Embodiments of the present invention provide a signal processing method, including: dividing a frequency band used to send a downlink synchronization symbol into at least two parts of frequency bands that do not overlap, where the two parts of frequency bands are a first frequency band and a second frequency band; alternately allocating frequencies in the first frequency band to a probe tone and a flag tone; and allocating all frequencies in the second frequency band to a probe tone; and modulating a downlink pilot sequence to probe tones in the first frequency band and the second frequency band, and sending the downlink pilot sequence to a peer device. The embodiments of the present invention further provide a signal processing apparatus and a network system.