CN106028455A - DF protocol based resource allocation method for two-way relay cognitive radio system - Google Patents

Abstract

The invention discloses a DF protocol based resource allocation method for a two-way relay cognitive radio system. The method comprises the following steps: utilizing the characteristic of volume maximization of the DF protocol to obtain a power relationship among a cognitive mobile user, a base station and various relays; utilizing the relationship, power limitation conditions of the cognitive user for signal transmission to the relays, and power limitation conditions of the base station for signal transmission to the relays, so as to obtain a signal-to-noise ratio of the two-way relay cognitive radio system during signal transmission through each relay; carrying out permutation and combination of all the signal-to-noise ratios, so as to obtain a signal-to-noise ratio combination, in which the sum of all the signal-to-noise ratios reaches the maximum value while satisfying interference limitation conditions; and obtaining the maximum system capacity, the corresponding relay, and the power of the relay for signal broadcasting according to the sum of all the signal-to-noise ratios in the obtained signal-to-noise ratio combination. The method provided by the invention has the advantages that the system capacity is enlarged; only the power of each relay for signal broadcasting needs to be obtained, so that the power obtaining process is simplified, and the complicity is reduced.

Description

Resource allocation methods in bi-directional relaying cognitive radio system based on DF agreement

Technical field

The present invention relates to a kind of resource allocation techniques relayed in cognitive radio system, especially relate to a kind of based on DF Resource allocation methods in the bi-directional relaying cognitive radio system of (Decode and Forward, decoding forwards) agreement.

Background technology

Wireless communication technology is developed rapidly in recent years, along with the increase of wireless application demand, and in short supply the asking of frequency spectrum Topic highlights day by day.Cognitive radio technology is by allowing cognitive user not affecting on the premise of authorized user normally works, dynamic State ground insertion authority frequency band, is effectively improved spectrum utilization efficiency.

In order to meet people's higher radio communication service demand, the wireless communication system of a new generation needs not only to provide Higher power system capacity, but also need the requirement that can meet user to service quality, such as the reliability of link and network Coverage etc..However, it is contemplated that the impact of the factor such as distance decline in the time-varying characteristics of wireless channel and signal transmission, The aspects such as the coverage making reliability and the network being wirelessly transferred encounter stern challenge.And cooperating relay technology has Effect ground improves the signal reliability caused in wireless environments because of the factor such as depth attenuation of geographical distribution and channel Reducing, cooperating relay technology will assist in and improves communication quality, the power system capacity increasing wireless communication system and expansion network Coverage, thus, cooperating relay technology is one of wireless communication technology of currently most receiving publicity.

Junction network in cognitive radio can be classified according to different forms.Junction network in cognitive radio Two kinds can be divided into: one-way junction network and bilateral relay network according to data flow direction.The total system of bidirectional relay system is held Amount is the twice of the entire system capacity of one-way junction system, and this makes bilateral relay network further be concerned.Double In relay system, bidirectional relay system based on physical-layer network coding is most widely used, and it just has only to two time slots Can complete the mutual of bi-directional data, thus the efficiency being doubled than traditional one-way junction system.In cognitive radio Junction network can be divided into again two kinds according to the duplex mode of via node: one is half-duplex junction network；Another kind is complete Duplex junction network.In view of implementation complexity, the most common relay system generally is half-duplex relay system.Use half The collaboration relay node of duplex mode according to signal processing strategy can be divided into AF (Amplify and Forward, amplification forwarding), DF (Decode and Forward, decoding forwards) and CC (Coded Cooperation, coding cooperative), wherein, DF agreement side Formula is that relaying is first decoded after receiving the signal of source node, relays to after then decoded data being recompiled Destination node.

In bi-directional relaying cognitive radio system, in order to obtain higher power system capacity, resource has been distributed into be optimized Problem.In resource distribution, relay selection is again a problem needing to solve.In relay selection, the single relaying of selection is had to carry out Signal transmits, and has the many relayings of selection to carry out signal transmission.Select single relaying that resource allocation optimization problem reduction is easily solved, but It is that power system capacity is limited.Select many relayings can make resource allocation optimization complication, but power system capacity can be improved.Two-way Relaying cognitive radio system in resource allocation optimization problem classics solution have three kinds, one be optimization problem is transferred to convex Optimization problem solves；Two is to apply Lagrange to combine subgradient method to solve；Three is application mean power method Solve.Owing to existing, cognitive user is launched the restriction of power and the restriction to authorized user's interference, therefore optimization problem is turned The methods and applications Lagrange carrying out solving for convex optimization problem combines subgradient method and carries out the complexity of the method solved Height, is difficult to solve；And the method applying mean power method to solve can not obtain higher power system capacity.

Summary of the invention

The technical problem to be solved is to provide a kind of bi-directional relaying cognitive radio system based on DF agreement In resource allocation methods, it can not only improve power system capacity, and can simplify power distribution, reduce complexity.

The present invention solves the technical scheme that above-mentioned technical problem used: a kind of bi-directional relaying based on DF agreement is cognitive Resource allocation methods in radio system, it is characterised in that comprise the following steps:

1. each channel set in bi-directional relaying cognitive radio system uses many Rayleigh fadings model；Set two-way in The cognitive radio system that continues is made up of a cognitive mobile subscriber, a base station, M relaying and an authorized user, wherein, and M > 1；Set and there is no direct link between cognitive mobile subscriber and base station, L relaying need to be selected to carry out signal transmission, wherein, 1≤L ≤M；

Setting each relay selection half-duplex operation, each relaying carries out the process of signal transmission when being divided into two Gap: the first time slot is multiple access time slot, in the first slot, base station is to all relay transmission signals, by the transmitting merit of base station Rate is designated as P_CB, the transmitting power of cognitive mobile subscriber, to all relay transmission signals, is designated as P by the most cognitive mobile subscriber_S, base Stand and time cognitive mobile subscriber transmits signal to same relay transmission signal；In the first slot, cognitive mobile subscriber All authorized user is produced interference with base station；Second time slot is time slot, and in the second time slot, it is received by each relaying The signal from base station and come autoepistemic mobile subscriber signal broadcast, by used during m-th repeat broadcast signal Power is designated asIn the second time slot, each relaying also produces interference to authorized user；Above-mentioned, 1≤m≤M；

