The mpsk signal unbound nucleus signal-noise ratio estimation method that Open-closed-loop combines
Technical field
The invention belongs to channel estimation technique, the mpsk signal non-data that a kind of Open-closed-loop combines is auxiliary
Help signal-noise ratio estimation method.
Background technology
The channel information provided by signal-to-noise ratio (SNR) estimation, can be effectively improved channel transport efficiency, is constantly pursuing
High performance today, signal-to-noise ratio (SNR) estimation technology has a wide range of applications.Such as, Tubo code, LDPC code are contour
The channel coding method of performance is required for utilizing signal-tonoise information to carry out additional interpretations, and adaptive coding modulation is also
Need the foundation that signal-tonoise information selects as coded modulation scheme, this external power control, adaptive equalization with
And the technical field such as Dynamic Resource Allocation for Multimedia is also required for utilizing signal-tonoise information to improve performance.
In terms of signal-to-noise ratio (SNR) estimation, forefathers have been carried out numerous studies, and these are studied and can be divided into two big classes: base
In data-aided method (DA) and method based on unbound nucleus (NDA).Data-aided method requirement
Insert pilot signal or training sequence known to receiving terminal in a stream.Obviously, adopt and can drop in this way
Low system transfers efficiency.In a lot of application scenarios, consider from the angle improving spectrum efficiency, unbound nucleus
Method is a kind of preferably selection.
According to estimate time the need of knowing carrier parameter, unbound nucleus SNR estimator again can be further
It is divided into photocarrier method (CA) and the big class of non-carrier aided algorithm two.Photocarrier method algorithm also has a variety of: online
SNR estimator, the signal-to-noise ratio estimation algorithm of iteration.The SNR ranges that online SNR estimator is suitable for (is estimated
Meter precision is interval close to the signal to noise ratio of theoretical limit) it is 0 to 6dB, its applicable SNR ranges can be extended
To-5 to 12dB.The signal-to-noise ratio estimation algorithm of iteration can reduce the estimated bias when low signal-to-noise ratio further,
But the complexity of this algorithm is the highest.But photocarrier method algorithm has a common problem, i.e. by carrier parameter
Estimated accuracy impact is bigger, it is necessary to could use after realizing accurate carrier recovery.For overcoming this problem, can
To estimate signal to noise ratio according to reception signal envelope, owing to this method is unrelated with carrier parameter, thus the most non-
Photocarrier method signal-to-noise ratio estimation algorithm.Non-carrier aided algorithm have second order Fourth-order moment (M2M4) algorithm and single order and
Second order estimates SNR method.Wherein single order and second order estimate that the method for signal to noise ratio is than M2M4 arithmetic accuracy
Height, when low signal-to-noise ratio, estimated bias is less, but the method has relatively when the symbolic number for estimating is less
Big estimated bias.
P.Gao,C.Tepedelenlioglu,“SNR estimation for nonconstant modulus
Constellations, " (IEEE Trans.Signal Processing, vol.53, no.3,
Pp.865-870,2005) literary composition proposes a kind of single order utilizing signal envelope and second order to estimate signal to noise ratio
Method, this method needs to utilize look-up table to realize.This method is higher than M2M4 arithmetic accuracy, at low letter
Make an uproar than time estimated bias less.But actual application is limited by look-up table size, during high s/n ratio, is estimated performance
Can increase along with signal to noise ratio and decline.Chao Gong,Bangning Zhang,Aijun Liu,Daoxing
Guo, " A High Accurate and Low Bias SNR Estimator:Algorithm and
Implementation ", (Radioegineering, 2011, Vol.12) literary composition is to proposing a kind of M1M2
The correction algorithm of method, and use the method for segmentation third degree curve matching to replace LUT Method.This side
But method precision higher hardware implementation complexity is bigger.Both approaches is all open loop method of estimation, is suitable for
The signal-to-noise ratio (SNR) estimation of short burst signal.And continuous signal open loop method of estimation is not being made full use of
With, estimated accuracy needs to be improved further.
