CN105282082A - Doppler estimation method based on combination of copy correlation and positive hole carriers - Google Patents

Abstract

The invention discloses a Doppler estimation method based on combination of copy correlation and positive hole carriers. The method comprises the following steps of modulating to-be-sent binary data into OFDM (Orthogonal Frequency Division Multiplexing) symbols inserted with positive hole carriers at a sending end; framing L OFDM symbols, and inserting chirp signals at the head and the tail of each frame signal; sampling reception signals at a receiving end, and performing Doppler estimation using copy correlation; obtaining the relative movement speed between the sending end and the receiving end through roughly-estimated Doppler factor calculation; and performing speed compensation of each OFDM symbol in a frame signal nearby the estimated relative movement speed, using DFT for obtaining the energy sum of each OFDM symbol at a positive hole carrier during speed compensation, and determining a speed corresponding to the minimum energy sum as a precisely-estimated speed, so as to obtain a precisely-estimated Doppler factor. The invention improves estimation precision, reduces the number of inserted chirp signals, and improves the communication rate while reducing the operand.

Description

A kind of based on the relevant Doppler estimation be combined with null subcarrier of copy

Technical field

The invention belongs to field of underwater acoustic communication, particularly relate to a kind of based on the relevant Doppler estimation be combined with null subcarrier of copy.

Background technology

Due to the complex environment of ocean, underwater acoustic channel exist serious noise, many ways time delay, Doppler frequency shift and time the feature such as change, had a strong impact on the quality of underwater sound communication.OFDM (OrthogonalFrequencyDivisionMultiplexing, OFDM) technology, due to features such as its band efficiency are high and anti-multi-path capability is strong, is widely used in field of underwater acoustic communication.Because OFDM is responsive to carrier wave frequency deviation, Doppler frequency shift destroys the orthogonality between OFDM subcarrier, has had a strong impact on its performance and communication quality, and therefore, the impact how reducing Doppler frequency shift is the key improving OFDM underwater sound communication quality.

At present, conventional in OFDM underwater sound communication Doppler estimation mainly contains following three kinds of methods:

(1) the simple signal frequency measurement estimation technique.The method is after transmitting terminal synchronizing signal, insert the CW signal of one section of given frequency, after synchronous, calculate the frequency receiving CW signal at receiving terminal to received signal, the CW signal of transmission and the CW signal frequency of reception are compared the Doppler factor that can calculate estimation.The precision that the method is estimated limits by CW signal length, and is subject to the interference of many ways and noise.

(2) Correlation Estimation Method is copied.The method inserts linear FM signal at transmitting terminal in the front and back of OFDM symbol, OFDM symbol length must be received at receiving terminal by copy correlative measurement, the OFDM symbol length of the OFDM symbol length received and transmission is compared the Doppler factor that can draw estimation.The precision that the method is estimated limits by the time-bandwidth product inserting signal, for ensureing the sharp-pointed of receiving terminal relevant peaks, the time-bandwidth product inserting signal should be enough large, and the method needs to insert linear FM signal before and after each OFDM symbol, insert signal frequency higher, operand is comparatively large, reduces message transmission rate.

(3) the null subcarrier estimation technique.The method in OFDM symbol, inserts null subcarrier at transmitting terminal, calculate the energy at OFDM symbol hollow sub-carrier positions place by compensating different doppler velocities at receiving terminal, energy and minimum corresponding speed are the doppler velocity of estimation, are translated into the Doppler factor that Doppler factor is estimation.The Doppler factor that the method is estimated is comparatively accurate, has good effect after compensating.But algorithm requires to insert null subcarrier in each ofdm symbol, reduce carrier wave utilance, and along with the increase of doppler velocity hunting zone and the raising of search precision, algorithm complex increases greatly.

Summary of the invention

The object of this invention is to provide that a kind of underwater sound OFDM is accurate, algorithm complex is little, easy realization, based on the relevant Doppler estimation be combined with null subcarrier of copy.

Based on the relevant Doppler estimation be combined with null subcarrier of copy, comprise the following steps,

Step one: at transmitting terminal, binary data to be sent is modulated into the OFDM symbol being inserted with null subcarrier;

Step 2: L OFDM symbol is carried out framing, inserts linear FM signal at every frame signal head and the tail;

Step 3: sample to received signal at receiving terminal, adopts copy to be correlated with and carries out Doppler's rough estimate, calculates Signal Compression and extension degree, obtain the Doppler factor of rough estimate by the relevant peaks of every frame signal head and the tail:

$\widetilde{\mathrm{\δ}}=\frac{T}{T^{\′}}-1$

Wherein T is the length of the frame signal without Doppler contribution, and T ' is the frame signal length through Doppler contribution recorded;

Step 4: the relative moving speed being calculated transmitting terminal and receiving terminal by the Doppler factor of rough estimate:

$\tilde{v}=\widetilde{\mathrm{\δ}}*c$

Wherein c is that sound wave is at water medium velocity;

Step 5: adopt null subcarrier method to carry out velocity compensation to OFDM symbol each in a frame signal near the relative moving speed estimated, when adopting DFT solving speed to compensate each OFDM symbol null subcarrier place energy and, energy and minimum corresponding speed are the speed accurately estimated, the speed accurately estimated are converted into Doppler factor and are the Doppler factor accurately estimated.

