CN101447967A - Pilot frequency sequence structure used in OFDM/OQAM system and the construction method thereof - Google Patents

Abstract

The invention provides a pilot frequency sequence structure used in OFDM/OQAM system and the construction method thereof; under the condition that two sides of pilot frequency reference channel are added by full 0 protection symbol, the odd number sequence number and even number sequence number of the sequence body part have the same symbols, so when the interference between symbols is removed, while the interference between sub-carriers in pilot frequency reference signals is removed. More important, through the pilot frequency signal design method of the invention, the receiving end channel does not need forming blurry function characteristic in estimating process, so, the receiving end avoids the complex calculation in signal processing, and greatly reduces the hardware implementing difficulty and system cost in OFDM/OQAM system. The invention is particularly suitable for the self-adapting OFDM/OQAM system and high-speed OFDM/OQAM system.

Description

A kind of pilot frequency sequence structure and building method thereof that is used for the OFDM/OQAM system

Technical field

The invention belongs to the channel estimation technique in the OFDM/OQAM system, particularly the structural design of pilot signal in the channel estimation technique.

Background technology

As everyone knows, in the existing communication technology, OFDMA technology (OFDM/offset QAM based on staggered quadrature amplitude modulation method, be called for short OFDM/OQAM) with its very high availability of frequency spectrum, good time-frequency focus characteristics, become one of main candidate technologies of following mobile multimedia communication.

The mathematic(al) representation of the transmission signal s (t) of OFDM/OQAM system is:

$s\left(t\right)=\underset{n}{\mathrm{\Σ}}\underset{m=0}{\overset{M-1}{\mathrm{\Σ}}}{a}_{m,n}g(t-{\mathrm{n\τ}}_0)j^{m+n}{e}^{j2\mathrm{\π}{\mathrm{mv}}_{0}t}---\left(1\right)$

$g_{m,n}=g(t-{\mathrm{n\τ}}_0)j^{m+n}{e}^{j2\mathrm{\π}{\mathrm{mv}}_{0}t}$

A wherein _{M, n}Be on m the subcarrier of n emission symbol, v ₀And τ ₀Represent OFDM/OQAM system subcarrier interval and send signal interval, g (t) is expressed as the mode filter function.Than traditional orthogonal frequency division multiplexi, the OFDM/OQAM system only satisfies strict orthogonality condition in real number field, and is as follows:

Suppose that the OFDM/OQAM signal has experienced a multidiameter fading channel, the channel pulse impulse response is h (t), white Gaussian noise n ₀(t), the mathematic(al) representation of OFDM/OQAM system received signal is:

$y\left(t\right)=h\left(t\right)*s\left(t\right)+n_0\left(t\right)={\∫}_0^{\mathrm{\Δ}}h(t,\mathrm{\τ})s(t-\mathrm{\τ})\mathrm{d\τ}+n_0\left(t\right)---\left(3\right)$

When receiving terminal is received the transmission signal, and after it was carried out the matched filtering operation, received signal y (t) was expressed as:

$y\left(t\right)=\mathrm{Re}\left\{(\underset{n}{\mathrm{\Σ}}\underset{n\′}{\mathrm{\Σ}}\underset{m=0}{\overset{M-1}{\mathrm{\Σ}}}\underset{m\′=0}{\overset{M-1}{\mathrm{\Σ}}}{a}_{m,n}\⟨g_{m,n}|g_{m\′,n\′}\⟩H_m\right\}+n_0\left(t\right)$

　　　　　　　　　　　　　　　　　　　　　　　　　　　　(4)

$=H_m{a}_{m,n}+\mathrm{Re}\left\{\underset{m\≠m\′,n\≠n\′}{\mathrm{\Σ}}{a}_{m\′,n\′}\⟨g_{m,n}|g_{m\′,n\′}\⟩H_m\right\}+n_0\left(t\right)$

Wherein $H_m={\∫}_0^{\mathrm{\Δ}}h\left(\mathrm{\τ}\right)e^{j2\mathrm{\π}{\mathrm{mv}}_0(-\mathrm{\τ})}\mathrm{d\τ},$ And $\mathrm{Re}\left\{\underset{m\≠m\′,n\≠n\′}{\mathrm{\Σ}}{a}_{m\′,n\′}\⟨g_{m,n}|g_{m\′,n\′}\⟩H_m\right\}$ All intersymbol interference and subcarrier interference have been represented, n ₀(t) be noise after the matched filtering.

