CN101409694B - Method and system for implementing single carrier frequency domain equilibrium - Google Patents

Method and system for implementing single carrier frequency domain equilibrium Download PDF

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CN101409694B
CN101409694B CN2008102259161A CN200810225916A CN101409694B CN 101409694 B CN101409694 B CN 101409694B CN 2008102259161 A CN2008102259161 A CN 2008102259161A CN 200810225916 A CN200810225916 A CN 200810225916A CN 101409694 B CN101409694 B CN 101409694B
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frequency domain
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吴昊
田金洁
方立
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BEIJING VIGA Co Ltd
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Abstract

The invention discloses a single carrier frequency domain equilibrium realizing method with low cost and a system thereof, comprising three parts of channel estimation, equalizer and channel tracking. A data frame adopted by the method/system comprises a training sequence part and a data transmission part. The training sequence part is arranged in the front part and comprises two same continuous training blocks. The data transmission part is arranged in the back part and comprises a plurality of continuous Fourier transforming blocks, namely FFT blocks. The length of every FFT block is the size of FFT. Any complete FFT block comprises a data block and a UW block. And the data block is in front, and the UW block is at back. The method/system utilizes the data of the two same training blocks for the channel estimation. Compared with a traditional continuous data format, the cost of useless data can be lowered. A noise prediction decision feedback equilibrium algorithm is adopted for the equilibrium treatment and a recursive least squares algorithm is adopted for the channel tracking treatment.

