CN100426708C - Signal-to-jamming ratio evaluating method - Google Patents

Abstract

The present invention discloses a method for estimating signal to interference ratio, which comprises the following steps: calculating the estimation value of the signal to interference ratio; inputting the estimation value of the signal to interference ratio to a low-pass filter, and the output value of the low-pass filter is an ultimate SIR estimation value. The low-pass filter is an IIR filter, and the low-pass filter is also an alpha filter. When a selected power control algorithm (PCA) is 1, the coefficient (alpha) of the alpha filter is 0.6. In the present invention, low-pass filtering is carried out for the original estimation value of the signal to interference ratio, and a value after the low-pass filtering is used as an SIR estimation value for carrying out command judgment. Experiments show that the method can further improve the performance of power control and system capacity.

Description

A kind of method of estimation of signal interference ratio

Technical field

The present invention relates to the power control techniques in Wideband Code Division Multiple Access (WCDMA) (WCDMA) system, particularly about the method for estimation of signal interference ratio (SIR).

Background technology

Power control techniques can be divided into open Loop Power control and closed power control.Open Loop Power control is a kind of rough estimate to decline, and the then effectively rapid fading of tracking signal of closed power control is estimated accurately to decline.Closed power control is divided into inner loop power control and exterior ring power control again.Inner loop power control is the signal interference ratio (SIR) of receiving terminal by measuring received signal, and compares with thresholding SIR, the transmitting power that the power control command adjustment of generation response is made a start, and inner loop power is controlled every time slot and is carried out once; Exterior ring power control is that receiving terminal is adjusted thresholding SIR according to the average Block Error Rate of received signal decoding, deinterleaving, and exterior ring power control is that polylith carries out once.Wherein, inner-loop power control is the crucial power control technology of decision systems performance.

In inner loop power control, each time slot all needs the signal quality according to receiving terminal, as SIR, compares with the signal quality of target and the power per liter or fall power of determining to make a start, thereby realizes the purpose of power control.In general, at first to estimate the SIR of receiving end signal,, then send and fall power command to making a start if the SIR of signal is higher than the SIR of target, reducing the value of SIR, on the contrary power per liter then.So, correct estimate the core that received signal SIR is an inner-loop power control.

In the WCDMA system, SIR estimates it is to carry out in the power control algorithm (PCA) on the frequency pilot sign of Dedicated Physical Control Channel (DPCCH).As shown in Equation (1), the signal of each symbol of receiving terminal DPCCH generally is made up of signal and noise two parts.

x(t)＝a(t)+n(t) (1)

Wherein a (t) is a signal section, and the variation of this part is very fast, but generally in a time slot this part more stable; N (t) is a noise.Suppose that a (t) is A in the time slot, n (t) is a Gaussian noise, and variance is σ ², so formula (1) can be as shown in Equation (2).

x(t)＝A+n(t) (2)

The purpose of estimating SIR is exactly signal energy and the noise energy that estimates each time slot, thereby obtains sir value.According to formula (2), the output of the signal amplitude estimation of M symbol as shown in Equation (3).

$x=A+\frac{1}{M}\mathrm{\Σn}\left(t\right)---\left(3\right)$

As shown in Equation (4), signal energy estimate be exactly amplitude x square.

$x^2=A^2+2A*\frac{1}{M}\mathrm{\Σn}\left(t\right)+\frac{1}{M^2}{\left(\mathrm{\Σn}\left(t\right)\right)}^2---\left(4\right)$

According to Statistics, the estimation of each time slot noise energy is exactly the variance of x (t), therefore, can estimate noise energy.Because noise energy is more stable,, obtain the noise energy σ of each time slot at last so the noise energy that each time slot is estimated is carried out filtering ²

Signal energy with each time slot is exactly the sir value of each time slot divided by noise energy, shown in formula (5).

$\mathrm{SIR}=[A^2+2A*\frac{1}{M}\mathrm{\Σn}\left(t\right)+\frac{1}{M^2}{\left(\mathrm{\Σn}\left(t\right)\right)}^2]/{\mathrm{\σ}}^2---\left(5\right)$

By formula as can be seen, the first in the formula (5) is real sir value; Second portion is the deviation that produces owing to noise, and average is 0, and variance is relevant with noise energy; Third part is because the positive bias that noise produces can be eliminated by revising.So just the SIR estimated value can be reduced to by real sir value and noise and form, noise energy and average M decision before wherein noise is estimated by SIR, as shown in Equation (6).

$\mathrm{SIR}=\frac{A^2}{{\mathrm{\σ}}^2}+n\left(t\right)---\left(6\right)$

Wherein a front part is a live part, and a back part will play negative effect.

In general, three aspects such as the time delay of inaccurate SIR estimated value, power control commands error of transmission and power control commands may cause the power control decreased performance of system, and the required Eb/N0 of receiving demodulation is increased, and reduce systematic function and capacity.Wherein, it doesn't matter in the estimation of power control commands error of transmission and SIR, and the power control commands time delay is not only relevant with the SIR estimation, also relevant with the propagation delay time of power control commands.So the SIR method of estimation can directly influence the precision of SIR estimated value and the time delay of power control commands.Very obvious, although the sir value average ideal that formula (6) estimates, because The noise, variance is very big, and current time slots SIR estimates inaccurate, influences the power control performance greatly.So reduce noise variance in the formula (6), can improve the power control performance of system as far as possible.Simultaneously, reduce the time that formula (6) is estimated as far as possible, the SIR of required time slot is estimated as soon as possible, also can improve the performance of system.

