CN101459962A - Resource distributing method having QoS requirement in CR OFDM system - Google Patents

Abstract

The invention provides a method with the QoS requirement for distributing resources in a CR OFDM system, which comprises the following steps: selecting a cognitive user whose gamma m is maximal from a to-be distributed cognitive user set UM, distributing the proper sub-carrier wave, power and bit number for the cognitive user according to the principle that the gain factor gamma mn is larger than the priority or the bit numbers are approximate, newly confirming to-be distributed sub-carrier wave sets SN and UM, newly calculating the interference I generated to the users by the cognitive users, if the I is bigger than the interference threshold value Ith of the authorized users, canceling the sub-carrier wave and the distributing of the power and the bits and finishing the distributing work, if the UM has no to-be distributed cognitive users and the SN still has the to-be distributed sub-carrier wave resources, then distributing the residual carrier waver resources. The method considers the two restraining conditions of the interference threshold and the QoS requirement of the users, thereby further improving the availability ratio of the frequency spectrum and the distributing of the recourses.

Description

The resource allocation methods that has qos requirement in the CR ofdm system

Technical field

The invention belongs to wireless communication technology field, especially a kind of cognitive radio (cognitive radio that is applied in, abbreviation CR) resource allocation algorithm in OFDM (orthogonal frequency division multiplexing the is called for short OFDM) system.

Background technology

Along with multimedia service being extensive use of in radio communication, radio communication has entered high speed data transfer epoch.Yet message transmission rate is high more, and intersymbol interference is severe more, and is also serious more to the influence of systematic function.The OFDM technology then can address this problem well, it passes through string and conversion with data flow at a high speed, become the relatively low data flow of transmission rate and on the experimental process carrier wave, transmit, alleviated the destruction of intersymbol interference greatly, improved the performance of system under high speed data transfer signal.

Cognitive radio is a kind of technology of the new raising availability of frequency spectrum, it can will temporarily not be authorized to user (licensed users in some zones, being called for short LU) frequency range used lends unauthorized user (be also referred to as cognitive user cognitive radio user, be called for short CRU) and makes and be used for improving the availability of frequency spectrum.Cognitive radio is the wireless communication system of an intelligence, and it can correspondingly dynamically adjust its transmission parameter by the study to radio environment.Because OFDM technology allocation of subcarriers neatly, and control its power, so the CR ofdm system that combines of CR and two kinds of technology of OFDM, become the important component part of future communications system.In the CR ofdm system, authorized user and cognitive user will often be used adjacent frequency spectrum resource simultaneously, and this will produce mutual interference, and this mutual interference is that cognitive user must be considered when use authority user's frequency range.Simultaneously, in the CR ofdm system, the business of cognitive user not only has traditional business such as voice-and-data, also have streaming media service such as ever-increasing real-time voice video, these multimedia services will be to QoS (Quality of Service, be service quality) different requirements is arranged, thereby must carry out QoS to various multimedia services and consider.If the resource of system assignment can not satisfy the demand of cognitive user QoS, will have a strong impact on the communication quality of cognitive user.Therefore, in the CR ofdm system, how allocation of subcarriers, power and bit resource just can make cognitive user produce the interference threshold that the interference of authorized user is no more than authorized user, and the qos requirement that can improve the availability of frequency spectrum of system simultaneously again and satisfy cognitive user has become important studying a question.

Summary of the invention

Purpose of the present invention aims to provide a kind of adaptive resource collocation method, realize that CR ofdm system cognitive user when the distributing carrier wave resource is no more than the interference threshold of authorized user to the interference of authorized user, satisfy the qos requirement of cognitive user simultaneously and improve the availability of frequency spectrum of system as far as possible.

The present invention is achieved by the following technical solutions:

The resource allocation methods that has qos requirement in a kind of CR ofdm system is characterized in that, comprises the following steps:

The resource allocation system of step 1. pair base station carries out initialization, finishes following work:

Set sub-carrier set S to be allocated _NWith cognitive user collection U to be allocated _MAnd the setting cognitive user is to the interference I=0 of authorized user; From the request resource information of cognitive user, obtain the minimum transmitted bit speed of cognitive user and convert a bit number demand R in the OFDM symbol to _mRequire BER, authorized user's interference threshold I from the signal of authorized user with the error rate upper limit _ThTransmitting power spectrum and send channel gain according to authorized user calculate the interference S that authorized user produces cognitive user signal on each subcarrier successively _Mn(d _n), the gain factor γ of each cognitive user on each subcarrier _Mn, the average gain factor of all cognitive user on each subcarrier

The performance number P that will distribute on each subcarrier _nWith the average gain factor of each cognitive user on all subcarriers

The resource allocation system of step 2. base station satisfies the resource allocation of qos requirement to cognitive user:

