CN101360084A - Inter-carrier interference eliminating method, apparatus, signal receiving method and receiver - Google Patents

Abstract

The invention discloses an eliminating method of inter-carrier interference, comprising the following: obtaining current sub-carrier channel response module value; if the module value is more than a threshold set in advance, a natural number n is selected from the natural numbers set in advance to be selected, so that 2n is most close to the module value square, and conj (Hk)/2n is taken as 1/Hk to calculate an interference factor that other sub-carriers interfere with the current sub-carrier; wherein, conj(. ) is conjugate operation, and Hk is the channel response estimation value of the current sub-carrier; if the module value is less than or equal to the threshold, the interference factor that other sub-carriers interfere with the current sub-carrier is set as 0; the product of the receiving data of other sub-carriers and the interference factor that corresponding sub-carrier interferes with the current sub-carrier is subtracted from the receiving data of the current sub-carrier, and the difference value is taken as a receiving data of the current sub-carrier after the interference is eliminated. The invention also discloses an eliminating device, a signal receiving method and a receiver of the inter-carrier interference. With the invention applied, the complexity of eliminating the interference can be lowered, and real time division operation can be avoided.

Description

Inter-carrier interference eliminating method, device and signal acceptance method and receiver

Technical field

The present invention relates to OFDM (OFDM) technology, particularly disturb the removing method and the device of (ICI) and signal acceptance method and the receiver of using this removing method between the ofdm system sub-carriers.

Background technology

OFDM (OFDM) system is and can resists distinctive multipath fading in the radio communication with more succinct means with respect to the advantage of traditional single-carrier system.Common OFDM receiver block diagram as shown in Figure 1.

In OFDM receiver shown in Figure 1, fast Fourier transform (FFT) module 101 is converted to frequency-region signal by the FFT conversion with time-domain signal.Wherein, the signal Y that receives on each subcarrier of frequency domain (sub-carrier) k _kCan be expressed as:

Y _k＝H _k*X _k+w _k，k＝0，1，2，…，N-1 (1)

X wherein _kBe the primary signal that on subcarrier k, sends, H _kBe the value of domain channel response on subcarrier k, w _kBe the noise on the subcarrier k.Carry out channel estimating through channel estimation module 102 among Fig. 1 and obtain H _kAfter, the balanced and judgement by simple single order just can recover and send signal X _k

But the equation relation of formula (1) is only applicable to the state of static state or low-speed motion.When being in high-speed motion, because the variability of time orientation channel has caused time selective fading, when entering the more serious time slice of fading ratio, continuous burst error can appear.Being reflected to influence on the frequency domain is to cause the Doppler frequency expansion, disturbs (ICI, Inter-Carrier Interference) to increase between subcarrier and can not ignore, and the signal expression that receives becomes:

$Y_k=\underset{i,i\≠k}{\mathrm{\Σ}}{H}_{i,k}*X_i+H_{k,k}*X_k+w_k,k=\mathrm{0,1,2},\·\·\·,N-1---\left(2\right)$

Wherein, H _{I, k}For subcarrier i (property the taken advantage of interference of i ≠ k) subcarrier k is caused,

Represent the ICI interference that data cause the last data of subcarrier k on other subcarriers.By formula (2) as seen, under the high-speed motion environment, received signal is polluted by the ICI interference and is caused mis-behave, utilizes contaminated pilot signal to carry out channel estimating simultaneously, also can reduce the accuracy of channel estimating.

At present, the problem of bringing at high-speed mobile can be eliminated by two types approach.First kind is to adopt time-interleaved means, with interweaving data is broken up making a start, and with deinterleaving data is recovered back original order again in receiving end.This method is not eliminated the interference that ICI brings, but a period of time signals disperse that can fading ratio is more serious comes, and is beneficial to subsequent channel decoding.

Another kind method is at formula (2), eliminates the ICI interference that other subcarriers bring on frequency domain.The principle of concrete ICI interference eliminated is suc as formula shown in (3.1) and (3.2).

r _k＝Y _k/H _k (3.1)

${\tilde{X}}_k=r_k-\underset{i,i\≠k}{\mathrm{\Σ}}\frac{H_{i,k}}{H_k}{r}_i,0\≤k\≤N-1---\left(3.2\right)$

By above-mentioned two formulas as seen, the method for present ICI elimination comprises:

Step 1 according to formula (3.1), is carried out the initial estimation r that equilibrium obtains sending signal to the reception data on the subcarrier _k

Step 2 is according to formula (3.2), from initial estimation r _kIn deduct the interference value of other subcarriers to current subcarrier, obtain final transmitting signal estimated value

More above-mentioned formula (3.2) and formula (2) are as seen disturbed for eliminating according to the transmitting signal estimated value that formula (3.2) obtains After estimated value, and, among the application will $A_i=\frac{H_{i,k}}{H_k}$ Be called the interference factor of subcarrier i to current subcarrier k.Wherein,

$H_{i,k}=\frac{1}{N-1}*\frac{{\mathrm{\ΔH}}_i}{\exp (j*2\mathrm{\π}*(i-k)/N)-1}---\left(3.3\right)$

N is the OFDM total number of sub-carriers of system, and the N value of ubiquitous system is 1024～8192.

In addition, because adjacent two subcarriers disturb maximum to the ICI of current subcarrier, and other subcarriers are less relatively to the ICI interference of current subcarrier, therefore, in the existing ICI removing method, usually only from initial estimation, deduct adjacent two subcarrier k-1 and k+1 current subcarrier is received the interference of data, and ignore the interference of all the other subcarriers.Promptly in step 2, i is k-1 and k+1.

