CN101951358B  OFDM (Orthogonal Frequency Division Multiplexing) timing synchronous system based on noise subspace  Google Patents
OFDM (Orthogonal Frequency Division Multiplexing) timing synchronous system based on noise subspace Download PDFInfo
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 CN101951358B CN101951358B CN201010501412A CN201010501412A CN101951358B CN 101951358 B CN101951358 B CN 101951358B CN 201010501412 A CN201010501412 A CN 201010501412A CN 201010501412 A CN201010501412 A CN 201010501412A CN 101951358 B CN101951358 B CN 101951358B
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Abstract
The invention discloses an OFDM timing synchronous system based on a noise subspace, comprising a fast Fourier transformation device, a phase compensation and conciliation device, a fast Fourier inverse transformation device, a square device, an addition device and a window minimum searching device, wherein the fast Fourier transformation device, the phase compensation and conciliation device, the fast Fourier inverse transformation device, the square device, the addition device and the window minimum searching device are sequentially connected. By introducing a noise subspace concept, the influence on an estimation result by multipath intersymbol interference is removed, thereby unbiased timing synchronous information can be obtained; and the Fourier positive/inverse transformation device has the characteristics of a highefficiency implementation structure and a fast algorithm, and the system implementation complexity is reduced by adopting large numbers of Fourier positive/inverse transformation devices. The timing synchronous system can be used for various block mode transmission systems including OFDM, with cyclic prefixes.
Description
Technical field
What the present invention relates to is the simultaneous techniques field timing synchronization sytem in a kind of mobile communication, in particular a kind of OFDM timing synchronization sytem based on noise subspace.
Background technology
Regularly be the prerequisite of GSM ability proper communication synchronously.In order to support highspeed data service, future mobile communication system will adopt the system of broadband, many (sending and receiving) antenna, and OFDM (OFDM) is the important candidate scheme of future mobile communication system.In ofdm system, traditional timing simultaneous techniques mainly is through training sequence is carried out autocorrelation computation, and the method for seeking peak value then finds the starting point of symbol.This timing simultaneous techniques can be worked finely in Gaussian channel, but for multidiameter fading channel, because related operation can't be removed the influence of disturbing between multipath, so the timing synchronizing information that obtains has inclined to one side.The present invention utilizes channel estimating to have the characteristics of noise subspace, has proposed a kind of timing synchronization sytem based on noise subspace.Because this technology can be removed the influence of disturbing between multipath effectively, so the timing synchronizing information that obtains is no inclined to one side.
Summary of the invention
Goal of the invention: the deficiency that the objective of the invention is to overcome prior art; A kind of OFDM timing synchronization sytem based on noise subspace is provided; Based on the highprecision symbol original position method of estimation of noise subspace, the timing simultaneous techniques that a kind of fast and reliable is provided, estimated accuracy is high, implementation complexity is low, is applicable to ofdm system.
Technical scheme: the present invention realizes through following technical scheme; The present invention includes fast fourier transformation apparatus, phase compensation reconciliation device, inverse fast fourier transform device, squaring device, adder and window minimum value searcher, wherein: fast fourier transformation apparatus, phase compensation reconciliation device, inverse fast fourier transform device, squaring device, adder link to each other with window minimum value searcher successively;
Described fast fourier transformation apparatus, the i of difference acknowledge(ment) signal, i+1; ...; I+G sampled point is that starting point is carried out the N point fast Fourier and changed (FFT), the frequencyregion signal that to obtain G+1 length be N, and i is any sampling location of reception signal in the window; G is the length of Cyclic Prefix, and N is the subcarrier number of ofdm system;
Device is conciliate in described phase compensation, and each subcarrier of each frequencyregion signal is carried out the respective phase compensation by sideplay amount and subcarrier sequence number, then to the frequencyregion signal after compensating divided by the known training sequence of receiving terminal;
Described inverse fast fourier transform device is done the inverse fast fourier transform (IFFT) that M is ordered to the frequencyregion signal of removing behind the modulation symbol, the timedomain signal that to obtain G+1 length be M, and M is the subcarrier number that training sequence takies;
Described squaring device is to MG mould square summation that is worth of each timedomain signal afterbody;
Described adder, to G+1 value obtaining in the squaring device with, be designated as ρ
_{i}
The ρ of minimum in the described window minimum value searcher, search window
_{i}, the start position of timing output OFDM symbol.
