CN107231327B - System and method for transmitting and receiving circularly symmetric preamble signals - Google Patents
System and method for transmitting and receiving circularly symmetric preamble signals Download PDFInfo
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- CN107231327B CN107231327B CN201610177565.6A CN201610177565A CN107231327B CN 107231327 B CN107231327 B CN 107231327B CN 201610177565 A CN201610177565 A CN 201610177565A CN 107231327 B CN107231327 B CN 107231327B
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2647—Arrangements specific to the receiver only
- H04L27/2655—Synchronisation arrangements
- H04L27/2689—Link with other circuits, i.e. special connections between synchronisation arrangements and other circuits for achieving synchronisation
- H04L27/2692—Link with other circuits, i.e. special connections between synchronisation arrangements and other circuits for achieving synchronisation with preamble design, i.e. with negotiation of the synchronisation sequence with transmitter or sequence linked to the algorithm used at the receiver
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/32—Carrier systems characterised by combinations of two or more of the types covered by groups H04L27/02, H04L27/10, H04L27/18 or H04L27/26
- H04L27/34—Amplitude- and phase-modulated carrier systems, e.g. quadrature-amplitude modulated carrier systems
- H04L27/38—Demodulator circuits; Receiver circuits
- H04L27/3845—Demodulator circuits; Receiver circuits using non - coherent demodulation, i.e. not using a phase synchronous carrier
- H04L27/3854—Demodulator circuits; Receiver circuits using non - coherent demodulation, i.e. not using a phase synchronous carrier using a non - coherent carrier, including systems with baseband correction for phase or frequency offset
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Abstract
The invention provides a system and a method for sending and receiving a circularly symmetric preamble signal, which generate a section of first time domain base symbol with the length of N; circularly shifting the first time domain base symbol by m sampling points left or right to obtain a second time domain base symbol with the length of N; repeatedly, alternately and cascade-expanding the first time domain base symbol and the second time domain base symbol to any length to form a leading symbol; cascading a signaling frame or a data frame after the leading symbol to form a leading baseband frame; and modulating the leading baseband frame into a radio frequency signal and transmitting the radio frequency signal. The system and the method for sending and receiving the circularly symmetric preamble signal have more accurate timing estimation and greatly improve the timing estimation performance; in the aspect of frequency offset estimation of a decimal carrier, the accuracy of frequency offset estimation is improved; fewer sampling points need to slide when the peak value is detected, and the detection time is shorter.
Description
Technical Field
The present invention relates to the technical field of mobile communication, and in particular, to a system and a method for transmitting and receiving a circularly symmetric preamble signal.
Background
In wireless networks such as Ad Hoc networks (Ad Hoc networks), before an initial link is established, both communication parties are not aware of frequency points at which signals are transmitted. At this time, the sending end generally sends a section of paging preamble signal at its working frequency point, so that the receiving end completes the capturing of the paging preamble signal within a certain capturing time window. The capture time window is generally much shorter than the length of the paging preamble signal, so as to ensure that the capture time window is within the duration of the paging preamble signal when the receiving end searches through a plurality of different frequency points. Because the frequency point adopted by the paging preamble signal to be captured is only one of the frequency points searched by the receiving end, the shorter the capture time window is, the more the frequency points which can be searched and traversed by the receiving end are, the wider the searched frequency band is, and the shorter the time for establishing the initial link is under the condition of the given working bandwidth.
The normal establishment of the link depends on the effective acquisition of the paging preamble signal sent by the sending end and the demodulation of the paging information by the receiving end. How to ensure that the receiving end quickly and accurately captures the paging preamble signal in a given scanning frequency point and capturing time window mainly depends on the optimal design and receiving algorithm of the paging preamble signal. In addition, after the paging preamble signal is detected, the receiving end needs to complete the time-frequency synchronization of the paging frame, so as to complete the subsequent paging information demodulation. The time-frequency synchronization of the paging frame mainly has the function of utilizing the preamble to carry out timing synchronization, decimal multiple and integral multiple carrier frequency offset estimation. After the time-frequency synchronization work is finished, the receiving end can enter the normal information demodulation process only through communication.
The paging preamble is mainly used in the establishment phase of the communication link, so that the paging preamble with optimized design is beneficial for a receiving end to find and detect whether the signal exists as soon as possible. Meanwhile, the paging preamble signal also ensures that the initial synchronization process is as simple and reliable as possible.
Moose, Paul h, in the article "a technical for orthogonal frequency dividing frequency offset correction", an algorithm for calculating a carrier frequency offset using two repeated OFDM symbols in the frequency domain is proposed. The research lays a foundation for the design of a leader structure. This cyclically repeated preamble has since been extensively studied in OFDM systems.
