U.S. patent application number 12/121826 was filed with the patent office on 2008-11-20 for spread spectrum communication method and system using diversity correlation and multi-user detection.
This patent application is currently assigned to Lot 41 Acquisition Foundation, LLC.. Invention is credited to STEVE J. SHATTIL.
Application Number | 20080285631 12/121826 |
Document ID | / |
Family ID | 26890234 |
Filed Date | 2008-11-20 |
United States Patent
Application |
20080285631 |
Kind Code |
A1 |
SHATTIL; STEVE J. |
November 20, 2008 |
SPREAD SPECTRUM COMMUNICATION METHOD AND SYSTEM USING DIVERSITY
CORRELATION AND MULTI-USER DETECTION
Abstract
A communication system transmits and receives a plurality of
spread-spectrum signals having differences in at least one
diversity parameter. The signals are highly correlated when their
diversity parameters are similar, and the signals are uncorrelated
when at least one diversity parameter is different Any combination
of a transmitter, a receiver, and a communication channel may
diversity-encode the signals to effect differences in their
diversity parameters. A receiver diversity-decoder compensates for
differences in a diversity-parameter of at least one received
signal to make the signal highly correlated with at least one other
received signal. A correlator combines at least two of the received
signals to recover an embedded information signal. The
communication system enables the use of true-noise signals for
spreading information signals, provides simplified receiver
designs, and enables antenna arrays to spatially process
spread-spectrum signals.
Inventors: |
SHATTIL; STEVE J.; (Boulder,
CO) |
Correspondence
Address: |
CONNOLLY BOVE LODGE & HUTZ LLP
1875 EYE STREET, N.W., SUITE 1100
WASHINGTON
DC
20006
US
|
Assignee: |
Lot 41 Acquisition Foundation,
LLC.
Wilmington
DE
|
Family ID: |
26890234 |
Appl. No.: |
12/121826 |
Filed: |
May 16, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09824264 |
Apr 2, 2001 |
7391804 |
|
|
12121826 |
|
|
|
|
60194633 |
Apr 4, 2000 |
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Current U.S.
Class: |
375/148 ;
375/150; 375/343; 375/347; 375/E1.002; 375/E1.003; 375/E1.02;
375/E1.032 |
Current CPC
Class: |
H04L 27/2278 20130101;
H04L 1/0618 20130101; H04B 7/0613 20130101; H04B 2201/709709
20130101 |
Class at
Publication: |
375/148 ;
375/150; 375/343; 375/347; 375/E01.002; 375/E01.003;
375/E01.02 |
International
Class: |
H04B 1/00 20060101
H04B001/00; H04B 1/69 20060101 H04B001/69; H04B 1/707 20060101
H04B001/707 |
Claims
1.-13. (canceled)
14. A method of extracting information signals from a plurality of
received spread-spectrum signals, the method comprising: receiving
the spread-spectrum signals, at least one of the spread-spectrum
signals being a diversity-encoded spread-spectrum signal, decoding
at least one of the diversity-encoded spread-spectrum signals to
obtain a decoded signal, and correlating the decoded signal with at
least one of the spread-spectrum signals to produce a correlation
signal that is indicative of information encoded in the
spread-spectrum signals.
15. A method of extracting information signals from a plurality of
received spread-spectrum signals, the method comprising: receiving
the spread-spectrum signals and at least one spectrum-decoding
signal, at least one of the spread-spectrum signals or the
spectrum-decoding signal being a diversity-encoded spread-spectrum
signal, decoding at least one of the diversity-encoded signals to
provide at least one diversity-decoded signal, and correlating the
diversity-decoded signal with at least one of the spread-spectrum
signals or the spectrum-decoding signal to produce a correlation
signal that is indicative of information encoded in the
spread-spectrum signals.
16.-17. (canceled)
18. A spread-spectrum receiver for extracting an information signal
from a plurality of spectrum-coded, diversity-coded signals, the
receiver comprising: a receiving system to receive the
spectrum-coded, diversity-coded signals, a diversity processor
coupled to the receiving system to diversity decode at least one of
the received signals to provide a plurality of signals that are
highly correlated, and a signal combiner coupled to the diversity
processor or otherwise combine the plurality of highly correlated
signals to generate a correlation signal indicative of the
information signal.
19. A spread-spectrum receiver for extracting an information signal
from at least one spectrum-coded, diversity-coded signal, the
receiver comprising: a receiving system to receive the at least one
spectrum-coded, diversity-coded signal and to receive at least one
despreading signal, the received despreading signal being separable
from the at least one spectrum-coded signal, a diversity processor
coupled to the receiving system to diversity decode at least one of
the received signals to generate a plurality of signals that are
highly correlated, and a signal combiner coupled to the diversity
processor or otherwise combine the plurality of highly correlated
signals to generate a correlation signal indicative of the
information signal.
20. The method according to claim 15, wherein said
spectrum-decoding signal is received distinctly from the
spread-spectrum signals.
21. The receiver according to claim 19, wherein said despreading
signal is received distinctly from the at least one spectrum-coded,
diversity-coded signal.
22. The receiver according to claim 18, wherein said receiving
system comprises an array of receiving elements.
23. The receiver according to claim 19, wherein said receiving
system comprises an array of receiving elements.
24. The receiver according to claim 18, wherein said signal
combiner comprises a multi-user detector.
25. The receiver according to claim 24, wherein said multi-user
detector comprises a weight-and-sum canceller.
26. The receiver according to claim 19, wherein said signal
combiner comprises a multi-user detector.
27. The receiver according to claim 26, wherein said multi-user
detector comprises a weight-and-sum canceller.
28. The method according to claim 14, wherein said correlating
comprises performing multi-user detection.
29. The method according to claim 28, wherein said multi-user
detection comprises weight-and-sum cancellation.
30. The method according to claim 14, further comprising:
generating a set of weighting factors to be used in said
combining.
31. The method according to claim 30, wherein said generating a set
of weighting factors is performed based on a received training
sequence of reference symbols.
32. The method according to claim 15, wherein said correlating
comprises performing multi-user detection.
33. The method according to claim 30, wherein said multi-user
detection comprises weight-and-sum cancellation.
34. The method according to claim 15, further comprising:
generating a set of weighting factors to be used in said
combining.
35. The method according to claim 34, wherein said generating a set
of weighting factors is performed based on a received training
sequence of reference symbols.
Description
CROSS-SECTION TO RELATED APPLICATIONS
[0001] This application is a divisional application of U.S.
Application No. 09/824,264, filed Apr. 2, 2001, which is a
continuation application of U.S. Provisional Patent Application No.
60/194,633, filed Apr. 4, 2000
FIELD OF THE INVENTION
[0002] The present invention relates to spread-spectrum
communication and radar systems. More specifically, the present
invention relates to a spread-spectrum communication system that
uses a diversity-processing system, such as an antenna array.
BACKGROUND OF THE INVENTION
[0003] In a spread-spectrum communication system, the transmitted
signal bandwidth is much greater than the bandwidth or rate of
information being sent. Also, some function other than the
information being sent is employed to provide the resulting
modulated radio-frequency (RF) bandwidth.
[0004] The desired signal is recovered by remapping the
expanded-bandwidth signal into the original information bandwidth.
