US 6,192,243 B1Granted

Method and apparatus for dynamically adjusting number of guard channels in a mobile communication system

AssigneeNortel Networks Limited

InventorsPing Yang, Hua Jiang

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Abstract

A wireless communications systems for servicing mobile subscribers which dynamically optimizes the absolute number of channels reserved for use only as guard channels to minimize the blocking of handoff as well as new calls even under widely varying traffic and mobility conditions. This is accomplished by periodically first incorporating values, representative of traffic and mobility data typically collected in cellular systems, obtained over a given period of time, into an equation developed by the present inventors and calculating the number of guard channels needed to obtain assumed values of new and handoff call blocking; second changing the number of guard channels to the calculated value; and then third gathering data for a new period of time before returning to the first step.

Claims10

Dependent claims

A method for determining an optimum number of guard channels reserved in a cell of a cellular communications system for handoff calls in order to achieve a predetermined handoff call blocking probability, the method comprising the steps of:

a. measuring traffic load of the cell for a predetermined time interval;
b. measuring the number of handoffs per call in the cell during the predetermined time interval;
c. determining an optimum number of guard channels reserved for handoff calls in the cell based on traffic load and mobility for the cell in order to achieve the predetermined handoff call blocking probability, by:
setting a value for new call blocking probability (pbn) to a blocking probability value equal to a given handoff blocking (pbh);
setting a number of guard channels (m) to zero;
setting pbn(0) to the same value as a previously set value of pbn. and setting a counter j to 1;
solving for pbn(j);
determining whether the absolute value of {pbn(j)−pbn(j−1)} divided by pbn(j) is less than a predetermined error value;
responsive to a determination that the absolute value of {pbn(j)−pbn(j−1)} divided by pbn(j) is not less than the predetermined error value, incrementing j and repeating the steps of solving for pbn(j) and checking the absolute value until the absolute value difference between successively obtained values of pbn is less than the predetermined error value;
responsive to a determination that the absolute value of {pbn(j)−pbn(j−1)} divided by pbn(j) is less than the predetermined error value, setting pbn equal to the last obtained value of new call blocking probability pbn(j);
calculating a handoff blocking probability (pbh(m)) for a previous set number of guard channels;
determining whether the calculated result pbh(m) is greater than the initially predetermined value of handoff blocking probability pbh;
responsive to a determination that pbh(m) is greater than pbh, incrementing m and returning to the step of setting pbn(0);
and
responsive to a determination that pbh(m) is less than or equal to pbh, setting the optimum number of guard channels equal to m and setting the call blocking probability to the last calculated value of pbn;
and
d. adjusting the number of guard channels reserved for handoff calls in the cell to a value corresponding to the optimum number of guard channels reserved for handoff calls determined in the previous step.

14 more elements

A method for determining an optimum number of channels reserved in a cell of a cellular communications system for handoff calls in order to achieve a predetermined handoff call blocking probability, the method comprising:

measuring a first traffic load value of the cell for a first predetermined time interval;
measuring a first mobility value of mobile radios in the cell during the first predetermined time interval;
determining a first optimum number of guard channels reserved for handoff calls in the cell based on first traffic load value and the first mobility value for the cell in order to achieve the predetermined handoff call blocking probability;
measuring a second traffic load value of the cell for a second predetermined time interval;
measuring a second mobility value of mobile radios in the cell during the second predetermined time interval;
determining a second optimum number of guard channels reserved for handoff calls in the cell based on second traffic load value and the second mobility value for the cell in order to achieve the second predetermined handoff call blocking probability;
adjusting the number of guard channels reserved for handoff calls in the cell to a value corresponding to the second determined optimum number of guard channels reserved for handoff calls;
determining a differential traffic value as the difference between the first traffic value and the second traffic value;
determining a differential mobility value as the difference between the first mobility value and the second mobility value;
determining whether either the differential traffic value is greater than a predetermined set upper threshold value of differential traffic value or the differential mobility value is greater than a predetermined set upper threshold values of differential mobility value;
in response to a determination that either the differential traffic value is greater than a predetermined set upper threshold value of differential traffic value or the differential mobility value is greater than a predetermined set upper threshold value of differential mobility value, setting a third predetermined time interval equal to the second predetermined time interval divided by a first constant greater than one;
in response to a determination that neither the differential traffic value is greater than a predetermined set upper threshold values of differential traffic value nor the differential mobility value is greater than a predetermined set upper threshold values of differential mobility value, determining whether either the differential traffic value is less than a predetermined set lower threshold values of differential traffic value or the differential mobility value is less than a predetermined set lower threshold values of differential mobility value;
in response to a determination that either the differential traffic value is less than a predetermined set lower threshold value of differential traffic value or the differential mobility value is less than a predetermined set lower threshold value of differential mobility value, setting a third predetermined time interval equal to the second predetermined time interval multiplied by a second constant greater than one;
in response to a determination that neither the differential traffic value is less than a predetermined set lower threshold value of differential traffic value nor the differential mobility value is less than a predetermined set lower threshold value of differential mobility value, setting a third predetermined time interval equal to the second predetermined time interval;
measuring a third traffic load value of the cell for the third predetermined time interval;
measuring a third mobility value of mobile radios in the cell during the third predetermined time interval;
determining a third optimum number of guard channels reserved for handoff calls in the cell based on third traffic load value and the third mobility value for the cell in order to achieve the predetermined handoff call blocking probability;
and
adjusting the number of guard channels reserved for handoff calls in the cell to a value corresponding to the third determined optimum number of guard channels reserved for handoff calls.

16 more elements

Dependencies are inferred from the claim text.