CN103107972B - A kind of QAM demodulation method - Google Patents

Abstract

The present invention relates to a kind of QAM demodulation method, the described method scope of data according to input signal, dynamically adjust soft demodulation correction factor α, to calculate the soft demodulating information of QAM mapping data.The QAM demodulation method of the present invention falls into the ratio of main region according to input signal data, selects modifying factor neatly so that the result of calculating is more accurate, thus adjusting the judgement credibility of the soft output of probabilistic information more accurately；It addition, the method for the present invention can avoid the defect of traditional method completely, power deviation is no longer sensitive.

Description

A kind of QAM demodulation method

Technical field

The present invention relates to the demodulation method in a kind of mobile radio system, be specifically related to a kind of based on the QAM demodulation method in CMMB (ChinaMobileMultimediaBroadcasting) standard.

Background technology

China Mobile multimedia broadcasting technology CMMB (ChinaMobileMultimediaBroadcasting) is CMMB (the being commonly called as mobile TV) industry standard formally promulgated by SARFT(The State Administration of Radio and Television) for 2006.The standard specifies in broadcasting service frequency range, the frame structure of mobile multimedia broadcast system broadcast channel transmission signal, Channel Coding and Modulation, suitable in the broadcasting service frequency in 30MHz to 3000MHz frequency range, the broadcast system of the multi-media signals such as TV, broadcast, data message is launched, it may be achieved whole nation roaming by satellite and/or terrestrial wireless.

In CMMB standard, have employed biphase phase shift keying BPSK (BinaryPhaseShiftKeying), QPSK QPSK (QuadraturePhaseShiftKeying) and three kinds of modulation systems of quadrature amplitude modulation QAM (QuadratureAmplitudeModulation) to improve bandwidth, be separately adapted to the channel of different situations.Wherein, the constellation modulating mode of QAM is more sensitive to interchannel noise, therefore that the performance requirement of demodulation is the highest.When data are demodulated by receiving terminal, conventional demodulation method has the hard solution soft demodulation of mediation.Hard demodulation is that reception data are forced judgement for corresponding modulation bit, it is achieved simple, but poor-performing；Soft demodulation is then according to the probability Soft Inform ation receiving the data each bit of output, it is achieved slightly complicated, but performance is fine.Channel circumstance in applying due to CMMB is generally relatively more severe, is therefore typically all and transfers to obtain good performance by soft solution.

In traditional soft demodulation, the qam constellation of CMMB standard maps and generally adopts equation below to be soft demodulated:

Pr (b3)=Real (Data (i))；

Pr (b2)=Imag (Data (i))；

$\mathrm{Pr}\left(b1\right)=\mathrm{abs}\left(\mathrm{Real}\left(\mathrm{Data}\left(i\right)\right)\right),2*\frac{1}{c};$

$\mathrm{Pr}\left(b0\right)=\mathrm{abs}\left(\mathrm{Imag}\left(\mathrm{Data}\left(i\right)\right)\right),2*\frac{1}{c};$

This computational methods are simple and better performances, but when reducing or increasing and cause the amplitude of data to be demodulated reduction unanimous on the whole occur or increase occur in the power inputting signal, the soft demodulating information of bit b1, b0 then can be a greater impact, and therefore causes that declining occurs in the performance of soft demodulation.

Summary of the invention

The technical problem to be solved is to provide a kind of QAM demodulation method, it is achieved that a kind of precision is high and realizes relatively simple QAM soft demodulating method.

The present invention is to solve above-mentioned technical problem, disclose a kind of QAM demodulation method, described method includes: the scope of data according to input signal, dynamically adjusts soft demodulation correction factor, to calculate the soft demodulating information of QAM mapping data.

Further, the described scope of data according to input signal, dynamically adjust soft demodulation correction factor α, the method to calculate the QAM soft demodulating information mapping data comprises the steps:

Acquisition input signal data Data (i), wherein i=1,2,3 ... n；

Fall into the ratio η of main region D according to input signal data Data (i), select soft demodulation correction factor α；

According to the parameter alpha that above-mentioned steps obtains, it is calculated as follows the probabilistic information soft output value of the bit b3 of data Data (i), b2, b1 and b0:

B3=Real (Data (i)),

B2=Imag (Data (i)),

$b1=\mathrm{abs}\left(\mathrm{Real}\left(\mathrm{Data}\left(i\right)\right)\right),\mathrm{\α}*2*\frac{1}{c},$

$b0=\mathrm{abs}\left(\mathrm{Imag}\left(\mathrm{Data}\left(i\right)\right)\right),\mathrm{\α}*2*\frac{1}{c},$

Wherein, Real () represents the function in realistic portion, and Imag () represents the function seeking imaginary part, and abs () represents the function seeking absolute value,For the power normalization factor, η is the number ratio with total number of input signal data Data (i) of input signal data Data (i) falling into main region D.

