CN107222444A - The receiving handling method of leading symbol in physical frame - Google Patents
The receiving handling method of leading symbol in physical frame Download PDFInfo
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Abstract
The invention provides a kind of receiving handling method of leading symbol in physical frame, including to being handled the data signal received to obtain baseband signal；Judge with the presence or absence of the leading symbol for expecting to receive in the baseband signal, wherein, the leading symbol for expecting to receive is that, based on time-domain OFDM symbol, its front portion has the spatial structure of modulated signal with cyclic prefix, its rear portion；In above-mentioned judged result in the case of being, determine position of the leading symbol in physical frame and solve the signaling information entrained by the leading symbol, the technical program is solved in current DVB_T2 standards and other standards, and leading symbol low complex degree receiving algorithm under complex frequency Selective Fading Channel detects the problem of probability of failure occur.
Description
The application is a divisional application of the original, the application number of the original is 201410326504.2, and the application date is 2014, 7 and 10, the invention and creation name of the method for receiving and processing the preamble symbol in the physical frame is' invented.
Technical Field
The present invention relates to the field of wireless broadcast communication technologies, and in particular, to a method for receiving and processing preamble symbols in a physical frame.
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 only one P1 symbol or a plurality of P1 symbols occur consecutively in each physical frame, which 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) detecting initial carrier frequency offset and timing error, and compensating to achieve frequency and timing synchronization;
4) emergency alerts or broadcast system wake-up.
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. Additionally, DBPSK differential decoding may also fail in complex frequency selective fading channels, such as long multipath. Moreover, since the DVB _ T2 has no cyclic prefix in the time domain structure, if the DVB _ T2 is combined with a frequency domain structure that needs to perform channel estimation, the performance of the frequency domain channel estimation is seriously degraded.
Disclosure of Invention
The invention solves the problem that the detection of preamble symbols in a low-complexity receiving algorithm under a complex frequency selective fading channel has failure probability in the current DVB _ T2 standard and other standards.
To solve the above problem, an embodiment of the present invention provides a method for receiving and processing preamble symbols in a physical frame, including the following steps: processing the received digital signal to obtain a baseband signal; judging whether a preamble symbol expected to be received exists in the baseband signal, wherein the preamble symbol expected to be received is a time domain OFDM symbol as a main body, and the front part of the preamble symbol is provided with a cyclic prefix and the rear part of the preamble symbol is provided with a time domain structure of a modulation signal; and if the judgment result is yes, determining the position of the preamble symbol in the physical frame and solving the signaling information carried by the preamble symbol.
Compared with the prior art, the technical scheme of the invention has the following beneficial effects:
whether a preamble symbol expected to be received exists in a received baseband signal (obtained by processing a received physical frame), wherein the preamble symbol is mainly a time domain OFDM symbol, the front part of the preamble symbol has a cyclic prefix, and the rear part of the preamble symbol has a time domain structure of a modulation signal. And under the condition that the judgment result is yes, determining the position of the preamble symbol in the physical frame and decoding the signaling information carried by the preamble symbol, thereby decoding the information of the subsequent data frame according to the indication of the signaling information.
The structure of the modulation signal of the time domain OFDM symbol and the time domain OFDM symbol ensures that an obvious peak value can be obtained by utilizing delay correlation at a receiving end. Moreover, the modulation signal of the time domain OFDM symbol can avoid that a 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 value occurs when the length of a guard interval in the received signal is the same as the length of the modulation signal.
Further, the frequency domain OFDM symbol corresponding to the time domain OFDM symbol in the preamble symbol includes: the system comprises effective subcarriers and zero sequence subcarriers, wherein the zero sequence subcarriers are positioned on two sides of the effective subcarriers; the effective subcarriers include fixed sequence subcarriers and signaling sequence subcarriers, and the fixed sequence subcarriers and the signaling sequence subcarriers are arranged in a parity-staggered manner. Through the specific frequency domain structure design, the fixed sequence can be used as the pilot frequency in the physical frame, thereby facilitating the receiving end to decode and demodulate the preamble symbol in the received physical frame.
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FIG. 1 is a diagram illustrating a CAB structure of preamble symbols in a physical frame according to the present invention;
fig. 2 is a schematic diagram of a CAB structure of preamble symbols for transmitting signaling information according to the present invention;
fig. 3 is a flowchart illustrating a method for receiving and processing preamble symbols in a physical frame according to an embodiment of the present invention.
Detailed Description
The inventor finds that in the current DVB _ T2 standard and other standards, preamble symbols have the problem of low complexity receiving algorithm detection failure probability under complex frequency selective fading channels.
In view of the above problems, the inventors have studied and provided a method for receiving and processing preamble symbols in a physical frame. The method is based on the characteristic of the time domain waveform of the preamble symbol, and the structure of the modulation signal of the time domain OFDM symbol and the time domain OFDM symbol is utilized to ensure that an obvious peak value can be obtained at a receiving end by utilizing delay correlation. Moreover, the modulation signal of the time domain OFDM symbol can avoid that a 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 value occurs when the length of a guard interval in the received signal is the same as the length of the modulation signal.
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 schematic diagram illustrating a CAB structure of preamble symbols in a physical frame according to the present invention. Referring to fig. 1, a segment a represents a time domain OFDM symbol, a segment C represents a cyclic prefix, and a segment B represents a modulated signal.
The time domain OFDM symbol is obtained by the sending end after the frequency domain OFDM symbol is subjected to inverse discrete Fourier transform. For example, for P1_ XiObtaining a time domain OFDM symbol after performing inverse discrete Fourier transform:
wherein M is the number of effective non-zero subcarriers.
