CN101729469B - Multi-rate processing system - Google Patents

Abstract

The invention discloses a multi-rate processing system. The multi-rate processing system comprises an anti-aliasing/anti-image filter, wherein the original mold of the anti-aliasing/anti-image filter adopts a lattice structure which is on the basis of a wave number filtering algorithm and is used for extracting anti-aliasing filter of down-sampling processing from synchronous information in an initial cell search process and interpolating anti-image filter of up-sampling processing into the synchronous information in a channel estimation process. The technical scheme of the invention adopts the lattice structure on the basis of the wave number filtering algorithm to realize the multi-rate processing in an LTE system, which has the advantages of narrow transition band, in-band proximate linear phase, high system stability, little influence caused by a filter coefficient and high computational efficiency.

Description

A kind of multi-rate processing system

Technical field

The present invention relates generally to communication technical field, refers to especially a kind of multi-rate processing system in the LTE system.

Background technology

In LTE (Long Term Evolution, Long Term Evolution) system, the many places critical process has related to multi-speed processing, the wherein most important extraction processing that comprises synchronizing information in the cell initial search process, and the interpolation processing in the channel estimation process.

LTE standard code synchronizing information is on 62 subcarriers (except the DC subcarrier) of centre, as shown in Figure 1.For the system of a unknown bandwidth, because synchronizing information all is over-sampling (OSR (over sampling ratio)＞1), should do first down-sampled processing before doing cell initial search (Initial Cell Search, ICS).According to the basic principle of multi-speed processing, do down-sampled before, must do first anti-aliasing filter.

On the contrary, be channel estimating (CHE, Channel Estimator) time, at specific resource particle (RE, Resource Element) known reference signal (RS is inserted in the position, Reference Signal) to calculate the locational channel estimating of this RE, then utilize the method for interpolation to obtain the locational channel estimating of other all RE, as shown in Figure 2.Clearly original channel estimating owes to sample, need to do to rise sampling processing, according to the basic principle of multi-speed processing, do rise sampling after, need to carry out anti-mirror image filtering.

Down-sampled process for cell initial search, the LTE system is defined in SCH (Supplemental Channel, Supplemental Channel) and PDSCH (Physical Downlink Shared Channel, 5 subcarriers are arranged Physical Downlink Shared Channel), can utilize these 5 subcarriers as the transition band of frequency overlapped-resistable filter, transition band is narrow comparatively speaking; And for the sampling process that rises of channel estimating, need the noise of giving consideration to channel, mirror image to disturb and multipath component.If therefore adopt the FIR design multirate filter of linear phase, all need very high exponent number during realization, complexity is very high, has limited the performance of multi-rate filtering.

Summary of the invention

The present invention proposes a kind of multi-rate processing system, employing realizes multi-speed processing in the LTE system based on the lattice structure of wavenumber filtering algorithm, has advantages of that transition band is narrow, approximately linear phase place in the band, stiffness of system are high, be subjected to that the filter coefficient variable effect is little and computational efficiency is high.

Technical scheme of the present invention is achieved in that

A kind of multi-rate processing system comprises:

Anti-aliasing/anti-mirror filter, described anti-aliasing/anti-mirror filter prototype adopts the lattice structure based on the wavenumber filtering algorithm, be used for cell initial search process synchronizing information is extracted the anti-mirror image filtering that interpolation rises sampling processing in the anti-aliasing filter of down-sampled processing and the channel estimation process.

Preferably, described anti-aliasing/anti-mirror filter is the infinite impulse response iir filter with approximately linear phase property.

Preferably, when the over-sampling multiple greater than 2 the time, the multi-term expression of described infinite impulse response iir filter is:

$H\left(z\right)=\underset{K=1}{\overset{M}{\mathrm{\Σ}}}{Z}^{-K+1}\×H_K\left(Z^M\right);$

Wherein, H _K(Z ^M) be the all-pass filter expression formula of K item, and determine H according to exponent number N and over-sampling multiple _K(Z ^M) exponent number.

Preferably, described anti-aliasing/anti-mirror filter comprises the multiplication unit after low bit quantization is processed.

Preferably, the bit number span of described multiplication unit is 4 to 8 bits.

Preferably, also comprise:

Selected cell is used for selecting according to the multi-path location that channel estimating obtains the cut-off frequency of described anti-mirror filter.

Preferably, also comprise:

Compensating unit is used for carrying out nonlinear compensation in the filtered sequence of channel estimation process antagonism mirror image.

