CN104954299A - Auxiliary pilot method used for FBMC (Filter Bank Multicarrier) system channel estimation - Google Patents

Abstract

FBMC (Filter Bank Multicarrier) is a special carrier communication mode. Being different from OFDM (Orthogonal frequency division multiplexing), subcarriers of the FBMC are not orthogonal to one another, so that intersymbol interference and inter-carrier interference naturally exist. A traditional OFDM channel estimation method is built on the basis of no intersymbol interference and inter-carrier interference, thereof, to carry out accurate channel estimation, the interference of surrounding symbols to a pilot symbol must be eliminated, and surrounding interference factors are definite under a certain filter bank structure and a prototype filter design. An auxiliary pilot method is such a method that an auxiliary pilot is placed nearby the position of an actual pilot, the value of the auxiliary pilot is determined by virtue of the values of the surrounding symbols and the corresponding interference factors, and the interference of the surrounding symbols to the pilot position is eliminated by virtue of the auxiliary pilot, so as to carry out accurate channel estimation.

Description

A kind of auxiliary pilot method for filter bank multi-carrier system channel estimating

Technical field

The invention belongs to the multi-carrier communication technical field in radio communication, more specifically, relate to a kind of auxiliary pilot method for filter bank multi-carrier system channel estimating.

Background technology

Multi-carrier modulation is a kind of effective transmission technology.By multi-carrier modulation, available channel is divided into several parallel subchannels, and every sub-channels has the subcarrier of associated.Some parallel low-rate input signals effectively can be converted into a two-forty signal by transmitter, then transmit in the channel.On the other hand, receiver must Perfect Reconstruction or well approximate reconstruction go out low-rate signal.Comprehensive analysis filterbank, multiplexing in other words multiplexing (Transmutiplexer, TMUX) structure, be multicarrier system core composition.Synthesis filter banks (Synthesis filter bank, SFB) is made up of one group of parallel emission filter, and analysis filterbank (Analysis filter bank, AFB) comprises and accepts filter accordingly.Because the field of bank of filters is very wide, there is a lot of implementations.In actual applications, the important criteria that designing filter group is followed is the complexity performed.In modulated filter bank method, all subchannel filter can be passed through to use cosine from comprehensive and analysis prototype filter, sinusoidal or index modulation.Not only design is efficient, and also very efficient from the angle performed.Therefore, modulated filter group technique owing to having very high calculated performance, usually as an important method of designing filter group.

There is a variety of multi-transceiver technology in the communications field, but OFDM (OFDM) certainly, is a kind of technology with dominant position.Such as, WLAN (wireless local area network) (WLAN), digital audio and video broadcasting (DAB, DVB-T, DVB-H), forth generation mobile communication (LTE), wireless MAN (WIMAX) etc. standard, all using OFDM as multi-carrier modulation method.From the angle of bank of filters, OFDM is used for modulation and demodulation based on inverse discrete Fourier transform (DFT) (IDFT) and discrete Fourier transform (DFT) (DFT) respectively as synthesis filter banks and analysis filterbank.In addition, the prototype filter of OFDM is a rectangular window, and the length of rectangular window is the OFDM symbol length of transmission.Concerning desired transmission channel, due to the orthogonality of subchannel, acknowledge(ment) signal can recover completely.In actual channel, particularly in wireless channel, owing to there is Multipath Transmission, having different time delays, can there is interference (ISI) in intersymbol.In order to resist multi-path jamming, OFDM needs to add Cyclic Prefix before symbol, and the length of Cyclic Prefix is greater than channel maximum path time delay.But due to subchannel not completely isolated, there is main lobe overlap between adjacent channel, and, in very wide frequency domain, there is larger secondary lobe and leak, first secondary lobe only 13dB lower than main lobe.These secondary lobes and main lobe can produce interference in whole frequency domain, in rapid fading with when there is frequency shift (FS), can cause serious inter-carrier interference problem.And disturb if existed between arrowband, the meeting of the hydraulic performance decline of ofdm system is very serious.Because the energy of arrowband interference can extend to a lot of adjacent sub-channel, so be difficult to simply the subchannel that there is interference be turned off.

