U.S. patent application number 10/619382 was filed with the patent office on 2004-06-03 for communication system using geographic position data.
This patent application is currently assigned to TeraTech Corporation. Invention is credited to Broadstone, Steven R., Chiang, Alice M., Velazquez, Scott R..
Application Number | 20040104839 10/619382 |
Document ID | / |
Family ID | 24930379 |
Filed Date | 2004-06-03 |
United States Patent
Application |
20040104839 |
Kind Code |
A1 |
Velazquez, Scott R. ; et
al. |
June 3, 2004 |
Communication system using geographic position data
Abstract
A wireless communication system employs directive antenna arrays
and knowledge of position of users to form narrow antenna beams to
and from desired users and away from undesired users to reduce
co-channel interference. By reducing co-channel interference coming
from different directions, spatial filtering with antenna arrays
improves the call capacity of the system. A space division multiple
access (SDMA) system allocates a narrow antenna beam pattern to
each user in the system so that each user has its own communication
channel free from co-channel interference. The position of the
users is determined using geo-location techniques. Geo-location can
be derived via triangulation between cellular base stations or via
a global positioning system (GPS) receiver. The system can be
optimized by applying partially adaptive processing algorithms,
which are seeded by geo-location data.
Inventors: |
Velazquez, Scott R.;
(Revere, MA) ; Broadstone, Steven R.; (Woburn,
MA) ; Chiang, Alice M.; (Weston, MA) |
Correspondence
Address: |
THOMAS O. HOOVER, ESQ.
BOWDITCH & DEWEY, LLP
161 Worcester Road
P.O. Box 9320
Framingham
MA
01701-9320
US
|
Assignee: |
TeraTech Corporation
77-79 Terrace Hall Avenue
Burlington
MA
01803
|
Family ID: |
24930379 |
Appl. No.: |
10/619382 |
Filed: |
July 14, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10619382 |
Jul 14, 2003 |
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09188835 |
Nov 9, 1998 |
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6593880 |
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09188835 |
Nov 9, 1998 |
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PCT/US97/18780 |
Oct 10, 1997 |
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PCT/US97/18780 |
Oct 10, 1997 |
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08729289 |
Oct 10, 1996 |
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6512481 |
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Current U.S.
Class: |
342/357.31 |
Current CPC
Class: |
G01S 19/53 20130101;
G01S 19/06 20130101; G01S 19/51 20130101; G01S 5/0027 20130101;
G01S 5/12 20130101; H04W 16/28 20130101 |
Class at
Publication: |
342/357.1 |
International
Class: |
G01S 005/14; G01S
001/00 |
Claims
What is claimed:
1. A communication system comprising: a first transceiver located
with a first user having a first processor and a first directional
antenna array; a second transceiver located with a second user
having a second processor and a second antenna array; a locator on
at least one of the first user and second user that determines a
physical location of one of the first and second antenna array; a
spatially multiplexed communication link formed between the first
and second transceivers, and an adaptive programmable beamformer
circuit in the first transceiver that shapes a communication beam
directed between the first antenna array and the second antenna
array, the adaptive programmable beamformer circuit having a single
integrated chip having a plurality of complex multipliers, a
plurality of down conversion circuits and a plurality of finite
impulse response (FIR) filters programmable with respect to a
plurality of delays and a steering circuit that adjusts the
plurality of delays to the programmable beamformer circuit.
2. The system of claim 1 wherein the first and second antenna
arrays are movable relative to one another and the programmable
beamformer updates the direction of the communication beam in
response to the relative motion.
3. The system of claim 1 wherein the communication beam is a radio
frequency beam.
4. The system of claim 1 wherein the locator is responsive to
location data from a satellite positioning system.
5. The system of claim 1 wherein the locator is responsive to
location data from a ground-based positioning system.
6. The system of claim 1 wherein the beamformer includes a nulling
circuit for suppressing signals outside of the direction of the
second antenna array.
7. The system of claim 1 wherein the beamformer includes an
adaptive processing module to alter the shape of the communication
beam over time.
8. An acoustic communication system comprising: a first transceiver
having a directional antenna array, the directional antenna array
having a first geographical position; a second transceiver on a
mobile unit having an antenna array, the antenna array being
movable relative to the directional antenna array; a spatially
multiplexed communication link between the first and second
transceivers formed by a communication signal between the antenna
arrays; a positioning system on the mobile unit that detects a
geographical position of the mobile antenna arrays, the position of
the mobile antenna array being communicated from the mobile
transceiver to the first transceiver over the communication link;
an adaptive programmable beamformer circuit in the first
transceiver that modifies the signal in response to the relative
motion of the antenna arrays, the adaptive programmable beamformer
circuit having a single integrated chip having a plurality of
complex multipliers, a plurality of down conversion circuits and a
plurality of finite impulse response (FIR) filters programmable
with respect to a plurality of weights and a steering circuit that
adjusts the plurality of weights to the programmable beamformer
circuit; and a nulling module coupled to the beamformer that
suppresses interference to the signal.
9. The system of claim 8 wherein the beamformer updates the shape
of the signal over time.
10. The system of claim 8 wherein the signal is a radio frequency
beam.
11. The system of claim 8 wherein the positioning system is
responsive to position data from a satellite positioning
system.
12. The system of claim 8 wherein the positioning system is
responsive to position data from a ground-based positioning
system.
13. The system of claim 8 wherein the beamformer includes a
plurality of programmable filter arrays.
14. The system of claim 8 further comprising a table of stored
antenna weights stored in memory, the table accessed by the nulling
module to modify the signal.
15. The system of claim 8 further comprising an adaptive processing
module to alter the shape of the beam over time.
16. The system of claim 8 wherein the mobile antenna array is a
directional antenna array.
17. A method for operating an acoustic communication system
comprising: operating a first transceiver at a first unit and
having a first processor and a first directional antenna array;
operating a second transceiver on a mobile unit having a second
processor and a second antenna array; determining the physical
location of the second antenna array relative to the first antenna
array; forming a spatially multiplexed communication link between
the first and second transceivers, the link including a
communication beam between the first antenna array and the second
antenna array; and in an adaptive programmable beamformer
integrated circuit chip in the first transceiver, responding to the
physical location of the second antenna array, by using a plurality
of complex multipliers, a plurality of down conversion circuits and
shaping the communication beam using a plurality of programmable
finite impulse response (FIR) filters with respect to a plurality
of weights and steering the beam to be directed between the first
antenna array and the second antenna array using the programmable
beamformer circuit.
