CN105282076B - Generation method of preamble symbol and generation method of frequency domain OFDM symbol - Google Patents

Abstract

The invention discloses a method for generating a frequency domain OFDM symbol and a method for generating a preamble symbol in a physical frame, wherein the method for generating the frequency domain OFDM symbol comprises the following steps: determining an average power ratio of the fixed sequence and the signaling sequence; respectively generating a fixed sequence and a signaling sequence set on a frequency domain according to the average power ratio R; selecting a signaling sequence from the signaling sequence set, filling a fixed sequence and the signaling sequence on the effective subcarriers, and arranging the fixed sequence and the signaling sequence 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; and the sequence number of the selected signaling sequence in the set is the signaling information carried by the OFDM symbol. The technical scheme solves the problem of the probability of failure of detection of the preamble symbol in a low-complexity receiving algorithm under a frequency selective fading channel in the current DVB _ T2 standard and other standards.

Description

Generation method of preamble symbol and generation method of frequency domain OFDM symbol

technical field

The present invention relates to the technical field of wireless broadcast communication, and in particular, to a method for generating an OFDM symbol in a frequency domain and a method for generating a preamble symbol in a physical frame.

Background technique

Usually, in order to enable the receiving end of the OFDM system to correctly demodulate the data sent by the transmitting end, the OFDM system must realize accurate and reliable time synchronization between the transmitting end and the receiving end. At the same time, since the OFDM system is very sensitive to the frequency offset of the carrier, the receiver of the OFDM system also needs to provide an accurate and efficient carrier spectrum estimation method to accurately estimate and correct the carrier frequency offset.

At present, the method for realizing time synchronization between the transmitting end and the receiving end in the OFDM system is basically realized based on the preamble symbol. The preamble symbol is a sequence of symbols known to both the transmitter and the receiver of the OFDM system. The preamble symbol is used as the beginning of a physical frame (named as a P1 symbol), and only one P1 symbol or multiple P1 symbols appear in each physical frame. symbol, which marks the beginning of the physical frame. Uses of the P1 symbol include:

1) Make the receiving end detect quickly to determine whether the signal transmitted in the channel is the signal expected to be received;

2) Provide basic transmission parameters (such as FFT points, frame type information, etc.) so that the receiving end can perform subsequent receiving processing;

3) Detect the initial carrier frequency offset and timing error, and achieve frequency and timing synchronization after compensation;

4) Emergency alarm or broadcast system wake up.

In the DVB_T2 standard, the P1 symbol design based on the CAB time domain structure is proposed, which better realizes the above functions. However, there are still some limitations on low-complexity receiving algorithms. For example, in a long multipath channel with 1024, 542, or 482 symbols, the use of the CAB structure to perform timing coarse synchronization will cause a large deviation, resulting in errors in estimating the carrier integer multiple frequency deviation in the frequency domain. In addition, DBPSK differential decoding may also fail in complex frequency selective fading channels, such as long multipath. Moreover, since there is no cyclic prefix in the time domain structure of DVB_T2, if it is combined with the frequency domain structure that needs to perform channel estimation, the problem of serious degradation of the frequency domain channel estimation performance will be caused.

SUMMARY OF THE INVENTION

The problem solved by the present invention is that in the current DVB_T2 standard and other standards, there is no cyclic prefix in the DVB_T2 time domain structure, which is not suitable for coherent detection, and the low-complexity reception algorithm detection failure probability of the preamble symbol in the complex frequency selective fading channel question.

In order to solve the above problem, an embodiment of the present invention provides a method for generating an OFDM symbol in a frequency domain, including the following steps: determining an average power ratio R of a fixed sequence and a signaling sequence; Sequence and signaling sequence set; select a signaling sequence from the signaling sequence set, fill the fixed sequence and the signaling sequence on the valid subcarriers, and the fixed sequence and the signaling sequence are arranged in an odd-even staggered arrangement; Zero-sequence sub-carriers are respectively filled on both sides of the effective sub-carrier to form a frequency-domain OFDM symbol of a predetermined length; wherein, the sequence number of the selected signaling sequence in the set is the signaling information carried by the OFDM symbol.

An embodiment of the present invention further provides a method for generating a preamble symbol in a physical frame, including the following steps: performing an inverse discrete Fourier transform on a frequency-domain OFDM symbol of a predetermined length to obtain a time-domain OFDM symbol; wherein the frequency-domain OFDM symbol The OFDM symbol is obtained according to the generation method of the above frequency domain OFDM symbol; the time domain OFDM symbol with the cyclic prefix length is intercepted from the time domain OFDM symbol as the cyclic prefix; the modulation is generated based on the above intercepted time domain OFDM symbol with the cyclic prefix length a signal; generating a preamble symbol based on the cyclic prefix, the time-domain OFDM symbol, and the modulated signal.

Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

According to the method for generating frequency-domain OFDM symbols provided by the embodiments of the present invention, the fixed sequence and signaling sequence are filled on the effective subcarriers in a parity interleaved manner. Through such a specific frequency-domain structure design, the fixed sequence can be used as a physical frame. In this way, it is convenient for the receiving end to decode and demodulate the preamble symbols in the received physical frame.

Further, in the method for generating a fixed sequence in the frequency domain, each element in the fixed sequence is a fixed value modulo, and the argument is a complex number with any value between 0 and 2π. In the method for generating a signaling sequence set in the frequency domain, the number of signaling sequences is an integer power of 2, and the root value in the CAZAC sequence generation formula is determined based on the length and number of signaling sequences, and a set of different signaling sequences is determined. The q value of , and the corresponding cyclic shift bit k, and the signaling sequence is calculated from this.

Moreover, the inventor obtained a fixed signaling with better effect in practice, the length and number of a group of signaling sequences with better effect and the corresponding four root values, and selected 128 groups of q in each root value. Value with the number of bits to rotate. Therefore, the subsequently generated preamble symbols have a lower peak to average power ratio (Peak to Average Power Ratio, PAPR), and the success probability of the receiving end detecting the preamble symbols is improved.

Furthermore, using the structure of the modulated 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 using the delay correlation at the receiving end. In addition, in the process of generating the preamble symbol, the modulated signal of the time-domain OFDM symbol is designed to avoid continuous wave interference or single-frequency interference at the receiving end, or the appearance of a multipath channel equal to the length of the modulated signal, or the guard interval in the received signal. False detection peaks occur when the length is the same as the modulated signal length.

Description of drawings

FIG. 1 is a schematic flowchart of a specific embodiment of a method for generating a frequency-domain OFDM symbol according to the present invention;

2 is a schematic flowchart of a specific embodiment of a method for generating a preamble in a physical frame of the present invention;

FIG. 3 is a schematic diagram of a time domain structure of a preamble symbol in a physical frame according to the present invention.

Detailed ways

The inventor found that in the current DVB_T2 standard and other standards, the low-complexity reception algorithm detection failure probability of the preamble symbol occurs in the frequency selective fading channel. In addition, there is no cyclic prefix in the DVB_T2 time domain structure, which cannot be applied to coherent detection, and the low-complexity reception algorithm detection of preamble symbols in frequency selective fading channels has the problem of failure probability.

In response to the above problems, the inventor has provided a method for generating a preamble symbol in a physical frame and a method for generating an OFDM symbol in the frequency domain, which ensures that the receiver can still process the received signal when the carrier frequency deviation is within the range of -500kHz to 500kHz.

In order to make the above objects, features and advantages of the present invention more clearly understood, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a schematic flowchart of a specific implementation manner of a method for generating a frequency-domain OFDM symbol according to the present invention. Referring to FIG. 1, a method for generating an OFDM symbol in a frequency domain includes the following steps:

Step S11: determine the average power ratio R of the fixed sequence and the signaling sequence;

Step S12: respectively generating a fixed sequence and a signaling sequence set in the frequency domain according to the average power ratio R;

Step S13: select a signaling sequence from the signaling sequence set, fill the fixed sequence and the signaling sequence on the valid subcarriers, and arrange the fixed sequence and the signaling sequence in an odd-even staggered arrangement;

Step S14: Filling zero sequence subcarriers on both sides of the effective subcarrier to form a frequency domain OFDM symbol of a predetermined length; wherein, the sequence number of the selected signaling sequence in the set is the signaling information carried by the OFDM symbol .

Specifically, as described in step S11, the average power ratio R of the fixed sequence and the signaling sequence is determined. Wherein, the fixed sequence includes relevant information that the receiver can use for carrier frequency synchronization and timing synchronization, and the sequence of the signaling sequence in the set is used to carry each basic transmission parameter.

Among them, the average power ratio R of the fixed sequence and the signaling sequence can be adjusted according to the actual application requirements. A larger R is selected to increase the power of the fixed sequence to obtain better channel estimation and bias estimation performance, or a smaller R is selected. The actual signal-to-noise ratio on the signalling carrier is increased by increasing the power of the signalling sequence to improve the signalling decoding performance. Therefore, the average power ratio R of the fixed sequence and the signaling sequence is determined according to the balanced consideration of the offset estimation performance, the channel estimation performance, the de-signaling performance and the timing synchronization performance.

