CN102025663B - Estimation method and device of orthogonal frequency division multiplexing (OFDM) synchronous position - Google Patents
Estimation method and device of orthogonal frequency division multiplexing (OFDM) synchronous position Download PDFInfo
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Abstract
The embodiment of the invention discloses an estimation method and device of an orthogonal frequency division multiplexing (OFDM) synchronous position. The method comprises the following steps of dividing a signal to be segmented into a first segmentation signal and a second segmentation signal after receiving the cycle prefix (CP) of an OFDM symbol; respectively carrying out separation on training sequences and data symbols in the first segmentation signal and the second segmentation signal; calculating the signal to noise ratio of the first segmentation signal and the second segmentation signal according to the separated training sequences and data symbols; searching a synchronous reference position of the OFDM symbol according to a bisection recursion mode by comparing the signal to noise ratios of the first segmentation signal and the second segmentation signal; and obtaining a synchronous initial position of an effective data part of the OFDM symbol according to the synchronous reference position. The embodiment of the invention can start synchronous estimation once receiving the CP, obtains the synchronous initial position of an OFDM effective data symbol through a recursion method by comparing the signal to noise ratios of the segmentation signals and has the advantages that the structure is simple and the synchronization speed is rapid.
Description
Technical Field
The present invention relates to the field of communications technologies, and in particular, to a CP (Cyclic Prefix) based OFDM (Orthogonal Frequency Division Multiplexing) position estimation method and apparatus.
Background
OFDM is a technique that modulates a high-rate data stream into multiple lower-rate sub-data streams and communicates via a physical channel that has been divided into multiple sub-carriers. OFDM technology has been applied in communication systems such as data broadcasting and digital television, as well as in the wireless local area network standards IEEE802.11 and wireless metropolitan area network IEEE 802.16. Since an OFDM symbol is formed by superimposing a plurality of subcarrier signals and each subcarrier is distinguished by orthogonality, in order to ensure orthogonality in an OFDM system, it is necessary for a receiving side and a transmitting side to perform strict time synchronization and carrier synchronization so as to correctly receive data.
The inventor finds that, in the research process of the prior art, an OFDM system in the prior art generally adopts a data-assisted method for synchronization, which needs to use a plurality of OFDM data blocks to transmit pilot symbols or training sequences, thereby causing resource waste; and the receiver needs to receive the complete data before starting the synchronization estimation, thereby bringing the loss of information rate.
Disclosure of Invention
In order to solve the above technical problems, embodiments of the present application provide an OFDM synchronization position estimation method and apparatus, so as to solve the problems that the existing synchronization position estimation method is prone to cause resource waste and brings information rate loss.
The embodiment of the application discloses the following technical scheme:
an OFDM synchronization position estimation method, comprising:
receiving a Cyclic Prefix (CP) of an OFDM symbol, wherein the CP comprises a training sequence and a data symbol with the same transmission power;
equally dividing a signal to be segmented into two segments of signals, namely a first segment of signal and a second segment of signal, wherein the signal to be segmented belongs to the CP;
respectively separating the training sequence and the data symbol in the first segment signal and the second segment signal;
calculating the signal-to-noise ratio of the first section of signal and the second section of signal according to the separated training sequence and the separated data symbol;
searching the synchronous reference position of the OFDM symbol according to a halving recursion mode by comparing the signal-to-noise ratio of the first section of signal and the second section of signal;
and obtaining the synchronization initial position of the effective data part of the OFDM symbol according to the synchronization reference position.
The calculating the signal-to-noise ratio of the first segment signal and the second segment signal according to the separated training sequence and the separated data symbol comprises:
calculating the autocorrelation function of the training sequence and the data symbol in the first segment signal and the second segment signal respectively;
respectively taking the estimation of the autocorrelation function of the data symbols in the first-stage signal and the second-stage signal as signal power estimation and the estimation of the training sequence as noise power estimation;
and respectively taking the ratio of the signal power estimation and the noise power estimation of the first section signal and the second section signal as the signal-to-noise ratio of the first section signal and the second section signal.
The searching for the synchronization reference position of the OFDM symbol according to the halving recursion mode includes:
when the difference value between the signal-to-noise ratio of the first section of signal and the signal-to-noise ratio of the second section of signal is within a preset range, outputting the position of a first sampling point after the second section of signal as the synchronous reference position of the OFDM symbol;
when the difference value of the signal-to-noise ratio of the first section signal and the signal-to-noise ratio of the second section signal is not within a preset range, if the signal-to-noise ratio of the first section signal is smaller than the signal-to-noise ratio of the second section signal, extracting the second section signal as the signal to be segmented, and returning to the step of equally dividing the signal to be segmented into the two sections of signals;
and when the difference value of the signal-to-noise ratio of the first section signal and the signal-to-noise ratio of the second section signal is not within a preset range, if the signal-to-noise ratio of the first section signal is greater than the signal-to-noise ratio of the second section signal, extracting the first section signal as the signal to be segmented, and returning to the step of equally dividing the signal to be segmented into the two sections of signals.