Simultaneously, to adjacent sub-carrier i=k-1 and k+1,, have because N is bigger:

$H_{k+1,k}=\frac{1}{N-1}*\frac{{\mathrm{\ΔH}}_{k+1}}{\exp (j*2\mathrm{\π}/N)-1}\≈\frac{1}{N-1}*\frac{{\mathrm{\ΔH}}_{k+1}}{j*\sin (2\mathrm{\π}/N)}\≈\frac{{\mathrm{\ΔH}}_{k+1}}{j*\left(2\mathrm{\π}\right)}$

$H_{k-1,k}=\frac{1}{N-1}*\frac{{\mathrm{\ΔH}}_{k-1}}{\exp (j*(-2\mathrm{\π})/N)-1}\≈\frac{1}{N-1}*\frac{{\mathrm{\ΔH}}_{k-1}}{-j*\sin (2\mathrm{\π}/N)}\≈\frac{{\mathrm{\ΔH}}_{k-1}}{-j*\left(2\mathrm{\π}\right)}$

Therefore, formula (3.2) can be reduced to

${\tilde{X}}_k=r_k-\frac{\left({\mathrm{\ΔH}}_{k-1}\right)/(-j2\mathrm{\π})}{H_k}{r}_{k-1}-\frac{\left({\mathrm{\ΔH}}_{k+1}\right)/\left(j2\mathrm{\π}\right)}{H_k}{r}_{k+1};0\≤k\≤N-1$

Wherein, Δ H _K-1The changing value of representing the response of a current OFDM symbol subcarrier k-1 and a last OFDM symbol subcarrier k-1 upper signal channel, Δ H _K+1The changing value of representing the response of a current OFDM symbol subcarrier k+1 and a last OFDM symbol subcarrier k+1 upper signal channel;

For sending signal X _kEstimated value, be used to separate mapping and obtain soft bit information and give the subsequent communication channel decoding unit and finish decoding.

The method that above-mentioned elimination ICI disturbs adds time-interleaved/deinterleaving, can improve the performance of receiver when high-speed motion effectively.But it also has several shortcomings:

1. implementation complexity is big, and especially the calculating of each subcarrier data all needs real-time division arithmetic;

2. when multipath transmisstion makes that certain subcarrier k fading rise is dark, in the ICI elimination process directly divided by H _k, because H _kValue very little through decline, therefore can introduce very big noise;

3. the frequency domain channel estimated value H that when equilibrium, uses _kThe auxiliary pilot estimation that normally utilizes known frequency domain to insert obtains, but because the influence of ICI, the data that receiving terminal obtains on the pilot frequency locations subcarrier are disturbed by ICI, cause channel estimating to be inaccurate and have than mistake, thereby influence the follow-up mapping block accuracy of separating.

Summary of the invention

In view of this, the invention provides a kind of ICI removing method, can reduce the complexity of interference eliminated, avoid real-time division arithmetic.

For achieving the above object, the present invention adopts following technical scheme:

The removing method that disturbs between one sub-carrier comprises:

Obtain the mould value of current sub-carrier channels response,, make 2 if this mould value greater than the thresholding that sets in advance, is then selected a natural number n in default natural number to be selected ⁿThe most approaching described mould value square, and will

As 1/H _k, calculate the interference factor of other default subcarriers to current subcarrier; Wherein, conj () represents conjugate operation, H _kChannel response estimated value for current subcarrier;

If described mould value is less than or equal to the thresholding that sets in advance, then described other subcarriers are put 0 to the interference factor of current subcarrier;

The reception data and the respective sub that deduct from the reception data of current subcarrier on other subcarriers are long-pending to the interference factor of current subcarrier, the reception data after the difference result is disturbed as the elimination of current subcarrier.

Preferably,

Described other default subcarriers are two adjacent sub-carriers of current subcarrier;

Described general

As 1/H _k, calculate other subcarriers the interference factor of current subcarrier comprised: utilize formula $\frac{\left(\mathrm{\Δ}{H}_{k-1}\right)/(-j2\mathrm{\π})*\mathrm{conj}\left(H_k\right)}{2^n}$ Calculate the interference factor A of the last subcarrier k-1 of current subcarrier _K-1, utilize formula $\frac{\left({\mathrm{\ΔH}}_{k+1}\right)/\left(j2\mathrm{\π}\right)*\mathrm{conj}\left(H_k\right)}{2^n}$ Calculate the interference factor A of a back subcarrier k+1 of current subcarrier _K+1

Preferably, will

Be expressed as binary constant, the m position that moves to right again utilizes shift result to replace constant 1/j2 π, is used to calculate interference factor, and described m is default constant.

Preferably, this method further comprises: before carrying out interference eliminated, determine the translational speed of receiver, when described translational speed is higher than default speed threshold, the reception data on each subcarrier is carried out ICI eliminate; Otherwise, process ends.

Preferably, the translational speed of described definite receiver comprises: utilize Doppler frequency shift to estimate to determine the translational speed of receiver.

A kind of method of reseptance of orthogonal frequency division multiplex OFDM signal comprises:

Carry out disturbing between subcarrier ICI to eliminate the reception data after the interference that is eliminated to the reception data on each subcarrier that obtains after handling through fast fourier transform FFT;

Utilize the reception data of eliminating after disturbing on each pilot sub-carrier to carry out channel estimating again, obtain the channel response of revising on each subcarrier;

Reception data after utilizing the channel response of revising on each subcarrier and eliminating interference are determined the transmitting signal estimated value on each subcarrier;

Wherein, the elimination that the reception data on the current subcarrier are carried out disturbing between subcarrier comprises:

Obtain the mould value of current subcarrier,, make 2 if this mould value greater than the thresholding that sets in advance, is then selected a natural number n in default natural number to be selected ⁿThe most approaching described mould value square, and will

As 1/H _k, be used to calculate the interference factor of other subcarriers to current subcarrier; Wherein, conj () represents conjugate operation, H _kChannel response estimated value for current subcarrier;

If described mould value is less than or equal to the thresholding that sets in advance, then other subcarriers are put 0 to the interference factor of current subcarrier;

The reception data and the respective sub that deduct from the reception data of current subcarrier on other subcarriers are long-pending to the interference factor of current subcarrier, the reception data after the difference result is disturbed as the elimination of current subcarrier.