In this embodiment, the average power ratio R of the fixed sequence and the signaling sequence is 1. When the fixed sequence length and the signaling sequence length are the same, the average power ratio is the power sum ratio.

After the average power ratio is determined, the amplitude ratio of the fixed sequence and the signaling sequence is obtained accordingly. When the average power ratio R is 1, and both the fixed sequence and the signaling sequence are constant-modulus sequences, the amplitude ratio of the corresponding fixed sequence and the signaling sequence is

As described in step S12, a fixed sequence and a signaling sequence set are respectively generated in the frequency domain according to the average power ratio R.

In this embodiment, generating a fixed sequence in the frequency domain may be implemented in the following specific manner:

Step S121: Determine the length of the fixed sequence; wherein, each element in the fixed sequence is a fixed value modulo, and the argument is a complex number with any value between 0 and 2π.

It should be noted that, in this embodiment, the length of the fixed sequence is less than half of the length of the OFDM symbol.

Step S122: Select a fixed sequence from all optional fixed sequences, and generate a signaling sequence set with good autocorrelation and cross-correlation, and based on the fixed sequence and any signaling sequence in the signaling sequence set The formed OFDM symbols satisfy the required power peak-to-average ratio after inverse Fourier transform.

Specifically, in all value spaces of the above fixed sequence (that is, each element is a complex number whose modulus is a fixed value and whose argument is any value between 0 and 2π), a fixed sequence is preferably selected. The selected fixed sequence needs to satisfy: the signaling sequence set generated by the fixed sequence has good autocorrelation and cross-correlation, and is based on the fixed sequence and any signaling sequence in the signaling sequence set. The frequency domain OFDM symbol has a lower peak-to-average power ratio (PAPR) after inverse Fourier transform, and the specific value (or value range) of the power peak-to-average ratio can be determined according to system requirements. .

In this embodiment, generating a signaling sequence set in the frequency domain may be implemented in the following specific manner:

Step S123: Determine the length of the signaling sequence and the number of signaling sequences contained in the signaling sequence set; wherein, the number of the signaling sequences is 2 to the power of N, and N is a positive integer;

Step S124: Generate M signaling sequence subsets respectively, and the number of signaling sequences in each signaling sequence subset is m ₁ to m _M respectively, and

Step S125: Arrange all the signaling sequences in each signaling sequence subset in order to form a signaling sequence set; and number them as 0 to 2 ^N -1;

Among them, the root values of each signaling sequence subset are different from each other, and the amplitude of each element in all signaling sequences is the same as the element amplitude in the fixed sequence.

Further, this embodiment also provides a preferred implementation manner of generating each signaling sequence subset in the above step S124, which is as follows:

Step S1241: Determine the root value in the CAZAC sequence generation formula based on the number of the signaling sequences; where the root value is greater than or equal to twice the number of signaling sequences.

In practice, root is a prime number, and preferably root=L, such that the autocorrelation value of the sequence is zero.

Step S1242: According to the selected root value, select a set of different q values to generate a CAZAC sequence, where the number of q values is equal to the number of signaling sequences, the value of q value is an integer and is greater than 0 and less than the root value, any The sum of the two q values is not equal to the root value;

Step S1243: Perform a cyclic shift on the generated CAZAC sequence; wherein, the number of bits of the cyclic shift is determined by the corresponding root value and q value.

In practical applications, the q value and the number of bits of the cyclic shift should be selected so that all signaling sequences have low cross-correlation, and the composed frequency domain OFDM symbols have low peak-average power after inverse Fourier transform. Ratio (Peak-to-Average Power Ratio, PAPR).

Step S1244: Calculate and obtain a required subset of signaling sequences according to the determined number of signaling sequences, the q value, and the number of bits of the cyclic shift.

For example, the fixed sequence and signaling sequence length L and root value are determined, and a set of q values and a set of cyclic shift bits (q _i , k _i , i=0～2 ^N -1) have been optimized, and the first The generation formula method of i signaling sequences:

First, generate the CAZAC sequence:

Then, cyclically shift it:

s _i ^* (n)=[s( _ki -1),s( _ki -1),...,S(root-1),s(0),...,s( _ki -1)]

Finally, a sequence of length L is truncated from the head of the above sequence:

SC _i (n)=s _i ^* (n), n=0～L-1

The obtained sequence SC _i (n) is the required i-th signaling sequence.

