U.S. patent application number 10/230762 was filed with the patent office on 2002-12-26 for carrier phase recovery of multi-rate signals.
Invention is credited to Garmonov, Alexander, Menyailov, Dmitry, Pogorilko, Dmitry, Savinsky, Peter, Shen, Qiang, Tong, Wen, Wang, Rui.
Application Number | 20020196733 10/230762 |
Document ID | / |
Family ID | 22740243 |
Filed Date | 2002-12-26 |
United States Patent
Application |
20020196733 |
Kind Code |
A1 |
Shen, Qiang ; et
al. |
December 26, 2002 |
Carrier phase recovery of multi-rate signals
Abstract
Method and apparatus for performing complex channel gain
estimation from a transformer output and a non-coherent combiner
output include a selector, an envelope detector, a weighting unit,
a controller, store units, and an averager. The device may perform
coherent complex channel gain estimation on link signals for
signals transmitted by IS-95 burst randomization, and may operate
on a power control group.
Inventors: |
Shen, Qiang; (Nepean,
CA) ; Savinsky, Peter; (Voronezh, RU) ; Wang,
Rui; (Ottawa, CA) ; Tong, Wen; (Ottawa,
CA) ; Menyailov, Dmitry; (Voronezh, RU) ;
Pogorilko, Dmitry; (Voronezh, RU) ; Garmonov,
Alexander; (Voronezh, RU) |
Correspondence
Address: |
GIBBONS, DEL DEO, DOLAN, GRIFFINGER & VECCHIONE
1 RIVERFRONT PLAZA
NEWARK
NJ
07102-5497
US
|
Family ID: |
22740243 |
Appl. No.: |
10/230762 |
Filed: |
August 28, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10230762 |
Aug 28, 2002 |
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09200080 |
Nov 25, 1998 |
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6463043 |
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Current U.S.
Class: |
370/208 ;
375/E1.032 |
Current CPC
Class: |
H04B 1/712 20130101;
H04B 1/7117 20130101; H04L 2027/0067 20130101 |
Class at
Publication: |
370/208 |
International
Class: |
H04J 011/00 |
Claims
What is claimed is:
1. An estimator for determining a complex channel gain estimation
from a transformer output and a non-coherent combiner output,
comprising: a selector for determining an orthogonal function index
from said non-coherent combiner output, and determining a
corresponding complex value from said transformer output using said
orthogonal function index, an envelope detector for calculating the
squared magnitude of said transformer output, and for generating at
least one M-ary real value, wherein M is an integer greater than
one, a weighting unit coupled to said envelope detector for
estimating a signal quality coefficient from said at least one
M-ary real value and generating at least one weighted symbol by
multiplying said signal quality coefficient by said corresponding
complex value, at least one store unit coupled to said weighting
unit for storing said at least one weighted symbol, an averager
coupled to said at least one store unit for averaging said at least
one weighted symbol, and a controller coupled to said non-coherent
combiner output, said at least one store unit, and said averager,
for resetting said at least one store unit and for controlling said
averager, thereby determining said complex channel gain
estimation.
2. An estimator according to claim 1, wherein said controller
resets said at least one store unit after said non-coherent
combiner output is at least one control group.
3. An estimator according to claim 1, wherein said weighting unit
is a multiplier for multiplying said at least one M-ary real value
and said corresponding complex value.
4. An estimator according to claim 1, wherein said averager
selectively combines said at least one weighted symbol from said at
least one store unit, according to a signal of said controller.
5. An method for determining a complex channel gain estimation from
a transformer output and a non-coherent combiner output,
comprising: determining an orthogonal function index from said
non-coherent combiner output, and determining a corresponding
complex value from said transformer output using said orthogonal
function index, calculating the squared magnitude of said
transformer output, and for generating at least one M-ary real
value, wherein M is an integer greater than one, estimating a
signal quality coefficient from said at least one M-ary real value
and generating at least one weighted symbol by multiplying said
signal quality coefficient by said corresponding complex value,
storing said at least one weighted symbol, averaging said at least
one weighted symbol, and controlling said averager, thereby
determining said complex channel gain estimation.