Preferably, describedly utilize on each pilot sub-carrier the reception data of eliminating after disturbing to carry out channel estimating again to comprise: with finite impulse response FIR filter as interpolation filter, reception data after eliminate disturbing on each pilot sub-carrier are carried out filtering interpolation, with the filtering result as the channel estimation value of revising on each subcarrier.

Preferably, this method further comprises: before the reception data on each subcarrier being carried out the ICI elimination, determine the translational speed of receiver, when described translational speed is higher than default speed threshold, reception data on each subcarrier are carried out ICI eliminate, and carry out the described reception data of eliminating after disturbing on each pilot sub-carrier of utilizing and carry out the operation of channel estimating again; Otherwise, directly utilize reception data on each subcarrier to determine transmitting signal estimated value on each subcarrier, perhaps the reception data on each subcarrier are carried out ICI and eliminate, and directly utilize the reception data of eliminating on former channel estimation value and each subcarrier behind the ICI to determine transmitting signal estimated value on each subcarrier.

Preferably, the translational speed of described definite receiver comprises: utilize Doppler frequency shift to estimate to determine the translational speed of receiver.

Interference blanking unit between one sub-carrier comprises: mould value computing unit, comparator unit, interference factor computing unit, selected cell and interference cancellation unit;

Described mould value computing unit is used to obtain the mould value of current subcarrier;

Described comparator unit is used for the mould value of more current subcarrier and the thresholding of presetting, if the mould value of current subcarrier greater than default thresholding, is then selected a natural number n in default natural number to be selected, makes 2 ⁿThe most approaching described mould value square, the natural number of selecting is exported to described interference factor computing unit, and trigger selector will be received from the interference factor output of described interference factor computing unit; Otherwise trigger described selector interference factor is put 0 also output;

Described interference factor computing unit, be used for

As 1/H _k, calculate the interference factor of other subcarriers, and the interference factor that calculates imported described selected cell current subcarrier; Wherein, conj () represents conjugate operation, H _kChannel response estimated value for current subcarrier;

Described selected cell is used for the control according to described comparing unit, and interference factor is exported to described interference cancellation unit;

Described interference cancellation unit is used for amassing the interference factor of current subcarrier is from reception data and respective sub that the reception data of current subcarrier deduct on other subcarriers, the reception data after the difference result is disturbed as the elimination of current subcarrier.

A kind of receiver of ofdm signal comprises FFT module, first extraction pilot module, channel estimation module and the equilibrium solution mapping block, and this receiver comprises that also ICI cancellation module, second extracts pilot module and channel response filtering interpolation module;

Described ICI cancellation module is used for that the reception data on each subcarrier of described FFT module output are carried out ICI and eliminates, and the reception data that are eliminated after disturbing are exported to second pilot extraction module and equilibrium solution mapping block;

Described second extracts pilot module, is used to extract the reception data of eliminating on each pilot sub-carrier after disturbing, and exports to described channel response filtering interpolation module;

Described channel response filtering interpolation module is used to utilize on each pilot sub-carrier the reception data of eliminating after disturbing to carry out channel estimating again, obtains the channel response revised on each subcarrier, and exports to described equilibrium solution map unit;

Described ICI cancellation module comprises: mould value computing unit, comparator unit, interference factor computing unit, selected cell and interference cancellation unit;

Wherein, described mould value computing unit is used to obtain the mould value of current subcarrier;

Described comparator unit is used for the mould value of more current subcarrier and the thresholding of presetting, if the mould value of current subcarrier greater than default thresholding, is then selected a natural number n in default natural number to be selected, makes 2 ⁿThe most approaching described mould value square, the natural number of selecting is exported to described interference factor computing unit, and trigger selector will be received from the interference factor output of described interference factor computing unit; Otherwise trigger described selector interference factor is put 0 also output;

Described interference factor computing unit, be used for

As 1/H _k, calculate the interference factor of other subcarriers, and the interference factor that calculates imported described selected cell current subcarrier; Wherein, conj () represents conjugate operation, H _kChannel response estimated value for current subcarrier;

Described selected cell is used for the control according to described comparing unit, and interference factor is exported to described interference cancellation unit;

Described interference cancellation unit is used for amassing the interference factor of current subcarrier is from reception data and respective sub that the reception data of current subcarrier deduct on other subcarriers, the reception data after the difference result is disturbed as the elimination of current subcarrier.

Preferably, described receiver further comprises Doppler's estimation module, be used to carry out the movement velocity that Doppler frequency deviation estimates to determine this receiver, when described movement velocity is higher than default speed threshold, start described ICI cancellation module and channel response filtering interpolation module; When described movement velocity is less than or equal to default speed threshold, close described ICI cancellation module and channel response filtering interpolation module, perhaps start described ICI cancellation module and close channel response filtering interpolation module;

Described ICI cancellation module further according to the control of described Doppler's estimation module, starts or closes the operation of itself;

Described channel response filtering interpolation module further according to the control of described Doppler's estimation module, starts or closes the operation of itself.

