U.S. patent application number 15/456233 was filed with the patent office on 2018-04-05 for apparatus and methods to provide communications to aerial platforms.
The applicant listed for this patent is UBIQOMM, LLC. Invention is credited to Ahmad Jalali.
Application Number | 20180097560 15/456233 |
Document ID | / |
Family ID | 61759149 |
Filed Date | 2018-04-05 |
United States Patent
Application |
20180097560 |
Kind Code |
A1 |
Jalali; Ahmad |
April 5, 2018 |
APPARATUS AND METHODS TO PROVIDE COMMUNICATIONS TO AERIAL
PLATFORMS
Abstract
Apparatus, systems and methods for the provision of high data
rate and high throughput communications link for drones, in a
bandwidth efficient manner. One set of embodiments describe
apparatus and methods to mitigate interference from other systems
when using the unlicensed radio frequency bands such as the
Industrial Scientific and Medical (ISM) bands. Apparatus and
methods are also described to enable association of the drone radio
sub-system with an "optimal" cell site, such as when the drone uses
a directional antenna beam to maximize system throughput.
Configurations of a mechanically steerable directional antenna
aperture are also disclosed. Other embodiments describe systems and
methods to mitigate excessive amounts of interference, and to
provide a reliable communications link for signaling and other
mission-critical messages.
Inventors: |
Jalali; Ahmad; (San Diego,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
UBIQOMM, LLC |
San Diego |
CA |
US |
|
|
Family ID: |
61759149 |
Appl. No.: |
15/456233 |
Filed: |
March 10, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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62404610 |
Oct 5, 2016 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04W 28/0268 20130101;
H04W 74/0833 20130101; H04W 84/005 20130101; H01Q 9/0407 20130101;
H04W 16/28 20130101; H04B 1/692 20130101; H01Q 3/04 20130101; H04W
36/30 20130101; H04W 84/12 20130101; H04B 7/18502 20130101; H04W
36/0061 20130101; H04W 72/046 20130101; H01Q 1/28 20130101; H01Q
3/06 20130101; H04W 24/08 20130101; H04L 25/08 20130101; H04B
7/18504 20130101; H04W 36/32 20130101; H04W 28/0236 20130101; H01Q
3/24 20130101; H04W 72/0446 20130101; H01Q 21/065 20130101; H04W
72/0453 20130101 |
International
Class: |
H04B 7/185 20060101
H04B007/185; H04W 16/28 20060101 H04W016/28; H04W 24/08 20060101
H04W024/08; H04W 36/30 20060101 H04W036/30; H04W 36/32 20060101
H04W036/32; H04B 1/692 20060101 H04B001/692; H04W 72/04 20060101
H04W072/04; H04W 36/00 20060101 H04W036/00; H01Q 9/04 20060101
H01Q009/04; H01Q 3/06 20060101 H01Q003/06; H01Q 3/24 20060101
H01Q003/24 |
Claims
1. Apparatus for receiving broadband access via a network of cell
sites comprising one or more base stations, each base station
comprising a cell radio sub-system, and a cell antenna sub-system
configured to form at least one directional beam; the apparatus
comprising: a drone radio sub-system, a position location
determination unit, and a drone antenna sub-system comprising an
antenna aperture configured to form a steerable directional beam;
wherein the drone radio sub-system is further configured to: store
a plurality of position locations associated with a plurality of
cell sites of the network of cell sites; instruct the drone antenna
sub-system to steer a beam toward a specific cell site based on a
drone position coordinate and a specific position coordinate of the
specific cell site; measure a downlink signal quality measurement
on a received signal from the specific cell site; and receive
uplink signal quality measurements provided within the received
signal from the specific cell site, wherein the uplink signal
quality measurements are associated with the specific cell
site.
2. The apparatus of claim 1, wherein the drone antenna sub-system
is further configured to steer the antenna aperture on at least one
axis to point the steerable directional beam toward the specific
cell site.
3. The apparatus of claim 2, wherein the drone antenna sub-system
comprises a mechanical steering mechanism configured to rotate the
antenna aperture from a center of the antenna aperture.
4. The apparatus of claim 1, wherein the drone radio sub-system is
further configured to: divide a network coverage area into a number
of contiguous geographic bins; maintain a candidate cell site
association table with an entry for each one of the number of
contiguous geographic bins; wherein the candidate cell site
association table comprises a list of cell sites that are available
to establish a communications link based on an uplink or downlink
signal quality; and for at least one candidate cell site within the
list of cell sites: measure the downlink signal quality for the at
least one candidate cell site; or receive the uplink signal quality
from the at least one candidate cell site; and associate with the
at least one candidate cell site based at least in part on the
uplink or downlink signal quality.
5. The apparatus of claim 4, wherein the drone radio sub-system
further configured to hand off to a different cell site when the
uplink or downlink signal quality of the communications link to the
at least one candidate cell site falls below an acceptable
threshold.
6. The apparatus of claim 4, wherein the drone radio sub-system is
further configured to hand off to a different cell site based on a
current position location and the candidate cell site association
table.
7. The apparatus of claim 1, wherein the antenna aperture comprises
an array of patch elements with at least one row and at least one
column of patch elements.
8. The apparatus of claim 1, wherein the drone radio sub-system is
configured to create one or more spread channels that spread
encoded bits in time or frequency.
9. The apparatus of claim 8, wherein the drone radio sub-system
communicates using an Institute of Electrical and Electronics
Engineers (IEEE) 802.11-compliant protocol.
10. The apparatus of claim 9, wherein the IEEE 802.11-compliant
protocol is further compliant with an IEEE 802.11ac standard.
11. The apparatus of claim 8, wherein the received signal is
received over the one or more spread channels.
12. The apparatus of claim 1, wherein the drone radio sub-system
communicates using a frequency band associated with an unlicensed
shared Industrial Scientific and Medical (ISM) band.
13. A method for receiving broadband access at a drone, comprising:
storing a plurality of position location data associated with a
network of cell sites; steering a beam toward a specific cell site
of the network of cell sites based at least on a drone position
coordinate, and a specific position coordinate of the specific cell
site as reflected in the data, the steered beam characterized by at
least a frequency within an unlicensed frequency band; measuring a
downlink signal quality measurement on a received signal from the
specific cell site; and receiving an uplink signal quality
measurements from the specific cell site.
14. The method of claim 13, wherein the steering comprises
mechanically rotating an antenna aperture about a fixed axis.
15. The method of claim 13, wherein the steering comprises
electrically forming the beam from a patch array of antenna
elements.
16. A method for providing broadband access to at least one drone,
comprising: forming at least one directional beam toward the at
least one drone within an unlicensed frequency band; receiving a
beam from the at least one drone; measuring the uplink signal
quality from the at least one drone; and transmitting the uplink
signal quality measurements to the at least one drone; wherein the
transmitted uplink signal quality measurements are configured to be
used by the drone in configuring at least a portion of the
broadband access.
17. A drone radio sub-system, comprising: a position location
determination sub-system configured to determine a drone position
coordinate; and a drone antenna sub-system configured to steer a
directional radio frequency beam; wherein the drone radio
sub-system is configured to: store data relating to a plurality of
position locations associated with a network of cell sites; steer
the directional radio frequency beam toward a specific cell site
based at least on an evaluation of (i) the drone position
coordinate, and (ii) a specific position coordinate of the specific
cell site; measure a downlink signal quality measurement on one or
more received signals from the specific cell site; and receive one
or more uplink signal quality measurements from the specific cell
site.
18. The drone radio sub-system of claim 17, wherein the drone
antenna sub-system is configured to generate the directional radio
frequency beam within an unlicensed frequency band.
19. The drone radio sub-system of claim 18, wherein the one or more
received signals from the specific cell site is/are received within
the unlicensed frequency band.
20. The drone radio sub-system of claim 19, wherein one or more
received signals from the specific cell site is/are multiplexed in
at least one of time and frequency within the unlicensed frequency
band.
Description
PRIORITY APPLICATIONS
[0001] This application claims the benefit of priority to
co-pending and co-owned U.S. Provisional Patent Application Ser.
No. 62/404,610, filed Oct. 5, 2016, and entitled "A NETWORK OF CELL
SITES TO PROVIDE COMMUNICATIONS TO AERIAL PLATFORMS", which is
incorporated herein by reference in its entirety.
