Method of synchronizing radio transmitters for synchronous radio transmission

• US 4,709,402 A
• Filed: 10/22/1986
• Issued: 11/24/1987
• Est. Priority Date: 12/09/1982
• Status: Expired due to Term

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Akerberg, Dag E.
• Primary Examiner(s): Griffin, Robert L.
• Assistant Examiner(s): Kuntz, Curtis
• Application Number:
  US06/921,740
• Time in Patent Office: 398 Days
• Field of Search: 455/18, 455/51, 455/53, 455/57, 455/52, 455/68, 455/69, 455/77, 455/76, 455/75, 340/825.44
• US Class Current: 455/503
• CPC Class Codes: G08B 3/1016 using wireless transmission calling systems using transmission by inductive loop H04B5/00
• CPC Class Codes: H04H 20/67 Common-wave systems, i.e. using separate transmitters operating on substantially the same frequency

Abstract

In transmission by radio of personal paging calls synchronous radio transmission from several transmitters is often used, i.e. the transmitters send on the same frequency. The characters of the call must also be sent simultaneously from the transmitters so that they shall be correctly comprehended by the receivers. A method and an apparatus are described here for synchronizing the separate transmitters (2:2, 3:16) such as to transmit on the same frequency.

Claims

1. In a radio communication system having a central radio station connected by lines to a plurality of other radio stations for transmitting messages to receivers, the method of controlling the transmitting frequency of the carrier signal of a first of the other radio stations to have a given relationship with the transmitting frequency of the carrier signal of a second of the radio stations comprising the steps of the central station sending on the lines to the first and second other radio stations order messages for ordering said other radio stations to adjust the transmitting frequencies of their carrier signals, the second other radio station in response to the receipt of said order message transmitting with its own transmitting frequency said order message over the air to said first other radio station,

said first other radio station in response to the receipt of said order message on a line from the central station being activated to receive over the air messages from the second radio station,

said first radio station comparing the transmission frequency of the order message received over the air from the second other radio station with its own carrier signal'"'"'s transmission frequency, said comparing step comprising counting a number of cycles of a signal derived from the order message received from the second radio station, counting a number of cycles of a signal derived from its own carrier frequency and comparing the counts, and

said first radio station adjusting its own carrier signal'"'"'s transmission frequency in accordance with the results of the comparision.

2. The method of claim 1 wherein when one of the counting steps of a given number of cycles is counted both counting steps are terminated.

3. The method of claim 2 wherein the amount of adjusting is a function of the difference between said given number of cycles and the number of cycles counted during the other of the counting steps.

4. In a transceiver having a receiver and a transmitter, apparatus for adjusting the frequency of the carrier signal of the transmitter with respect to the carrier frequency of a signal received by the receiver comprising controllable oscillator means for generating the carrier signal, said oscillator means having an input means receiving a count value for controlling the frequency of the carrier signal, first counting means responsive to said oscillator means for counting the number of cycles carrier signal, second counting means responsive to said receiver for counting the number of cycles of the received signal, comparing means comparing the counts accumulated by said counting means over a given time interval for generating a count value representing the difference of said counts, and means for feeding the count value generated by said comparing means to the input means of said controllable oscillator means.

5. In a transceiver including a receiver of the double superheterodyne type having first and second local oscillators with first and second intermediate frequencies which receives message carrier signals and having a transmitter which transmits modulated carrier signals, apparatus for adjusting the frequency of the carrier signal of the transmitter to the frequency of the message carrier signals comprising:

a voltage controlled oscillator for generating a signal which has a frequency equal to 1/N of the frequency of the carrier signal of the transmitter;

first frequency divider means connected to the first local oscillator for generating a first frequency divided signal having a frequency equal to 1/N of the frequency of the first intermediate frequency;

second frequency divider means connected to the second local oscillator means for generating a second frequency divided signal having a frequency equal to 1/N of the frequency of the second intermediate frequency;

a first mixer means having a first input for receiving the signal from said voltage controlled oscillator, a second input for receiving the signal from said first frequency divider means and an output for generating a signal having a frequency equal to the difference in the frequencies of the signals received at said first and second inputs;

a second mixer means having a first input for receiving the signal from the output of said first mixer means, a second input for receiving the signal from said second frequency divider means and an output for transmitting a signal having a frequency which is the difference in frequencies of the signals received at the first and second inputs; and

comparing means having first and second compare inputs for receiving signals after heterodyning by the receiver and the signal from the output of said second mixer means and an output for generating a control signal which is a function of the difference in frequencies of the signals received at the inputs;

control means utilizing said control signal for controlling the frequency of said voltage controlled oscillator; and

means in said transmitter for utilizing the signal from said voltage controlled oscillator to produce the carrier signal.

6. The apparatus of claim 5 wherein said comparing means comprises counting means for counting the number of cycles of each of the signals received at said compare inputs over a period of time, and means for generating said control signal having a value related to the difference in the counts.