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Method for synchronizing downlink time and frequency of OFDM system

A technology of frequency synchronization and time synchronization, which is applied in the field of communication, can solve problems such as the increase of error in the calculation process, achieve the effects of increasing speed, avoiding multiple traversal searches, and reducing FFT calculation time

Inactive Publication Date: 2010-06-23
BEIJING XINWEI TELECOM TECH
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Problems solved by technology

[0023] The above two methods of calculating frequency offset have their defects. The autocorrelation method can only calculate the fractional frequency offset, while the cross-correlation algorithm requires multiple FFT operations, and is affected by the fractional frequency offset. The process error becomes larger

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  • Method for synchronizing downlink time and frequency of OFDM system
  • Method for synchronizing downlink time and frequency of OFDM system
  • Method for synchronizing downlink time and frequency of OFDM system

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Embodiment Construction

[0039] Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0040] figure 1 It is a structure representing the training symbols at the sending end and the local training symbols at the receiving end to which the present invention is applied. Figure 101 shows the time-domain structure of the sending training symbol, which is composed of two identical sub-symbols and a cyclic prefix, and each sub-symbol has a duration T u us, CP (cyclic prefix) length is T g us, so the total duration of the originating training symbols is (2*T u +T g ). T.M.Schmidl's literature proposes to send two adjacent identical training symbols, but the present invention only requires sending one training symbol with adjacent identical sub-symbols. The frequency domain structure of the training symbol is shown in Figure 102. This symbol has even subcarriers vacant, and the training sequence is only placed on the odd subcarrier. The train...

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Abstract

The invention provides a method for synchronizing a downlink time and a frequency of an OFDM system, which comprises that: a sending end sends a training symbol for marking different cells, wherein the training symbol consists of two identical subsymbols and a cyclic prefix in a time domain, the time length of each subsymbol is Tuus, and the time length of the cyclic prefix is Tgus; a receiving end carries out autocorrelation calculation on a received signal and searches an autocorrelation platform in an autocorrelation value of the received signal; after the effective autocorrelation platform is detected, an initial position of the autocorrelation platform is determined as a time synchronization position, and a decimal frequency offset can be calculated by using the autocorrelation value of the autocorrelation platform. The invention further can intercept the received signal to carry out mutual correlation with the local training symbol from the time synchronization position acquired by the method, more accurately determines the time synchronization position and an integer frequency offset according to a double correlation peak generated by the structure of the training symbol, and at the same time can finely adjust the decimal frequency offset and distinguish different cells.

Description

technical field [0001] The present invention relates to the technical field of communication, and more precisely, relates to a downlink time and frequency synchronization method of an OFDM system. Background technique [0002] OFDM has attracted more and more attention due to its high data transmission rate, strong anti-multipath interference ability, and high spectrum efficiency. OFDM modulation has been successfully used in wired and wireless communications. Such as: LTE (Long Time Evolution), Wimax, IEEE802.11, DAB (Digital Audio Broadcasting), DVB and HyperLAN / 2 of European ETSI. One of the main reasons for choosing OFDM is that this modulation method can resist frequency selective fading and narrowband interference very well. In a single carrier system, a fading or interference will cause the entire link to fail, but in a multicarrier system, at a certain moment Only a small number of subchannels are affected by deep fading. [0003] One of the weaknesses of OFDM tec...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): H04L27/26
Inventor 严振亚郑磊李航黄俊
Owner BEIJING XINWEI TELECOM TECH
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