RELATED APPLICATIONS
[0002] This application is related to co-owned, co-pending U.S.
patent application Ser. No. 15/225,240, entitled "UNMANNED AERIAL
VEHICLE (UAV) BEAM POINTING AND DATA RATE OPTIMIZATION FOR HIGH
THROUGHPUT BROADBAND ACCESS", filed Aug. 1, 2016, co-owned,
co-pending U.S. patent application Ser. No. 14/711,427, entitled
"GROUND TERMINAL AND GATEWAY BEAM POINTING TOWARD AN UNMANNED
AERIAL VEHICLE (UAV) FOR NETWORK ACCESS", filed on May 13, 2015,
co-owned, co-pending U.S. patent application Ser. No. 14/626,698,
entitled "BEAM FORMING AND POINTING IN A NETWORK OF UNMANNED AERIAL
VEHICLES (UAVS) FOR BROADBAND ACCESS", filed on Feb. 19, 2015,
co-owned, co-pending U.S. patent application Ser. No. 14/516,491,
entitled "UNMANNED AERIAL VEHICLE (UAV) BEAM FORMING AND POINTING
TOWARD GROUND COVERAGE AREA CELLS FOR BROADBAND ACCESS", filed on
Oct. 16, 2014, co-owned, co-pending, U.S. patent application Ser.
No. 14/486,916, entitled "ANTENNA BEAM MANAGEMENT AND GATEWAY
DESIGN FOR BROADBAND ACCESS USING UNMANNED AERIAL VEHICLE (UAV)
PLATFORMS", filed on Sep. 15, 2014, co-owned, co-pending, U.S.
patent application Ser. No. 14/295,160, entitled "METHODS AND
APPARATUS FOR MITIGATING FADING IN A BROADBAND ACCESS SYSTEM USING
DRONE/UAV PLATFORMS", filed on Jun. 3, 2014, co-owned, co-pending,
U.S. patent application Ser. No. 14/222,497, entitled "BROADBAND
ACCESS TO MOBILE PLATFORMS USING DRONE/UAV", filed on Mar. 21,
2014, and co-owned, co-pending, U.S. patent application Ser. No.
14/223,705, entitled "BROADBAND ACCESS SYSTEM VIA DRONE/UAV", filed
on Mar. 24, 2014, each of the foregoing incorporated by reference
herein in its entirety.
COPYRIGHT
[0003] A portion of the disclosure of this patent document contains
material that is subject to copyright protection. The copyright
owner has no objection to the facsimile reproduction by anyone of
the patent document or the patent disclosure, as it appears in the
Patent and Trademark Office patent files or records, but otherwise
reserves all copyright rights whatsoever.
BACKGROUND
1. Technological Field
[0004] The present disclosure describes aspects of a system for
providing communications and/or data access including e.g.,
broadband internet and network access (also generally referred to
as "internetworks"), to aerial platforms such as general aviation
aircraft, commercial aircraft, and drones, using a network of
terrestrial cell sites. In exemplary aspects, the present
disclosure describes systems, apparatus, and methods to mitigate
interference received in the communications link between an aerial
platform and a cell site e.g., from other interfering cell sites
and transmitters of extraneous systems. These systems, apparatus,
and methods, inter alia, maximize the throughput and link
reliability of the proposed aerial platform communications
system.
2. Description of Related Technology
[0005] It is expected that drones will be deployed in large numbers
for applications such as package delivery, surveillance, data
collection in sectors such as for example construction and
agriculture, firefighting, and emergency response. Drones will
require connectivity to an air traffic control system, as well as
to internetworks such as the Internet and data centers. Many drones
will collect large amounts of video data in segments (such as e.g.,
construction, farms, firefighting, and emergency response), and
will require high speed data links to upload the data to data
centers in real time for processing.
[0006] Unfortunately, interference poses specific problems for such
large scale deployments of aerial platforms at broadband access
speeds. In particular, new technologies are needed to deliver
broadband access to drones at high data rate, low cost, and
ubiquitously. Examples of current broadband delivery systems to
drones include conventional cellular networks and satellite
systems. These current broadband access systems have a number of
shortcomings for providing broadband access, including particularly
to drones. For instance, usage projections forecast that the drone
population will continue to expand (e.g., as many as 10,000 drones
per metropolitan area), and a commensurate amount of capacity in
the conventional cellular networks will be needed to service them.
The additional capacity requirement may result in a shortfall of
available service for smart phones, and/or potentially increase
wireless data plan prices due to the limited nature of the
commodity.
[0007] Geo-stationary satellites are another option. In
metropolitan areas, satellite capacity is typically more expensive
than that of the terrestrial solutions. Moreover, since drones
generally use small antennas with limited reception capabilities,
the satellite must compensate by providing a higher gain link to
maintain the drone to satellite communications link. Such increased
gain requirements for satellites can also increase the operational
cost of the satellite-based drone connectivity.
[0008] Hence, what are needed are methods and apparatus for
providing broadband access to drones, including one or more of the
attributes of high data rate, high throughput, reliable, cost
effective, and/or ubiquity.
SUMMARY
[0009] The present disclosure describes, inter alia, systems,
apparatus, and methods to mitigate interference received in the
communications link between an aerial platform and a cell site
e.g., from other interfering cell sites and transmitters of
extraneous systems.
[0010] In a first aspect, a system to provide broadband access to
drones is disclosed. In one embodiment, the system includes: a
network of cell sites comprising one or more base stations, each
base station comprising a cell radio sub-system, and a cell antenna
sub-system configured to form at least one directional beam; a
plurality of drones that each comprise a drone radio sub-system, a
position location determination unit, and a drone antenna
sub-system comprising an antenna aperture configured to form a
steerable directional beam. In one exemplary configuration, each
drone radio sub-system is further configured to: store a plurality
of position locations associated with a plurality of cell sites of
the network of cell sites; instruct the drone antenna sub-system to
steer a beam toward a specific cell site based on a drone position
coordinate and a specific position coordinate of the specific cell
site; measure a downlink signal quality measurement on a received
signal from the specific cell site; and receive uplink signal
quality measurements provided within the received signal from the
specific cell site. The uplink signal quality measurements are
e.g., associated with the specific cell site.
[0011] In one variant, the drone antenna sub-system is further
configured to steer the antenna aperture on at least one axis to
point the steerable directional beam toward the specific cell site.
In one case, the drone antenna sub-system comprises a mechanical
steering mechanism configured to rotate the antenna aperture from a
center of the antenna aperture.
[0012] In another variant, the drone radio sub-system is further
configured to: divide a network coverage area into a number of
contiguous geographic bins; and maintain a candidate cell site
association table with an entry for each one of the number of
contiguous geographic bins. The candidate cell site association
table comprises for example a list of cell sites that are available
to establish a communications link based on an uplink or downlink
signal quality. For at least one candidate cell site within the
list of cell sites, the drone radio sub-system measures the
downlink signal quality for the at least one candidate cell site
(or receives the uplink signal quality from the at least one
candidate cell site), and associates with the at least one
candidate cell site based at least in part on the uplink or
downlink signal quality. In one such implementation, the drone
radio sub-system is further configured to hand off to a different
cell site when the uplink or downlink signal quality of the
communications link to the at least one candidate cell site falls
below an acceptable threshold or otherwise meets a prescribed
criterions. In another such implementation, the drone radio
sub-system is further configured to hand off to a different cell
site based on a current position location and the candidate cell
site association table.
[0013] In one variant, the antenna aperture comprises an array of
patch elements with at least one row and/or at least one column of
patch elements.
[0014] In another variant, at least one of the cell radio
sub-system and drone radio sub-system creates one or more spread
channels that spread encoded bits in time or frequency. In one
case, at least one of the cell radio sub-system and drone radio
sub-system communicate using an Institute of Electrical and
Electronics Engineers (IEEE) 802.11-compliant protocol. The IEEE
802.11-compliant protocol may be compliant with for instance IEEE
802.11ac. In still another variant, the received signal is received
over the one or more spread channels.
[0015] In yet another variant, at least one of the cell radio
sub-system and drone radio sub-system communicate using a frequency
band associated with an unlicensed shared Industrial Scientific and
Medical (ISM) band.
[0016] A method for receiving broadband access at a drone is also
disclosed. In one embodiment, the method includes: storing a
plurality of position locations associated with a network of cell
sites; steering a beam toward a specific cell site of the network
of cell sites based on a drone position coordinate and a specific
position coordinate of the specific cell site; measuring a downlink
signal quality measurement on a received signal from the specific
cell site; and receiving an uplink signal quality measurements from
the specific cell site. The steered beam is characterized for
example by a frequency within an unlicensed frequency band.
[0017] In one variant, the steering comprises mechanically rotating
an antenna aperture about a fixed axis. In other variants, the
steering comprises electrically forming the beam from a patch array
of antenna elements.
[0018] A method for providing broadband access to at least one
drone is further disclosed. In one embodiment, the method includes:
forming at least one directional beam toward the at least one drone
within an unlicensed frequency band; receiving a beam from the at
least one drone; measuring the uplink signal quality from the at
least one drone; and transmitting the uplink signal quality
measurements to the at least one drone.
