Method of operating a communications system, a communications system and a secondary station for use in the system

• US 5,375,254 A
• Filed: 12/04/1991
• Issued: 12/20/1994
• Est. Priority Date: 12/14/1990
• Status: Expired due to Fees

• Current Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Original Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Inventors: Owen, Frank C. G.
• Primary Examiner(s): Eisenzopf, Reinhard J.
• Assistant Examiner(s): Charouel, Lisa
• Application Number:
  US07/804,255
• Time in Patent Office: 1,112 Days
• Field of Search: 455/33.1, 455/33.2, 455/54.1, 455/56.1, 455/62, 455/63, 455/161.1, 455/161.2, 455/161.3, 455/127, 455/343, 379/58, 379/59, 379/63
• US Class Current: 455/525
• CPC Class Codes: H04M 1/72511 Searching for available channels
• CPC Class Codes: H04M 1/72516 with means for out-of-range alerting
• CPC Class Codes: H04M 1/73 Battery saving arrangements
• CPC Class Codes: H04M 2250/08 home cordless telephone systems using the DECT standard
• CPC Class Codes: H04W 36/08 Reselecting an access point
• CPC Class Codes: H04W 48/20 Selecting an access point
• CPC Class Codes: H04W 52/0241 where no transmission is received, e.g. out of range of the transmitter
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

A communications system, such as the DECT, comprises a plurality of geographically separate primary stations and a plurality of secondary stations which are able to roam relative to the primary stations. Communication between a primary and a secondary station is by way of any of a plurality of time division duplex radio channels. An idle primary station transmits an idle beacon signal. When a secondary station roams out of the coverage area of a primary station and so can longer lock to that primary station, it scans all of the radio channels for an idle beacon signal. To conserve battery power, instead of continuously rescanning all channels, the successive rescans are made less frequently as the time interval from when the secondary station was last in lock increases, until a predetermined maximum interval has been reached between successive rescans.

Claims

1. A method of operating a communications system comprising a plurality of primary stations and at least one secondary station, said primary stations and said secondary station each having radio transceiving means which provide a plurality of radio channels for communication between said secondary station and each of said primary stations, said secondary station being able to roam in and out of radio range with at least one of said primary stations;

said method comprising the steps of;

transmitting by each primary station, when idle, an idle beacon signal to which said secondary station can lock when it is in radio range of an idle primary station;

scanning of said plurality of channels by said secondary station to search for the idle beacon signal to which it can lock; and

periodic rescanning of said channels by the secondary station at a rescan frequency which decreases in relation to an increase in the time interval from when the secondary station was last in lock with the idle beacon signal.

2. A method as claimed in claim 1, wherein the rescan frequency is decreased in predetermined steps in relation to the increase in the time interval from when the secondary station was last in lock with the idle beacon signal.

3. A method as claimed in claim 2, wherein the rescan frequency is maintained at a last of said predetermined steps until said secondary station either locks to the idle beacon signal or is de-energized.

4. A method as claimed in claim 1, wherein the rescan frequency is adapted in accordance with operating characteristics of the system.

5. A communications system comprising a plurality of primary stations and at least one secondary station, the primary stations and the secondary station each having radio transceiving means which provide a plurality of radio channels for communication between the secondary station and each of the primary stations;

each primary station, when idle, transmitting an idle beacon signal to which the secondary station can lock when received thereby;

the secondary station scanning the plurality of channels to search for the idle beacon signal to which it can lock;

characterized in that the secondary station comprises control means for causing periodic rescanning of said plurality of channels at a rescan frequency which decreases in relation to an increase in the time interval from when the secondary station was last in lock with the idle beacon signal.

6. A communications system as claimed in claim 5, wherein said control means decreases the rescan frequency in predetermined steps until a predetermined maximum interval has been reached between successive rescans.

7. A secondary station for use in a communications system which comprises at least one said secondary station and a plurality of primary stations, said secondary station and the primary stations each having radio transceiving means which provide a plurality of radio channels between said secondary station and each of the primary stations, each primary station, when idle transmitting an idle beacon signal to which said secondary station can lock when received thereby;

characterized in that said secondary station includes control means for causing scanning of said plurality of channels to search for the idle beacon signal to which it can lock, and to periodically rescan said plurality of channels at a rescan frequency which decreases in relation to an increase in the time interval from when said secondary station was last in lock with the idle beacon signal.

8. A secondary station as claimed in claim 7, wherein said control means decreases the rescan frequency in predetermined steps until a predetermined maximum interval has been reached between successive rescans.