U.S. patent application number 09/766153 was filed with the patent office on 2001-09-27 for phased array spread spectrum receiver.
Invention is credited to Schilling, Donald L..
Application Number | 20010024466 09/766153 |
Document ID | / |
Family ID | 23015931 |
Filed Date | 2001-09-27 |
United States Patent
Application |
20010024466 |
Kind Code |
A1 |
Schilling, Donald L. |
September 27, 2001 |
Phased array spread spectrum receiver
Abstract
A spread spectrum phased array receiver has a set of phased
array antennas. The set of phased array antennas receive a spread
spectrum signal containing a plurality of channels. The receiver
outputs timed versions of the received signal. Each timed version
is associated with a respective one out of the set of phased array
antennas. A plurality of despread signals is produced by
despreading each timed version of the received signal using a
plurality of chip code sequences associated with the channels. The
despread signals are combined as a despread signal. A magnitude of
the combined despread signal is determined for obtaining a present
and a prior magnitude. The present and prior magnitude are
compared. A delay associated with the timed versions is adjusted in
response to the comparison so antenna beams are steered towards
components of the spread spectrum signal with a highest combined
magnitude.
Inventors: |
Schilling, Donald L.; (Sands
Point, NY) |
Correspondence
Address: |
VOLPE AND KOENIG, PC
DEPT ICC
SUITE 400, ONE PENN CENTER
1617 JOHN F. KENNEDY BOULEVARD
PHILADELPHIA
PA
19103
US
|
Family ID: |
23015931 |
Appl. No.: |
09/766153 |
Filed: |
January 19, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09766153 |
Jan 19, 2001 |
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09280328 |
Mar 29, 1999 |
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6256340 |
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09280328 |
Mar 29, 1999 |
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08859522 |
May 20, 1997 |
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5926502 |
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08859522 |
May 20, 1997 |
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08625254 |
Apr 1, 1996 |
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5633889 |
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08625254 |
Apr 1, 1996 |
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08266769 |
Jun 28, 1994 |
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5659572 |
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08266769 |
Jun 28, 1994 |
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08155173 |
Nov 22, 1993 |
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5422908 |
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Current U.S.
Class: |
375/148 ;
342/423; 375/E1.001; 375/E1.002 |
Current CPC
Class: |
H04B 7/0894 20130101;
H01Q 3/2682 20130101; G01S 3/42 20130101; H04B 1/707 20130101; H01Q
3/22 20130101; H04B 7/084 20130101; H01Q 3/26 20130101; H04B 1/69
20130101; H01Q 3/2605 20130101; H04B 1/1081 20130101; H04L 1/06
20130101 |
Class at
Publication: |
375/148 ;
342/423 |
International
Class: |
H04K 001/00 |
Claims
What is claimed is:
1. A method for use in a spread spectrum communication system of
steering antenna beams of a phased array receiver, the receiver
having a set of phased array antennas, the method comprising:
receiving a spread spectrum signal containing a plurality of
channels by the set of phased array antennas; outputting timed
versions of the received signal, each timed version associated with
a respective one out of said set of phased array antennas;
producing a plurality of despread signals by despreading each timed
version of the received signal using a plurality of chip code
sequences associated with the plurality of channels; combining the
despread signals as a combined despread signal; determining a
magnitude of the combined despread signal for obtaining a present
and a prior magnitude; comparing the present magnitude with the
prior magnitude; and adjusting a delay associated with the timed
versions in response to the comparison so antenna beams associated
with the set of phased array antennas are steered towards
components of the spread spectrum signal with a highest combined
magnitude.
2. The method of claim 1 wherein the timed versions are the
received signal and a delayed version of the received signal.
3. The method of claim 1 wherein the combining of the despread
signals comprises: despreading in-phase and quadrature phase
components of the timed versions for each channel; and combining
the despread in-phase and the despread quadrature phase components
as the combined despread signal.
4. The method of claim 1 further comprising: converting the spread
spectrum signal received by each one of said set of phased array
antennas to a respective intermediate frequency signal after the
step of outputting timed versions.