Channel gain between setting base station and each relaying, the channel between cognitive mobile subscriber and each relaying increase The channel gain between channel gain, base station and authorized user between mobile subscriber beneficial, cognitive and authorized user, each relaying And the channel gain between authorized user is all known, the channel gain between base station and m-th are relayed, cognitive mobile use Channel gain between family and m-th relaying, the channel gain between cognitive mobile subscriber and authorized user, base station are used with mandate Channel gain between family, m-th relaying is corresponding with the channel gain between authorized user is designated as g₁、g₂、g₃、g₄、g₅,g₃=| h^S-PU|², g₄=| h^CB-PU|²,Wherein, 1≤m≤M, symbol " | | " is the symbol that takes absolute value,Represent the channel coefficients between base station and m-th relaying,Represent that cognition is mobile Channel coefficients between user and m-th relaying, h^S-PURepresent the channel coefficients between cognitive mobile subscriber and authorized user, h^CB-PURepresent the channel coefficients between base station and authorized user,Represent the channel between m-th relaying and authorized user Coefficient；Set cognitive mobile subscriber and authorized user is concurrently accessed frequency spectrum and carries out signal transmission；Set bi-directional relaying cognition wireless All noises in electricity system are all σ_n ²Additive white Gaussian noise；

2. will be designated as by the speed of the bi-directional relaying cognitive radio system under DF agreement during m-th relay transmission signalSpeed, m-th that the speed that relays to m-th according to cognitive mobile subscriber, base station to m-th relay are relayed to base station Speed, m-th is relayed to the speed of cognitive mobile subscriber and m-th relaying can process the maximum limiting speed of signal, willIt is described as:And according to aromatic law, willIt is described as:Then in conjunction withWithObtain And then obtain

Wherein, 1≤m≤M, min () for taking minimum value function, R₁Represent that cognitive mobile subscriber is to m in the first slot The speed of individual relaying,R₂Represent the speed that base station relays in the first slot to m-th,R₃Represent that m-th is relayed to the speed of base station in the second time slot,R₄Represent that m-th is relayed to the speed of cognitive mobile subscriber in the second time slot,R₅Represent that m-th relaying can process the maximum limiting speed of signal in the second time slot,SNR_mRepresent and recognized by the bi-directional relaying under DF agreement during m-th relay transmission signal Know the signal to noise ratio of radio system；

3. build the optimized allocation of resources problem in the bi-directional relaying cognitive radio system under DF agreement, be described as:

$\underset{P_S,P_{CB},P_{{\mathrm{RS}}_m},{\mathrm{\ϵ}}_m}{\max }{R}_{DF}=\frac{1}{2}{\log }_2(1+\underset{m=1}{\overset{M}{\Σ}}{\mathrm{\ϵ}}_m\×{\mathrm{SNR}}_m)$

$\begin{array}{cc}s.t.& 0\≤P_S\≤\stackrel{\‾}{P_S}\end{array}$

$0\≤P_{CB}\≤\stackrel{\‾}{P_{CB}}$

$0\≤P_{{\mathrm{RS}}_m}\≤\stackrel{\‾}{P_{{\mathrm{RS}}_m}},\∀m=1,2,\mathrm{...},M$

P_S×g₃+P_CB×g₄≤I_th

$\underset{m=1}{\overset{M}{\Σ}}{\mathrm{\ϵ}}_m\×P_{{\mathrm{RS}}_m}\×g_5\≤I_{th}$

${\mathrm{\ϵ}}_m\∈\{0,1\},\∀m=1,2,\mathrm{...},M$

Wherein, max represents " making maximization ", ε_mFor the selective factor B of m-th relaying, work as ε_m=1 interval scale m-th relaying Selected, work as ε_m=0 interval scale m-th relaying is the most selected, R_DFRepresent select L relaying carry out signal transmit time DF agreement under The power system capacity of bi-directional relaying cognitive radio system, s.t. represent " constrained in ... ",Represent cognitive mobile subscriber Restriction power,Represent the restriction power of base station,Represent the restriction power of m-th relaying, I_thRepresent authorized user institute Receptible maximum interference value, the 1st constraints is P_SRestrictive condition, the 2nd constraints is P_CBRestrictive condition, 3 constraintss areRestrictive condition, the 4th constraints represents that cognitive mobile subscriber is in m-th in the first slot Continue the interference and base station pair when m-th relay transmission signal, base station that when transmitting signal, authorized user is produced by cognition mobile subscriber The interference sum that authorized user produces is less than the receptible maximum interference value of authorized user, and the 5th constraints represents In second time slot, during M repeat broadcast signal, its interference producing authorized user is less than the receptible maximum of authorized user Interference value, the 6th constraints represents ε_mValue limit；

4. solution procedure 3. in optimized allocation of resources problem, in solution procedure use the maximized spy of DF protocol capacity Point, solves the power relation obtained between cognitive mobile subscriber, base station and each relaying；Then time with each repeat broadcast signal Power used represents that cognitive mobile subscriber power used when this relay transmission signal and base station pass to this relaying Power used during defeated signal, it is thus achieved that by the bi-directional relaying cognitive radio system under DF agreement during each relay transmission signal The value of signal to noise ratio；Then pass through the value to all signal to noise ratios and carry out permutation and combination, find a kind of signal to noise ratio combination, this signal to noise ratio The value of all signal to noise ratios in combination and value meet step 3. in optimized allocation of resources problem in the 5th constraints Lower maximum；Further according to find signal to noise ratio combination in all signal to noise ratios value and value, it is thus achieved that the bi-directional relaying under DF agreement The maximum system capacity of cognitive radio system and maximum system capacity corresponding L relaying and L the respective broadcast singal of relaying The power of Shi Suoyong.

Described step detailed process 4. is:

4. _ 1, according to the maximized feature of DF protocol capacity, R is worked as₁=R₃And R₂=R₄Time, R_DFValue is maximum；Then basisAnd R₁=R₃, obtainAnd according toAnd R₂=R₄, obtainThen according toWithWillIt is converted into And obtainWith

4. _ 2, basisWithWill

$\underset{P_S,P_{CB},P_{{\mathrm{RS}}_m},{\mathrm{\ϵ}}_m}{\max }{R}_{DF}=\frac{1}{2}{\log }_2(1+\underset{m=1}{\overset{M}{\Σ}}{\mathrm{\ϵ}}_m\×{\mathrm{SNR}}_m)$

$\begin{array}{cc}s.t.& 0\≤P_S\≤\stackrel{\‾}{P_S}\end{array}$

$0\≤P_{CB}\≤\stackrel{\‾}{P_{CB}}$

It is converted into

P_S×g₃+P_CB×g₄≤I_th

$\underset{m=1}{\overset{M}{\Σ}}{\mathrm{\ϵ}}_m\×P_{{\mathrm{RS}}_m}\×g_5\≤I_{th}$

