CN100539571C - Signal-noise ratio estimation method under a kind of quadrature amplitude modulation mode - Google Patents

Abstract

The present invention proposes the signal-noise ratio estimation method under a kind of quadrature amplitude modulation mode, use quadrature amplitude modulation in the communication link, choose one section restituted signal sequence and carry out signal-to-noise ratio (SNR) estimation: the mean value of the in-phase component of computation of modulation signals constellation point and the quadratic sum of quadrature component, with the mean value of the in-phase component of modulation signal constellation point and quadrature component absolute value sum square, the proportionality coefficient C between two values; Calculate square D of the mean value of restituted signal in-phase component and quadrature component absolute value sum ²Estimate the restituted signal power P _S=CD ²Utilize maximum-likelihood criterion that restituted signal is adjudicated, the decision signal constellation point is A _m', estimating noise power: see the bottom right formula; According to P _SWith P _n, estimated snr SNR _Est=P _S/ P _nUse the method among the present invention, can simply and accurately estimate the signal to noise ratio under the communication link current state when using quadrature amplitude modulation in the communication link.

Description

A Method for Estimating Signal-to-Noise Ratio in Quadrature Amplitude Modulation

(1) Technical field

The present invention relates to a signal processing method in a digital communication system, more specifically, to a method for estimating a signal-to-noise ratio (Signal to Noise Ratio) in a quadrature amplitude modulation (Quadrature Amplitude Modulation) mode, which is applied in the present invention The method can simply and accurately estimate the signal-to-noise ratio in the current state of the communication link when quadrature amplitude modulation is used in the communication link.

(2) Background technology

With the development of modern communication technology, the demand for high-speed, stable, and anytime, anywhere communication is increasing. The third-generation mobile communication technology, as an evolution technology after the first-generation and second-generation mobile communication technologies, aims to provide high-speed, stable , Large-capacity mobile communication system solutions, so that while meeting the needs of voice communication anytime and anywhere, it can also provide high-quality communication services for multimedia services such as data, video and images.

Therefore, in the third-generation mobile communication system, a series of adaptive modulation and coding (Adaptive Modulation and Coding), hybrid automatic repeat (Hybrid Automatic Repeat on Request), multi-antenna transmission and multi-antenna reception (Multiple Input Multiple Output) were proposed. In order to support high-speed data transmission, the adaptive coding and modulation technology means that the wireless transmitter adaptively selects different modulation methods and channel coding according to the state parameter information of the current wireless channel: when the wireless channel is in a fading state, that is When the channel transmission quality is poor, the transmitter will select a more robust (Robust) modulation method and channel coding, that is, a lower-order modulation method and a channel coding with stronger error correction capability and lower coding efficiency to resist channel fading. Adverse effects caused by the communication process; when the wireless channel is in an enhanced state, that is, when the channel transmission quality is better, the transmitter will select a more efficient modulation method and channel coding, that is, a higher-order modulation method and a weaker error correction capability. Channel coding with higher coding efficiency to improve the spectrum resource utilization of the communication system. By adaptively adjusting the modulation mode and channel coding of the wireless transmitter, the state parameter characteristics of the current wireless channel are fully utilized to adapt to the fluctuation state changes of the wireless channel, and the data throughput of the communication system can be maximized.

Based on the above characteristics of adaptive modulation and coding technology, whether the state parameter information of the current wireless channel can be accurately obtained, so as to select a suitable modulation method and channel coding is a key factor determining the performance of adaptive modulation and coding. The signal-to-noise ratio in the current state of the communication link is a commonly used channel state parameter, which can reflect the transmission quality of the current channel. When the wireless channel is in a fading state, the signal-to-noise ratio in the current state of the communication link is low, and the corresponding transmission quality of the channel in the current period is poor; when the wireless channel is in an enhanced state, the communication link in the current state The signal-to-noise ratio of the channel is high, and correspondingly, the transmission quality of the channel during the current period is relatively high. Therefore, when using adaptive modulation and coding technology, the wireless transmitter can know the fluctuation state of the wireless channel according to the signal-to-noise ratio in the current state of the communication link, so as to adaptively adjust the modulation method and channel coding.