6. A method according to claim 5, wherein said controlling further
comprises resetting said at least one store unit after said
non-coherent combiner output is at least one control group.
7. A method according to claim 5, wherein said weighted symbol is
derived by multiplying said at least one M-ary real value and said
corresponding complex value.
8. A method according to claim 5, further comprising controlling
said averaging by selectively combining said stored at least one
weighted symbol.
9. An apparatus for determining a complex channel gain estimation
from a transformer output and a non-coherent combiner output,
comprising: a selector means for determining an orthogonal function
index from said non-coherent combiner output, and determining a
corresponding complex value from said transformer output using said
orthogonal function index, an envelope detector means for
calculating the squared magnitude of said transformer output, and
for generating at least one M-ary real value, wherein M is an
integer greater than one, a weighting unit means coupled to said
envelope detector means for estimating a signal quality coefficient
from said at least one M-ary real value and generating at least one
weighted symbol by multiplying said signal quality coefficient by
said corresponding complex value, at least one store unit means
coupled to said weighting unit means for storing said at least one
weighted symbol, an averager means coupled to said at least one
store unit means for averaging said at least one weighted symbol,
and a controller means coupled to said non-coherent combiner
output, said at least one store unit means, and said averager
means, for resetting said at least one store unit means and for
controlling said averager means, thereby determining said complex
channel gain estimation.
10. An apparatus according to claim 9, wherein said controller
means resets said at least one store unit after said non-coherent
combiner output is at least one control group.
11. An apparatus according to claim 9, wherein said weighting unit
means is a multiplier means for multiplying said at least one M-ary
real value and said corresponding complex value.
12. An apparatus according to claim 9, wherein said averager means
selectively combines said at least one weighted symbol from said at
least one store unit means, according to a signal of said
controller means.
13. A system for performing carrier phase recovery of multi-rate
signals which include in-phase and quadrature phase portions,
comprising: a despreader capable of despreading at least one code
from said multi-rate signals and obtaining said in-phase and
quadrature phase signals; a transformer coupled to said despreader
capable of transforming said in-phase and quadrature phase signals
and obtaining a plurality of M-ary complex values, wherein M is an
integer greater than one; a buffer coupled to said transformer
capable of storing said plurality of M-ary complex values; a
non-coherent combiner coupled to said transformer, capable of
combining said non-coherent portions of said plurality of M-ary
complex values; an estimator coupled to said transformer and said
non-coherent combiner, configured to estimate a channel complex
gain from said plurality of M-ary complex values and combining said
non-coherent portions of said plurality of M-ary complex values;
and, a coherent combiner coupled to said buffer and said estimator,
configured to perform maximal ratio combining of said stored
plurality of M-ary complex values and said channel complex gain
estimation, thereby generating a plurality of real value vectors,
said combinations representative of carrier phase of said
multi-rate signals.
14. The system according to claim 13 wherein said transformer
performs a fast Hadamard transform.
15. The system according to claim 13 wherein said plurality of
M-ary complex values are Walsh spectrums, wherein M is an integer
greater than one.
16. The system according to claim 13 wherein said coherent combiner
performs maximal ratio combining by multiplying a complex conjugate
of said channel complex gain estimation to a plurality of
corresponding finger outputs and combining all said fingers.
17. A system for performing carrier phase recovery of multi-rate
signals which include in-phase and quadrature phase portions
comprising: despreader means for despreading at least one code from
said multi-rate signals and obtaining said in-phase and quadrature
phase signals; transformer means coupled to said despreader means
for transforming said in-phase and quadrature phase signals and
obtaining a plurality of M-ary complex values, wherein M is an
integer greater than one, and, wherein M-ary complex values contain
non-coherent portions; buffer means coupled to said transformer
means for storing said plurality of M-ary complex values;
non-coherent combiner means coupled to said transformer means for
combining said non-coherent portions of said plurality of M-ary
complex values; estimator means coupled to said transformer means
and said non-coherent combiner means, for estimating a channel
complex gain from said plurality of M-ary complex values and said
combination of non-coherent portions of said plurality of M-ary
complex values; and, coherent combiner means coupled to said buffer
means and said estimator means, for performing maximal ratio
combining of said stored plurality of M-ary complex values and said
channel complex gain estimation, thereby generating a plurality of
real value vectors, said combinations representative of carrier
phase of said multi-rate signals.
