A Correlating Receiver for OFDM at Low SNR

By extending OFDM symbols, acceptable BER performance can be achieved at low SNRs. Two alternative differential receiver architectures are presented, a receiver based on a FX correlator (Fourier transformation before correlation) and based on an XF correlator (correlation before Fourier transformation). To reduce the complexity and hence the power consumption of both the ADC and the first digital processing stage single- or two bit quantization is used. The receiver based on the XF correlator is more suited to exploit such coarse quantization. Two basic effects are visible if coarse quantization is used. First, the BER performance is reduced due to the introduction of quantization errors. Second, beyond certain SNR levels, the BER performance does not increase due to the correlation between quantization errors. Furthermore, oversampling increases BER performance considerably. For single bit quantization with oversampling, acceptable BERs (<; 10^-3) can be achieved for a limited SNR range for symbol extension factors of 32 and 64. In case of two bit quantization without oversampling, the results are comparable with single bit quantization with two times oversampling. For two bit quantization in combination with two times oversampling, acceptable BERs are achieved for symbol extension factors 8, 16, 31 and 64.