Method of controlling handover in a multicellular radio communications network, and speed estimation methods relating thereto

A method of controlling handover in a multicellular radio communications network, the network including cells of layer m, where m ranges from 1 up to M, a cell of layer m+1 including a base station intended to communicate with mobile stations generally moving more rapidly than mobile stations with which base stations of cells of layer m are intended to communicate, the method comprising:

• measuring communication parameters between a mobile station assigned to a source cell and one of the base station of the source cell and at least one base station of a neighboring cell, the measured communication parameters including a level of at least one signal received by the mobile station from the base station of a neighboring cell, the at least one signal being received and measured by the mobile station at successive measurement instants spaced apart by a constant measurement interval;
• analyzing the measured communication parameters to determine instants at which the mobile station satisfies a first handover criterion for handover from the source cell of layer m+1 to a target cell of layer m;
• estimating a movement speed of the mobile station with respect to the target cell base station when the first handover criterion is satisfied, wherein the estimating is performed based on the measured levels of the signal received by the mobile station before said first handover criterion is satisfied;
• performing a handover of the mobile station to the target cell if the estimated speed is below a first speed threshold, and maintaining the assignment to the source cell if the estimated speed is above the first speed threshold, wherein,
• estimating the movement speed of the mobile station with respect to the base station of the target cell comprises the steps of:
• calculating, over a sliding window, average values of the measured levels of the signal received by the mobile station from the target cell base station until an instance N0 when the handover criterion is satisfied, an average value R(i), relating to a measurement instant i, being an average of the signal levels measured at instants from i-L+1 to i, where L is an integer representing a size of the sliding window;
• obtaining at least Nmin average values relating to Nmin consecutive measurement instants immediately preceding the instant N0, where Nmin is an integer;
• determining an oldest measurement instant N0-J, where at least Nmin and at most Jmax measurement intervals occur before the instant N0, Jmax being an integer at least equal to Nmin and the absolute value of the difference E(j,k)=›(1-k/j).R(N0)+(k/j).R(N0-j)!-R(N0-k) is less than a predetermined threshold for every pair of integers j, k, where 1.ltoreq.k.ltoreq.J;
• and
• estimating the speed at the instant N0 based on the gradient ›R(N0)-R(N0-J)!/J.

A method of controlling handover in a multicellular radio communications network, the network including cells of layer m, where m ranges from 1 up to M, a cell of layer m+1 including a base station intended to communicate with mobile stations generally moving more rapidly than mobile stations with which base stations of cells of layer m are intended to communicate, the method comprising:

• measuring communication parameters between a mobile station assigned to a source cell and one of the base station of the source cell and at least one base station of a neighboring cell, the measured communication parameters including a level of at least one signal received by the mobile station from the base station of a neighboring cell, the at least one signal being received and measured by the mobile station at successive measurement instants spaced apart by a constant measurement interval;
• analyzing the measured communication parameters to determine instants at which the mobile station satisfies a first handover criterion for handover from the source cell of layer m+1 to a target cell of layer m;
• estimating a movement speed of the mobile station with respect to the target cell base station when the first handover criterion is satisfied, wherein the estimating is performed based on the measured levels of the signal received by the mobile station before said first handover criterion is satisfied;
• performing a handover of the mobile station to the target cell if the estimated speed is below a first speed threshold, and maintaining the assignment to the source cell if the estimated speed is above the first speed threshold, wherein,
• when estimating the movement speed of the mobile station with respect to the target cell base station at an instant N0, occurring after the handover criterion is satisfied and values X(N0-P+1) to X(N0) of the signal level have been obtained at instants N0-P+1 to N0, where P is a predetermined integer, the estimating step comprises:
• determining a straight line exhibiting a minimum distance with points (N0-p,X(N0-p)) where 0.ltoreq.p<P, by linear interpolation;
• and
• estimating the movement speed of the mobile station at the instant N0 based on said minimum distance.

A method for estimating speed of movement of a mobile radio communications station with respect to a base station of a cellular network, comprising the steps of:

• measuring levels of a radio signal received by one of the two stations from the other station at successive measurement instants spaced apart by a constant measurement interval;
• calculating, over a sliding window, average values of the measured signal levels, an average value R(i) relating to a measurement instant i being an average of the signal levels measured at instants i-L+1 to i, where L is an integer representing the size of the sliding window;
• having obtained at least Nmin average values relating to Nmin consecutive measurement instants immediately preceding a measurement and estimation instant N0, where Nmin is an integer, determining an oldest measurement instant N0-J before the instant N0 by at least Nmin measurement intervals and at most Jmax measurement intervals, where Jmax is an integer at least equal to Nmin, such that, for every pair of integers j, k, where 1.ltoreq.k.ltoreq.J, a difference E(j,k)=›(1-k/j).R(N0)+(k/j).R(N0-j)!-R(N0-k) is less than a predetermined threshold;
• and
• estimating the movement speed at the instant N0 on the basis of the gradient ›R(N0)-R(N0-J)!/J.

A method for estimating the speed of movement of a mobile radio communications station with respect to a base station of a cellular network, comprising the steps of:

• measuring levels of a radio signal received by one of the two stations from the other station at successive measurement instants spaced apart by a constant measurement interval;
• having obtained values X(N0-P+1) to X(N0) of the signal level at instants N0-P+1 to N0, where N0 designates a measurement and estimation instant and P designates a predetermined integer, determining a straight line exhibiting a minimum distance with points (N0-p,X(N0-p)) where 0.ltoreq.p<P, by linear interpolation;
• and
• estimating the movement speed at the instant N0 on the basis of said minimum distance.