For example, determine the average power ratio R to be 1; the length of the fixed sequence is 353 and the amplitude is 1, and an optimal fixed sequence is calculated as follows:

Among them, the values of ω _n are arranged in rows from left to right in order as shown in the following table:

5.43 2.56 0.71 0.06 2.72 0.77 1.49 6.06 4.82 2.10 5.62 4.96 4.93 4.84 4.67 5.86 5.74 3.54 2.50 3.75 0.86 1.44 3.83 4.08 5.83 1.47 0.77 1.29 0.16 1.38 4.38 2.52 3.42 3.46 4.39 0.61 4.02 1.26 2.93 3.84 3.81 6.21 3.80 0.69 5.80 4.28 1.73 3.34 3.08 5.85 1.39 0.25 1.28 5.14 5.54 2.38 6.20 3.05 4.37 5.41 2.23 0.49 5.12 6.26 3.00 2.60 3.89 5.47 4.83 4.17 3.36 2.63 3.94 5.13 3.71 5.89 0.94 1.38 1.88 0.13 0.27 4.90 4.89 5.50 3.02 1.94 2.93 6.12 5.47 6.04 1.14 5.52 2.01 1.08 2.79 0.74 2.30 0.85 0.58 2.25 5.25 0.23 6.01 2.66 2.48 2.79 4.06 1.09 2.48 2.39 5.39 0.61 6.25 2.62 5.36 3.10 1.56 0.91 0.08 2.52 5.53 3.62 2.90 5.64 3.18 2.36 2.08 6.00 2.69 1.35 5.39 3.54 2.01 4.88 3.08 0.76 2.13 3.26 2.28 1.32 5.00 3.74 1.82 5.78 2.28 2.44 4.57 1.48 2.48 1.52 2.70 5.61 3.06 1.07 4.54 4.10 0.09 2.11 0.10 3.18 3.42 2.10 3.50 4.65 2.18 1.77 4.72 5.71 1.48 2.50 4.89 4.04 6.12 4.28 1.08 2.90 0.24 4.02 1.29 3.61 4.36 6.00 2.45 5.49 1.02 0.85 5.58 2.43 0.83 0.65 1.95 0.79 5.45 1.94 0.31 0.12 3.25 3.75 2.35 0.73 0.20 6.05 2.98 4.70 0.69 5.97 0.92 2.65 4.17 5.71 1.54 2.84 0.98 1.47 6.18 4.52 4.44 0.44 1.62 6.09

5.86 2.74 3.27 3.28 0.55 5.46 0.24 5.12 3.09 4.66 4.78 0.39 1.63 1.20 5.26 0.92 5.98 0.78 1.79 0.75 4.45 1.41 2.56 2.55 1.79 2.54 5.88 1.52 5.04 1.53 5.53 5.93 5.36 5.17 0.99 2.07 3.57 3.67 2.61 1.72 2.83 0.86 3.16 0.55 5.99 2.06 1.90 0.60 0.05 4.01 6.15 0.10 0.26 2.89 3.12 3.14 0.11 0.11 3.97 5.15 4.38 2.08 1.27 1.17 0.42 3.47 3.86 2.17 5.07 5.33 2.63 3.20 3.39 3.21 4.58 4.66 2.69 4.67 2.35 2.44 0.46 4.26 3.63 2.62 3.35 0.84 3.89 4.17 1.77 1.47 2.03 0.88 1.93 0.80 3.94 4.70 6.12 4.27 0.31 4.85 0.27 0.51 2.70 1.69 2.18 1.95 0.02 1.91 3.13 2.27 5.39 5.45 5.45 1.39 2.85 1.41 0.36 4.34 2.44 1.60 5.70 2.60 3.41 1.84 5.79 0.69 2.59 1.14 5.28 3.72 5.55 4.92 2.64

It is determined that the number of signaling sequences is 512, and the signaling sequence set includes 4 signaling sequence subsets, each signaling sequence subset includes 128 signaling sequences, and the length of the signaling sequence is 353.

According to the above fixed sequence, the parameters used for calculating the signaling sequence in each signaling sequence subset are as follows:

1) The root value of the first signaling sequence subset is 353;

The value of q is all the values in the following table:

The number of bits for the cyclic shift is all values in the following table:

2) The root value of the second signaling sequence subset is 367;

The value of q is all the values in the following table:

The number of bits for the cyclic shift is all values in the following table:

3) The root value of the third signaling sequence subset is 359;

The value of q is all the values in the following table:

The number of bits for the cyclic shift is all values in the following table:

4) The root value of the fourth signaling sequence subset is 373;

The value of q is all the values in the following table:

The number of bits for the cyclic shift is all values in the following table:

As described in step S13, a signaling sequence is selected from the signaling sequence set, and the fixed sequence and the signaling sequence are filled on valid subcarriers, and the fixed sequence and the signaling sequence are arranged in an odd-even staggered arrangement.