In modern mobile communication systems, quadrature amplitude modulation has gained more and more attention and applications because of its efficient spectrum resource utilization. The quadrature amplitude modulation signal s(t) can be expressed as: s(t)=a _k cos2πf _c t+b _k sin2πf _c t, k=1, 2, ..., K, where a _k is the quadrature amplitude modulation signal constellation The in-phase component of the point, b _k is the quadrature component of the quadrature amplitude modulation signal constellation point, K is the number of modulation signal constellation points, that is, the order of quadrature amplitude modulation, and f _c is the carrier frequency. 16QAM modulation refers to quadrature amplitude modulation in which the number K of modulated signal constellation points is 16. In the existing third generation mobile communication system standard, 16QAM modulation is one of the modulation modes defined in adaptive modulation and coding technology. Therefore, when the 16QAM modulation mode is adopted in the communication link, as mentioned above, how to obtain the signal-to-noise ratio in the current state of the communication link is a technical problem that needs to be solved.

For a more detailed description of the adaptive modulation and coding technology in the third generation mobile communication system standard, please refer to the documents 3GPP TS25.213, 3GPP TS 25.223, 3GPP TR 25.855, 3GPP TR 25.858 and 3GPP TR 25.950 (3GPP website www.3gpp.org Documentation downloads are available in ).

(3) Contents of the invention

The purpose of this invention is to solve the above-mentioned problem of how to obtain the signal-to-noise ratio under the current state of the communication link when the quadrature amplitude modulation mode is adopted in the communication link, and to provide a signal-to-noise ratio under the quadrature amplitude modulation mode. The estimation method can simply and accurately estimate the signal-to-noise ratio in the current state of the communication link when the quadrature amplitude modulation method is used in the communication link.

The above-mentioned object of the invention is achieved by the following method of the present invention: a method for estimating signal-to-noise ratio under a quadrature amplitude modulation mode, wherein quadrature amplitude modulation is used in the communication link, and the quadrature amplitude modulation signal constellation point is A _k , A _k = a _k + jb _k , k=1, 2,..., K, a _k is the in-phase component of the modulation signal constellation point, b _k is the quadrature component of the modulation signal constellation point, and K is the number of modulation signal constellation points number, the occurrence probability of each modulated signal constellation point is equal and independent; the demodulated signal at the receiver is D _m , D _m =I _m +jQ _m , m=1, 2, L, and _Im is the demodulated signal In-phase component, Q _m is the quadrature component of the demodulated signal, m is the serial number of the demodulated signal, it is characterized in that: intercept a section of demodulated signal sequence m=i, i+1,..., i+M-1, M≥ 1. Estimating the signal-to-noise ratio based on the intercepted demodulated signal sequence, including the following steps:

为判决信号星座点的同相分量，

为判决信号星座点的正交分量；估计噪声功率P_n，a. Estimate demodulated signal power _PS and noise power P _n : calculate the average value of the sum of squares of the in-phase component and quadrature component of the modulated signal constellation point, and the sum of the absolute values of the in-phase component and quadrature component of the modulated signal constellation point The square of the mean value of , the coefficient of proportionality C between the two values, $C=\frac{\frac{1}{K}\underset{k=1}{\overset{K}{\mathrm{\Σ}}}(a_k^2+b_k^2)}{{\left[\frac{1}{2K}\underset{k=1}{\overset{K}{\mathrm{\Σ}}}(\left|a_k\right|+\left|b_k\right|)\right]}^2};$ Calculate the square D ² of the average value of the sum of the absolute values of the in-phase component and the quadrature component of the demodulated signal, ${\mathrm{D.}}^2={\left[\frac{1}{2m}\underset{m=i}{\overset{i+m-1}{\mathrm{\Σ}}}(\left|I_m\right|+\left|Q_m\right|)\right]}^2;$ Estimate the demodulated signal power P _S , P _S =C D ² ; use the Maximum Likelihood Criterion (Maximum Likelihood Criterion), namely the Minimum Euclidean Distance criterion (Minimum Euclidean Distance) to judge the demodulated signal, and the judgment signal constellation point is $A_m^{\′}=a_m^{\′}+{\mathrm{jb}}_m^{\′}=\underset{k=\mathrm{1,2},\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;K}{\min }\left({|{\mathrm{D.}}_m-A_k|}^2\right),$ m=i, i+1, ..., i+M-1,

