Tdma system timer for maintaining timing to multiple satellite simultaneously

Abstract

A method for timing correction in a communications receiver includes the steps of (a) setting a timer to a known value; (b) defining a first window by defining a first rollover value; (c) defining a second window by defining a second rollover value; (d) defining a first receive gate transition relative to the first rollover value; (e) defining a second receive gate transition relative to the second rollover value; (f) starting the timer; (g) receiving a first receive burst in the first window; (h) receiving a second receive burst in the second window; (i) if a first receive burst is received after the first receive gate transition, increasing the second rollover value, and decreasing the first rollover value by an equal amount; (j) if the first receive burst is received before the first receive gate transition, decreasing the second rollover value, and increasing the first rollover value by an equal amount; (k) if the second receive burst is received after the second receive gate transition, increasing the first rollover value, and decreasing the second rollover value by an equal amount; (l) if the second receive burst is received before the second receive gate transition, decreasing the first rollover value, and increasing the second rollover value by an equal amount; (m) if the first receive burst is received after the second receive gate transition, and the second receive burst is received after the second receive gate transition by a similar amount, increasing one of the first rollover value and the second rollover value at least one frame and then restoring the one of the first rollover value and the second rollover value; (n) if the first receive burst is received before the first receive gate transition, and the second receive burst is received before the second receive gate transition by a similar amount, decreasing one of the first rollover value and the second rollover value at least one frame and then restoring the one of the first rollover value and the second rollover value; (o) if the first receive burst is received time-shifted relative to the first receive gate transition, and the second receive burst is received time-shifted relative to the second receive gate transition by a different amount, adjusting the second rollover value including: if the second receive burst is received after the second receive gate transition, increasing the first rollover value, and decreasing the first rollover value by an equal amount; and if the second receive burst is received before the second receive gate transition, decreasing the first rollover value, and increasing the second rollover value by an equal amount; and then adjusting the first rollover value including: if a first receive burst is received after the first receive gate transition, increasing the second rollover value, and decreasing the first rollover value by an equal amount; and in the event the first receive burst is received before the first receive gate transition, decreasing the second rollover value, and increasing the first rollover value by an equal amount; and then adjusting the first rollover value to match an error between the second receive burst and the second receive gate transition.