CN104954309B - The generation method of leading symbol and the generation method of frequency-domain OFDM symbol - Google Patents
The generation method of leading symbol and the generation method of frequency-domain OFDM symbol Download PDFInfo
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- CN104954309B CN104954309B CN201410121324.0A CN201410121324A CN104954309B CN 104954309 B CN104954309 B CN 104954309B CN 201410121324 A CN201410121324 A CN 201410121324A CN 104954309 B CN104954309 B CN 104954309B
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- 238000013507 mapping Methods 0.000 description 4
- 230000009897 systematic effect Effects 0.000 description 3
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2602—Signal structure
- H04L27/261—Details of reference signals
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2602—Signal structure
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- H—ELECTRICITY
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- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L25/00—Baseband systems
- H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
- H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
- H04L25/03006—Arrangements for removing intersymbol interference
- H04L25/03012—Arrangements for removing intersymbol interference operating in the time domain
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2626—Arrangements specific to the transmitter only
- H04L27/2627—Modulators
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Abstract
The invention discloses a kind of generation method of leading symbol in physical frame and the generation methods of frequency-domain OFDM symbol, and wherein the generation method of leading symbol includes: to generate fixed sequence program and signaling sequence respectively on frequency domain in physical frame；Fixed sequence program and signaling sequence are filled to effective subcarrier, and arranged between the fixed sequence program and signaling sequence in oem character set；Fill null sequence subcarrier respectively in effective subcarrier two sides to form the frequency-domain OFDM symbol of predetermined length；Inverse discrete fourier transform is made to obtain time-domain OFDM symbol to the frequency-domain OFDM symbol；Generate the modulated signal of the time-domain OFDM symbol；Leading symbol is generated based on the time-domain OFDM symbol and the modulated signal.The technical program solves in current DVB_T2 standard and other standards, and the problem of probability of failure occurs in leading symbol low complex degree receiving algorithm detection under frequency selective fading channels.
Description
Technical Field
The present invention relates to the field of wireless broadcast communication technologies, and in particular, to a method for generating preamble symbols in a physical frame and a method for generating frequency domain OFDM symbols.
Background
Generally, in order for a receiving end of an OFDM system to correctly demodulate data transmitted by a transmitting end, the OFDM system must implement accurate and reliable time synchronization between the transmitting end and the receiving end. Meanwhile, since the OFDM system is very sensitive to the carrier frequency offset, the receiving end of the OFDM system needs to provide an accurate and efficient carrier frequency spectrum estimation method to accurately estimate and correct the carrier frequency offset.
At present, a method for implementing time synchronization between a transmitting end and a receiving end in an OFDM system is basically implemented based on preamble symbols. The preamble symbol is a symbol sequence known to both the transmitting end and the receiving end of the OFDM system, and serves as the start of a physical frame (named P1 symbol), and the P1 symbol appears only once in each physical frame, and marks the start of the physical frame. The P1 symbols have the following uses:
1) enabling a receiving end to quickly detect whether a signal transmitted in a channel is an expected received signal;
2) providing basic transmission parameters (such as FFT point number, frame type information and the like) so that a receiving end can perform subsequent receiving processing;
3) and detecting initial carrier frequency offset and timing error, and compensating to achieve frequency and timing synchronization.
The DVB _ T2 standard provides a P1 symbol design based on a CAB time domain structure, and the functions are well realized. However, there are still some limitations on low complexity reception algorithms. For example, in a long multipath channel with 1024, 542, or 482 symbols, a large deviation occurs in timing coarse synchronization using the CAB structure, which results in an error in estimating the carrier integer multiple frequency offset in the frequency domain. In addition, DPSK differential decoding may also fail in frequency selective fading channels.
Disclosure of Invention
The invention solves the problem that the detection of preamble symbols in a low-complexity receiving algorithm under a frequency selective fading channel has failure probability in the current DVB _ T2 standard and other standards.