Further, the described power normalization factorFor

Further, described n is total number of data subcarrier in adjacent OFDM symbol in a time slot, one or more, when bandwidth is 2M, and n=522*F；When bandwidth is 8M, n=2610*F；Wherein, F is the OFDM symbol number chosen, 1≤F≤53.

Further, described main region D is the border circular areas D on qam constellation mapped plan, and described border circular areas D is:

Wherein, I, Q represent the real axis on qam constellation mapped plan and the coordinate figure on imaginary axis direction respectively.

Further, the computational methods of the described ratio η falling into main region D according to input signal data Data (i) include:

Calculate $\sqrt{{\left|\mathrm{Real}\left(\mathrm{Data}\left(i\right)\right)\right|}^2+{\left|\mathrm{Imag}\left(\mathrm{Data}\left(i\right)\right)\right|}^2}=R;$

IfThen represent that input data Data (i) falls into main region D；

Otherwise input data Data (i) does not fall within main region D；

Calculate total number of number/input signal data Data (i) of input signal data Data (i) of η=fall into main region D.

Further, the described ratio η falling into main region D according to input signal data Data (i), the method selecting soft demodulation correction factor α is:

As η > 0.98, α=0.7；

When 0.91 < η≤0.98, α=0.8；

When 0.84 < η≤0.91, α=1；

When 0.75 < η≤0.84, α=1.3；

When 0.69 < η≤0.75, α=1.6；

When 0.65 < η≤0.69, α=2.1；

When 0.60 < η≤0.65, α=2.9；

Otherwise, α=4.1.

The invention described above technical scheme is adopted to provide the benefit that: the QAM soft demodulating method of present invention design falls into the ratio of main region according to input signal data, select soft demodulation correction factor flexibly, make the result calculated more accurate, thus adjusting the judgement credibility of the soft output of probabilistic information more accurately；It addition, the method for the present invention then completely avoid the defect of traditional method, power deviation is no longer sensitive, improve judgement credibility and the precision of the soft output of probabilistic information, realize simple simultaneously.

Accompanying drawing explanation

Fig. 1 is the qam constellation mapping graph in embodiment of the present invention CMMB standard；

Fig. 2 is the ber curve figure emulating the present invention obtained and conventional qam mode in the embodiment of the present invention.

Detailed description of the invention

Below in conjunction with accompanying drawing, principles of the invention and feature being described, example is served only for explaining the present invention, is not intended to limit the scope of the present invention.

Fig. 1 show the qam constellation mapping graph in CMMB standard, every 4 bits of QAM correspond to 1 constellation symbol, the Bit data of FEC coding output is split into the symbol (b3b2b1b0) that 4 bits are a group, the constellation mapping of this symbol is in-phase component I=b1b0, quadrature component Q=b3b2, as it can be seen, the value of I and the Q corresponding to constellation isWith

The embodiment of the present invention is for the QAM in CMMB standard, it is provided that a kind of QAM soft demodulating method, and described method is the scope of data according to input signal, dynamically adjusts soft demodulation correction factor, to calculate the soft demodulating information of QAM mapping data.Comprise the steps:

Step one, acquisition input signal data Data (i), wherein i=1,2,3 ... n；

In a specific embodiment of the present invention, described n is total number of data subcarrier in adjacent OFDM symbol in a time slot, one or more, when bandwidth is 2M, and n=522*F；When bandwidth is 8M, n=2610*F；Wherein, described F is positive integer, the number of the OFDM symbol in the time slot that expression is chosen, and 1≤F≤53.

Step 2, falls into the ratio η of main region D according to input signal data Data (i), selects soft demodulation correction factor α；

In embodiment of the present invention, described main region D is the border circular areas D on qam constellation mapped plan, and described border circular areas D is:Wherein, I, Q represent the real axis on qam constellation mapped plan and the coordinate figure on imaginary axis direction respectively.

In this embodiment, the computational methods of the described ratio η falling into main region D according to input signal data Data (i) include:

First calculate $\sqrt{{\left|\mathrm{Real}\left(\mathrm{Data}\left(i\right)\right)\right|}^2+{\left|\mathrm{Imag}\left(\mathrm{Data}\left(i\right)\right)\right|}^2}=R;$

IfThen represent that input data Data (i) falls into main region D；

Otherwise input data Data (i) does not fall within main region D；

The situation falling into main region D finally according to input data Data (i) calculates η, wherein total number of number/input signal data Data (i) of input signal data Data (i) of η=fall into main region D.

In the present embodiment, the described ratio η falling into main region D according to input signal data Data (i), the method selecting soft demodulation correction factor α is:

As η > 0.98, α=0.7；

When 0.91 < η≤0.98, α=0.8；

When 0.84 < η≤0.91, α=1；

When 0.75 < η≤0.84, α=1.3；

When 0.69 < η≤0.75, α=1.6；

When 0.65 < η≤0.69, α=2.1；

When 0.60 < η≤0.65, α=2.9；

Otherwise, α=4.1.