In direct sequence CDMA (DS-CDMA) systems, removal or demodulation
of the spectrum-spreading modulation is accomplished by
multiplication with a local reference identical in structure and
synchronized in time with the received signal. Correlation is a
method of time-domain analysis that is particularly useful for
detecting signals buried in noise, establishing coherence between
random signals, and determining the sources of signals and their
transmission times. In DS-CDMA systems, the prime purpose of a
correlator is to match the local reference signal to a desired
incoming signal and thereby reproduce the embedded
information-bearing carrier as an output.
[0005] Frequency reuse is the process of using the same frequency
in multiple separate geographic regions for a plurality of distinct
communication links. Frequencies can be reused provided that the
regions are attenuated or isolated from each other by a minimum
value for signal rejection by user receivers in each region. U.S.
Pat. No. 4,901,307 describes the process of creating marginal
isolation, which provides an increase in frequency reuse in DS-CDMA
systems. In DS-CDMA, even small reductions in the overall power
level of the system allow for increased system capacity. One
particularly effective method for creating isolation and improving
frequency reuse is spatial division multiple access (SDMA). SDMA
applications to multiple access communication systems including
adaptive array processing are discussed in U.S. Pat. No. 5,642,353,
U.S. Pat. No. 5,592,490, U.S. Pat. No. 5,515,378, and U.S. Pat. No.
5,471,647. In addition to frequency reuse, antenna arrays also
increase processing gain and improve interference rejection.
[0006] The advantage of using adaptive antenna arrays for DS-CDMA
communications is that adaptive antenna arrays could provide
significant improvements in range extension, interference
reduction, and capacity increase. To identify a particular user, a
DS-CDMA system demodulates Walsh codes after converting the
received signal from RF to digital. Therefore, an adaptive antenna
array requires information about the user codes from CDMA radio, or
it needs to demodulate many different incoming RF signals to track
mobile users. These methods are complex processes and are more
difficult to implement than tracking users in non-CDMA systems.
Major changes in CDMA radio architecture are required to implement
adaptive array processing. These changes may be the major obstacle
for adaptive array deployment in the near future.
[0007] Phased-array antenna systems employ a plurality of
individual antennas or subarrays of antennas that are separately
excited to cumulatively produce a highly directional
electromagnetic wave. The radiated energy from each antenna element
or subarray has a different phase so that an equiphase beam front
(the cumulative wave front of electromagnetic energy radiated from
all of the antenna elements in the array) travels in a selected
direction. The difference in phase or timing between the antenna's
activating signals determines the direction in which the cumulative
wave front from all of the individual antenna elements is
transmitted. Similarly, phase analysis of received electromagnetic
energy detected by the individual array elements enables
determination of the direction from which received signals
arrive.
[0008] Beamforming, which is the adjustment of the relative phase
of the actuating signals for the individual antennas, can be
accomplished by electronically shifting the phases of the actuating
signals. Beamforming can also be performed by introducing a time
delay in the different actuating signals to sequentially excite the
antenna elements that generate the desired transmission direction.
However, phase-based electronically controlled phased-array systems
are relatively large, heavy, complex, and expensive. These
electronic systems require a large number of microwave components
(such as phase shifters, power splitters, and waveguides) to form
the antenna control system. This arrangement results in a system
that is relatively lossy, electromagnetically sensitive,
hardware-intensive, and has a narrow tunable bandwidth.
SUMMARY OF THE INVENTION
[0009] It is the principle objective of the present invention to
provide a novel and improved method and apparatus for processing
spread-spectrum signals received by an antenna array. The foregoing
is accomplished by using diversity parameters (such as
directionality, time, polarization, frequency, mode, spatial
subchannels, and phase space) to correlate a plurality of desired
signals and decorrelate interfering signals received by the
array.
[0010] Diversity parameters of received signals can be adjusted by
either or both the transmitters and the receivers. This ensures
separability of interfering signals and enables optimization of the
correlation process. A related objective of the invention is to
optimize the correlation process by adjusting either or both the
receivers and the transmitters.
[0011] Correlation processing at antenna arrays allows a small
number of antenna elements to separate a large number of unknown
signals. Long Baseline Interferometry maybe used to increase the
number of resolvable signals that can be processed by the array.
Consequently, an objective of the invention is to reduce the number
of antenna elements needed for array processing of spread-spectrum
signals.
[0012] A communication channel may be used to adjust diversity
parameters of the transmitted signals. Thus, another objective of
the invention is to exploit distortion (such as multipath effects)
in a communication channel to enhance signal quality and increase
system capacity for spread-spectrum communications. Different
communication channels, including communication channels associated
with co-located transceivers, can provide distinct variations to
diversity parameters of transmitted signals. For example, signals
may change with respect to polarization, delay spread, spatial gain
distribution, directional gain distribution, frequency-dependent
gain distribution, mode distribution, phase space, etc. These
variations can be used as unique signatures to identify signals
received from different transmitters. There are many preferred
methods, including correlation, that may be used to separate
signals transmitted by different transmitters.
[0013] The correlation process may be combined with multi-user
detection that removes interference and noise in a spread-spectrum
receiver. Multi-user detection includes cancellation and
constellation techniques that provide multiple algebraically unique
combinations of unknown signals (including desired signals,
interference, and noise). The objective of multi-user detection is
to separate interfering signals in order to optimize
signal-to-noise, signal-to-interference, or
signal-to-noise-plus-interference ratios. Thus, an objective of the
invention is to improve frequency reuse in a spread-spectrum
communication system.
[0014] Further objectives of the invention include using true noise
sources to encode information signals in a spread-spectrum
communication system and simplifying receiver designs. An
additional objective is to provide a bandwidth-efficient means of
transmitting a decoding signal along with an information-modulated
spread spectrum signal. This objective serves to simplify the
receiver design, enable the transmitter to use spreading codes and
noise-like signals that do not need to be duplicated by the
receiver, and overlay a decoding signal in the same frequency band
as its associated coded information signal.
[0015] The objectives of the present invention recited above, as
well as additional objects, are apparent in the description of the
preferred embodiments.
BRIEF DESCRIPTION OF TUE DRAWINGS
[0016] FIG. 1 shows a spread-spectrum receiver system of the
present invention that uses an antenna array and a correlator to
decode received spread-spectrum signals.
[0017] FIG. 2 is a plot of a carrier beam pattern and a correlation
beam pattern of a receiver array.
[0018] FIG. 3A is a plot of an amplitude-versus-time profile of a
narrowband signal arriving at a receiver in a multipath
environment.
[0019] FIG. 3B is a plot of a delay profile of a signal arriving at
a receiver in a multipath environment.
[0020] FIG. 4A shows two decorrelated direct-sequence signals
arriving from an angle .theta..sub.i relative to an array having
two spatially separated receivers.
[0021] FIG. 4B shows two decorrelated noise signals arriving from
an angle .theta..sub.i relative to an array having two spatially
separated receivers.
[0022] FIG. 5A is a functional diagram of a multi-input correlator
system of the present invention.
[0023] FIG. 5B is a functional diagram of a multi-input correlator
system of the present invention.
[0024] FIG. 5C is a functional diagram of a multi-input correlator
system of the present invention.