2.1, resource allocation system is from cognitive user collection U to be allocated _MSelect

Maximum cognitive user is according to gain factor γ _MnGreatly the approaching principle of principle of priority or bit number is distributed suitable subcarrier, power and bit number to cognitive user, and redefines sub-carrier set S to be allocated _NWith cognitive user collection U to be allocated _M

2.2, recomputate the interference value I that cognitive user produces main user, if interference value I is greater than the interference threshold value I of authorized user _Th, then cancel this subcarrier and go up power and the distribution of bit and sharing out the work of ends with system, otherwise enter step 2.3;

If 2.3 cognitive user collection U _MIn do not had cognitive user to be allocated and sub-carrier set S to be allocated _NIn still have sub-carrier resources to be allocated, then jump to step 3, otherwise enter step 2.4;

If 2.4 sub-carrier set S to be allocated _NIn do not had sub-carrier resources to be allocated sharing out the work of ends with system so, otherwise jump to step 2.1;

The resource allocation system of step 3. base station is reallocated to the residue sub-carrier resources:

3.1, according to gain factor γ _MnGreatly principle of priority is distributed suitable subcarrier, power and bit number to cognitive user, and redefines sub-carrier set S to be allocated _N:

3.2, recomputate the interference value I that cognitive user produces authorized user, if interference value I is greater than the interference threshold value I of authorized user _Th, then cancel this subcarrier and go up power and the distribution of bit and sharing out the work of ends with system, otherwise enter step 3.3;

If 3.3 sub-carrier set S to be allocated _NIn do not had sub-carrier resources to be allocated sharing out the work of ends with system so, otherwise jump to step 3.1.

Wherein, described step 2 specific implementation method is as follows:

(1) selects cognitive user collection U to be allocated _MIn Maximum cognitive user m ^*, and select it at sub-carrier set S to be allocated _NIn have the maximum gain factor subcarrier n ^*, calculate the bit number b that this cognitive user can be got by (5) formula on this subcarrier,

$b=\mathrm{round}\left({\log }_2(1+{\mathrm{\γ}}_{m*n*}{P}_{n*})\right)---\left(5\right)$

In the above-mentioned formula, round represents the computing that rounds up,

Expression cognitive user m ^*At subcarrier n ^*On gain factor,

Expression subcarrier n ^*On power,

Bit number b is carried out the judgement and the operation of following process:

I) if b equals 0, then with this subcarrier n ^*The performance number of last distribution and bit number all are changed to 0, and from sub-carrier set S to be allocated _NMiddle this subcarrier of deletion;

If ii) b is greater than 0 and the bit number that needs less than cognitive user

Then press gain factor γ _MnGreatly principle of priority is given cognitive user m with this subcarrier allocation ^*, and the watt level on this subcarrier is assigned as $P_{n*}=\frac{2^b-1}{{\mathrm{\γ}}_{m*n*}},$ Bit number is assigned as b, with cognitive user m ^*The bit number that needs to distribute is changed to $R_{m*}=R_{m*}-b,$ With subcarrier n ^*From sub-carrier set S to be allocated _NMiddle deletion;

If iii) b is more than or equal to the bit number of cognitive user needs And smaller or equal to

α is the adjustable reflection availability of frequency spectrum and holds the parameter that cognitive user is counted importance degree that its value is then pressed gain factor γ more than or equal to 0 _MnGreatly principle of priority is given cognitive user m with this subcarrier allocation ^*, and the watt level on this subcarrier is assigned as $P_{n*}=\frac{2^b-1}{{\mathrm{\γ}}_{m*n*}},$ Bit number is assigned as b, with subcarrier n ^*From sub-carrier set S to be allocated _NMiddle deletion is with cognitive user m ^*From cognitive user collection U to be allocated _MMiddle deletion;

If iv) b greater than

Then press bit number near the new subcarrier of principle search

$n*=\arg \underset{n\∈S_N}{\min }\left(|{\log }_2(1+{\mathrm{\γ}}_{m*n}{P}_n)-R_{m*}|\right),$ And this subcarrier will satisfy $\mathrm{round}\left({\log }_2(1+{\mathrm{\γ}}_{m*n}{P}_n)\right)\≥R_{m*},$ Give cognitive user m with this subcarrier allocation ^*, and the allocation bit number is $b=\mathrm{round}\left({\log }_2(1+{\mathrm{\γ}}_{m*n}{P}_{n*})\right),$ Watt level is $P_{n*}=\frac{2^b-1}{{\mathrm{\γ}}_{m*n*}},$ With this subcarrier from sub-carrier set S to be allocated _NMiddle deletion is with cognitive user m ^*From cognitive user collection U to be allocated _MMiddle deletion;

(2) dispensed subcarrier n ^*And when going up power and bit number and increasing to the interference of authorization user signal $\mathrm{\ΔI}=P_{n*}{\mathrm{IF}}_{n*},$ Upgrade the interference value I=I+ Δ I that cognitive user produces authorized user, if I is greater than the interference threshold value I of authorized user _Th, then cancel this subcarrier and go up power and the distribution of bit and sharing out the work of ends with system, otherwise enter step (3);

(3) if S _MIn do not had cognitive user to be allocated and S _NIn still have sub-carrier resources to be allocated, then jump to step 3, otherwise enter step (4);

(4) if S _NIn do not had sub-carrier resources to be allocated to finish so to distribute, otherwise jump to step (1).

