Interference effects in high spectrum efficiency M-QAM radio systems

With a view to determining the actual spectral efficiency obtainable with a multilevel quadrature amplitude modulation (M-QAM) system, adjacent and cochannel interference effects are investigated; consequently, degradations in signal-to-noise ratio required to guarantee a fixed error probability are evaluated. The algorithm proposed, which is also compared and checked with different, alternative methods already published, can achieve both accuracy of the results and efficiency in computing time. Thus it allows rapid system investigation whatever the value of spectrum efficiency, i.e. for any choice of radiofrequency channel spacing and any number of modulation states. The numerical results, obtained with different values of rolloff factor, emphasise the ever increasing sensitivity of system performance to adjacent and cochannel interference when M increases.<>