CN101621489B - Channel estimation method for four-phase modulation system - Google Patents

Abstract

The invention discloses a channel estimation method for a four-phase modulation system, which belongs to the digital communication field. The method comprises the following steps: a sending terminal performing four-phase modulation to a binary sequence Bt(m) to obtain a frequency-domain symbol sequence Xt(k), performing the FFT or the DFT to the symbol sequence Xt(k) to obtain a transmitted time-domain sequence xt(n), a receiving terminal performing FFT or DFT to the received time-domain sequence xt(n) to obtain a received frequency-domain sequence Yr(k), calculating the amplitude and the phase of the frequency-domain sequence Yr(k) to obtain an amplitude sequence AH(k) and a phase sequence Phi(k), the amplitude sequence AH(k) being namely the amplitude of a channel response H, performing the phase rotation to the phase sequence Phi(k) to obtain a phase sequence Theta H<0>(k), performing the phase correction to the phase sequence Theta H<0>(k) to obtain a corrected phase sequence Theta H(k) which is namely the phase of the channel response H. The invention directly utilizes the received four-phase modulation symbol to perform channel estimation without decision feedback and avoids the influence of wrong judgment to the channel estimation accuracy.

Description

A kind of channel estimation methods that is used for four phase Modulation OFDM systems

Technical field

The invention belongs to digital communicating field, be specifically related to a kind of channel estimation methods that is used for four phase Modulation OFDM systems.

Background technology

(Orthogonal Frequency Division Multiplexing, OFDM) in the system, accuracy of channel estimation directly influences the portfolio effect of frequency-region signal, and then influences the performance of whole OFDM system at OFDM.Channel estimation methods in traditional ofdm system comprises two kinds of non-blind channel estimation method and blind channel estimation methods.Non-blind channel estimation method adopts the mode of inserting training sequence or inserting pilot tone to carry out channel estimating usually.This method has increased redundant information, has reduced system transmissions efficient, but can the real-time tracking channel variation.In order to reach high as far as possible data transmission efficiency, some ofdm system does not send training sequence and the pilot tone that is specifically designed to channel estimating, therefore can't adopt non-blind channel estimation method to carry out channel estimating.

Blind channel estimation method mainly comprises the method for estimation based on decision-feedback, and this method need not to increase redundant information, and efficiency of transmission is high.A kind of blind channel estimation method commonly used is based on the channel estimation methods of decision-feedback.Data after this method will be adjudicated carry out feeding back to channel estimator after the symbol-modulated, and channel estimator is removed modulation intelligence through the division arithmetic that will receive between the modulating data after data and the judgement, thereby obtains channel response estimation result.But this method is owing to need adjudicate data, and accuracy of channel estimation depends on the correctness of judgement data.When certain number of sub-carrier is in deep fade for a long time or receive influencing that single-frequency disturbs for a long time, be prone to the error propagation phenomenon, cause bigger channel estimation errors.

Summary of the invention

The objective of the invention is to propose a kind of channel estimation methods that is used for four phase Modulation OFDM systems that is applicable under the inapparent channel condition of time-varying characteristics; It directly utilizes the four phase modulation signals that receive to estimate the amplitude and the phase place of channel response respectively, and then obtains channel response estimation result.

The technical scheme of channel estimation methods of the present invention is following:

A kind of channel estimation methods that is used for four phase Modulation OFDM systems, its step comprises:

A) transmitting terminal is with binary sequence B _t(m) carry out four modulation mutually, obtain symbol sebolic addressing X _t(k);

B) with the frequency domain symbol sequence X _t(k) carry out IFFT (Inverse Fast Fourier Transform, inverse fast Fourier transform) or IDFT (Inverse Discrete Fourier Transform, inverse discrete Fourier transform), the time domain sequences x that obtains sending _t(n), this time domain sequences x _t(n) arrive receiving terminal through channel, receiving terminal receives time domain sequences y _r(n);

C) receiving terminal is with the time domain sequences y that receives _r(n) carry out FFT (Fast Fourier Transformation, fast Fourier transform) or DFT (Discrete Fourier Transform, discrete Fourier transform), the frequency domain sequence Y that obtains receiving _r(k);

D) calculate frequency domain sequence Y _r(k) amplitude and phase place obtain the amplitude sequence A _H(k) and phase sequence

This amplitude sequence A _H(k) be the amplitude of channel response H.

