CN101958874A - D-OFDMA (Dual-Orthogonal Frequency Division Multiple Access) cellular system based on angular multiplexing - Google Patents

Abstract

The invention provides a D-OFDMA (Dual Orthogonal Frequency Division Multiple Access) cellular system based on angular multiplexing, aiming at a root reason for forming ICI (Inter-Cell Interference) in a traditional OFMDA cellular system, which is that all cells have identical modulation basis functions on the same subcarrier. The invention provides the D-OFDMA cellular system based on FrFT (Fractional Fourier Transform) angular multiplexing and realizes the orthogonality of the modulation basis functions on different subcarriers in the cells and the approximate orthogonality of the modulation basis functions of adjacent cells on the same subcarrier by optimally distributing an FrFT angle as a resource in all the cells in the cellular system. Accordingly, a target user receiving end can carry out MMSE (Multiuse Mission Support Equipment) balance and relative detection in an FrFT domain of a corresponding angle of each service cell to effectively suppress the ICI and improve the cell margin throughput.

Description

Biorthogonal frequency division multiple access cellular system based on angular multiplexing

Technical field:

The present invention relates to multi-carrier communication and technical fields such as inter-cell interference cancellation and coordination.

Background technology:

Along with transmission rate request growing in the radio communication, the multi-carrier transmission technology is just more and more studied and is used in recent years.Multi-transceiver technology transmits data by high-speed data-flow being divided into several parallel bit streams, make every channel that a much lower bit rate all be arranged, and the data on every subchannel is respectively by different carrier modulation.OFDM (OFDM) is a kind of multi-carrier modulation technology of special uniformly-spaced frequency overlap, OFDM technology itself and and the technology of other communication system combinations become the most important developing direction and the trend of following high speed data transfer technical field.

In OFDM (OFDMA) cellular system, serial data stream at a high speed is divided into a plurality of parallel low rate data streams, be modulated to respectively then on the subcarrier of different quadratures and transmit, thereby the elongation sign cycle effectively overcomes the interference effect among symbols that multipath causes.In at present traditional OFDMA cellular system, all with the complex exponential signal of quadrature as subcarrier, by contrary discrete Fourier transform (DFT) (IDFT) and discrete Fourier transform (DFT) (DFT) realization subcarrier-modulated and demodulation.Each sub-carrier frequencies is

Wherein, N is the subcarrier number, T _sBe the duration (or cycle) of OFDM symbol, frequency interval is

If the discrete signal of transmitting terminal is available d after digital modulation, insertion pilot tone _kExpression, the system subcarrier number is N, and the symbol energy on each subcarrier is E _s=1, the baseband signal that does not then add Cyclic Prefix can be expressed as:

$s\left(n\right)=\frac{1}{N}\underset{k=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{d}_k{\mathrm{<figure-callout\; id="2"\; label="e\; j"\; filenames="HSA00000315963500022.png,HSA00000315963500031.png"\; state="\{\{state\}\}">e</figure-callout>}}^j,n=\mathrm{0,1},...,N-1---\left(2\right)$

Or be expressed as with matrix form:

s＝F ^H·d (3)

Wherein, F ^HBe the IDFT matrix; D=[d ₀, d ₁..., d _N-1] ^TAt receiving terminal, the targeted customer also receives from interference signal outside the sub-district and additive white Gaussian noise (AWGN) except receiving the desired signal from persistent district.The baseband receiving signals that received signal obtains after removing Cyclic Prefix and doing discrete Fourier transform (DFT) is:

$y=\underset{i=1}{\overset{N_{\mathrm{BS}}}{\mathrm{\&Sigma;}}}{\mathrm{FH}}_i{F}^H{d}^{\left(i\right)+\mathrm{Fn}---\left(4\right)}$

Wherein, N _BSSub-district number for whole system; FH _iF ^HBe the frequency equivalent channel transmission matrix of i cell base station to the targeted customer; The transmission data of representing i cell base station; N is the AWGN vector.

By (4) formula as seen, for traditional OFDMA cellular system, except useful signal, also be mixed with co-channel interference signal in targeted customer's the received signal from other cell base stations from serving BS.Especially when the targeted customer was in cell edge, presence of intercell interference was often very serious, and communication quality obviously descends.In fact, the basic reason that presence of intercell interference forms in the legacy system is that the modulation basic function of each sub-district on same sub-carrier is identical, and receiving terminal can't suppress or eliminates by means such as simple filtering.At present, often adopt technology such as power control, the access of chance formula frequency spectrum, adaptive fractional channeling, array antenna, adaptive beamforming to carry out interference coordination or elimination.But these technology all do not tackle the problem at its root, and just by improving the communication quality of Cell Edge User on the basis of sacrificing frequency domain resource utilance or sacrifice central user performance.

