WO2001095282A2

WO2001095282A2 - Alignment of narrow beam transmission

Info

Publication number: WO2001095282A2
Application number: PCT/US2001/018540
Authority: WO
Inventors: Andrew Pavelchek; Victor J. Chan; Eric Shoquist
Original assignee: Airfiber, Inc.
Priority date: 2000-06-05
Filing date: 2001-06-05
Publication date: 2001-12-13
Also published as: WO2001095282A3

Abstract

A system of aligning narrow beam links encodes information on the transmitter indicative of the transmitter's position. When the receiver sees the transmitter's beam, it sends back information from the encoded information, and causes the transmitter to return to the position of alignment.

Description

ALIGNMENT OF NARROW BEAM TRANSMISSION

CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of prior U.S. provisional application serial no. 60/209,510, filed June 5, 2000.

BACKGROUND The present invention relates generally to alignment of narrow beam transmission.

Transmitters and receivers can communicate over a narrow beam link. In order to communicate in this way, each transmitter needs to be aligned to point at a corresponding receiver.

SUMMARY The present application teaches a new way of aligning these narrow beam links so that transmitter of each narrow beam link points at the receiver of an other narrow beam link. This is done by coding orientation information on the transmitter, so that the receiver obtains this orientation information at the time when the alignment occurs .

BRIEF DESCRIPTION OF THE DRAWINGS These and other aspects will now be described in detail with reference to the accompanying drawings wherein: Fig. 1 shows a basic topology of the system;

Fig. 2 shows a detailed topology of a transmitter and receiver;

Fig. 3 shows a block diagram of a control system; and

Fig. 4 shows a flowchart of operation.

DETAILED DESCRIPTION When two elements need to point at one another, each side of the pointing system may have an uncertainty about where to point. Each element may be considered to have an uncertainty of N possible pointing orientations, only one of which will align its transmitted beam to the other element. Testing all possible such orientations of the 2 transceivers entails testing N x N combinations. The present invention teaches how the two may operate so that they do not need to resolve simultaneously. Given a receiver field of view that is wider than the transmit beam, resulting in an uncertainty in pointing orientation of M possibilities, where M is less than N, it is possible to resolve the alignment by testing, in the worst case, on the order of (N x M) 4- N/M combinations.

A basic layout of this system is shown in Figure 1. A plurality of buildings 100, 102, 103, 104 are shown, each including a narrow beam transmission system 120 associated with the building. The narrow beam transmission system includes at least one transmitter, here 122 and 124, and at least one receiver, here 126 and 128. Each transmitter such as 122 transmits information to a receiver in another building 104. The transmitters can also be connected to receive an uplink connection from a broadband source, e.g., broadband content. The receivers receive information from other transmitters in other buildings, and deliver that information to a broadband sink.

The basic narrow beam system 120 includes a control system shown as 130, and also includes an out of band channel transceiver element 132 which may be a non- optical link. The out of band link transceiver may produce a broadband non-directional signal 134 which is transmitted to the other buildings such as 102. A corresponding receiver 136 on each of the buildings may receive the transmission from the out of band link. The out of band link can be, for example, an RF link, a cellular phone link, or any other type of link. The cellular phone allows other units to be specifically addressed by telephone number, for example. This system may be used for emergency control signals, and for special control signals, such as the alignment operation.

In operation, the system includes a plurality of transmitters and a plurality of receivers. Figure 2 shows one specific transmitter 200, and a specific receiver 210. The transmitter transmits a beam of light radiation 202 with a relatively narrow beam width and divergence, a "pencil beam". The pencil beam 202 includes information which is produced by a modulation source shown as 205. The transmitter is capable of transmitting in a variety of different directions controlled by translator 206.

The receiver 210 receives a beam of light 202. The receiver field of view 212, has a solid angle a that may be wider than 'the angle of divergence of the transmission, e.g., ten times as wide. The receiver also includes a demodulator shown as 215 which receives information that is modulated on the beam 202. The information can be demodulated and used in a standard way.

A more detailed block diagram of each of the transceivers is shown in Figure 3. The transmitter 200 is driven by a transmitter driver 300, which is driven by a modulator 305. The modulator can modulate information onto the light beam in any desired way. For example, the information can be modulated by on and off modulation, frequency modulation, phase or polarization modulation or by any other way of changing the light according to applied information. The modulator is controlled by a processor which may itself control other parts of the system. The receiver 210 includes receiver electronics 315. A demodulator 320 receives the information that is encoded on the light beam, which also feeds the processor 310. The system also includes servo motors shown generally as block 330 which can adjust the relative pointing angles of the transmitter 200 and the receiver 210. An angle sense element 335 senses the relative positions in space of the transmitter and/or receiver drivers, and provides that information to the processor 310. An out of band communication element 340, as described above, carries out communication with other nodes in the system.

