OFDM performance with odd-even quantisation in Cartesian ΔΣ upconverters

This paper studies the odd-quantisation technique when subjected to OFDM input signals in a Cartesian Delta Sigma (ΔΣ) upconverter. The results will be compared to the even-quantisation method of [9] to establish whether there is an improvement in performance. The overall performance of the odd-quantisation scheme has about 5dB reduced adjacent channel power (ACP) compared to the even-quantisation scheme. The smaller first quantisation step results in lower quantisation noise for small signals, leading to a lower noise floor. When the signal is frequency offset, a number of distortions become visible in the spectrum. The third harmonic is the biggest distortion contributor followed by the image. Interestingly, the overall better noise performance of the odd-quantisation scheme does not improve the distortion spectra. Best performance occurs when frequency offsetting is avoided.