The present invention traces sth. to its source exactly, from changing the angle of subcarrier-modulated basic function, has proposed a kind of biorthogonal frequency division multiple access (D-OFDMA) cellular system based on fraction Fourier conversion (FrFT) angular multiplexing.Its main thought is that a kind of new resource is regarded as in the FrFT angle, optimum allocation is carried out in minizone at whole cellular system, make and the nearly orthogonal of modulation basic function on the neighbor cell same sub-carrier reach the effect of utilizing simple coherent detection to suppress presence of intercell interference thus.Give the optimum allocation criterion of FrFT angle resource among the present invention simultaneously.

Summary of the invention

In this system, the translation-angle of fraction Fourier conversion is counted as between a kind of new different districts of time-frequency combination resource in whole system and carries out optimum allocation.According to the network configuration of cellular system,, select 3 different angles { β as long as in the optional scope of FrFT angle ₁, β ₂, β ₃Or 7 different angles { β ₁, β ₂..., β ₇Carry out the minizone distribution, just can guarantee the angle difference (as shown in Figure 3 and Figure 4) between any neighbor cell, and if the suitable modulation basic function nearly orthogonal of neighbor cell on same sub-carrier that can also make of angle Selection.The optimization criterion of its 3 angle and 7 angular distribution is respectively:

$\{{\mathrm{\&beta;}}_1,{\mathrm{\&beta;}}_2,{\mathrm{\&beta;}}_3\}=\arg \underset{N_1,{\mathrm{<figure-callout\; id="2"\; label="N"\; filenames="HSA00000315963500022.png,HSA00000315963500031.png"\; state="\{\{state\}\}">N</figure-callout>}}_2,N_3\&Element;\mathrm{\&Theta;}}{\min }\underset{i,j=1}{\overset{3}{\mathrm{\&Pi;}}}{\mathrm{\&rho;}}_{i,j}---\left(5\right)$

$\{{\mathrm{\&beta;}}_1,{\mathrm{\&beta;}}_2,...,{\mathrm{\&beta;}}_7\}=\arg \underset{N_1,{\mathrm{<figure-callout\; id="2"\; label="N"\; filenames="HSA00000315963500022.png,HSA00000315963500031.png"\; state="\{\{state\}\}">N</figure-callout>}}_2,...,{\mathrm{<figure-callout\; id="7"\; label="N"\; filenames="HSA00000315963500021.png"\; state="\{\{state\}\}">N</figure-callout>}}_7\&Element;\mathrm{\&Theta;}}{\min }\underset{i,j=1}{\overset{7}{\mathrm{\&Pi;}}}{\mathrm{\&rho;}}_{i,j}---\left(6\right)$

Wherein,

The optional scope of expression FrFT angle, Δ G _fBe intercarrier protection interval.

The average correlation of representing two sub-district basic functions;

The expression angle is β _i-β _j(k, k) the individual element of fraction Fourier conversion matrix.The optimum FrFT angle that obtains of criterion can make the modulation basic function of any neighbor cell on same sub-carrier satisfy nearly orthogonal thus.

As seen, the biorthogonality of cellular system proposed by the invention mainly shows: the orthogonality of modulation basic function on the different sub carrier in the sub-district, and the nearly orthogonal of modulating basic function between neighbor cell on same sub-carrier.And corresponding therewith legacy system is a kind of based on multiplexing single OFDM (S-OFDMA) cellular system (as shown in Figure 2) in Fourier transform list angle, and the angle of each cell allocation all is a pi/2.

After supposing to have carried out the optimal corner resource allocation according to criterion (5), the FrFT angle that the note cell i is assigned to is α _i(or claim that the FrFT exponent number is p _i=2 α _i/ π), the downlink transmission data of this cell base station utilizes angle to be α _iContrary discrete fraction rank Fourier transform (α _i-IDFrFT) modulate, wherein the data on k subcarrier can be formulated as after ovennodulation:

$s_k^{\left(i\right)}=f_{-d_i,k}{d}_k^{\left(i\right)}---\left(7\right)$

Wherein,

For angle is α _iThe IDFrFT matrix

K row,

The data symbols that the expression cell i sends on k subcarrier.Be without loss of generality, the hypothetical target user is linked into sub-district 1, and each cell base station is H to targeted customer's channel response matrix _i, then received signal is:

$r_k=\underset{i=1}{\overset{N_{\mathrm{BS}}}{\mathrm{\&Sigma;}}}{H}_i{s}_k^{\left(i\right)}+v_k---\left(8\right)$

Wherein, v _kExpression AWGN vector.Because the targeted customer is linked into sub-district 1, then utilizes angle to be α ₁Fraction Fourier conversion carry out demodulation and obtain:

$Y_k=F_{d_1}{H}_1{s}_k^{\left(1\right)}+\underset{i=2}{\overset{N_{\mathrm{BS}}}{\mathrm{\&Sigma;}}}{F}_{d_j}{H}_i{s}_k^{\left(i\right)}+V_k---\left(9\right)$

At α ₁The estimation of useful signal is carried out obtaining after the balanced and coherent detection of MMSE in-FrFT territory:

${\hat{d}}_k^{\left(1\right)}=E_{s,1}^2{f}_{-d_1,k}^H{H}_1^H{F}_{d_1}^H{R}_{\mathrm{YY}}^{-1}{Y}_k---\left(10\right)$

Wherein,

Be noise variance; Be signal power from cell i.