18. The method of claim 17 further comprising the steps of: moving
the first and second antenna arrays relative to one another, and in
the beamformer, updating the direction of the signal over time in
response to the relative movement.
19. The method of claim 17 wherein the communication beam is a
radio frequency beam.
20. The method of claim 17 wherein the second transceiver in a
mobile unit may function as the first transceiver and the first
transceiver may function as the second transceiver.
21. The method of claim 17 wherein the step of determining the
physical position is responsive to position data from a satellite
positioning system.
22. The method of claim 17 wherein the step of determining the
physical position is responsive to position data from a
ground-based positioning system.
23. The method of claim 17 wherein the beamformer includes a
nulling circuit to suppress signals outside the direction of the
second antenna array.
24. The method of claim 17 wherein the beamformer includes an
adaptive processing module for altering the shape of the
communication beam over time.
25. A method of operating an acoustic communication system
comprising: operating a first transceiver having a first
directional antenna, the first directional antenna having a fixed
geographical position; operating a mobile transceiver on a mobile
unit having a second directional antenna, the second antenna being
movable relative to the first directional antenna; forming a
spatially multiplexed communication link between the first and
mobile transceivers by a communication signal between the antennas;
in a positioning system on the mobile unit, detecting the
geographical position of the mobile antenna, the position of the
mobile antenna being communicated to the first transceiver over the
communication link; and in a first adaptive programmable beamformer
integrated circuit chip in the first transceiver and a second
programmable beamformer integrated circuit chip in the mobile
transceiver, modifying the signal in response to the relative
motion of the antennas by using a plurality of complex multipliers,
a plurality of down conversion circuits and shaping the
communication signal using a plurality of finite impulse response
(FIR) filters programmable with respect to a plurality of weights,
and steering a beamformed signal.
26. The method of claim 25 wherein the step of modifying the signal
comprises updating the direction of the signal over time in
response to the relative movement of the antennas.
27. The method of claim 25 wherein the step of modifying comprises
determining the range between the first antenna and the mobile
antenna and, when the range is less than a specific range,
modifying the signal to be omnidirectional.
28. The method of claim 25 wherein the signal is a radio frequency
beam.
29. The method of claim 25 wherein the step of detecting comprises
receiving position data from a satellite positioning system.
30. The method of claim 25 wherein the step of detecting comprises
receiving position data from a ground-based positioning system.
31. The method of claim 25 wherein the beamformers include a
plurality of programmable filter arrays.
32. The method of claim 25 wherein the step of modifying the signal
comprises providing antenna weights from a table stored in
memory.
33. The method of claim 25 wherein the step of modifying the signal
comprises performing adaptive processing to alter the shape of the
signal over time.
34. The method of claim 25 wherein the step of modifying the signal
comprises suppressing interference with the signal in a nulling
module.
35. The method of claim 25 wherein the step of forming the
communication link comprises a spatially multiplexed signal.
36. A beamforming circuit for an acoustic communication system
comprising: a plurality of sampling circuits for receiving
communication signals; a plurality of programmable finite impulse
response (FIR) filters, each FIR filter being connected to a
sampling circuit; a summing circuit that sums filtered signals from
the plurality of FIR filters; and a directional communication
signal formed from the summed signals.
37. The circuit of claim 36 wherein the sampling circuits, the
plurality of programmable FIR filters and the summing circuit are
formed on a single integrated circuit.
38. The circuit of claim 36 further comprising a multiplier
connected to each sampling circuit to generate an in-phase channel
and a quadrature channel, each channel being connected to a filter,
a converter and one of the FIR filters.
39. The circuit of claim 36 wherein the communication system
comprises an acoustic network including a plurality of transceivers
that communicate by a communication link with mobile transceiver
units, and further including a unit having an adaptive array
processor providing weighting signals to the FIR filters.
Description
CROSS REFERENCES TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 09/188,835, filed on Nov. 9, 1998, which is a continuation of
International Application Number PCT/US97/18780, filed on Oct. 10,
1997, Publication No. WO98/16077, which is a continuation-in-part
of U.S. Ser. No. 08/729,289, filed on October 10, 1996, now U.S.
Pat. No. 6,512,481, issued Jan. 28, 2003, the entire teachings of
which are both incorporated herein by reference in their
entirety.
BACKGROUND OF THE INVENTION
[0002] At present, the communications spectrum is at a premium,
with projected high capacity requirements of Personal Communication
Systems (PCS) adding to the problem. Although all modulation
techniques for wireless communications suffer capacity limitations
due to co-channel interference, spread spectrum, or Code Division
Multiple Access (CDMA), is a modulation technique which is
particularly suited to take advantage of spatial processing to
increase user capacity. Spread spectrum increases signal bandwidth
from R (bits/sec) to W (Hz), where W>>R, so multiple signals
can share the same frequency spectrum. Because they share the same
spectrum, all users are considered to be co-channel interferers.
Capacity is inversely proportional to interference power, so
reducing the interference increases the capacity.
[0003] Some rudimentary spatial processing can be used to reduce
interference, such as using sector antennas. Instead of using a
single omnidirectional antenna, three antennas each with a 120
degree sector can be used to effectively reduce the interference by
three, because, on average, each antenna will only be looking at
1/3 of the users. By repeating the communications hardware for each
antenna, the capacity is tripled.
[0004] Ideally, adaptive antenna arrays can be used to effectively
eliminate interference from other users. Assuming infinitesimal
beamwidth and perfect tracing, adaptive array processing (AAP) can
provide a unique, interference-free channel for each user. This
example of space division multiple access (SDMA) allows every user
in the system to communicate at the same time using the same
frequency channel. Such an AAP SDMA system is impractical, however,
because it requires infinitely many antennas and complex signal
processing hardware. However, large numbers of antennas and
infinitesimal beamwidths are not necessary to realize the practical
benefits of SDMA.
[0005] SMDA allows more users to communicate at the same time with
the same frequency because they are spatially separated. SDMA is
directly applicable to a CDMA system. It is also applicable to a
time division multiple access (TDMA) system, but to take full
advantage of SDMA, this requires monitoring and reassignment of
time-slots to allow spatially separated users to share the same
time-slot simultaneously. SDMA is also applicable to a frequency
division multiple access (FDMA) system, but similarly, to take full
advantage of SDMA, this requires monitoring and reassignment of
frequency-slots to allow spatially separated users to share the
same frequency band at the same time.
