PN long code shift for access attempt

• US 8,391,412 B1
• Filed: 07/17/2009
• Issued: 03/05/2013
• Est. Priority Date: 07/17/2009
• Status: Expired due to Fees

• Current Assignee: Sprint Spectrum LP (Deutsche Telekom AG)
• Original Assignee: Sprint Spectrum LP (Deutsche Telekom AG)
• Inventors: Oroskar, Siddharth S., Vargantwar, Sachin R., Rai, Deveshkumar, Khanka, Bhagwan, Shetty, Manoj
• Primary Examiner(s): Payne, David C.
• Assistant Examiner(s): Stevens, Brian J
• Application Number:
  US12/505,121
• Time in Patent Office: 1,327 Days
• Field of Search: 375/308, 375/302, 375/295, 370/335, 370/328
• US Class Current: 375/308
• CPC Class Codes: H04W 64/00 Locating users or terminals or network equipment for network management purposes, e.g. mobility management
• CPC Class Codes: H04W 72/00 Local resource management
• CPC Class Codes: H04W 74/004 in the uplink, i.e. towards network
• CPC Class Codes: H04W 88/06 adapted for operation in multiple networks or having at least two operational modes, e.g. multi-mode terminals

Abstract

A method and system is disclosed for shifting the phase of a PN long code for access attempts by an access terminal in a wireless communication network. An access terminal may seek to acquire access from a base station that is detected by the access terminal above a threshold power level, even if the access terminal is further away from the base station than a threshold distance beyond which access is not normally granted. According to one embodiment, the access terminal will, upon determining that it is beyond the threshold distance, embed in an access request message an apparent distance that is smaller than the threshold distance, by phase-shifting a timing signal and encoding the access request message with the phase-shifted timing signal. The access terminal will then transmit the access request message on an air interface communication link to the base station.

Claims

1. In an access terminal that operates in a wireless communication system that includes a base station, a method comprising:

making a determination that the access terminal is located greater than a threshold distance from the base station;

responsive to at least the determination, embedding in an access request message an apparent distance that is smaller than the threshold distance by phase-shifting a timing signal and encoding the access request message with the phase-shifted timing signal; and

transmitting the access request message on an air interface communication link to the base station, the access request message being a request by the access terminal for wireless access,

wherein the wireless communication system operates according to a CDMA family of protocol, including IS-2000 and IS-856,

wherein the threshold distance is a cell radius measured from the base station,

wherein the timing signal is a pseudo-random number (PN) long code,

and wherein embedding in the access request message an apparent distance that is smaller than the threshold distance by phase-shifting the timing signal comprises;

computing a difference between (i) a distance from the access terminal to the base station and (ii) the cell radius; and

phase-shifting the PN long code by a particular number of chips corresponding to at least the difference, thereby generating a shifted PN long code.

2. The method of claim 1, wherein making the determination that the access terminal is located greater than a threshold distance from the base station comprises:

determining a distance between the access terminal and the base station by comparing location coordinates of the access terminal with location coordinates of the base station; and

comparing the distance between the access terminal and the base station with the threshold distance.

3. The method of claim 1, wherein embedding in the access request message an apparent distance that is smaller than the threshold distance is further responsive to determining that a signal received from the base station is detected above a threshold power level by the access terminal.

4. The method of claim 3, wherein the wireless communication system operates according to a CDMA family of protocol, including IS-2000 and IS-856,

wherein the signal received from the base station is a pilot signal,

and wherein determining that the signal received from the base station is detected above a threshold power level comprises determining that the pilot signal is detected above a threshold strength.

5. The method of claim 1, wherein the PN long code is generated so as to have a reference phase that is determined in part by a long code mask, and wherein phase-shifting the PN long code by the particular number of chips comprises:

determining a modified long code mask that will cause the PN long code to be generated so as to have a modified phase that is shifted with respect to the reference phase by the particular number of chips; and

using the modified long code mask to generate the shifted PN long code.

6. The method of claim 1, wherein the access request message is an access probe, and wherein encoding the access request message with the phase-shifted timing signal comprises modulating the access probe with the shifted PN long code.

7. The method of claim 6, wherein transmitting the access request message on the air interface communication link to the base station comprises transmitting at least one modulated access probe to the base station.

8. The method of claim 1, wherein making the determination that the access terminal is located greater than a threshold distance from the base station comprises determining a current distance between the access terminal and the base station,

and wherein phase-shifting the timing signal comprises:

determining an expected phase shift that would result from a propagation delay of transmitting the timing signal across the current distance;

determining an artificial phase shift that would result from a propagation delay of transmitting the timing signal across a distance that is smaller than the threshold distance; and

advancing a phase of the timing signal by an amount at least as large as a difference between the expected phase shift and the artificial phase shift.

9. The method of claim 8, wherein the timing signal is pseudo-random number (PN) long code,

wherein the expected phase shift corresponds a first number of chips and the artificial phase shift corresponds to a second number of chips,

and wherein advancing the phase of the timing signal by an amount at least as large as a difference between the expected phase shift and the artificial phase shift comprises shifting the PN long code by a third number of chips, the third number being at least as large as a difference between the first number and the second number.

