U.S. patent application number 13/342468 was filed with the patent office on 2012-05-03 for transponder systems and methods for radio-over-fiber (rof) wireless picocellular systems.
Invention is credited to Jacob George, William Carl Hurley, Andrey Kobyakov, Michael Sauer.
Application Number | 20120105208 13/342468 |
Document ID | / |
Family ID | 39675673 |
Filed Date | 2012-05-03 |
United States Patent
Application |
20120105208 |
Kind Code |
A1 |
George; Jacob ; et
al. |
May 3, 2012 |
TRANSPONDER SYSTEMS AND METHODS FOR RADIO-OVER-FIBER (RoF) WIRELESS
PICOCELLULAR SYSTEMS
Abstract
Transponder systems and methods for radio-over-fiber (RoF)
wireless picocellular system are disclosed. One type of transponder
system includes a RoF transponder used in combination with at least
one radiation-reflector assembly to provide for enhanced antenna
directivity of the transponder. Another type of transponder system
is a transponder node assembly, wherein two or more transponders
are integrated into a single assembly, thereby reducing cost while
facilitating RoF wireless picocellular system deployment. Another
type of transponder system provides one or more transponders in a
RoF wireless picocellular system with radio-frequency
identification (RFID) tags, and uses an RFID tag reader to locate
and read information from the transponders, as well as to perform
transponder mode selection. Another type of transponder system is
directed to a tether cable assembly that includes a
dispensible/retractable coiled tether cable housed in a protective
housing for connecting the tether cable to a transponder.
Inventors: |
George; Jacob; (Horseheads,
NY) ; Sauer; Michael; (Corning, NY) ;
Kobyakov; Andrey; (Painted Post, NY) ; Hurley;
William Carl; (Hickory, NC) |
Family ID: |
39675673 |
Appl. No.: |
13/342468 |
Filed: |
January 3, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11703016 |
Feb 6, 2007 |
8111998 |
|
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13342468 |
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Current U.S.
Class: |
340/10.1 |
Current CPC
Class: |
G06K 19/0723 20130101;
H04B 10/25756 20130101; H04W 88/085 20130101; G06K 7/10178
20130101 |
Class at
Publication: |
340/10.1 |
International
Class: |
G06K 7/01 20060101
G06K007/01 |
Claims
1. A transponder unit, comprising: at least one transponder
configured to receive downlink radio-frequency (RF) service signals
in a distributed antenna system and distribute the downlink RF
service signals to at least one antenna to be transmitted
wirelessly; and a RFID tag positioned relative to the at least one
transponder, the RFID tag configured to receive an RFID
interrogation signal from a RFID reader and provide a return RFID
signal to the RFID reader in response.
2. The transponder unit of claim 1, wherein the return RFID signal
includes no RFID tag data.
3. The transponder unit of claim 1, wherein the return RFID tag
signal contains RFID tag data that includes at least one property
selected from a group of properties comprising: a transponder
location, GPS coordinates, an installation date, a maintenance
history, an operating frequency or frequencies, and an antenna
location or locations.
4. The transponder unit of claim 1, wherein the RFID tag is
electrically connected to the at least one transponder, wherein the
RFID tag is adapted to provide an electrical signal to the at least
one transponder, wherein the at least one transponder has two or
more operational modes, and wherein the at least one transponder is
adapted to be responsive to said electrical signal to switch its
operation mode.
5. The transponder unit of claim 1, wherein the RFID interrogation
signal is comprised of a ping signal.
6. The transponder unit of claim 1, wherein the RFID tag is
addressable by the RFID interrogation signal.
7. The transponder unit of claim 1, wherein the RFID tag is
electrically coupled to at least one transponder.
8. The transponder unit of claim 7, wherein the RFID tag is further
configured to communicate receipt of the RFID interrogation signal
to at least one transponder.
9. The transponder unit of claim 8, wherein the RFID tag is
configured to communicate a mode signal to the at least one
transponder based on the receipt of the RFID interrogation signal
by the RFID tag.
10. The transponder unit of claim 9, wherein the at least one
transponder is configured to change operational mode based on
receipt of the mode signal.
11. The transponder unit of claim 1, wherein the RFID tag is
configured to receive the RFID interrogation signal over a downlink
communication link carrying the downlink RF service signals.
12. The transponder unit of claim 1, wherein the RFID tag is
comprised of: a microcircuit configured to process the RFID
interrogation signal; a memory unit electrically coupled to the
microcircuit, the memory unit configured to store at least one of
RFID tag data and data associated with the at least one
transponder; and an antenna electrically coupled to the
microcircuit, the antenna configured to receive the RFID
interrogation signal.
13. The transponder unit of claim 1, wherein the RFID tag is
further configured to be powered by the RFID interrogation
signal.
14. The transponder unit of claim 1, wherein the at least one
transponder is located in a housing of the at least one
transponder.
15. The transponder unit of claim 1, wherein the at least one
transponder is located in a communications cable configured to
carry the downlink RF service signals.
16. The transponder unit of claim 1, wherein the at least one
transponder is further configured to receive uplink RF service
signals from a client device through the at least one antenna and
distribute the uplink RF service signals to a head-end unit.
17. The transponder unit of claim 1, wherein the at least one
transponder is comprised of at least one RoF transponder configured
to receive optical radio-frequency (RF) service signals.
18. The transponder unit of claim 17, wherein the at least one RoF
transponder further comprises an optical-to-electrical (O-E)
converter configured to convert the optical RF service signals to
electrical RF service signals.
19. The transponder unit of claim 17, wherein the at least one RoF
transponder further comprises an electrical-to-optical (E-O)
converter configured to convert the electrical RF service signals
to optical RF service signals.
20. A transponder radio-frequency identification (RFID) system,
comprising: a RFID reader configured to communicate a RFID
interrogation signal to a RFID tag and cause the RFID tag to emit a
return RFID signal in response; a plurality of transponders each
configured to receive downlink radio-frequency (RF) service signals
in a distributed antenna system and distribute the downlink RF
service signals to at least one antenna to be transmitted
wirelessly; and a RFID tag positioned relative to each of the
plurality of transponders, the RFID tags each configured to receive
the RFID interrogation signal from the RFID reader and provide the
return RFID signal to the RFID reader in response, wherein the
return RFID signal comprises RFID tag data.
21. The transponder RFID system of claim 20, wherein the RFID
interrogation signal is comprised of a ping signal.
22. The transponder RFID system of claim 20, wherein the RFID tag
is configured to receive the RFID interrogation signal over a
downlink communication link carrying the downlink RF service
signals.
23. The transponder RFID system of claim 20, further comprising a
head-end unit configured to distribute the downlink RF service
signals to the plurality of transponders.
24. The transponder RFID system of claim 23, wherein the RFID
reader is included in the head-end unit.
25. The transponder RFID system of claim 20, wherein each of a
plurality of RFID tags are addressable by the RFID interrogation
signal.
26. The transponder RFID system of claim 20, further comprising at
least one database associated with the RFID reader, the at least
one database configured to store RFID tag information associated
with the plurality of transponders.
27. The transponder RFID system of claim 25, wherein the RFID
reader is further configured to sequentially poll each of the
plurality of RFID tags.
28. The transponder RFID system of claim 20, wherein the RFID
reader is further configured to communicate the RFID tag data to a
network.
29. The transponder RFID system of claim 28, wherein the RFID
reader is further configured to communicate the RFID tag data to a
network wirelessly.
30. The transponder RFID system of claim 20, wherein the RFID
reader further comprises a global positioning system (GPS) unit
configured to provide GPS data.
31. The transponder RFID system of claim 30, wherein the RFID
reader is further configured to store the GPS data associated with
the RFID tag data to store location information for the plurality
of transponders.
32. The transponder RFID system of claim 30, wherein the RFID
reader is further configured to communicate the GPS data with the
RFID tag data to communicate location information for the plurality
of transponders.
33. The transponder RFID system of claim 20, wherein at least one
transponder is further configured to receive uplink RF service
signals from a client device through the at least one antenna and
distribute the uplink RF service signals to a head-end unit.
34. The transponder RFID system of claim 20, wherein the at least
one transponder is comprised of at least one RoF transponder
configured to receive optical radio-frequency (RF) service signals.
Description
RELATED APPLICATION
[0001] The present application is a continuation of U.S. patent
application Ser. No. 11/703,016 filed on Feb. 6, 2007, the content
of which is relied upon and incorporated herein by reference in its
entirety, and the benefit of priority under 35 U.S.C. .sctn.120 is
hereby claimed.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to wireless
communication systems, and in particular relates to transponders
and transponder systems and methods used in optical-fiber-based
wireless picocellular systems for radio-over-fiber (RoF)
communication.
[0004] 2. Technical Background
[0005] Wireless communication is rapidly growing, with
ever-increasing demands for high-speed mobile data communication.
As an example, so-called "wireless fidelity" or "WiFi" systems and
wireless local area networks (WLANs) are being deployed in many
different types of areas (coffee shops, airports, libraries, etc.).
Wireless communication systems communicate with wireless devices
called "clients," which must reside within the wireless range or
"cell coverage area" in order to communicate with the access point
device.
[0006] One approach to deploying a wireless communication system
involves the use of "picocells," which are radio-frequency (RF)
coverage areas having a radius in the range from about a few meters
up to about 20 meters. Because a picocell covers a small area,
there are typically only a few users (clients) per picocell.
Picocells also allow for selective wireless coverage in small
regions that otherwise would have poor signal strength when covered
by larger cells created by conventional base stations.
[0007] In conventional wireless systems, picocells are created by
and centered on a wireless access point device connected to a
head-end controller. The wireless access point device includes
digital information processing electronics, a RF
transmitter/receiver, and an antenna operably connected to the RF
transmitter/receiver. The size of a given picocell is determined by
the amount of RF power transmitted by the access point device, the
receiver sensitivity, antenna gain, and the RF environment, as well
as by the RF transmitter/receiver sensitivity of the wireless
client device. Client devices usually have a fixed RF receiver
sensitivity, so that the above-mentioned properties of the access
point device mainly determine the picocell size. Combining a number
of access point devices connected to the head-end controller
creates an array of picocells that cover an area called a
"picocellular coverage area." A closely packed picocellular array
provides high per-user data-throughput over the picocellular
coverage area.
[0008] Prior art wireless systems and networks are wire-based
signal distribution systems where the access point devices are
treated as separate processing units linked to a central location.
This makes the wireless system/network relatively complex and
difficult to scale, particularly when many picocells need to cover
a large region. Further, the digital information processing
performed at the access point devices requires that these devices
be activated and controlled by the head-end controller, which
further complicates the distribution and use of numerous access
point devices to produce a large picocellular coverage area.
[0009] While RoF wireless picocellular systems are generally
robust, there are some limitations. One limitation relates to the
radiation pattern from the transponder antenna. Though microstrip
antennas have a directional radiation pattern, they are generally
more expensive and more complicated to integrate into a RoF cable
than the simpler and less expensive dipole antennas. However,
dipole antennas in the form of wires radiate omnidirectionally in a
plane perpendicular to the RoF cable. This wastes energy and also
interferes with other picocells, such as those formed in the floor
above the ceiling in which the RoF cable is deployed.
