CN1852406A - Method for controlling digital automatic electric-level gain - Google Patents

Abstract

A digital automatic level gain control method belongs to the technical field of digital signal transmission. The present invention is realized by an automatic level gain control loop, and the automatic level gain control loop includes two complex multipliers, a square root detector, a logarithmic operator, a real number subtractor, a real multiplier, an integral Device, and antilog operator; the complex signal obtained after signal demodulation is composed of I road and Q road, which is (XI(n)+jXQ(n)), and multiplied by the control signal M of digital AGC, Obtain the output signal (YI(n)+jYQ(n)); send it to a signal power detector, take the square of the imaginary and real parts, add them up, and take the logarithm; then subtract it from a preset reference value R, Get the error signal ERR; multiply it by a gain value K; average again; take the logarithm of the output to get the AGC control signal M; this method effectively controls and compensates the received signal level, reducing the signal power range of fluctuations. And can be widely used in the data level control of each module of the system.

Description

Control Method of Digital Automatic Level Gain

technical field

The invention relates to a method in the technical field of digital signal transmission, in particular to a digital automatic level gain control method suitable for a digital television terrestrial broadcast receiver.

technical background

In a high-speed digital signal wireless transmission system, such as digital high-definition television (HDTV), the signal is affected by the transmission channel during the wireless transmission process, and has been affected by the use of the receiving antenna. The signal power at the receiving end will have a wide range. fluctuation. In actual situations, for example, in the case of vehicle movement, when entering and leaving the shelter of a building, the receiver is likely to receive a signal level of 3uV at a certain moment, and at another moment, it may just leave the building The signal received by the occlusion may be 1V. Therefore, an adjustment range of nearly 110dB is required for the received signal. Figure 1 shows the spectrum diagram of ADTB-T OQAM system data plus double pilot, which illustrates the relative amplitude of the spectrum. But the problem is that in the receiver, due to the limited quantization precision of the A/D converter, the signal range that can be represented is smaller than the dynamic range of the received signal amplitude. Therefore, an automatic level gain control AGC circuit is commonly used in the receiver to control and compensate the received signal level.

Generally speaking, AGC can be divided into two types according to the form of control signal: namely, analog AGC and digital AGC. In practical applications, the combination of analog AGC and digital AGC is often used to work. Coarse adjustment with analog AGC and fine adjustment with digital AGC. The present invention is mainly based on digital AGC adjustment as a fine adjustment link.

After searching the literature of the prior art, it was found that in the Chinese patent "AGC circuit" published on February 16, 2005 with the patent number "CN200410056346.X", an AGC-controlled circuit was proposed. The control signal in the AGC proposed by this patent is an analog signal, which can be adjusted in a large range, but if it is applied to the ADTB-T advanced digital terrestrial broadcasting system, the accuracy may not be enough.

ADTB-T advanced digital terrestrial broadcasting system, its transmission system is based on OQAM offset quadrature amplitude modulation. Since the OQAM coherent demodulation is processed to output two channels of I and Q, the control information can be jointly extracted from the signals of the I and Q channels. However, VSB actually only has one channel signal available, and the available information is less. However, the I and Q paths of the QAM modulation system are independent of each other and do not form a Hilbert change relationship. Therefore, in the application of ADTB-T advanced digital terrestrial broadcasting system, it is possible to make full use of I and Q two-way information to improve the performance of the AGC control circuit.

Contents of the invention

Aiming at the deficiencies of the prior art, the invention provides a digital automatic level gain control method of a receiver in digital TV terrestrial broadcasting. The invention solves the problem that the signal power of the receiving end will fluctuate in a large range due to the influence of the transmission channel during the wireless transmission process of the digital signal, thereby affecting the receiving quality.

The present invention is realized by adopting the following technical solutions. A digital automatic level gain control method suitable for digital television terrestrial broadcast receivers includes: adjusting the received signal through an automatic level gain control loop; Wherein, the automatic level gain control loop includes: two complex multipliers, a square root detector, a logarithmic operator, a real number subtractor, a real multiplier, an integrator, and an antilogarithmic operator The complex signal that the OQAM signal is processed after demodulation in the receiver is made up of two-way signals, and they are respectively I road and Q road, and complex signal is expressed as (XI(n)+jXQ(n)); Above-mentioned complex signal Respectively through a complex multiplier, multiplied by the control signal M of the digital AGC to obtain the output signal (YI(n)+jYQ(n)); the signal is sent to a signal power detector, and the real part and the imaginary part are respectively After taking the square and adding, what is basically obtained is the signal power; taking the logarithm of the above signal power; subtracting the logarithmic signal power from a preset reference value R to obtain an error signal ERR; The signal is sent to a real multiplier and multiplied by a gain value K; the output of the above real multiplier is then sent to an integrator for averaging to reduce noise interference; the control signal of the digital AGC is obtained after the logarithm operation is performed on the output of the above integrator M; send the control signal M of the digital AGC back to the multiplexer of the I and Q paths, so that the signal level of the output (YI(n)+jYQ(n)) remains stable.

In the ADTB-T advanced digital terrestrial broadcasting system, in the receiver of the OQAM offset quadrature amplitude modulation splitting system, a digital automatic level gain control loop is used after A/D sampling to quantize the quantized data after A/D Estimate the size based on the statistical average, that is, the square of the sampled data (that is, the power of the signal), and use this mean as a direct estimate of the signal power.

The automatic level gain control loop (AGC loop) can be to carry out the automatic level gain control to the data after the down-conversion of the receiver and the A/D sampling, also can be the carrier wave after the A/D sampling Data recovery loop for automatic level gain control.

