U.S. patent application number 10/124997 was filed with the patent office on 2004-10-21 for system for acquiring and maintaining reliable optical wireless links.
Invention is credited to Keller, Robert C., Melendez, Jose L..
Application Number | 20040208616 10/124997 |
Document ID | / |
Family ID | 23090800 |
Filed Date | 2004-10-21 |
United States Patent
Application |
20040208616 |
Kind Code |
A1 |
Melendez, Jose L. ; et
al. |
October 21, 2004 |
SYSTEM FOR ACQUIRING AND MAINTAINING RELIABLE OPTICAL WIRELESS
LINKS
Abstract
Disclosed is apparatus and method for establishing and
maintaining optical data transfer between a first optical
communications device (202) and a second optical communications
device (204). The devices have a feedback communications link (216)
therebetween. An optical signal (214), having a predetermined
signal profile (306), is transmitted from a transmission source
(104) within the first optical communications device to an optical
receiver (112) within the second optical communications device. The
predetermined signal profile is transmitted from the first device,
via the feedback communications link, to the second device. The
signal profile (408) of the optical signal as received by the
optical receiver is determined, and compared with the predetermined
signal profile to quantify any misalignment or movement of the
optical signal with respect to the optical receiver. The
transmission of the optical signal is then adjusted by a directing
member (106) responsive to the results of the compared profiles to
align and center the optical signal with respect to the optical
receiver. Once properly align, the optical signal may be utilized
for high speed, high bandwidth data transmission.
Inventors: |
Melendez, Jose L.; (Plano,
TX) ; Keller, Robert C.; (Plano, TX) |
Correspondence
Address: |
TEXAS INSTRUMENTS INCORPORATED
P O BOX 655474, M/S 3999
DALLAS
TX
75265
|
Family ID: |
23090800 |
Appl. No.: |
10/124997 |
Filed: |
April 18, 2002 |
Current U.S.
Class: |
398/156 |
Current CPC
Class: |
H04B 10/1127
20130101 |
Class at
Publication: |
398/156 |
International
Class: |
H04B 010/00; H04B
010/04 |
Claims
What is claimed is:
1. A method of establishing optical data transfer between first and
second optical communications devices, having a feedback
communications link therebetween, comprising the steps of:
transmitting an optical signal, having a predetermined signal
profile, from a transmission source within the first optical
communications device to an optical receiver within the second
optical communications device; transmitting the predetermined
signal profile from the first communications device, via the
feedback communications link, to the second communications device;
determining a reception profile of the optical signal as received
by the optical receiver; comparing the reception profile to the
predetermined signal profile to quantify misalignment of the
optical signal with the optical receiver; adjusting the
transmission source responsive to the quantified misalignment to
align the optical signal with optical receiver; and utilizing the
optical signal to transmit data.
Description
FIELD OF THE INVENTION
[0001] The present invention relates in general to optical wireless
communications and, more particularly, to apparatus and methods for
establishing and maintaining a reliable optical wireless data link
between to transmitting and receiving units.
BACKGROUND OF THE INVENTION
[0002] Modern data communications technologies have greatly
expanded the ability to communicate large amounts of data over many
types of communications facilities. This explosion in
communications capability not only permits the communication of
large databases, but has also enabled the digital communication of
audio and video content. This multimedia communication requires
high bandwidth communication, which is now carried out over a
variety of facilities, including telephone lines (e.g., fiber optic
and twisted pair), coaxial cable (e.g., as supported by cable
television service providers), dedicated network cabling within an
office or home location, satellite links, and wireless
telephony.
[0003] Each of these conventional communications facilities
involves certain limitations in their deployment. In the case of
communications over the telephone network, high-speed data
transmission, such as that provided by digital subscriber line
(DSL) services, must be carried out at a specific frequency range
to not interfere with voice traffic, and is currently limited in
the distance that such high-frequency communications can travel. Of
course, communications over "wired" networks, including the
telephone network, cable network or dedicated network, requires the
running of the physical wires among the locations to be served.
This physical installation and maintenance is costly, as well as
limiting to the user of the communications network.