The obtaining of the synchronization start position of the effective data part of the OFDM symbol according to the synchronization reference position includes:
taking the position of the first sampling point of the CP as a reference point, and judging whether the distance between the synchronous reference position and the reference point is less than half of the length of the CP or not;
and if the distance is less than half of the CP length, taking the position of the synchronization reference position plus the CP length as the synchronization starting position of the effective data part of the OFDM symbol, and if the distance is more than half of the CP length, taking the synchronization reference position as the synchronization starting position of the effective data part of the OFDM symbol.
Before equally dividing the signal to be segmented into two segments of signals, the method further comprises the following steps:
judging whether the number of sampling points of the signal to be segmented is more than 1;
and if the number of the sampling points is more than 1, equally dividing the signal to be segmented into two segments of signals, and if the number of the sampling points is equal to 1, outputting the position of the sampling point as the synchronous reference position of the OFDM symbol.
An OFDM synchronous position estimating apparatus comprising:
a receiving unit, configured to receive a cyclic prefix CP of an OFDM symbol, where the CP includes a training sequence and a data symbol with the same transmit power;
the segmentation unit is used for equally dividing a signal to be segmented into two segments of signals, namely a first segment of signal and a second segment of signal, wherein the signal to be segmented belongs to the CP;
a separation unit, configured to separate the training sequence and the data symbol in the first segment of signal and the second segment of signal respectively;
a calculating unit, configured to calculate signal-to-noise ratios of the first segment signal and the second segment signal according to the separated training sequence and the data symbol;
the searching unit is used for searching the synchronous reference position of the OFDM symbol according to a halving recursion mode by comparing the signal-to-noise ratio of the first section of signal and the second section of signal;
and the obtaining unit is used for obtaining the synchronization initial position of the effective data part of the OFDM symbol according to the synchronization reference position.
The calculation unit includes:
an autocorrelation function calculation unit, configured to calculate autocorrelation functions of the training sequence and the data symbols in the first segment of signal and the second segment of signal, respectively;
a power estimation unit, configured to use estimates of autocorrelation functions of data symbols in the first segment signal and the second segment signal as signal power estimates, and use estimates of training sequences as noise power estimates, respectively;
and the signal-to-noise ratio acquisition unit is used for respectively taking the ratio of the signal power estimation and the noise power estimation of the first section signal and the second section signal as the signal-to-noise ratio of the first section signal and the second section signal.
The search unit includes:
the first comparison unit is used for comparing whether the difference value of the signal-to-noise ratio of the first section signal and the signal-to-noise ratio of the second section signal is within a preset range or not;
the first execution unit is used for outputting the position of a first sampling point after the second section of signal as the synchronous reference position of the OFDM symbol when the difference value of the signal-to-noise ratio of the first section of signal and the signal-to-noise ratio of the second section of signal is within a preset range;
the second comparison unit is used for comparing the signal-to-noise ratio of the first section signal with the signal-to-noise ratio of the second section signal when the difference value of the signal-to-noise ratio of the first section signal and the signal-to-noise ratio of the second section signal is not in a preset range;
and the second execution unit is used for extracting the second section signal as the signal to be segmented when the signal-to-noise ratio of the first section signal is smaller than that of the second section signal, returning to the segmentation unit to execute a corresponding function, and extracting the first section signal as the signal to be segmented when the signal-to-noise ratio of the first section signal is larger than that of the second section signal, returning to the segmentation unit to execute a corresponding function.
The obtaining unit includes:
a distance determining unit, configured to determine whether a distance between the synchronous reference position and the reference point is less than half of the length of the CP, using a position where a first sampling point of the CP is located as a reference point;
a synchronization position determining unit, configured to, if the distance is smaller than half of the CP length, use a position obtained by adding the CP length to the synchronization reference position as a synchronization starting position of the OFDM symbol valid data portion, and if the distance is larger than half of the CP length, use the synchronization reference position as a synchronization starting position of the OFDM symbol valid data portion.
Further comprising:
the judging unit is used for judging whether the number of sampling points of the signal to be segmented is more than 1 or not;
and the execution unit is used for triggering the segmentation unit to execute a corresponding function if the number of the sampling points is greater than 1, and outputting the position of the sampling point as the synchronous reference position of the OFDM symbol if the number of the sampling points is equal to 1.