18. The System according to claim 17 wherein said transformer means
performs a fast Hadamard transform.
19. The system according to claim 17 wherein said plurality of
M-ary complex values are Walsh spectrums.
20. The system according to claim 17 wherein said coherent combiner
means performs maximal ratio combining by multiplying a complex
conjugate of said channel complex gain estimation to a plurality of
corresponding finger outputs and combining all said fingers.
21. In a system, a method of performing carrier phase recovery of
multi-rate signals which include in-phase and quadrature phase
portions, comprising: despreading at least one code from said
multi-rate signals and obtaining said in-phase and quadrature phase
signals, using a despreader; transforming said in-phase and
quadrature phase signals and obtaining a plurality of M-ary complex
values, wherein M is an integer greater than one, and, wherein
M-ary complex values contain non-coherent portions, using a
transformer coupled to said despreader; storing said plurality of
M-ary complex values, using a buffer coupled to said transformer;
combining said non-coherent portions of said plurality of M-ary
complex values, using a non-coherent combiner coupled to said
transformer; estimating a channel complex gain from said plurality
of M-ary complex values and said combination of non-coherent
portions of said plurality of M-ary complex values, using an
estimator coupled to said transformer and said non-coherent
combiner; performing maximal ratio combining of said stored
plurality of M-ary complex values and said-channel complex gain
estimation, using a coherent combiner coupled to said buffer and
said estimator; and, generating a plurality of real value vectors
from said coherent combiner, said combinations representative of
carrier phase of said multi-rate signals.
22. The method according to claim 21, wherein the step of
transforming comprises using a fast Hadamard transform.
23. The method according to claim 21, wherein said plurality of
M-ary complex values are Walsh spectrums.
24. The method according to claim 21, wherein the step of
performing maximal ratio combining further comprises: multiplying a
complex conjugate of said channel complex gain estimation to a
plurality of corresponding finger outputs and combining all said
fingers.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This is a division of U.S. patent application Ser. No.
09/200,080 filed Nov. 25, 1998, now pending.
FIELD OF THE INVENTION
[0002] This invention relates generally to the field of wireless
communications systems and, more particularly, to apparatus and
methods for recovering carrier phase of multi-rate signals.
BACKGROUND OF THE INVENTION
[0003] In typical wireless communication systems a Cell Site Modem
(CSM) is used for communication between the base station and the
mobile station. Among other things, the CSM recovers the carrier
phase of the link signal from the mobile to base station. Carrier
phase recovery (sometimes referred to as phase referencing) is the
operation of extracting a phase coherent reference carrier from a
received carrier.
[0004] The base station transmits a pilot channel as a reference
channel. This allows the mobile station to acquire the timing of
the forward channel and thus provides a phase reference for the
mobile station. However, the IS-95 standard does not provide for
the mobile station transmitting a reference channel to the base
station. Therefore the base station must use the link signal to
estimate the carrier phase.
[0005] Generally, CSMs use non-coherent demodulation. The drawback
of this method is the signal to noise ratio degradation at each
demodulator. In addition, non-coherent demodulation prevents rake
receivers from using more sophisticated combining methods to
achieve higher combining gain for a multipath fading channel.
[0006] Coherent demodulation provides a better signal to noise
ratio than non-coherent techniques. However, it is difficult to
recover carrier phase when the link signal is the only signal to
work from. Carrier recovery used for coherent demodulation is
complicated further by the fact that IS-95 uses a data burst
randomizer to transmit multi-rate data.
[0007] When the signal received by the base station is at the full
rate, conventional systems and methods of carrier recovery for
coherent demodulation may be employed. However, when the signal
received by the base station is a series of random bursts, each
burst having the length of one power control group (i.e. 6 Walsh
symbols in IS-95), conventional CSMs do not effectively estimate
carrier phase for use in coherent demodulation. This is because
conventional CSMs do not perform complex (i.e. magnitude and phase)
channel gain estimation on a single power control group. Thus,
sufficient gains are difficult to achieve for the different data
rates.