[0004] Wireless communication facilities of course overcome the
limitation of physical wires and cabling, and provide great
flexibility to the user. Conventional wireless technologies involve
their own limitations, however. For example, in the case of
wireless telephony, the frequencies at which communications may be
carried out are regulated and controlled. Furthermore, current
wireless telephone communication of large data blocks, such as
video, is prohibitively expensive, considering the per-unit-time
charges for wireless services. Additionally, wireless telephone
communications are subject to interference among the various users
within a nearby area. Radio frequency data communication must be
carried out within specified frequencies, and is also vulnerable to
interference from other transmissions. Satellite transmission is
also currently expensive, particularly for bidirectional
communications (i.e., beyond the passive reception of television
programming).
[0005] Recently, attention has turned to optical wireless
networking for data communications. Using this technology, data is
transmitted by modulating a light beam, in much the same manner as
in the case of fiber optic telephone communications. A
photo-receiver receives the modulated light, and demodulates the
signal to retrieve the data. As opposed to fiber optic-based
optical communications, however, this approach does not use a
physical wire for transmission of the light signal. In the case of
directed optical communications, a line-of-sight relationship
between the transmitter and the receiver permits a modulated light
beam, such as that produced by a laser, to travel without the
waveguide of a fiber optic cable.
[0006] Hence, optical wireless networks could provide numerous
important advantages over other conventional communications
systems. First, high frequency light modulation can provide for
high bandwidth data communication (e.g., .about.100 Mbps-Gbps).
This high bandwidth need not be shared among multiple users,
especially when carried out over line-of-sight optical
communications between transmitters and receivers. Without other
users on the communications link, of course, the bandwidth is not
limited by interference from other users, as in the case of
wireless telephony. Modulation can also be quite simple, as
compared with multiple-user communications that require time or
code multiplexing of multiple communications signals.
Bi-directional communication can also be readily implemented
utilizing this technology. Furthermore, optical frequencies are not
currently regulated, and as such no licensing is required for the
deployment of extra-premises networks.
[0007] These attributes of optical wireless networks make this
technology attractive both for local networks within a building,
and also for external networks. Indeed, it is contemplated that
optical wireless communications may be useful in data communication
within a room, such as for communicating video signals from a
computer to a display device, such as a video projector. The costs
and effort associated with routing and placing cables in congested,
space constrained areas can be eliminated using optical wireless
links. If reliable enough, modems using optical wireless links
would be especially valuable in mobile product devices such as
laptop computers and handheld organizers.
[0008] A common problem with some conventional optical wireless
links, however, is that they utilize relatively wide, diffuse
optical beams to facilitate the acquisition and maintenance of a
light link. The ability to correctly aim a transmitted light beam
at a receiver is of importance in optical communications
technology. Wider beams can allow for greater tracking tolerance,
because exact positioning of a transmitting beam on a receiver is
not required to maintain a nominal communication link. The use of
wider beams, however, either decreases the intensity (i.e., power)
of the beam at the receiver or increases the power required to
deliver a high data rate signal, and can result in severe
limitations in the usable bandwidth of the data link(s)
established, thus decreasing the usefulness of link for many
communication applications.
[0009] Some conventional systems attempt to use narrower, more
tightly focused optical beams (e.g., laser generated collimated
beams) to provide greater communications bandwidth. When utilizing
laser-generated collimated beams, which can have quite small spot
sizes, the reliability and signal-to-noise ratio of the transmitted
signal are degraded if the aim of the transmitting beam strays from
an optimum point at the receiver. Considering that many
contemplated applications of this technology are in connection with
equipment that will not be precisely located, or that may move over
time, it is necessary to be able to rapidly and reliably adjust the
aim of the light beam.
[0010] Because the integrity of communications does rely on precise
optical alignment, conventional solutions can also present problems
in circumstances where transceiver units are subject to some
vibration or sway (e.g., a building to building link, or a mobile
to stationary link). Many conventional systems rely on a low
bandwidth direct feedback channel between transceivers, such as a
secondary telephone line modem, and some gross mechanical
adjustment (e.g., a motorized mechanical assembly housing one or
more of the transceivers) to maintain transceiver alignment. Such
conventional systems can have problems responding when high
frequency vibrations occur, and make it difficult, if not
impossible, to successfully track and maintain communications with
a moving transceiver. Finally, such conventional systems are often
not able to translate changes in signal strength, which is a common
method of measuring the integrity of a communications link, into
usable positioning information for the mechanical assembly.