Due to the above-mentioned defect of OFDM, researcher has invented more multi-transceiver technology, such as Discrete Wavelet Multitone (Discrete wavelet multitone, DWM), filtering multitone (Filtered multitone, FMT), cosine-modulation multitone (cosine modulated mutitone, CMT), based on the technology of OFDM/OQAM, based on the technology etc. improving DFT, these technology have abandoned simple IDFT/DFT structure, the substitute is the filter bank structure with very high frequency selectivity.Macroscopically say, these technology all belong to the category of filter bank multi-carrier (FBMC), realize the object improving frequency selectivity by use is longer with the well-designed prototype filter of spectral shape.Due to the design of good prototype filter, the secondary lobe of frequency response leaks and have dropped compared with OFDM a lot.Like this, all execution to well comprising frequency spectrum, and create good anti-arrowband interference performance.Next, in order to make adjacent sub-carrier signal separate, only need the execution in the middle of it to leaving a blank just.But perform while frequency selectivity in raising, continuous print symbol waveform can high superposed in time domain, namely inherently there is intersymbol interference, so there is no necessaryly as OFDM, add Cyclic Prefix.

Different with OFDM, what FBMC transmitted is OQAM symbol.The PHYDYAS project team in Europe carries out devising a prototype filter, and devises effective filter bank structure.Due to the existence disturbed in FBMC, cause FBMC cannot carry out pilot settings and channel estimating as OFDM, because traditional pilot design and channel estimation methods cannot exclusive PCR, the channel value of estimation can severe deviations, causes receiver accurately to recover to transmit.

Summary of the invention

In order to solve the problems of the technologies described above, invent a kind of Auxiliary Pilot Channel method of estimation herein, near actual pilot, position is chosen a position and is placed auxiliary pilot, the value of auxiliary pilot is determined by surrounding symbol and interference coefficient, this auxiliary pilot can eliminate the interference of surrounding symbol to pilot tone, thus carries out accurate channel estimating, then utilizes interpolation algorithm, carry out the channel estimating of whole transmission frame, and then recover to transmit.

To achieve these goals, the invention provides a kind of auxiliary pilot method for filter bank multi-carrier system channel estimating, described method comprises the steps:

(1) the interference coefficient t of calculating filter group multicarrier system _k,n;

(2) Design assistant pilot frequency locations;

(3) pilot value is placed at pilot frequency locations place

(4) calculate except auxiliary pilot position other position symbols to the interference value of pilot frequency locations $u_{k_0,n_0}=\underset{(k,n)\∈{\mathrm{\Ω}}_{k_0,n_0},(k,n)\≠(k_0,n_0),(k,n)\≠(k_a,n_a)}{\mathrm{\Σ}}{d}_{k,n}{t}_{k_0-k,n_0-n},$ Wherein for the interference coefficient at distance objective Resource Block (k, n) place;

(5) value of pilot tone is calculated wherein k _a, n _afor the position of auxiliary pilot;

(6) transmitting terminal is launched by IFFT and PPN, and receiving terminal is received by PPN and FFT;

(7) auxiliary pilot is utilized to carry out channel estimating in formula represent the Received signal strength at actual pilot place, represent the actual pilot data that transmitting terminal is placed, then according to interpolation algorithm, calculate the channel value of whole frame time-frequency domain;

(8) channel value is utilized to carry out Received signal strength equilibrium and transmitting data recovery, x in formula _k,nthe signal that pickup receives, d _k,nrepresent restoring signal.

In one embodiment of the invention, Design assistant pilot frequency locations is the maximum position of interference coefficient in described step (2).

In one embodiment of the invention, described filter is PHYDYAS prototype filter.

In one embodiment of the invention, the interference coefficient in described step (1) is determined according to following table:

Wherein, transverse axis represents transmission frame symbol number, and the longitudinal axis represents transmission frame subchannel number.

Due in FBMC system, when utilizing pilot tone to carry out channel estimating, pilot tone can be subject to the solid noisy impact of system, cannot carry out channel estimating accurately.By the intrinsic interference that the inventive method is subject to owing to can eliminate pilot tone, therefore channel estimating accurately can be carried out.

Accompanying drawing explanation

Fig. 1 is FBMC-OQAM system configuration of the present invention;

Fig. 2 carries out the result of MATLAB emulation.

Embodiment

In order to make object of the present invention, technical scheme and advantage clearly understand, below in conjunction with drawings and Examples, the present invention is further elaborated.Should be appreciated that specific embodiment described herein only in order to explain the present invention, be not intended to limit the present invention.In addition, if below in described each execution mode of the present invention involved technical characteristic do not form conflict each other and just can mutually combine.

