CN102075475A - Combined tracking method for timing deviation and sampling frequency offset - Google Patents
Combined tracking method for timing deviation and sampling frequency offset Download PDFInfo
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- CN102075475A CN102075475A CN2009102018418A CN200910201841A CN102075475A CN 102075475 A CN102075475 A CN 102075475A CN 2009102018418 A CN2009102018418 A CN 2009102018418A CN 200910201841 A CN200910201841 A CN 200910201841A CN 102075475 A CN102075475 A CN 102075475A
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Abstract
The present invention discloses a combined tracking method for timing deviation and sampling frequency offset, which is suitable for a digital mobile multimedia broadcasting system. The method comprises the steps of: according to channel impulse response information obtained by estimation, firstly estimating timing deviation for OFDM symbols and determining timing adjusting information for the next time slot; and then estimating sampling frequency offset according to the position information of the strongest path in the channel impulse response and the timing adjusting information for the last time slot, thereby realizing the combined adjusting of the timing deviation and the sampling frequency offset. The combined tracking method of the invention can not only track a symbol timing error brought by multipath distribution characteristic of a transmission channel, but also track and correct the sampling frequency offset brought by the inconsistency between two local oscillators for transmitting and receiving terminals; stable operation can also be realized even in the time division working mode of a receiver and the receiver can stably work by flexibly changing the estimation size of the sampling frequency offset according to the length of the time division working time of the receiver.
Description
Technical field
The present invention relates to the transmission of wireless signals field, particularly relate to a kind of timing offset of digital mobile multi-media broadcasting system and associating tracking of sampling frequency offset of being applicable to.
Background technology
To OFDM (Orthogonal Frequency Division Multiplexing, OFDM) system, regularly synchronous and sample frequency all is one of its core technology synchronously.Because ofdm system has been introduced Cyclic Prefix as protection at interval, ofdm system is comparatively loose to regularly synchronous requirement.Only in the scope of Cyclic Prefix, change as long as guarantee the original position of FFT (fast Fourier transform) computing window, just can not disturb (ISI) between created symbol.But in wireless propagation environment, because the existence of scattering object on every side, wireless signal can arrive receiver through a plurality of propagation paths usually.Can there be tangible time delay in a plurality of signal copies for receiver receives between them usually.So wireless channel all is a multipath channel usually, and according to the conversion of receiver receiving position and the conversion of communication environments on every side, tangible conversion also can take place in corresponding multipath channel.The multidiameter delay characteristic of channel has increased ofdm system time delay expansion sensitivity, and only first signal copy of guaranteed transmitting signal and last signal copy all drop in the Cyclic Prefix, and ofdm system just can be evaded the influence of intersymbol interference.In order to reduce the influence of this negative factor as far as possible, therefore in the wireless OFDM system of reality, need to reduce regularly synchronous error as far as possible.Common way is to introduce the timing offset track loop to follow the tracks of in the multipath channel conversion trend corresponding to the first footpath of first signal copy in receiver.
And sampling frequency offset is present in all digital communication systems, and the main cause that produces sampling frequency offset is that transmitter and receiver local oscillator between the two exists certain frequency departure and phase deviation.Concerning the OFDM receiver, iff there being the sampling phase deviation, only can cause the phase place rotation of each sub-carrier signal, the OFDM receiver utilizes channel estimating can compensate the influence of this phase place rotation, therefore can not cause too much influence to signal to noise ratio.And if also have sampling frequency deviation simultaneously, concerning digital system, will show as on the time domain in identical duration, bring the increase or the minimizing of sampled point, and the increase of this sampled point or reduce can the progressively accumulation along with the variation of time.This variation can bring the initial moment of system's FFT window to drift about on the one hand, disturbs between created symbol; Can destroy the orthogonality between subcarrier on the other hand, cause inter-carrier interference (ICI, InterCarrier Interference).
The method of at present more general estimation sampling frequency offset is to utilize frequency domain training sequence to obtain the domain channel response of channel, the conjugation multiplication of twice domain channel response before and after utilizing then, after the unfavorable response of removing propagation channel, ask sampling frequency deviation according to residual phase deviation information.This method is applicable to the ofdm system that adopts the time-frequency two-dimensional pilot structure, but needs to increase the channel frequency domain response information that certain storage resources is stored a moment.
