U.S. patent application number 10/013327 was filed with the patent office on 2002-12-05 for hybrid universal broadband telecommunications using small radio cells interconnected by free-space optical links.
Invention is credited to Acampora, Anthony.
Application Number | 20020181444 10/013327 |
Document ID | / |
Family ID | 21884286 |
Filed Date | 2002-12-05 |
United States Patent
Application |
20020181444 |
Kind Code |
A1 |
Acampora, Anthony |
December 5, 2002 |
Hybrid universal broadband telecommunications using small radio
cells interconnected by free-space optical links
Abstract
Diverse communication terminals attach via broadband radio to a
communications network at any of typically three hierarchical cell
sizes increasing from, typically, a single building to a city to a
region. Almost all telecommunications traffic transpires, however,
within lowest-level "picocells 1" to and from low cost "base
stations 11" that have typically one radio transceiver 111, four
optical transceivers 112, an ATM switch 113 and an ATM controller
114. Each local "base station 11" is interconnected to a regional
"end office switch 12", where is realized connection to a worldwide
wire/fiber line communications backbone 4, upon a multi-hop mesh
network 100 via short highly-focused free-space broadband
directional optical links 10. By this free-space wireless broadband
access the need for new broadband access cabling the "last mile" to
subscriber/users is totally surmounted. Subscriber service is of
the order of 20 Mb/s peak rate, and 10 Mb/s average rate.
Inventors: |
Acampora, Anthony; (La
Jolla, CA) |
Correspondence
Address: |
FUESS & DAVIDENAS
ATTN: William C. Fuess
Suite 11-G
10951 Sorrento Valley Road
San Diego
CA
92121-1613
US
|
Family ID: |
21884286 |
Appl. No.: |
10/013327 |
Filed: |
November 6, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10013327 |
Nov 6, 2001 |
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09527087 |
Mar 16, 2000 |
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6314163 |
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09527087 |
Mar 16, 2000 |
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08994800 |
Dec 19, 1997 |
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6049593 |
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60035698 |
Jan 17, 1997 |
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Current U.S.
Class: |
370/352 ;
370/351 |
Current CPC
Class: |
H04B 10/11 20130101;
H04W 16/32 20130101; H04W 36/04 20130101; H04B 10/25753 20130101;
H04B 10/1125 20130101; H04B 10/25752 20130101 |
Class at
Publication: |
370/352 ;
370/351 |
International
Class: |
H04L 012/66 |
Claims
What is claimed is:
1. A telecommunications apparatus comprising: a communications
switch; a first transceiver, electrically coupled to the
communications switch, for wirelessly telecommunicating externally
to the apparatus in a first portion of the electromagnetic
spectrum; a second transceiver, electrically coupled to the
communications switch, for wirelessly telecommunicating externally
to the apparatus in a second portion of the electromagnetic
spectrum that is of higher frequency than is the first portion; and
a controller for causing the communications switch to first-route
telecommunications traffic between the first transceiver and the
second transceiver; wherein wireless telecommunications are
first-routed between a first and a second, higher frequency,
portion of the electromagnetic spectrum.
2. The telecommunications apparatus according to claim 1 wherein
the first transceiver comprises: a radio transceiver electrically
connected to the communications switch for wirelessly
telecommunicating externally to the apparatus in the radio portion
of the electromagnetic spectrum.
3. The telecommunications apparatus according to claim 2 wherein
the second transceiver comprises: a transceiver of free-space
optical telecommunications signals electrically connected to the
communications switch; wherein wireless telecommunications are
first-routed between radio and optical portions of the
electromagnetic spectrum.
4. The telecommunications apparatus according to claim 2 wherein
the second transceiver comprises: a millimeter wavelength radio
transceiver of millimeter wavelength telecommunications signals;
wherein wireless telecommunications are first-routed between a
first radio portion of the electromagnetic spectrum and a second,
millimeter wavelength, portion of the electromagnetic spectrum that
is of higher frequency than is the first portion.
5. The telecommunications apparatus according to claim 1 wherein
the communications switch comprises: an Asynchronous Transfer Mode
switch that is electrically connected to both the first transceiver
and the second transceiver.
6. The telecommunications apparatus according to claim 1 wherein
the first transceiver comprises: a radio transceiver,
wire-connected to the communications switch, for telecommunicating
externally to the apparatus by radio signals.
7. The telecommunications apparatus according to claim 6 wherein
the radio transceiver comprises: a cellular radio receiver and a
receive antenna; and a cellular radio transmitter and a transmit
antenna.
8. The telecommunications apparatus according to claim 1 wherein
the second transceiver comprises: a transceiver of free-space
optical signals, wire-connected to the communications switch, for
telecommunicating externally to the apparatus by free space optical
signals.
9. The telecommunications apparatus according to claim 8 wherein
the optical transceiver comprises: a plurality of optical receivers
each receiving free-space optical telecommunications signals over a
different free-space optical path; and a plurality of optical
transmitters each transmitting free-space optical
telecommunications signals over a different free-space optical
path; wherein free-space optical telecommunications may be
maintained over a plurality of different free-space optical
paths.
10. The telecommunications apparatus according to claim 9 wherein
the controller is further for causing that the communications
switch should second route telecommunications traffic from the
optical receivers to the optical transmitters; wherein wireless
telecommunications are not only first-routed between the first
portion of the electromagnetic spectrum and a free space optical
portion of the electromagnetic spectrum, but are also second-routed
between free-space optical paths.
11. The telecommunications apparatus according to claim 10 situated
in a wireless telecommunications mesh of a multiplicity of
identical apparatus wherein wireless telecommunications in the
first portion of the electromagnetic spectrum are local to a
locally-situated first transceiver; wherein wireless free-space
optical telecommunications in the optical portion of the
electromagnetic spectrum are between physically proximately located
second, optical, transceivers; and wherein telecommunications are
not only first-routed between the first portion of the
electromagnetic spectrum and the free-space optical portion of the
electromagnetic spectrum, but are also second-routed between the
plurality of free-space optical paths all of which paths are in the
optical portion of the electromagnetic spectrum.
12. The telecommunications apparatus according to claim 1 wherein
the second transceiver comprises: a transceiver of millimeter
wavelength radio signals, wire-connected to the communications
switch, for telecommunicating externally to the apparatus by
millimeter wavelength radio signals.
13. The telecommunications apparatus according to claim 12 wherein
the millimeter wavelength radio transceiver comprises: a plurality
of millimeter wavelength radio receivers each receiving millimeter
wavelength radio telecommunications signals over a different
free-space path; and a plurality of millimeter wavelength radio
transmitters each transmitting free-space millimeter wavelength
radio telecommunications signals over a different free-space path;
wherein free-space millimeter wavelength radio telecommunications
may be maintained over a plurality of different free-space
paths.
14. The telecommunications apparatus according to claim 13 wherein
the controller is further for causing that the communications
switch should second route telecommunications traffic from the
millimeter wavelength radio receivers to the millimeter wavelength
radio transmitters; wherein wireless telecommunications are not
only first-routed between the first portion of the electromagnetic
spectrum and a millimeter wavelength radio portion of the
electromagnetic spectrum, but are also second-routed between
free-space millimeter wavelength radio paths.
15. The telecommunications apparatus according to claim 14 situated
in a wireless telecommunications mesh of a multiplicity of
identical apparatus wherein wireless telecommunications in the
first portion of the electromagnetic spectrum are local to a
locally-situated first transceiver; wherein wireless free-space
millimeter radio telecommunications in the millimeter wavelength
radio portion of the electromagnetic spectrum are between
physically proximately located second, millimeter wavelength radio,
transceivers; and wherein telecommunications are not only
first-routed between the first portion of the electromagnetic
spectrum and the millimeter wavelength radio portion of the
electromagnetic spectrum, but are also second-routed between the
plurality of millimeter wavelength radio paths all of which paths
are in the millimeter wavelength radio portion of the
electromagnetic spectrum.
16. The telecommunications apparatus according to claim 1 wherein
the second transceiver comprises: at least one transceiver of
free-space optical signals, wire-connected to the communications
switch, for telecommunicating externally to the apparatus by free
space optical signals; and at least one transceiver of millimeter
wavelength radio signals, also wire-connected to the communications
switch, for telecommunicating externally to the apparatus by
millimeter wavelength radio signals; wherein telecommunications
external to the apparatus in the second portion of the
electromagnetic spectrum is hybrid by both free-space optical
signals and millimeter wavelength radio signals.
17. A telecommunications method comprising: first-telecommunicating
a local omnidirectional first-frequency first signal by use of an
omnidirectional first-frequency first wireless transceiver;
second-telecommunicating a plurality of local directional second
signals of a second frequency, higher than is the first frequency,
by use of an associated plurality of directional second-frequency
second wireless transceivers; converting between (i) the first
signal, as is telecommunicated with the first wireless transceiver,
and (i) some particular one of a second signals, as is associated
with a particular second wireless transceiver, in accordance with a
protocol for telecommunicating along a chosen directional path;
while cross-communicating between the second transceivers so that
all second signals directionally telecommunicated by use of any one
of the second transceivers is further telecommunicated by use of
another one of the second transceivers so as to advance further
telecommunicate each second signal, as well as the converted first
signal, along a chosen directional path in accordance with the
protocol; wherein, although both first-telecommunicating and
second-telecommunicating are of local signals, the omnidirectional
first-frequency first signal is immediately converted to a
second-frequency directional second signal, and is then further
directionally telecommunicated, while the directionally
telecommunicated second-frequency signals are still further
directionally telecommunicated, along the chosen directional
path.
18. The telecommunications method according to claim 17 wherein the
first-telecommunicating of the local omnidirectional
first-frequency first signal by use of the omnidirectional
first-frequency first wireless transceiver comprises;
first-telecommunicating a local omnidirectional radio signal by use
of an omnidirectional radio wireless transceiver.
19. The telecommunications method according to claim 17 wherein the
second-telecommunicating of the plurality of local directional
second signals of the second frequency by use of the associated
plurality of directional second-frequency second wireless
transceivers comprises: second-telecommunicating a plurality of
local directional free-space optical signals by use of the
associated plurality of directional free-space optical
transceivers.
20. The telecommunications method according to claim 17 wherein the
second-telecommunicating of the plurality of local directional
second signals of the second frequency by use of the associated
plurality of directional second-frequency second wireless
transceivers comprises: second-telecommunicating a plurality of
local directional free-space millimeter-wavelength radio by use of
the associated plurality of directional millimeter-wavelength radio
transceivers.
21. The telecommunications method according to claim 17 wherein the
second-telecommunicating of the plurality of local directional
second signals of the second frequency by use of the associated
plurality of directional second-frequency second wireless
transceivers comprises: second-telecommunicating both (i) a
plurality of local directional free-space optical signals by use of
the associated plurality of directional free-space optical
transceivers and (ii) a plurality of local directional free-space
millimeter-wavelength radio by use of the associated plurality of
directional millimeter-wavelength radio transceivers.
22. A telecommunications apparatus comprising: a communications
switch; a broadband radio first transceiver, electrically connected
to the communications switch, for wirelessly telecommunicating
omnidirectinally externally to the apparatus by broadband radio in
a first, radio, portion of the electromagnetic spectrum; a second
transceiver, electrically connected to the communications switch,
for wirelessly telecommunicating directionally externally to the
apparatus in a second portion of the electromagnetic spectrum; and
a controller for causing the communications switch to first-route
telecommunications traffic between the broadband radio first
transceiver and the second transceiver.
23. The telecommunications apparatus according to claim 22 wherein
the second transceiver comprises: an optical transceiver wirelessly
directionally telecommunicating across free-space optical
links.
24. The telecommunications apparatus according to claim 23 wherein
the optical transceiver comprises: a plurality of optical receivers
each receiving free-space optical telecommunications signals over a
different-direction free-space optical path; and a plurality of
optical transmitters each transmitting free-space optical
telecommunications signals over a different-direction free-space
optical path; wherein free-space optical telecommunications may be
maintained over a plurality of different-direction free-space
optical paths.
25. The telecommunications apparatus according to claim 24 wherein
the controller is further causing the communications switch to
second-route telecommunications traffic from the optical receivers
to the optical transmitters; wherein wireless telecommunications
are not only first-routed between the first portion of the
electromagnetic spectrum and a free space optical portion of the
electromagnetic spectrum, but are also second-routed between
free-space optical paths.
26. The telecommunications apparatus according to claim 22 wherein
the second transceiver comprises: a millimeter wavelength radio
transceiver wirelessly directionally telecommunicating across
free-space radio links.
27. The telecommunications apparatus according to claim 26 wherein
the millimeter wavelength radio transceiver comprises: a plurality
of millimeter wavelength radio receivers each directionally
receiving free-space radio telecommunications signals over a
different-direction free-space path; and a plurality of millimeter
wavelength radio transmitters each directionally transmitting
free-space radio telecommunications signals over a
different-direction free-space path; wherein free-space millimeter
wavelength radio telecommunications may be maintained over a
plurality of different-direction free-space paths.
28. The telecommunications apparatus according to claim 27 wherein
the controller is further causing the communications switch to
second-route telecommunications traffic from the millimeter
wavelength radio receivers to the millimeter wavelength radio
transmitters; wherein wireless telecommunications are not only
first-routed between the radio portion of the electromagnetic
spectrum and a millimeter wavelength radio portion of the
electromagnetic spectrum, but are also second-routed between
millimeter wavelength radio free-space paths.
29. The telecommunications apparatus according to claim 22 wherein
the second transceiver comprises: at least one optical transceiver
wirelessly directionally telecommunicating across free-space
optical links; and at least one millimeter wavelength radio
transceiver wirelessly directionally telecommunicating across
free-space radio links.
30. The telecommunications apparatus according to claim 22 situated
in a wireless telecommunications mesh of a multiplicity of
identical apparatus wherein omnidirectional wireless
telecommunications in the first, radio, portion of the
electromagnetic spectrum are local to a locally-situated radio
first transceiver; and wherein wireless directional free space
telecommunications in the second portion of the electromagnetic
spectrum are directionally between second transceivers of
physically proximately located apparatus.
31. The telecommunications apparatus according to claim 30 wherein
the second transceiver comprises: a plurality of receivers each
receiving directional telecommunications signals over a
different-direction free-space path; and a plurality of
transmitters each transmitting directional telecommunications
signals over a different-direction free-space path; wherein
free-space telecommunications may be maintained over a plurality of
different-direction free-space paths.
32. The telecommunications apparatus according to claim 31 wherein
the controller is further causing the communications switch to
second-route telecommunications traffic from the second receivers
to the second transmitters; wherein telecommunications are not only
first-routed between the first portion of the electromagnetic
spectrum and the second portion of the electromagnetic spectrum,
but are also second-routed between the plurality of free-space
paths, all of which paths are in the second portion of the
electromagnetic spectrum.