[0019] Further, a drone radio sub-system is disclosed. In one
embodiment, the drone radio sub-system includes: a position
location determination sub-system configured to determine a drone
position coordinate; and a drone antenna sub-system configured to
steer a directional beam. In one configuration, the drone radio
sub-system is adapted to: store a plurality of position locations
associated with a network of cell sites; steer the directional beam
toward a specific cell site based on the drone position coordinate
and a specific position coordinate of the specific cell site;
measure a downlink signal quality measurement on a received signal
from the specific cell site; and receive uplink signal quality
measurements from the specific cell site.
[0020] In one variant, the drone antenna sub-system is configured
to generate the directional beam within an unlicensed frequency
band. In one such variant, the received signal from the specific
cell site is received within the unlicensed frequency band.
Additionally, the received signal from the specific cell site may
be multiplexed in at least one of time and frequency within the
unlicensed frequency band.
[0021] In another aspect, apparatus to provide broadband access to
a drone are disclosed. In one embodiment, the apparatus include: a
cell radio sub-system configured to transmit and/or receive signals
to one or more aerial platforms via a cell antenna sub-system; the
cell antenna sub-system configured to form at least one directional
beam. In one variant, the cell radio sub-system is further
configured to: partition a frequency band into one or more
sub-frequency channels; partition at least one of the one or more
sub-frequency channels into one or more data channels; and
associate a first aerial platform to a first data channel of the
one or more data channels.
[0022] In one variant, the one or more data channels occupy a
number of time slots and at least one of the one or more
sub-frequency channels. In some cases, a subset of the one or more
data channels are allocated for shared data traffic that may be
arbitrarily allocated to one or more applications or users. In some
cases, a subset of the one or more data channels are allocated for
dedicated data traffic that is allocated to a specific application
or user. In still other cases, a subset of the one or more data
channels are allocated for a random access channel for data
transmission without an explicit bandwidth reservation.
[0023] In another variant, the cell radio sub-system is configured
to transmit announcement messages via a first directional beam. In
one such variant, the cell radio sub-system is further configured
to receive association messages from the first aerial platform via
a second directional beam. In some situations, the second
directional beam is wider than the first directional beam.
[0024] In still other variants, the at least one directional beam
can be dynamically adjusted to compensate for changing channel
conditions.
[0025] A method for receiving broadband access at a drone is
disclosed. In one embodiment, the method includes: steering a beam
toward a specific cell site of the network of cell sites based at
least on a drone position coordinate, and a specific position
coordinate of the specific cell site; searching for announcement
messages sent from the specific cell site; determining a frequency
band of the specific cell site, the frequency band comprising one
or more sub-frequency channels partitioned into one or more data
channels; and when a received announcement message for the specific
cell site satisfies an association criteria, transmitting an
association message on an uplink channel of the specific cell
site.
[0026] In one variant, the association criteria comprises a minimum
signal quality associated with the frequency band.
[0027] In another variant, the association criteria comprises a
higher signal quality associated with the frequency band compared
to a signal quality associated with another cell site.
[0028] In still another variant, the method further includes
determining at least one channel assignment for the uplink channel
via the received announcement message.
[0029] In still other variants, the method includes transmitting
the association message on the uplink channel of the specific cell
site comprises a number of transmissions. In one such case, the
number of transmissions is based on the number of uplink sub-beams
used by the specific cell site.
[0030] A drone apparatus is disclosed. In one embodiment, the drone
apparatus includes a drone radio sub-system configured to transmit
and/or receive signals to one or more ground terminals via a drone
antenna sub-system; and a drone antenna sub-system configured to
steer a directional radio frequency beam. In one embodiment, the
drone radio sub-system is configured to: determine a frequency band
of a specific cell site, the frequency band comprising one or more
sub-frequency channels partitioned into one or more data channels
steer the directional radio frequency beam toward the specific cell
site; and associate with the specific cell site.
[0031] In one variant, the one or more data channels comprise at
least shared data traffic that may be arbitrarily allocated to one
or more applications or users.
[0032] In another variant, the one or more data channels comprise
at least dedicated data traffic that is allocated to a specific
application or user.
[0033] In still other variants, the frequency band comprises an
unlicensed frequency band.
[0034] In one such variant, the one or more data channels are each
allocated one or more time slots and one or more sub-frequency
channels.
[0035] These and other aspects shall become apparent when
considered in light of the disclosure provided herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0036] In the following figures, where appropriate, similar
components are identified using the same reference label.
[0037] FIG. 1 is a graphical depiction of an exemplary terrestrial
network of base stations useful in conjunction with various
embodiments described herein.
[0038] FIGS. 2A and 2B are graphical depictions of exemplary base
stations communicating with drones in conjunction with some
embodiments described herein.
[0039] FIG. 3 is a graphical depiction of an exemplary cell site
with different size beamwidths for uplink and downlink beams in
conjunction with some embodiments described herein.
[0040] FIGS. 4A and 4B are graphical depictions of an exemplary
drone antenna sub-system in conjunction with some embodiments
described herein.
[0041] FIG. 5A is a logical representation of time periods with
different uplink beamwidth antenna beams, in accordance with the
principles described herein.
[0042] FIG. 5B is a logical representation of time periods with
different uplink and downlink beamwidth antenna beams, in
accordance with the principles described herein.
[0043] FIG. 6 is a graphical depiction of an exemplary cell site
with multiple sub-sectors per each sector.
[0044] FIG. 7 is a graphical depiction of exemplary time periods of
a downlink and uplink shared and dedicated channel bandwidth
schedule for use within a time division duplex (TDD) system with
multiple sub-sectors per sector.
[0045] FIG. 8 is a graphical depiction of an exemplary aerial
platform based communications system useful in conjunction with
various embodiments described herein.
[0046] FIG. 9 is a graphical depiction of exemplary radio equipment
of an aerial platform useful in conjunction with various
embodiments described herein.
[0047] FIG. 10 is a graphical depiction of exemplary radio
equipment of a ground terminal useful in conjunction with various
embodiments described herein.
[0048] All Figures .COPYRGT. Copyright 2016-2017 Ubiqomm, LLC. All
rights reserved.
DETAILED DESCRIPTION
[0049] The present disclosure describes, inter alia, aspects of a
system designed to provide broadband access to aerial platforms
such as drones.
[0050] The capital expenditure cost of a cellular network includes
the spectrum acquisition cost, hardware cost of the base stations
that are installed at each cell site, and the cost of base station
installation. Generally speaking, a significant amount of bandwidth
(e.g., at least 20 Megahertz (MHz)) is needed to provide adequate
throughput for large numbers of drones (e.g., more than 10,000
drones within a metropolitan area). 20 MHz of licensed spectrum
nationwide has auctioned for billions of dollars in recent years.
On the other hand, there is about 500 MHz of unlicensed spectrum
available in the 5 GHz Industrial Scientific and Medical (ISM)
radio band for use without any license cost. The ISM band is,
however, shared by many users/systems and subject to limits on the
device and base station transmit power. It is desirable to provide
connectivity to drones using unlicensed assets such as the 5 GHz
ISM band. However, in order to provide high data rate and reliable
communications in the ISM band, techniques must be devised to
significantly mitigate interference received from, e.g., other
systems deployed in the band.
[0051] In this disclosure, one set of exemplary embodiments
describe systems and methods to filter out the interference
received from other systems, and to make the drone communications
link highly robust to excessive amounts of interference. These
techniques allow use of the exemplary ISM band for drone
communications, resulting in significant spectrum cost saving as
noted supra. Moreover, the techniques described herein may be
broadly applicable to (i) any unlicensed band including without
limitation future additions to the ISM band and/or reclaimed
frequency allocations, or (ii) licensed bands where the
cost/benefit calculation warrants use of such band.
[0052] As mentioned above, base station hardware cost and
installation at the cell sites is also a major capital expenditure
for building networks that provide broadband access to cell phones
or drones. Therefore, it is desirable to minimize the number of
cell sites needed in the network to provide adequate capacity for
communications to the drones. In order to reduce the number of
required cell sites, the data throughput by the base station in
each cell site should be maximized. The embodiments in this
disclosure also describe systems and methods to maximize the data
throughput of each cell site.
Beamwidth and Directionality Selection--
[0053] FIG. 1 illustrates a wireless network including a number of
cell sites 110-j. At each cell site, a base station 120-j including
a radio sub-system 122-j and an antenna sub-system 124-j is
installed, where j is an integer identifying different occurrences
of the same sub-system. The base station radio sub-system 122 is
comprised of at least a transmitter, a receiver, a processor, and a
non-transitory computer readable medium. In FIG. 1, the base
station antenna is shown on top of towers. The base stations and
their antennas may alternatively be installed on top of tall
buildings with open view over a large area, or in yet other modes,
such as atop a natural topological feature such as a hill. Drones
140-j are comprised of a radio sub-system 142-j and an antenna
sub-system 144-j. The drone radio sub-system 142 is comprised of at
least a transmitter, receiver, a processor, and a non-transitory
computer readable medium. In some embodiments, the drone radio
sub-system is also equipped with a position location determination
device such as GPS (Global Positioning System) or other similar
systems such as Global Navigation Satellite System (GLONASS),
Assisted-GPS (A-GPS), etc. Drones 140-j communicate with the cell
sites 120-j from which they receive the strongest signal quality
such as the highest Signal to Interference plus Noise Ratio (SINR).
