The present application is a divisional application of the original, and the title "method for generating preamble symbol in physical frame" was invented and invented in application No. 201410168180.4 of the original, application date 2014, 4 and 24.
Disclosure of Invention
The invention solves the problems that in the current DVB _ T2 standard and other standards, a DVB _ T2 time domain structure has no cyclic prefix, so that the DVB _ T2 standard and other standards cannot be applied to coherent detection, and the detection of preamble symbols in a complex frequency selective fading channel by a low-complexity receiving algorithm has failure probability.
In order to solve the above problem, an embodiment of the present invention provides a method for generating a preamble symbol in a physical frame, including the following steps: performing inverse discrete Fourier transform on the frequency domain OFDM symbol with the preset length to obtain a time domain OFDM symbol; determining a cyclic prefix length; intercepting part of the time domain OFDM symbols with the length of the cyclic prefix from the rear part of the time domain OFDM symbols as the cyclic prefix; generating a modulation signal according to the part of the time domain OFDM symbols; generating a preamble symbol based on the cyclic prefix, the time domain OFDM symbol, and the modulation signal.
Optionally, the determining the cyclic prefix length includes: the cyclic prefix length is determined according to the length of the multipath against which the wireless broadcast communication system needs to contend.
Optionally, generating a modulation signal according to the part of the time domain OFDM symbol includes: setting a frequency shift sequence; multiplying the partial time domain OFDM symbol by the frequency shift sequence to obtain the modulated signal.
Optionally, the generating a preamble symbol based on the cyclic prefix, the time domain OFDM symbol, and the modulation signal includes: and splicing the cyclic prefix at the front part of the time domain OFDM symbol as a guard interval, and splicing the modulation signal at the rear part of the OFDM symbol as a modulation frequency offset sequence to generate a preamble symbol.
Optionally, before performing inverse discrete fourier transform on the frequency domain OFDM symbol with the predetermined length to obtain the time domain OFDM symbol, the method further includes the following steps: respectively generating a fixed sequence and a signaling sequence on a frequency domain; filling a fixed sequence and a signaling sequence onto effective subcarriers, wherein the fixed sequence and the signaling sequence are arranged in a parity staggered manner; and filling zero sequence subcarriers on two sides of the effective subcarriers respectively to form frequency domain OFDM symbols with preset length.
Optionally, the fixed sequence is a complex sequence, and a modulus of each complex number in the complex sequence is 1.
Optionally, the nth complex number in the complex number sequence isn is 0,1,. 349; wherein, ω isnThe values of (A) are arranged in rows from left to right in sequence as shown in the following table:
optionally, the generating the signaling sequence in the frequency domain includes the following steps: generating a reference sequence; the reference sequence is cyclically shifted to generate a signaling sequence.
Optionally, the reference sequence is represented as:n is 0-349; the signaling sequence generated after the cyclic shift is performed on the reference sequence is represented as:wherein k isiFor the shift values, the following table shows:
optionally, the length of the fixed sequence is equal to the length of the signaling sequence, and the length is smaller than 1/2 of the predetermined length.
Optionally, the filling zero sequence subcarriers at two sides of the effective subcarrier to form a frequency domain OFDM symbol with a predetermined length respectively includes: and filling zero sequence subcarriers with equal length on two sides of the effective subcarriers respectively to form frequency domain OFDM symbols with preset length.
Optionally, the length of the zero sequence subcarrier filled on each side is greater than a critical length value, and the critical length value is determined by the system sampling rate, the symbol rate and the predetermined length.
Optionally, the predetermined length is 1024.
Optionally, the cyclic prefix length is 512.
Compared with the prior art, the technical scheme of the invention has the following beneficial effects:
according to the method for generating the preamble symbol in the physical frame provided by the embodiment of the invention, the cyclic prefix length is determined according to different channel environments, and a part of the time domain OFDM symbol with the cyclic prefix length is intercepted from the rear part of the time domain OFDM symbol to be used as the cyclic prefix, so that the problem of the reduction of the frequency domain channel estimation performance is solved. And the part of time domain OFDM symbols are utilized to generate modulation signals, so that the generated preamble symbols have good small frequency offset and timing synchronization performance.