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. Wherein, the predetermined length is 1024, but it can also be changed according to system requirements in practical applications.

Taking the predetermined length of 1024 as an example, let the length of the fixed sequence be L (that is, the number of valid subcarriers that carry the fixed sequence is L), and the length of the signaling sequence is P (that is, the number of valid subcarriers that carry the signaling sequence is L). The number is P), in this embodiment, L=P. In other embodiments, L may also be slightly larger than P.

The fixed sequence and the signaling sequence are arranged in an odd-even staggered arrangement, that is, the fixed sequence is filled to the position of the even subcarrier (or odd subcarrier), and correspondingly, the signaling sequence is filled to the position of the odd subcarrier (or even subcarrier) On the effective subcarriers in the frequency domain, the distribution state of the fixed sequence and the signaling sequence parity staggered is presented. It should be noted that when the lengths of the fixed sequence and the signaling sequence are inconsistent (for example, P>L), the fixed sequence and the signaling sequence can be arranged in parity and staggered manner by means of zero-padded sequence subcarriers.

As described in step S14, zero-sequence sub-carriers are padded on both sides of the effective sub-carrier to form a frequency-domain OFDM symbol of a predetermined length: wherein, the sequence number of the selected signaling sequence in the set is the one carried by the OFDM symbol signaling information.

In a preferred embodiment, this step includes: filling zero sequence sub-carriers of equal length on both sides of the effective sub-carrier respectively to form a frequency-domain OFDM symbol of a predetermined length.

Following the example with a predetermined length of 1024, the length of the zero sequence subcarriers is G=1024-L-P, and the two sides are filled with (1024-L-P)/2 zero sequence subcarriers.

Further, in order to ensure that the receiver can still process the received signal when the carrier frequency deviation is in the range of -500kHz to 500kHz, the value of (1024-LP)/2 is usually greater than the critical length value (set as TH), which is determined by the system. The symbol rate and predetermined length are determined. For example, if the predetermined length is 1024, the system symbol rate of 7.61M, and the sampling rate of 9.14M, then For example, L=P=353, then G=318, and 159 zero sequence subcarriers are padded on both sides.

Therefore, subcarriers (ie, frequency-domain OFDM symbols) P1_X ₀ , _{P1_X 1} , .

Among them, the fixed sequence subcarriers Signaling sequence subcarriers The parity positions are interchangeable.

FIG. 2 is a schematic flowchart of a specific implementation manner of a method for generating a preamble in a physical frame according to the present invention. Referring to Fig. 2, the generation method of the preamble symbol in the physical frame includes the following steps:

Step S21: Perform an inverse discrete Fourier transform on a frequency-domain OFDM symbol of a predetermined length to obtain a time-domain OFDM symbol; wherein, the frequency-domain OFDM symbol is generated according to the above-mentioned method for generating a frequency-domain OFDM symbol;

Step S22: intercepting a time-domain OFDM symbol with a cyclic prefix length from the time-domain OFDM symbol as a cyclic prefix;

Step S23: generating a modulated signal based on the time-domain OFDM symbol with the cyclic prefix length intercepted above;

Step S24: Generate a preamble symbol based on the cyclic prefix, the time-domain OFDM symbol and the modulated signal.

In this embodiment, as described in step S21, inverse discrete Fourier transform is performed on a frequency-domain OFDM symbol of a predetermined length to obtain a time-domain OFDM symbol.

The inverse discrete Fourier transform described in this step is a commonly used method for converting a frequency-domain signal into a time-domain signal, and details are not described here.

After P1_X _i is inverse discrete Fourier transform, the time-domain OFDM symbol is obtained:

Wherein, L is the number of fixed sequence carriers, P is the number of signaling sequence carriers, and R is the average power ratio of the fixed sequence to the signaling sequence.

As described in step S22, a time-domain OFDM symbol with a cyclic prefix length is intercepted from the time-domain OFDM symbol as a cyclic prefix.

In this embodiment, the cyclic prefix length is equal to or smaller than the predetermined length. Taking the predetermined length as 1024 as an example, the cyclic prefix length may be 1024 or less than 1024. Preferably, the length of the cyclic prefix is 520, and the second half (length of 520) of the time-domain OFDM symbol is usually intercepted as the cyclic prefix, so as to solve the problem that the performance of frequency-domain channel estimation is degraded.