In the absence of extraneous interference from other systems, the
closest cell site to the drone is the one from which the drone
receives the strongest signal strength and best quality.
[0054] The available frequency spectrum is in the illustrated
configuration divided into a set of contiguous frequency bands;
each of the contiguous frequency bands is referred to as a
frequency channel. For instance, the IEEE 802.11ac standard divides
the available spectrum in the 5 GHz ISM band into frequency
channels of bandwidths 20, 40 or 80, or 160 MHz each. Each
frequency channel is referred to by the frequency bandwidth it
occupies, e.g. a 20 MHz frequency channel describes a frequency
channel that occupies 20 MHz of contiguous frequency spectrum. It
will be appreciated, however, that use of contiguous bands is not
essential.
[0055] FIG. 2A shows an exemplary diagram of a six (6) sector cell
site. The bulb shaped coverage footprints 125-j represent the beams
produced by sector antennas for each sector numbered j. Each beam
is characterized by a coverage area based on an angular coverage
(or beamwidth) and a coverage distance. Still other antenna
configurations and/or coverage areas may be substituted with
equivalent success by those of ordinary skill in the related arts,
given the contents of the present disclosure. For example, a
multi-antenna array may be used to create a beam-formed coverage
area so as to e.g., compensate for environmental or other
effects.
[0056] As a brief aside, a so-called "omnidirectional" antenna
radiates (generally) equal power in all radial directions. A
"directional" antenna has a peak effective radiated power within a
so-called "main lobe." The main lobe can be pointed e.g., toward a
transceiver for optimal link performance. The term "beamwidth"
refers to an angular coverage of a directional antenna. Typically,
the beamwidth is defined as the angular region where the antenna
provides at least half (e.g., -3 decibels (dB)) of the peak
effective radiated power of the main lobe.
[0057] As shown in the system of FIG. 2A, the downlink (cell site
to drone) and uplink (drone to cell site) beams have substantially
the same beamwidth (only one beam and label 125-j is used to depict
the uplink and downlink beams in each sector). In subsequently
described embodiments, the downlink and uplink beams have different
beamwidths (see e.g., FIG. 3). If the cell site base station
simultaneously transmits to drones in all six (6) sectors on the
same frequency channel as shown in FIG. 2A, then the signals in
adjacent sectors will cause inter-sector interference and result in
low signal-to-interference-plus-noise ratio (SINR) for drone
receivers that are close to the sector boundaries. For example, as
the drone 140 moves closer to the boundary between sectors 125-1
and 125-2 (which are using the same frequency channel), the drone
140 will be unable to differentiate between the sectors. Reduced
SINR directly corresponds to reduced data rates in the affected
regions. In one embodiment, adjacent sectors are assigned different
frequency channels, in order to improve the SINR at the sector
boundaries.
[0058] FIG. 2B illustrates a system where adjacent sectors use
different frequency channels in order to minimize inter-sector
interference at sector boundaries, thereby increasing data rate in
those regions. For instance, in the so-called "frequency reuse" of
two (2) depicted in FIG. 2B, the available spectrum is divided into
two sets of channels (F.sub.1 and F.sub.2), each of the two sets
assigned to alternating sectors so that no two adjacent sectors use
the same frequency channel. The two types of dashed lines shown for
beams on FIG. 2B pictorially illustrate that the corresponding
beams are transmitting/receiving on different frequencies. More
generally, the term "frequency reuse" refers to frequency
allocation schemes that stagger geographical or spatial use of a
number of frequency bands so as to minimize interference between
areas using the same frequency. Higher order frequency reuse
factors (e.g., three (3), four (4), or higher) can be used to
provide more separation and better performance, but may require
complex network management. Moreover, it will be appreciated that
the frequency reuse within a given system (or portion of the
system) may be asymmetric; e.g., applied to only a subset of the
spatial distribution of the system, and/or applied differently in
different portions of the system.
[0059] Referring back to the system of FIGS. 2A, 2B, in one
embodiment each sector radio sub-system transmits an announcement
message 212 which may be received by the drones in the
corresponding sector. The announcement message contains system
information such as sector identification and system operational
parameters. The drone radio sub-system 142 searches for
announcement messages from the cell sites, until it detects at
least one announcement message. Alternatively, the drone(s) may
"ping" one or more cell sites (or a given geographic area
generally) to elicit a response (announcement) from one or more
such cell sites.
[0060] The detected announcement message contains network and
sector specific information that can be used by the drones to
associate with the network and the sector. Upon receiving one or
more announcement messages 212, the drone selects a sector with the
strongest announcement message and sends an association message 312
to the selected sector. The association message 312 requests an
association (or to associate) with the corresponding sector. In one
embodiment, once a drone is associated with a sector, the drone
receives/transmits data to the wireless network and/or broader
internet (or Internet) via the corresponding sector until, as
described later herein, the drone switches association to a
different sector or cell site. For instance, the drone may handover
to a different sector/cell site when the signal quality between the
drone and its currently associated sector falls below acceptable
thresholds, and/or where the drone may receive a stronger signal
from the other sector or cell site. Alternatively, other criteria
or considerations may drive the handover decision process (or at
least be part of it), such as economic ramifications of use of one
sector/cell site) over another, past reliability or performance
history, anticipated future "crossover" of a cell site where
communication may be lost (see discussion below), or yet other
factors.
[0061] In one exemplary embodiment, the beamwidth of the antenna
beams at the drone and the base station are narrowed in at least
the azimuthal dimension so as to filter out interference from
extraneous and/or external systems operating in the ISM unlicensed
band. Moreover, narrow beamwidth base station/drone antenna beams
may also serve to filter interference from other cell sites/drones
of the same system, thereby allowing the reuse of all available
spectrum at each cell site. Furthermore, narrow azimuthal beams can
be used to maximize received SINR at the base station/drone
receiver to achieve high data rates and throughput. It will further
be appreciated that other "beam-shaping" techniques (including
narrowing in dimensions other than azimuth, such as elevation) may
also be employed consistent with the present disclosure in order to
maximize received SINR.
[0062] Artisans of ordinary skill in the related arts will readily
appreciate that reusing as much spectrum as possible at each cell
site increases the data throughput of the network. To these ends,
narrower beamwidths of an antenna in one or more dimensions (e.g.,
elevation, azimuth, etc.) can be created with a larger sized
antenna in that dimension. For example, a base station sector
antenna that is operating at 5.5 GHz and having an aperture area
about 0.5 square meters has a peak gain of at least 31 dBi
(decibels isotropic; a measure of the gain of an antenna compared
with an ideal isotropic antenna that uniformly distributes energy
in all directions) and a half power beamwidth of about 5 degrees.
Certain deployment scenarios can accommodate large sized antennas
(e.g., an antenna of size about 0.5 square meter) at the cell site
in each sector; e.g., there may be adequate physical space at the
cell site tower or on top of a building. In one exemplary
embodiment, an antenna with about 31 dBi peak gain and beamwidth of
about 5 degrees, provides a narrow beamwidth to filter significant
amount of interference from other systems or drones, and high
enough gain to achieve high data rate on the uplink.
[0063] Unfortunately, there is limited space and weight allocation
available for existing drone platforms. To these ends, solutions
for a drone antenna structure that has a narrow beamwidth in
azimuth while minimizing the size of the antenna and the structure
that supports the antenna are desired. In one embodiment, the base
station and drone antennas support two (2) polarizations which may
be e.g., two (2) linear or two (2) circular polarizations. In some
embodiments, the base station and drone radio sub-systems transmit
two (2) parallel streams of data, one on each of the two (2)
antenna polarizations, in in order to increase the data rate and
the system throughput.
[0064] One exemplary mechanically steerable drone antenna mechanism
is pictorially depicted in FIG. 4A. The antenna system includes an
antenna aperture 144a and a mechanical steering structure 144m. One
candidate antenna aperture 144a design is a patch array with rows
and columns of patch antenna elements 145-j. The mechanical
steering structure 144m rotates the antenna aperture 144a in at
least one dimension (e.g., in the azimuthal dimension). The drone
radio sub-system 142 computes the direction toward which the
antenna aperture 144a may point to maximize received signal
quality, and instructs the mechanical steering mechanism 144m to
steer the antenna aperture 144a in the corresponding direction. In
one embodiment, the antenna aperture is steered from the bottom
center of the antenna aperture (as shown in FIG. 4A) so as to
minimize the space that the antenna sub-system will occupy as the
antenna aperture 144a rotates in 360 degrees. In this case, as the
antenna aperture with width w and height h is rotated around its
bottom center, the antenna aperture will occupy a cylindrical
volume of diameter w and height h. This scheme minimizes the volume
and the weight that the antenna sub-system occupies while steering
a high gain and narrow beamwidth beam in e.g., a 360 degrees of
azimuth.