And intercepting the time domain OFDM symbol with the length of the cyclic prefix from the time domain OFDM symbol as the cyclic prefix, wherein the length of the cyclic prefix is equal to or less than the length of the time domain OFDM symbol. The determined cyclic prefix length is determined according to any one or more factors of the multi-path length which the wireless broadcast communication system usually needs to resist, the minimum length of a robust correlation peak value obtained by the system at the lowest receiving threshold and the number of bits of the time domain structure transmission signaling. If only the signaling needs to be transmitted in the frequency domain structure, and the time domain structure is fixed and no signaling needs to be transmitted, only one or two of the multipath length to be countered and the minimum length of the robust correlation peak obtained by the system at the lowest receiving threshold need to be considered. In general, the longer the length of the cyclic prefix, the better the performance against long multipath, and the longer the length of the cyclic prefix and the length of the modulated signal, the more robust the peak of its delay correlation. Generally, the length of the cyclic prefix and the length of the modulation signal are required to be greater than or equal to the minimum length of the robust correlation peak obtained by the system at the lowest receiving threshold.
And generating a modulation signal based on the intercepted time domain OFDM symbol with the cyclic prefix length.
In practical application, a frequency offset sequence may be set, and then the time domain OFDM symbol with the cyclic prefix length or a part of the time domain OFDM symbol with the cyclic prefix length is multiplied by the frequency offset sequence to obtain the modulation signal.
Let NcpFor determined cyclic prefix length, LenBIs the modulation signal length.
The frequency offset sequence isWherein f isSHMay be selected as the frequency domain subcarrier spacing (i.e., 1/N) corresponding to the time domain OFDM symbolAT), where T is the sampling period, NAIs the length of the time domain OFDM symbol. In this example, NAIs 1024, take fSH1/1024T. In other examples, to sharpen the correlation peak, fSHCan also be selected to be 1/(Len)BT). When LenB＝NCPWhen f is presentSH＝1/NCPAnd T. Such as LenB＝NCPWhen is 512, fSH＝1/512T。
In other embodiments, m (t) may also be designed into other sequences, such as an m-sequence or some simplified window sequence.
The modulation signal of the partial time domain OFDM symbol is P1_ b (t), P1_ b (t) is obtained by multiplying the partial time domain OFDM symbol by the frequency offset sequence m (t), i.e., P1_ b (t) is:
n1 is the sampling point number of the time domain OFDM symbol selected to be copied to the start of the modulation signal segment.
The length of the modulation signal can obtain robust correlation by the system at the lowest receiving thresholdThe minimum length of the peak. Typically the modulation signal length is equal to or greater than the minimum length. Let NASetting the sampling point serial number of the time domain OFDM symbol as 0,1, … N for the length of the time domain OFDM symbolAAnd 1, setting N1 as the sampling point sequence number of the time domain OFDM symbol corresponding to the starting point selected to be copied to the modulation signal segment, and setting N2 as the sampling point sequence number of the time domain OFDM symbol corresponding to the end point selected to be copied to the modulation signal segment. Wherein,
N2＝N1+LenB-1
for convenience of description, the time domain OFDM symbol is divided into 2 parts, the first part is a part of the time domain OFDM symbol (generally, the front part of the time domain OFDM symbol) which is not truncated as a cyclic prefix, and the second part is a part of the time domain OFDM symbol (generally, the rear part of the time domain OFDM symbol) which is truncated as a cyclic prefix. If all the time domain OFDM symbols are intercepted as cyclic prefixes, the length of the first section is 0. N1 must fall within the second segment, i.e., the portion of the time domain OFDM symbol selected for the modulated signal segment does not span beyond the portion of the time domain OFDM symbol truncated as a cyclic prefix.
The modulation signal is only modulated by frequency offset or other signals, so that the correlation value of the modulation signal and the cyclic prefix and the correlation value of the modulation signal and the time domain OFDM symbol can be used for timing synchronization and small offset estimation. In practical applications, the modulated signal length typically does not exceed the length of the cyclic prefix portion. The modulation signal can avoid the receiving end from continuous wave interference or single frequency interference, or the occurrence of a multipath channel with the same length as the modulation signal, or the occurrence of a false detection peak when the length of a guard interval in the received signal is the same as the length of the modulation signal.
As shown in fig. 1, the cyclic prefix is spliced at the front of the time domain OFDM symbol as a guard interval, and the modulated signal is spliced at the rear of the OFDM symbol as a modulated frequency offset sequence to generate a preamble symbol of a CAB structure.
For example, the preamble symbol may be based on employing the time domain expression:
in a preferred embodiment, the predetermined length NA＝1024；NcpIs half of said predetermined length, i.e. when NAWhen is 1024, Ncp＝512。
Further, different cyclic prefixes and modulation signals are generated, so that finally formed preamble symbols are different, when a receiving end demodulates the preamble symbols in the received physical frame, delay correlation operation can be performed on the preamble symbols, different delays are set according to attempts, and only when delay values are matched with design parameters of the preamble symbols, an obvious correlation peak value can be obtained, so that different preamble symbols are distinguished, and the purpose of transmitting signaling information in a time domain structure in the preamble symbols is achieved.
The embodiment of the invention provides a method for intercepting a time domain OFDM symbol with a cyclic prefix length by selecting different initial positions in the time domain OFDM symbol for intercepting the time domain OFDM symbol with a modulation signal length to generate a modulation signal, so that a finally formed preamble symbol transmits signaling information through the different initial positions.
The transmitted signaling information is exemplified as an emergency alert or a broadcast system identity EAS _ flag.
For example, the time domain OFDM symbol has a length of 1024, NCPIs 512+ L, LenB512-L, the length of the whole preamble symbol is 2048, wherein the modulation frequency offset value fSH1/1024T, the emergency alert or broadcast system identity EAS _ flag is signaled by selecting a different starting position N1 for transmission of the 1-bit signaling.
If EAS _ flag is equal to 1, taking N1 as 512-L, i.e. N is equal toAAnd the corresponding sampling point with the serial number of 512-L to 1023-2L of the OFDM symbol of 1024 generates B after modulating the frequency offset sequence, and the B is placed at the rear part of A.
If EAS _ flag is equal to 0, N1 is equal to 512+ L, i.e. N is equal toAAnd the corresponding sampling point with the serial number of 512+ L-1023 of the 1024 OFDM symbol generates B after modulating the frequency offset sequence, and the B is placed at the rear part of A.