In order to solve the above problem, an embodiment of the present invention provides a method for generating a preamble symbol in a physical frame, including the following steps: respectively generating a fixed sequence and a signaling sequence on a frequency domain; filling the fixed sequence and the signaling sequence onto effective subcarriers, wherein the fixed sequence and the signaling sequence are arranged in a parity staggered manner; filling zero sequence subcarriers on two sides of the effective subcarriers respectively to form frequency domain OFDM symbols with preset length; performing inverse discrete Fourier transform on the frequency domain OFDM symbol to obtain a time domain OFDM symbol; generating a modulation signal of the time domain OFDM symbol; and generating a preamble symbol based on the time domain OFDM symbol and the modulation signal.
Optionally, the length of the fixed sequence is equal to the length of the signaling sequence, and the length is smaller than 1/2 of the predetermined length.
Optionally, the filling zero sequence subcarriers at two sides of the effective subcarrier to form a frequency domain OFDM symbol with a predetermined length respectively includes: and filling zero sequence subcarriers with equal length on two sides of the effective subcarriers respectively to form frequency domain OFDM symbols with preset length.
Optionally, the length of the zero sequence sub-carrier padded on each side is greater than a critical length value, and the critical length value is determined by the systematic symbol rate and a predetermined length.
Optionally, the generating the modulation signal of the time domain OFDM symbol includes: setting a frequency shift sequence; and multiplying the time domain OFDM symbol by the frequency shift sequence to obtain a modulation signal of the time domain OFDM symbol.
Optionally, the length of the frequency shift sequence is equal to or less than the length of the time domain OFDM symbol.
Optionally, generating a preamble symbol based on the time domain OFDM symbol and the modulation signal refers to: and taking the modulation signal as a guard interval of the time domain OFDM symbol, and splicing the guard interval at the front part of the time domain OFDM symbol to generate a preamble symbol.
Optionally, the predetermined length is 1024.
Optionally, the fixed sequence is a pseudo-random binary sequence.
Optionally, the step of generating a fixed sequence and a signaling sequence in the frequency domain, and the step of filling the fixed sequence and the signaling sequence into the effective subcarriers, and further includes the following steps between the fixed sequence and the signaling sequence in a parity-even staggered arrangement: and respectively carrying out DBPSK mapping on the fixed sequence and the signaling sequence to obtain the mapped fixed sequence and the mapped signaling sequence.
The embodiment of the invention also provides a method for generating the frequency domain OFDM symbol, which comprises the following steps: respectively generating a fixed sequence and a signaling sequence on a frequency domain; filling the fixed sequence and the signaling sequence onto effective subcarriers, wherein the fixed sequence and the signaling sequence are arranged in a parity staggered manner; and filling zero sequence subcarriers on two sides of the effective subcarriers respectively to form frequency domain OFDM symbols with preset length.
Compared with the prior art, the technical scheme of the invention has the following beneficial effects:
the structure of the modulation signal of the time domain OFDM symbol and the time domain OFDM symbol (as a preamble symbol) ensures that an obvious peak value can be obtained by utilizing delay correlation at a receiving end. Further, in the process of generating the preamble symbol, designing the modulation signal of the time domain OFDM symbol can avoid that the receiving end is subjected to continuous wave interference or single frequency interference, or a multipath channel with the same length as the modulation signal occurs, or a false detection peak occurs when the guard interval length in the received signal is the same as the length of the modulation signal.
Drawings
Fig. 1 is a flowchart illustrating a method for generating preamble symbols in a physical frame according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of the generation of a fixed sequence using a pseudo-random binary sequence generator in accordance with the present invention;
fig. 3 is a schematic diagram of frequency domain carrier distribution of frequency domain OFDM symbols generated in the method for generating preamble symbols in physical frames according to the present invention.