[0065] In addition to mechanical steering, artisans of ordinary
skill in the related arts will readily appreciate that a patch
array of antenna elements can be used to electrically form a
directional beam. Electrical formation of an antenna beam is based
on signal processing techniques that combine transmission or
reception elements in a phased array such that desired signal(s)
constructively interfere while undesirable signals and noise
experience destructive interference. Common additional signal
processing techniques that are readily appreciated by those of
ordinary skill in the related arts (given the present disclosure)
and which may further improve electrical beam forming performance
include e.g., signal filtering and/or spreading.
[0066] FIG. 4B illustrates a drone directional antenna design
according to another embodiment, comprised of a number of antenna
apertures 144a-j, where j denotes the different occurrences of the
antenna aperture, and an antenna aperture beam selection sub-system
146. Each antenna aperture 144a-j forms a beam toward a specific
direction in 360 degrees. FIG. 4B shows an exemplary drone antenna
with four (4) antenna apertures placed around the four (4) sides of
the box. The drone radio sub-system: (i) determines the direction
that the drone antenna beam should point so as to maximize received
signal quality, (ii) selects the appropriate antenna aperture for
the corresponding beam pointing direction, and (iii) instructs the
antenna aperture beam selection sub-system 146 to transmit to
and/or receive from the cell site using the corresponding selected
antenna aperture. The antenna aperture of FIG. 4B shows a number of
antenna elements 145-k, where k is an integer denoting different
occurrences of the antenna element, which are phased to form a beam
for the corresponding antenna aperture. One candidate antenna
aperture design is a patch array with patch elements 145-k. Note
that the antenna aperture beam selection sub-system 146 may be
instructed by the drone radio sub-system, to combine two (2)
adjacent antenna apertures 144a-j to form and steer a beam in a
given direction. Combining two (2) antenna apertures will result in
a higher beam gain at the boundary of two (2) antenna
apertures.
[0067] Artisans of ordinary skill in the related arts will, given
this disclosure, readily appreciate that base station antennas that
are optimized to point toward horizon or a few degrees above the
horizon may have very low gain at very high elevation angles above
horizon. Similarly, the gain of the drone antenna at large angles
below the horizon may be very low if the drone antenna aperture is
mainly designed to point toward the horizon. Therefore, the gains
of the base station and drone antennas may be too low to close the
link between the drone and the base station when the drone is above
a cell site, or is at high elevation angles relative to the cell
site. One solution to providing connectivity to a drone when the
drone is in the vicinity of a cell site is to have the drone
communicate with a distant cell site but at a lower data rate until
the drone moves away from the cell site.
[0068] In another embodiment, the cell site may be equipped with an
antenna that e.g., points substantially upwards and is
characterized by high gains toward high elevation angles. For
example, an upwards pointing antenna beam is illustrated by the
dotted circle 126 in FIG. 6. When a drone is in the vicinity of the
cell site, the drone radio sub-system may communicate with the base
station radio sub-system using the upwards pointed antenna aperture
(126 in FIG. 6). Similarly, the drone antenna sub-system may also
be equipped with an antenna aperture that points downwards to
provide high gain toward a cell site that is in the vicinity of the
drone. In such implementations, the drone radio sub-system may use
the antenna aperture with the downward-pointing beam that has a
high gain at large angles below the horizon to communicate with the
base station radio sub-system when the drone is in the vicinity of
the base station. In one embodiment, the upwards pointing base
station antenna beam (126 in FIG. 6) operates on a different
frequency channel than the frequency channels used by beams 125-j
(125-1 through 125-6 in FIG. 6), in order to minimize
cross-interference between the beams (125-1 through 125-6 in FIG.
6) covering distant locations from the cell site and the beam
covering locations near the cell site (126 in FIG. 6) as described
above.
[0069] At initial drone radio sub-system power up, the drone radio
sub-system 142 instructs the drone antenna sub-system 144 to point
the antenna aperture 144a toward one of the plurality of the cell
sites 110-j in the network. In one embodiment, the drone radio
sub-system 142 has a position location determination device such as
a GPS unit that provides the position coordinates of the drone, and
is also configured to access or obtain the geographic position
coordinates of all the cell sites in the network which are close
enough to the drone to be able to establish a communications link
with the drone. Yet other schemes may be used, such as a sector- or
raster-scan approach looking for peaks in signal strength or other
RF parameters when the positions of cells are not known a priori to
the drone or are otherwise not accessible (see discussion
below).
[0070] In one embodiment, the drone radio sub-system 142 may
instruct the antenna sub-system 144 to steer its aperture 144a
toward the cell site that is closest to the drone at initial drone
radio power up. As mentioned above, the drone radio sub-system 142
searches for announcement messages 212 sent by the base stations
120-j. Extraneous interference at the closest cell site may prevent
reliable communication in some scenarios; consequently, the drone
radio sub-system may need to choose a cell site that has the
highest SINR for initial association. The interference seen by the
cell site radio sub-system 122-j when pointing a beam toward a
drone 140 may be different from the interference that the drone 140
measures when pointing its antenna beam toward the cell site 120-j.
Therefore, the drone radio sub-system 142 may consider both the
SINR seen on the drone to cell site (uplink) and the cell site to
drone (downlink) directions to choose a cell site which will
provide adequate SINR in both directions.
[0071] Since the drone antenna may be highly directional, the drone
radio sub-system may only be able to measure downlink signal
quality from at most one cell site toward which the drone antenna
aperture is pointing. In some variants, a mechanism for measuring
uplink and downlink signal quality from multiple cell sites is
needed to find a cell site with adequate uplink and downlink signal
quality. Downlink signal quality may be measured from the
announcement message sent by all sectors. In one such variant, the
drone radio sub-system sequentially instructs the drone antenna
sub-system 144 to steer the drone antenna aperture 144a toward a
set of candidate cell sites and measure the downlink SINR to each
cell site (based on the announcement message).
[0072] Next, the drone radio sub-system chooses a cell site with
highest SINR, from among a set of candidate cell sites with
adequate downlink SINR, with which to associate.
[0073] Once the drone associates with a given cell site, the radio
sub-system of the corresponding cell site will measure the SINR
received from the drone on the uplink, and if the SINR is not
adequate will inform the drone radio system so that the drone radio
sub-system can try another cell site from among the candidate cell
sites with adequate downlink SINR to communicate with. In other
words, the drone radio sub-system may sequentially associate with a
number of candidate cell sites to measure SINRs on the downlink
from each candidate cell site, and also transmit to each candidate
cell site so that each candidate cell site radio sub-system may
measure the uplink SINR from the drone and report the measured
uplink SINR to the drone radio sub-system.
[0074] In one exemplary embodiment, the radio sub-system chooses a
cell site with adequate SINR on uplink and downlink based on
certain metrics. Artisans of ordinary skill in the related arts,
given the contents of the present disclosure, will appreciate that
any number of other signal quality metrics besides SINR may also be
used (whether alone or in combination) to determine a cell site
with adequate signal quality with which to reliably communicate.
Common examples of such metrics include without limitation: signal
quality (e.g., as measured by SINR), latency, bit error rate (BER),
block error rate (BLER), packet error rate (PER) and throughput.
More generally, any number of connectivity metrics may be
substituted with equivalent success, by one of ordinary skill given
the contents of the present disclosure. For example, some
embodiments may additionally consider network congestion, power
consumption, historical reliability, and/or compatibility.
[0075] In one embodiment, the drone radio sub-system determines a
cell site with which to associate without knowledge of the drone's
position coordinate or the position coordinates of the cell sites.
In this embodiment, the drone antenna sub-system may be instructed
to steer its beam in multiple directions e.g., in 360 degrees of
azimuth and/or various degrees of elevation (e.g., the horizon and
below), and search for announcements messages in each direction.
The drone radio sub-system measures the signal quality on the
received announcements messages, identifies the cell sites from
which it receives announcements messages, and determines a list of
cell sites from which the drone radio sub-system receives high
enough signal quality with which to reliably communicate. The drone
radio sub-system transmits messages to a subset of cell sites on
the aforementioned list, and receives uplink signal quality
measurements from the corresponding cell sites. Then, based on the
downlink and uplink signal quality measurements from the cell
sites, the drone radio sub-system chooses a cell site with adequate
signal quality on both links with which to associate, according to
some criterion. Common examples of such criterion may include
without limitation, signal quality, network congestion, quality of
service, cost considerations, power consumption, and/or
compatibility. For example, the drone radio sub-system may select
the link with the highest downlink throughput. In another example,
the drone radio sub-system may select the link with the shortest
uplink and downlink latencies.