[0008] Others have attempted to recover carrier phase from the
mobile to base station link signal using phase locked loop systems.
However these systems do not provide adequate carrier phase. Phase
locked loop systems require continuous signal input and cannot
operate at lower transmission rates when signals become
intermittent. While more gain may be achieved for full rate
transmissions, losses can occur for other lower transmission rates.
Systems which utilize tentative non-coherent demodulation and
moving average complex estimation also require continuous signal
input and experience similar problems at lower rate
transmissions.
[0009] Other proposals which utilize aided symbol or aided signal
technologies require modification of IS-95 standard devices and
methods. These proposals would be incompatible with, the existing
wireless communication infrastructure.
[0010] Accordingly there exists a need for systems and methods of
performing coherent complex channel gain estimation on link signals
which is effective for signals transmitted by IS-95 burst
randomization.
[0011] There also exists a need for such systems which operate on a
power control group.
[0012] Accordingly it is an object of the present invention to
provide systems and methods for performing coherent complex channel
gain estimation on link signals which is effective for signals
transmitted by IS-95 burst randomization.
[0013] It is also an object of the present invention to provide
systems and methods which operate on a power control group.
SUMMARY OF THE INVENTION
[0014] In accordance with the teachings of the present invention,
these and other objects may be accomplished by the present
invention, which is a system for performing complex channel gain
estimation from a transformer output and a non10 coherent combiner
output. A selector determines an orthogonal function index from the
non-coherent combiner output, and may use the orthogonal function
index to determine a corresponding complex value from the
transformer output.
[0015] An envelope detector may calculate the squared magnitude of
the transformer output and generate M-ary real values, where M is
an integer greater than one. A weighting unit coupled to the
envelope detector may estimate a signal quality coefficient from
the M-ary real values and generating weighted symbols by
multiplying the signal quality coefficient by the corresponding
complex value.
[0016] Store units may be coupled to the weighting unit for storing
the weighted symbol. Also, an averager may be coupled to the store
units for averaging the weighted symbols. A controller may be
coupled to the non-coherent combiner output, the store units, and
the averager, for resetting the store units and for controlling the
averager, thereby determining complex channel gain estimation.
[0017] Another embodiment of the present invention is a system for
performing carrier phase recovery of multi-rate signals which
include in-phase and quadrature phase portions. An embodiment of
the present invention includes a despreader capable of despreading
at least one code from the multi-rate signals. The despreader is
also capable of despreading the inphase and quadrature phase
signals of the multi-rate signals.
[0018] This embodiment also includes a transformer which is coupled
to the despreader. The transformer is capable of transforming the
in-phase and quadrature phase signals and obtaining a plurality of
M-ary complex values, where M is an integer greater than one.
[0019] A buffer, non-coherent combiner, and estimator are coupled
to the transformer. The buffer is capable of storing the plurality
of M-ary complex values. The non-coherent combiner is capable of
combining the non-coherent portions of the plurality of M-ary
complex values. The estimator is both coupled to the transformer
and the non-coherent combiner. The estimator is configured to
estimate a complex channel gain from the plurality of M-ary complex
values and the non-coherent combining of the plurality of M-ary
complex values of all fingers (branches).
[0020] In addition a coherent combiner is coupled to the buffer and
the estimator. The coherent combiner is configured to perform
maximal ratio combining of the stored plurality of M-ary complex
values and the channel complex gain estimation. The output of the
coherent combiner is a plurality of real value vectors.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] The invention will be more clearly understood by reference
to the following detailed description of an exemplary embodiment in
conjunction with the accompanying drawings, in which:
[0022] FIG. 1 is a general block diagram of a coherent,
maximal-ratio combining System in accordance with the present
invention.
[0023] FIG. 1B is a flowchart diagram illustrating the operation of
the system in accordance with the present invention.
[0024] FIG. 2 is a diagram of the non-coherent combiner.
[0025] FIG. 3 is a diagram of the coherent combiner.
[0026] FIG. 4A is a diagram of the channel complex gain
estimator.
[0027] FIG. 4B is a flowchart diagram illustrating the operation of
the channel complex gain estimator in accordance with the present
invention.