33. A telecommunications method for and upon a communications mesh
network of arrayed nodes, the method comprising: wirelessly locally
radio telecommunicating to a radio transceiver at each node by
radio; wirelessly locally directionally optically free-space
telecommunicating between each of a plurality of optical
transceivers, co-located with each other and with the radio
transceiver at each node, by a plurality of directional free-space
optical signals to a plurality of nearby nodes; and first-routing,
at each node, telecommunications to and from the radio transceiver
and a selected one of the plurality of optical receivers that is so
selected in accordance with a protocol for telecommunicating along
a chosen path upon the mesh; while second-routing, at each node,
telecommunications received at one or more of the plurality of
local directional optical transceivers to another one or ones of
the plurality of local directional optical transceivers so to
establish and maintain optical telecommunications along a path upon
the mesh that is chosen in accordance with the protocol; wherein,
by the radio telecommunicating and the optical telecommunicating,
and by the first-routing and the second-routing, telecommunications
transpires (i) omnidirectionally at each node by radio, and (ii)
directionally between nodes upon the path upon the mesh by
optics.
34. The telecommunications method according to claim 33 wherein the
wirelessly locally radio telecommunicating is by broadband radio in
a broadband radio transceiver.
35. The telecommunications method according to claim 33 wherein the
wirelessly locally radio telecommunicating is in accordance with
Asynchronous Transfer Mode protocol.
36. The telecommunications method according to claim 33 wherein the
wirelessly locally optically free-space telecommunicating is in
accordance with Asynchronous Transfer Mode protocol.
37. The telecommunications method according to claim 33 wherein the
protocol for the telecommunicating along a chosen path upon the
mesh is developed at a node, called an end-office, that is common
to all paths.
38. The telecommunications method according to claim 33 wherein the
protocol for the telecommunicating is implemented at (i) the node,
called an end-office, that is common to all paths, and at (ii) all
nodes along the path upon the mesh that is chosen in accordance
with the protocol.
39. The telecommunications method according to claim 33 wherein the
protocol for the telecommunicating is implemented collectively at
(i) the node, called an end-office, that is common to all paths,
and at (ii) all the arrayed nodes of the mesh, including both those
nodes that are along the path upon the mesh that is chosen in
accordance with the protocol and those nodes that are not along
this path; wherein arrayed nodes of the mesh that are not along the
path do not become involved in actively implementing the
communications protocol until, and unless, the path changes, as
will be the case when and if the wirelessly locally radio
telecommunicating by the radio transceiver changes to a new node,
at which time even then only those nodes that are newly along a new
path upon the mesh that is chosen in accordance with the protocol
will become involved; wherein the protocol for the
telecommunicating is kept upon all the arrayed nodes of the entire
mesh, but is at any one time actively implemented by only those
nodes that are along a telecommunications path.
40. A telecommunications apparatus, called a base station, located
within a multi-hop free-space optical telecommunications mesh
consisting of a large number of identical base stations
geographically dispersed, each base station of the mesh comprising:
a communications switch; a first transceiver, electrically
connected to the communications switch, for wirelessly
telecommunicating locally externally to the base station; a
plurality of optical transceivers, electrically connected to the
communications switch, for wirelessly directionally
telecommunicating externally to the base station by an associated
free-space directional optical link; and a controller for causing
the communications switch to route (i) telecommunications traffic
telecommunicated with the first transceiver to one of the plurality
of optical transceivers, and (ii) also optical telecommunications
traffic received at one directional optical transceiver to another
directional optical transceiver for further free-optical optical
transmission, all to the consistent purpose and end that
telecommunications traffic to and from the first transceiver should
be routed through a selected co-located directional optical
transceiver and then through the further directional optical
transceivers of whatsoever number of other base stations as are
required until reaching a particular base station called an end
office; wherein radio and free-space optical communications upon
the mesh support telecommunications between, on the one hand, (i) a
first transceiver of a base station and, on the other hand, (ii) a
particular base station called the end office.
41. The base station telecommunications apparatus according to
claim 40 wherein the first transceiver comprises: a radio
transceiver for wirelessly telecommunicating locally externally to
the base station by radio.
42. The base station telecommunications apparatus according to
claim 40 wherein the controller is causing the communications
switch to route (ii) optical telecommunications traffic received at
one directional optical transceiver to another directional optical
transceiver for further free-optical optical transmission through
the further directional optical transceivers of whatsoever number
of other base stations as are required until reaching a selected
optical transceiver of a particular base station called an end
office; wherein radio and free-space optical communications upon
the mesh support telecommunications between, on the one hand, (i) a
first transceiver of a base station and, on the other hand, (ii) a
optical transceiver of the particular base station called the end
office.
43. The base-station telecommunications apparatus according to
claim 42 located within a radio and multi-hop free-space optical
telecommunications mesh of a large number of identical base
stations geographically distributed wherein the particular base
station called the end office comprises: an end-office
communications switch; a connection between the end-office switch
and a communications backbone external to the system to which
backbone other end-offices also connect; a plurality of end-office
transceivers, electrically connected to the end-office
communications switch, for wirelessly telecommunicating externally
to the end-office in order to (i) receive across free-space
telecommunications links the telecommunications traffic received by
all the radio transceivers of all the base stations, and (ii)
transmit across the free-space telecommunications links
telecommunications traffic received from the communications
backbone to a particular radio transceiver of a particular base
station; and a controller for causing the end-office communications
switch to route communications traffic between, on the one hand,
the wired connection to the external communications backbone and,
on the other hand, the plurality of end-office transceivers;
wherein both (i) radio, and (ii) free-space telecommunications
across free-space telecommunications links, are bi-directional
between the end-office and each radio transceiver of all base
stations.
44. The base-station telecommunications apparatus according to
claim 43 wherein the end office's plurality of transceivers
comprise: optical transceivers for wirelessly optically
telecommunicating externally to the end-office in order to (i)
receive across the free-space optical telecommunications links the
telecommunications traffic received by all the radio transceivers
of all the base stations, and (ii) transmit telecommunications
traffic received from the communications backbone across the
free-space optical telecommunications links to a particular radio
transceiver of a particular base station; wherein the controller is
causing the end-office communications switch to route
communications traffic between, on the one hand, the wired
connection to the external communications backbone and, on the
other hand, the plurality of end-office optical transceivers;
wherein both (i) radio, and (ii) free-space optical
telecommunications, are bi-directional between the end-office and
each radio transceiver of all base stations.
45. The base-station telecommunications apparatus according to
claim 43 wherein the end office's plurality of transceivers
comprise: millimeter wavelength radio transceivers for wirelessly
millimeter radio telecommunicating externally to the end-office in
order to (i) receive across the free-space millimeter radio
telecommunications links the telecommunications traffic received by
all the radio transceivers of all the base stations, and (ii)
transmit telecommunications traffic received from the
communications backbone across the free-space millimeter radio
telecommunications links to a particular radio transceiver of a
particular base station; wherein the controller is causing the
end-office communications switch to route communications traffic
between, on the one hand, the wired connection to the external
communications backbone and, on the other hand, the plurality of
end-office millimeter radio transceivers; wherein both (i) radio,
and (ii) free-space millimeter radio telecommunications, are
bi-directional between the end-office and each radio transceiver of
all base stations.
46. A communications system comprising: an end-office having a
communications switch, a hardwired connection between the switch
and a communications backbone external to the system to which
communications backbone other end-offices also connect, a plurality
of optical transceivers, electrically connected to the
communications switch, for telecommunicating externally to the
end-office optically through free space, and a controller for
causing the communications switch to route communications traffic
between (i) the hardwired connection to the external communications
backbone and (ii) the plurality of optical transceivers; and a
multi-hop mesh of radio-telecommunicating and
optically-free-space-telecommunicating base stations each having a
communications switch, a plurality of optical transceivers,
electrically connected to the communications switch, for wirelessly
telecommunicating externally to the base station by free-space
optical links, and a controller for causing the communications
switch to route received optical communications traffic from a
receiving to a transmitting optical transceiver to the purpose and
the end that telecommunications traffic at any individual base
station will be free-space optically communicated though whatsoever
number of base stations is required until telecommicatively
connecting to the end office and to the communications backbone;
wherein free-space optical communications upon the mesh are
variably routed from one base station to another.
47. The communications system according to claim 46 wherein the
multi-hop mesh of optically-free-space-telecommunicating base
stations is further of base stations that are additionally
radio-telecommunicating, and wherein each of these
radio-telecommunicating and optically-free-space-te-
lecommunicating base stations further has, in addition to its
communications switch, its plurality of optical transceivers, and
its controller: a radio transceiver, electrically connected to the
communications switch, for wirelessly communicating by radio
externally to the base stations; wherein the controller is further
causing the switch to route communications traffic between the
radio transceiver and the optical transceivers.
48. A communications system comprising: an end-office having a
communications switch, a hardwired connection between the switch
and a communications backbone external to the system to which
communications backbone other end-offices also connect, a plurality
of optical transceivers, electrically connected to the
communications switch, for wirelessly telecommunicating externally
to the end-office optically through free space, and a controller
for causing the communications switch to route communications
traffic between (i) its hardwired connection to the external
communications backbone and (ii) the plurality of optical
transceivers; and a multi-hop mesh of free-space
optically-communicating base stations each having a communications
switch, a radio transceiver, electrically connected to the
communications switch, for wirelessly telecommunicating by radio
locally externally to the base station, a plurality of optical
transceivers, electrically connected to the communications switch,
for wirelessly communicating regionally externally to the base
station by free-space optical links, and a controller for causing
the communications switch (i) to route telecommunications traffic
between the radio transceiver and the optical transceivers, and
(ii) to route received optical communications traffic from a
receiving to a transmitting optical transceiver, to the purpose and
the end that local telecommunications traffic at the radio
transceiver is free-space optically communicated step-wise
regionally through the optical transceivers of whatsoever number of
base stations are required to and from the end office, and upon the
communications backbone; wherein radio telecommunications local to
one base station are free-space optically telecommunicated upon the
mesh until ultimately communicatively interconnecting to the
communications backbone.
49. A communications method comprising: bi-directionally
wire/cable-communicating information between a communications
switch at a particular, end-office, site and a hardwired connection
to a communications backbone which backbone is external to the
end-office site and to which other end-office sites also connect;
end-office-wire/cable-s- witching the information between the
end-office communications switch and a selected one of a plurality
of wireless first transceivers, co-located at the end office with
and electrically wire/cable connected to the communications switch,
where the selected one of the plurality of wireless first
transceivers at the end office is so selected in accordance with
the information telecommunicated; first
wirelessly-telecommunicating the information through the selected
one of the plurality of wireless first transceivers into free
space, and onto a mesh of a multiplicity of free-space wireless
communication transceivers; further first
wirelessly-telecommunicating the information upon successive links
in free space upon the mesh, and through successive selected ones
of the multiplicity of wireless first transceivers as are each
located at a geographically separated mesh node, the successive
selections of which ones of the wireless first transceivers are
invoked for telecommunication upon the mesh, and the direction of
the telecommunication of the information upon the mesh, all being
in accordance with the information, until a mesh telecommunications
linkage is ultimately made with a wireless first transceiver at a
particular selected, base station, mesh node;
base-station-wire/cable-switching, in a switch at the selected base
station mesh node that wire/cable connected to the wireless first
transceiver at this selected base station mesh node, the
information between the wireless first transceiver at this selected
base-station node and a wireless second transceiver that is
co-located at this selected base-station node along with the first
transceiver; and second wirelessly-telecommunicating the
information with and through the second transceiver to a
telecommunicating device in the local geographical region of the
selected base-station node; wherein communications and
telecommunications have transpired by, inter alia,
wire/cable-communicating at the end-office, first
wirelessly-telecommunic- ating over free-space mesh network links
between the end-office and the selected base station node, and
second wirelessly-telecommunicating at the selected base station
node to the telecommunicating device.
50. The communications method according to claim 49 wherein the
end-office-switching of the information is between the end-office
communications switch and a selected one of a plurality of
directional optical first transceivers; wherein the
wirelessly-optically-telecommunic- ating of the information is
through the selected one of a plurality of directional optical
first transceivers into free space, and onto a mesh of a
multiplicity of free-space directional optical telecommunication
first transceivers; wherein the further
wirelessly-telecommunicating of the information is optically in
free space upon the mesh through successive selected ones of the
multiplicity of directional optical telecommunication first
transceivers; wherein the base-station switching, in a switch at
the selected base station node, is of the information between the
optical first transceiver at this selected base-station node and a
radio second transceiver that is co-located at this selected
base-station node along with the optical first transceiver; and
wherein the wirelessly-telecommunicating of the information is from
the radio second transceiver to a radio-telecommunicating device in
the local geographical region of the selected base-station
node.
51. A hybrid telecommunications system where both (i)
omnidirectional telecommunications, and (ii) directional
telecommunications, transpire upon at least some of a multiplicity
of communications paths between a corresponding multiplicity of
end-users and a cable-based communications backbone, the system
CHARACTERIZED IN THAT each of the multiplicity of end-users
telecommunicates, via an omnidirectional telecommunications signal,
with the system at a one of a plurality of system cells that are
upon each of a plurality of hierarchical system cell levels, an
end-user that proves unable to telecommunicate with the system
through a system cell located at a lowest system cell hierarchical
level attempting to communicate with a system cell at a next higher
system cell hierarchical level and so on until telecommunications
access to the system is finally obtained; where IF omnidirectional
telecommunications access to the system is successfully achieved at
a system cell that is upon the lowest system cell hierarchical
level THEN, starting from this particular lowest-hierarchical-level
system cell where the telecommunications access has been so
achieved, telecommunication then transpires by directional
telecommunications signals directionally across directional
telecommunications links organized as a mesh until a particular,
end-office, system cell is reached which end-office cell is,
nonetheless to being upon the lowest system cell hierarchical
level, communicatively connected to a cable-based communications
backbone, whereupon telecommunications with the end user that has
been in part (i) omnidirectional, and in part (ii) directional, is
summarily, at this end-office system cell, communicatively joined
to the cable-based communications backbone; and ELSE IF, upon such
times as omnidirectional telecommunications access to the system is
not achieved at the lowest system cell hierarchical level but is
instead achieved only a higher system cell hierarchical level,
THEN, system cells upon these higher hierarchical system cell
levels being directly communicatively connected to the cable-based
communications backbone, the telecommunications with the end user
that has been omnidirectional, is summarily, and at this
higher-hierarchical-level system cell, communicatively joined to
the cable-based communications backbone; wherein upon
telecommunications upon at least some of the multiplicity of
communications paths between the corresponding multiplicity of
end-users and the cable-based communications backbone are (i) in
part omnidirectional and (ii) in part directional.
52. The hybrid radio and optical telecommunication system according
to claim 51 FURTHER CHARACTERIZED IN THAT omnidirectional
telecommunications are by radio, with an omnidirectional radio
telecommunications signal.
53. The hybrid radio and optical telecommunication system according
to claim 51 FURTHER CHARACTERIZED IN THAT directional
telecommunications are optical, over directional free-space optical
links.
54. The hybrid radio and optical telecommunication system according
to claim 51 FURTHER CHARACTERIZED IN THAT directional
telecommunications are by millimeter wavelength radio, over
directional millimeter wavelength radio links.