[0010] Another limitation relates to the need for having a
transponder for each picocell. The typical RoF transponder includes
a mechanical housing, a laser, a photodetector, a printed circuit
board with RF electronics, optical connectors, and electrical
connectors. The relatively small size of picocells typically
requires that the transponders be spaced apart by between 5 to 10
meters or so. A RoF wireless picocellular system would be easier to
deploy and be less expensive if the number of transponders could be
reduced.
[0011] A further limitation relates to locating RoF transponders
after they are deployed. The typical RoF wireless picocellular
system includes one or more RoF cables that are hidden in a
building's infrastructure, such as above a suspended ceiling. This
makes it difficult for service personnel to locate a problematic
transponder.
[0012] Another limitation relates to deploying the RoF
transponders. One way of deploying transponders is to tether them
to respective access points in the RoF cable using a tether cable.
However, the position of each transponder relative to the RoF cable
tends to be different, requiring different lengths of tether cable.
This requires that the slack in some of the tether cables be
addressed by coiling the tether or otherwise storing the excess
tether cable. In addition, tether cabling needs to be packaged for
shipping in a manner that lends itself to ease of installation
since quicker system installation translates into cost savings.
SUMMARY OF THE INVENTION
[0013] One aspect of the invention is a transponder system with
enhanced antenna directivity, for use in a RoF wireless
picocellular system. The system includes a transponder having a
converter pair unit adapted to convert radio-frequency (RF)
electrical signals into optical signals and vice versa, and an
antenna system having at least one antenna element operably coupled
to the converter pair unit. The system also includes at least one
radiation-reflecting member arranged relative to the at least one
antenna element so as to provide enhanced antenna directivity as
compared to not having the at least one radiation-reflecting
member.
[0014] Another aspect of the invention is a transponder node
assembly for a RoF wireless picocellular system. The system
includes two or more converter pairs, with each converter pair
adapted to convert RF electrical signals into RF optical signals
and vice versa. The system also includes corresponding two or more
antenna systems electrically connected to the corresponding two or
more converter pairs. The system also includes a protective housing
that houses the two or more converter pairs.
[0015] Another aspect of the invention is a transponder
radio-frequency identification (RFID) system that includes a
radio-over-fiber (RoF) transponder adapted to convert
radio-frequency (RF) electrical signals to RF optical signals and
vice versa. The system also includes a RFID tag positioned relative
to the transponder and adapted to produce a RFID-tag signal. In one
case, the RFID-tag signal contains RFID tag data that includes at
least one property of the transponder. In another case, the
RFID-tag signal contains no RFID tag data and acts as a ping signal
to locate the RFID tag. The system also includes a RFID tag reader
adapted to cause the RFID tag to emit the RFID-tag signal and to
detect and process the RFID tag signal.
[0016] Another aspect of the invention is a tether cable assembly
for a RoF wireless picocellular system having an optical fiber
cable. The assembly includes a tether cable having at least one
optical fiber, at least one electrical wire, and proximal and
distal ends. The assembly also includes a spool around which the
tether cable can be coiled and uncoiled. The assembly further
includes a housing surrounding the spool and having a first slot
sized to pass the tether cable. The assembly also has a RoF
transponder connected to the tether cable proximate end. The tether
cable distal end is adapted to operably couple to the optical fiber
cable.
[0017] Additional features and advantages of the invention are set
forth in the detailed description that follows, and will be readily
apparent to those skilled in the art from that description or
recognized by practicing the invention as described herein,
including the detailed description that follows, the claims, and
the appended drawings.
[0018] It is to be understood that both the foregoing general
description and the following detailed description present
embodiments of the invention, and are intended to provide an
overview or framework for understanding the nature and character of
the invention as it is claimed. The accompanying drawings are
included to provide a further understanding of the invention, and
are incorporated into and constitute a part of this specification.
The drawings illustrate various embodiments of the invention and,
together with the description, serve to explain the principles and
operations of the invention.
[0019] Accordingly, various basic electronic circuit elements and
signal-conditioning components, such as bias tees, RF filters,
amplifiers, power dividers, etc., are not all shown in the drawings
for ease of explanation and illustration. The application of such
basic electronic circuit elements and components to the systems of
the present invention will be apparent to one skilled in the
art.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a schematic diagram of a generalized embodiment of
an optical-fiber-based wireless picocellular system showing a
head-end unit optically coupled to a transponder via an optical
fiber RF communication link, along with the picocell formed by the
transponder and a client device within the picocell;
[0021] FIG. 2 is a detailed schematic diagram of an example
embodiment of the system of FIG. 1, showing the details of the
head-end unit, the optical fiber RF communication link and the
transponder;
[0022] FIG. 3 is a close-up view of an alternative example
embodiment for the transponder of the wireless system of FIG. 2,
wherein the transponder includes a transmitting antenna and a
receiving antenna within the transponder housing, and the converter
pair unit includes the DC power converter;
[0023] FIG. 4 is a schematic diagram of an example embodiment of an
optical-fiber-based wireless picocellular system according to the
present invention that utilizes a central head-end station and
multiple transponders arranged along an optical fiber cable;
[0024] FIG. 5 is a detailed schematic diagram of an example
embodiment of the central head-end station of the system of FIG.
4;
[0025] FIG. 6A is a close-up cut-away view of the optical fiber
cable of the system of FIG. 4, showing two transponders, the
downlink and uplink optical fibers, and the electrical power line
that powers the transponders;
[0026] FIG. 6B is a schematic diagram similar to FIG. 6,
illustrating an example embodiment wherein transponders lie outside
of the protective outer jacket of the optical fiber cable.
[0027] FIG. 7 is schematic diagram illustrating a transponder in
the optical fiber cable along with the corresponding picocell, and
showing the exchange of electromagnetic RF service signals
(downlink and uplink signals) between the transponder and client
devices within the picocell;
[0028] FIG. 8 is a close-up schematic diagram of a section of
optical fiber cable and a transponder incorporated therein,
illustrating an example embodiment of the present invention wherein
the transponder includes a single dipole antenna element and a
radiation-reflector assembly arranged on the optical fiber cable
relative to the single dipole antenna;
[0029] FIG. 9 and FIG. 10 are close-up schematic diagrams of the
antenna element and radiation-reflector assembly of FIG. 8,
illustrating how an upward-traveling downlink electromagnetic
signal is reflected by the radiation-reflector assembly;
[0030] FIG. 11 is a perspective schematic diagram of an example
embodiment of the radiation-reflector assembly of the present
invention;
[0031] FIG. 12 is an edge-on view of the radiation-reflector
assembly of FIG. 11;
[0032] FIG. 13 is a schematic diagram similar to FIG. 8, showing an
example embodiment of a transponder that includes two antenna
elements that operate at different frequencies and two
corresponding radiation-reflector assemblies;
[0033] FIG. 14 is a detailed schematic side view of an example
embodiment wherein a transponder is attached to the side of an
optical fiber cable;
[0034] FIG. 15 is a schematic diagram illustrating an end-on view
of the optical fiber cable and transponder of FIG. 14;
[0035] FIG. 16 is a schematic diagram of an example embodiment
wherein the transponder is located remote from the optical fiber
cable;
[0036] FIG. 17 is a schematic diagram similar to FIG. 16,
illustrating an example embodiment wherein each antenna element has
associated therewith a pair of radiation-reflector assemblies
arranged on adjacent sides of the transponder housing;
[0037] FIG. 18 is a schematic cross-sectional diagram of a building
infrastructure and an optical fiber cable deployed therein,
illustrating an example application of the transponder illustrated
in FIG. 17;
[0038] FIG. 19 is a schematic diagram similar to FIG. 16,
illustrating a transponder wherein the antenna elements are located
in optical fiber cable rather than within the remotely located
transponder housing, and wherein the radiation-reflector assemblies
are fixed to the optical fiber cable relative to the antenna
elements;
[0039] FIG. 20 is a schematic diagram similar to FIG. 16,
illustrating an example embodiment wherein a single
radiation-reflector assembly is used to reflect radiation from two
separate antenna elements;
[0040] FIG. 21 is a schematic diagram of an example embodiment of a
transponder node assembly according to the present invention that
integrates two or more transponders, with the transponder node
assembly shown incorporated into an optical fiber cable;
[0041] FIG. 22 is a close-up detailed schematic diagram of an
example embodiment of the transponder node assembly of FIG. 21;
[0042] FIG. 23 is a close-up schematic diagram of a portion of the
building infrastructure shown in FIG. 18, including an optical
fiber cable deployed in the ceiling space above the drop-ceiling,
with remote transponders operably coupled to the optical fiber
cables with respective tether cables;
[0043] FIG. 24 is a close-up view of FIG. 23, illustrating an
example embodiment of the transponder therein having a transponder
RFID tag, and also showing a RFID-tag reader in the room below the
drop ceiling, wherein the transponder RFID tag and the RFID-tag
reader comprise a transponder RFID system;
[0044] FIG. 25 is a more detailed schematic diagram of the
transponder RFID system of FIG. 24, shown in a different
orientation for ease of illustration, wherein the RFID tag system
includes a database unit operably coupled to the RFID-tag
reader;
[0045] FIG. 26 is a schematic diagram of an example embodiment of
the transponder RFID system of the present invention similar to
that shown in FIG. 23, illustrating an example embodiment wherein
transponders are located remote from optical fiber cable via tether
cables and wherein the RFID tags are located on the optical fiber
cable at or near where the tether cables connect to the optical
fiber cable;
[0046] FIG. 27 is a schematic diagram of an example embodiment of
the transponder RFID system of the present invention similar to
that shown in FIG. 26, but wherein the transponders and the
associated RFID tags are located within optical fiber cable;
[0047] FIG. 28 is a schematic diagram illustrating an example
embodiment of the transponder RFID system of the present invention
similar to that shown in FIG. 24, wherein the RFID tag is
electrically connected to the transponder;
[0048] FIG. 29 is a perspective schematic diagram similar to FIG.
26, illustrating an example of how the optical fiber cable and the
remote transponder can be arranged in the ceiling space above a
section of the drop-ceiling using a tether cable;
[0049] FIG. 30 is a top-down view of an example tether cable
assembly according to the present invention wherein the tether
cable is stored within a housing and deployed and refracted as
needed;
[0050] FIG. 31 is a side view of the tether cable assembly of FIG.