The whole physical layer process flow process of this system as shown in Figure 1, the finding the solution and will provide in detail below of the derivation of its process and the optimum allocation of FrFT angle.Content of the present invention at first briefly introduce fraction Fourier conversion (FrFT) and discrete form (DFrFT) thereof below in order better to illustrate.

FrFT is a kind of generalized form of Fourier transform.As a kind of new time frequency analyzing tool, FrFT can be interpreted as signal and be rotated counterclockwise method for expressing on the fractional order Fourier domain that constitutes after a certain angle around initial point at time-frequency plane internal coordinate axle.The FrFT of signal x (t) is defined as:

$X_d\left(u\right)=\left\{F_d\right[x\left(t\right)\left]\right\}\left(u\right)={\&Integral;}_{-\&infin;}^{+\&infin;}x\left(t\right)K_d(t,u)\mathrm{dt}---\left(11\right)$

Wherein, α is the angle of fractional order Fourier domain and frequency domain, is called the FrFT angle, F _d[] is the FrFT operator notation, K _d(t u) is the transformation kernel of FrFT:

$K_d(t,u)=\left\{\begin{array}{cc}\sqrt{\frac{1-j\cot d}{2k}}\exp \{\mathrm{<figure-callout\; id="2"\; label="j\; t"\; filenames="HSA00000315963500022.png,HSA00000315963500031.png"\; state="\{\{state\}\}">j</figure-callout>}\frac{t^{}}{}\frac{{}^2+u^2}{2}\cot d-\mathrm{jut}\csc d\},& d\&NotEqual;\mathrm{Dk}\\ j(t-u),& d=2\mathrm{Dk}\\ \mathrm{\&delta;}(t+u),& \mathrm{\&alpha;}=(2D+1)\mathrm{\&pi;}\end{array}\right.---\left(12\right)$

FrFT is inversely transformed into:

$x\left(t\right)={\&Integral;}_{-\&infin;}^{+\&infin;}{X}_d\left(u\right)K_{-d}(t,u)\mathrm{du}---\left(13\right)$

In the practical application, need the calculating of discrete form.Input and output to FrFT are sampled with interval of delta t and Δ u respectively, when the output sampling number M of fractional order Fourier domain more than or equal to time domain input sample points N, and the sampling interval satisfy

Δu·Δt＝|S|·2k·sin?d/M (14)

Wherein, | S| is the integer (often be taken as 1) relatively prime with M, and DFrFT can be expressed as:

$X_d\left(m\right)=\left\{\begin{array}{cc}{A}_d{e}^{\frac{\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="HSA00000315963500022.png,HSA00000315963500031.png"\; state="\{\{state\}\}">j</figure-callout>}}{2}\cot d\&CenterDot;{\mathrm{<figure-callout\; id="2"\; label="m"\; filenames="HSA00000315963500022.png,HSA00000315963500031.png"\; state="\{\{state\}\}">m</figure-callout>}}^2\&CenterDot;{\mathrm{\&Delta;u}}^2}\underset{n=-(N-1)/2}{\overset{(N-1)/2}{\mathrm{\&Sigma;}}}{\mathrm{<figure-callout\; id="2"\; label="e\; j"\; filenames="HSA00000315963500022.png,HSA00000315963500031.png"\; state="\{\{state\}\}">e</figure-callout>}}^{\frac{j}{}}x\left(n\right),& d\&NotEqual;\mathrm{Dk}\\ x\left(m\right),& d=2\mathrm{Dk}\\ x(-m),& \mathrm{\&alpha;}=(2D+1)\mathrm{\&pi;}\end{array}\right.---\left(15\right)$

Wherein, D is an integer.

