Peak power reduction of flexible OFDM waveforms for cognitive radio

High peak-to-average power ratio (PAPR) is one of the major issues in practical orthogonal frequency division multiplexing (OFDM) transmissions. Due to high PAPR and power amplifier nonlinearity, it is typical to observe an increase in the out-of-band (OOB) interference caused by the OFDM transmissions and the bit-error rate at the receiver. The dynamic spectrum access system in this demonstration applies PAPR reduction to frequency-agile and bandwidth-adaptive OFDM transmissions, without sending any side information to the receivers. Partial transmission sequences (PTS) are adopted for PAPR reduction to be compatible with the cyclostationary signatures, embedded into OFDM waveforms for frequency acquisition and bandwidth estimation. In addition, by rotating the signal constellation properly, there is no need to send PTS-related side information to the receivers. The demonstration system is built upon the highly flexible Iris software radio platform, which is capable of providing the runtime reconfigurability needed.