${\mathrm{\ϵ}}_m\∈\{0,1\},\∀m=1,2,\mathrm{...},M$

$\underset{P_S,P_{CB},P_{{\mathrm{RS}}_m},{\mathrm{\ϵ}}_m}{\max }{R}_{DF}=\frac{1}{2}{\log }_2(1+\underset{m=1}{\overset{M}{\Σ}}{\mathrm{\ϵ}}_m\×{\mathrm{SNR}}_m)$

$\begin{array}{cc}s.t.& 0\≤\frac{P_{{\mathrm{RS}}_m}\×g_1}{g_2}\≤\stackrel{\‾}{P_S}\end{array}$

$0\≤\frac{P_{{\mathrm{RS}}_m}\×g_2}{g_1}\≤\stackrel{\‾}{P_{CB}}$

Then in conjunction with

$\frac{P_{{\mathrm{RS}}_m}\×g_1}{g_2}\×g_3+\frac{P_{{\mathrm{RS}}_m}\×g_2}{g_1}\×g_4\≤I_{th}$

$\underset{m=1}{\overset{M}{\Σ}}{\mathrm{\ϵ}}_m\×P_{{\mathrm{RS}}_m}\×g_5\≤I_{th}$

${\mathrm{\ϵ}}_m\∈\{0,1\},\∀m=1,2,\mathrm{...},M$

$\underset{P_S,P_{CB},P_{{\mathrm{RS}}_m},{\mathrm{\ϵ}}_m}{\max }{R}_{DF}=\frac{1}{2}{\log }_2(1+\underset{m=1}{\overset{M}{\Σ}}{\mathrm{\ϵ}}_m\×{\mathrm{SNR}}_m)$

$\begin{array}{cc}s.t.& 0\≤\frac{P_{{\mathrm{RS}}_m}\×g_1}{g_2}\≤\stackrel{\‾}{P_S}\end{array}$

$0\≤\frac{P_{{\mathrm{RS}}_m}\×g_2}{g_1}\≤\stackrel{\‾}{P_{CB}}$

In front 4 constraintss, obtain

$\frac{P_{{\mathrm{RS}}_m}\×g_1}{g_2}\×g_3+\frac{P_{{\mathrm{RS}}_m}\×g_2}{g_1}\×g_4\≤I_{th}$

$\underset{m=1}{\overset{M}{\Σ}}{\mathrm{\ϵ}}_m\×P_{{\mathrm{RS}}_m}\×g_5\≤I_{th}$

${\mathrm{\ϵ}}_m\∈\{0,1\},\∀m=1,2,\mathrm{...},M$

Then according to

Will

$\underset{P_S,P_{CB},P_{{\mathrm{RS}}_m},{\mathrm{\ϵ}}_m}{\max }{R}_{DF}=\frac{1}{2}{\log }_2(1+\underset{m=1}{\overset{M}{\Σ}}{\mathrm{\ϵ}}_m\×{\mathrm{SNR}}_m)$

$\begin{array}{cc}s.t.& 0\≤\frac{P_{{\mathrm{RS}}_m}\×g_1}{g_2}\≤\stackrel{\‾}{P_S}\end{array}$

$0\≤\frac{P_{{\mathrm{RS}}_m}\×g_2}{g_1}\≤\stackrel{\‾}{P_{CB}}$

It is converted into

$\frac{P_{{\mathrm{RS}}_m}\×g_1}{g_2}\×g_3+\frac{P_{{\mathrm{RS}}_m}\×g_2}{g_1}\×g_4\≤I_{th}$

$\underset{m=1}{\overset{M}{\Σ}}{\mathrm{\ϵ}}_m\×P_{{\mathrm{RS}}_m}\×g_5\≤I_{th}$

${\mathrm{\ϵ}}_m\∈\{0,1\},\∀m=1,2,\mathrm{...},M$

$\underset{P_{{\mathrm{RS}}_m},{\mathrm{\ϵ}}_m}{\max }{R}_{DF}=\frac{1}{2}{\log }_2(1+\underset{m=1}{\overset{M}{\Σ}}{\mathrm{\ϵ}}_m\×{\mathrm{SNR}}_m)$

$\begin{array}{cc}s.t.& P_{{\mathrm{RS}}_m}=\min (\frac{\stackrel{\‾}{P_S}\×g_2}{g_1},\frac{\stackrel{\‾}{P_{CB}}\×g_1}{g_2},\frac{I_{th}}{\frac{g_1\×g_2}{g_2}+\frac{g_2\×g_4}{g_1}},\stackrel{\‾}{P_{{\mathrm{RS}}_m}});\end{array}$

$\underset{m=1}{\overset{M}{\Σ}}{\mathrm{\ϵ}}_m\×P_{{\mathrm{RS}}_m}\×g_5\≤I_{th}$

${\mathrm{\ϵ}}_m\∈\{0,1\},\∀m=1,2,\mathrm{...},M$

4. _ 3, R is worked as₁=R₃And R₂=R₄Time, willIt is converted into Then basisAndWithSolveObtain SNR_mValue；

The value that 4. _ 4, step 4. _ 3 solves M the signal to noise ratio obtained carries out permutation and combination, when selecting 1 relaying, in ContinuePlanting and select, signal to noise ratio hasPlant combination；When selecting 2 relayings, relaying hasPlanting and select, signal to noise ratio hasKind Combination；The like, when selecting M relaying, relaying hasPlanting and select, signal to noise ratio hasPlant combination；Then every kind is calculated Signal to noise ratio combination in all signal to noise ratios value and value；Then fromIndividual and value is found out satisfiedMaximum, be designated as SNR_max；In conjunction with SNR_maxWith $\underset{P_{{\mathrm{RS}}_m},{\mathrm{\ϵ}}_m}{\max }{R}_{DF}=\frac{1}{2}{\log }_2(1+\underset{m=1}{\overset{M}{\Σ}}{\mathrm{\ϵ}}_m\×{\mathrm{SNR}}_m)$

Obtain

$\underset{m=1}{\overset{M}{\Σ}}{\mathrm{\ϵ}}_m\×P_{{\mathrm{RS}}_m}\×g_5\≤I_{th}$

${\mathrm{\ϵ}}_m\∈\{0,1\},\∀m=1,2,\mathrm{...},M$

And then obtain R_DFValue, this value is the bi-directional relaying cognition wireless under DF agreement The maximum system capacity of electricity system, and obtain L relaying corresponding to maximum system capacity and L relaying respective broadcast singal time institute Power.

