Directional antenna physical layer steering for WLAN
View Patent ↗A technique for steering a directional antenna such as may be used in a Wireless Local Area Network (WLAN) device. The technique detects signal parameters during reception of short sync pulses in the very beginning portion of a Packet Protocol Data Unit (PPDU) frame. As a result, the antenna can be steered to an optimum direction for reception prior to receiving other portions of a preamble that may be needed to acquire carrier signal phase and frequency.
1. A method for controlling a directional angle of a steerable antenna array, wherein a radio signal received via the array contains a preamble portion and a data portion, the method comprising the steps of:
configuring the antenna array for receiving the radio signal in an omni-directional mode;
receiving an initial part of the preamble;
determining a quality metric of the initial part of the preamble;
setting the array to a candidate angle;
receiving a subsequent part of the preamble;
determining a quality metric for the subsequent part so received;
repeating the steps of setting the array, receiving a subsequent preamble part and determining a quality metric for at least one additional candidate angle; and
selecting a candidate angle based on the quality metrics,
wherein the preamble portion comprises short synchronization pulses and long synchronization pulses, and wherein the step of selecting a candidate angle is completed prior to reception of the long synchronization pulses.
2. A method as in claim 1 additionally comprising:
after the step of configuring the array for receiving in an omni-directional mode, but before receiving an initial part of the preamble, setting an automatic gain control.
3. A method as in claim 1 additionally comprising:
receiving additional preamble signal parts with the array set to the candidate angle.
4. A method as in claim 3 additionally comprising:
using a subsequent preamble part for frequency estimation.
5. A method as in claim 1 wherein the radio signal contains a Packet Protocol Data Unit (PPDU) frame that provides the preamble portion.
6. A method as in claim 1 wherein the radio signal contains a Physical Layer Convergent Procedure (PLCP) comprising multiple short sync pulses, the short sync pulses comprising the preamble parts.
7. A method as in claim 6 wherein the quality metric is determined by the steps of:
performing a Fast Fourier Transform (FFT) on a received short sync pulse and selecting FFT bins corresponding to a desired signal;
performing a first inverse FFT to create a time domain result of the desired signal;
selecting bins not selected in the first step of performing an FFT as bins-not-selected to provide a noise estimate;
performing a second inverse FFT on the bins-not-selected to create a time domain result of noise signals;
establishing a pseudo signal-to-noise ratio estimate as the metric, from a ratio of the two inverse FFT results.
8. A method as in claim 1 wherein the step of determining a quality metric additionally comprises:
correlating a subsequent preamble part against an expected received preamble part.
9. A method as in claim 8 wherein the expected received preamble part is a stored optimum response.
10. A method as in claim 8 wherein the expected received preamble part is recorded from a previous radio signal reception.
11. A method as in claim 1 wherein the preamble comprise a series of synchronization pulses, each pulse having a first section and a second section, the first and second pulse section having symmetry about an in-phase and quadrature time axis.
12. A method as in claim 11 wherein the step of determining a quality metric determines a quality metric for two candidate angles from a single preamble part, by determining a metric for a first candidate angle from first pulse section and determining a second candidate angle from the second pulse section.