Non-coherent, non-data-aided pseudo-noise synchronization and carrier synchronization for QPSK or OQPSK modulated CDMA system
First Claim
Patent Images
1. A method for synchronizing a received signal with a transmitted signal comprising the steps of:
- (a) converting the received signal into in-phase (I) and quadrature phase (Q) components using an estimate of frequency error (Δ
f) and phase offset (Δ
φ
) between the received signal and the transmitted signal;
(b) determining a delay ({circumflex over (τ
)}) between the received signal and the transmitted signal with respect to a pseudo-noise (PN) spreading sequence applied to the transmitted and received signals using the I and Q components of the received signal;
(c) determining a value for the estimate of the frequency delay (Δ
f) and the phase offset (Δ
φ
) between the received signal and the transmitted signal using the delay ({circumflex over (τ
)}); and
(d) feeding back the value for the estimate determined in step (c) to be used as the estimate for converting in step (a).
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Abstract
A non-coherent method for (PN) code synchronization and eliminates the need for prior clock synchronization between a transmitter and receiver. The method further eliminates any need for prior knowledge of a transmitted data sequence to provide synchronization. In the method, based on a coarse estimation of the carrier frequency, a received CDMA intermediate frequency (IF) signal is baseband converted to in-phase (I) and quadrature-phase (Q) components. The baseband I and Q components are then used to calculate an estimated delay {circumflex over (τ)} at a PN synchronization roll-over point. The estimated delay {circumflex over (τ)} is used in an intermediate data sequence in the synchronization roll-over calculation process to more accurately estimate carrier frequency error and phase offset for the IF carrier signal used in the baseband conversion process. The estimated carrier signal is then provided as feed back to correct for the coarse estimate of the carrier frequency error and phase offset, thus adaptively correcting for Doppler shift in a received signal.
13 Citations
7 Claims
-
1. A method for synchronizing a received signal with a transmitted signal comprising the steps of:
-
(a) converting the received signal into in-phase (I) and quadrature phase (Q) components using an estimate of frequency error (Δ
f) and phase offset (Δ
φ
) between the received signal and the transmitted signal;
(b) determining a delay ({circumflex over (τ
)}) between the received signal and the transmitted signal with respect to a pseudo-noise (PN) spreading sequence applied to the transmitted and received signals using the I and Q components of the received signal;
(c) determining a value for the estimate of the frequency delay (Δ
f) and the phase offset (Δ
φ
) between the received signal and the transmitted signal using the delay ({circumflex over (τ
)}); and
(d) feeding back the value for the estimate determined in step (c) to be used as the estimate for converting in step (a). - View Dependent Claims (2, 3, 4, 5, 6, 7)
where; x(t+τ
)=I(t+τ
)Q(t+τ
)IPN(t)QPN(t); and
x′
(t+τ
)=I′
(t+τ
)Q′
(t+τ
)IPN(t)QPN(t), andwhere, t=η
T, where η
=0,1,2, . . . N−
1Tc is a duration of a PN chip, τ
b is a delay at a beginning of a search window for delay estimation,τ
e is a delay at an end of a search window for delay estimation,N is an integer indicating a desired number of samples, IPN(t) is an in-phase short PN spreading sequence, and QPN(t) is a quadrature-phase short PN spreading sequence.
-
-
3. The method of claim 2, wherein the frequency error (Δ
- f) between the received signal and the transmitted signal from step (c) is determined according to the following equation;
where s(t′
)=x(t′
+{circumflex over (τ
)})+i·
x′
(t′
+{circumflex over (τ
)}),t′
=η
Tc, where η
′
=0,1,2, . . . M−
1,Δ
ft is a frequency tolerance, andM is an integer indicating a desired number of samples.
- f) between the received signal and the transmitted signal from step (c) is determined according to the following equation;
-
4. The method of claim 3, wherein the phase offset (Δ
- φ
) between the received signal and the transmitted signal from step (c) is determined according to the following equation;
- φ
-
5. The method of claim 2 wherein the frequency error Δ
- f between the received signal and the transmitted signal is within a frequency tolerance Δ
ft such that Δ
ft<
{fraction (1/16)}·
1/N·
fs, where fs is a sampling rate of the I and Q components of the received signal.
- f between the received signal and the transmitted signal is within a frequency tolerance Δ
-
6. The method of claim 1, wherein the delay ({circumflex over (τ
- )}) is determined using the following equation;
where; x(t+τ
)=I(t+τ
)Q(t+τ
)IPN(t)QPN(t),x′
(t+τ
)=I′
(t+τ
)Q′
(t+τ
)IPN(t)QPN(t),t=η
T, where η
=0,1,2, . . . N−
1,Tc is a duration of a PN chip, τ
b is a delay at a beginning of a search window for delay estimation,τ
e is a delay at an end of a search window for delay estimation,N is an integer indicating a desired number of samples, IPN(t) is an in-phase short PN spreading sequence, and QPN(t) is a quadrature-phase short PN spreading sequence, Δ
ft is a frequency tolerance, xLP(t+τ
) is an output of a low pass filter provided with the signal x(t+τ
) as an input, the low pass filter receiving the signal x(t+τ
) having a cutoff frequency at approximately twice the frequency tolerance, andxLP′
(t+τ
) is an output of a low pass filter provided with the signal x′
(t+τ
) as an input, the low pass filter receiving the signal x′
(t+τ
) having a cutoff frequency at approximately twice the frequency tolerance.
- )}) is determined using the following equation;
-
7. The method of claim 6 wherein the frequency error Δ
- f between the received signal and the transmitted signal is within the frequency tolerance Δ
ft such that Δ
ft≧
{fraction (1/16)}·
1/N·
fs, where fs, is the sampling rate of the I and Q components of the received signal.
- f between the received signal and the transmitted signal is within the frequency tolerance Δ
Specification
-
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Current AssigneeAnritsu Corporation
-
Original AssigneeAnritsu Corporation
-
InventorsSheba, Mahbuba
-
Primary Examiner(s)Pham, Chi
-
Assistant Examiner(s)Nguyen, Dung X.
-
Application NumberUS09/247,425Time in Patent Office972 DaysField of Search375/367, 375/149, 375/326, 375/147, 375/355US Class Current375/326CPC Class CodesH04B 1/70718 with asynchronous demodulat...H04B 1/7075 with code phase acquisitionH04B 1/70775 Multi-dwell schemes, i.e. m...H04B 1/7087 Carrier synchronisation asp...H04B 2001/70706 using a code tracking loop,...H04L 27/2273 associated with quadrature ...