The main implementation procedure of described step 3 is as follows:

(1) presses gain factor γ _MnGreatly principle of priority is selected sub-carrier set S to be allocated _NMiddle gain factor γ _MnMaximum subcarrier n ^*With corresponding cognitive user m ^*, and with subcarrier n ^*Distribute cognitive user m ^*, the allocation bit number is $b=\mathrm{round}\left({\log }_2(1+{\mathrm{\γ}}_{m*n*}{P}_{n*})\right),$ Distribute watt level to be $P_{n*}=\frac{2^b-1}{{\mathrm{\γ}}_{m*n*}},$ With this subcarrier from sub-carrier set S to be allocated _NMiddle deletion;

(2) calculate $\mathrm{\ΔI}=P_{n*}{\mathrm{IF}}_{n*},$ Upgrade I=I+ Δ I.If I is greater than interference threshold I _Th, then cancel this subcarrier and go up power and the distribution of bit and sharing out the work of ends with system, otherwise enter step (3)

(3) if S _NIn do not had sub-carrier resources to be allocated to finish so to distribute, otherwise jump to step (1).

The performance number P that will distribute on described each subcarrier _nProcessing method is as follows:

(i) calculate λ, P according to (3), (4) formula _n,

$\mathrm{\λ}=\frac{N}{(I_{\mathrm{th}}+{\mathrm{\Σ}}_{n=1}^N\frac{{\mathrm{IF}}_n}{\stackrel{\‾}{{\mathrm{\γ}}_n}})\ln 2}---\left(3\right)$

$P_n=\frac{1}{{\mathrm{\λIF}}_n\ln 2}-\frac{1}{\stackrel{\‾}{{\mathrm{\γ}}_n}}---\left(4\right)$

N=1 in the formula, 2 ..., N, I _ThBe the interference threshold value of authorized user, IF _nBe the interference factor of subcarrier n to authorized user, the size of interference is measured with watt (W), ${\mathrm{IF}}_n=T_s{\∫}_{d_n-W_i/2}^{d_n+W_i/2}{\left|g_n\right|}^2{\left(\frac{\sin \mathrm{\π}{\mathrm{fT}}_s}{\mathrm{\π}{\mathrm{fT}}_s}\right)}^2\mathrm{df}$ , T _sThe symbol period of expression OFDM, d _nExpression subcarrier n is to the spectral distance at authorized user service band center, W _lThe channel width of expression authorized user, N is the sub-carrier number that cognitive user can be used, g _nThe expression base station is to the channel gain of authorized user on subcarrier n, and f represents frequency variable;

If (ii) P _n(n=1,2 ..., value is arranged less than 0 in N), then with the negative value P of minimum _nAssignment is 0, and removes this subcarrier, returns step (i); If P _n(n=1,2 ..., void value is less than 0 in N), and then this calculating finishes.

The present invention has following advantage with respect to prior art:

1, the present invention has considered the interference threshold of authorized user and two constraintss of qos requirement of cognitive user simultaneously when design, according to the relation between mutual interference and the spectral distance, when the system assignment resource, at first satisfy the qos requirement of cognitive user, further improve the resource allocation of the availability of frequency spectrum again.The invention enables system when Resources allocation, cognitive user is no more than the interference threshold of authorized user to the interference of authorized user, satisfies the qos requirement (comprising that the minimum bit transmission rate and the error rate upper limit require) of cognitive user simultaneously and improves the availability of frequency spectrum of system as far as possible.

2, also designed a parameter alpha that reflects the availability of frequency spectrum and hold the importance degree of number of users among the present invention, its value is more than or equal to 0.When $R_{m*}\≤b\≤R_{m*}+\mathrm{\α}$ The time, press greatly priority principle of gain factor, give user m with the subcarrier allocation that had before found ^*When $b>R_{m*}+\mathrm{\α}$ The time, distribute near principle by bit number, promptly search new subcarrier again, the bit number of meeting consumers' demand is simultaneously given user m near the subcarrier allocation of the bit number of user's request again ^*, its result is exactly the lowest bit number that the user obtains its demand.The α value is big more, illustrates that the importance degree of the availability of frequency spectrum is high more, and at this moment the availability of frequency spectrum of system is also high more; The α value is more little, illustrates that the importance degree that holds number of users is high more, and at this moment system's number of users that can hold is also many more.System can determine the availability of frequency spectrum and the importance degree that holds the cognitive user number by the size of adjusting the α value.

