Method and apparatus for reducing amplitude variations and interference in communication signals, such as in wireless communication signals employing inserted pilot symbols

• US 6,310,869 B1
• Filed: 08/31/1998
• Issued: 10/30/2001
• Est. Priority Date: 08/31/1998
• Status: Expired due to Term

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Razoumov, Leonid, Terasawa, Daisuke, Holtzman, Jack
• Primary Examiner(s): Marcelo, Melvin
• Application Number:
  US09/144,402
• Time in Patent Office: 1,156 Days
• Field of Search: 370/335, 370/342, 375/144, 375/145, 375/148
• US Class Current: 370/335
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04B 1/7103 the interference being multiple access interference
• CPC Class Codes: H04B 2201/70701 featuring pilot assisted reception
• CPC Class Codes: H04B 2201/70706 with means for reducing the peak-to-average power ratio
• CPC Class Codes: H04J 13/004 Orthogonal
• CPC Class Codes: H04J 13/0048 Walsh
• CPC Class Codes: H04J 13/12 Generation of orthogonal codes
• CPC Class Codes: H04L 2025/03777 characterised by the signalling
• CPC Class Codes: H04L 27/2615 Reduction thereof using coding
• CPC Class Codes: H04W 52/04 TPC

Abstract

Several methods and corresponding apparatus reduce peak to average power in signals transmitted in a wireless communications system, particularly with respect to pilot symbols transmitted from a base station to several user stations. A large peak to average amplitude of inserted pilot symbols has been found to result from a common sign chip position that exists in orthogonal codes, such as Walsh codes. In a first embodiment, the Walsh codes are multiplied by a random value of ±1. Under a second embodiment, the common sign chip position is eliminated in each Walsh code. The user station then inserts the missing chip position to regain orthogonality. In a third embodiment, the base station transmits pilot symbols, on a separate pilot channel, in only symbol positions that user stations expect to find pilot symbols. Under a fourth embodiment, each Walsh code is randomly shifted.

Claims

1. In a communication system having a base station and a plurality of user stations that exchange communication signals with the base station, a method for reducing transmission signal power of transmitted communication signals, the method comprising:

receiving channel data for transmission on a plurality of channels, wherein the channel data includes pilot symbol data;

combining orthogonal codes with the received channel data, wherein each orthogonal code has at least one common chip position, and wherein the common chip position has a same value for each orthogonal code; and

before transmitting the channel data combined with the orthogonal codes, altering the common chip position of at least one of the orthogonal codes to reduce a combined amplitude resulting from simultaneous transmission and addition of the common chip position for the plurality of channels.

2. The method of claim 1 wherein the orthogonal codes are Walsh codes, and wherein the common chip position has a same sign for each Walsh code,

wherein altering the common chip position includes multiplying a random value of +1 or − 1 to each Walsh code before combining the orthogonal code with the received pilot symbol data,

wherein receiving channel data includes receiving channel data for transmission on a plurality of channels to the plurality of user stations, and wherein combining orthogonal codes and altering the common chip position are performed at the base station.

3. The method of claim 1 wherein altering the common chip position includes altering each orthogonal code by a phase value between 0 and 360 degrees.

4. The method of claim 1 wherein altering the common chip position includes sequentially multiplying each orthogonal code by a value selected from the series +1, −

1, +1, −

1, +1, . . . , but non-sequentially assigning orthogonal codes to each new set of channel data for each new user.

5. The method of claim 1 wherein the orthogonal codes are Walsh codes, wherein the common chip position is a first chip in each Walsh code, and wherein altering the common chip position includes omitting the first chip position in each Walsh code.

6. The method of claim 1 wherein altering the common chip position includes omitting the common chip position in at least some of the orthogonal codes.

7. The method of claim 1 wherein altering the common chip position includes attenuating the common chip position in at least some of the orthogonal codes.

8. The method of claim 1 wherein altering the common chip position includes shifting chip positions of at least some of the orthogonal codes.

9. The method of claim 1, further comprising:

at the base station, transmitting to the user station information regarding the altering of the common chip position; and

at the user station removing the alteration of the common chip position.

