Summary of the invention
The object of the present invention is to provide a kind of employing software approach centering frequency deviation difference to carry out estimation approach and device, realize automatic intermediate frequency estimation of deviation and the carrier deviation of receiving baseband signal is proofreaied and correct.
To achieve the object of the present invention, we provide a kind of carrier deviation bearing calibration of wireless communication system, comprise the steps: a) receiving slot baseband signal; B), calculate the carrier frequency offset estimator according to this phase pushing figure and the chip time interval according to the phase pushing figure between baseband signal estimation portable terminal and the wireless base station; C), carry out carrier deviation and proofread and correct according to the carrier frequency offset estimator.
According to another aspect of the present invention, we provide a kind of carrier deviation means for correcting of wireless communication system, it is connected between the frequency mixer and baseband processor of transceiver equipment, be used for time slot signal sampling according to mobile communication system, calculating carrier frequency offset according to chip-spaced estimates, according to the carrier deviation estimator, the baseband signal that receives is carried out carrier deviation proofread and correct then.
Described device, described carrier deviation estimation unit comprises: carrier deviation estimation module and carrier deviation correction module, wherein said carrier deviation estimation module is used to receive the sampling from time slot signal, calculate carrier frequency offset at certain chip in the time interval, and this deviation is outputed to the carrier deviation correction module; The carrier deviation estimator of described carrier deviation correction module by obtaining carried out carrier deviation to the baseband signal that receives and proofreaied and correct.
Described device, wherein said carrier deviation estimation unit further comprises carrier wave precorrection module, it is connected on the transmission channel between baseband processor and the frequency mixer, be connected with the carrier deviation estimation module simultaneously, the carrier deviation of reception carrier estimation of deviation module output is estimated, the baseband signal that send is carried out carrier wave precorrection.
Described device, described carrier deviation estimation unit comprises: carrier deviation estimation module and AFC module, wherein said carrier deviation estimation module is used to receive the sampling from time slot signal, calculates carrier frequency offset at certain chip in the time interval, and this deviation is outputed to the AFC module; Described AFC module is according to the deviation that receives, calculate frequency correction value that obtains and the relation of controlling voltage of needing, and according to resulting control voltage or digital control word control voltage controlled oscillator, the local frequency that makes frequency mixer is more near the local frequency of transmitter.
Described device, described carrier deviation estimation unit comprises: carrier deviation estimation module, AFC module and carrier deviation correction module, wherein said carrier deviation estimation module is used to receive the sampling from time slot signal, calculate carrier frequency offset according to certain chip in the time interval, and this deviation is outputed to AFC module and carrier deviation correction module; The carrier deviation estimator of described carrier deviation estimation module by obtaining carried out carrier deviation to the baseband signal that receives and proofreaied and correct; Described AFC module is according to the deviation that receives, and calculates the relation that needs the frequency correction value that obtains and control voltage, and according to resulting control voltage or digital control word control voltage controlled oscillator, makes local frequency more near the local frequency of transmitter.
Hence one can see that, the invention provides a kind of mobile terminal side intermediate frequency local oscillator that makes and keep consistent with wireless base station side intermediate frequency local oscillator frequency, and the method and apparatus that baseband signal is proofreaied and correct, different be to use idea of Software Radio, use software that the carrier deviation of portable terminal and wireless base station is estimated, and can realize that parameter can adjust, the terminal that is suitable for different IF is carried out the carrier deviation of AFC and baseband signal and is proofreaied and correct.The inventive method is simple, uses software to realize, because the inventive method is implemented on the baseband signal, so amount of calculation is little, flexibility is good, and is functional, do not need the hardware frequency discriminator, phase discriminator, and perhaps phase-locked loop, cost is low.
Embodiment
Below in conjunction with accompanying drawing specific embodiments of the invention are described.
Need to prove that method and apparatus of the present invention can be applied to the down channel of receiving terminal,, also can be applied to the ascending time slot channel (UpPTS) that the base station receives as the DwPTS (descending guiding time slot) of the terminal of TD-SCDMA system.Embodiments of the invention are that example describes with the DwPTS time slot signal of the down channel of portable terminal receiving terminal mainly, but this embodiment and can be not as a limitation of the invention.
Figure 1 shows that the transmitter principle block diagram, in Fig. 1, S (t) through frequency mixer and local oscillator mixing, obtains intermediate frequency Modulation band-limited signal g (t) for information source simulation complex baseband signal, it is sent into radio-frequency module carry out up-conversion and power amplification, launches then.
