Wireless communication systems routinely employ frequency-hopping spread-spectrum techniques. These techniques typically involve transmitting wireless signals using multiple frequency channels. In these techniques, both transmitters and receivers quickly switch among the multiple frequency channels, where the switching occurs in a pseudo-random order. Frequency-hopping spread-spectrum techniques are often useful since they help to reduce the effects of electromagnetic interference and other interference and noise. As a particular example, these techniques are often useful in industrial control systems where large amounts of interference and noise are generated by industrial processes.
Frequency-hopping spread-spectrum techniques often require synchronization between the transmitters and the receivers. Typically, this involves synchronizing all transmitters and all receivers to the same frequency-hopping pattern and offset or phase. A frequency-hopping pattern represents a sequence of frequency channels, which identifies the order of the channels used during communications. The offset or phase identifies a current location in the frequency-hopping pattern used by the transmitters. When synchronized to the transmitters' frequency-hopping pattern and offset or phase, the receivers know the channel frequency that the transmitters use at any given time.
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