55. A hybrid telecommunications system where both (i) radio
telecommunications, and (ii) free-space optical telecommunications,
transpire upon at least some of a multiplicity of communications
paths between a corresponding multiplicity of end-users and a
cable-based communications backbone, the system CHARACTERIZED IN
THAT each of the multiplicity of end-users telecommunicates, via a
radio telecommunications signal, with the system at a one of a
plurality of system cells that is upon each of a plurality of
hierarchical system cell levels, an end-user that proves unable to
telecommunicate with the system through a system cell at a lowest
system cell hierarchical level attempting to communicate with a
system cell at a next higher system cell hierarchical level and so
on until radio telecommunications access to the system is finally
obtained; where, upon such times as radio telecommunications access
to the system is successfully achieved at the lowest system cell
hierarchical level, then, starting from a particular
lowest-hierarchical-level system cell where this telecommunications
access is so achieved, telecommunication then transpires across
free-space optical links organized as a mesh until a particular,
end-office, system cell is reached which end-office cell is,
nonetheless to being upon the lowest hierarchical system cell
level, communicatively connected to a cable-based communications
backbone, whereupon the telecommunications with the end user that
have been (i) in part by radio, and (ii) in part by free-space
optical, are summarily, and at this end-office system cell,
communicatively joined to the cable-based communications backbone;
and where, upon such times as radio telecommunications access to
the system is not achieved at the lowest system cell hierarchical
level but is instead achieved only a higher system cell
hierarchical level, then, system cells upon these higher
hierarchical system cell levels being directly communicatively
connected to the cable-based communications backbone, the
telecommunications with the end user that has transpired by radio,
is summarily, and at this higher-hierarchical-level system cell,
communicatively joined to the cable-based communications backbone;
wherein upon at least some of the multiplicity of communications
paths between the corresponding multiplicity of end-users and the
cable-based communications backbone telecommunications are (i) in
part by radio and (ii) in part by free-space optical links.
56. The hybrid radio and optical telecommunication system according
to claim 55 FURTHER CHARACTERIZED IN THAT the radio
telecommunications are omnidirectional, by an omnidirectional radio
telecommunications signal.
57. The hybrid radio and optical telecommunication system according
to claim 55 FURTHER CHARACTERIZED IN THAT the free-space optical
telecommunications are directional, by directional free-space
optical telecommunications links.
58. A broadband free-space network access system for providing
broadband telecommunications services to stationary and mobile user
devices comprising: multiple sets of plural
geographically-localized uniquely-identified first-tier
telecommunication stations called base stations, each base station
bi-directionally wirelessly telecommunicating by a broadband
free-space first signal with a plurality of user devices within a
small-size area geographically local to the base station, each set
of plural base stations providing in combination broadband
free-space wireless telecommunications to most, but not necessarily
all, of the user devices that are within a medium-size geographical
area that includes the small-size geographical areas local to each
base station of the set; a free-space broadband communications
network for communicatively interconnecting, by free-space second
signals that are of different frequency than are the first signals,
the multiple sets of plural geographically-localized
uniquely-identified first-tier telecommunication base stations to a
communications backbone; and a multiplicity of second-tier stations
each within a medium-size geographical area, each second-tier
station bi-directionally wirelessly telecommunicating again by the
broadband free-space first signal with any user devices within the
medium-size geographical area which user devices are not otherwise
telecommunicating with first-tier telecommunication base stations,
and communicatively interconnecting these user devices to the
communications backbone; wherein any individual user device can,
and most commonly does, wirelessly telecommunicate through a
first-tier telecommunications base station within a small
geographical area local to the device in order to, after
communicating further across the free-space broadband
communications network, communicatively interconnect with the
communications backbone; but wherein any individual user device can
alternatively wirelessly telecommunicate within the medium-size
geographical area through a second-tier telecommunications station
in order to communicatively interconnect with the same
communications backbone.
59. The broadband radio network access system according to claim 58
wherein the collective base stations of each of the multiple sets
of plural geographically-localized first-tier telecommunications
base stations collectively provide radio telecommunications to the
majority of the user devices that are within a medium-size
geographical area including the small-size geographical areas that
are local to each base stations of the set; wherein most of the
radio telecommunications in each medium-sized geographical area is
through the first tier base stations, rather than through the
second-tier station.
60. The broadband radio network access system according to claim 59
wherein the first-tier telecommunication stations comprise: radio
station bi-directionally wirelessly telecommunicating by a
broadband radio signals.
61. The broadband radio network access system according to claim 60
wherein the free-space broadband communications-network comprises:
a network of optical transceivers for communicatively
interconnecting by free-space optical signals that are of different
frequency than are the radio signals.
62. The broadband radio network access system according to claim 59
wherein the second-tier telecommunication stations comprise: radio
stations bi-directionally wirelessly telecommunicating by a
broadband radio signals.
63. The broadband radio network access system according to claim 58
further comprising: a multiplicity of third-tier stations each
within a large-size geographical area subsuming a plurality of
medium-sized geographical areas where are located the second-tier
stations, each third-tier station bi-directionally wirelessly
telecommunicating again by the broadband free-space first signal
with any user devices within the large-size geographical area which
user devices are not otherwise telecommunicating with neither the
first-tier telecommunication base stations nor the second-tier
stations, and communicatively interconnecting these user devices to
the communications backbone; wherein any individual user device
can, and most commonly does, wirelessly telecommunicate through a
first-tier telecommunications base station within a small
geographical area local to the device, or alternatively, through a
second-tier telecommunications station within the medium-size
geographical area, but still can, further alternatively, wirelessly
telecommunicate within the large-size geographical area through a
third-tier telecommunications station in order to communicatively
interconnect with the same communications backbone. wherein
communications with and between user devices within the network
access system preferably transpires at a lowest system level of the
first-tier stations, but can if necessary transpire to and through
second-tier stations telecommunicating to user devices within a
medium geographical area, or even to and through third-tier
stations telecommunicating to user devices within a large
geographical area.
64. The broadband radio network access system according to claim 63
wherein the collective base stations of each of the multiple sets
of plural geographically-localized first-tier telecommunications
base stations, and the collective second-tier telecommunications
stations, collectively provide telecommunications to the vast
majority of the user devices that are within a large-size
geographical area including the medium-size geographical areas that
include the small-sized geographical areas that are local to each
base stations of the set; wherein most of the radio
telecommunications in each medium-sized geographical area is
through the first tier base stations, and a lessor amount is
through the second-tier station, and a still lessor amount is
through the third-tier station.
65. The broadband radio network access system according to claim 63
wherein the first-tier telecommunication stations comprise: radio
stations bi-directionally wirelessly telecommunicating by a
broadband radio signals; wherein the second-tier telecommunication
stations comprise: radio stations bi-directionally wirelessly
telecommunicating by a broadband radio signals; and wherein the
third-tier telecommunication stations comprise: radio stations
bi-directionally wirelessly telecommunicating by a broadband radio
signals.
67. The broadband radio network access system according to claim 66
wherein the free-space broadband communications network comprises:
a network of optical transceivers for communicatively
interconnecting by free-space optical signals that are of different
frequency than are the radio signals.
68. A communications system comprising: a mesh network
telecommunicatively interconnecting a multiplicity of communication
switches by and upon free-space telecommunications links; and means
for establishing virtual communication paths upon the mesh network
between ones of the multiplicity of communication switches.
69. The communications system according to claim 68 wherein the
mesh network is telecommunicatively interconnecting the
multiplicity of communication switches by and upon free-space
optical telecommunications links.
70. The communications system according to claim 68 wherein the
mesh network is telecommunicatively interconnecting the
multiplicity of communication switches by and upon free-space
millimeter wavelength radio telecommunications links.
71. The communications system according to claim 68 wherein the
means for establishing virtual communication paths upon the mesh
network between ones of the multiplicity of communication switches
is so establishing the virtual communications links in form of a
tree, the virtual communication paths from the multiplicity of
communication switches focusing to a root node communication switch
called an end office.
72. The communications system according to claim 71 wherein the
means for establishing virtual communication paths upon the mesh
network between ones of the multiplicity of communication switches
is located at the end office.
73. The communications system according to claim 71 wherein the
means for establishing virtual communication paths upon the mesh
network between ones of the multiplicity of communication switches
is distributed between the end office and some other ones of the
multiplicity of communication switches.
74. The communications system according to claim 71 wherein the
means for establishing virtual communication paths upon the mesh
network between ones of the multiplicity of communication switches
is distributed between among all the multiplicity of communication
switches.
Description
RELATION TO THE RELATED PATENT APPLICATIONS
[0001] The present patent application is related to U.S.
Provisional Patent Application Ser. No. 60/035/698 filed on Jan.
17, 1997, for a METHOD AND APPARATUS FOR HIGH CAPACITY RADIO ACCESS
SYSTEM. The related provisional patent application is to the
selfsame Anthony Acampora who is the inventor of the invention of
the present application.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention generally concerns wide area
multimedia broadband telecommunications systems and services,
particularly systems and services for homes, offices, outdoor
and/or remote locations where telecommunication terminals are
attached to a wire- or fiber-based telecommunications network via
wireless links, thereby permitting users of the telecommunications
terminals the ability to roam freely and obviating any requirement
that a wired "telecommunications outlet" should be available.
[0004] The present invention particularly concerns the
partitionment of wide area multimedia broadband telecommunications
systems and services both (i) in the media--radio, free-space
optical, or wire and fiber--over which communications traffic from
point to point and from time to time transpires, and also (ii) in
the system hardware, and among the system protocols, for handling
this communications traffic (upon the various media). All
partitionment is to the end of ensuring universal low-cost
high-performance wide-area (tele) communications availability. In
particular, the present invention will be seen to be concerned with
how to connect the existing world communications "backbone" which
is, in America circa 1997, based primarily on wire and optical
fiber lines, to the typical subscriber household and office--the
so-called "last mile" problem.
[0005] 2. Description of the Prior Art
[0006] 2.1 General Challenges Besetting Universal Communications
Systems and Services
[0007] For the past several years, the telecommunications industry
has witnessed an explosive growth in the demand for (1) non-voice
types of services (driven by so called multimedia traffic, and
suggestive of some unspecified combination of low and high speed
data, voice, image, and video); and (2) service to non-stationary,
mobile, end terminals. See D. Wright, Broadband: Business Services,
Technologies, and Strategic Impact, Artech House, Boston, 1993; A.
S. Acampora, An Introduction to Broadband Networks, Plenum Press,
New York, 1994; IEEE Communications Magazine, issue on Introducing
the Internet Technology Series, Vol. 35, No. 1, January 1997; T. S.
Rappaport, Wireless Communications Principles and Practice,
Prentice Hall, New Jersey, 1996; and IEEE Personal Communications,
issue on Wireless ATM, Vol. 3, No. 4, August 1996.
[0008] Despite this demand, three primary technical problems remain
to be solved before a communications infrastructure adequate to
meet modern demand can be created.
[0009] The first of these problems involves the inadequate capacity
afforded by the copper wires which typically presently, circa 1997,
serve to connect homes and offices to core, or "end-office",
switches within the existing U.S. national telecommunications
network. These wires are additionally characterized by their
inflexibility to accommodate new and added communications devices
at the user portal; exactly where changes are most likely to occur.
In other words, even if all the copper wire in the U.S. was to be
instantaneously converted to high-bandwidth fiber optics, the
locations, and the physical connections, of new telephones or
computers or televisions or other devices to the wire and fiber
communications network would remain troublesome, effectively
mandating extensive and expensive manual services to "wire" and
"re-wire" the home or office site every time site service
requirements change appreciably.
[0010] It would obviously be useful if some "magic box" existed in
the attic, or the communications closet, which permitted that any
communications device brought within the home or building, whether
permanently or temporarily, could be immediately wirelessly
integrated into the communications network totally without the use
of skilled labor. The "magic box" would preferably be universal,
inexpensive, and supportive of a high communications capacity.
Although this "magic box" might occasionally have to be upgraded if
new and very large communications requirements were to arise at the
home or office site, the requirement of expensively "custom wiring"
the communications of the home or office would be obviated.
[0011] The second problem concerns the limited available bandwidth
of the radio spectrum to meet the demand for non-stationary and/or
flexible communications services. The "black box" of the previous
section could clearly be a cellular radio transceiver serving to
link diverse communications devices, whether portable or not, to a
communications grid by radio. Alas, the radio spectrum that is both
now (i.e., in 1997) allocated, and reasonably allocatable, for
general telecommunications services is already crowded, and
incapable of meeting all the demands for real-time multimedia
communication arising over any extended populated geographical
area.
[0012] The third problem concerns the desire, if not the political
necessity, of guaranteeing universally (i) available and (ii)
affordable communications services. It is clearly possible to
auction the radio spectrum, and to let those who can afford more
use more. It is clearly possible to cost-effectively service
certain metropolitan areas while leaving communication "backwaters"
that are not fully enfranchised with evolving equipments and
services. However, in a democracy there are limits in allocating
the God-given public resource of the radio spectrum purely on
financial grounds.
[0013] At the same time the existing U.S. national communications
infrastructure presents challenges to future upgrading, it also
presents opportunity. As reported by author and futurist George
Gilder in his book "Into the Fibersphere", and in his columns of
the "Telecosm Series" appearing in Forbes Magazine, "the ultimate
source of bandwidth expansion is the immense capacity of optical
fiber. Now comprising a global installed base of 40 million miles
(25 million miles in North America), each optical fiber, as Paul
Green of IBM estimated to Forbes ASAP four years ago [i.e., in
1992] commands and intrinsic available bandwidth of 25,000
gigahertz." How much bandwidth is this? It is more than all the
radio telecommunications--from ultra low frequency communication
with submarines to K band satellite links--that are at any one time
transpiring on the entire planet. Yes, each single strand of 40
million miles of optic fiber already existing can potentially
handle all the radio traffic in the entire world.
[0014] Where then exactly is located this wonderful pipeline to all
the world's information? In America it is close by, but has not yet
reached the average American doorstep. Five years ago each American
household was an average of 1,000 households away from a fiber
node, now it is but 100. At the beginning of 1996 15% of U.S. cable
TV subscribers directly connected to fiber optics; at the end of
1996, 30%. Being that nut all American households presently have,
or even can have, cable television, the average separation in feet
of a U.S. household or business from an optic fiber is still
several hundred feet. And, due to the first problem discussed
above, many Americans in metropolitan areas literally have optic
fiber "at their feet" but are unable to effectively connect to
it.
[0015] It will be seen to be the objective of the present invention
to solve all three problems, and to cost-effectively and equitably
avail all the world's peoples of the opportunity to communicate
into the growing fiber optic communications "backbone" of the
United States and of the world.
[0016] The capacity and flexibility problem at the user interface
will be, by and large, solved by the present invention. The user
will be able to add new telecommunications devices at will within
broad limits. Although these devices will often be bi-directionally
communicating, and are in general used for purposes such as
Internet access, pay-per-view, programming on demand, and
multimedia communication that are quite different from traditional
broadcast radio and television, they will require no more
"installation" than, for example, does a store-purchased radio or
television receiving broadcast signals.
[0017] The limited available bandwidth of the radio spectrum will
likewise seen to be solved--without repealing physical laws--by the
expedient of reusing most portions of the radio spectrum.