It can be seen from the foregoing embodiments that, after receiving a CP of an OFDM symbol, an embodiment of the present application equally divides a signal to be segmented into a first segment signal and a second segment signal, respectively separates a training sequence and a data symbol in the first segment signal and the second segment signal, calculates signal-to-noise ratios of the first segment signal and the second segment signal according to the separated training sequence and data symbol, searches a synchronization reference position of the OFDM symbol according to a halving recursion manner by comparing the signal-to-noise ratios of the first segment signal and the second segment signal, and obtains a synchronization start position of an effective data portion of the OFDM symbol according to the synchronization reference position. The embodiment of the application can start synchronous estimation after receiving the CP, obtains the synchronous initial position of the OFDM effective data symbol by comparing the signal-to-noise ratio of the segmented signals and a recursion method, and has simple calculation and high synchronous speed; compared with the prior art, the method does not need to superpose the training sequence and the pilot frequency on the effective data part to be transmitted, so that the transmission rate of the effective data part is not influenced, the redundancy of the system is reduced, and the synchronization can be completed in a short time.
Drawings
In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a flowchart illustrating a first embodiment of an OFDM synchronization position estimation method according to the present invention;
FIG. 2A is a flowchart illustrating a second embodiment of the OFDM synchronization position estimation method of the present application;
FIG. 2B is a schematic diagram of an OFDM symbol of the present application;
FIG. 3 is a block diagram of a first embodiment of an OFDM synchronization position estimation apparatus according to the present application;
fig. 4 is a block diagram of a second embodiment of the OFDM synchronous position estimation apparatus of the present application.
Detailed Description
The following embodiments of the present invention provide a method and an apparatus for estimating an OFDM synchronization position. The embodiment of the application estimates the synchronous initial position of the effective data part of the OFDM symbol by utilizing the signal-to-noise ratio difference between signals after the CP is segmented.
In order to make the technical solutions in the embodiments of the present invention better understood and make the above objects, features and advantages of the embodiments of the present invention more comprehensible, the technical solutions in the embodiments of the present invention are described in further detail below with reference to the accompanying drawings.
Referring to fig. 1, a flowchart of a first embodiment of the OFDM synchronization position estimation method of the present application is shown.
Step 101: a CP of an OFDM symbol is received, the CP including a training sequence and a data symbol having a same transmit power.
In the embodiment of the present application, half of the data of the cyclic prefix portion is a training sequence portion, and half is a data symbol portion. Therefore, when the transmitting end transmits the OFDM symbols, the transmission power of the training sequence and the data symbols in the cyclic prefix portion is half of the total transmission power respectively.
Step 102: and equally dividing the signal to be segmented into a first segment signal and a second segment signal, wherein the signal to be segmented belongs to the CP.
Step 103: and respectively separating the training sequence and the data symbol in the first segment signal and the second segment signal.
Taking the first segment signal as an example, when the training sequence and the data symbol in the first segment signal are separated, denoising processing may be adopted to obtain the data symbol, and then the data symbol is subtracted from the first segment signal, so as to obtain the training sequence of the first segment signal.
Step 104: and calculating the signal-to-noise ratio of the first segment signal and the second segment signal according to the separated training sequence and the data symbols.
Specifically, autocorrelation functions of training sequences and data symbols in the first segment of signals and the second segment of signals are respectively calculated, estimates of the autocorrelation functions of the data symbols in the first segment of signals and the second segment of signals are respectively used as signal power estimates, estimates of the training sequences are respectively used as noise power estimates, and ratios of the signal power estimates and the noise power estimates of the first segment of signals and the second segment of signals are respectively used as signal-to-noise ratios of the first segment of signals and the second segment of signals.
Step 105: and searching the synchronous reference position of the OFDM symbol according to a halving recursion mode by comparing the signal-to-noise ratio of the first section of signal and the second section of signal.
Specifically, when the difference between the signal-to-noise ratio of the first segment of signal and the signal-to-noise ratio of the second segment of signal is within a preset range, the position of a first sampling point after the second segment of signal is output is used as the synchronous reference position of the OFDM symbol; when the difference value of the signal-to-noise ratio of the first section signal and the signal-to-noise ratio of the second section signal is not within a preset range, if the signal-to-noise ratio of the first section signal is smaller than the signal-to-noise ratio of the second section signal, extracting the second section signal as the signal to be segmented, and returning to the step of equally dividing the signal to be segmented into the two sections of signals; and when the difference value of the signal-to-noise ratio of the first section signal and the signal-to-noise ratio of the second section signal is not within a preset range, if the signal-to-noise ratio of the first section signal is greater than the signal-to-noise ratio of the second section signal, extracting the first section signal as the signal to be segmented, and returning to the step of equally dividing the signal to be segmented into the two sections of signals.