Chunrng Kan and Tingchang Wang disclose that the preamble structure is adopted in a short-wave communication system in the article A synchronization acquisition and synchronization using pilot symbols for OFDM in HF communications, and propose a scheme for overcoming synchronization errors caused by fading characteristics of a short-wave channel by adopting a repeated m sequence as a preamble symbol. Simulation shows that the algorithm has obvious advantages in detection rate and synchronization performance under low signal-to-noise ratio.
For the above-mentioned cyclic repetition scheme, in order to ensure that a peak occurs to determine whether a detected signal exists, a minimum correlation period (i.e. a minimum window length of a sliding window) is required to be 2N, and a minimum correlation length is N, that is, a minimum of three symbol lengths is required to successfully detect a signal. Where N is the length of one OFDM symbol or one preamble symbol.
However, in the above scheme, continuous peaks occur during synchronization by using the autocorrelation operation of the preamble sequence. The peak continues until one symbol length before the start of the data segment of the preamble symbol. Thus, the timing position in this scheme can be determined from the falling edge of the peak plateau. However, due to the multipath characteristics of the channel and the influence of noise, the error of the falling edge of the detection platform will be large; when the phase information of the timing position is used for frequency offset estimation, the performance of frequency offset estimation is also affected because only the phase information of one position is available.
Therefore, the above solution has the following two drawbacks:
(1) the resulting peak plateau will cause timing estimation ambiguity;
(2) since there is only one timing location information, the reference information for frequency offset estimation will also be less.
In order to overcome the problem of a peak platform brought by a direct repeated cascade structure during autocorrelation operation, the method comprises the following steps of (1) TrungThanhNguyen; hanwen Cao; guven, A.B. et al analyzed the preamble structure employed in DVB-T2 in the article "Robust specific sensing of DVB-T2signal using the first preamble symbol". The preamble symbol used in DVB-T2 is a structure of [ CA B ]. Wherein, the length of "C" and "B" is 542 and 482, respectively, and the time domain data of "A" is generated after frequency shift. The structure overcomes the timing error caused by the peak platform and improves the accuracy of the leading symbol detection. However, this scheme is mainly used in application scenarios where the carrier frequency is known or insensitive to detection time.
Disclosure of Invention
In view of the above-mentioned shortcomings of the prior art, the present invention provides a system and method for transmitting and receiving a cyclic symmetric preamble signal, which can achieve normal and fast establishment of a communication link and perform more accurate timing synchronization and frequency offset estimation.
In order to achieve the above and other related objects, the present invention provides a transmission system of a cyclic symmetric preamble signal, which includes a time domain base symbol generation module, a base symbol cyclic shift replica symbol generation module, a cascade extension module, a signaling frame/data frame cascade module, and an RF transmission module; the time domain base symbol generating module is used for generating a section of first time domain base symbol with the length of N; the base symbol cyclic shift replica symbol generating module is used for cyclically shifting the first time domain base symbol by m sampling points left or right to obtain a second time domain base symbol with the length of N, wherein m is more than or equal to 1 and less than or equal to N-1; the cascade expansion module is used for repeatedly, alternately and cascade-expanding the first time domain base symbol and the second time domain base symbol to any length to form a leading symbol; the signaling frame/data frame cascade module is used for cascading a signaling frame or a data frame after the leading symbol to form a leading baseband frame; the RF transmitting module is used for modulating the leading baseband frame into a radio frequency signal and transmitting the radio frequency signal.
The transmission system of the circularly symmetric preamble according to the above, wherein: the first time domain base symbol is obtained by OFDM modulation of a constant modulus zero autocorrelation sequence.
Correspondingly, the invention also provides a receiving system of the circularly symmetric preamble signal, which comprises an RF receiving module, a sliding dual autocorrelation module and a peak detection module;
the RF receiving module is used for modulating a received radio frequency signal into a discrete baseband signal;
the sliding dual autocorrelation module is used for slidingly intercepting a sequence with the length of 2N from the discrete baseband signal and performing sliding dual autocorrelation operation on the intercepted sequence according to the cyclic shift number m of a first time domain base symbol of a sending end to generate a sliding dual autocorrelation output sequence; wherein, N is the length of the first time domain base symbol of the sending end;
the peak detection module is used for carrying out energy peak detection on the sliding dual autocorrelation output sequence so as to obtain a correlation value with maximum energy in a sampling value range.
The system for receiving a cyclically symmetric preamble according to the above, wherein: in the sliding dual autocorrelation module, the intercepted sequence is represented as the cascade of 2 sequences with the length of N;
when the truncated sequence is subjected to sliding dual autocorrelation operation, if the first time domain base symbol of the sending end is circularly shifted left by m sampling values, the sliding dual autocorrelation output sequence c (n) is represented as:
when the truncated sequence is subjected to sliding dual autocorrelation operation, if the first time domain base symbol of the sending end circularly shifts to the right by m sampling values, the sliding dual autocorrelation output sequence c (n) is represented as:
wherein y (n) represents a discrete baseband signal,
and
representing the phase adjustment factor.