Detailed Description
The inventor finds that in the current DVB _ T2 standard and other standards, preamble symbols have a problem of a probability of failure in detection by a low-complexity reception algorithm under a frequency selective fading channel.
In view of the above problems, the inventors have studied and provided a method for generating preamble symbols in a physical frame, which ensures that a receiving end can still process a received signal with a carrier frequency deviation within a range of-500 kHz to 500 kHz.
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below.
Fig. 1 is a flowchart illustrating a method for generating preamble symbols in a physical frame according to an embodiment of the present invention. Referring to fig. 1, a method for generating preamble symbols in a physical frame includes the steps of:
step S11: respectively generating a fixed sequence and a signaling sequence on a frequency domain;
step S12: filling a fixed sequence and a signaling sequence onto effective subcarriers, wherein the fixed sequence and the signaling sequence are arranged in a parity staggered manner;
step S13: filling zero sequence subcarriers on two sides of the effective subcarriers respectively to form frequency domain OFDM symbols with preset length;
step S14: performing inverse discrete Fourier transform on the frequency domain OFDM symbol to obtain a time domain OFDM symbol;
step S15: generating a modulation signal of the time domain OFDM symbol;
step S16: and generating a preamble symbol based on the time domain OFDM symbol and the modulation signal.
It should be noted that the preamble symbol can be described from two domains, i.e., a time domain and a frequency domain. In this embodiment, the preamble symbol is generated by generating a frequency domain OFDM symbol in the frequency domain, and generating a preamble symbol in the time domain based on a modulation signal of the frequency domain OFDM symbol and a corresponding time domain OFDM symbol.
Specifically, as described in step S11, the fixed sequence and the signaling sequence are generated in the frequency domain, respectively. The fixed sequence includes the relevant information that the receiving end can use to do carrier frequency synchronization and timing synchronization, and the signaling sequence includes each basic transmission parameter.
In this embodiment, the fixed sequence may be a pseudo-random binary sequence.
For example, let fixed sequence be FC0,FC1,…，FCN-2The pseudo random binary sequence generator (PRBS) can be used for generating, and the specific generation process is as shown in fig. 2, which uses the pseudo random binary sequence generator to generate a schematic diagram of a fixed sequence. In practical applications, other types of sequences may be selected for the fixed sequence.
The signaling sequence is used to transmit P bits of information (e.g., various signaling), and has a total of 2PEach possibility is mapped to a signalling sequence of length M. The sequence group has 2PThe sequences are not related to each other, and are not related to known fixed sequences.
In other embodiments, DBPSK mapping may be performed on the fixed sequence and the signaling sequence according to system requirements.
In particular, for a fixed sequence FC0,FC1,…,FCN-2Performing DBPSK mapping to FC0,FC1,…,FCN-2Is mapped intoThe formula is as follows:
for the signaling sequence (set to SC)0,SC1,…，) Performing DBPSK mapping to SC0,SC1,,SCM-2Is mapped asThe formula is as follows:
the fixed sequence and the signaling sequence are padded on the active subcarriers and are arranged in a parity staggered manner as described in step S12.
In a preferred embodiment, the length of the fixed sequence is equal to the length of the signaling sequence, and the length is less than 1/2 of the predetermined length. The predetermined length is 1024, but it can be changed according to the system requirement in practical application.
Taking the predetermined length as 1024 as an example, let the length of the fixed sequence be N (that is, the number of effective subcarriers carrying the fixed sequence be N), and the length of the signaling sequence be M (that is, the number of effective subcarriers carrying the signaling sequence be M), in this embodiment, M = N. In other embodiments, N may also be slightly larger than M.
The fixed sequence and the signaling sequence are arranged in a parity staggered manner, namely the fixed sequence is filled to the position of even subcarrier (or odd subcarrier), correspondingly, the signaling sequence is filled to the position of odd subcarrier (or even subcarrier), thereby the distribution state of the parity staggered arrangement of the fixed sequence and the signaling sequence is presented on the effective subcarrier of the frequency domain. It should be noted that, when the lengths of the fixed sequence and the signaling sequence are not consistent (for example, M > N), the parity interleaving of the fixed sequence and the signaling sequence may be implemented by means of zero padding sequence subcarriers.