[0076] In another embodiment, the coverage area of the network may
be divided into a number of bins, and a table may be stored in each
drone radio sub-system which contains the previously measured
uplink/downlink SINRs of a set of cell sites close to the drone
position in each of the geographic bins, referred to as the
candidate cell site association table. The drone radio sub-system
makes downlink SINR measurements, receives uplink SINR measurements
from the cell site radio sub-systems, and updates the
uplink/downlink SINRs for each position bin of the aforementioned
table as the drone travels. At any time, the drone radio sub-system
can reference a position bin in the candidate cell site association
table where the drone is located, in order to determine a cell site
with adequate downlink/uplink SINR with which to associate.
[0077] As a brief aside, interfering sources may be transmitting
only part of the time and thus may only intermittently interfere.
Thus, the cell site radio sub-system may need to make multiple
uplink SINR measurements on the uplink messages sent by the drone
in order to measure the uplink SINR under different interference
conditions. Additionally, the drone radio sub-system may store the
statistics of the uplink and downlink measured SINRs at each cell
site sector in the aforementioned table for future reference.
Previously gathered statistics ensure that the drone can reliably
select a cell site sector with adequate uplink/downlink signal
quality for communications on an as needed basis (e.g., without
updating interference measurements).
[0078] As mentioned previously, the drone radio sub-system measures
the downlink SINR, or some other signal quality metric, on the
received messages from its associated cell site, and also receives
uplink SINR/signal quality measurements from its associated cell
site radio sub-system on measurements made on uplink messages sent
by the drone. The drone radio sub-system may initiate a change of
association to another cell site if the measured uplink/downlink
SINRs fall below a threshold. In some cases, the drone may
predictively switch associations based on e.g., the position of the
drone within the network or historic quality measurements. Once the
drone radio sub-system determines that an association with another
cell site may be needed to provide a higher quality communications
link, in one embodiment the drone may look up the entry of the
candidate cell site association table within whose geographic bin
the drone currently resides and choose a new cell site with which
to associate. In another embodiment, the drone antenna sub-system
may sequentially steer the drone antenna aperture toward a number
of candidate association cell sites based on the position of the
drone, measure the downlink signal quality from each cell site,
receive uplink signal quality measurement from the corresponding
cell sites, and choose a sector with adequate uplink/downlink
signal quality with which to associate.
[0079] Once a cell site has been chosen as a candidate association
cell site, the drone radio sub-system initiates association with
the candidate cell site by sending a message to its currently
associated cell site notifying the current associated cell site of
the impending transfer to the candidate association cell site. The
message includes the identification of the candidate cell site that
the drone radio sub-system intends to associate with, and a
corresponding frequency channel. The drone radio sub-system may
also report its position coordinates to the currently associated
cell site.
[0080] In other embodiments, the currently associated cell site
sub-system may also be configured with the candidate cell site
association table mentioned above. The currently associated cell
site radio sub-system can initiate association of the drone with a
new cell site (the candidate cell site) by sending a message to the
drone that includes information on the chosen candidate cell site,
and instructing the drone to steer its antenna beam and a frequency
channel to tune to in order to associate with the candidate
association cell site.
[0081] Once the drone radio sub-system steers its antenna beam
toward the candidate association cell site, the drone radio
sub-system searches for any announcement messages sent by the
candidate association cell site. The specific sector of the cell
site that provides the highest signal quality to the drone
typically depends on the position of the drone relative to the
position of cell site. Therefore, the drone radio sub-system will
tune to a frequency channel that is expected to correspond to the
strongest signal from the cell site, and search for announcement
messages from the cell site on the tuned frequency channel. If
after a certain time interval the drone radio sub-system does not
receive an announcement message from the cell site, the drone radio
sub-system may attempt to search other frequencies by tuning to a
different frequency channel and searching for announcement messages
on the new frequency channel until the announcement message is
detected.
[0082] The above discussion considered the case where the drone
needs to associate with a different cell site than it is currently
associated with (where the drone is "handing over" to a different
cell site). As previously noted, each cell site in the exemplary
embodiment has multiple sectors, thus the drone may also need to
change the sector of the cell site that it is communicating with as
the drone travels. In one such case, the drone radio sub-system
monitors the signal quality on the downlink from the sector and
when the signal quality falls below a threshold or otherwise
satisfies a handover criteria (e.g., based on the position of the
drone, historic performance, etc.), the drone radio sub-system
initiates an association with a neighboring sector of the cell
site. During the association processes, the drone radio sub-system
tunes to the frequency channel of the neighboring candidate
association sector(s), and measures the downlink signal quality.
The drone radio sub-system chooses the sector with the higher
signal quality for association. Once a new sector has been
determined, the drone radio sub-system sends an association message
to the cell site, requesting to start communications with the new
sector of the cell site.
[0083] As mentioned previously, the beam for the downlink and
uplink directions as shown in FIGS. 2A and 2B are of roughly the
same size, and are identified with the same label 125-j. In
alternative embodiments, the cell site may allocate different size
beamwidth beams on the downlink and uplink, and have asymmetric
capabilities. For instance, if the uplink beam of the cell site
sector has a narrower beamwidth than the downlink beam, then the
uplink beam will filter out more interference from other sources of
interference in the network. A narrower uplink beamwidth may also
provide higher SINR on the uplink, higher data rates and more
reliable communications links between the drone and the cell site.
FIG. 3, illustrates a case where the uplink beam 125u beamwidth is
half of the downlink beam 125d. As shown in FIG. 3, the uplink
includes two (2) sub-beams that correspond to each downlink beam in
a given sector. Each uplink sub-beam will have three (3) decibels
(dB) more gain (approximately a factor of two (2)) toward the
desired drone. Moreover, the improved interference rejection of
extraneous systems/transmitter noise could potentially result in
more than three (3) dB of increase in SINR on the uplink
direction.
Shared and Dedicated Channel Operation --
[0084] In some aspects of the present disclosure, the aggregate
bandwidth of the link may be partitioned for use in a number of
different ways. For example, the available frequency (bandwidth) on
a given frequency channel may be further divided into a set of
sub-frequency channels. Each sub-frequency channel be subdivided
into multiple data channels that simultaneously transmit and/or
receive. In one configuration, each data channel occupies a number
of time slots and one or more sub-frequency channels; in some
cases, the data channel may occupy the entire frequency channel.
The combination of time slots and the sub-frequency channels
assigned to a data channel determines the amount of bandwidth
allocated to the data channel.
[0085] As a brief aside, two (2) types of data channels are
described herein. So-called "shared" data channels are data
channels that carry data that may be arbitrarily allocated among a
variety of applications and/or number of users (e.g., via a
broadcast or multicast paradigm). So-called "dedicated" data
channels carry data that are dedicated for e.g., a particular user
or a particular application, such as where QoS (quality of service)
or other requirements must be met. Artisans of ordinary skill in
the related arts will readily appreciate that such a distinction is
made purely for illustrative purposes, other types of data channels
and/or hybrids thereof may be substituted with equivalent success,
given the contents of the present disclosure. For example, a shared
or dedicated data channel may occupy all the sub-frequency channels
of a given frequency channel during multiple time slots. For
instance, the Institute of Electrical and Electronics Engineers
(IEEE) 802.11ac standard assigns an entire frequency channel in the
uplink or downlink to one device at a time.
[0086] Referring now to FIG. 5A, an exemplary drone and base
station radio sub-system can send signaling messages such as
announcements and association messages on shared uplink and
downlink channels. One uplink shared channel is a so-called "random
access channel". A drone can send messages such as association and
bandwidth request as well as short data packets on the random
access channel. The remaining time slots and frequency channels may
be allocated to dedicated channels where bandwidth is a priori
reversed for specific drones on the uplink and downlink.
[0087] When there are multiple uplink sub-beams per one downlink,
the base station radio sub-system may determine which uplink
sub-beam to search/scan, so as to detect messages sent by the
drone. During the initial drone association with a cell site, the
base station antenna sub-system forms an analog beam to communicate
with the drone. The drone radio sub-system searches for
announcement messages sent by the cell site as described in
previous embodiments that are transmitted on the analog beam. Upon
receiving the announcement message (and when announcement message
satisfies association criteria), the drone sends an association
message on the uplink. In one embodiment, the base station's uplink
beam (for receiving the association message) has a substantially
wider beamwidth compared to the downlink beam (for transmitting the
announcement message) such that the base station radio sub-system
can detect the association message sent by the drone on the uplink
beam. In other words, the base station uses a wider beamwidth for
receiving the association message so as to account for drone
movement and/or other signaling mismatches.
[0088] In some embodiments, the shared random access channel can be
used by any (or all) drones to send small amounts of data to the
base station without an explicit bandwidth reservation/assignment
by the drone/base station. For example, as shown in FIG. 5A, the
time interval may be divided into two (2) sections, shown by dotted
and solid lines. During the dotted time interval (FIG. 5A), the
base station radio sub-system expects association or random access
messages from the drones, and uses a wider beam to search for
messages from the drones. During the solid time intervals of FIG.
