Apparatus and method for frequency channel selection in a radiotelephone system

• US 4,166,927 A
• Filed: 07/21/1978
• Issued: 09/04/1979
• Est. Priority Date: 07/21/1978
• Status: Expired due to Term

• Current Assignee: BC Telecom, Inc. (Telus Corporation)
• Original Assignee: BC Telecom, Inc. (Telus Corporation)
• Inventors: Hamaoki, Roy T.
• Primary Examiner(s): Olms, Douglas W.
• Application Number:
  US05/926,985
• Time in Patent Office: 410 Days
• Field of Search: 179/2 EB, 179/2 EA, 325/52, 325/468, 325/469, 325/470
• US Class Current: 455/455
• CPC Class Codes: H03J 7/183 combined with selection between different stations transmitting the same programm, e.g. by analysis of the received signal strength
• CPC Class Codes: H04W 72/02 Selection of wireless resources by user or terminal

Abstract

In a mobile radiotelephone system, N separate modulated carrier signals in N frequency channels are applied to a demodulating radio receiver which provides a succession of N different output signals each having idle and busy states. An idle and signal-to-noise detector monitors each of the output signals of the radio receiver. The detector provides a first logic signal when one of the output signals concurrently exhibits an idle state and has at least a predetermined minimum signal-to-noise level, and provides a second logic signal at all other times. A receiver switching circuit, in response to the second logic signal, causes the receiver to cyclically switch to each of the N frequency channels. When the receiver switches to a carrier signal which causes the detector to produce a first logic signal, the switching circuit causes the receiver to lock onto that particular carrier signal. Improved operation results from a gain control circuit which reduces the gain sensitivity of the receiver upon a change in state of the detector output signal from a first logic signal to a second logic signal. The gain sensitivity is then slowly increased as the receiver cyclically switches to each of the N frequency channels. When an idle receiver output signal is detected having at least the minimum level of signal-to-noise, the receiver switching circuit locks the receiver onto the particular carrier signal. This technique assures that the first such detected signal will provide the best frequency channel for the demodulating radio receiver.

Claims

1. In a mobile radiotelephone system having N separated radio frequency channels, apparatus for selecting the particular idle frequency channel having the best signal-to-noise ratio, said apparatus comprising:

demodulating receiver means for receiving N different modulated carrier signals in each of said N radio frequency channels, said demodulator means under the control of switching means providing at an output a succession of N different output signals, and each output signal having idle and busy mutually exclusive states corresponding to the idle and busy state of the corresponding radio frequency channel;

first detector means having a first input terminal connected to the output of said receiver means and having a first output terminal, said detector means providing a first logic signal when one of said receiver output signal concurrently exhibits an idle state and has at least a predetermined minimum signal-to-noise level, and said detector means providing a second logic signal at all other times;

subscriber handset means having an input connected to said receiver means output and having a second output terminal, said handset means having on-hook and off-hook mutually exclusive states;

a call-in-progress state detector for detecting the on-hook and off-hook states of said handset means, said state detector having an input connected to said second output terminal and also having a third output terminal providing an on-hook and off-hook output signal indicative of the on-hook and off-hook states respectively of said handset means;

receiver switching means having an output and second and third input terminals, said output adapted for connection to said receiver means, said second input terminal connected to said first output terminal, and said third input terminal connected to said third output terminal, said switching means for cyclically switching said receiver means to each of said N frequency channels in response either to said first logic signal or to said off-hook signal; and

gain control means having an output and fourth and fifth input terminals, said output adapted for connection to said receiver means, said fourth input terminal connected to said first output terminal, and said fifth input terminal connected to said third output terminal, said gain control means producing a control output signal for causing a decrease in the gain sensitivity of said receiver means from a predetermined maximum gain to a predetermined minimum gain and thereafter for causing an increase in said gain sensitivity to said predetermined maximum, said gain increase occurring at a rate substantially slower than the rate of gain decrease so that the period of time required for said switching means to switch said receiver means to each of said N frequency channels at least once is substantially greater than the time required for the gain sensitivity to increase from said minimum to said maximum, said control output signal being produced in response to either

(a) a change in state of said first detector means output signal from said first logic signal to said second logic signal or

(b) in response to a predetermined timed interval after a change in output state of said first detector means from said first logic signal to said second logic signal unless an off-hook output signal is produced by said call-in-progress detector, and

said gain control means being inhibited from generating said control output signal whenever an off-hook indication from said call-in-progress detector means is produced.

2. Apparatus as in claim 1 wherein said gain control means comprises:

a ramp generator having an input and producing said control output signal when the proper signal is applied to its input;

an AND gate having an output coupled to the input of said ramp generator and also having a non-inverting input and an inverting input, said inverting input coupled to said third output terminal;

a first OR gate having an output coupled to the noninverting input of said AND gate and first and second inputs, said second input coupled to said first output terminal;

timer means having an output coupled to the first input of said first OR gate and also having an inhibit input connection, said timer means periodically producing a third logic signal after a predetermined timed interval; and

a second OR gate having first and second input and an output, said output coupled to the inhibit input connection of said timer means, said first input coupled to said third output terminal, and said second input coupled to said first output terminal, said OR gate causing said timer means to be inhibited from producing said third logic signal

(a) so long as said first detector means provides a second logic signal or

(b) so long as said call-in-progress state detector provides an off-hook output signal.