Partially block-interleaved CDMA coding and decoding

• US 6,359,874 B1
• Filed: 05/21/1998
• Issued: 03/19/2002
• Est. Priority Date: 05/21/1998
• Status: Expired due to Term

• Current Assignee: Ericsson, Inc. (Telefonaktiebolaget LM Ericsson)
• Original Assignee: Ericsson, Inc. (Telefonaktiebolaget LM Ericsson)
• Inventors: Dent, Paul W.
• Primary Examiner(s): Olms, Douglas
• Assistant Examiner(s): Sam, Phirin
• Application Number:
  US09/082,722
• Time in Patent Office: 1,398 Days
• Field of Search: 370/342, 370/335, 370/320, 370/318, 370/333, 370/432, 370/441, 370/203, 370/209, 370/210, 370/212, 375/130, 375/135, 375/140, 375/146
• US Class Current: 370/342
• CPC Class Codes: H04J 11/005 of intercell interference
• CPC Class Codes: H04J 13/0048 Walsh
• CPC Class Codes: H04J 13/18 Allocation of orthogonal codes
• CPC Class Codes: H04L 1/08 by repeating transmission, e.g. Verdan system H04L1/1858 and H04L1/189 take precedence

Abstract

The present invention discloses a CDMA coding method including the steps of converting the information to be transmitted into digital form, error-correction coding the digital information, and assembling the coded symbols into frames having N symbols. Each coded information symbol within a frame is then repeated a first number of times L1 in succession and the sign of select repeated symbols, determined by a spreading code generator, is changed to produce a symbol block of N×L1 symbols. The symbol block is then repeated a second umber of times L2, where for each block repeat, a block sign change is applied to all symbols of the same block; the sign for each block may also be supplied by the spreading code generator. The resulting L2×N×L1 coded and repeated symbols are then modulated upon a radio frequency carrier and transmitted to a receiver simultaneously with similar symbols intended for other receivers, where different information is transmitted to a plurality of receivers. Signals coded for simultaneous transmission to different receivers may include a greater number of information symbols repeated a reduced number L1 times or a lesser number of information symbols repeated a greater number L1 times, while still maintaining the same number of repeated symbols in a block. By assigning specific block-spreading sequences to groups of signals in various adjacent service areas or according to transmitter-receiver distance, strong signals can be better discriminated from weak signals and inter-cell interference can be reduced.

Claims

1. A method for communicating information between a first station and a number of second stations located in a communications service area, comprising the steps of:

converting information to digital symbols for transmission;

repeating each of said symbols a first number of times;

altering a sign of select repeated symbols using a first access code sequence;

assembling a number of symbols repeated said first number of times into blocks of repeated symbols; and

repeatedly transmitting each of said blocks of symbols a second number of times, using a block sign or phase change determined by the digits of a second access code sequence.

2. The method of claim 1 wherein said converting step comprises analog-to-digital conversion.

3. The method of claim 1 wherein said converting step comprises error correction or detection coding.

4. The method of claim 3 wherein said error correction coding is Reed-Solomon block coding.

5. The method of claim 3 wherein said error correction coding is convolutional coding.

6. The method of claim 1 wherein said converting step comprises error correction coding combined with interleaving.

7. The method of claim 1 wherein said first access code sequence is one of a number of orthogonal code sequences assigned to transmit different information signals.

8. The method of claim 1 wherein said first access code sequence is one of a set of Walsh Hadamard codes bitwise combined with a masking code sequence assigned for use in a given service area.

9. The method of claim 1 wherein said second number of times is two, and said block sign sequence is either ++ and +−

or +− and

++.

10. The method of claim 1 wherein said block phase changes from one of a number of orthogonal Fourier sequences.

11. The method of claim 1 wherein said step of repeatedly transmitting blocks of symbols includes modulating a radio frequency carrier using said symbols.

12. The method of claim 1 wherein said second access code sequence is varied between adjacent service areas in order to reduce interference from transmissions in one service area to communications in an adjacent service area.

13. The method of claim 1 wherein said second access code sequence is assigned for communication with a particular second station based on the distance between said first station and the particular second station.

14. The method of claim 1 wherein a known sequence of symbols is transmitted before a first block repeat of said repeated block transmissions.

15. The method of claim 1 wherein a known sequence of symbols is transmitted after a last block repeat of said repeated block transmissions.

16. The method of claim 1 wherein a known sequence of symbols is transmitted before a first block repeat and after a last block repeat of said repeated block transmissions.

17. The method of claim 16 wherein said known sequence of symbols is of duration at least equal to a delay difference between an earliest expected multipath ray and a latest expected multipath ray.

18. The method of claim 1 wherein a number of the symbols from an end of a last repeated block are appended for transmission just before a first block repeat.

19. The method of claim 18 wherein said number of symbols is selected to have a transmission duration equal to a delay difference between an earliest expected multipath ray and a latest expected multipath ray.

20. The method of claim 1 wherein a number of the symbols from a start of a first block repeat are transmitted again following a last block repeat.

21. The method of claim 20 wherein said number of symbols is selected to have a transmission duration equal to a delay difference between an earliest expected multipath ray and a latest expected multipath ray.

22. The method of claim 1 wherein said step of repeatedly transmitting blocks of symbols includes forming a complex modulating waveform corresponding to said symbols and adding, through the use of weighting factors, a number of complex modulating waveforms corresponding to different information signals to be transmitted using different ones of said first or second access code sequences.

23. The method of claim 22 wherein said weighting factors are varied to adjust a relative power of transmission of information to different ones of said second stations.

24. A method for communicating information between a first station and a number of second stations located in a communication service area, comprising the steps of:

converting a received signal to a representative stream of complex numerical samples;

assembling said complex numerical samples into a frame corresponding to a given number of repeatedly transmitted symbol blocks;

combining corresponding samples from different block-repeats within said frame by removing the sign or phase difference between block-repeats according to a second access code sequence and then adding to obtain a first compressed frame of samples; and

further combining samples from said first compressed frame of samples using a first access code sequence to obtain a doubly compressed frame of samples; and

processing said doubly compressed frame of samples using an error correction decoder to reproduce said information.

25. The method of claim 24 wherein said further combining of samples is performed by a RAKE receiver algorithm.

26. A transmitter for transmitting digital symbols from a first station to a plurality of second stations in a Code Division Multiple Access (CDMA) environment, said transmitter comprising:

a first CDMA repeat coder for repeating each digital symbol to be transmitted a first number of times and for altering a sign of select repeated symbols in accordance to a first access code sequence; and

a second CDMA repeat coder for assembling a number of symbols repeated said first number of times into blocks of repeated symbols, for repeating each block a second number of times, and for altering a sign or phase of select repeated blocks in accordance to a second access code sequence.

27. The transmitter according to claim 26 wherein said first access code sequence is one of a number of orthogonal code sequences assigned to transmit different information signals.

28. The transmitter according to claim 26 wherein said first access code sequence is one of a set of Walsh Hadamard codes bitwise combined with a masking code sequence assigned for use in a given service area.

29. The transmitter according to claim 26 wherein said second number of times is two, and said block sign sequence is either ++ and +−

or +− and

++.

30. The transmitter according to claim 26 wherein said block phase changes from one of a number of orthogonal Fourier sequences.

31. The transmitter according to claim 26 wherein said second access code sequence is varied between adjacent service areas in order to reduce interference from transmissions in one service area to communications in an adjacent service area.

32. The transmitter according to claim 26 wherein said second access code sequence is assigned for communication with a particular second station based on the distance between said first station and the particular second station.