[0018] Finally, the (i) availability and (ii) affordability of
universal communications services will also be seen to be dealt
with effectively in the present invention, where any system user is
but little burdened with the cost of the communications network if
he or she is but a light user of its services. The un-subsidized
cost of, for example, "life line" telecommunications services, even
in remote areas, should be commensurate with what it is now. This
is true even though an immediate "next" user who is adjacently
located both geographically and logically in the communications
network may volitionally use awesomely large telecommunications
services, incurring the costs therefore.
SUMMARY OF THE INVENTION
[0019] The present invention contemplates a new type of broadband
access system for providing high quality, bandwidth-upon-demand,
communication services to homes and offices. The invention is a
candidate architecture for immediate implementation as a
significant portion of the United States national communications
infrastructure in the twenty-first century, and is suitable for
world-wide use. This portion is particularly between (i) diverse
(tele)communicating equipments that are located in American homes
and offices and (ii) the U.S. national and world communications
"backbone" which is, by and large, presently based on copper wire
and on fiber optics. This portion of the U.S. national
communications infrastructure--which is the portion primarily dealt
with by the present invention--is commonly called the "last
mile".
[0020] 1. System General Description
[0021] In the communications system of the present invention,
diverse communication terminals attach to a communications network
via short radio links. Terminal users can roam freely within a
house or building unencumbered by availability of wired
communications outlets. Basic service is extended within this
region by and through small, high capacity, broadband radio cells
called "base stations".
[0022] Typically large grid arrays of base stations are
interconnected, each base station to several of its neighbors, via
short, highly focused free-space broadband optical or millimeter
wave links in a multi-hop mesh network. Stepwise multi-hop
communication upon the mesh ultimately leads to an "end office"
where access to a wire, or fiber, communications "backbone" is
made. By this totally free-space broadband access any need for new
broadband access cabling over the "last mile" is totally
surmounted.
[0023] A multi-tiered arrangement of radio cells further extends
radio telecommunications service both to out-of-building pedestrian
and to vehicular users. The projected several tiers of free-space
radio cells will ultimately provide universal broadband radio
telecommunications service over the entirety of the planet.
[0024] This approach of the present invention presents issues
involving reliability, availability, capacity, and hand-off. These
issues are identified and addressed in this specification. The
obtainable service rate is of the order of 20 Mb/s peak rate, and
10 Mb/s average rate, to each and all subscribers, universally
within a geographical area projected in the first instance be the
continental U.S.
[0025] The systems approach of the present invention surmounts
three broadband access challenges. The preferred system uses three
tiers of radio cells, with some possibly large number of
lower-tiered cells nested within each higher-tiered cell. To avoid
extensive re-wiring, short, free-space optical or millimeter wave
links interconnect the base stations of the lowest-tiered
cells.
[0026] The overwhelmingly greatest fraction of access traffic is
handled by cells in the lowest tier. Here, each of a large number
of geographically small, high capacity radio cells (called
"picocells") is responsible for serving some small number (perhaps
one) of homes and/or offices. Most service subscribers will, in
most cases, attach to the network via their home or office base
station and, through this base station, enjoy complete freedom to
roam within the building and its immediate surroundings.
[0027] A cluster of contiguous picocells thereby serves a large
population of users, each of whom is served via a home or office
picocellular base station. A packet mode of wireless access,
similar to if not identical with the Asynchronous Transfer Mode
(ATM), supports the bandwidth-upon-demand needs of multimedia
traffic. See M. de Prycker, Asynchronous Transfer Mode, Ellis
Horwood Limited, West Sussex, 1992.
[0028] Imbedded virtual connection trees maintain
quality-of-service guarantees while permitting rapid, decentralized
hand-off of live connections among adjacent picocells. See A. S.
Acampora and M. Naghshineh, An Architecture and Methodology for
Mobile-Executed Hand-Off in Cellular ATM Networks, IEEE J. Sel.
Areas Comm., Vol. 12, No. 8, October 1994; A. S. Acampora and M.
Naghshineh, Control and QoS Provisioning in High Speed
Microcellular Networks, IEEE Personal Communications, Vol. 1, No.
2, 2Q 1994; M. Naghshineh and A. S. Acampora, Design and Control of
Micro-Cellular Networks with QoS Provisioning for Real Time
Traffic, J. High Speed Networks, Vol. 5, No. 1, 1996; and M.
Naghshineh and A. S. Acampora, Design and Control of Micro-Cellular
Networks with Supporting Multiple Lanes of Traffic, Wireless
Networks. Vol. 2, No. 3, August 1996.
[0029] See also U.S. Pat. Nos. 5,528,583 for a METHOD AND APPARATUS
FOR SUPPORTING MOBILE COMMUNICATIONS IN MOBILE COMMUNICATIONS
NETWORKS; U.S. Pat. No. 5,497,504 for a SYSTEM AND METHOD FOR
CONNECTION CONTROL IN MOBILE COMMUNICATIONS; and U.S. Pat. No.
5,487,065 for a METHOD AND APPARATUS FOR SUPPORTING MOBILE
COMMUNICATIONS IN ASYNCHRONOUS TRANSFER MODE BASED NETWORKS to the
selfsame A. Acampora who is the inventor of the present invention.
The contents of these prior patents are incorporated herein by
reference.
[0030] In the preferred embodiment, the picocellular base stations
are themselves interconnected by a dense mesh of highly focused,
free-space optical or millimeter wave links which are physically
short in length, i.e. under several hundred feet. As will be shown,
the shortness of these links, and their highly focused nature,
provides excellent margin against fog and other atmospheric
disturbances (essentially 100% availability). Also, although the
transmitters and receivers of the free-space optical links must be
spatially aligned, the tolerances are such that the links can
easily withstand extreme mechanical disturbances such as strong
wind force. In an alternative arrangement, the picocell base
stations are interconnected by highly-focused, point-to-point,
millimeter wave beams.
[0031] By means of these free-space optical (or millimeter wave)
links, traffic generated within (or delivered to) any picocell
will, in general, be relayed among a sequence of base stations in a
multi-hop arrangement, eventually entering (or leaving) the wired
network at a regional "end office". The picocellular base station,
itself, is a small stand-alone unit containing a power supply,
antenna, radio equipment, baseband processing equipment, a small
packet switch (needed to relay traffic), and several optical (or
millimeter wave) transceivers, each aimed at a different one of the
neighboring picocellular base stations. The richness of the
optically-based (millimeter-wave-based) interconnecting mesh, and
its alternative routing capabilities, serve to balance the traffic
among the optical links and, also, to vastly improve system
reliability. For communications upon a hardware- and
software-scalable optical network (employing wavelength-routing,
wavelength reuse and multi-hop packet switching; not all of which
features are required in the system of the present invention) see
The Scalable Lightwave Network by A. S. Acampora appearing in IEEE
Communications Magazine, Vol. 32, No. 12, December 1994.
[0032] The second tier of cells is more conventional in appearance.
Each "standard cell" covers an area with a diameter measured in
terms of miles or tens of miles, and a variable number of picocells
(ranging from zero to, perhaps, several thousand) is contained
within its footprint. The base station of a standard cell attaches
directly to an end office. Each standard cell serves three
purposes: (1) extension of service to any location not served by a
picocell; (2) extension of service to any vehicles traveling at a
speed too great to be accommodated via picocellular handoff; and
(3) provisioning of an alternate means to access the service office
in the event of a picocellular failure and/or interruption of all
of its optical links. Since a standard cell handles only the
overflow traffic not served by its subtended picocells, it is
envisioned that its telecommunications traffic burden will remain
modest.
[0033] The highest tier contains a contiguous raster of megacells,
each with a typical diameter of several hundred miles. The
megacells (1) provide access from locations covered by neither a
picocell nor by a standard cell, and (2) insure universal
availability. It is envisioned that the megacells will be created
by a constellation of Low Earth Orbit (LEO) satellites. Once again,
since a megacell handles only the overflow traffic from its
subtended standard cells and picocells, its traffic burden should
remain modest.
[0034] Because the footprint of a picocell is so small, its
bandwidth is shared by only a small number of users (possibly only
one), and each subscriber thereby enjoys broadband service. By
re-using the radio spectrum sufficiently often, the problem of
limited availability of spectrum is surmounted. Furthermore, since
each picocellular base station is served by its free-space optical
and/or millimeter radio links, new buried broadband cabling
apparatus is unnecessary, and the capacity constraint of existing
copper wiring is surmounted. Finally, the standard cells and
megacells extend service to regions not covered by picocells,
improve reliability, and serve high-velocity vehicles for which
hand-off among picocells might be problematic; assuring universal
service with no blackout regions.
[0035] Note that broadband access is not only extended to homes and
offices but, moreover, the access enjoys the additional virtue of
being tetherless. Both pedestrians and vehicles are readily
served.
[0036] The preferred telecommunications system is based on
Asynchronous Transfer Mode (ATM) transport. Although this
assumption is not essential, ATM supports the type of virtual
connectivity and instantaneous, on-demand access to bandwidth
presently preferred for serving newly emerging types of non-voice
traffic. Thus, all interfaces (radio at all three tiers, free-space
optical, and serving office) are assumed to be ATM. For the
preferred system, the radio links support a peak data rate of,
typically, 20 Mbits/sec, and no optical link is operated at a rate
greater than, typically, 155 Mbits/sec. Also, although it is not
mandatory, it is further assumed that the backbone wired network is
based on ATM.
[0037] 2. First Aspect of the Invention: A Dual-Spectrum
Telecommunications Apparatus
[0038] In accordance with a first aspect of the present invention,
a telecommunications apparatus includes (i) a communications
switch, (ii) a first transceiver, electrically coupled to the
communications switch, for wirelessly telecommunicating externally
to the apparatus in a first portion of the electromagnetic
spectrum, and (iii) at least one second transceiver, electrically
coupled to the communications switch, for wirelessly
telecommunicating externally to the apparatus in a second portion
of the electromagnetic spectrum that is of higher frequency than is
the first portion. A controller causes the communications switch to
route telecommunications traffic between the first transceiver and
the second transceiver. Accordingly, by operation of the apparatus
wireless telecommunications are routed between a first and a
second, higher frequency, portion of the electromagnetic
spectrum.
[0039] The first transceiver is preferably a radio transceiver. The
second transceiver is preferably a transceiver of free-space
optical telecommunications signals. In this embodiment wireless
telecommunications are routed between radio and optical portions of
the electromagnetic spectrum.
[0040] The communications switch preferably operates under the
Asynchronous Transfer Mode protocol.
[0041] In the preferred embodiment, the optical transceiver
includes at least one, and preferably four or more,
optical-receivers--each receiving free-space optical
telecommunications signals over a different free-space optical
path--coupled with a like number of optical transmitters--each
transmitting free-space optical telecommunications signals over a
different free-space optical path. By this construction free-space
optical telecommunications may be simultaneously maintained over a
plurality of different free-space optical paths.
[0042] The controller preferably further acts to cause the
communications switch to further route telecommunications traffic
from the optical receivers to the optical transmitters. In this
manner wireless telecommunications are not merely routed between
the radio and the optical portions of the electromagnetic spectrum,
but are also routed between free-space optical paths.
[0043] The telecommunications apparatus so constructed, and so
operating, is typically situated in a wireless telecommunications
mesh of a large number of identical apparatus. Wireless
telecommunications in the radio portion of the electromagnetic
spectrum are local to each radio transceiver in each apparatus.
Wireless free space optical telecommunications transpire between
the optical transceivers of apparatus that are physically
proximately located. Telecommunications are thus not only routed
between the radio and the optical portions of the electromagnetic
spectrum, but are also second-routed between a number of free-space
optical paths (all of which paths are, or course, in the optical
portion of the electromagnetic spectrum).
[0044] This first aspect of the present invention may be
equivalently considered to be embodied in a dual-spectrum
telecommunications method. In the method a locally wirelessly
telecommunicated signal of a first frequency (i.e., radio) is
telecommunicated in a first-frequency local transceiver. A number
of locally wirelessly telecommunicated signals of a second
frequency (i.e., optical) are telecommunicated in a plurality of
directional transceivers suitable to this second frequency, which
is higher than the first frequency. Conversion is performed between
the first-frequency wirelessly telecommunicated signal at the
first-frequency local transceiver and a second-frequency wirelessly
telecommunicated signal at a selected one of the plurality of
second-frequency local transceivers. Which particular one of the
second-frequency local transceiver is so selected, and converted,
is in accordance with a system-wide protocol for telecommunicating
along a chosen directional path. Meanwhile second-frequency (i.e.,
optical) signals locally telecommunicated at any one of the
plurality of second-frequency local transceivers are cross-coupled
to another one of the plurality of second-frequency local
transceivers, thereby to advance the second-frequency signal along
a chosen directional path that is also in accordance with the
protocol.
[0045] By this method, and even though all transceivers are local,
the first-frequency signal is immediately converted to a
second-frequency signal, and is further telecommunicated,
whensoever and wheresoever received. Meanwhile the second-frequency
signals are further telecommunicated along a chosen directional
path.
[0046] 3. Second Aspect of the Invention: A Telecommunications
Method Upon a Mesh Network
[0047] In accordance with a second aspect of the present invention,
a telecommunications method is conducted upon a mesh network of
arrayed nodes. The method includes (i) wirelessly locally radio
telecommunicating to a radio transceiver at a node by radio, and
(ii) wirelessly locally directionally optically free-space
telecommunicating to each of a plurality of optical transceivers,
co-located with each other and with the radio transceiver at the
node, by a plurality of directional free-space optical signals.
[0048] Telecommunications to and from the radio transceiver are
routed to and a selected one of the plurality of optical receivers.
The optical receiver is so selected in accordance with a protocol
for telecommunicating along a chosen path upon the mesh.
[0049] Meanwhile, telecommunications received at one or more of the
plurality of second-frequency local transceivers at the same node
are routed to another one or ones of the plurality of
second-frequency local transceivers. By this routing
telecommunications is established and maintained along a path upon
the mesh that is chosen in accordance with the protocol.
[0050] The wireless local radio telecommunicating is preferably by
broadband radio in a broadband radio transceiver. Moreover, the
radio telecommunicating preferably transpires in accordance with
Asynchronous Transfer Mode wireless telecommunications protocol--as
does, preferably also, the wireless local optical free-space
telecommunicating.
[0051] In greater detail, the protocol for all this
telecommunicating along a chosen path upon the mesh is developed at
a node, called an end-office, that is common to all paths.
Implementation of this protocol may be shared with selected
processors distributed among the arrayed nodes, which processors
are upon the chosen path, or may even be done entirely among these
distributed processors. If the telecommunicating device at the
telecommunicating cell identifies itself as roaming, or commences
to roam, then the implementation of the protocol may even be
distributed among all the processors of all the arrayed nodes of
the mesh.
