Method of selectively directing a mobile station to retry system access in a radio telecommunication system

• US 6,081,713 A
• Filed: 05/18/1998
• Issued: 06/27/2000
• Est. Priority Date: 05/18/1998
• Status: Expired due to Term

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Desgagne, Michel
• Primary Examiner(s): Bost, Dwayne D.
• Assistant Examiner(s): Vuong, Quochien B.
• Application Number:
  US09/081,481
• Time in Patent Office: 771 Days
• Field of Search: 455/436, 455/437, 455/438, 455/439, 455/63, 455/453, 455/446, 455/447, 455/525, 370/331, 370/332
• US Class Current: 455/436
• CPC Class Codes: H04W 16/06 Hybrid resource partitioning, e.g. channel borrowing
• CPC Class Codes: H04W 36/20 for optimising the interference level

Abstract

A method of reducing co-channel interference in a cellular telecommunication system having a congested serving cell, a plurality of neighbor cells controlled by a mobile switching center (MSC), and an accessing mobile station attempting to access the cellular system in the serving cell. The MSC fetches signal strength information from mobile stations camped on the serving cell'"'"'s digital control channel (DCCH). The signal strength information includes received signal strengths at the camped mobile stations from the serving cell and the neighbor cells. The MSC then fetches signal strength information from busy mobile stations involved in on-going calls in the serving cell. For each busy and camped mobile station, the expected downlink signal strength from each neighbor cell is subtracted from the maximum downlink signal strength from the serving cell. The mobile station/neighbor cell combination with the numerically least difference causes the least co-channel interference when the identified mobile station is moved into the identified neighbor cell. If the identified mobile station is the accessing mobile station, the MSC redirects the accessing mobile station to access the cellular system in the identified neighbor cell. If the identified mobile station is a busy mobile station involved in a call, the MSC forces a handoff of the identified mobile station to the identified neighbor cell.

Claims

1. A method of reducing co-channel interference in a cellular telecommunication system having a congested serving cell, a plurality of neighbor cells controlled by a mobile switching center (MSC), and an accessing mobile station attempting to access the cellular system in the serving cell, said method comprising the steps of:

camping the accessing mobile station on the serving cell'"'"'s digital control channel (DCCH);

fetching signal strength information from the accessing mobile station, said signal strength information including received signal strength at the accessing mobile station from the serving cell and the neighbor cells;

fetching signal strength information from a plurality of busy mobile stations involved in on-going calls in the serving cell, said signal strength information including received signal strength at each busy mobile station from the serving cell and the neighbor cells;

identifyig a mobile station/neighbor cell combination which causes the least co-channel interference when an identified mobile station is moved into an identified neighbor cell;

determining in the MSC whether the identified mobile station is the accessing mobile station;

redirecting the identified mobile station to access the cellular system in the identified neighbor cell, upon determining that the identified mobile station is the accessing mobile station; and

forcing a handoff of the identified mobile station to the identified neighbor cell, upon determining that the identified mobile station is a busy mobile station involved in a call.

2. The method of reducing co-channel interference of claim 1 wherein said step of identifying a mobile station/neighbor cell combination which causes the least co-channel interference includes the steps of:

finding a difference, for each mobile station in the network, between the maximum downlink signal strength of the serving cell and the expected downlink signal strength from each neighbor cell; and

identiiying a mobile station/neighbor cell combination for which the difference between the maximum signal strength of the serving cell and the expected signal strength from the neighbor cell is numerically least, the combination identifying the identified mobile station and the identified neighbor cell.

3. The method of reducing co-channel interference of claim 1 further comprising, after the step of identifying a mobile station/neighbor cell combination which causes the least co-channel interference, the steps of:

determining whether the accessing mobile station is still in the serving cell; and

stopping the process upon determining that the accessing mobile station is no longer in the serving cell.

4. The method of reducing co-channel interference of claim 3 wherein the step of determining whether the accessing mobile station is still in the serving cell includes determining that the accessing mobile station has performed a cell reselection and an automatic origination in one of the neighbor cells.

5. The method of reducing co-channel interference of claim 3 wherein the step of determining whether the accessing mobile station is still in the serving cell includes determining that the accessing mobile station has performed a cell reselection and an automatic page response in one of the neighbor cells.

6. The method of reducing co-channel interference of claim 1 further comprising, after the step of fetching signal strength information from the accessing mobile station, the steps of:

determining whether the serving cell is still congested; and

providing access to the accessing mobile station upon determining that the serving cell is no longer congested.

7. A method of minimizing co-channel interference in a cellular telecommunication system having a congested serving cell, a plurality of neighbor cells controlled by a mobile switching center (MSC), a plurality of busy mobile stations engaged in calls, and a plurality of accessing mobile station attempting to access the cellular system in the serving cell, said method comprising the steps of:

fetching signal strength measurements from each of the plurality of accessing mobile stations, said signal strength measurements including received signal strength at each of the accessing mobile stations from the serving cell and the neighbor cells;

fetching signal strength measurements from each of the plurality of busy mobile stations, said signal strength measurements including received signal strength at each of the busy mobile stations from the serving cell and the neighbor cells; and

minimizing co-channel interference in the cellular system, said minimizing step comprising the steps of;

identifying a mobile station/neighbor cell combination for which a difference between the maximum downlink signal strength of the serving cell and the expected downlink signal strength from each neighbor cell is the numerically least of all possible mobile station/neighbor cell combinations; and

moving the identified mobile station to the identified neighbor cell.

8. The method of minimizing co-channel interference of claim 7 wherein the step of moving the identified mobile station to the identified neighbor cell includes the steps of:

determining in the MSC whether the identified mobile station is one of the plurality of accessing mobile stations;

redirecting the identified mobile station to access the cellular system in the identified neighbor cell, upon determining that the identified mobile station is one of the plurality of accessing mobile stations; and

forcing a handoff of the identified mobile station to the identified neighbor cell, upon determining that the identified mobile station is one of the plurality of busy mobile stations.

9. The method of minimizing co-channel interference of claim 7 wherein the step of minimizing co-channel interference in the cellular system includes calculating the maximum downlink signal strength of the serving cell (MaxServSS_i) utilizing the equation:

space="preserve" listing-type="equation">MaxServSS.sub.i =SSserv.sub.i +ATT.sub.i -BO.sub.CC-DTC,

where SSserv_i is the measured downlink signal strength on the serving channel for a mobile station (MS_i), ATT_i is attenuation of power on the serving channel relative to the maximum transmitted power on the digital traffic channel DTC) for MS_i, and BO_CC-DTC is the difference between the maximum transmitted power on the digital control channel (DCCH) and the maximum transmitted power on the DTC.

10. The method of minimizing co-channel interference of claim 7 wherein the step of minimizing co-channel interference in the cellular system includes calculating the expected downlink signal strength from each neighbor cell (ExpNeighSS_i,j) utilizing the equation:

space="preserve" listing-type="equation">ExpNeighSS.sub.i,j =SSNeigh.sub.i,j -BO.sub.CC-DTCj,

where SSNeigh_i,j is the measured downlink signal strength for MS_i from neighbor cell_j, and BO_CC-DTCj is the difference between the maximum transmitted power on the digital control channel (DCCH) of neighbor cell_j and the digital traffic channels (DTCs) of neighbor cell_j.