METHOD, USER EQUIPMENT AND RADIO BASE STATION FOR RANDOM ACCESS IN A CELLULAR TELECOMMUNICATIONS SYSTEM TECHNICAL FIELD OF THE INVENTION

• US 20090161599A1
• Filed: 04/07/2006
• Published: 06/25/2009
• Est. Priority Date: 04/07/2006
• Status: Active Grant

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Dahlman, Erik, Haartsen, Jacobus Cornelius
• Granted Patent: US 9,363,778 B2
• Time in Patent Office: Days
• US Class Current: 370/326
• CPC Class Codes: H04W 56/00 Synchronisation arrangements
• CPC Class Codes: H04W 56/0045 compensating for timing error by altering transmission time
• CPC Class Codes: H04W 74/0891 for synchronized access

Abstract

The present invention relates to a random access process in a cellular communications system and to a user equipment (UE) and a NodeB adapted for performing the process. A problem with the random access is that the time slot for receiving a random access request (RA-request) has a long unused guard portion. When the UE transmits the RA-request, the distance to the receiving NodeB is unknown, and the purpose of the guard portion is to accommodate for propagation delay. The disadvantage is the inefficient use of the random access channel which results in long delays for UEs to access the network. The present invention solves the problem with a method in which the UE position is determined and the distance and propagation delay between the UE and NodeB is calculated before the transmission of the RA-request, and the timing of the transmission is advanced by the propagation delay.

Claims

1. A method for a user equipment in a cellular communication system comprising the steps of:

scanning radio channels of the communication system, to find available downlink broadcast channels;

synchronising to the downlink broadcast channel of a first Base station;

and, further comprising the steps of;

receiving parameters indicating the first Base station position;

receiving synchronisation signals from at least 3 time synchronised positioning nodes;

receiving information on the position of said positioning nodes;

determining the distance between the user equipment and the first Base station;

calculating the propagation delay between the user equipment and the first base station prior to the transmitting step;

transmitting a random access request on a time slotted random access channel of the first Base station and advancing the timing of said transmitting of the random access request by the propagation delay.

2. A method according to claim 1 wherein the information on positions of the positioning nodes is received with the synchronisation signals.

3. A method according to claim 1 wherein the information on positions of the positioning node is retrieved from a data base that is loaded in the user equipment prior to the transmitting step.

4. A method according to claim 1, wherein the position nodes consist of GPS satellites.

7. A method according to claim 1, wherein the position nodes comprises said first Base station and a second and a third Base station.

8. A method according to claim 1 wherein said advancing step is made relative to the synchronisation to the downlink broadcast channel.

9. A method according to claim 1, wherein the random access channel is divided into time slots of a predefined period, and the random access request occupies 95% or more of the time slot period.

5. A method according to 4 wherein first Base station position parameters are received on the broadcast channel of the first Base station.

6. A method according to 4 wherein first Base station identity is received on the broadcast channel of the first Base station, and the position of the first Base station is retrieved from a database that is downloaded in the user equipment prior to the transmitting step.

10. A user equipment for a cellular communication system comprising,

a receiver arranged to synchronize to a broadcast channel transmitted by a first Base station and receiving information on the uplink random access channel structure when the user equipment is in idle mode,

a transmitter, time synchronised with the received broadcast channel and arranged for transmitting a random access request on said random access channel to said first Base station, further comprising:

a distance calculator arranged for, receiving information on a geographical position of said user equipment via an input from a GPS receiver and receiving information for identifying the geographical position of said first Base station, or alternatively, receiving at least mutual difference in synchronisation signals received via said receiver from the first Base station and at least two other Base stations together with information for identifying the position of said three or more Base stations, and for, calculating the propagation delay between the user equipment and said first Base station;

a time alignment controller with an input from the distance calculator and an output to the transmitter and arranged to advance the transmission timing of said random access request to compensate for the propagation delay to said Base station.

11. A user equipment according to claim 10 further comprising a controller controlling the operation of the receiver, the distance calculator, and the transmitter.

12. A user equipment according to claim 10 wherein the distance calculator is connected to, or comprises, a memory for storing a database of Base station positions and further is arranged to retrieve the position of a Base station by reference to its identity.

13. A radio base station adapted for receiving random access requests of a specific length, from a multiplicity of UEs on a first and on a second physical random access channel comprising dedicated time slots repeated regularly, wherein the time slots of the first physical random access channel have a duration of said specific length plus a guard space of maximum 5% of said specific length and the time slots of said second physical random access channel have a duration of the specific length plus a guard space of 20% of said specific length or more.

14. The base station of claim 13 wherein the time slots of the first physical random access channel are repeated with a shorter interval than the time slots of the second physical random access channel.

15. The base station of claim 13 arranged for broadcasting its geographical position.

16. The base station of claim 13 arranged for broadcasting its identity.

17. The base station of claim 13, broadcasting a synchronisation signal and being synchronised with at least two neighbouring Base stations with an accuracy of at least 50 μ

s.

18. The base station of claim 13, wherein the random access requests transmitted on the first physical random access channel have a longer duration than the random access requests transmitted on the second physical random access channel.