Method and apparatus for frequency offset estimation and interleaver synchronization using periodic signature sequences
First Claim
1. A method for estimating the frequency offset in an OFDM communication system, comprising the steps of:
- allocating certain locations in an OFDM frame to a signature sequence;
transmitting said signature sequence with data to a receiver, wherein said data and said signature sequence are encoded using a differential encoding performed in frequency; and
estimating the frequency offset at said receiver by determining whether a correlated peak associated with said signature sequence is in an expected location.
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Abstract
A method and apparatus are disclosed for frequency offset estimation and interleaver synchronization, using periodic signature sequences, such as Barker codes. The periodic signature sequence is used for interleaver synchronization or frequency offset estimation or both. The periodic signature sequence is transmitted over a certain number of bins in both the upper and lower sides of the DAB signal. Since the signature sequences are assigned to specific bins known to the receiver, any shift of the correlated peak from the expected location due to frequency offset errors can be estimated by the frequency offset algorithm. If the Barker sequence is placed, for example, in the last column of the DAB interleaver, the location of the Barker sequence upon correlation of the received digital signal identifies the beginning of an interleaver block. A Barker sequence is transmitted over a signature frame every L data frames on each side band, where L is generally the number of OFDM frames that can fill the interleaver memory. If the maximum frequency offset is M, then the frequency offset algorithm utilizes a search window of size n+2M (between bins N−M through N+n+M), and attempts to maintain the Barker sequence in the center of the search window. At the receiver, the Barker sequence is mapped to the OFDM signature bins that do not belong to uncertainty regions (the group of bins that can fall out of the receiver processing range for maximum positive and negative frequency offset values). Thus, the Barker sequence bins are processed by the disclosed receiver as long as the frequency offset does not exceed the specified maximum frequency offset.
66 Citations
30 Claims
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1. A method for estimating the frequency offset in an OFDM communication system, comprising the steps of:
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allocating certain locations in an OFDM frame to a signature sequence; transmitting said signature sequence with data to a receiver, wherein said data and said signature sequence are encoded using a differential encoding performed in frequency; and estimating the frequency offset at said receiver by determining whether a correlated peak associated with said signature sequence is in an expected location. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A method for estimating the frequency offset in an OFDM communication system, comprising the steps of:
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receiving a digital signal, wherein said received digital signal contains a signature sequence in an expected location, wherein said received digital signal is encoded using a differential encoding performed in frequency; correlating said received digital signal using a filter matched to said signature sequence; and identifying whether a correlated peak associated with said received digital signal is an expected location. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19, 20, 21)
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22. A method for synchronizing interleavers in an OFDM communication system, comprising the steps of:
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allocating certain locations in an OFDM frame to a signature sequence; transmitting said signature sequence with data to a receiver, wherein said data and said signature sequence are encoded using a differential encoding performed in frequency; and identifying a beginning of an interleaver block based on a location of a correlated peak associated with said signature sequence. - View Dependent Claims (23, 24, 25, 26, 27, 28)
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29. A receiver in an OFDM communication system for receiving a digital signal containing a signature sequence in an expected location, comprising:
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a filter matched to said signature sequence for correlating said received digital signal, wherein said received digital signal is encoded using a differential encoding performed in frequency; and a frequency offset estimator that identifies whether a correlated peak associated with said received digital signal is an expected location.
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30. A receiver in an OFDM communication system, comprising:
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means for receiving a digital signal having a signature sequence in certain locations, wherein said received digital signal is encoded using a differential encoding performed in frequency; a filter matched to said signature sequence for correlating said received digital signal; and an interleaver synchronizer that identifies a beginning of an interleaver block based on a location of a correlated peak associated with said signature sequence.
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Specification