Wireless LAN with distributed access points for space management

• US 7,057,555 B2
• Filed: 11/27/2002
• Issued: 06/06/2006
• Est. Priority Date: 11/27/2002
• Status: Expired due to Fees

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: Lewis, Michael E.
• Primary Examiner(s): Tarcza, Thomas H.
• Assistant Examiner(s): Mull, Fred H
• Application Number:
  US10/305,570
• Publication Number:
  US 20040102157A1
• Time in Patent Office: 1,287 Days
• Field of Search: 342/372, 342/377, 342/373, 455/63.4, 455/25, 455/562.1, 455/41.2, 455/41.3
• US Class Current: 342/372
• CPC Class Codes: H01Q 3/30 varying the relative phase between the radiating elements of an array H01Q3/2605, H01Q3/2658, H01Q3/2682, H01Q3/44 take precedence
• CPC Class Codes: H04B 7/0408 using two or more beams, i.e. beam diversity
• CPC Class Codes: H04W 84/12 WLAN [Wireless Local Area Networks]
• CPC Class Codes: H04W 88/02 Terminal devices
• CPC Class Codes: H04W 88/08 Access point devices

Abstract

A directional antenna system is disclosed in which a plurality of RF nodes are provided for cooperatively forming a directional antenna array for transmitting and receiving wireless signals between a wireless client at a predetermined position in space. One or more network interface assemblies are provided for exchanging signals between the plurality of RF nodes and a network. Preferably, the plurality of RF nodes are distributed in space with respect to each other and the network interface assembly. The network interface includes a beamformer for applying a plurality of antenna weighting factors to the respective RF nodes, for introducing phase differences in the respective transmitted and received wireless signals that produce a directional steering vector for the wireless signals. In one embodiment of the invention, a processing arrangement is provided for deriving an array manifold, which includes a respective plurality of antenna weighting factors corresponding respectively to distances between each of the plurality of RF nodes, for producing the directional steering vector for the wireless signals. In another embodiment of the invention, a subspace beamforming arrangement is provided for building a covariance matrix from sampled values of a wireless client signal at each RF node, and deriving dominant eigenvectors corresponding to each RF node. The dominant eigenvectors are used as the respective antenna weighting factors for producing the directional steering vectors for the wireless signals.

Claims

1. A directional antenna system comprising:

a plurality of RF nodes cooperatively forming a directional antenna array for transmitting and receiving wireless signals between a wireless client at a predetermined position in space;

at least one network interface assembly for exchanging signals between the plurality of RF nodes and a network, wherein the plurality of RF nodes are distributed in space with respect to each other and the network interface assembly;

wherein the plurality of RF nodes converts wireless signals from the wireless client to baseband signals that are sent to the at least one network interface assembly;

wherein the plurality of RF nodes converts baseband signals from the at least one network interface assembly to wireless signals sent to the wireless client;

wherein the at least one network interface comprises;

a beamformer for applying a plurality of antenna weighting factors to the respective RF nodes, for introducing phase differences in the respective transmitted and received wireless signals that produce a directional steering vector for the wireless signals; and

a processing arrangement for deriving an array manifold including a respective plurality of antenna weighting factors corresponding respectively to distances between each of the plurality of RF nodes, for producing the directional steering vector for the wireless signals.

2. The directional antenna system of claim 1, further comprising a local positioning system, the local positioning system comprises:

a correlator respectively associated with each of the plurality of RF nodes, for measuring a signal time delay between each RF node, to thereby derive distance measurements between each RF node;

wherein the correlator receives a long correlation signal from a second of the plurality of RF nodes and cross-correlates the long correlation signal with a copy of the long correlation signal maintained at each of the plurality of RF nodes; and

wherein the correlator further comprising a plurality of taps for receiving a predetermined number of time sequenced points wherein the long correlation signal is processed in parallel and each predetermined point is forwarded to a respective tap which multiplies the respective point by the complex conjugate of the of the respective corresponding point maintained at the node, and wherein the sum of the products has a peak corresponding to the time delay in transmission from the second of the plurality of RF nodes.

3. The directional antenna system of claim 1 further comprising an adder between the beamformer and the network interface for summing the respective received signals with applied antenna weighting factors, for forwarding to the network.

4. The directional antenna system of claim 1 wherein each of the plurality of RF nodes comprises:

an antenna for transmitting and receiving the wireless signals;

a radio assembly, comprising a local oscillator, for respectively modulating and demodulating the transmitted and received wireless signals;

a converter, comprising a clock, for respectively converting signals between analog wireless signals and digital network signals;

wherein the respective plurality of local oscillators and clocks are mutually coherent in frequency and phase.

5. The directional antenna system of claim 1 wherein the at least one network interface assembly comprises a PHY for exchanging signals with the plurality of radio nodes, and a MAC for converting the exchanged signals respectively to and from a network protocol.

6. The directional antenna system of claim 1 wherein the at least one network interface comprises a plurality of network interfaces, each of which for cooperating with at least one of the plurality of RF nodes.

7. The directional antenna system of claim 1 wherein each of the plurality of RF nodes comprises a wired connection for connecting to the at least one network interface.

8. The directional antenna system of claim 1 wherein the antenna weighting factors are calculated front a received client signal in order to triangulate the client'"'"'s position.