As seen from the above technical solution, when disturbing ICI to eliminate, obtain the mould value of current sub-carrier channels response among the present invention,, make 2 if this mould value greater than the thresholding that sets in advance, is then selected a natural number n in default natural number to be selected ⁿThe most approaching described mould value square, and will

As 1/H _k, calculate the interference factor of other default subcarriers to current subcarrier; Under this account form, avoided directly divided by H _kOperation, be converted to that conjugation is taken advantage of and shifting function; If described mould value is less than or equal to the thresholding that sets in advance, other subcarriers that then will preset put 0 to the interference factor of current subcarrier, thereby avoid introducing big noise at the darker carrier wave place of decline; Next, the reception data and the respective sub that deduct from the reception data of current subcarrier on other subcarriers are long-pending to the interference factor of current subcarrier, reception data after the difference result disturbed as the elimination of current subcarrier, under this account form, directly utilize to receive data and calculate, avoid according to a preliminary estimate in the computational process directly divided by H _kOperation.By the interference elimination method of the invention described above, avoided real-time division arithmetic on the one hand, also avoided the darker carrier wave place of decline to introduce big noise on the other hand, reduce receptivity.

Description of drawings

Fig. 1 is existing OFDM receiver block diagram.

The flow chart of ICI removing method in Fig. 2 embodiment of the invention.

Fig. 3 is the structure chart of ICI cancellation element among the present invention.

Fig. 4 is the specific implementation structure chart of unit in the ICI cancellation element.

Fig. 5 is the block diagram of OFDM receiver among the present invention.

Fig. 6 is the OFDM receiver block diagram of controlled ICI elimination and channel estimating filtering interpolation module.

Embodiment

For making purpose of the present invention, technological means and advantage clearer,, the present invention is described in further details below in conjunction with accompanying drawing.

Basic thought of the present invention is: in ICI elimination process, avoid real-time division arithmetic, thereby reduce the complexity of interference eliminated, improve the receptivity of receiver.

At first, the real-time divide operations when avoiding according to a preliminary estimate, among the present invention no longer to the r after according to a preliminary estimate _kCarry out interference eliminated, but direct reception data Y from current subcarrier k _kIn deduct the default interference value of other subcarriers i on current subcarrier, carry out interference eliminated with reception data to current subcarrier k, no longer carry out process according to a preliminary estimate, also just avoided the real-time divide operations in this operating process.Promptly according to formula ${\tilde{Y}}_k=Y_k-\underset{i,i\≠k}{\mathrm{\Σ}}{H}_{i,k}*Y_i$ Receive the interference eliminated of data.Wherein, can determine the value of other subcarriers i according to the requirement of system's receptivity.

Secondly, calculating the interference factor of other subcarriers to current subcarrier $A_i=\frac{H_{i,k}}{H_k}$ Process in, for avoiding real-time divide operations, the molecule and the denominator of interference factor be multiply by conj (H respectively _k), i.e. H _kConjugation, obtain $A_i=\frac{H_{i,k}*\mathrm{conj}\left(H_k\right)}{{\left|H_k\right|}^2},$ Utilize 2 again ⁿReplace denominator | H _k| ²Thereby, can utilize conjugation multiplication and binary shift to replace divided by | H _k| ²Operation.Promptly utilized formula (4) calculate interference factor.

$\frac{H_{i,k}*\mathrm{conj}\left(H_k\right)}{2^n}---\left(4\right)$

By above-mentioned two aspects, just can avoid interference the real-time division arithmetic in the elimination process.In addition, during multipath transmisstion because the decline of some subcarriers is darker, cause to introduce bigger noise divided by the channel response of this subcarrier, for avoiding introducing this noise like, among the present invention, only the channel response amplitude on subcarrier surpasses when presetting thresholding, carries out ICI according to the improvement of above-mentioned two aspects and eliminates, if the channel response amplitude on the subcarrier does not surpass default thresholding, then no longer the reception data on the subcarrier are carried out interference eliminated.

Represent that by the form of formula the ICI interference elimination method among the present invention is:

${\tilde{Y}}_k=Y_k-\underset{i,i\≠k}{\mathrm{\Σ}}{H}_{i,k}*Y_i$

$A_i=\left\{\begin{array}{cc}\frac{H_{i,k}*\mathrm{conj}\left(H_k\right)}{2^n},& {\left|H_k\right|}^2>\mathrm{threshold}\\ 0,& {\left|H_k\right|}^2\≤\mathrm{threshold}\end{array}\right.$

Below by specific embodiment explanation the specific embodiment of the present invention.

The flow chart of ICI removing method in Fig. 2 embodiment of the invention.In this flow process, to carry out the ICI elimination at current subcarrier k is that example describes, and select two the adjacent sub-carrier k-1 and the k+1 of current subcarrier interference maximum are carried out interference eliminated, from the reception data of current subcarrier k, eliminate the interference value of adjacent sub-carrier on current subcarrier.As shown in Figure 2, eliminating the method flow that current subcarrier k goes up ICI comprises:

Step 201 is obtained current sub-carrier channels response H _kThe mould value.

This step is obtained the mould value of the channel response of current subcarrier k | H _k|.

Whether step 202, the mould value of judging the response of current sub-carrier channels greater than default thresholding, if then execution in step 203, otherwise execution in step 204.

In the present invention,, utilize the mode of step 203 to determine the interference factor of adjacent two subcarriers, and carry out interference eliminated during in the mould value of current sub-carrier channels response receiving data to current subcarrier greater than default thresholding.When the mould value of current sub-carrier channels response is less than or equal to default thresholding, the channel response decline that current subcarrier is described is bigger, then in step 204, adjacent sub-carrier is put 0 to the interference factor of current subcarrier, thereby shield this ICI and eliminate process, avoid the big noise of introducing divided by less channel response.