[0006] In a cellular application, SDMA directly improves frequency
re-use (the ability to use the same frequency spectrum in adjoining
cells) in all three modulation schemes by reducing co-channel
interference between adjacent cells. SDMA can be directly applied
to the TDMA and FDMA modulation schemes even without re-assigning
time or frequency slots to null co-channel interferers from nearby
cells, but the capacity improvement is not as dramatic as if the
time and frequency slots are re-assigned to take full advantage of
SDMA.
SUMMARY OF THE INVENTION
[0007] Instead of using a fully adaptive implementation of SDMA,
exploitation of information on users' position changes the antenna
beamforming from an adaptive problem to deterministic one, thereby
simplifying processing complexity. Preferably, a beamformer uses a
simple beam steering calculation based on position data. Smart
antenna beamforming using geo-location significantly increases the
capacity of simultaneous users, but without the cost and hardware
complexity of an adaptive implementation. In a cellular application
of the invention, using an antenna array at the base station (with
a beamwidth of 30 degrees for example) yields an order of magnitude
improvement in call capacity by reducing interference to and from
other mobile units. Using an antenna array at the mobile unit can
improve capacity by reducing interference to and from other cells
(i.e., improving frequency reuse). For beamforming, the accuracy of
the position estimates for each mobile user and update rates
necessary to track the mobile users are well within the
capabilities of small, inexpensive Global Positioning System (GPS)
receivers.
[0008] In general, the present invention is a communication system
with a plurality of users communicating via a wireless link. A
preferred embodiment of the invention is a cellular mobile
telephone system. Each user has a transmitter, receiver, an array
of antennas separated in space, a device and method to determine
its current location, hardware to decode and store other users'
positions, and beamformer hardware. The beamformer uses the stored
position information to optimally combine the signals to and from
the antennas such that the resulting beam pattern is directed
toward desired users and away from undesired users.
[0009] An aspect of the invention uses a deterministic direction
finding system. That system uses geo-location data to compute an
angle of arrival for a wireless signal. In addition, the
geo-location data is used to compute a range for the wireless
signal. By using the determined angel of arrival and range, a
system in accordance with the invention can deterministically
modify the wireless signal beam between transceivers.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The foregoing and other objects, features and advantages of
the invention, including various novel details of construction and
combination of parts will be apparent from the following more
particular drawings and description of preferred embodiments of the
communication system using geographic position data in which like
references characters refer to the same parts throughout the
different views. It will be understood that the particular
apparatus and methods embodying the invention are shown by way of
illustration only and not as a limitation of the invention,
emphasis instead of being placed upon illustrating the principles
of the invention. The principles and features of this invention may
be employed in various and numerous embodiments without departing
from the scope of the invention.
[0011] FIG. 1 is a schematic diagram of a cellular communication
system.
[0012] FIG. 2 is a schematic block diagram of components in a base
station and a mobile unit of FIG. 1.
[0013] FIG. 3 is a schematic diagram of a general adaptive antenna
array.
[0014] FIG. 4 is a schematic diagram of a mobile-to-base
communications link in cellular communications using AAP SDMA.
[0015] FIG. 5 is a schematic diagram of a base-to-mobile
communications link in cellular communications using AAP SDMA.
[0016] FIG. 6 is a schematic diagram of a general SDMA
communications system employing geo-location techniques.
[0017] FIG. 7 is a schematic block diagram of two communicating
users of FIG. 6.
[0018] FIG. 8 is a flow chart of a method of operating a cellular
telephone system using geo-location data.
[0019] FIG. 9 is a schematic diagram of a cellular telephone system
using geo-location data.
[0020] FIG. 10 is a schematic block diagram of a steering
circuit.
[0021] FIG. 11 is a schematic block diagram of a nulling
circuit.
[0022] FIG. 12 is a schematic block diagram of a receiver module
for a mobile unit beamformer.
[0023] FIG. 13 is a schematic block diagram of a transmitter module
for a mobile unit beamformer.
[0024] FIG. 14 is a schematic block diagram of a receiver module
for a base station beamformer.
[0025] FIG. 15 is a schematic block diagram of a transmitter module
for a base station beamformer.
[0026] FIG. 16 is a schematic block diagram of a preferred base
station employing real-valued FIR filtering at IF.
[0027] FIG. 17 is a schematic block diagram of a preferred base
station employing complex-valued FIR filtering at base band.
[0028] FIG. 18 is a schematic block diagram of a beamshaping
circuit based on an adaptive-array processing algorithms.
DETAILED DESCRIPTION OF THE INVENTION
[0029] FIG. 1 is a schematic diagram of a general land-based
cellular wireless communications system. The geographic area
serviced by this communications system 1 is divided into a
plurality of geographic cells 10, each cell 10 having a respective
geographically fixed base station 20. Each cell 10 can have an
arbitrary number of mobile cellular units 30, which can travel
between and among the cells 10.
[0030] FIG. 2 is a schematic block diagram of components in a base
station 20 and a mobile unit 30 of FIG. 1. As shown, each base
station 20 includes a transceiver 210 having a transmitter 212 and
a receiver 214, control hardware 220, and a set of antennas 25 to
communicate with a plurality of mobile units 30. The mobile units
are free to roam around the entire geographic service area. Each
mobile unit 30 includes a transceiver 310 having a transmitter 312
and a receiver 314, control hardware 320, a handset 8, and an
antenna or antennas 35 to allow for simultaneous sending and
receiving of voice messages to the base station 20. The base
station 20 communicates with a mobile telecommunications switching
office (MTSO) 5 to route the calls to their proper destinations
2.
[0031] The capacity of a spread spectrum cellular communication
system can be expressed as:
N=(W/R)(N.sub.O/E.sub.b)(1/D)F G (1)
[0032] where W is the bandwidth (typically 1.25 MHz);
[0033] R is the data rate (typically 9600 bps);
[0034] E.sub.b/N.sub.O is the energy-to-noise ratio (typically 6
dB);
[0035] D is the voice duty-cycle (assumed to be 0.5);
[0036] F is the frequency reuse (assumed to be 0.6);
[0037] G is the number of sectors per cell (assumed to be 1, or
omnidirectional); and
[0038] N is the number of simultaneous users.
[0039] As such, a typical cell can support only about 25-30
simultaneous calls. Space division multiple access (SDMA)
techniques can be used to increase capacity.
