CN104348775A - Wireless signal receiving machine and wireless signal receiving method - Google Patents

Abstract

The invention discloses a wireless signal receiving machine. The wireless signal receiving machine has a larger Doppler frequency offset compensation range, and the transmission quality of a business channel can be further improved. The receiving machine comprises a circulation prefix removing unit, a merging unit and n branch processing modules, wherein the circulation prefix removing unit is used for receiving downlink wireless signals, and carries out circulation prefix removing processing on the received wireless signals, in addition, the signals are divided into n branch signals according to different multi-path frequency offset, and each branch signal is respectively input into the corresponding branch processing module; each branch processing module is used for decoding the input branch signal, and the decoding signal of the corresponding branch is obtained and is input into the merging unit; the merging unit is used for merging the input decoding signals of each branch and outputting the merged signals. The invention also discloses a wireless signal receiving method.

Description

A kind of wireless signal receiver and radio signal receiving method

Technical field

The application relates to wireless communication technology field, particularly relates to a kind of wireless signal receiver and radio signal receiving method.

Background technology

OFDM (OFDM) technology is adopted to be main implementation in LTE system down link, ofdm system adds symbol period, make this system more responsive to frequency shift (FS), more strict to synchronous requirement, otherwise the orthogonality can destroyed between subcarrier, increase the crosstalk between subchannel, thus have a strong impact on systematic function.One of LTE system main purpose will provide high rate data transmission for mobile subscriber, and this just has higher requirement to the transmission reliability of business datum high order modulation.And the demodulation of higher order signal is more responsive to frequency departure, usual frequency departure is greater than 50Hz, will have influence on the demodulation performance of 64QAM.

In practical application scene, the terminal of high-speed mobile brings larger Doppler frequency shift to communication system, brings very large impact to the performance of terminal.Therefore, for reducing the impact that frequency shift (FS) causes, being necessary to carry out Frequency offset estimation and compensation to received signal, ensureing that receiving terminal is consistent with the frequency of transmitting terminal, improving the timing estimation performance of ofdm system, ensureing transmission quality.

At present, the scheme of carrying out thin frequency deviation estimation for ofdm system mainly contains based on synchronizing signal with based on nonsynchronous signal two kinds, mainly contains following three kinds in LTE system based on the frequency deviation estimating method of synchronizing signal:

Carry out related operation according to synchronizing signal, and then obtain estimated value;

Frequency deviation estimating method based on non-pilot symbol can utilize the Cyclic Prefix of OFDM symbol and tail data to ask relevant, and then obtains frequency deviation estimated value;

Or, utilize pilot signal to carry out related operation, and then obtain frequency deviation estimated value.

It is the common method that solution receiver and transmitter exist frequency deviation that receiver adopts frequency offset correction algorithm to carry out compensate of frequency deviation, but general frequency offset correction algorithm is as utilized synchronizing signal, there is certain frequency offset estimation range, go beyond the scope, systematic function sharply declines, and system may be caused to work.In high-speed railway communication system, the mode of distributed base station is a kind of solution cell merge better scheme frequently.In distributed base station system, a baseband processing unit (BBU) connects multiple Remote Radio Unit (RRU), when high ferro is between two RRU, namely away from a RRU close another one RRU simultaneously, the signal of two RRU that terminal receives has larger Doppler shift and the positive and negative difference of frequency deviation, such two Signal averaging cause inter-sub-carrier interference, especially in high order modulation situation, are difficult to meet service feature requirement by the method for above-mentioned frequency offset correction.Thus, being necessary to design a kind of receiver for having larger Doppler's compensate of frequency deviation scope, improving the transmission quality of Traffic Channel further.

Summary of the invention

This application provides wireless signal receiver, this receiver has larger Doppler's compensate of frequency deviation scope, can improve the transmission quality of Traffic Channel further.

A kind of wireless signal receiver that the embodiment of the present application provides, comprising: go cyclic prefix unit, merge cells and n branch road processing module,

Described cyclic prefix unit of going, for receiving downstream wireless signals, is carried out removal circulation prefix processing to the wireless signal received, and is divided into n tributary signal according to the difference of multipath frequency deviation, each tributary signal is input to respectively corresponding branch road processing module; N be more than or equal to 2 natural number;

The tributary signal of each branch road processing module described to input carries out corresponding compensate of frequency deviation and decoding, obtains the decoded signal of corresponding branch road and is input to merge cells;

Merge cells is used for the decoded signal of each branch road of input to merge, and exports the signal after merging.

Wireless signal receiver according to claim 1, is characterized in that, described n equals 2 or 3.

Wireless signal receiver according to claim 1, is characterized in that, the decoded signal of each branch road of input is merged into by described merge cells: the decoded signal of each branch road of input is carried out equal gain combining by merge cells.