[0052] This may sound more complex than it is. All that happens is
that a virtual path is established between communicating entities
on the net. The only pertinent questions are: (i) where and how is
this virtual path established; and (ii) which nodes need to know
about the virtual path so established? . Establishing such a
virtual communication path is routine in cellular
telephony--although the present invention is the first instance, as
will be explained, to conventionally so compute and to so use a
virtual path that lies in substantial part upon a mesh network. The
answers are: (i) at the end office, and (ii) some selected nodes,
up to potentially all nodes. It is in particular not troublesome
that, in the case of a roaming radio transceiver, a node upon the
mesh which node is physically remote from that node where the radio
transceiver is currently located should, nonetheless to this node's
current non-involvement in the current communications path, keep
track of a virtual path which would, it the roaming radio
transceiver was someday to enter this node, permit of communication
upon the mesh because, after all, resource is only consumed when
the virtual communications path becomes a real communications path.
If an extremely large number of virtual paths were to be constantly
dynamically established and re-established upon the net such as
might be due, for example, to thousands of simultaneously roving
radio transceivers (for example, cellular telephones), then the
communication and simultaneous maintenance of associated thousands
of virtual paths at and upon all the nodes of the net could result
in a communications control "overhead". However, it must be
realized that the vast number of radio transceivers are not
roaming, and are instead stationary or semi-stationary in single
cells comprising buildings or the like. Consequently, there is no
insurmountable challenge to calculating and to maintaining all
necessary virtual, and to exercising all real, communications
paths.
[0053] 4. Third Aspect of the Invention: A Telecommunications
Station, Called a "Base Station"
[0054] In accordance with a third aspect of the present invention,
a telecommunications station, called a "base station", is located
within both (i) a radio cell, and (ii) a multi-hop free-space
optical telecommunications mesh of a large number of identical base
stations geographically dispersed.
[0055] Each such base station includes (i) a communications switch,
(ii) a radio transceiver, electrically connected to the
communications switch, for wirelessly telecommunicating by radio
locally externally to the base station, and (iii) a number
(preferably four, at each point of the compass) of optical
transceivers, electrically connected to the communications switch,
for wirelessly telecommunicating externally to the base stations by
associated free-space optical links.
[0056] A (iv) controller causes the communications switch to route
(i) telecommunications traffic received by the radio transceiver to
the optical transceivers, and (ii) also optical telecommunications
traffic received at one optical transceiver to another optical
transceiver for free-optical optical transmission.
[0057] All this routing, and all this telecommunicating, is to the
consistent purpose and end that telecommunications traffic to and
from the radio transceiver (i) is first routed through a co-located
optical transceiver and (ii) is then further routed through the
optical transceivers (of whatsoever number of other base stations
as are required) until reaching a selected optical transceiver of a
particular base station (called an "end office" base station).
[0058] Accordingly, radio and free-space optical communications
upon the mesh support telecommunications between, on the one hand,
(i) a radio transceiver of a base station and, on the other hand,
(ii) a optical transceiver of the particular base station called
the "end office".
[0059] The "end office" base station has a communications switch
connected to a communications backbone external to the system.
Other "end-office" base stations also connect to this
communications backbone.
[0060] A number, typically four, of optical transceivers that are
electrically connected to the "end-office" communications switch
wirelessly optically externally telecommunicate. They do so in
order to (i) receive across the free-space optical
telecommunications links the telecommunications traffic received by
all the radio transceivers of all the base stations, and in order
to (ii) transmit telecommunications traffic received from the
communications backbone to a particular radio transceiver of a
particular base station.
[0061] A controller causes the "end-office" communications switch
to route communications traffic between, on the one hand, the wired
connection to the external communications backbone and, on the
other hand, the plurality of "end-office" optical transceivers.
[0062] By this operation both (i) radio, and (ii) free-space
optical telecommunications are bi-directional between the
end-office and each radio transceiver of all base stations.
[0063] 5. Fourth Aspect of the Invention: A Telecommunications
System
[0064] In accordance with a fourth aspect of the present invention,
the "base station" and the "end office" telecommunications stations
just discussed in the previous section 3 can be combined into an
entire telecommunications system.
[0065] In such a telecommunications system an "end-office" includes
(i) a communications switch, (ii) a hardwired connection between
the switch and a communications backbone external to the system to
which communications backbone other end-offices also connect, (iii)
a number of optical transceivers, electrically connected to the
communications switch, for telecommunicating externally to the
end-office optically through free space, and (iv) a controller for
causing the communications switch to route communications traffic
between the hardwired connection to the external communications
backbone and the plurality of optical transceivers.
[0066] This "end office" is used with, and as a part of, a
multi-hop mesh of radio-telecommunicating and
optically-free-space-telecommunicating "base stations". Each "base
station" includes (i) a communications switch, (ii) a number of
optical transceivers, electrically connected to the communications
switch, for wirelessly telecommunicating externally to the base
station by free-space optical links, and (iii) a controller for
causing the communications switch to route received optical
communications traffic from a receiving to a transmitting optical
transceiver. The routing is to the purpose and the end that
telecommunications traffic at any individual base station will be
free-space optically communicated though whatsoever number of base
stations is required until it is telecommicatively connecting to
the "end office" (and then to the communications backbone).
[0067] Notably, and as is characteristic of meshes, the free-space
optical communications upon the mesh are variably routed from one
base station to another.
[0068] To this mesh optical telecommunications system--which is
already arguably of an interesting form employing as it does both
free-space optical links and dynamic link routing--the present
invention preferably makes the momentous addition of cellular
radio.
[0069] Such an "enhanced" telecommunications system is, of course,
a multi-hop mesh of optically-free-space-telecommunicating base
stations that are additionally radio-telecommunicating. Each of
these radio-telecommunicating and
optically-free-space-telecommunicating base stations has, in
addition to its communications switch and its optical transceivers
and its controller, certain additional components.
[0070] Namely, a radio transceiver is electrically connected to the
communications switch for wirelessly communicating by radio
externally to the base stations. When this radio receiver is
present the controller is further causes the switch to route
communications traffic between the radio transceiver and the
optical transceivers.
[0071] More particularly, the controller causes the communications
switch (i) to route telecommunications traffic between the radio
transceiver and the optical transceivers, and (ii) to route
received optical communications traffic from a receiving to a
transmitting optical transceiver. All routing is to the purpose and
the end that local telecommunications traffic at the radio
transceiver is free-space optically communicated step-wise
regionally through the optical transceivers of whatsoever number of
base stations are required to and from the end office, and upon the
communications backbone. In this manner, radio telecommunications
local to one base station are free-space optically telecommunicated
upon the mesh until ultimately communicatively interconnecting to
the communications backbone--the forte of the present
invention.
[0072] 6. Fifth Aspect of the Invention: A Hybrid
Telecommunications System
[0073] By this time it should be clear that the present invention
is most significantly manifest in a telecommunications system (i)
where some telecommunication is local within a cell (normally at a
lower frequency, typically radio) and (ii) where some, related and
continuing, telecommunication transpires upon the links of mesh
network (normally at higher frequency, and typically upon free
space optical links).
[0074] The present invention is thus found in a hybrid
telecommunications system typically having both (i) radio
telecommunications, and (ii) optical telecommunications. Such a
hybrid telecommunications system is characterized in that
telecommunication from each of a great multiplicity of end users
into the system is by cellular radio at a one of a plurality of
hierarchical cell levels. A user radio transceiver that is unable
to telecommunicate into the system at a lower cell level will
attempt to communicate into the system at a next higher cell level
and so on until access is finally obtained.
[0075] If and when cellular radio telecommunications access is
achieved at a lowest system level, which is overwhelmingly the most
common case, ensuing telecommunications will transpire across
optical links organized as a mesh. Optical links at each node of
the mesh direct merge such individual cellular radio
telecommunications as may be from time to time accessed at that
node of the mesh into other optical communications traffic carried
upon the mesh. This continues until, optical communication links
having been joined throughout the mesh, the cellular radio
telecommunication at each node is ultimately communicatively
interconnected to a central, end-office, node or the mesh.
[0076] If the cellular radio communications access transpires at a
system level other than the lowest, then the ensuing
telecommunications signals will be carried directly between the
station where access is achieved and the end-office switch by means
of a conventional point-to-point communications link such as wire,
fiber, or directed radio beam.
[0077] Telecommunication with at least some (and normally all)
optical links (as do access cellular radio telecommunications)
preferably transpires by free space optical links. Communication
with the central node or end-office is, in addition to optical
communication links upon the mesh, preferably also by fiber optic
cable.
[0078] The present invention may similarly be found in a hybrid
radio and optical telecommunication method that includes in the
same telecommunications system both (i) telecommunicating by radio,
and (ii) telecommunicating by optics. Such a method is
characterized in that each of a great number of end users
telecommunicate into the telecommunications system by cellular
radio at a one of a plurality of hierarchical cell levels. A user
radio transceiver that is unable to telecommunicate into the system
at a lower cell level will attempt to communicate into the system
at a next higher cell level and so on until access is finally
obtained.
[0079] After cellular radio telecommunications access to the system
is so finally obtained, telecommunicating will then most commonly
transpire across optical links organized as a mesh, the optical
links at each node of the mesh merging such local cellular radio
telecommunications as is from time to time accessed at that node
into other optical communications traffic carried upon the mesh
until, optical communication links being joined throughout the
mesh, cellular radio telecommunication at each mesh node is
ultimately communicatively interconnected to a central node, or
end-office.
[0080] 7. Sixth Aspect of the Invention: A Virtual Communications
Upon a Mesh Network, Particularly as Exists in Free Space
[0081] The present invention employs a routing algorithm of a
conventional nature to establish a virtual connection path between
two communicating entities--a terminal device at a base station and
a home office--so that Quality of Service (QOS) for the entire
network is maintained. (If it is impossible to establish a
communications path while maintaining minimum QOS, communications
is normally denied.) For the communications routing back and forth
between each base station and the end office, all connections are
virtual, or "virtual connections". The route selection process, or
algorithm, establishes these virtual connections.
[0082] At the onset, it may be noted that the communications
traffic that is carried upon the communications paths between each
base station and the end office is of nature, typically voice or
digital data, that has heretofore been carried to the end-user on
dedicated lines or links called "pipes". As just stated, the
present invention is opposite, establishing and using virtual
trees, and virtual connections, for all communications between base
stations and the end offices.
[0083] In so doing, the present system is somewhat reminiscent of
cellular telephony, where connections in the form of pipes of a
limited duration are established and re-established as a
telecommunicating device roams within a telecommunications area.
There are differences, however. To the best knowledge of the
inventor, the present invention is the first to ever contemplate
establishing, and using, virtual connections on a mesh network,
particularly one that is (i) in free space and/or such as may be
implemented by (ii) free-space optical links and/or millimeter
wavelength radio.
[0084] Moreover, some of the links of the mesh network (as are
associated with some one or some few of the base stations) may
permissibly be, as has been explained, a direct optical, or a
radio, or a wire, or a fiber, link between some base station and an
end office. (To the extent that the link is wire or fiber, then to
that extent the mesh network is no longer 100% "free space".)
Notably, the virtual connectivity principle of the present
invention still holds true. Virtual connections are readily made
upon mesh networks having different links, including even such wire
and fiber links as have heretofore been inflexibly associated with
pipes, just as surely (and easily) as they are made upon mesh
networks uniformly consisting of only free-space optical, or
millimeter wavelength radio, links. Therefore the present invention
will also be realized to occasionally use types of communications
channels associated with pipes--i.e., wire and optic fiber--in a
virtual communications network where these channel types have not
previously been found.
[0085] Therefore, the present invention may be considered to be
embodied in a communications system having a mesh network
communicatively interconnecting a multiplicity of communication
switches, and logic for establishing virtual communication paths
upon the mesh network between ones of the multiplicity of
communication switches. The communications system's mesh network
preferably telecommunicatively interconnects the multiplicity of
communication switches, typically (but not exclusively) by and on
free-space telecommunications links that may typically (but not
exclusively) be free-space optical telecommunications links and/or
free-space millimeter wavelength radio telecommunications
links.
[0086] The logic establishing virtual communication paths upon the
mesh network between ones of the multiplicity of communication
switches so establishes the virtual communications links in form of
a tree (the virtual communication paths from the multiplicity of
communication switches focusing to a root node communication switch
called an end office).
[0087] The logic for establishing virtual communication paths upon
the mesh network between ones of the multiplicity of communication
switches may be (i) located at the end office, (ii) distributed
between the end office and some other ones of the multiplicity of
communication switches or (iii) distributed between among all the
multiplicity of communication switches.
[0088] These and other aspects and attributes of the present
invention will become increasingly clear upon reference to the
following drawings and accompanying specification.
BRIEF DESCRIPTION OF THE DRAWINGS
[0089] FIG. 1 is a diagram of a multi-tier radio-access
telecommunications system in accordance with the present invention;
three tiers are illustrated.
[0090] FIG. 2 is a diagram of the optical interconnection of
picocells by and within a dense optical mesh in the multi-tier
radio-access telecommunications system in accordance with the
present invention previously seen in FIG. 1.
[0091] FIG. 3a is a schematic block diagram of a first embodiment
of a base station apparatus used within each picocell of the
multi-tier radio-access telecommunications system in accordance
with the present invention previously seen in FIG. 1.
[0092] FIG. 3b is a diagrammatic view of a typical installation of
the first embodiment of the base station apparatus previously seen
in FIG. 3a.
[0093] FIG. 3c is a diagrammatic view of a typical installation of
a second, millimeter wavelength radio linked, embodiment of a base
station apparatus.
[0094] FIG. 3d is a diagrammatic view of a typical installation of
a base station apparatus similar to that of FIGS. 3a and 3b, or
FIG. 3c, now installed in an end office, the apparatus having when
so installed wired connection to communications switching
equipments which are in turn connected to a world-wide wire/fiber
line backbone.
[0095] FIG. 4 is a diagram of the optical mesh, including
end-office links, by which optical interconnection of picocells
transpires in the multi-tier radio-access telecommunications system
in accordance with the present invention.
[0096] FIG. 5 is a diagram of the optical mesh, including one
end-office link, previously seen in FIGS. 2 and 4; equal-traffic
"zones" to the end-office link being illustrated.
[0097] FIG. 6 is a diagram of a regular rectangular optical mesh,
including multiple end-office links, by which optical
interconnection of picocells transpires in the multi-tier
radio-access telecommunications system in accordance with the
present invention.
[0098] FIG. 7a is a diagram of a first case, wherein message
traffic is restricted within a domain, of message traffic occurring
on the regular rectangular optical mesh previously seen in FIG.
6.
[0099] FIG. 7b is a diagram of certain particular, cross, links
arising in the first case of the message traffic restricted within
a domain previously seen in FIG. 7a.
[0100] FIG. 8, consisting of FIG. 8a through FIG. 8d, are diagrams
of a second case, wherein message traffic is restricted within a
quadrant, of message traffic occurring on the regular rectangular
optical mesh previously seen in FIG. 6.
[0101] FIG. 9, consisting of FIG. 9a through FIG. 9c, are diagrams
of a third case, wherein message traffic is restricted within a
semi-quadrant, of message traffic occurring on the regular
rectangular optical mesh previously seen in FIG. 6.
[0102] FIG. 10a is a diagram of a first virtual connection tree for
the optical mesh, by which optical mesh optical interconnection of
picocells transpires in the multi-tier radio-access
telecommunications system in accordance with the present
invention.
[0103] FIG. 10b is a diagram of a second virtual connection tree
for the optical mesh, alternative to the connection tree of FIG.