Step 3, according to the parameter alpha that above-mentioned steps obtains, is calculated as follows the probabilistic information soft output value of the bit b3 of data Data (i), b2, b1 and b0:

B3=Real (Data (i)),

B2=Imag (Data (i)),

$b1=\mathrm{abs}\left(\mathrm{Real}\left(\mathrm{Data}\left(i\right)\right)\right),\mathrm{\&alpha;}*2*\frac{1}{c},$

$b0=\mathrm{abs}\left(\mathrm{Imag}\left(\mathrm{Data}\left(i\right)\right)\right),\mathrm{\&alpha;}*2*\frac{1}{c};$

Wherein, Real () represents the function in realistic portion, Imag () represents the function seeking imaginary part, abs () represents the function seeking absolute value, η is the number ratio with total number of input signal data Data (i) of input signal data Data (i) falling into main region DFor the power normalization factor, the described power normalization factorFor

Fig. 2 is the ber curve figure emulating the present invention obtained and conventional qam mode in the embodiment of the present invention, as shown in the figure, in simulations, employing is that LDPC (LowDensityParityCheckCode, the i.e. low density parity check code) code of 1/2 code check in CMMB standard is as error correcting code, when the bit error rate is 0, the signal to noise ratio of traditional method is about 7.9dB, and the method for the present invention is 7.3dB, therefore, relative to traditional method, the method for the present invention has the gain of 0.6dB.

The foregoing is only presently preferred embodiments of the present invention, not in order to limit the present invention, all within the spirit and principles in the present invention, any amendment of making, equivalent replacement, improvement etc., should be included within protection scope of the present invention.

Claims (3)

1. a QAM demodulation method, it is characterised in that described method includes: the scope of data according to input signal, dynamically adjusts soft demodulation correction factor, to calculate the soft demodulating information of QAM mapping data；

The described scope of data according to input signal, dynamically adjusts soft demodulation correction factor α, and the method to calculate the QAM soft demodulating information mapping data comprises the steps:

Acquisition input signal data Data (i), wherein i=1,2,3 ... n；

Described n is total number of data subcarrier in adjacent OFDM symbol in a time slot, one or more, when bandwidth is 2M, and n=522*F；When bandwidth is 8M, n=2610*F；Wherein, F is the OFDM symbol number chosen, 1≤F≤53；

Fall into the ratio η of main region D according to input signal data Data (i), select soft demodulation correction factor α；Described main region D is the border circular areas D on qam constellation mapped plan, and described border circular areas D is:Wherein, I, Q represent the real axis on qam constellation mapped plan and the coordinate figure on imaginary axis direction respectively；

According to the parameter alpha that above-mentioned steps obtains, it is calculated as follows the probabilistic information soft output value of the bit b3 of data Data (i), b2, b1 and b0:

B3=Real (Data (i)),

B2=Imag (Data (i)),

$\begin{array}{cc}b1=abs\left(\mathrm{Re}al\right(Data\left(i\right)\left)\right)& \mathrm{\&alpha;}*2*\frac{1}{c}\end{array},$

$\begin{array}{cc}b0=abs\left(\mathrm{Im}ag\right(Data\left(i\right)\left)\right)& \mathrm{\&alpha;}*2*\frac{1}{c}\end{array},$

Wherein, Real () represents the function in realistic portion, and Imag () represents the function seeking imaginary part, and abs () represents the function seeking absolute value,For the power normalization factor, η is the number ratio with total number of input signal data Data (i) of input signal data Data (i) falling into main region D；

The described ratio η falling into main region D according to input signal data Data (i), the method selecting soft demodulation correction factor α is:

As η > 0.98, α=0.7；

When 0.91 < η≤0.98, α=0.8；

When 0.84 < η≤0.91, α=1；

When 0.75 < η≤0.84, α=1.3；

When 0.69 < η≤0.75, α=1.6；

When 0.65 < η≤0.69, α=2.1；

When 0.60 < η≤0.65, α=2.9；

Otherwise, α=4.1.

2. QAM demodulation method according to claim 1, it is characterised in that the described power normalization factorFor

3. QAM demodulation method according to claim 1, it is characterised in that the computational methods of the described ratio η falling into main region D according to input signal data Data (i) include:

Calculate $\sqrt{\left|\mathrm{Re}al\left(Data\right(i)\right){|}^2+\left|\mathrm{Im}ag\left(Data\right(i)\right){|}^2}=R;$

IfThen represent that input data Data (i) falls into main region D；

Otherwise input data Data (i) does not fall within main region D；

Calculate total number of number/input signal data Data (i) of input signal data Data (i) of η=fall into main region D.