Referring to fig. 2, another CAB structure for transmitting a preamble symbol of an emergency alert or broadcast system flag EAS _ flag is shown. Wherein the value of L is 8.
The time domain expression is:
if EAS _ flag is 1
If EAS _ flag is equal to 0
As another example, the predetermined length is 1024, NCPIs 512+ 15L, LenBFor 512, N1 may take 512+ i × L, and i is greater than or equal to 0 and less than 16, which may indicate 16 different fetching methods for transmitting 4-bit signaling information. For example, different transmitters may transmit their corresponding identification TXID by taking a different N1, the same transmitter may also transmit transmission parameters by changing N1 in time. Preferably, L is 16.
As another example, the predetermined length is 1024, NCPIs 512+ 7L, LenBFor 512, N1 can take 512+ i L, i is more than or equal to 0 and less than 7, and 3bit signaling information is transmitted. Preferably, L is 16.
The above is the generation method of the preamble symbol and the characteristic of the preamble symbol of the CAB structure in the embodiment of the present invention. At the receiving end, the characteristics of the preamble symbol can be used to determine whether a received baseband signal (obtained by processing the received physical frame) has a signal expected to be received, and if the determination result is yes, the position of the preamble symbol in the physical frame is determined and the signaling information carried by the preamble symbol is decoded, so as to decode the information of the subsequent data frame according to the indication of the signaling information.
Fig. 3 is a flowchart illustrating a specific embodiment of a method for receiving and processing preamble symbols in a physical frame according to the present invention. Referring to fig. 3, the reception processing method includes the steps of:
step S11: processing the received physical frame to obtain a baseband signal;
step S12: judging whether a preamble symbol expected to be received exists in the baseband signal, wherein the preamble symbol expected to be received is a time domain OFDM symbol as a main body, and the front part of the preamble symbol is provided with a cyclic prefix and the rear part of the preamble symbol is provided with a time domain structure of a modulation signal;
step S13: and if the judgment result is yes, determining the position of the preamble symbol in the physical frame and solving the signaling information carried by the preamble symbol.
As described in step S11, the received physical frame is processed to obtain a baseband signal. Generally, a signal received by a receiving end is an analog signal, and therefore, it is necessary to perform analog-to-digital conversion on the signal to obtain a digital signal, and then perform processing such as filtering and down-sampling on the digital signal to obtain a baseband signal. If the receiving end receives the intermediate frequency signal, the receiving end needs to perform spectrum shifting after performing analog-to-digital conversion on the intermediate frequency signal, and then performs processing such as filtering and down-sampling to obtain a baseband signal.
In step S12, it is determined whether there is a preamble symbol expected to be received in the baseband signal, wherein the preamble symbol expected to be received is a time domain OFDM symbol as a main body, and has a time domain structure with a cyclic prefix at the front part and a modulated signal at the rear part.
Specifically, first, the receiving end determines whether there is a preamble symbol expected to be received in the received baseband signal, i.e., whether the received signal conforms to the receiving standard, for example, the receiving end needs to receive data of the DVB _ T2 standard, and then needs to determine whether the received signal is based on the DVB _ T2 standard (e.g., whether there is a preamble symbol in the DVB _ T2 format in a physical frame).
In this embodiment, the determining whether the preamble symbol expected to be received exists in the baseband signal includes the following steps:
step S12A: according to the delay relationship and the modulation frequency offset relationship between each two of a cyclic prefix, a time domain OFDM symbol and a modulation signal in a preamble symbol expected to be received, performing delay sliding correlation and demodulation frequency offset on a baseband signal to obtain three delay correlation accumulated values;
step S12B: performing mathematical operation based on one, two or three of the three delay correlation accumulated values, and performing peak detection on an absolute value of a result of the mathematical operation;
step S12C: and if the peak detection result meets a preset condition, determining that the expected received signal exists in the baseband signal.
Specifically, referring to the above embodiment, the time domain expression of the preamble symbol is:
wherein N isAIs the length of the time domain OFDM symbol, NcpFor the length of the cyclic prefix, N1 is the sampling point number of the time domain OFDM symbol selected to be copied to the start of the modulation signal segment. Such as NAWhen is 1024, Ncp＝520，LenBN1 is 504 or 520, 504.
Since the preamble symbol desired to be received is a time domain OFDM symbol as a main body, the front part thereof has a cyclic prefix and the rear part thereof has a time domain structure of a modulated signal. Then the received signal, if it contains the desired preamble symbol, contains one or more multipaths each having the structure described above.
OFDM symbol based on cyclic prefix and time domainThe delay correlation of the received signal is performed by delay sliding correlation, and the delay correlation expression U is1(n) and delay correlation accumulated value U1' (n) is as follows:
U1(n)＝r(n)r*(n-NA)
can select the U pair1' (n) normalizing the energy to obtain U1s'(n)。
Namely, it is
Based on the delay relation and modulation frequency offset value between the modulation signal and the cyclic prefix, the received signal is delayed slide-correlated and the frequency offset is demodulated, and attention is paid to the delay correlation expression U2(n) and delay correlation accumulated value U2' (n) is as follows:
also can select the pair U2' (n) normalizing the energy to obtain U2s'(n)。
Based on the delay relation between the modulation signal and the time domain OFDM symbol and the modulation frequency offset value, the delay sliding correlation is carried out on the received signal, and the delay correlation expression U is expressed3(n) and delay correlation accumulated value U3' (n) is as follows:
also can select the pair U3' (n) normalizing the energy to obtain U3s'(n)。
Wherein corr _ len can take 1/fSHT to avoid continuous wave interference or LenBSo that the peak is sharp.
Using delayed correlation accumulation values U1'(n)、U2'(n)、U3' (n) performing mathematical operations, e.g. U2'(n)·U3'*(n), or U1'(n-NA+N1)·U2'(n)·U3'*And (n) acquiring the preamble symbol, and judging whether the baseband signal has the expected received signal.