Step 106: and obtaining the synchronization starting position of the effective data part of the OFDM symbol according to the synchronization reference position.
Specifically, the position of the first sampling point of the CP is used as a reference point, and whether the distance between the synchronous reference position and the reference point is less than half of the length of the CP is judged; and if the distance is less than half of the CP length, taking the position of the synchronization reference position plus the CP length as the synchronization starting position of the effective data part of the OFDM symbol, and if the distance is more than half of the CP length, taking the synchronization reference position as the synchronization starting position of the effective data part of the OFDM symbol.
Referring to fig. 2A, a flow chart of a second embodiment of the OFDM synchronization position estimation method of the present application is shown:
step 201: a CP of an OFDM symbol is received, the CP including a training sequence and a data symbol having a same transmit power.
Fig. 2B is a schematic diagram of an OFDM symbol structure according to the present application. Each OFDM symbol consists of a cyclic prefix portion, which is typically the last data of the valid data portion, and a valid data portion. In this embodiment of the present application, before transmitting an OFDM symbol, a transmitting end needs to insert a training sequence known to both the transmitting end and the receiving end into a cyclic prefix. Specifically, the training sequence is repeated multiple times to form a sequence equal to the cyclic prefix, and then the sequence and the cyclic prefix are weighted to generate a new cyclic prefix portion with a weighting coefficient of 0.5, that is, as shown in fig. 2B, half of the data of the cyclic prefix portion is the training sequence portion and half is the data symbol portion. Therefore, when the transmitting end transmits the OFDM symbols, the transmission power of the training sequence and the data symbols in the cyclic prefix portion is half of the total transmission power respectively. The training sequence in the embodiment of the present application may be a time domain pseudorandom sequence, and satisfy the characteristic of mutual orthogonality, for example, an m sequence.
At the transmitting end, the modulation of the OFDM symbols is performed by using IFFT (inverse fast fourier transform), so the transmitted OFDM symbols are discrete data, and the discrete data is composed of a plurality of samples, so each OFDM symbol can also be regarded as being composed of a plurality of samples.
When receiving an OFDM symbol, a receiving end receives a cyclic prefix portion first, and the length of the cyclic prefix may be set to be 4 to 5 times of the delay spread, so that the receiving end can know whether the cyclic prefix portion has been received according to the length (or the number of samples) of received data.
Step 202: judging whether the number of sampling points of the signal to be segmented is more than 1, if so, executing a step 203; otherwise, step 216 is performed.
In the embodiment of the application, when a CP is initially received, a signal to be segmented is the complete CP, and then, after signal-to-noise ratio comparison, the returned signal to be segmented is a part of the CP, that is, in the process of performing halving recursion, the signal to be segmented all belong to the CP.
Step 203: and equally dividing the signal to be segmented into a first segment signal and a second segment signal.
Step 204: and respectively separating the training sequence and the data symbol in the first segment signal and the second segment signal.
Taking the first segment signal as an example, when the training sequence and the data symbol in the first segment signal are separated, denoising processing may be adopted to obtain the data symbol, and then the data symbol is subtracted from the first segment signal, so as to obtain the training sequence of the first segment signal.
Step 205: the autocorrelation functions of the training sequences and data symbols in the first segment of the signal and the second segment of the signal are calculated, respectively.
Taking the first segment of signal as an example, let the data symbol separated from the first segment of signal be x (n), and the separated training sequence be r (n), then the corresponding autocorrelation functions are calculated according to the following formulas:
Rxx(m)＝E[x*(n)x(n+m)]
Rrr(m)＝E[r*(n)r(n+m)]
in the above formula, Rxx(m) is the autocorrelation function of the data symbols, Rrr(m) is the autocorrelation function of the training sequence. Wherein, assuming that there are K samples in the first segment of signal, m represents any one of the K samples.
The calculation process of the autocorrelation function of the training sequence and the data symbols of the second segment signal is the same as that of the first segment signal, and is not repeated herein.
Step 206: and respectively taking the estimation of the autocorrelation function of the data symbols in the first-stage signal and the second-stage signal as the signal power estimation and taking the estimation of the training sequence as the noise power estimation.
Taking the first segment signal as an example, taking a sampling time sequence of the data symbols and the training sequence in the first segment signal, and calculating the autocorrelation function estimation of the data symbols and the training sequence by a time averaging method according to the following formula:
in the above formula, N is the number of samples in the sampling time series, x (N) { x (0), x (1), …, x (N-1) },
is an estimate of the autocorrelation function for the data symbols,
is estimated for the autocorrelation function of the training sequence.
Further, according to the following formula:
wherein τ is an integer of from ∞ to + ∞.