Step 203 is selected a natural number n in default natural number to be selected, make 2 ⁿApproach most current sub-carrier channels response mould value square, and will

As 1/H _kCalculate the interference factor of adjacent two subcarriers to current subcarrier, execution in step 205 again.

In this step, choose the most approaching | H _k| ²2 ⁿ, wherein, n is one in the default natural number a plurality of to be selected.Like this, can utilize

Replace 1/H _k, be used to calculate the interference factor of adjacent two subcarriers to current subcarrier.Preferably, the mould value scope that the sub-carrier channels that obtains according to long-time statistical responds is determined natural number value to be selected.

When calculating adjacent two subcarriers, can adopt the approximate calculation mode of mentioning in the background technology, and utilize the interference factor of current subcarrier

Replace 1/H _k, that is to say and utilize formula $A_{k-1}=\frac{\left({\mathrm{\ΔH}}_{k-1}\right)/(-j2\mathrm{\π})*\mathrm{conj}\left(H_k\right)}{2^n}$ Calculate the interference factor A of the last subcarrier of current subcarrier to current subcarrier _K-1Utilize formula $A_{k+1}=\frac{\left({\mathrm{\ΔH}}_{k+1}\right)/\left(j2\mathrm{\π}\right)*\mathrm{conj}\left(H_k\right)}{2^n}$ Calculate the interference factor A of a back subcarrier of current subcarrier to current subcarrier _K+1Wherein, conj (H _k) can realize 1/2 by the conjugation multiplication ⁿCan realize by the binary shift computing; Because 1/ (j2 π) be constant, so this division also can be with simple multiplication and shift operation replacement, particularly, can with

Be expressed as binary constant, the m position that moves to right again utilizes shift result to replace constant 1/j2 π, and m is default constant.For example, the m value is 10, then can utilize 163/ (j*2 ¹⁰) replacement 1/j2 π.Like this, promptly avoided the real-time division arithmetic in the interference factor computational process.

Step 204 all puts 0 with adjacent two subcarriers to the interference factor of current subcarrier, and execution in step 205.

As previously mentioned, multipath transmisstion may cause that certain subcarrier fading rise is darker, at this moment, if still calculate interference factor according to formula (4), then because | H _k| too small, and cause interference factor to increase, thus make Y _K-1* A _K-1And Y _K+1* A _K+1Amplitude may surpass Y _kAnd in fact, the ICI of adjacent sub-carrier influence should not surpass this subcarrier on amplitude, so among the present invention, when the channel response mould value of current subcarrier is less than or equal to default thresholding, directly interference factor is put 0, does not calculate the ICI interference.

Step 205, the reception data and the respective sub that deduct from the reception data of current subcarrier on adjacent two subcarriers are long-pending to the interference factor of current subcarrier, the reception data after the difference result is disturbed as the elimination of current subcarrier.

In this step, utilize formula ${\tilde{Y}}_k=Y_k-Y_{k-1}*A_{k-1}-Y_{k+1}*A_{k+1}$ Obtain the reception data of eliminating the current subcarrier after disturbing

So far, the flow process of ICI removing method finishes in the present embodiment.In the foregoing description, current carrier wave has been carried out the ICI elimination, and consider that adjacent two subcarriers are bigger to the interference of current subcarrier, and other subcarriers are less to the interference of current subcarrier, therefore, when carrying out the ICI elimination, only the interference eliminated that the reception data on adjacent two subcarriers are brought is fallen.In fact, also can further eliminate and receive the interference that data are brought on other subcarriers, concrete processing mode is same as described above, promptly calculate the interference factor of corresponding subcarrier to current subcarrier, the reception data and the respective sub that further deduct other subcarriers again from the reception data of current subcarrier are long-pending to the interference factor of current subcarrier.

In addition, the ICI removing method of the invention described above is at disturbing between the subcarrier that the Doppler frequency shift expansion is brought under the high-speed motion environment, and under static state or low-speed motion state, not existing ICI or ICI to hang down can ignore, at this moment just needn't utilize said method to carry out ICI and eliminate, to save the system power resource.Particularly, can be before above-mentioned ICI removing method carries out interference eliminated, determine the translational speed of receiver, when this translational speed during greater than default speed threshold, carry out method shown in Figure 1 and carry out interference eliminated, when this translational speed is less than or equal to default speed threshold, no longer carries out interference eliminated, but directly utilize the reception data estimation on the subcarrier to send signal.Wherein preferably, can utilize Doppler frequency shift to estimate to determine the translational speed of receiver.

Further, the ICI removing method of the invention described above can be used in ICI cancellation element shown in Figure 3.As shown in Figure 3, this ICI cancellation element comprises: mould value computing unit, comparator unit, interference factor computing unit, selected cell and interference cancellation unit.

In this ICI cancellation element, mould value computing unit is used to obtain the mould value of current subcarrier.Comparator unit is used for the mould value of more current subcarrier and the thresholding of presetting, if the mould value of current subcarrier greater than default thresholding, is then selected a natural number n in default natural number to be selected, makes 2 ⁿThe most approaching described mould value square, the natural number of selecting is exported to described interference factor computing unit, and trigger selector will be received from the interference factor output of described interference factor computing unit; Otherwise trigger described selector interference factor is put 0 also output.The interference factor computing unit is used for

As 1/H _k, calculate the interference factor of other subcarriers, and the interference factor that calculates imported described selected cell current subcarrier; Wherein, conj () represents conjugate operation, H _kChannel response estimated value for current subcarrier.Selected cell is used for the control according to described comparing unit, and interference factor is exported to described interference cancellation unit.Interference cancellation unit is used for amassing the interference factor of current subcarrier is from reception data and respective sub that the reception data of current subcarrier deduct on other subcarriers, the reception data after the difference result is disturbed as the elimination of current subcarrier.