E.g. NA＝1024，Ncp＝520，LenB504, 520, N1,
delaying a received signal by 1024 sampling points to perform sliding correlation on the received signal to obtain a first delay correlation accumulated value;
carrying out sliding correlation on 1528 sampling points of the received signal delay and the received signal after frequency offset demodulation to obtain a second delay correlation accumulated value;
and delaying the received signal by 504 sampling points and performing sliding correlation on the received signal after demodulation frequency offset to obtain a third delay correlation accumulated value.
And as such NA＝1024，Ncp＝512，LenB512, N1,
delaying a received signal by 1024 sampling points to perform sliding correlation on the received signal to obtain a first delay correlation accumulated value;
delaying the received signal by 1536 sampling points and performing sliding correlation on the received signal after frequency offset demodulation to obtain a second delay correlation accumulated value;
and delaying the received signal by 512 sampling points and performing sliding correlation on the received signal after demodulation frequency offset to obtain a third delay correlation accumulated value.
When a preamble symbol occurs, U2'(n)·U3'*(n) or U1'(n-NA+N1)·U2'(n)·U3'*The absolute value of (n) will peak. Thus can pass through the pair U2'(n)·U3'*(n) or U1'(n-NA+N1)·U2'(n)·U3'*(n) or U after energy normalization2s'(n)·U3s'*(n) or U1s'(n-NA+N1)·U2s'(n)·U3s'*And (n) adopting various peak detection algorithms to judge whether the expected received signal exists in the baseband signal. And if the peak value detection result meets a preset condition, determining that the pilot symbol expected to be received and the signal expected to be received exist in the baseband signal. For example, the peak maximum value is compared with a fixed threshold, if the peak maximum value exceeds the threshold, the preamble symbol and signal expected to be received exist, otherwise, the peak maximum value does not exist.
The determining the position of the preamble symbol in the physical frame in step S12 includes: the position of the preamble symbol in the physical frame is determined based on the result of peak detection satisfying a preset condition.
Specifically, if there is a preamble symbol expected to be received, the position of the preamble symbol in the physical frame is determined according to the part of the value or the maximum value where the peak value is large.
Fractional frequency offset estimation can also be carried out by using the peak value detection result, and the fractional frequency offset estimation can be obtained by weighting the value calculated by the following 2 methods by taking the peak value.
The method comprises the following steps:
wherein N isfThe point number with large peak value participating in statistics shows how many points on the peak value are taken to participate in calculation, and the calculation can also be carried out by taking the maximum value.
The method 2 comprises the following steps:
wherein k is equal to U1' (k) the point where the absolute value is maximum.
Further, since the transmitting end can use N1 (i.e. different starting positions in the time domain OFDM symbol intercepting the length of the modulation signal) to transmit signaling information, the expected received preamble symbol has the following characteristics:
1) intercepting a time domain OFDM symbol with a cyclic prefix length from the time domain OFDM symbol as a cyclic prefix;
2) generating a modulation signal based on the intercepted time domain OFDM symbol with the cyclic prefix length;
the OFDM signal transmission method comprises the steps that in a time domain OFDM symbol for intercepting a cyclic prefix length, different initial positions are selected to intercept the time domain OFDM symbol with a modulation signal length to generate a modulation signal, so that a finally formed preamble symbol transmits signaling information through the different initial positions;
in this case, based on different starting positions, several different delay relationships between the modulation signal and the cyclic prefix and between the modulation signal and the time domain OFDM symbol are generated, so as to determine whether there is a preamble symbol expected to be received in the baseband signal. And if the judgment result is yes, determining the position of the preamble symbol in the physical frame.
According to the delay relations between a plurality of different modulation signals and cyclic prefixes and between the modulation signals and time domain OFDM symbols, further obtaining a plurality of delay related accumulated value groups, wherein each group comprises delay sliding correlation and demodulation frequency deviation of the baseband signals according to the delay relations and modulation frequency deviation relations between every two of the cyclic prefixes, the time domain OFDM symbols and the modulation signals in the expected received preamble symbols, so as to obtain three delay related accumulated values;
computing one, two or three delay correlation accumulated values in each delay correlation accumulated value group, and carrying out peak value detection on the absolute value of the multiplication result;
and if the result of one group of peak value detection meets a preset condition, determining that the pilot symbol expected to be received exists in the baseband signal.
For example, when the preamble symbols use different N1 to transmit Q-bit signaling, the delay sliding correlation with N1 defined as a fixed value is a group. Each group containing the 3 delay-correlated accumulated values described above. Receiving end simultaneous 2QThe delay correlation set above for different values of N1, then from 2QEach U2'(n)·U3'*(n) or U1'(n-NA+N1)·U2'(n)·U3'*In the absolute value of (n), it is determined whether or not a desired preamble symbol exists.
If none of the absolute values exceeds the threshold, it indicates that the desired received signal is not present in the baseband signal. For example, when N1 is 504 or 520 is used to transmit a 1-bit emergency alert or broadcast system identifier, where N1-520 is denoted as a normal preamble symbol and N1-504 is denoted as an emergency alert or broadcast system, the above-mentioned delay correlation group of 2 groups is performed.
The group with the emergency alert broadcast flag 0, i.e., N1-520, is taken
Delaying a received signal by 1024 sampling points to perform sliding correlation on the received signal;
1528 sampling points of the received signal delay are in sliding correlation with the received signal after frequency offset demodulation;
the received signal delays 504 sampling points and carries out sliding correlation on the received signal after frequency offset demodulation;
the group with the emergency alert broadcast flag 1, i.e., N1 ═ 504, takes
The received signal is delayed by 1024 sampling points and is subjected to sliding correlation with the received signal after frequency offset demodulation;
carrying out sliding correlation on the received signal subjected to frequency offset demodulation by 1544 sampling points;
the received signal is delayed by 520 sampling points and is subjected to sliding correlation with the received signal after frequency offset demodulation. If the set of maximum values N1-520 exceeds the threshold, indicating that the baseband signal is the desired signal and the preamble symbol is present, EAS _ flag is 0; conversely, if the set of maximum values of N1-504 exceeds the threshold, it indicates that EAS _ flag-1; if none of the 2 sets exceeds the threshold, it indicates that the baseband signal is not the desired signal.