10a, by which optical mesh optical interconnection of picocells
transpires in the multi-tier radio-access telecommunications system
in accordance with the present invention.
[0104] FIG. 11 is a graph of the power budget of an optical link on
the optical mesh of the multi-tier radio-access telecommunications
system in accordance with the present invention.
[0105] FIG. 12 is a graph of the bit error rate and an optimal
threshold, OOK modulation being employed, of an optical link on the
optical mesh of the multi-tier radio-access telecommunications
system in accordance with the present invention.
[0106] FIG. 13 is a graph of the atmospheric absorption at 2 km
above sea level of an optical link on the optical mesh of the
multi-tier radio-access telecommunications system in accordance
with the present invention.
[0107] FIG. 14 is a graph of the visual range compared to
attenuation at 800 nm wavelength for an optical link on the optical
mesh of the multi-tier radio-access telecommunications system in
accordance with the present invention.
[0108] FIG. 15 is a graph of the attenuation due to rain (at 800 nm
wavelength) for an optical link on the optical mesh of the
multi-tier radio-access telecommunications system in accordance
with the present invention.
[0109] FIG. 16 is a graph of the attenuation due to snow (at 800 nm
wavelength) for an optical link on the optical mesh of the
multi-tier radio-access telecommunications system in accordance
with the present invention.
[0110] FIG. 17 is a graph of the scintillation effect on beam
intensity for an optical link on the optical mesh of the multi-tier
radio-access telecommunications system in accordance with the
present invention.
[0111] FIG. 18 is a graph of the wind bending effect on the support
poles for an optical link on the optical mesh of the multi-tier
radio-access telecommunications system in accordance with the
present invention.
[0112] FIG. 19 is a diagrammatic view of the preferred embodiment
of a base station optical transceiver on the optical mesh of the
multi-tier radio-access telecommunications system in accordance
with the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0113] The basic approach to a multi-tier radio-access
telecommunications system in accordance with the present invention
is discussed in section 1. Section 2 contains a discussion of
considerations in routing signals upon the optical mesh. Section 3
contains a description of the handoff of signals, and explains the
concept of an embedded virtual connection tree. Section 4 contains
descriptions of exemplary radio and optical links of the
telecommunications system of the present invention, along with some
representative calculations of system's capacity and of the
performance margins of its optical links.
[0114] 1. Description of the Multi-tier Radio-access
Telecommunications System
[0115] A multi-tier radio-access telecommunications system in
accordance with the present invention where large radio cells are
superimposed upon smaller radio cells in a multi-tiered hierarchy
(three tiers are representative, and illustrated) is depicted in
FIG. 1. Each of many picocells 1 (tier 1) is created by a small,
station, enjoy complete freedom to roam within the home or office
premises-bases or near-premises-based, base station (to soon be
shown in FIG. 3). Subscribers normally attach for communicating via
their home or office base station and, through this base
environment and, to some extent, externally to the building as
well.
[0116] If a subscriber should leave the area served by his or her
home or office base station, then service is handed to either the
base station serving the adjacent building, if there was to be no
gap in coverage, or else to the base station of one of a number of
standard cells 2, the service domain of each which spans from zero
to many picocells 1. Finally, if a user should enter some
environment serviced neither by any of the standard cells 2 nor by
any picocells 1, then service is extended via one of a number or
megacells 3, having a range of coverage that spans zero to many
standard cells 2. Service among megacells 3 is contiguous.
[0117] The tier-1 base station may be, essentially, an item of
consumer electronics that is either sold or leased to the
residential or business subscriber. Alternatively, the tier-1 base
station may be owned by the service provider and installed on
property owned or leased by the service provider. If a subscriber
places a call through his or her own subscriber unit, billing for
the service will be to that unit. If the subscriber places a call
through a neighboring subscriber unit, then the subscriber's
terminal equipment (e.g., his or her cellular telephone), must
request third party billing at call set-up time so that the home
subscriber unit, and not the neighboring unit servicing the call,
will be billed for service. Hand-off is fully supported, both among
peer cells at the same tier and among cells at different levels in
the hierarchy.
[0118] The primary purpose of tier 1 is to provide adequate
capacity to serve most users, thereby dramatically reducing the
demand placed upon tier 2. Selected base stations at tier 2 connect
directly to core, or end-office (network) switches 12, as shown in
FIG. 1. Understand that FIG. 1 is a schematic diagram, and not a
physical map. The end-office switches 12 are commonly physically
located directly among the picocells 1 that they serve to
communicatively interconnect. However, since tier 1 base stations
are residential or office units, new means must be provided to
interconnect these stations to the core network.
[0119] As shown in FIG. 2, these new means include short,
free-space, bi-directional optical links interconnecting the tier-1
base stations in a rich optical mesh. Each tier-1 base station
thereby serves two functions. First, it accepts information from
(and delivers information to) each terminal unit within its
footprint service area (a one of the picocells 1) via radio.
Second, it serves as a cooperating relay station, accepting
information (in the form of addressed data packets, possibly ATM
cells) from in-bound optical links and routing such information
onto the correct outbound optical link.
[0120] As shown in FIG. 3a, the apparatus of a tier-1 base station
includes (i) several optical transmitters and receivers, or optical
transceivers 112,(ii) the radio and baseband equipment illustrated
as receive antennas and demodulator 111, (iii) a small electronic
packet switch, preferably an ATM switch 112, and (iv) a small
control processor 114 to manage the base station and serve as the
local representative of the network control system. The radio
equipment 111 includes all apparatus needed to accept/deliver
signals from/to the ATM switch 113 and deliver/accept these to/from
the antennas 111 (partial).
[0121] FIG. 3b is a diagrammatic representation of the physical
installation of the apparatus of the base station as it might be
installed in the attic of a home. The optical transceivers 112 are
located in free space outside any building. The remaining radio and
baseband equipment 111, ATM switch 113 and control processor 114,
including the baseband antenna 111 (partial) are normally housed
inside a building, and are represented by the labels "electronics"
and "antenna".
[0122] An equivalent diagrammatic view of a typical installation of
a second, millimeter wavelength radio, embodiment of the base
station apparatus is shown in FIG. 3b. Everything is the same as in
FIG. 3b except radio transceivers 112a (operative in millimeter
wavelength radio spectral regions, and not to be confused with the
baseband radio 111) replace the optical transceivers 112 (shown in
FIGS. 3a and 3b).
[0123] Each transceiver of the optical (FIGS. 3a, 3b) or millimeter
wavelength radio (FIG. 3c) types communicates, normally by line of
sight, to a transceiver of a like type.
[0124] A diagrammatic view of a typical installation of a base
station apparatus similar to that of FIGS. 3a and 3b, or FIG. 3c,
as is now installed in an end office switch 12 (shown in FIGS. 1
and 2) is shown in FIG. 3d. The apparatus so installed has a wired
connection to conventional (end-office) communications switching
equipments. These equipments which are in turn connected to a
world-wide wire/fiber line backbone.
[0125] Returning to FIG. 3a, the packet, or ATM switch 113 is
needed so that, in addition to serving as source and sink of the
traffic placed onto the optical network, each base station can
relay (hop) packets from one optical link to the next. These
multi-hopping transmissions occur along a route (a set of links)
chosen at connection set-up time so as to maintain
Quality-of-Service (QoS) guarantees. Each packet hops along
successive links in accordance with information contained within
the packet until it arrives at an entry/exit port of the core
network (for packets traveling along the access network toward the
core network), or else at the terminating tier-1 base station (for
packets being distributed from the core network to the tier-1 base
stations of the access network). Multi-hopping is important to
permit use of very short free-space optical links as are needed to
insure freedom from atmospheric disturbances and good link
availability, and as are needed in certain areas to overcome
obstacles such as hills and buildings.
[0126] The preferred dimensionality of the packet (or ATM) switch
is at least 5.times.5, so that, in addition to the signals arriving
from/ being sent to the radio interface, at least four optical
transceivers can be supported. Note that this small packet switch
is normally an electronic switch; both radio and optical packets
are first converted to baseband electronic signals prior to
switching, as in most multi-hop arrangements.
[0127] The multi-hop architecture is well-known within the field of
multi-wavelength optical networks. However, its present application
to free-space optical networks is believed to be novel, as is the
overall approach whereby tiers of base stations are created, the
lowest tier being interconnected by a new free-space optical
network so as to avoid local wireline bottlenecks. See A. S.
Acampora, A Multichannel Multi-hop Local Lightwave Network,
Conference Record, 1987, Globecom, Tokyo; and C. A. Brackett and A.
S. Acampora, et al., A Scalable Muitiwavelength Multi-hop Optical
Network, IEEE J. Lightwave Tech., Vol. 11, No. 5/6, May/June
1993.
[0128] The actual interconnection pattern of the optical
interconnection network in accordance with the present invention
may be that of a recursive grid, a quasi-rectangular mesh in which
nesting of access stations (tier-1 base stations, in the present
case) into sub-levels is permitted so as to make possible the easy
addition of new access stations (modular growth) without disturbing
any more than one pre-existing link. See A. S. Acampora, The
Scalable Lightwave Network, IEEE Comm. Mag., Vol. 32, No. 12,
December 1994; and A. S. Acampora, Architectures for Hardware and
Software Scalable Multiwavelength Networks, Photonics Networks,
Kluwer Academic Publications, 1997.
[0129] An additional benefit of the recursive grid is its
compatibility with existing scalable routing algorithms, meaning
that the computational complexity associated with the establishment
of a multi-hop route for a new virtual connection scales but
linearly with the number of nodes in the grid. That is, the
computational complexity per node is independent of the number of
nodes. Since, for the purposes of this specification disclosure,
any topology can be chosen for the optical mesh, the interested
reader is referred to the literature for additional information
concerning general background to the recursive grid.
[0130] Multi-hop routing for the preferred radio access system of
the present invention is easiest to explain assuming fixed-point
service, that is, with no handoff; routing with hand-off will be
covered in Section 3. For fixed-point service, the route either to
or from a given base station--which route will be taken by the
packets associated with a given virtual connection flow--is
comprised of a sequence of links chosen by an Admission Controller
at call set-up time. When choosing this route, the Admission
Controller must guarantee that all Quality-of-Service (QoS)
objectives are met. This means not only that each optical link in
the sequence can accommodate the new virtual connection without
unacceptable QoS degradation but, also, that the terminal radio
cell can accommodate the new virtual connection. If hand-off is
supported (both among clusters of picocells, and between picocells
and standard cells), then, as will be explained in Section s, the
admission decision must also guarantee that the overall traffic
intensity (new calls plus pre-existing calls) presented to the cell
cluster remains acceptable.
[0131] Signaling for new connection requests is handled in a quite
conventional fashion. Namely, a permanent signaling virtual channel
connection exists between each base station and a control computer
located within the end-office. When the control computer receives a
request for communications from, or to, a (radio-telecommunicating)
subscriber device at a subscriber base station, then it calculates
the multi-hop routing of packets on the optical network to
establish this communication. In this regard the control computer
is functioning no differently than a standard (wired) telephone
network switching computer, or at least those that manage
communications over multiple paths that offer redundancy.
[0132] Finally, to vastly improve dependability of the free-space
optical mesh, a set of back-up virtual routes is established at the
time that the admission decision is made. The back-up routes are
established so that, in the event of a link failure or transient
interruption of the optical beam, alternate routing can be
instantaneously effected with minimal information loss. In general,
virtual resources must be reserved on each optical link to
accommodate instantaneous alternate routing. Although this back-up
routing can readily be realized simply by devoting more system
resource to each communications path (consider, for example, that
two complete paths might be established at each admission
decision), optimization of this back-up remains an open issue not
addressed in this specification disclosure. Back-up routing would
preferably involve the selection of primary and alternate routes so
that, in the event of a single link failure, the additional traffic
burden placed on the surviving links would be minimized, that is,
the virtual resources reserved for failure recovery should comprise
only a small fraction of a link's capacity. This suggests that
primary and alternate routes be chosen such that in the event of a
link failure or transient disruption, the re-routed traffic be
smeared over as many disjoint paths as possible.
[0133] 2. Routing in the Optical Mesh
[0134] Of primary consideration to the flow of traffic along the
links of the optical mesh is the avoidance of traffic bottlenecks
or "hot" spots. The situation depicted in FIG. 4 is drawn for a
simple topology in which the optical mesh consists of a rectangular
grid and each cross-point represents a single tier-1 base
station.
[0135] A portion of the tier-1 access network is shown in FIG. 4.
The purpose of this portion is to deliver traffic generated within
the picocells to the end-offices (of which two such are
illustrated), and to distribute traffic from the end-offices to the
picocells. Each end-office attaches to some number of neighboring
tier-1 base stations by means of short free-space optical links.
Note that the base stations that are connected to an end-office
need an additional optical transceiver beyond the number needed by
other base stations.
[0136] To maintain their dependability, the optical links must be
kept short, and the number of base stations connected to an
end-office is correspondingly limited. The objective is to route
each virtual connection such that the flow of traffic is evenly
distributed among the limited number of optical links leading
directly to/from an end-office.
[0137] Some simple calculations are in order. Suppose that all
picocells generate the same level of traffic intensity, C, and
suppose that each end-office is responsible for N base stations.
Let each end-office be equipped with L optical links. Then,
assuming that traffic can be "balanced" among these L links each
must handle a traffic intensity C.sub.L=NC/L. (Note that, in
general, other optical links will handle a lesser traffic intensity
since, in the preferred multi-hopping arrangement, the traffic
handled by the optical links grows as traffic is relayed toward the
end-offices).
[0138] A traffic intensity C.sub.L=NC/L provides a "best case"
relationship among the number of optical links needed per
end-office (L), the multi-hop capacity deflator (C.sub.L/C, the
ratio of the required link capacity normalized by the delivered
user or picocell capacity), and the number of picocells supportable
by an end-office. It is the objective of routing in the optical
mesh to "smear" so that this traffic relationship applies as best
as is possible. While "optimum" routing should be considered to be
an open research problem, some simple observations and heuristics
permit developing reasonable approach to routing.
[0139] 2.1. A "Zoned" Approach to Routing
[0140] First, it is possible to define a Ozone associated with each
"finger", or optical link, emanating from an end-office. Referring
to FIG. 5, a zone is defined to be a set of base stations chosen
such that (1) traffic associated with all base stations of a given
zone enters/exits the end-office through a common finger, and (2)
the same traffic intensity is associated with all zones.
[0141] The objective of the routing algorithm, then, is to choose a
route for each new call attempt such that all traffic associated
with a given zone enters/exits the end-office through that zone's
finger. Such zones may be permanently defined based on the average
traffic intensity presented by each picocell. Alternatively, to
achieve better routing efficiency, zones may be dynamically defined
in response to instantaneous traffic patterns. For example, in the
latter case, the zone associated with a currently lightly-loaded
finger might be adaptively enlarged to include a greater number of
base stations, while the zone associated with an adjacent
heavily-loaded finger might be reduced to include a smaller number
of base stations, such that, for future calls, it is more likely
that a route will be chosen through the lightly-loaded finger.
Then, as new virtual connections are made and old ones are
terminated, the boundaries of the zones will continuously adapt in
an attempt to maintain load balance among the fingers.