Provide the specific embodiment of an ICI cancellation element below.Wherein, specifically provided the embodiment of obtaining the related plurality of units of interference factor.In this embodiment, be example with the last subcarrier k-1 that obtains current subcarrier therefore to the interference of current subcarrier, introduce the specific implementation of correlation unit.Fig. 4 is the structure chart of this specific implementation.

As shown in Figure 4,

Preserve the channel estimation value H ' of a last OFDM symbol in a, the buffer unit _k, utilize adder to calculate the channel estimation value H of the current OFDM symbol of current input _kChannel estimation value H ' with a last OFDM symbol in the buffer unit _kPoor, obtain changing value Δ H _k

The channel estimation value H of the current OFDM symbol of b, input _kInput-buffer unit (for example, a buffer) preserves simultaneously, uses calculating channel to estimate transformed value in order to next symbol.

C, Δ H _kOperation divided by j2 π can replace by multiplication described in the abovementioned steps 203 and shifting function.

D, the value that c is obtained also postpone with register holds, become (the Δ H of a last subcarrier correspondence of current subcarrier _K-1)/(-j2 π), utilize the channel response value H of conjugation multiplier and current subcarrier again _kConjugate multiplication, and get negatively, obtain (Δ H _K-1)/(-j2 π) * conj (H _k), export to shift cells right.

E, to the channel estimation value H of current OFDM symbol of input _kAsk range value, i.e. the mould value | H _k|, and utilize comparator bank with the mould value | H _k| compare with thresholding and one group of natural number of setting.If | H _k| the thresholding greater than setting, then further compare | H _k| ²With 2 ⁱ, the one group natural number of i for setting finds and | H _k| ²Immediate 2 ⁱSelected i is exported to shift cells right as n, and the control selected cell, output is received from the interference factor A of shift cells right _K-1If | H _k| be less than or equal to the thresholding of setting, think that then this subcarrier decline is too big, for avoiding introducing big noise, do not carry out ICI and eliminate, the control selected cell directly puts 0 with interference factor.

F, shift cells right obtain the ICI interference factor of subcarrier k-1 to this subcarrier to the result of the d n position that moves right, and export to selected cell.

G, selected cell select output according to the control signal of comparator between the interference factor and 0 that receives, then final selected cell output be exactly definite interference factor A _K-1

As seen by above-mentioned, the buffer unit among Fig. 4, adder, complex multiplier, delay cell, conjugation multiplier and shift unit are finished the function of interference factor computing unit among Fig. 3 jointly.And Fig. 4 is only to calculate interference factor A _K-1For example describes.Similar to the above to the interference factor computing unit of current subcarrier for other subcarriers, just the time of delay of delay cell and position difference to some extent just repeats no more here.

Wait to obtain other subcarriers behind the interference factor on the current subcarrier, it can be inputed to interference cancellation unit, by the reception data Y of interference cancellation unit from the current subcarrier _kIn deduct the interference of other subcarriers, for example deduct the interference Y of adjacent two subcarriers _K-1* A _K-1And Y _K+1* A _K+1, the current subcarrier that obtains " totally " receives data

Among the present invention, further, in the OFDM receiver, can use above-mentioned ICI removing method, and after the reception data of disturbing that are eliminated, further carry out channel estimating again, can access channel estimation value more accurately, further improve the receptivity under the mobile channel according to these data.Particularly, the ofdm signal method of reseptance of using above-mentioned ICI removing method comprises:

A, the reception data on each subcarrier that obtains after handling through fast fourier transform FFT are carried out disturbing between subcarrier the elimination of ICI, reception data after disturbing are eliminated; For the reception data on each subcarrier, utilize method shown in Figure 1 to carry out ICI and eliminate;

B, utilize on each pilot sub-carrier the reception data of eliminating after disturbing to carry out channel estimating again, obtain the channel response of revising on each subcarrier; Particularly, can be with finite impulse response (FIR) filter as interpolation filter, carry out filtering interpolation to the reception data of eliminating after disturbing on each pilot sub-carrier, with the filtering result as the channel estimation value of revising on each subcarrier;

C, utilize the channel response revised on each subcarrier and eliminate reception data after disturbing, determine the transmitting signal estimated value on each subcarrier.

Moving speed estimation is similar with adding in the above-mentioned ICI removing method, uses in the ofdm signal method of reseptance after ICI eliminates, and also can add the step of moving speed estimation, thereby whether control carries out reappraising of ICI elimination and channel response.

Particularly, can be before the reception data on each subcarrier being carried out the ICI elimination, determine the translational speed of receiver, when described translational speed is higher than default speed threshold, reception data on each subcarrier are carried out ICI to be eliminated, and utilize the reception data of eliminating after disturbing on each pilot sub-carrier to carry out channel estimating again, last carry out equilibrium, determine the transmitting signal estimated value on each subcarrier according to the reception data of carrying out again eliminating on the resulting result of channel estimating and each subcarrier behind the ICI.When described translational speed is less than or equal to default speed threshold, can carry out no longer that ICI eliminates and channel reappraises, but directly utilize the reception data on each subcarrier, determine the transmitting signal estimated value on each subcarrier; Perhaps, also can only carry out ICI and eliminate, and carry out channel estimating no longer again, the reception data after utilizing former channel estimation results and eliminating ICI are determined the transmitting signal estimated value on each subcarrier.

With the block diagram of the corresponding OFDM receiver of above-mentioned OFDM method of reseptance as shown in Figure 5, wherein, the module before the FFT is identical with existing OFDM receiver shown in Figure 2, dispenses here.In receiver shown in Figure 5, ICI cancellation module, second pilot extraction module and channel response filtering interpolation module have been increased newly with respect to existing receiver.

