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Table 2 FWT versus FFT sensing complexity comparison

From: Optimized spectrum sensing algorithms for cognitive LTE femtocells

FWT FFT
A single FWT operation per LTE OFDM symbol (5 slots × 7 FWT operations) The five LTE slots are divided into FFT blocks according to the FFT size, the average FFT of these blocks is the output of the FFT sensing module
Complexity = 2 × (Number of samples per LTE OFDM Symbol) × 7 × 5 × M × L Complexity = (Number of FFT blocks per 5 LTE slots) × FFT_Size × log2(FFT_Size)
Daubechies (dbN) wavelets are used where N is the filter order 256 and 512 point FFT modules are used
1598520 computations for db2 FWT
3197040 computations for db4 FWT
1599488 computations for 256-point FFT
1797120 computations for 512-point FFT