CN105553909B - A kind of method that iteration limit filtration reduces ofdm signal peak-to-average force ratio - Google Patents
A kind of method that iteration limit filtration reduces ofdm signal peak-to-average force ratio Download PDFInfo
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Abstract
A kind of method that iteration limit filtration reduces ofdm signal peak-to-average force ratio, first calculating OFDM time-domain signal power, will be more than power threshold P according to clipping factor-alpha0OFDM real part and imaginary part carry out amplitude limiting processing respectively；It secondly is that OFDM frequency-region signal carries out frequency domain filtering by FFT transform by the OFDM time-domain signal after amplitude limiting processing；Then the signal after frequency domain filtering is transformed to OFDM time-domain signal by IFFT and completes 1 iteration limit filtration processing；Above-mentioned iteration limit filtration treatment process is finally repeated according to maximum number of iterations, method in the present invention does not need ofdm system and transmits additional information, the influence for carrying out extra process compensation originator amplitude limiting processing to ofdm signal in receiving end is not needed yet, by proper choice of clipping factor-alpha, it only needs to complete amplitude limiting processing by add operation, and processing result can be directly by carrying out frequency domain filtering after FFT transform；The work clock that can be used in iteration limit filtration operation higher than sample rate is multiplexed FFT/IFFT converter unit, saves the realization resource that peak-to-average force ratio inhibits.
Description
Technical field
The invention belongs to digital wireless communication transmission technique fields, are related to a kind of iteration limit filtration reduction ofdm signal peak
The method of ratio.
Background technique
Orthogonal frequency division multiplexing (Orthogonal Frequency Division Multiplexing, OFDM) technology is one
The advantages that planting multi-carrier modulation technology, relying on its higher transmission rate, stronger ability of anti-multipath is widely used in wireless
The communications field is one of the core technology of forth generation land mobile communication.
The basic principle of OFDM technology is that the input traffic of high speed serialization is modulated to NsThe mutually orthogonal low speed in road is simultaneously
On capable subcarrier, so that the information rate of every subcarriers data flow is reduced to the 1/N of input trafficsTimes, data symbol
Period expansion is the N of input datasTimes.The modulating/demodulating process of OFDM generallys use inverse Fourier transform/Fourier transformation
(Inverse Fast Fourier Transform, IFFT/FFT) is realized, therefore baseband OFDM symbols are expressed as
Wherein, X (k) is the data on k-th of subcarrier, NsFor the size of IFFT.
It can be seen that ofdm modulation signal by N from the expression formula of OFDM baseband signalsA independent and orthogonal subcarrier is folded
Add.Work as NsThere may be biggish peak values when a subcarrier in-phase stacking, lead to the peak-to-average power of ofdm system
(Peak-to-Average Power Ratio, PAPR) is higher.PAPR is defined as ofdm signal peak signal peak power and letter
The ratio between number mean power, is expressed as
Wherein, x (n) is OFDM baseband signal, and E [] indicates to calculate expectation.Measuring the most common method of PAPR performance is
It compensates cumulative distribution function (Complementary Cumulative Distribution Function, CCDF), indicates number
PAPR according to block is more than the probability of given thresholding λ: CCDF=P { PAPR > λ }.
Since ofdm signal has biggish PAPR, usually require that transmitter intermediate power amplifier there must be biggish line
Property dynamic range, especially when the work of transmitter nonlinear power amplifier is when close to saturation point, signal can generate frequency outside serious band
Spectrum leakage and inband distortion cause monkey chatter and bit error rate (Bit Error Rate, BER) performance to decline.Commonly
PAPR suppression technology is broadly divided into three classes, i.e. predistortion technology, signal coding technology, probability class technology.Wherein, Signal coding skill
Art and probability class technology need transmitting additional information to demodulate for receiving end, and companding transform technology needs are connecing in predistortion technology
Receiving end carries out solution companding processing.Comprehensively consider the performance and hardware realization complexity of PAPR suppressing method, changes in predistortion technology
It is relatively simple practical PAPR suppressing method for limit filtration technology.