10. In an access terminal that operates in a wireless communication system that includes a base station, a method comprising:

detecting a signal above a threshold power level from a base station that is greater than a threshold distance from the access terminal, the access terminal being located at a current location;

responsive to the detection, phase-shifting a timing signal by at least an amount corresponding to a propagation delay that would result from transmitting the timing signal across a differential distance between the current location and a location that is closer than the threshold distance to the base station;

encoding an access request message with the phase-shifted timing signal; and

transmitting the access request message on an air interface communication link to the base station, the access request message being a request by the access terminal for wireless access,

wherein the wireless communication system operates according to a CDMA family of protocol, including IS-2000 and IS-856,

wherein the timing signal is a pseudo-random number (PN) long code,

and wherein phase-shifting the timing signal by at least an amount corresponding to a propagation delay that would result from transmitting the timing signal across a differential distance between the current location of the access terminal and a location that is closer than the threshold distance to the base station comprises phase-shifting the PN long code by a particular number of chips corresponding to at least the differential distance, thereby generating a shifted PN long code.

11. The method of claim 10, wherein the wireless communication system operates according to a CDMA family of protocol, including IS-2000 and IS-856,

wherein the signal received from the base station is a pilot signal,

and wherein detecting the signal above the threshold power level from a base station comprises determining that the pilot signal is detected above a threshold strength.

12. The method of claim 10, wherein detecting the signal above the threshold power level from a base station that is greater than the threshold distance from the access terminal comprises determining that the current location is greater than the threshold distance from the base station.

13. The method of claim 12, wherein determining that the current location is greater than the threshold distance from the base station comprises:

determining the current location; and

determining a location of the base station.

14. The method of claim 10, wherein the PN long code is generated so as to have a reference phase that is determined in part by a long code mask, and wherein phase-shifting the PN long code by the particular number of chips comprises:

determining a modified long code mask that will cause the PN long code to be generated so as to have a modified phase that is shifted with respect to the reference phase by the particular number of chips; and

using the modified long code mask to generate the shifted PN long code.

15. The method of claim 10, wherein the access request message is an access probe,

wherein the threshold distance is a cell radius measured from the base station,

and wherein encoding the access request message with the phase-shifted timing signal comprises embedding in the access probe an apparent distance that is smaller than the cell radius by modulating the access probe with the shifted PN long code.

16. The method of claim 15, wherein transmitting the access request message on the air interface communication link to the base station comprises transmitting at least one modulated access probe to the base station.

17. An access terminal configured for operation in a wireless communication system that includes a base station, the access terminal comprising:

means for detecting a signal above a threshold power level from a base station that is greater than a threshold distance from the access terminal;

means for, responsive to the detection, phase-shifting a timing signal by at least an amount corresponding to a propagation delay that would result from transmitting the timing signal across a differential distance between a current location of the access terminal and a location that is closer than the threshold distance to the base station;

means for encoding an access request message with the phase-shifted timing signal; and

means for transmitting the access request message on an air interface communication link to the base station, wherein the access request message is a request by the access terminal for wireless access,

wherein the wireless communication system operates according to a CDMA family of protocol, including IS-2000 and IS-856,

wherein the timing signal is a pseudo-random number (PN) long code,

and wherein means for phase-shifting the timing signal by at least an amount corresponding to a propagation delay that would result from transmitting the timing signal across a differential distance between the current location of the access terminal and a location that is closer than the threshold distance to the base station comprise means for shifting the PN long code by a particular number of chips corresponding to at least the differential distance, thereby generating a shifted PN long code.

18. The access terminal of claim 17, wherein operation of the wireless communication system is according to a CDMA family of protocol, including IS-2000 and IS-856,

wherein the signal received from the base station is a pilot signal,

and wherein means for detecting the signal above the threshold power level from a base station comprise means for determining that the pilot signal is detected above a threshold strength.

19. The access terminal of claim 17, wherein means for detecting the signal above the threshold power level from a base station that is greater than the threshold distance from the access terminal comprise means for determining that the current location is greater than the threshold distance from the base station.

20. The access terminal of claim 19, wherein means for determining that the current location is greater than the threshold distance from the base station comprise:

means for determining the current location; and

means for determining a location of the base station.

21. The access terminal of claim 17, wherein the PN long code is generated so as to have a reference phase that is determined in part by a long code mask, and wherein means for phase-shifting the PN long code by the particular number of chips comprise:

means for determining a modified long code mask that will cause the PN long code to be generated so as to have a modified phase that is shifted with respect to the reference phase by the particular number of chips; and

means for using the modified long code mask to generate the shifted PN long code.

22. The access terminal of claim 17, wherein the access request message is an access probe,

wherein the threshold distance is a cell radius measured from the base station,

and wherein means for encoding the access request message with the phase-shifted timing signal comprise means for embedding in the access probe an apparent distance that is smaller than the cell radius by modulating the access probe with the shifted PN long code.

23. The access terminal of claim 22, wherein means for transmitting the access request message on the air interface communication link to the base station comprise means for transmitting at least one modulated access probe to the base station.