[0025] FIG. 5D is a functional diagram of a single-input correlator
system of the present invention.
[0026] FIG. 5E is a functional diagram of a multi-input correlator
system of the present invention.
[0027] FIG. 5F is a functional diagram of a single-input correlator
system of the present invention.
[0028] FIG. 6 shows a relative time-domain representation of two
time-offset signal samples that each includes a plurality of
multipath components of a spread-spectrum signal.
[0029] FIG. 7A shows signal levels and noise levels measured at the
output of a correlator having a first time offset.
[0030] FIG. 7B is a plot of signal levels and noise levels measured
at the output of a correlator having a second time offset.
[0031] FIG. 8 is a process diagram that shows the operation of a
three-input weight-and-sum canceller used for multi-user
detection.
[0032] FIG. 9A shows a spread-spectrum communication system of the
present invention that uses multipath to produce multiple
time-offset versions of a transmitted signal.
[0033] FIG. 9B shows a spread-spectrum communication system of the
present invention in which a transmitter produces multiple
time-offset versions of a transmitted signal.
[0034] FIG. 9C shows a spread-spectrum communication system of the
present invention in which a receiver array generates multiple
time-offset versions of a received signal.
[0035] FIG. 9D shows a spread-spectrum communication system in
which a transmitter array generates multiple time-offset versions
of a transmitted signal.
[0036] FIG. 9E shows a spread-spectrum communication system of the
present invention that includes transmitter and receiver
arrays.
[0037] FIG. 10A shows a spread-spectrum communication system that
transmits a despreading signal having a time offset from a
transmitted spread-spectrum signal.
[0038] FIG. 10B shows a spread-spectrum communication system that
transmits a despreading signal having a different diversity
parameter from a transmitted spread-spectrum signal.
[0039] FIG. 10C shows a spread-spectrum communication system that
transmits a despreading signal from a separate transmitting
element.
[0040] FIG. 10D shows a spread-spectrum communication system that
transmits a duplicate spread-spectrum signal having at least one
diversity parameter with a unique value.
[0041] FIG. 10E shows a spread-spectrum communication system that
transmits a duplicate spread-spectrum signal from a separate
transmitting element. The transmitted signals may have different
values of at least one diversity parameter.
[0042] FIG. 11 shows a receiver having a correlation system and a
multi-user detector.
[0043] FIG. 12A shows a single-input correlator that includes at
least one diversity processor.
[0044] FIG. 12B shows a multiple-input correlator that includes at
least one diversity processor.
[0045] FIG. 13 shows a spread-spectrum receiver of the present
invention that includes a correlator processor.
[0046] FIG. 14A is a process diagram of a transmission method of
the invention.
[0047] FIG. 14B shows steps of an alternative transmission method
of the invention.
[0048] FIG. 14C is a process diagram of steps that may follow the
transmission methods shown in FIG. 14A and FIG. 14B.
[0049] FIG. 15A shows steps of a process diagram for receiving
spread-spectrum signals.
[0050] FIG. 15B is a process diagram for an alternative reception
technique.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0051] FIG. 1 shows a spread-spectrum receiver system of the
present invention. An array 140 including at least two receivers
140.1 and 140.N receives a plurality of signals s.sub.n(t) from a
plurality of directions of arrival, such as directions 61, 62, and
63, in a communication channel (not shown). Different directions
(such as directions 61, 62, and 63) of arrival result in a
plurality of different signal delays .DELTA.t.sub.i occurring
between signals received by the two receivers 140.1 and 140.N.
Signal responses of the receivers 140.1 and 140.N are output at one
or more receiver outputs, such as outputs 160.1 and 160.N. The
receiver-output signals are coupled into a plurality of correlators
161, 162, and 163. The output of each correlator 161, 162, and 163
is coupled to a multi-user detector 103.
[0052] Three transmitted signals s.sub.1(t), s.sub.2(t), and
s.sub.3(t) arrive at the array 140 from the directions 61, 62, and
63, respectively. This simple case is shown for the purpose of
facilitating an understanding of the function of the
spread-spectrum receiver array. It will be appreciated that this
understanding may be extended to more complex cases involving
multipath components, distortions, noise, and large numbers of
desired and/or interfering signals. The signals s.sub.1(t),
s.sub.2(t), and s.sub.3(t) are assumed to be spread-spectrum
signals, defined herein to mean any signal having a processing gain
that exceeds one. It is preferable that the signals s.sub.1(t),
s.sub.2(t), and s.sub.3(t) have high autocorrelation-to-cross
correlation ratios (i.e., the signals are highly correlated with
synchronized versions of themselves and substantially uncorrelated
with other signals). It is preferable that the signals s.sub.1(t),
s.sub.2(t), and s.sub.3(t) be substantially uncorrelated with
unsynchronized versions of themselves.
[0053] The angle of arrival 61, 62, and 63 of each signal
s.sub.1(t), s.sub.2(t), and s.sub.3(t), respectively, and the
separation between the receivers 140.1 and 140.N determines the
relative delay .DELTA.t.sub.i of the signals entering the
correlators 161, 162, and 163. If the relative delay .DELTA.t.sub.i
between samples of a particular signal s.sub.n(t) is less than the
inverse of the signal bandwidth, the samples of the signal
s.sub.n(t) from each receiver 140.1 and 140.N will be correlated.
Additional delays may be provided by either or both receivers 140.1
and 140.N, or by the correlators 161, 162, and/or 163 to adjust the
correlations of the received signals.
[0054] FIG. 2 shows a carrier beam pattern 40 and a correlation
beam pattern 50 of an array 140 of receivers (or transmitters). The
beam patterns 40 and 50 represent reception sensitivity or
transmission-signal magnitude with respect to angular direction
relative to the array 140. The carrier beam pattern 40 has a main
beam 41, a plurality of sidelobes (such as sidelobe 42), and
possibly, secondary main lobes (such as secondary main lobe 43).
The correlation beam pattern 50 has a main beam 51 resulting from a
correlation peak. The correlation beam pattern 50 does not have
sidelobes, but it may have minor correlation peaks (not shown).
[0055] Carrier beam patterns are well known in the prior art. The
main beam 41 results from a coherent combining of signals received
by receivers in the array 140. Sidelobes result from minor
coherencies between received signals. Secondary main lobes (such as
secondary main lobe 43) can result from a coherent combining of
received signals from array elements that are separated by a large
distance.
[0056] Correlation beam patterns (such as beam pattern 50) result
from variations of relative delay with respect to angle of arrival
and/or angle of transmission. Ideally, the correlation beam pattern
50 will not have secondary main lobes for a particular
spread-spectrum signal s.sub.n(t), no matter how far the receivers
are separated, because the signal s.sub.n(t) is uncorrelated for
relative delay magnitudes in excess of the signal's s.sub.n(t)
inverse bandwidth.
[0057] The main-beam width of the correlation beam pattern 50 is
much larger than the main-beam width of the carrier beam pattern 40
shown in FIG. 2 because the carrier frequency is typically much
larger than the signal bandwidth. Reducing the beam width of the
correlation beam pattern 50 can be done by increasing the signal
s.sub.n(t) bandwidth or by increasing the separation between
receivers in the array 140. Methods of Long Baseline Interferometry
(LBI) or Very Long Baseline Interferometry (VLBI) are appropriate
methods for carrying out methods of the present invention.