Suppose that transmitter local oscillator centre frequency is ω
0, the output signal amplitude is A, then wherein the transmitter modulated intermediate frequency signal can be expressed as:
Fig. 2 is the receiver principle block diagram of first embodiment of the invention, in Fig. 2,
Be expressed as receiver intermediate frequency received signal, with its input mixer, carry out quadrature demodulation after, obtain zero intermediate frequency analog baseband signal Sr (t).If the receiver local frequency is ω
1, then:
Ideally, ω
0=ω
1, therefore can recover the signal that transmitting terminal sends fully, that is:
Yet in actual conditions, do not have the on all four crystal oscillator of frequency characteristic, the local frequency of wireless base station and portable terminal can not full coherent.Cause ω
0≠ ω
1, the analog baseband signal that is obtained in this case should be following form:
Δ ω=ω in the formula
0-ω
1Be the frequency departure between wireless base station and the travelling carriage, Δ =Δ ω t is the phase difference that gives expression in time of frequency departure for this reason.
As mentioned above, because the local frequency characteristic is inconsistent, can cause and in receiver side zero intermediate frequency analog baseband signal, have by the residual modulation voltage of frequency departure, cause baseband signal to be the distortion of amplitude modulation shape, if directly baseband signal is carried out corresponding Base-Band Processing thus, this deviation will be accumulated to the symbol data after the despreading, thereby can cause symbol phase deviation after the despreading to reduce the signal to noise ratio of symbol after the despreading, improve the error rate.
Therefore,, improve communication quality, must remove this frequency departure for correctly obtaining despread data.
The present invention uses software to be implemented in the function that Δ ω is estimated and removed to receiving terminal.Referring to Fig. 2, as can be seen from Figure 2, receiver of the present invention is except comprising RF (radio frequency) module, frequency mixer, local oscillator (this local oscillator is a voltage controlled oscillator) and baseband processor, also comprise a carrier deviation estimation unit, this device is connected between frequency mixer and the baseband processor, is used for the time slot signal sampling according to mobile communication system, calculates carrier frequency offset according to chip-spaced and estimates, according to the carrier deviation estimator, the baseband signal that receives is carried out carrier deviation proofread and correct then.This carrier deviation estimation unit comprises: carrier deviation estimation module, AFC module and carrier deviation correction module, wherein the carrier deviation estimation module is used to receive the sampling from the descending guiding time slot signal of A/D converter (not shown), calculate carrier frequency offset at certain chip in the time interval, and this deviation is outputed to AFC module and carrier deviation correction module; And the carrier deviation estimator of carrier deviation estimation module by obtaining carries out carrier deviation to the baseband signal that receives to proofread and correct; And while AFC module is according to the deviation that receives, calculate frequency correction value that obtains and the relation of controlling voltage or control word of needing, and according to resulting control voltage employing D/A converter (not shown) or digital control word control voltage controlled oscillator, make local frequency more near the local frequency of transmitter, like this, by repeating repeatedly to make local frequency consistent with the local frequency of transmitter.
The idiographic flow of carrier deviation method of estimation of the present invention is described referring to Fig. 6:
At step S61, receive descending guiding time slot (DwPTS) signal of 96chip, and adopt 8 samplings to quantize value, obtain like this
Sr(n)=AS(n)e
jΔamT=AS(n)e
jnΔ (1)
T is the sampling interval in the formula, in the TD-SCDMA system when adopting 8 times of speed samplings, T=0.09765625 μ s.
At step S62, in the carrier deviation estimation module, realize estimation to Δ =Δ ω t, method is:
Carry out normalization to receiving digital baseband by its mould value, and take absolute value, obtain:
f(n)=Sr′(n)=|e
jnΔ| (2)
Receive data to 96*8 and do following computing:
Wherein N is a sampling number, in TD-SCDMA, and N=8
Corresponding each e (n) tries to achieve its phase angle Ψ (n),
ψ(n)=arg[e(n)] (4)
For guaranteeing consistency and the validity of gained departure Δ , be averaged:
At step S63, receiving baseband signal is removed phase deviation:
l(n)=Sr(n)e
-jnΔ (6)
The frequency offset signal l (n) that goes that obtains thus sends into rear end digital baseband processing, and l (n) is the baseband signal of going the overfrequency deviation.
At step S64, the gained result is scaled intermediate frequency control voltage of voltage-controlled oscillator or control word sends into VCO (voltage controlled oscillator) as control voltage, realize AFC.The specific implementation process is as follows: establishing pressuring controlling oscillator frequency/voltage slope is k, according to the phase deviation of gained in the sampling interval:
As can be known: the IF-FRE deviation is:
So according to the characteristic k of local oscillator voltage controlled oscillator, can controlled voltage be:
This is controlled the voltage-controlled input that voltage is sent to local oscillator voltage controlled oscillator (VCO), to adjust local frequency.
At step S65, the reception of beginning next frame data, and repeat above step 1-4.
Need to prove that at this step S63 in above-mentioned steps and S64 not necessarily carry out in proper order, are executed in parallel sometimes, carry out respectively according to the structure of different carrier deviation devices sometimes, this point can be understood in following several embodiment.
Specify below and implement several preferred embodiments of the present invention.
