Multichannel radio telephone system

• US 4,281,413 A
• Filed: 12/03/1979
• Issued: 07/28/1981
• Est. Priority Date: 12/03/1979
• Status: Expired due to Term

• Current Assignee: Ericsson GE Mobile Communications Inc (Telefonaktiebolaget LM Ericsson)
• Original Assignee: General Electric Company
• Inventors: Forrest, Robert T.
• Primary Examiner(s): Bookbinder, Marc E.
• Application Number:
  US06/099,551
• Time in Patent Office: 603 Days
• Field of Search: 455/31-34, 455/50, 455/53, 455/54, 455/63, 455/62, 179/2 EB
• US Class Current: 455/455
• CPC Class Codes: H04B 7/2621 using frequency division multiple access [FDMA] H04B7/2615 takes precedence

Abstract

Phantom signals resulting from intermodulation between a busy channel and an idle channel with idle tone cause scanning radio stations to lock on a phantom idle channel and miss communications. Locking on a phantom idle channel is prevented by transmitting a busy tone on each channel having communication so that any phantom signals resulting from intermodulation will include busy tone. A scanning station is arranged to lock on a channel with only idle tone, and not lock on any channel (real or phantom) with busy tone.

Claims

1. In a communication system having a plurality of spaced radio channels on which intermodulation signals may be present, and having means for transmitting an idle tone on a selected one of said channels to indicate that said one channel is idle and available for communication, the improvement comprising means for transmitting a busy tone on each channel that is being used for communication, whereby intermodulation signals which are present include both said idle channel tone and said busy tone, and said idle channel includes said idle tone without said busy tone.

2. The communication system of claim 1, and further comprising a receiver that is rendered operable on said idle channel by said idle tone only but that is not rendered operable by both said idle tone and said busy tone.

3. The communication system of claim 2 wherein said receiver is a scanning receiver which, when rendered operable by said idle tone, renders an associated transmitter operable on said idle channel.

4. An improved multichannel radio telephone system comprising:

(a) a plurality of stations each having a transmitter and receiver;

(b) a central terminal connected to each of said stations for selectively activating a station to transmit an idle tone when said selected station is available for use, and to transmit a busy tone when said selected station is being used for communicating;

(c) and a plurality of satellite stations each having a transmitter and receiver, said satellite stations each further having scanning means for selecting a radio channel having only an idle tone, and for rejecting any radio channel having both an idle tone and a busy tone, or only a busy tone.

5. In a multichannel radio telephone system comprising:

(a) at least one fixed station having transmitter means capable of transmitting on each of a plurality of radio channels, and further capable of transmitting an idle signal on a channel that is designated for communication;

(b) a plurality of mobile stations each having a transmitter and receiver capable of being tuned to operate on each of said plurality of radio channels;

the improvement comprising;

(c) means at said fixed station for transmitting a busy signal along with communication information transmitted on each of said channels;

(d) and means at each of said mobile stations for tuning said transmitter and receiver to each of said channels, continuing said tuning in response to a busy signal on a channel, and stopping said tuning in response to only an idle signal on a channel.

6. The improvement of claim 5 wherein said idle signal and said busy signal are audio tones.

7. The improvement of claim 5 or claim 6 wherein said means for tuning further continue said tuning in the absence of any signal on a channel.

8. In a multichannel radio telephone system in which a plurality of spaced radio channels are used for providing communication for a plurality of stations, a method for preventing a station from locking on a channel because of intermodulation, comprising the steps of:

(a) at a station, transmitting a busy signal on each channel having communication thereon;

(b) at said station, transmitting an idle signal on a selected channel designated for communication;

(c) at another station, scanning each of said channels;

(d) at said scanning station, continuing said scanning in response to each channel having said busy signal thereon or having said busy signal and said idle signal thereon;

(e) at said scanning station, stopping said scanning on the channel having only said idle signal thereon;

(f) and at said stopped scanning station, rendering said station operable on said channel having only said idle signal thereon.