Patent ID: 8532228
Filing Date: 2013-09-10
Classification: H04L

Abstract:
1. A method for automatic frequency offset compensation in a zero-intermediate frequency receiver demodulating minimum-shift keying (MSK) signals, comprising the steps of: receiving a radio frequency (RF) signal in an automatic frequency control (AFC) module; running a coarse carrier frequency offset estimation of the received RF signal in said AFC module; running a fine carrier frequency offset estimation of the received RF signal in said AFC module; determining whether an expected preamble of a MSK signal has been detected, wherein if the expected preamble has not been detected then continue running the coarse and fine carrier frequency offset estimations, and if the expected preamble has been detected then stop running the coarse and fine carrier frequency offset estimations; calculating an absolute difference between the coarse and fine carrier frequency offset estimations in said AFC module; determining whether the absolute difference is less than a threshold value, wherein if the absolute difference is less than the threshold value then using the fine carrier frequency offset estimation for compensating the carrier frequency offset, and if the absolute difference is equal to or greater than the threshold value then adjusting the fine carrier frequency offset estimation by adding or subtracting 180 degrees per period thereto until the absolute difference is less than the threshold value, and thereafter using the adjusted fine carrier frequency offset estimation for compensating the carrier frequency offset.