5. The method of claim 1 further comprising: storing the present
magnitude for use as a subsequent prior magnitude.
6. A spread spectrum phased array receiver, the receiver having a
set of phased array antennas, t he set of phased array antennas for
receiving a spread spectrum signal containing a plurality of
channels, the receiver comprising: a delay device for outputting
timed versions of the received signal, each timed version
associated with a respective one out of said set of phase array
antennas; a despreader and a combiner for producing a plurality of
despread signals by despreading each timed version of the received
signal using chip code sequences associated with the plurality of
channels and combining the despread signals as a combined despread
signal; a magnitude device for determining a magnitude of the
combined despread signal for obtaining a present and a prior
magnitude; a comparator for comparing the present magnitude with
the prior magnitude; and a counter for adjusting a delay associated
with the timed versions in response to the comparison so antenna
beams associated with the set of phased array antennas are steered
towards components of the spread spectrum signal with a highest
combined magnitude.
7. The receiver of claim 6 wherein the delay device is a digital
delay device for generating a delayed version of the received
signal; wherein the timed versions are the received signal and the
delayed version.
8. The receiver of claim 6 wherein: the despreader for despreading
in-phase and quadrature phase components of the timed versions for
each channel; and the combiner for combining the despread in-phase
and despread quadrature phase components as the combined despread
signal.
9. The receiver of claim 6 further comprising: a respective set of
RF/IF sections coupled to a respective antenna out of the set of
antennas for converting the spread spectrum signal received by each
antenna out of the set to a respective intermediate frequency
signal.
10. The receiver of claim 6 further comprising: a shift register
for storing the present magnitude as a subsequent prior magnitude.
Description
RELATED PATENTS
[0001] This patent stems from a continuation application of parent
application having Ser. No. 08/625,254, filed Apr. 1, 1996, now
U.S. Pat. No. 5,633,889 with issue date May 27, 1997, which is a
continuation application of Ser. No.. 08/266,769, filed Jun. 28,
1994, which was a continuation-in-part application of patent
application entitled, PHASED ARRAY SPREAD SPECTRUM SYSTEM AND
METHOD, having Ser. No. 08/155,173, and filing date Nov. 22, 1993,
now U.S. Pat. No. 5,422,908 with issue date Jun. 6, 1995. The
benefit of the earlier filing date of the parent patent
applications is claimed for common subject matter pursuant to 35
U.S.C. .sctn. 120.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to spread-spectrum is
communications and more particularly to a method and apparatus for
enhancing communications by using phased array principles for
increasing signal-to-noise ratio for a spread spectrum signal with
multipath arriving at a receiver.
DESCRIPTION OF THE RELEVANT ART
[0003] Achieving sufficient signal strength when a received signal
comes from two paths is a problem when communicating with
spread-spectrum modulation in a multipath environment. The received
signal from the two paths may have phase cancellation, yielding no
reception, or reception with an unacceptable error rate.
[0004] Phased arrays, as is well known in the art, require N
antenna elements for distinguishing up to N-1 signals arriving at
the phased array from different paths or directions. This concept
of spatial diversity is well developed in antenna theory.
SUMMARY OF THE INVENTION
[0005] A general object of the invention is an improved system and
method for receiving spread-spectrum signals in a multipath
environment.
[0006] Another object of the invention is to increase the received
signal-to-noise ratio or reduce the probability of error of a
spread-spectrum signal arriving from two or more paths.
[0007] Another object of the invention is to receive a plurality of
spread-spectrum signals arriving at the antenna from a multiplicity
of different directions, independent of the number of antenna
elements.
[0008] According to the present invention, as embodied and broadly
described herein, a phased array spread-spectrum system is provided
comprising receiving means, delaying means, combining means,
despreading means, generating means, storing means, and comparing
means. The receiving means receives a plurality of spread-spectrum
signals and a plurality of phased-versions of the plurality of
spread-spectrum signals. Typically, the plurality of
spread-spectrum signals is received by a first plurality of
receivers coupled to a first antenna, and the plurality of phased
versions of the plurality of spread-spectrum signals is received by
a second plurality of receivers coupled to a second antenna. The
plurality of received spread-spectrum signals and the plurality of
phased versions of the plurality of spread-spectrum signals are
digitized. The delaying means can delay the plurality of received
spread-spectrum signals with respect to the plurality of phased
versions of the plurality of spread-spectrum signals by a plurality
of delays. The plurality of received spread-spectrum signals
consequently becomes a plurality of delayed signals.