In the digital automatic level gain control method of the present invention, the preset reference value R can select the average signal power of the data information transmitted by the system. The preset reference value R may also be selected as 20.

The beneficial effect of the scheme of the present invention is that the given digital automatic level gain control means can effectively control and compensate the received signal level, reduce the fluctuation range of the signal power, and adopt the digital control signal at the same time, which has a relatively High precision. And can be widely used in the data level control of each module of the system.

Description of drawings

Figure 1 is the spectrum diagram of ADTB-T OQAM system data plus double pilot

Fig. 2 is the digital AGC loop that adopts in the inventive method

Detailed ways

The present invention will be further described below in conjunction with the examples.

The present invention adjusts the received signal through an automatic level gain control loop, and Fig. 2 shows a digital AGC loop adopted in the method of the present invention. The AGC loop includes two complex multipliers, a square root detector, a logarithmic operator, a real number subtractor, a real multiplier, an integrator, and an antilog operator, and the control method is specifically:

In a communication system based on OQAM modulation, after the OQAM signal arrives at the receiver, it is demodulated first, and the complex signal obtained after demodulation is composed of two signals of I and Q, using (XI(n)+jXQ(n) ) to represent; (XI(n)+jXQ(n)) The I and Q two-way signals formed by (XI(n)+jXQ(n)) pass through a multiplexer respectively, and are multiplied with the control signal M of the digital AGC to obtain the output signal (YI(n)+jYQ (n)), this control signal M comes from the output of the AGC loop; the signal (YI(n)+jYQ(n)) is sent to a signal power detector, and the real and imaginary parts are squared and added. Basically what is obtained is the signal power; take the logarithm of the above signal power; subtract the logarithmic signal power from a preset reference value R to obtain an error signal ERR; send the above error signal into a real multiplier Multiplier, multiplied by a gain value K; the output of the above-mentioned real multiplier is sent to an integrator for averaging to reduce noise interference; the control signal M of the digital AGC is obtained after the logarithmic operation of the output of the above-mentioned integrator; the digital AGC The control signal M is sent back to the multiplexer of the I and Q paths, so that the signal level of the output (YI(n)+jYQ(n)) remains stable.

In the above process, if the power of the input signal detected by the receiver is less than the expected power, the result after taking the logarithm is subtracted from the preset reference value R to obtain a positive number. After going through the real multiplier and integrator, it is still a positive number. After the operation of negating the antilog, the positive number finally becomes a number M greater than 1. This M will be used as a control signal and multiplied with the input signal to increase the energy of the input signal.

Conversely, if the power of the input signal detected by the receiver is greater than the expected power, then the logarithmic result is subtracted from the preset reference value R to obtain a negative number. After going through the real multiplier and integrator, it is still a negative number. After the antilog operation, the negative number finally becomes a number M less than 1. This M will be used as a control signal and multiplied with the input signal to reduce the energy of the input signal.

Finally, through the continuous adjustment of the loop, if the setting of the loop parameters is appropriate, the input signal power will be equal to the expected power, and then the result after taking the logarithm and subtracting the preset reference value R will be zero. After going through the real multiplier and integrator, it is still zero. The control signal M becomes 1, and the energy of the input signal remains constant on average.

The logarithm and antilog operations are used in the loop to make the control signal M adjust the input signal through multiplication. Without the logarithm and antilog operations, the control signal would be adding and subtracting to condition the input signal. Generally speaking, the use of multiplication can greatly improve the convergence speed and convergence results of the loop.

The integrator in the loop functions as an averager. Because the signal is randomly distributed, the average energy has practical research significance. It is also beneficial to improve the convergence speed of the loop.

Claims (4)

1. the control method of a digital automatic electric-level gain, it is characterized in that: realize received signal is regulated by an automatic electric-level gain control loop, in based on the OQAM communication system for modulation, the OQAM signal arrives after the receiver, at first pass through demodulation, form by I and Q two paths of signals through the complex signal that the demodulation reprocessing obtains, represent with (XI (n)+jXQ (n)); I that (XI (n)+jXQ (n)) forms and Q two paths of signals are respectively through a multiplier, multiply each other with the control signal M of digital AGC, obtain output signal (YI (n)+jYQ (n)), this control signal M is from the output of AGC loop, (YI (n)+jYQ (n)) sends into a signal power detector with signal, to real part and each squared back addition of imaginary part;

What obtain basically is signal power, and above-mentioned signal power is taken the logarithm, and the signal power after taking the logarithm and a reference value R who sets in advance are subtracted each other, and obtains an error signal ERR; Above-mentioned error signal is sent into a reality take advantage of device, be multiplied by a yield value K; Above-mentioned reality is taken advantage of device output to send into an integrator again and is done on average, to cut down noise jamming, to obtaining the control signal M of this digital AGC after the operation of above-mentioned integrator output negate logarithm, the control signal M of digital AGC is sent back to the multiplier on I and Q road, make the signal level of output (YI (n)+jYQ (n)) keep stable.

2. the control method of digital automatic electric-level gain according to claim 1, it is characterized in that, described automatic electric-level gain control loop, be to after the receiver down-conversion and the data after the A/D sampling carry out automatic electric-level gain control, or the data in the A/D sampling back institute tool carrier recovery loop are carried out automatic electric-level gain control.

3. the control method of digital automatic electric-level gain according to claim 1 is characterized in that, the average power signal of the data message of the reference value R selective system transmission that sets in advance.

4. according to the control method of claim 1 or 3 described digital automatic electric-level gains, it is characterized in that the reference value R that sets in advance is chosen as 20.

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