Patent ID: 6236860
Filing Date: 2001-05-22
Classification: H04W

Abstract:
A scanning method for initiating handover of a call or roaming in a duplex radio communication system comprising radio access units and at least one remote radio communication unit, said radio access units and the or each remote radio communication unit being arranged for establishing a call at a radio link between a remote radio communication unit and a radio access unit, which radio link is selected from a plurality of predetermined radio links, and for switching a call in progress at a first radio link between a remote radio communication unit and a first radio access unit to a second radio link between said remote radio communication unit and a second radio access unit, wherein each or clusters of radio access units are operated in a mutually time asynchronous manner forming an asynchronous radio environment and said remote radio communication unit is synchronised to a first radio access unit, said method comprises the following steps performed by said remote radio communication unit:a) scanning said radio environment for radio access units which operate in a time synchronous manner with said first radio access unit using a scan window having a width and/or position in time such to essentially retrieve synchronisation data and control data exchanged during a predetermined time period at a radio link operating time synchronous with said first radio link,b) scanning said radio environment for radio access units which operate in a time asynchronous manner with said first radio access unit using a scan window having a width and position in time such to retrieve synchronisation data and control data essentially exchanged outside said predetermined time period,c) maintaining a list of synchronous and asynchronous radio links available for handover, andd) evaluating said list on the basis of predetermined radio link criteria such to determine whether handover or roaming has to be initiated.