The system for receiving a cyclically symmetric preamble according to the above, wherein: the timing estimation module is used for determining the corresponding time position of the transmitted first time domain base symbol in the discrete baseband signal according to the sampling value serial number of the correlation value with the maximum energy.
The system for receiving a cyclically symmetric preamble according to the above, wherein: the frequency deviation estimation module is used for determining the frequency deviation between the discrete baseband signal and the transmitted preamble baseband frame signal according to the phase of the correlation value with the maximum energy.
In addition, the invention also provides a method for sending the circularly symmetric preamble signal, which comprises the following steps:
generating a first time domain base symbol with the length of N;
circularly shifting the first time domain base symbol by m sampling points left or right to obtain a second time domain base symbol with the length of N, wherein m is more than or equal to 1 and less than or equal to N-1;
repeatedly, alternately and cascade-expanding the first time domain base symbol and the second time domain base symbol to any length to form a leading symbol;
cascading a signaling frame or a data frame after the leading symbol to form a leading baseband frame;
and modulating the leading baseband frame into a radio frequency signal and transmitting the radio frequency signal.
According to the above method for transmitting cyclic symmetric preamble, wherein: the first time domain base symbol is obtained by OFDM modulation of a constant modulus zero autocorrelation sequence.
Correspondingly, the invention also provides a method for receiving the circularly symmetric preamble signal, which comprises the following steps:
modulating the received radio frequency signal into a discrete baseband signal;
the method comprises the steps of intercepting a sequence with the length of 2N in a sliding mode from a discrete baseband signal, and carrying out sliding dual autocorrelation operation on the intercepted sequence according to the cyclic shift number m of a first time domain base symbol of a sending end to generate a sliding dual autocorrelation output sequence; wherein, N is the length of the first time domain base symbol of the sending end;
and carrying out energy peak detection on the sliding dual autocorrelation output sequence to obtain a correlation value with the maximum energy in the sampling value range.
The method for receiving a cyclically symmetric preamble signal comprises: the truncated sequence is represented as a cascade of 2 sequences of length N;
when the truncated sequence is subjected to sliding dual autocorrelation operation, if the first time domain base symbol of the sending end is circularly shifted left by m sampling values, the sliding dual autocorrelation output sequence c (n) is represented as:
when the truncated sequence is subjected to sliding dual autocorrelation operation, if the first time domain base symbol of the sending end circularly shifts to the right by m sampling values, the sliding dual autocorrelation output sequence c (n) is represented as:
wherein y (n) represents a discrete baseband signal,
and
representing the phase adjustment factor.
The method for receiving a cyclically symmetric preamble signal comprises: and determining the corresponding time position of the transmitted first time domain base symbol in the discrete baseband signal according to the sampling value serial number of the correlation value with the largest energy.
The method for receiving a cyclically symmetric preamble signal comprises: further comprising determining a frequency offset between the discrete baseband signal and the transmitted preamble baseband frame signal according to the phase of the correlation value having the largest energy.
As described above, the system and method for transmitting and receiving a cyclic symmetric preamble signal according to the present invention have the following advantages:
(1) when the autocorrelation operation is carried out in a receiving system, a clear peak value is generated, and timing ambiguity caused by a peak value platform is avoided, so that the timing estimation is more accurate, and the timing estimation performance is greatly improved;
(2) in the aspect of frequency offset estimation of a decimal carrier, the accuracy of frequency offset estimation is improved;
(3) a peak value exists in one symbol period, and only a receiving signal with the length of three symbols can ensure that one peak value is detected; therefore, fewer sampling points need to slide when the peak value is detected, and the detection time is shorter.
Drawings
Fig. 1 is a schematic structural diagram of a transmission system of a cyclic symmetric preamble according to the present invention;
FIG. 2 is a schematic diagram of a cyclic symmetric preamble receiving system according to the present invention;
FIG. 3 is a diagram illustrating an embodiment of sliding dual autocorrelation values when the transmitter cyclically shifts left by m samples in the present invention;
FIG. 4 is a schematic diagram of an embodiment of a preamble baseband frame in a reference scheme;
FIG. 5 is a schematic diagram of a preamble baseband frame according to an embodiment of the present invention;
FIG. 6 is a schematic diagram showing the comparison of the detection characteristics of the reference scheme and the scheme employed in the present invention;
FIG. 7 is a diagram of a simulated frame of a leading baseband frame in the reference scheme of the present invention
FIG. 8 is a diagram of a simulated frame of a leading baseband frame according to the present invention
FIG. 9 is a diagram showing a comparison of autocorrelation energy simulations of a reference scheme and a preferred scheme of the present invention;
FIG. 10 is a schematic diagram showing a comparison of the timing error cumulative distribution functions of the reference scheme and the preferred scheme of the present invention;
FIG. 11 is a schematic diagram illustrating a comparison of frequency offset estimation error accumulation distribution functions of a reference scheme and a preferred scheme of the present invention;
fig. 12 is a flowchart illustrating a method for transmitting a cyclic symmetric preamble according to the present invention;
fig. 13 is a flowchart of a method for receiving a cyclic symmetric preamble according to the present invention.