Traditional iteration limit filtration method (Iterative Clipping and Filtering, ICF) includes clipping
With filtering two-step pretreatment.Amplitude limiting processing is by J times of over-sampling of ofdm signal { xu(n), n=0 ..., JNs- 1 } amplitude and thresholding A
It compares, amplitude limiting processing is carried out to the amplitude for being more than A, is expressed as
Wherein, xcuIt (n) is clipping treated ofdm signal, | xu(n) | it is ofdm signal amplitude before amplitude limiting processing,
For ofdm signal phase before amplitude limiting processing.By being inserted into N to centres(J-1) a zero frequency-region signalCarry out JNsPoint IFFT converts to obtain J times of over-sampling
Ofdm signal.
In order to reduce the out of band spectrum interference of amplitude limiting processing introducing, frequency domain low-pass usually is carried out to the signal after clipping
Wave.Firstly, by the signal { x after clippingcu(n), n=0 ..., JNs- 1 } pass through JNsThe FFT transform of point obtains frequency domain letter to frequency domain
Number { Xcu(k), k=0 ..., JNs-1}；Then, by { Xcu(k), k=0 ..., JNs- 1 } intermediate Ns(J-1) a sampling zero setting.By
It will lead to ofdm signal peak regeneration in filtering processing, therefore need that ofdm signal is repeated several times above-mentioned limit filtration processing, obtain
Obtain preferable PAPR rejection.
The angle analysis realized from method, traditional iteration limit filtration method are needed signal x (n) before amplitude limiting processing
=A (n) ejθ(n)Be transformed to amplitude A (n) and phase theta (n) under polar coordinates from real part and imaginary part, according to clipping thresholding to amplitude into
Row clipping, phase remain unchanged, the amplitude A (n) of signal under polar coordinates and phase theta (n) are transformed to right angle after amplitude limiting processing
The real part Re { x (n) } and imaginary part Im { x (n) } of ofdm signal under coordinate.It follows that in the amplitude limiting processing of 1 iterative process
In just need to carry out 2 coordinate transforms, therefore the iterative process of such ICF method realize it is complex.
Summary of the invention
Present invention solves the technical problem that are as follows: overcome the deficiencies of the prior art and provide a kind of iteration limit filtration reduction
The method of ofdm signal peak-to-average force ratio.This method first according to limit ratio γ to the real part of OFDM time-domain signal and imaginary part respectively according to
Clipping factor-alpha carries out amplitude limiting processing；Then, OFDM frequency-region signal is filtered and constellation extension, and transforms to time domain continuation
Next iteration amplitude limiting processing.The amplitude limiting processing unit of this method according to clipping Factor minute safety pin to the real part of signal and imaginary part into
Row clipping, by proper choice of the clipping factor, amplitude limiting processing only needs add operation, and interative computation unit is set using repeatedly multiplexing
Meter can obtain preferable system performance while reducing complexity.