The decoding of the signaling information carried by the preamble symbol in step S13 includes the following steps: and solving signaling information carried by the preamble symbol by using all or part of the time domain waveform of the preamble symbol and/or a frequency domain signal obtained by performing Fourier transform on all or part of the time domain waveform of the preamble symbol.
Specifically, in this step, since the sending end may use N1 (i.e., different starting positions in the time domain OFDM symbol where the modulation signal length is truncated) to transmit the signaling information, the sending end may also use the signaling sequence subcarriers in the frequency domain OFDM symbol corresponding to the time domain OFDM symbol to transmit the signaling information. Therefore, the receiving end will correspondingly solve the signaling information based on the two different signaling information transmission modes, and the specific implementation process is as follows:
the transmitting end utilizes N1 to transmit signaling information:
as described above, the receiving end can solve the signaling information carried by the preamble symbol according to the condition that the determination result is yes. If the result of the peak detection of a certain group meets the preset condition, the signaling corresponding to the initial position of the modulation signal segment corresponding to the group is the transmission signaling.
The transmitting terminal utilizes the signaling sequence subcarrier in the frequency domain OFDM symbol corresponding to the time domain OFDM symbol to transmit signaling
Information:
specifically, the frequency domain OFDM symbol corresponding to the time domain OFDM symbol includes: the system comprises effective subcarriers and zero sequence subcarriers, wherein the zero sequence subcarriers are positioned on two sides of the effective subcarriers; the effective subcarriers include fixed sequence subcarriers and signaling sequence subcarriers, and the fixed sequence subcarriers and the signaling sequence subcarriers are arranged in a parity-staggered manner. That is, the fixed sequence is filled to the position of even subcarrier (or odd subcarrier), and 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. When the lengths of the fixed sequence and the signaling sequence are not consistent, the parity staggering arrangement of the fixed sequence and the signaling sequence can be realized by a zero padding sequence subcarrier mode.
The signaling sequence and the fixed sequence may be generated by: and selecting a fixed sequence from all the selectable fixed sequences, generating a signaling sequence set with good autocorrelation and cross-correlation, and enabling an OFDM symbol formed based on any signaling sequence in the fixed sequence and the signaling sequence set to meet the required power peak-to-average ratio after being subjected to inverse Fourier transform.
In a particular embodiment, the first and second electrodes are,
the fixed sequence has a length of 353 and an amplitude of 1, as represented by:
wherein, ω isnThe values of (A) are arranged in rows from left to right in sequence as shown in the following table:
the number of the signaling sequences is 512, the signaling sequence set comprises 4 signaling sequence subsets, each signaling sequence subset comprises 128 signaling sequences, and the length L of each signaling sequence is 353.
The method for generating the signaling sequence comprises the following steps:
number of cyclically shifted bits (q)i,ki,i＝0～2N-1) where N-7 means that each sub-set of signalling sequences contains 128 signalling sequences for a total of 4 sub-sets of 512 signalling sequences;
first, a CAZAC sequence is generated:
then, it is cyclically shifted:
si *(n)＝[s(ki-1),s(ki),...,S(root-1),s(0),...,s(ki-1)]
finally, the sequence of length L is truncated from the head of the sequence:
SCi(n)＝si *(n),n＝0～L-1
the resulting sequence SCi(n) is the required ith signaling sequence.
R is the average power ratio of the fixed sequence to the signaling sequence, which is 1 in this example.
1) The root value of the first signaling sequence subset is 353;
the values of q are all in the following table:
| 1 | 9 | 10 | 16 | 18 | 21 | 28 | 29 | 32 | 35 | 49 | 51 | 53 | 54 | 55 |
| 57 | 59 | 60 | 61 | 65 | 68 | 70 | 74 | 75 | 76 | 77 | 78 | 82 | 84 | 85 |
| 86 | 88 | 90 | 95 | 96 | 103 | 113 | 120 | 123 | 125 | 126 | 133 | 134 | 135 | 137 |
| 138 | 140 | 141 | 142 | 145 | 147 | 148 | 150 | 151 | 155 | 156 | 157 | 161 | 163 | 165 |
| 167 | 170 | 176 | 178 | 179 | 181 | 182 | 184 | 185 | 187 | 194 | 200 | 201 | 204 | 209 |
| 210 | 217 | 222 | 223 | 224 | 225 | 229 | 232 | 234 | 235 | 237 | 239 | 241 | 244 | 246 |
