Random access orthogonal frequency division multiplex system and method

• US 5,909,436 A
• Filed: 08/28/1996
• Issued: 06/01/1999
• Est. Priority Date: 08/28/1995
• Status: Expired due to Term

• Current Assignee: Intellectual Ventures I LLC (Intellectual Ventures LLC)
• Original Assignee: Telia AB (Government of Norway)
• Inventors: Wahlqvist, Mattias, Engstrom, Bo, Ostberg, Christer, Larsson, Roger
• Primary Examiner(s): Olms, Douglas W.
• Assistant Examiner(s): HOM, SHICK C
• Application Number:
  US08/704,809
• Time in Patent Office: 1,007 Days
• Field of Search: 370/344, 370/343, 370/335, 370/206, 370/207, 370/208, 370/209, 370/210, 370/342, 370/336, 370/318, 370/337, 375/202, 375/261, 375/362, 455/63, 455/422, 455/517
• US Class Current: 370/343
• CPC Class Codes: H04L 27/2613 Structure of the reference signals
• CPC Class Codes: H04L 27/2656 Frame synchronisation, e.g. packet synchronisation, time division duplex [TDD] switching point detection or subframe synchronisation
• CPC Class Codes: H04L 5/0007 the frequencies being orthogonal, e.g. OFDM(A), DMT
• CPC Class Codes: H04L 5/0048 Allocation of pilot signals, i.e. of signals known to the receiver
• CPC Class Codes: H04L 5/0053 Allocation of signaling, i.e. of overhead other than pilot signals
• CPC Class Codes: H04W 52/322 Power control of broadcast channels
• CPC Class Codes: H04W 52/50 at the moment of starting communication in a multiple access environment
• CPC Class Codes: H04W 56/00 Synchronisation arrangements
• CPC Class Codes: H04W 74/08 Non-scheduled access, e.g. ALOHA hybrid access H04W74/02

Abstract

A random access protocol system and method for communicating between a mobile station and a base station in a multi-access digital radio communication system, including the steps of cyclically repeating a random access sequence and transmitting each cyclically repeated random access sequence in an orthogonal frequency division multiplex format from the mobile station as an uplink transmission.

Claims

1. A random access protocol method for communicating between a mobile station and a base station in a multi-access digital radio communications system comprising the steps of:

cyclically repeating a random access sequence; and

transmitting each cyclically repeated random access sequence in an orthogonal frequency division multiplex format from the mobile station as an uplink transmission to the base station, which receives and combines the random access sequence that is cyclically repeated in said cyclically repeating step so as to improve a probability of detecting an access request by said mobile station.

2. The random access protocol method as claimed in claim 1, wherein said transmitting step comprises transmitting said random access sequence in the frequency division orthogonal frequency division multiplex format.

3. The random access protocol method as claimed in claim 2, further comprising the steps of:

transmitting a pilot channel from said base station;

detecting said pilot channel at said mobile station;

synchronizing at said mobile station to an orthogonal frequency division multiplex symbol of said orthogonal frequency division multiplex format transmitted by said base station;

listening at said mobile station to a broadcast control channel for said random access sequence and a sub-carrier number which corresponds to an access grant channel;

transmitting at said mobile station said random access sequence in the random access channel for a plurality of cycles; and

checking said access grant channel by said mobile station to determine whether said base station has granted said mobile station access.

4. The random access protocol method as claimed in claim 3, wherein said transmitting step comprises:

transmitting said random access sequence at a power determined by data carried on the access grant channel AGCH channel, and if said mobile station is not granted access to said base station as checked in said checking step, said mobile station retransmits said random access sequence at a higher power.

5. The random access protocol method as claimed in claim 3, further comprising the steps of:

detecting said random access sequence at said base station;

raising a busy flag in said broadcast control channel at said base station in response to detecting said random access sequence in said detecting step, said raising step comprising,

removing said random access sequence from said broadcast control channel;

transmitting at said base station timing advance information on said access grant channel by said base station;

adjusting at said mobile station a mobile station timing advance in accordance with said timing advance information; and

transmitting at said mobile station a second random access sequence to verify the mobile station timing advance adjustment made by said mobile station in said adjusting step.

6. The random access protocol method as claimed in claim 5, further comprising the steps of:

transmitting at said base station an acknowledgement upon receipt of said second random access sequence, said acknowledgment comprising data informing said mobile station which of plural sub-carriers will be employed for a dedicated information channel and a dedicated control channel, said acknowledgment transmitted on said access grant channel;

receiving said acknowledgement at said mobile station;

transmitting at said mobile station a randomly selected number; and

echoing the randomly selected number at the base station which was transmitted by said mobile station at said transmitting step, said echoing step for identifying the mobile station in order to prevent data collisions with other mobile stations.

7. The random access protocol method as claimed in claim 1, wherein said transmitting step comprises transmitting a m-sequence as said random access sequence.

8. The random access protocol method as claimed in claim 1, wherein said transmitting step comprises transmitting as said random access sequence a Gold sequence.

9. The random access protocol method as claimed in claim 1, wherein said transmitting step comprises transmitting as said random access sequence a first four phase sequence which is capable of being cross-correlated with a second four phase sequence.

10. The random access protocol method as claimed in claim 1, wherein said transmitting step comprises applying said random access sequence to all of a set of sub-carriers.

11. The random access protocol method as claimed in claim 10, wherein said transmitting step comprises transmitting at a higher power a first subset of said set of sub-carriers dedicated to a random access channel than transmitting of the other sub-carriers to which said random access sequence is also applied.

12. The random access protocol method as claimed in claim 1, wherein said transmitting step comprises the steps of:

applying said random access sequence only to a subset of a set of sub-carriers, said subset of said set of sub-carriers dedicated to a random access channel; and

transmitting only said subset of said set of said set of sub-carriers.

