CN110120925B - Time delay estimation method based on short wave diversity signals - Google Patents

Time delay estimation method based on short wave diversity signals Download PDF

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CN110120925B
CN110120925B CN201910358390.2A CN201910358390A CN110120925B CN 110120925 B CN110120925 B CN 110120925B CN 201910358390 A CN201910358390 A CN 201910358390A CN 110120925 B CN110120925 B CN 110120925B
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time delay
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frame
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张存林
董彬虹
曹蕾
蔡沅沅
李�昊
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University of Electronic Science and Technology of China
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    • H04—ELECTRIC COMMUNICATION TECHNIQUE
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Abstract

The hair isThe invention discloses a multipath time delay estimation method based on multipath diversity signals under a short wave channel, belongs to the technical field of channel parameter estimation in wireless communication, and relates to an estimation method based on multipath diversity signals, low in complexity and free of channel prior information time delay. Under the condition of non-data assistance, the estimation method can be favorable for resisting the poor transmission characteristic of a short wave channel and finishing the estimation of multipath time delay and relative time delay by only using single-channel data, utilizing multiple channels carrying the same information, counting independent and fading uncorrelated signals and utilizing a segmented frequency domain matching correlation mode taking method. Simulation results show that the estimation precision is only 10 at a lower signal-to-noise ratio‑4And when the signal is in s magnitude, the estimation of the multipath time delay and the relative time delay of the signal can still keep higher accuracy.