The length G of described Cyclic Prefix is greater than the maximum delay expansion of wireless multipath channel.
The subcarrier number M that the length G of described Cyclic Prefix takies less than training sequence, the subcarrier number M that training sequence takies is smaller or equal to the subcarrier number N of ofdm system.
Device is conciliate in described phase compensation; Each subcarrier to each frequencyregion signal carries out the respective phase compensation by sideplay amount and subcarrier sequence number, realizes through the k number of subcarrier to i+n frequencyregion signal multiply by
.
Beneficial effect:, removed the influence of disturbing between multipath estimated result, thereby can obtain not have inclined to one side timing synchronizing information through introducing the notion of noise subspace; Fourier just/inverse transformation device exists implementation structure and algorithm efficiently fast, through adopt a large amount of Fouriers just/inverse transformation device, alleviated system's implementation complexity; The timing synchronization sytem that the present invention proposes can be used to comprise the various block transmission systems that Cyclic Prefix is arranged of OFDM.
Description of drawings
Fig. 1 is a structural representation of the present invention;
Fig. 2 is the flow chart of work of the present invention.
Embodiment
Elaborate in the face of embodiments of the invention down, present embodiment provided detailed execution mode and concrete operating process, but protection scope of the present invention is not limited to following embodiment being to implement under the prerequisite with technical scheme of the present invention.
As depicted in figs. 1 and 2; Present embodiment comprises fast fourier transformation apparatus, phase compensation reconciliation device, inverse fast fourier transform device, squaring device, adder and window minimum value searcher, and wherein: fast fourier transformation apparatus, phase compensation reconciliation device, inverse fast fourier transform device, squaring device, adder link to each other with window minimum value searcher successively.
The number of sub carrier wave that ofdm system comprised is N, and the length of Cyclic Prefix is G.Synchronizing symbol is that multiple pseudorandom (PN) sequence of M=N/2 is formed by length, takies the even bit subcarrier in the N number of subcarrier.
Described fast fourier transformation apparatus, the i of difference acknowledge(ment) signal, i+1; ...; I+G sampled point is that starting point is carried out the N point fast Fourier and changed, the frequencyregion signal that to obtain G+1 length be N, and i is any sampling location of reception signal in the window; G is the length of Cyclic Prefix, and N is the subcarrier number of ofdm system;
Device is conciliate in described phase compensation, and each subcarrier of each frequencyregion signal is carried out the respective phase compensation by sideplay amount and subcarrier sequence number, then to the frequencyregion signal after compensating divided by the known training sequence of receiving terminal;
Described inverse fast fourier transform device is done the inverse fast fourier transform that M is ordered to the frequencyregion signal of removing behind the modulation symbol, the timedomain signal that to obtain G+1 length be M, and M is the subcarrier number that training sequence takies;
Described squaring device is to MG mould square summation that is worth of each timedomain signal afterbody;
Described adder, to G+1 value obtaining in the squaring device with, be designated as ρ
_{i}
The ρ of minimum in the described window minimum value searcher, search window
_{i}, the start position of timing output OFDM symbol.
The length G of described Cyclic Prefix is greater than the maximum delay expansion of wireless multipath channel.
The subcarrier number M that the length G of described Cyclic Prefix takies less than training sequence, the subcarrier number M that training sequence takies is smaller or equal to the subcarrier number N of ofdm system.
Device is conciliate in described phase compensation; Each subcarrier to each frequencyregion signal carries out the respective phase compensation by sideplay amount and subcarrier sequence number, realizes through the k number of subcarrier to i+n frequencyregion signal multiply by
.