30;
[0051] FIG. 32 is a cross-sectional diagram of an example
embodiment of the tether cable used in the tether cable assembly of
FIG. 31, wherein the tether cable has a rectangular cross-section
and supports two optical fibers and two electrical power lines;
[0052] FIG. 33 is a schematic diagram of the tether cable assembly
similar to the side view of FIG. 31, but without the housing,
showing an example internal configuration that includes a spool
operably connected to a retracting member, and a locking device
that engages the tether cable;
[0053] FIG. 34 is a top-down view of the spool shown in FIG. 33,
but with the top flange removed to show the coiled tether cable
with one tether cable end located within the hollow central
post;
[0054] FIG. 35 is a top-down view similar to FIG. 34, but
illustrating an example embodiment wherein the tether cable winds
around the central post in both directions so that both tether
cable ends can reside outside of the tether cable assembly
housing;
[0055] FIG. 36 is a schematic cut-away diagram of an example
embodiment wherein the tether cable assembly includes a transponder
and is used to connect the transponder to an optical fiber cable;
and
[0056] FIG. 37 is a schematic diagram similar to FIG. 29, showing
how a tether cable assembly with the dual winding configuration of
FIG. 35 is used to remotely connect a transponder to an optical
fiber cable.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0057] Reference is now made in detail to the present preferred
embodiments of the invention, examples of which are illustrated in
the accompanying drawings. Whenever possible, the same or analogous
reference numbers are used throughout the drawings to refer to the
same or like parts.
Generalized Optical-Fiber-Based Rof Wireless Picocellular
System
[0058] FIG. 1 is a schematic diagram of a generalized embodiment of
an optical-fiber-based RoF wireless picocellular system 10
according to the present invention. System 10 includes a head-end
unit 20, one or more transponder units ("transponder") 30 and an
optical fiber RF communication link 36 that optically couples the
head-end unit to the transponder. In an example embodiment, optical
fiber RF communication link 36 includes at least one optical fiber,
and preferably two optical fibers (e.g., uplink and downlink
optical fibers, as discussed below). As discussed in detail below,
system 10 is adapted to form a picocell 40 substantially centered
about transponder 30. The one or more transponders 30 form a
picocellular coverage area 44. Head-end unit 20 is adapted to
perform or to facilitate any one of a number of RF-over-fiber
applications, such as radio-frequency identification (RFID),
wireless local-area network (WLAN) communication, or cellular phone
service. Shown within picocell 40 is a client device 45 in the form
of a computer. Client device 45 includes an antenna 46 (e.g., a
wireless card) adapted to receive and/or send electromagnetic RF
signals.
[0059] FIG. 2 is a detailed schematic diagram of an example
embodiment of system 10 of FIG. 1. In an example embodiment,
head-end unit 20 includes a service unit 50 that provides
electrical RF service signals for a particular wireless service or
application. In an example embodiment, service unit 50 provides
electrical RF service signals by passing (or conditioning and then
passing) such signals from one or more outside networks 52, as
described below. In a particular example embodiment, this includes
providing WLAN signal distribution as specified in the IEEE 802.11
standard, i.e., in the frequency range from 2.4 to 2.5 GHz and from
5.0 to 6.0 GHz. In another example embodiment, service unit 50
provides electrical RF service signals by generating the signals
directly. In another example embodiment, service unit 50
coordinates the delivery of the electrical RF service signals
between client devices within picocellular coverage area 44.
[0060] Service unit 50 is electrically coupled to an
electrical-to-optical (E/O) converter 60 that receives an
electrical RF service signal from the service unit and converts it
to corresponding optical signal. In an example embodiment, E/O
converter 60 includes a laser suitable for delivering sufficient
dynamic range for the RF-over-fiber applications of the present
invention, and optionally includes a laser driver/amplifier
electrically coupled to the laser. Examples of suitable lasers for
E/O converter 60 include laser diodes, distributed feedback (DFB)
lasers, Fabry-Perot (FP) lasers, and vertical cavity surface
emitting lasers (VCSELs).
[0061] Head-end unit 20 also includes an optical-to-electrical
(O/E) converter 62 electrically coupled to service unit 50. O/E
converter 62 receives an optical RF service signal and converts it
to a corresponding electrical signal. In an example embodiment, O/E
converter is a photodetector, or a photodetector electrically
coupled to a linear amplifier. E/O converter 60 and O/E converter
62 constitute a "converter pair unit" 66.
[0062] In an example embodiment, service unit 50 includes a RF
signal modulator/demodulator unit 70 that generates an RF carrier
of a given frequency and then modulates RF signals onto the
carrier, and that also demodulates received RF signals. Service
unit 50 also includes a digital signal processing unit ("digital
signal processor") 72, a central processing unit (CPU) 74 for
processing data and otherwise performing logic and computing
operations, and a memory unit 76 for storing data, such as RFID tag
information or data to be transmitted over the WLAN. In an example
embodiment, the different frequencies associated with the different
signal channels are created by modulator/demodulator unit 70
generating different RF carrier frequencies based on instructions
from CPU 74. Also, as described below, the common frequencies
associated with a particular combined picocell are created by
modulator/demodulator unit 70 generating the same RF carrier
frequency.
[0063] With continuing reference to FIG. 2, in an example
embodiment transponder 30 includes a converter pair 66, wherein the
E/O converter 60 and the O/E converter 62 therein are electrically
coupled to an antenna system 100 via a RF signal-directing element
106, such as a circulator. Signal-directing element 106 serves to
direct the downlink and uplink electrical RF service signals, as
discussed below. In an example embodiment, antenna system 100
includes one or more patch antennas, such as disclosed in U.S.
patent application Ser. No. 11/504,999 filed Aug. 16, 2006, which
is assigned to the present assignee and which patent application is
incorporated herein by reference. Transponder 30 also includes a
housing 102 that in an example embodiment houses some or all of the
various transponder elements. In an example embodiment, some or all
of antenna system 100 lies outside of housing 102. In an example
embodiment, housing 102 houses only the elements making up
converter pair unit 66.
[0064] FIG. 3 is a close-up view of an alternative example
embodiment for transponder 30 that includes two antennae: a
transmitting antenna 100T electrically coupled to O/E converter 62,
and a receiving antenna 100R electrically coupled to O/E converter
60. The two-antenna embodiment obviates the need for RF
signal-directing element 106. Note also that the example embodiment
of transponder 30 in FIG. 3 includes DC power converter 180 within
converter pair unit 66, and that antenna system 100 is within
housing 102.
[0065] Transponders 30 of the present invention differ from the
typical access point device associated with wireless communication
systems in that the preferred embodiment of the transponder has
just a few signal-conditioning elements and no digital information
processing capability. Rather, the information processing
capability is located remotely in head-end unit 20, and in a
particular example, in service unit 50. This allows transponder 30
to be very compact and virtually maintenance free. In addition, the
preferred example embodiment of transponder 30 consumes very little
power, is transparent to RF signals, and does not require a local
power source, as described below.
[0066] With reference again to FIG. 2, an example embodiment of
optical fiber RF communication link 36 includes a downlink optical
fiber 136D having an input end 138 and an output end 140, and an
uplink optical fiber 136U having an input end 142 and an output end
144. The downlink and uplink optical fibers 136D and 136U optically
couple converter pair 66 at head-end unit 20 to the converter pair
at transponder 30. Specifically, downlink optical fiber input end
138 is optically coupled to E/O converter 60 of head-end unit 20,
while output end 140 is optically coupled to O/E converter 62 at
transponder 30. Similarly, uplink optical fiber input end 142 is
optically coupled to E/O converter 60 of transponder 30, while
output end 144 is optically coupled to O/E converter 62 at head-end
unit 20.
[0067] In an example embodiment, the optical-fiber-based wireless
picocellular system 10 of the present invention employs a known
telecommunications wavelength, such as 850 nm, 1300 nm, or 1550 nm.
In another example embodiment, system 10 employs other less common
but suitable wavelengths such as 980 nm.
[0068] Example embodiments of system 10 include either single-mode
optical fiber or multimode optical fiber for downlink and uplink
optical fibers 136D and 136U. The particular type of optical fiber
depends on the application of system 10. For many in-building
deployment applications, maximum transmission distances typically
do not exceed 300 meters. The maximum length for the intended
RF-over-fiber transmission needs to be taken into account when
considering using multi-mode optical fibers for downlink and uplink
optical fibers 136D and 136U. For example, it has been shown that a
1400 MHz.km multi-mode fiber bandwidth-distance product is
sufficient for 5.2 GHz transmission up to 300 m.
[0069] In an example embodiment, the present invention employs 50
.mu.m multi-mode optical fiber for the downlink and uplink optical
fibers 136D and 136U, and E/O converters 60 that operate at 850 nm
using commercially available VCSELs specified for 10 Gb/s data
transmission. In a more specific example embodiment, OM3 50 .mu.m
multi-mode optical fiber is used for the downlink and uplink
optical fibers 136D and 136U.
[0070] Wireless system 10 also includes a power supply 160 that
generates an electrical power signal 162. Power supply 160 is
electrically coupled to head-end unit 20 for powering the
power-consuming elements therein. In an example embodiment, an
electrical power line 168 runs through the head-end unit and over
to transponder 30 to power E/O converter 60 and O/E converter 62 in
converter pair 66, the optional RF signal-directing element 106
(unless element 106 is a passive device such as a circulator), and
any other power-consuming elements (not shown). In an example
embodiment, electrical power line 168 includes two wires 170 and
172 that carry a single voltage and that are electrically coupled
to a DC power converter 180 at transponder 30. DC power converter
180 is electrically coupled to E/O converter 60 and O/E converter
62, and changes the voltage or levels of electrical power signal
162 to the power level(s) required by the power-consuming
components in transponder 30. In an example embodiment, DC power
converter 180 is either a DC/DC power converter, or an AC/DC power
converter, depending on the type of power signal 162 carried by
electrical power line 168. In an example embodiment, electrical
power line 168 includes standard electrical-power-carrying
electrical wire(s), e.g., 18-26 AWG (American Wire Gauge) used in
standard telecommunications and other applications. In another
example embodiment, electrical power line 168 (dashed line) runs
directly from power supply 160 to transponder 30 rather than from
or through head-end unit 20. In another example embodiment,
electrical power line 168 includes more than two wires and carries
multiple voltages.
[0071] In an example embodiment, head-end unit 20 is operably
coupled to an outside network 52 via a network link 224.
General Method of Operation
[0072] With reference to the optical-fiber-based wireless
picocellular system 10 of FIG. 1 and FIG. 2, service unit 50
generates an electrical downlink RF service signal SD ("electrical
signal SD") corresponding to its particular application. In an
example embodiment, this is accomplished by digital signal
processor 72 providing the RF signal modulator 70 with an
electrical signal (not shown) that is modulated onto a RF carrier
to generate a desired electrical signal SD.
[0073] Electrical signal SD is received by E/O converter 60, which
converts this electrical signal into a corresponding optical
downlink RF signal SD' ("optical signal SD'"), which is then
coupled into downlink optical fiber 136D at input end 138. It is
noted here that in an example embodiment optical signal SD' is
tailored to have a given modulation index. Further, in an example
embodiment the modulation power of E/O converter 60 is controlled
(e.g., by one or more gain-control amplifiers, not shown) to vary
the transmission power from antenna system 100. In an example
embodiment, the amount of power provided to antenna system 100 is
varied to define the size of the associated picocell 40, which in
example embodiments range anywhere from about a meter across to
about twenty meters across.