[0058] In some cases, it may be advantageous to remove the carriers
from each received signal before correlation. Removing the carriers
or otherwise compensating for the carrier beam pattern can reduce
the effect that coherencies between the carriers may have on
correlation.
[0059] FIG. 3A shows an amplitude-versus-time profile 132 of a
narrowband component of a signal s.sub.n(t) arriving at a receiver
(not shown). In a multipath environment, a narrowband signal's
intensity changes with respect to time due to flat fading. Delays
between multipath components may be determined by processing one or
more narrowband components. Simple amplitude-versus-time analysis
may be used over one or more narrowband components, or over a
wideband signal. A Fourier-type of analysis may also be used to
determine a delay profile, such as the delay profile shown in FIG.
3B.
[0060] FIG. 4A shows a direct-sequence signal s.sub.n(t) arriving
at an angle .theta..sub.i relative to an array 140 having two
receivers 140.1 and 140.N separated by a distance d. The
path-length difference between the signal s.sub.n(t) arriving at
each of the receivers 140.1 and 140.N is D.sub.i=d sin
.theta..sub.i. The relative delay is .DELTA.t.sub.i=D.sub.i/c,
where c is the speed of electromagnetic radiation in the medium in
which the array 140 is located. In this case, the delay
.DELTA.t.sub.i exceeds the chip rate of the direct-sequence code in
signal s.sub.n(t). Thus an applied delay of .DELTA.t.sub.i (which
may be achieved by an additional effective path length D.sub.i)
applied at receiver 140.1 will enable correlation of the signal
s.sub.n(t) received by the receivers 140.1 and 140.N. It will be
appreciated that information may be modulated onto one or more of
the received direct-sequence signal s.sub.n(t).
[0061] FIG. 4B shows a noise signal s.sub.n(t) arriving from an
angle .theta..sub.i relative to an array 140 having two receivers
140.1 and 140.N separated by a distance d. The processing method
used for compensating for a relative delay .DELTA.t.sub.i between
signals received by the receivers 140.1 and 140.N is identical to
the method described with respect to FIG. 4A. If the relative delay
.DELTA.t.sub.i is greater than the inverse of the bandwidth of the
noise signal, the received samples of the signal s.sub.n(t) will be
uncorrelated. It will be appreciated that an information signal
maybe impressed onto one or more of the noise signals
s.sub.n(t).
[0062] A notable characteristic of the receiver shown in FIG. 1 is
that it may use only two elements to separate three received
signals s.sub.1(t), s.sub.2(t), and s.sub.3(t). The number of
separable signals can be larger (in fact, much larger) than the
number of receiving elements because each correlator 161, 162, and
163 is capable of generating an algebraically unique combination of
received signals. In fact, any non-linear process may be used to
generate an algebraically unique combination of received signals.
In the present case, the signals s.sub.1(t), s.sub.2(t), and ss(t)
are separable because different relative delays .DELTA.t.sub.i are
used to characterize each signal s.sub.n(t). These relative delays
.DELTA.t.sub.i are associated with different angles of arrival
(such as 61, 62, and 63 shown in FIG. 1). The relative delays
.DELTA.t.sub.i may be associated with multipath phenomena that
cause multiple reflections of a given signal s.sub.n(t) to arrive
at a receiver at different times. Thus, a single receiver element
may be used instead of a receiver array to separate multiple
received signals and/or remove interference (and/or noise) from at
least one desired signal s.sub.n(t).
[0063] FIG. 5A is a functional diagram of a correlator system (such
as correlators 161, 162, and/or 163) that may be used in the
receiver shown in FIG. 1. Correlator inputs are coupled to the
receiver outputs 160.1 and 160.N. A weighting system 164 is capable
of applying a complex weight to signals received from a receiver
output, such as receiver output 160.1. One possible implementation
of the weighting system 164 is shown in a functional diagram of a
correlator depicted in FIG. 5B. The weighting system 164 may
include a delay device 165 that is capable of providing at least
one relative delay .DELTA.t.sub.i between signals received from the
receiver outputs 160.1 and 160.N. A gain controller 167 is capable
of providing amplitude adjustment to at least one delay-adjusted
signal. The order in which the gain controller 167 and the delay
device 165 are placed may be reversed. A plurality of samples, some
of which may be delayed and/or gain adjusted, are combined in a
signal combiner 168 capable of correlating the input samples and
providing an output signal to an output 171.
[0064] The combiner 168 may also be referred to as a correlator. A
combiner, such as the combiner 168, may provide any of a set of
combining functions including, but not limited to, multiplication,
summation, sampling, sampling and combining, convolution,
integration, averaging, and transformation relative to any
invertable transform function.
[0065] FIGS. 5C through 5F show additional correlator designs.
Single-input correlators may be coupled to a single receiver output
(such as receiver output 160.1), or to multiple receiver outputs
(such as receiver outputs 160.1 to 160.N). Each of a pair of signal
samples may be delayed by a different value of delay .DELTA.t.sub.i
before correlation. Different delays .DELTA.t.sub.i may be used to
obtain multiple correlations of one or more signals. Different
delays .DELTA.t.sub.i may also be used to obtain different signals
having optimum correlation at particular delays .DELTA.t.sub.i.
Correlation may include multiplying or otherwise combining more
than two signal samples.
[0066] FIG. 6 shows a relative time-domain representation of two
samples of a received signal s.sub.n(t) and its multipath
components. Two samples are obtained for three delayed versions of
a received signal s.sub.n(t). A first sample of received signals
includes three multipath components 71, 72, and 73. Components 72
and 73 have relative delays of .DELTA.t.sub.1 and .DELTA.t.sub.3,
respectively. A second sample of received signals also includes
three multipath components 81, 82, and 83. Components 82 and 83
also have relative delays of
.DELTA.t.sub.2-.DELTA.t.sub.1=.DELTA.t.sub.1 and
.DELTA.t.sub.4-.DELTA.t.sub.1=.DELTA.t.sub.3, respectively. The
samples may be taken from separate receivers or one or more samples
may be split (or otherwise replicated) from the first sample taken
from a receiver.
[0067] The second sample is time-shifted by an amount of
.DELTA.t.sub.1 so that component 72 lines up with component 81.
This will cause components 72 and 81 to be correlated, whereas the
other components will all be substantially uncorrelated.
[0068] The output of each correlator 161, 162, and 163 is coupled
to the multi-user detector 103 shown in FIG. 1. Either the
correlators 161, 162, and 163 and/or the multi-user detector 103
may include a sampler (not shown) that samples the correlator
output over a predetermined time interval, such as the period of
any information signal embedded in the signal s.sub.n(t). A
decision system (not shown) may be employed to interpret or
otherwise process signals output by the sampler (not shown).
[0069] Noise at a correlator's output originates from several
sources:
1. Environment and circuit noise. 2. Undesired signals. 3. Desired
signals having time offsets. Noise output due to environment and
circuit noise is typically negligible compared to noise due to
undesired signals (such as jamming and other interference). Before
synchronization, or during imperfect synchronization, a part of the
desired signal is output as noise. The amount of output noise
depends on the degree of synchronization. When there is no
synchronization (the reference and target signals are more than one
code chip apart, or they are separated by more than the inverse
bandwidth of a true noise or other wideband signal), the output
produced is all noise.