In order to simplify calculating, get M=N usually.When α ≠ D π, (15) formula can be write as following matrix form:

X _d＝F _d·x (16)

Wherein, X _d=[X _d(0), X _d(1) ..., X _d(N-1)] ^T, x=[x (0), x (1) ..., x (N-1)] ^T, F _αBe N * N matrix, its element is Equally, IDFrFT can be written as:

x＝F _-α·X _α (17)

Wherein, F _αBe unitary matrix, character promptly arranged:

According to above to the analysis of tradition based on the OFDMA cellular system deficiency of Fourier transform, in the present invention, we propose the angle of FrFT as a kind of new resource (calling the angle resource), carry out optimum allocation in whole cellular system, the angle that each cell allocation arrives is preserved as this sub-district base attribute.During downlink transfer, data source at first through forming the data of serial after chnnel coding and the digital modulation, obtains parallel data stream through behind the serial to parallel conversion again.After every group of parallel data inserted pilot tone, by Serving cell corresponding angle α _iIDFrFT carry out subcarrier-modulated, generate a α _i-OFDM symbol.Each α in the cell i like this _iThe subcarrier of-OFDM symbol becomes linear frequency modulation (LFM, or the Chirp) signal with identical frequency modulation rate, different reference frequencies.The frequency that is k subcarrier in the cell i is:

Reference frequency as each Chirp signal of subcarrier-modulated basic function is spaced apart Δ s=2k/T _sBy (18) formula as can be seen, its frequency changes in an OFDM symbol period, and the Changing Pattern of any two neighbor cells is also inequality, and this is constant with traditional ofdm system sub-carriers base index function frequency to be different.Disturb for fear of between subcarrier, frequency range is less than the subcarrier reference frequency at interval in symbol period to require to satisfy each subcarrier-modulated basic function With intercarrier protection interval delta G _fPoor, promptly require:

$\max \left|\mathrm{\&Delta;}{s}_k^{\left(i\right)}\right|=\left|T_s\cot d_i\right|<\mathrm{\&Delta;s}-{\mathrm{\&Delta;G}}_f,\&ForAll;i\&Element;\{\mathrm{1,2},...,N_{\mathrm{BS}}\}---\left(19\right)$

The desirable scope that obtains each sub-district FrFT angle thus is:

$\mathrm{\&Theta;}=\{k-\mathrm{arccot}(\frac{2k}{T_s^2}-\frac{{\mathrm{\&Delta;G}}_f}{T_s}),\mathrm{arccot}(\frac{2k}{T_s^2}-\frac{{\mathrm{\&Delta;G}}_f}{T_s})\}---\left(20\right)$

From whole OFDMA cellular system, the data of different districts on same sub-carrier are had the Chirp signal modulation of same datum frequency, different frequency modulation rates.Be without loss of generality, the hypothetical target user is linked into sub-district 1.At first, establishing the data vector that the OFDM symbol after digital modulation need transmit in the cell i is According to (16) formula, obtain through α _iThe OFDM symbol of-IDFrFT modulation

For:

$S^{\left(i\right)}=F_{-d_i}\&CenterDot;d^{\left(i\right)}---\left(21\right)$

Signal after the subcarrier-modulated adds the Cyclic Prefix of certain-length again, and converts serial data to, can carry out rf modulations and emission afterwards.For the transmission data on the subcarrier k

Signal after the modulation For:

$s_k^{\left(i\right)}=f_{-d_i,k}{d}_k^{\left(i\right)}---\left(22\right)$

Wherein, Be α _iK the subcarrier that-IDFrFT produces raises the system basic function, promptly K row.

Suppose that the channel maximum delay is L, then the circulating prefix-length of system is chosen as L, can effectively reduce intersymbol interference like this.The process of inserting Cyclic Prefix can be expressed as with the form of matrix product:

${\tilde{s}}_k^{\left(i\right)}=T_{\mathrm{CP}}\&CenterDot;s_k^{\left(i\right)}={[s_{N-L}^{\left(i\right)},s_{N-L+1}^{\left(i\right)},...,s_{N-1}^{\left(i\right)},s_0^{\left(i\right)},s_1^{\left(i\right)},...,s_{N-1}^{\left(i\right)}]}^T---\left(23\right)$

Wherein,

P=N+L; I _NWith

Be respectively N * N unit matrix and I _NThe matrix that back L row element is formed.

Suppose channel impulse response h (n, l) (n=0,1 ..., P-1, l=0,1 ..., L-1), then pass through channel after, the signal that the targeted customer receives is:

${\tilde{r}}_k={\tilde{H}}_1{\tilde{s}}_k^{\left(1\right)}+\underset{i=2}{\overset{N_{\mathrm{BS}}}{\mathrm{\&Sigma;}}}{\tilde{H}}_i{\tilde{s}}_k^{\left(i\right)}+{\tilde{v}}_k---\left(24\right)$

Wherein,

Be the channel matrix of i sub-district, that is: to the targeted customer

Be additive white Gaussian noise (AWGN) vector.

