of 147 dB.
For applications where higher data throughputs are needed the additional increase in spectrum efficiency can be gained by D8PSK and 16-DEQAM modulation formats. However, compared to π/4-DQPSK, an increase in overall communication efficiency cannot be expected, while there is the inevitable penalty in power efficiency characteristic.
ETSI EN 300 113-1 V1.6.2 (2009-11), Electromagnetic compatibility and Radio spectrum Matters (ERM), Part 1: Technical characteristics and methods of measurement. European Standard. ETSI, 11/2009.
ETSI EN 302 561 V1.2.1 (2009-12), Electromagnetic compatibility and Radio spectrum Matters (ERM), Land Mobile Service; Radio Equipment using constant or non-constant envelope modulation operating in a channel bandwidth of 25 kHz, 50 kHz, 100 kHz or 150 kHz; Harmonized EN covering essential requirements of article 3.2 of the R&TTE Directive. European Standard. ETSI, 12/2009.
ETSI EN 301 166-1 V1.3.2 (2009-11), Electromagnetic compatibility and Radio spectrum Matters (ERM), Part 1: Technical characteristics and methods of measurement. European Standard. ETSI, 11/2009.