Patent ID: 7577180

Claim:
A method for maintaining synchronization of a base unit and a portable unit in a standby mode over a frequency-hopping radio link comprising: transiting the base unit and the portable unit to a resynchronization state during the standby mode in a resynchronization period, wherein the resynchronization period is a product of a positive number and a period of time of frequency hopping on each channel of multiple communication channels that are used by the base unit and the portable unit for communications; transmitting at least one link synchronization message from the base unit to the portable unit at every resynchronization period; adjusting a timing clock of the portable unit based on the at least one synchronization message received from the base unit; responding to the at least one link synchronization message when required by the base unit; and after receiving the response to the at least one link synchronization message, transiting the base unit and the portable unit from the resynchronization state to a low-power state, wherein the link synchronization message is one of a link synchronization checking message and a link synchronization confirmation message, and wherein the link synchronization confirmation message requires a response from the portable unit, the method further comprising transmitting the link synchronization checking message for (M−1)synchronization periods and a first link synchronization confirmation message at M-th period, wherein M is an integer greater than 2.