Targeted customer's receiving terminal at first will receive and handle the baseband signal obtain and carry out serial to parallel conversion, go the process of Cyclic Prefix can use received signal premultiplication matrix R equally then _CP=[0 _{N * L}, I _N] _{N * P}Be expressed as:

$r_k=R_{\mathrm{CP}}{\tilde{r}}_k=\underset{i=1}{\overset{N_{\mathrm{BS}}}{\mathrm{\&Sigma;}}}{R}_{\mathrm{CP}}{\tilde{H}}_i{T}_{\mathrm{CP}}{s}_k^{\left(i\right)}+v_k=\underset{i=1}{\overset{N_{\mathrm{BS}}}{\mathrm{\&Sigma;}}}{H}_i{s}_k^{\left(i\right)}+v_k---\left(26\right)$

Wherein, $H_i=R_{\mathrm{CP}}{\tilde{H}}_i{T}_{\mathrm{CP}}.$

At this moment, the signal that removes behind the Cyclic Prefix shown in (26) formula is carried out α ₁-DFrFT subcarrier demodulation obtains:

$Y_k=F_{d_1}(\underset{i=1}{\overset{N_{\mathrm{BS}}}{\mathrm{\&Sigma;}}}{H}_i{s}_k^{\left(i\right)}+v_k)=\underset{i=1}{\overset{N_{\mathrm{BS}}}{\mathrm{\&Sigma;}}}{\stackrel{\&OverBar;}{H}}_i{s}_k^{\left(i\right)}+v_k---\left(27\right)$

Wherein, Be α ₁The equivalent channel transmission matrix in-FrFT territory, it can be expressed as: Become or slow time varying channel h when non- _i(n, l)=h (l), then H _iIt is a circular matrix.In order to eliminate the influence of multipath, the signal after the demodulation is carried out α based on least mean-square error (MMSE) criterion ₁The equilibrium of-DFrFT territory.If the weight vector of equalizer is W, then can be expressed as through the signal after the equilibrium:

${\hat{s}}_k^{\left(i\right)}={\mathrm{WY}}_k---\left(28\right)$

According to the MMSE criterion, filter W should make following error function reach minimum:

$J_k=E\left\{{(s_k^{\left(1\right)}-{\hat{s}}_k^{\left(1\right)})}^H(s_k^{\left(1\right)}-{\hat{s}}_k^{\left(1\right)})\right\}---\left(29\right)$

Launching after (28) formula substitution (29) formula, W is asked local derviation and makes it equal 0, try to achieve the equalizer weight vector and be:

$W=E_{s,1}^2{H}_i^H{F}_{d_1}^H{R}_{\mathrm{YY}}^{-1}---\left(30\right)$

Wherein,

$R_{\mathrm{YY}}=E\left\{Y_k{Y}_k^H\right\}=\underset{i=1}{\overset{N_{\mathrm{BS}}}{\mathrm{\&Sigma;}}}{E}_{s,i}^2\left\{F_{d_1}{H}_i{f}_{-d_i,k}{f}_{-d_i,k}^H{H}_i^H{F}_{d_1}^H\right\}+E_v^2{I}_N---\left(31\right)$

Pass through α ₁-DFrFT territory MMSE equalizer, and utilize

Between nearly orthogonal (if the angle resource allocation is reasonable), carry out obtaining receiver after the simple coherent detection and be output as:

${\hat{d}}_k^{\left(1\right)}=E_{s,1}^2{f}_{-d_1,k}^H{H}_i^H{f}_{d_1}^H{R}_{\mathrm{YY}}^{-1}{Y}_k---\left(32\right)$

Last signal is through digital demodulation, and operation such as channel-decoding back forms receiver output.

So far, we have provided the implementation method of DFrFT territory MMSE equalizer and coherent detection, but the quality of detection effect depends on

The correlation size, i.e. angle resource { β ₁, β ₂, β ₃Be distributed among the design extremely important.

For traditional OFDMA cellular system, all sub-districts adopt identical base index to come the modulating data code element on same sub-carrier, and co-channel interference seriously seriously descends communication quality outside the sub-district owing to being subjected to cause edge customer thus.In fact, presence of intercell interference produces and is difficult to suppress and the basic reason coordinated is exactly the complete correlation of modulating basic function on the same sub-carrier in the legacy system.So, among the present invention with on the carrier wave between neighbor cell the modulation basic function average correlation as cost function.Consider angle beta _iAnd β _jTwo basic functions on k the subcarrier that the fractional Fourier inverse transformation produces

With

Between correlation, utilize the character of fraction Fourier conversion to obtain:

$J_k(N_i,N_j)=f_{-N_i,k}^H{f}_{-N_j,k}={\left(F_{-N_i}^H{F}_{-N_j}\right)}_{k,k}=F_{N_i-N_j}(k,k)---\left(33\right)$

Can see by following formula, for traditional OFDMA cellular radio structure (as shown in Figure 2), all cell selecting equal angular, i.e. N _i=N _j=N=k/2, substitution (35) formula obtain J (N, N)=I _N(k, k)=1.Represent that k the basic function on the subcarrier is relevant fully this moment, and angular multiplexed distance is R (R is a station spacing).Thus also as can be seen, traditional OFDMA cellular system is a special case of native system.