The following formula can be obtained:
the estimates of the signal power and the noise power can be directly estimated from the autocorrelation function, i.e., as follows:
wherein,
in order to estimate the power of the signal,
is a noise power estimate. The method for calculating the signal-to-noise ratio can simplify the complexity of the system, and the relative error in the whole calculation process is small.
The calculation process of the signal power estimation and the noise power estimation of the second segment signal is the same as that of the first segment signal, and is not described herein again.
Step 207: and respectively taking the ratio of the signal power estimation and the noise power estimation of the first-stage signal and the second-stage signal as the signal-to-noise ratio of the first-stage signal and the second-stage signal.
The SNR is defined as the ratio of the average power of the signal to the average power of the noise, and the SNR calculated from the first-segment signal is SNR1, which is calculated according to the following formula:
similarly, the signal-to-noise ratio of the second segment signal is obtained as SNR 2.
Step 208: judging whether the difference value of the signal-to-noise ratio of the first section signal and the signal-to-noise ratio of the second section signal is within a preset range, if so, executing a step 212; otherwise, step 209 is performed.
The absolute value of the difference between the signal-to-noise ratios of the first segment signal and the second segment signal is calculated, and if the absolute value of the difference is within a preset range, the signal-to-noise ratios of the two segments of signals are considered to be approximately equal. For example, SNR1 and SNR2 satisfy the following approximate relationship:
|SNR1-SNR2|≤0.01～0.09
step 209: judging whether the signal-to-noise ratio of the first section of signal is smaller than that of the second section of signal, if so, executing a step 210; otherwise, step 211 is executed.
Step 210: and extracting the second segment signal as the signal to be segmented, and returning to the step 202.
Step 211: and extracting the first segment signal as a signal to be segmented, and returning to the step 202.
Since the training sequence is inserted into the cyclic prefix in the embodiment of the present application, it can be considered that noise is added to the data of the cyclic prefix portion, so that the signal-to-noise ratio when the signal-to-noise ratio is calculated at the receiving end is smaller than that when the noise is not added, and because delay spread occurs, if the data of the received cyclic prefix portion is superimposed with data of other subcarriers, such as an effective data symbol, the signal power can be considered to be increased, and thus the signal-to-noise ratio can be increased. Therefore, in the foregoing step 210 and step 211, a segment of signal with a large signal-to-noise ratio is taken out as a signal to be segmented, and the step 202 is returned to continue to find the synchronization reference position of the OFDM symbol.
Step 212: and the position of the first sampling point after the second section of signal is output is used as the synchronous reference position of the OFDM symbol.
Step 213: judging whether the distance between the synchronous reference position and the reference point is less than half of the CP length, if so, executing step 214; otherwise, step 215 is performed.
Taking the position of the first sampling point of the CP as a reference point;
step 214: and taking the position of the synchronous reference position added with the CP length as the synchronous initial position of the effective data part of the OFDM symbol, and finishing the current flow.
Step 215: and taking the synchronous reference position as the synchronous starting position of the effective data part of the OFDM symbol, and ending the current flow.
Step 216: and outputting the position of the sampling point as the synchronous reference position of the OFDM symbol, and returning to step 213.
When the number of sampling points is equal to 1, the halving recursion judgment is finished, and the position of the output sampling point is the synchronous reference position of the OFDM symbol. Because the signal to be segmented is judged before the signal-to-noise ratio is calculated, the number of sampling points of the signal to be segmented is not less than 1, and the situation that the number of the sampling points is less than 1 does not need to be considered.
The embodiment can start synchronous estimation after receiving the CP, obtains the synchronous initial position of the OFDM effective data symbol by comparing the signal-to-noise ratio of the segmented signals and a recursion method, and has simple calculation and high synchronous speed; compared with the prior art, the method does not need to superpose the training sequence and the pilot frequency on the effective data part to be transmitted, so that the transmission rate of the effective data part is not influenced, the redundancy of the system is reduced, and the synchronization can be completed in a short time.
Further, the synchronization starting position of the OFDM symbol effective data obtained in the embodiment of the present application is used to calculate the position relationship between the synchronization starting point and the whole cyclic prefix end, and the position relationship information is transmitted to the back-end processing part, so that the position relationship information can be used as a reference for subsequent channel estimation, equalization, and other processing. Meanwhile, because the training sequence inserted into the cyclic prefix is a training sequence known by both the transmitting end and the receiving end, performance indexes such as bit error rate and the like can be calculated by referring to the difference between the received training sequence and the known training sequence.
Corresponding to the embodiment of the OFDM synchronous position estimation method, the application also provides an embodiment of an OFDM synchronous position estimation device.
Referring to fig. 3, a block diagram of a first embodiment of an OFDM synchronization position estimation apparatus according to the present application is shown:
the device includes: a receiving unit 310, a segmentation unit 320, a separation unit 330, a calculation unit 340, a lookup unit 350 and an obtaining unit 360.