[0142] Note that, with such a "zoned" approach, traffic originating
or terminating within a base station at the boundary of two zones
may be bifurcated to best achieve load balance. In a similar
spirit, traffic originating or terminating within a base station on
the boundary of two zones served by two different end-offices may
be bifurcated among those offices (furthermore, when adapting the
"footprint" of a zone to the prevailing traffic, a given base
station can be re-assigned, for future calls, to a different
end-office if this will facilitate load balancing).
[0143] Note further that the geometrical boundaries of the zones
may be quite irregular. It is the intent to capture a common
traffic intensity within all zones (for permanently assigned
zones), and to tailor the zonal boundaries to the remaining
available capacity of the fingers (for dynamically assigned zones).
Both the traffic generated within a given picocell, and the
geometrical deployment of picocells, are very much demographically
dependent. In general, one should not expect uniform spacing of the
picocells as might be (incorrectly) implied from FIG. 5, which is
intended only to show a connectivity pattern among cells but which
does not speak at all to their spacing.
[0144] Finally, note also that the richness of the mesh, the
possibility of bifurcating traffic among fingers and end-offices,
the ability to enter/exit an end-office via any of several fingers,
and the ability to select alternate routes, collectively provide
substantial protection against disruption of an optical link or a
set of links (either as a result of equipment failure, atmospheric
impairment, or transient interruption of an optical beam due,
perhaps, to a migrating bird!). It is envisioned that, as part of
fault management, a diagnostic routine should be continuously
executed which permits the base stations to rapidly sense
disruption of an optical link and to initiate corrective action
(alternate routing). Not only can the surviving optical links be
used to communicate management and control commands during the
restoration phase subsequent to link disruption but, if necessary,
the radio interfaces can also be used to deliver these fault
management messages.
[0145] 2.2 Conditions for Avoiding "Hot" Spots on the Mesh
[0146] One problem associated with the zoned approach just
described in the previous section 2.1 is its loss of trunking
efficiency; if the finger associated with a given zone is loaded to
capacity (meaning that no additional virtual connections can be
added without unacceptably degrading the QoS guarantees) even
though adjacent fingers are underutilized, it is not possible (at
least with fixed zones) to accept additional traffic generated
within the zone associated with the fully loaded finger at another
finger. Thus, virtual connections that might have been accepted by
an underutilized finger will be blocked.
[0147] Consequently, it is useful to examine conditions under which
better trunking efficiency might be realized. In fact, there exist
some simple conditions under which a routing algorithm may ensure
that the loading of all optical cross-links not leading directly to
an end office (the "mesh links") is always less than the loading on
an optical link that does lead directly (the "direct links" or
"fingers") to an end office. In such a case, a simple Erlang
blocking formulae can be applied, independent of the detailed
traffic distribution among the picocells.
[0148] To begin, consider FIG. 6 drawn for a rectangular mesh.
Suppose that each direct link has a capacity of C.sub.L virtual
cells, and each picocell generates traffic of value
C.ltoreq.C.sub.L. (Alternatively, each picocell may terminate
traffic of value C.ltoreq.C.sub.L; it is readily shown that for
either traffic inbound to an end office or outbound from an end
office, each bi-directional mesh link is used in only one direction
and, therefore, by symmetry, the Erlang blocking formulae are
independently applicable for each direction.) Further, assume that
each mesh link can carry traffic load of C.sub.L. Let us define
each base-station (which forms a picocell) to be a node. The nodes
directly connected to an end-office are called "index nodes" (FIG.
6). The unit distance between two adjacent nodes is called a "hop".
Let us impose the constraint that a node can communicate only with
its closest (in terms of the minimum number of hops) end-office.
Then, the rectangular mesh may be sub-divided into "domains". A
domain consists of an end-office and all the nodes communicating
with it. A node may belong to more than one domain if it is
equidistant to more than one end-office. The index node,
geographically closest to the end-office it is associated with, is
called the "primary index node".
[0149] Let us now consider FIG. 7, in which there are exactly four
direct links to the end-office, i.e., the maximum traffic intensity
which can be handled by the end-office is 4C.sub.L. The traffic
generated within the domain must be routed to the end-office in the
domain. In each "quadrant" of the domain, concentric loops can be
drawn as shown in FIG. 7a. A "loop" connects nodes along the
boundary of a rectangle. If, in any quadrant, the generated traffic
is less than or equal to C.sub.L, we can use those mesh links
within the quadrant not associated with the mesh links comprising
the loop to first route the traffic to the outermost loop in the
quadrant. The direct link attached to this loop can then be used to
route the traffic to the end-office. If, on the other hand, the
traffic generated in a given quadrant exceeds C.sub.L, i.e., is
between C.sub.L and 4C.sub.L, then traffic in excess of C.sub.L can
be redirected to neighboring quadrants using the mesh links between
the quadrants (not shown in FIG. 7). Note from FIG. 7b that there
will be at least four mesh links leading out of a quadrant and,
hence, it is always possible to redirect excess traffic of up to
3C.sub.L to the neighboring quadrants, thereby uniformly
distributing the traffic among the quadrants. As long as no node
generates more than C.sub.L units of traffic, and as long as the
total traffic is less than 4C.sub.L, then the only blocking
encountered is due to the direct links being fully loaded. The call
blocking probability can then be computed using the Erlang blocking
formula given by 1 P b ( , M ) = M / M ! k = 0 M k k !
[0150] where the number of available circuits is M and the load is
.rho.. In the above case, if the load generated in the domain is
.rho..sub.D, the call blocking probability is given by
P.sup.b(.rho..sub.D, 4C.sub.L).
[0151] Next impose the constraint that all traffic generated within
a quadrant must reach the end-office by using only those direct
links which lead into that quadrant (FIG. 8). Furthermore, the
route taken by any call is constrained to lie entirely within the
quadrant. Let K be the number of direct links from the end-office
into a quadrant. It is essential that the value of K be less than
or equal to 5 in order to avoid blockage on the mesh links (to be
discussed later).
[0152] Now, consider a quadrant is of size R.times.R. Let N=[K/2],
where [x] is the closest integer greater than or equal x. Suppose
that R.gtoreq.N. In such a case, it is always possible to draw M
=[R/2] loops in the quadrant (sometimes a loop may consist of just
a single node). Label the loops as shown in FIG. 8a and 8b, with
the innermost loop bearing the highest index number, that is, loop
i+1 would always lie within loop i. Mesh links which belong to a
loop are called loop links, and the mesh links interconnecting
loops are called inter-loop links (See FIG. 8b).
[0153] For this case, we can redistribute the calls by first
routing all calls generated by nodes in the inner M-N loops to loop
N using inter-loop links (note that these do not belong to any
loop). Since the number of inter-loop links from loop i+1 to loop i
is equal to 4 (R-2i) , it is possible to route all calls from the
innermost M-N loops onto loop N. Note that, when R is even, the
maximum value of i is (R/2)-1, and for this value of i, the number
of links out of the innermost loop is eight. If R is odd, then i is
at most and the number of links out of the innermost loop will be
four. However, since there is exactly one node in the innermost
loop when R is odd, it is possible to route calls from the
innermost M-N loops to loop N.
[0154] As an example, in FIG. 8b it is possible to route up to
4C.sub.L calls (the maximum number which can be generated in loop
3) from loop 3 to loop 2. Thus, at the conclusion of this process,
all the traffic is concentrated on loops 1 through N (the outermost
loops) Now, if K.ltoreq.4, then the total traffic generated is less
than or equal to 4C.sub.L. Since no traffic has as yet been flowed
onto the inter-loop links interconnecting the outermost two loops,
these links can now be used to uniformly distribute the traffic
among these two loops. (Note that, for this process, no inter-loop
link can be used which will subsequently be used to attach an inner
loop to the direct link serving that loop. For example, referring
to FIG. 8a, inter-loop links a and b cannot be used to redistribute
traffic among the loops since they will subsequently be used to
attach loop 3, via node X, to node Y, which is an index node)
[0155] Furthermore, having accomplished this, neither loop carries
traffic in excess of 2C.sub.L (note that loops are bi-directional).
If K=5, the traffic intensity may be as great as 5C.sub.L and, in
such a case, using an identical procedure, one may uniformly
distribute the traffic among loops 1, 2 and 3 (the outermost three
loops).
[0156] Since it is possible to carry up to 2C.sub.L calls on each
loop (C.sub.L in the clock-wise direction and the other C.sub.L in
the counter-clockwise direction), the entire traffic can
successfully be routed to the corner node on the loop, closest to
the end-office, without encountering blockage on the mesh links.
The inter-loop links connected to this node lead directly to an
index node (See FIGS. 8a and 8b). Thus, using these links, the
traffic can now be routed to the end-office.
[0157] Note that it may be impossible to distribute traffic
uniformly among the outer three loops if the total load generated
is in excess of 5C.sub.L. This is illustrated in FIGS. 8c and 8d.
Let all the traffic be generated by a cluster of nodes at a corner
of the quadrant. If a maximum load of 5C.sub.L is generated by a
cluster of five nodes in a corner of the quadrant, then, since
there are five mesh links leading out of this cluster, it will
always possible to re-distribute the load (FIG. 8c) among the outer
three loops as described earlier. However, if a maximum load of,
say, 6C.sub.L is generated by a cluster of six nodes in a corner of
the quadrant as shown in FIG. 8d, then its will be impossible to
route this traffic to the end-office without blocking up to C.sub.L
calls since there are only five links (at least six links are
necessary) leading out of the cluster. Thus, if the number of
direct links, K, from the end-office into a quadrant is greater
than five, given that the traffic within the quadrant is less than
K C.sub.L, one cannot guarantee that there will be no blockage on
the mesh links. (Note that, this, in turn, implies that there may
be up to 20 links total leading out of an end-office).
[0158] Now, suppose R.ltoreq.N. For this case, one may subdivide
the quadrant into arcs as shown in FIG. 8d (there are 4 arcs shown
in FIG. 8d). Note that the inner N arcs (an arc may consist of a
single node, i.e., the primary index node) are connected to index
nodes. It is readily apparent that all the traffic may be routed
from the outer arcs to the inner N arcs, and redistributed among
these N arcs (using the cross links between arcs), such that if an
arc is connected to j index nodes, it carries a traffic of j
C.sub.L. The total traffic on an arc may then be routed to the end
office through the index nodes on that arc. It is to be noted that,
again, if K>5, it may be impossible to deliver the traffic to
the inner N arcs, due to conditions similar to those described in
the previous paragraph.
[0159] Thus, we have shown that if the number of links leading
directly to an end office, K, is less than or equal to five per
quadrant, and are symmetrically arranged as shown in FIG. 8a, then
call blocking can be computed using the Erlang blocking formula.
Let the traffic intensity generated in a quadrant be .rho..sub.q.
Referring to Equation (1), the probability that a call is blocked
is then equal to P.sub.b(.rho..sub.q, 5C.sub.L).
[0160] If the number of direct links from the end-office into a
quadrant is six (i.e., the total number of links leading out of the
end office is now 24), one can eliminate blocking on mesh links by
imposing the additional constraint that routes taken by calls
generated within a semi-quadrant (See FIGS. 9a and 9b), in order to
reach the end-office, must be constrained to lie entirely within
the semi-quadrant. Adjacent diagonal nodes belong to different
semi-quadrants. Semi-loops may be drawn within a semi-quadrant as
shown in FIG. 9. Since the number of direct links is 6, at least 3
semi-loops can be drawn in a semi-quadrant (in the limiting case, a
semi-loop may have just a column of nodes).
[0161] If the maximum traffic generated within a semi-quadrant is
less than or equal to 3C.sub.L, it is possible to distribute the
traffic among the three outermost semi-loops such that the traffic
carried by any semi-loop is less than or equal to C.sub.L. Note
that if the traffic is greater than 3C.sub.L, blockage may be
encountered on the mesh links. For example, let the traffic
generated be 4C.sub.L. If all the traffic is generated in the
cluster of four nodes at the corner of the semi-quadrant adjacent
to the diagonal (FIG. 9a) then, since there are only 3 links
leading out of this cluster, C.sub.L calls must be blocked. Thus,
the maximum load which can be routed to the end-office without
encountering blockage on mesh links within a semi-quadrant is
3C.sub.L. Referring to Equation (1), the probability of a call
being blocked under such constraints is therefore
P.sub.b(.rho..sub.S, 3C.sub.L), where .rho..sub.S is the total
traffic intensity generated in the semi-quadrant.
[0162] 3. Cell Hand-Off
[0163] Routing in the optical mesh, as described in Section 2,
assumes that, for its entire duration, a given virtual connection
flows to/from the base station from which it was originally
generated over a fixed set of optical links. In reality, since
users are free to roam among radio cells, the virtual connections
must be "handed off" among radio cells as a user "travels" among a
sequence of cells. At the time of hand-off, it is required that (1)
a new route be found leading from the newly-serving base station
back to the end office, and (2) new routing instructions be
provided to the switch contained in each base station along the new
route. Implicit in the selection of a new route is the ability to
maintain QoS over each link in the new route and within the radio
cell accepting responsibility for the hand-off call. Insuring that
QoS objectives are met can present a critical real-time processing
challenge, especially when hand-offs occur very frequently such as
might be expected in a picocellular system. Delivering new routing
instructions to the switches, after QoS has been ascertained, is a
further challenge. Both challenges are adequately met by the
virtual connection tree.
[0164] The basis of the virtual connection tree is the creation, at
call set-up time, of a set of virtual connections for that call,
each originating from a root node and each terminating in a
different base station or leaf (actually two trees are set up: one
leading to the root node, one leading from the root node, such that
duplex connections can be handled). At call set-up time, an
admission controller determines whether or not a new call can
safely be admitted to the tree. For a new call to be admissible, it
must be determined that on a statistical basis, and as a result of
user mobility, the likelihood that too many calls will exist within
a leaf of the tree, or flow on any given branch (link) of the tree,
are acceptably low. If too many calls exist within a cell or flow
on some given branch, then that cell or branch is said to be in
overload, meaning that the QoS objectives cannot be met. Overload,
then, either causes an unacceptable (but transient) degradation in
service (i.e., delay or lost packet objectives are temporarily not
met) or causes the call which caused overload to be dropped (as
might occur, for example, for real time traffic such as voice). In
essence, at call set-up time, the admission controller is making a
guarantee: each new user can freely roam among all leaves (base
stations) in the tree and, only occasionally (that is, with some
guaranteed low probability) will unconstrained notion of the users
cause an overload condition to arise. To maintain this guarantee,
the admission controller blocks new call requests at some
pre-determined threshold.
[0165] If a newly-requested virtual connection is admitted, a route
in each direction will is chosen by that user.