The determining of the cyclic prefix length is based on any of the multipath length that the wireless broadcast communication system usually needs to fight against, the minimum length of the robust correlation peak that the system can obtain when the system is at the lowest reception threshold, and the number of bits of the time domain structure transmission signaling. one or more factors. If it is only necessary to transmit signaling in the frequency domain structure, but the time domain structure is fixed and no signaling is required, it is only necessary to consider the length of the multipath that needs to be confronted, and the minimum length of the robust correlation peak that the system can obtain at the lowest reception threshold. One or two. Generally, 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 modulating signal, the more robust its delay-related peaks are. Usually, the length of the cyclic prefix and the length of the modulated signal should be greater than or equal to the minimum length that the system can obtain a robust correlation peak at the lowest receiving threshold.

As described in step S23, a modulated signal is generated based on the truncated time-domain OFDM symbols of the cyclic prefix length. In practice, the length of the modulated signal generally does not exceed the length of the cyclic prefix part.

Specifically, this step includes:

1) Set a frequency offset sequence;

2) Multiplying the time-domain OFDM symbols of the cyclic prefix length or part of the time-domain OFDM symbols of the cyclic prefix length by the frequency offset sequence to obtain the modulated signal.

For example, let N _cp be the determined cyclic prefix length, and Len _B be the modulated signal length. The modulated signal length is determined by the minimum length at which the system can obtain a robust correlation peak at the lowest receive threshold. Usually the length of the modulated signal is greater than or equal to the minimum length. Let NA be the length of the time _- domain OFDM symbol, and let the sampling point numbers of the time-domain OFDM symbol be 0, ₁ , ... NA -1. Let N1 be the sampling of the time-domain OFDM symbol corresponding to the start point of the modulated signal segment selected and copied Point sequence number, N2 is the sequence number of the sampling point of the time domain OFDM symbol corresponding to the end point of the selected and copied to the modulated signal segment. in,

N2=N1+Len _B -1

For the convenience of description, the time-domain OFDM symbol is divided into two parts, the first part is the part of the time-domain OFDM symbol that is not intercepted as the cyclic prefix (usually the front part of the time-domain OFDM symbol), and the second part is intercepted as the cyclic prefix. Part of the time-domain OFDM symbol (usually the latter part of the time-domain OFDM symbol). If all the truncated time-domain OFDM symbols are used as cyclic prefixes, the length of the first segment is 0. N1 must fall in the second segment, that is, the range of the part of the time-domain OFDM symbols selected for the modulated signal segment will not exceed the range of the part of the time-domain OFDM symbols truncated as the cyclic prefix.

The modulated signal part and the cyclic prefix part are the same as part of the information in the time-domain OFDM symbol. The modulated signal part is only modulated with frequency offset or other signals, so the correlation value between the modulated signal part and the cyclic prefix part and the correlation value between the modulated signal part and the time-domain OFDM symbol can be used for timing synchronization and small offset estimation. In practice, the modulated signal length generally does not exceed the cyclic prefix length. If the length of the modulated signal is greater than the length of the cyclic prefix, the excess part will increase the overhead of the system, resulting in a decrease in transmission efficiency, and it can only enhance the robustness of the correlation value between the modulated signal part and the time-domain OFDM symbol, while maintaining the same Under the overhead, this part length should be added to the cyclic prefix part, which will bring more performance benefits.

As shown in Figure 3, segment A represents the time-domain OFDM symbol, segment C represents the cyclic prefix, and segment B represents the modulated signal. The frequency offset sequence is Wherein, f _SH can be selected as the frequency-domain subcarrier spacing (ie, 1/NA _T ) corresponding to the time-domain OFDM symbol, where T is the sampling period, and NA is the length of the time _- domain OFDM symbol. In this example, NA is 1024, and f _{SH =} 1/1024T is taken. In other instances, f _SH may also be chosen to be 1/(Len _B T) in order to sharpen the correlation peak. When Len _B =N _CP , f _SH =1/N _CP T. For example, when Len _B =N _CP =512, f _SH =1/512T.

In other embodiments, M(t) can also be designed to be other sequences, such as m sequences or some simplified window sequences.

The modulation signal of this part of the time-domain OFDM symbol is P1_B(t), and P1_B(t) is obtained by multiplying this part of the time-domain OFDM symbol by the frequency offset sequence M(t), that is, P1_B(t) is:

Wherein, N1 is the sampling point sequence number selected to be copied to the time-domain OFDM symbol corresponding to the start point of the modulated signal segment.

