Low-power wireless system for telephone services

• US 5,987,099 A
• Filed: 10/07/1994
• Issued: 11/16/1999
• Est. Priority Date: 10/16/1992
• Status: Expired due to Term

• Current Assignee: RPX Clearinghouse LLC (RPX Corporation)
• Original Assignee: Northern Telecom Limited (Nortel Networks Corporation)
• Inventors: Ploeg, David Charles, Matsushita, Shoji, Wong, Jin Kue, Redmond, Alan Morris, O'Neill, Keith Daniel, Bird, William Owen, Mah, Garry Don, Gale, Peter David, Szpilfogel, Christian Jacques
• Primary Examiner(s): Kuntz, Curtis
• Assistant Examiner(s): Oehling, G. J.
• Application Number:
  US08/320,849
• Time in Patent Office: 1,866 Days
• Field of Search: 379/58, 379/59, 379/60, 379/63, 455/33.1, 455/33.2, 455/33.4, 455/54.1, 455/54.2, 455/56.1, 455/67.1
• US Class Current: 455/436
• CPC Class Codes: H04W 36/08 Reselecting an access point
• CPC Class Codes: H04W 36/30 by measured or perceived connection quality data
• CPC Class Codes: H04W 48/20 Selecting an access point
• CPC Class Codes: H04W 68/00 User notification, e.g. alerting and paging, for incoming communication, change of service or the like
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

A wireless telephone system provides telecommunications services for personal wireless telephone sets over an area which is divided into service cells. Each of the cells is defined by reception characteristics of a plurality of radio base stations within the cell. The telephone system includes a service controller and a port being wireline connected between each radio base station and the service controller. The service controller selects radio base stations for setting up radio links with wireless sets of calling or called persons. A base station which serves a wireless set and surrounding idle base stations monitor strengths of radio signals received from the wireless set and report running averages of the monitored signal strengths to the service controller. Movement of the wireless set from one cell to another cell during a call is detected as a drop in the running average reported by the serving base station. The service controller selects an idle base station to which the call is handed off based on the running averages reported by the idle base stations only idle base stations having a running average greater than the serving base station report their running average.

Claims

1. In a telephone system having a plurality of cells for wireless communication with portable sets each having a preassigned identity, wherein each cell includes a plurality of radio base stations, any one of which is operable to provide a radio link with a portable set over any one of a plurality of radio frequency channels, and wherein a portable set is operable to initiate the radio link by identifying at least one vacant radio frequency channel and then periodically broadcasting, in the identified radio frequency channel, a radio signal including a coded message corresponding to a preassigned identity of the portable set, a method for completing the radio link comprising the steps of:

a) in one of the radio base stations detecting a receive signal strength indication (RSSI) level of the broadcast radio signal on said vacant radio frequency channel;

b) registering the received RSSI level at said radio base station;

c) in response to the RSSI level being greater than a portable originating link setup (POLS) threshold level, broadcasting, from said radio base station, an acknowledgement radio signal being indicative of the channel and the RSSI level of the broadcast radio signal with said portable set, to a first cell manager associated with the radio base station;

d) completing a telephone wireless connection between the radio base station and the portable set on said vacant radio frequency channel if, the RSSI level of the broadcast radio signal on said vacant radio frequency channel is at least a value of an arbitration threshold;

e) forwarding the detected RSSI level of the broadcast radio signal of said vacant radio frequency channel to base stations of neighboring cells if the RSSI level of the broadcast radio signal is below the arbitration threshold;

f) detecting at base stations of neighboring cells the RSSI level of the broadcast radio signal on said vacant radio frequency channel;

g) instructing base stations in neighboring cells to send registered RSSI levels of the broadcast radio signal, to the first cell manager, if the RSSI level detected by neighboring base stations is of a greater value than the RSSI level of the broadcast radio signal received from the first cell manager;

h) receiving, at the first cell manager, the registered RSSI levels of base stations associated with neighboring cells to compare with the RSSI level of the broadcast radio signal; and

i) enabling completion of a radio link at a base station having the greatest RSSI level.