The present invention is a kind of based on the relevant Doppler estimation be combined with null subcarrier of copy, can also comprise:

The precision of velocity compensation is Δ, and compensation number of times is n, then compensation range is

The amplitude solving each null subcarrier place after doppler velocity compensation through DFT computing is:

Y _i＝Ζ×W

Wherein, Y _i=[y ₀, y ₁... y _k-1], in frame data, each OFDM symbol is expressed as Ζ=[z ₀, z ₁... z _n-1], each OFDM symbol null subcarrier number is K, and null subcarrier position is Κ=[k ₁, k ₂... k _k], i-th Doppler effect correction speed is v _i, i=1,2 ... n, W are that a N × K ties up matrix;

The energy that then i-th doppler velocity compensation obtains null subcarrier place is:

E(v _i)＝Y _iY _i ^H

Compensate E (v n time _i) in speed corresponding to minimum value be the relative moving speed of the accurate estimation obtained:

$\hat{v}=\arg \min E\left(v_i\right)$

The Doppler factor of accurate estimation is:

$\widehat{\mathrm{\δ}}=\frac{\hat{v}}{c}.$

Beneficial effect:

The present invention carries out quadratic estimate to Doppler factor, improves estimated accuracy; In units of frame, carry out Doppler's estimation, decrease the insertion number of linear FM signal, while improving traffic rate, reduce operand; Adopt copy to be correlated with and rough estimate is carried out to Doppler, decrease null subcarrier algorithm speed search number, while guaranteeing accuracy, reduce the complexity of algorithm.

Accompanying drawing explanation

Fig. 1 is the idiographic flow that the present invention realizes OFDM underwater sound communication;

Fig. 2 is that the present invention realizes OFDM underwater sound communication one frame signal structure;

Fig. 3 is the idiographic flow that Doppler of the present invention estimates.

Embodiment

Below in conjunction with accompanying drawing, the present invention is described in further details.

The object of the present invention is to provide that a kind of underwater sound OFDM is accurate, algorithm complex is little, the Doppler estimation of easy realization.

The object of the present invention is achieved like this:

(1) at transmitting terminal, binary data to be sent is modulated into the OFDM symbol being inserted with null subcarrier;

(2) multiple OFDM symbol is carried out framing, insert linear FM signal at every frame signal head and the tail;

(3) sample to received signal at receiving terminal, adopt copy to be correlated with and carry out Doppler's rough estimate, calculate Signal Compression and extension degree by the relevant peaks of every frame signal head and the tail, obtain the Doppler factor of rough estimate:

(4) transmitting terminal and receiving terminal relative moving speed is roughly calculated by the Doppler factor of rough estimate:

(5) null subcarrier method is adopted to carry out different velocity compensations to OFDM symbol each in a frame signal near the relative moving speed estimated, adopt DFT to solve when friction speed compensates each OFDM symbol null subcarrier place energy and, energy and minimum corresponding speed are the speed accurately estimated, the speed of estimation are converted into Doppler factor and are the Doppler factor accurately estimated.

The invention discloses a kind of based on the relevant Doppler estimation be combined with null subcarrier of copy.The method is applied to underwater sound ofdm communication, and multiple OFDM symbol being inserted with null subcarrier is formed a frame by transmitting terminal, and the head and the tail of a frame signal are inserted linear FM signal; First receiving terminal adopts the relevant method of copy to carry out the rough estimate of Doppler, calculates relative moving speed roughly; Then adopt null subcarrier method to carry out the accurate estimation of Doppler, near the relative moving speed estimated, different speed search is carried out to a frame signal, obtain accurate Doppler factor.The present invention carries out quadratic estimate to Doppler factor, improves estimated accuracy; In units of frame, carry out Doppler's estimation, decrease the insertion number of linear FM signal, while improving traffic rate, reduce operand; Adopt copy to be correlated with and rough estimate is carried out to Doppler, decrease null subcarrier algorithm speed search number, while guaranteeing accuracy, reduce the complexity of algorithm.