As described in step S24, a preamble symbol is generated based on the cyclic prefix, the time-domain OFDM symbol and the modulated signal.

Specifically, the cyclic prefix is spliced in the front part of the time-domain OFDM symbol as a guard interval, and the modulated signal is spliced in the rear part of the OFDM symbol as a modulation frequency offset sequence to generate a preamble symbol, as shown in the figure 3 shown.

For example, the leading symbol can take the following time domain expression according to:

In a preferred embodiment, when the predetermined length N _A =1024, N _cp =520, Len _B =504, and N1 is 504 or 520.

Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can use the methods and technical contents disclosed above to improve the present invention without departing from the spirit and scope of the present invention. The technical solutions are subject to possible changes and modifications. Therefore, any simple modifications, equivalent changes and modifications made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solutions of the present invention belong to the technical solutions of the present invention. protected range.

Claims (7)

1. A method for generating frequency domain OFDM symbols, comprising the steps of:

determining an average power ratio R of the fixed sequence and the signaling sequence;

respectively generating a fixed sequence and a signaling sequence set on a frequency domain according to the average power ratio R;

selecting a signaling sequence from a signaling sequence set, filling a fixed sequence and the signaling sequence on an effective subcarrier, and arranging the fixed sequence and the signaling sequence in a parity staggered manner;

filling zero sequence subcarriers on two sides of the effective subcarrier respectively to form frequency domain OFDM symbols with preset length: wherein, the sequence number of the selected signaling sequence in the set is the signaling information carried by the OFDM symbol,

wherein generating the set of signaling sequences comprises:

all signaling sequences within a subset of signaling sequences are arranged together in order to form a set of signaling sequences,

generating each subset of signaling sequences comprises:

determining root values in a CAZAC sequence generation formula based on the number of the signaling sequences;

selecting a different set of q values to generate a CAZAC sequence based on the selected root value,

the parameters for generating each subset of signaling sequences are:

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:

8 9 10 15 19 21 31 34 39 49 58 59 71 76 80 119 120 121 123 140 142 151 154 162 166 171 184 186 188 190 191 193 194 195 198 203 204 207 208 209 210 211 212 214 215 219 220 221 222 223 224 226 228 230 232 233 235 236 237 239 240 241 243 245 249 250 252 254 257 259 260 261 262 263 264 265 266 267 269 271 272 273 275 276 277 278 281 282 283 284 285 286 289 294 297 299 302 303 306 307 310 311 312 313 314 316 317 321 322 323 326 327 329 331 332 334 338 340 342 344 345 347 349 351 356 361 363 366

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:

300 287 80 119 68 330 93 359 17 93 355 308 106 224 20 18 226 165 320 339 352 316 241 336 119 166 258 273 302 275 46 26 259 330 206 46 10 308 165 195 314 330 208 148 275 15 214 251 8 27 264 169 128 207 21 246 14 291 345 114 306 179 109 336 322 149 270 253 207 152 26 190 128 137 196 268 36 40 253 29 264 153 221 341 116 24 55 60 171 25 100 202 37 93 115 174 239 148 170 37 328 37 253 237 355 39 288 225 223 140 163 145 264 75 29 282 252 270 30 262 271 305 122 78 27 127 92 6

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

。

2. the method for generating frequency domain OFDM symbols according to claim 1, wherein generating the fixed sequence in the frequency domain comprises the steps of:

determining the length of the fixed sequence; wherein, each element in the fixed sequence is a complex number with a modulus of a constant value and an argument of any value between 0 and 2 pi;

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.

3. The method of generating frequency domain OFDM symbols of claim 1, wherein generating a set of signaling sequences in the frequency domain comprises:

determining the length of the signaling sequence and the number of the signaling sequences contained in the signaling sequence set; the number of the signaling sequences is the power of N of 2, and N is a positive integer;

respectively generating M signaling sequence subsets, wherein the number of the signaling sequences in each signaling sequence subset is M₁～m_MAnd is and

arranging all the signaling sequences in each signaling sequence subset together in sequence to form a signaling sequence set;

wherein, the root values of each signaling sequence subset are different, and the amplitude of each element in all the signaling sequences is the amplitude of the element in the fixed sequence

4. The method of generating frequency domain OFDM symbols of claim 3, wherein generating each subset of signaling sequences comprises:

determining root values in a CAZAC sequence generation formula based on the number of the signaling sequences; wherein the root value is greater than or equal to twice the number of signaling sequences;

according to the selected root value, selecting a group of different q values to generate a CAZAC sequence, wherein the number of the q values is equal to the number of the signaling sequences, the value of the q values is an integer and is greater than 0 and smaller than the root value, and the sum of any two q values is not equal to the root value;

performing cyclic shift on the generated CAZAC sequence; wherein, the bit number of the cyclic shift is determined by the corresponding root value and q value;

and calculating to obtain a required signaling sequence subset according to the determined number of the signaling sequences, the q value and the cyclic shift digit.