Further, in the process of generating the frequency domain OFDM symbol, the fixed sequence and the signaling sequence are filled onto the effective subcarriers in a parity interleaving manner, and through such a specific frequency domain structure design, the fixed sequence can be used as a pilot in a physical frame, so that a receiving end can decode and demodulate a preamble symbol in a received physical frame conveniently.
Moreover, since the fixed sequence adopts the complex sequence, and the modulus of each complex number in the complex sequence is 1, the preamble symbol generated subsequently has a lower Peak to Average Power Ratio (PAPR), and the success probability of detecting the preamble symbol by the receiving end is improved.
Furthermore, the structure of the modulation signal using the time domain OFDM symbol and the time domain OFDM symbol (as a preamble symbol) ensures that a distinct peak can be obtained at the receiving end using delay correlation. In addition, in the process of generating the preamble symbol, the modulation signal of the time domain OFDM symbol is designed to avoid that the receiving end is subjected to continuous wave interference or single frequency interference, or that a multipath channel with the same length as the modulation signal occurs, or that a false detection peak occurs when the guard interval length in the received signal is the same as the length of the modulation signal.
Detailed Description
The inventor finds that in the current DVB _ T2 standard and other standards, the DVB _ T2 time domain structure has no cyclic prefix, and the preamble symbol has the problem of low complexity receiving algorithm detection failure probability under a frequency selective fading channel.
In view of the above problems, the inventors have studied and provided a method for generating preamble symbols in a physical frame. The problem of the performance reduction of frequency domain channel estimation is solved, and the part of time domain OFDM symbols are utilized to generate modulation signals, so that the generated preamble symbols have good small frequency offset and timing synchronization performance. Further, the receiving end can still process the received signal within the range of-500 kHz to 500kHz by ensuring the carrier frequency deviation.
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below.
Fig. 1 is a flowchart illustrating a method for generating preamble symbols in a physical frame according to an embodiment of the present invention. Referring to fig. 1, a method for generating preamble symbols in a physical frame includes the steps of:
step S14: performing inverse discrete Fourier transform on the frequency domain OFDM symbol with the preset length to obtain a time domain OFDM symbol;
step S15: determining a cyclic prefix length;
step S16: intercepting part of the time domain OFDM symbols with the length of the cyclic prefix from the rear part of the time domain OFDM symbols as the cyclic prefix;
step S17: generating a modulation signal according to the part of the time domain OFDM symbols;
step S18: generating a preamble symbol based on the cyclic prefix, the time domain OFDM symbol, and the modulation signal.
It should be noted that, in the process of generating the preamble symbol, how to generate the frequency domain OFDM symbol is not limited. In practice, the skilled person can generate frequency domain OFDM symbols using existing techniques.
In the embodiment of the present invention, the inventor provides a method for generating a frequency domain OFDM symbol through research. Fig. 2 is a schematic flow chart of a method for generating frequency domain OFDM symbols in a method for generating preamble symbols in a physical frame according to the present invention. Referring to fig. 2, the method for generating a frequency domain OFDM symbol includes the steps of:
step S11: respectively generating a fixed sequence and a signaling sequence on a frequency domain;
step S12: filling a fixed sequence and a signaling sequence onto effective subcarriers, wherein the fixed sequence and the signaling sequence are arranged in a parity staggered manner;
step S13: and filling zero sequence subcarriers on two sides of the effective subcarriers respectively to form frequency domain OFDM symbols with preset length.
Specifically, as described in step S11, the fixed sequence and the signaling sequence are generated in the frequency domain, respectively. The fixed sequence includes the relevant information that the receiving end can use to do carrier frequency synchronization and timing synchronization, and the signaling sequence includes each basic transmission parameter.