[0009] The combining means combines the plurality of delayed
signals and the plurality of phased versions of the plurality of
spread-spectrum signals as a plurality of combined signals. An
in-phase component of each delayed signal is combined with an
in-phase component of each phased version of each spread-spectrum
signal, respectively. A quadrature-phase component of each delayed
signal is combined with a quadrature-phase component of each phased
version of each spread-spectrum signal, respectively.
[0010] The despreading means despreads the plurality of combined
signals as a plurality of despread signals. This may be
accomplished using a plurality of product detectors with a
plurality of chipping sequences matched to the plurality of
received spread-spectrum signals, respectively, or a plurality of
matched filters having a plurality of impulse functions matched to
the plurality of chipping sequences of the plurality of received
spread-spectrum signals, respectively.
[0011] The generating means generates from the plurality of
despread signals a plurality of magnitude values. Each magnitude
value may be an absolute value, or the square of the in-phase
component and quadrature-phase component of the despread
signal.
[0012] The storing means stores a plurality of previous-magnitude
values previously generated by the generating means and a plurality
of present-magnitude values presently generated by the generating
means. The plurality of previous-magnitude values and the plurality
of present-magnitude values, respectively, are compared by the
comparing means. In response to the result of this comparison, the
comparing means outputs a plurality of comparison signals. The
delaying means may change any or all of the plurality of delays
based on the plurality of comparison signals, respectively.
[0013] The present invention also includes a method for maximizing
the signal strength of a plurality of spread-spectrum signals with
multipath comprising the steps of receiving the plurality of
spread-spectrum signals and a plurality of phased versions of the
plurality of spread-spectrum signals. The received plurality of
spread-spectrum signals is delayed with respect to the plurality of
phased versions of the spread-spectrum signals by a plurality of
delays, to generate a plurality of delayed signals. The plurality
of delayed signals and the plurality of phased versions of the
plurality of spread-spectrum signals are combined as a plurality of
combined signals, and the plurality of combined signals is despread
as a plurality of despread signals, respectively.
[0014] The method includes generating a plurality of magnitude
values from the plurality of despread signals, and storing a
plurality of previous-magnitude values and a plurality of
present-magnitude values. The plurality of previous-magnitude
values and the plurality of present-magnitude values are compared,
and a plurality of comparison signals is output based on this
comparison. Using the plurality of comparison signals, the
plurality of delays is changed. The step of generating the
plurality of magnitude values is a way of locating a maximum. Other
procedures for locating a maximum or equivalent may be used.
[0015] Additional objects and advantages of the invention are set
forth in part in the description which follows, and in part are
obvious from the description, or may be learned by practice of the
invention. The objects and advantages of the invention also may be
realized and attained by means of the instrumentalities and
combinations particularly pointed out in the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The accompanying drawings, which are incorporated in and
constitute a part of the specification, illustrate preferred
embodiments of the invention and, together with the description,
serve to explain the principles of the invention.
[0017] FIG. 1 is a block diagram illustrating the general concept
of the invention;
[0018] FIG. 2 shows two multipath signals being received by a
user;
[0019] FIG. 3 is a block diagram for adjusting a phase between two
receivers;
[0020] FIG. 4 is a block diagram for adjusting a phase for a
plurality of spread-spectrum signals; and
[0021] FIG. 5 is a block diagram for adjusting a phase between two
sets of receivers for a plurality of spread-spectrum signals.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0022] Reference now is made in detail to the present preferred
embodiments of the invention, examples of which are illustrated in
the accompanying drawings, wherein like reference numerals indicate
like elements throughout the several views.