In addition, when rapid fading speed was slow, power control can improve systematic function greatly, but when rapid fading speed when very fast, power control has caused that systematic function descends, this is that power control does not catch up with fast-changing decline because the power control time delay is suitable with rapid fading.But because power control remedies the effect of path loss in addition, although power control has inevitably influenced systematic function, power control must exist.So, current SIR method of estimation, just formula (6) can't have been avoided power control side effect to system when quick rapid fading.

Summary of the invention

In view of this, the invention provides a kind of method of estimation of signal interference ratio,, effectively improve power control performance and systematic function to avoid power control side effect to system when the quick rapid fading.

A kind of method of estimation of signal interference ratio is to realize like this.

Calculate the signal interference ratio estimated value;

With signal interference ratio estimated value input infinite impulse response (IIR) filter, the output valve of iir filter is final SIR estimated value.

Described iir filter is the alpha filter.

When selecting power control algorithm (PCA) to be 1, the factor alpha of described alpha filter is 0.6.

The present invention carries out low-pass filtering with the estimated value of original signal interference ratio by iir filter, to carry out the order judgement as the SIR estimated value through the value after the low-pass filtering, experiment shows that this method can avoid power control side effect to system when quick rapid fading, and further improves the performance and the power system capacity of power control.

Embodiment

Core content of the present invention is to carry out low-pass filtering one time on former SIR estimated value basis, just the result to each time slot of estimating in the formula (6) carries out low-pass filtering, then the value after the low-pass filtering is carried out the power control commands judgement as the estimated value of SIR.

Describe technical scheme of the present invention in detail below in conjunction with the drawings and specific embodiments.

Low pass filter has two kinds of infinite impulse response (IIR) and finite impulse responses (FIR).Iir filter can obtain high selectivity with lower exponent number, but phase nonlinear is very serious.The FIR filter can obtain strict linear phase, but must be with reaching high selectivity than higher exponent number, so cost is higher, it is bigger to delay time.Because the FIR filter order is big more, time delay is big more, and the SIR estimation is very tight to delay requirement, so adopt iir filter here.

By formula (6) and as can be seen, the SIR estimated value is carried out filtering will cause following two influences in conjunction with the characteristic of low pass filter:

1) to the useful part A in the SIR estimated value ²/ σ ²Will cause certain time delay, especially as signal energy A ²The variation of reflected signal energy in time of SIR estimated value might cause the power control performance decrease like this when changing.This also is the reason of the SIR estimated value not being carried out filtering, if adopt low-pass filtering, filter bandwidht is the bigger the better.

2) effectively suppress the SIR estimated value deviation that invalid part n (t) causes in the SIR estimated value, noise energy fluctuation that the SIR estimated value is caused just.SIR estimated value variance is more little, and it is accurate more to estimate, helps power control performance and power system capacity like this.From this view point, the bandwidth of low pass filter is more little, and effect is good more.

The SIR estimated value is carried out low-pass filtering also have the another one important function.The front is mentioned, and power control not only can remedy the influence of path fading to systematic function, can remedy rapid fading more to Effect on Performance.If but it is too fast to decline, power control will be played side effect.In wireless channel, rapid fading means that fading frequency exists simultaneously from 0 decline to maximum fading frequency.Therefore, the SIR estimated value is carried out low-pass filtering can effectively suppress the SIR estimated value variation that the too fast rapid fading of the rapidity of fading causes, can reduce the negative effect of power control like this quick rapid fading.Can also keep at a slow speed rapid fading to the influence of SIR estimated value, the performance power control remedies the effect of rapid fading at a slow speed.

Therefore, from top analysis as can be seen, the SIR estimated value is carried out the existing favourable one side of filtering, disadvantageous one side is also arranged.But, because being carried out filtering, the SIR estimated value will influence systematic function in many aspects, existing positive influences also have negative effect, so the definite optimum bandwidth of filter finally is to obtain with emulation by experiment.Experiment shows, if can select suitable bandwidth, still helps the improvement of systematic function.

Be that example illustrates the solution of the present invention with the alpha filter below.

The alpha filter is the simplest iir filter, and this filter can be expressed as shown in the formula (7).

y(n)＝a×x(n)+(1-a)×y(n-1) (7)

Wherein, x (n) expression current time slots input value, y (n) expression current time slots output valve, y (n-1) represents last time slot output valve; The bandwidth of coefficient a decision filter.Repeatedly test and emulation through system, when power control algorithm (PCA) was 1, a in the formula elected 0.6 as, and this low pass filter can farthest improve systematic function, improved power system capacity.

The present invention is with original SIR estimated value input low pass filter, and the output valve of getting low pass filter is last sir value.Experiment shows, selects suitable low pass filter and suitable bandwidth that the estimated value of SIR is carried out low-pass filtering, can reduce negative effect as far as possible, improves positive influences, improves systematic function, improves power system capacity.

Claims (3)

1, the method for estimation of a kind of signal interference ratio (SIR) is characterized in that, this method may further comprise the steps:

Calculate the signal interference ratio estimated value;

With signal interference ratio estimated value input infinite impulse response (IIR) filter, the output valve of iir filter is final SIR estimated value.

2, method according to claim 1 is characterized in that, described iir filter is the alpha filter.

3, method according to claim 2 is characterized in that, when selecting power control algorithm (PCA) to be 1, the factor alpha of described alpha filter is 0.6.