The technical solution that the present invention solves are as follows: a kind of method that iteration limit filtration reduces ofdm signal peak-to-average force ratio, step
It is as follows:
(1) extract OFDM time domain baseband signals x (n), n=0 ..., Ns- 1 } real and imaginary parts calculate OFDM time domain base
Band signal power P (n), n=0 ..., Ns- 1 }, it is expressed as
P (n)=(Re { x (n) })2+(Im{x(n)})2
In formula, Re { x (n) } and Im { x (n) } be respectively in OFDM time domain baseband signals the real part of n-th sampling x (n) and
Imaginary part；OFDM time domain baseband signals x (n), n=0 ..., Ns- 1 } expression formula is
In formula, NdFor the effective sub-carrier number of OFDM frequency domain, NsFor the size of IFFT/FFT transformation, X (k) is k-th of subcarrier
The frequency domain data of upper modulation, by being N by lengthdThe multiple random sequence of MPSK/MQAM modulation to be mapped to OFDM frequency domain mutual
Orthogonal NsThe N of a subcarrierdOn a low frequency component, (Ns-Nd) a high fdrequency component zero padding, obtain OFDM frequency domain sequence
(2) will be calculated in step (1) OFDM time domain baseband signals power P (n), n=0 ..., Ns- 1 } and amplitude gate
Limit P0It compares, according to the clipping factor-alpha of setting, preferably 0 < α < 1, to more than P0Ofdm signal sampling real part and imaginary part carry out
Clipping is expressed as
In formula, xCIt (n) is the OFDM time domain baseband signals after clipping, clipping thresholding P0By the limit ratio γ and OFDM set
Time domain baseband signals x (n), n=0 ..., Ns- 1 } mean power E [| x (n) |2] determine, i.e. P0=10γ/10·E[|x(n)
|2]。
(3) the OFDM time domain baseband signals { x after the clipping for obtaining step (2)C(n), n=0 ..., Ns- 1 } pass through NsPoint
FFT transform obtains frequency-region signal { XC(k), k=0 ..., Ns- 1 }, by { XC(k), k=0 ..., Ns- 1 } intermediate Ns-NdA sampled value
Zero setting, the signal { X after obtaining frequency domain filteringCF(k), k=0 ..., Ns- 1 }, it is expressed as
(4) by the signal { X after step (3) frequency domain filteringCF(k), k=0 ..., Ns- 1 } pass through NsPoint IFFT converts to obtain 1
OFDM time-domain signal { x after secondary limit filtrationCF(n), n=0 ..., Ns-1}；
(5) the OFDM time-domain signal { x for setting maximum number of iterations as I, after the limit filtration that step (4) is obtainedCF(n),
N=0 ..., Ns- 1 } replace step (1) in input OFDM time domain baseband signals x (n), n=0 ..., Ns- 1 }, step is repeated
(1)~(4), until the number of iterations meets the maximum number of iterations I of setting, after the limit filtration that I time step (4) is obtained
OFDM time-domain signal { xCF(n), n=0 ..., Ns- 1 } value, as OFDM time-domain signal { y (n), the n after iteration limit filtration
=0 ..., Ns-1}。
The peak-to-average power ratio (PAPR) of ofdm signal is expressed as OFDM time-domain signal peak signal peak power and signal is flat
Equal power ratio, is expressed as
In formula, x (n) is OFDM baseband signal, and E [] indicates to calculate expectation.
The compensation cumulative distribution function (CCDF) for measuring ofdm signal PAPR performance is expressed as
CCDF=P { PAPR > λ }
In formula, λ is thresholding given when measuring PAPR performance.
The peak OFDM of OFDM time domain baseband signals based on above-mentioned transmitting terminal, iteration limit filtration proposed by the invention is equal
Than suppressing method realization structure as shown in Figure 1, having follow steps:
(1) signal power is calculated
OFDM baseband signal x (n), n=0 ..., Ns- 1 } it is complex signal, calculates OFDM base according to its real and imaginary parts
Band signal power P (n), n=0 ..., Ns- 1 }, it is expressed as
P (n)=(Re { x (n) })2+(Im{x(n)})2
In formula, Re { x (n) } and Im { x (n) } be respectively in OFDM time domain baseband signals the real part of n-th sampling x (n) and
Imaginary part.
