Comparison of spectrum efficiencies of 4- and 16-QAM in mobile cellular environment

The spectrum efficiencies of linear multilevel quadrature amplitude modulation (QAM) schemes are compared in mobile cellular environment taking into account the impact of the bandwidth efficiency (bit/s/Hz) and the frequency re-use efficiency (comparable to the C/I requirement). 16-QAM needs about 6 dB higher co-channel interference protection than 4-QAM in ideal conditions. This implies that 16-QAM requires twice as many cells per frequency re-use cluster as 4-QAM when the distance dependence propagation exponent α equals 4. The bandwidth of 16-QAM is half of the bandwidth of 4-QAM which indicates that 4- and 16-QAM have about the same overall spectrum efficiency. Indoors α is typically larger than 4 and 16-QAM is slightly more spectrum efficient whereas outdoors 4-QAM is more spectrum efficient (α<4)