Wireless signal receiver according to claim 2, it is characterized in that, when described n equals 3, the 1st branch road processing module and the 3rd branch road processing module adopt positive and negative maximum doppler frequency to carry out compensate of frequency deviation respectively, and the 2nd branch road processing module adopts synchronizing signal correlation method to carry out compensate of frequency deviation.

Preferably, each branch road processing module described comprises frequency shift unit, fast Fourier transform unit, channel estimating unit and balanced unit.

The embodiment of the present application additionally provides a kind of radio signal receiving method, comprising:

Receive downstream wireless signals, removal circulation prefix processing is carried out to the wireless signal received, and is divided into n tributary signal according to the difference of multipath frequency deviation;

Respectively compensate of frequency deviation and decoding are carried out to each tributary signal, obtains the decoded signal of corresponding branch road;

The decoded signal of each branch road is merged, and exports the signal after merging.

As can be seen from the above technical solutions, utilize signal to produce different frequency displacements by multipath channel, and the decline of each multipath signal is uncorrelated mutually, the Doppler shift of channel is larger, and each tributary signal will become more uncorrelated later.Receiver, by carrying out corresponding compensate of frequency deviation respectively to the multipath signal received, produces different diversity branch signals, and therefore these diversity branch signals merged can provide diversity gain.In high-speed railway communication system, adopt the base station case of distributed RRU, the increase being by RRU people has the multipath signal of different Doppler shift, and therefore technical scheme is particularly useful for high-speed railway communication system.

Accompanying drawing explanation

Fig. 1 is the distributed base station scene schematic diagram of high ferro communication system in the embodiment of the present application;

What Fig. 2 provided for the embodiment of the present application adopts based on the block diagram of the receiver of Doppler diversity at receiving terminal;

Fig. 3 is a kind of MPS process scene schematic diagram of the high ferro communication system in the embodiment of the present application;

Fig. 4 is that the Doppler diversity method of reseptance that the embodiment of the present application proposes compares schematic diagram with the simulation experiment result of frequency offset correction algorithm conventional in prior art.

Embodiment

In high-speed railway communication system, because train can reach very high speed, therefore can with larger doppler spread, the Doppler shift that carrier frequency 2.6GHz, 300km/h are corresponding is 722Hz, and now channel is quick time-varying channel, has time selectivity.The frequency bias compensation method that the application proposes, its fundamental design idea is exactly utilize signal to produce different frequency displacements by multipath channel later, and the decline of each multipath signal is uncorrelated mutually, and the Doppler shift of channel is larger, and each tributary signal will become more uncorrelated.Therefore these diversity branch signals merged can provide diversity gain.。Receiver, by carrying out corresponding compensate of frequency deviation respectively to the multipath signal received, produces different diversity branch signals,

In high-speed railway communication system, adopt the base station case of distributed RRU, the increase being by RRU people has the multipath signal of different Doppler shift, and at high speeds, there is larger Doppler shift, by suitable signal transacting, just can obtain many mutual incoherent paths, namely can obtain Doppler diversity gain, and frequency offset correction can only make the frequency deviation of receiving terminal and transmitting terminal reduce as far as possible, extra gain can not be obtained.

For making the know-why of technical scheme, feature and technique effect clearly, below in conjunction with specific embodiment, technical scheme is described in detail.

The response of wireless multi-path time-varying channel impulse is

$h(t,\mathrm{\τ})=\frac{1}{\sqrt{N_p}}\mathrm{\Σ}{\mathrm{\α}}_p{e}^{j2\mathrm{\π}{f}_{{D_p}^t}}\mathrm{\δ}(\mathrm{\τ}-{\mathrm{\τ}}_p)---\left(1\right)$

Wherein, N _p, α _p, and τ _pbe respectively multipath number, the decline of p footpath channel, Doppler frequency shift and time delay. at [-f _d, f _d] upper equally distributed.

Consider that the OFDM comprising N number of subcarrier sends symbol:

$s\left(t\right)=\frac{1}{N}\underset{n=0}{\overset{N-1}{\mathrm{\Σ}}}{d}_n{e}^{j\frac{2\mathrm{\π}}{N}{f}_{n}t}g\left(t\right)---\left(2\right)$

Wherein, d _nbe modulation symbol, g (t) is into window function, f _nfor the frequency that subcarrier n is corresponding.OFDM sends signal after transmission, can represent and become:

$x\left({\mathrm{kT}}_s\right)=\frac{1}{\sqrt{N_{p}N}}\underset{p=1}{\overset{N_p}{\mathrm{\Σ}}}{\mathrm{\α}}_p{e}^{j2\mathrm{\π}{f}_{{D_p}^{{\mathrm{kT}}_s}}}\underset{i=0}{\overset{N-1}{\mathrm{\Σ}}}{d}_i{e}^{j\frac{2\mathrm{\π}}{N}{f}_i({\mathrm{kT}}_s-{\mathrm{\τ}}_p)}+n\left({\mathrm{kT}}_s\right)---\left(3\right)$

Wherein, T _s, n (kT _s) be respectively time-domain sampling interval and additive noise.

