METHOD FOR PREVENTING PIN-PONG HANDOVER EFFECT IN MOBILE WIMAX NETWORKS

• US 20090274118A1
• Filed: 12/22/2008
• Published: 11/05/2009
• Est. Priority Date: 12/21/2007
• Status: Active Grant

• Current Assignee: RPX Corporation
• Original Assignee: Nokia Siemens Networks SPA (Nokia Corporation), NOKIA SIEMENS NETWORKS OY OF CASSINA, NOKIA SIEMENS NETWORKS OY OF CASSINA
• Inventors: De Sanctis, Alessandro, Rastell, Marco, Tortora, Daniele
• Granted Patent: US 8,379,597 B2
• Time in Patent Office: Days
• US Class Current: 370/331
• CPC Class Codes: H04W 36/008375 based on historical data
• CPC Class Codes: H04W 36/38 by fixed network equipment

Abstract

To prevent a handover ping-pong effect between base-station in WiMAX-compliant networks, a priority level is firstly assigned to the trigger causes for handover, and the prioritized causes are coded. Then codes are subdivided into a first class of unrestricted handovers and a second class of handover subjected to restriction. The first class includes the highest priority handovers. The second class includes a given subset of handovers with a high or normal priority intended for optimizing resources. Outside this subset the second class also includes handovers for power budget having a normal priority level. When an outgoing handover is decided, the actual serving BS either permits or selectively suppresses the Handover Request to the target BS when the latter is corresponding to the preceding serving BS for that mobile. The selection mechanism operates on the second class of restricted handovers, during a penalty time triggered by the occurrence of handover causes included in the given subset of the second class.

Claims

1. A method for controlling handovers of a radio connection to a mobile station between base stations of a cellular communication network, comprising:

assigning a priority level to handover trigger causes includible in a handover request or confirm message and coding the prioritized handover trigger causes to obtain codes;

subdividing the codes into a first class associated with unrestricted handovers and a second class associated with handovers subjected to restriction;

storing an identifier of a previous serving base station for an incoming handover accepted for a mobile station;

starting a penalty timer if the code of the prioritized handover trigger cause of an accepted handover belongs to a given subset of the second class;

deciding a new valid condition to trigger a handover request for the mobile station, comprising;

detecting if a target base station identifier is equal to the stored identifier,

detecting if the code of the prioritized handover trigger cause of the new valid condition belongs to the second class, and

determining that a penalty elapsed time is below a configurable value; and

suppressing issuance of a handover request for the mobile station if all the conditions of the deciding step are simultaneously met, otherwise issuing a handover request including the handover trigger cause.

2. The method of claim 1, wherein the second coding class includes codes of handover trigger causes dealing with network resources allocation optimization and traffic distribution, including load balancing, having a priority level high or normal.

3. The method of claim 1, wherein the first coding class includes codes of handover trigger causes dealing with imperative handovers, including Power Level, Quality of transmission, alarms, having a highest priority level.

4. The method of claim 1, wherein the code of a prioritized power budget handover trigger cause, having normal priority level, is outside the given subset of the second coding class.

5. The method of claim 1, wherein the handover trigger causes are transmitted by vendor specific Type/Length/Value information elements included in handover request messages and handover confirm messages.

6. The method of claim 1, wherein handover performance counters are provided for handover causes.

7. The method of claim 1, wherein the cellular telecommunication network has a radio interface based on an OFDMA or SOFDMA technique.