Handset
[0023] The present invention provides a unique phased array
spread-spectrum system comprising receiving means, delaying means,
combining means, despreading means, generating means, storing
means, and comparing means. The delaying means is coupled between
the receiving means and the combining means. The despreading means
is coupled between the combining means and the generating means.
The storing means is coupled between the generating means and the
comparing means, and the comparing means is coupled to the delaying
means.
[0024] The receiving means of FIG. 1 receives a spread-spectrum
signal and a phased version of the spread-spectrum signal. The term
"phased version" as used herein includes a version of the
spread-spectrum signal having a phase different from the received
spread-spectrum signal, and/or a version of the spread-spectrum
signal having a time delay with respect to the received
spread-spectrum signal. The different phase and/or time delay
arises, as shown in FIG. 2, from the spread-spectrum signal 15 and
the phased version of the spread-spectrum signal 16 arriving from
different paths, such as bouncing off different buildings 17, 18.
The phased array spread-spectrum system may be implemented at a
base station or, as shown in FIG. 2, at a remote subscriber unit
(RSU) such as a handset 19. The phase change occurs upon each
reflection, since a first spread-spectrum signal 15 has one
reflection and a second ray, such as the phased version of the
spread-spectrum signal 16, has two reflections. As a result of the
difference in time between the two signals, the multipath signals
can undergo phase cancellation and cause a fade. The phased array
spread-spectrum system of FIG. 1 delays or phase shifts one of the
two antennas 11, 12 enough to steer the beam from the two antennas
to either building, or ray path having maximum signal strength.
[0025] Typically, the receiving means, as shown in FIG. 1, includes
a first antenna 11 and a second antenna 12. The spread-spectrum
signal d(t)g(t)cos.omega..sub.0t is received with a first receiver
coupled to the first antenna 11, and the phased version of the
spread-spectrum signal
d(t-.tau.)g(t-.tau.)cos.omega..sub.0(t-.tau.) is received with a
second receiver coupled to the second antenna 12. The first
receiver and the second receiver include radio frequency (RF) and
intermediate frequency (IF) amplifiers and filters, as appropriate.
The received spread-spectrum signal and the phased version of the
spread-spectrum signal may be digitized.
[0026] The delaying means, shown in FIG. 1 as a delay device 13,
can delay the received spread-spectrum signal with respect to the
phased version of the spread-spectrum signal by a delay. The
received spread-spectrum signal consequently becomes a delayed
signal, with the delay approximately equal to a delay of the phased
version of the spread-spectrum signal. A preferred embodiment
employs digital signal processing. Accordingly, the delaying means
would include a digital delay device such as a shift register.
Alternatively, analog circuitry would employ an analog delay
device, or a phase shifter.
[0027] Although illustrated with two antennas, the receiving means
may include additional antennas for enhanced performance. The
delaying means would have appropriate delaying circuits to
accommodate the multiple antennas.
[0028] The combining means, shown in FIG. 1 as a combiner 14,
combines the delayed signal and the phased version of the
spread-spectrum signal as a combined signal. The delayed signal and
the phased version of the spread-spectrum signal have approximately
the same phase or time delay. Thus, an in-phase component of the
delayed signal combines with an in-phase component of the phased
version of the spread-spectrum-signal, and a quadrature-phase
component of the delayed signal combines with a quadrature-phase
component of the phased version of the spread-spectrum signal.
[0029] The despreading means despreads the combined signal as a
despread signal. This may be accomplished using a product detector
with a chipping sequence matched to the received spread-spectrum
signal, or a matched filter such as a surface acoustic wave (SAW)
device having an impulse function matched to the chipping sequence
of the received spread-spectrum signal. Product detectors, digital
signal processors and SAW devices for despreading spread-spectrum
signals are well known in the art.
[0030] The generating means generates a magnitude value from the
despread signal. The magnitude value may be an absolute value, the
square of the in-phase component and quadrature-phase component of
the despread signal, or other metric of the despread signal for
determining a relative signal strength value. A magnitude value
currently being generated by the generating means is referred to
herein as a present-magnitude value. A magnitude value previously
generated by the generating means is referred to herein as a
previous-magnitude value. The invention is taught with the
previous-magnitude value being generated just before the
present-magnitude value, although a previous-magnitude value may be
separated in time and other magnitude values from the present
magnitude value. Also, more than one previous-magnitude value may
be used. The concept of the present invention is taught with one
previous-magnitude value.