(2) amplitude limiting processing of real part and imaginary part
To be calculated in step (1) OFDM baseband signal power P (n), n=0 ..., Ns- 1 } with clipping thresholding P0Phase
Than according to clipping factor-alpha (usually taking 0 < α < 1) to more than P0Ofdm signal sampling real part and imaginary part carry out clipping, indicate
For
In formula, xCIt (n) is clipping treated ofdm signal.Clipping thresholding P0By limit ratio γ and average power signal E [|
x(n)|2] determine, γ=10log10(E[|x(n)|2]/(α2P0)), when E [| x (n) |2When]=1, P0=10γ/10/α2。
(3) FFT transform and frequency domain filtering
Signal { x after the clipping that step (2) is obtainedC(n), n=0 ..., Ns- 1 } pass through NsPoint FFT transform obtains frequency domain
Signal { XC(k), k=0 ..., Ns-1}.By { XC(k), k=0 ..., Ns- 1 } intermediate Ns-NdA sampled value zero setting obtains frequency domain filter
Signal { X after waveCF(k), k=0 ..., Ns- 1 }, it is expressed as
In formula, NdFor effective sub-carrier number of ofdm signal, NsFor IFFT/FFT size.
(4) IFFT is converted
By the signal { X after frequency domain filteringCF(k), k=0 ..., Ns- 1 } pass through NsPoint IFFT converts to obtain 1 limit filtration
OFDM time-domain signal { x afterwardsCF(n), n=0 ..., Ns-1}。
If maximum number of iterations is I, the signal { x obtained to step (4)CF(n), n=0 ..., Ns- 1 } step (1) is repeated
~(4), the OFDM time-domain signal { y until the maximum number of iterations I of the number of iterations satisfaction setting, after obtaining iteration limit filtration
(n), n=0 ..., Ns-1}.Wherein, the selection of maximum number of iterations I need to comprehensively consider system peak-to-average force ratio inhibit require with
And the implementation complexity that peak-to-average force ratio inhibits.
Clipping calculates the realization structure with reuse plan in the iteration limit filtration method that Main Analysis is proposed below.
1. clipping calculates: when by selecting the value of clipping factor-alpha to be superimposed for 2 integral number power, in above-mentioned steps (2)
Multiplying can be completed by addition.By taking the real part clipping operation of signal as an example, limit width factor-alpha=α12-1+α22-2…+αl2-lThere is l in the binary number of expression0Position is 1, l-l0Position is 0, and data sampling is quantified as M-bit binary number in the implementation.Letter
Steps are as follows for the amplitude limiting processing of change:
It (a) will be more than thresholding P0The M-bit binary number of ofdm signal real part move to right to obtain l respectively0A binary number, and
By l0A binary number is added；
(b) M-bit binary number can be obtained by truncating the result being added in step (a), after as 1 iteration amplitude limiting processing
Ofdm signal real part numerical value.
2. reuse plan: in iteration limit filtration method, each iteration needs to calculate separately 1 FFT transform and 1 time
IFFT transformation.In the implementation, by being higher than sample rate L0It repeats that 1 FFT unit is called to complete successive ignition under clock again
The mode that FFT/IFFT is converted in operation, it is possible to reduce FFT computing unit needed for ICF method realization process is saved and realized
Resource.
The advantages of the present invention over the prior art are that:
(1) iteration limit filtration method of the invention does not need to transmit additional information for receiving end demodulation, is not required to yet
To carry out additional operation compensation method for suppressing peak to average ratio in receiving end influences, it is only necessary in transmitting terminal according to limit ratio to signal
Real and imaginary parts according to the clipping factor carry out simple process；
(2) iteration limit filtration method of the invention is in step (2), can be to avoid by properly selecting the clipping factor
Multiplication operation only completes amplitude limiting processing by add operation, and amplitude limiting processing result can be carried out directly by FFT transform to frequency domain
Frequency domain filtering processing；
(3) iteration limit filtration method of the invention is in step (3) and step (4), by using higher than ofdm signal
The work clock of sample rate repeats the IFFT/FFT operation during calling FFT unit to realize successive ignition, has saved OFDM hair
Penetrate the hardware realization resource that peak-to-average force ratio inhibits in machine；
(4) iteration limit filtration method of the invention has lower implementation complexity, in identical the number of iterations and limit
Under the conditions of amplitude ratio, by proper choice of the clipping factor, it can obtain in situation similar in performance of BER and change better than tradition
For the peak-to-average ratio inhibition performance of limit filtration.