[0074] Optical signal SD' travels over downlink optical fiber 136
to output end 140, where it is received by O/E converter 62 in
transponder 30. O/E converter 62 converts optical signal SD' back
into electrical signal SD, which then travels to signal-directing
element 106. Signal-directing element 106 then directs electrical
signal SD to antenna 100. Electrical signal SD is fed to antenna
system 100, causing it to radiate a corresponding electromagnetic
downlink RF signal SD'' ("electromagnetic signal SD''").
[0075] Because client device 45 is within picocell 40,
electromagnetic signal SD'' is received by client device antenna
46, which may be part of a wireless card, or a cell phone antenna,
for example. Antenna 46 converts electromagnetic signal SD'' into
electrical signal SD in the client device (signal SD is not shown
therein). Client device 45 then processes electrical signal SD,
e.g., stores the signal information in memory, displays the
information as an e-mail or text message, etc.
[0076] In an example embodiment, client device 45 generates an
electrical uplink RF signal SU (not shown in the client device),
which is converted into an electromagnetic uplink RF signal SU''
(electromagnetic signal SU''") by antenna 46.
[0077] Because client device 45 is located within picocell 40,
electromagnetic signal SU'' is detected by transponder antenna
system 100, which converts this signal back into electrical signal
SU. Electrical signal SU is directed by signal-directing element
106 to E/O converter 60, which converts this electrical signal into
a corresponding optical uplink RF signal SU' ("optical signal
SU'"), which is then coupled into input end 142 of uplink optical
fiber 136U. Optical signal SU' travels over uplink optical fiber
136U to output end 144, where it is received by O/E converter 62 at
head-end unit 20. O/E converter 62 converts optical signal SU' back
into electrical signal SU, which is then directed to service unit
50. Service unit 50 receives and processes signal SU, which in an
example embodiment includes one or more of the following: storing
the signal information; digitally processing or conditioning the
signals; sending the signals on to one or more outside networks 52
via network links 224; and sending the signals to one or more
client devices 45 in picocellular coverage area 44. In an example
embodiment, the processing of signal SU includes demodulating this
electrical signal in RF signal modulator/demodulator unit 70, and
then processing the demodulated signal in digital signal processor
72.
[0078] System with central head-end station and optical fiber
cable
[0079] FIG. 4 is a schematic diagram of an example embodiment of an
optical-fiber-based wireless picocellular system 200 that includes
a central head-end station 210. Central head-end station 210 can be
thought of as a head-end unit 20 adapted to handle one or more
service units 50 and one or more transponders 30. Central head-end
station 210 is optically coupled to an optical fiber cable 220 that
includes multiple transponders 30. Optical fiber cable 220 is
constituted by multiple optical fiber RF communication links 36,
with each link optically coupled to a corresponding transponder 30.
In an example embodiment, multiple transponders 30 are spaced apart
along the length of optical fiber cable 220 (e.g., at 8 meter
intervals) to create a desired picocell coverage area 44 made up of
picocells 40, which in practice overlap at the edges.
[0080] FIG. 5 is a detailed schematic diagram of an example
embodiment of central head-end control station 210. Rather than
including multiple head-end units 20 of FIG. 1 directly into
head-end control station 210, in an example embodiment the head-end
units are modified to allow for each service unit 50 to communicate
with one, some, or all of transponders 30, depending on the
particular application of a given service unit. Service units 50
are each electrically coupled to a RF transmission line 230 and a
RF receiving line 232. In FIG. 5, three of six service units 50A
through 50F are shown for the sake of illustration.
[0081] In an example embodiment, system 200 further includes a main
controller 250 operably coupled to service units 50 and adapted to
control and coordinate the operation of the service units in
communicating with transponders 30. In an example embodiment,
controller 250 includes a central processing unit (CPU) 252 and a
memory unit 254 for storing data. CPU 252 is adapted (e.g., is
programmed) to process information provided to controller 250 by
one or more of service units 50. In an example embodiment,
controller 250 is or includes a programmable computer adapted to
carry out instructions (programs) provided to it or otherwise
encoded therein on a computer-readable medium.
[0082] Central head-end station 210 further includes a downlink RF
signal multiplexer ("downlink multiplexer") 270 operably coupled to
controller 250. Downlink multiplexer unit 270 has an input side 272
and an output side 274. Transmission lines 230 are electrically
connected to downlink multiplexer 270 at input side 272.
[0083] In an example embodiment, downlink multiplexer 270 includes
a RF signal-directing element 280 (e.g., a RF switch) that allows
for selective communication between service units 50 and
transponders 30, as described below. In an example, the selective
communication involves sequentially addressing transponders 30 for
polling corresponding picocells 40. Such sequential polling can be
used, for example, when one of service units 50 is a RFID reader
searching for RFID tags 290 in picocells 40 (FIG. 4). In an example
embodiment, RFID tags 290 are attached to an item 292 to be tracked
or otherwise monitored via the attached RFID tag. In another
example embodiment, the selective communication involves
simultaneously addressing some or all of transponders 30. Such
simultaneous addressing can be used, for example, when one of
service units 50 is a cellular phone transmitter or a RF-signal
feed-through unit that provides simultaneous coverage of some or
all of picocells 40.
[0084] Central head-end station 210 also includes an uplink RF
signal multiplexer ("uplink multiplexer") 320 operably coupled to
controller 250 and having an input side 322 and an output side 324.
Receiving lines 232 are electrically connected to uplink
multiplexer 320 at output side 324. In an example embodiment,
uplink multiplexer 320 includes a RF signal-directing element
328.
[0085] Central head-end station 210 also includes a number of E/O
converters 60 that make up an E/O converter array 360, and a
corresponding number of O/E converters 62 that make up an O/E
converter array 362. E/O converters 60 are electrically coupled to
output side 274 of downlink multiplexer 270 via electrical lines
330, and are optically coupled to input ends 138 of corresponding
downlink optical fibers 136D. O/E converters 62 are electrically
coupled to input side 322 of uplink multiplexer 320 via electrical
lines 332, and are optically coupled to output ends 144 of
corresponding uplink optical fiber 136U. Downlink optical fibers
136D constitute a downlink optical fiber cable 378 and uplink
optical fibers 136U constitute an uplink optical fiber cable
380.
[0086] FIG. 6A is a close-up schematic diagram of optical fiber
cable 220 showing downlink and uplink optical fibers 136D and 136U
and two of the six transponders 30. Also shown is electrical power
line 168 electrically coupled to transponders 30. In an example
embodiment, optical fiber cable 220 includes a protective outer
jacket 344. In an example embodiment, transponders 30 reside
completely within out jacket 344.
[0087] FIG. 6B is a schematic diagram similar to FIG. 6A,
illustrating an example embodiment wherein transponders 30 lie
outside of protective outer jacket 344. Having transponders 30 lie
outside of protective outer jacket 344 makes it easier to arrange
the transponders relative to a building infrastructure after the
optical fiber cable is deployed, as described below.
Method of Operation
[0088] With reference to FIGS. 4, 5, 6A and 6B, optical-fiber-based
wireless picocellular system 200 operates as follows. At central
head-end station 210, service units 50A, 50B, . . . 50F each
generate or pass through from one or more outside networks 52
respective electrical signals SD that correspond to the particular
application of the given service unit. Electrical signals SD are
transmitted over RF transmission lines 230 to downlink multiplexer
270. Downlink multiplexer 270 then combines (in frequency) and
distributes the various signals SD to E/O converters 60 in E/O
converter array 360. In an example embodiment, downlink multiplexer
270 and RF signal-directing element 280 therein are controlled by
controller 250 via a control signal 51 to direct signals SD to one,
some or all of E/O converters 60 in E/O converter array 360 and
thus to one, some or all of transponders 30, based on the
particular service unit application. For example, if service unit
50A is a cellular phone unit, then in an example embodiment signals
SD therefrom (e.g., passing therethrough from one or more outside
networks 52) are divided (and optionally amplified) equally by RF
signal-directing element 280 and provided to each E/O converter 60
in E/O converter array 360. This results in each transponder 30
being addressed. On the other hand, if service unit 50F is a WLAN
service unit, then RF signal-directing element 280 may be adapted
(e.g., programmed) to direct signals SD to select ones of E/O
converters 60 in E/O converter array 360 so that only select
transponders 30 are addressed.
[0089] Thus, one, some or all of E/O converters 60 in E/O converter
array 360 receive electrical signals SD from downlink multiplexer
270. The addressed E/O converters 60 in E/O converter array 360
convert electrical signals SD into corresponding optical signals
SD', which are transmitted over the corresponding downlink optical
fibers 136D to the corresponding transponders 30. The addressed
transponders 30 convert optical signals SD' back into electrical
signals SD, which are then converted into electromagnetic signals
SD'' that correspond to the particular service unit
application.
[0090] FIG. 7 is a close-up view of one of transponders 30 in
optical fiber cable 220, illustrating the corresponding picocell 40
and the exchange of downlink and uplink electromagnetic signals
SD'' and SU'' between the transponder and client devices 45 within
the picocell. In particular, electromagnetic signals SU'' are
received by the corresponding transponder 30 and converted to
electrical signals SU, and then to optical signals SD'. Optical
signals SD' then travel over uplink optical fiber 136U and are
received by O/E converter array 362 and the corresponding O/E
converters 62 therein for the addressed transponders 30. The O/E
converters 60 convert optical signals SU' back to electrical
signals SU, which then proceed to uplink multiplexer 320. Uplink
multiplexer 320 then distributes electrical signals SU to the
service unit(s) 50 that require(s) receiving these electrical
signals. The receiving service units 50 process signals SU, which
in an example embodiment includes one or more of: storing the
signal information; digitally processing or conditioning the
signals; sending the signals on to one or more outside networks 52
via network links 224; and sending the signals to one or more
client devices 45 in picocellular coverage area 44.
[0091] In an example embodiment, uplink multiplexer 320 and RF
signal-directing element 328 therein are controlled by controller
250 via a control signal S2 to direct electrical signals SU to the
service unit(s) 50 that require(s) receiving electrical signals
SU.
[0092] In an example embodiment, the different services from some
or all of service units 50 (i.e. cellular phone service, WiFi for
data communication, RFID monitoring, etc.) are combined at the RF
signal level by frequency multiplexing.
[0093] In an example embodiment, a single electrical power line 168
from power supply 160 at central control station 210 is
incorporated into optical fiber cable 220 and is adapted to power
each transponder 30, as shown in FIG. 6. Each transponder 30 taps
off the needed amount of power, e.g., via DC converter 180 (FIG.
2). Since the preferred embodiment of transponder 30 has relatively
low functionality and power consumption, only relatively low
electrical power levels are required (e.g., .about.1 watt),
allowing high-gauge wires to be used (e.g., 20 AWG or higher) for
electrical power line 168. In an example embodiment that uses many
transponders 30 (e.g., more than 12) in optical fiber cable 220, or
if the power consumption for transponders 30 is significantly
larger than 1 watt due to their particular design, lower-gauge
wires or multiple wires are employed in electrical power line 168.