13. The random access protocol method as claimed in claim 12, wherein said transmitting step comprises applying said random access sequence to said subset of said set of sub-carriers, said subset of said set of sub-carriers being unequally spaced from each other.

14. The random access protocol method as claimed in claim 1, wherein said cyclically repeating step comprises cyclically repeating said random access sequence without any guard space between each repeated cycle of said random access sequence.

15. The random access protocol method as claimed in claim 14, wherein said transmitting step comprises transmitting said random access sequence in a random access channel and transmitting in another channel modulated data as at least one channel symbol having guard spaces, wherein said guard spaces have respective durations which are in an integer relationship to a duration of a symbol of said random access sequence.

16. The random access protocol method as claimed in claim 1, further comprising the steps of:

detecting if said random access sequence is properly received at said base station in an at least two consecutive data frames; and

responding at a base station to said mobile station only if said random access sequence is detected in at least two consecutive data frames in said detecting step.

17. The random access protocol method as claimed in claim 1, wherein said transmitting step comprises transmitting said cyclically repeated random access sequence as a first random access sequence from a first mobile station and transmitting a cyclically repeated second random access sequence from a second mobile station, wherein said first random access sequence and said second random access sequence are transmitted to at least one base station.

18. A method of measuring performance of a random access sequence transmitted in a mobile radio communication system comprising the steps of:

generating a signal comprising a random access sequence, said generating step comprising,

modulating said random access sequence onto a plurality of sub-carriers to form said signal;

processing said signal via an inverse fast Fourier transform; and

introducing a time shift into said signal;

subjecting said signal to a multi-path effect said subjecting step comprising the steps of,

processing said signal to create a delay spread, and

processing said signal to create a doppler shift;

passing said signal to a receiver;

detecting at said receiver said random access sequence in said signal; and

estimating a timing advance based on said signal in said receiver, said timing advance indicative of said performance.

19. The method as claimed in claim 18, wherein said subjecting step further comprises injecting a noise into said signal.

20. The method as claimed in claim 19, wherein said injecting step comprises injecting punctuated noise.

21. An apparatus for measuring performance of a cyclically repeated random access sequence in an uplink transmission from a mobile station comprising:

inverse Fast Fourier Transform means for inverse Fast Fourier transform processing a signal comprising the random access sequence to be tested, said signal modulated onto a plurality of sub-carriers;

time shift means for introducing into the signal a random time shift which is uniformly distributed over a duration of one symbol;

simulating means for simulating an effect of delay spread and an effect of doppler shift on said signal;

receiving means for detecting said random access sequence in said signal; and

estimating means for estimating the timing shift.

22. The apparatus as claimed in claim 21, further comprising noise generating means for injecting noise into said signal.

23. The apparatus as claimed in claim 22, wherein said noise generating means is adapted to generate punctuated noise.

24. A mobile radio telecommunications system comprising:

a plurality of base stations;

a plurality of mobile stations which use a frequency division orthogonal frequency division multiplex format for uplink communications with said plurality of base stations, and employing a random access protocol comprising transmitting a random access sequence, wherein

said mobile station and a base station of said plurality of based stations establish a communication link by said mobile station listening for a pilot channel transmitted by said base station,

after detection of said pilot channel, said mobile station synchronizes to an orthogonal frequency division multiplex symbol transmitted by said base station, said mobile station then transmits said random access sequence in a random access channel,

said mobile station listens to a broadcast control channel for a random access sequence that is not occupied by another of said plurality of mobile stations and for a sub-carrier number corresponding to an access grant channel,

after transmission of a plurality of cycles of said random access sequence, said mobile station checks said access grant channel to determine whether, or not, said base station has granted said mobile station access,

said random access sequence is transmitted by said mobile station at a power determined by a set of data carried on the access grant channel AGCH channel,

if said mobile station is not granted access to said base station, said mobile station retransmits said random access sequence at a higher power,

on detection of said random access sequence, said base station raises a busy flag in said broadcast control channel by removing said random access sequence from said broadcast control channel,

said base station transmits timing advance information on the access grant channel,

said mobile station adjusts a mobile station timing advance in accordance with said timing advance information,

said mobile station transmits a second random access sequence to verify the timing advance adjustment made by said mobile station,

on receipt of said second random access sequence, said base station transmits an acknowledgment on said access grant channel together with a second data informing said mobile station which of a set of sub-carriers will be employed for a dedicated information channel and a dedicated control channel,

said mobile station then transmits a randomly selected number, and

the base station echoes said randomly selected number so to identify the mobile station in order to prevent data collisions with the other of said plurality of mobile stations and

said mobile station cyclically repeats said random access sequence.

25. The mobile radio telecommunications system as claimed in claim 24, wherein said random access sequence comprises an m-sequence.

26. The mobile radio telecommunications system as claimed in claim 24, wherein said random access sequence comprises a Gold sequence.

27. The mobile radio telecommunications system as claimed in claim 24, wherein said random access sequence comprises a four phase sequence capable of being crosscorrelated with a second four phase sequence.

28. The mobile radio telecommunications system as claimed in claim 24, wherein said mobile station comprises means for applying said random access sequence to all available of said sub-carriers.

29. The mobile radio telecommunications system as claimed in claim 28, wherein said means for applying applies said random access sequence to a subset of said sub-carriers dedicated to a random access channel, and said means, for applying further comprises power control means adapted to cause said subset of said sub-carriers to be transmitted at a higher power than other sub-carriers, to which said random access sequence is also applied.

30. The mobile radio telecommunications system as claimed in claim 24, wherein said mobile station further comprises means for applying said random access sequence to only certain of said sub-carriers, which are dedicated to a random access channel.