The receiving unit 310 is configured to receive a cyclic prefix CP of an OFDM symbol, where the CP includes a training sequence and a data symbol with the same transmit power;
a segmenting unit 320, configured to equally divide a signal to be segmented into two segments of signals, namely a first segment of signal and a second segment of signal, where the signal to be segmented belongs to the CP;
a separating unit 330, configured to separate the training sequence and the data symbol in the first segment of signal and the second segment of signal, respectively;
a calculating unit 340, configured to calculate signal-to-noise ratios of the first segment signal and the second segment signal according to the separated training sequence and data symbol;
a searching unit 350, configured to search a synchronous reference position of the OFDM symbol according to a halving recursive manner by comparing signal-to-noise ratios of the first segment signal and the second segment signal;
an obtaining unit 360, configured to obtain a synchronization start position of the effective data portion of the OFDM symbol according to the synchronization reference position.
Referring to fig. 4, a block diagram of a second embodiment of the OFDM synchronization position estimation apparatus of the present application is shown:
the device includes: a receiving unit 410, a determining unit 420, an executing unit 430, a segmenting unit 440, a separating unit 450, a calculating unit 460, a searching unit 470 and an obtaining unit 480.
The receiving unit 410 is configured to receive a cyclic prefix CP of an OFDM symbol, where the CP includes a training sequence and a data symbol with the same transmit power;
a determining unit 420, configured to determine whether the number of sampling points of the signal to be segmented is greater than 1;
an executing unit 430, configured to trigger the segmenting unit 440 to execute a corresponding function if the number of samples is greater than 1, and output a position where the sample is located as a synchronization reference position of the OFDM symbol if the number of samples is equal to 1;
a segmenting unit 440, configured to equally divide a signal to be segmented into two segments of signals, namely a first segment of signal and a second segment of signal, where the signal to be segmented belongs to the CP;
a separating unit 450, configured to separate the training sequence and the data symbol in the first segment of signal and the second segment of signal, respectively;
a calculating unit 460, configured to calculate signal-to-noise ratios of the first segment signal and the second segment signal according to the separated training sequence and data symbol;
a searching unit 470, configured to search the synchronous reference position of the OFDM symbol according to a halving recursive manner by comparing signal-to-noise ratios of the first segment signal and the second segment signal;
an obtaining unit 480, configured to obtain a synchronization start position of the effective data portion of the OFDM symbol according to the synchronization reference position.
In particular, the calculation unit 460 may comprise (not shown in fig. 4): an autocorrelation function calculation unit, configured to calculate autocorrelation functions of the training sequence and the data symbols in the first segment of signal and the second segment of signal, respectively; a power estimation unit, configured to use estimates of autocorrelation functions of data symbols in the first segment signal and the second segment signal as signal power estimates, and use estimates of training sequences as noise power estimates, respectively; and the signal-to-noise ratio acquisition unit is used for respectively taking the ratio of the signal power estimation and the noise power estimation of the first section signal and the second section signal as the signal-to-noise ratio of the first section signal and the second section signal.
In particular, the lookup unit 470 may include (not shown in fig. 4): the first comparison unit is used for comparing whether the difference value of the signal-to-noise ratio of the first section signal and the signal-to-noise ratio of the second section signal is within a preset range or not; the first execution unit is used for outputting the position of a first sampling point after the second section of signal as the synchronous reference position of the OFDM symbol when the difference value of the signal-to-noise ratio of the first section of signal and the signal-to-noise ratio of the second section of signal is within a preset range; the second comparison unit is used for comparing the signal-to-noise ratio of the first section signal with the signal-to-noise ratio of the second section signal when the difference value of the signal-to-noise ratio of the first section signal and the signal-to-noise ratio of the second section signal is not in a preset range; and the second execution unit is used for extracting the second section signal as the signal to be segmented when the signal-to-noise ratio of the first section signal is smaller than that of the second section signal, returning to the segmentation unit to execute a corresponding function, and extracting the first section signal as the signal to be segmented when the signal-to-noise ratio of the first section signal is larger than that of the second section signal, returning to the segmentation unit to execute a corresponding function.
In particular, the obtaining unit 480 may include (not shown in fig. 4): a distance determining unit, configured to determine whether a distance between the synchronous reference position and the reference point is less than half of the length of the CP, using a position where a first sampling point of the CP is located as a reference point; a synchronization position determining unit, configured to, if the distance is smaller than half of the CP length, use a position obtained by adding the CP length to the synchronization reference position as a synchronization starting position of the OFDM symbol valid data portion, and if the distance is larger than half of the CP length, use the synchronization reference position as a synchronization starting position of the OFDM symbol valid data portion.