Summary of the invention
The technical problem to be solved in the present invention provides a kind of timing offset of digital mobile multi-media broadcasting system and associating tracking of sampling frequency offset of being applicable to, when the signal timing mistake that can cause distributing because of propagation channel multipath distribution character is followed the tracks of, the sampling frequency deviation of the inconsistent generation of transmitting-receiving two-end local oscillator is followed the tracks of and rectified a deviation, even also can steady operation under receiver time-division mode of operation, and can change the estimation size of sampling frequency offset according to the length of operating time receiver time-division neatly, make the receiver steady operation.
For solving the problems of the technologies described above, the associating tracking of timing offset of the present invention and sampling frequency offset comprises the steps:
Step 2, performance number is asked in pointwise to the channel impulse response sequence, and searches maximum performance number and corresponding sampling point position, and this performance number and sampling point position are respectively the power P of most powerful path in the channel impulse response
MaxAnd the position I of most powerful path
Max(n), n is used to identify current time slots constantly;
Step 3, according to average power P
ePower P with most powerful path
MaxObtain the multipath detection threshold ξ of current time slots
1, ξ
1=max (k
1P
e, P
Max/ k
2); Desirable average power P
eK
1Doubly size and most powerful path power P
MaxK
2Higher value in/one size is the multipath detection threshold; Wherein, k
1And k
2Delay character according to propagation channel is configured, and need satisfy k
1And k
2It all is positive number greater than 1;
Step 4, according to multipath detection threshold ξ
1In the channel impulse response sequence, carry out effective diameter identification, promptly select all power greater than multipath detection threshold ξ
1Effective diameter; Find out the first path position I of current time slots multipath in distributing according to described effective diameter
f(n), thus determine the most powerful path time delay τ of current time slots
Max(n), τ
Max(n)=I
Max(n)-I
f(n), I
Max(n) be the position of the most powerful path in the step 2;
Step 5, the first path position I that estimates according to last effective time slot signal
f(n-1) and current time slots estimate the first path position I obtain
f(n), obtain the estimated value D of current time slots timing offset
e=I
f(n)-I
f(n-1), this estimated value being fed back to the timing offset adjustment loop was rectified a deviation to timing offset before next effective time slot signal arrives; The position of estimating the most powerful path of next effective time slot signal simultaneously is I '
Max(n+1)=I
Max(n)+D
e
The position I ' of step 6, the most powerful path estimated according to last effective time slot signal
Max(n) and current time slots estimate to obtain most powerful path position I
Max(n), estimate to obtain both sampling point deviation K=I '
Max(n)-I
Max(n);
Step 7, according to duration T at interval between the twice effective time slot signal in front and back
uWith the sampling point deviation K that estimates, obtain the estimated value γ=K/T of sampling frequency offset
u, feed back this estimated value to digital sample module sample frequency rectified a deviation.
The present invention is directed to Chinese digital mobile multi-media broadcasting system (China Mobile MultimediaBroadcasting, CMMB) time-multiplexed physical frame structure, in conjunction with timing simultaneous techniques and sample frequency simultaneous techniques, realize the estimation of uniting to timing offset and sampling frequency offset.The present invention can be when the signal timing mistake cause be followed the tracks of because propagation channel multipath distribution character distributes, and the sampling frequency deviation of the inconsistent generation of transmitting-receiving two-end local oscillator is followed the tracks of and rectified a deviation.This method is specially adapted to this broadcast system with time-division mode of operation of CMMB.Method of the present invention is different with general ofdm system, a plurality of business are with the identical frequency resource of the mode time division multiplexing of time slot in the CMMB system, receiver can only engrave to receive when the time slot at current business place and send signal, and close the reception link constantly at other, thereby reach the purpose of receiver economize on electricity, so the received signal that receiver receives not is continuous; The present invention can be at this discontinuous received signal, and the estimation size according to changing to the flexible in size of duration sampling frequency offset between the useful signal at interval makes the receiver steady operation.
Description of drawings
The present invention is further detailed explanation below in conjunction with accompanying drawing and embodiment:
Fig. 1 is a CMMB physical layer frame structure schematic diagram;
Fig. 2 is method one an embodiment schematic flow sheet of the present invention.
Embodiment
Referring to shown in Figure 1, according to the protocol definition of CMMB, its physical layer signal is unit with the physical frame, and frame length is 1 second.Each physical frame signal is divided into 40 time slots again, and each time slot duration is 25 milliseconds.The beginning that is fixed on each time slot signal sends two known synchronizing signals, is used for the bearer service data after the synchronizing signal.Each business can take a plurality of time slots and send business datum, takies identical frequency spectrum resource in the mode of time-division and sends broadcasting service.This time-multiplexed physical frame definition helps receiver and adopts time slot handoff technique (Timing Slice) to choose the time slot signal that will receive neatly in a plurality of time slot signals, keeps mourning in silence on other time slot signals, to reduce the power consumption of receiver.But increased simultaneously the requirement to timing offset tracking module and sampling frequency offset tracking module, what make that receiver must also can be stable in flexible and changeable received signal combination estimates timing offset and sampling frequency offset, and is in time rectified a deviation.