Detailed description of the invention
Fig. 1 is the realization structure chart that iteration limit filtration proposed by the invention reduces Peak-to-Average Power Ratio method；
Fig. 2 is the method flow diagram that iteration limit filtration proposed by the invention reduces Peak-to-Average Power Ratio method；
Fig. 3 is the CCDF curve using iteration limit filtration method and conventional method (ICF) of the invention；
Fig. 4 is the BER performance schematic diagram using iteration limit filtration method and conventional method (ICF) of the invention.
Specific embodiment
Basic ideas of the invention are as follows: a kind of method that iteration limit filtration reduces ofdm signal peak-to-average force ratio calculates first
OFDM time-domain signal power will be more than power threshold P according to clipping factor-alpha0OFDM real part and imaginary part carry out at clipping respectively
Reason；It secondly is that OFDM frequency-region signal carries out frequency domain filtering by FFT transform by the OFDM time-domain signal after amplitude limiting processing；Then will
Signal after frequency domain filtering is transformed to OFDM time-domain signal by IFFT and completes 1 iteration limit filtration processing；Last basis is most
Big the number of iterations repeats above-mentioned iteration limit filtration treatment process, and the method in the present invention does not need ofdm system and transmits additionally
Information does not need the influence for carrying out extra process compensation originator amplitude limiting processing to ofdm signal in receiving end, by suitably selecting yet
Select clipping factor-alpha, it is only necessary to amplitude limiting processing be completed by add operation, and processing result can be directly by carrying out after FFT transform
Frequency domain filtering；The work clock that can be used in iteration limit filtration operation higher than sample rate is multiplexed FFT/IFFT converter unit,
Save the realization resource that peak-to-average force ratio inhibits.
With reference to the accompanying drawing with specific implementation example, the present invention is described in further detail.Following instance is for illustrating this
Invention, but it is not limited to use scope of the invention.
Main idea is that: a kind of method that iteration limit filtration reduces ofdm signal peak-to-average force ratio is provided.It is mentioned
Iteration limit filtration method out does not need transmitting additional information or carries out extra process in receiving end, it is only necessary in transmitting terminal root
Amplitude limiting processing is carried out according to clipping factor-alpha according to real and imaginary parts of the limit ratio γ to ofdm signal.Iteration clipping filter of the invention
Wave reduce ofdm signal peak-to-average force ratio method realization structure as shown in Figure 1 firstly, according to ofdm signal x (n), n=0 ...,
Ns- 1 } real part and imaginary part calculate signal power P (n), n=0 ..., Ns-1}；Secondly, according to clipping factor-alpha to more than power
Thresholding P0The real part and imaginary part of the signal of (being calculated by limit ratio γ) carry out clipping, by selecting clipping factor-alpha secondary for 2 integer
Power superposition, amplitude limiting processing can operate to avoid multiplication, only be realized by add operation；Then, by the signal { x after clippingC(n),
N=0 ..., Ns- 1 } pass through NsPoint FFT transform to frequency domain, and by frequency-region signal centre Ns-NdFrequency is completed in a sampled value zero setting
Domain filtering；Finally, the signal after frequency domain filtering is passed through NsThe IFFT of point is transformed to after time domain obtains 1 iteration limit filtration
Ofdm signal.It repeats the above steps, until the number of iterations is equal to the maximum number of iterations I of setting, completion OFDM peak-to-average ratio inhibits.