Compared with prior art, it is an advantage of the current invention that:

1) the inventive method selects several relayings to carry out signal transmission, and selecting multiple relaying to carry out signal transmission can make Power system capacity promotes further.

2) the inventive method is special by utilizing DF protocol capacity to maximize during solving-optimizing resource allocation problem Point, obtains the power relation between cognitive mobile subscriber, base station and each relaying；Then this relation and cognitive mobile subscriber are utilized The power limitation condition that power limitation condition used when relay transmission signal, base station are used when relay transmission signal, To the value by the signal to noise ratio of the bi-directional relaying cognitive radio system under DF agreement during each relay transmission signal, then pass through The value of all signal to noise ratios is carried out permutation and combination, finds a kind of signal to noise ratio combination, all signal to noise ratios in the combination of this signal to noise ratio Value and value maximum under satisfied interference restrictive condition, further according to the sum of the value of all signal to noise ratios in the signal to noise ratio combination found Value, it is thus achieved that the maximum system capacity of the bi-directional relaying cognitive radio system under DF agreement and relaying corresponding to maximum system capacity The power used with during repeat broadcast signal；The process of the inventive method solving-optimizing resource allocation problem is short and sweet, not only Improve power system capacity, and represent that cognitive mobile subscriber relays to this with power used during each repeat broadcast signal During transmission signal, power used and base station power used when this relay transmission signal, the most only solves each repeat broadcast Power used during signal, simplifies power solution procedure, thus reduces the complexity solved.

Accompanying drawing explanation

Fig. 1 is the composition schematic diagram of bi-directional relaying cognitive radio system；

Fig. 2 be the inventive method totally realize block diagram；

Fig. 3 a is for being σ at additive white Gaussian noise_n ²=10^-4W, relaying number M=4, the receptible maximum of authorized user Interference value I_thValue when being 10dBm, cognitive mobile subscriber limit power, base station limit power and the restriction of each relaying The value of power is from-10dBm～30dBm, the inventive method and the many relay selection method of existing two-way, two-way list relay selection The power system capacity of method and the many relay selection method of single channel is with the comparison diagram of the change curve limiting power；

Fig. 3 b is for being σ at additive white Gaussian noise_n ²=10^-4W, relaying number M=4, the receptible maximum of authorized user Interference value I_thValue when being 20dBm, cognitive mobile subscriber limit power, base station limit power and the restriction of each relaying The value of power is from-10dBm～30dBm, the inventive method and the many relay selection method of existing two-way, two-way list relay selection The power system capacity of method and the many relay selection method of single channel is with the comparison diagram of the change curve limiting power；

Fig. 4 a is for being σ at additive white Gaussian noise_n ²=10^-4W, relaying number M=4, the restriction merit of cognitive mobile subscriber Rate, base station value 20dBm limiting power limiting power and each relaying time, the receptible maximum interference of authorized user Value I_thValue from-10dBm～40dBm, the inventive method and the many relay selection method of existing two-way, two-way list relay selection The comparison diagram of the change curve that the power system capacity of method and the many relay selection method of single channel limits with interference；

Fig. 4 b is for being σ at additive white Gaussian noise_n ²=10^-4W, relaying number M=4, the restriction merit of cognitive mobile subscriber Rate, base station value 25dBm limiting power limiting power and each relaying time, the receptible maximum interference of authorized user Value I_thValue from-10dBm～40dBm, the inventive method and the many relay selection method of existing two-way, two-way list relay selection The comparison diagram of the change curve that the power system capacity of method and the many relay selection method of single channel limits with interference.

Detailed description of the invention

Below in conjunction with accompanying drawing embodiment, the present invention is described in further detail.

Resource allocation methods in a kind of based on DF agreement the bi-directional relaying cognitive radio system that the present invention proposes, its Totally realize block diagram as in figure 2 it is shown, it comprises the following steps:

1. each channel set in bi-directional relaying cognitive radio system uses many Rayleigh fadings model；Set two-way in The cognitive radio system that continues is made up of, by cognition a cognitive mobile subscriber, a base station, M relaying and an authorized user Mobile subscriber, base station, m-th relaying and authorized user's correspondence are designated as S, CB, RS_mAnd PU, as it is shown in figure 1, wherein, M > 1, at this Embodiment takes M=4,1≤m≤M；Set and there is no direct link between cognitive mobile subscriber and base station, need to select L is gone on Row signal transmits, wherein, and 1≤L≤M.

Setting each relay selection half-duplex operation, each relaying carries out the process of signal transmission when being divided into two Gap: the first time slot is multiple access time slot, in the first slot, base station is to all relay transmission signals, by the transmitting merit of base station Rate is designated as P_CB, the transmitting power of cognitive mobile subscriber, to all relay transmission signals, is designated as P by the most cognitive mobile subscriber_S, base Stand and time cognitive mobile subscriber transmits signal to same relay transmission signal；In the first slot, cognitive mobile subscriber All authorized user is produced interference with base station；Second time slot is time slot, and in the second time slot, it is received by each relaying The signal from base station and come autoepistemic mobile subscriber signal broadcast, by used during m-th repeat broadcast signal Power is designated asIn the second time slot, each relaying also produces interference to authorized user；Above-mentioned, 1≤m≤M.

Channel gain between setting base station and each relaying, the channel between cognitive mobile subscriber and each relaying increase The channel gain between channel gain, base station and authorized user between mobile subscriber beneficial, cognitive and authorized user, each relaying And the channel gain between authorized user is all known, the channel gain between base station and m-th are relayed, cognitive mobile use Channel gain between family and m-th relaying, the channel gain between cognitive mobile subscriber and authorized user, base station are used with mandate Channel gain between family, m-th relaying is corresponding with the channel gain between authorized user is designated as g₁、g₂、g₃、g₄、g₅,g₃=| h^S-PU|², g₄=| h^CB-PU|²,Wherein, 1≤m≤M, symbol " | | " is the symbol that takes absolute value, as it is shown in figure 1,Represent the channel coefficients between base station and m-th relaying,Represent Channel coefficients between cognitive mobile subscriber and m-th relaying, h^S-PURepresent the letter between cognitive mobile subscriber and authorized user Road coefficient, h^CB-PURepresent the channel coefficients between base station and authorized user,Represent between m-th relaying and authorized user Channel coefficients, in bi-directional relaying cognitive radio system, channel information between base station and m-th relaying, cognitive mobile Channel information between user and m-th relaying, channel information, base station and mandate between cognitive mobile subscriber and authorized user The channel information between channel information and m-th relaying and authorized user between user is known；Set cognitive mobile subscriber with Authorized user is concurrently accessed frequency spectrum and carries out signal transmission；Without loss of generality, the institute in bi-directional relaying cognitive radio system is set Having noise is all σ_n ²Additive white Gaussian noise, take σ in the present embodiment_n ²=10^-4W。

