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Directional antenna physical layer steering for wlanDirectional antenna physical layer steering for wlan description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070008219, Directional antenna physical layer steering for wlan. Brief Patent Description - Full Patent Description - Patent Application Claims
RELATED APPLICATIONS [0001] This application is a continuation of U.S. application Ser. No. 10/675,583, filed on Sep. 30, 2003, which claims the benefit of U.S. Provisional Application No. 60/414,947 filed Sep. 30, 2002 and U.S. Provisional Application No. 60/415,847 filed Oct. 3, 2002. The entire teachings of the above applications are incorporated herein by reference. BACKGROUND OF THE INVENTION [0002] Wireless Local Area Network (WLAN) equipment continues to be used as a solution for many different data connectivity applications. WLANs are now viewed as an ideal solution for providing access to wireless equipped personal computers within home networks, mobile access to laptop computers and personal digital assistants (PDAs), as well as providing robust and convenient access in business applications. [0003] Indeed, at the present time many laptop computers are shipped from the factory with WLAN interface cards. Certain microprocessor manufacturers, such as Intel, have also announced intentions to incorporate WLAN capability directly into processor chip platforms. These and other initiatives will continue to drive the integration of WLAN equipment into personal computers of all types. [0004] It is already the case that in many cities, WLAN access equipment operating in accordance with the IEEE 802.11a, 802.11b, and 802.11g standards is in wide use. In these cities one can now find "hot spots" that provide network connectivity. Unfortunately, having tens, if not hundreds, of closely spaced wireless networks using the same radio spectrum means that interference becomes a problem. That is, although the 802.11 standards provide for robust signaling in the form of spread spectrum radio frequency modulation, and using orthogonal frequency division multiplexing over modulated subcarriers, crowding of the radio spectrum still increases noise and therefore decreases performance for all users. [0005] It is recognized that directional antenna arrays can be used to steer radio frequency energy between a transmitter and receiver. This greatly reduces the amount of interference that would otherwise be created for concurrent users of the spectrum. The use of such arrays in wireless subscriber equipment has been described in U.S. Pat. No. 6,100,843 entitled "Adaptive Antenna for Use in Same Frequency Networks"; U.S. Pat. No. 6,400,317 entitled "Methods and Apparatus for Antenna Control in a Communications Network"; and in U.S. Pat. No. 6,473,036 entitled "Method Apparatus for Adapting Antenna Array to Reduce Adaptation Time While Increasing Array Performance". Each of these patents is assigned to Tantivity Communications, Inc., the assignee of the present application. [0006] However, WLAN signaling has special considerations in that communication is expected to be on a peer-to-peer basis with extremely short packet lengths. It has heretofore been thought quite difficult to require WLAN subscriber equipment to steer an antenna array, to one of many possible candidate angles, during such very short intervals. SUMMARY OF THE INVENTION [0007] The present invention is a technique for implementing an antenna steering at the physical layer of a Wireless Local Area Network (WLAN) device. Implementing the antenna steering decision at the physical layer eliminates involving higher communication layers, which would otherwise require modification of standardized communication processing software, such as the Media Access Control (MAC) or Link layers. [0008] In one embodiment, the invention provides techniques for signal detection during short sync symbol reception in the very beginning of a preamble portion of a WLAN frame. Specifically, in the context of an 802.11a or 802.11g Packet Protocol Data Unit (PPDU) frame (packet), this may be concluded within only a few initial training sequence symbols of the Physical Layer Convergent Procedure (PLCP) preamble portion. Operating very quickly during these so-called short sync pulses, the antenna will be steered to an optimum direction prior to receiving other portions of the preamble. This permits the radio receiver equipment to use the remainder of the preamble to acquire carrier phase lock and frequency synchronization, in just about the same manner as if no directional antennal were present. The remaining preamble portions can thus be processed according to standard WLAN frame processing. [0009] One specific technique employed is to set an antenna array to an omni-directional mode prior to reception of the first short sync pulse. This permits Automatic Gain Control (AGC) circuitry in the receiver to track for an initial short sync pulse. During reception of the next one or two short sync pulses, a signal metric such as a correlation is used to evaluate the observed response against an expected response. The expected response can either be a stored response that is the optimum expected for a short sync. Alternatively, the expected response can be a stored version of a measured response received with an omni setting during the initial short sync pulse. [0010] In accordance with certain other aspects of the invention, correlations can be performed over a first and second half of a short sync pulse by swapping real and imaginary samples. This provides twice as many candidate angles to be tested for each subsequent short sync pulse. [0011] With either of these two techniques, by the time of arrival of the fourth short sync pulse, the antenna array has been steered to a candidate direction. This provides at least five to six additional short sync pulses that may be used by the receiver to acquire frequency and phase lock. [0012] A third technique involves the use of finite impulse response comb filtering. This may be performed through the use of inverse Fast Fourier Transforms. The process here is to implement an ideal comb type filter response for both signal and noise and then convolve it with the received short sync signal. An approximate estimate of a signal to noise ratio can be derived as a ratio of observed signal and noise filter responses. The candidate angle exhibiting the strongest signal to noise ratio is then selected to be used. BRIEF DESCRIPTION OF THE DRAWINGS [0013] The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. [0014] FIG. 1 is a block diagram of a typical wireless local area network (WLAN) receiver showing the location of implementation of an antenna steering algorithm according to the present invention. [0015] FIG. 2 is a high level diagram of a Packet Protocol Data Unit (PPDU) used in an 802.11a or 802.11g network. [0016] FIG. 3 is a more detailed view of the preamble portion of the header. [0017] FIG. 4 is a time domain representation of the real and imaginary portions of a PLCP preamble or "short sync" pulse. [0018] FIG. 5 is a more detailed view of the short sync pulse showing the real and imaginary parts, as well as a magnitude portion. [0019] FIG. 6 is a frequency domain plot of the magnitude of the short sync pulse. [0020] FIG. 7 is a three-dimensional view showing the frequency to main amplitude and phase response of the short sync pulse in the frequency domain. Continue reading about Directional antenna physical layer steering for wlan... Full patent description for Directional antenna physical layer steering for wlan Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Directional antenna physical layer steering for wlan patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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