Low-delay rate detection for variable rate communication systems

• US 6,222,875 B1
• Filed: 07/11/1997
• Issued: 04/24/2001
• Est. Priority Date: 07/11/1997
• Status: Expired due to Term

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Dahlman, Erik, Ovesjö, Fredrik
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): PARK, ALBERT C
• Application Number:
  US08/890,794
• Time in Patent Office: 1,383 Days
• Field of Search: 375/200-210, 375/367, 370/342, 370/335, 370/441
• US Class Current: 375/130
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04B 2201/70703 using multiple or variable rates
• CPC Class Codes: H04J 13/0048 Walsh
• CPC Class Codes: H04J 13/18 Allocation of orthogonal codes
• CPC Class Codes: H04L 1/0025 Transmission of mode-switching indication

Abstract

Variable rate data transmissions are accommodated having BRI transmitted in the same frame as the data itself. When Walsh code spreading is employed, the despreading process can be split into two separate despreading operations, with buffering between the two operations. Buffering is made of the intermediate symbols between the despreading stages, and can be made at the maximum user data rate instead of the much higher chip rate. In this way, the size of the buffer in the receiver can be significantly reduced.

Claims

1. A receiver comprising:

means for receiving a spread spectrum signal including at least two physical channels;

means for partially despreading one of said at least two physical channels using a first code;

means for buffering said partially despread signal; and

means for despreading said buffered signal using a second code.

2. The receiver of claim 1, wherein said spread spectrum signal is received at a chip rate and said means for buffering stores said partially despread signal at less than said chip rate.

3. The receiver of claim 1, wherein said at least two physical channels include a control channel and a first data channel.

4. The receiver of claim 1, wherein said one of said at least two physical channels can be received at any of a plurality of data rates and said first code is selected based upon said plurality of data rates.

5. The receiver of claim 3, further comprising:

means for demodulating and decoding said control channel to obtain bit rate information associated with said first data channel; and

means for supplying said bit rate information to said means for despreading said buffered signal using at least a second code.

6. The receiver of claim 5, wherein said second code is selected based upon said bit rate information.

7. The receiver of claim 3, wherein said at least two physical channels further include a second data channel.

8. The receiver of claim 7, wherein said means for partially despreading also despreads said second data channel using said first code.

9. The receiver of claim 8, further comprising:

means for demodulating and decoding said control channel to obtain bit rate information associated with each of said first and second data channels; and

wherein said despreading means selects said second code and a third code for despreading said first and second data channels, respectively, based upon said bit rate information.

10. The receiver of claim 9, wherein said bit rate information includes spreading factors for each of said first and second data channels.

11. The receiver of claim 5, wherein said bit rate information is a spreading factor.

12. The receiver of claim 8, wherein said first code is selected based upon code bits which are common to said first and second data channels.

13. A method for despreading a data frame comprising the steps of:

(a) despreading said data frame using a first code;

(b) buffering an output of step (a);

(c) determining a rate at which said data frame was transmitted; and

(d) despreading said buffered output using a second code, said second code selected based upon said determined rate.

14. The method of claim 13, wherein step (b) further comprises the step of:

buffering said output at a rate that is less than a chip rate of said data frame.

15. The method of claim 13, wherein step (c) further comprises the step of:

obtaining said rate by despreading and decoding a control channel.

16. The method of claim 13, wherein step (a) further comprises the step of:

determining said first code based upon a plurality of rates at which said data frame can be transmitted.

17. A receiver comprising:

a first despreader for despreading a received spread spectrum signal;

a buffer connected to said first despreader for storing an output thereof; and

a second despreader, connected to said buffer, for despreading said stored output wherein said first despreader despreads said received spread spectrum signal using at least two branches, each branch using a same first code to despread said received spread spectrum signal.

18. The receiver of claim 17, wherein said second despreader despreads said stored output using at least two branches, each branch using a code which is different from other codes used in said at least two branches.

19. The receiver of claim 17, wherein said first despreader descrambles said received spread spectrum signal using a scrambling code.