L sub-carrier is through diversity branch frequency displacement f _xafter, signal y (j, the f of output _x) be

$y(l,f_x)=\frac{1}{\sqrt{N}}\underset{k=0}{\overset{N-1}{\mathrm{\Σ}}}x\left(k\right)e^{-j2\mathrm{\π}{f}_{x}k}{e}^{-j2\mathrm{\πl\Δfk}}=y_s(l,f_x)+y_{\mathrm{ICI}}+n---\left(4\right)$

Wherein, y _s(l, f _x) be useful signal, y _iCIfor inter-sub-carrier interference signal, n represents noise item.

y _s(l,f _x)＝d _lH(l,f _x) (5)

D _lthe symbol that subcarrier l sends, H (l, f _x) be signal gain on subcarrier l,

$H(l,f_x)=\frac{1}{N\sqrt{N_p}}\underset{p=1}{\overset{N_p}{\mathrm{\Σ}}}{\mathrm{\α}}_p{e}^{-j2\mathrm{\πl\Δf}{\mathrm{\τ}}_p}{e}^{\mathrm{j\π}(N-1)(f_{D_p}-f_x)}\frac{\sin \mathrm{N\π}(f_{D_p}-f_x)}{\sin \mathrm{\π}(f_{D_p}-f_x)}---\left(6\right)$

So, frequency-shifted components is respectively with two branch roads on cross-correlation can be expressed as

$R^l(f_{x_1},f_{x_2})={\mathrm{\σ}}_d^2{R}_{\mathrm{HH}}^l(f_{x_1},f_{x_2})$

$=\frac{{\mathrm{\σ}}_{\mathrm{\α}}^2{\mathrm{\σ}}_d^2}{N^2{N}_p}\underset{p=1}{\overset{N_p}{\mathrm{\Σ}}}E\left\{e^{\mathrm{j\π}(N-1)(f_{x_2}-f_{x_1})}\frac{\sin \mathrm{N\π}(f_{D_p}-f_{x_1})\sin \mathrm{N\π}(f_{D_p}-f_{x_2})}{\sin \mathrm{\π}(f_{D_p}-f_{x_1})\sin \mathrm{\π}(f_{D_p}-f_{x_2})}\right\}---\left(7\right)$

From above formula, the Doppler diversity branch road of different frequency displacement is that uncorrelated or part is correlated with mutually.Inter-sub-carrier interference in formula (4) can be expressed as

$y_{\mathrm{ICI}}(l,f_x)=\frac{1}{N\sqrt{N_p}}\underset{p=1}{\overset{N_p}{\mathrm{\Σ}}}{\mathrm{\α}}_p\underset{i=0,i\≠l}{\overset{N-1}{\mathrm{\Σ}}}{d}_i{e}^{-j2\mathrm{\πi\Δf}{\mathrm{\τ}}_p}{e}^{\mathrm{j\π}(N-1)[(i-l)\mathrm{\Δf}+f_{D_p}-f_x]}\×$ (8)

$\frac{\sin \mathrm{N\π}[(i-l)\mathrm{\Δf}+f_{D_p}-f_x]}{\sin \mathrm{\π}[(i-l)\mathrm{\Δf}+f_{D_p}-f_x]}$

Because the symbol carried between subcarrier is zero-mean and mutually independently, the interference therefore between subcarrier is incoherent mutually.Based on this, the radio signal receiving method that the application provides comprises:

Receive downstream wireless signals, removal circulation prefix processing is carried out to the wireless signal received, and is divided into n tributary signal according to the difference of multipath frequency deviation;

Respectively compensate of frequency deviation and decoding are carried out to each tributary signal, obtains the decoded signal of corresponding branch road;

The decoded signal of each branch road is merged, and exports the signal after merging.

Radio communication scene under a kind of high-speed railway in the embodiment of the present application as shown in Figure 1, in order to reduce high ferro cell merge frequently, the mode connecting multiple RRU by a BBU expands the covering radius of community, multiple RRU is evenly arranged along high ferro circuit, distance between adjacent R RU is 4km, and the vertical range of each RRU and high ferro circuit is 400m.When high ferro travels with 300km/h, and when being in the position of black rectangle shown in Fig. 1, the signal frequency deviation receiving RRU2 and RRU3 is respectively 722Hz and-722Hz.