[0028] FIG. 5 is a table showing an example of the contents used in
the complex gain estimator.
DETAILED DESCRIPTION OF THE INVENTION
[0029] The conventional technology of code division multiple access
(CDMA) employs a technique that allows users to simultaneously
share the same radio frequency band. It achieves this by modulating
the radio frequency signal with a spreading sequence known as a
pseudonoise (PN-code) digital signal. Other pseudo-random sequences
(i.e. codes) can be mixed to the signals to make them more
resistant to noise, multi-path propagation, fading, and time
jitter. For example a code that reduces the effect of multi-path
propagation, time jitter (imprecise implementation errors) is an
orthogonal code. In the preferred embodiment, a Walsh coded
orthogonal spectrum is received. However, other types of orthogonal
codes are well known. Thus, the Walsh codes can be supplemented by
other orthogonal codes and still be within the scope of the present
invention.
[0030] In accordance with the present invention, a system
decorrelates the unique codes mixed with the carrier signals. In
addition, the system can use the link signal to estimate the
carrier phase. FIG. 1 illustrates a system in accordance with the
present invention for using the recovered carrier phase of
multi-rate signals. The apparatus shown may be used at a wireless
network base station, mobile station, or any other wireless
communication station such as a communication satellite.
[0031] The received signals, which include in-phase (I) and
quadrature (Q) components, are applied to the inputs of a
despreader 20. The despreader 20 decorrelates the PN-code from the
received signals. The output of the despreader is the orthogonal
(i.e. Walsh) codes in complex form.
[0032] A transformer 30 is coupled to the output of the despreader
20. The transformer 30 operates on the I and Q phase components of
the orthogonal signals using a Fast Hadamard Transform (a type of
Discrete Fourier Transform). Those skilled in the art will
appreciate that other known transforms may be used instead of the
Fast Hadamard Transform, such as Fast Walsh Transform, Fast
Rademacher Transform, Fast Hartley Transform and the like, and
still be within the scope of the invention. The output of the
transformer is the complex orthogonal spectrum with M-ary complex
values, where M is an integer (e.g. 64).
[0033] A delay unit 40 is also coupled to the transformer 30. The
delay unit 40 stores the orthogonal spectrums (within one power
control group) from the transformer 30 for further processing after
the channel complex gain estimation is available. A complex gain
estimator 70 determines the channel complex gain estimation from
the output values of each finger output (i.e. the output of the
transformer 30 and noncoherent combiner 60). Once the complex
estimation is ready, the delay 40 feeds the stored data to a
coherent combiner 50 with the corresponding complex gain estimate.
For example, the delay 40 unit may store the complex signal for up
to a 6 Walsh symbol duration. The 6 Walsh symbol spectrum in one
power control group can use the same one estimate or use several
estimates, depending on the implementation.
[0034] A noncoherent combiner 60 is also coupled to the output of
the transformer 30. The noncoherent combiner 60 performs diversity
combining to all branches of the orthogonal spectrum with
noncoherent output. One method of obtaining diversity combining of
noncoherent values is to use equal gain combining. However other
methods for performing noncoherent diversity combining can be used
and still be within the scope of the invention.
[0035] The coherent combiner 50 is coupled to the delay 40 and the
complex gain estimator 70. The coherent combiner 50 performs
diversity combining to all branches with coherent output. This can
be accomplished by performing maximal ratio combining on all
branches with complex gain weights. Maximal ratio combining is
accomplished by multiplying the complex conjugate of the complex
gain estimate to the corresponding finger output and then combining
all the fingers. The coherent combiner output is the real value
vector of M (e.g. M=64) elements for M-ary orthogonal modulation.
FIG. 1B is a flowchart diagram illustrating the operation of the
coherent, maximal ratio combining system and further illustrates
the signal flow and processing of the complex value input in
accordance with the present invention.
[0036] FIG. 2 is a detailed diagram of the noncoherent combiner 60.