The inevitable voltage drop along electrical power line 168 within
cable 220 typically requires large-range (-30 volts) voltage
regulation at each transponder 30. In an example embodiment, DC
power converters 180 at each transponder 30 perform this voltage
regulation function. If the expected voltage drop is known, then in
an example embodiment controller 250 carries out the voltage
regulation. In an alternative embodiment, remote voltage sensing at
each transponder 30 is used, but this approach is not the preferred
one because it adds complexity to the system.
Transponder System with Enhanced Antenna Directivity
[0094] FIG. 8 is a close-up schematic diagram of a section of
optical fiber cable 220 and transponder 30 therein, illustrating an
example embodiment of the present invention wherein the transponder
includes an antenna system 100 having a single dipole antenna
element 300A connected to converter pair unit 66 via a section of
coaxial cable 302A. FIG. 8 includes X-Y coordinates 305 for the
sake of reference for the discussion below, wherein the X-direction
is horizontal and the Y-direction is vertical. Also shown in FIG. 8
is a radiation-reflector assembly 310A that includes a
radiation-reflecting member 312A supported by a support member
314A. In an example embodiment, radiation-reflecting member 312A is
movable, e.g., adjustable via rotation about its long and/or short
axes. Transponder 30 and radiation-reflecting member 312A (or
alternatively, the entire radiation-reflector assembly 310A) make
up a "transponder system."
[0095] Radiation-reflector assembly 310A is shown mounted atop
optical fiber cable 220 so as to be above and parallel to antenna
element 300A, with support member 314A engaged with a mounting
member 320A fixed to optical fiber cable 220. The distance between
antenna element 300A and radiation reflecting member 312A is DA. In
general, radiation-reflecting member 312A is arranged relative to
antenna element 300A so as to provide enhanced antenna directivity
as compared to not having the radiation-reflecting member so
arranged.
[0096] In an example embodiment, distance DA is equal to or is
about .lamda..sub.RA/4, where .lamda..sub.RA is the center
wavelength of the operating band of antenna element 300A and thus
the downlink and uplink electromagnetic radiation signals SD'' and
SU'' transmitted therefrom and received thereby. This allows the
reflected signals to be in phase with the non-reflected signals by
accumulating a total phase of .lamda..sub.RA/2 by traveling to and
from radiation-reflecting member 312A as well as another phase
accumulation of .lamda..sub.RA/2 upon reflection.
[0097] In an example embodiment, radiation-reflecting member 312A
is made of metal, such as copper. Also in an example embodiment,
support member 314A is made of a dielectric material such as
plastic, and is adapted to snap-engage mounting member 320A.
[0098] In operation, electromagnetic downlink signals SD'' are
emitted from antenna element 300A in both the +Y and -Y directions,
as illustrated in the close-up schematic diagram of FIG. 9. The
electromagnetic signals SD'' that propagate in the +Y direction
encounter radiation-reflecting member 312A, which reflects these RF
radiation signals so that they propagate in the -Y direction, as
illustrated in FIG. 10. In the preferred case where distance DA is
equal to or about .lamda..sub.RA/4, the reflected and non-reflected
signals SD'' are in phase. Electromagnetic uplink signals SU'' from
one or more client devices (not shown in FIG. 9 and FIG. 10) are
reflected by radiation-reflecting member 312A and are received by
antenna element 300A in a similar manner.
[0099] FIG. 11 and FIG. 12 show respective close-up perspective and
close-up edge-on views of radiation-reflector assembly 310A. In an
example embodiment, reflecting member 312A is curved (e.g.,
cylindrically concave) to enhance the directionality of the
reflected downlink signals SD'', as well as the gain associated
with received uplink signals SU''. In an example embodiment,
radiation-reflecting member 312A has a long dimension L about the
same as that of the length of the corresponding antenna element
300A, and preferably having about 5% more resonant length. By way
of example, for a 5.2 GHz antenna element 300A having a length of
.lamda..sub.RA/4, an example length L of radiation-reflecting
member 312A is given by
1.05(.lamda..sub.RA/4)=(c)/(4f.sub.RA)=(3.times.10.sup.12
mm/s)/(4)(5.2.times.10.sup.9 Hz).about.15 mm, where c is the speed
of light and f.sub.RA is the frequency that corresponds to
wavelength .lamda..sub.RA. For a frequency .lamda..sub.RA=2.4 GHz,
L.about.33 mm.
[0100] FIG. 13 is a schematic diagram similar to that of FIG. 8,
illustrating an example embodiment wherein antenna system 100 of
transponder 30 includes two antenna elements 300A and 300B operably
connected to converter pair unit 66 via respective coaxial cables
302A and 302B. In an example embodiment, antenna elements 300A and
300B operate at different frequencies, thus forming two different
picocells (not shown). In an example embodiment, antenna element
300A transmits downlink signals SD'' and receives uplink signals
SU'' in the 5 GHz band (having a center wavelength .lamda..sub.RA),
while antenna element 300B transmits downlink signals SD'' and
receives uplink signals SU'' in the 2.4 GHz band (having a center
wavelength .lamda..sub.RB). Transponder 30 thus includes two
radiation-reflector assemblies 310A and 310B arranged relative to
corresponding antenna elements 300A and 300B at respective
distances DA and DB. In an example embodiment, DA is equal to or
about .lamda..sub.RA/4, and DB is equal to or about
.lamda..sub.RB/4. Note that transponder 30 of FIG. 13 shows only
one pair of downlink and uplink optical fibers 136D and 136U even
though there are two antenna elements 300A and 300B operating at
different frequencies. In this example embodiment, transponder 30
is adapted to multiplex and demultiplex the different RF
frequencies associated with the different antenna elements onto the
downlink and uplink optical fibers. In another example embodiment,
downlink and uplink optical fibers 136D and 136U are provided for
each antenna element, such as shown in FIG. 14, discussed
below.
[0101] FIG. 14 is a detailed schematic side view of an example
embodiment wherein a transponder 30 similar to that shown in FIG.
13 is attached to the side of optical fiber cable 220. Note that in
FIG. 14, four optical fibers connect to transponder 30, namely a
pair of downlink and uplink optical fibers 136D and 136U for each
antenna 300A and 300B. Thus, respective pairs of downlink and
uplink optical fibers carry the respective RF frequencies
associated with the different antenna elements. FIG. 15 is an
end-on view of the optical fiber cable of FIG. 14, showing how
transponder 30 of FIG. 14 is arranged relative to optical fiber
cable 220.
[0102] FIG. 16 is a schematic diagram of an example embodiment of
transponder 30 and optical fiber cable 220, wherein the transponder
is located remote from the optical fiber cable. One or two pairs of
downlink and uplink optical fibers 136D and 136U (only one pair is
shown for the sake of illustration) and electrical power line 168
extend from optical fiber cable 220 to remotely located transponder
30. In an example embodiment, the optical fibers and the electrical
power line are included in a single tether cable, as discussed in
greater detail below. Antenna system 100 is located within housing
102 so that radiation-reflector assemblies 310A and 310B are
mounted atop housing 102 relative to the corresponding antenna
elements 300A and 300B.
[0103] FIG. 17 is similar to FIG. 16, and illustrates an example
embodiment wherein each antenna element 300A and 300B has
associated therewith a pair of radiation-reflector assemblies 310A
and a pair of radiation-reflector assemblies 310B, respectively,
mounted to adjacent sides of housing 102 relative to the
corresponding antenna element. This arrangement provides additional
directivity for downlink signals SD'' and uplink signals SU''.
[0104] FIG. 18 is a schematic cross-sectional diagram of a building
infrastructure 400 illustrating an example application of the
example transponder 30 as illustrated in FIG. 17. Building
infrastructure 400 includes a first floor 401 that partly defines a
corresponding first-floor room 401R, and includes a second floor
402 that partly defines a corresponding second-floor room 402R. A
drop ceiling 410 is suspended by suspension lines 412 connected to
the second floor and that depend downwards a certain distance
towards the first floor 401. Building infrastructure 400 also
includes an outer wall 420. Drop ceiling 410, second floor 402, and
outer wall 420 define a ceiling space 430 within which pipes,
wires, ducts and other building utilities are run. An optical fiber
cable 220 is arranged in ceiling space 430 and has the example
transponder 30 of FIG. 17 operably incorporated therewith.
Transponder 30 is arranged next to outer wall 420. In this
arrangement, it is often undesirable for downlink signals SD''
and/or uplink signals SU'' to be transmitted to or received from
second-floor room 402R and/or to and from an outside environment
440 on the outside of outer wall 420. Transponder 30 thus serves to
direct downlink signals SD'' of first and second frequencies from
the respective first and second antennas 300A and 300B into a
portion of first-floor room 401R, thereby defining a highly
localized two-frequency picocell 40 that does not extend with any
significant power either to second-floor room 402R or to outside
environment 440. Such an arrangement is particularly useful when
outside wall 420 does not significantly attenuate RF signals.
[0105] FIG. 19 is a schematic diagram illustrating an example
embodiment of transponder 30 similar to that of FIG. 16, but
wherein antenna elements 300A and 300B are located in optical fiber
cable 220 rather than within housing 102. Antenna elements 300A and
300B are electrically connected to converter pair unit 66 via an
antenna cable 450 that includes respective coaxial cables 302A and
302B as discussed above. In this embodiment, radiation-reflector
assemblies 310A and 310B are attached to optical fiber cable 220,
e.g., via mounting members 320A and 320B fixed thereto. It is worth
noting that in a particular example of this example embodiment,
distances D.sub.A and D.sub.B are equal to or about
.lamda..sub.RA/4 and .lamda..sub.RB/4, respectively.
[0106] FIG. 20 is a schematic diagram similar to FIG. 16,
illustrating an example embodiment wherein a single
radiation-reflector assembly 310C is used to reflect radiation
associated with two or more antenna elements--here, two antenna
elements 300A and 300B. Radiation-reflector assembly 310C has a
reflecting member 312C located a distance DC away from the plane of
antennas 300A and 300B and has dimensions (particularly in the
X-direction) sufficient for it to cover or substantially cover
(i.e., reside above) both antenna elements. Radiation-reflecting
assembly 310C also includes support member 314C and mounting member
320C that engages the support member.
[0107] In an example embodiment, distance DC is at or about
.lamda..sub.R/4 of one of the wavelengths from either antenna
element 300A or 300B. In another example embodiment, distance DC is
given by (.lamda..sub.RA/4+.lamda..sub.RB/4)/2, wherein
.lamda..sub.RA and .lamda..sub.RB are the aforementioned center
wavelengths of the frequency bands of antenna elements 300A and
300B, respectively. In another example embodiment, distance DC is
set to be at or about .lamda..sub.RA/4 or .lamda..sub.RB/4.
[0108] While the single radiation-reflector assembly 310C does not
typically provide the same degree of efficiency as an arrangement
where each antenna element has its own radiation-reflector
assembly, it still is able to provide an effective degree of
radiation directivity and isolation, and thus enhanced transponder
performance.
[0109] In general, at least one radiation-reflecting member is
arranged relative to either a corresponding at least one antenna
element or to one or more antenna elements, so as to provide
enhanced antenna directivity as compared to not having the at least
one radiation-reflecting member so arranged.