Zero sequence subcarriers are padded on both sides of the effective subcarrier to form frequency domain OFDM symbols of a predetermined length, respectively, as described in step S13.
In a preferred embodiment, this step comprises: and filling zero sequence subcarriers with equal length on two sides of the effective subcarriers respectively to form frequency domain OFDM symbols with preset length.
Following the example of a predetermined length of 1024, G =1024-M-N of the length of the zero sequence subcarrier, both sides are filled with (1024-M-N)/2 zero sequence subcarriers.
Further, in order to ensure that the receiving end can still process the received signal within the carrier frequency deviation range of-500 kHz to 500kHz, the value of (1024-M-N)/2 is usually larger than the critical length value (set to TH), which is determined by the systematic symbol rate and the predetermined length. E.g., a systematic symbol rate of 1024, 7.56M, length, thenFor example, M = N =350, then G =324, with both sides each filled with 162 zero-sequence subcarriers.
Accordingly, subcarriers (i.e., frequency domain OFDM symbols) P1_ X of a predetermined length (1024) are provided0,P1_X1,…，Pl_X1023Generated by filling in the following way:
wherein,the parity positions may be interchanged.
Fig. 3 is a schematic diagram illustrating a frequency domain carrier distribution of frequency domain OFDM symbols generated by the method for generating preamble symbols in a physical frame according to the present invention.
As shown in step S14, the frequency domain OFDM symbol is inverse discrete fourier transformed to obtain a time domain OFDM symbol.
The inverse discrete fourier transform described in this step is a common way of converting a frequency domain signal into a time domain signal, and is not described herein again.
Performing inverse discrete Fourier transform on P1_ Xi to obtain a time domain OFDM symbol:
a modulated signal of the time domain OFDM symbol is generated as described in step S15.
Specifically, the method comprises the following steps: 1) setting a frequency shift sequence; 2) and multiplying the time domain OFDM symbol by the frequency shift sequence to obtain a modulation signal of the time domain OFDM symbol.
For example, let the frequency shift sequence beWherein f isSH1/(1024T). M (t) can also be designed into other sequences, such as m-sequence or some simplified window sequence.
The modulation signal of the time domain OFDM symbol is P1_ b (t), and P1_ b (t) is obtained by multiplying P1_ a (t) by the frequency shift sequence m (t) (i.e., P1_ b (t) ═ P1_ a (t) × m (t)), and is used as the guard interval of P1_ a (t).
A preamble symbol is generated based on the time domain OFDM symbol and the modulation signal as described in step S16.
Specifically, the method comprises the following steps: and taking the modulation signal as a guard interval of the time domain OFDM symbol, and splicing the guard interval at the front part of the time domain OFDM symbol to generate a preamble symbol.
For example, the preamble symbol may be generated according to the following formula:
the length of the guard interval may also be smaller than the length of the time domain OFDM symbol, the length of the guard interval is set to be B _ len, the length of the time domain OFDM symbol is set to be a, and the front B _ len part of a is taken for modulation, that is:
the embodiment of the invention also provides a method for processing the receiving signal of the receiving end. The method comprises the following specific steps:
step S21: receiving a signal, which is r (t).
Step S22: demodulating the received signal by M (t); for example, fSH＝1/(1024T)Then, multiply the received signal to order
Step S23: delaying the demodulated signal; for example, let r2(t)＝r1(t-1024)。
Step S24: correlating the delayed signal with the received signal (i.e., r)2(t) correlates with r (t) to obtain a correlation value (i.e., the location where the timing coarse synchronization is obtained).