What Fig. 2 provided for the embodiment of the present application adopts based on the block diagram of the receiver of Doppler diversity at receiving terminal, this receiver comprises CP unit, merge cells and n branch road processing module, the structure of each branch road processing module is identical, wherein i-th branch road processing module comprises the i-th frequency shift unit, the i-th fast Fourier transform (FFT) unit, the i-th channel estimating unit and the i-th balanced unit.

In distributed RRU high-speed railway communication system, because receiving terminal receives the composite signal with multiple RRU signals of different frequency deviation, the signal on multiple RRU is uncorrelated mutually, therefore has diversity gain.

First, the signal that receiver receives can be divided into Liang Ge branch, adopts f1 frequency to carry out compensate of frequency deviation to Doppler diversity branch 1, adopts f2 frequency to carry out compensate of frequency deviation to Doppler diversity branch 2.Two Doppler diversity branch roads are adopted in this example.

Secondly, solution OFDM modulation, channel estimation and equalization are carried out to different compensate of frequency deviation two Doppler diversity tributary signals, solves the symbol on this branch road.

Finally, the signal on two branch roads is merged, as equal gain combining.Signal after being combined carries out the subsequent operations such as planisphere mapping.

Another one embodiment is as follows,

Radio communication scene under high-speed railway is as follows, in order to reduce high ferro cell merge frequently, can by increasing transmitting power, and the mode strengthening cell coverage area solves, namely as shown in Figure 3.

Under above-mentioned scene, receiving terminal receives has the multipath channel of different frequency deviation, becomes and incoherent mutually when each multipath channel is quick, and therefore the carrying out of each multipath signal merges, and can obtain diversity gain.

First, the signal that receiver receives can be divided into three branches.Because maximum Doppler frequency offset correspond to the maximum power of channel, therefore two branch roads can utilize positive and negative maximum Doppler frequency offset to carry out compensate of frequency deviation respectively, and another one branch road can utilize conventional frequency excursion algorithm to carry out compensate of frequency deviation.

Secondly, solution OFDM modulation, channel estimation and equalization are carried out to the multiple Doppler diversity tributary signal of different compensate of frequency deviation, solves the symbol on this branch road.

Finally, the signal on two branch roads is merged, as equal gain combining.Signal after being combined carries out the subsequent operations such as planisphere mapping.

Can be obtained by Fig. 4, when employing 64QAM modulation and under being in high speed 500km/h situation, frequency deviation correcting method conventional in prior art can not make system worked well; And the frequency bias compensation method based on Doppler diversity adopting the embodiment of the present application to provide, when SNR is at 29dB, the BLER of system drops to 0.1.

The foregoing is only the preferred embodiment of the application; not in order to limit the protection range of the application; within all spirit in technical scheme and principle, any amendment made, equivalent replacements, improvement etc., all should be included within scope that the application protects.

Claims (6)

1. a wireless signal receiver, is characterized in that, comprising: go cyclic prefix unit, merge cells and n branch road processing module,

Described cyclic prefix unit of going, for receiving downstream wireless signals, is carried out removal circulation prefix processing to the wireless signal received, and is divided into n tributary signal according to the difference of multipath frequency deviation, each tributary signal is input to respectively corresponding branch road processing module; N be more than or equal to 2 natural number;

The tributary signal of each branch road processing module described to input carries out corresponding compensate of frequency deviation and decoding, obtains the decoded signal of corresponding branch road and is input to merge cells;

Merge cells is used for the decoded signal of each branch road of input to merge, and exports the signal after merging.

2. wireless signal receiver according to claim 1, is characterized in that, described n equals 2 or 3.

3. wireless signal receiver according to claim 1, is characterized in that, the decoded signal of each branch road of input is merged into by described merge cells: the decoded signal of each branch road of input is carried out equal gain combining by merge cells.

4. wireless signal receiver according to claim 2, it is characterized in that, when described n equals 3, the 1st branch road processing module and the 3rd branch road processing module adopt positive and negative maximum doppler frequency to carry out compensate of frequency deviation respectively, and the 2nd branch road processing module adopts synchronizing signal correlation method to carry out compensate of frequency deviation.

5. the wireless signal receiver according to any one of Claims 1-4, is characterized in that, each branch road processing module described comprises frequency shift unit, fast Fourier transform unit, channel estimating unit and balanced unit.

6. a radio signal receiving method, is characterized in that, comprising:

Receive downstream wireless signals, removal circulation prefix processing is carried out to the wireless signal received, and is divided into n tributary signal according to the difference of multipath frequency deviation;

Respectively compensate of frequency deviation and decoding are carried out to each tributary signal, obtains the decoded signal of corresponding branch road;

The decoded signal of each branch road is merged, and exports the signal after merging.