[0070] FIG. 7A shows signal levels and noise levels measured at the
output of a correlator. A desired signal level 75A results from the
correlation of the time-shifted components 72 and 81 shown in FIG.
6. A noise level 85A results from desired signal components that
are not correlated, such as from mixing signal 71 with signals 81,
82, and 83, signal 72 with signals 82 and 83, and signal 73 with
signals 81, 82, and 83. A noise level 95A results from undesired
signals. As the noise levels (such as noise levels 85A and 95A)
increase, the determination of desired signal values in a
measurement comprising a superposition of noise and desired signal
values becomes uncertain.
[0071] The ratio of the desired signal level 75A (correlated
desired signal components) to the noise level 85A resulting from
uncorrelated desired signal components depends on the delay
.DELTA.t.sub.i applied to the signal components shown in FIG. 6.
For example, the signal levels shown in FIG. 7A may correspond to
noise and desired signal levels when the second sample is
time-shifted by an amount of .DELTA.t.sub.1 so that component 72
lines up with component 81. FIG. 7B shows different signal and
noise levels that occur when the second sample is time-shifted by
an amount of .DELTA.t.sub.3, which causes component 73 to line up
with component 81.
[0072] Two algebraically unique equations of a desired signal's
level (represented by 75A and 75B) and uncorrelated desired signal
components (represented by 85A and 85B) may be adequate to
substantially separate uncorrelated desired signal components from
the desired signal's level. A third correlation process using a
different relative delay .DELTA.t.sub.i between samples may provide
a third algebraically unique equation, which could be useful in
removing noise due to cross correlations of undesired signals.
[0073] Interference at a correlator's output originates from
several sources: [0074] 1. Other correlations of multipath
components of the desired signal. [0075] 2. Correlations of
undesired signals.
[0076] The desired signal may have multiple correlations for a
given relative delay .DELTA.t.sub.i. Interference due to
time-shifted versions of the desired signal can cause distortion
and intersymbol interference of the desired correlation. Multiple
correlations of signals having different delays .DELTA.t.sub.i can
provide algebraically unique combinations of interfering signals.
Thus, a multi-user detector (such as the multi-user detector 103
shown in FIG. 1) can separate interfering signals by various
techniques including cancellation and constellation methods.
[0077] FIG. 8 illustrates the operation of a three-input
weight-and-sum canceller 103 used for multi-user detection. Three
inputs 201, 202, and 203 receive signals y.sub.1(t), y.sub.2(t),
and y.sub.3(t) that have transmit components s.sub.1(t),
s.sub.2(t), and s.sub.3(t) from three correlator outputs, such as
the correlators 161, 162, and 163 shown in FIG. 1.
y.sub.1(t)=.beta..sub.11s.sub.1(t)+.beta..sub.12s.sub.2(t)+.beta..sub.13-
s.sub.3(t)+n.sub.1
y.sub.2(t)=.beta..sub.21s.sub.1(t)+.beta..sub.22s.sub.2(t)+.beta..sub.23-
s.sub.3(t)+n.sub.2
y.sub.3(t)=.beta..sub.31s.sub.1(t)+.beta..sub.32s.sub.2(t)+.beta..sub.33-
s.sub.3(t)+n.sub.3
where n.sub.1, n.sub.2, and n.sub.3 are noise signals and
.beta..sub.mn are complex proportionality terms similar to spatial
gain terms described in U.S. Pat. No. 6,008,760, which is hereby
incorporated by reference.
[0078] The proportions of the proportionality terms .beta..sub.mn
of the components s.sub.n(t) must differ such that the equations
for y.sub.m(t) are unique for all m. For m=1,2,3, this provides
three equations with three unknowns. Each solution of the three
equations provides an estimate of one of the signal components
s.sub.1(t), s.sub.2(t), and s.sub.3(t) at an output 251, 252, and
253.
[0079] Each input signal y.sub.m(t) is sampled twice or split into
two samples. One of the y.sub.1(t) samples goes through a first
weighting process 211 where the signal y.sub.1(t) remains
unchanged. The weighting processes are illustrated as amplifiers to
indicate that a buffering process occurs when signals are weighted.
Signals added to the output of a buffer do not affect the value of
signals input to the buffer. The signal y.sub.1(t) is then combined
with a weighted version of component y.sub.2(t) that receives a
weight of -g.sub.12 from a weighting element 213. The signals
y.sub.1(t) and -g.sub.12y.sub.2(t) are summed to produce signal
y.sub.12(t). The second sample of y.sub.1(t) goes through a second
weighting process 212 where it is changed by gain -g.sub.31. This
weighted signal is combined with an unweighted version of signal
y.sub.3(t) that is processed with unity gain 215 to produce signal
y.sub.31(t). An unweighted version of signal y.sub.2(t) is output
after a unity gain buffer 214 and is combined with a weighted
version of signal y.sub.3(t) to produce signal y.sub.23(t). The
signal y.sub.3(t) receives a weight of -g.sub.23 from a weighting
process 216.
[0080] An unweighted version of signal y.sub.12(t) passes through a
buffering process 231 and is combined with a -g.sub.41 weighted
version of signal y.sub.31(t) that is acted on by a weighting
process 232. The resulting signal is y.sub.41(t). A second version
of signal y.sub.12(t) acquires a weight of -g.sub.42 in a weighting
process 233 before being combined with signal y.sub.23(t), which
passes through a buffering process 234. This produces signal
y.sub.42(t). Signal y.sub.42(t) passes through a buffering process
244 and is combined with a weighted version of y.sub.31(t) to
provide an estimated signal s'.sub.2(t) at the output 252. The
signal y.sub.31(t) has a weight of -g.sub.52 applied by a weighting
process 243. An estimated signal s'.sub.1(t) at output 251 results
from the summation of signal y.sub.41(t) with a version of signal
y.sub.23(t), which has a weight of -g.sub.51 applied by a weighting
process 242. The signal y.sub.41(t) is unchanged as it passes
through a buffering process 241. The combining of unweighted signal
y.sub.31(t) with a weighted signal y.sub.42(t) produces an
estimated signal s'.sub.31(t) at output 253. The unweighted signal
y.sub.31(t) is buffered by a process 246, and signal y.sub.42(t) is
multiplied by a weight value of -g.sub.53 during a weighting
process 245.
[0081] The estimated signal values are given by the following
equations:
s 1 ' ( t ) = ( .beta. 11 - .beta. 21 g 12 - ( .beta. 31 - g 31
.beta. 11 ) g 41 - ( .beta. 21 - .beta. 31 g 23 ) g 51 ) s 1 ( t )
+ ( .beta. 12 - .beta. 22 g 12 - ( .beta. 32 - g 31 .beta. 12 ) g
41 - ( .beta. 22 - .beta. 32 g 23 ) g 51 ) s 2 ( t ) + ( .beta. 13
- .beta. 23 g 12 - ( .beta. 33 - g 31 .beta. 13 ) g 41 - ( .beta.
