CN102387113B - Digital AGC (automatic gain control) rapid adjustment method applied to OFDM (orthogonal frequency division multiplexing) - Google Patents
Digital AGC (automatic gain control) rapid adjustment method applied to OFDM (orthogonal frequency division multiplexing) Download PDFInfo
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Abstract
The invention relates to a digital AGC (automatic gain control) rapid adjustment method applied to OFDM (orthogonal frequency division multiplexing), which comprises the following steps of: (1) calculating the power of a received signal by way of combining FIR (finite impulse response) and IIR (infinite-duration impulse response); (2) converting the power of the received signal into a corresponding logarithmic form p_dB (n); and (3) comparing the power of the current signal with an ideal power of the signal so as to obtain a difference value, then calculating a corresponding adjusted gain value according to the difference value, and carrying out feedback adjustment. In the invention, the power of the received signal is calculated by way of combining FIR and IIR, so that a good compromise between an adjusted speed and adjusted stability can be found.
Description
Technical field
The present invention relates to the radio sensing network communications field, particularly relate to the digital Auto Gain control fast adjustment method in a kind of OFDM of being applied to.
Background technology
Wireless sensor network (Wireless Sensor Network, be called for short " WSN ") " intelligence " network of being formed by the microsensor node with radio communication, perception and computing capability, it relates to, and multidisciplinary height intersects, the integrated hot research field, forward position of knowledge height, has now been widely used in the various fields such as military affairs, agricultural, environment measuring, health care, industry, intelligent transportation.Along with the application of wireless sensor network, the distance of communication is increased, the speed of communication is increased, generally adopt at present OFDM (Orthogonal Frequency Division Multiplexing is called for short " OFDM ") communication system for middle-high speed wireless sensor network application.
OFDM technology puts forward in eighties of last century 50～sixties.Whole transmission bandwidth is divided into a series of mutually orthogonal subcarriers by it, needs only the shared bandwidth of single sub-carrier enough narrow, and the channel frequency response on it just can be regarded as smooth.Frequency selective fading channels is converted into a series of flat fading sub-carrier channels like this.Each time domain OFDM symbol is sent to before transmission, add the Cyclic Prefix that is greater than the expansion of channel maximum delay, can eliminate in radio communication, due to the channel multi-path serious intersymbol interference that causes (Inter-Symbol Interference is called for short " ISI ") that declines.But that OFDM receiver performance is affected by signal amplitude size is larger, the signal amplitude that receives is excessive or too smallly all can produce considerable influence to receptivity, causes the even frame losing of the larger error rate.Therefore need to carry out automatic gain control (Automatic Gain Control is called for short " AGC ") at receiver, signal amplitude can be adjusted to automatically to the scope that is applicable to demodulation, receptivity can not occur to affect because signal is excessive, too small.
AGC method of adjustment is mainly divided into two classes, and the first kind is simulation AGC, and Equations of The Second Kind is digital AGC.Simulation AGC is that radio-frequency head is surveyed the amplitude that receives signal by analog circuit, automatically generate corresponding feedback adjusting voltage according to the amplitude detecting, and then the voltage of adjusting radio frequency VGA, change radio circuit voltage gain, make to receive signal amplitude and meet demodulation requirement; Digital AGC is that baseband module is by the digital signal receiving, detect digital signal amplitude, calculate in requisition for the amplitude difference of adjusting by digital algorithm, calculate the digital value of feedback voltage, after transforming, DA controls VGA, change radio circuit voltage gain, make to receive signal amplitude and meet demodulation requirement.Because digital AGC is realized simply, regulate the speed fast, obtain increasing application, be particularly suitable for resource-constrained wireless sensor network application.AGC method is regulated the speed and stability is double-edged sword, regulate the speed fast, can stablize in the short period of time and receive signal amplitude, can reduce AGC and adjust expense, improve data user rate, but it is fast to regulate the speed, and will cause larger fluctuation, less noise all may cause that mistuning is whole, poor stability.Vice versa.
Summary of the invention
Technical problem to be solved by this invention is to provide the digital Auto Gain control fast adjustment method in a kind of OFDM of being applied to, and the stability that can occasionally find AGC to adjust and the compromise of regulating the speed reduce because signal amplitude changes caused performance decline.
The technical solution adopted for the present invention to solve the technical problems is: the fast adjustment method of the digital Auto Gain control in a kind of OFDM of being applied to is provided, comprises the following steps:
(1) mode of utilizing FIR and IIR to combine is calculated the power that receives signal;
(2) received signal power is changed into corresponding logarithmic form p_dB (n);
(3) compare the power of current demand signal and the ideal power difference of signal, calculate the corresponding yield value of adjusting according to difference, carry out feedback adjusting.
