CA2535535A1

CA2535535A1 - Random access in a mobile telecommunications system

Info

Publication number: CA2535535A1
Application number: CA002535535A
Authority: CA
Inventors: Riaz Esmailzadeh
Original assignee: Individual
Current assignee: Telefonaktiebolaget LM Ericsson AB
Priority date: 1996-10-18
Filing date: 1997-10-14
Publication date: 1998-04-30
Anticipated expiration: 2017-10-14
Also published as: CA2535535C

Abstract

A mobile communications system is provided for significantly reducing the time required to process a random access mobile-originated call. During call setup, a mobile station transmits a random access packet that includes a preamble and a plurality of fields. The information provided in these fields is used by the base station to facilitate a more efficient call setup and more quickly allocate channel resources. A system is also provided for detecting, identifying and receiving multiple random access requests.
Each mobile station transmits one of a plurality of different preamble symbol patterns in a random access request packet.
The base station receiver includes a plurality of accumulators, each of which is tuned to a different preamble symbol pattern. Consequently, the base station receiver can distinguish between simultaneous random access requests.
This preamble symbol arrangement can also be used in conjunction with power-ramping processes, such as those used in IS-95 and CODIT systems, to provide individual power control for mobile stations making multiple random access attempts.

Claims

1. A signal format for a random access request in a mobile communications system, the signal format comprising:
a preamble, said preamble including at least one of a plurality of signature patterns; and at least one of a plurality of facilitating fields, said plurality of facilitating fields including a mobile identity field, a service field, a short data field and an air time field.

2. The signal format according to claim 1, wherein said at least one of said plurality of signature patterns is orthogonal to another one.

3. The signal format according to claim 1 or 2, wherein said at least one of said plurality of facilitating fields comprises a forward error correction coded field.

4. The signal format according to any one of claims 1 to 3, further comprising pilot tones for facilitating coherent demodulation at a base station.

5. A method of acquiring access to a random access mobile system by a mobile station, the method comprising:
acquiring synchronization with an intended base station;
determining a starting time for a random access request frame from a received broadcast/pilot channel information of said base station;
estimating a Doppler fading rate and a number of significant rays existing in a transmission channel by measuring the level and rate of change of received broadcast/pilot channel signals;
estimating the shadowing and distance attenuation of the transmission channel by measuring a path loss over a plurality of fading periods;
calculating, based on the estimation steps and on a degree of transmission diversity required by the mobile system, the transmission power level required for a random access request message to be received at the intended base station with a predetermined signal-to-interference ratio, said random access request message including a preamble; and including at least one of a plurality of facilitating fields, said plurality of facilitating fields including a mobile identity field, a service field, a short data field and an air time field; and as a last step, generating and transmitting the random access request message.

6. The method of claim 5, wherein said preamble comprises at least one of a plurality of signature patterns.

7. The method according to claim 6, further comprising the step of selecting a unique signature pattern from said plurality of signature patterns from an internal memory location of the mobile station.

8. The method according to claim 7, wherein said plurality of signature patterns comprises a first signature pattern and a second signature pattern orthogonal to said first signature pattern.

9. The method according to claim 7 or 8, wherein the step of generating and transmitting said random access request message comprises the step of inserting said unique signature pattern into a preamble of said random access request message.

10. The method according to any one of claims 6 to 8, wherein pilot tones are inserted in the random access request frame for facilitating coherent demodulation at the base station.

11. A method in a base station for demodulating a plurality of random access requests, the method comprising:
receiving a first random access request;
applying said first random access request to at least one matched filter to produce a despread result;
accumulating said despread result using a plurality of different signature patterns to produce a plurality of accumulation results; and detecting at least a first peak signal from said plurality of accumulation results, wherein said random access requests are received substantially simulatenously.

12. The method of claim 11, wherein said first random access request comprises a first signature pattern.

13. The method according to claim 12, wherein said first random access request comprises a first random access request frame, said first random access request frame having a preamble that includes said first signature pattern.

14. The method according to claim 11 or 12, wherein said step of applying said first random access request to at least one matched filter to produce a despread result further comprises the step of applying said first random access request to said at least one matched filter using a specific preamble spreading code.

15. The method according to claim 11 or 12, wherein said step of accumulating said despread result using a plurality of different signature patterns to produce a plurality of accumulation results further comprises the step of accumulating said despread result recursively.

16. The method according to claim 11, further comprising the step of:
receiving a second random access request, said second random access request including a signature pattern, said first signature pattern being different from said second signature pattern, wherein said step of applying said first random access request to at least one matched filter to produce a despread result further comprises a step of applying said second random access request to said at least one matched filter to produce said despread result; and said step of detecting at least a first peak signal from said plurality of accumulation results further comprises the step of detecting a second peak signal from said plurality of accumulation results.

17. The method according to claim 16, wherein said steps of receiving a first random access request and receiving a second random access request occur substantially simultaneously.

18. The method according to claim 16, wherein said at least a first peak signal and said second peak signal are detected from said plurality of accumulation results substantially simultaneously.

19. The method according to claim 16, further comprising the step of differentiating said first random access request from said second random access request based, at least in part, on said at least a first peak signal and said second peak signal.