5A, the time slots are assigned/dedicated to specific drones, and
the base station radio sub-system uses a narrow uplink beam to
search for the drone's messages.
[0089] More generally, as will be appreciated by those of ordinary
skill in the related arts, wider beamwidths can provide larger
coverage areas. In contrast, narrower beamwidths can provide more
gain and/or provide higher data rates. Accordingly, a selection of
beamwidth may be tailored for particular reception requirements
(e.g., area coverage, data rate). Moreover, beamwidth may be
dynamically adjusted to compensate for changing channel conditions
and/or connectivity requirements, including altitude changes of the
drone itself (e.g., from a gust of wind).
[0090] In one embodiment, the drone radio sub-system is configured
to include the drone's latest position coordinates in the "uplink"
association message (the term "uplink" being used in the present
context to refer to a mobile-to-cell site communication). Once the
drone has associated with a cell site, the drone radio sub-system
periodically sends the drone's position so that the cell site radio
sub-system has substantially real time knowledge of the drone's
position (within the reporting period granularity). The cell site
radio sub-system can determine the optimal sub-beam on the uplink
to search for the messages the corresponding drone sends based on
the real time drone position. Specifically, the base station radio
sub-system can assume that the drone is pointing an antenna beam
toward the cell site location, thus the base station radio
sub-system can determine which sub-beam of the uplink the drone is
pointing its antenna beam at. The base station radio sub-system can
use the optimal uplink sub-beam to search for uplink messages.
[0091] In one embodiment, the drone radio sub-system sequentially
transmits an association message multiple times. In one such
variant, the association message is transmitted a number of times
that corresponds to the number of uplink sub-beams of the cell site
radio sub-system.
[0092] Following the transmission of the announcement message, the
cell site radio sub-system sequentially switches from one uplink
sub-beam to the next so that it can detect at least one of the
multiple sequential association messages sent by the drone radio
sub-system on at least one of the uplink sub-beams. Once the cell
site radio sub-system detects one of the drone's association
message, the cell site radio sub-system records the drone's
position coordinates and thereafter performs a finer granularity
search via its uplink sub-beam where the drone antenna is pointing
based on the drone's position. When digital beamforming is employed
at the base station radio sub-system, the base station's baseband
processor may generate multiple uplink sub-beams digitally and
search each of the digitally formed uplink sub-beams until it
detects the uplink message from the drone.
[0093] In one exemplary embodiment, the throughput of the system
described in conjunction with FIGS. 2A and 2B may be further
enhanced by using all frequency channels in all six (6) sectors
simultaneously (referred to as frequency reuse factor of one (1)
scheme). FIG. 6 shows one such cell site sectorization design
including six (6) sectors delineated by solid lines, and two
sub-sectors in each sector delineated by dotted lines. As
illustrated in FIG. 6, both sets of frequency channels (F.sub.1 and
F.sub.2) are simultaneously used in all sectors, but in only one of
the two (2) sub-sectors of each sector. More directly, by no two
(2) adjacent sub-sectors are simultaneously transmitting/receiving
on the said frequency channels so as to maintain spatial isolation.
The improved isolation results in higher SINR at the
sub-sector/sector boundaries than would otherwise be achievable,
while still providing all available spectrum in each sector. Such a
configuration effectively doubles throughput as compared to a
scheme of frequency reuse factor two (2) previously described. The
base station radio sub-system of FIG. 6, divides the time slots in
the uplink and downlink direction into two (2) sets, where each set
is assigned to a different sub-sector of a sector. During one set
of time slots, the base station radio sub-system transmits and
receives data from drones in one of the sub-sectors. The base
station radio sub-system does not simultaneously transmit or
receive data on two (2) adjacent sub-sectors.
[0094] While FIG. 6 shows two (2) sub-sectors, artisans of ordinary
skill in the related arts will readily appreciate that any number
of sub-sectors may be substituted with equivalent success, given
the contents of the present disclosure. The number of sub-sectors
may be adjusted based on the beamwidth of the sector antenna;
beamwidth is typically limited by the size of the antenna. For
example, in a 5 GHz band, a 0.5 square meter antenna can support as
many as eight (8) sub-sectors.
[0095] The foregoing discussion is generally illustrative of
embodiments with a fixed number of downlink and uplink sub-beams
per sector and/or a different number of sub-beams on the uplink and
downlink. As noted above, uplink and downlink beams may adaptively
be formed toward each drone during the uplink and downlink
dedicated channels such that data is being received from and/or
transmitted to one drone at a time. More generally, adaptive beam
forming allows a base station antenna sub-system to point the peak
of the beam toward each drone, thereby maximizing the SINR and the
associated data rate.
[0096] In another aspect of the disclosure, the base station may
receive messages sent by the drones on the shared uplink channels,
such as the uplink random access channel, and also send messages on
the downlink to multiple drones at a time in the shared downlink
channels. As shown in FIG. 5B, the time axis may be divided into
time periods where the uplink/downlink shared and uplink/downlink
dedicated data channels are active. Then, during the shared
uplink/downlink data channel time periods, the uplink/downlink
beams may be formed to be wide enough to receive or transmit
messages from or to all drones in the base station sector's
coverage area. In some variants, the shared uplink/downlink beams
may be formed wide enough to receive or transmit messages from or
to a subset of the drones in the base station sector's coverage
area; the subset may be based on drone position location. For
example, as previously noted above, the drones may send their
position location to the base station; this position location
information allows the base station to adaptively group similarly
located drones and form narrow beams toward the subset of drones
during the appropriate channel time periods.
Example Operation --
[0097] The following discussion provides an illustrative
description of systems and methods whereby a narrow beam can be
tailored to transmit or receive both shared and dedicated data
channels in the sub-sectors. In the illustrative embodiment, the
base station radio sub-system determines the drones that are
located in each sub-sector so as to dynamically adjust
transmissions on only a subset of the sub-sectors to minimize
inter-sector interference. For example, the base station radio
sub-system can allocate a shared downlink channel for each
sub-sector to transmit announcement messages on the beam of the
corresponding sub-sectors. In each sub-sector, the drones which
have not associated with any base station can transmit an
association message to the corresponding base station on the
scheduled uplink shared channel for each sub-sector (responsive to
receiving the announcement message). The association message will
include the drone's position location coordinates e.g., to enable
beamwidth selection and/or shared and dedicated channel spatial
adjustments.
[0098] Once the base station has received one or more association
messages, the base station radio sub-system divides or allocates
the remaining bandwidth (time slots and sub-frequency channels) for
dedicated data channels among the different sub-sectors of a given
sector based on the number of drones in each sub-sector, and the
amount of traffic to/from those drones. FIG. 7 is an exemplary
illustration of how the time is divided between uplink and downlink
shared and dedicated channels for a TDD system where each sector is
composed of two (2) sub-sectors. In FIG. 7, the solid time line
illustrates the time allotted to downlink channels, and the dotted
time line illustrates the time allotted to the uplink channels. In
an FDD (Frequency Division Duplex) system, the available uplink and
downlink channels are similarly divided between the different
sub-sectors, but with the uplink and downlink channels assigned to
a sub-sector running concurrently on different frequency bands.
[0099] The base station radio sub-system schedules bandwidth for
each sub-sector and each drone, and sends a drone specific
dedicated bandwidth schedule to each drone on the downlink shared
channels. Drones may continuously monitor the downlink for data
destined to them, or wake up to listen to the channel during the
time slots where data is scheduled to the drone and of which the
drone is a priori informed. The base station radio sub-system
scheduler ensures that the sub-sectors that are simultaneously
transmitting are sufficiently isolated (via e.g., spatial
distances, time slots, frequency bands, spreading codes, and/or
other multiplexing techniques) such that the inter-sector
interference received at the drone from those sub-sectors is below
a threshold in order to achieve high signal quality and data rates.
In one embodiment of a TDD system where the base stations and
drones alternately transmit at different times on the same
frequency channel, the transmit time slots of all sub-sectors and
all sectors that are simultaneously transmitting will be
synchronized in order to avoid inter-sector interference.
Therefore, all resources of the sub-sectors of a cell can be
maximally utilized by either simultaneously receiving or
simultaneously transmitting and the timing of the time slot
boundaries of all sub-sectors are synchronized.
[0100] Once a drone and a cell site are associated and begin data
transmission, the base station and drone radio sub-systems
determine the highest data rate that can be supported by the
uplink/downlink data channel e.g., the data rate corresponding to
the probability of correctly decoded data packets based on the
signal quality at the receiver. The base station and drone radio
sub-systems can each maintain a table of the highest
downlink/uplink data rates the base station and drone may reliably
transmit in each geographic position bin where the drone may be
located; in one such implementation, the table of data rates is
referred to as the data rate indicator table.