Step S25: and performing Fast Fourier Transform (FFT) on the correlation value to obtain a frequency domain 1K signal, and removing the fixed sequence from the signal frequency domain shift point to obtain a channel estimation value of the fixed sequence point.
Step S26: and performing inverse Fourier transform (IFFT) on the channel estimation value to a time domain, wherein if an obvious peak value exists, the shift number is correct integer frequency offset, and the peak value also marks the position of the strongest path.
Step S27: after the time domain compensates the integral multiple frequency offset, the time domain sequence corresponding to the fixed sequence on the frequency domain is utilized to carry out local correlation, thereby calculating the decimal frequency offset and obtaining the accurate timing synchronization position.
Step S28: and interpolating a channel estimation value of the signaling sequence by utilizing the channel estimation value of the fixed sequence point in a frequency domain, and then carrying out coherent demodulation to obtain the signaling.
The embodiment of the invention also provides a method for generating the frequency domain OFDM symbol, which comprises the following steps:
step S31: respectively generating a fixed sequence and a signaling sequence on a frequency domain;
step S32: filling a fixed sequence and a signaling sequence onto effective subcarriers, wherein the fixed sequence and the signaling sequence are arranged in a parity staggered manner;
step S33: and filling zero sequence subcarriers on two sides of the effective subcarriers respectively to form frequency domain OFDM symbols with preset length.
In this embodiment, the specific implementation processes of step S31 to step S33 for generating the frequency domain OFDM symbol may refer to the detailed descriptions of step S11 to step S13 in the method for generating the preamble symbol in the physical frame, which are not described herein again.
That is to say, based on the method for generating the frequency domain OFDM symbol provided in this embodiment, a person skilled in the art may use other embodiments (not limited to the foregoing steps S14 to S16) to process the frequency domain OFDM symbol to generate the preamble symbol in the time domain.
In summary, the technical solution ensures that an obvious peak can be obtained at a receiving end by using delay correlation by using the modulation signal of the time domain OFDM symbol and the structure of the time domain OFDM symbol (as a preamble symbol). Further, in the process of generating the preamble symbol, designing the modulation signal of the time domain OFDM symbol can avoid that the receiving end is subjected to continuous wave interference or single frequency interference, or a multipath channel with the same length as the modulation signal occurs, or a false detection peak occurs when the guard interval length in the received signal is the same as the length of the modulation signal.
Although the present invention has been described with reference to the preferred embodiments, it is not intended to limit the present invention, and those skilled in the art can make variations and modifications of the present invention without departing from the spirit and scope of the present invention by using the methods and technical contents disclosed above.
Claims (3)
1. A method for generating preamble symbols in a physical frame, comprising the steps of:
obtaining a time domain OFDM symbol;
generating a modulated signal of the time domain OFDM symbol,
generating a preamble symbol based on the time domain OFDM symbol and the modulation signal,
the modulation signal is used as a guard interval of the time domain OFDM symbol, the length of the modulation signal is smaller than that of the time domain OFDM symbol, the front part of the guard interval in the time domain OFDM symbol is taken for modulation to obtain the modulation signal, and the modulation signal is spliced at the rear part of the time domain OFDM symbol; the time domain OFDM symbol is obtained by performing inverse discrete Fourier transform on a frequency domain OFDM symbol with a preset length, wherein the preset length is 1024.
2. The method of generating preamble symbols in a physical frame according to claim 1,
the generating the modulation signal of the time domain OFDM symbol comprises:
setting a frequency shift sequence;
and multiplying the time domain OFDM symbol by the frequency shift sequence to obtain a modulation signal of the time domain OFDM symbol.
3. The method of generating preamble symbols in a physical frame according to claim 2,
the length of the frequency shift sequence is equal to or less than the length of the time domain OFDM symbol.