Ofdm signal has the feature that in iteration limit filtration method of the invention
(1) in OFDM transmitting terminal, if the effective sub-carrier number of OFDM frequency domain is Nd, the size of IFFT/FFT transformation is Ns.By length
For NdMPSK/MQAM modulation multiple random sequence be mapped to the mutually orthogonal N of OFDM frequency domainsThe N of a subcarrierdOn a low frequency component,
(Ns-Nd) a high fdrequency component zero padding, obtain OFDM frequency domain sequence
By OFDM frequency domain sequence X (k), k=0 ..., Ns- 1 } N is carried outsThe IFFT of point converts to obtain OFDM time domain baseband signals, is expressed as
In formula, X (k) is the frequency domain data modulated on k-th of subcarrier.
(2) peak-to-average power ratio (PAPR) of ofdm signal is expressed as OFDM time-domain signal peak signal peak power and signal
The ratio between mean power is expressed as
In formula, x (n) is OFDM baseband signal, and E [] indicates to calculate expectation.
(3) the compensation cumulative distribution function (CCDF) for measuring ofdm signal PAPR performance is expressed as
CCDF=P { PAPR > λ }
In formula, λ is thresholding given when measuring PAPR performance.
The peak OFDM of OFDM time domain baseband signals based on above-mentioned transmitting terminal, iteration limit filtration proposed by the invention is equal
Than suppressing method flow chart as shown in Fig. 2, having follow steps:
(1) signal power is calculated
OFDM baseband signal x (n), n=0 ..., Ns- 1 } it is complex signal, calculates OFDM base according to its real and imaginary parts
Band signal power P (n), n=0 ..., Ns- 1 }, it is expressed as
P (n)=(Re { x (n) })2+(Im{x(n)})2
In formula, Re { x (n) } and Im { x (n) } be respectively in OFDM time domain baseband signals the real part of n-th sampling x (n) and
Imaginary part.
(2) amplitude limiting processing of real part and imaginary part
To be calculated in step (1) OFDM baseband signal power P (n), n=0 ..., Ns- 1 } with clipping thresholding P0Phase
Than according to clipping factor-alpha (usually taking 0 < α < 1) to more than P0Ofdm signal sampling real part and imaginary part carry out clipping, indicate
For
In formula, xCIt (n) is clipping treated ofdm signal, the value of clipping factor-alpha can pass through diplomatic copy invented party
The peak-to-average ratio inhibition performance and BER performance of method determine.Clipping factor-alpha value is too small, will lead to the BER of signal after peak-to-average force ratio inhibits
Performance is poorer；Clipping factor-alpha value is excessive, will lead to peak-to-average ratio inhibition performance under identical the number of iterations and is deteriorated, thus clipping because
The preferred scope of sub- α is 0.8≤α < 1.Clipping thresholding P0By the limit ratio γ that sets and average power signal E [| x (n) |2] really
It is fixed, P0=10γ/10·E[|x(n)|2], when E [| x (n) |2When]=1, P0=10γ/10.In the nothing based on IEEE802.11 standard
Line local area network (WLAN), forth generation land mobile communication etc. using OFDM system system in, the usual value of limit ratio γ be 3≤
γ < 8 (unit: dB).
(3) FFT transform and frequency domain filtering
Signal { x after the clipping that step (2) is obtainedC(n), n=0 ..., Ns- 1 } pass through NsPoint FFT transform obtains frequency domain
Signal { XC(k), k=0 ..., Ns-1}.By { XC(k), k=0 ..., Ns- 1 } intermediate Ns-NdA sampled value zero setting obtains frequency domain filter
Signal { X after waveCF(k), k=0 ..., Ns- 1 }, it is expressed as
In formula, NdFor effective sub-carrier number of ofdm signal, NsFor IFFT/FFT size.