Description

A kind of single carrier frequency domain equalization implementation method and system
Technical field
The invention belongs to broadband wireless transmission transferring technology field, relate in particular to a kind of single carrier frequency domain equalization implementation method and system.
Background technology
(single carrier frequency domain equalization SC-FDE) is a kind of effectively method that anti-multipath is disturbed in the broadband wireless transmission to single carrier frequency domain equalization.In wireless communication system, except receiving various interference of noise, the multipath transmisstion that transmits also affects the error rate of transfer of data, cause intersymbol interference (inter symbol interference, ISI).Along with the bigger raising of access and message transmission rate, increasingly high transmission bandwidth has caused serious time dispersive, receives the multipath ripple that has comprised experience decay and time delay in the signal, causes frequency selective fading, thereby causes serious ISI.If single alleviate ISI with time domain equalization, need more filter tap just can obtain acceptable portfolio effect this time, is difficult to reach the real-time requirement like this, and along with the increase of multidiameter delay expansion, complexity of equalization even possibly increase by exponentially.
In the 4th generation,, (4G) GSM speed can reach several 10Mbps even 100Mbps, and the time domain equalization under high like this system transmissions speed is unpractiaca.(Cyclic Prefix CP), makes the frequency domain equalization of receiving terminal become simple so people have at first proposed Cyclic Prefix; The eighties in 20th century; Along with high-speed digital signal is handled (Digital Signal Processing; DSP) fast development of chip; The appearance of large scale integrated circuit makes that the realization of fast Fourier transform (FFT) technology no longer is the obstacle that is difficult to go beyond, and therefore the complexity of signal time-frequency conversion has also obtained reducing greatly.Like this, the equilibrium on the traditional time domain transforms to and realizes just becoming possibility on the frequency domain.(Orthogonal Frequency Division Multiplexing OFDM) is suggested under such background with SC-FDE just based on the major technique OFDM of the piecemeal of CP transmission.CP is used for ofdm system at first, and OFDM is a kind of modulation system efficiently, has the advantage of high spectrum efficiency and strong anti-ISI.Yet; Laboratory research at OFDM is day by day ripe; Its peak-to-average force ratio (Peak-to-Average Power Ratio, when PAPR) too high weakness became the bottleneck that system realizes improving with performance gradually, people initiated the technological discussion to SC-FDE again; And with regard to principle and the performance of SC-FDE, and special symbolic construction and the signal processing algorithm of this system begun research.SC-FDE has similar identical complexity, spectrum efficiency and antijamming capability with OFDM, and the performance of SC-FDE has bigger advantage than OFDM.
SC-FDE adopts frequency domain equalization to eliminate the influence of frequency-selective channel to signal.Frequency-domain equalization technology generally also is criterion and the algorithm that adopts in traditional time domain equalization, and the algorithm of different with time domain equalization is frequency domain equalization is handled on frequency domain, has simplified the tap number like this, handles simple.Simultaneously, because the channel status of wireless channel is time dependent, so balance module need be followed the tracks of this variation.Adaptive tracing algorithm commonly used have least fibre method (Least Mean square, LMS), recurrent least square method (Recursive Least Square, RLS) etc.
The structure of single-carrier frequency domain equalization system is as shown in Figure 1; It comprises channel estimation module, balance module and channel tracking module; Wherein channel estimation module is used for carrying out channel estimating according to receiving signal r, thereby obtains the initial frequency domain equalization coefficient W1 of balance module; Balance module is used for to received signal that r carries out equilibrium treatment, obtains equalizing signal d, and its concrete scheme obtains equalization data for adopting the frequency domain equalization coefficient to multiply by mutually with reception signal frequency-domain data; The channel tracking module is used for carrying out channel tracking treatment according to frequency domain equalization coefficient W and error signal e that reception signal r, balance module transmission come, calculates the frequency domain equalization coefficient that makes new advances, and gives balance module to upgrade the frequency domain equalization coefficient W of balance module.
Under the continuous transmission mode; The traditional scheme of single-carrier frequency domain equalization system adopts transmission structure shown in Figure 2 usually, and two identical unique words (Unique Word, UW) pieces are arranged between the adjacent data blocks; Wherein first UW piece is as Cyclic Prefix, and second UW then is used for channel estimating.
Continuous transmission structure shown in Figure 2 because the adjacent data interblock needs two UW, has therefore increased overhead.
Summary of the invention
The technical problem that the present invention will solve provides a kind of lower-cost single carrier frequency domain equalization implementation method and system.
For solving the problems of the technologies described above, single carrier frequency domain equalization implementation method of the present invention comprises:
Channel estimation steps, equalization step and channel tracking step; Wherein said channel estimation steps is used for carrying out channel estimating according to receiving signal, thereby obtains supplying the initial frequency domain equalization coefficient of said equalization step use; Said equalization step is used for carrying out to received signal equilibrium treatment; Said channel tracking step is used for through channel tracking, and the frequency domain equalization coefficient that said equalization step is used upgrades;
The Frame that said each step adopts comprises training sequence part and transmission data division, and wherein said training sequence part is preceding, and it comprises two continuous identical training pieces; Said transmission data division after, it comprises that several continuous Fourier transform pieces are fft block, the length of any said fft block is FFT size; Any complete said fft block is formed by a data block and UW piece, and said data block is preceding, said UW piece after;
Particularly, said channel estimation steps is to utilize said two identical training blocks of data to carry out channel estimating.
As preferred version of the present invention, said equalization step is to adopt the noise prediction decision feedback equalization algorithm to carry out equilibrium treatment.
As another kind of preferred version of the present invention, said channel tracking step is to adopt recursive least squares to carry out channel tracking treatment.
For solving the problems of the technologies described above, single carrier frequency domain equalization realization of the present invention system comprises:
Channel estimation module, balance module and channel tracking module;
The Frame that this system adopts comprises training sequence part and transmission data division, and wherein said training sequence part is preceding, and it comprises two continuous identical training pieces; Said transmission data division after, it comprises that several continuous Fourier transform pieces are fft block, the length of any said fft block is FFT size; Any complete said fft block is formed by a data block and UW piece, and said data block is preceding, said UW piece after;
Said channel estimation module is used for carrying out channel estimating according to said two identical training blocks of data, thereby obtains supplying the initial frequency domain equalization coefficient of said balance module use;
Said balance module is used for carrying out to received signal equilibrium treatment;
Said channel tracking module is used for through channel tracking, and the frequency domain equalization coefficient that said balance module is used upgrades.