[0011] Thus, when either a high degree of transceiver mobility is
required, or when transceivers may be subject to high frequency or
small scale vibrations, conventional systems are typically
incapable of providing reliable, high bandwidth communication.
SUMMARY OF THE INVENTION
[0012] Therefore, a versatile system for acquiring and maintaining
reliable optical wireless links that provides for simple and
cost-effective high performance optical communications, especially
where fixed optical units are subject to high frequency vibrations
or where optical units are in motion relative to one another, is
now needed, providing for efficient and practical utilization of
optical wireless communications in mobile products and devices
while overcoming the aforementioned limitations of conventional
methods.
[0013] The present invention provides a system for implementing an
optical communications network. The present invention determines
optical beam position information with respect to time at a
receiver of an optical wireless link unit. The optical beam is
transmitted from a second optical wireless link unit in response to
a predetermined beam steering input. The relative motion of the
units in relation to one another, and with respect to time, will
result yield beam position profiles over time. A beam steering
element effectively separates the motion into two components. The
first component corresponds directly to the beam steering input,
which is predetermined. The second component corresponds to the
relative motion, which can be of variable frequency or amplitude. A
high bandwidth return channel is provided to relay a high
resolution portrait of the beam location profile over time. The
present invention processes and utilizes this information to adjust
the beam steering element, correcting for the motion or vibrations
and maintaining the optical data link between the units. The
present invention thus provides robust and efficient optical
wireless communications within a given fixed or mobile network or
system.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] For a more complete understanding of the present invention,
including its features and advantages, reference is made to the
following detailed description, taken in conjunction with the
accompanying drawings. Corresponding numerals and symbols in the
different figures refer to corresponding parts unless otherwise
indicated.
[0015] FIG. 1 illustrates an optical transceiver in accordance with
the present invention;
[0016] FIG. 2 illustrates one embodiment of an optical
communications system in accordance with the present invention;
[0017] FIG. 3 illustrates one embodiment of a raster pattern in
accordance with the present invention;
[0018] FIG. 4 illustrates the effects of raster movement according
to the present invention; and
[0019] FIG. 5 illustrates a number of raster and detector
configurations in accordance with the present invention.
DETAILED DESCRIPTION
[0020] The present invention defines a system, comprising various
structures and methods, implementing an optical communications
network. The present invention determines optical beam position
information with respect to time at a receiver of an optical
wireless link unit. The optical beam is transmitted from a second
optical wireless link unit in response to a predetermined beam
steering input. The relative motion of the units in relation to one
another and with respect to time, will result yield beam position
profiles over time. A beam steering element effectively separates
the motion into two components. The first component corresponds
directly to the beam steering input, which is predetermined. The
second component corresponds to the relative motion, which can be
of variable frequency or amplitude. A high bandwidth return channel
is provided to relay a high resolution portrait of the beam
location profile over time. This information is processed and
utilized by the present invention to adjust the beam steering
element, correcting for the motion or vibrations and maintaining
the optical data link between the units. The present invention
provides robust and efficient optical wireless communications
within a given fixed or mobile network or system.
[0021] It should be understood that the principles and applications
disclosed herein can be applied to a wide range of optical
communications systems utilizing a variety of optical transmission
and reception technologies. For purposes of explanation and
illustration, the present invention is hereafter described in
reference to several specific embodiments of high performance
optical communication systems. The present invention, however, is
equally applicable in any number of communication networks that
might enjoy the benefits and advantages provided by the present
invention.
