Blind handover technique

• US 20050202821A1
• Filed: 03/09/2005
• Published: 09/15/2005
• Est. Priority Date: 03/10/2004
• Status: Active Grant

• Current Assignee: Orange S.A.
• Original Assignee: Orange S.A.
• Inventors: Pischella, Mylene
• Granted Patent: US 7,224,972 B2
• Time in Patent Office: Days
• US Class Current: 455/436
• CPC Class Codes: H04W 36/00837 Determination of triggering parameters for hand-off
• CPC Class Codes: H04W 36/0085 Hand-off measurements
• CPC Class Codes: H04W 36/14 Reselecting a network or an air interface

Abstract

In a mobile telecommunications system, when it is determined that a mobile terminal should be handed over from a first cell (primary cell) to a second cell (target cell), the target cell is chosen based on measurements of link quality in the primary network at the time when it is determined that handover is necessary, as well as on stored data indicative of the respective probabilities that different potential target cells will be the best handover target from a particular primary cell. This enables an appropriate choice of target cell to be made even in a case where it is not possible to make measurements on the target cells at the time when it is determined that handover is necessary (for example because handover is to a target cell that operates at a different frequency from that of the primary cell).

Claims

1. A method of performing a blind handover of a mobile terminal from a primary cell (A_j) in a primary network of a mobile telecommunications system to a target cell (T_k) in a target network, wherein said primary network comprises a control entity, the method comprising the steps of:

evaluating the quality of communications links available to the mobile terminal in the primary network; and

selecting the target cell for the handover based on the evaluated quality measurement(s) (M) and on data (B_k,j) indicating the respective probabilities that different cells (T_k) in the target network will be the best cell to use as the target cell in a handover from different cells (A_j) in the primary network, wherein the target cell for the handover is selected by weighting said probability data (B_j,k) based on the evaluated quality measurements (M).

2. The blind handover method according to claim 1, wherein:

the evaluating step comprises the step of identifying a number (N) of cells (A₁, A₂, . . . , A_N) in the primary network that provide the best link quality for the mobile terminal; and

the target cell selecting step comprises the steps of calculating, for different cells (T_k) in the target network, weighted probabilities (P_k) such that;

$P_k,=\underset{i=1}{\overset{N}{\sum <br><br>}}<br><br>B_{k,i}\times <br><br>\frac{M_i}{M_1}÷<br><br>\underset{i=1}{\overset{N}{\sum <br><br>}}<br><br>\frac{M_i}{M_1}$

where B_k,i is predetermined probability data indicating the probability that target cell T_k will be the best target cell in a transfer from primary cell A_i, the primary cells are ordered according to the evaluated link quality associated therewith such that primary cell A₁ is the primary cell with highest link quality and primary cell A_N is the primary cell with N-^th highest evaluated link quality, and M_i is the quality measurement for primary cell A_i.

3. The blind handover method according to claim 1, wherein the predetermined probability data comprises a plurality of sets of data, each set of data indicating probabilities that, when link quality in the target network is evaluated using a respective different quality-measurement parameter, different cells (T_k) in the target network will be the best cell to use as the target cell in a handover.

4. The blind handover method according to claim 1, and comprising the step of deciding whether or not handover of the mobile terminal is desirable by comparing link quality data obtained in the evaluating step with a threshold level (T_limit);

wherein the predetermined probability data comprises a plurality of sets of data, each set of data indicating probabilities that, when the threshold level (T_limit) takes a respective different value, different cells (T_k) in the target network will be the best cell to use as the target cell in a handover.

5. A blind handover method according to claim 1, wherein the primary network and the target network form part of the same mobie telecommunications system but have different operating frequencies.

6. A blind handover method according to claim 1, wherein the primary network and the target network form part of two different mobile telecommunications systems.

7. A control entity for use in a mobile telecommunications network, the control entity being adapted, in use, to instruct blind handovers of a mobile terminal from a primary cell of said network to a target cell in a different network, the control entity comprising:

input means for receiving data indicating the quality of communications links available to the mobile terminal in the primary network;

retrieval means for accessing data (B_j,k) indicating the respective probabilities that different cells (T_k) in the target network will be the best cell to use as the target cell in a handover from a different cells (A_j) in the primary network; and

computing means for selecting the target cell for the handover based on the evaluated quality measurement(s) (M) and on the accessed probability data relating to cells in the target network, the computing means being adapted to weight the accessed probability data (B_k,j) based on the evaluated quality measurements (M).

8. The control entity according to claim 7, and comprising identification means, cooperating with the input means, for identifying a number (N) of cells (A₁, A₂, . . . , A_N) in the primary network that provide the best link quality for the mobile terminal;

wherein the computing means is adapted to compute, for different cells (T_k) in the target network, weighted probabilities (P_k) such that;

$P_k,=\underset{i=1}{\overset{N}{\sum <br><br>}}<br><br>B_{k,i}\times <br><br>\frac{M_i}{M_1}÷<br><br>\underset{i=1}{\overset{N}{\sum <br><br>}}<br><br>\frac{M_i}{M_1}$

where B_k,i is predetermined probability data indicating the probability that target cell T_k will be the best target cell in a transfer from primary cell A_i, the primary cells are ordered according to the evaluated link quality associated therewith such that primary cell A₁ is the primary cell with highest link quality and primary cell A_N is the primary cell with N-^th highest evaluated link quality, and M_i is the quality measurement for primary cell A_i.

9. The control entity according to claim 7, and comprising means for selecting different sets of probability data for use by the computing means dependent upon different types of link quality evaluation parameter, the selected set of probability data depending upon which link quality evaluation parameter is appropriate for the target network.

10. The control entity according to claim 7, and comprising:

comparison means for comparing with a threshold level (T_limit) link quality measurement data obtained via the input means; and

means for selecting different sets of probability data for use by the computing means dependent upon the value of the threshold level (T_limit) used by the comparison means.

11. A mobile telecommunications network adapted to implement blind handover of a mobile terminal from a primary cell in which the mobile terminal is operating to a target cell in a different network, the mobile telecommunications network comprising a control entity according to claim 7.