As a kind of preferred version, said balance module is to adopt the noise prediction decision feedback equalization algorithm to carry out equilibrium treatment.
As another kind of preferred version, said channel tracking module is to adopt recursive least squares to carry out channel tracking treatment.
Beneficial effect of the present invention is:
The present invention has adopted a kind of structure of successive frame efficiently, and frame head adopts two continuous identical training sequences, can accomplish apace synchronously and channel estimating.Insert a UW between the data block as Cyclic Prefix.Than traditional continuous data form, the present invention has reduced the expense of hash.The present invention simultaneously adopts and carries out equilibrium treatment to received signal based on the decision-feedback adaptive equalization algorithm of noise prediction; And utilize feedforward error signal and noise prediction error signal to remove to upgrade feedforward and feedback equalization coefficient respectively independently; Have characteristics such as systematic function is good, simple in structure, and have advantages of high practicability.
Description of drawings
Fig. 1 is the structural principle sketch map of single-carrier frequency domain equalization system;
Fig. 2 is the tcp data segment sketch map in the common frame structure that adopts of single-carrier frequency domain equalization system;
Fig. 3 is the structural representation of the Frame of single-carrier frequency domain equalization system employing of the present invention;
Fig. 4 is the balance module principle schematic that the present invention adopts.
Embodiment
Below in conjunction with accompanying drawing and embodiment the present invention is done further explain.
Fig. 3 is the structural representation of the Frame of single-carrier frequency domain equalization system employing of the present invention; As shown in the figure, frame signal comprise two identical training pieces (Pilot Block, PB); These two identical training pieces are used for channel estimating, Q continuous in succession thereafter fft block.A complete fft block is combined by a data block and a UW piece, and the block length N of fft block is the FFT size, and wherein the UW segment length is M.
The unique word sequence is generally the chu sequence or the frank-zadaff sequence of IEEE802.16a standard code, and its length is generally 2 whole power.
Single carrier frequency domain equalization realization of the present invention system comprises channel estimation module, balance module and channel tracking module; Wherein the channel estimation module utilization receives the PB segment data completion channel estimating in the signal data frame; And calculate the initial frequency domain equalization coefficient W1 of balance module, give balance module and be used for initialization; The balance module transmission data in the Frame to received signal carries out equilibrium and obtains equalizing signal d, and balance module is given the channel tracking module with current frequency domain equalization coefficient W, error signal e simultaneously; Frequency domain equalization coefficient W and error signal e that the channel tracking module utilizes balance module to provide, and, calculate the frequency domain equalization coefficient W that makes new advances according to receiving signal r, give the equilibrium that equalizer is used for next fft block.
Elaborate in the face of each module of system of the present invention down:
One, channel estimation module
Channel estimation module at first calculates channel impulse response.Two training piece parts of acknowledge(ment) signal r are transformed to frequency domain data R through FFT; Odd number value of frequency point according to the frequency domain transform data of two identical block of character of Fourier transform is 0; The FFT data X that R is positioned at value and the PB data of even number frequency is divided by and obtains channel frequency domain response estimation value H, obtains time domain channel impulse response estimated value h through inverse Fourier transform (IFFT).Through noise reduction process, h is truncated to UW segment length M and zero padding to fft block length N, obtain the frequency domain response estimation value H behind the noise reduction.Simultaneously, to the estimation values sigma that on average obtains noise variance of square asking of the odd number value of frequency point of R 2
Obtain domain channel response and σ 2After, calculate the frequency domain equalization coefficient W of j frequency according to following formula j:
Figure GDA0000155550120000051
H wherein jBe the frequency domain response value of j frequency, 1≤j≤N.
Two, balance module
In the present embodiment, balance module adopts NP-DFE (noise prediction decision feedback equalization) structure, and its operation principle is as shown in Figure 4.Than common DFF, the feedforward of NP-DFE and feedback fraction are independent calculating, are very suitable for the application scenario that adaptive channel is followed the tracks of.Because NP-DFE and DFE (decision feedback equalization when tap number is unlimited; Decision Feedback Equalization) has identical performance; And the corresponding time domain tap of frequency domain equalization is unlimited, therefore adopts NP-DFE to compare the loss that can not bring on any performance with DFE.
In the NP-FDE structure, utilize the error signal e between feedforward filtering signal z and the decision signal d to remove to upgrade feed-forward coefficients W, utilize the error signal e 1 between noise prediction signal z_np and the decision signal d to remove to upgrade feedback factor c.Feed-forward coefficients W upgrades by the Fourier transform piece, carries out at frequency domain.W, the e that preceding piece obtains gives the channel tracking module and calculates the frequency domain equalization coefficient W that makes new advances, and receives the equalizing coefficient of data as next piece.The time domain that is updated in of feedback factor is carried out, and adopts the LMS algorithm to upgrade feedback factor c, and computing formula is:
c(n+1)＝c(n)+μe 1e *(n)
C=[c wherein 1..., c B], e (n)=[e N-1..., c N-B], B is the feedback tap number, μ is a step factor.
Three, channel tracking module
Because channel becomes when slow, need constantly adjust equalizing coefficient to follow the tracks of this variation.The channel tracking module adopts RLS (Recursive Least Squares, recurrence least square) algorithm, for the k in the transmission frame (the individual Fourier transform piece of 1≤k≤Q), the target error function expression is:
Σ i = 1 k λ k - i | | e i | | 2 = Σ i = 1 k λ k - i | | E i | | 2 = Σ i = 1 k λ k - i | | diag ( W k ) · R i - D i | | 2
= Σ i = 1 k λ k - i Σ j = 1 N | W k , j R i , j - D i , j | 2 = Σ j = 1 N [ Σ i = 1 k λ k - i | W k , j R i , j - D i , j | 2 ]
E wherein iBe the time domain data of i fft block error vector, E iBe the frequency domain data of i fft block error vector, R iFor receiving signal frequency-domain data, D iFrequency domain data for decision signal.1≤j≤N, j represent that the data of its qualification are j data in this Fourier transform piece.
Can know that from above-mentioned function expression the frequency domain equalization coefficient is independently updated at each frequency.Adopt N dimension equalizing coefficient vector W kMinimize the target error function, can obtain:
K k , j = P k - 1 , j R k , . j * / ( λ + P k - 1 , j | R i , j | 2 )
P k，j＝(P k-1，j-K k，jR i，j?P k-1，j)/λ
W k，j＝W k-1，j+K k，jE k，j(1≤j≤N)
Wherein, K is a gain vector, representes k fft block; P is the contrary of correlation matrix; Na Muda is a forgetting factor.W KjRepresent j equalizing coefficient that data are corresponding in k the fft block, can draw the frequency domain equalization coefficient W of k fft block in view of the above k
Above-described specific embodiment; The object of the invention, technical scheme and beneficial effect have been carried out further explain; Institute it should be noted; The above is merely specific embodiment of the present invention, and those skilled in the art can carry out various changes and modification to the present invention and not break away from the spirit and scope of the present invention.Like this, belong within the scope of technical scheme and equivalent technologies thereof of claim record of the present invention if of the present invention these are revised with modification, then the present invention also is intended to comprise these changes and modification interior.