is the in-phase component of the decision signal constellation point,

is the orthogonal component of the decision signal constellation point; the estimated noise power P _n ,

${\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; m</span>}}\underset{\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; i</span>}}{\overset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; |</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ;</span>$

b. Estimate the signal-to-noise ratio SNR _est : ${\mathrm{SNR}}_{\mathrm{est}}=\frac{P_S}{P_{\mathrm{no}}}.$

According to one aspect of the present invention, it is characterized in that the digital communication system to which the method is applicable is any one of digital communication systems using quadrature amplitude modulation.

According to another aspect of the present invention, it is characterized in that 16QAM modulation is used in the communication link.

According to yet another aspect of the present invention, it is characterized in that the average value of the sum of the squares of the in-phase component and the quadrature component of the modulated signal constellation point, and the average value of the sum of the absolute values of the in-phase component and the quadrature component of the modulated signal constellation point The square of , the coefficient of proportionality C between the two values is equal to 2.5.

According to still another aspect of the present invention, it is characterized in that the length of the intercepted demodulated signal sequence is 44 16QAM modulation symbols, that is, M=44.

According to still another aspect of the present invention, it is characterized in that the noise in the communication link is additive white Gaussian noise (Additive White Gaussian Noise).

(4) Description of drawings

The purpose and features of the present invention will be described in detail through embodiments in conjunction with the accompanying drawings, and these embodiments are illustrative and not restrictive.

Figure 1 shows the modulation signal constellation diagram under the 16QAM modulation mode. The numbers in the brackets marked in the figure represent the horizontal and vertical coordinate values of the modulation signal constellation points, that is, the in-phase component values and quadrature component values of the modulation signal constellation points.

FIG. 2 shows a comparison diagram between the estimated SNR _est obtained by using the method of the present invention and the set SNR reference value.

(5) Specific implementation methods

1 and 2 show an embodiment of the present invention.

In the digital communication system, when the 16QAM modulation mode is used in the communication link, the constellation point of the 16QAM modulation signal is A _k , A _k = a _k + jb _k , k=1, 2, ..., 16, a _k is the modulation signal The in-phase component of the constellation point, b _k is the quadrature component of the modulated signal constellation point, K is the number of modulated signal constellation points, a _k ∈ {1, -1, 3, -3}, b _k ∈ {1, - 1, 3, -3}, as shown in Figure 1, the numbers in the brackets marked in the figure indicate the abscissa and ordinate values of the modulation signal constellation point, that is, the in-phase component value and the quadrature component value of the modulation signal constellation point, each The probability of occurrence of modulated signal constellation points is equal and independent; at the receiver, in order to obtain the signal-to-noise ratio in the current state of the communication link, the received signal after channel transmission is demodulated, and the demodulated signal is D _m , D _m =I _m +jQ _m , m=1, 2,..., Im is the in-phase component of the demodulated signal, Q _m is the quadrature component of the demodulated signal, _m is the sequence number of the demodulated signal; intercept a section of demodulated Signal sequence m=i, i+1,..., i+M-1, M=44, carry out signal-to-noise ratio estimation according to this segment demodulation signal sequence, comprise steps as follows:

$A_m^{\&prime;}=a_m^{\&prime;}+{\mathrm{jb}}_m^{\&prime;}=\underset{k=\mathrm{1,2},\&CenterDot;\&CenterDot;\&CenterDot;16}{\min }\left({|D_m-A_k|}^2\right),$ m＝i，i+1，L，i+43，