2. In a telephone system having a plurality of cells for wireless communication with portable sets each having a preassigned identity, wherein each cell includes a plurality of radio base stations, any one of which is operable to provide a radio link with a portable set over any one of a plurality of radio frequency channels, a method of establishing a call between a radio base station and a portable set, wherein an originating radio link is established from a radio base station to the portable set of a called party over a vacant radio frequency channel, comprising the steps of:

a) receiving an incoming call request for a called party associated with a portable set;

b) estimating the location of the portable set from amongst said plurality of cells;

d) selecting radio base stations having vacant radio frequency channels in cells located near a probable location of the portable set;

e) broadcasting a radio signal including a coded message corresponding to the preassigned identity of a called portable set in at least one vacant radio frequency channel of each selected radio base station;

f) after each radio signal broadcast, monitoring the at least one vacant radio frequency channel for a portable set response broadcast including the identity of the called portable set;

g) registering the portable set response broadcast at a first radio base station if the portable set response broadcast is of a received signal strength indication (RSSI) level greater than a switch originating link setup (SOLS) threshold level, and broadcasting a radio signal indicative of the channel and the RSSI level of the radio link with the called portable set to a first cell manager associated with said first radio base station;

h) establishing a radio link between the first base station and the portable set on said vacant radio frequency channel if, the RSSI level of the response broadcast on said vacant radio frequency channel is at least a value of an arbitration threshold;

i) forwarding the RSSI level of the response broadcast to base stations of neighboring cells if the RSSI level of the response broadcast is below the arbitration threshold;

j) instructing base stations in neighboring cells to send registered RSSI levels of the response broadcast, associated with the vacant radio frequency channel used by the portable set, to the first cell manager, if the RSSI level is of a greater value than the RSSI level of the response broadcast received from the first cell manager;

k) receiving, at the first cell manager, the registered RSSI levels of the response broadcast from base stations associated with neighboring cells to compare with the RSSI level at said first radio base station; and

l) enabling completion of a radio link on said vacant radio frequency channel at a base station having the greatest RSSI level.

3. A method as defined in claim 2 wherein the location of said portable set is estimated, by:

identifying and searching a first half of said plurality of cells;

identifying and searching a second half of said plurality of cells if the portable set was not found in the first half; and

searching all cells of said plurality of cells if the searches of the first and second half failed to locate the portable set.

4. A method as defined in claim 2, wherein the location of said portable set is estimated, by:

randomly polling, at regular intervals, all portable sets;

maintaining a positional histogram for each registered portable set, relative each cell in said plurality of cells.

5. A method as defined in claim 2, wherein the location of said portable set is estimated, by:

forwarding a list of vacant frequency radio channels to each base station associated with separate groups of cells; and

instructing a radio base station in a cell to select a vacant radio frequency channel on said list for searching for the portable set, wherein each cell which uses a radio base station for searching is separated by at least one cell from any other cells which also uses a radio base station for searching the portable set.

6. A method of maintaining wireless telephony service for a portable telephone set communicating with a first radio base station during mobile operation of the portable set while it is able to traverse a cell of established operation toward any neighbouring cell, the method comprising the steps of:

a) periodically monitoring, at said first radio base station and at idle base stations of neighbouring cells, the radio channel used for communication between said portable telephone set and said first radio base station, to maintain a record of the RSSI level on said radio channel;

b) generating a running average of a receive signal strength indication (RSSI) level at said first and idle radio base stations;

c) storing said running average in a memory at said idle base stations in said neighbouring cells;

d) in response to a predetermined drop in the running average, at said first base station, generating a handoff request to neighbouring base stations via an associated cell manager, said request providing an indication of the RSSI level of said monitored radio channel of the cell of established operation;

e) each idle radio base station of neighbouring cells responding to said handoff request if its stored running average is greater, by a predetermined amount, than the RSSI level indicated in said request;

f) forwarding the stored running average to said associated cell manager;

g) selecting in response to the received RSSI levels of idle radio base stations in a neighbouring cell, a target radio base station to act on said handoff request; and

h) transferring the radio link to the target radio base station whereby the neighbouring cell of the target base station becomes the cell of established operation and repeating steps a), b), c) and d).