[0022] The present invention is now described beginning in
reference to FIG. 1, which illustrates an optical transceiver 100
according to the present invention. Transceiver 100 comprises a
housing 102, light source 104 disposed within housing 102, beam
directing member 106 disposed within housing 102, transmit aperture
108, receive aperture 110, optical detector 112 disposed within
housing 102, and a processor member 114. Housing 102 may comprise
any application appropriate structure that will house the necessary
elements, such as a molded plastic enclosure or even a
semiconductor substrate. Source 104 may comprise a number of
appropriate devices and systems, but for purposes of explanation
and illustration, will be depicted and treated as a collimated beam
generating laser. Source 104 will operate responsive to processor
114, or some other processor means, to transmit high speed data
communications via the light that it sources. Generally, member 106
will be interposed, either directly or indirectly, between source
104 and aperture 108 such that a transmitted light path 116 from
source 104 is directed to member 106 and then out of housing 102
through aperture 108 to a receiving unit. Aperture 108 may comprise
any desired structure, from a simple opening in housing 102 to any
number of optical filters or lenses.
[0023] Beam directing member 106 is responsively coupled via link
118 to processor 114, and comprises an optical element or elements
that provide the ability to manipulate and redirect light path 116
at very high speed and with very fine resolution. While there are a
number of possible configurations and apparatus (e.g., series of
optical lenses and filters) that would suffice, one embodiment of
element 106 comprises an analog, 2-axis micro mirror. As those
skilled in the art should be aware, such a micromicron provides for
electromagnetic control responsive to processor 114, providing very
fast light deflection in very fine increments. Other elements have
similar responsiveness may be utilized according to the present
invention.
[0024] Detector 112 may comprise any suitable photo detection
device, or array of devices, disposed within housing 102 in
proximity to aperture 110 to receive an incoming light path 120.
Alternatively, detector 112 could be disposed directly within
aperture 110 or directly upon an outer surface of housing 102.
Detector 112 is coupled to processor 114 via link 122. Processor
114 may be disposed within, or as part of, housing 102, or
alternatively, may be remotely located apart from housing 102. In
the latter case, links 118 and 122 may comprise appropriate
physical (e.g., wiring) or wireless (e.g., RF) signal paths between
housing 102 and processor 114. Processor 114 may comprise any
appropriate processor device (e.g., DSP) or processing capacity
(e.g., personal computer) providing the ability to process data and
algorithms in accordance with this invention. Finally, source 104
may be responsively coupled to processor 114 via link 124, or
alternatively, may be activated responsive to some other desired
external stimulus (e.g., another separate processor). In operation,
source 104 initiates data communications via light path 116
responsive to some stimulus (e.g., a signal from processor 114).
Light path 116 proceeds to member 106 where the direction of path
116 may be altered in varying degrees as it is directed onto and
out of aperture 108 towards a desired target. Processor 114 can
signal member 106 to alter, in varying degrees, the direction of
path 116. Incoming light path 120 is received through aperture 110
by detector 112, and desired data is delivered to processor 114 via
link 122.
[0025] Referring now to FIG. 2, a simple communication system 200
according to the present invention is illustrated. System 200
comprises a first optical transceiver 202 and a second optical
transceiver 204 of the type described in reference to FIG. 1.
Although particular configuration may be varied depending upon
system requirements, actual materials used, and desired
performance, for ease of reference FIG. 2 depicts the transmit
aperture 206 of transceiver 202 aligned with the receive aperture
208 of transceiver 204. Similarly, the receive aperture 210 of
transceiver 202 is aligned with the transmit aperture 212 of
transceiver 204. Generally, these initial alignments can be made
manually to within a few degrees accuracy. Assuming that
transceiver 202 is initiating communications, it will direct a
transmit communications beam 214 at transceiver 204. System 200
will have a feedback path established between transceivers 202 and
204. This feedback path may take the form of a separate physical or
wireless communications link 216 between the transceivers, or may
comprise communication via a communications beam 218 from
transceiver 204 to transceiver 202. In general, this feedback path
will be used to communicate a variety of information between the
transceivers to successfully target beam 214 and, once successfully
targeted, to keep the high speed data transfer occurring through
beam 214 locked on. A separate link 216 may be used as a temporary
feedback path only to initiate communications, at which point
feedback operation may be switched to a direct optical link 218
between the two transceivers. Alternatively, a diffuse optical beam
link between the two transceivers may be used as the initial
feedback link, until the high speed direct optical communications
can be established. A number of such possibilities, depending upon
particular design and performance requirements, will be apparent
upon reference to this specification to those skilled in the
art.