5. The method of generating frequency domain OFDM symbols of claim 1, wherein the fixed sequence and the signaling sequence have an average power ratio R of 1.

6. The method of claim 2, wherein the fixed sequence length is 353, modulo 1, expressed as:

FC(n)＝e^jωn

wherein, ω is_nThe values of (A) are arranged in rows from left to right in sequence as shown in the following table:

5.43 2.56 0.71 0.06 2.72 0.77 1.49 6.06 4.82 2.10 5.62 4.96 4.93 4.84 4.67 5.86 5.74 3.54 2.50 3.75 0.86 1.44 3.83 4.08 5.83 1.47 0.77 1.29 0.16 1.38 4.38 2.52 3.42 3.46 4.39 0.61 4.02 1.26 2.93 3.84 3.81 6.21 3.80 0.69 5.80 4.28 1.73 3.34 3.08 5.85 1.39 0.25 1.28 5.14 5.54 2.38 6.20 3.05 4.37 5.41 2.23 0.49 5.12 6.26 3.00 2.60 3.89 5.47 4.83 4.17 3.36 2.63 3.94 5.13 3.71 5.89 0.94 1.38 1.88 0.13 0.27 4.90 4.89 5.50 3.02 1.94 2.93 6.12 5.47 6.04 1.14 5.52 2.01 1.08 2.79 0.74 2.30 0.85 0.58 2.25 5.25 0.23 6.01 2.66 2.48 2.79 4.06 1.09 2.48 2.39 5.39 0.61 6.25 2.62 5.36 3.10 1.56 0.91 0.08 2.52 5.53 3.62 2.90 5.64 3.18 2.36 2.08 6.00 2.69 1.35 5.39 3.54 2.01 4.88 3.08 0.76 2.13 3.26 2.28 1.32 5.00 3.74 1.82 5.78 2.28 2.44 4.57 1.48 2.48 1.52 2.70 5.61 3.06 1.07 4.54 4.10 0.09 2.11 0.10 3.18 3.42 2.10 3.50 4.65 2.18 1.77 4.72 5.71 1.48 2.50 4.89 4.04 6.12 4.28 1.08 2.90 0.24 4.02 1.29 3.61 4.36 6.00 2.45 5.49 1.02 0.85 5.58 2.43 0.83 0.65 1.95 0.79 5.45 1.94 0.31 0.12 3.25 3.75 2.35 0.73 0.20 6.05 2.98 4.70 0.69 5.97 0.92 2.65 4.17 5.71 1.54 2.84 0.98 1.47 6.18 4.52 4.44 0.44 1.62 6.09 5.86 2.74 3.27 3.28 0.55 5.46 0.24 5.12 3.09 4.66 4.78 0.39 1.63 1.20 5.26 0.92 5.98 0.78 1.79 0.75 4.45 1.41 2.56 2.55 1.79 2.54 5.88 1.52 5.04 1.53 5.53 5.93 5.36 5.17 0.99 2.07 3.57 3.67 2.61 1.72

2.83 0.86 3.16 0.55 5.99 2.06 1.90 0.60 0.05 4.01 6.15 0.10 0.26 2.89 3.12 3.14 0.11 0.11 3.97 5.15 4.38 2.08 1.27 1.17 0.42 3.47 3.86 2.17 5.07 5.33 2.63 3.20 3.39 3.21 4.58 4.66 2.69 4.67 2.35 2.44 0.46 4.26 3.63 2.62 3.35 0.84 3.89 4.17 1.77 1.47 2.03 0.88 1.93 0.80 3.94 4.70 6.12 4.27 0.31 4.85 0.27 0.51 2.70 1.69 2.18 1.95 0.02 1.91 3.13 2.27 5.39 5.45 5.45 1.39 2.85 1.41 0.36 4.34 2.44 1.60 5.70 2.60 3.41 1.84 5.79 0.69 2.59 1.14 5.28 3.72 5.55 4.92 2.64

。

7. the method for generating frequency domain OFDM symbols according to claim 3, wherein the number of the signaling sequences in the generated signaling sequence set is 512, and the signaling sequence set comprises 4 signaling sequence subsets, each signaling sequence subset comprises 128 signaling sequences, and the length of the signaling sequence is 353.