Description of the element reference numerals
11 time domain base symbol generating module
12-base symbol cyclic shift replica symbol generation module
13 cascaded expansion module
14 signaling frame/data frame cascade module
15 RF transmitting module
21 RF receiving module
22 sliding dual autocorrelation module
23 peak detection module
Detailed Description
The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention. It is to be noted that the features in the following embodiments and examples may be combined with each other without conflict.
It should be noted that the drawings provided in the following embodiments are only for illustrating the basic idea of the present invention, and the components related to the present invention are only shown in the drawings rather than drawn according to the number, shape and size of the components in actual implementation, and the type, quantity and proportion of the components in actual implementation may be changed freely, and the layout of the components may be more complicated.
Referring to fig. 1, the transmission system of the cyclic symmetric preamble signal of the present invention includes a time domain base symbol generation module 11, a base symbol cyclic shift replica symbol generation module 12, a cascade extension module 13, a signaling frame/data frame cascade module 14, and an RF transmission module 15.
The time domain base symbol generating module 11 is configured to generate a time domain base symbol a with a length N.
Wherein, the time domain base symbol A is obtained by OFDM modulation of a specific symbol sequence. Preferably, the specific symbol sequence employs a constant-modulus zero auto-correlation sequence.
The base symbol cyclic shift replica symbol generating module 12 is configured to cyclically shift the time domain base symbol a left or right by m sampling points to obtain a time domain base symbol a' with a length N, where m is greater than or equal to 1 and less than or equal to N-1.
The cascade expansion module 13 is connected to the time domain base symbol generation module 11 and the base symbol cyclic shift replica symbol generation module 12, and is configured to repeatedly, alternately, cascade-expand the time domain base symbol a and the time domain base symbol a' to an arbitrary length to form a preamble symbol P.
Specifically, the structure of the obtained leader symbol P is AA'.
The signaling frame/data frame cascading module 14 is connected to the cascading expansion module 13, and is configured to cascade the signaling frame or the data frame after the preamble symbol P to form a preamble baseband frame S.
The RF transmitting module 15 is connected to the signaling frame/data frame cascade module 14, and is configured to modulate the leading baseband frame S into a radio frequency signal and transmit the radio frequency signal.
Specifically, the preamble baseband frame S is modulated into a radio frequency signal by up-conversion and transmitted.
Referring to fig. 2, the system for receiving a cyclic symmetric preamble signal of the present invention includes an RF receiving module 21, a sliding dual autocorrelation module 22, and a peak detection module 23, which are connected in sequence.
The RF receiving module 21 is configured to modulate the received radio frequency signal into a discrete baseband signal y (n).
Specifically, the RF receiving module down-converts the received radio frequency signal into a baseband signal, and then performs a/D sampling to form a discrete baseband signal y (n).
The sliding dual autocorrelation module 22 is configured to slide and intercept a sequence Y with a length of 2N from the discrete baseband signal Y (N), and perform a sliding dual autocorrelation operation on the intercepted sequence Y according to the cyclic shift number m of the time domain base symbol a at the transmitting end to generate a sliding dual autocorrelation output sequence c (N).
In particular, the sequence Y can be represented as a cascade of 2 sequences Y1 and Y2 of length N. Fig. 3 is a schematic diagram of the sliding dual autocorrelation value when the transmitting end circularly shifts m sampling values to the left.
When the intercepted sequence Y is subjected to sliding dual autocorrelation operation, if a time domain base symbol A at a transmitting end circularly moves left by m sampling values, the sampling value of m points before Y1 is subjected to conjugate multiplication corresponding to the sampling value of m points after Y2, the sampling value of N-m points after Y1 is subjected to conjugate multiplication corresponding to the sampling value of N-m points before Y2, and finally the two products are subjected to phase compensation and then are combined. Therefore, the sliding dual autocorrelation output sequence c (n) can be expressed by the equation:
wherein
And
is introduced for adjusting the phase interval. The transmission data passes through the channel and is affected by frequency deviation, the normalized frequency deviation is represented by epsilon, and the relation between the received data y (n) and the transmitted data x (n) is as follows:
y(n)＝x(n)*ej2πεn/N
the invention adopts sliding dual autocorrelation, which can cause the phase difference of the front part and the rear part to be different,
and
namely, the method is introduced for ensuring that the sliding dual autocorrelation operation has a constant phase difference, and a specific value can be obtained by the magnitude of the position difference of two parts of sampling points multiplied by conjugates. To adjust for the difference in phase difference, it is preferable
The reciprocal of the phase difference between the sampling value at m points before Y1 and the sampling value at m points after Y2;
is the inverse of the phase difference between the N-m samples after Y1 and the N-m samples before Y2.