| 247 | 248 | 249 | 251 | 252 | 253 | 254 | 255 | 262 | 270 | 272 | 273 | 280 | 282 | 290 |
| 291 | 306 | 307 | 308 | 309 | 311 | 313 | 314 | 315 | 317 | 320 | 326 | 327 | 330 | 331 |
| 333 | 336 | 338 | 340 | 342 | 345 | 347 | 349 |
the number of bits of the cyclic shift is all the values in the following table:
| 105 | 244 | 172 | 249 | 280 | 251 | 293 | 234 | 178 | 11 | 63 | 217 | 83 | 111 | 282 |
| 57 | 85 | 134 | 190 | 190 | 99 | 180 | 38 | 191 | 22 | 254 | 186 | 308 | 178 | 251 |
| 277 | 261 | 44 | 271 | 265 | 298 | 328 | 282 | 155 | 284 | 303 | 113 | 315 | 299 | 166 |
| 342 | 133 | 115 | 225 | 13 | 26 | 326 | 148 | 195 | 145 | 185 | 121 | 58 | 162 | 118 |
| 151 | 182 | 230 | 39 | 249 | 305 | 309 | 144 | 188 | 181 | 265 | 140 | 212 | 137 | 10 |
| 298 | 122 | 281 | 181 | 267 | 178 | 187 | 177 | 352 | 4 | 353 | 269 | 38 | 342 | 288 |
| 277 | 88 | 124 | 120 | 162 | 204 | 174 | 294 | 166 | 157 | 56 | 334 | 110 | 183 | 131 |
| 171 | 166 | 321 | 96 | 37 | 261 | 155 | 34 | 149 | 156 | 267 | 332 | 93 | 348 | 300 |
| 245 | 101 | 186 | 117 | 329 | 352 | 215 | 55 |
2) root value of the second subset of signaling sequences is 367;
the values of q are all in the following table:
the number of bits of the cyclic shift is all the values in the following table:
| 198 | 298 | 346 | 271 | 345 | 324 | 160 | 177 | 142 | 71 | 354 | 290 | 69 | 144 | 28 |
| 325 | 100 | 55 | 237 | 196 | 271 | 210 | 187 | 277 | 8 | 313 | 53 | 53 | 194 | 294 |
| 36 | 202 | 69 | 25 | 18 | 179 | 318 | 149 | 11 | 114 | 254 | 191 | 226 | 138 | 179 |
| 341 | 366 | 176 | 64 | 50 | 226 | 23 | 181 | 26 | 327 | 141 | 244 | 179 | 74 | 23 |
| 256 | 265 | 223 | 288 | 127 | 86 | 345 | 304 | 260 | 139 | 312 | 62 | 360 | 107 | 201 |
| 301 | 263 | 257 | 184 | 329 | 300 | 81 | 121 | 49 | 196 | 201 | 94 | 147 | 346 | 179 |
| 59 | 212 | 83 | 195 | 145 | 3 | 119 | 152 | 310 | 31 | 134 | 54 | 187 | 131 | 63 |
| 276 | 294 | 142 | 246 | 54 | 181 | 121 | 273 | 276 | 36 | 47 | 16 | 199 | 243 | 235 |
| 194 | 348 | 95 | 262 | 52 | 210 | 115 | 250 |
3) the root value of the third subset of signaling sequences is 359;
the values of q are all in the following table:
| 1 | 3 | 5 | 6 | 9 | 12 | 14 | 22 | 29 | 30 | 32 | 34 | 60 | 63 | 65 |
| 67 | 72 | 74 | 76 | 78 | 83 | 84 | 87 | 88 | 89 | 90 | 91 | 92 | 94 | 95 |
| 96 | 99 | 112 | 115 | 123 | 124 | 128 | 137 | 141 | 143 | 145 | 149 | 152 | 153 | 154 |
| 155 | 159 | 164 | 165 | 169 | 175 | 179 | 183 | 186 | 187 | 188 | 189 | 192 | 197 | 199 |
| 201 | 202 | 203 | 211 | 215 | 219 | 220 | 221 | 223 | 226 | 227 | 228 | 229 | 230 | 234 |
| 237 | 238 | 239 | 243 | 246 | 248 | 249 | 250 | 252 | 254 | 257 | 258 | 261 | 262 | 273 |
| 274 | 280 | 282 | 284 | 286 | 288 | 290 | 297 | 298 | 300 | 303 | 308 | 309 | 310 | 312 |
| 313 | 314 | 317 | 318 | 319 | 320 | 321 | 322 | 323 | 324 | 326 | 333 | 334 | 335 | 336 |
| 339 | 341 | 342 | 344 | 349 | 351 | 352 | 355 |
the number of bits of the cyclic shift is all the values in the following table:
4) the root value of the fourth signaling sequence subset is 373;
the values of q are all in the following table:
| 26 | 28 | 29 | 34 | 38 | 40 | 43 | 49 | 54 | 57 | 58 | 62 | 64 | 65 | 79 |
| 80 | 81 | 83 | 85 | 86 | 87 | 101 | 102 | 187 | 189 | 190 | 191 | 193 | 194 | 195 |
| 196 | 198 | 199 | 200 | 202 | 204 | 205 | 206 | 208 | 209 | 211 | 213 | 214 | 216 | 217 |
| 218 | 219 | 220 | 221 | 222 | 223 | 224 | 225 | 227 | 228 | 230 | 232 | 233 | 236 | 237 |
| 241 | 243 | 245 | 246 | 247 | 248 | 249 | 250 | 251 | 252 | 253 | 255 | 256 | 259 | 260 |
| 261 | 262 | 263 | 265 | 266 | 267 | 275 | 276 | 280 | 282 | 283 | 284 | 285 | 289 | 295 |
| 297 | 300 | 301 | 302 | 303 | 305 | 307 | 317 | 320 | 322 | 323 | 325 | 327 | 328 | 332 |
| 338 | 341 | 342 | 343 | 348 | 349 | 351 | 352 | 353 | 355 | 356 | 357 | 358 | 359 | 360 |
| 361 | 362 | 363 | 364 | 367 | 369 | 370 | 372 |
the number of bits of the cyclic shift is all the values in the following table:
| 333 | 337 | 177 | 125 | 169 | 270 | 254 | 88 | 123 | 310 | 96 | 273 | 120 | 239 | 157 |
| 224 | 62 | 119 | 19 | 235 | 136 | 117 | 237 | 100 | 244 | 181 | 295 | 249 | 356 | 9 |
| 289 | 139 | 82 | 171 | 178 | 292 | 158 | 308 | 257 | 42 | 55 | 210 | 320 | 294 | 100 |
| 75 | 79 | 163 | 195 | 80 | 303 | 97 | 271 | 179 | 359 | 178 | 241 | 281 | 367 | 58 |
| 91 | 7 | 179 | 39 | 267 | 245 | 213 | 286 | 349 | 172 | 35 | 301 | 361 | 102 | 301 |
| 155 | 1 | 34 | 96 | 293 | 202 | 87 | 176 | 248 | 319 | 301 | 168 | 280 | 154 | 244 |
| 215 | 370 | 260 | 117 | 30 | 329 | 42 | 149 | 112 | 125 | 50 | 249 | 197 | 273 | 230 |
| 13 | 142 | 244 | 335 | 57 | 21 | 261 | 48 | 370 | 110 | 296 | 326 | 224 | 77 | 112 |
| 31 | 262 | 121 | 38 | 283 | 323 | 93 | 94 |
and combining the 4 signaling sequence subsets to obtain a signaling sequence subcarrier set.
