Waveform shaping techniques for bandwidth-efficient digital modulations
Wireless communications systems and networks
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Orthogonal frequency division multiplexing (OFDM) is a popular transmission technique that is employed in applications such as digital audio broadcasting, asymmetric digital subscriber line and wireless LAN. We consider design of modulating waveforms for OFDM in the presence of the delay spread and system impairments such as frequency offset and timing mismatch. We give a complete parameterization of OFDM modulating waveforms. Increasing robustness of OFDM to frequency offsets requires using long modulating waveforms. To make the implementation of OFDM systems with long modulating waveforms feasible we propose fast implementation algorithms. Some preliminary modulating waveform design examples are presented. The presented waveforms demonstrate that the robustness of OFDM systems to impairments can be improved by allowing certain degradation of unnecessarily good performances of the state of the art OFDM systems in ideal operating conditions.