2. will be designated as by the speed of the bi-directional relaying cognitive radio system under DF agreement during m-th relay transmission signalSpeed, m-th that the speed that relays to m-th according to cognitive mobile subscriber, base station to m-th relay are relayed to base station Speed, m-th is relayed to the speed of cognitive mobile subscriber and m-th relaying can process the maximum limiting speed of signal, willIt is described as:And according to aromatic law, willIt is described as:Then in conjunction withWith ObtainAnd then obtain

Wherein, 1≤m≤M, min () for taking minimum value function, R₁Represent that cognitive mobile subscriber is to m in the first slot The speed of individual relaying,R₂Represent the speed that base station relays in the first slot to m-th,R₃Represent that m-th is relayed to the speed of base station in the second time slot,R₄Represent that m-th is relayed to the speed of cognitive mobile subscriber in the second time slot,R₅Represent that m-th relaying can process the maximum limiting speed of signal in the second time slot,SNR_mRepresent and recognized by the bi-directional relaying under DF agreement during m-th relay transmission signal Know the signal to noise ratio of radio system.

3. build the optimized allocation of resources problem in the bi-directional relaying cognitive radio system under DF agreement, be described as:

$\underset{P_S,P_{CB},P_{{\mathrm{RS}}_m},{\mathrm{\ϵ}}_m}{\max }{R}_{DF}=\frac{1}{2}{\log }_2(1+\underset{m=1}{\overset{M}{\Σ}}{\mathrm{\ϵ}}_m\×{\mathrm{SNR}}_m)$

$\begin{array}{cc}s.t.& 0\≤P_S\≤\stackrel{\‾}{P_S}\end{array}$

$0\≤P_{CB}\≤\stackrel{\‾}{P_{CB}}$

$0\≤P_{{\mathrm{RS}}_m}\≤\stackrel{\‾}{P_{{\mathrm{RS}}_m}},\∀m=1,2,\mathrm{...},M$

P_S×g₃+P_CB×g₄≤I_th

$\underset{m=1}{\overset{M}{\Σ}}{\mathrm{\ϵ}}_m\×P_{{\mathrm{RS}}_m}\×g_5\≤I_{th}$

${\mathrm{\ϵ}}_m\∈\{0,1\},\∀m=1,2,\mathrm{...},M$

Wherein, max represents " making maximization ", ε_mFor the selective factor B of m-th relaying, work as ε_m=1 interval scale m-th relaying Selected, work as ε_m=0 interval scale m-th relaying is the most selected, R_DFRepresent select L relaying carry out signal transmit time DF agreement under The power system capacity of bi-directional relaying cognitive radio system, s.t. represent " constrained in ... ",Represent cognitive mobile subscriber Restriction power,Represent the restriction power of base station,Represent the restriction power of m-th relaying,With's Value is all it is known that I_thRepresent the authorized user institute's receptible maximum interference value restriction of the authorized user (disturb), I_thValue it is known that 1st constraints is P_SRestrictive condition, the 2nd constraints is P_CBRestrictive condition, the 3rd constraints is's Restrictive condition, the 4th constraints represents that cognitive mobile subscriber cognition when m-th relay transmission signal moves in the first slot Employ interference and the base station interference that authorized user is produced by base station when m-th relay transmission signal that authorized user is produced by family Sum is less than the receptible maximum interference value of authorized user, and the 5th constraints represents that M relaying is wide in the second time slot When broadcasting signal, its interference producing authorized user is less than the receptible maximum interference value of authorized user, the 6th constraint article Part represents ε_mValue limit.

4. solution procedure 3. in optimized allocation of resources problem, in solution procedure use the maximized spy of DF protocol capacity Point, solves the power relation obtained between cognitive mobile subscriber, base station and each relaying；Then time with each repeat broadcast signal Power used represents that cognitive mobile subscriber power used when this relay transmission signal and base station pass to this relaying Power used during defeated signal, it is thus achieved that by the bi-directional relaying cognitive radio system under DF agreement during each relay transmission signal The value of signal to noise ratio；Then pass through the value to all signal to noise ratios and carry out permutation and combination, find a kind of signal to noise ratio combination, this signal to noise ratio The value of all signal to noise ratios in combination and value meet step 3. in optimized allocation of resources problem in the 5th constraints Lower maximum；Further according to find signal to noise ratio combination in all signal to noise ratios value and value, it is thus achieved that the bi-directional relaying under DF agreement The maximum system capacity of cognitive radio system and maximum system capacity corresponding L relaying and L the respective broadcast singal of relaying The power of Shi Suoyong.

In this particular embodiment, step detailed process 4. is:

4. _ 1, according to the maximized feature of DF protocol capacity, R is worked as₁=R₃And R₂=R₄Time, R_DFValue is maximum；Then basisAnd R₁=R₃, obtainAnd according toAnd R₂=R₄, obtainThen according toWithWillIt is converted intoAnd obtainWith

4. _ 2, basisWithWill

$\underset{P_S,P_{CB},P_{{\mathrm{RS}}_m},{\mathrm{\ϵ}}_m}{\max }{R}_{DF}=\frac{1}{2}{\log }_2(1+\underset{m=1}{\overset{M}{\Σ}}{\mathrm{\ϵ}}_m\×{\mathrm{SNR}}_m)$

$\begin{array}{cc}s.t.& 0\≤P_S\≤\stackrel{\‾}{P_S}\end{array}$

$0\≤P_{CB}\≤\stackrel{\‾}{P_{CB}}$

It is converted into

P_S×g₃+P_CB×g₄≤I_th

$\underset{m=1}{\overset{M}{\Σ}}{\mathrm{\ϵ}}_m\×P_{{\mathrm{RS}}_m}\×g_5\≤I_{th}$

${\mathrm{\ϵ}}_m\∈\{0,1\},\∀m=1,2,\mathrm{...},M$

$\underset{P_S,P_{CB},P_{{\mathrm{RS}}_m},{\mathrm{\ϵ}}_m}{\max }{R}_{DF}=\frac{1}{2}{\log }_2(1+\underset{m=1}{\overset{M}{\Σ}}{\mathrm{\ϵ}}_m\×{\mathrm{SNR}}_m)$

