Method and apparatus for adaptive beamforming in an antenna array system for wireless communications
A novel system for performing adaptive beamforming in a slow frequency hopping environment is disclosed. The presence of slow frequency hopping means that conventional mechanisms of using beamforming weights from previous time slots are inapplicable. The inventive system calculates a series of beamforming weights from an estimate of the spatial location of the mobile subscriber in the previous frame, which is impervious to slow frequency hopping and the data that precedes the training sequence data of the current frame. The beamforming weights and the spatial location of the mobile are updated with the arrival of the entirety of the current frame. The initial beamforming weight estimate is sufficient to permit processing on a real-time basis of the current frame even if the inventive system is implemented as an appliqué system interposed between the antenna array and a conventional base station.
1. A method of adaptively beamforming data for an antenna array, comprising the steps of:
(a) receiving in a current frame, an RF signal emanating from a mobile station;
(b) obtaining a spatial location associated with a previous frame of the signal;
(c) calculating beamforming weights based on pre-training sequence data of the current frame of the signal and the spatial location;
(d) applying the beamforming weights to the antenna array data to process the current frame; and
(e) estimating an updated spatial location associated with the current frame based on training sequence data of the current frame; and
(f) maintaining the updated spatial location for use with a future frame of the signal.
2. A method according to claim 1 , comprising the step of:
(g) applying the beamforming weights to the antenna array data for receipt by the base station.
3. A method according to claim 1 , wherein the step of estimating is calculating a direction of arrival (DoA).
4. A method according to claim 3 , wherein the step of calculating a direction of arrival (DoA) comprises using Capon's method.
5. A method according to claim 3 , wherein the step of calculating a direction of arrival (DoA) comprises combining Capon's method with adaptive beamforming.
6. A method according to claim 1 , further comprising, after step (e), of the step:
(e1) validating the beamforming weights calculation of step (c) using the training sequence data of the current frame.
7. A method according to claim 6 , wherein the step of validating comprises detecting silence.
8. A method according to claim 7 , wherein the step of detecting silence comprises comparing a received signal strength indicator (RSSI) against a pre-determined threshold.
9. A method according to claim 7 , wherein the step of detecting silence comprises comparing a ratio of a magnitude of a correlation peak to a received signal strength indicator (RSSI) measurement against a predetermined threshold.
10. A method according to claim 6 , wherein the step of validating comprises detecting burst synchronization.
11. A method according to claim 1 , wherein the step of estimating comprises calculating a spatial signature of the signal emanating from the mobile station.
12. A method according to claim 1 , further comprising, after step (e) of the step:
(e2) recalculating beamforming weights based on the training sequence of the current frame of the signal.
13. An adaptive beamforming system for a base station, comprising:
a plurality of antenna elements for receiving in frames an RF signal emanating from a mobile station;
a spatial location database for storing a spatial location associated with a previous frame of the signal;
a beamforming weight calculator for determining a set of beam weights based on the stored spatial location;
a beamforming network for applying the set of beam weights to retrieve a current frame of the signal; and
a spatial location estimator for calculating a spatial location associated with the current frame for updating the spatial location database.