E) phase sequence

is carried out the phase place rotation, obtain phase sequence

F) to phase sequence

Carry out the phase place correction, obtain revised phase sequence θ _H(k).This phase sequence θ _H(k) be the phase place of channel response H.

Further, above-mentioned steps a) in, to binary sequence B _t(m) carry out four mutually the modulation method following:

Successively with sequence B _t(m) per two input bits are mapped as a modulation symbol according to four phase modulation constellation in.Wherein, The amplitude of four constellation point on the planisphere is identical; The phase place of adjacent constellation point differs pi/2, and the phase place of the constellation point of first quartile is the arbitrary value between

.

Further; Above-mentioned steps e) in; The method of phase sequence

being carried out phase place rotation is following: to each phase value in the phase sequence

take advantage of 4 successively, mould 2 π and remove 4 computings, thereby obtain phase sequence

Further; Above-mentioned steps f) in; The method of phase sequence

being carried out the phase place correction is following: thresholding T is set; Begin from second frequency of phase sequence , carry out successively as judging:

(1) calculates this frequency

With previous frequency

Phase difference $\mathrm{\&Delta;\; \&theta;}={\mathrm{\&theta;}}_H^0\left(k_0\right)-{\mathrm{\&theta;}}_H^0(k_0-1);$

(2) as if Δ θ>=T, ${\mathrm{\&theta;}}_H^0\left(k_0\right)={\mathrm{\&theta;}}_H^0\left(k_0\right)-\frac{\mathrm{\&pi;}}{2};$ If Δ θ≤-T, ${\mathrm{\&theta;}}_H^0\left(k_0\right)={\mathrm{\&theta;}}_H^0\left(k_0\right)+\frac{\mathrm{\&pi;}}{2};$ Otherwise, if | Δ θ |＜T,

Remain unchanged, the frequency sequence number adds 1, i.e. k ₀=k ₀+ 1;

(3) repeating step (1) and (2) are up to the phase place correction of accomplishing last frequency.

Advantage of the present invention and technique effect are:

1, the present invention directly utilizes four phase modulation symbols of reception to carry out channel estimating, need not to carry out decision-feedback, avoids the influence of mistaken verdict for precision of channel estimation.

2, the amplitude and the phase place of channel response are estimated that separately its amplitude is obtained by the amplitude of four phase modulation symbols, its phase place is obtained by phase place rotation and phase correction procedure.

3, phase place rotation and phase correction procedure only need displacement, comparison, sum operation, realize simply, complexity is low.

Description of drawings

The transmitter architecture block diagram that Fig. 1 the present invention proposes;

The channel estimation methods that Fig. 2 the present invention proposes is implemented block diagram;

The four phase modulation constellation that Fig. 3 the present invention proposes;

Fig. 4 (a) is the channel estimating phase curve before the phase place correction;

Fig. 4 (b) is the revised channel estimating phase curve of phase place;

The amplitude curve of the channel estimating that the channel estimation method that Fig. 5 (a) provides for employing the present invention obtains;

The phase curve of the channel estimating that the channel estimation method that Fig. 5 (b) provides for employing the present invention obtains.

Embodiment

Specify the channel estimation methods that is used for four-phase modulation system that is applicable under the inapparent channel condition of time-varying characteristics of the present invention below in conjunction with accompanying drawing, but be not construed as limiting the invention.

As shown in Figure 1, the present invention proposes at transmitting terminal, to binary sequence B _t(m) carry out four modulation mutually, obtain the frequency domain symbol sequence X _t(k).Wherein, four phase modulation constellation are as shown in Figure 3, and α representes the phase place of the constellation point of first quartile.Then, with the frequency domain symbol sequence X _t(k) carry out IFFT or IDFT, the time domain sequences x that obtains sending _t(n).