Referring to shown in Figure 2, be that example is set forth implementation process of the present invention in one embodiment of this invention with CMMB, specifically comprise the steps:
Step 2, degree of rectificating are the power P of most powerful path in 2048 the channel impulse response
MaxAnd the position I of most powerful path
Max(n).For example, performance number is asked in pointwise to the channel impulse response sequence, and searches the power P of wherein maximum performance number as most powerful path
Max, and corresponding sampling point position is the position I of most powerful path
Max(n), n is used to identify current time slots constantly.
Step 3, according to average power P
ePower P with most powerful path
MaxObtain the multipath detection threshold ξ of current time slots
1, ξ
1=max (k
1P
e, P
Max/ k
2).
Step 4, according to multipath detection threshold ξ
1In the channel impulse response sequence, carry out effective diameter identification, promptly select all power greater than multipath detection threshold ξ
1Effective diameter.Find out the first path position I of current time slots multipath in distributing according to effective diameter
f(n), thus determine the most powerful path time delay τ of current time slots
Max(n)=I
Max(n)-I
f(n).
Step 5, the first path position I that estimates according to last effective time slot signal
f(n-1) and current time slots estimate the first path position I obtain
f(n), obtain the estimated value D of current time slots timing offset
e=I
f(n)-I
f(n-1), this estimated value being fed back to the timing offset adjustment loop was rectified a deviation to timing offset before next effective time slot signal arrives; Simultaneously, the position of estimating the most powerful path of next effective time slot signal is I '
Max(n+1)=I
Max(n)+D
e
The position I ' of step 6, the most powerful path estimated according to last effective time slot signal
Max(n) and current time slots estimate to obtain most powerful path position I
Max(n), obtain both sampling point deviation K=I '
Max(n)-I
Max(n).
Step 7, according to duration T at interval between the twice effective time slot signal in front and back
uWith the sampling point deviation K that estimates, obtain the estimated value γ=K/T of sampling frequency offset
u, feed back this estimated value to digital sample module sample frequency rectified a deviation.
Here interval duration T between twice effective time slot signal before and after
uSpan from 25 milliseconds to 1 second, minimum change of scale is 25 milliseconds.If former and later two time slots all are effective received signals, so between former and later two effective time slot signals at interval duration be 25 milliseconds, the sampling frequency deviation of K the big or small 40*K of sampling point deviation correspondence then, unit is a hertz.If only comprise the useful signal of a time slot in 1 second the physical frame of duration, the interval duration between former and later two effective time slots is 1 second so, and then K the corresponding size of sampling point deviation is the sampling frequency deviation of K, and unit is a hertz.This shows that even under the time slot mode of operation, receiver also can change the estimation size of sampling frequency offset neatly according to the variation of duration at interval between effective time slot signal, reaches the purpose of steady operation.
In described step 6, if the sampling point deviation K that estimates to obtain is greater than a certain given threshold k
1The time, can think that a same time slot signal of current time slots signal compares, great changes have taken place in most powerful path, can force to set K=0 this moment, even to guarantee that the sampling frequency offset loop also keeps steady operation under the fast time variant channel.
More than by embodiment the present invention is had been described in detail, but these are not to be construed as limiting the invention.Under the situation that does not break away from the principle of the invention; those skilled in the art also can make many distortion and improvement; for example; though being example with CMMB, top description specifically sets forth embodiments of the present invention; but thought of the present invention is not limited in CMMB; can be applicable to the ofdm system that other have training sequence, these also should be considered as protection scope of the present invention.