According to the network configuration of cellular system, according to the neighbor cell principle of shared same angle not, 3 different FrFT angle { β of minimum needs ₁, β ₂, β ₃Realize (as shown in Figure 3) that its angular multiplexed distance is

The definition selected angle is β _iAnd β _jTwo sub-districts between the average correlation of subcarrier basic function:

${\mathrm{\&rho;}}_{i,j}=\frac{1}{N}\underset{k=0}{\overset{N-1}{\mathrm{\&Sigma;}}}\left|J_k({\mathrm{\&beta;}}_i,{\mathrm{\&beta;}}_j)\right|---\left(34\right)$

Therefore, 3 angle { β ₁, β ₂, β ₃Optimize criterion and can be defined as:

$\{{\mathrm{\&beta;}}_1,{\mathrm{\&beta;}}_2,{\mathrm{\&beta;}}_3\}=\arg \underset{N_1,{\mathrm{<figure-callout\; id="2"\; label="N"\; filenames="HSA00000315963500022.png,HSA00000315963500031.png"\; state="\{\{state\}\}">N</figure-callout>}}_2,N_3\&Element;\mathrm{\&Theta;}}{\min }\underset{i,j=1}{\overset{3}{\mathrm{\&Pi;}}}{\mathrm{\&rho;}}_{i,j}---\left(35\right)$

By optimizing criterion (35), can be so that the average correlation minimum of subcarrier-modulated basic function between neighbor cell, then utilize simple coherent detection just can suppress radius well to be Presence of intercell interference in the scope.For this extraneous interference, owing to the inhibition of having passed through more serious path loss and coherent detection makes it less to detecting performance impact.Equally, if select 7 angle { β ₁, β ₂..., β ₇In cellular system, distribute (as shown in Figure 4), angular multiplexed distance is reached

7 angles of its correspondence are optimized criterion and can be defined as:

$\{{\mathrm{\&beta;}}_1,{\mathrm{\&beta;}}_2,...,{\mathrm{\&beta;}}_7\}=\arg \underset{N_1,{\mathrm{<figure-callout\; id="2"\; label="N"\; filenames="HSA00000315963500022.png,HSA00000315963500031.png"\; state="\{\{state\}\}">N</figure-callout>}}_2,...,{\mathrm{<figure-callout\; id="7"\; label="N"\; filenames="HSA00000315963500021.png"\; state="\{\{state\}\}">N</figure-callout>}}_7\&Element;\mathrm{\&Theta;}}{\min }\underset{i,j=1}{\overset{7}{\mathrm{\&Pi;}}}{\mathrm{\&rho;}}_{i,j}---\left(36\right)$

Each sub-district can suppress its radius and is thus

Presence of intercell interference in the scope.Equally, for this extraneous interference, owing to the inhibition of having passed through serious path loss and coherent detection makes it very little to detecting performance impact.

Character according to the DFrFT matrix:

Top optimization problem can be reduced to the mean allocation in the optional scope of angle, in order to make inter-carrier interference less, require intercarrier spacing big as far as possible simultaneously, can determine earlier that one of them angle is a pi/2, then with this as benchmark, uniformly-spaced choose to both sides.In addition, in actual applications, only consider 3 angle optimizations and 7 angle optimized distribution usually, its reason mainly is the increase along with the angle number, and the equispaced must reduce between angle, and the relation of being inversely proportional to (as shown in Figure 7) between correlation and the differential seat angle.

The advantage of system of the present invention mainly shows the following aspects:

(1) solved simply and effectively in traditional OFDMA cellular system, owing to all sub-districts problem of inter-cell interference that shared same base index function causes on same sub-carrier;

(2) all sub-districts can be transmitted by full frequency band, have improved band efficiency;

(3) but because edge customer need not limit its transmission band and transmitting power, simplified control of upper strata power and resource scheduling algorithm, can effectively improve the cell edge throughput simultaneously;

Because there is fast algorithm in DFrFT, can realize that (4) therefore, the computational complexity of system and the traditional ofdm system based on Fourier transform are suitable with fast Fourier transform (FFT);

(5) the optimal corner resource allocation just can be decided when system's network planning without real-time update and feedback.Simultaneously, utilize the character of FrFT, complicated angle resource optimization assignment problem is converted into angle uniformly-spaced chooses, be easy to realize.

