Method and system for code reuse and capacity enhancement using null steering

• US 8,553,746 B2
• Filed: 04/03/2012
• Issued: 10/08/2013
• Est. Priority Date: 11/02/2001
• Status: Active Grant

• Current Assignee: Interdigital Technology Corporation (InterDigital, Inc.)
• Original Assignee: Interdigital Technology Corporation (InterDigital, Inc.)
• Inventors: Bolourchi, Nadar, Kazakevich, Leonid, Yang, Rui
• Primary Examiner(s): Tran, Khai
• Application Number:
  US13/438,635
• Publication Number:
  US 20120189035A1
• Time in Patent Office: 553 Days
• Field of Search: 375/142, 375/130, 375/141, 375/267, 375/295, 375/304, 375/347, 342/153, 342/347, 342/367, 342/368, 455/456, 455/562
• US Class Current: 375/142
• CPC Class Codes: H01Q 3/2611 Means for null steering; Adaptive interference nulling
• CPC Class Codes: H04B 7/0617 for beam forming
• CPC Class Codes: H04B 7/0669 using different channel coding between antennas space-time coding H04L1/0618
• CPC Class Codes: H04J 13/0077 Multicode, e.g. multiple codes assigned to one user
• CPC Class Codes: H04W 88/08 Access point devices

Abstract

The number of users and data capacity of wireless systems are increased by employing apparatus and method for increasing the number of spreading codes available in the system by providing a mechanism to reuse the already allocated spreading code or use the codes that may correlate to those already being used within the same sector/cell. This, in return, provides capacity improvement proportional to the number of added base station (BS) antennas for each cell. An antenna null steering technique for code allocation maintains the cross correlation properties of the codes only for the desired user and to obtain a gain in capacity improvement.

Claims

1. A base station employing null beam steering of wireless communication signals to a plurality of users, comprising:

an antenna array having a plurality of antennas;

a spreading code generator for selecting spreading codes for the plurality of users that correlate to spreading codes already being used with the same cell;

a plurality of weight modulators for modulating data d_i, for i=1, . . . , N, intended for one of N users with N+1 complex weights w_i, for i=1, . . . , N+1, each modulated signal being directed to one of the N+1 antennas;

wherein the complex weights are selected to create a null at one of the plurality of users, such that a gain of a composite channel from the base station to the nulled user is zero and a gain of a composite channel from the base station to another user is maximized;

wherein each element of the complex weights is a function of the channel impulse responses from the antenna array to locations of the users; and

a summer for summing the weight modulated data signals.

2. The base station of claim 1, wherein the weight modulator is configured to generate complex weights w_i as a function of the number of antennas in the array.

3. The base station of claim 1, wherein the antenna array is comprised of at least three antennas.

4. A method implemented by a base station employing null beam steering, transmitting data to N users, including data d_A to a first user A and data dB to second user B, wherein the user A and the user B are located within a given cell or sector and positioned at different angular directions relative to the base station, the base station transmitting the data d_A and the data d_B over an antenna array having N+1 antennas, comprising:

simultaneously applying one of a same and a correlated spreading code to the data d_A and the data d_B;

separately applying the data d_A and the data dB with first and second different sets of complex weights where each set of weights includes N+1 complex weight modulators w_i (for i=1, 2, . . . N+1), each weight modulator having an output signal directed to one of the N antennas;

wherein each weight modulator is a function of the channel impulse responses from the antenna array to locations of each of user A and user B;

selecting the complex weights to create a null at one of user A and user B, such that a gain of a composite channel from the base station to the nulled user is zero and a gain of a composite channel from the base station to the other user is maximized;

summing the weight modulated data signals intended for each of the user A and the user B; and

transmitting the summed signals from the antenna array to the user A and the user B.

5. The method of claim 4 wherein the complex weight modulators w_i of the first and second sets of complex weights are applied to specific ones of the N antennas.

6. The method of claim 4 further comprising arranging the antennas in the antenna array in a linear manner.

7. The method of claim 6 further comprising spacing the antennas at the base station by predetermined distances.

8. The method of claim 6 further comprising spacing the antennas at the base station by 0.75 meters.