Random access preamble coding for initiation of wireless mobile communications sessions

• US 20040264550A1
• Filed: 06/08/2004
• Published: 12/30/2004
• Est. Priority Date: 06/11/1999
• Status: Active Grant

• Current Assignee: Anand G. Dabak
• Original Assignee: Anand G. Dabak
• Inventors: Dabak, Anand G.
• Granted Patent: US 7,324,485 B2
• Time in Patent Office: Days
• US Class Current: 375/142
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04B 1/7075 with code phase acquisition
• CPC Class Codes: H04B 1/7093 Matched filter type
• CPC Class Codes: H04J 13/0048 Walsh
• CPC Class Codes: H04J 13/18 Allocation of orthogonal codes
• CPC Class Codes: H04L 7/041 using special codes as synchronising signal

Abstract

A wireless communications network, including a base station (10) and wireless units (UE), is disclosed. The wireless units (UE) request a connection with the base station (10) by the transmission of a preamble within time slots designated by the base station (10). The disclosed preambles are Walsh Hadamard code symbols, repeated a number of times so as to have the same length as a cell-specific scrambling code. The wireless unit (UE) requesting a connection pseudo-randomly selects a time slot from those available, and one of the Walsh Hadamard code symbols, replicates the code symbol into a spread interleaved bitstream, scrambles this bitstream and transmits it to the base station (10). Upon receipt, the base station (10) applies the incoming bitstream to a matched filter (98) to descramble the signal, following which the symbol is de-interleaved by way of a sequence of delay lines (100). Despreaders (102) generate each bit of the symbol from corresponding taps of the delay lines (100), and the symbol is applied to a correlator (104, 126, 136) to determine the transmitted preamble.

Claims

1-24. -24. (Canceled)

25. A method of decoding a preamble, comprising the steps of:

extracting a first number of groups of signals having a second number of signals in each group from a data stream having a predetermined length, wherein each group has a third number of subgroups;

applying one signal from each subgroup to each respective despreader circuit of a third number of despreader circuits, each despreader circuit producing a respective output signal; and

producing a first number of transforms from the output signal from each respective despreader circuit of each subgroup, each transform having the third number of signals.

26. A method as in claim 25, comprising summing a respective signal corresponding to each transform at a third number of sum circuits, thereby producing the third number of sum signals.

27. A method as in claim 26, wherein a product of the first and second numbers is equal to the predetermined length.

28. A method as in claim 27, wherein the first number is 4, the second number is 1024, the third number is 16, and the predetermined length is 4096.

29. A method as in claim 26, wherein the transform is a Walsh Hadamard transform.

30. A method as in claim 26, wherein the respective signal corresponding to each transform is a square of the amplitude of the transform signal.

31. A method as in claim 26, wherein the sum signal corresponds to a match between data stream and one of the plurality of codes.

32. A method as in claim 25, comprising:

producing a plurality of products, each product comprising a respective transform signal and complex conjugates of another respective transform signal; and

summing a plurality of the products at each of a third number of sum circuits, thereby producing the third number of sum signals.

37. A method of decoding a data sequence having a group of signals repeated a predetermined number of times, comprising the steps of:

applying one signal from each group to a respective despreader circuit of a plurality of despreader circuits, each despreader circuit of the plurality of despreader circuits producing a respective output signal; and

producing a first number of transforms from the output signal from each respective despreader circuit, each transform having a second number of signals.

38. A method as in claim 37, wherein the plurality of despreader circuits comprises 64 despreader circuits.

39. A method as in claim 37, wherein the first number of transforms is 4.

40. A method as in claim 37, wherein each transform is a Walsh Hadamard transform.

41. A method as in claim 37, wherein the plurality of sum signals corresponds to a match between the group of signals and one of the plurality of codes.

42. A method as in claim 37, comprising summing a respective signal corresponding to each transform at a respective sum circuit, thereby producing a plurality of sum signals.

43. A method as in claim 37, comprising:

producing a plurality of products, each product comprising a respective transform signal and complex conjugates of another respective transform signal; and

summing a plurality of the products at each of a plurality of sum circuits, thereby producing a plurality of sum signals.

44. A method of encoding a preamble, comprising the steps of:

selecting a first code from a plurality of orthogonal codes;

repeating the first code a plurality of times to produce a sequence having a predetermined length; and

combining the sequence with a second code having the predetermined length.

45. A method as in claim 44, wherein the plurality of orthogonal codes are Walsh Hadamard codes corresponding to users in a wireless cell and wherein the second code is a scrambling code corresponding to a wireless cell.