10. In a communication system having a base station and a plurality of user stations that exchange communication signals with the base station, an apparatus for reducing transmission signal power of transmitted communication signals, the apparatus comprising:

means for receiving channel data for transmission on a plurality of channels, wherein the channel data includes pilot symbol data;

means for combining orthogonal codes with the received channel data, wherein each orthogonal code has at least one common chip position, and wherein the common chip position has a same value for each orthogonal code; and

means, coupled to the means for combining, for altering the common chip position of at least one of the orthogonal codes to reduce a combined amplitude resulting from simultaneous transmission and addition of the common chip position for the plurality of channels.

11. The apparatus of claim 10 wherein the orthogonal codes are Walsh codes, and wherein the common chip position has a same sign for each Walsh code,

wherein the means for altering the common chip position includes means for multiplying a random value of +1 or − 1 to each Walsh code before combining the orthogonal code with the received pilot symbol data, and

wherein the means for receiving channel data includes means for receiving channel data for transmission on a plurality of channels to the plurality of user stations.

12. The apparatus of claim 10 wherein the means for altering the common chip position includes altering each orthogonal code, or each orthogonal code as combined with the received channel data, by a phase value between 0 and 360 degrees.

13. The apparatus of claim 10 wherein the means for altering the common chip position includes means for sequentially multiplying each new set of channel data for each new user station by a value selected from the series +1, −

1, +1, −

1, +1, . . . , but non-sequentially assigning orthogonal codes to each new set of channel data for each new user.

14. The apparatus of claim 10 wherein the orthogonal codes are Walsh codes, wherein the common chip position is a first chip in each Walsh code, and wherein the means for altering the common chip position includes means for omitting the first chip position in each Walsh code.

15. The apparatus of claim 10 wherein the means for altering the common chip position includes means for omitting the common chip position in at least some of the orthogonal codes.

16. The apparatus of claim 10 wherein the means for altering the common chip position includes means for attenuating the common chip position in at least some of the orthogonal codes.

17. The apparatus of claim 10 wherein the means for altering the common chip position includes means for shifting chip positions of at least some of the orthogonal codes.

18. The apparatus of claim 10, further comprising:

means for transmitting to the user station information regarding the altering of the common chip position so that the user station may remove the alteration of the common chip position.

19. In a communication system having a base station and a plurality of user stations that exchange communication signals with the base station, an apparatus for reducing transmission signal power of transmitted communication signals, the apparatus comprising:

an input node that receives channel data for transmission on a plurality of channels, wherein the channel data includes pilot symbol data;

an orthogonal code generator combining orthogonal codes, wherein each orthogonal code has at least one common chip position, and wherein the common chip position has a same value for each orthogonal code; and

a common chip position altering circuit, coupled to the input node and the orthogonal code generator, that alters the common chip position of at least one of the orthogonal codes before combining the channel data combined with the orthogonal codes to reduce a combined amplitude resulting from addition of the common chip position for the plurality of channels.

20. The apparatus of claim 19 wherein the orthogonal codes are Walsh codes, and wherein the common chip position has a same sign for each Walsh code,

wherein the altering circuit includes a multiplier that multiplies a random value of +1 or − 1 to each Walsh code before combining the orthogonal code with the received pilot symbol data,

wherein the input node receives channel data for transmission on a plurality of channels to the plurality of user stations, and wherein the code generator and the altering circuit form part of the base station.

21. The apparatus of claim 19 wherein the altering circuit includes a combiner that combines a phase value between 0 and 360 degrees to each orthogonal code or to the orthogonal code as combined with the received channel data.

22. The apparatus of claim 19 wherein the altering circuit includes a multiplier that sequentially multiplies each orthogonal code for each new user station by a value selected from the series +1, −

1, +1, −

1, +1, . . . , but non-sequentially assigns orthogonal codes to each new set of channel data for each new user.

23. The apparatus of claim 19 wherein the orthogonal codes are Walsh codes, wherein the common chip position is a first chip in each Walsh code, and wherein the altering circuit includes a decimator that omits the first chip position in each Walsh code.

24. The apparatus of claim 19 wherein the altering circuit includes a decimator that omits the common chip position in at least some of the orthogonal codes.

25. The apparatus of claim 19 wherein the altering circuit includes a chip shifting circuit that shifts chip positions of at least some of the orthogonal codes.

26. The apparatus of claim 19, further comprising:

a processor that transmits to the user station information regarding the altering of the common chip position.

27. The apparatus of claim 19 wherein the orthogonal code generator and the altering circuit form a single code generating circuit.