Wherein, the ICI cancellation module is used for that the reception data on each subcarrier of FFT module output are carried out ICI and eliminates, and the reception data that are eliminated after disturbing are exported to second pilot extraction module and equilibrium solution mapping block.The realization of concrete this ICI cancellation module just repeats no more as shown in Figure 3 here.Second extracts pilot module, is used to extract the reception data of eliminating on each pilot sub-carrier after disturbing, and exports to channel response filtering interpolation module.Channel response filtering interpolation module, be used to utilize the reception data of eliminating after disturbing on each pilot sub-carrier to carry out channel estimating again, obtain the channel response revised on each subcarrier, and export to the equilibrium solution map unit, be used to estimate the transmission signal on each subcarrier.Particularly, this channel response filtering interpolation module can adopt the FIR filter, for example:

$\tilde{H}\left(k\right)=\underset{i=-L}{\overset{L}{\mathrm{\Σ}}}H(k+i|(k+i){\∈P}_{\mathrm{pilot}})*w_{\mathrm{fil}}\left(i\right)$

Wherein,

Be the channel estimation value that subcarrier k upgrades, L is a filter order, w _Fil(i) be filter coefficient, H (k+i| (k+i) ∈ P _Pilot) the subcarrier k+i that is illustrated in pilot set go up to utilize eliminates the channel response value that the ICI data after interference obtains again.This interpolation filter may be same or similar with the channel estimation module before the ICI cancellation module, but because the input pilot data of this filter had been eliminated the ICI interference, therefore can estimate more precise channels response.

In addition, preferably, above-mentioned OFDM receiver can further include the control circuit of an energy to ICI cancellation module and channel filtering interpolation module difference On/Off.Since these two modules need be to the reception data of all subcarriers recomputate corresponding with channel, power consumption is had relatively high expectations, when static or low-speed motion, can close these two modules to save power consumption by control circuit.

A kind of implementation of this control circuit is that the time domain before the FFT conversion partly increases Doppler's spread estimation module, is used for the estimating Doppler frequency displacement, and then obtains the estimation of movement velocity and determine whether to close this two modules.This implementation as shown in Figure 6.

By the specific implementation of the invention described above as seen, when the receiver high-speed motion, the ICI that the present invention can effectively eliminate between the subcarrier disturbs and provides channel estimation value more accurately, to improve receiver performance., by Doppler's estimation module, can control and close one or two module of the present invention, during static or low-speed motion when receiver to save power consumption.

Being preferred embodiment of the present invention only below, is not to be used to limit protection scope of the present invention.Within the spirit and principles in the present invention all, any modification of being done, be equal to replacement, improvement etc., all should be included within protection scope of the present invention.

Claims (12)

1, the removing method that disturbs between a sub-carrier is characterized in that, this method comprises:

Obtain the mould value of current sub-carrier channels response,, make 2 if this mould value greater than the thresholding that sets in advance, is then selected a natural number n in default natural number to be selected ⁿThe most approaching described mould value square, and will

As 1/H _k, calculate the interference factor of other default subcarriers to current subcarrier; Wherein, conj () represents conjugate operation, H _kChannel response estimated value for current subcarrier;

If described mould value is less than or equal to the thresholding that sets in advance, then described other subcarriers are put 0 to the interference factor of current subcarrier;

The reception data and the respective sub that deduct from the reception data of current subcarrier on other subcarriers are long-pending to the interference factor of current subcarrier, the reception data after the difference result is disturbed as the elimination of current subcarrier.

2, method according to claim 1 is characterized in that,

Described other default subcarriers are two adjacent sub-carriers of current subcarrier;

Described general

As 1/H _k, calculate other subcarriers the interference factor of current subcarrier comprised: utilize formula $\frac{\left(\mathrm{\Δ}{H}_{k-1}\right)/(-j2\mathrm{\π})*\mathrm{conj}\left(H_k\right)}{2^n}$ Calculate the interference factor A of the last subcarrier k-1 of current subcarrier _K-1, utilize formula $\frac{\left(\mathrm{\Δ}{H}_{k-1}\right)/(-j2\mathrm{\π})*\mathrm{conj}\left(H_k\right)}{2^n}$ Calculate the interference factor A of a back subcarrier k+1 of current subcarrier _K+1

3, method according to claim 2 is characterized in that, will

Be expressed as binary constant,

The m position that moves to right again utilizes shift result to replace constant 1/j2 π, is used to calculate interference factor, and described m is default constant.

4, according to arbitrary described method in the claim 1 to 3, it is characterized in that this method further comprises: before carrying out interference eliminated, determine the translational speed of receiver, when described translational speed is higher than default speed threshold, the reception data on each subcarrier is carried out ICI eliminate; Otherwise, process ends.

5, method according to claim 4 is characterized in that, the translational speed of described definite receiver comprises: utilize Doppler frequency shift to estimate to determine the translational speed of receiver.

6, a kind of method of reseptance of orthogonal frequency division multiplex OFDM signal is characterized in that, this method comprises:

Carry out disturbing between subcarrier ICI to eliminate the reception data after the interference that is eliminated to the reception data on each subcarrier that obtains after handling through fast fourier transform FFT;

Utilize the reception data of eliminating after disturbing on each pilot sub-carrier to carry out channel estimating again, obtain the channel response of revising on each subcarrier;

Reception data after utilizing the channel response of revising on each subcarrier and eliminating interference are determined the transmitting signal estimated value on each subcarrier;

Wherein, the elimination that the reception data on the current subcarrier are carried out disturbing between subcarrier comprises:

Obtain the mould value of current subcarrier,, make 2 if this mould value greater than the thresholding that sets in advance, is then selected a natural number n in default natural number to be selected ⁿThe most approaching described mould value square, and will As 1/H _k, be used to calculate the interference factor of other subcarriers to current subcarrier; Wherein, conj () represents conjugate operation, H _kChannel response estimated value for current subcarrier;

If described mould value is less than or equal to the thresholding that sets in advance, then other subcarriers are put 0 to the interference factor of current subcarrier;

The reception data and the respective sub that deduct from the reception data of current subcarrier on other subcarriers are long-pending to the interference factor of current subcarrier, the reception data after the difference result is disturbed as the elimination of current subcarrier.