23 - .beta. 33 g 23 ) g 51 ) s 3 ( t ) ##EQU00001## s 2 ' ( t ) = (
( .beta. 21 - g 31 .beta. 31 ) - ( .beta. 11 - .beta. 21 g 12 ) g
42 - ( .beta. 31 - .beta. 11 g 31 ) g 52 ) s 1 ( t ) + ( ( .beta.
22 - g 31 .beta. 32 ) - ( .beta. 12 - .beta. 22 g 12 ) g 42 - (
.beta. 32 - .beta. 12 g 31 ) g 52 ) s 2 ( t ) + ( ( .beta. 23 - g
23 .beta. 33 ) - ( .beta. 13 - .beta. 23 g 12 ) g 42 - ( .beta. 33
- .beta. 13 g 31 ) g 52 ) s 3 ( t ) ##EQU00001.2## s 3 ' ( t ) = (
.beta. 31 - .beta. 11 g 31 - ( ( .beta. 21 - g 23 .beta. 31 ) - (
.beta. 21 - .beta. 31 g 23 ) g 42 ) g 53 ) s 1 ( t ) + ( .beta. 32
- .beta. 12 g 31 - ( ( .beta. 22 - g 23 .beta. 32 ) - ( .beta. 22 -
.beta. 32 g 23 ) g 42 ) g 53 ) s 2 ( t ) + ( .beta. 33 - .beta. 13
g 31 - ( ( .beta. 23 - g 23 .beta. 33 ) - ( .beta. 23 - .beta. 33 g
23 ) g 42 ) g 53 ) s 3 ( t ) ##EQU00001.3##
If the weights g.sub.ij are selected to completely cancel
interfering signals, the interference components s.sub.p(t) (where
p.noteq.k) of each estimated signal s'.sub.k(t) are zero. In this
case, all weights g.sub.ij are functions of proportionality terms
.beta..sub.mn. In order to minimize the sum of interference and
noise contributions to the estimated signals s'.sub.k(t), it is
desirable to adjust the weights g.sub.ij used in the spatial
demultiplexer 206. Thus, a small amount of interference may be
added to the signals s'.sub.k(t) in order to reduce the total noise
plus interference.
[0082] Assuming that noise levels for each input signal y.sub.m(t)
are the same (and defined as no), corresponding values of noise
n.sub.k in the estimated signals s'.sub.k(t) are related to the
absolute values of the weights used in the spatial demultiplexer
206. This is shown by the following equations:
n.sub.1=((1+|g.sub.12|)+(1+|g.sub.31|)|g.sub.41|+(1+|g.sub.12|)|g.sub.51-
|)n.sub.0
n.sub.2=((1+|g.sub.23|)+(1+|g.sub.21|)g.sub.42+(1+|g.sub.31)|g.sub.52|)n-
.sub.0
n.sub.3=((1+|g.sub.31|)+((1+|g.sub.23|)+(1+|g.sub.12|)|g.sub.42|)|g.sub.-
53|)n.sub.0
[0083] A training sequence may be used to establish the values of
the weights g.sub.ij. A training sequence involves sending known
reference signals such that the spatial gain characteristics of
each received signal can be determined. This may be accomplished by
sending a reference signal at a predetermined time or after
interrogation or by sending a reference signal on a different
communication channel (such as a frequency channel or a CDMA code
channel). The rate of change of the proportionality terms may be
determined from the reference signals and then used to adapt the
weights to compensate for predicted changes in the proportionality
terms. The weights may also be determined by estimation methods in
addition to or in place of reference signals.
[0084] Other cancellation methods may be used in addition to or in
place of the method described. One such method involves taking the
inverse of the matrix .beta..sub.mn that describes the
proportionality terms of the received signals y.sub.m(t) and then
applying the inverse to the received signals y.sub.m(t). Another
technique for diagonalizing the matrix .beta..sub.mn is known as
Cramer's method. These techniques, as well as others, may be used
together. Different cancellation methods often provide the best
signal reception for different received spatial gain
distributions.
[0085] The multi-user detector 103 can be used to remove both noise
and interference. Parameters of the multi-user detector 103 may be
controlled in order to optimize any signal-quality measurement,
such as signal to noise, signal to interference, and signal to
noise plus interference. Control of the correlators may also be
provided to optimize any signal-quality parameter.
[0086] FIG. 9A shows a spread-spectrum communication system of the
present invention. A spread-spectrum transmission system includes
an information-signal source 90, a wideband-signal source 92, a
modulator 94, and a transmitter 99. The modulator 94 is coupled to
the information-signal source 90 and the wideband-signal source 92
for modulating or otherwise coupling an information signal onto a
wideband signal to provide spreading of the information signal.
Modulation may also involve modulating signals onto one or more
carrier signals. Modulation may be accomplished by adding the
information to the spectrum-spreading code before it is used as
spreading modulation. Alternatively, information may be used to
modulate a carrier before spreading it. This type of modulation can
be accomplished by some form of angle modulation. The wideband
signal may be any type of coded or true noise signal. The
spread-spectrum information signal is coupled into a communication
channel by the transmitter 99. The transmitter 99 may include
signal-processing circuits (not shown), such as amplifiers (not
shown) and filters (not shown).
[0087] Transmitted signals propagate through the channel and arrive
at a receiver 140 after reflecting off of one or more objects, such
as object 177. Thus, the receiver 140 receives a plurality of
time-shifted versions of the transmitted signal. The received
signals are coupled to a correlator processor 169, which may
include a plurality of correlators (not shown). The correlator
processor 169 splits (or otherwise duplicates) the received signals
for providing a plurality of samples. The correlator processor 169
may apply at least one delay to at least one sample of the received
signals prior to correlating a plurality of the samples. A
multi-user detector 103 is coupled to the correlator processor 169
to remove noise and/or interference from the correlated
signals.
[0088] Signals transmitted by a plurality of spread-spectrum
transmission systems are separable by a receiving system of the
present invention provided that the delay profiles of the
transmitted signals arriving at the receiver system are unique for
each associated transmission system. Such uniqueness may be ensured
by spatially separating the transmission systems so each
transmitted signal experiences a unique multipath environment. The
transmission systems may each have a different directionality that
causes the signals transmitted by each system to experience a
different multipath environment. Thus, multiple transmission
systems may be co-located but have different directionality to
ensure separability of signals received by a receiver.
[0089] FIG. 9B shows a spread-spectrum communication system having
similar components to the system shown in FIG. 9A. The transmitter
99 generates multiple time-offset versions of the spread
information signal. Thus, multipath effects are not necessary for
providing time offsets to the transmitted signals. Delay
characteristics of received signals may be adjusted by the
transmitter to ensure unique delay profiles and/or otherwise
compensate for a multipath environment. Similarly, spatial
location, transmitter directionality, and/or receiver
directionality may be adjusted to compensate for a particular
multipath environment and/or ensure that delay profiles of signals
received by a receiver are unique.
[0090] The transmitter 99 may transmit a correlation signal or any
type of despreading code that is time-offset from the transmitted
spread-spectrum information signal. A correlation signal or
despreading code includes any signals that may be used by a
receiver to decode, decrypt, or otherwise extract an information
signal from a received signal. For example, the transmitter 99 may
be coupled to the wideband-signal source 92, which may input one or
more wideband signals that are time offset from the spread-spectrum
information signal. The transmitted wideband signal may be received
and correlated with the transmitted spread-spectrum information
signal to recover the information signal.