Below in conjunction with accompanying drawing citing, the present invention will be further described:

(1) as shown in Figure 1, at transmitting terminal, binary data to be sent is modulated into the OFDM symbol being inserted with null subcarrier;

(2) the OFDM underwater sound communication frame structure of Fig. 2 designed by the present invention, carries out framing by multiple OFDM symbol, inserts linear FM signal at every frame signal head and the tail;

(3) the Doppler's algorithm for estimating of the present invention according to Fig. 3, sample to received signal at receiving terminal, adopt copy to be correlated with and carry out Doppler's rough estimate, calculate Signal Compression and extension degree by the relevant peaks of every frame signal head and the tail, obtain the Doppler factor of rough estimate:

$\widetilde{\mathrm{\δ}}=\frac{T}{T^{\′}}-1;$

Wherein T is the length of the frame signal without Doppler contribution, and T ' is the frame signal length through Doppler contribution recorded;

(4) transmitting terminal and receiving terminal relative moving speed is roughly calculated by the Doppler factor of rough estimate:

$\tilde{v}=\widetilde{\mathrm{\δ}}*c;$

Wherein c is that sound wave is at water medium velocity;

(5) null subcarrier method is adopted to carry out different velocity compensations to OFDM symbol each in a frame signal near the relative moving speed estimated, adopt DFT to solve when friction speed compensates each OFDM symbol null subcarrier place energy and, energy and minimum corresponding speed are the speed accurately estimated, the speed of estimation are converted into the accurate Doppler factor that Doppler factor is estimation.

(6) suppose that compensation speed precision is Δ, compensation number of times is n, then compensation range is ; Receiving terminal carries out sampling to received signal and synchronously obtains frame valid data, and in frame data, each OFDM symbol can be expressed as Ζ=[z ₀, z ₁... z _n-1], suppose that each OFDM symbol null subcarrier number is K, null subcarrier position is Κ=[k ₁, k ₂... k _k], i-th Doppler effect correction speed is v _i(i=1,2 ... n), then through DFT computing solve doppler velocity compensate after the amplitude at each null subcarrier place be Y _i=[y ₀, y ₁... y _k-1], then

Y _i＝Ζ×W；

Wherein W is that a N × K ties up matrix,

Wherein f _sfor sample frequency, f _cfor initial frequency, Δ f is the carrier spacing.

The energy that then i-th doppler velocity compensation obtains null subcarrier place is:

E(v _i)＝Y _iY _i ^H；

Compensate E (v n time _i) in speed corresponding to minimum value be the relative moving speed of the accurate estimation obtained:

$\hat{v}=\arg \min E\left(v_i\right);$

Be translated into Doppler factor:

$\widehat{\mathrm{\δ}}=\frac{\hat{v}}{c};$

Wherein be the Doppler factor of required accurate estimation.

Claims (2)

1., based on the relevant Doppler estimation be combined with null subcarrier of copy, it is characterized in that: comprise the following steps,

Step one: at transmitting terminal, binary data to be sent is modulated into the OFDM symbol being inserted with null subcarrier;

Step 2: L OFDM symbol is carried out framing, inserts linear FM signal at every frame signal head and the tail;

Step 3: sample to received signal at receiving terminal, adopts copy to be correlated with and carries out Doppler's rough estimate, calculates Signal Compression and extension degree, obtain the Doppler factor of rough estimate by the relevant peaks of every frame signal head and the tail:

$\widetilde{\mathrm{\δ}}=\frac{T}{T^{\′}}-1$

Wherein T is the length of the frame signal without Doppler contribution, and T ' is the frame signal length through Doppler contribution recorded;

Step 4: the relative moving speed being calculated transmitting terminal and receiving terminal by the Doppler factor of rough estimate:

$\tilde{v}=\widetilde{\mathrm{\δ}}*c$

Wherein c is that sound wave is at water medium velocity;

Step 5: adopt null subcarrier method to carry out velocity compensation to OFDM symbol each in a frame signal near the relative moving speed estimated, when adopting DFT solving speed to compensate each OFDM symbol null subcarrier place energy and, energy and minimum corresponding speed are the speed accurately estimated, the speed accurately estimated are converted into Doppler factor and are the Doppler factor accurately estimated.

2. according to claim 1 a kind of based on the relevant Doppler estimation be combined with null subcarrier of copy, it is characterized in that: the precision of described velocity compensation is Δ, and compensation number of times is n, then compensation range is $\left[\begin{array}{cc}\tilde{v}-\frac{n}{2}\mathrm{\Δ}& \tilde{v}+\frac{n}{2}\mathrm{\Δ}\end{array}\right],$ The amplitude solving each null subcarrier place after doppler velocity compensation through DFT computing is:

Y _i＝Ζ×W

Wherein, Y _i=[y ₀, y ₁... y _k-1], in frame data, each OFDM symbol is expressed as Ζ=[z ₀, z ₁... z _n-1], each OFDM symbol null subcarrier number is K, and null subcarrier position is Κ=[k ₁, k ₂... k _k], i-th Doppler effect correction speed is v _i, i=1,2 ... n, W are that a N × K ties up matrix;

The energy that then i-th doppler velocity compensation obtains null subcarrier place is:

$E\left(v_i\right)=Y_i{Y}_i^H$

Compensate E (v n time _i) in speed corresponding to minimum value be the relative moving speed of the accurate estimation obtained:

$\hat{v}=\arg \min E\left(v_i\right)$

The Doppler factor of accurate estimation is:

$\widehat{\mathrm{\δ}}=\frac{\hat{v}}{c}.$