[0110] A transponder 30 having enhanced directionality has a number
of important advantages over a transponder that does not have an
associated radiation-reflector assembly. One advantage is reduced
interference with other transponders by substantially reducing the
amount of radiation that travels in an unwanted direction or to an
unwanted location. For example, as described above in connection
with FIG. 18, blocking downlink signals SD'' from traveling to
different rooms in a building prevents multi-floor interference
between picocells.
[0111] Enhanced antenna directivity also decreases the amount of
cross-talk between picocells 40 that use the same subcarrier
frequency. Thus, one can achieve small picocell size without an
increase in the cross-talk penalty.
[0112] The enhanced directivity of transponder 30 of the present
invention also improves communication efficiency by redirecting
otherwise wasted radiation back into the picocell associated with
the transponder. This also has the effect of improved wireless
security by blocking unwanted leakage of the picocell to unwanted
areas, such as outside of a building or other offices or common
areas of a building, as described above in connection with FIG.
18.
[0113] The enhanced directivity of transponder 30 of the present
invention also facilitates the formation of wireless-free zones.
Such zones may be desired in certain locations, such as
laboratories where very sensitive measuring equipment is located,
or in hospitals where RF wireless signals might interfere with
patient care.
[0114] Also, as discussed above, the enhanced directivity of
transponder 30 of the present invention can be used to optimize
wireless performance in particular regions of a building. For
example, transponders located next to a wall are likely to have a
large portion of its energy absorbed by or transmitted through the
wall. By orienting the radiation patterns of such transponders
using one or more radiation-reflector assemblies (see, e.g., FIG.
18), improved or optimized performance for a given situation can be
obtained. Likewise, certain RoF wireless picocellular system
deployment scenarios may require or otherwise benefit from
directional antennas. For instance, wireless access in a stairwell
is made possible by a transponder with an antenna system having an
antenna radiation pattern tailored to the stairwell geometry.
[0115] The radiation-reflector assembly of the present invention is
also preferably adapted for quick deployment, using for example
so-called snap-engagement of the different parts of the assembly.
This allows for quick and efficient installation of the associated
RF wireless picocellular system.
Transponder Node Assembly
[0116] Conventional ROF wireless picocellular systems have a single
transponder 30 associated with each picocell 40, as shown in FIG.
4. For such systems, the spacing between transponders 30 (or, more
precisely, the associated antenna systems 100) can be made
relatively large, e.g., larger than the 5-10 meters typically
employed to obtain full wireless coverage for a given area without
the picocells having substantial spatial overlap. However, this
relatively small spatial separation between transponders allows for
the use of relatively short lengths of coax cables to carry the RF
signals to the transponder antenna systems. This allows for
integrating two or more transponders into a single assembly,
referred to herein as a "transponder node assembly."
[0117] FIG. 21 is a schematic diagram of an example embodiment of a
transponder node assembly 500 according to the present invention,
as shown incorporated into optical fiber cable 220. Transponder
node assembly 500 includes a converter pair assembly 566 to which
is electrically coupled two or more antenna elements 300. In the
example transponder node assembly 500 shown in FIG. 21, three
antenna elements 300A, 300B and 300C are shown, wherein antenna
elements 300B and 300C are electrically coupled to converter pair
assembly 566 via respective coaxial cable sections 302B and 302C,
while antenna element 300A is connected directly to the converter
pair assembly (i.e., the coaxial cable is internal to housing 102).
Three optical fiber RF communication links 36 are optically coupled
to transponder node assembly 500, preferably via a multi-fiber
optical connector 570.
[0118] FIG. 22 is a close-up schematic diagram of an example
embodiment of transponder node assembly 566. Transponder node
assembly 566 includes two or more converter pair units 66, such as
the three shown in the present example embodiment. A single DC
power converter 180 is employed, rather than having one for each
converter pair unit 66. Also, in an example embodiment, transponder
node assembly 500 includes a single heat sink 590 in thermal
communication with converter pairs 66, rather than three separate
heat sinks for each converter pair unit. Likewise, the various
electronic elements (not shown) used in transponder 30 are
preferably placed on a single printed circuit board (not shown)
rather than having a separate printed circuit board for each
transponder 30. Similarly, a single protective housing 102 is used
rather than separate housings for each transponder, and a single
electrical power connector 596 is also used to connect to
electrical power line 168. In general, the consolidation and
integration of the various parts of the two or more transponders 30
into transponder node assembly 500 results in a significant cost
savings--estimated to be about 20% to 30% when integrating five
transponders into a single transponder node assembly. In addition,
transponder node assembly 500 can be made very compact (e.g.,
nearly the size of a single transponder unit 30) by using a light
source array (e.g., VCSEL arrays), a photodetector array, optical
connectors, and other like components normally used for integrating
and/or packaging micro-optical and integrated optical systems. In
an example embodiment, transponder node assembly 500 includes two
or more antenna systems arranged to provide a picocell spacing of
at least five meters. Here, "picocell spacing" means the distance
from the center of one picocell to the center of the adjacent
picocell.
[0119] By way of example, for a transponder node assembly 500
having the capability of five transponders and for a node
(picocell) spacing of 5 meters, the longest length of coaxial cable
302 for antenna elements 300 is 10 meters. Using commercially
available coaxial cable such as Astrolab 3205 cable (available from
www.astrolab.com), the RF loss over the 10 meters is only about 5
dB, which is acceptably low for RoF wireless picocellular systems.
The transponder node assembly of the present invention thus enables
a method of forming picocells in a radio-over-fiber (RoF) wireless
picocellular system. This method includes forming transponder node
assembly 500 as described above, e.g., by combining two or more
converter units 66 into housing 102 and connecting respective two
or more antenna systems 100 to the corresponding two or more
converter units. The method also includes distributing the two or
more antenna systems 100 to corresponding two or more locations,
e.g., throughout optical fiber cable 220 so as to form two or more
corresponding picocells 40 (such as formed in FIG. 4 with separate
transponders 30). Picocells 40 have respective two or more spatial
locations corresponding to the relative locations of the respective
two or more antenna systems 100. In an example embodiment, the
method includes providing a separation between adjacent antenna
systems of between about 2 m and about 10 m.
Transponder RFID System
[0120] A typical cable installation scenario associated with
deploying a RoF wireless picocellular system involves placing
optical fiber cable 220 and the transponders 30 either incorporated
therein or operably coupled thereto atop ceiling tiles in a
building. FIG. 23 is a close-up of a portion of the building
infrastructure shown in FIG. 18, including an optical fiber cable
220 deployed above drop-ceiling 410 in ceiling space 430. Two
transponders 30 are shown, wherein the transponders are located
remote from optical fiber cable and are operably coupled thereto
via respective tethers 602 that include downlink and uplink optical
fibers 136D and 136U, along with electrical power line 168 (not
shown). Transponders 30 may be separated by, for example, 5 to 10
meters and might lay 1 to 2 meters away from optical fiber cable
220.
[0121] While such hidden installation is preferred for aesthetic
reasons, it is often difficult to locate transponders after
installation, either for maintenance, repair or other adjustments
such as position adjustment to adjust the location or coverage of
the corresponding picocell. Since optical fiber cable 220 is hidden
by drop ceiling 410, quick location of a given transponder 30 is a
difficult and time-consuming task.
[0122] Accordingly, an aspect of the present invention involves
providing at least one transponder 30 (and preferably most if not
all of the transponders in a RoF wireless picocellular system) with
a RFID tag. FIG. 24 is a close-up view of FIG. 23, illustrating an
example embodiment of transponder 30 having a RFID tag 640, and
also showing a RFID-tag reader 650 in room 401R below drop ceiling
410. Note that the example transponder 30 of FIG. 24 has its
antenna system 100 located within housing 102 for the sake of
illustration. Transponder 30, along with RFID tag 640 and RFID tag
reader 650, constitute what is referred to herein as "transponder
RFID system" 700.
[0123] FIG. 25 is a more detailed schematic diagram of transponder
RFID system 700 shown in a different orientation than that of FIG.
24 for ease of illustration and explanation. RFID tag 640 includes
a receive/transmit antenna 642 and a microcircuit 644 (e.g., in the
form of a microchip) electrically connected to the antenna. A
memory unit 646 (e.g., a memory chip) is electrically connected to
microcircuit 644. Memory unit 646 is adapted to store information
("RFID tag data"), which in an example embodiment includes at least
one property of the associated transponder 30, but more typically
includes a number of such properties, such as the date of
installation, the operating frequency band or bands, maintenance
history, output power, the number of antenna systems and/or antenna
elements, the distance to the nearest transponders (e.g., as
measured along the optical fiber cable), and the like. In an
example embodiment, RFID tag signal ST (discussed below) is
representative of a unique RFID tag number that has associated
therewith one or more properties (such as the transponder
properties mentioned above) that are stored in RFID tag reader 650
and/or an RFID database 710 (discussed below).
[0124] RFID reader 650 includes a receive/transmit antenna 662, a
signal processing circuit 664 electrically connected thereto, and a
memory unit 666 electrically connected to the signal processing
circuit. RFID tag reader 650 also includes other electronic
components that are not essential to the present invention and so
are not shown. In an example embodiment, RFID tag reader 650
includes a GPS unit 668 adapted to provide GPS data to signal
processing circuit 664 and/or to memory unit 666.
[0125] With continuing reference to FIG. 25, in the operation of
transponder RFID system 700, signal processing circuit 664
generates an interrogation signal SI and transmits it via antenna
662 to RFID tag 640 as an electromagnetic interrogation signal
SI''. In an example embodiment, signal processing circuit 664 is
also adapted to either generate or pass along a "write signal" SW
that carries information to be written to a write-able type of RFID
tag 640 via a corresponding electromagnetic write signal SW''. The
information in the write signals is based on, for example,
information either stored in memory unit 666, entered into the RFID
tag reader directly by a user, or communicated to it from a
database unit, as described below.
[0126] Microcircuit 644 in RFID tag 640 is adapted to receive at
antenna 642 interrogation signal SI'' and to process this signal.
The processing includes, for example, comparing the received
interrogation signal SI'' to a corresponding bit sequence stored in
memory unit 646. In an example embodiment, microcircuit 644 is
adapted to use the energy in interrogation signal SI'' to power
itself. If the proper content of the received interrogation signal
SI'' is confirmed, then microcircuit 644 is adapted to generate a
RFID tag signal ST representative of the stored RFID tag data and
to transmit this signal via antenna 642 to RFID reader 650 as an
electromagnetic tag signal ST'' to be read by the RFID tag reader.
In an example embodiment, RFID tag reader 650 is adapted to
generate a "ping" interrogation signal SI'' that simply elicits a
"ping" electromagnetic tag signal ST'' from RFID tag 640, wherein
the ping form of signal ST'' is used located the RFID tag.
[0127] In an example embodiment, at least some of the RFID tags 640
are adapted to generate RFID tag signals ST'' at a frequency
suitable for long-range RFID-tag reading, such at the 915 MHz band
or the 2.45 GHz band. Such RFID tags are best suited for aerial or
aboveground applications, or more generally for RFID-tag locations
that are not buried or otherwise obstructed by an intervening
RF-frequency-absorbing medium. Suitable RFID tags for the present
invention are available from Alien Technologies, Inc., as Model
Nos. ALL-9440 and ALL-9350.