The above has described an integrated transceiver, but a separate transmitter and receiver can be used. The optical axis 203 of each transmitter must be line-of-site aligned to the optical axis 214 of its corresponding receiver. A previous way of aligning required that one or both of the transmitter or receiver raster-scanned through all different positions until alignment was reached. Alignment was signaled from receiver to transmitter, at which time the scanning was stopped. The raster scanning needed to be slow enough so that overshoot of the positions did not occur between the time of signaling and the time when the scanning stopped. If the transmitter continued moving after alignment was reached, the alignment would be lost.

The present system, in contrast, can operate at any desired speed and is not limited by any kind of overshoot problem described above. In operation, the processor 310 carries out the operation shown in the flowchart of Figure 4.

Each transmitter is caused to scan at 400 at a very fast rate of speed. The scanning can be raster scanning, i.e., moving from left to right, indexing up or down, and then moving from right to left and repeating this sequence. Optimally the scanning pattern should approximate the probability density of the correct alignment, for example, a spiral pattern covers the highest probability areas of a Gaussian distribution first, minimizing the mean time to alignment.

At each angle β, where β can be, for example, the angle of transmission of the transmitter, the position information is updated at 405. At 410, the new position information is modulated unto the transmitter driver 300, and thereby onto the beam of the transmitter 200. The information can be transmitted, for example, by changing the frequency or amplitude of the laser, by digitally encoding information on the laser, or in any other desired way.

At 415, the receiver determines whether it has detected a transmitter beam. When the orientation is detected, a "detect" message is sent at 420 using the out of band communication element 340. The detect is sent by the receiver, to the transmitter from which the information originated. The detect message can include the orientation information which modulated on the laser beam at the time of reception. In this way, the information sent back at 420 represents the orientation of alignment.

At 425, alignment is carried out based on the transmitted information. The transmitter is commanded to go the orientation of alignment represented by the information in the modulation. This can be done by sending the information from the receiver back to the transmitter, or by sending that information to a central alignment system, and using that central system to command all elements to the desired orientation.

Although only a few embodiments have been disclosed in detail above, other modifications are possible. For example, while the above has described the operation occurring via a laser beam, it could occur via any other narrow beam communication. In addition, while the above has described solely the transmitter scanning, both the transmitter and receiver could scan. Alternatively, only the transmitter could scan. All such modifications are intended to be encompassed within the following claims.

Claims

What is Claimed is:

1. A method comprising: transmitting a beam which includes orientation information modulated thereon from a transmitter to a receiver; periodically changing an orientation of said transmitting beam, and changing a content of said orientation information to match the position of said transmitting; and receiving said beam at said receiver, and taking the orientation on said beam as indicating an orientation of alignment.

2. A method as in claim 1, further comprising communicating said orientation of alignment back from said receiver to said transmitter.

3. A method as in claim 2, wherein said communicating is via a cellular telephone link.

4. A method as in claim 2, wherein the transmission is via out of band communication.

5. A method as in claim 1, wherein said

transmitter has a beam divergence of γ which is narrower than a field of view of said receiver.

6. A method as in claim 1, wherein said modulating comprises changing one of frequency or amplitude or DC level of the beam.

7. A method as in claim 2, wherein said taking comprises detecting a message being received, detecting orientation information in the message that is received, and sending said orientation information to said transmitter.

8. A method as in claim 1, wherein said changing is carried out at rate faster than an ability of said receiver to report back a caught message.

9. A method as in claim 1, wherein said modulating comprises digitally modulating information on the beam.

10 . A system, comprising : a transmitter having a first angle of transmission, and transmitting a beam which includes orientation information modulated thereon; a receiver, having a second angle of reception, where said second angle of reception is wider than said angle of transmission; a beam moving element, operating to change an orientation of said transmitting beam, and produce a signal that changes a content of said orientation information to match the orientation of said transmitter; and an orientation detecting element, coupled to said receiver, determining said orientation information at said time of alignment.

11. A system as in claim 10, further comprising an out-of-band communication element, transmitting said orientation of alignment from said receiver to said transmitter.

12. A system as in claim 11, wherein said out-of- band communication element is a cellular telephone link.

13. A system as in claim 11, wherein said transmitter moving element moves said transmitter to said orientation of alignment.

14. A system as in claim 13, wherein said modulating comprises changing one of frequency or amplitude or DC level of the transmitted beam.

15. A system as in claim 13, wherein said modulating comprises digitally modulating information on the transmitted beam.