$\begin{array}{cc}s.t.& 0\≤\frac{P_{{\mathrm{RS}}_m}\×g_1}{g_2}\≤\stackrel{\‾}{P_S}\end{array}$

$0\≤\frac{P_{{\mathrm{RS}}_m}\×g_2}{g_1}\≤\stackrel{\‾}{P_{CB}}$

Then in conjunction with

$\frac{P_{{\mathrm{RS}}_m}\×g_1}{g_2}\×g_3+\frac{P_{{\mathrm{RS}}_m}\×g_2}{g_1}\×g_4\≤I_{th}$

$\underset{m=1}{\overset{M}{\Σ}}{\mathrm{\ϵ}}_m\×P_{{\mathrm{RS}}_m}\×g_5\≤I_{th}$

${\mathrm{\ϵ}}_m\∈\{0,1\},\∀m=1,2,\mathrm{...},M$

$\underset{P_S,P_{CB},P_{{\mathrm{RS}}_m},{\mathrm{\ϵ}}_m}{\max }{R}_{DF}=\frac{1}{2}{\log }_2(1+\underset{m=1}{\overset{M}{\Σ}}{\mathrm{\ϵ}}_m\×{\mathrm{SNR}}_m)$

$\begin{array}{cc}s.t.& 0\≤\frac{P_{{\mathrm{RS}}_m}\×g_1}{g_2}\≤\stackrel{\‾}{P_S}\end{array}$

$0\≤\frac{P_{{\mathrm{RS}}_m}\×g_2}{g_1}\≤\stackrel{\‾}{P_{CB}}$

In front 4 constraintss, obtain

$\frac{P_{{\mathrm{RS}}_m}\×g_1}{g_2}\×g_3+\frac{P_{{\mathrm{RS}}_m}\×g_2}{g_1}\×g_4\≤I_{th}$

$\underset{m=1}{\overset{M}{\Σ}}{\mathrm{\ϵ}}_m\×P_{{\mathrm{RS}}_m}\×g_5\≤I_{th}$

${\mathrm{\ϵ}}_m\∈\{0,1\},\∀m=1,2,\mathrm{...},M$

Then according to

Will

$\underset{P_S,P_{CB},P_{{\mathrm{RS}}_m},{\mathrm{\ϵ}}_m}{\max }{R}_{DF}=\frac{1}{2}{\log }_2(1+\underset{m=1}{\overset{M}{\Σ}}{\mathrm{\ϵ}}_m\×{\mathrm{SNR}}_m)$

$\begin{array}{cc}s.t.& 0\≤\frac{P_{{\mathrm{RS}}_m}\×g_1}{g_2}\≤\stackrel{\‾}{P_S}\end{array}$

$0\≤\frac{P_{{\mathrm{RS}}_m}\×g_2}{g_1}\≤\stackrel{\‾}{P_{CB}}$

It is converted into

$\frac{P_{{\mathrm{RS}}_m}\×g_1}{g_2}\×g_3+\frac{P_{{\mathrm{RS}}_m}\×g_2}{g_1}\×g_4\≤I_{th}$

$\underset{m=1}{\overset{M}{\Σ}}{\mathrm{\ϵ}}_m\×P_{{\mathrm{RS}}_m}\×g_5\≤I_{th}$

${\mathrm{\ϵ}}_m\∈\{0,1\},\∀m=1,2,\mathrm{...},M$

$\underset{P_{{\mathrm{RS}}_m},{\mathrm{\ϵ}}_m}{\max }{R}_{DF}=\frac{1}{2}{\log }_2(1+\underset{m=1}{\overset{M}{\Σ}}{\mathrm{\ϵ}}_m\×{\mathrm{SNR}}_m)$

$\begin{array}{cc}s.t.& P_{{\mathrm{RS}}_m}=\min (\frac{\stackrel{\‾}{P_S}\×g_2}{g_1},\frac{\stackrel{\‾}{P_{CB}}\×g_1}{g_2},\frac{I_{th}}{\frac{g_1\×g_2}{g_2}+\frac{g_2\×g_4}{g_1}},\stackrel{\‾}{P_{{\mathrm{RS}}_m}})\end{array}.$

$\underset{m=1}{\overset{M}{\Σ}}{\mathrm{\ϵ}}_m\×P_{{\mathrm{RS}}_m}\×g_5\≤I_{th}$

${\mathrm{\ϵ}}_m\∈\{0,1\},\∀m=1,2,\mathrm{...},M$

4. _ 3, R is worked as₁=R₃And R₂=R₄Time, willIt is converted intoThen basisAndWithSolveObtain SNR_mValue.

The value that 4. _ 4, step 4. _ 3 solves M the signal to noise ratio obtained carries out permutation and combination, when selecting 1 relaying, in ContinuePlanting and select, signal to noise ratio hasPlant combination；When selecting 2 relayings, relaying hasPlanting and select, signal to noise ratio hasKind Combination；The like, when selecting M relaying, relaying hasPlanting and select, signal to noise ratio hasPlanting combination, table 1 gives works as M All of signal to noise ratio combination when=4, totally 15 kinds of signal to noise ratio combinations；Then all signal to noise ratios in the combination of every kind of signal to noise ratio are calculated Value and value；Then fromIndividual and value is found out satisfiedMaximum, be designated as SNR_max；In conjunction with SNR_maxWith

Obtain

$\underset{m=1}{\overset{M}{\Σ}}{\mathrm{\ϵ}}_m\×P_{{\mathrm{RS}}_m}\×g_5\≤I_{th}$

${\mathrm{\ϵ}}_m\∈\{0,1\},\∀m=1,2,\mathrm{...},M$

And then obtain R_DFValue, this value is the bi-directional relaying cognition wireless under DF agreement The maximum system capacity of electricity system, and obtain L relaying corresponding to maximum system capacity and L relaying respective broadcast singal time institute Power.

Table 1 is the combination of all of signal to noise ratio as M=4

In order to further illustrate feasibility and the effectiveness of the inventive method, carry out following emulation.

All channels in bi-directional relaying cognitive radio system assume that as the independent and many Rayleigh fadings of obedience, additivity height This white noise is σ_n ²=10^-4W, relays number M=4.

