Frequency shift compensation, such as for use in a wireless meter reading environment

Abstract

Methods and apparatus for computing the carrier frequency of a transmitter using frequency modulated digital data to compensate for frequency shifting of the transmitter and the receiver local oscillators and for bandwidth adjustment of the receiver's filter. In particular, methods and apparatus are disclosed for binary systems transmitting “1” and “0” data using decoded or undecoded received signals.

1 - 24 . (canceled) 
     
     
         25 . In an automatic utility meter reading system that transmits utility data signals, an adjustable bandwidth receiving apparatus, comprising:
 a memory module for storing data, instructions, or both;   a receiver for receiving utility meter data signals:   a processor coupled with the memory module and the receiver, wherein the receiver and the processor are configured to:
 match a receiver local oscillator (LO) frequency to a carrier (SC) frequency of the receiver signals to compensate for a frequency difference, wherein the matching comprises: 
 receiving a first signal representing a first binary value at a first data rate; 
 mixing the first signal with a signal generated by the LO, wherein the LO frequency is an expected SC frequency; 
 filtering the first mixed signal; 
 receiving a second signal representing a second binary value at the first data rate; 
 mixing the second signal with the signal generated by the LO; 
 filtering the second mixed signal; 
 computing an average value of only the two filtered signals, wherein the computed average value is a difference between the SC and the LO frequencies; 
 adjusting the LO frequency by the computed average value; adjusting the bandwidth based on the computed average value to allow a signal with an estimated maximum frequency error to pass; and 
 receiving subsequent data signals at a second data rate that is higher than the first data rate; and 
   wherein data signals are frequency modulated (FM), and wherein the first binary value is transmitted by a frequency that is a sum of a deviation frequency and the SC frequency and the second binary value is transmitted by a frequency that is a difference of the SC frequency and the deviation frequency.   
     
     
         26 . The apparatus of  claim 25 , wherein the processor provides a compensation signal to match the LO frequency to the SC frequency based on the computed value, and adjusts the bandwidth around the matched LO frequency, based on the computed value. 
     
     
         27 . The apparatus of  claim 25 , wherein one of the two filtered signals is a baseband in-phase signal and the other filtered signal is a baseband quadrature signal. 
     
     
         28 . In a wireless utility meter reading system of data receivers and transmitters, a method of adjusting a receiver, wherein transmitters transmit frequency modulated (FM) binary data, and wherein a first binary value is transmitted by adding a deviation frequency to a local oscillator (LO) frequency of the transmitter and a second binary value is transmitted by subtracting the deviation frequency from the transmitter's LO frequency, the method comprising:
 receiving a signal representing the first binary value;   down-converting the received signal with a signal generated by a LO of the receiver, wherein a frequency of the receiver's LO is substantially similar to an estimation of the transmitter's LO frequency;   filtering the down-converted signal;   computing a difference between the transmitter's LO frequency and the receiver's LO frequency, using a single received signal, by subtracting the deviation frequency from the filtered signal, if the received signal represented the first binary value, or by adding the deviation frequency to the filtered signal, if the received signal represented the second binary value;   compensating the receiver's LO frequency by the computed difference if the receiver's LO frequency needs to be altered; and   adjusting a bandwidth of the receiver filter to allow an estimated maximum frequency error to pass, if the receiver's bandwidth needs to be adjusted.   
     
     
         29 . The method of  claim 28 , wherein a compensation signal associated with the computed difference adjusts the bandwidth of a variable filter based on an estimated worst case frequency error. 
     
     
         30 . The method of  claim 28 , wherein the bandwidth of the receiver is narrowed around the adjusted frequency based on the computed difference. 
     
     
         31 . In a wireless communication system, a method of adjusting receiver bandwidth using a difference between a transmitter local oscillator (LO) frequency and its corresponding receiver LO frequency, the method comprising:
 a means for matching the receiver's LO frequency to the transmitter's LO frequency to compensate for frequency shifting, the matching comprising:
 a means for receiving at least one signal representing one binary value that is frequency modulated (FM); 
 a means for down-converting the at least one signal by a signal imitating the frequency of the transmitter's LO; 
 a means for filtering the down-converted signal; a means for computing a difference between the transmitter's LO frequency and the receiver's LO frequency based on the one filtered signal; and 
 a means for matching the receiver's LO frequency to the transmitter's LO frequency, using the computed difference; and 
   a means for adjusting the bandwidth of the receiver based on the computed difference, if the bandwidth needs to be adjusted.   
     
     
         32 . In an automatic utility meter reading system that transmits utility data signals, a process of transmitting data via a transmitter, the process comprising:
 transmitting an initial signal representing a first binary value at a first data rate, wherein the initial signal is configured for adjusting a difference between a carrier frequency of the transmitter and a carrier frequency of a utility data collection receiver; and   transmitting the utility data signals at a second data rate that is higher than the first data rate after transmission of the initial signal.   
     
     
         33 . A method of data communication in a utility data collection device used in an automatic utility meter reading system that transmits utility data signals, the method comprising:
 widening a receiver bandwidth to receive initial communication data at a first data rate;   adjusting a local oscillator based on the received data; and   narrowing the receiver bandwidth to receive subsequently transmitted data at a second data rate that is higher than the first data rate.