In described step (1), replaced the power of signal by amplitude amount, the power of described signal is p (n)=(1-ρ) p (n-1)+ρ z (n), wherein, ρ is weighted factor, 0 < ρ < 1, z (n) is the range value amount of single sampled point signal.
Described weighted factor ρ=0.125.
The range value amount of described single sampled point signal
M is progressive average, with regulate the speed relevant, M >=0; Y (n) is for receiving signal.
Described reception signal y (n) is complex signal, by I, and Q two-way composition, the range value amount of described single sampled point signal
In described step (2), pass through form p_dB (the n)=log of logarithm
10(p (n)).
In described step (3), the feedback adjusting in n+1 moment gain output valve is A (n+1), A (n+1)=(1-α) A (n)+α [R-p_dB (n)], wherein, A (n) is the yield value of exporting in the n moment, α is weighted factor, 0 < α < 1, logarithm value corresponding to ideal power that R is signal.
Feedback adjusting is two sections of adjustment methods in described step (3), and first paragraph is coarse regulation, judges whether signal transships, excessive or too small; Second segment is fine control, after first paragraph adjustment completes end, carries out.
Beneficial effect
Owing to having adopted above-mentioned technical scheme, the present invention compared with prior art, there is following advantage and good effect: the mode that the present invention adopts FIR and IIR to combine is calculated the power that receives signal, can regulate the speed and adjust between stability and find one to compromise preferably.The present invention utilizes the amplitude amount of signal to replace quantity of power, by adopting Taylor expansion close approximation, can in meeting performance, greatly reduce the complexity realizing.The present invention adopts two sections of methods of adjustment, adapts to dynamic range large, regulates the speed fast, can comparatively fast stablize simultaneously.
Brief description of the drawings
Fig. 1 is the structural representation of realizing the inventive method;
Fig. 2 is flow chart of the present invention.
Embodiment
Below in conjunction with specific embodiment, further set forth the present invention.Should be understood that these embodiment are only not used in and limit the scope of the invention for the present invention is described.In addition should be understood that those skilled in the art can make various changes or modifications the present invention after having read the content of the present invention's instruction, these equivalent form of values fall within the application's appended claims limited range equally.
The present invention relates to the digital Auto Gain control fast adjustment method in a kind of OFDM of being applied to, below a specific embodiment of the present invention in wireless sensor network application is elaborated.
Fig. 1 is that numeral is adjusted the structural representation that gain is controlled automatically, and it adopts OFDM to communicate, and this digital auto gain control method is negative feedback.Shown in Fig. 2 is method flow of the present invention:
First estimate the power that receives signal, in the present embodiment, adopt range value to replace quantity of power, to reduce the complexity of calculating.After signal power is the amplitude by obtaining single sampled point, then obtain the amplitude signal p (n) through certain filtering elimination high-frequency impulse noise jamming by IIR method, replace the power of signal with this amplitude signal.The power of signal is p (n)=(1-ρ) p (n-1)+ρ z (n), wherein, ρ is weighted factor, 0 < ρ < 1, the specific value of establishing ρ=0.125, z (n) is the range value amount of single sampled point signal, and its computing formula is
wherein, the reception signal of y (n) for transforming through AD, please illustrate Re[] representative gets real part and Im[] representative gets the portion that needs.Reception signal y (n) in the present embodiment is complex signal, by I, and Q two-way composition, therefore its computing formula utilizes FIR method can be changed into
Wherein, M is progressive average, with regulate the speed relevant, M >=0, and along with adjusting the difference of hop count difference, in first paragraph adjustment, M value is less, make can faster speed adjustment, concrete span is according to the difference of sampling rate and difference, in the system that the sampling rate of setting is in the present embodiment 20MHz, first paragraph adjusted value M value is 2,4,8,16,32 ...; During second segment is adjusted, M value is larger, is greater than the adjustment value of first paragraph, makes to adjust to have higher stability.
As can be seen here, the mode that the present invention adopts FIR and IIR to combine is calculated the power that receives signal, can regulate the speed and adjust between stability and find one to compromise preferably.The present invention utilizes the amplitude amount of signal to replace quantity of power, by adopting Taylor expansion close approximation, can in meeting performance, greatly reduce the complexity realizing.
