Method and system for controlling the power at which an access packet is sent by a mobile in a mobile radio system

DETAILED DESCRIPTION The invention consists in a method of controlling the power at which an access packet is transmitted by a mobile on an access channel to a base transceiver station of a mobile radio system, said base transceiver station transmitting on a broadcast channel regularly, wherein: at the base transceiver station the broadcast channel transmits a power indication representing the transmit power of said channel; at the mobile the power received on said channel is measured, the measured power is compared with the transmit power indicated by the transmit power indication on the broadcast channel to deduce an estimated propagation loss from said mobile to said base transceiver station, and an optimal transmit power for said access packet is determined on the basis of the estimated propagation loss and parameters of said mobile radio system.
The method according to the invention thus enables the mobile to optimize the power at which the access packet is transmitted.
The constraints in respect of the base station receivers are therefore much less severe, which helps to simplify their design and reduce their cost.
Additionally, the method according to the invention offers better use of the electrical energy stored in the mobiles and can reduce interference generated by the mobiles.
In another aspect the invention consists in a mobile radio system comprising a plurality of base transceiver stations communicating with a set of mobiles, each base transceiver station being adapted to transmit regularly on a broadcast channel, implementing the method as defined above, wherein at least one of said base transceiver stations is adapted to transmit on said broadcast channel an indication of the power transmitted on said channel and at least one mobile in the access phase in a cell managed by said base transceiver station comprises means for measuring the power at which said broadcast channel is received, means for comparing the measured power with the transmitted power and supplying an estimate of the propagation loss between said mobile and said base transceiver station, and means for adjusting the power at which an access packet is transmitted to an optimal transmit power level calculated from the estimated propagation loss and parameters of said system