Timing alignment in an LTE system
A method for use in a user terminal in a cellular communications system. According to the method, the user terminal applies a first timing advance value to its transmissions to a controlling node, and the user terminal requests communication with the controlling node in a contention based procedure by transmitting an access request (MSG 1), in response to which the controlling node transmits an initiation message (MSG 2) along with a second timing advance value. According to the method, the user terminal uses the first timing advance value if the user terminal loses the contention based procedure, i.e. if the controlling node subsequently continues the initiated communication with said other user terminal.
1. A method implemented in a user terminal of a communication system, the method comprising:
applying a first timing advance value to transmissions to a controlling node;
requesting communication with the controlling node in a contention based procedure by transmitting a random access preamble;
receiving, in response to the transmission of the random access preamble, a random access response along with a second timing advance value from the controlling node; and
ignoring the second timing advance value when the first timing advance value is valid and continue applying the first timing advance value to a transmission to the controlling node that is subsequent to the receipt of the random access response;
wherein said first timing advance value is associated with a timer and is valid when the timer is running.
2. The method of claim 1 , wherein the user terminal uses the second timing advance value in a message which is subsequent to said random access response.
3. The method of claim 1 , wherein the method is applied if the first timing advance value is considered valid by the user terminal.
4. The method of claim 1 , wherein the first and second timing advance values in the user terminal are associated with respective first and second timers and are considered valid for the duration of said respective first and second timers, the respective first and second timers being started upon reception of a corresponding predefined message from the controlling node.
5. The method of claim 1 , wherein a user terminal which has a valid timing alignment value uses this value regardless of receipt of a second timing alignment value.
6. The method of claim 1 , wherein the communication system comprises a Long Term Evolution (LTE) system, and wherein the user terminal comprises an LTE UE and the controlling node comprises an LTE eNodeB.
7. The method of claim 6 , wherein the method is applied in an LTE Random Access procedure.
8. A user terminal in a communication system, the user terminal configured to:
apply a first timing advance value to transmissions to a controlling node;
request communication with the controlling node in a contention based procedure by transmitting a random access preamble;
receive, in response to the transmission of the random access preamble, a random access response along with a second timing advance value from the controlling node; and
ignore the second timing advance value when the first timing advance value is valid and continue applying the first timing advance value in a transmission to the controlling node that is subsequent to the receipt of the random access response;
wherein said first timing advance value is associated with a timer and is valid when the timer is running.