Therefore, the decoding of the signaling information carried by the preamble symbol by the receiving end includes: and performing operation on the signal containing the signaling sequence subcarrier and the signaling sequence subcarrier set or a time domain signal corresponding to the signaling sequence subcarrier set to solve the signaling information carried by the signaling sequence subcarrier in the preamble symbol.
Wherein the signal containing signaling sequence subcarriers comprises: all or part of the time domain waveform of the received preamble symbol, or a frequency domain OFDM symbol obtained by intercepting the time domain OFDM symbol from the preamble symbol and performing Fourier transform. The signaling sequence subcarrier set is a set formed by filling each signaling sequence in the signaling sequence set onto an effective subcarrier.
In particular, the N corresponding to the ODFM symbol body is truncatedACarrying out Fourier transformation on the time domain signal with the length to obtain a frequency domain OFDM symbol; then, removing zero carrier, and taking out the received frequency domain signaling subcarrier according to the signaling subcarrier position. And performing specific mathematical operation on the channel estimation value and the known signaling subcarrier set to complete the frequency domain decoding function.
For example, let i equal to 0: M-1, M be the number of signaling subcarriers, and j equal to 0:2P-1, P is the number of signalling bits transmitted in the frequency domain, i.e. the corresponding set of signalling subcarriers has a total of 2PEach element corresponding to a sequence of length M, HiFor each channel estimation value corresponding to a signaling subcarrier, SC _ reciFor the received frequency domain signaling subcarrier values,and an ith value is taken for the jth element in the signaling subcarrier set. ThenTake max (corr)j) And corresponding j, obtaining the signaling information transmitted by the frequency domain.
In other embodiments, the above process may also be performed in the time domain, and a time domain signaling waveform set corresponding to a known signaling subcarrier set after fourier inverse transformation is directly and synchronously correlated with a time domain received signal at an accurate multipath position, and the one with the largest absolute value of a correlation value is taken, so that signaling information transmitted in the frequency domain may also be solved, which is not described herein again.
Further, the receiving end can also use the fixed sequence to perform integer frequency offset estimation or channel estimation.
Specifically, the present embodiment further includes the following steps: 1) intercepting a signal containing a fixed subcarrier according to the determined position of the preamble symbol in the physical frame; 2) and carrying out operation on the signal containing the fixed subcarrier and a frequency domain fixed subcarrier sequence or a time domain signal corresponding to the frequency domain fixed subcarrier sequence to obtain integral multiple frequency offset estimation or channel estimation.
Wherein the signal containing the fixed subcarriers comprises: all or part of the time domain waveform of the received preamble symbol, or a frequency domain OFDM symbol obtained by intercepting the time domain OFDM symbol from the preamble symbol and performing Fourier transform.
Two methods for performing integer frequency offset estimation at the receiving end are described in detail below.
The method comprises the following steps:
and intercepting all or part of the time domain waveform of the received preamble symbol according to the position of the detected preamble symbol in the physical frame. A frequency sweeping manner is adopted, that is, the partial time domain waveform is modulated with different frequency offsets by a fixed frequency change step diameter (for example, corresponding to an integral multiple frequency offset interval), so that a plurality of time domain signals are obtained:t is the sampling period, fsIs the sampling frequency. The time domain signal corresponding to the inverse fourier transform of the known frequency domain fixed sequence subcarrier is a2, a2 is used as a known signal, and a1 is assigned to each of the known signalsyPerforming sliding correlation, and selecting the A1 with the largest correlation peakyThen the frequency offset value y modulated by the frequency offset is the estimated integer frequency offset value.
Wherein, the sweep frequency range corresponds to the frequency deviation range that the system needs to resist, for example, the frequency deviation of plus or minus 500K needs to resist, the sampling rate of the system is 9.14M, the length of the preamble symbol main body is 1K, and the sweep frequency range isI.e., -57,57]。
The method 2 comprises the following steps:
and intercepting a time domain signal corresponding to the ODFM symbol main body in the preamble symbol, performing Fourier transform to obtain a frequency domain OFDM symbol, performing cyclic shift in the sweep frequency range on the frequency domain OFDM symbol obtained by the transform, performing 2-point-separated differential multiplication, performing correlation operation on the frequency domain OFDM symbol and a 2-point-separated differential multiplication value of a known fixed sequence subcarrier to obtain a series of correlation values, and selecting the cyclic shift corresponding to the maximum correlation value to correspondingly obtain an integer frequency offset estimation value.
The received signal containing the fixed sequence subcarrier and the known frequency domain fixed sequence subcarrier and/or the time domain signal corresponding to the inverse fourier transform are used to complete channel estimation, and may be performed in the time domain and/or in the frequency domain, which is not described herein again.
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 (10)
1. A method for receiving and processing preamble symbols in a physical frame, comprising the steps of:
processing the received digital signal to obtain a baseband signal;
judging whether a pilot symbol expected to be received exists in the baseband signal, wherein the pilot symbol expected to be received takes a time domain OFDM symbol as a main body, has a cyclic prefix and has a time domain structure of a modulation signal;
if the result is yes, determining the position of the preamble symbol in the physical frame and decoding the signaling information carried by the preamble symbol,
wherein determining whether the preamble symbol expected to be received exists in the baseband signal comprises:
according to the delay relationship and the modulation frequency offset relationship between each two of a cyclic prefix, a time domain OFDM symbol and a modulation signal in a preamble symbol expected to be received, performing delay sliding correlation and/or demodulation frequency offset on a baseband signal to obtain three delay correlation accumulated values;
performing mathematical operation on one, two or three of the three delay correlation accumulated values, and performing peak value detection on the absolute value of the operation result;
and if the peak value detection result meets a preset condition, determining that the pilot symbol expected to be received exists in the baseband signal.
2. The method as claimed in claim 2, wherein the determining the position of the preamble symbol in the physical frame comprises:
the position of the preamble symbol in the physical frame is determined based on the result of peak detection satisfying a preset condition.