28. The apparatus of claim 19 wherein the orthogonal code generator includes a table of orthogonal codes stored in a memory, and wherein the altering circuit includes a pseudo random number generator.

29. In a communication system having a base station and a plurality of user stations that exchange signals with the base station, an apparatus for reducing transmission signal power of transmitted signals, the apparatus comprising:

an input node that receives data for transmission on a plurality of channels, wherein the data includes pilot symbols;

an altered orthogonal code generator, wherein each of a plurality of unaltered orthogonal codes have at least one common chip position having a same value, and wherein the altered orthogonal code generator alters at least some of the unaltered orthogonal codes by a phase value between 0 and 360 degrees to produce phase altered orthogonal codes; and

a combining circuit that combines at least some of the pilot symbols for some of the plurality of channels with the phase altered orthogonal codes to reduce a combined amplitude resulting from addition of the common chip position for the plurality of channels.

30. The apparatus of claim 29 wherein the plurality of unaltered orthogonal codes are Walsh codes, and wherein the common chip position has a same sign for each Walsh code, and

wherein the altered orthogonal code generator multiplies a random value of +1 or − 1 to each Walsh code.

31. The apparatus of claim 29 wherein the altered orthogonal code generator sequentially multiplies each unaltered orthogonal code by a value selected from the series +1, −

1, +1, −

1, +1, . . . , but non-sequentially assigns phase altered orthogonal codes to each new set of channel data for each new user.

32. The apparatus of claim 29, further comprising:

a transmitter that transmits to the user station information regarding the phase value of the phase altered orthogonal code.

33. The apparatus of claim 29 wherein the altered orthogonal code generator includes a generator that generates the unaltered orthogonal codes, and a random phase generating circuit.

34. The apparatus of claim 29 wherein the altered orthogonal code generator includes a table of unaltered orthogonal codes stored in a memory, and a pseudo random number generator.

35. In a communication system having a base station and a plurality of user stations that exchange signals with the base station, an apparatus for reducing transmission signal power of transmitted signals, the apparatus comprising:

an input node that receives data for transmission on a plurality of channels, wherein the data includes pilot symbols;

an altered orthogonal code generator, wherein each of a plurality of unaltered orthogonal codes has at least one common chip position having a same value, and wherein the altered orthogonal code generator attenuates the common chip position in at least some of the unaltered orthogonal codes to produce altered orthogonal codes; and

a combining circuit that combines at least some of the pilot symbols for some of the plurality of channels with the altered orthogonal codes to reduce a combined amplitude resulting from addition of the common chip position for the plurality of channels.

36. The apparatus of claim 35 wherein the plurality of unaltered orthogonal codes are Walsh codes, and wherein the common chip position has a same sign for each Walsh code, and

wherein the altered orthogonal code generator eliminates the common chip position in each Walsh code.

37. The apparatus of claim 35, further comprising:

a transmitter that transmits to the user station information regarding an attenuation value of the altered orthogonal code.

38. The apparatus of claim 35 wherein the altered orthogonal code generator includes a generator that generates the unaltered orthogonal codes, and a common chip position decimating circuit.

39. The apparatus of claim 35 wherein the altered orthogonal code generator includes a table of unaltered orthogonal codes stored in a memory.

40. A user station for use in a communication system having a base station and a plurality of other user stations, wherein all of the user stations exchange communication signals with the base station, the user station comprising:

a receiver that receives channel data from one of a plurality of channels, wherein the channel data includes pilot symbol data encoded with one of a plurality of orthogonal codes, wherein each orthogonal code has at least one common chip position, wherein the common chip position has a same value for each orthogonal code, and wherein the common chip position of the one received orthogonal code is altered; and

a processor, coupled to the receiver, that returns the altered one received orthogonal code to an original state.

41. The user station of claim 40 wherein the orthogonal codes are Walsh codes, and wherein the common chip position has a same sign for each Walsh code;

and

wherein the processor determines that the one received orthogonal code was multiplied by a value of +1 or −

1.

42. The user station of claim 40 wherein the processor determines that the one received orthogonal code was combined with a phase value between 0 and 360 degrees.

43. The user station of claim 40 wherein the processor determines that the common chip position was eliminated in the one received orthogonal code.

44. The user station of claim 40 wherein processor determines that the chip positions of the one received orthogonal code were shifted.

45. The user station of claim 40 wherein the receiver receives:

information regarding the altering of the common chip position in the one received orthogonal code.