For the difference of adjusting hop count, after wait different time, the amplitude amount of signal is converted into logarithm component, the time that first paragraph is waited for is shorter, and the second segment stand-by period is greater than first paragraph, and stand-by period and M are worth arranging similar.After logarithm transforms, logarithmic form p_dB (the n)=log obtaining
10(p (n)).
Obtain when after the signal amplitude value in region the last period, by more current amplitude amount and the desirable amplitude components gap requiring, the corresponding adjustment yield value that obtains feedback.The feedback adjusting gain output valve in n+1 moment is A (n+1), A (n+1)=(1-α) A (n)+α [R-p_dB (n)], wherein A (n) is the yield value of exporting in the n moment, α is weighted factor, 0 < α < 1, R is the logarithm value corresponding to desirable amplitude of signal, the value of R is relevant with the resolution of AD converter, and the signal amplitude requiring in OFDM can be set to R=log
10(0.75*2
n), the figure place that wherein N is AD converter.In feedback adjusting process, adopt two sections of adjustment methods to adjust, first paragraph is coarse regulation, regulates the speed fast, adjusts precision low, mainly judges whether signal transships, excessive or too small; Second segment is fine control, regulates the speed slow, adjusts precision high, substantially information is adjusted constantly, only after first paragraph adjustment completes end, enters second segment adjustment again.Be not difficult to find, the present invention adopts two sections of methods of adjustment, adapts to dynamic range large, regulates the speed fast, can comparatively fast stablize simultaneously.
Claims (5)
1. be applied to the digital Auto Gain control fast adjustment method in OFDM, it is characterized in that, comprise the following steps:
(1) mode of utilizing FIR and IIR to combine is calculated the power that receives signal; Wherein, after the power of signal is the amplitude by obtaining single sampled point, eliminated after filtering again the amplitude signal p (n) of high-frequency impulse noise jamming by IIR method, p (n)=(1-ρ) p (n-1)+ρ z (n), wherein, ρ is weighted factor, 0 < ρ < 1, and z (n) is the range value amount of single sampled point signal; The range value amount of described single sampled point signal
m is progressive average, with regulate the speed relevant, M>=0; Y (n) is for receiving signal; Described reception signal y (n) is complex signal, and by I, Q two-way composition, utilizes the range value amount of described single sampled point signal of FIR method
(2) received signal power is changed into corresponding logarithmic form p_dB (n);
(3) compare the power of current demand signal and the ideal power difference of signal, calculate the corresponding yield value of adjusting according to difference, carry out feedback adjusting.
2. the digital Auto Gain control fast adjustment method being applied in OFDM according to claim 1, is characterized in that described weighted factor ρ=0.125.
3. the digital Auto Gain control fast adjustment method being applied in OFDM according to claim 1, is characterized in that, passes through form p_dB (the n)=log of logarithm in described step (2)
10(p (n)).
4. the digital Auto Gain control fast adjustment method being applied in OFDM according to claim 1, it is characterized in that, in described step (3), the feedback adjusting in n+1 moment gain output valve is A (n+1), A (n+1)=(1-α) A (n)+α [R-p_dB (n)], wherein, A (n) is the yield value of exporting in the n moment, α is weighted factor, 0 < α < 1, logarithm value corresponding to ideal power that R is signal.
5. the digital Auto Gain control fast adjustment method being applied in OFDM according to claim 1, is characterized in that, feedback adjusting is two sections of adjustment methods in described step (3), and first paragraph is coarse regulation, judges whether signal transships, excessive or too small; Second segment is fine control, after first paragraph adjustment completes end, carries out.
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| CN101257472A (en) * | 2008-04-09 | 2008-09-03 | 浙江大学 | Orthogonal frequency division multiplexing receiver system and its automatic gain control method |
| CN101490997A (en) * | 2006-07-14 | 2009-07-22 | 高通股份有限公司 | Multi-carrier receiver for wireless communication |
| CN101895507A (en) * | 2010-08-09 | 2010-11-24 | 复旦大学 | Orthogonal frequency division multiplexing receiver system and automatic gain control method thereof |
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| CN101490997A (en) * | 2006-07-14 | 2009-07-22 | 高通股份有限公司 | Multi-carrier receiver for wireless communication |
| CN101257472A (en) * | 2008-04-09 | 2008-09-03 | 浙江大学 | Orthogonal frequency division multiplexing receiver system and its automatic gain control method |
| CN101895507A (en) * | 2010-08-09 | 2010-11-24 | 复旦大学 | Orthogonal frequency division multiplexing receiver system and automatic gain control method thereof |
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