Adaptive Modulation For OFDM Signals

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Adaptive Modulation For OFDM Signals. The sub band Signal To Noise Ratio in an OFDM communications channel varies by as much as 30 dB. In order to optimise the bandwidth efficiency of OFDM signalling it is desirable to adapt the chosen modulation technique such as M-ary QAM to the SNR available in sub bands. In this way high quality channels transmit the highest bit rates, whilst low quality channels accommodate the lowest bit rates. The net result is that the capacity of the communications link does not have to be limited by designing for worst case conditions.