When the intercepted sequence Y is subjected to sliding dual autocorrelation operation, if a time domain base symbol A at a transmitting end circularly moves to the right by m sampling values, the sampling value of the front N-m point of Y1 is correspondingly and conjointly multiplied with the sampling value of the rear N-m point of Y2, the sampling value of the rear m point of Y1 is correspondingly and conjointly multiplied with the sampling value of the front m point of Y2, and the two products are combined after phase compensation. Therefore, the sliding dual autocorrelation output sequence c (n) can be expressed by the equation:
wherein, it is preferable
The reciprocal of the phase difference between the sampling value of the point N-m before Y1 and the sampling value of the point N-m after Y2;
is the inverse of the phase difference between the m samples after Y1 and the m samples before Y2.
The peak detection module 23 is configured to perform energy peak detection on the sliding dual autocorrelation output sequence C (n) to obtain a correlation value C' (n) with the largest energy in the sampling value range.
Preferably, a timing estimation module is also included.
The timing estimation module is connected with the peak detection module and is used for determining the corresponding time position of the transmitted time domain base symbol A in the discrete baseband signal y (n) according to the sampling value serial number n of the correlation value C' (n) with the largest energy.
Preferably, a frequency offset estimation module is further included.
The frequency deviation estimation module is connected with the peak value detection module and used for determining the frequency deviation between the discrete baseband signal y (n) and the transmitted leading baseband frame signal according to the phase of the correlation value C' (n) with the largest energy.
Since the transmission signal is transmitted through the channel, the frequency offset referred to herein is a frequency offset existing between the transmission-side signal and the reception-side signal due to the influence of the channel characteristics.
As shown in fig. 4, in the defined reference scheme, a preamble baseband frame is formed by repeatedly concatenating a plurality of time-domain base symbols a and then concatenating signaling frames.
As shown in fig. 5, in the scheme adopted by the present invention, the leading baseband frame S includes a leading symbol P and a signaling frame. The preamble symbol P is formed by alternately cascading and expanding a plurality of time domain base symbols A and copied time domain base symbols A' circularly shifted to the left by A1 or circularly shifted to the right by A2.
The comparison of the detection characteristics of the reference protocol and the protocol employed in the present invention is shown in fig. 6. As can be seen from the figure, the solution adopted by the present invention has the following advantages:
1) in terms of rapid detection of signals
In the scheme adopted by the invention, one peak value exists in one symbol period, so that only a receiving signal with the length of three symbols is needed to ensure that one peak value is detected. Therefore, fewer sampling points need to be slid to detect the peak, and the detection time is shorter.
2) In terms of timing estimation of symbols
The scheme adopted by the invention has definite peak values when the self-correlation operation is carried out in the receiving system, and avoids timing ambiguity caused by a peak value platform generated in a reference scheme. Therefore, the timing estimation of the scheme adopted by the invention is more accurate, and the timing estimation performance is greatly improved compared with the reference scheme.
3) In the aspect of decimal carrier frequency offset estimation
The improvement of timing accuracy is beneficial to improving the accuracy of frequency offset estimation, so that the scheme adopted by the invention also has certain performance advantage in the aspect of decimal carrier frequency offset estimation compared with a reference scheme.
The following describes an embodiment of a preamble signal transmission/reception system according to the present invention with reference to a specific embodiment.
As shown in fig. 7, in the defined reference scheme, a preamble baseband frame is formed by concatenating a plurality of time-domain base symbols a repeatedly, and then concatenating data frames.
Since the constant Amplitude Zero Auto-correlation (CAZAC) sequence has ideal periodic autocorrelation characteristics, good cross-correlation characteristics, and other properties, in a preferred embodiment of the present invention, the CAZAC sequence is used to generate preamble symbols, and for convenience of explanation, the number of cyclic shifts is 1/2 equal to the length of the time-domain base symbol a, that is, m is 1/2N. Therefore, as shown in fig. 8, the leading baseband frame S includes a leading symbol P and a data frame. Wherein the preamble symbol P is formed by repeatedly and alternately cascading the time domain base symbol a and the time domain base symbol a' in this specific embodiment.