Description of drawings

Fig. 1 uses a model for the frequency spectrum of CR ofdm system down link;

Fig. 2 is greedy algorithm and the inventive method emulation number of users and system break probabilistic relation figure under a specific embodiment;

Fig. 3 is a system resource allocation flow process of the present invention.

Embodiment

The following description of example of the present invention, MatLab emulation is adopted in system emulation, and parameter setting does not influence generality.Adopt Fig. 1 intermediate frequency spectrum to use a model, base station (base station, BS) 1 authorized user of service and 4 cognitive user u in the system ₁, u ₂, u ₃, u ₄, bandwidth was W in the middle of authorized user used _lThe frequency range of=0.3125Hz, transmitting power are 1W, and interference threshold is I _Th=0.002W, power spectral density replaces cognitive user to use adjacent frequency range with the white noise signal through oval filtering.The authorized user power spectrum specifically adopts the logical elliptic filter of band in the MatLab specific implementation, and parameter is set to:

The frequency band range of filter is 0 to 5.3125MHz, passband ripple maximum attenuation R _p=3dB, stopband ripple minimal attenuation R _s=40, passband normalization cut-off frequency $W_p=\left[\begin{array}{cc}\frac{81}{170}& \frac{89}{170}\end{array}\right],$ Stopband normalization cut-off frequency $W_s=\left[\begin{array}{cc}\frac{8}{17}& \frac{9}{17}\end{array}\right],$ Use [n, W _n(Rp Rs) obtains minimum exponent number n and the passband normalization width W that band leads to elliptic filter to]=ellipord for Wp, Ws _n, use [b, a]=ellip (n, Rp, Rs, W _n) obtain normalization coefficient.The symbol that uses in the band pass filter and subordinate's symbol are irrelevant.

4 cognitive user are used 16 subcarriers on both sides, use s ₁, s ₂..., s ₁₆Expression.The bandwidth of subcarrier is W _c=0.3125MHz, they are respectively 6,9,9,7 bits at the bit number demand in an OFDM symbol, and it all is 10 that the error rate upper limit requires ^-5OFDM symbol period T _sBe 4ms, physical layer adopts MQAM modulation and Gray code associating.The channel gain h of cognitive user and authorized user _Mn, g _nBe independent identically distributed, all obey variance and be 1 Rayleigh and distribute the power spectral density N of additive white Gaussian noise ₀=10 ^-8W/Hz.The adaptive resource allocation method that has qos requirement in the CR ofdm system as shown in Figure 3, system postulation is the channel gain that can correctly find out each user, so h _Mn, g _nBe system's known conditions.

Now be located in the OFDM mark space cognitive user u ₁, u ₂, u ₃, u ₄Channel gain on 16 subcarriers is h _Mn:

The channel gain g of authorized user _n:

Carry out the detailed process of embodiment below

1. base station initialization:

(1) sets sub-carrier set S to be allocated _N={ s ₁, s ₂..., s ₁₆, cognitive user collection U to be allocated _M={ u ₁, u ₂, u ₃, u ₄And cognitive user to the interference I=0 of authorized user.

(2) from the request resource information of cognitive user, obtain the minimum transmitted bit speed of cognitive user and convert a bit number demand R in the OFDM symbol to _M={ 6,9,9, the 7} and the error rate upper limit require BER=10 ^-5, authorized user's interference threshold I from the signal of authorized user _Th=0.002W.

(3) calculate the interference size S of authorized user generation according to the transmitting power spectrum and the send channel gain of authorized user according to (1) formula to cognitive user signal on each subcarrier _Mn(d _n):

$S_{\mathrm{mn}}\left(d_n\right)={\∫}_{d_n-W_c/2}^{d_n+W_c/2}{\left|h_{\mathrm{mn}}\right|}^2{\mathrm{\Φ}}_P\left(f\right)\mathrm{df}---\left(1\right)$

D wherein _nExpression subcarrier n is to the spectral distance at authorized user service band center, Φ _P(f) be the power spectral density of authorization user signal, specifically realize by the above-mentioned MatLab program that has illustrated.

