Patent US3482646A successfully refreshed from Google Patents.
Patent EP0730357A2 successfully refreshed from Google Patents.
EP0730357A2
Expired / Lapsed
EP
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Frequency and frame synchronisation for OFDM
Assignee: Telia Co AB
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Filing: 1996-02-23
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Granted: —
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Expires: 2016-02-23
Abstract
Abstract The present invention is a method and device for synchronization at OFDM-systems. A signal is read into the synchronization block in the time domain, i.e. before fourier transforming of the signal via the FFT-processor, according to Figure 1. In the synchronization block the frame clock for start and input of data in the FFT-processor is regained. For OFDM-reception it is very important that this input starts at the right point of time to make possible detection of data. The point of time for the input to the FFT-processor is therefore adjusted in relation to the regained frame clock. When the frame clock has been regained the frequency error can be estimated, which is also performed in the synchronization block. The frequency error is utilized in a control loop for feed back to an oscillator which generates a complex rotating vector which is multiplied by the input signal for compensation of the frequency error. The invention can be utilized at OFDM-system with guard space or OFDM-system with pulse forming.
Inventors
- 👤 Mikael Isaksson
- 👤 Bo ENGSTRÖM
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-01 09:11
CPC Classifications
H; H04; H04L; H04L27/00; H04L27/26; H04L27/2601; H04L27/2647; H04L27/2655; H04L27/2662; H04L27/2665; H04L27/2657
Claims Analysis
Total Claims: 17
Claim 1
Independent Claim
77 words
Method for synchronization at OFDM-systems, where a digitized signal is divided into a number of channels, and the signal is read into a synchronization block, characterized in that the synchronization block from the signal determines the position of a frame clock, that the synchronization block transmits a frame clock signal to an FFT-block and a frequency control signal to an oscillator, and that the synchronization of the system is made before FFT is performed on the signal.
Claim 2
Dependent Claim
28 words
Method according to patent claim 1, characterized in that the signal includes a symbol and a repeated part of the symbol in the allocated space of the signal.
Claim 3
Dependent Claim
27 words
Method according to patent claim 2, characterized in that the signal is cross correlated at which the repeated part of the signal is given a positive contribution.
Claim 4
Dependent Claim
19 words
Method according to patent claim 3, characterized in that the cross correlation is calculated by multiplication and sliding mean.
Claim 5
Dependent Claim
78 words
Method according to patent claim 2, characterized in that the repeated part of the signal is complex conjugated and multiplied by corresponding part of the signal, at which a second signal is created, which second signal is shifted a number of samples corresponding to the repeated part in the signal, the result of which is subtracted from the second signal and a third signal is created which is integrated and that a filtered cross correlation sequence is obtained.
Claim 6
Dependent Claim
44 words
Method according to patent claim 5, characterized in that the absolute value of the third signal is determined and that a saw-tooth signal is obtained, which is utilized for generation of the frame clock by utilization of the peak values of the third signal.
Claim 7
Dependent Claim
33 words
Method according to patent claim 3, characterized in that a frequency error in the system is determined by calculation of the phase of the cross correlation when the cross correlation has its maximum.
Claim 8
Dependent Claim
24 words
Method according to patent claim 7, characterized in that the phase shift of the cross correlation is proportional to the length of the symbol.
Claim 9
Dependent Claim
56 words
Device for synchronization at OFDM-systems where a synchronization device is arranged to receive a signal, which signal is digitized and divided into a number of channels, characterized in that a correlation of the signal is performed by the synchronization devices at which a synchronization signal is transmitted, and that the synchronization is performed before an FFT-function.
Claim 10
Dependent Claim
23 words
Device according to patent claim 9, characterized in that the synchronization device is arranged to transmit a frame clock signal to an FFT-processor.
Claim 11
Dependent Claim
28 words
Device according to patent claim 9, characterized in that the synchronization device is arranged to transmit a frequency signal to an oscillator, and that the frequency is correlated.
Claim 12
Dependent Claim
42 words
Device according to patent claim 9, characterized in that the signal includes a symbol (L) and that the symbol at least to a part is repeated in the signal, which repeated signal (R) preferably is placed after the symbol within the signal.
Claim 13
Dependent Claim
60 words
Device according to patent claims 9 and 12, characterized in that a complex conjugation is performed on the repeated signal (R) whereafter a multiplication by corresponding part in the symbol (L) is performed in a multiplication device, and that a device for sliding mean is arranged to produce the synchronization signal out of the obtained signal (N) from the multiplication.
Claim 14
Dependent Claim
62 words
Device according to patent claim 13, characterized in that the device for sliding mean includes a shift device which is arranged to shift the signal (N) a number of steps corresponding to the length of the repeated signal (R), the result of which is subtracted from the original signal (N), and that the obtained signal (E) is integrated in an integration device.
Claim 15
Dependent Claim
48 words
Device according to patent claims 9 and 14, characterized in that the synchronization device is arranged to calculate the absolute value of the signal (C), and that a signal (T) including a sequence of triangular signals is produced, which signal generates the frame clock signal to the FFT-processor.
Claim 16
Dependent Claim
36 words
Device according to patent claim 15, characterized in that a frequency error is determined in the synchronization device by determining the phase shift of the cross correlation, which phase shift is proportional to the frequency error.
Claim 17
Dependent Claim
18 words
Device according to patent claim 16, characterized in that the frequency error preferably is measured at correlation maxima.
References Cited (Backward Citations)
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