Claims (6)

1. a single carrier frequency domain equalization implementation method comprises channel estimation steps, equalization step and channel tracking step, it is characterized in that:
The Frame that said each step adopts comprises training sequence part and transmission data division, and wherein said training sequence part is preceding, and it comprises two continuous identical training pieces; Said transmission data division after, it comprises that several continuous Fourier transform pieces are fft block, the length of any said fft block is FFT size; Any complete said fft block is formed by a data block and UW piece, and said data block is preceding, said UW piece after;
Said channel estimation steps is to utilize said two identical training blocks of data to carry out channel estimating.
2. single carrier frequency domain equalization implementation method according to claim 1 is characterized in that:
Said equalization step is to adopt the noise prediction decision feedback equalization algorithm to carry out equilibrium treatment.
3. single carrier frequency domain equalization implementation method according to claim 1 and 2 is characterized in that:
Said channel tracking step is to adopt recursive least squares to carry out channel tracking treatment.
4. a single carrier frequency domain equalization is realized system, comprises channel estimation module, balance module and channel tracking module, it is characterized in that:
The Frame that this system adopts comprises training sequence part and transmission data division, and wherein said training sequence part is preceding, and it comprises two continuous identical training pieces; Said transmission data division after, it comprises that several continuous Fourier transform pieces are fft block, the length of any said fft block is FFT size; Any complete said fft block is formed by a data block and UW piece, and said data block is preceding, said UW piece after;
Said channel estimation module is used for carrying out channel estimating according to said two identical training blocks of data, thereby obtains supplying the initial frequency domain equalization coefficient of said balance module use;
Said balance module is used for carrying out to received signal equilibrium treatment;
Said channel tracking module is used for through channel tracking, and the frequency domain equalization coefficient that said balance module is used upgrades.
5. single carrier frequency domain equalization according to claim 4 is realized system, it is characterized in that:
Said balance module is to adopt the noise prediction decision feedback equalization algorithm to carry out equilibrium treatment.
6. realize system according to claim 4 or 5 described single carrier frequency domain equalizations, it is characterized in that:
Said channel tracking module is to adopt recursive least squares to carry out channel tracking treatment.
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