Mobile communications system

• US 6,278,881 B1
• Filed: 06/29/1998
• Issued: 08/21/2001
• Est. Priority Date: 06/30/1997
• Status: Expired due to Term

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Balck, Kenneth
• Primary Examiner(s): Hunter, Daniel
• Assistant Examiner(s): Chow, C.
• Application Number:
  US09/106,363
• Time in Patent Office: 1,149 Days
• Field of Search: 455/444, 455/443, 455/434, 455/436, 455/437, 455/439, 455/446, 455/464, 379/59
• US Class Current: 455/444
• CPC Class Codes: H04W 36/04 Reselecting a cell layer in multi-layered cells

Abstract

In a cellular communications network including microcells and macrocells, a mobile device preferably communicates with an appropriate one of the microcells. When a handover from one microcell to another is imminent, a backup channel in the macrocell layer is allocated to the mobile device, for use if the handover is not successfully completed.

Claims

1. A method of managing a handover in a mobile communications system comprising a plurality of base stations associated with respective cells and a plurality of mobile stations, in which a mobile station is in communication with a first base station in a first cell on a first channel, the method comprising:

detecting that the mobile station is approaching an edge of the first cell;

allocating a second channel in a second cell to the mobile station;

determining that the mobile station should handover communications to a third channel in a third cell; and

if the mobile station fails to handover communications to the third channel in the third cell, beginning communications with the mobile station on the second channel.

2. A method of managing a handover as claimed in claim 1, wherein the second cell is at a higher level than the first cell.

3. A method of managing a handover as claimed in claim 2, wherein the second cell is at a level immediately higher than the level of the first cell.

4. A method of managing a handover as claimed in claim 2, wherein the first cell is a micro cell, and the second cell is a macro cell.

5. A method of managing a handover as claimed in claim 1, comprising detecting that the mobile station is approaching an edge of the first cell by determining that the signal strength on the first channel has fallen below a predetermined threshold.

6. A method of managing a hangover as claimed in claim 1, comprising detecting that the mobile station is approaching an edge of the first cell by determining that the rate at which signal strength on the First channel is falling exceeds a predetermined threshold.

7. A method of managing a handover as claimed in claim 1, comprising detecting that the mobile station is approaching an edge of the first cell by determining that the path loss on the first channel has exceeded a predetermined threshold.

8. A method of managing a handover as claimed in claim 1, comprising detecting that the mobile station is approaching an edge of the first cell by determining that the rate at which path loss on the first channel is rising exceeds a predetermined threshold.

9. A method of managing a handover as claimed in claim 1, comprising detecting that the mobile station is approaching an edge of the first cell by determining that the distance of the mobile station from the first base station exceeds a predetermined threshold.

10. A method of managing a handover of a mobile device from a first base station to a second base station in a first lower layer of a cellular communications network, the method comprising:

determining that a handover may be imminent;

allocating a reserve channel in a second higher layer to the mobile device;

if required, instructing the mobile device to handover to the second base station; and

if the handover is unsuccessful, communicating with the mobile device over the reserve channel.

11. A method of managing a handover as claimed in claim 10, comprising detecting that the mobile station is approaching an edge of the first cell by determining that the signal strength on the first channel has fallen below a predetermined threshold.

12. A method of managing a handover as claimed in claim 10, comprising detecting that the mobile station is approaching an edge of the first cell by determining that the rate at which signal strength on the first channel is falling exceeds a predetermined threshold.

13. A method of managing a handover as claimed in claim 10, comprising detecting that the mobile station is approaching an edge of the first cell by determining that the path loss on the first channel has exceeded a predetermined threshold.

14. A method of managing a handover as claimed in claim 10, comprising detecting that the mobile station is approaching an edge of the first cell by determining that the rate at which path loss on the first channel is rising exceeds a predetermined threshold.

15. A method of managing a handover as claimed in claim 10, comprising detecting that the mobile station is approaching an edge of the first cell by determining that the distance of the mobile station from the first base station exceeds a predetermined threshold.

16. A base station controller, for use in a cellular communications network, having a first base station and a second base station in a first lower layer and a third base station in a second higher layer, the first, second and third base stations operating on first, second and third channels respectively, and the controller comprising:

means for receiving signal strength measurements from a mobile device communicating with the first base station on the first channel;

means for determining from the received signal strength measurements a handover may be imminent;

means for allocating the third channel to the mobile device as a reserve channel;

if required, instructing the mobile device to handover to the second base station; and

if the handover is unsuccessful, communicating with the mobile device over the reserve channel.

17. A mobile communications device, for use in a cellular communications network, the device comprising:

a transceiver, for communicating with a designated base station on a designated channel;

means for making signal strength measurements, and for reporting those measurements to the designated base station;

means for receiving channel assignments, including handover instructions;

means for determining whether an existing connection with a base station can be maintained;

means for storing details of a backup channel allocated to the mobile device; and

if it is determined that an existing connection with a base station cannot be maintained, but no handover instruction has been received, means for handing over to the backup channel.

18. A mobile communications device as claimed in claim 17, wherein the means for storing details of the backup channel is controlled by a timer to store said details for a predetermined time period.

19. A cellular communications network comprising:

a first cell including a first base station;

a second cell including a second base station;

a third cell including a third base station, wherein the third cell includes the first and second cells;

means for detecting that a mobile device is going to handover from the first cell to the second cell;

means for allocating a channel in the third cell to the mobile device;

means for notifying the mobile device of the allocation of the channel;

means for instructing the mobile device to handover from the first cell to the second cell; and

means for performing handover to the channel in the third cell if the mobile device fails to access the second base station and fails to reconnect to the first base station.

20. The cellular communications system of claim 19, wherein the first and second cells are microcells and the third cell is a macrocell.