7, method according to claim 6, it is characterized in that, describedly utilize on each pilot sub-carrier the reception data of eliminating after disturbing to carry out channel estimating again to comprise: with finite impulse response FIR filter as interpolation filter, reception data after eliminate disturbing on each pilot sub-carrier are carried out filtering interpolation, with the filtering result as the channel estimation value of revising on each subcarrier.

8, according to claim 6 or 7 described methods, it is characterized in that, this method further comprises: before the reception data on each subcarrier being carried out the ICI elimination, determine the translational speed of receiver, when described translational speed is higher than default speed threshold, reception data on each subcarrier are carried out ICI eliminate, and carry out the described reception data of eliminating after disturbing on each pilot sub-carrier of utilizing and carry out the operation of channel estimating again; Otherwise, directly utilize reception data on each subcarrier to determine transmitting signal estimated value on each subcarrier, perhaps the reception data on each subcarrier are carried out ICI and eliminate, and directly utilize the reception data of eliminating on former channel estimation value and each subcarrier behind the ICI to determine transmitting signal estimated value on each subcarrier.

9, method according to claim 8 is characterized in that, the translational speed of described definite receiver comprises: utilize Doppler frequency shift to estimate to determine the translational speed of receiver.

10, interference blanking unit between a sub-carrier is characterized in that, this device comprises: mould value computing unit, comparator unit, interference factor computing unit, selected cell and interference cancellation unit;

Described mould value computing unit is used to obtain the mould value of current subcarrier;

Described comparator unit is used for the mould value of more current subcarrier and the thresholding of presetting, if the mould value of current subcarrier greater than default thresholding, is then selected a natural number n in default natural number to be selected, makes 2 ⁿThe most approaching described mould value square, the natural number of selecting is exported to described interference factor computing unit, and trigger selector will be received from the interference factor output of described interference factor computing unit; Otherwise trigger described selector interference factor is put 0 also output;

Described interference factor computing unit, be used for

As 1/H _k, calculate the interference factor of other subcarriers, and the interference factor that calculates imported described selected cell current subcarrier; Wherein, conj () represents conjugate operation, H _kChannel response estimated value for current subcarrier;

Described selected cell is used for the control according to described comparing unit, and interference factor is exported to described interference cancellation unit;

Described interference cancellation unit is used for amassing the interference factor of current subcarrier is from reception data and respective sub that the reception data of current subcarrier deduct on other subcarriers, the reception data after the difference result is disturbed as the elimination of current subcarrier.

11, a kind of receiver of ofdm signal, comprise FFT module, first extraction pilot module, channel estimation module and the equilibrium solution mapping block, it is characterized in that this receiver comprises that also ICI cancellation module, second extracts pilot module and channel response filtering interpolation module;

Described ICI cancellation module is used for that the reception data on each subcarrier of described FFT module output are carried out ICI and eliminates, and the reception data that are eliminated after disturbing are exported to second pilot extraction module and equilibrium solution mapping block;

Described second extracts pilot module, is used to extract the reception data of eliminating on each pilot sub-carrier after disturbing, and exports to described channel response filtering interpolation module;

Described channel response filtering interpolation module is used to utilize on each pilot sub-carrier the reception data of eliminating after disturbing to carry out channel estimating again, obtains the channel response revised on each subcarrier, and exports to described equilibrium solution map unit;

Described ICI cancellation module comprises: mould value computing unit, comparator unit, interference factor computing unit, selected cell and interference cancellation unit;

Wherein, described mould value computing unit is used to obtain the mould value of current subcarrier;

Described comparator unit is used for the mould value of more current subcarrier and the thresholding of presetting, if the mould value of current subcarrier greater than default thresholding, is then selected a natural number n in default natural number to be selected, makes 2 ⁿThe most approaching described mould value square, the natural number of selecting is exported to described interference factor computing unit, and trigger selector will be received from the interference factor output of described interference factor computing unit; Otherwise trigger described selector interference factor is put 0 also output;

Described interference factor computing unit, be used for As 1/H _k, calculate the interference factor of other subcarriers, and the interference factor that calculates imported described selected cell current subcarrier; Wherein, conj () represents conjugate operation, H _kChannel response estimated value for current subcarrier;

Described selected cell is used for the control according to described comparing unit, and interference factor is exported to described interference cancellation unit;

Described interference cancellation unit is used for amassing the interference factor of current subcarrier is from reception data and respective sub that the reception data of current subcarrier deduct on other subcarriers, the reception data after the difference result is disturbed as the elimination of current subcarrier.

12, receiver according to claim 11, it is characterized in that, described receiver further comprises Doppler's estimation module, be used to carry out the movement velocity that Doppler frequency deviation estimates to determine this receiver, when described movement velocity is higher than default speed threshold, start described ICI cancellation module and channel response filtering interpolation module; When described movement velocity is less than or equal to default speed threshold, close described ICI cancellation module and channel response filtering interpolation module, perhaps start described ICI cancellation module and close channel response filtering interpolation module;

Described ICI cancellation module further according to the control of described Doppler's estimation module, starts or closes the operation of itself;

Described channel response filtering interpolation module further according to the control of described Doppler's estimation module, starts or closes the operation of itself.

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