[0040] The capacity improvement by using an adaptive array at the
base station 20 in the mobile-base link is summarized below in
Table I. The results are valid for various antenna beamwidths at a
fixed outage probability of 10.sup.-3.
1TABLE I Base Station Antenna Beamwidth vs. Call Capability in
Mobile-to-Base Link Beamwidth (degrees) Capacity (calls/cell) 360
(omni) 31 120 75 60 160 30 320
[0041] FIG. 3 is schematic diagram of an M-element adaptive antenna
array 35a, 35b, 35c and beamformer 54. Each element has N adaptive
linear filters (ALFs) 55, where N is the number of users per cell.
Each of the ALFs 55 are adapted in real time to form a beam to and
from each mobile unit 30 via a combiner 57. The ALFs 55 use a
variety of techniques to form an optimal beam, such as using
training sequences, dynamic feedback, and property restoral
algorithms. Preferably, the ALFs 55 are single chip adaptive
filters as described in U.S. Pat. No. 5,535,150 to Chiang, the
teachings of which are incorporated herein by reference.
[0042] The M-element array is capable of nulling out M-1 co-channel
interference sources. However, all the users in a CDMA cell share
the same frequency band and therefore, are all co-channel
interferers in the mobile-to-base link. Because the number of
users, N, far exceeds the number of antennas, M, subspace methods
of direction-of-arrival estimation are not applicable. Instead, a
Constant Modulus Algorithm (CMA) adaptive beamforming approach is
more applicable.
[0043] For the base-to-mobile link, the co-channel interferers are
the neighboring base stations. Conceivably, the number of antennas
in the adaptive array at the mobile could be approximately the same
as the number of neighboring base stations, so subspace methods of
direction-of-arrival estimation may be applicable to null out the
interfering base stations. The computational complexity of both
types of AAP algorithms is approximately equal.
[0044] The majority of the computational complexity incurred by
using AAP in a cellular system is due to covariance formulation and
copy processing. The covariance is a sum of a sequence of matrices,
each of which is an outer product of complex array samples. Each
term of this outer product is a complex product. The computation
requires on the order of K.sup.2 computations, where K is the
number of antennas. Using the covariance, the AAP algorithm
computes the antenna weight vector, which is applied to the
received signal vectors. This is a matrix inversion, which copies
the desired signal. The covariance is updated periodically, and
each desired signal is copied in real time.
[0045] Overall about 1/2 to 2/3 of the computational complexity
incurred by using AAP SDMA in a cellular system is due to the
covariance formulation alone, and the remaining complexity resides
in the matrix inversion for copy weight generation. The complexity,
size, power consumption, and cost of implementing AAP SDMA has thus
far prevented it from gaining acceptance. In preferred embodiments,
the present invention achieves substantially the same results as a
fully adaptive implementation of SDMA but with significantly less
hardware complexity, smaller size, lower power consumption, and
lower cost.
[0046] FIG. 4 is a schematic diagram of a mobile-to-base
communication link in a cellular communications system using AAP
SDMA. Illustrated are the antenna array SDMA transmission beam
patterns 150 from the mobile units 30 to the base station 20 along
a central direction 155. Also illustrated is interference 170 which
would exist without SDMA.
[0047] Assuming the base station 20 employs a multi-antenna
adaptive array while the mobile unit 30 uses a single
omnidirectional antenna, in the reverse channel (uplink, or
mobile-to-base), the base station array reduces interference from
other users both in-cell and out-of-cell, as illustrated in FIG. 4,
by pointing its reception beam only towards the desired mobile unit
30.
[0048] For a 120 degree beamwidth, about 1/3 of the mobile units 30
in a cell 10 are visible to the array, so the capacity is
approximately tripled. Similarly, for a 30 degree beamwidth, about
{fraction (1/12)} of the mobile units 30 in a cell 10 are visible
to the array, so the capacity is increased by a factor of
approximately 12.
[0049] Assuming that both the base station 20 and the mobile unit
30 employ multi-element antenna arrays, for the reverse channel,
this system significantly reduces interference from out-of-cell
mobile transmitters, because they are forming beams toward their
own base station 20. Ideally, this would improve the frequency
reuse, F, from 0.6 to nearly 1.0, thereby increasing the capacity
by nearly 2/3. Simulations on such a system show that a frequency
re-use factor of F=0.8826 with a 60 degree beamwidth from the
mobile unit improves capacity by 47% over the omnidirectional case
(F=0.6).
[0050] Improvement due to adaptive arrays on the mobile units 30
are not as dramatic as those achieved with adaptive arrays at the
base station 20. In addition, complexity, size, power, and cost can
make the application of antenna arrays in mobile units 30
impractical for most situations. The reduction in inter-cell
interference afforded by adaptive arrays in mobile units 30 may,
however, be critical in high-traffic environments and for mobile
units 30 near the cell boundaries where interference is the
greatest.
[0051] FIG. 5 is a schematic diagram of a base-to-mobile
communication link in a cellular communications system using AAP
SDMA. Assuming the base station 20 employs a multi-antenna array
while the mobile unit 30 uses a single omnidirectional antenna, in
the base-to-mobile link, the base station 20 antenna array reduces
interference to other users both in-cell 180 and out-of-cell 175,
as illustrated in FIG. 4. Results for this channel for various
beamwidths are summarized below in Table II.
2TABLE II Base Station Antenna Beamwidth vs. Call Capacity in
Base-to-Mobile Channel Beamwidth (degrees) Capacity (calls/cell)
360 (omni) 30 75 (5 antennas) 120 55 (7 antennas) 165
[0052] Assuming that both the base station 20 and the mobile units
30 employ multi-element adaptive antenna arrays, for the forward
channel, this system significantly reduces interference from
out-of-cell base stations, because the mobile units 30 are forming
beams toward their own base station 20. As in the reverse channel,
ideally, this would improve the frequency re-use, F, from 0.6 to
nearly 1.0, thereby increasing the capacity by nearly 2/3.
[0053] FIG. 6 is a schematic diagram of a general SDMA
communications system employing geo-location techniques. As
illustrated, a first user 301 and a second user 302 are in
communication. The first user 301 computes the direction of the
desired user 302 and a beam pattern 314 is formed along the desired
direction 316. In addition to desired users 302, the first user 301
wants to avoid projecting a beam in the direction 317 of an
undesired user 303. Furthermore, the first user 301 wants to avoid
receiving a beam from any direction other than the desired
direction 316. These goals are accomplished by utilizing a narrow
directional radio beam.