Claims (2)
1. the associating tracking of timing offset and sampling frequency offset is characterized in that, comprises the steps:
Step 1, in the current time slots signal, obtain the channel impulse response sequence that length is N according to the synchronizing signal that comprises, and ask the average power P of channel impulse response sequence
e
Step 2, ask the power P of most powerful path in the channel impulse response
MaxAnd the position I of most powerful path
Max(n), n is used to identify current time slots constantly;
Step 3, according to average power P
ePower P with most powerful path
MaxObtain the multipath detection threshold ξ of current time slots
1, ξ
1=max (k
1P
e, P
Max/ k
2); Wherein, k
1And k
2Delay character according to propagation channel is configured, and need satisfy k
1And k
2It all is positive number greater than 1;
Step 4, according to multipath detection threshold ξ
1In the channel impulse response sequence, carry out effective diameter identification, promptly select all power greater than multipath detection threshold ξ
1Effective diameter; Find out the first path position I of current time slots multipath in distributing according to described effective diameter
f(n), thus determine the most powerful path time delay τ of current time slots
Max(n)=I
Max(n)-I
f(n);
Step 5, the first path position I that estimates according to last effective time slot signal
f(n-1) and current time slots estimate the first path position I obtain
f(n), obtain the estimated value D of current time slots timing offset
e=I
f(n)-I
f(n-1), this estimated value being fed back to the timing offset adjustment loop was rectified a deviation to timing offset before next effective time slot signal arrives; The position of estimating the most powerful path of next effective time slot signal simultaneously is I '
Max(n+1)=I
Max(n)+D
e
The position I ' of step 6, the most powerful path estimated according to last effective time slot signal
Max(n) and current time slots estimate to obtain most powerful path position I
Max(n), estimate to obtain both sampling point deviation K=I '
Max(n)-I
Max(n);
Step 7, according to duration T at interval between the twice effective time slot signal in front and back
uWith the sampling point deviation K that estimates, obtain the estimated value γ=K/T of sampling frequency offset
u, feed back this estimated value to digital sample module sample frequency rectified a deviation.
2. method according to claim 1 is characterized in that: the sampling point deviation K that estimates to obtain when step 6 is greater than a certain given threshold k
1The time, think that then a same time slot signal of current time slots signal compares most powerful path great changes have taken place, force to set K=0 this moment, even to guarantee that the sampling frequency offset loop also keeps steady operation under the fast time variant channel.
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| CN102255864A (en) * | 2011-08-30 | 2011-11-23 | 豪威科技(上海)有限公司 | Low-complexity general sampling recovery method and device |
| CN102685875A (en) * | 2012-05-03 | 2012-09-19 | 京信通信系统（中国）有限公司 | Method and device for timing synchronization adjustment between base stations |
| CN104735011A (en) * | 2013-12-24 | 2015-06-24 | 卓胜微电子（上海）有限公司 | Device and method for sample frequency deviation robust estimation in complex channel environment |
| CN105897304A (en) * | 2016-05-31 | 2016-08-24 | 西安空间无线电技术研究所 | Rapid sync method of frequency hopping communication system |
| CN109525524A (en) * | 2018-06-28 | 2019-03-26 | 大唐联仪科技有限公司 | A kind of signal synchronizing method and device |
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| CN102685875B (en) * | 2012-05-03 | 2015-07-15 | 京信通信系统（中国）有限公司 | Method and device for timing synchronization adjustment between base stations |
| CN104735011A (en) * | 2013-12-24 | 2015-06-24 | 卓胜微电子（上海）有限公司 | Device and method for sample frequency deviation robust estimation in complex channel environment |
| CN104735011B (en) * | 2013-12-24 | 2019-01-29 | 江苏卓胜微电子股份有限公司 | Device and method for Robust Estimation sampling frequency deviation under Complex Channel environment |
| CN105897304A (en) * | 2016-05-31 | 2016-08-24 | 西安空间无线电技术研究所 | Rapid sync method of frequency hopping communication system |
| CN109525524A (en) * | 2018-06-28 | 2019-03-26 | 大唐联仪科技有限公司 | A kind of signal synchronizing method and device |
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| CN102075475B (en) | 2013-04-24 |
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Effective date of registration: 20151111 Address after: 214072 Jiangsu province Binhu District of Wuxi City Liyuan Development Zone 530 No. 1 building twelve room 1203 Patentee after: JIANGSU MAXSCEND TECHNOLOGY CO., LTD. Address before: 201203, 7 floor, building No. 4, Zhang Jiang microelectronics port, No. 690 blue wave road, Shanghai, Pudong New Area Patentee before: Maxscend Technologies Inc. |
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Address after: 214072 Jiangsu province Binhu District of Wuxi City Liyuan Development Zone 530 No. 1 building twelve room 1203 Patentee after: Jiangsu Zhuo Sheng microelectronics Limited by Share Ltd Address before: 214072 Jiangsu province Binhu District of Wuxi City Liyuan Development Zone 530 No. 1 building twelve room 1203 Patentee before: JIANGSU MAXSCEND TECHNOLOGY CO., LTD. |
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