Spatially switched router for wireless data packets

Optical: systems and elements – Deflection using a moving element – Using a periodically moving element

Reexamination Certificate

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C343S753000, C370S351000, C370S338000, C370S389000, C370S410000

Reexamination Certificate

active

06426814

ABSTRACT:

TECHNICAL FIELD
The present invention relates to the field of wireless communication in general, and in particular, to a router for switched array antennas for high capacity wireless broadband networks.
BACKGROUND ART
Wireless communication at high frequencies in the range of 1 GHz to more than 100 GHz are used extensively for point-to-point (PP) and point-to-multi point (PMP) communication. For these high frequencies, three types of antennas are commonly used for spatial directional data transmission. Parabolic reflector antennas are used for a fixed narrow spatial direction of transmission. Sectorial horn antennas are used for fixed wide area transmission. Patch antennas are used for fixed direction transmission as well. Those antennas have fixed lobe patterns aligned towards transceivers located in a well defined spatial sector. Once the data link is defined the antennas transmit and receive data from those fixed directions, based on the MAC (Media Access Control) layer either in a circuit connection form, in broadcast form or in a polling form. In PP and PMP systems, the transceivers' antennas at both sides of each link have to be aligned to face each other and the antennas' alignment is usually done manually during the initial link commissioning. When setting up a PMP link, the antenna beams at both sites have to be aligned simultaneously towards each other to reach maximum received signal. In PMP systems, the base station often includes fixed sectorial antennas that are set initially to radiate in well defined sectors, e.g. four low gain antennas of 90 degrees that are positioned to cover 360 degrees. Thus, a subscriber's antenna has a narrower spatial divergence to increase its gain, is aligned towards the base station location in azimuth and elevation until maximum reception is achieved. This alignment guarantees that the base station is also receiving maximum transmission signal via its large lower gain fixed sectorial antenna.
Data packets transmitted and received by the antennas are coming from the same directions. In the case of PMP system that uses FDM B frequency division multiplexing, or TDM B time division multiplexing, or other modulation technique, the base station can broadcast information dedicated to specific transceivers located in a sector. All other transceivers in the same sector will receive the data, decode it, but will ignore it once it is found that the data is not aimed for them. However, by sharing the sector among many transceivers, only a limited amount of data packets can be forwarded simultaneously among the transceivers when transmitting at the same frequency.
The process of alignment in both PP links or in the case of adding a new subscriber at a PMP system is done off-line prior to service activation and involves accurate mechanical adjustment while monitoring the received signal level. In DBS (Direct Broadcast System—a PMP using a satellite), antenna alignment is done in a similar way to terrestrial PMP system. At the subscriber location, the antenna is aligned towards a geostationary satellite until a good signal is detected, and then it is fixed mechanically towards that direction. In all of the above-described cases, the antenna's aperture is aligned mechanically towards the broadcasting source or towards each other before establishing the communication link and starting the service. Based on the received signal level, the direction is mechanically adjusted, sometimes by motor driven antenna, and fixed to the specified direction of maximum reception and transmission.
Few techniques are used to route or direct data towards different transmission directions. The most common is to locate a base station with multiple transceivers, each one with its own separate antenna, where each antenna covers a different sector. The base station MAC layer switches the data at baseband to the transmitter, which covers the sector that contains the subscriber transceiver site where the data packets are aimed. At a PMP base station, typical sectorial antennas such as horn antennas are designed to cover fixed 90, 45, 30 or 15 degree lobes in the horizontal plane and about 7 degrees in the vertical plane. The subscriber antenna, on the other hand, is designed with much narrower beam sensitivity, i.e. higher gain, with similar divergence in horizontal and vertical planes, usually less than 7 degrees. Horn antennas, lens corrected horns and parabolic antennas are commonly used for the subscriber transceiver. Other PMP systems use a subscriber radio with an antenna that receives the down-stream data from the base station in one polarization, say horizontal, and transmits upstream in a perpendicular polarization, say vertical, towards the base station, thus increasing network capacity. In all of the above cases, the spatial capacity in a sector is fixed by the alignment of the antennas.
Phased array antennas allow beam steering by controlling the phase of each antenna element relative to phase of the other elements thus allows beam steering. Those antennas are complicated to control in a very short duration imposed by the burst nature of the packets of data. Thus, phased array antennas are currently used only in some advanced cellular base stations to establish circuit connections for relatively long duration data transmissions, such as in circuit oriented networks where the duration of voice conversation is relatively much longer than packets of data. Phased array antennas are used primarily at low frequencies, typically less than 2.5 GHz, to get high directionality in a multireflections environment. The complexity, high cost and high loss of components, namely phase shifters, at high frequencies prevent use for mass commercial applications.
A simple solution for switching data packets towards different transceivers at different directions is by fast switching the final output energy between different sectorial antennas located in different angles, in say the horizontal plane, thus covering a large field of view. This configuration, however, demands a multiplicity of antennas, each one aimed in a different direction with a multiplicity of transmitters and connection lines to feed those antennas. RF energy needs to be switched and then transported, via long waveguides or coax, to each antenna. The distance from the switches to the antennas creates large signal attenuation, which increases at higher frequencies, and demands increased antenna structural dimensions, cost, and can be environmentally objectionable. Thus, an objective is to control a very fast switch for millimeter waves using a high frequency switched antenna array, with the switch located in close proximity to the antenna array. This is needed to allow high bit rate packets modulating high frequency RF to be efficiently switched towards different transceivers in different spatial directions.
SUMMARY OF THE INVENTION
An example of spatial routing of data packets in the space between arbitrarily distributed wireless nodes is described by Berger at el. in U.S. patent application Ser. No. 09/187,665 entitled “Broadband Wireless Mesh Topology Networks”, filed Nov. 5, 1998, incorporated by reference herein. The wireless network nodes are designed to select a transmission direction and a receive direction based on the routing address of the data packets to be sent and/or received. The selection of a transmission or receiving direction is done instantaneously to accommodate short bursts of data packets arriving from nodes located at different directions or transmitted towards nodes located at different directions, as defined by the scheduler of the MAC layer of the network nodes, as explained in the prior applications. A communication protocol that is designed to support the scheduling of spatially routed packets between network nodes in any generic topology such as mesh, tree and branch and PMP, is described by Aaronson at el. in U.S. patent application Ser. No. 09/328,105 entitled “Communication Protocol for Packet Data Particularly in Mesh Topology Wireless Networks”, filed Jun. 8, 19

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