[0031] The storing means stores the previous-magnitude value
previously generated by the generating means and the
present-magnitude value presently generated by the generating
means. In a digital implementations the storing means might be
embodied as a shift register or, equivalently, as gates for
performing the storing function. In an analog implementation, the
storing means might be embodied as two or more capacitors for
storing the previous-magnitude value and the present-magnitude
value.
[0032] The previous-magnitude value and the present-magnitude value
are compared by the comparing means. In response to this
comparison, the comparing means outputs a comparison signal. The
comparing means, for example, may output a comparison signal to
increase the delay .tau. of the delaying means, if the
present-magnitude value were greater than the previous-magnitude
value; conversely, the comparing means may output a comparison
signal to decrease the delay T of delaying means, if the
present-magnitude value were less than the previous-magnitude
value. The delaying means changes the first delay based on the
comparison signal. If a plurality of previous-magnitude values were
used, then a scheme may be implemented with the comparing means to
weight the plurality of previous-magnitude values.
[0033] The present invention provides improvement if the delay
.tau. is less than the time of a chip T.sub.c. The present
invention works on in-close multipath. For far-out multipath, noise
is produced. Thus, the present invention finds applications in
buildings or within areas where .tau.<T.sub.c. For
.tau.>T.sub.c a RAKE system should be used.
[0034] In the exemplary arrangement shown in FIG. 3, the receiving
means is embodied as the first antenna 11, a first RF/IF section
21, a first analog-to-digital converter 23, the second antenna 12,
a second RF/IF section 22, and a second analog-to-digital converter
24. The first RF/IF section 21 is coupled between the first antenna
11 and the first analog-to-digital converter 23. The second RF/IF
section 22 is coupled between the second antenna 12 and the second
analog-to-digital converter 24. Typically, the first RF/IF section
21 generates an in-phase component and a quadrature-phase component
of the received spread-spectrum signal. The second RF/IF section 22
generates an in-phase component and quadrature-phase component of
the phased-version of the spread-spectrum signal.
[0035] As illustratively shown in FIG. 3, the outputs of the first
analog-to-digital converter 23 and the second analog-to-digital
converter 24 may go to other sections for processing different
channels of the spread spectrum signal 25, 26.
[0036] The delaying means is embodied as a first digital delay
device 27. The delaying means additionally may include a second
digital delay device 28. The first digital delay device 27 is
coupled to the first analog-to-digital converter 23. If a second
digital delay device 28 were employed, then the second digital
delay device 28 is coupled to the second analog-to-digital
converter 24.
[0037] The combining means is embodied as a first summer 29 and a
second summer 30. The first summer 29 is coupled to the first
digital-delay device 27 and to the second digital-delay device 28.
The second summer 30 is coupled to the first digital-delay device
27 and to the second digital-delay device 28. If the second digital
delay device 28 were not employed, then the first summer 29 is
coupled to the first digital-delay device 27 and to the second
analog-to-digital converter 24, and the second summer 30 is coupled
to the first digital-delay device 27 and to the second
analog-to-digital converter 24.
[0038] The despreading means is embodied as a despreader 31. The
despreader 31 may be embodied as a product device coupled to an
appropriate chipping-sequence generator and synchronization
circuitry for despreading the received spread spectrum signal.
Alternatively, the despreader 31 may be a digital signal processor
which includes the appropriate product devices, or a matched filter
having an impulse response matched to the chipping sequence of the
received spread spectrum signal. As is well known in the art, a
surface acoustic wave (SAW) device having an impulse response
matched to the chipping sequence may be employed.
[0039] The generating means is embodied as a magnitude device 32.
The magnitude device 32 is coupled to the despreader 31. Normally,
the despreader 31 is coupled to additional circuitry for
demodulating data embedded in the received spread spectrum
signal.