Fig. 2 has provided the channel estimation methods enforcement block diagram that the present invention proposes, and specifically describes as follows:

The 1--receiving terminal is with the time domain sequences y that receives _r(n) carry out FFT or DFT, the frequency domain sequence Y that obtains receiving _r(k).

2--calculates frequency domain sequence Y _r(k) amplitude and phase place obtain the amplitude sequence A _H(k) and phase sequence

This amplitude sequence A _H(k) be the amplitude of channel response H.

3--carries out the phase place rotation with phase sequence

; It is following to obtain its phase place spinning solution of phase sequence

: to each phase value in the phase sequence

take advantage of 4 successively, mould 2 π and remove 4 computings, thereby obtain phase sequence

4--is to phase sequence Carry out the phase place correction, obtain revised phase sequence θ _H(k).This phase sequence θ _H(k) be the phase place of channel response H.Its phase correction method is following: thresholding T is set; Begin from second frequency of phase sequence

, carry out successively as judging:

(1) calculates this frequency

With previous frequency

Phase difference $\mathrm{\&Delta;\; \&theta;}={\mathrm{\&theta;}}_H^0\left(k_0\right)-{\mathrm{\&theta;}}_H^0(k_0-1).$

(2) as if Δ θ>=T, ${\mathrm{\&theta;}}_H^0\left(k_0\right)={\mathrm{\&theta;}}_H^0\left(k_0\right)-\frac{\mathrm{\&pi;}}{2};$ If Δ θ≤-T, ${\mathrm{\&theta;}}_H^0\left(k_0\right)={\mathrm{\&theta;}}_H^0\left(k_0\right)+\frac{\mathrm{\&pi;}}{2};$ Otherwise, if | Δ θ |＜T,

Remain unchanged, the frequency sequence number adds 1, i.e. k ₀=k ₀+ 1.

(3) repeating step (1) and (2) are up to the phase place correction of accomplishing last frequency.

Enumerate a concrete embodiment below the channel estimation methods that the present invention proposes is described.If total number of sub carrier wave of ofdm system is 256, effectively number of sub carrier wave is 210.The constellation point phase place α of first quartile is taken as 0 in the four phase modulation constellation.Binary sequence B _t(m) to modulation symbol sequence X _t(k) mapping relations adopt the Gray code mapping, and are as shown in the table.Transmitting terminal is with X _t(k) carry out 256 IFFT, the time domain sequences x that obtains sending _t(n).This time domain sequences x _t(n) arrive receiving terminal through Gaussian channel, receiving terminal receives time domain sequences y _r(n).

Receiving terminal is with time domain sequences y _r(n) carry out 256 FFT, choose 210 complex values on effective subcarrier as frequency domain sequence Y _r(k).Calculate Y _r(k) amplitude and phase place obtain the amplitude sequence A _H(k) and phase sequence

Wherein, amplitude sequence A _H(k) be the amplitude of channel response H.With phase sequence

In each phase value take advantage of 4 successively, mould 2 π and remove 4 phase place rotary manipulation, obtain phase sequence

For example,

Behind the phase place rotary manipulation, $\{{\mathrm{\&theta;}}_H^0\left(1\right),{\mathrm{\&theta;}}_H^0\left(2\right),...,{\mathrm{\&theta;}}_H^0\left(10\right)\}=\{\mathrm{1.2848,1.2724,1.2601},\mathrm{1.2479,1.2391,1.2309,1.2113,1.2011},$ $\mathrm{1.1872,1.1810}\}.$

Then;

carries out following phase place correction operations to phase sequence: thresholding

is set begins from second frequency of phase sequence

, carry out successively as judging:

(1) calculates this frequency With previous frequency

Phase difference $\mathrm{\&Delta;\; \&theta;}={\mathrm{\&theta;}}_H^0\left(k_0\right)-{\mathrm{\&theta;}}_H^0(k_0-1).$

(2) as if Δ θ>=T, ${\mathrm{\&theta;}}_H^0\left(k_0\right)={\mathrm{\&theta;}}_H^0\left(k_0\right)-\frac{\mathrm{\&pi;}}{2};$ If Δ θ≤-T, ${\mathrm{\&theta;}}_H^0\left(k_0\right)={\mathrm{\&theta;}}_H^0\left(k_0\right)+\frac{\mathrm{\&pi;}}{2};$ Otherwise, if | Δ θ |＜T,

Remain unchanged, the frequency sequence number adds 1, i.e. k ₀=k ₀+ 1.