Description of drawings

Fig. 1-based on the D-OFDMA cellular system physical layer block diagram of FrFT angular multiplexing;

Fig. 2-tradition is based on the multiplexing S-OFDMA cellular system networks structure chart in the single angle of 1-FFT;

Fig. 3-based on the D-OFDMA cellular system structure chart of 3-FrFT angular multiplexing;

Fig. 4-based on the D-OFDMA cellular system structure chart of 7-FrFT angular multiplexing;

During Fig. 5-3-FrFT angular multiplexing, the modulation basic function of each sub-district on subcarrier 10;

During Fig. 6-3-FrFT angular multiplexing, the modulation basic function of each sub-district on subcarrier 40;

Fig. 7-basic function average correlation is with the change curve of differential seat angle;

Under Fig. 8-awgn channel, based on the D-OFDMA cellular system of 3-FrFT angular multiplexing and the bit error rate performance curve comparison diagram of legacy system;

Under Fig. 9-TU channel, based on the D-OFDMA cellular system of 3-FrFT angular multiplexing and the bit error rate performance curve comparison diagram of legacy system;

Embodiment

The present invention is further described below in conjunction with accompanying drawing and example.

According to the argumentation of front summary of the invention part, will be summarized as follows based on the embodiment of the D-OFDMA cellular system of FrFT angular multiplexing below in conjunction with Fig. 1 and Fig. 2.In order concentrate to describe the enforcement of key component involved in the present invention, in the following description, we still describe by the baseband system of equivalence, omit links such as rf modulations in the real system, sampling.Simultaneously, in order to set forth conveniently, the hypothetical target user is linked into sub-district 1.

For D-OFDMA cellular system based on the FrFT angular multiplexing, when carrying out the network planning, at first determine the number (selecting for use several FrFT angle to distribute) of FrFT angle in the minizone, carry out optimum allocation according to (34) or (35) diagonal angle resource then, according to Fig. 3 or Fig. 4 it is assigned to each sub-district, preserves as the base attribute of each sub-district.When each cell base station and its access user communicate, all according to separately sub-district assigned angle carry out IDFrFT modulation and the DFrFT demodulation of signal thereafter.

At targeted customer's serving BS transmitting terminal, at first will send data and form the data symbols after the baseband modulation through chnnel coding, digital modulation.The base band data code element of the serial after will modulating is afterwards carried out serial to parallel conversion, data symbols after the modulation that obtains walking abreast.Insert pilot frequency code element in the data symbols after parallel modulation, concrete pilot frequency code element form is the same with traditional ofdm system with inserted mode.Then, by (17) formula the parallel data code element that has pilot code is made the contrary discrete fraction rank Fourier transform of this sub-district institute corresponding angle, the concrete conversion number of subcarriers that can be comprised by an OFDM symbol as required of counting determines.Then, by the Cyclic Prefix of the described adding certain-length of (23) formula, length is determined by system channel time delay situation.At last parallel signal is carried out serial to parallel conversion, obtain the base-band data signal of serial.

Like this, each sub-district just becomes a series of stacks with linear FM signal of identical frequency modulation rate, different reference frequencies by the OFDM symbol that the IDFrFT of corresponding angle separately carries out generating after the subcarrier-modulated, and each sub-carrier frequencies is shown in (18) formula.And modulation basic function reference frequency is identical on the neighbor cell same sub-carrier, and difference only shows frequency modulation rate difference.

At targeted customer's receiving terminal, pass through α except having in the received signal (24) from persistent district ₁The useful signal of-IDFrFT modulation also comprises from other sub-districts through α _iThe interference signal and the additive white Gaussian noise of-IDFrFT (i ≠ 1) modulation.To receive and carry out serial to parallel conversion, and remove Cyclic Prefix by (26) formula through the baseband signal that processing such as down-conversion obtain.Then, by shown in (16) formula, the DFrFT that uses the persistent district corresponding angle carries out subcarrier demodulation to signal, obtains the data-signal after the subcarrier demodulation.Utilize the pilot frequency information that contains in the signal, can carry out channel estimating, obtain the equivalent transmission matrix of channel the signal after the subcarrier demodulation.The method of concrete channel estimating can not be a content of the present invention with reference to the existing method in traditional ofdm system, repeats no more.Carry out fractional order Fourier domain MMSE equilibrium and coherent detection to received signal by (32) formula then.At last, form output stream by digital demodulation, channel-decoding etc.

For the validity of system of the present invention and algorithm is described, we have carried out the system emulation experiment, and simulation parameter sees Table 1.

Fig. 5 and Fig. 6 have provided the modulation basic function of different districts on different sub carrier, and wherein optimizing 3 angles that obtain is { 0.35 π, 0.5 π, 0.65 π }, distributes in whole system according to Fig. 3.This shows that the modulation basic function of all neighbor cells on same sub-carrier is different.Fig. 7 has provided correlation between the basic functions different on these different districts same sub-carrier about the change curve of differential seat angle, and therefrom differential seat angle is in [0, π] scope as can be seen, and correlation is inversely proportional to it.When differential seat angle reached 0.1 π, its correlation can be regarded nearly orthogonal as substantially less than 0.1.

