Random access preamble coding for initiation of wireless mobile communications sessions

• US 8,174,955 B2
• Filed: 01/25/2008
• Issued: 05/08/2012
• Est. Priority Date: 06/11/1999
• Status: Expired due to Term

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Dabak, Anand G.
• Primary Examiner(s): BLANTON, JOHN D
• Application Number:
  US12/011,250
• Publication Number:
  US 20080130482A1
• Time in Patent Office: 1,565 Days
• Field of Search: None
• US Class Current: 370/203
• 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. A communication circuit, comprising:

a first circuit coupled to receive a first plurality of repetitions of a first code having a length, the first code selected from a plurality of orthogonal codes; and

a multiplier circuit coupled to receive the first plurality of repetitions of a first code and a second code having the length, the multiplier circuit producing a product of the first plurality of repetitions of a first code and the second code.

2. A communication circuit as in claim 1, comprising a modulator circuit coupled to receive the product, the modulator circuit producing a modulated product.

3. A communication circuit as in claim 1, wherein the modulated product comprises an in-phase component and a quadrature component.

4. A communication circuit as in claim 1, wherein the first plurality is 4 and the length is 64.

5. A communication circuit as in claim 1, wherein the first code is a Walsh Hadamard code.

6. A communication circuit as in claim 1, wherein the first code corresponds to a user in a wireless cell.

7. A communication circuit as in claim 1, wherein the second code is a scrambling code.

8. A communication circuit as in claim 1, wherein the second code corresponds to a base station in a wireless cell.

9. A method of communicating with a remote device, 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 length;

combining the sequence with a second code having the length; and

transmitting the sequence to the remote device.

10. A method as in claim 9, comprising the step of modulating the product.

11. A method as in claim 10, wherein the step of modulating comprises modulating an in-phase component and a quadrature component.

12. A method as in claim 9, wherein the plurality is 4 and the length is 64.

13. A method as in claim 9, wherein the first code is a Walsh Hadamard code.

14. A method as in claim 9, wherein the first code corresponds to a user in a wireless cell.

15. A method as in claim 9, wherein the second code is a scrambling code.

16. A method as in claim 9, wherein the second code corresponds to a base station in a wireless cell.

17. A method of operating a wireless communications unit to request a connection with a remote device, comprising the steps of:

receiving a signal indicating at least one time slot within which a preamble may be transmitted by the wireless communications unit;

selecting one of a plurality of orthogonal codes for the preamble;

generating a spread code using the selected orthogonal code repeated a selected number of repetitions;

multiplying the spread code by a scrambling code associated with the remote device, wherein the spread code has a length equal to a length of the scrambling code; and

transmitting, to the remote device, a preamble signal corresponding to the multiplied spread code.

18. The method of claim 17, wherein the set of orthogonal codes consists of a set of Walsh Hadamard codes having a length of sixteen, wherein the generating step repeats a symbol of the Walsh Hadamard code 256 times, and wherein the length of the scrambling code is 4096 chips.

19. The method of claim 17, wherein the set of orthogonal codes consists of a set of Walsh Hadamard codes having a length of sixteen, wherein the generating step repeats a symbol of the Walsh Hadamard code 240 times, and wherein the length of the scrambling code is 3840 chips.

20. The method of claim 17, wherein the plurality of orthogonal codes corresponds to a set of Walsh Hadamard codes.

21. The method of claim 17, wherein the selecting step comprises executing a pseudo-random selection algorithm.

22. The method of claim 17, wherein the receiving step receives a signal indicating a plurality of time slots within which the preamble may be transmitted by the wireless communications unit;

and further comprising;

selecting one of the plurality of time slots for transmission of the preamble.