Access channel slot sharing

• US 6,167,056 A
• Filed: 11/09/1998
• Issued: 12/26/2000
• Est. Priority Date: 11/10/1997
• Status: Expired due to Term

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Vijayan, Rajiv, Levin, Jeffrey A., Miller, David S., Zehavi, Ephraim
• Primary Examiner(s): Vu, Huy D.
• Assistant Examiner(s): Harper, Kevin C.
• Application Number:
  US09/189,357
• Time in Patent Office: 778 Days
• Field of Search: 370/320, 370/329, 370/330, 370/331, 370/335, 370/342, 370/441, 370/479, 370/350, 375/130, 375/140, 375/134, 375/367, 375/149
• US Class Current: 370/441
• CPC Class Codes: H04B 1/7077 Multi-step acquisition, e.g. multi-dwell, coarse-fine or validation
• CPC Class Codes: H04B 1/708 Parallel implementation
• CPC Class Codes: H04B 7/18532 Arrangements for managing transmission, i.e. for transporting data or a signalling message
• CPC Class Codes: H04B 7/216 Code division or spread-spectrum multiple access [CDMA, SSMA]
• CPC Class Codes: H04B 7/2637 for logical channel control

Abstract

The present invention is a system and method for increasing user capacity on a slotted random access channel in a spread spectrum communications system by using a multi-part access probe. First and second parts of the access probe are modulated using a short PN code sequence, and the entire access probe is modulated using a long PN code sequence. Information to be transmitted by the access probe is modulated on the second part of the access probe, and the access probe is transmitted so that the first part of the probe falls within the boundaries of an access channel slot. In one embodiment, time slots in access channels used for access signal reception are made the length of the first part. In a further embodiment, time slots in a plurality of adjacent access channels used for access signal reception may be longer than said first part but are offset in time from each other by the length or period of the first part.

Claims

1. A system for transmitting multi-part access probes over a slotted random access communications channel having a plurality of access channel slots, each of said access probes including an access message, the system comprising:

a first modulator for modulating a first part and a second part of the access probe with a short pseudonoise sequence;

a second modulator for modulating said second part of the access probe with a long pseudonoise sequence;

a data modulator for modulating said second part with the access message; and

a transmitter for transmitting the access probe so that said first part falls within one of the access channel slots.

2. The system of claim 1, wherein the length of said short PN sequence is 2⁸ chips.

3. The system of claim 1, wherein the length of said long PN sequence is 2⁴² chips.

4. The system of claim 1, wherein said short PN sequence is a pair of quadrature short pseudonoise sequences.

5. The system of claim 1, wherein each of said access channel slots has first and second guard bands, wherein said means for transmitting further comprises:

means for transmitting the access probe so that said first part falls within one of the access channel slots between said first and second guard bands.

6. A system for receiving a multi-part access probe over a slotted random access communications channel having a plurality of access channel slots, each of the access probes including a first part modulated with a short pseudonoise sequence and a second part modulated with the short pseudonoise sequence and a long pseudonoise sequence, the system comprising:

a plurality of demodulators for demodulating the access probe; and

a searcher receiver for acquiring and despreading the access probe and passing said despread access probe to one of said plurality of demodulators.

7. The system of claim 6, wherein the slotted random access communications is a slotted ALOHA channel.

8. A method for transmitting multi-part access probes over a slotted random access communications channel having a plurality of access channel slots, each of said access probes including an access message, the method comprising the steps of:

modulating a first part and a second part of the access probe with a short pseudonoise sequence;

modulating a second part of the access probe with a long pseudonoise sequence;

modulating said second part with the access message; and

transmitting the access probe so that said first part falls within one of the access channel slots.

9. The method of claim 8, wherein the length of said short pseudonoise sequence is 2⁸ chips.

10. The method of claim 8, wherein the length of said long pseudonoise sequence is 2⁴² chips.

11. The method of claim 8, wherein said short pseudonoise sequence is a pair of quadrature short pseudonoise sequences.

12. The method of claim 8, wherein each of said access channel slots has first and second guard bands, further comprising the step of:

transmitting the access probe so that said first part falls within one of the access channel slots between said first and second guard bands.

13. A method for transmitting a plurality of access signals over at least one access channel, each including preamble and message portions with the preamble having first and second stages, comprising the steps of:

modulating the first stage and second stage of the preamble by a first signal;

modulating the second stage of the preamble also by a second signal;

modulating the message with said first signal and said second signal; and

transmitting said modulated access signal in the form of said first stage, said modulated second stage, and said modulated message so that said preamble falls within one of a plurality of preselected time slots whose length corresponds substantially to that of said first stage.

14. The method of claim 13, wherein more than one access signal is transmitted in time such that a second stage or message portion overlaps the first stage of one or more other transmitted access signals.

15. The method of claim 13, further comprising guard bands forming boundaries for said preselected time slots.

16. The method of claim 13, wherein said modulated first stage of the preamble is transmitted for a sufficient time for a receiver to acquire a timing of said first signal.

17. The method of claim 16, wherein said modulated second stage of the preamble is transmitted for a sufficient time for a receiver to acquire a timing of said second signal.

18. The method of claim 13, wherein said first signal is a pair of quadrature spreading, pseudonoise sequences.

19. The method of claim 18, wherein said second signal is a channelizing pseudonoise sequence.

20. The method of claim 19, wherein said access signal comprises a message following said preamble, said message modulated by said first code sequence and said second code sequence.

21. A method for using an access signal in a wireless communication system comprising:

transmitting an access signal including a preamble and a message, said preamble having a first stage of a predetermined first length and a second stage, said first stage having data modulated by a first signal, said second stage having data modulated by a second signal and said first signal; and

receiving said access signal over an access channel divided into signal reception time slots that are substantially the same length as said first stage.

22. The method of claim 21, wherein the first stage of the preamble is comprised of null data.

23. The system of claim 21, wherein the second stage of the preamble is comprised of null data.

24. The method of claim 21, wherein said first signal and said second signal are PN sequences.

25. A method for using an access signal in a wireless communication system comprising:

transmitting an access signal including a preamble and a message, said preamble having a first stage of a predetermined first length and a second stage, said first stage having data modulated by a first signal, said second stage having data modulated by a second signal and said first signal; and

receiving said access signal over a plurality of an access channels divided into signal reception time slots that are time offset from each other by a period substantially the same length as said first stage.

26. The method of claim 25, wherein the first stage of the preamble is comprised of null data.

27. The method of claim 25, wherein said first signal and said second signal are PN sequences.

28. The method of claim 25, further comprising guard bands forming boundaries for said signal reception time slots.

29. A method for acquiring a transmission at a receiver from a transmitter, the transmission having a preamble, the preamble having a first stage and a second stage, the method comprising the steps of:

performing a coarse search on the transmission received by the receiver during the first stage of the preamble, wherein the first stage of the preamble is modulated by a first signal, said coarse search to determine a timing offset of said first signal;

performing a fine search on the transmission received by the receiver during the second stage of the preamble, wherein the second stage of the preamble is modulated by said first signal and a second signal, said fine search to determine a timing offset of said second signal, wherein said timing offset of said second signal is determined using said first signal and said timing offset of said first signal; and

demodulating the transmission using said first signal, said second signal, said timing offset of said first signal, and said timing offset of said second signal.