(4) by the signal { X after frequency domain filteringCF(k), k=0 ..., Ns- 1 } pass through NsPoint IFFT converts to obtain 1 clipping
Filtered OFDM time-domain signal { xCF(n), n=0 ..., Ns-1}。
If maximum number of iterations is I, when the number of iterations is less than I, signal { x that step (4) is obtainedCF(n), n=
0,…,Ns- 1 } input signal as step (1) repeats step (1)-(4)；When the number of iterations is equal to I, step (4) are obtained
Signal { the x arrivedCF(n), n=0 ..., Ns- 1 } as after iteration limit filtration OFDM time-domain signal y (n), n=0 ..., Ns-
1}.Wherein, the peak-to-average force ratio that the selection of maximum number of iterations I needs to comprehensively consider system inhibits the reality required and peak-to-average force ratio inhibits
Existing complexity, i.e. maximum number of iterations I is bigger, and the peak-to-average ratio inhibition performance of this method is better, but realizes that process is more complicated, needs
Hardware realization resource it is more.The usual value range of maximum number of iterations I is 1≤I≤20.
Clipping calculates the realization structure with reuse plan in the iteration limit filtration method that Main Analysis is proposed below.
1. clipping calculates: when by selecting the value of clipping factor-alpha to be superimposed for 2 integral number power, in above-mentioned steps (2)
Multiplying can be completed by addition.By taking the real part clipping operation of signal as an example, limit width factor-alpha=α12-1+α22-2…+αl2-lThere is l in the binary number of expression0Position is 1, l-l0Position is 0, when wherein l is the integral number power superposition that clipping factor representation is 2
The sum of sum term, and data sampling is quantified as M-bit binary number in realization.Simplify in iteration amplitude limit method of the invention
Steps are as follows for amplitude limiting processing:
It (a) will be more than thresholding P0The M-bit binary number of ofdm signal real part move to right to obtain l respectively0A binary number, and
By l0A binary number is added；
(b) M-bit binary number can be obtained by truncating the result being added in step (a), after as 1 iteration amplitude limiting processing
Ofdm signal real part numerical value.
2. reuse plan: in iteration limit filtration method, each iteration needs to calculate separately 1 FFT transform and 1 time
IFFT transformation.In the implementation, by being higher than sample rate L0It repeats that 1 FFT unit is called to complete successive ignition under clock again
The mode that FFT/IFFT is converted in operation, it is possible to reduce FFT computing unit needed for ICF method realization process is saved and realized
Resource.
Effect of the invention can further be illustrated by following emulation.
In ofdm communication system, if sub-carrier number Ns=256, the effective sub-carrier number N of useru=180, signal bandwidth is
Bw=3MHz, subcarrier spacing are Δ f=15kHz, up-sample multiple L=19, clipping factor-alpha=2-1+2-2+2-3+2-4=
0.9375, limit ratio γ=5dB, maximum number of iterations I=12.
Fig. 3, Fig. 4 are the CCDF curve and BER using iteration limit filtration method and traditional IC F method of the invention
Energy.As can be seen that in limit ratio γ, the identical situation of maximum number of iterations I, when clipping factor-alpha=0.9375, the present invention
The PAPR rejection of method is better than traditional IC F method, and BER performance is close with traditional IC F method.As CCDF=0.1%,
The PAPR value of OFDM original signal is more than 11.33dB, can be reduced to the PAPR value of ofdm signal using traditional IC F method
8.30dB can be reduced to 8.18dB using iteration limit filtration method proposed by the invention.
Non-elaborated part of the present invention belongs to techniques well known.
