Low Complexity Synchronization for Offset Tolerant DFT-Based BFSK Demodulator

A DFT-based demodulator for BFSK is used for applications where the received signal experiences a carrier frequency offset (CFO) much larger than the data rate. It is particularly interesting for emerging ultra-narrowband communications for wireless sensor networks and loT. The drawback is that the synchronization algorithm proposed for such a demodulator involves calculating the DFT for a window sliding over the whole preamble. This imposes a large computational load which is not desired in low power applications. To overcome CFO the sampling frequency should be larger than the signal bandwidth. Thus, the spectral range of the DFT is larger than the signal bandwidth. This means that only a subset of DFT bins have information about the signal; however, due to unknown CFO, the conventional synchronization algorithm needs all bins of the DFT. In this work, a novel synchronization algorithm is proposed which only needs a subset of DFT bins. Such algorithm can simplify implementation because efficient Single Bin Sliding DFT (SB-SDFT) algorithms can be used. Moreover, to be able to use the SB-SDFT algorithm, it is modified to incorporate zero-padding. The proposed algorithm and its implementation using the modified SB-SDFT reduce the number of complex multiplications, complex additions and memory usage by 28%, 64% and 81%, respectively, while achieving the same BER performance for the demodulator.