In this embodiment, the fixed sequence is a complex sequence, and the modulus of each complex number in the complex sequence is 1. The signaling sequence is used to transmit P bits of information (e.g., various signaling), and has a total of 2PEach possibility is mapped to a signalling sequence of length M. The sequence group has 2PThe sequences are not related to each other, and are not related to known fixed sequences.
The fixed sequence and the signaling sequence are padded on the active subcarriers and are arranged in a parity staggered manner as described in step S12.
In a preferred embodiment, the length of the fixed sequence is equal to the length of the signaling sequence, and the length is less than 1/2 of the predetermined length. The predetermined length is 1024, but it can be changed according to the system requirement in practical application.
Taking the predetermined length as 1024 as an example, let the length of the fixed sequence be N (that is, the number of the effective subcarriers carrying the fixed sequence be N), and the length of the signaling sequence be M (that is, the number of the effective subcarriers carrying the signaling sequence be M), where M is equal to N in this embodiment. In other embodiments, N may also be slightly larger than M.
The fixed sequence and the signaling sequence are arranged in a parity staggered manner, namely the fixed sequence is filled to the position of even subcarrier (or odd subcarrier), correspondingly, the signaling sequence is filled to the position of odd subcarrier (or even subcarrier), thereby the distribution state of the parity staggered arrangement of the fixed sequence and the signaling sequence is presented on the effective subcarrier of the frequency domain. It should be noted that, when the lengths of the fixed sequence and the signaling sequence are not consistent (for example, M > N), the parity interleaving of the fixed sequence and the signaling sequence may be implemented by means of zero padding sequence subcarriers.
Zero sequence subcarriers are padded on both sides of the effective subcarrier to form frequency domain OFDM symbols of a predetermined length, respectively, as described in step S13.
In a preferred embodiment, this step comprises: and filling zero sequence subcarriers with equal length on two sides of the effective subcarriers respectively to form frequency domain OFDM symbols with preset length.
Following the example of a predetermined length of 1024, the length G of the zero-sequence subcarrier is 1024-M-N, and (1024-M-N)/2 zero-sequence subcarriers are padded on both sides.
Further, in order to ensure that the receiving end can still process the received signal within the carrier frequency deviation range of-500 kHz to 500kHz, the value of (1024-M-N)/2 is usually larger than the critical length value (set to TH), which is determined by the systematic symbol rate and the predetermined length. E.g. a systematic symbol rate of 1024, 7.61M, and a sampling rate of 9.14M, the predetermined length is then 1024For example, when M is 350, G is 324, and each side is padded with 162 zero-sequence subcarriers.
Accordingly, subcarriers (i.e., frequency domain OFDM symbols) P1_ X of a predetermined length (1024) are provided0,P1_X1,…,P1_X1023Generated by filling in the following way:
wherein,the parity positions may be interchanged.
Fig. 3 is a schematic diagram illustrating a frequency domain carrier distribution of the frequency domain OFDM symbol generated by the method for generating the frequency domain OFDM symbol illustrated in fig. 2.
By adopting the method for generating the frequency domain OFDM symbol in the method for generating the preamble symbol in the physical frame according to the embodiment of the present invention, the inventor has studied to obtain a specific implementation for generating the fixed sequence and the signaling sequence in the frequency domain, with respect to the step S11.
The example of the predetermined length being 1024 and the length of the fixed sequence being equal to the length of the signaling sequence (both being 350) is used.
Specifically, the fixed sequence is a sequence of complex numbers, each complex number in the sequence of complex numbers having a modulo 1. For example, the nth complex number in the complex number sequence isn is 0,1,. 349; wherein, ω isnThe values of (A) are arranged in rows from left to right in sequence as shown in the following table:
wherein n in the first row is 0-9 corresponding to omeganThe value of (a) and the second row are n is 10-19 corresponding to omeganBy analogy, in the 35 th row, n is 340-349 corresponding to omeganThe value of (a).
A signalling sequence for transmitting P (e.g. P-8) bits of information, having a total of 28Each possibility is mapped to a signalling sequence of length 350.