3. The method as claimed in claim 1, wherein the preamble symbol expected to be received has the following characteristics: 1) intercepting a time domain OFDM symbol with a cyclic prefix length from the time domain OFDM symbol as a cyclic prefix; 2) generating a modulation signal based on the intercepted time domain OFDM symbol with the cyclic prefix length;
the OFDM signal transmission method comprises the steps that in a time domain OFDM symbol for intercepting a cyclic prefix length, different initial positions are selected to intercept the time domain OFDM symbol with a modulation signal length to generate a modulation signal, so that a finally formed preamble symbol transmits signaling information through the different initial positions;
and generating a plurality of different delay relations between the modulation signal and the cyclic prefix and between the modulation signal and the time domain OFDM symbol based on different initial positions so as to judge whether the baseband signal has the preamble symbol expected to be received or not.
4. The method for receiving and processing preamble symbols in a physical frame according to claim 3,
and if the judgment result is yes, determining the position of the preamble symbol in the physical frame and solving the signaling information carried by the preamble symbol.
5. The method as claimed in claim 3, wherein the generating a plurality of different delay relationships between the modulation signal and the cyclic prefix and between the modulation signal and the time domain OFDM symbol based on different start positions to determine whether there is a preamble symbol expected to be received in the baseband signal comprises:
according to the delay relations between a plurality of different modulation signals and cyclic prefixes and between the modulation signals and time domain OFDM symbols, further obtaining a plurality of delay related accumulation value groups, wherein each group comprises delay sliding correlation and demodulation frequency deviation of the baseband signals according to the delay relations and/or modulation frequency deviation relations between the cyclic prefixes, the time domain OFDM symbols and the modulation signals in the expected received preamble symbols, so as to obtain three delay related accumulation values;
computing one, two or three delay correlation accumulated values in each delay correlation accumulated value group, and carrying out peak value detection on the absolute value of the multiplication result;
and if the result of one group of peak value detection meets a preset condition, determining that the pilot symbol expected to be received exists in the baseband signal.
6. The method for receiving and processing preamble symbols in a physical frame according to claim 5,
if the result of the peak detection of a certain group meets the preset condition, the signaling corresponding to the initial position of the modulation signal segment corresponding to the group is the transmitted signaling information.
7. The method as claimed in claim 1, wherein the performing delay sliding correlation on the baseband signal according to the delay relationship and/or modulation frequency offset relationship between two of the cyclic prefix, the time domain OFDM symbol and the modulation signal in the preamble symbol expected to be received comprises:
delaying a received signal by 1024 sampling points to perform sliding correlation on the received signal to obtain a first delay correlation accumulated value;
delaying 1528 sampling points or 1536 sampling points of the received signal, and performing sliding correlation on the received signal after frequency offset demodulation to obtain a second delay correlation accumulated value;
and delaying the received signal by 504 sampling points or 512 sampling points to perform sliding correlation on the received signal after demodulating the frequency offset so as to obtain a third delay correlation accumulated value.
8. The method for receiving and processing preamble symbols in a physical frame according to claim 5,
the method comprises two delay correlation accumulation value groups, wherein the corresponding emergency alarm broadcast flag is 0 or 1;
the group with the emergency alert broadcast flag of 0, takes the following delay slip correlation process:
delaying a received signal by 1024 sampling points to perform sliding correlation on the received signal;
1528 sampling points of the received signal delay are in sliding correlation with the received signal after frequency offset demodulation;
the received signal delays 504 sampling points and carries out sliding correlation on the received signal after frequency offset demodulation; the group with the emergency alert broadcast flag of 1, takes the following delay slip correlation process:
the received signal is delayed by 1024 sampling points and is subjected to sliding correlation with the received signal after frequency offset demodulation;
carrying out sliding correlation on the received signal subjected to frequency offset demodulation by 1544 sampling points;
the received signal is delayed by 520 sampling points and is subjected to sliding correlation with the received signal after frequency offset demodulation.
9. The method for receiving and processing preamble symbols in a physical frame according to claim 1,
peak detection is performed based on a value of the delay correlation accumulated value after mathematical operation, and fractional frequency offset estimation is performed by using a maximum value of the peak value or a plurality of values with large peak values.
10. The method as claimed in claim 1, wherein the frequency domain OFDM symbol corresponding to the time domain OFDM symbol comprises:
the system comprises effective subcarriers and zero sequence subcarriers, wherein the zero sequence subcarriers are positioned on two sides of the effective subcarriers; the effective subcarriers comprise fixed sequence subcarriers and signaling sequence subcarriers, and the fixed sequence subcarriers and the signaling sequence subcarriers are arranged in a parity staggered manner or in an even-odd staggered manner;
the decoding of the signaling information carried by the preamble symbol includes:
and performing operation on the signal containing the signaling sequence subcarrier and the signaling sequence subcarrier set or a time domain signal corresponding to the signaling sequence subcarrier set to solve the signaling information carried by the signaling subcarrier in the preamble symbol.
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| CN111294181B (en) * | 2019-02-28 | 2022-11-18 | 展讯通信（上海）有限公司 | Symbol data transmitting and receiving method, storage medium, transmitting end device and receiving end device |
| CN111769920A (en) * | 2019-04-02 | 2020-10-13 | 上海朗帛通信技术有限公司 | Method and apparatus in a node used for wireless communication |
| CN111769920B (en) * | 2019-04-02 | 2022-11-18 | 上海朗帛通信技术有限公司 | Method and apparatus in a node used for wireless communication |
Also Published As
| Publication number | Publication date |
|---|---|
| CN109743278B (en) | 2021-10-22 |
| CN107222444B (en) | 2020-02-14 |
| CN105245479B (en) | 2019-03-19 |
| CN109743278A (en) | 2019-05-10 |
| CN106685880A (en) | 2017-05-17 |
| CN107070831A (en) | 2017-08-18 |
| CN105245479A (en) | 2016-01-13 |
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