(4) calculate the gain factor γ of each cognitive user on each subcarrier according to (2) formula _Mn

${\mathrm{\γ}}_{\mathrm{mn}}=\frac{{\left|h_{\mathrm{mn}}\right|}^2}{\mathrm{\Γ}(N_0{W}_c+S_{\mathrm{mn}})}---\left(2\right)$

Γ represents the amount of redundancy related with physical level coded modulation, Γ=-ln (5 * 10 ^-5)/1.5=6.6023.Obtain γ _MnValue be:

(5) according to γ _MnCalculate the average gain factor of all users on each subcarrier

Value is:

By formula ${\mathrm{IF}}_n=T_s{\∫}_{d_n-W_i/2}^{d_n+W_i/2}{\left|g_n\right|}^2{\left(\frac{\sin \mathrm{\π}{\mathrm{fT}}_s}{\mathrm{\π}{\mathrm{fT}}_s}\right)}^2\mathrm{df}$ Calculate IF _nValue be:

According to the power P that will distribute on following each subcarrier of method iterative computation _n(n=1,2 ..., 16) value is:

(i) calculate λ, P according to (3), (4) formula _n, N is the sub-carrier number that cognitive user can be used in the formula, I _ThBe the interference threshold value of authorized user, IF _nBe the interference factor of subcarrier n to authorized user.The size of disturbing is measured with watt (W).

$\mathrm{\λ}=\frac{N}{(I_{\mathrm{th}}+{\mathrm{\Σ}}_{n=1}^N\frac{{\mathrm{IF}}_n}{\stackrel{\‾}{{\mathrm{\γ}}_n}})\ln 2}---\left(3\right)$

$P_n=\frac{1}{{\mathrm{\λIF}}_n\ln 2}-\frac{1}{\stackrel{\‾}{{\mathrm{\γ}}_n}}---\left(4\right)$

If (ii) P _n(n=1,2 ..., value is arranged less than 0 in N), then with the negative value P of minimum _nAssignment is 0, and removes this subcarrier, returns step (i); If P _n(n=1,2 ..., N) in void value then calculate to finish less than 0.

(6) according to γ _MnCalculate four cognitive user u ₁, u ₂, u ₃, u ₄The average gain factor on all subcarriers respectively For: 28.4483,31.1468,31.3829,54.9049.

Step 2. satisfies the resource allocation of user's qos requirement:

(1) basis Size at first select cognitive user collection U to be allocated _MIn Maximum cognitive user u ₄, and by gain factor greatly principle of priority select it at sub-carrier set S to be allocated _NIn have the maximum gain factor subcarrier s ₁, calculate the bit number b=5 that this cognitive user can be distributed by (5) formula on this subcarrier,

b＝round(log ₂(1+γ ₄₁P ₁)) (5)

Because b=5 is less than cognitive user u ₄The bit number R that needs ₄=7, so with subcarrier s ₁Distribute to cognitive user u ₄, and the watt level on this subcarrier is assigned as $P_1=\frac{2^5-1}{{\mathrm{\γ}}_{41}}=0.1118W,$ Bit number is assigned as 5, with cognitive user u ₄The bit number that needs to distribute is changed to R ₄=R ₄-b=2 is with subcarrier s ₁From sub-carrier set S to be allocated _NMiddle deletion, upgrading sub-carrier set to be allocated is S _N={ s ₂, s ₃..., s ₁₆.Dispensed subcarrier s ₁And increase interference Δ I=P when going up power and bit to authorization user signal ₁IF ₁=2.0217 * 10 ^-4W upgrades I=I+ Δ I=2.0217 * 10 ^-4W.I is less than the interference threshold I of authorized user _Th=0.002W is because cognitive user u ₄The bit number demand also be not met and still have subcarrier to be allocated, so can continue to cognitive user u ₄Carry out resource allocation.

(2) select sub-carrier set S to be allocated _NThe subcarrier s of middle gain factor maximum ₁₆, calculate cognitive user u ₄Can be at subcarrier s ₁₆The bit number b=6 of last distribution, at this moment b=6 is greater than cognitive user u ₄The bit number R that also needs ₄=2 with parameter alpha=2 and, therefore need press bit number and seek new subcarrier allocation to cognitive user u near principle ₄Search subcarrier s by bit number near principle ₂, can distribute to cognitive user u on it ₄Bit number be 3, the most approaching and greater than cognitive user u in remaining subcarrier ₄The bit number 2 of Xuing also is therefore with subcarrier s ₂Distribute to cognitive user u ₄, and the watt level on this subcarrier is assigned as $P_2=\frac{2^3-1}{{\mathrm{\γ}}_{42}}=0.2027W,$ Bit number is assigned as 3, with subcarrier s ₂From sub-carrier set S to be allocated _NMiddle deletion, upgrading sub-carrier set to be allocated is S _N={ s ₃, s ₄..., s ₁₆, with cognitive user u ₄From cognitive user collection U to be allocated _MMiddle deletion, upgrading cognitive user collection to be allocated is U _M={ u ₁, u ₂, u ₃.Dispensed subcarrier s ₂And increase interference Δ I=P when going up power and bit to authorization user signal ₂IF ₂=2.4727 * 10 ^-4W upgrades I=I+ Δ I=4.4944 * 10 ^-4W.I is less than the interference threshold I of authorized user _Th=0.002W can continue remaining cognitive user is carried out resource allocation.