Description

Time delay estimation method based on short wave diversity signals
Technical Field
The invention belongs to the technical field of channel parameter estimation in wireless communication, and relates to an estimation method based on multi-path diversity signals, which is low in complexity and does not need channel prior information time delay.
Background
In short-wave communication, there are many problems such as multipath delay, doppler shift and frequency selective fading, which bring great difficulty to the reception and processing of signals, so diversity technology is often adopted to combat the poor transmission characteristics of channels. The invention can utilize diversity signal, without test or pilot frequency sequence to estimate the multi-path time delay of channel parameter and relative time delay of diversity signal.
The diversity technique is a method for improving the rate of correctly determining a received signal by providing a plurality of replicas of a transmitted signal, and is used for compensating for fading channel loss and resisting adverse effects caused by fading. Diversity specifically refers to both distributed transmission and centralized reception, where distributed transmission enables a receiving end to obtain multiple statistically independent fading signals carrying the same information. Concentrated reception is where the receiver combines multiple statistically independent fading signals received to reduce the effects of fading. In accordance with the principles of information theory, copies of the original transmitted signal having other degrees of attenuation are provided to the receiver opportunity to facilitate a correct decision of the received signal.
Currently, there are three types of commonly used multipath delay estimation models. The first type: estimating the time delay between a transmission pulse and an echo based on single-channel data, wherein the auxiliary pilot frequency data is required to have good correlation performance; the second type: also based on single-channel data, the receiving end knows that the transmitted pilot frequency auxiliary data has good correlation; in the third category: based on the multi-channel data, the time difference between different position receivers is used for estimation. There are many classical algorithms under these three models: such as correlation algorithms, algorithms based on cost functions, algorithms based on signal space characteristics, etc., but these algorithms all require the receiver to know the particular test sequence or pilot signal transmitted, which is difficult to achieve in uncooperative communications. Therefore, the scheme of the invention considers a time delay estimation method under a new scene, namely the prior knowledge of unknown transmitted signals of a receiver is only based on single-channel multi-path diversity signals to complete the estimation of the multi-path time delay of the channel and the relative time delay between the signals.
Disclosure of Invention
The invention creatively utilizes the multi-path diversity signals commonly used by the short wave channel to estimate the multi-path time delay of the short wave channel and the relative time delay between the signals. And matching the multi-channel signal in a segmented frequency domain to obtain a mode, searching a reasonable secondary mode while obtaining the relative time delay of the signal, wherein the difference between the two modes is the estimated value of the multi-path time delay of the channel. The channel of the scheme is modeled by the combination of a fading process representing a direct path and a fading process representing a reflection path, a received signal comprises two path components, the method is suitable for an MFSK modulation mode of a frequency selective fading short-wave channel, the algorithm complexity is low, the required information only comprises a symbol rate and a sampling frequency, other prior information is not required to be known, and the method can also be used for a non-cooperative communication scene. Simulation shows that the scheme has accurate estimation on multipath time delay and relative time delay and can still ensure ideal performance under a lower signal-to-noise ratio.
The technical scheme of the invention is as follows:
and respectively framing the multi-path input signals in a non-overlapping way according to the length of five symbols, carrying out frequency domain matching correlation on the multi-path data frame by frame, enabling the position of the maximum correlation value of each frame to correspond to the relative time delay estimation value of the frame, and taking the mode of the relative time delay of each frame as the final relative time delay estimation value of the signals. And searching a secondary mode meeting the requirement in each frame of relative time delay, wherein the difference between the secondary mode and the final estimated value is not more than the short wave channel multipath time delay empirical value and is not less than two sampling points. And the difference between the final relative delay estimation value and the secondary mode is the multi-path delay of the channel.
The invention relates to a multipath time delay estimation method based on multipath diversity signals under a short wave channel, which comprises the following steps:
step 1, receiving signals r of two pathsm(t), m is 1,2 is sampled with a sampling frequency Fs to obtain { r [ (r) ]m(n), m is 1, 2; n is 1,2,., N }, m represents the number of paths of the diversity signals, and N represents the data length of each path;
step 2, framing the two paths of signals respectively;
the number of sampling points Nsamp in a symbol is obtained from the known symbol rate Symr and the sampling frequency Fs, the signals are divided into frames without overlapping by using the frame length fl as 5, if the frame length of the last frame is not enough, the last frame is abandoned, so the total frame number is large
Figure GDA0002824161970000021
The m-th receiving sequence r with the length of Nm(n) becomes after framing
Figure GDA0002824161970000022
Wherein each element represents a frame of data after framing;
step 3, performing frequency domain matching correlation on the two paths of signals frame by frame, and recording peak positions;
respectively carrying out fast Fourier transform on each frame data of the two paths of signals to obtain the frequency spectrum Y of the two paths of signalsm(k) M is 1, 2; and (k) multiplying the k by the conjugate, performing inverse Fourier transform, and obtaining a correlation value set C after modulus value extractionk(fr), k ═ 1,2,. ann, fn; fr 1, 2.., fl, and finally the correlation peak position p (k) max (C) is recordedk(fr)),k＝1,2,...,fn；fr＝1,2,...,fl；
Step 4, taking the mode P of the peak position P (k) of the correlation valuemObtaining two paths of signals relative time delay Rdelay ═ Pm-1; if the relative delay Rdelay' is greater than
Figure GDA0002824161970000023
The correction delay is rfl-Rdelay', otherwise, rdlay is maintained;
step 5, searching the secondary mode P meeting the requirementsm；
Calculating the number of sampling points Ns (Fs x Mdelay ') corresponding to Mdelay ' according to the sampling frequency Fs and the empirical value Mdelay ' of the maximum multipath time delay of the short wave channel; for the correlation value peak position { P (k) ·, k ═ 1, 2.. times, fn }, the set Φ ═ P (k) |2 < | P (k) — P) satisfying the condition that the difference from the final correction delay Rdelay is greater than two sample points and less than the number Ns of sample points constitutes the set Φ ═ P (k) |2 < | P (k) > -PmNs < k 1,2, fn, P, phismThe obtained secondary mode is obtained;
step 6, the multipath time delay Mdelay is the corrected time delay Rdelay and the sub-mode PsmThe difference, i.e. Mdelay |. Rdelay-Psm|。
The invention has the beneficial effects that: under the condition of non-data assistance, the estimation method can be favorable for resisting the poor transmission characteristic of a short wave channel and finishing the estimation of multipath time delay and relative time delay by only using single-channel data, utilizing multiple channels carrying the same information, counting independent and fading uncorrelated signals and utilizing a segmented frequency domain matching correlation mode taking method. Simulation results show that the estimation precision is only 10 at a lower signal-to-noise ratio-4And when the signal is in s magnitude, the estimation of the multipath time delay and the relative time delay of the signal can still keep higher accuracy.
Drawings
Fig. 1 is a flow chart of delay estimation.
FIG. 2 is a block diagram of a short-wave ionospheric channel model.
Fig. 3 is a diagram of performance simulation of the inventive scheme versus delay estimation.
Fig. 4 is a simulation diagram of the performance of multipath delay estimation in the scheme of the present invention.
Detailed Description
The technical scheme of the invention is detailed below by combining the accompanying drawings and the embodiment. It should be understood that the scope of the present invention is not limited to the following examples, and any techniques implemented based on the present disclosure are within the scope of the present invention.
The simulation parameters are set as follows:
taking 2FSK modulation signal as an example, let symbol rate Symr be 200sps and sampling frequency Fs be 9600Hz, and the number of sampling points Nsamp in one symbol be 48. The selected simulation channel is a frequency selective fading channel with interference at the middle latitude, and the channel model is shown in fig. 2. Assume that the input signal: s (t) ═ cos (2 pi ft) or s (t) ═ ej2πft. Tau is the multipath time delay, fdIn order to maximize the doppler shift frequency,
Figure GDA0002824161970000031
describing the fading characteristics of a short wave channel, and outputting a signal if two variances are equal to obey a time-varying fading coefficient with a mean value of zero complex Gaussian distribution:
Figure GDA0002824161970000032
the steps of estimating the multipath time delay using the multipath diversity signal are as follows:
step 1, receiving signals r of two pathsm(t), m is 1,2 with 9600Hz sampling frequency to get { r-m(n), m is 1, 2; n is 1, 2.,. N }, where m denotes the number of paths of the diversity signal and N denotes the data length of each path.
Step 2, framing the two paths of signals respectively;
the number of sampling points 48 in a symbol is obtained from the known symbol rate 200sps and sampling frequency 9600Hz, the signal is divided into frames without overlapping by sampling points with the frame length 240, if the last frame data is not enough, the last frame is discarded, so the total frame number is the same
Figure GDA0002824161970000041
The m-th receiving sequence r with the length of Nm(n) becomes after framing
Figure GDA0002824161970000042
Wherein each element represents a frame of data after framing.
Step 3, performing frequency domain matching correlation on the two paths of signals frame by frame, and recording peak positions;
respectively carrying out fast Fourier transform on each frame data of the two paths of signals to obtain the frequency spectrum Y of the two paths of signalsm(k) M is 1, 2; and (k) multiplying the k by the conjugate, performing inverse Fourier transform, and obtaining a correlation value set C after modulus value extractionk(fr), k ═ 1,2,. ann, fn; fr 1, 2.., fl, and finally the correlation peak position p (k) max (C) is recordedk(fr)),k＝1,2,...,fn；fr＝1,2,...,fl。
Step 4, taking P (k), k being 1,2mObtaining two paths of signals relative time delay Rdelay ═ Pm-1; if the relative time delay Rdelay 'is larger than 120 sampling points, the corrected time delay is Rdelay-240-Rdelay', otherwise, the Rdelay is kept;
step 5, searching the secondary mode P meeting the requirementsm；
Calculating the number 19 of sampling points corresponding to 2ms according to 9600Hz of sampling frequency and the empirical value of the maximum multipath time delay of the simulation channel for 2 ms; for { P (k), k ═ 1, 2.., fn }, the set of estimates satisfying a difference from the final relative delay greater than 2 and less than 19 samples constitutes the set Φ ═ P (k) |2 < | P (k) -PmI < 19, k ═ 1,2,.., fn }, P, ΦsmI.e. the desired secondary mode.
Step 6, the multipath time delay Mdelay is the corrected time delay Rdelay and the sub-mode PsmThe difference, i.e. Mdelay |. Rdelay-Psm|。
The performance simulation results for multipath delay and relative delay estimation are shown in fig. 3 and fig. 4, respectively, and the results show that: under the short wave frequency selective fading channel, when the signal-to-noise ratio EbN0 is 20dB and the estimation precision is 0.2ms, the method of the invention can still keep a higher precision for the estimation of the multipath time delay and the relative time delay.

