MBMS acknowledgements on RACH
The present invention relates to multicast communication systems and in particular to the implementation of a random access uplink channel, which can be used, e.g., for transmission of acknowledgement messages for received data. In order to prevent frequent collisions on said channel, the transmission of acknowledgement messages is spread at least over time or, additionally, with regard to another distinguishing channel property, e.g. a RACH sub-channel or RACH-signature.
1. A method for avoiding collisions on a random access channel of a telecommunication system providing Multimedia Broadcast/Multicast Services (MBMS) to a plurality of subscribing user equipments, said method comprising the steps of:
dividing an MBMS session into a first period for transmission of MBMS data to user equipments and a subsequent second period for receiving feedback information, by determining a delay time period for each subscribing user equipment after the lapse of which said user equipment starts transmission of feedback information on the random access channel for acknowledgement of successfully received MBMS data portions; and
selecting a preamble signature for use on a sub-channel of a random access channel for the subscribing user equipments; then,
forwarding said respective delay time periods and preamble signature to the user equipments; then
transmitting one or more MBMS data portions on a downlink channel to the group of subscribing user equipments; and
receiving feedback information from the plurality of user equipments.
2. The method according to claim 1 , wherein said delay time period starts counting at a user equipment from the successful reception of said one or more MBMS-data portions.
3. The method according to claim 1 , wherein said delay time period is calculated from a unique identifier of the user equipment.
4. The method according to claim 1 , wherein said delay time period constitutes a randomly determined value within a given time period.
5. A method in a user equipment of a telecommunication system subscribing to a Multimedia Broadcast/Multicast Service (MBMS), said method comprising the steps of:
determining a delay time period based on dividing an MBMS session into a first period for transmission of MBMS data to the user equipment and a subsequent second period for transmitting feedback information by the user equipment;
using a preamble signature on a sub-channel of a random access channel for transmission of said feedback information by the user equipment; and
transmitting by the user equipment, after the lapse of said delay time period, feedback information on the random access channel using the preamble signature for acknowledgement of successfully received MBMS-data portions.