(3) according to giving cognitive user u ₄The method that Resources allocation is identical, according to Order is from big to small given cognitive user u successively ₃, u ₂, u ₁Resources allocation, u ₃The subcarrier that distributes is s ₃, s ₁₆, the power that distributes on two subcarriers is respectively 0.7436W, 0.2694W, and bit number is respectively 6,4; u ₂The subcarrier that distributes is s ₅, s ₁₅, the power that distributes on two subcarriers is respectively 0.9719W, 1.9860W, and bit number is respectively 5,4; u ₁The subcarrier that distributes is s ₁₃, the power that distributes on the subcarrier is 2.3605W, bit number is 6; Simultaneously, at assigning process sub-carriers s ₈, s ₄, s ₁₄Going up assignable bit number is 0, all is 0 with power on them and Bit Allocation in Discrete therefore, and they are deleted from assignable sub-carrier set.

(4) four satisfied cognitive user u of Yi Shang distribution ₁, u ₂, u ₃, u ₄QoS (lowest bit rate and the error rate upper limit) requirement, allocation of subcarriers is I=0.0016W to the interference that authorized user produces, remains assignable sub-carrier set S _NBe { s ₆, s ₇, s ₉, s ₁₀, s ₁₁, s _I2.Disturb the interference threshold that does not surpass authorized user, and still have remaining sub-carrier resources also unallocated, therefore also can carry out the residue sub-carrier resources reallocation of step 3.

Step 3: the reallocation of residue sub-carrier resources,

(1) according to gain factor principle of priority greatly, from sub-carrier set S to be allocated _NThe middle γ that selects _MnMaximum subcarrier s ₁₂Cognitive user u with correspondence ₁, find that assignable bit is 0, therefore, with subcarrier s ₁₂The power that distributes is 0, and the bit number of distribution is 0, and with it from sub-carrier set S to be allocated _NMiddle deletion.

(2) surplus resources continue to distribute, and according to gain factor principle of priority greatly, the subcarrier of Fen Peiing is s successively ₇, s ₉, s ₆, s ₁₁, s ₁₀With the cognitive user of correspondence be u ₄, u ₁, u ₃, u ₂, u ₃Wherein has only subcarrier s ₁₁Going up assignable bit is 1, and remaining all is 0.Therefore, with subcarrier s ₁₁Distribute to cognitive user u ₂, the power of distribution is 0.0559W, and the bit number of distribution is 1, and the interference that increases authorized user is 9.2287 * 10 ^-5W upgrades I=I+ Δ I=0.0017W.And with these subcarriers from sub-carrier set S to be allocated _NMiddle deletion.

To sum up obtain four cognitive user u after three steps ₁, u ₂, u ₃, u ₄The bit number that distributes is assigned as the power and the bit that distribute on 6,12,10,8,16 subcarriers and is respectively:

Power: 0.1118 0.2027 0.7436 0 0.9717 000000000 1.98600.2694.

Bit number: 5360500000106064.

Generation is 0.0018W to the interference of authorized user, does not surpass interference threshold.

Compare for the ease of the inventive method and existing greedy algorithm, the basic thought of greedy algorithm is to divide timing only to distribute a bit at every turn, and it increases the interference minimum to authorized user, reaches the interference threshold of authorized user up to interference, distributes and finishes.Fig. 2 has provided the performance comparison of the situation that outage probability (user who promptly can not get service request accounts for total user's ratio) and the availability of frequency spectrum under two kinds of methods change with number of users, and its performance curve is 1000 statistical average performances.The error rate upper limit of cognitive user is less demanding in 10 among Fig. 2 ^-5, when the Minimum requirements bit number in OFDM symbol was uniformly distributed in integer on the interval [3,10], outage probability (total promptly can not get the ratio that the user of service request accounts for the user) and the availability of frequency spectrum were with the emulation of the situation of number of users variation.

As can be seen from Figure 2, because greedy algorithm does not carry out subcarrier and Bit Allocation in Discrete according to the QoS demand of cognitive user, its outage probability just begins to become big at number of users seldom the time.And ARAQ algorithm (algorithm of this paper method is realized) carries out subcarrier and Bit Allocation in Discrete by user QoS demand, and the number of users that QoS is met will be much larger than the number of users under the greedy algorithm.Simultaneously, than when the α=∞, system can satisfy more user QoS demand in α=0 o'clock.The number of users that holds during 0＜α＜∞ will be between the number of users of two end points.