[0101] One example of a uplink/downlink data rate calculation may
be based on the link budget using knowledge of the base station and
drone EIRP (Effective Radiated Isotropic Power) and the distance
between the cell site and the drone for each geographic bin in
which the drone resides. The link budget uses the transmitter and
receiver parameters and the path loss between the
transmitter/receiver to compute the SINR, or some other signal
quality, at each receiver to determine the highest data rate
achievable at the computed SINR values.
[0102] The values of the data rate indicator table may be
dynamically updated using actual measurements of SINR (as described
herein). For example, the drone and cell site make uplink and
downlink SINR measurements and report the corresponding SINR values
to each other during the course of ongoing communications. The base
station and drone radio sub-systems each update the highest
achievable data rates for their end of the link based on the
measured SINR values.
[0103] As a brief aside, another technique that is very powerful in
mitigating interference is spreading the data at the transmitter in
time and in frequency, and de-spreading the data at the receiver to
reduce the effect of interference. For instance, in the IEEE
802.11ac standard, the lowest modulation is BPSK (Binary Phase
Shift Keying) specified in the 802.11ac so called MCS0 data
channel. Coded BPSK modulation can decode the data packet with low
probability of error (e.g., as low as two (2) dB of SINR). Consider
an uncorrelated interferer with the same power as the desired
signal e.g., a scenario where the received SINR of the MCS0 data
channel is less than zero (0) dB; under such circumstances the
coded MCS0 data channel would not be successfully decoded as it
does not exceed the minimum tolerable SINR (two (2) dB). By
transmitting the coded BPSK symbol twice, the received SINR can be
increased with processing gain even in presence of the uncorrelated
interferer. A perfect processing gain of the retransmitted signal
would double the SINR (i.e., a gain of three (3) dB), which is more
than adequate to decode the desired signal with low probability of
error. More generally, repeating the BPSK symbol N times, can
enable successful decode of the desired signal in the presence of
up to N uncorrelated interferers with equal power as that of the
desired signal. The spreading, repetition of coded symbols, may be
done in any multiplexing domain (e.g., time, frequency, spreading
code or other.)
[0104] In order to ensure that messages carrying critical system
parameters and signaling information are delivered reliably, a
number of time slots are assigned on one or more frequency
channels, such as 20 MHz channel in the IEEE 802.11 family of
standards, with spreading to mitigate extraneous interference from
other systems. The amount of spreading to achieve a low packet
error rate (e.g., less than 1%) may be determined based on the
statistics of the measured interference, the higher the variance of
interference power the higher the amount of spreading. The
resulting time/frequency channel is referred to as the spread
signaling channel. A spread signaling channel can reliably deliver
messages such as the IEEE 802.11 base station beacon, registration,
encryption, bandwidth request, bandwidth grant, and other critical
messages.
[0105] The drone radio sub-system associates with a cell site using
the systems and methods described in the previous embodiments.
Depending on the interference levels, the association procedure may
be carried out on the spread signaling channel described above or
on the nominal channels. For instance, the drone may attempt to
detect the announcement message of the cell sites on a nominal
channel, and to send the corresponding association message on the
nominal channels. If the association procedure is not successful,
the drone radio sub-system may then switch to the more reliable
spread channels to attempt the association procedure.
Apparatus --
[0106] FIG. 8 shows one exemplary embodiment of an aerial platform
810. The aerial platform communicates with a network of terrestrial
sites. In one exemplary embodiment, the aerial platform is an
unmanned aerial vehicle (UAV). More generally however, the
principles described herein may be used with any aerial platform
such as general aviation aircraft, commercial aircraft, and drones.
In one exemplary embodiment, the network of terrestrial sites
comprises a broadband ground terminal 820. Common examples of such
broadband ground terminals include e.g., cellular base stations,
IEEE 802.11-based access points, etc. More generally however, the
principles described herein may be used with any ground terminal
including terminals at home or enterprises to provide network
connectivity to an internetwork (e.g., the Internet). The ground
terminal may be a fixed ground terminal or mobile terminal
including devices attached to platforms such as vehicles, boats,
ship, airplanes, trucks, or other vehicles. Some mobile ground
terminals are standalone mobile devices (e.g., handheld devices,
etc.) In one exemplary embodiment, the ground terminal comprises a
cellular base station.
[0107] In one exemplary embodiment, the drone 810 has a drone radio
sub-system 812, a message switch sub-system 816, and at least one
drone antenna aperture sub-system 814 to communicate with the
ground terminal 820. During operation, the UAV is configured to
cruise or patrol an "orbit" while maintaining communication with
the ground terminal 820. The ground terminal 820 may be connected
to broader Internet networks 826 via a gateway radio sub-system 822
thereby allowing the ground terminals 820 Internet access and/or
access to the terrestrial network. In one exemplary embodiment, the
UAV comprises a drone.
[0108] FIG. 9 illustrates one exemplary embodiment of an unmanned
aerial vehicle (UAV) radio sub-system 912 that includes five (5)
sub-systems: (i) a receiver 918 that is configured to demodulate
and decode a signal received from a drone antenna aperture
sub-system 914; a transmitter 916 that is configured to modulate
data received from a processor 914 and send the resulting signal
through the drone antenna aperture sub-system 814; a processor
sub-system 914 that is configured to carry out functions such as:
(i) configuring the receiver 918 and transmitter 916 sub-systems,
(ii) processing the data received from the receiver 918 sub-system,
(iii) determining the data to be transmitted through the
transmitter sub-system 916, and (iv) controlling the antenna
sub-system 814; a non-transitory computer readable memory
sub-system 912 that is configured to store one or more program code
instructions, data, and/or configurations, and system parameter
information that are accessed by the processor 914; and (v) a
gyroscope/accelerometer/global positioning system (GPS) sub-system
919 that is configured to determine a position and orientation of
the UAV such as roll or pitch angles.
[0109] Depending on the altitude of the UAV, each UAV covers an
area on the ground; in one embodiment the area covered has a radius
of as low as a few tens of kilometers (km) to as much as 200 km or
more. The UAV's radio sub-system sends aggregated data to/from the
internetwork via one or more of the ground terminals 820 of a
terrestrial network. Since the ground terminal 820 may handle
aggregated data from UAVs 810, practical implementations of the
present disclosure may support higher data rates than necessary for
a single UAV 810. Accordingly, in one embodiment the gain of the
ground terminal 820 antenna sub-system is much larger than the UAV
810, and may transmit at higher power than the UAV 810. Those of
ordinary skill in the related arts will readily appreciate the wide
variety of techniques which may be used to increase gain, including
without limitation, increasing transmit and receive power,
increasing bandwidth, increasing processing gain, increasing coding
gain, etc.
[0110] Referring back to the embodiment of FIG. 8, the ground
terminal (GT) 820 has two (2) main sub-systems: a ground terminal
radio sub-system 822, and a ground terminal antenna sub-system 824.
As shown in FIG. 10, the GT radio sub-system 822 comprises four (4)
sub-systems: (i) the receiver 1018 that demodulates and decodes the
signal from the drone antenna sub-system; (ii) the transmitter
sub-system 1016 that modulates the data and sends the resulting
signal through the antenna sub-system 1024; (iii) the processor
sub-system 1014 that carries out functions such as: configuring the
receiver 1018 and transmitter 1016 sub-systems, processing the data
received from the receiver 1018 sub-system, determining the data to
be transmitted through the transmitter sub-system 1016, as well as
controlling the antenna sub-system 824; and (iv) the memory
sub-system 1012 that contains program code, configuration data, and
system parameters information that are accessed by the processor
1014.
[0111] It will be recognized that while certain embodiments of the
present disclosure are described in terms of a specific sequence of
steps of a method, these descriptions are only illustrative of the
broader methods described herein, and may be modified as required
by the particular application. Certain steps may be rendered
unnecessary or optional under certain circumstances. Additionally,
certain steps or functionality may be added to the disclosed
embodiments, or the order of performance of two or more steps
permuted. All such variations are considered to be encompassed
within the disclosure and claimed herein.
[0112] While the above detailed description has shown, described,
and pointed out novel features as applied to various embodiments,
it will be understood that various omissions, substitutions, and
changes in the form and details of the device or process
illustrated may be made by those skilled in the art without
departing from principles described herein. The foregoing
description is of the best mode presently contemplated. This
description is in no way meant to be limiting, but rather should be
taken as illustrative of the general principles described herein.
The scope of the disclosure should be determined with reference to
the claims.
[0113] It will be further appreciated that while certain steps and
aspects of the various methods and apparatus described herein may
be performed by a human being, the disclosed aspects and individual
methods and apparatus are generally
computerized/computer-implemented. Computerized apparatus and
methods are necessary to fully implement these aspects for any
number of reasons including, without limitation, commercial
viability, practicality, and even feasibility (i.e., certain
steps/processes simply cannot be performed by a human being in any
viable fashion).
* * * * *