Specifically, generating the signaling sequence in the frequency domain includes the following steps:
1) generating a reference sequence;
2) the reference sequence is cyclically shifted to generate a signaling sequence.
Wherein the reference sequence is a partial Zadoff-Chu sequence. For example, the reference sequence may be expressed as:
the signaling sequence generated after the cyclic shift is performed on the reference sequence is represented as:wherein k isiFor the shift values, the following table shows:
in other embodiments, 8 of the 256 sequences (corresponding to P being 3), 16 (corresponding to P being 4), 32 (corresponding to P being 5), 64 (corresponding to P being 6), 128 (corresponding to P being 7) and 256 (corresponding to P being 8) may be selected for transmission of signaling of P bits that meet system requirements, and the smaller the value of P, the lower the peak-to-average power ratio (PAPR) of the selected subset of sequences will be.
Finally, subcarriers (i.e., frequency domain OFDM symbols) of a predetermined length (1024) P1_ X0,P1_X1,…,P1_X1023Generated by filling in the following way:
whereinThe parity locations may be interchanged.
With continued reference to fig. 1, as depicted in step S14, an inverse discrete fourier transform is performed on the frequency domain OFDM symbol with the predetermined length to obtain a time domain OFDM symbol.
The inverse discrete fourier transform described in this step is a common way of converting a frequency domain signal into a time domain signal, and is not described herein again.
P1_XiObtaining a time domain OFDM symbol after performing inverse discrete Fourier transform:
the cyclic prefix length is determined as described in step S15.
Unlike the prior art, in the embodiment, a Cyclic Prefix (CP) needs to be added before the time domain OFDM symbol, and the wireless broadcast communication system can determine the length of the CP (set to N) according to different channel environmentscp). For example, the cyclic prefix length may be determined based on the length of the multipath against which the wireless broadcast communication system needs to contend. That is, when generating the preamble symbol, the wireless broadcast communication system can determine the multipath length that the preamble symbol needs to contend with, and thus determine the cyclic prefix.
As stated in step S16, a part of the time domain OFDM symbol with the cyclic prefix length is truncated from the rear of the time domain OFDM symbol as the cyclic prefix.
In this embodiment, taking the predetermined length as 1024 as an example, the cyclic prefix length is 512. That is, in this step, the latter half (length of 512) of the time domain OFDM symbol is truncated as a cyclic prefix, thereby solving the problem of degraded performance of frequency domain channel estimation.
A modulated signal is generated from the partial time domain OFDM symbol as described in step S17.
Specifically, the method comprises the following steps:
1) setting a frequency shift sequence;
2) multiplying the partial time domain OFDM symbol by the frequency shift sequence to obtain the modulated signal.
For example, let the frequency shift sequence beWherein f isSH1/(1024T). M (t) can also be designed into other sequences, such as m-sequence or some simplified window sequence.
The modulation signal of the 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 shift sequence m (t), i.e., P1_ b (t) is:
a preamble symbol is generated based on the cyclic prefix, the time domain OFDM symbol and the modulation signal as described in step S18.
Specifically, the cyclic prefix is spliced at the front part of the time domain OFDM symbol as a guard interval, and the modulation signal is spliced at the rear part of the OFDM symbol as a modulation frequency offset sequence to generate a preamble symbol.
For example, the preamble symbol may be based on employing the time domain expression:
wherein N iscpIs 512.
In other embodiments, if the predetermined length takes on another value (i.e., not 1024), then 1024 in the above equation P1(t) will be changed to the corresponding value (i.e., consistent with the predetermined length), and N will be the same as NcpIt may also be changed to other values, preferably NcpIs half of the predetermined length。
In summary, the technical solution solves the problem of performance degradation of frequency domain channel estimation, and generates a modulation signal by using the part of time domain OFDM symbols, so that the generated preamble symbol has good small frequency offset and timing synchronization performance. Further, the receiving end can still process the received signal within the range of-500 kHz to 500kHz by ensuring the carrier frequency deviation.
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.