First embodiment
As shown in Figure 2, wherein local oscillator is a voltage controlled oscillator, needs in this embodiment voltage controlled oscillator is controlled, with the difference of the local oscillator of the local oscillator of further dwindling receiver and transmitter.Its concrete operating process is as follows:
1. receive the descending DwPTS signal of 96chip, and adopt 8 samplings to quantize value;
2. in the carrier deviation estimation module, realize estimation, the result of gained is outputed to AFC module and carrier deviation correction module Δ =Δ ω t;
3. the carrier deviation correction module is estimated the baseband signal that receives is removed phase deviation according to the carrier deviation of input, and the signal that will remove deviation is thus sent into rear end digital baseband device and handled;
4.AFC module estimates to be scaled the intermediate frequency control voltage of voltage-controlled oscillator according to the carrier deviation of input or control word is sent into VCO as control voltage, realizes AFC.
Second embodiment
As shown in Figure 3, local oscillator among this embodiment is non-variable-frequency oscillator, can not carry out AFC, in Fig. 3, described carrier deviation estimation unit is different with the carrier deviation device of first embodiment, because it can not carry out AFC, so do not comprise the AFC module in this carrier deviation device, specific operation process is as follows:
1. receive the descending DwPTS signal of 96chip, and adopt 8 samplings to quantize value.
2. realize the estimation to Δ =Δ ω t in the carrier deviation estimation module, the result of gained outputs to the carrier deviation correction module.
3. the carrier deviation correction module is estimated receiving baseband signal is removed phase deviation according to the carrier deviation of input. and the signal of the removal deviation that will obtain is thus sent into rear end digital baseband device and is handled.
The 3rd embodiment
As shown in Figure 4, under the good situation of the frequency stability characteristics of local oscillator, can not need to carry out carrier deviation through AFC and proofread and correct, the AFC control of only carrying out frequency mixer just can realize purpose of the present invention.Therefore, carrier deviation device shown in Figure 4 is compared with first embodiment and is not needed the carrier deviation correction module.Its concrete operating process is as follows:
1. receive the descending DwPTS signal of 96chip, and adopt 8 samplings to quantize value;
2. in the carrier deviation estimation module, realize estimation, resulting result is outputed to the AFC module Δ =Δ ω t;
3. the baseband signal that receives directly being sent into the rear end baseband processor handles;
4.AFC module estimates to be scaled the intermediate frequency control voltage of voltage-controlled oscillator according to the carrier deviation of input or control word is sent into VCO as control voltage, realizes AFC.
The 4th embodiment
As shown in Figure 5, in order to proofread and correct carrier deviation more accurately at mobile communication terminal and base station both sides, consider the transmitting-receiving process in time-division (TD) system and mobile terminal side simultaneously, carry out carrier deviation and proofread and correct (portable terminal is received and handled) and predistortion (portable terminal is sent out processing), in carrier deviation means for correcting shown in Figure 5, different with second embodiment of the invention is to also have a carrier wave precorrection module on the transmission channel between baseband processor and the frequency mixer, it is connected between baseband processor and the frequency mixer, be connected with the carrier deviation estimation module simultaneously, the carrier deviation of reception carrier estimation of deviation module output is estimated, the baseband signal that will send is carried out carrier wave precorrection, make the carrier wave baseband signal of emission approaching consistent like this, to guarantee carrier wave consistency in base station side with the baseband signal of the carrier wave of base station.Its concrete operating process is as follows:
1. receive the descending DwPTS signal of 96chip at receiving slot, and adopt 8 samplings to quantize value;
2. in the carrier deviation estimation module, realize estimation, resulting result is outputed to receive path carrier deviation correction module and sendaisle carrier wave predistortion module Δ =Δ ω t;
3. the carrier deviation correction module is estimated receiving baseband signal is removed phase deviation according to the carrier deviation of input, and the signal of the removal deviation that obtains is thus sent into baseband processor and handled;
4. at transmission time slot, sendaisle carrier wave predistortion module is carried out carrier wave predistortion according to the carrier deviation amount of estimating in the receiving slot to obtain to the baseband signal that needs send, the baseband signal through predistortion that obtains is sent into intermediate frequency Modulation, and on radio frequency, send.
Need to prove at this, though method and apparatus of the present invention is described at descending guiding time slot, but this method and apparatus goes for up guiding time slot (UpPTS) equally, as in up guiding time slot, at first receive the up UpPTS signal of 160chip (chip), that is to say that this device not only can use in terminal, and can use in the base station.Simultaneously, method of the present invention is described and is adopted 8 samplings and according to single-time sampling interval calculation phase deviation and frequency departure, but this method can be used the 2/4/8/16/32/... sampling equally, and phase deviation and frequency departure is calculated according to the 2/4/8/.. sampling interval.
In sum, description of the invention, describe in detail and above-mentioned accompanying drawing be not be used for limiting of the present invention.To those skilled in the art, under instruction of the present invention, can carry out various corresponding modification and can not exceed the spirit and scope of the present invention, but this variation should be included within claim of the present invention and the equivalent scope thereof.