[0091] FIG. 9C shows a spread-spectrum communication system having
an array of receivers 140.1 to 140.N coupled to the communication
channel. The receivers 140.1 to 140.N may be uniformly spaced or
non-uniformly spaced. Other components in the system are similar to
the components shown in FIG. 9A. The array of receivers 140.1 to
140.N provide an effective multipath to received signals. The angle
of arrival of the received signals determines the delay profile of
the signals received by the receivers 140.1 to 140.N.
[0092] In FIG. 9D, a plurality of transmitters 99.1 to 99.N
provides an effective multipath delay profile to signals received
by a single receiver 140. In FIG. 9E, an array of transmitters 99.1
to 99.N and an array of receivers 140.1 to 140.N are used to
provide and/or enhance delay profiles of signals that are
transmitted and received by the spread-spectrum communication
system.
[0093] FIG. 10A shows a spread-spectrum communication system that
transmits a despreading signal having a time offset .DELTA.t.sub.i
from a transmitted spread-spectrum signal. Components shown in FIG.
10A are similar to the components listed in FIG. 9B. The modulator
94 modulates an information signal s.sub.n(t) from an
information-signal source 90 onto a wideband signal generated by a
wideband-signal source 92 for providing a spread spectrum signal.
The wideband signal may be any type of coded or noise signal. The
wideband-signal source 92 and the modulator 94 are coupled to a
transmitter 99. A wideband signal from the wideband-signal source
92 is delayed by at least one delay element, such as delay element
96.1, before being coupled into the transmitter 99. The transmitter
99 couples the spread-spectrum signal and the delayed wideband
signal into a communication channel. The spread-spectrum signal may
be delayed. For example, a delay element (not shown) may be coupled
between the modulator 94 and the transmitter 99 instead of (or in
addition to) the delay element 96.1 shown in FIG. 10A. At a
receiver, at least one sample of the received transmission signal
is delayed by an amount .DELTA.t.sub.i in a correlator processor
169. The correlator processor 169 then matches the time-offset
wideband signal to a desired spread-spectrum signal and thereby
reproduces the embedded information-bearing signal as an
output.
[0094] In the transmission system shown in FIG. 10A, the modulation
technique employed is preferably a form of phase-shift key
modulation. However, any type of modulation scheme may be used,
including amplitude modulation, frequency modulation, polarization
modulation, code modulation, etc. In some applications,
differential modulation schemes are preferable. A preferred
embodiment of the invention uses a constant-modulus modulation
scheme. The modulation scheme used in the transmission systems
shown in FIG. 9A to 9E is one that preferably facilitates
discrimination between transmitted symbols after correlation. Thus,
differential amplitude modulation is one of many candidate
modulation schemes that may be used.
[0095] FIG. 10B illustrates a diversity transmitter of the present
invention having similar elements as the transmitter shown in FIG.
10A. A diversity encoder 96 adjusts at least one diversity
characteristic of a wideband signal generated by a wideband-signal
source 92. Diversity characteristics include any parameter that can
be used to differentiate or otherwise separate signals. Diversity
characteristics include, but are not limited to, polarization,
frequency, directionality, time, phase space, spatial separation,
and subspace channels. In one set of preferred embodiments, one or
more diversity parameters are adjusted in such a way as to not
increase the frequency band of the transmission.
[0096] The diversity encoder 96 may be a delay element (such as the
delay element 96.1 shown in FIG. 10A) in order to provide time
diversity to the wideband signal. The transmitter 99 may include an
array of transmission elements (not shown) and the diversity
encoder 96 may include a coupling system (not shown) that connects
the diversity encoder 96 to individual transmission elements (not
shown).
[0097] FIG. 10C illustrates a diversity transmitter of the present
invention having similar elements as the transmitter shown in FIG.
10B. The diversity encoder 96 may comprise part of a transmitter
99, particularly if the diversity encoder 96 encodes signals with
respect to spatial separation, polarization, or directionality. The
transmitter 99 includes a first transmission system 99.1 and a
second transmission system 99.2. The diversity encoder 96 is
coupled to the second transmission system 99.2.
[0098] FIG. 10D and FIG. 10E show diversity transmitters of the
present invention in which a diversity encoder 96 encodes a
spread-spectrum signal coupled out of a modulator 94. It will be
appreciated that a communication channel can provide diversity
encoding with respect to at least one diversity parameter. The
orientation of one or more diversity transmitters may be selected
to achieve one or more desirable channel-encoded diversity
characteristics.
[0099] FIG. 11 shows a receiver that correlates a plurality of
received signals and separates multi-user interference and/or noise
from the correlation signals. A correlator processor 169 has a
plurality of inputs 160.1 to 160.N coupled to a plurality of
correlators 169.1 to 169.N. Correlator 169.1 includes at least one
diversity processor, such as diversity processors 164.1 to 164.K
The diversity processors 164.1 to 164.K are coupled to a signal
combiner 168.1 that correlates or otherwise combines a plurality of
input signals. Similarly, Correlator 169.N includes at least one
diversity processor, such as diversity processors 164.L to 164.M.
The diversity processors 164.L to 164.M are coupled to a signal
combiner 168.N that correlates or otherwise combines a plurality of
input signals. The correlator processor 169 is coupled to a
multi-user detector 103.
[0100] In this case, the multi-user detector 103 is shown as a
two-input weight-and-sum canceller. A first input signal is split
or otherwise duplicated to provide two samples that are each
weighted by a weighting system 211 and 213. A second input signal
is split or otherwise duplicated to provide two samples that are
each weighted by a weighting system 212 and 214. A first weighted
sample of the first input signal is combined with a first weighted
sample of the second input signal in a first combining system 424.
A second weighted sample of the first input signal is combined with
a second weighted sample of the second input signal in a second
combining system 426, The combining systems 424 and 426 are adapted
to output signals that are substantially free from multi-user
interference.
[0101] FIG. 12A shows a correlator 169.1 that is one possible
embodiment of any of the correlators shown in FIG. 11. The
correlator 169.1 includes at least one diversity processor, such as
diversity processors 164.1 to 164.K. The diversity processors 164.1
to 164.K process input signals to create a signal output
characterized by at least one particular diversity parameter.
[0102] A diversity parameter may be any type of physical or logical
signal characteristic that enables multiple access and/or
multi-user detection. For example, the diversity parameter
exploited by the processors 164.1 to 164.K may be time, in which
case the diversity processors 164.1 to 164.K apply a time delay to
an input signal. Other diversity parameters may be exploited
instead of (or in addition to) time including, but not limited to,
frequency, polarization, directionality, spatial separation, and
phase space. It will be appreciated that a diversity processor
(such as the processors 164.1 to 164.K) may include receiving
elements (not shown). A diversity processor (such as any of the
processors 164.1 to 164.K) may provide a pass through without
adjusting the diversity properties of an input signal.
[0103] FIG. 12B shows another design for a correlator 169.1 that
includes a plurality of signal-input terminals 160.1 to 160.K.
Correlators, as well as diversity processors, may be nested to
increase the number of unique combinations of unknown signals (as
well as interference and noise). Different types of diversity
processors may also be used in combination. One function of the
diversity processors 164.1 to 164.K is to provide a plurality of
unique proportions of interfering signals (and even noise) at the
correlator outputs. This enables a multi-user detector to remove
interference, to remove noise, and/or to separate desired
signals.
