| 摘要 |
<p>A method of detecting a set up signal having a predetermined frequency and used for data transmissions over a communication network (4, 6, 8) comprises filtering (32) the received signal by a Butterworth filter having a passband including the predetermined frequency, determining an energy level of the filtered received signal and comparing (50) the determined energy level of the filtered received signal with a first predetermined value and providing a first detect signal when the determined energy level is greater than the first predetermined value. The method further comprises identifying (36) a component of the received signal at the predetermined frequency and determining an energy level of the identified component, comparing (60) the determined energy level of the identified component with a second predetermined value and providing a second detect signal when the determined energy level is greater than the second predetermined value. In addition, an autocorrelation function is performed (38, 64) on the received signal to discriminate between the set up signal and other signals in the received signal and a check signal is provided when the autocorrelation function identifies the set up signal. The set up signal in the received signal is detected (44, 66, 68) in response to the first and the second detect signals and the check signal. A method of detecting phase reversals in the set up signal is also disclosed.</p> |
