Method and system for code reuse and capacity enhancement using null steering
First Claim
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 di, for i=1, . . . , N, intended for one of N users with N+1 complex weights wi, 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.
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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.
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Citations
8 Claims
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1. A base station employing null beam steering of wireless communication signals to a plurality of users, comprising:
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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 di, for i=1, . . . , N, intended for one of N users with N+1 complex weights wi, 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. - View Dependent Claims (2, 3)
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4. A method implemented by a base station employing null beam steering, transmitting data to N users, including data dA 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 dA and the data dB over an antenna array having N+1 antennas, comprising:
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simultaneously applying one of a same and a correlated spreading code to the data dA and the data dB; separately applying the data dA and the data dB with first and second different sets of complex weights where each set of weights includes N+1 complex weight modulators wi (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. - View Dependent Claims (5, 6, 7, 8)
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Specification