Technical scheme of the present invention adopts based on the multi-speed processing in the lattice structure realization LTE system of wavenumber filtering algorithm, the multirate filter of realizing based on this algorithm can overcome the restriction of traditional iir filter and FIR design of filter, has advantages of that transition band is narrow, approximately linear phase place in the band, stiffness of system are high, be subjected to that the filter coefficient variable effect is little and computational efficiency is high.

Description of drawings

In order to be illustrated more clearly in the embodiment of the invention or technical scheme of the prior art, the below will do to introduce simply to the accompanying drawing of required use in embodiment or the description of the Prior Art, apparently, accompanying drawing in the following describes only is some embodiments of the present invention, for those of ordinary skills, under the prerequisite of not paying creative work, can also obtain according to these accompanying drawings other accompanying drawing.

Fig. 1 is the schematic diagram of synchronizing information position in the LTE system;

Fig. 2 is the distribution schematic diagram of resource particle in the LTE system (RE);

Fig. 3 is the structural representation of a kind of multi-rate processing system preferred embodiment of the present invention;

Fig. 4 is a kind of structural representation of the lattice filter prototype based on the wavenumber filtering algorithm;

Fig. 5 is that another kind is based on the structural representation of the lattice filter prototype of wavenumber filtering algorithm;

Fig. 6 is the schematic diagram that synchronizing information extracts down-sampled processing in the cell initial search process.

Embodiment

Below in conjunction with the accompanying drawing in the embodiment of the invention, the technical scheme in the embodiment of the invention is clearly and completely described, obviously, described embodiment only is the present invention's part embodiment, rather than whole embodiment.Based on the embodiment among the present invention, those of ordinary skills belong to the scope of protection of the invention not making the every other embodiment that obtains under the creative work prerequisite.

With reference to Fig. 3, show the structural representation of a kind of multi-rate processing system preferred embodiment of the present invention.Described multi-rate processing system comprises anti-aliasing/anti-mirror filter and selected cell, compensating unit.

Described anti-aliasing/anti-mirror filter prototype adopts the lattice structure based on the wavenumber filtering algorithm, be used for cell initial search process synchronizing information is extracted the anti-mirror image filtering that interpolation rises sampling processing in the anti-aliasing filter of down-sampled processing and the channel estimation process.

Described anti-aliasing/anti-mirror filter comprises the multiplication unit after low bit quantization is processed.The bit number span of described multiplication unit is 4 to 8 bits, and described multiplication unit is hanged down bit quantization, can reduce hard-wired complexity.

Described selected cell is used for selecting according to the multi-path location that channel estimating obtains the cut-off frequency of described anti-mirror filter.

Described compensating unit is used for carrying out nonlinear compensation in the filtered sequence of channel estimation process antagonism mirror image.

LTE system multi-speed processing is stricter to being with interior performance and transition band to require, and therefore will guarantee under the not high prerequisite of hardware implementation complexity the approximately linear phase place in the realization band and the transition band of sharp cut-off.

Thereby what time following the main consideration of filter prototype design is:

1, filter order N is not less than 7, thereby guarantees the transition band of sharp cut-off.

2, filter order N is not more than 15, thereby guarantees Systems balanth, reduces the complexity of design.

3, make N+1 equal the integral multiple of over-sampling multiple as far as possible, thereby be convenient to multinomial decomposition.

4, first the many logical modellings with the branch above the lattice structure are single order, other be designed to two rank models, thereby guarantee approximately linear phase place in the band.

With reference to Fig. 4, Fig. 5, show two kinds based on the structural representation of the lattice filter prototype of wavenumber filtering algorithm, the described structural correspondence of Fig. 4 [(N+1)/4] ∈ Z wherein, the described structural correspondence of Fig. 5 [(N-1)/4] ∈ Z.

Preferably, according to OFDM (Orthogonal Frequency Division Multiplexing, OFDM) to being with interior nonlinear phase than more sensitive characteristics, described anti-aliasing/anti-mirror filter adopts the infinite impulse response iir filter with approximately linear phase property.

When the sampling multiple greater than 2 the time, at first obtain the ψ at equivalent zero point of iir filter prototype _BK(K=1......N) and equivalent limit ψ _AK(K=1......N), then obtain the polynomial expression formula of iir filter:

$H\left(z\right)=\underset{K=1}{\overset{M}{\mathrm{\Σ}}}{Z}^{-K+1}\×H_K\left(Z^M\right);$

Wherein, H _K(Z ^M) be the all-pass filter expression formula of K item, and determine H according to exponent number N and over-sampling multiple _K(Z ^M) exponent number.