Claims (4)

1, the resource allocation methods that has qos requirement in a kind of CR ofdm system is characterized in that, comprises the following steps: that the resource allocation system of step 1. pair base station carries out initialization, finishes following work:

Set sub-carrier set S to be allocated _NWith cognitive user collection U to be allocated _MAnd the setting cognitive user is to the interference I=O of authorized user; From the request resource information of cognitive user, obtain the minimum transmitted bit speed of cognitive user and convert a bit number demand R in the OFDM symbol to _mRequire BER, authorized user's interference threshold I from the signal of authorized user with the error rate upper limit _ThTransmitting power spectrum and send channel gain according to authorized user calculate the interference S that authorized user produces cognitive user signal on each subcarrier successively _Mn(d _n), the gain factor γ of each cognitive user on each subcarrier _Mn, the average gain factor of all cognitive user on each subcarrier

The performance number P that will distribute on each subcarrier _nWith the average gain factor of each cognitive user on all subcarriers

The resource allocation system of step 2. base station satisfies the resource allocation of qos requirement to cognitive user:

2.1, resource allocation system is from cognitive user collection U to be allocated _MThe middle selection

Maximum cognitive user is according to gain factor γ _MnGreatly the approaching principle of principle of priority or bit number is distributed suitable subcarrier, power and bit number to cognitive user, and redefines sub-carrier set S to be allocated _NWith cognitive user collection U to be allocated _M

2.2, recomputate the interference value I that cognitive user produces main user, if interference value I is greater than the interference threshold value I of authorized user _Th, then cancel this subcarrier and go up power and the distribution of bit and sharing out the work of ends with system, otherwise enter step 2.3;

If 2.3 cognitive user collection U _MIn do not had cognitive user to be allocated and sub-carrier set S to be allocated _NIn still have sub-carrier resources to be allocated, then jump to step 3, otherwise enter step 2.4;

If 2.4 sub-carrier set S to be allocated _NIn do not had sub-carrier resources to be allocated sharing out the work of ends with system so, otherwise jump to step 2.1;

The resource allocation system of step 3. base station is reallocated to the residue sub-carrier resources:

3.1, according to gain factor γ _MnGreatly principle of priority is distributed suitable subcarrier, power and bit number to cognitive user, and redefines sub-carrier set S to be allocated _N

3.2, recomputate the interference value I that cognitive user produces authorized user, if interference value I is greater than the interference threshold value I of authorized user _Th, then cancel this subcarrier and go up power and the distribution of bit and sharing out the work of ends with system, otherwise enter step 3.3;

If 3.3 sub-carrier set S to be allocated _NIn do not had sub-carrier resources to be allocated sharing out the work of ends with system so, otherwise jump to step 3.1.

2, the resource allocation methods that has qos requirement in a kind of CR ofdm system according to claim 1 is characterized in that, described step 2 specific implementation method is as follows:

(1) selects cognitive user collection U to be allocated _MIn

Maximum cognitive user m ^*, and select it in sub-carrier set SN to be allocated, to have the subcarrier n of the maximum gain factor ^*, be calculated as follows the bit number b that this cognitive user can be got on this subcarrier,

$b=\mathrm{round}\left({\log }_2(1+{\mathrm{\γ}}_{m*n*}{P}_{n*})\right)$

In the above-mentioned formula, round represents the computing that rounds up,

Expression cognitive user m ^*At subcarrier n ^*On gain factor,

Expression subcarrier n ^*On power,

Bit number b is carried out the judgement and the operation of following process:

I) if b equals 0, then with this subcarrier n ^*The performance number of last distribution and bit number all are changed to 0, and from sub-carrier set S to be allocated _NMiddle this subcarrier of deletion;

If ii) b is greater than 0 and the bit number that needs less than cognitive user Then press gain factor γ _MnGreatly principle of priority is given cognitive user m with this subcarrier allocation ^*, and the watt level on this subcarrier is assigned as $P_{n*}=\frac{2^{b-1}}{{\mathrm{\γ}}_{m*n*}},$ Bit number is assigned as b, with cognitive user m ^*The bit number that needs to distribute is changed to $R_{m*}=R_{m*}-b,$ With subcarrier n ^*From sub-carrier set S to be allocated _NMiddle deletion;

If iii) b is more than or equal to the bit number of cognitive user needs

And smaller or equal to

α is the adjustable reflection availability of frequency spectrum and holds the parameter that cognitive user is counted importance degree that its value is then pressed gain factor γ more than or equal to 0 _MnGreatly principle of priority is given cognitive user m with this subcarrier allocation ^*, and the watt level on this subcarrier is assigned as $P_{n*}=\frac{2^{b-1}}{{\mathrm{\γ}}_{m*n*}},$ Bit number is assigned as b, with subcarrier n ^*From sub-carrier set S to be allocated _NMiddle deletion is with cognitive user m ^*From cognitive user collection U to be allocated _MMiddle deletion;