为判决信号星座点的同相分量，为判决信号星座点的正交分量；估计噪声功率P_n， $P_n=\frac{1}{44}\underset{m=i}{\overset{i+43}{\mathrm{\&Sigma;}}}{|D_m-A_m^{\&prime;}|}^2;$ 1. Estimate demodulated signal power _PS and noise power P _n : Calculate the average value of the sum of squares of the in-phase component and quadrature component of the modulated signal constellation point, and the sum of the absolute values of the in-phase component and quadrature component of the modulated signal constellation point The square of the mean value of , the coefficient of proportionality C between the two values, $C=\frac{\frac{1}{16}\underset{k=1}{\overset{16}{\mathrm{\&Sigma;}}}(a_k^2+b_k^2)}{{\left[\frac{1}{32}\underset{k=1}{\overset{16}{\mathrm{\&Sigma;}}}(\left|a_k\right|+\left|b_k\right|)\right]}^2}=\frac{\frac{1}{16}(16\&times;3^2+16\&times;1^2)}{{\left[\frac{1}{32}(16\&times;3+16\&times;1)\right]}^2}=2.5;$ Calculate the square D ² of the average value of the sum of the absolute values of the in-phase component and the quadrature component of the demodulated signal, ${\mathrm{D.}}^2={\left[\frac{1}{88}\underset{m=i}{\overset{i+43}{\mathrm{\&Sigma;}}}(\left|I_m\right|+\left|Q_m\right|)\right]}^2;$ Estimate the demodulated signal power P _S , P _S =2.5·D ² ; use the maximum likelihood criterion to judge the demodulated signal, and the constellation point of the judged signal is

$A_m^{\&prime;}=a_m^{\&prime;}+{\mathrm{jb}}_m^{\&prime;}=\underset{k=\mathrm{1,2},\&Center\; Dot;\&Center\; Dot;\&CenterDot;16}{\min }\left({|{\mathrm{D.}}_m-A_k|}^2\right),$ m=i, i+1, L, i+43,

is the in-phase component of the decision signal constellation point, is the orthogonal component of the decision signal constellation point; the estimated noise power P _n , $P_{\mathrm{no}}=\frac{1}{44}\underset{m=i}{\overset{i+43}{\mathrm{\&Sigma;}}}{|{\mathrm{D.}}_m-A_m^{\&prime;}|}^2;$

2. Estimated signal-to-noise ratio SNR _est : SNR ${\mathrm{SNR}}_{\mathrm{est}}=\frac{P_S}{P_{\mathrm{no}}}.$

Use the method of the present invention in order to examine, carry out the performance of signal-to-noise ratio estimation, emulate the above-mentioned communication link using 16QAM modulation mode, by setting different additive white Gaussian noise powers or changing the power of the transmitted signal in the emulation Change the signal-to-noise ratio in the communication link, then perform signal-to-noise ratio estimation according to the calculation steps in the above-mentioned embodiments; compare the resulting signal-to-noise ratio estimate SNR _est with the signal-to-noise ratio reference value set in the simulation, and Get points to draw a curve, as shown in Figure 2, the abscissa in the figure represents the signal-to-noise ratio value set in the simulation, and the ordinate represents the estimated value SNR _est of the signal-to-noise ratio in the figure; As a reference, it is assumed that the estimated value of the SNR is the SNR value set in the simulation, as shown in the blue curve in the figure, under the SNR set in the simulation, using the The estimated signal-to-noise ratio SNR _est obtained in the calculation step is shown in the red curve in the figure; comparing the two curves in the figure, it can be seen that the estimated signal-to-noise ratio SNR obtained by using the signal-to-noise ratio estimation method in the above-mentioned embodiment _est basically agrees with the signal-to-noise ratio value set in the simulation.

By increasing the length of the demodulated signal sequence intercepted during SNR estimation, that is, increasing the M value, the average time in the calculation process of SNR estimation is increased, or through some existing filtering techniques, the resulting SNR A further revision of the ratio estimate SNR _est can further improve the performance of the signal-to-noise ratio estimation method.