Specifically, in a preferred embodiment of the present invention, the preamble symbol is obtained by the following steps:
1) generating a frequency domain symbol with 72 points by using a CAZAC sequence;
2) zero padding is carried out on the obtained sequence to obtain a 128-point sequence;
3) performing inverse Fourier transform (IFFT) on the 128-point sequence to convert the frequency domain symbol into a time domain to obtain a time domain base symbol A;
4) circularly shifting 1/2 the symbol length of the time domain base symbol A to obtain a time domain base symbol A';
5) the time domain base symbol a and the time domain base symbol a' are alternately and repeatedly concatenated.
In the frame structures of the two schemes, the preamble symbols are set to be four symbols in length. Meanwhile, in order to be similar to the actual application scene, a data frame is accessed afterwards.
In the actual simulation, an Additive White Gaussian Noise (AWGN) channel is sent, the signal-to-Noise ratio is 5dB, and a normalized frequency offset is added, where the normalized frequency offset is set to 0.01. In order to obtain statistical results, the simulation loops 1000 times for the reference scheme and the preferred scheme of the invention, and the timing and frequency offset errors of each time are counted.
Fig. 9 shows a simulation comparison of normalized autocorrelation energy curves for two schemes. As can be seen, the autocorrelation curve of the reference solution (defined as solution one) has a peak plateau, and the timing estimation is based on the falling edge position of the plateau. However, in a noisy environment, the position of the falling edge is easily blurred to a large extent. The timing performance of the reference scheme is relatively poor. The preferred scheme (defined as scheme two) of the present invention has an obvious peak after the autocorrelation operation, and one symbol length is one peak period. The timing estimation is carried out according to the peak position, the timing ambiguity problem of a reference scheme is solved, the peak is more obvious, and therefore the timing estimation performance is improved.
Fig. 10 is a graph comparing the cumulative distribution function of timing errors for two schemes. As can be seen from the figure, the timing performance of the preferred embodiment of the present invention is significantly better than the reference embodiment. The reason is that the optimal scheme of the invention has obvious peak values after autocorrelation operation, has higher accuracy of detecting the peak value position and overcomes the timing ambiguity problem caused by a peak value platform in a reference scheme.
Fig. 11 is a graph comparing frequency offset estimation error accumulation profiles. As can be seen from the figure:
1) the maximum frequency offset estimation error of the reference scheme is smaller than that of the preferred scheme of the present invention, because when the frequency offset estimation is performed by using the phase of the autocorrelation peak for the preamble symbol composed of the same symbol concatenation, the autocorrelation peak is continuous, i.e. there is no specific autocorrelation peak, so the phase of the autocorrelation peak is not sensitive to the timing error, i.e. the phase of the estimated autocorrelation peak and the autocorrelation values in the vicinity thereof can be both used for frequency offset estimation, without causing significant estimation performance loss.
2) The optimal scheme of the invention overcomes the problem of a peak platform of a reference scheme, and achieves great timing performance improvement; but simultaneously, because a local unique optimal correlation peak value is generated when the self-correlation operation is carried out on the leading symbol, namely the self-correlation peak value is sensitive to the timing error. When the autocorrelation timing error is caused by noise, etc., the estimated autocorrelation peak will contain the autocorrelation interference components of the adjacent symbols, which interference components will increase with the increase of the timing error and affect the phase of the estimated correlation peak, thereby causing the frequency offset estimation error thereof to increase.
Referring to fig. 12, the method for transmitting a cyclic symmetric preamble signal according to the present invention includes the steps of:
and step S11, generating a time domain base symbol A with the length of N.
Wherein, the time domain base symbol A is obtained by OFDM modulation of a specific symbol sequence. Preferably, the specific symbol sequence employs a constant-modulus zero auto-correlation sequence.
And step S12, circularly shifting the time domain base symbol A left or right by m sampling points to obtain a time domain base symbol A' with the length of N, wherein m is more than or equal to 1 and less than or equal to N-1.
And step S13, repeatedly, alternately and cascade-expanding the time domain base symbol A and the time domain base symbol A' to any length to form a preamble symbol P.
Specifically, the structure of the obtained leader symbol P is AA'.
Step S14, concatenating the signaling frame or data frame after the preamble symbol P to form a preamble baseband frame S.
And step S15, modulating the leading baseband frame S into a radio frequency signal and transmitting the radio frequency signal.
Specifically, the preamble baseband frame S is modulated into a radio frequency signal by up-conversion and transmitted.
Referring to fig. 13, the method for receiving a cyclic symmetric preamble signal according to the present invention includes the steps of:
step S21, modulate the received rf signal into a discrete baseband signal y (n).
Specifically, the RF receiving module down-converts the received radio frequency signal into a baseband signal, and then performs a/D sampling to form a discrete baseband signal y (n).