Fig. 8 has provided under the awgn channel, the multiplexing S-OFDMA cellular system bit error rate performance curve comparison diagram of D-OFDMA cellular system and traditional single FFT angle based on the 3-FrFT angular multiplexing, wherein the legacy system error rate does not adopt in system edge customer is carried out obtaining under the presence of intercell interference inhibition algorithm conditions such as frequency band limits and power control, adopt QPSK and 16QAM digital modulation mode as seen from the figure, its performance all has the lifting of nearly 20dB.

Fig. 9 has provided under the channel of typical cities and towns (TU), 6 footpath, the multiplexing S-OFDMA cellular system bit error rate performance curve comparison diagram of D-OFDMA cellular system and the single angle of traditional FFT based on the 3-FrFT angular multiplexing, wherein the legacy system error rate does not adopt in system edge customer is carried out obtaining under the presence of intercell interference inhibition algorithm conditions such as frequency band limits and power control, adopt QPSK and 16QAM digital modulation mode as seen from the figure, its performance still has the lifting of nearly 20dB.

Table 1 system emulation parameter

Claims (6)

1. biorthogonal frequency division multiple access (D-OFDMA) cellular system based on fraction Fourier conversion (FrFT) angular multiplexing, it is characterized in that: the transmitting terminal of neighbor cell utilizes the mutually different contrary fraction Fourier conversion (IFrFT) of angle that the data vector is modulated, make and satisfy mutually orthogonal property between the modulation basic function on the different sub carrier in the sub-district, satisfy nearly orthogonal between the modulation basic function on the same sub-carrier between neighbor cell simultaneously; Targeted customer's receiving terminal utilizes the FrFT of its Serving cell institute corresponding angle to receive the demodulation of vector, carries out equilibrium and coherent detection simultaneously on the FrFT territory of corresponding angle, suppresses presence of intercell interference.

2. the D-OFDMA cellular system based on the FrFT angular multiplexing according to claim 1 is characterized in that: the IFrFT modulation of data vector is carried out according to the FrFT angle that is assigned to separately in each sub-district; User's receiving terminal carries out demodulation according to the assigned FrFT angle of Serving cell.Modulation and demodulation formula availability vector form is expressed as respectively between i sub-district and its access user:

With

Wherein, α _iFor distribute to the FrFT angle of cell i by certain criterion;

Be the data vector that comprises in OFDM symbol in the cell i;

Be that i sub-district internal object user receiving terminal removes reception vector to be demodulated behind the Cyclic Prefix, wherein be mixed with interference signal and additive white Gaussian noise from a plurality of base station sent outside the sub-district;

With

Be discrete contrary fraction Fourier conversion (IDFrFT) matrix and discrete fraction rank Fourier transforms (DFrFT) matrix.

3. the D-OFDMA cellular system based on the FrFT angular multiplexing according to claim 1 is characterized in that: interior k the subchannel rise of an OFDM symbol system basic function frequency is in the cell i

T wherein _sBe the duration (or cycle) of OFDM symbol, and t ∈ (0, T _s).

4. the D-OFDMA cellular system based on the FrFT angular multiplexing according to claim 1, it is characterized in that: disturb for fear of between the subcarrier, frequency range is less than the subcarrier reference frequency at interval in symbol period to require to satisfy on each subchannel the modulation basic function With intercarrier protection interval delta G _fPoor, the optional scope that obtains each FrFT angle, sub-district thus is:

。

5. the D-OFDMA cellular system based on the FrFT angular multiplexing according to claim 1, it is characterized in that: the FrFT angle is counted as between a kind of new different districts of time-frequency combination resource in whole system carries out optimum allocation, promptly according to the network configuration of cellular system, as long as in the optional scope in FrFT angle, select 3 different angles { β ₁, β ₂, β ₃Or 7 different angles { β ₁, β ₂..., β ₇Carry out the minizone distribution, can guarantee angle difference between any neighbor cell, and if the suitable modulation basic function nearly orthogonal of neighbor cell on same sub-channel that make of angle Selection, the optimization criterion of its 3 angle and 7 angular distribution is respectively:

Wherein,

The average correlation of representing two sub-district basic functions; The expression angle is β _i-β _jThe DFrFT matrix the (this criterion can make the modulation basic function average correlation on the neighbor cell same sub-channel reach minimum for k, k) individual element.

6. the D-OFDMA cellular system based on the FrFT angular multiplexing according to claim 1 is characterized in that: utilize the nearly orthogonal of modulation basic function on the different districts same sub-channel, carry out coherent detection at FrFT, suppress presence of intercell interference.

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