The envelope detector 100 performs on each finger output M-ary
complex value, which is the output of the transformer 30. A summer
110 sums the M-ary complex values of each finger from each envelope
detector 100 and returns a M-ary real value by computing the square
of the magnitude of each complex value. Other fingers 120 may also
be coupled to the summer 110. The output is thus the diversity
combining of all the branches of the orthogonal spectrum with
noncoherent output.
[0037] FIG. 3 is a detailed diagram of the coherent combiner 50. A
conjugator 150 returns the complex conjugate of the channel
estimation 160 coming from the estimator 70. The complex conjugate
is then multiplied with the delayed orthogonal spectrums 170 by a
multiplier 175, where the delayed orthogonal spectrum comes from
the delay 40. The multiplied output 180 is then summed by a summer
200. Other fingers 190 may also be summed together. The real part
of the complex value from the summer 200 is then obtained using a
real value unit 210. The output is the diversity combination of all
the branches of the orthogonal spectrum with coherent output.
[0038] FIG. 4 is a detailed description of the complex gain
estimator. A selector 300 takes the noncoherent combiner 60 output
and the transformer 30 output of the corresponding finger and
determines the orthogonal function index. This index is
corresponding to the maximum value of the orthogonal spectrum
received from the non-coherent combiner 60, and is used to select a
corresponding complex value from the transformer 30 output. The
output of the selector 300 is the complex value corresponding to
that orthogonal function index in the transformer 30 output. The
index may be a Walsh index, Gold index, Rademacher index, Hartley
index, or the like and still be within the scope of the invention.
The corresponding element in the transformer 30 output is fed into
a store unit 310 after being weighted by a weighting unit 320.
[0039] An envelope detector 360 calculates the squared magnitude of
the complex value from the transformer 30 and returns M-ary real
values, where M is an integer (e.g. 64). The weighting unit 320
estimates the signal quality (e.g. signal to noise ratio) from the
output of the envelope detector 360 and uses this estimation (in
the form of weighting coefficients) to weigh the selector 300
output. The weighting unit 320 can be a simple multiplier. It may
optionally be omitted, thus creating a weighting factor of one.
Those skilled in the art will realize that various noise quality
coefficients may be determined from a signal. The preferred
embodiment uses a signal to noise ratio coefficient determined by
dividing 323 the average 322 and maximum value 321 of the output
from the envelope detector
[0040] The store unit 310 may be a shift register with a tapped
delay line, or other memory device, with a size of N, where N is
the number of symbols in one power control group. For example, if
Walsh symbols are used N may be equal to 6. However since other
types of symbols can be used and still be within the scope of this
invention and other symbols have different size power control
groups, N may be any integer. The symbols may be Walsh symbols,
Gold symbols, Rademacher symbols, Hartley symbols, or the like and
still be within the scope of the invention. These complex values
are then selectively fed into an averager 330 according to certain
control logic from a controller 340. The controller 340 unit counts
the symbol index, and at the end of every N symbols (i.e. one power
control group), resets the contents of the store unit (i.e. resets
the memory or shift register). It also controls which elements of
the store unit 310 are used in the channel gain estimation
according to the index the system is operating on. FIG. 4B is a
flowchart diagram illustrating the operation of the channel
estimator and further describes the signal flow through the channel
estimator in accordance with the present invention.
[0041] The averager 330 averages the contents of the store unit
310. The controller 340 decides which contents the averager 330
will use in the averaging. For example, four summing operators
perform averaging over different sets of Walsh symbol values as
shown in FIG. 5.
[0042] In the table shown in FIG. 5, B.sub.l (i=1, 2, . . . 6) are
the contents in the store unit 310. They are selectively used in
the averager according to each Walsh symbol the channel estimation
is for. Note that there are N=6 Walsh symbols in one power control
group according to the IS-95 standard. Optionally, the control
signal 370 to the averager 330 can be omitted, which means all
N(=6) Walsh symbols in one power control group use one channel gain
estimation which is the average of all N contents from the store
unit 310. Those skilled in the art will realize that a more
sophisticated weighted summation (filtering) can be used in place
of the simple averager 330 shown. Also, tap adaptation (i.e.
adjusting the poles and/or zeros) of such filtering may also be
utilized.
[0043] Having described the invention, what is claimed as new and
secured by Letters Patent is:
* * * * *