[0026] The present invention communicates a variety of information
between the optical communication units. Utilizing the present
invention, a transmit beam 214 may be initiated with a known signal
strength, and rastered in a predetermined pattern. This information
is communicated to the receiving unit 204 via the feedback path.
Unit 204 then compares, via the appropriate processor algorithms,
the signal strength and profile as measured at its detector with
the predetermined signal information. Any deviation or difference
data is analyzed and communicated back, via the feedback path to
transmitting unit 202, which may then use that data to adjust, via
its beam directing member, the direction of beam 214. This process
is described in greater detail with reference now to FIGS. 3 and
4.
[0027] FIG. 3a depicts an illustrative raster pattern scheme 300. A
transmitted light beam is traced in a pattern 302 around detector
304. Although not completely symmetrical, pattern 302 is
effectively centered on detector 304. FIG. 3b depicts a plot 306
illustrating the characteristics of the signal received at detector
304 at various points t.sub.0, t.sub.1, t.sub.2, and t.sub.3 along
pattern 302. Plot 306 provides a profile of specific signal
intensity and duration data that can be algorithmically compared
and analyzed to determine whether the raster pattern 302 is
centered on detector 304 or not. FIG. 4 provides an illustration of
effects on signal profile if the transmitted raster pattern is
moved or moving off center. FIG. 4 depicts four instances 400, 402,
404, and 406 of raster pattern 302 as it is gradually moved off
center to the side of detector 304. Plot 408 depicts the signal
profile data as measured over four t.sub.3 intervals corresponding
to the four instances 400-406 of raster pattern 302.
[0028] As illustrated, plot 408 deviates measurably from the
predetermined pattern in plot 306. The profile information for the
transmitted beam raster pattern is communicated, via the feedback
path, to the receiving unit. The processor of the receiving unit
utilizes this information to determine any deviation in the raster
pattern it actually receives at its detector. This deviation is
analyzed, and associated with either the static variance from
center, or movement away from center, of pattern 302. Once the
variance or movement is analyzed, this information may be
communicated back to the transmitting unit so that it makes
appropriate adjustments, via its processor and beam steering
member, to center the transmitted beam, effectively locking it on.
This process is iterated continuously to maintain stable high speed
optical communication between the two transceivers.
[0029] As illustrated in FIG. 5, a large number of raster and
detector array patterns are possible. Depending upon particular
design and application constraints, raster patterns and detector
configurations may be optimized. Symmetrical raster patterns,
although useful, are not absolutely necessary; only patterns in
which some variance in the regularity of the pattern and its
resulting signal profile may be readily identified. As an
alternative to, or in addition to, rastering the transmit beam, one
embodiment includes a primary signal detector, which would be
utilized for actual data communications, arrayed with a number of
positional detectors, which would be utilized only to analyze the
relative positional intensity of the transmitted beam. In this
embodiment, the additional detectors provide a positional
distribution, increasing accuracy of the signal profile and
tracking process. Such an embodiment could detect relative movement
faster (i.e., without completing an entire raster cycle), and thus
increase the speed and efficiency of the tracking process. In
addition, certain applications may incorporate the use of light
pipes or other light directing devices to better analyze varying
beam widths and intensities; enhancing detector responsiveness and
profile characteristics. All such variations are comprehended by
the present invention.
[0030] Thus, utilizing the present invention, designers can provide
a high speed, high bandwidth communications utilizing optical
wireless technology. Data communications will be reliable and cost
effective, providing the ability to implement optical wireless
technology in a number of applications where such technology was
impossible or impractical to use.
[0031] While this invention has been described with reference to
illustrative embodiments, this description is not intended to be
construed in a limiting sense. Upon reference to the description,
it will be apparent to persons skilled in the art that various
modifications and combinations of the illustrative embodiments as
well as other embodiments of the invention can be made without
departing from the spirit and scope of the invention. It is
therefore intended that the appended claims encompass any such
modifications or embodiments.
* * * * *