Claims (1)

1. A multipath time delay estimation method based on multipath diversity signals under a short wave channel comprises the following steps:
step 1, receiving signals r of two pathsm(t), m is 1,2 is sampled with a sampling frequency Fs to obtain { r [ (r) ]m(n), m is 1, 2; n is 1,2,., N }, m represents the number of paths of the diversity signals, and N represents the data length of each path;
step 2, framing the two paths of signals respectively;
the number of sampling points Nsamp in a symbol is obtained from the known symbol rate Symr and the sampling frequency Fs, the signals are divided into frames without overlapping by using the frame length fl as 5, if the frame length of the last frame is not enough, the last frame is abandoned, so the total frame number is large
Figure FDA0002824161960000011
The m-th receiving sequence r with the length of Nm(n) becomes after framing
Figure FDA0002824161960000012
Wherein each element represents a frame of data after framing;
step 3, performing frequency domain matching correlation on the two paths of signals frame by frame, and recording peak positions;
respectively carrying out fast Fourier transform on each frame data of the two paths of signals to obtain the frequency spectrum Y of the two paths of signalsm(k) M is 1, 2; and (k) multiplying the k by the conjugate, performing inverse Fourier transform, and obtaining a correlation value set C after modulus value extractionk(fr), k ═ 1,2,. ann, fn; fr 1, 2.., fl, and finally the correlation peak position p (k) max (C) is recordedk(fr)),k＝1,2,...,fn；fr＝1,2,...,fl；
Step 4, taking the mode P of the peak position P (k) of the correlation valuemObtaining two paths of signals relative time delay Rdelay ═ Pm-1; if the relative delay Rdelay' is greater than
Figure FDA0002824161960000013
The correction delay is rfl-Rdelay', otherwise, rdlay is maintained;
step 5, searching the secondary mode P meeting the requirementsm；
According to the sampling frequency Fs and shortCalculating the sampling point number Ns (Fs) Mdelay ' corresponding to the Mdelay ' according to the empirical value Mdelay ' of the maximum multipath time delay of the wave channel; for the correlation value peak position { P (k) ·, k ═ 1, 2.. times, fn }, the set Φ ═ P (k) |2 < | P (k) — P) satisfying the condition that the difference from the final correction delay Rdelay is greater than two sample points and less than the number Ns of sample points constitutes the set Φ ═ P (k) |2 < | P (k) > -PmNs < k 1,2, fn, P, phismThe obtained secondary mode is obtained;
step 6, the multipath time delay Mdelay is the corrected time delay Rdelay and the sub-mode PsmThe difference, i.e. Mdelay |. Rdelay-Psm|。
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