Load estimation and load management in a cellular communications network
A cellular communications network 10 comprises a plurality of basestations 12, 14, 16 and 18 connected to each other through an interface and to a core network through another interface. Each basestation has a coverage area referred to as a cell k. There are provided methods for estimating the load imparted on a cell in the cellular communications network by user equipments in the cell. The methods make it possible to estimate any potential increase in the load that may impact onto a target cell due to the handover of a UE from a serving cell.
1. A method for estimating a load imparted on a cell in a cellular communications network by user equipments in the cell, the method comprising:
calculating an average power of the cell by a basestation associated with the cell;
calculating an bit rate achieved for each currently scheduled user equipment in the cell;
estimating a current value of the load imparted on the cell as a sum of required bit rates for each currently scheduled user equipment in the cell divided by a sum of the calculated achieved bit rates for each user equipment in the cell, multiplied by the calculated average power of the cell divided by a maximum power available in the cell;
estimating an actual load imparted on the cell as a sum of a fraction taken of a previous value of the load imparted on the cell and a fraction taken of the estimated current value of the load imparted on the cell; and
adjusting the fraction taken of the previous value of the load and the fraction taken of the estimated current value of the load by:
calculating a variability of the estimated current value of the load imparted on the cell; and
adjusting the fraction taken of the previous value of the load and the fraction taken of the estimated current value of the load based on the calculated variability of the estimated current value of the load imparted on the cell.
2. A method as claimed in claim 1 ,
wherein the sum of the fraction taken of the previous value of the load and the fraction taken of the estimated current value of the load equals 1.
3. A method as claimed in claim 1 , wherein the sum of the calculated achieved bit rates for each user equipment in the cell comprises a sum of the calculated achieved bit rates for each currently scheduled user equipment in the cell or a sum of the calculated achieved bit rates for each active user equipment in the cell.
4. A method as claimed in claim 1 , wherein the fraction taken of the previous value of the load and the fraction taken of the estimated current value of the load are adjusted by:
determining whether the calculated variability of the estimated current value of the load imparted on the cell is less than a target value minus a first hysteresis value; and
if the calculated variability is less than the target value minus the first hysteresis value:
reducing the fraction taken of the previous value of the load and increasing the fraction taken of the estimated current value of the load.
5. A method as claimed in claim 1 , wherein the fraction taken of the previous value of the load and the fraction taken of the estimated current value of the load are adjusted by:
determining whether the calculated variability of the estimated current value of the load imparted on the cell is less than a target value minus a first hysteresis value; and
if the calculated variability is not less than the target value minus the first hysteresis value:
determining whether the calculated variability is greater than the target value plus a second hysteresis value;
if the calculated variability is not greater than the target value plus the second hysteresis value:
repeating the calculating the variability of the estimated current value of the load imparted on the cell and the adjusting the fraction taken of the previous value of the load and the fraction taken of the estimated current value of the load; and
if the calculated variability is greater than the target value plus the second hysteresis value:
increasing the fraction taken of the previous value of the load and reducing the fraction taken of the estimated current value of the load.
6. A method as claimed in claim 1 , wherein the variability of the estimated current value of the load imparted on the cell is calculated as a standard deviation of the estimated current value of the load imparted on the cell divided by a mean of the estimated current value of the load imparted on the cell.
7. A method as claimed in claim 1 , wherein the step of calculating the bit rate achieved for each currently scheduled user equipment in the cell comprises:
if a particular user equipment is not currently scheduled:
calculating the bit rate achieved for the particular user equipment as a fraction taken of a previous value of the bit rate achieved for the user equipment; or
if a particular user equipment is currently scheduled:
calculating the bit rate achieved for the particular user equipment as the sum of a fraction taken of a previous value of the bit rate achieved for the user equipment and a fraction taken of a current bit rate allocated to the user equipment, wherein the sum of the fraction taken of the previous value of the bit rate achieved for the user equipment and the fraction taken of the current bit rate allocated to the user equipment equals 1.
8. A basestation for estimating a load imparted on a cell in a cellular communications network by user equipments in the cell, the basestation comprising a processor and a memory and configured for:
calculating an average power of the cell;
calculating an bit rate achieved for each currently scheduled user equipment in the cell;
estimating a current value of the load imparted on the cell as a sum of required bit rates for each currently scheduled user equipment in the cell divided by a sum of the calculated achieved bit rates for each user equipment in the cell, multiplied by the calculated average power of the cell divided by a maximum power available in the cell;
estimating an actual load imparted on the cell as the sum of a fraction taken of a previous value of the load imparted on the cell and a fraction taken of the estimated current value of the load imparted on the cell; and
adjusting the fraction taken of the previous value of the load and the fraction taken of the estimated current value of the load by:
calculating a variability of the estimated current value of the load imparted on the cell; and
adjusting the fraction taken of the previous value of the load and the fraction taken of the estimated current value of the load based on the calculated variability of the estimated current value of the load imparted on the cell.
9. The basestation as claimed in claim 8 ,
wherein the sum of the fraction taken of the previous value of the load and the fraction taken of the estimated current value of the load equals 1.
10. The basestation as claimed in claim 8 , wherein the sum of the calculated achieved bit rates for each user equipment in the cell comprises a sum of the calculated achieved bit rates for each currently scheduled user equipment in the cell or a sum of the calculated achieved bit rates for each active user equipment in the cell.
11. The basestation as claimed in claim 8 , wherein the fraction taken of the previous value of the load and the fraction taken of the estimated current value of the load are adjusted by:
determining whether the calculated variability of the estimated current value of the load imparted on the cell is less than a target value minus a first hysteresis value; and
if the calculated variability is less than the target value minus the first hysteresis value:
reducing the fraction taken of the previous value of the load and increasing the fraction taken of the estimated current value of the load.
12. The basestation as claimed in claim 8 , wherein the variability of the estimated current value of the load imparted on the cell is calculated as a standard deviation of the estimated current value of the load imparted on the cell divided by a mean of the estimated current value of the load imparted on the cell.
13. The basestation as claimed in claim 8 , wherein the step of calculating the bit rate achieved for each currently scheduled user equipment in the cell comprises:
if a particular user equipment is not currently scheduled:
calculating the bit rate achieved for the particular user equipment as a fraction taken of a previous value of the bit rate achieved for the user equipment; or
if a particular user equipment is currently scheduled:
calculating the bit rate achieved for the particular user equipment as the sum of a fraction taken of a previous value of the bit rate achieved for the user equipment and a fraction taken of a current bit rate allocated to the user equipment, wherein the sum of the fraction taken of the previous value of the bit rate achieved for the user equipment and the fraction taken of the current bit rate allocated to the user equipment equals 1.