[0040] The storing means is embodied as a shift register 33. The
shift register 33 is coupled to the magnitude device 32. The
storing means alternatively may be embodied as a plurality of
gates, registers, or other circuitry for storing magnitude
values.
[0041] The comparing means may be embodied as a comparator 34 and
an up/down counter 35. The comparator 34 typically has two inputs
coupled to the shift register 33. The up/down counter 35 is coupled
to the output of the comparator 34 and to the first digital-delay
device 27 and/or the second digital-delay device 28.
[0042] The first antenna 11 receives the spread-spectrum signal
which is amplified by the first RF/IF section 21. The first RF/IF
section 21 outputs an in-phase component and a quadrature-phase
component to the first analog-to-digital converter 23. The first
analog-to-digital converter 23 converts the in-phase component and
the quadrature-phase component to a digitized in-phase component
and a digitized quadrature-phase component. These components may be
processed by modules similar to the phase compensation circuitry
40, by coupling to the outputs of the first analog-to-digital
converter 23 at the outputs 25, 26.
[0043] Similarly, a phased version of the spread-spectrum signal is
received by the second antenna 12 and then amplified and filtered
by the second RF/IF section 22. The second RF/IF section 22 has
outputs for an in-phase component and a quadrature-phase component
which are fed to the second analog-to-digital converter 24. The
outputs 26 of the second analog-to-digital converter can go to
modules similar to the phase compensation circuitry 40 for
processing different chipping sequences. For example, a spread
spectrum signal may have a plurality of spread-spectrum channels,
with each spread-spectrum channel defined by a different chipping
sequence. Accordingly, each module 40 would be used for a
corresponding spread-spectrum channel, for processing with that
particular chipping sequence.
[0044] The first digital-delay device 27 delays the digitized
spread-spectrum signal by a first delay. The output of the first
digital-delay device 27 is the first delayed signal. The second
digital-delay device 28 delays the digitized phased version of the
spread-spectrum signal by a second delay. The output of the second
digital-delay device 28 is a second delayed signal. The second
digital-delay device 28 is optional, and is not required for use of
the present invention. If the second digital-delay device 28 were
not employed, then the term second delayed signal refers to the
digitized phased version of the spread-spectrum signal, outputted
from the second analog-to-digital converter 24.
[0045] The first summer 29 combines the quadrature-phase components
of the first delayed signal from the first digital-delay device 27,
with the quadrature-phase components of the second delayed signal
from the second digital-delay device 28. The output of the first
summer 29 is a first combined signal.
[0046] The second summer 30 combines an in-phase component from the
first digital-delay device 27, with an in-phase component from the
second digital-delay device 28. Accordingly, the in-phase
components of the first delayed signal and the second delayed
signal are combined as a second combined signal.
[0047] The despreading device 31 despreads the first combined
signal and the second combined signal as a despread
quadrature-phase signal and a despread in-phase signal,
respectively. The despread in-phase signal and the despread
quadrature-phase signal can be processed by further processing
devices, not shown, for demodulating data embedded in the received
spread-spectrum signal.
[0048] The magnitude device 32 generates a magnitude value from the
despread in-phase signal and the despread quadrature-phase signal.
The magnitude value may be an absolute value determined from the
despread in-phase signal and the despread quadrature-phase signal,
or a square of the despread in-phase signal plus a square of the
despread quadrature-phase signal. Other metrics may be used for
accomplishing the same function of determining a relative signal
strength value. The function of the magnitude value is to compare
the signal strength of a present-magnitude value with a
previous-magnitude value.
[0049] The shift register 33 stores the previous-magnitude value
and the present-magnitude value in order that a comparison may be
made by the comparator 34. The comparator 34, when comparing the
previous-magnitude value with the present-magnitude value, outputs
a comparison signal. The comparison signal can control the up/down
counter 35 to increase or decrease a delay of the first
digital-delay device 27. Optionally, the up/down counter 35 may
increase or decrease a second delay of the second digital-delay
device 28.
