Code assignment in a CDMA wireless system

• US 7,035,238 B1
• Filed: 07/13/1999
• Issued: 04/25/2006
• Est. Priority Date: 06/04/1999
• Status: Expired due to Term

• Current Assignee: WSOU Investments, LLC (WSOU Holdings, LLC)
• Original Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Inventors: Papadias, Constantinos Basil, Foschini, Gerard Joseph, Chen, Jiunn-Tsair
• Primary Examiner(s): Pham, Chi
• Assistant Examiner(s): HOANG, THAI D
• Application Number:
  US09/353,460
• Time in Patent Office: 2,478 Days
• Field of Search: 455/3.02, 455/3.05, 455/3.06, 455/434, 455450-455, 455/500, 455/509, 455/511, 455/515, 455/517, 455/63, 455/103, 370/320, 370329-330, 370335-336, 370/342, 370/436, 370/441
• US Class Current: 370/335
• CPC Class Codes: H04B 1/7097 Interference-related aspects
• CPC Class Codes: H04J 13/004 Orthogonal
• CPC Class Codes: H04J 13/18 Allocation of orthogonal codes

Abstract

A CDMA wireless communication system for communicating with wireless terminals. The system comprises a channel estimator for determining characteristics of the wireless channels of the wireless terminals. The channel characteristics are used by a code optimizer to assign spreading codes to the wireless terminals. In one embodiment, the code optimizer utilizes an iterative code optimization algorithm and maintains a processing set of wireless terminals. The code optimizer chooses target wireless terminals and performs a random code search in order to find an improved code for the target wireless terminal. The improved code found in the random code search is further improved by performing a gradient search of codes in the signal space in the vicinity of the improved code and by performing a gradient search of transmission delays. The improved codes are transmitted to the wireless terminals for use in reverse link communication.

Claims

1. A method for updating spreading codes assigned to wireless terminals in a CDMA wireless communication system, comprising:

(a) identifying a target wireless terminal having a signal to interference-plus-noise ratio below a predetermined threshold;

(b) assigning a new spreading code to the target wireless terminal identified in paragraph (a), by searching for an optimal signal signature corresponding to the new spreading code so as to reduce signal interference between the wireless terminals when in reverse link communication with a base station, wherein the act of searching for an optimal signal signature corresponding to the new spreading code comprises selecting a random spreading code out of a set of unused spreading codes associated with a region of signal space that is less dense when compared other regions of signal space;

(c) forwarding the new spreading code to the target wireless terminal identified in paragraph (a); and

(d) updating spreading codes assigned to wireless terminals in a CDMA wireless communication system by repeating operational acts specified in paragraphs (a), (b), and (c) on an iterative basis.

2. The method as recited in claim 1, further comprising adjusting a transmission delay of the target wireless terminal identified in paragraph (a).

3. The method as recited in claim 1, further comprising testing the randomly selected code to ascertain whether there is an improvement of the signal to interference-plus-noise ratio for the identified wireless terminal.

4. The method as recited in claim 1, further comprising testing the randomly selected code to ascertain whether there is an improvement of the signal to interference-plus-noise ratio for the identified wireless terminal;

and selecting another spreading code in proximity to the set of unused spreading codes associated with a region of signal space that is less dense if there is no improvement in the signal to interference-plus-noise ratio for the identified wireless terminal.

5. The method as recited in claim 1, wherein the searching for an optimal signal signature corresponding to the new spreading code described in paragraph (b) further comprises performing a gradient search for the optimal signal signature.

6. A method for assigning codes to wireless terminals in a CDMA wireless communication system, comprising:

estimating propagation characteristics of at least one channel used to communicate from at least one of the wireless terminals to a base station in a reverse link of the CDMA wireless communication system;

assigning spreading codes to the wireless terminals based on the estimated propagation characteristics of the at least one channel, wherein the act of assigning the spreading codes comprises;

(a) identifying a target wireless terminal having a signal to interference-plus-noise ratio below a predetermined threshold;

(b) assigning a new spreading code to the target wireless terminal identified in paragraph (a), by searching for an optimal signal signature corresponding to the new spreading code so as to reduce signal interference between the wireless terminals when in reverse link communication, wherein the act of searching for an optimal signal signature corresponding to the new spreading code comprises selecting a random spreading code out of a set of unused spreading codes associated with a region of signal space that is less dense when compared other regions of signal space;

(c) forwarding, in a forward link of the CDMA wireless communication system, the new spreading code to the target wireless terminal identified in paragraph (a); and

(d) updating spreading codes assigned to wireless terminals in a CDMA wireless communication system by repeating operational acts specified in paragraphs (a), (b), and (c) on an iterative basis.

7. A system for assigning codes to wireless terminals, the system comprising:

means for estimating propagation characteristics of at least one channel used to communicate from at least one of the wireless terminals to a base station in a reverse link of the CDMA wireless communication system;

means for assigning spreading codes to the wireless terminals based on the estimated propagation characteristics of the at least one channel, wherein the act of assigning the spreading codes comprises;

(a) means for identifying a target wireless terminal having a signal to interference-plus-noise ratio below a predetermined threshold;

(b) means for assigning a new spreading code to the target wireless terminal identified in paragraph (a), by searching for an optimal signal signature corresponding to the new spreading code so as to reduce signal interference between the wireless terminals when in reverse link communication, wherein the act of searching for an optimal signal signature corresponding to the new spreading code comprises selecting a random spreading code out of a set of unused spreading codes associated with a region of signal space that is less dense when compared other regions of signal space;

c) means for forwarding, in a forward link of the CDMA wireless communication system, the new spreading code to the target wireless terminal identified in paragraph (a); and

(d) means for updating spreading codes assigned to wireless terminals in a CDMA wireless communication system by repeating operational acts specified in paragraphs (a), (b), and (c) on an iterative basis.

8. Apparatus for communicating with a plurality of wireless terminals via a plurality of channels, said apparatus comprising:

a channel estimator for estimating channel propagation characteristics;

a code optimizer for assigning spreading codes to the plurality of wireless terminals based on the estimated channel propagation characteristics, wherein the codes are spreading codes;

wherein the code optimizer comprises a memory storing computer program instructions;

a processor for executing said stored computer program instructions;

the computer program instructions defining acts of assigning spreading codes to the plurality of wireless terminals by;

(a) identifying a target wireless terminal having a signal to interference-plus-noise ratio below a predetermined threshold;

(b) assigning a new spreading code to the target wireless terminal identified in paragraph (a), by searching for an optimal signal signature corresponding to the new spreading code so as to reduce signal interference between the wireless terminals when in reverse link communication, wherein the act of searching for an optimal signal signature corresponding to the new spreading code comprises selecting a random spreading code out of a set of unused spreading codes associated with a region of signal space that is less dense when compared other regions of signal space;

(c) forwarding, in a forward link of the CDMA wireless communication system, the new spreading code to the target wireless terminal identified in paragraph (a); and

(d) updating spreading codes assigned to wireless terminals in a CDMA wireless communication system by repeating operational acts specified in paragraphs (a), (b), and (c) on an iterative basis for other wireless terminals.