[0128] In an example embodiment, RFID tag reader 650 and one or
more of RFID tags 640 are adapted with encryption capability so
that the interrogation signal SI and the RFID tag signal ST can be
encrypted to prevent third parties from reading or overwriting RFID
tag data.
[0129] RFID tag reader 650 is also adapted to receive
electromagnetic RFID tag signal ST'' via antenna 662, which
converts this signal back into electrical RFID tag signal ST.
Signal processing circuit 664 is further adapted to extract the
RFID tag data from this signal and store this data in memory unit
666.
[0130] In an example embodiment, transponder RFID system 700
includes a database unit 710 operably coupled to RFID reader 650 so
that information can be transmitted to and receive from the
database unit. In an example embodiment, database unit 710 includes
a transmit/receive antenna 712 used to wirelessly communicate with
RFID tag reader 650, through a WiFi network or through the cellular
phone network, as examples. In another example embodiment, database
unit 710 is operably coupled to RFID tag reader 650 via a
non-wireless (e.g., an electrical or optical) communication link
720, such as an Ethernet link.
[0131] Database unit 710 includes a microprocessor 730 operably
connected thereto, a memory unit 734 operably coupled to the
microprocessor, and a display 740 operably coupled to the
microprocessor. In an example embodiment, database unit 710 is or
otherwise includes a computer, such as a laptop computer, personal
computer or workstation. In an example embodiment, database unit
710 is mobile (e.g., as a laptop computer or hand-held device) and
is brought out to the field to be accessible to those working in
the field to deploy or maintain the RoF wireless picocellular
system. Also in an example embodiment, database unit 710 supports a
graphical user interface (GUI) so that a database-unit user can
view graphical images and interact with interactive graphical
images on display 740.
[0132] In an example embodiment, RFID tag reader 650 transmits RFID
tag data to database unit 710 either non-wirelessly via a
non-wireless data signal S1 sent over communication link 720, or
wirelessly via electromagnetic data signal S1''. Database unit 710
then stores and processes the RFID tag data, such as described
below.
[0133] Also in an example embodiment, database unit 710 either
wirelessly and/or non-wirelessly transmits write information in
respective write signals SW and/or (electromagnetic) signal SW'' to
RFID tag reader 650. The write signals are then sent by RFID tag
reader 650 as an electromagnetic write signal SW'' to one or more
write-able RFID tags 640 and stored therein as RFID tag data.
[0134] Microprocessor 730 in database unit 710 is adapted to
process the RFID tag data in RFID tag signals ST to glean useful
information about the corresponding transponders 30. In an example
embodiment, this information is displayed on display 740. In an
example embodiment, the information is represented as graphics, and
further is presented by database unit 710 in the form of one or
more interactive maps of the RoF wireless picocellular system that
include the location of one or more transponders 30. In an example
embodiment, the location information includes GPS coordinates
supplied by GPS unit 668.
[0135] FIG. 26 is a schematic diagram of transponder RFID system
700 similar to that shown in FIG. 23, illustrating an example
embodiment wherein transponders 30 are located remote from optical
fiber cable 220 via tether cables 602, and wherein RFID tags 640
are located on the optical fiber cable, e.g., at or near the
location where tether cables 602 are attached to the optical fiber
cable.
[0136] FIG. 27 is a schematic diagram of transponder RFID system
700 similar to FIG. 26, but wherein the transponders and thus the
RFID tags 640 are located within optical fiber cable 220.
Transponder Mode Selection via the RFID Tag
[0137] In an example embodiment of the present invention, when
transponders 30 are not in use, they are adapted to transition from
a "fully operational" mode to a "stand-by" power-saving mode by
turning off main energy consuming elements therein. One approach to
returning transponder 30 to the fully operational mode or placing
the transponder directly into the stand-by mode is to do so via
RFID tag 650.
[0138] FIG. 28 is a schematic diagram illustrating an example
embodiment of the transponder RFID system of the present invention,
wherein RFID tag 640 is electrically connected to transponder 30
via an electrical connection 780. When RFID tag 640 is addressed
with an appropriate signal, such as interrogation signal SI'' (or a
particular sequence of such signals), or via a particular write
signal SW'', a mode signal SM is generated in the RFID tag and sent
to transponder 30 over electrical connection 780. Signal SM is then
used to change the operational mode of transponder 30.
[0139] This example embodiment is particularly effective if RFID
tag 640 is of the chargeable type, which tends to have a longer
read range. When RFID tag 640 is chargeable, then in an example
embodiment, power from transponder 30 is sent over electrical
connection 780 in the form of power signal SP to the RFID tag to
charge the RFID tag.
Tether Cable Assembly
[0140] FIG. 29 is a perspective schematic diagram similar to FIG.
26, showing an example of how optical fiber cable 220 can be
arranged in ceiling space 430 above a section of drop-ceiling 410.
Optical fiber cable 220 includes one or more connectors 804 that
serve as access points for corresponding one or more tether cables
602 each having first and second ends 606 and 608. The first
("proximal") tether cable end 606 is shown connected to transponder
30 while the second ("distal") tether cable end 608 is shown
connected to optical fiber cable 220 via connector 804. Another
connector 804 (not shown) can also be used at transponder 30 to
connect tether cable end 606 to the transponder.
[0141] After optical fiber cable 220 is deployed, the usual
procedure is to then connect the tether cable ends 606 and 608 to
transponder 30 and to optical fiber cable 220, respectively, and
then place the transponder in its final position according to the
desired picocell location for that transponder. In the usual case
where tether cables 602 are all of a fixed length, there is
typically some amount of slack that requires a portion 603 of the
tether cable to be coiled and neatly stored. Also, conventional
tether cables 602 are usually coiled for packaging and shipping and
then uncoiled when the transponders are deployed.
[0142] FIG. 30 is a plan schematic diagram of an example embodiment
of a tether cable assembly 850 according to the present invention,
and FIG. 31 is a side view of the same assembly. Assembly 850
includes a housing 854 that contains tether cable 602. FIG. 32 is a
close-up cross-sectional view of an example embodiment of a
ribbon-type tether cable 602 used in tether cable assembly 850.
Ribbon tether cable 602 includes at least one optical fiber and at
least one wire, and in a preferred embodiment includes downlink and
uplink optical fibers 136D and 136U and at least one electrical
power line 168 (two such power lines are shown in FIG. 32).
[0143] With reference again to FIG. 30 and FIG. 31, housing 854
includes a slot 856 (e.g., a rectangular slot) sized so that
ribbon-type tether cable 602 passes therethrough when dispensed
from or retracted into the housing. Thus, housing 854 houses some
or all of tether cable 602 in coiled form, depending on how much of
the tether cable is dispensed from the housing.
[0144] FIG. 33 is a side-view of tether cable assembly 850 with
housing 854 removed. Tether cable assembly 850 further includes in
an example embodiment a spool 860 having a first flange 864
(referred to herein the "upper flange") and an opposing flange 868
(referred to herein as the "lower flange"). A central post 870
extends between the two flanges and the tether cable is coiled
around the central post. In an example embodiment, central post 870
is connected to lower flange 868, which rotates with respect to
upper flange so that rotating the lower flange dispenses (uncoils)
or retracts (coils) tether cable 602.
[0145] In an example embodiment, lower flange 868 and/or central
post 870 is/are operably connected to a retracting unit 872 so that
tether cable 602 can be either automatically or selectively
retracted (coiled). In an example embodiment, retracting unit 872
is or includes a spring.
[0146] In an example embodiment having such a retracting unit,
tether cable assembly 850 also preferably includes a locking
mechanism 874 that selectively engages and disengages (e.g., via
manual operation) tether cable 602 so that a select amount of the
tether cable can be dispensed and remain dispensed if not otherwise
held in place.
[0147] FIG. 34 is a top-down view of spool 860 with upper flange
864 removed to show a portion of tether cable 602 wound around
central post 870. In an example embodiment, central post 870 is
hollow and includes a wall 876 that defines a central post interior
877. Wall 876 includes an aperture 878 formed therein sized to
accommodate tether cable 602 at proximate tether cable end 606 so
that this end can reside in and/or pass through central post
interior 877. With reference again to FIG. 31, in an example
embodiment, proximate tether cable end 606 passes through central
post interior 873 and passes outside of housing 854, e.g., through
an aperture 879 formed in the underside of the housing at the
location of central post 872.
[0148] Most optical fibers are strongly affected by small-radius
bends. For example, standard single-mode fiber such as SMF-28 from
Corning, Inc., has a high attenuation at small bending radii.
Accordingly, assembly 850 is adapted to control the amount of
bending of ribbon-type tether cable 602.
[0149] With continuing reference to FIG. 34, central post 870 has
an outer radius R.sub.O. Outer radius R.sub.O is greater than a
certain minimum tether cable bend radius R.sub.C so that when
tether cable 602 is wound around spool 860, the tether cable always
maintains a sufficiently large bend radius (i.e., is always greater
than the minimum bending radius R.sub.C) to prevent significant
optical power loss due to bending of the one or more optical fibers
in tether cable 602. In an example embodiment, minimum radius
R.sub.C is --10 mm.
[0150] In an example embodiment illustrated in FIG. 34, central
post 870 includes a curved wall portion 880 formed in wall 876
adjacent aperture 878 and having a bending radius R.sub.B. Curved
wall portion 880 is curved so as to control the bending of tether
cable 602 near proximate tether cable end 606 that passes through
aperture 878 and into or through central post interior 877.
Proximate tether cable end 606 can be attached to either
transponder 30 or to optical fiber cable 220, e.g., through housing
aperture 879. Note that curved wall portion 880 need not be
circular, and in such a case can still be defined by a radius of
curvature that represents the greatest amount of curvature (i.e.,
smallest radius).
[0151] In an example embodiment, curved wall portion 880 has radius
of curvature .about.R.sub.B<5 mm. For certain,
bending-loss-resistant optical fibers such as those developed by
Corning, Inc., a quarter-turn bend at 5 mm causes about a 0.025 dB
power loss. Ten additional bends of such optical fiber at 10 mm
would add about another 0.10 dB power loss.
[0152] FIG. 35 is a schematic diagram similar to FIG. 34, showing
an example embodiment wherein housing 854 includes a second slot
(aperture) 857 and tether cable 602 winds around central post 870
in both directions so that both tether cable ends 606 and 608 can
reside outside of the tether cable assembly housing 854 when the
tether cable is deployed.
[0153] FIG. 36 is a schematic cut-away diagram of an example
embodiment of wherein tether cable assembly 850 includes a
transponder within its housing 854 and is used to connect the
transponder to optical fiber cable 220. In FIG. 36, only some of
the components of tether cable assembly 850 are shown for the sake
of clarity in cut-away section 900. In the example embodiment of
FIG. 36, transponder 30 is included within housing 854 and is
operably coupled to tether cable 602 at proximate tether cable end
606 while tether cable distal end 608 is connected to optical fiber
cable 220.