[0050] The present invention also includes a method for maximizing
signal strength of a spread-spectrum signal with multipath
comprising the steps of receiving the spread-spectrum signal and a
phased version of the spread-spectrum signal. The in-phase and
quadrature-phase components of the received spread-spectrum signal
are delayed with respect to the in-phase and quadrature-phase
components of the phased version of the spread-spectrum signal by a
delay, to generate a delayed signal. The in-phase component and the
quadrature-phase component of the delayed signal and the in-phase
component and the quadrature-phase component of the phased version
of the spread-spectrum signal are combined, respectively, as the
in-phase component and quadrature-phase component of a combined
signal, and the combined signal is despread as an in-phase
component and a quadrature-phase component of a despread
signal.
[0051] The method includes generating a magnitude value from the
in-phase component and the quadrature-phase component of the
despread signal, and storing a previous-magnitude value and a
present-magnitude value. The previous-magnitude value and the
present-magnitude value are compared, and a comparison signal is
output based on this comparison. Using the comparison signal, the
delay is changed.
Base Station
[0052] The present invention may be extended to the base station,
with the unique phased array spread-spectrum system processing a
plurality of spread-spectrum signals. In this embodiment, the
receiving means receive a plurality of spread-spectrum signals and
a plurality of phased versions of the plurality of spread-spectrum
signals. As shown in FIG. 2, the different phases and.backslash.or
time delays arise from the spread-spectrum signal 15 and the phased
version of the spread-spectrum signal 16 arriving from different
paths, such as bouncing off different buildings 17, 18. Typically,
the receiving means, as shown in FIGS. 3, 4, and 5, includes the
first antenna 11 and second antenna 12. The receiving means may
further include appropriate RF and IF amplifiers and filters. The
received plurality of spread-spectrum signals and the received
plurality of phased versions of the plurality of spread-spectrum
signals may be digitized.
[0053] The delaying means, shown in FIG. 4 as delay device 121,
delay device 122, . . . , delay device 123, can delay the received
plurality of spread-spectrum signals, with respect to the received
plurality of phased versions of the plurality of spread-spectrum
signals, by a plurality of delays, respectively. The received
plurality of spread-spectrum signals consequently become a
plurality of delayed signals, with the delay for each of the
plurality of delayed signals approximately equal to a delay of the
respective phased version of the received spread-spectrum signal. A
preferred embodiment would include digital signal processing.
Accordingly, the delay means would include a digital delay device
such as a shift register. Alternatively, analog circuitry would
employ an analog delay device, or phase shifter.
[0054] The combining means, shown in FIG. 4 as a combiner 14,
combines the plurality of delayed signals and the plurality of
phased versions of the plurality of spread-spectrum signals as a
combined signal. The output of the combining means may include
appropriate RF circuitry and/or IF circuity 124.
[0055] Each of the plurality of the delayed signals, and each of
the respective phased versions of the plurality of spread-spectrum
signals, respectively, have the same phase or time delay. Thus, an
in-phase component of the delayed signal combines with an in-phase
component of the phased version of a spread-spectrum signal, and a
quadrature-phase component of the delayed signal combines with a
quadrature-phase component of the phased version of the
spread-spectrum signal.
[0056] The despreading means despreads the combined signal as a
plurality of despread signals. This may be accomplished, as shown
in FIG. 4, using a plurality of despreading devices, 131, 132, . .
. , 133. Each despreading device may be implemented using a product
detector or mixer with a chipping sequence matched to the received
spread-spectrum signal for a particular channel. Alternatively, the
despreader may be implemented using a matched filter, such as
surface acoustic wave device, having an impulse function matched to
the chipping sequence of the received spread-spectrum signal for
the particular channel. Product detectors, mixers, digital signal
processors and SAW devices for despreading spread-spectrum signal
are well known in the art.
[0057] The controller means changes the plurality of delays of the
delay means, in response to the plurality of despread signals. The
controlling means, as illustrated in FIG. 4, is embodied as a
plurality of control circuitry 141, 142, . . . , 143. The
controlling means outputs a plurality of comparison signals to the
plurality of delay devices 121, 122, . . . , 123.