When the over-sampling multiple equals 2, use the unit delay unit to replace an exponent part of lattice filter prototype; First all-pass filter of other unit, two rank is removed, and keep the unit delay unit, thereby obtain the filter of half band structure, thereby saved half amount of calculation and system resource.

With reference to Fig. 6, show the schematic diagram that synchronizing information in the cell initial search process extracts down-sampled processing.

Always have as can be known from Fig. 16 kinds of over-samplings, wherein the highest over-sampling is 16 times, for the frequency overlapped-resistable filter design, need very low cut-off frequency to come the outer interference of inhibition zone, and the complexity of filter reduces and rapid growth with cut-off frequency, and 16 the process of therefore falling multiple and be splits into 8X and two down-sampled processes of 2X; Down-sampled multiple is that 12 process splits into 4X and two down-sampled processes of 3X.

According to above decomposition, down-sampled process can design as follows:

1, design is based on the lattice filter group of wave number algorithm, and wherein the cut-off frequency of single filter is respectively pi/2 (half band structure), π/3 (three filters), π/4 (four filters), π/8 (eight filters).

2, the sample rate of supporting according to radio frequency integrated circuit RFIC is determined down-sampled multiple, wherein when over-sampling multiple OSR＜10, directly chooses corresponding desampling fir filter.

3, when over-sampling multiple OSR 〉=10, if OSR=12, successively by 4X, 3X desampling fir filter; If OSR=16 is successively by 8X, 2X desampling fir filter.

The sampling processing that rises for sequence interpolations in the channel estimation process is described as follows:

The original channel estimation results of LTE system regulation is 6 times to be owed to sample, so interpolation filter all is based on 6 times of many speed designs of over-sampling, is 6 poly phase filter with design of filter.

Consider the impact of multipath in the actual channel, the prototype filter of K cut-off frequency of design, suitable cut-off frequency is selected in the position of the multipath that selected cell obtains according to channel estimating.

Because the original series of channel estimating does not carry out pulse-shaping, and the limited length of sequence, special in the situation of smaller bandwidth, most of sequence is affected clearly by the transient response of iir filter all in the filtering interpolation process, is compensated by compensating unit according to following mode.

1, at first judges and take the ratio F=abs of amplitude by first sampled point of sequence (x (1)/FS), setting compensation thresholding X do not need to do compensation when F≤X; When F＞X, then need to compensate.

2, the exponent number N according to filter determines compensating length L, when bandwidth is to get L=N in a preset value and the situation of F greater than another preset value; Otherwise get L=min (M/2, N/2), wherein M is the length of sequence.

3, employing compensates based on the way of 2 rank fitting of a polynomials of least square;

4, the afterbody of sequence carried out same compensation process.

One of ordinary skill in the art will appreciate that; the above only is preferred embodiment of the present invention, and is in order to limit the present invention, within the spirit and principles in the present invention not all; any modification of doing, be equal to replacement, improvement etc., all should be included within protection scope of the present invention.

Claims (5)

1. a multi-rate processing system is characterized in that, comprising:

Anti-aliasing/anti-mirror filter, described anti-aliasing/anti-mirror filter prototype adopts the lattice structure based on the wavenumber filtering algorithm, be used for cell initial search process synchronizing information is extracted the anti-mirror image filtering that interpolation rises sampling processing in the anti-aliasing filter of down-sampled processing and the channel estimation process;

Described anti-aliasing/anti-mirror filter is the infinite impulse response iir filter with approximately linear phase property;

Wherein, when the over-sampling multiple greater than 2 the time, the multi-term expression of described infinite impulse response iir filter is:

$H\left(z\right)=\underset{K=1}{\overset{M}{\mathrm{\Σ}}}{Z}^{-K+1}\×H_K\left(Z^M\right);$

Wherein, H _K(Z ^M) be the all-pass filter expression formula of K item, and determine H according to exponent number N and the over-sampling multiple of described iir filter _K(Z ^M) exponent number.

2. multi-rate processing system according to claim 1 is characterized in that, described anti-aliasing/anti-mirror filter comprises the multiplication unit after low bit quantization is processed.

3. multi-rate processing system according to claim 1 is characterized in that, the bit number span of described multiplication unit is 4 to 8 bits.

4. according to claim 1 to 3 each described multi-rate processing systems, it is characterized in that, also comprise:

Selected cell is used for selecting according to the multi-path location that channel estimating obtains the cut-off frequency of described anti-mirror filter.

5. multi-rate processing system according to claim 4 is characterized in that, also comprises:

Compensating unit is used for carrying out nonlinear compensation in the filtered sequence of channel estimation process antagonism mirror image.

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