7. A method as defined in claim 6, wherein said handoff request includes the RSSI level of the monitored radio channel in the cell of established operation plus a delta value representing said predetermined amount.

8. A method as defined in claim 6, wherein a handoff request is generated by said first base station in response to a drop in the running average being more than a predetermined amount, wherein the predetermined amount of drop in the running average is a first delta when the running average is within a first range of RSSI levels and a second delta when the running average is within a second range of RSSI levels.

9. A method as defined in claim 8, wherein said second delta is of a lesser value than said first delta and wherein running averages within said second range of RSSI levels are of lesser value than running averages within said first range of RSSI levels.

10. A method as defined in claim 8, wherein the predetermined amount of drop in the running average is predetermined to be proportional to a most recent apex in the level of the running average.

13. A method as defined in claim 6, wherein the running averages are computed for a period having a length between 5 seconds and 15 seconds.

11. A wireless telephone system for maintaining a communication between a portable telephone set and a first radio base station during mobile operation of the portable set while it is able to traverse a cell of established operation toward any neighbouring cell, comprising:

a) monitoring means, at said first radio base station and at idle base stations of neighbouring cells, for periodically monitoring the radio channel used for communication between said portable telephone set and said first radio base station, to maintain a record of the RSSI level on said radio channel;

b) generating means for generating a running average of a received signal strength indication (RSSI) level at said first and idle radio base stations;

c) means for storing said running average in a memory at said idle base stations in said neighbouring cells;

d) means for generating a handoff request to neighbouring base stations via an associated cell manager in response to a predetermined drop in the running average at said first base station, said request providing an indication of the RSSI level of said monitored radio channel of the cell of established operation;

e) means for responding, at each idle radio base station of neighbouring cells, to said handoff request by forwarding the stored running average if greater, by a predetermined amount, than the RSSI level indicated in said request; and

f) a service controller for selecting, in response to the received RSSI levels of idle radio base stations in a neighbouring cell, a target radio base station to act on said handoff request and for transferring the radio link to the target radio base station whereby the neighbouring cell of the target base station becomes the cell of established operation.

12. In a telephone system having a plurality of cells for wireless communication with portable sets each having a preassigned identity, wherein each cell includes a plurality of radio base stations, any one of which is operable to provide a radio link with a portable set over any one of a plurality of radio frequency channels, said system operating to establish a call between a radio base station and a portable set, wherein an originating radio link is established from a radio base station to the portable set of a called party, comprising:

a) means for receiving an incoming call request for a called party associated with a portable set;

b) means for estimating the location of the portable set from amongst said plurality of cells;

d) service controller means for selecting radio base stations having vacant radio frequency channels in cells located near a probable location of the portable set;

e) means for broadcasting, in at least one vacant channel of each selected radio base station, a radio signal including a coded message corresponding to the preassigned identity of a called portable set;

f) means for monitoring the at least one radio frequency channel, after each radio signal broadcast, for a portable set response including the identity of the called portable set;

g) means for receiving the portable set response broadcast at a first radio base station if the portable set response broadcast is of a received signal strength indication (RSSI) level greater than a switch originating link setup (SOLS) threshold level;

h) means for broadcasting a radio signal indicative of the channel and the RSSI level of the radio link with the called portable set to a first cell manager associated with said first radio base station;

i) means for establishing a radio link between the first base station and the portable set on said indicated channel if, the RSSI level of the radio link therebetween is at least a value of an arbitration threshold;

j) means for forwarding the RSSI level of the radio link to base stations of neighboring cells if the RSSI level of the radio link is below the arbitration threshold;

k) means for instructing base stations in neighboring cells to send registered RSSI levels, associated with the channel used by the portable set, to the first cell manager, if the RSSI level is of a greater value than the RSSI level of the radio link received from the first cell manager;

l) means for receiving, at the first cell manager, the registered RSSI levels of base stations associated with neighboring cells to compare with the RSSI level of the radio link; and

m) means for enabling completion of a radio link at a base station having the greatest RSSI level.