As can be seen from the description of the above embodiment, after receiving the CP of the OFDM symbol, the embodiment of the present application equally divides the signal to be segmented into the first segment signal and the second segment signal, respectively separates the training sequence and the data symbol in the first segment signal and the second segment signal, calculates the signal-to-noise ratio of the first segment signal and the second segment signal according to the separated training sequence and data symbol, searches the synchronous reference position of the OFDM symbol according to a halving recursion manner by comparing the signal-to-noise ratios of the first segment signal and the second segment signal, and obtains the synchronous start position of the effective data portion of the OFDM symbol according to the synchronous reference position. The embodiment of the application can start synchronous estimation after receiving the CP, obtains the synchronous initial position of the OFDM effective data symbol by comparing the signal-to-noise ratio of the segmented signals and a recursion method, and has simple calculation and high synchronous speed; compared with the prior art, the method does not need to superpose the training sequence and the pilot frequency on the effective data part to be transmitted, so that the transmission rate of the effective data part is not influenced, the redundancy of the system is reduced, and the synchronization can be completed in a short time.
Those skilled in the art will readily appreciate that the techniques of the embodiments of the present invention may be implemented as software plus a required general purpose hardware platform. Based on such understanding, the technical solutions in the embodiments of the present invention may be essentially or partially implemented in the form of a software product, which may be stored in a storage medium, such as ROM/RAM, magnetic disk, optical disk, etc., and includes several instructions for enabling a computer device (which may be a personal computer, a server, or a network device, etc.) to execute the method according to the embodiments or some parts of the embodiments.
The embodiments in the present specification are described in a progressive manner, and the same and similar parts among the embodiments are referred to each other, and each embodiment focuses on the differences from the other embodiments. In particular, for the system embodiment, since it is substantially similar to the method embodiment, the description is simple, and for the relevant points, reference may be made to the partial description of the method embodiment.
The above-described embodiments of the present invention do not limit the scope of the present invention. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (8)
1. An OFDM synchronization position estimation method, comprising:
receiving a Cyclic Prefix (CP) of an OFDM symbol, wherein the CP comprises a training sequence and a data symbol with the same transmitting power, the CP is the training sequence which is known by a transmitting end and a receiving end and is inserted into the cyclic prefix before the transmitting end transmits the OFDM symbol, and the CP is specifically operated in the way that the training sequence is repeated for multiple times into a sequence which is equal to the cyclic prefix, then the sequence and the cyclic prefix are weighted to generate a new cyclic prefix part, and the weighting coefficient is 0.5;
equally dividing a signal to be segmented into two segments of signals, namely a first segment of signal and a second segment of signal, wherein the signal to be segmented is the CP;
respectively separating the training sequence and the data symbol in the first segment signal and the second segment signal;
calculating the signal-to-noise ratio of the first section of signal and the second section of signal according to the separated training sequence and the separated data symbol;
searching the synchronous reference position of the OFDM symbol according to a halving recursion mode by comparing the signal-to-noise ratio of the first section of signal and the second section of signal;
obtaining a synchronization start position of the effective data part of the OFDM symbol according to the synchronization reference position, comprising: taking the position of the first sampling point of the CP as a reference point, and judging whether the distance between the synchronous reference position and the reference point is less than half of the length of the CP or not; and if the distance is less than half of the CP length, taking the position of the synchronization reference position plus the CP length as the synchronization starting position of the effective data part of the OFDM symbol, and if the distance is more than half of the CP length, taking the synchronization reference position as the synchronization starting position of the effective data part of the OFDM symbol.
2. The method of claim 1, wherein calculating the signal-to-noise ratio of the first segment signal and the second segment signal according to the separated training sequence and data symbols comprises:
calculating the autocorrelation function of the training sequence and the data symbol in the first segment signal and the second segment signal respectively;
respectively taking the estimation of the autocorrelation function of the data symbols in the first-stage signal and the second-stage signal as signal power estimation and the estimation of the training sequence as noise power estimation;
and respectively taking the ratio of the signal power estimation and the noise power estimation of the first section signal and the second section signal as the signal-to-noise ratio of the first section signal and the second section signal.
3. The method of claim 1, wherein said finding the synchronization reference position of the OFDM symbol in a halved recursive manner comprises:
when the difference value between the signal-to-noise ratio of the first section of signal and the signal-to-noise ratio of the second section of signal is within a preset range, outputting the position of a first sampling point after the second section of signal as the synchronous reference position of the OFDM symbol;
when the difference value of the signal-to-noise ratio of the first section signal and the signal-to-noise ratio of the second section signal is not within a preset range, if the signal-to-noise ratio of the first section signal is smaller than the signal-to-noise ratio of the second section signal, extracting the second section signal as the signal to be segmented, and returning to the step of equally dividing the signal to be segmented into the two sections of signals;
and when the difference value of the signal-to-noise ratio of the first section signal and the signal-to-noise ratio of the second section signal is not within a preset range, if the signal-to-noise ratio of the first section signal is greater than the signal-to-noise ratio of the second section signal, extracting the first section signal as the signal to be segmented, and returning to the step of equally dividing the signal to be segmented into the two sections of signals.