[0104] FIG. 13 shows a spread-spectrum receiver of the present
invention. A receiver 140 receives a plurality of spread-spectrum
signals from a communication channel. The receiver 140 may include
a receiver array (not shown). The receiver 140 is coupled to a
correlator processor 169 that includes a diversity-processing
system 164 (such as a weighting system) including one or more
diversity processors 164.1 to 164.L. The diversity-processing
system 164 is coupled to a signal combiner 168 that combines a
plurality of processed output signals. The signal combiner 168 may
include multiple combining systems (not shown) that combine pairs
of processed output signals and/or more than two output signals at
a time. The multiple combining systems (not shown) may be nested.
The signal combiner 168 may include one or more correlators (not
shown). Output signals from a plurality of outputs 171.1 to 171.N
of the correlator processor 169 may be processed in a multi-user
detector (not shown).
[0105] The diversity processors 164.1 to 164.L may share a single
receiver system (not shown) in the receiver 140, or the receiver
140 may include multiple receiving elements (not shown) and/or
systems (not shown) that are used exclusively by each of the
diversity processors 164.1 to 164.L. A diversity processor, such as
processors 164.1 to 164.L, may comprise a receiving system (not
shown) of the receiver 140. For example, a diversity processor may
include a polarized receiver (not shown), a spatially separated
receiver (not shown), a feed to a dish antenna (not shown), one or
more detectors in a lens system (not shown), and/or an
array-processing system (not shown). A diversity processor, such as
processors 164.1 to 164.L, may include at least one polarizer (not
shown), filter (not shown), delay device (not shown), phase-shifter
(not shown), and/or spread-spectrum decoder (not shown).
[0106] FIG. 14A outlines steps of a transmission method of the
present invention. A wideband signal is produced in a
signal-generation step 170. The wideband signal maybe any type of
coded or true-noise signal. Information is coupled into the
wideband signal in a coupling step 172. An information signal may
be modulated onto the wideband signal or the information signal may
be used to generate the wideband signal to produce a
spread-spectrum signal. A duplicating step 174 creates at least one
replica of the spread-spectrum signal. For example, the
spread-spectrum signal may be split into a plurality of
spread-spectrum signals having similar signal characteristics. A
diversity-encoding step 176 provides adjustment of at least one
diversity parameter of at least one of the spread-spectrum
signals.
[0107] FIG. 14B shows steps of a transmission method of the
invention. A plurality of wideband signals is generated in a
signal-generation step 171. The wideband signals may include any
type of coded or true-noise signals. Information is coupled into at
least one of the wideband signals in a coupling step 172 to provide
at least one spread-spectrum signal. A diversity-encoding step 176
provides adjustment of at least one diversity parameter of at least
one of the spread-spectrum signals and/or at least one of the
wideband signals.
[0108] FIG. 14C shows transmission-signal processing steps that may
follow the transmission methods shown in FIG. 14A and FIG. 14B.
Spread-spectrum and/or wideband signals may be modulated onto at
least one carrier signal in a modulation step 178. Spread-spectrum
and/or wideband signals may be coupled into a communication channel
in a channel-coupling step 180.
[0109] FIG. 15A shows steps of a reception method of the invention.
A plurality of duplicate spread-spectrum signals is received in a
reception step 181. At least one of the received duplicate signals
has been diversity-encoded by the communication channel and/or a
transmitter (not shown) that generated the signal and coupled it
into the channel. A diversity-decoding step 182 decodes at least
one of the received diversity-encoded signals to provide at least
two signals that are highly correlated. The signals are correlated
in a correlation step 184 to provide a correlation output signal
that is indicative of at least one information signal modulated on
the received spread-spectrum signals.
[0110] FIG. 15B shows steps of a reception method of the invention.
At least one spread-spectrum signal and at least one despreading
signal are received in a reception step 181. A despreading signal
is any signal that may be correlated or otherwise combined with a
spread-spectrum signal to recover a spread information signal. At
least one of the received spread-spectrum and/or despreading
signals has been diversity-encoded by the communication channel
and/or a transmitter (not shown) that generated the signal and
coupled it into the channel. A diversity-decoding step 183 decodes
at least one of the received diversity-encoded signals to provide
at least two signals that are highly correlated. The signals are
correlated in a correlation step 184 to provide a correlation
output signal that is indicative of at least one information signal
modulated on the received spread-spectrum signals.
[0111] Although the drawings and specification imply simple in-line
correlation, heterodyne correlation may also be used. A heterodyne
correlator produces a correlated signal output at a different
center frequency than the input signal. In the process of
despreading or removing the code modulation (or noise), the
information-bearing signal is translated to a new center frequency.
This avoids the possibility of direct feedthrough and, in some
instances, simplifies receiver design because the circuitry
following a heterodyne correlator can operate at a lower frequency.
Correlators described herein and shown in the figures may sample,
sum, sample and sum, multiply, or otherwise combine two or more
signal inputs over at least one time interval.
[0112] In the preferred embodiments, several kinds of
interferometry multiplexing are demonstrated to provide a basic
understanding of diversity reception and spatial demultiplexing.
With respect to this understanding, many aspects of this invention
may vary. Multi-user detectors illustrated and described herein
have been of the cancellation type. However, other types of
multi-user detection systems (such as constellation processors)
maybe used, as described in U.S. Pat. No. 6,008,760, U.S. Pat. No.
6,211,671, PCT Appl. No. WO95/03686, U.S. Prov. Pat. Appl.
60/163,141, and U.S. patent application Ser. Nos. 08/862,859,
09/324,206, and 09/347,182, which are all incorporated by
reference. Multi-user detection may be performed with respect to
any type of optimization technique, such as, but not limited to
maximal combining. The invention described herein may be integrated
with any of the diversity-processing methods described in U.S.
Prov. Pat. Appl. 60/163,141.
[0113] The communication channel may be a free-space channel or any
type of guided-wave channel. The invention described herein is
applicable to optical-fiber communications.
[0114] A CPU may be used to perform constellation processing,
weight-and-sum operations, or equivalent types of cancellation
processes associated with multi-user detection. Similarly,
correlation and other signal-combining processes may be performed
by digital signal processing methods.
[0115] Although the wireless interface in the invention is
described with regard to RF and microwave frequencies, the
principles of operation of the invention apply to any frequency in
the electromagnetic spectrum. Additionally, diversity processing
(such as encoding and decoding) may include combinations of space,
frequency, time, phase-space, mode, code, and
polarization-diversity processing methods. In this regard, it
should be understood that such variations, as well as other
variations, fall within the scope of the present invention, its
essence lying more fundamentally with the design realizations and
discoveries achieved than merely the particular designs
developed.
[0116] The foregoing discussion and the claims that follow describe
the preferred embodiments of the present invention. With respect to
the claims, it should be understood that changes could be made
without departing from the essence of the invention. To the extent
such changes embody the essence of the present invention, each
naturally falls within the breadth of protection encompassed by
this patent. This is particularly true for the present invention
because its basic concepts and understandings are fundamental in
nature and can be broadly applied.
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