Claims (3)
1. a kind of method that iteration limit filtration reduces ofdm signal peak-to-average force ratio, it is characterised in that steps are as follows:
(1) extract OFDM time domain baseband signals x (n), n=0 ..., Ns- 1 } real and imaginary parts calculate OFDM time-domain baseband letter
Number power P (n), n=0 ..., Ns- 1 }, it is expressed as
P (n)=(Re { x (n) })2+(Im{x(n)})2
In formula, Re { x (n) } and Im { x (n) } are respectively the real and imaginary parts of n-th of sampling x (n) in OFDM time domain baseband signals；
OFDM time domain baseband signals x (n), n=0 ..., Ns- 1 } expression formula is
In formula, NdFor the effective sub-carrier number of OFDM frequency domain, NsFor the size of IFFT/FFT transformation, X (k) is k-th of subcarrier up-regulation
The frequency domain data of system, by being N by lengthdThe multiple random sequence of MPSK/MQAM modulation to be mapped to OFDM frequency domain mutually orthogonal
NsThe N of a subcarrierdOn a low frequency component, (Ns-Nd) a high fdrequency component zero padding, obtain OFDM frequency domain sequence
(2) will be calculated in step (1) OFDM time domain baseband signals power P (n), n=0 ..., Ns- 1 } with clipping thresholding P0
It compares, according to the clipping factor-alpha of setting to more than P0Ofdm signal sampling real part and imaginary part carry out clipping, be expressed as
In formula, xCIt (n) is the OFDM time domain baseband signals after clipping, clipping thresholding P0By the limit ratio γ and OFDM time domain set
Baseband signal x (n), n=0 ..., Ns- 1 } mean power E [| x (n) |2] determine, i.e. P0=10γ/10·E[|x(n)|2]；
The real part and imaginary part of ofdm signal sampling carry out the implementation method of clipping are as follows: by selecting the value of clipping factor-alpha are 2
Integral number power superposition completes multiplying by addition, and wherein clipping factor-alpha indicates are as follows: α=α12-1+α22-2…+αl2-l,
This group of binary number α1,α2…αlIn have l0Position is 1, l-l0Position is 0, and data sampling is quantified as M-bit binary number in the implementation,
Steps are as follows:
It a) will be more than thresholding P0Ofdm signal real part or the M-bit binary number of imaginary part move to right to obtain l respectively0A binary number, and
By l0A binary number is added；
B) M-bit binary number can be obtained by truncating the result being added in step a), the OFDM letter after as 1 iteration amplitude limiting processing
Number real part or imaginary numbers；
(3) the OFDM time domain baseband signals { x after the clipping for obtaining step (2)C(n), n=0 ..., Ns- 1 } pass through NsPoint FFT
Transformation obtains frequency-region signal { XC(k), k=0 ..., Ns- 1 }, by { XC(k), k=0 ..., Ns- 1 } intermediate Ns-NdA sampled value is set
Zero, the signal { X after obtaining frequency domain filteringCF(k), k=0 ..., Ns- 1 }, it is expressed as
(4) by the signal { X after step (3) frequency domain filteringCF(k), k=0 ..., Ns- 1 } pass through NsPoint IFFT converts to obtain 1 limit
Filtered OFDM time-domain signal { xCF(n), n=0 ..., Ns-1}；
(5) the OFDM time-domain signal { x for setting maximum number of iterations as I, after the limit filtration that step (4) is obtainedCF(n), n=
0,…,Ns- 1 } replace step (1) in input OFDM time domain baseband signals x (n), n=0 ..., Ns- 1 }, repeat step (1)~
(4), until the number of iterations meets the maximum number of iterations I of setting, after the iteration limit filtration that I time step (4) is obtained
OFDM time-domain signal { xCF(n), n=0 ..., Ns- 1 } value, as OFDM time-domain signal { y (n), the n after iteration limit filtration
=0 ..., Ns-1}。
2. the method that a kind of iteration limit filtration according to claim 1 reduces ofdm signal peak-to-average force ratio, it is characterised in that:
The peak-to-average power ratio (PAPR) of the OFDM time domain baseband signals is expressed as OFDM time-domain signal peak signal peak power and letter
The ratio between number mean power, is expressed as
In formula, x (n) is OFDM baseband signal, and E [] indicates to calculate expectation.
3. the method that a kind of iteration limit filtration according to claim 1 reduces ofdm signal peak-to-average force ratio, it is characterised in that:
The compensation cumulative distribution function (CCDF) for measuring the OFDM time domain baseband signals PAPR performance is expressed as
CCDF=P { PAPR > λ }
In formula, λ is thresholding given when measuring PAPR performance.
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