[0054] The radio-beam extends from the transmitting unit at a
beamwidth angle B.sub.o. The distance from the transmitting unit to
the receiving unit is designated as r.sub.m. The beamwidth at the
receiving unit is B.sub.m. In a cellular system, a base unit is
located at the center of a geographical cell of radius R and the
receiving unit is generally mobile and moves with a velocity V.
[0055] FIG. 7 is a schematic block diagram of communicating users
of FIG. 6. As illustrated, the first user 301 and the second user
302 receive geo-location data from a satellite system 90. The users
301, 302 communicate using a respective antenna array 52 controlled
by a respective beamformer circuit 34. In addition to the standard
transceiver 310 and control hardware 320, a Global Positioning
System (GPS) circuit 350 communicates with a global positioning
satellite system 90 to command the beamformer 34. Although a
satellite system 90 is illustrated, the geo-location data can be
provided by or derived from a ground-based positioning system.
Furthermore, a differential global positioning system using both
ground and satellite based transmitters can be employed to provide
a higher resolution location.
[0056] FIG. 8 is a flow chart of a method of operating a cellular
telephone system using geo-location data. As a part of the initial
establishment of the wireless link (step 500) between the mobile
unit 30 and the base station 20, the mobile unit 30 must determine
its current position. The GPS receiver may not already be tracking
satellites and could take several minutes to get an accurate
position estimate (cold start). If the GPS receiver 350 is cold
starting (step 510), the base station 20 provides a rough location
estimate to orient the GPS receiver and significantly expedite the
position acquisition (step 512). It can send an estimate of the
mobile unit's location via triangularization from adjacent base
stations. This information can be sent along with a Channel
Assignment Message (which informs the mobile unit of a Traffic
Channel on which to send voice and data) via a Paging Channel.
Users share the Paging Channel to communicate information necessary
for the establishment of calls.
[0057] Then the base station 20 transmits its position to the
mobile unit 30 via the Paging Channel (Step 520). If the mobile
unit 30 is employing a directive antenna array 35', it uses the
base station position and its current position and heading
information to form a beam pattern toward the base station 20 as
described above (step 530). The mobile tunes to the Traffic Channel
and starts sending a Traffic Channel preamble and the current
mobile location information to the base station via a Reverse
Traffic Channel (step 540). Every two seconds, the GPS location is
updated and sent to the base station via the Reverse Traffic
Channel.
[0058] If the mobile unit 30 is employing a directive antenna array
35', every two seconds it uses the current heading information and
compares its updated position information to the stored location of
the current base station to update the beam pattern toward the base
station. Also, the base station 20 receives the updated mobile unit
location information and updates its beam pattern toward the mobile
unit (step 550). During hand-off between base stations (step 560),
the directivity of the mobile antenna array, if employed, is
disabled (step 570) to allow the user to communicate with other
base stations.
[0059] FIG. 9 is a schematic diagram of a cellular telephone system
using geo-location data. A preferred embodiment is an
implementation of SDMA using knowledge of user position in a
cellular spread spectrum communication system. Fixed base stations
20 communicate with roving mobile units 30 within a prescribed
geographic cell 10. Each base station 20 consists of a transceiver
210, a directional antenna array 25' and associated beamformer
hardware 24, control hardware 220, and a transmission link with a
mobile telecommunications switching office (MTSO) 5 to route calls.
The mobile unit 30 consists of handset 8 with a microphone and a
speaker, a transceiver 310, a GPS receiver 350 (or other hardware
to determine position of the mobile), and an omnidirectional
antenna 35 or optionally a directional antenna array 35' and
associated beamformer hardware 34.
[0060] A preferred embodiment of the invention employs a
conventional CDMA base station but with the addition of a
10-element directional antenna array 25' capable of forming antenna
patterns with a beamwidth of 36 degrees, beamformer hardware 24,
and additional modems to accommodate the order of magnitude
increase in call capacity. The beamformer hardware 24 takes as
input the current latitude and longitude of each mobile unit,
compares it with the known location of the base station 20 to
determine the angle of arrival (AOA) of each mobile unit's signal,
and generates a set of complex antenna weights to apply to each
antenna output for each mobile unit such that the combined signal
represents a beam pattern steered in the direction of the desired
mobile unit for both the transmit and receive signals. The complex
antenna weights are calculated to simply steer the antenna
beam.
[0061] Instead of calculating the weights in real-time, a set of
weights can be stored in a Programmable Read-Only Memory (PROM) for
a finite set of angles of arrival, and can be recalled and
immediately applied. The beam pattern is preferably widened as the
mobile unit 30 approaches the base station 20 (as described below)
because the beam coverage decreases as the mobile unit 30
approaches the base station 20. Furthermore, the assumption that
multipath components propagate from approximately the same location
as the mobile unit 30 becomes less valid as the mobile unit 30
approaches the base station. Optionally, the beamformer hardware 24
can track multiple mobile units simultaneously and place nulls on
interfering mobile units, but this is more computationally complex
(although not as complex as a fully adaptive array).
[0062] The base station antenna array forms an antenna pattern with
beamwidth B.sub.0=30 degrees. Assuming the cell radius is R=6 km,
the mobile unit is at radius r.sub.m (m), the maximum velocity of
the mobile unit is V=100 (km/h), and the location estimate is
updated at U=2 times per second, examination of the pie-slice
geometry of the antenna pattern reveals that the antenna beam width
at the mobile unit's location is B.sub.m=2.pi.r.sub.m (B.sub.0/360)
meters, which decreases as the mobile unit 30 approaches the base
station 20. Once a location estimate has been determined for the
mobile unit 30 and transmitted to the base station 20, the base
station 20 forms an antenna pattern with the main lobe centered on
the mobile unit 30.
[0063] In the worst case, this estimate is wrong by T=30 m. In an
update cycle, the mobile travels V/U (m), and as long as this
distance is less than B.sub.m/2 (half the beamwidth in meters at
the mobile location) minus the error in the location estimate, T,
then the mobile will remain within the antenna main lobe:
V/U.ltoreq.(B.sub.m/2)-T . Evaluating this equation with the
typical numerical values and solving for the mobile location yields
r.sub.m.gtoreq.167.6 m at a velocity V=100 km/h. Therefore the
mobile unit 30 remains in the beam coverage area as long as it is
further than 167.6 m from the base station 20.