It is σ that Fig. 3 a gives at additive white Gaussian noise_n ²=10^-4W, relaying number M=4, authorized user institute receptible Maximum interference value I_thValue when being 10dBm, cognitive mobile subscriber limit power, base station limit power and each relaying Limit the value of power from-10dBm～30dBm, the inventive method and the many relay selection method of existing two-way, two-way list relaying The power system capacity of system of selection and the many relay selection method of single channel is with the comparison diagram of the change curve limiting power；Fig. 3 b gives It is σ at additive white Gaussian noise_n ²=10^-4W, relaying number M=4, receptible maximum interference value I of authorized user_thValue During for 20dBm, cognitive mobile subscriber limit power, base station the value limiting power limiting power and each relaying from- 10dBm～30dBm, the inventive method relay selection method many with existing two-way, two-way list relay selection method and single channel are many The power system capacity of relay selection method is with the comparison diagram of the change curve limiting power.

Analysis chart 3a and Fig. 3 b understands, when receptible maximum interference value I of authorized user_thValue be 10dBm, cognitive When the value of the restriction power limiting power and each relaying limiting power, base station of mobile subscriber is less than 5dBm, four kinds of sides The power system capacity of method is continuously increased with the increase limiting power, and when restriction power, the restriction of base station of cognitive mobile subscriber When the value limiting power of power and each relaying is more than 5dBm, the inventive method and the system of the many relay selection method of single channel Capacity is held essentially constant, and the power system capacity of two-way many relay selection method and two-way single relay selection method is with limiting power Increase and constantly reduce；When receptible maximum interference value I of authorized user_thValue be 20dBm, cognitive mobile subscriber's When the value of the restriction power limiting power and each relaying limiting power, base station is less than 15dBm, the system of four kinds of methods is held Measure and be continuously increased with limiting the increase of power, and limit power, the restriction power of base station and each as cognitive mobile subscriber When the value limiting power of relaying is more than 15dBm, the power system capacity of the inventive method relay selection method many with single channel is basic Keep constant, and the power system capacity of the many relay selection method of two-way and two-way list relay selection method with limit power increase and Constantly reduce；Being contrasted from simulation result, the inventive method makes power system capacity higher.

It is σ that Fig. 4 a gives at additive white Gaussian noise_n ²=10^-4W, relaying number M=4, the restriction of cognitive mobile subscriber Power, base station value 20dBm limiting power limiting power and each relaying time, the receptible maximum dry of authorized user Disturb value I_thValue from-10dBm～40dBm, the inventive method and the many relay selection method of existing two-way, the relaying choosing of two-way list The comparison diagram of the change curve that the power system capacity of selection method and the many relay selection method of single channel limits with interference；Fig. 4 b gives Additive white Gaussian noise is σ_n ²=10^-4W, relaying number M=4, restriction power, the restriction power of base station of cognitive mobile subscriber And the value limiting power of each relaying is when being 25dBm, receptible maximum interference value I of authorized user_thValue from- 10dBm～40dBm, the inventive method relay selection method many with existing two-way, two-way list relay selection method and single channel are many The comparison diagram of the change curve that the power system capacity of relay selection method limits with interference.

Analysis chart 4a and Fig. 4 b understands, when restriction power, the restriction power of base station and each relaying of cognitive mobile subscriber Limit power value be 20dBm, receptible maximum interference value I of authorized user_thValue less than 15dBm time, four kinds The power system capacity of method is with receptible maximum interference value I of authorized user_thThe increase of value and be continuously increased, and when authorizing Receptible maximum interference value I of user_thValue more than 15dBm time, the inventive method and the many relay selection method of single channel Power system capacity is held essentially constant, and the power system capacity of the many relay selection method of two-way and two-way list relay selection method is with authorizing use Receptible maximum interference value I in family_thThe increase of value and constantly reduce；When cognitive the restriction power of mobile subscriber, base station The value limiting power limiting power and each relaying be 25dBm, receptible maximum interference value I of authorized user_th's When value is less than 25dBm, the power system capacity of four kinds of methods is with receptible maximum interference value I of authorized user_thThe increasing of value Add and be continuously increased, and when receptible maximum interference value I of authorized user_thValue more than 25dBm time, the inventive method with The power system capacity of the many relay selection method of single channel is held essentially constant, the many relay selection method of two-way and two-way list relay selection side The power system capacity of method is with receptible maximum interference value I of authorized user_thThe increase of value and constantly reduce；By simulation result Contrast understands, and the inventive method makes power system capacity higher.

Claims (2)

1. the resource allocation methods in a bi-directional relaying cognitive radio system based on DF agreement, it is characterised in that include with Lower step:

1. each channel set in bi-directional relaying cognitive radio system uses many Rayleigh fadings model；Setting bi-directional relaying is recognized Know that radio system is made up of a cognitive mobile subscriber, a base station, M relaying and an authorized user, wherein, M > 1；If There is no direct link between fixed cognitive mobile subscriber and base station, L relaying need to be selected to carry out signal transmission, wherein, 1≤L≤M；

Setting each relay selection half-duplex operation, each relaying carries out the process of signal transmission and is divided into two time slots: the One time slot is multiple access time slot, and in the first slot, the transmitting power of base station, to all relay transmission signals, is designated as by base station P_CB, the transmitting power of cognitive mobile subscriber, to all relay transmission signals, is designated as P by the most cognitive mobile subscriber_S, base station and recognizing Know mobile subscriber when transmitting signal to same relay transmission signal；In the first slot, cognitive mobile subscriber and base station All authorized user is produced interference；Second time slot is time slot, in the second time slot, each relaying to its receive from The signal of the signal of base station and next autoepistemic mobile subscriber is broadcasted, by power note used during m-th repeat broadcast signal ForIn the second time slot, each relaying also produces interference to authorized user；Above-mentioned, 1≤m≤M；

Set the channel gain between base station and each relaying, channel gain between cognitive mobile subscriber and each relaying, recognize Know the channel gain between the channel gain between mobile subscriber and authorized user, base station and authorized user, each relaying and award Channel gain between power user is all known, the channel gain between base station and m-th are relayed, cognitive mobile subscriber with Channel gain between m-th relaying, the channel gain between cognitive mobile subscriber and authorized user, base station and authorized user it Between channel gain, m-th relaying corresponding with the channel gain between authorized user be designated as g₁、g₂、g₃、g₄、g₅,g₃=| h^S-PU|², g₄=| h^CB-PU|²,Wherein, 1≤m≤M, symbol " | | " is the symbol that takes absolute value,Represent the channel coefficients between base station and m-th relaying,Represent that cognition is mobile to use Channel coefficients between family and m-th relaying, h^S-PURepresent the channel coefficients between cognitive mobile subscriber and authorized user, h^CB-PU Represent the channel coefficients between base station and authorized user,Represent the channel coefficients between m-th relaying and authorized user； Set cognitive mobile subscriber and authorized user is concurrently accessed frequency spectrum and carries out signal transmission；Set bi-directional relaying cognitive radio system In all noises be all σ_n ²Additive white Gaussian noise；

