Method and apparatus for aligning a digital receiver

An automatic frequency controller, coupled to a receiver element, wherein the receiver element receives and demodulates a frequency modulated (FM) signal, and wherein the FM signal includes a plurality of data symbols, and wherein each data symbol modulates the FM signal at one of a plurality of frequency deviations, and wherein each of the plurality of frequency deviations has one of two opposite polarities, the automatic frequency controller comprising:

• an error detector, coupled to said receiver element, wherein said error detector determines error rates of at least two subsets of the data symbols, each subset comprising a plurality of the data symbols modulated at a unique one of the plurality of frequency deviations, and wherein the at least two subsets of the data symbols comprise data symbols of the two opposite polarities;
• a frequency controller, coupled to said error detector, wherein said frequency controller generates a frequency control signal based on the error rates of the at least two subsets of the data symbols;
• and
• a local oscillator, coupled to said frequency controller, wherein said local oscillator is controlled by the frequency control signal to align said receiver element to the FM signal.

A selective call receiver for processing a frequency modulated (FM) signal, wherein the FM signal includes data symbols, and wherein each data symbol modulates the FM signal at one of a plurality of frequency deviations, and wherein each of the plurality of frequency deviations has one of two opposite polarities, and wherein the FM signal further includes a selective call address, the selective call receiver comprising:

• a receiver element which receives and demodulates the FM signal;
• a control circuit, coupled to said receiver element, which decodes the data symbols and the selective call address included in the FM signal, and which generates an alert signal when the selective call address matches an address stored in the selective call receiver;
• a sensible alert, coupled to the control circuit, which is responsive to the alert signal for generating a sensible alert signal;
• and
• an automatic frequency controller, coupled to said receiver element and said control circuit, the automatic frequency controller comprising
• an error detector, coupled to said control circuit, wherein said error detector determines error rates of at least two subsets of the data symbols, each subset comprising a plurality of the data symbols modulated at a unique one of the plurality of frequency deviations, and wherein the at least two subsets comprise data symbols of the two opposite polarities,
• a frequency controller, coupled to said error detector, wherein said frequency controller generates a frequency control signal based on the error rates of the at least two subsets of the data symbols, and
• a local oscillator, coupled to said frequency controller and said receiver element, wherein said local oscillator is controlled by the frequency control signal to align said receiver element to the FM signal.

A method used in a receiver for aligning the receiver to a frequency modulated (FM) signal, wherein the FM signal includes data symbols, and wherein each of the data symbols modulates the FM signal at one of a plurality of frequency deviations, and wherein each of the plurality of frequency deviations has one of two opposite polarities, and wherein the receiver includes a receiver section which is aligned by a local oscillator, the method comprising the steps of:

• intercepting and demodulating the FM signal, including the data symbols;
• determining error rates of at least two subsets of the data symbols, each of the at least two subsets other of the data symbols comprising a plurality of the data symbols modulated at a unique one of the plurality of frequency deviations, and wherein the at least two subsets comprise the data symbols of the two opposite polarities;
• generating a frequency control signal based on the error rates determined in said determining step;
• and
• aligning the receiver section to the FM signal by controlling the local oscillator responsive to the frequency control signal.