[0154] FIG. 37 is a schematic diagram similar to FIG. 29,
illustrating an example embodiment of wherein tether cable assembly
850 is used to connect transponder 30 to optical fiber cable 220,
wherein the tether cable assembly employs the tether-cable winding
configuration illustrated in FIG. 35. Here, transponder 30 is
located outside of tether cable housing 854. Note that tether cable
602 need not be coiled outside of housing 854 and that only as much
tether cable as needed can be dispensed. Note that dispensing the
tether cable from first and second slots 856 and 857 in housing 854
(FIG. 35) results in the tether cable assembly residing about half
way between where tether cable distal end 608 connects to optical
fiber cable 220 and where the tether cable proximal end 606
connects to the transponder.
[0155] Tether cable assembly 850 can be constructed to store
various lengths of tether cable 602. By way of example, a tether
cable assembly having a central post outer radius R.sub.O of 10.2
mm and a housing radius R.sub.H of 27.5 mm would have an
extractable tether-cable length of about 500 mm for a cable
thickness of 0.9 mm and 10 loops of the tether cable around spool
860. Tether cable assembly 850 has an extended tether-cable length
of 1000 mm when housing radius R.sub.H is extended to 35 mm. Thus,
a tether cable assembly 850 with a housing 854 having a diameter of
just over 3 inches could store about a meter of tether cable
602.
[0156] The number of fibers or conductors carried by tether cable
602 may also be varied. In an example embodiment, a short length of
spring steel (not shown) is included with or attached to tether
cable 602 as the retracting element to provide sufficient
tether-cable stiffness to deploy and retract the tether cable. The
spring action required for the retraction of the tether could be
provided by using copper clad steel wire, in which case the steel
would be a spring steel such as silicon-manganese steel or
chrome-vanadium steel.
[0157] In an example embodiment such as that shown in FIG. 36, a
connector 805 that is mate-able with connector 804 of optical fiber
cable 202 is provided at tether cable distal end 608 to provide for
easy connection of tether cable 602 to optical fiber 202.
[0158] Tether cable assembly 850 has the advantage of being
self-contained, compact, and is preferably constructed to be
rugged. In an example application of tether cable assembly 850,
after optical fiber cable 220 has been installed, the tether cables
are attached to optical fiber cable 220 (and to transponder 30 if
one is not included in the tether cable assembly). The tether cable
is then dispensed (and locked, if necessary via locking mechanism
874) and the transponder and assembly placed in their desired final
position. In the event that transponders 30 of a deployed RoF
wireless picocellular system need to be upgraded with new
transponders, the existing tether assemblies and transponders can
be removed and replaced with new tether assemblies and
transponders. The tether cable is adjusted to the desired length
and any slack tether cable is neatly stored by coiling it around
spool 860 within the assembly rather than atop the drop ceiling or
other location where it might present a hazard or
inconvenience.
[0159] Various embodiments of the present invention are adapted to
include bend performance optical fibers. One example of bend
performance optical fiber is a microstructured optical fiber having
a core region and a cladding region surrounding the core region,
the cladding region comprising an annular hole-containing region
comprised of non-periodically disposed holes such that the optical
fiber is capable of single mode transmission at one or more
wavelengths in one or more operating wavelength ranges. The core
region and cladding region provide improved bend resistance, and
single mode operation at wavelengths preferably greater than or
equal to 1500 nm, in some embodiments also greater than about 1310
nm, in other embodiments also greater than 1260 nm. The optical
fibers provide a mode field at a wavelength of 1310 nm preferably
greater than 8.0 microns, more preferably between about 8.0 and
10.0 microns. In preferred embodiments, optical fiber disclosed
herein is thus single-mode transmission optical fiber.
[0160] In some embodiments of the present invention, the
microstructured optical fibers disclosed herein comprises a core
region disposed about a longitudinal centerline and a cladding
region surrounding the core region, the cladding region comprising
an annular hole-containing region comprised of non-periodically
disposed holes, wherein the annular hole-containing region has a
maximum radial width of less than 12 microns, the annular
hole-containing region has a regional void area percent of less
than about 30 percent, and the non-periodically disposed holes have
a mean diameter of less than 1550 nm.
[0161] By "non-periodically disposed" or "non-periodic
distribution", it is meant that when one takes a cross-section
(such as a cross-section perpendicular to the longitudinal axis) of
the optical fiber, the non-periodically disposed holes are randomly
or non-periodically distributed across a portion of the fiber.
Similar cross sections taken at different points along the length
of the fiber will reveal different cross-sectional hole patterns,
i.e., various cross-sections will have different hole patterns,
wherein the distributions of holes and sizes of holes do not match.
That is, the holes are non-periodic, i.e., they are not
periodically disposed within the fiber structure. These holes are
stretched (elongated) along the length (i.e. in a direction
generally parallel to the longitudinal axis) of the optical fiber,
but do not extend the entire length of the entire fiber for typical
lengths of transmission fiber.
[0162] For a variety of applications, it is desirable for the holes
to be formed such that greater than about 95% of and preferably all
of the holes exhibit a mean hole size in the cladding for the
optical fiber which is less than 1550 nm, more preferably less than
775 nm, most preferably less than 390 nm. Likewise, it is
preferable that the maximum diameter of the holes in the fiber be
less than 7000 nm, more preferably less than 2000 nm, and even more
preferably less than 1550 nm, and most preferably less than 775 nm.
In some embodiments, the fibers disclosed herein have fewer than
5000 holes, in some embodiments also fewer than 1000 holes, and in
other embodiments the total number of holes is fewer than 500 holes
in a given optical fiber perpendicular cross-section. Of course,
the most preferred fibers will exhibit combinations of these
characteristics. Thus, for example, one particularly preferred
embodiment of optical fiber would exhibit fewer than 200 holes in
the optical fiber, the holes having a maximum diameter less than
1550 nm and a mean diameter less than 775 nm, although useful and
bend resistant optical fibers can be achieved using larger and
greater numbers of holes. The hole number, mean diameter, max
diameter, and total void area percent of holes can all be
calculated with the help of a scanning electron microscope at a
magnification of about 800.times. and image analysis software, such
as ImagePro, which is available from Media Cybernetics, Inc. of
Silver Spring, Md., USA.
[0163] The optical fibers disclosed herein may or may not include
germania or fluorine to also adjust the refractive index of the
core and or cladding of the optical fiber, but these dopants can
also be avoided in the intermediate annular region and instead, the
holes (in combination with any gas or gases that may be disposed
within the holes) can be used to adjust the manner in which light
is guided down the core of the fiber. The hole-containing region
may consist of undoped (pure) silica, thereby completely avoiding
the use of any dopants in the hole-containing region, to achieve a
decreased refractive index, or the hole-containing region may
comprise doped silica, e.g. fluorine-doped silica having a
plurality of holes.
[0164] In one set of embodiments, the core region includes doped
silica to provide a positive refractive index relative to pure
silica, e.g. germania doped silica. The core region is preferably
hole-free. In some embodiments, the core region comprises a single
core segment having a positive maximum refractive index relative to
pure silica .DELTA..sub.1 in %, and the single core segment extends
from the centerline to a radius R1. In one set of embodiments,
0.30%<.DELTA..sub.1<0.40%, and 3.0 .mu.m<R1<5.0 .mu.m.
In some embodiments, the single core segment has a refractive index
profile with an alpha shape, where alpha is 6 or more, and in some
embodiments alpha is 8 or more. In some embodiments, the inner
annular hole-free region extends from the core region to a radius
R2, wherein the inner annular hole-free region has a radial width
W12, equal to R2-R1, and W12 is greater than 1 .mu.m. Radius R2 is
preferably greater than 5 .mu.m, more preferably greater than 6
.mu.m. The intermediate annular hole-containing region extends
radially outward from R2 to radius R3 and has a radial width W23,
equal to R3-R2. The outer annular region 186 extends radially
outward from R3 to radius R4. Radius R4 is the outermost radius of
the silica portion of the optical fiber. One or more coatings may
be applied to the external surface of the silica portion of the
optical fiber, starting at R4, the outermost diameter or outermost
periphery of the glass part of the fiber. The core region and the
cladding region are preferably comprised of silica. The core region
is preferably silica doped with one or more dopants. Preferably,
the core region is hole-free. The hole-containing region has an
inner radius R2 which is not more than 20 .mu.m. In some
embodiments, R2 is not less than 10 .mu.m and not greater than 20
.mu.m. In other embodiments, R2 is not less than 10 .mu.m and not
greater than 18 .mu.m. In other embodiments, R2 is not less than 10
.mu.m and not greater than 14 .mu.m. Again, while not being limited
to any particular width, the hole-containing region has a radial
width W23 which is not less than 0.5 .mu.m. In some embodiments,
W23 is not less than 0.5 .mu.m and not greater than 20 .mu.m. In
other embodiments, W23 is not less than 2 .mu.m and not greater
than 12 .mu.m. In other embodiments, W23 is not less than 2 .mu.m
and not greater than 10 .mu.m.
[0165] Such fiber can be made to exhibit a fiber cutoff of less
than 1400 nm, more preferably less than 1310 nm, a 20 mm macrobend
induced loss at 1550 nm of less than 1 dB/turn, preferably less
than 0.5 dB/turn, even more preferably less than 0.1 dB/turn, still
more preferably less than 0.05 dB/turn, yet more preferably less
than 0.03 dB/turn, and even still more preferably less than 0.02
dB/turn, a 12 mm macrobend induced loss at 1550 nm of less than 5
dB/turn, preferably less than 1 dB/turn, more preferably less than
0.5 dB/turn, even more preferably less than 0.2 dB/turn, still more
preferably less than 0.01 dB/turn, still even more preferably less
than 0.05 dB/turn, and a 8 mm macrobend induced loss at 1550 nm of
less than 5 dB/turn, preferably less than 1 dB/turn, more
preferably less than 0.5 dB/turn, and even more preferably less
than 0.2 dB-turn, and still even more preferably less than 0.1
dB/turn.
[0166] The fiber of some embodiments of the present invention
comprises a core region that is surrounded by a cladding region
that comprises randomly disposed voids which are contained within
an annular region spaced from the core and positioned to be
effective to guide light along the core region. Other optical
fibers and microstructured fibers may be used in the present
invention. Additional features of the microstructured optical
fibers of additional embodiments of the present invention are
described more fully in pending U.S. patent application Ser. No.
11/583,098 filed Oct. 18, 2006, and provisional U.S. patent
application Ser. Nos. 60/817,863 filed Jun. 30, 2006; 60/817,721
filed Jun. 30, 2006; 60/841,458 filed Aug. 31, 2006; and 60/841,490
filed Aug. 31, 2006; all of which are assigned to Corning
Incorporated and the disclosures of which are incorporated by
reference herein.
[0167] It will be apparent to those skilled in the art that various
modifications and variations can be made to the present invention
without departing from the spirit and scope of the invention. Thus,
it is intended that the present invention cover the modifications
and variations of this invention provided they come within the
scope of the appended claims and their equivalents.
* * * * *
References