Summary of the invention
It is an object of the invention to provide the mpsk signal unbound nucleus signal-to-noise ratio (SNR) estimation that a kind of Open-closed-loop combines
Method, this method speed is fast, precision is high, hardware implementation complexity is low.
The technical solution realizing the object of the invention is: the mpsk signal non-data that a kind of Open-closed-loop combines is auxiliary
Helping signal-noise ratio estimation method, step is as follows:
The first step, envelope information obtains, i.e. according to two-way orthogonal signalling r receivedInAnd rQn, determine that it wraps
Network second order information un, then recycle unDetermine envelope first moment information vn;
Second step, statistical parameter calculates, i.e. one section N number of first moment information v receiving signalnSum square
M1, and second moment information unSum M2, pass through M1And M2Determine statistical parameter γ;
3rd step, signal-to-noise ratio (SNR) estimation, i.e. utilize the mapping relations one by one between the λ of statistical parameter γ and signal to noise ratio,
According to γ-value, signal to noise ratio λ is estimated;
4th step, closed loop smothing filtering, i.e. utilize a second-order loop filter to above using open-loop method
Obtain signal to noise ratio to be worth according to a preliminary estimate and smooth, improve estimated accuracy further, the letter obtained after smothing filtering
Compared estimate value of making an uproar is as final output result ρ.
In the first step, envelope second moment information unFormula is:
Wherein q is for receiving data-measuring figure place.
In the first step, envelope second moment information vnFormula is:
Wherein q is for receiving data-measuring figure place.
In second step, statistical parameter γ formula is:
Wherein δ is corrected parameter, and 0≤δ≤1.
In 3rd step, signal-to-noise ratio (SNR) estimation value λ is as follows with the mapping relations of statistical parameter γ:
I in formula0() is zero Bessel function;I1() is first-order bessel function.
In 4th step, the initial value of closed loop smoothing filter output register obtains for receiving data by first paragraph
Open loop signal-to-noise ratio (SNR) estimation value.
The present invention compared with prior art, its remarkable advantage: (1) estimating speed is fast, first carries out owing to have employed
The method that open loop is estimated, it is only necessary to tens symbols are obtained with one and are worth according to a preliminary estimate;(2) estimated accuracy
Height, the open loop estimation equation used has an advantage that estimated bias is little, and uses the method for loop filtering can
To improve precision further;(3) hardware implementation complexity is low;(4) present invention is by receiving signal carrier parameter
The impact of estimated accuracy;(5) present invention need not any auxiliary information;(6) this method has taken into full account quantization
Impact, be therefore especially suitable for hardware realize.
Accompanying drawing explanation
Fig. 1 is that entirety of the present invention realizes block diagram.
Fig. 2 is statistical parameter of the present invention and signal to noise ratio mapping relations curve.
Fig. 3 is that second-order loop filter of the present invention realizes schematic diagram.
Detailed description of the invention
Below in conjunction with the accompanying drawings the present invention is described in further detail.
The entirety of the present invention realizes flow process as it is shown in figure 1, be described in detail each step below:
(1) envelope information obtains
Simple mpsk signal has the feature of constant-envelope, and the actual signal that receives all comprises noise.Noise
The mpsk signal envelope received can be made to produce rise and fall, it is big that the change severe degree of envelope has reacted signal to noise ratio
Little.Therefore, it can the envelope utilizing mpsk signal to estimate signal to noise ratio.
The first step of the present invention seeks to obtain signal envelope information.The mpsk signal received is divided into a length of N
Some sections, process the most piecemeal.The mpsk signal received have passed through quadrature frequency conversion, can be divided into two
Road signal rInAnd rQn, n represents one section of nth data received in signal, and span is 0 to N-1.
Hardware is required for logarithm value in realizing and carries out quantification treatment, represents quantization digit with q, and at this, we take
q=8.First calculate and receive signal envelope second moment information un, method is as follows:
In formula, floor represents and rounds to 0 direction.When hardware realizes, square operation can cause data bits to add
Times.R in this exampleInAnd rQnThe number obtained after quadratic sum is 16 quantizations, for keep fixed quantisation figure place need into
Row cut position processes, and removes least-significant byte.Therefore, in formula after quadratic sum computing by the value that obtains divided by 2q.Real
Now, by rInAnd rQnThe low q position of quadratic sum value cuts out, and gets final product in above formula divided by 2qAnd round to 0 direction
Computing.The u obtained by said methodnIt it is the positive integer of a q position quantization.
