On-line signal quality monitoring method, apparatus, and system

The invention relates to an on-line signal quality monitoring method, apparatus, and system. The monitoring method comprises: according to signal to noise ratios, obtained at a transmission initialization stage, of all sub carriers, the sub carrier with the highest signal to noise ratio is set as a pilot sub carrier and other sub carriers are set as data sub carriers; bit distribution and power distribution of the pilot sub carrier and bit distribution and power distribution of all data sub carriers are determined; according to the bit distribution of all data sub carriers, signal to noise ratio measurement threshold values based on data decisions are set for all data sub carriers; and the signal to noise ratios, obtained by signal to noise ratio measurement based on data decisions, of all data sub carriers at the transmission stage are compared with the signal to noise ration measurement threshold values of all data sub carriers; and when the signal to noise ration of the certain data sub carrier is smaller than the signal to noise measurement threshold value, pilot-frequency-based signal to noise ratio measurement on the data sub carrier is started. Therefore, on-line signal quality monitoring with time continuity can be provided and accuracy of the monitoring result can be guaranteed.