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| CN201611013939.7A CN106603456A (en) | 2014-03-28 | 2014-03-28 | Generation method of preamble symbol and generation method of frequency-domain OFDM symbol |
| CN201611013351.1A CN106685877A (en) | 2014-03-28 | 2014-03-28 | Processing method of received signals of receiving end |
| CN201410121324.0A CN104954309B (en) | 2014-03-28 | 2014-03-28 | The generation method of leading symbol and the generation method of frequency-domain OFDM symbol |
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| CN201611013939.7A Division CN106603456A (en) | 2014-03-28 | 2014-03-28 | Generation method of preamble symbol and generation method of frequency-domain OFDM symbol |
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| CN105024963A (en) * | 2014-04-30 | 2015-11-04 | 上海数字电视国家工程研究中心有限公司 | Frequency domain OFDM symbol generation method and preamble symbol generation method |
| CN105007145B (en) * | 2014-04-16 | 2018-12-18 | 上海数字电视国家工程研究中心有限公司 | The generation method of leading symbol and the generation method of frequency-domain OFDM symbol |
| CN111490957B (en) * | 2020-03-10 | 2023-06-16 | 北京睿信丰科技有限公司 | Method and device for generating preamble sequence in time domain |
| CN115173952B (en) * | 2022-06-29 | 2023-08-11 | 苏州大学 | Optimized receiving method of optical universal filtering multi-carrier optical access network |
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| CN1081416C (en) * | 1999-01-04 | 2002-03-20 | 北京邮电大学 | Frame structure suitable for wide-band code division multiple access signal transmission |
| US8599764B2 (en) * | 2003-09-02 | 2013-12-03 | Qualcomm Incorporated | Transmission of overhead information for reception of multiple data streams |
| CN1937604B (en) * | 2005-09-20 | 2013-01-16 | 中兴通讯股份有限公司 | Initial access frame synchronizing method and device for orthogonal frequency division multiplexing system |
| CN101374131B (en) * | 2007-08-20 | 2013-01-30 | 株式会社Ntt都科摩 | Method and apparatus of timing synchronization, leading symbol as well as method and apparatus for generating the same |
| CN101132268B (en) * | 2007-09-13 | 2011-07-13 | 中兴通讯股份有限公司 | Frame generation method based on orthogonal frequency division multiplexing technology in TDD mode |
| CN101170534B (en) * | 2007-10-31 | 2010-06-23 | 中兴通讯股份有限公司 | A timing rough synchronization capturing method for mobile multimedia broadcast system |
| US8248910B2 (en) * | 2008-01-29 | 2012-08-21 | Nokia Corporation | Physical layer and data link layer signalling in digital video broadcast preamble symbols |
| CN101437005B (en) * | 2008-12-12 | 2012-11-14 | 中国人民解放军理工大学通信工程学院 | Method for estimating integer multiple frequency deviation with timing error during communication synchronization process |
| CN101938444B (en) * | 2009-06-30 | 2014-06-18 | 中兴通讯股份有限公司 | Method and device for estimating and correcting frequency offset of orthogonal frequency division multiplexing system |
| CN101945071A (en) * | 2009-07-10 | 2011-01-12 | 中兴通讯股份有限公司 | Confirming method of synchronization sequence in multipoint collaborative environment, synchronizing method and device |
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| CN103581096B (en) * | 2013-03-25 | 2017-05-10 | 上海数字电视国家工程研究中心有限公司 | OFDM modulating and demodulating method and digital signal emitting and receiving system |
| CN103532898B (en) * | 2013-04-22 | 2017-03-22 | 上海数字电视国家工程研究中心有限公司 | OFDM training symbol synchronization method based on CAZAC sequence |
| CN103532899B (en) * | 2013-07-31 | 2016-07-06 | 上海数字电视国家工程研究中心有限公司 | Time domain OFDM synchronizing symbol generates and demodulation method, data frame transmission method |
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- 2014-03-28 CN CN201410121324.0A patent/CN104954309B/en active Active
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| CN106603456A (en) | 2017-04-26 |
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