Then according to unObtain envelope first moment information vn, computational methods are as follows.
Open radical sign computing due to above formula existence and open radical sign computing, it is achieved this computing can use multiple method, this example
The method utilizing look-up table realizes.unBeing the positive integer of a q position quantization, possible value number has 2qIndividual.
By each unThe v that value is correspondingnValue one look-up table of write, writing address is un.For keeping quantization digit, vnValue
It is also adopted by q position to quantify.It is thus desirable to setting up a size is 2qThe look-up table of × q realizes unTo vnOne by one
Map.Use unV just can be directly read as addressnValue.
(2) statistical parameter calculates
This step can be subdivided into again two steps.First, one section of N number of first moment information v receiving signaln
Square M of sum1, and second moment information unSum M2, as follows:
Then according to M1And M2, further counting statistics parameter γ according to the following formula:
γ=2q(1-δ)(M1/N2-δ(M2/N))(M2/ N) (5)
δ is modifying factor, and span is 0 to 1, takes δ=0.8 in this example.
(3) signal to noise ratio is searched
Exist between signal to noise ratio and statistical parameter γ and be shown below relation:
In formula, λ is snr value, function I0(·)、I1() is respectively zero Bessel function and single order Bezier
Function.This is a monotonically increasing function, and therefore statistical parameter γ and signal to noise ratio are worth between λ according to a preliminary estimate
There are mapping relations one by one.This is also a nonlinear function simultaneously, it is difficult to obtained the Analytical Expression of λ by γ
Formula.For by statistical parameter γ obtain signal to noise ratio be worth λ according to a preliminary estimate can in a number of different ways, such as piecewise fitting
Method, approximation abbreviation method, loop up table etc..This example uses and is suitable for the LUT Method that FPGA realizes, due to letter
Make an uproar and represent than usual decibels, therefore realize inverse function by look-up table
λdB=10log10(λ)=10log10f-1(γ).Its mapping relations are as shown in Figure 2.Signal-to-noise ratio (SNR) estimation precision is
0.1dB, signal-to-noise ratio (SNR) estimation interval is-2dB to 12dB, and 8 quantizations can be used to represent.γ is 8 amounts
Changing, therefore look-up table size is 256*8.γ-value i.e. can find out the signal to noise ratio of correspondence directly as address.
(4) closed loop smothing filtering
Step 1 achieves signal to noise ratio open loop to 3 and estimates.In the case of not considering that signal to noise ratio changes over, open
Ring estimated accuracy depends on the size of N, and N the biggest estimation progress is the biggest.But under practical situation, signal to noise ratio
Changing often, can only be considered as fixed value at short notice, therefore data length N can not be excessive, otherwise
Within this segment data persistent period, signal to noise ratio may have occurred and that large change.Which limits in actual application and open
The precision of ring method of estimation.For improving estimation progress further, loop filter can be used to estimate with open loop
The method that device combines.This example employing one obtains second-order loop filtering as shown in Figure 3 and carries out value according to a preliminary estimate
Filtering.In figure, D1 and D2 is two depositors.When obtaining first paragraph snr of received signal estimated value, cut
Changing switch placed below, it is placed in top in the time.Thus make the output register in loop filter
D2 initial value is first time open loop signal-to-noise ratio (SNR) estimation value, and remaining time is filtered estimated value.The most permissible
Realize loop filter quickly enters lock, ensure that again enough output accuracies.Filter coefficient α and β
Can require to be adjusted according to signal to noise ratio change speed and estimated accuracy.This example takes α=0.016 He
β=0.025。
By using the present invention, signal-to-noise ratio (SNR) estimation error can be made less than 0.1dB, there is estimating speed fast, essence
Spend high advantage.