2. will be designated as by the speed of the bi-directional relaying cognitive radio system under DF agreement during m-th relay transmission signal Speed that the speed that relays to m-th according to cognitive mobile subscriber, base station to m-th relay, m-th are relayed to the speed of base station Rate, m-th are relayed to the speed of cognitive mobile subscriber and m-th relaying can process the maximum limiting speed of signal, willRetouch State for:And according to aromatic law, willIt is described as: Then in conjunction withWithObtainAnd then obtain

Wherein, 1≤m≤M, min () for taking minimum value function, R₁Represent that cognitive mobile subscriber relays to m-th in the first slot Speed,R₂Represent the speed that base station relays in the first slot to m-th,R₃ Represent that m-th is relayed to the speed of base station in the second time slot,R₄Represent in the second time slot M-th is relayed to the speed of cognitive mobile subscriber,R₅Represent m-th relaying in the second time slot The maximum limiting speed of signal can be processed,SNR_mRepresent by m-th relay transmission The signal to noise ratio of the bi-directional relaying cognitive radio system under DF agreement during signal；

3. build the optimized allocation of resources problem in the bi-directional relaying cognitive radio system under DF agreement, be described as:

$\underset{P_S,P_{CB},P_{{\mathrm{RS}}_m},{\mathrm{\ϵ}}_m}{max}{R}_{DF}=\frac{1}{2}{\log }_2(1+\underset{m=1}{\overset{M}{\Σ}}{\mathrm{\ϵ}}_m\×{\mathrm{SNR}}_m)$

$\begin{array}{cc}s.t.& 0\≤P_S\≤\stackrel{\‾}{P_S}\end{array}$

$0\≤P_{CB}\≤\stackrel{\‾}{P_{CB}}$

$0\≤P_{{\mathrm{RS}}_m}\≤\stackrel{\‾}{P_{{\mathrm{RS}}_m}},\∀m=1,2,...,M$

P_S×g₃+P_CB×g₄≤I_th

$\underset{m=1}{\overset{M}{\Σ}}{\mathrm{\ϵ}}_m\×P_{{\mathrm{RS}}_m}\×g_5\≤I_{th}$

${\mathrm{\ϵ}}_m\∈\{0,1\},\∀m=1,2,...,M$

Wherein, max represents " making maximization ", ε_mFor the selective factor B of m-th relaying, work as ε_m=1 interval scale m-th relaying is selected In, work as ε_m=0 interval scale m-th relaying is the most selected, R_DFRepresent select L relaying carry out signal transmission time DF agreement under pair To relaying cognitive radio system power system capacity, s.t. represent " constrained in ... ",Represent the limit of cognitive mobile subscriber Power processed,Represent the restriction power of base station,Represent the restriction power of m-th relaying, I_thRepresent that authorized user can connect The maximum interference value being subject to, the 1st constraints is P_SRestrictive condition, the 2nd constraints is P_CBRestrictive condition, the 3rd Constraints isRestrictive condition, the 4th constraints represents that cognitive mobile subscriber relays to m-th in the first slot During transmission signal cognition mobile subscriber interference that authorized user is produced and base station when m-th relay transmission signal base station to awarding The interference sum that power user produces is less than the receptible maximum interference value of authorized user, and the 5th constraints represents the In two time slots, during M repeat broadcast signal, its interference producing authorized user is less than the receptible maximum dry of authorized user Disturbing value, the 6th constraints represents ε_mValue limit；

4. solution procedure 3. in optimized allocation of resources problem, in solution procedure use the maximized feature of DF protocol capacity, Solve the power relation obtained between cognitive mobile subscriber, base station and each relaying；Then with each repeat broadcast signal time institute Power represent that cognitive mobile subscriber power used when this relay transmission signal and base station are to this relay transmission Power used during signal, it is thus achieved that by the bi-directional relaying cognitive radio system under DF agreement during each relay transmission signal The value of signal to noise ratio；Then pass through the value to all signal to noise ratios and carry out permutation and combination, find a kind of signal to noise ratio combination, this signal to noise ratio group The value of all signal to noise ratios in conjunction and value meet step 3. in optimized allocation of resources problem in the 5th constraints under Maximum；Further according to find signal to noise ratio combination in all signal to noise ratios value and value, it is thus achieved that the bi-directional relaying under DF agreement is recognized When knowing the maximum system capacity of radio system and L relaying corresponding to maximum system capacity and L the respective broadcast singal of relaying Power used.

Resource allocation methods in bi-directional relaying cognitive radio system based on DF agreement the most according to claim 1, It is characterized in that described step detailed process 4. is:

4. _ 1, according to the maximized feature of DF protocol capacity, R is worked as₁=R₃And R₂=R₄Time, R_DFValue is maximum；Then basisAnd R₁=R₃, obtainAnd according toAnd R₂=R₄, obtainThen according toWithWillIt is converted intoAnd ObtainWith

4. _ 2, basisWithWill

It is converted into

Then in conjunction with

In front 4 constraintss, obtain

Then according to

Will

It is converted into

4. _ 3, R is worked as₁=R₃And R₂=R₄Time, willIt is converted into Then basisAnd WithSolveObtain SNR_mValue；

The value that 4. _ 4, step 4. _ 3 solves M the signal to noise ratio obtained carries out permutation and combination, and when selecting 1 relaying, relaying hasPlanting and select, signal to noise ratio hasPlant combination；When selecting 2 relayings, relaying hasPlanting and select, signal to noise ratio hasPlant combination； The like, when selecting M relaying, relaying hasPlanting and select, signal to noise ratio hasPlant combination；Then every kind of signal to noise ratio is calculated The value of all signal to noise ratios in combination and value；Then fromIndividual and value is found out satisfied's Maximum, is designated as SNR_max；In conjunction with SNR_maxWith ObtainAnd then obtain R_DFValue, this value is the bi-directional relaying cognitive radio system under DF agreement The maximum system capacity of system, and obtain when L relaying corresponding to maximum system capacity and L the respective broadcast singal of relaying used Power.