[0064] The base station 20 uses the location information to sense
when the mobile unit 30 is closer than 167.6 m and widens the beam
pattern to omnidirectional (or optionally to 120 degrees). The
widening does not significantly increase interference to other
users because the low power is used for nearby mobile units 30. The
complex antenna weights for the widened beams are preferably stored
in memory for a finite set of angles of arrival, and they can be
recalled and immediately applied.
[0065] The mobile units 30 include a conventional handset 8
preferably augmented with an integrated GPS receiver 350 and
modifications to the control logic 320 to incorporate the GPS
position data in the transmission to the base station 20. Mobile
units 30 embodied in automobiles preferably employ a three-element
directional antenna array 35' mounted on the automobile and
beamformer hardware 34 in addition to the handset with the build-in
GPS receiver as described above. The beamformer hardware 34 stores
the current base station's latitude and longitude, compares it with
its own current latitude and longitude, and computes its current
heading via GPS doppler in information to determine the angle of
the arrival of the base station signal. A look-up table (for
example in a ROM) provides the antenna weights to steer the
transmit and receive beam pattern toward the base station.
Optionally the beamformer hardware can track multiple base stations
simultaneously and place nulls on interfering base stations.
[0066] The necessary accuracy of the mobile position determination
depends on the width of the antenna beam. Assuming the location can
be determined to within a tolerance of T=30 m (i.e., the location
can be determined with high probability to be within a circle of
radius T=30 m), as the mobile unit 30 moves, the antenna beam must
cover the entire area in which the mobile unit 30 can move in the
two seconds before the position is checked again and the antenna
beam pattern is updated. Because of the pie-slice geometry of the
beam pattern, as the mobile unit 30 approaches the base station 20,
the beam coverage decreases and must be widened to cover the area
in which the mobile unit 30 could travel in the two second update
cycle.
[0067] Mobile units employing the antenna array 35' can form an
antenna pattern with beamwidth B.sub.1=120 degrees. Assuming the
cell radius is R=6 km, the mobile is at radius r.sub.m (meters),
the maximum rotation of the mobile unit is .OMEGA.=45
degrees/second (i.e., the mobile can turn a 90 degree corner in 2
seconds), and the location estimate is updated at U=2 times per
second, examination of the pie-slice geometry of the antenna
pattern yields a location tolerance at the base station of
T.sub.b=360T/(2.pi.r.sub.m) (degrees), which increases as the
mobile unit 30 approaches the base station 20.
[0068] In addition to location, the mobile unit 30 needs to know
its direction of travel so it can determine the orientation of its
antenna array. This direction vector can be deduced from GPS
doppler data or from a compass.
[0069] Once a location estimate has been determined, the mobile
unit 30 forms an antenna pattern with the main lobe centered on the
base station 20. In the worse case, this estimate is wrong by
T.sub.b (degrees) and the mobile unit 30 is turning at maximum
rotation .OMEGA.=45 degrees/s. In an update cycle, the mobile's
main lobe rotates .OMEGA./U (degrees), and as long as this angle is
less than B.sub.1/2 (half the mobile beamwidth in degrees) minus
the error in the location estimate, T.sub.b (degrees), then the
base station 20 will remain within the mobile antenna's main lobe,
.OMEGA./U .ltoreq.(B.sub.1/2)-T.sub.b. Evaluating this equation
with the numerical values above and solving for the mobile location
yields r.sub.m.gtoreq.45 m . Therefore the base station 20 remains
in the beam coverage area as long as it is further than 45 m from
the mobile unit 30.
[0070] The mobile unit 30 uses its location information to sense
when it is closer than 45 m to the base station 20 and widens the
beam pattern to omnidirectional. Again, this widening does not
significantly increase interference to other users because the
power transmitted is low. A look-up table in a ROM provides the
antenna weights to change the beam pattern to omnidirectional when
the mobile unit 30 is within 45 m of the beam station or during
call hand-ff when the mobile unit 30 is communicating with more
than one base station 20.
[0071] A preferred embodiment of the invention includes an aspect
which reduces interference and improves capacity as long as the
multipath components propagate from approximately the same
direction as the line-of-sight (LOS) component, which is a fair
assumption. Typically, a multipath signal is limited to a
5-10.degree. arc relative to the receiver. As such, various
techniques can be employed to identify and null the multipath
component of a received signal.
[0072] Aspects of the invention can be practiced even if some users
are not equipped with SDMA capability. In the case that a
particular user does not employ an antenna array, the user will not
use position information and will default to conventional
omnidirectional transmission and/or reception. Similarly, in the
case that the user does not provide position information, other
users will default to conventional omnidirectional transmission to
and/or reception from that user. As conventional users are phased
out and SDMA equipped users are phased in, the capacity of the
system will increase as the fraction of SDMA equipped users
increases.
[0073] FIG. 10 is a schematic block diagram of a steering circuit.
The steering circuit 52 includes a GPS receiver 522 connected to a
GPS antenna 520 for receiving GPS signals from satellites. The GPS
receiver 522 computes the unit's latitude and longitude. A
deterministic direction finder 524 processes the mobile unit
latitude LAT.sub.M and longitude LNG.sub.M data as well as the base
station latitude LAT.sub.B and longitude LNG.sub.B data using a
first look-up table to compute an angle of arrival (AOA) and a
range (RNG) based on the following equations: 1 AOA = tan - 1 ( LNG
M - LNG B LAT M - LAT B ) ( 2 ) RNG = ( LAT M - LAT B ) 2 + ( LNG M
- LNG B ) 2 ( 3 )
[0074] The AOA and RNG values are processed by a second look-up
table in an antenna steering unit 526 which converts the values
into antenna weights. The antenna weights are calculated to steer
the beam in the direction of the angle of arrival. That is, the
antenna weights unity (i.e., omnidirectional) when the range is
below a prescribed threshold (i.e., the mobile unit is very close
to the base station) and for the mobile unit during handoff. The
antenna weights are provided to the beamformer.
[0075] FIG. 11 is a schematic block diagram of a nulling circuit.
