| 摘要 |
A method of determining propagation-delay changes in the send-and-receive transmission paths connecting two communications units (A, B) in a communications system employs a multi-stage process in which, in first stage - in which it assumed that the propagation delays are equal - approximations (tp1*, tp2*) of the propagation delays (tp1, tp2) are derived in the two units, a value (dt) of the phase difference between the two clocks driving the respective processors of the two units is derived and initial values of the propagation delays are calculated using the approximations and the phasedifference value. Subsequently, in one or more further stages further approximations (tp1*, tp2*) of the propagation delays (tp1, tp2) are derived and, using these further approximations and the phase-difference value (dt), further values of propagation delay are calculated, these being taken as the actual new propagation-delay values. This process continues in a cyclical fashion, with changes of propagation delay being detectable by simple comparison of successive corresponding delay values. Also disclosed is a method of detecting drift between the two processor clocks, in which the method just described is basically followed and the propagation-delay approximations are monitored to detect opposite changes in the pair of approximations. When opposite changes are detected, the rate of change is determined and, if it is below a predetermined rate, it is concluded that clock drift has occurred. In a preferred embodiment, once drift has been established an actual change measured between successive approximations is used to adjust the initial value of the clock phase difference and thereafter each new updated value, thereby compensating for the drift.
|