If iv) b greater than

Then press bit number near the new subcarrier of principle search

$n*=\arg \underset{n\∈S_N}{\min }\left(\right|{\log }_2(1+{\mathrm{\γ}}_{m*n*}{P}_n)-R_{m*}\left|\right),$ And this subcarrier will satisfy $\mathrm{round}\left({\log }_2(1+{\mathrm{\γ}}_{m*n*}{P}_{n*})\right)\≥R_{m*},$ Give cognitive user m with this subcarrier allocation ^*, and the allocation bit number is $b=\mathrm{round}\left({\log }_2(1+{\mathrm{\γ}}_{m*n*}{P}_{n*})\right),$ Watt level is $P_{n*}=\frac{2^{b-1}}{{\mathrm{\γ}}_{m*n*}},$ With this subcarrier from sub-carrier set S to be allocated _NMiddle deletion is with cognitive user m ^*From cognitive user collection U to be allocated _MMiddle deletion;

(2) dispensed subcarrier n ^*And when going up power and bit number and increasing to the interference of authorization user signal $\mathrm{\ΔI}=P_{n*}I{F}_{n*},$ Upgrade the interference value I=I+ Δ I that cognitive user produces authorized user, if I is greater than the interference threshold value I of authorized user _Th, then cancel this subcarrier and go up power and the distribution of bit and sharing out the work of ends with system, otherwise enter step (3);

(3) if S _MIn do not had cognitive user to be allocated and S _NIn still have sub-carrier resources to be allocated, then jump to step 3, otherwise enter step (4);

(4) if S _NIn do not had sub-carrier resources to be allocated to finish so to distribute, otherwise jump to step (1).

3, according to the resource allocation methods that has qos requirement in the described a kind of CR ofdm system of claim 1, it is characterized in that the main implementation procedure of described step 3 is as follows:

(1) presses gain factor γ _MnGreatly principle of priority is selected sub-carrier set S to be allocated _NMiddle gain factor γ _MnMaximum subcarrier n ^*With corresponding cognitive user m ^*, and with subcarrier n ^*Distribute cognitive user m ^*, the allocation bit number is $b=\mathrm{round}\left({\log }_2(1+{\mathrm{\γ}}_{m*n*}{P}_{n*})\right),$ Distribute watt level to be $P_{n*}=\frac{2^{b-1}}{{\mathrm{\γ}}_{m*n*}},$ With this subcarrier from sub-carrier set S to be allocated _NMiddle deletion;

(2) calculate $\mathrm{\ΔI}=P_{n*}I{F}_{n*},$ Upgrade I=I+ Δ I.If I is greater than interference threshold I _Th, then cancel this subcarrier and go up power and the distribution of bit and sharing out the work of ends with system, otherwise enter step (3)

(3) if S _NIn do not had sub-carrier resources to be allocated to finish so to distribute, otherwise jump to step (1).

4, the resource allocation methods that has qos requirement in a kind of CR ofdm system according to claim 1 is characterized in that the performance number P that will distribute on described each subcarrier _nProcessing method is as follows:

(i) calculate λ, P according to following formula 3, formula 4 _n,

$\mathrm{\λ}=\frac{N}{(I_{\mathrm{th}}+{\mathrm{\Σ}}_{n=1}^N\frac{{\mathrm{IF}}_n}{\stackrel{\‾}{{\mathrm{\γ}}_n}})\ln 2}---\left(3\right)$

$P_n=\frac{1}{\mathrm{\λ}{\mathrm{IF}}_n\ln 2}-\frac{1}{\stackrel{\‾}{{\mathrm{\γ}}_n}}---\left(4\right)$

N=1 in the formula, 2 ..., N, I _ThBe the interference threshold value of authorized user, IF _nBe the interference factor of subcarrier n to authorized user, the size of interference is measured with watt (W), ${\mathrm{IF}}_n=T_s{\∫}_{d_n-W_l/2}^{d_n+W_l/2}{\left|g_n\right|}^2{\left(\frac{\sin \mathrm{\π}{\mathrm{fT}}_s}{\mathrm{\πf}{T}_s}\right)}^2\mathrm{df},$ T _sThe symbol period of expression OFDM, d _nExpression subcarrier n is to the spectral distance at authorized user service band center, W _lThe channel width of expression authorized user, N is the sub-carrier number that cognitive user can be used, g _nThe expression base station is to the channel gain of authorized user on subcarrier n, and f represents frequency variable; If (ii) P _n(n=1,2 ..., value is arranged less than 0 in N), then with the negative value P of minimum _nAssignment is 0, and removes this subcarrier, returns step (i); If P _n(n=1,2 ..., void value is less than 0 in N), and then this calculating finishes.

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