Position data from each user is processed by a GPS circuit
521.sub.a, . . . ,521.sub.k. For a particular user "a", a desired
latitude LAT.sub.Ma and longitude LNG.sub.Ma data are received and
for other users undesirable latitude LAT.sub.Mb, . . . ,LAT.sub.Mk
and longitude LNG.sub.Mb, . . . ,LNG.sub.Mk data are received. A
first look-up table in a deterministic direction finder unit 523
converts the latitude and longitude data from the mobile units into
desired AOA.sub.a and undesired AOA.sub.b, . . . ,AOA.sub.k angles
of arrival and a desired range RNG based on the base station
latitude LAT.sub.B and longitude LNG.sub.B data. This information
for each user is passed to a second look-up table in a nulling unit
525 which computes antenna weights which are calculated to steer
the beam in the direction of the desired angle of arrival AOA.sub.a
and away from the undesired angle of arrivals AOA.sub.b, . . .
,AOA.sub.k (i.e., a circuit nulls undesired users). The antenna
weights can become unity as described above. The antenna weights
from the nulling unit 525 are provided to the beamformer.
[0076] FIG. 12 is a schematic block diagram of a receiver module
for a mobile unit beamformer. The circuit receives a plurality of
RF signals IN.sub.a, IN.sub.b, IN.sub.c over a respective antenna
35'a, 35'b, 36'c of a directional antenna array 35'. The RF signals
are processed into three baseband signal channels by a
three-channel receiver 312. Each baseband signal is processed by a
programmable filter 342a, 342b, 342c. A GPS signal from a GPS
receiver (not shown) is received by a steering/nulling circuit 344
operating as described above. The steering/nulling circuit 344
controls the programmable filters 342a, 342b, 342c. The outputs
from the programmable filters are combined by a RF combiner 346 to
produce an output signal OUT.
[0077] FIG. 13 is a schematic block diagram of a transmitter module
for a mobile unit beamformer. The input signal IN is split three
ways and processed by respective programmable filters 341a, 341b,
341c. The programmable filters 341 are controlled by a
steering/nulling circuit 343 based on inputs from a GPS receiver
(not shown) as described above. Three channels of baseband signals
result from the programmable filters and are fed to a three-channel
transmitter 314 which sends RF signals OUT.sub.a, OUT.sub.b,
OUT.sub.c to a respective antenna 35'a, 35 b, 35'c in the antenna
array 35'. In a preferred embodiment of the invention, the system
implements programmable filtering by including a vector-matrix
product processing system as described in U.S. Pat. No. 5,089,983
to Chiang, the teachings of which are incorporated herein by
reference.
[0078] FIG. 14 is a schematic block diagram of a receiver module
for a base station beamformer. As illustrated, the antenna array
25' of the base station includes 10 antennas 25'.sub.1, . . .
,25'.sub.10. The input signals IN.sub.1, . . . ,IN.sub.10 are
received by a ten-channel receiver 212 which yields ten channels of
baseband signals. Each channel of baseband signal is processed by a
programmable filter array 242, each of which includes a respective
programmable filter for each of N possible users. The programmable
filters 242 are controlled by a steering/nulling circuit 244 for
each user based on GPS data received from each user as described
above. The outputs from the programmable filters 242 are combined
by an RF combiner 246 into N outputs OUT.
[0079] FIG. 15 is a schematic block diagram of a transmitter module
for a base station beamformer. The transmitter section receives an
input signal IN which is split ten ways into ten channels. Each
channel is processed by a programmable filter array 241 having a
programmable filter for each N possible users. The programmable
filters are controlled by a steering/nulling circuit 243 for each
user based on GPS data from each mobile user as described above.
The programmable filters yield N baseband signals divided into ten
channels which are transmitted to the antenna array 25' by a
ten-channel transmitter 214. Each antenna 25'.sub.1, . . .
,25'.sub.10 receives a respective RF output signal OUT.sub.1, . . .
,OUT.sub.10 from the transmitter 214.
[0080] In a preferred embodiment of the invention, a cellular base
station includes sufficient signal-processing hardware to support
the use of geo-location information, received from mobile
transmitters, to optimally shape the receiving antenna-array
pattern. This approach is an alternative to using a fully adaptive
antenna-array that requires a significantly greater cost in terms
of hardware and software.
[0081] To implement a fully-adaptive base station receiver, an
array of antenna inputs must be processed to yield a set of
complex-valued weights that are fed back to regulate the gain and
phase of the incoming signals. The need for multiple weights
applied to a single input signal implies frequency independence.
The weight or weights are applied to each input signal as either a
real-valued Finite Impulse Response (FIR) filter at a chosen
intermediate frequency (IF) (as depicted in FIG. 16 below) or as
complex-valued FIR filter at base band (as depicted in FIG. 17
below). Following the application of the appropriate weights, the
outputs from each antenna-channel are summed to yield a beamformed
output from the array.
[0082] FIG. 16 is a schematic block diagram of a preferred base
station employing real-valued FIR filtering at IF. In particular,
the base station 1020 employs a sample-data beam shaping system for
downconverted and band limited signals. The mobile unit 30
communicates with the base station 1020 through a plurality of N
receiver units 1010.sub.1, 1010.sub.2, . . . , 1010.sub.N. Each
receiver includes a respective antenna 1022.sub.1, 1022.sub.2, . .
. , 1022.sub.N. Received signals are transmitted from the antennas
1022.sub.1, 1022.sub.2, . . . , 1022.sub.N through a bandpass
filer, 1024.sub.1, 1024.sub.2, . . . , 1024.sub.N; a gain
controllable amplifier 1026.sub.1, 1026.sub.2, . . . , 1026.sub.N;
a multiplier 1028.sub.1, 1028.sub.2, . . . , 1028.sub.N; and a
second bandpass filter 1030.sub.1, 1030.sub.2, . . . , 1030.sub.N
to form N receiver output signals.
[0083] The receiver output signals are input to a processing chip
1040 which includes a sampling circuit 1042.sub.1, 1042.sub.2, . .
. , 1042.sub.N and a programmable FIR filter 1044.sub.1,
1044.sub.2, . . . , 1044.sub.N for each input signal. The outputs
of the FIR filters are summed by a summing circuit 1046. A
postprocessor 1048 communicates with an off-chip automatic gain
control (AGC) circuit 1032 to provide a control signal to the
amplifiers 1026.sub.1, 1026.sub.2, . . . , 1026.sub.N to vary the
amplifier gains.
[0084] The postprocessor 1048 also communicates with an off-chip
geo-location controller 1038 which provides geo-location data to a
weighted circuit 1046. The weighting circuit 1036 provides weights
to the on-chip programmable filters 1044.sub.1, 1044.sub.2, . . . ,
1044.sub.N.