Ignore channel and noise effect, concerning a desirable FBMC-OQAM system, Received signal strength with the d that transmits _k,nrelation as follows:

$x_{k_0,n_0}=\underset{k\∈M}{\Σ}\underset{n=-\mathrm{\∞}}{\overset{\mathrm{\∞}}{\Σ}}{d}_{k,n}{t}_{k_0-k,n_0-n}---\left(0.1\right)$

Wherein, d _k,nrepresenting transmitting after OQAM modulation, is pure real number; for the interference coefficient at distance objective Resource Block (k, n) place, (k, n) represents transmission frame resource block location.Consider the impact of channel and noise, then acknowledge(ment) signal is:

$x_{k_0,n_0}=h_{k_0,n_0}(d_{k_0,n_0}+{\mathrm{ju}}_{k_0,n_0})+{\mathrm{\η}}_{k_0,n_0}---\left(0.2\right)$

the channel response coefficient at place, for white Gaussian noise, represent the intrinsic interference that acknowledge(ment) signal is subject to.If do not eliminate interference cannot estimate the channel at pilot frequency locations place.

The auxiliary pilot algorithm for estimating core that the present invention proposes is the interference suffered by transmitting terminal calculating pilot tone, by designing an auxiliary pilot position, by the interference nulling at pilot tone place, to carry out channel estimating and date restoring.Specific algorithm is as follows:

(1) the interference coefficient t of computing system _k,n, in the present embodiment, have employed PHYDYAS prototype filter, interference coefficient is determined by prototype filter and filter bank structure, as shown in table 1 below:

Table 1

Wherein, transverse axis represents transmission frame symbol number, and the longitudinal axis represents transmission frame subchannel number.In upper table, be illustrated for 14 symbols and 11 subcarriers.

(2) Design assistant pilot frequency locations, supposes that the position of pilot frequency locations in frame emission time-frequency domain is for (k ₀, n ₀), according to interference coefficient Design assistant pilot frequency locations, general Design assistant pilot frequency locations is the maximum position of interference coefficient, supposes that the position of auxiliary pilot is k _a, n _a, as shown in the table:

Wherein, transverse axis represents transmission frame symbol number, and the longitudinal axis represents transmission frame subchannel number.In upper table, be illustrated for 14 symbols and 11 subcarriers.P represents actual pilot position, and A represents auxiliary pilot position

(3) pilot value is placed in auxiliary pilot position

(4) calculate except auxiliary pilot position other position symbols to the interference value of pilot frequency locations

$u_{k_0,n_0}=\underset{(k,n)\∈{\mathrm{\Ω}}_{k_0,n_0},(k,n)\≠(k_0,n_0),(k,n)\≠(k_a,n_a)}{\Σ}{d}_{k,n}{t}_{k_0-k,n_0-n}---\left(0.3\right)$

(5) value of pilot tone is calculated

$d_{k_a,n_a}=-\frac{u_{k_0,n_0}}{t_{k_0-k_a,n_0-n_a}}---\left(0.4\right)$

(6) transmitting terminal is launched by IFFT and PPN, by wireless channel, adds noise.Receiving terminal is received by PPN and FFT.

(7) auxiliary pilot is utilized to carry out channel estimating, in formula represent the Received signal strength at actual pilot place, represent the actual pilot data that transmitting terminal is placed

$h_{k_0,n_0}=\frac{x_{k_0,n_0}}{d_{k_0,n_0}}---\left(0.5\right)$

Then according to interpolation algorithm, the channel value of whole frame time-frequency domain is calculated.

(8) channel value is utilized to carry out Received signal strength equilibrium and transmitting data recovery.X in formula _k,nthe signal that pickup receives, d represents restoring signal.

$d_{k,n}=\frac{x_{k,n}}{h_{k,n}}---\left(0.6\right)$

Below in conjunction with specific embodiment, the inventive method is described, concrete implementation step comprises:

(1) calculate interference coefficient according to PHYDYAS prototype filter and filter bank structure, in this is implemented, have employed PHYDYAS prototype filter, then its interference coefficient is as shown in table 1;

(2) pilot frequency locations is designed, in this is implemented, frequency domain places a pilot tone every five carrier waves, time domain places a pilot tone every 6 symbols, pilot-frequency expense is 1/5 × 1/6, as shown in table 2, illustrates that this is implemented emulation and says the frame structure and pilot tone and auxiliary pilot design that adopt for 11 subcarriers and 14 OQAM symbols, wherein transverse axis conventional letter numbering, the longitudinal axis represents subcarrier number;

(3), after producing transmission data, pilot value is placed at pilot frequency locations place.

(4) calculate except auxiliary pilot position other position symbols to the interference value of pilot frequency locations

$u_{k_0,n_0}=\underset{(k,n)\∈{\mathrm{\Ω}}_{k_0,n_0},(k,n)\≠(k_0,n_0),(k,n)\≠(k_a,n_a)}{\Σ}{d}_{k,n}{t}_{k_0-k,n_0-n}---\left(0.7\right)$

As shown in table 3, in this is implemented, have chosen three kinds of interference windows, one is large window, and one is wicket, also has one to be all interference be included.