(3) repeating step (1) and (2) are up to the phase place correction of accomplishing last frequency.

Figure 4 shows the phase correction, respectively before and after the channel estimation phase curve (ie, phase sequence and

).

Revised phase sequence θ _H(k) be the phase place of channel response H.Can see that the phase place correction operations has been eliminated the trip point in the phase curve, make phase curve become continuous.Shown in Figure 5 is under Gaussian channel, and signal to noise ratio is 31dB, the amplitude curve and the phase curve of the channel estimating that the channel estimation method that adopts the present invention to provide obtains.Consider the influence of making a start in the system and receiving the end low pass filter, amplitude is approximate consistent with the amplitude and the phase place theoretical curve of Gaussian channel with the phase estimation curve.

Although disclose practical implementation method of the present invention and accompanying drawing for the purpose of illustration; Its purpose is to help to understand content of the present invention and implement according to this; But it will be appreciated by those skilled in the art that: in the spirit and scope that do not break away from the present invention and appended claim, various replacements, variation and modification all are possible.The present invention should not be limited to this specification and the disclosed content of accompanying drawing, and the scope that the present invention requires to protect is as the criterion with the scope that claims define.

Claims (3)

1. channel estimation methods that is used for four phase Modulation OFDM systems, its step comprises:

A) transmitting terminal is with binary sequence B _t(m) carry out four modulation mutually, obtain the frequency domain symbol sequence X _t(k);

B) with the frequency domain symbol sequence X _t(k) carry out inverse fast Fourier transform or inverse discrete Fourier transform, the time domain sequences x that obtains sending _t(n), this time domain sequences x _t(n) arrive receiving terminal through channel, receiving terminal receives time domain sequences y _r(n);

C) receiving terminal is with the time domain sequences y that receives _r(n) carry out fast Fourier transform or discrete Fourier transform, the frequency domain sequence Y that obtains receiving _r(k);

D) calculate frequency domain sequence Y _r(k) amplitude and phase place obtain the amplitude sequence A _H(k) and phase sequence

This amplitude sequence A _H(k) be the amplitude of channel response H;

E) to phase sequence

In each phase value take advantage of 4 successively, mould 2 π and remove 4 computings, thereby obtain phase sequence ${\mathrm{\&theta;}}_H^0\left(k\right);$

F) to phase sequence

Carry out the phase place correction, obtain revised phase sequence θ _H(k), this phase sequence θ _H(k) be the phase place of channel response H; Its method is:

Thresholding T is set; Begin from second frequency of phase sequence

, carry out successively as judging:

1) calculates this frequency

With previous frequency

Phase difference $\mathrm{\&Delta;\; \&theta;}={\mathrm{\&theta;}}_H^0\left(k_0\right)-{\mathrm{\&theta;}}_H^0(k_0-1);$

2) as if Δ θ>=T, ${\mathrm{\&theta;}}_H^0\left(k_0\right)={\mathrm{\&theta;}}_H^0\left(k_0\right)-\frac{\mathrm{\&pi;}}{2};$ If Δ θ≤-T, ${\mathrm{\&theta;}}_H^0\left(k_0\right)={\mathrm{\&theta;}}_H^0\left(k_0\right)+\frac{\mathrm{\&pi;}}{2};$ Otherwise, if | Δ θ |＜T,

Remain unchanged, the frequency sequence number adds 1, i.e. k ₀=k ₀+ 1;

3) repeating step 1) and 2), up to the phase place correction of accomplishing last frequency.

2. the method for claim 1 is characterized in that, above-mentioned steps a) in, successively with sequence B _t(m) per two input bits are mapped as a modulation symbol according to four phase modulation constellation in.

3. method as claimed in claim 2; It is characterized in that; The amplitude of four constellation point on the planisphere is identical; The phase place of adjacent constellation point differs pi/2, and the phase place of the constellation point of first quartile is the arbitrary value between

.

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