[0085] FIG. 17 is a schematic block diagram of a preferred base
station employing complex-valued FIR filtering at base band. As
with FIG. 16, the base station 1020' includes a plurality of
receivers that provides an input signal to a processing chip 1050.
The processing chip 1050 yields two channels of output to an
off-chip postprocessor 1034 which decodes, encodes and equalizes
the channels. The postprocessor 1034 transmits a signal to the AGC
circuit 1032 to control the receiver amplifiers 1026.sub.1, . . . ,
1026.sub.N and is in communication with the geo-location controller
1038. Geo-location data from the geo-location controller 1038 is
processed by a weight-update circuit 1036' to calculate weights for
a 2N M stage FIR filter array.
[0086] The base station includes a beamshaping circuit using a two
channel downconversion system. The processing chip 1050 includes,
for each of N receivers, a sampling circuit 1052.sub.1, . . . ,
1052.sub.N and a multiplier 1054.sub.1, . . . , 1054.sub.N. The
multipliers 1054.sub.1, . . . , 1054.sub.N each provide an in-phase
(I) channel 1056.sub.1-I, . . . , 1054.sub.N-I and a quadrature (2)
channel 1056.sub.1-Q, . . . , 1056.sub.N-Q. The respective channels
are passed to respective low pass filters 1058.sub.1-I, . . . ,
1058.sub.N-Q. Each channel is then down-converted by downconversion
circuit 1060.sub.1-I, . . . , 1060.sub.N-Q. The down-converted
channels are fed to respective programmable FIR filters
1062.sub.1-I, . . . , 1062.sub.N-Q. These filters are programmed
based on the weight inputs from the weighting circuit 1038. The I
and Q channels are individually summed at summing circuits 1064-I,
1064-Q for output to the postprocessing system 1034.
[0087] The effect of the weights is to electronically shape the
antenna-array response. Ideally, mobile transmitters that are
interfering with the desired user are suppressed or nulled out,
while the transmitter of interest is given at least unity gain.
Using a fully adaptive antenna array, the weights are updated with
time as the mobile unit moves or as propagation conditions change.
The update of the weights, however, is computationally intensive
requiring the computation of the covariance matrix of the array
response.
[0088] In comparison, a preferred base station uses position
information obtained from the mobile transmitter (or from the
base-station network) to automatically compute the weights to be
applied to the input signals from each antenna. As in the
fully-adaptive system, the weights are updated as the mobile
transmitter moves. The potential difficulty with this approach is
that it does not explicitly account for changes in the propagation
conditions between the mobile transmitter and the base station.
[0089] In an effort to characterize the propagation conditions
between a mobile transmitter and a base station, a series of
operations were performed using a fully operational digital-TDMA
cellular system. The base station comprised 6 receiving antennas
that can be located with arbitrary spacings. A single, mobile
transmitter is used to characterize the propagation conditions.
Based on the signals received at the base station, profiles of the
signal-propagation delay versus time are mathematically computed.
Using these results, the worst case angle-of-arrival is computed.
For this case, the delayed signal is assumed to arrive from a
reflector along a line perpendicular to a line joining the base
station and the mobile.
[0090] For geo-location-based array-processing to operate, the true
location of the transmitter is preferably very close to the angle
of arrival (AOA) of the primary propagation path from the
mobile.
[0091] When the true location and the AOA of the primary
propagation path differ, the beam pattern produced by geo-location
information will not exactly produce the desired gain and nulling
of the mobiles' signal. This condition produces suppression of the
undesired mobile's signal, but may not completely cancel or null
out the transmission.
[0092] For worst-case propagation conditions, this implies that the
electronically synthesized beam pattern does not provide the
optimal gain for receiving this mobile, nor does it completely null
out the undesired signals. The difference between the ideal (fully
adaptive) array beam pattern and one constructed using only
geo-location information is not too great, however, when the true
position of the mobile and the AOA of the primary propagation path
vary by less than a few degrees.
[0093] In practice, the preceding situation occurs when the primary
propagation between the mobile and the base station are not
line-of-sight. This often occurs in urban canyons, where large
buildings block line-of-sight transmission from the mobile to the
base station (and vice versa); thereby, placing the mobile's
transmission in a "deep fade." To counteract this effect, a
preferred base station includes partially adaptive array-processing
to incrementally refine the initial beam pattern that is obtained
using only geo-location information. Candidate approaches for
partially-adaptive array processing can be readily found in the
literature for fully-adaptive array processing (e.g., "Novel
Adaptive Array Algorithms and Their Impact on Cellular System
Capacity," by Paul Petrus incorporated herein by reference).
[0094] The approaches to computing a mobile's true location have
been investigated in detail for CDMA signal communication (see
"Performance of Hyperbolic Position Location Techniques for
Code-Division Multiple Access," by George A. Mizusawa, incorporated
herein by reference). Implementing a GPS receiver in the phone is
one candidate for providing accurate geo-location information to
the base station. Alternatively, at least three base stations can
be employed to triangulate the mobile location using a variety of
algorithms.
[0095] FIG. 18 is a schematic block diagram of a beamshaping
circuit based on an adaptive-array processing algorithms. As
illustrated, the circuitry 1080 is essentially identical to that
illustrated in FIG. 17. The postprocessing circuit, however,
communicates with an adaptive-array processing algorithm in the
module 1039 provides the weighting signal to the on-chip
programmable FIR filters 1062.sub.1-I, . . . , 1062.sub.N-Q. The
processing chip 1050 can be similarly employed to accommodate other
cellular communication techniques.
[0096] Although preferred embodiments of the invention have been
described in the context of a cellular communication system, the
principles of the invention can be applied to any communication
system. For example, geo-location data and associated beamforming
can be embodied in any radio frequency communication system such as
satellite communication systems. Furthermore, the invention can be
embodied in acoustic or optical communication systems.
Equivalents
[0097] While the invention has been particularly shown and
described with reference to preferred embodiments thereof, it will
be understood by those skilled in the art that various changes in
form and details may be made therein without departing from the
spirit and scope of the invention as defined by the appended
claims. In particular, the various aspects of the invention can be
embodied in hardware, software or firmware.
[0098] These and all other equivalents are intended to be
encompassed by the following claims.
[0099] The claims should not be read as limited to the described
order or elements unless stated to that effect. Therefore, all
embodiments that come within the scope and spirit of the following
claims and equivalents thereto are claimed as the invention.
* * * * *