Work as a _{M, n}When being m subcarrier of pilot frequency sequence (known array that designs in order to estimate channel specially), then the OFDM/OQAM system based on the mathematic(al) representation of the channel estimating of pilot frequency sequence is:

$H_m\≈\frac{y\left(t\right)}{a_{m,n}+\left\{\underset{m\≠m\′,n\≠n\′}{\mathrm{\Σ}}{a}_{m\′,n\′}\⟨g_{m,n}|g_{m\′,n\′}\⟩\right\}}+\frac{n_0\left(t\right)}{a_{m,n}+\left\{\underset{m\≠m\′,n\≠n\′}{\mathrm{\Σ}}{a}_{m\′,n\′}\⟨g_{m,n}|g_{m\′,n\′}\⟩\right\}}---\left(5\right)$

Wherein $\frac{n_0\left(t\right)}{a_{m,n}+\left\{\underset{m\≠m\′,n\≠n\′}{\mathrm{\Σ}}{a}_{m\′,n\′}\⟨g_{m,n}|g_{m\′,n\′}\⟩\right\}}$ After having represented that the OFDM/OQAM system is through channel and matched filter, be superimposed upon the Gaussian noise on the pilot reference signal.The structural relation of visible pilot signal realizes to channel estimation method from the mathematic(al) representation of top channel estimating complexity and realizability.

The design of at present nearly all pilot frequency sequence structure all is at based on the ofdm system of complex field orthogonality condition, but for the OFDM/OQAM system of real number field orthogonality condition, the plural characteristic of multidiameter fading channel can be destroyed OFDM/OQAM system orthogonal property, make between the pilot reference signal created symbol disturb and subcarrier between disturb, and in the formula 5

Part can not be zero..Therefore the pilot signal structure of the channel estimating in the conventional orthogonal Frequency Division Multiplexing system no longer is applicable to the OFDM/OQAM system, need design new pilot signal structure for OFDM/OQAM.

At document (C.Lele, P.Siohan, R.Legouable.Preamble-based channel estimation techniquesfor OFDM/OQAM over the powerline, IEEE International Symposium on Power LineCommunications and Its Applications, Pisa, Italy, 2007,: a kind of pilot signal structure at the OFDM/OQAM system has been proposed 59-64), this pilot signal structure is: at first add complete 0 protection symbol at the pilot reference signal two ends, be used to eliminate intersymbol interference; Establish then and whenever face two symbols mutually and partner, two symbols in the every pair of symbol are identical, and promptly all odd numbers are identical to symbol, and all even-even symbols are also identical, but odd number to the even-even symbol be opposite, mathematical expression is: a _4n+1=a _4n+2=1, a _4n+3=a _4n+4=-1.The purpose of this design and benefit make in the formula 5 Part has reached maximum, thereby reduces the influence of white Gaussian noise to the OFDM/OQAM system.

But in fact, disturb between intersymbol interference in the OFDM/OQAM system and subcarrier and be only the principal element that influences systematic function, the key that therefore improves the pilot signal performance is how to eliminate intersymbol interference and subcarrier intersymbol interference factor.In addition, at existing channel estimation methods based on pilot signal, receiving terminal need be known the ambiguity function＜g of transmitting terminal forming filter in advance _{M, n}| g _{M ', n '}Characteristic, calculate then in the formula 5

And then utilize pilot reference signal to estimate the wireless channel fading characteristic, therefore existing channel estimation methods complexity based on pilot frequency sequence design method is too high.What is more important, for the OFDM/OQAM system with adaptive characteristic, transmitting terminal can select to have the formed filter of different time-frequency focusings by the different scattering propertiess of multipath time varying channel, and ambiguity function＜g _{M, n}| g _{M ', n '}Also can change, thereby increased the computation complexity of formula 5 in self adaptation OFDM/OQAM system, therefore there is certain limitation in existing OFDM/OQAM system pilot Design of Signal method. thereupon

Summary of the invention

The problem that the present invention is directed to existing OFDM/OQAM system channel estimation provides a kind of new pilot design structure and method.Eliminate interference sections between intersymbol interference in the pilot reference signal and subcarrier by rational pilot signal design, promptly in the formula described in the background technology 5 $\left\{\underset{m\≠m\′,n\≠n\′}{\mathrm{\Σ}}{a}_{m\′,n\′}\⟨g_{m,n}|g_{m\′,n\′}\⟩\right\}$ Be approximately zero.

The structure of the OFDM/OQAM system pilot sequence that the present invention proposes is: pilot signal sequence is made up of for three sections leading portion, stage casing and back segment; wherein leading portion and back segment all are complete zero (being protection sequence parts); the stage casing is the main part of pilot signal structure, every bit sign a of described main part _nBe to choose (value is 1 or-1) from polarity sign, even bit symbols all in the main part is identical, and all odd bits symbols are also identical, even bit symbol and odd bits symbol can be identical also can be opposite.

Building method is:

Step 1: with the main body sequence part (a of pilot reference signal ₁a ₂a ₃... a _n) the symbol (a of odd indexed ₁, a ₃, a ₅..., a _2m-1) all identical, and value is 1 or-1 (a ₁=a ₃=a ₅...=a _2m+1=± 1), again with each bit sign (a in the even number sequence number ₀, a ₂, a ₄..., a _2m) all identical, and value is 1 or-1 (a ₀=a ₂=a ₄...=a _2m=± 1), still, can be identical between even number sequence number symbol and the odd indexed symbol also can be opposite;

Step 2: add entirely 0 at the two ends of the formed main body sequence of step 1 part, the number of every end 0 equals sub-carrier number.