Therefore, using the method of the present invention, when the quadrature amplitude modulation method is used in the communication link, the signal-to-noise ratio in the current state of the communication link can be estimated simply and accurately, so as to know that the channel Therefore, when using adaptive modulation and coding technology, the wireless transmitter can adaptively adjust the modulation mode and channel coding according to the obtained signal-to-noise ratio in the current state of the communication link, so that the data throughput of the communication system rate reaches the maximum.

Claims (5)

1. the signal-noise ratio estimation method under the quadrature amplitude modulation mode wherein uses quadrature amplitude modulation in the communication link, and the quadrature amplitude modulation signal constellation point is A _k, A _k=a _k+ jb _k, k=1,2 ..., K, a _kBe the in-phase component of modulation signal constellation point, b _kBe the quadrature component of modulation signal constellation point, K is the number of modulation signal constellation point, and the probability of occurrence of each modulation signal constellation point equates and be independent; Signal after the receiver end demodulation is D _m, D _m=I _m+ jQ _m, m=1,2 ..., I _mBe the in-phase component of restituted signal, Q _mBe the quadrature component of restituted signal, m is the sequence number of restituted signal, it is characterized in that: intercept one section restituted signal sequence m=i, and i+1 ..., i+M-1, signal-to-noise ratio (SNR) estimation is carried out according to this section restituted signal sequence of intercepting in M 〉=1, comprises that step is as follows:

A. estimate the restituted signal power P _SWith noise power P _n: the mean value of the in-phase component of computation of modulation signals constellation point and the quadratic sum of quadrature component, with the mean value of the in-phase component of modulation signal constellation point and quadrature component absolute value sum square, the proportionality coefficient C between two values, $C=\frac{\frac{1}{K}\underset{k=1}{\overset{K}{\mathrm{\&Sigma;}}}(a_k^2+b_k^2)}{{\left[\frac{1}{2K}\underset{k=1}{\overset{K}{\mathrm{\&Sigma;}}}\left(\right|a_k|+|b_k\left|\right)\right]}^2};$ Calculate square D of the mean value of restituted signal in-phase component and quadrature component absolute value sum ², $D^2={\left[\frac{1}{2M}\underset{m=i}{\overset{i+M-1}{\mathrm{\&Sigma;}}}\left(\right|I_m|+|Q_m\left|\right)\right]}^2;$ Estimate the restituted signal power P _S, P _S=CD ²Utilize maximum-likelihood criterion that restituted signal is adjudicated, the decision signal constellation point is A ' _m, $A_m^{\&prime;}=a_m^{\&prime;}+j{b}_m^{\&prime;}=\underset{k=\mathrm{1,2},\&CenterDot;\&CenterDot;\&CenterDot;K}{\min }\left({|D_m-A_k|}^2\right),$ M=i, i+1 ..., i+M-1,

Be the in-phase component of decision signal constellation point,

Quadrature component for the decision signal constellation point; Estimating noise power P _n,

$P_n=\frac{1}{M}\underset{m=i}{\overset{i+M-1}{\mathrm{\&Sigma;}}}{|D_m-A_m^{\&prime;}|}^2;$

B. estimated snr SNR _Est: ${\mathrm{SNR}}_{\mathrm{est}}=\frac{P_S}{P_n}.$

2. the method for claim 1 is characterized in that described quadrature amplitude modulation adopts the 16QAM modulation system.

3. method as claimed in claim 2, the mean value that it is characterized in that the quadratic sum of the in-phase component of described modulation signal constellation point and quadrature component, with the mean value of the in-phase component of modulation signal constellation point and quadrature component absolute value sum square, the proportionality coefficient C between two values equals 2.5.

4. method as claimed in claim 3, the restituted signal sequence that it is characterized in that described intercepting are 44 16QAM modulation symbols.

5. as the described method of one of claim 1 to 4, it is characterized in that the noise in the described communication link is an additive white Gaussian noise.

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