Patent ID: 8265480

Claim:
A method for light mark demodulation, comprising: photoelectrically converting an optical signal modulated with a mark comprising a frequency and an interval into an electrical signal, and converting the electrical signal into a digital signal; and sampling the digital signal to obtain the frequency, controlling a counter to count according to a sampling result, and determining a particular mark according to the frequency and a counting result of the counter; wherein the sampling the digital signal to obtain the frequency, controlling the counter to count according to the sampling result, and determining the particular mark according to the frequency and the counting result of the counter comprises: sampling the converted electrical signal in a time period to obtain a frequency of the electrical signal in a sampling time window according to data in the sampling time window; assigning a counter to the frequency; sampling in a next time window, processing sampled data to determine if a frequency equal to the frequency of the electrical signal exists in the sampling time window; repeatedly sampling, if the frequency equal to the frequency of the electrical signal exists in the sampling window, processing sampled data to determine if a frequency equal to the frequency of the electrical signal in the sampling time window exists in the sampling time window; and adding, if the frequency equal to the frequency of the electrical signal does not exist in the sampling time window, 1 to the counter value and performing the following: sampling in another adjacent time window, processing sampled data to determine if a frequency is equal to the above frequency exists in the sampling time window; repeatedly sampling, if the frequency equal to the above frequency exists in the sampling time window, processing sampled data to determine if a frequency is equal to the above frequency in the sampling time window; adding, if the frequency equal to the above frequency does not exist in the sampling time window, 1 to the counter value and repeatedly performing this step until a frequency equal to the above frequency appears in the sampling time window; stopping, if the frequency equal to the above frequency exists in the sampling time window, counting, storing the counter value, and resetting the counter to zero; and determining the particular mark according to the frequency and the stored counter value.