Step S22, slide and intercept the sequence Y with length of 2N from the discrete baseband signal Y (N), and perform a sliding dual autocorrelation operation on the intercepted sequence Y according to the cyclic shift number m of the time domain base symbol a at the transmitting end to generate a sliding dual autocorrelation output sequence c (N).
In particular, the sequence Y can be represented as a cascade of 2 sequences Y1 and Y2 of length N. Fig. 3 is a schematic diagram of the sliding dual autocorrelation value when the transmitting end circularly shifts m sampling values to the left.
When the intercepted sequence Y is subjected to sliding dual autocorrelation operation, if a time domain base symbol A at a transmitting end circularly moves left by m sampling values, the sampling value of m points before Y1 is subjected to conjugate multiplication corresponding to the sampling value of m points after Y2, the sampling value of N-m points after Y1 is subjected to conjugate multiplication corresponding to the sampling value of N-m points before Y2, and finally the two products are subjected to phase compensation and then are combined. Therefore, the sliding dual autocorrelation output sequence c (n) can be expressed by the equation:
is convenient to use
The reciprocal of the phase difference between the sampling value at m points before Y1 and the sampling value at m points after Y2;
is the inverse of the phase difference between the N-m samples after Y1 and the N-m samples before Y2.
When the intercepted sequence Y is subjected to sliding dual autocorrelation operation, if a time domain base symbol A at a transmitting end circularly moves to the right by m sampling values, the sampling value of the front N-m point of Y1 is correspondingly and conjointly multiplied with the sampling value of the rear N-m point of Y2, the sampling value of the rear m point of Y1 is correspondingly and conjointly multiplied with the sampling value of the front m point of Y2, and the two products are combined after phase compensation. Therefore, the sliding dual autocorrelation output sequence c (n) can be expressed by the equation:
wherein, it is preferable
The reciprocal of the phase difference between the sampling value of the point N-m before Y1 and the sampling value of the point N-m after Y2;
is the inverse of the phase difference between the m samples after Y1 and the m samples before Y2.
Step S23, performing energy peak detection on the sliding dual autocorrelation output sequence C (n) to obtain a correlation value C' (n) with the maximum energy in the sampling value range.
Preferably, the method further comprises determining the corresponding time position of the transmitted time-domain base symbol a in the discrete baseband signal y (n) according to the sampling value serial number n of the correlation value C' (n) with the largest energy.
Preferably, the method further comprises determining a frequency deviation between the discrete baseband signal y (n) and the transmitted preamble baseband frame signal according to the phase of the correlation value C' (n) with the largest energy.
Since the transmission signal is transmitted through the channel, the frequency offset referred to herein is a frequency offset existing between the transmission-side signal and the reception-side signal due to the influence of the channel characteristics.
In summary, the system and method for transmitting and receiving a circularly symmetric preamble signal of the present invention have a clear peak value when performing autocorrelation operation in a receiving system, thereby avoiding timing ambiguity caused by a peak platform, so that timing estimation is more accurate, and timing estimation performance is greatly improved; in the aspect of frequency offset estimation of a decimal carrier, the accuracy of frequency offset estimation is improved; a peak value exists in one symbol period, and only a receiving signal with the length of three symbols can ensure that one peak value is detected; therefore, fewer sampling points need to slide when the peak value is detected, and the detection time is shorter. Therefore, the invention effectively overcomes various defects in the prior art and has high industrial utilization value.
The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical spirit of the present invention be covered by the claims of the present invention.
Claims (12)
1. A system for receiving a cyclically symmetric preamble, comprising: the device comprises an RF receiving module, a sliding dual autocorrelation module and a peak detection module;
the RF receiving module is used for modulating a received radio frequency signal into a discrete baseband signal;
the sliding dual autocorrelation module is used for slidingly intercepting a sequence with the length of 2N from the discrete baseband signal and performing sliding dual autocorrelation operation on the intercepted sequence according to the cyclic shift number m of a first time domain base symbol of a sending end to generate a sliding dual autocorrelation output sequence; wherein, N is the length of the first time domain base symbol of the sending end; the sending end generates a first time domain base symbol with the length of N; circularly shifting the first time domain base symbol by m sampling points left or right to obtain a second time domain base symbol with the length of N, wherein m is more than or equal to 1 and less than or equal to N-1; repeatedly, alternately and cascade-expanding the first time domain base symbol and the second time domain base symbol to any length to form a preamble symbol;
the peak detection module is used for carrying out energy peak detection on the sliding dual autocorrelation output sequence so as to obtain a correlation value with maximum energy in a sampling value range.
