Areal spectrum utilization efficiency in digital radio link networks

Areal spectral efficiencies of three digital modulation methods (QPSK, 8-PSK and 16-QAM) used in digital radio relay systems are studied. It turns out that the key feature to efficient total spectrum space usage is the interference tolerance of the used modulation method. Star point analyses indicate that QPSK (quadrature phase-shift keying) allows the smallest angles between neighbouring hops and that the total node capacity with QPSK is the highest for small and moderate fading margins. Analyses of a mesh network model accentuates the observation showing that the areal spectrum efficiencies of QPSK, 8-PSK and 16-QAM are related as 10:3:1 independently of fading margins under relatively general assumptions