Invention essence and effect:

The present invention is under the prerequisite of complete 0 symbol of protecting in conjunction with OFDM/OQAM system orthogonality condition at the pilot reference signal two ends, makes between the middle conventional letter of formula (4) and interference sections between subcarrier

In intersymbol interference partly be approximately equal to 0, disturb between the only remaining subcarrier of the residual interference item in the interference sections, but approximate representation is:

By analyzing＜g _{M, n}| g _{M ', n}Find that it is the odd symmetry character at center that this function has with subcarrier m ', that is:

〈g _m′-1，n|g _m′，n〉＝-〈g _m′+1，n|g _m′，n〉　　(7)

Therefore, if set the identical a of being of each pilot reference sub-carriers adjacent-symbol _{M '=m-1, n}=a _{M '=m+1, n}, that then represents interference sections is approximately zero promptly: $\left\{\underset{m\≠m\′,n\≠n\′}{\mathrm{\Σ}}{a}_{m\′,n\′}\⟨g_{m,n}|g_{m\′,n\′}\⟩\right\}\≈0.$ Therefore estimate channel calculating formula can be reduced to: $H_m\≈\frac{y\left(t\right)}{a_{m,n}}+\frac{n_0\left(t\right)}{a_{m,n}}.$

Comprehensive above the analysis; essence of the present invention and effect are: pilot reference channel both sides add complete 0 the protection symbol prerequisite under at first eliminated intersymbol interference; then by staggered designs thought; make odd indexed have identical symbol respectively with the even number sequence number; thereby disturb between the subcarrier in the elimination pilot reference signal, the structure of therefore above-mentioned pilot signal sequence can be eliminated between intersymbol interference that multipath channel introduces and subcarrier and disturb.Of paramount importancely be, by pilot signal design method of the present invention, the ambiguity function characteristic that does not need forming filter in the receiving terminal channel estimation process, therefore receiving terminal has been avoided the complicated calculations in the signal processing, and the hardware that greatly reduces the OFDM/OQAM system is implemented difficulty and system cost.The present invention is specially adapted to self adaptation OFDM/OQAM system and high speed FDM/OQAM system.

Embodiment

Embodiment one:

All even bit symbols of main body sequence part all are 1 (or all being-1) in the pilot frequency sequence, and all odd bits symbols all are-1 (or all being 1).The method of constructing this sequence is:

Step 1: each bit sign of the odd indexed in the main body sequence part of pilot frequency sequence all is changed to 1 (a ₁=a ₃=a ₅...=a _2m+1=1) or-1 (a ₁=a ₃=a ₅...=a _2m+1=-1), each bit sign is 1 (a in odd indexed ₁=a ₃=a ₅...=a _2m+1=1) time, then each bit sign with the even number sequence number in the main body sequence part of pilot frequency sequence all is changed to-1 (a ₀=a ₂=a ₄...=a _2m=-1); Each bit sign of odd indexed in the main body sequence part of pilot frequency sequence is-1 (a ₁=a ₃=a ₅...=a _2m+1=-1) time, then the value with each bit sign of the even number sequence number in the main body sequence of the pilot frequency sequence part all is changed to 1 (a ₀=a ₂=a ₄...=a _2m=1).

Step 2: respectively add the complete 0 protection symbol of subcarrier number in the both sides of main body sequence part.

Embodiment two:

All symbols of the main part of pilot frequency sequence all are 1 or all are-1.The method of constructing this sequence is:

Step 1: with all symbols of the main part of pilot frequency sequence all is 1 (a ₁=a ₂=a ₃...=a _n=1) or-1 (a ₁=a ₂=a ₃...=a _n=-1)

Step 2: the complete 0 protection symbol that respectively adds the subcarrier number in the both sides of main body sequence part.

Claims (3)

1, a kind of pilot frequency sequence structure that is used for the OFDM/OQAM system, form for three sections by leading portion, stage casing and back segment, wherein leading portion and back segment all are complete zero, the stage casing is the main part of pilot signal structure, every bit sign an of main part be from value be 1 or-1, it is characterized in that: even bits all in the described main part is identical, and all odd bits symbols are also identical, even bit symbol and odd bits symbol can be identical also can be opposite.

2, the building method of claim 1 pilot frequency sequence is characterized in that:

Step 1: the value of each bit sign of odd indexed in the main body sequence part of pilot frequency sequence all is changed to 1 or-1, when main body sequence each bit sign of odd indexed partly of pilot frequency sequence was 1, then the value with each bit sign in the main body sequence even number sequence number partly of pilot frequency sequence all was changed to-1; When main body sequence each bit sign of odd indexed partly of pilot frequency sequence was-1, then the value with each bit sign in the even number sequence number all was changed to 1,

Step 2: respectively add subcarrier several complete 0 protection symbols in the both sides of main body sequence part respectively.

3, the building method of claim 1 pilot frequency sequence is characterized in that:

Step 1: with all sign bits of the main part of pilot frequency sequence all is 1 or-1;

Step 2: respectively add subcarrier several complete 0 protection symbols in the both sides of main body sequence part respectively.