2. The system for receiving a cyclically symmetric preamble according to claim 1, wherein: in the sliding dual autocorrelation module, the intercepted sequence is represented as the cascade of 2 sequences with the length of N;
when the truncated sequence is subjected to sliding dual autocorrelation operation, if the first time domain base symbol of the sending end is circularly shifted left by m sampling values, the sliding dual autocorrelation output sequence c (n) is represented as:
when the truncated sequence is subjected to sliding dual autocorrelation operation, if the first time domain base symbol of the sending end circularly shifts to the right by m sampling values, the sliding dual autocorrelation output sequence c (n) is represented as:
wherein y (n) represents a discrete baseband signal,
and
representing the phase adjustment factor.
3. The system for receiving a cyclically symmetric preamble according to claim 1, wherein: the timing estimation module is used for determining the corresponding time position of the transmitted first time domain base symbol in the discrete baseband signal according to the sampling value serial number of the correlation value with the maximum energy.
4. The system for receiving a cyclically symmetric preamble according to claim 1, wherein: the frequency deviation estimation module is used for determining the frequency deviation between the discrete baseband signal and the transmitted preamble baseband frame signal according to the phase of the correlation value with the maximum energy.
5. The system for receiving a cyclically symmetric preamble according to claim 1, wherein: the transmitting system of the circularly symmetric leading signal comprises a time domain base symbol generating module, a base symbol circularly shifting and copying symbol generating module, a cascading expansion module, a signaling frame/data frame cascading module and an RF transmitting module;
the time domain base symbol generating module is used for generating a section of first time domain base symbol with the length of N;
the base symbol cyclic shift replica symbol generating module is used for cyclically shifting the first time domain base symbol by m sampling points left or right to obtain a second time domain base symbol with the length of N, wherein m is more than or equal to 1 and less than or equal to N-1;
the cascade expansion module is used for repeatedly, alternately and cascade-expanding the first time domain base symbol and the second time domain base symbol to any length to form a leading symbol;
the signaling frame/data frame cascade module is used for cascading a signaling frame or a data frame after the leading symbol to form a leading baseband frame;
the RF transmitting module is used for modulating the leading baseband frame into a radio frequency signal and transmitting the radio frequency signal.
6. The system for receiving a cyclically symmetric preamble according to claim 5, wherein: the first time domain base symbol is obtained by OFDM modulation of a constant modulus zero autocorrelation sequence.
7. A method for receiving a cyclic symmetric preamble, comprising: the method comprises the following steps:
modulating the received radio frequency signal into a discrete baseband signal;
the method comprises the steps of intercepting a sequence with the length of 2N in a sliding mode from a discrete baseband signal, and carrying out sliding dual autocorrelation operation on the intercepted sequence according to the cyclic shift number m of a first time domain base symbol of a sending end to generate a sliding dual autocorrelation output sequence; wherein, N is the length of the first time domain base symbol of the sending end; the sending end generates a first time domain base symbol with the length of N; circularly shifting the first time domain base symbol by m sampling points left or right to obtain a second time domain base symbol with the length of N, wherein m is more than or equal to 1 and less than or equal to N-1; repeatedly, alternately and cascade-expanding the first time domain base symbol and the second time domain base symbol to any length to form a preamble symbol;
and carrying out energy peak detection on the sliding dual autocorrelation output sequence to obtain a correlation value with the maximum energy in the sampling value range.
8. The method of receiving a cyclically symmetric preamble according to claim 7, wherein: the truncated sequence is represented as a cascade of 2 sequences of length N;
when the truncated sequence is subjected to sliding dual autocorrelation operation, if the first time domain base symbol of the sending end is circularly shifted left by m sampling values, the sliding dual autocorrelation output sequence c (n) is represented as:
when the truncated sequence is subjected to sliding dual autocorrelation operation, if the first time domain base symbol of the sending end circularly shifts to the right by m sampling values, the sliding dual autocorrelation output sequence c (n) is represented as:
wherein y (n) represents a discrete baseband signal,
and
representing the phase adjustment factor.
9. The method of receiving a cyclically symmetric preamble according to claim 7, wherein: and determining the corresponding time position of the transmitted first time domain base symbol in the discrete baseband signal according to the sampling value serial number of the correlation value with the largest energy.
10. The method of receiving a cyclically symmetric preamble according to claim 7, wherein: further comprising determining a frequency offset between the discrete baseband signal and the transmitted preamble baseband frame signal according to the phase of the correlation value having the largest energy.
11. The method of receiving a cyclically symmetric preamble according to claim 7, wherein: the method for sending the circularly symmetric preamble signal comprises the following steps:
cascading a signaling frame or a data frame after the leading symbol to form a leading baseband frame;
and modulating the leading baseband frame into a radio frequency signal and transmitting the radio frequency signal.
12. The method of receiving a cyclically symmetric preamble according to claim 11, wherein: the first time domain base symbol is obtained by OFDM modulation of a constant modulus zero autocorrelation sequence.
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