Table 3

-2	0	0.0006	-0.0001	0	0	0	-0.0001	0.0006	0
										-1	0.0054	j0.0429	-0.1250	j0.2058	0.2393	j0.2058	-0.1250	j0.0429	0.0054
0	0	-0.06680	0.0002	0.5644	1	0.5644	0.00020	-0.0668	0
										1	0.0054	-j0.0429	-0.1250	j0.2058	0.2393	j0.2058	-0.1250	j0.0429	0.0054
2	0	0.0006	-0.0001	0	0	0	-0.0001	0.0006	0

Wicket

Large window

(5) value of auxiliary pilot is calculated

$d_{k_a,n_a}=-\frac{u_{k_0,n_0}}{t_{k_0-k_a,n_0-n_a}}---\left(0.8\right)$

(6) transmitting terminal is launched by IFFT and PPN, by channel, adds noise.Receiving terminal is received by PPN and FFT

(7) receiving terminal pilot value is utilized to carry out channel estimating

$h_{k_0,n_0}=\frac{x_{k_0,n_0}}{d_{k_0,n_0}}---\left(0.9\right)$

(8) channel value is utilized to carry out Received signal strength equilibrium and transmitting data recovery

$d_{k,n}=\frac{x_{k,n}}{h_{k,n}}---\left(0.10\right)$

(9) for different SNR circulation emulation, statistical system bit error rate

Simulation result as shown in Figure 2, can obtain as drawn a conclusion from figure:

If 1 arranges auxiliary pilot, channel estimating cannot be carried out.

2, wicket eliminates major part interference, can carry out channel estimating, but also has part interference not eliminate, and channel estimation accuracy declines, and is directly reflected in the error rate.

3, compared with OFDM, wicket auxiliary pilot performance when signal to noise ratio is little is better, and along with the raising of signal to noise ratio, its performance will be poorer than OFDM, this be due to signal to noise ratio high time major effect performance factor be residual interference.

4, when signal to noise ratio is low, performance is all similar.But time signal to noise ratio is high, the bottleneck of wicket has just embodied, now residual interference has become the bottleneck of performance.

Large window is almost the same with the performance of complete window, all in performance, has larger lifting than wicket.Therefore we should select large window, high performancely reduce amount of calculation in acquisition simultaneously.

Those skilled in the art will readily understand; the foregoing is only preferred embodiment of the present invention; not in order to limit the present invention, all any amendments done within the spirit and principles in the present invention, equivalent replacement and improvement etc., all should be included within protection scope of the present invention.

Claims (4)

1. for an auxiliary pilot method for filter bank multi-carrier system channel estimating, it is characterized in that, described method comprises the steps:

(1) the interference coefficient t of calculating filter group multicarrier system _k,n;

(2) Design assistant pilot frequency locations;

(3) pilot value is placed at pilot frequency locations place

(4) calculate except auxiliary pilot position other position symbols to the interference value of pilot frequency locations $u_{k_0,n_0}=\underset{(k,n)\∈{\mathrm{\Ω}}_{k_0,n_0},(k,n)\≠(k_0,n_0),(k,n)\≠(k_a,n_a)}{\mathrm{\Σ}}{d}_{k,n}{t}_{k_0-k,n_0-n},$ Wherein for the interference coefficient at distance objective Resource Block (k, n) place;

(5) value of pilot tone is calculated wherein k _a, n _afor the position of auxiliary pilot;

(6) transmitting terminal is launched by IFFT and PPN, and receiving terminal is received by PPN and FFT;

(7) auxiliary pilot is utilized to carry out channel estimating in formula represent the Received signal strength at actual pilot place, represent the actual pilot data that transmitting terminal is placed, then according to interpolation algorithm, calculate the channel value of whole frame time-frequency domain;

(8) channel value is utilized to carry out Received signal strength equilibrium and transmitting data recovery, x in formula _k,nthe signal that pickup receives, d _k,nrepresent restoring signal.

2. the method for claim 1, is characterized in that, Design assistant pilot frequency locations is the maximum position of interference coefficient in described step (2).

3. method as claimed in claim 1 or 2, it is characterized in that, described filter is PHYDYAS prototype filter.

4. method as claimed in claim 3, it is characterized in that, the interference coefficient in described step (1) is determined according to following table:

Wherein, transverse axis represents transmission frame symbol number, and the longitudinal axis represents transmission frame subchannel number.