[0058] The controlling means may include generating means, storing
means, and comparing means. The generating means can generate a
plurality of magnitude values from the plurality of despread
signals. The storing means stores a plurality of previous-magnitude
values and a plurality of present-magnitude values generated by the
generating means. The comparing means compares the plurality of
previous-magnitude values with the plurality of present-magnitude
values, and outputs a plurality of comparison signals. An
embodiment of the generating means storing means and comparing
means is illustrated in FIG. 3.
[0059] In response to the plurality of comparison signals, the
delay means changes the plurality of delays, respectively. FIG. 4
broadly illustrates how the control circuitry 141, 142, 143 is
coupled to the delay device 121, 122, . . . , 123, respectively. As
apparent to one skilled to the art, the control circuitry shown in
FIG. 4 may be implemented using circuitry in FIG. 3 for each spread
spectrum channel.
[0060] FIG. 5 illustrates an alternative embodiment, with a signal
delay device 13 coupled to the antenna 11. Also shown is an RF/IF
amplifier 21 coupled through the delay device 13 to the antenna 11,
and an RF/IF amplifier 22 coupled to the antenna 12. In FIG. 5 each
spread spectrum channel, defined by chipping sequences g.sub.1(t),
g.sub.2(t), . . . , g.sub.k(t), is despread by the plurality of
despreaders 151, 152, . . . , 153 for the plurality of
spread-spectrum channels. Similarly, the plurality of phased
versions of the plurality of spread-spectrum channels are despread
by the plurality of despreaders 161, 162, . . . , 163, using
chipping sequences g.sub.1(t), g.sub.2(t), . . . , g.sub.k(t).
[0061] The delay device 13 delays the plurality of spread-spectrum
signals with respect to the received plurality of phased versions
of the plurality of spread-spectrum signals by a delay, thereby
generating the plurality of delayed signals. The combiner 153
combines the plurality of delayed signals and the plurality of
phased versions of the spread-spectrum signals as a combined
signal. In response to the combined signal, the control circuitry
166 changes the delay of the delay device 13.
[0062] In use, the phased array spread-spectrum system and method
may be used at a base station or a remote unit. A spread-spectrum
signal being received by the phased array spread spectrum system
and method is received by the first antenna 11 and the second
antenna 12, processed by the first and second RF/IF sections 21,
22, and converted to a digital form by first analog-to-digital
converter 23 and second analog-to-digital converter 24. Preferably,
digital signal processing is used and may be embodied in an
application-specific integrated circuit (ASIC). The digitized
spread-spectrum signal from the first analog-to-digital converter
23 is preferably delayed with respect to the digitized phased
version of the spread-spectrum signal from the second
analog-to-digital converter 24. The first digital-delay device 27
is adjusted by an up/down counter 35 until the phase and/or time
delay between the digitized spread-spectrum signal, and the
digitized phased version of the spread-spectrum signal, are more
closely aligned. The alignment accrues due to the variations of the
up/down counter 35 in response to comparisons by the comparator 34
of a present-magnitude value and a previous-magnitude value stored
in register 33.
[0063] Thus, the spread-spectrum signal and a phased version of the
spread-spectrum signal are received, processed to an intermediate
frequency or base band, and digitized. In-phase and
quadrature-phase components are used and delayed and added. The
resulting in-phase component and quadrature-phase component are
then despread. The magnitude of the despread spread-spectrum signal
is then taken; this represents the power or signal strength of the
desired signal. The present-magnitude value and the
previous-magnitude value are input to the shift register 33 and
compared by the comparator 34. The comparator 34 tells the up/down
counter 35 to count as an increase or decrease, i.e., up or down,
thereby controlling the delay. Thus, an increase in count might
increase the delay, whereas a decrease in count would decrease the
delay. Various control algorithms may be used with the up/down
counter 35, for more efficiency.
[0064] The phased array spread-spectrum system steers an antenna
beam formed by the first antenna 11 and the second antenna 12 in
the direction of the strongest multipath. This function can be
performed continually, so as to be continually looking for the
optimal multipath. This beam steering can be done at a base station
and at a handset, i.e, a remote subscriber unit.
[0065] It will be apparent to those skilled in the art that various
modifications can be made to the base station phased
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