4. The method of claim 1, wherein before equally dividing the signal to be segmented into two segments, the method further comprises:
judging whether the number of sampling points of the signal to be segmented is more than 1;
and if the number of the sampling points is more than 1, equally dividing the signal to be segmented into two segments of signals, and if the number of the sampling points is equal to 1, outputting the position of the sampling point as the synchronous reference position of the OFDM symbol.
5. An OFDM synchronous position estimating apparatus, comprising:
a receiving unit, configured to receive a cyclic prefix CP of an OFDM symbol, where the CP includes a training sequence and a data symbol with the same transmit power, and the CP is a training sequence known by both a transmitting end and a receiving end and inserted in the cyclic prefix before the transmitting end transmits the OFDM symbol, and is specifically configured to repeat the training sequence multiple times into a sequence equal to the cyclic prefix, and then weight the sequence and the cyclic prefix to generate a new cyclic prefix portion, where a weighting coefficient is 0.5;
the segmentation unit is used for equally dividing a signal to be segmented into two segments of signals, namely a first segment of signal and a second segment of signal, wherein the signal to be segmented is the CP;
a separation unit, configured to separate the training sequence and the data symbol in the first segment of signal and the second segment of signal respectively;
a calculating unit, configured to calculate signal-to-noise ratios of the first segment signal and the second segment signal according to the separated training sequence and the data symbol;
the searching unit is used for searching the synchronous reference position of the OFDM symbol according to a halving recursion mode by comparing the signal-to-noise ratio of the first section of signal and the second section of signal;
an obtaining unit, configured to obtain a synchronization start position of the effective data portion of the OFDM symbol according to the synchronization reference position, including: a distance determining unit, configured to determine whether a distance between the synchronization reference position and the reference point is less than half of the CP length by using a position where a first sampling point of the CP is located as a reference point, and a synchronization position determining unit, configured to, if the distance is less than half of the CP length, use a position obtained by adding the CP length to the synchronization reference position as a synchronization start position of the OFDM symbol valid data portion, and if the distance is greater than half of the CP length, use the synchronization reference position as a synchronization start position of the OFDM symbol valid data portion.
6. The apparatus of claim 5, wherein the computing unit comprises:
an autocorrelation function calculation unit, configured to calculate autocorrelation functions of the training sequence and the data symbols in the first segment of signal and the second segment of signal, respectively;
a power estimation unit, configured to use estimates of autocorrelation functions of data symbols in the first segment signal and the second segment signal as signal power estimates, and use estimates of training sequences as noise power estimates, respectively;
and the signal-to-noise ratio acquisition unit is used for respectively taking the ratio of the signal power estimation and the noise power estimation of the first section signal and the second section signal as the signal-to-noise ratio of the first section signal and the second section signal.
7. The apparatus of claim 5, wherein the lookup unit comprises:
the first comparison unit is used for comparing whether the difference value of the signal-to-noise ratio of the first section signal and the signal-to-noise ratio of the second section signal is within a preset range or not;
the first execution unit is used for outputting the position of a first sampling point after the second section of signal as the synchronous reference position of the OFDM symbol when the difference value of the signal-to-noise ratio of the first section of signal and the signal-to-noise ratio of the second section of signal is within a preset range;
the second comparison unit is used for comparing the signal-to-noise ratio of the first section signal with the signal-to-noise ratio of the second section signal when the difference value of the signal-to-noise ratio of the first section signal and the signal-to-noise ratio of the second section signal is not in a preset range;
and the second execution unit is used for extracting the second section signal as the signal to be segmented when the signal-to-noise ratio of the first section signal is smaller than that of the second section signal, returning to the segmentation unit to execute a corresponding function, and extracting the first section signal as the signal to be segmented when the signal-to-noise ratio of the first section signal is larger than that of the second section signal, returning to the segmentation unit to execute a corresponding function.
8. The apparatus of claim 5, further comprising:
the judging unit is used for judging whether the number of sampling points of the signal to be segmented is more than 1 or not;
and the execution unit is used for triggering the segmentation unit to execute a corresponding function if the number of the sampling points is greater than 1, and outputting the position of the sampling point as the synchronous reference position of the OFDM symbol if the number of the sampling points is equal to 1.
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