Specific algorithm is following:
I sampled point to receive signal is starting point, and after the FFT conversion, its frequencydomain expression can be write as:
Wherein: k representes the subcarrier sequence number; n
_{ε}Expression timing error, and n
_{ε}≤i≤n
_{ε}+ G; V (k) representes additive white Gaussian noise; H (k) is the frequency domain response of channel, can be expressed as:
Wherein: T representes the sampling period, and L representes the distinguishable footpath of channel number.Because synchronizing symbol is to be modulated on the even bit subcarrier, thus phase compensation with remove modulation symbol and also on the even bit subcarrier, carry out, that is:
Then, be the IFFT of M through length, obtain:
Suppose to receive signal and do not have timing error this moment, i.e. n
_{ε}=0, so
Be exactly the estimated value of multipath channel, because the expansion of the maximum delay of channel is a G sampled point at most, so the average power of noise subspace is:
In order to improve the precision of estimation; Calculate simultaneously with i sampled point; I+1 sampled point;, the noise subspace power when i+G sampled point is starting point
is also asked their additions on average, that is:
At last, in predefined window, minimum ρ (n
_{ε}) pairing sampled point n
_{ε}Be the starting point of OFDM symbol.
Fast fourier transformation apparatus is accomplished the computing that comprises in formula (1) and the formula (2); Phase compensation and demodulating equipment are accomplished formula (3); The inverse fast fourier transform device is accomplished formula (4); The quadratic sum adder is accomplished formula (5) and formula (6), and the minimum value searcher is accomplished the search of minimum value and confirming of starting point in the window.
Claims (4)
1. OFDM timing synchronization sytem based on noise subspace; It is characterized in that: comprise fast fourier transformation apparatus, phase compensation reconciliation device, inverse fast fourier transform device, squaring device, adder and window minimum value searcher; Wherein: fast fourier transformation apparatus, device, inverse fast fourier transform device are conciliate in phase compensation; Squaring device, adder links to each other with window minimum value searcher successively;
Described fast fourier transformation apparatus, the i of difference acknowledge(ment) signal, i+1; ...; I+G sampled point is that starting point is carried out the N point fast Fourier and changed, the frequencyregion signal that to obtain G+1 length be N, and i is any sampling location of reception signal in the window; G is the length of Cyclic Prefix, and N is the subcarrier number of ofdm system;
Device is conciliate in described phase compensation, and each subcarrier of each frequencyregion signal is carried out the respective phase compensation by sideplay amount and subcarrier sequence number, then to the frequencyregion signal after compensating divided by the known training sequence of receiving terminal;
Described inverse fast fourier transform device is done the inverse fast fourier transform that M is ordered to the frequencyregion signal of removing behind the modulation symbol, the timedomain signal that to obtain G+1 length be M, and M is the subcarrier number that training sequence takies;
Described squaring device is to MG mould square summation that is worth of each timedomain signal afterbody;
Described adder, to G+1 value obtaining in the squaring device with, be designated as ρ
_{i}
The ρ of minimum in the described window minimum value searcher, search window
_{i}, the start position of timing output OFDM symbol.
2. the OFDM timing synchronization sytem based on noise subspace according to claim 1 is characterized in that: the length G of described Cyclic Prefix is greater than the maximum delay expansion of wireless multipath channel.
3. the OFDM timing synchronization sytem based on noise subspace according to claim 1; It is characterized in that: the subcarrier number M that the length G of described Cyclic Prefix takies less than training sequence, the subcarrier number M that training sequence takies is smaller or equal to the subcarrier number N of ofdm system.
4. the OFDM timing synchronization sytem based on noise subspace according to claim 1; It is characterized in that: device is conciliate in described phase compensation; Each subcarrier to each frequencyregion signal carries out the respective phase compensation by sideplay amount and subcarrier sequence number, realizes through the k number of subcarrier to i+n frequencyregion signal multiply by
.
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EP1162803A1 (en) *  20000605  20011212  Telefonaktiebolaget L M Ericsson (Publ)  Frequency tracking device and method for a receiver of a multicarrier communication system 
CN101188447A (en) *  20061115  20080528  华为技术有限公司  A method and device for carrier frequency deviation estimation 
CN101616110A (en) *  20080624  20091230  鼎桥通信技术有限公司  A kind of frequency deviation estimating method and device 
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EP1162803A1 (en) *  20000605  20011212  Telefonaktiebolaget L M Ericsson (Publ)  Frequency tracking device and method for a receiver of a multicarrier communication system 
CN101188447A (en) *  20061115  20080528  华为技术有限公司  A method and device for carrier frequency deviation estimation 
CN101616110A (en) *  20080624  20091230  鼎桥通信技术有限公司  A kind of frequency deviation estimating method and device 
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张静 等.强信号背景下基于噪声子空间扩充的弱信号DOA估计方法.《系统工程与电子技术》.2009, * 
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