[0166] As applied to our hybrid radio-optical link broadband access
network, a connection tree might appear as shown in FIG. 10a. Note
that the root of the tree is an end-office, and branches of the
tree extend to every base station served by that end-office. Note
further that, as shown in FIG. 10a, the "fingers" leading to each
end-office are "main branches" of the tree, that is, the tree is
defined such that the zones of Section 3a are maintained and
load-balancing among the fingers is provided for. Finally, note
also that since each "leaf" can be reached through any of several
"branches", it is possible to choose the "branches" for a
newly-requested virtual connection such that (1) each base station
is included in the tree and (2) load balancing is achieved among
branches at a given distance from the root. Thus, when setting up a
tree for a new call, each base station served by a given end-office
would be included, but the path leading to each leaf would be
chosen such that as users roam among cells, all branches at a given
depth from the root node carry, on average, the same traffic
intensity.
[0167] It is also possible to define the root of the tree as shown
in FIG. 10b, in which case an ATM switch behind the end-offices
serves as the root node for some larger tree, the footprint of
which includes the base stations served by several end offices.
Also shown in FIG. 10b is the inclusion of the base station of a
standard cell as one leaf in the tree, so that a user can also
choose service from a standard cell if conditions warrant (i.e., if
the user has roamed to some vicinity not served by any
picocell).
[0168] 4. Optical and Radio Link Calculations
[0169] Discussion in this section demonstrates that, because of the
relatively short range of adjacent lasercom transceiver nodes
(100-200 meters) envisioned in the picocell network architecture of
the present invention, a pico cell free-space optical link,
hereinafter called the "lasercom link", can have all weather
availability at OC-3 and higher data rates by use of an
inexpensive, compact, low power, eyesafe transceiver. Estimates for
the target capacity of the radio picocell are also provided.
[0170] The overall system performance of a lasercom link is easily
quantified using a link budget, the techniques being similar to
those used to evaluate microwave links. There are three important
parameters, transmitter power, propagation losses, and receiver
sensitivity. The receiver sensitivity relates the amount of optical
power needed to maintain the signal-to-noise ratio required to
achieve a desired quality of service.
[0171] The received signal power can be calculated from: 2 P R = P
T A R d 2 2 e - d
[0172] where
[0173] P.sub.R=received power
[0174] P.sub.T=transmitted power
[0175] .intg.=optical efficiency
[0176] A.sub.R=area of receiving aperture
[0177] .delta.=angular divergence of the transmitted beam
[0178] .alpha.=atmospheric attenuation factor, and
[0179] d=distance between transmitter and receiver
[0180] For relatively clear air the exponential term is small and
received laser power scales with 1/d.sup.2 and 1/.delta..sup.2; for
propagation conditions of heavy attenuation, such as fog, it scales
exponentially.
[0181] The amount of background radiation collected by the
transceiver is dependent on the receiver's field of view and its
optical bandwidth. The field of view cannot be made arbitrarily
narrow due to alignment issues discussed below and the optical
bandwidth cannot be made arbitrarily small due to poor absolute
transmission through most narrow dielectric filters. The received
background power, P.sub.Back, is calculated from: 3 P Back = 0.2 w
a t t s m 2 nm sr A R F BW FOV 2 N
[0182] where
[0183] m=meters,
[0184] nm=nanometers,
[0185] sr=steradians
[0186] F.sub.BW=filter bandwidth, and
[0187] .delta..sup.2.sub.FOV=angular field-of-view
[0188] The value for irradiance of the sky was measured at 10
degrees from the sun using a specially calibrated
telescope/detector assembly.
[0189] The noise equivalent power of the detector/preamp module can
be calculated from a double-sided noise density usually expressed
in watts{square root}Hz. FIG. 11 shows the received signal power
P.sub.rec, background power P.sub.back, and noise equivalent power
P.sub.dark as a function of range for the following set of
parameters:
1 Telescope Diameter 10 cm Laser Power 20 mW Laser Divergence 2
mrad Telescope Efficiency 0.5 Atmospheric Attenuation Varies Data
Rate OC-3 (155 Mb/sec)
[0190] In order to determine the availability of the link in all
weather conditions, an attenuation of 392 dB/km, the worst (and
very rarely experienced) fog was assumed in the calculation.
[0191] The Bit Error Rate (BER) for the PIN detector (a unity gain
photodiode) circuit can be calculated using the previously obtained
values. See S. G. Lambert and W. L. Casey, Laser Communications in
Space, Artech House, Norwood, Mass., 1995.
[0192] This circuit has an overall transimpedance gain of 10.sup.6.
FIG. 12 shows the calculated BER versus range for this case. The
BER was calculated assuming equally likely ones and zeros and
on-off keyed (OOK) modulation with direct detection. The threshold
value was chosen at each range point with the criterion of
minimizing BER at that point. Clearly the system is capable of very
low (equivalent to fiber optic) BER at ranges of 100 meters or less
in the most attenuating condition. For the avalanche photodiode
detector, the range for a given BER is increased by approximately
15 meters.
[0193] Eye safety is always an issue when working with laser
systems. The wavelength employed here is not inherently eyesafe
(i.e., light can pass through the cornea to be imaged on the
retina) . ANZI standards Z131.1-1986 maintain that the maximum flux
entering the eye at this wavelength is 2 mW/cm.sup.2. See American
National Standard for the Safe Use of Lasers, The Laser Institute
of American, Orlando, Fla., 1986. Transmit laser power of 20 mW
implies a transmit aperture of 10 cm.sup.2 minimum, a criterion
easily met by our conceptual transceiver.
[0194] Path loss in an optical communications link is affected by
atmospheric absorption, scattering, and turbulence, however, the
magnitude of each loss mechanism varies greatly. FIG. 13 shows sea
level atmospheric transmission for a 350 meter path as a function
of wavelength calculated using MODTRAN IV. Fortunately, for
available semiconductor laser diode wavelengths of 810 nm, 1300 nm,
and 1550 nm, path loss is negligible due to molecular absorption.
See W. G. Driscoll and W. Vaughan, Handbook of Optics, McGraw-Hill,
USA, 1978.
[0195] Path loss due to scattering is a function of optical
radiation wavelength, number density and size of scatters in the
path. In order to quantify the amount of scattering attenuation
along a particular path, an approximation based on Mie scattering
and visibility range can be used. See W. G. Driscoll and W.
Vaughan, Handbook of Optics, McGraw-Hill, USA, 1978. The most
severe path losses at near infra red wavelengths come about due to
fog. Fog occurs when the relative humidity of an air particle
approaches its saturation value. Some of the nuclei then condense
into water droplets forming the fog. FIG. 14 shows attenuation
versus visual ranges up to one km. See W. K. Pratt, Laser
Communications Systems, John Wiley & Sons, N.Y., 1969.
Precipitation in the form of rain occurs when the water droplets
condense up to millimeter sizes. This causes both scattering and
water absorption losses along the path with the size distribution
of the drops determining the relative magnitude of these effects.
The difference in fog and water droplet size, three orders of
magnitude, accounts for the orders of magnitude difference in
attenuation for typical rain (FIG. 15) versus typical fog.
Additionally, the relatively large size of typical raindrops
compared with near infra red wavelengths, permits the drops to
forward scatter a significant fraction of incident optical power.
Attenuation due to snow has been measured by several groups and is
displayed in FIG. 16 for snow rates up to one foot per hour.
Typically the path loss due to snow lies somewhere between fog and
rain, however, the relationship is very complex and is best
measured experimentally.
[0196] Path loss fading due to scintillation can be very
significant (25-30 dB) for long range paths through the atmosphere.
Scintillation is caused by thermal fluctuations which induce random
fluctuations in the index of refraction along the path contained in
the beam's cross section. This causes the air to act like sets of
small prisms and lenses which deflect the beam of light. In the
plane of the receiver a speckle-like pattern appears with light and
dark cells which have a characteristic size that scales like the
square root of wavelength times path length. The generally accepted
form for the probability distribution of the expected intensity is
log normal for weak scintillations, however, this tends to saturate
at variances near 0.35 for heavily scintillated paths. The
log-normal distribution for the intensity and variance of intensity
is given by: 4 P ( I , x 2 ) = 1 2 I 2 x 2 exp [ - ( ln I + 2 x 2 )
2 8 x 2 ]
[0197] This is plotted in FIG. 17 for the calculated variances
along 100 meter and 1 km horizontal paths. For the 100 meter case
of the pico cell backbone the effect is nearly zero and the
distribution of intensity is Gaussian. For the 1 km case the path
is highly scintillated and a typical threshold detection scheme
would require nearly 25 dB additional margin of transmitted signal
power. Beam wander due to changes in index of refraction is about
0.1 microradians, negligible compared to the two milliradian beam
divergence for the pico cell backbone system considered here.
[0198] A final issue to consider is misalignment of the
transceivers to each other due to wind or thermal expansion causing
an angular displacement of either end of the link. FIG. 18 shows
the calculated deflection of 10 inch diameter hollow poles made
from steel, aluminum, and wood, applied wind pressure of 15 lbs,
per square inch, considered hurricane force, and no allowance for
aerodynamic flow. For steel and aluminum the deflection angle is
not significant compared with 2 milliradians for pole lengths near
forty feet. Since we envision much shorter poles, much smaller
diameter pipe may be used. Thermal expansion of a three to four
story building over temperature ranges of 50 degrees Celsius causes
less than 50 microradians of angular displacement, a negligible
effect for our case.
[0199] Given the previously discussed issues a potential conceptual
design for a picocell backbone optical communications transceiver
operating at OC-3 data rate (or higher), range of 100 meters or
less, all weather operation, and BER of less than 10.sup.-9 is
shown in FIG. 19. Since the beam divergences used in this unit are
over two orders of magnitude above the diffraction limit, extremely
inexpensive plastic optics can be used throughout, and alignment
tolerances become very forgiving permitting inexpensive
manufacture. The aperture size is four inches making the unit
relatively small, and could be made a factor of two smaller without
affecting performance significantly. The smaller the transceiver
can be made the easier and less expensive it is to build. Another
benefit of small size and wide beam divergence is that relatively
inexpensive acquisition and alignment systems can be used for
potential autonomous alignment and alignment maintenance
systems.
[0200] Turning now to the radio link, it is reasonable to assume an
available spectrum of 10 MHz, equally split between tiers 1 and 2
(tier 3, created by Low Earth Orbiting (LEO) satellites, uses a
different spectrum and will not be considered). In tier 1, since
the cell diameter is so small, the path loss is low and we can
safely consider the use of some higher-level digital modulation,
say 16 QAM. Allowing a signaling rate of 1 symbol/sec/Hz, this
translates to 20 Mb/s peak rate per picocell. We further envision
the use of a smart array processor at the base station which,
coupled with admission control, allows, on average, 10 Mb/s per
picocell, that is, a peak rate of 20 Mb/s and an effective average
frequency re-use factor of 50%.
[0201] For the standard cell, more array elements would be used to
provide 100% frequency re-use, but the greater path loss limits the
modulation to 4f-PSK, and both the peak and average rate within a
standard cell are 10 Mb/s.
[0202] 5. Summary
[0203] The present invention is embodied in a system and a method
for a general-purpose wireless local access network. The use of
very small radio cells with frequency re-use at the lowest tier
insures very high bandwidth per subscriber. The use of a dense mesh
of short, free-space optical links in a multi-hop arrangement
allows signals to flow between picocellular base stations and an
end-office, thereby eliminating any dependence on copper and/or
optical cabling to the subscriber. Finally, the use of
higher-tiered cells insures universal service availability (both
from a radio coverage perspective and from a failure recovery
perspective). The proposed system can equally well serve
fixed-point, pedestrian, and vehicular users; all access is via a
high capacity radio link, and handoff among cells is fully
supported.
[0204] Although the use of free-space optical links might suggest a
somewhat less-than-robust service availability, sample link
calculations show that the shortness of the link provides excellent
immunity against even extreme weather-related impairments. (For
longer spans, millimeter-wave radio links may be considered, but
this might substantially escalate the cost of a subscriber's
premises-based equipment.) Moreover, the richness of the optical
mesh, the high data rate of each link, and the existence of
higher-tiered radio cells; combine to provide excellent immunity
against outage caused by equipment failure. Routing in the mesh can
be adapted to prevailing traffic conditions such that optical link
bottlenecks as the traffic flows toward the head end are avoided,
and the approach is compatible with embedded virtual connection
trees to facilitate hand-off while maintaining QoS guarantees for
each of several traffic classes (multimedia traffic). Exemplary
capacity calculations suggest that 20 Mb/s peak rate, and 10 Mb/s
average rate can be provided to each subscriber, and no optical
link need operate at a rate exceeding 155 Mb/s.
[0205] In accordance with the preceding explanation, variations and
adaptations of the telecommunications system and method in
accordance with the present invention will suggest themselves to a
practitioner of the wireless communication system arts.
[0206] For example, narrow band millimeter or microwave radio could
be substituted, at a generally increased cost, for some or for all
of the optical links of the system. A mesh communication network
over a very wide area, or over very rugged terrain, might warrant
such a selective substitution of directional millimeter or
microwave radio for optical links. If some of the mesh
communication links at a single base station are optical, and some
are millimeter radio, then the base station is clearly a "hybrid".
(Each and any link may be redundant, and may be continually
operated redundantly or the communication modes may be substituted
for each other depending upon conditions such as atmospheric
interference.) If some mesh communication links are optical, and
some are millimeter radio, then the system is clearly a "hybrid".
These variations are not a problem, and are anticipated by the
present invention. Indeed, if some mesh links, whether optical or
millimeter radio, prove over time and actual use to be unreliable
for certain base stations, then the links may well be substituted
for by a link of another type.
[0207] Still another type of "hybrid" system is contemplated by the
present invention in that some of the mesh links may be, or may
become, conventional copper cable and/or optical fiber. Consider
the final links just short of an end office, which links were shown
as lines radiating from each end office in FIG. 6. If
communications traffic, or evolving communications traffic
dictates, any or all of these links can be made to be copper cable
and/or optical fiber as may generally be made to carry greater
communications traffic to an from a particular "sector" relative to
the end office then, for example, a standard optical or millimeter
radio link.
[0208] Still further, any individual one or ones of the base
stations may bypass the free-space network altogether, and
communicate direct to the end office via (i) radio, (ii) optics, or
(iii) copper cable and/or optical fiber. This "hard-wired" base
station may serve to communicate only such communications traffic
as is associated with its own picocell, or it may continue to mount
(in addition to its wire or fiber access) the system standard
optical and/or millimeter radio transceivers, using these
transceivers to siphon some communications traffic off the mesh and
thus helping to ameliorate the communications burden at other base
stations and other regions on the mesh. The "hard-wired" base
station thus becomes a "constrictor", and just one more of several
places where communications traffic can be interfaced to the
mesh.
[0209] Herein lies a great flexibility in the system of the present
invention. Clearly it has always been possible to add new base
stations (as well as new telecommunicating equipments at existing
base stations) to the mesh networks of the present invention as the
area, and/or the areal density, of broadband wireless
communications expands. The addition of new base stations can be
accomplished, of course, without any new copper cables or fiber
optics. However, should a new copper cable or a fiber optic be
installed to some new or existing base station point in an existing
mesh, then increased communications traffic can henceforth flow
thru this point without disruption to the existing mesh and
existing network.
[0210] In accordance with these and other possible variations and
adaptations of the present invention, the scope of the invention
should be determined in accordance with the following claims, only,
and not solely in accordance with that embodiment within which the
invention has been taught.
* * * * *