CN104507038A - Access overload control method of RAN (Radio Access Network) layer in clustered M2M (Machine to Machine) network - Google Patents

Abstract

The invention discloses an access overload control method of an RAN layer in a clustered M2M network. The method comprises the following steps: (1) dividing MTC equipment in a base station into time delay sensitive equipment and time delay insensitive equipment according to a preset time delay sensitivity limit; (2) acquiring the quantity of users requesting to access in a current time slot by the base station, obtaining a corresponding pilot frequency partition ratio beta * when the total quantity of successfully accessed MTC equipment is maximum, and then acquiring the quantity of pilot-frequency resources allocated to the time delay sensitive equipment and the quantity of pilot-frequency resources allocated to the time delay insensitive equipment according to the corresponding pilot frequency partition ratio beta * when the total quantity of successfully accessed MTC equipment is maximum; (3) realizing user access by adopting an ACB mechanism according to the quantity of the allocated pilot-frequency resources by the time delay sensitive equipment, and realizing user access by adopting the ACB mechanism according to the allocated pilot-frequency resources by the time delay insensitive equipment. The method disclosed by the invention can be used for effectively increasing the access rate of the MTC equipment.

Description

The access overload controlling method of RAN layer in a kind of sub-clustering type M2M network

Technical field

The invention belongs to M2M communication technical field, relate to the access overload controlling method of RAN layer in a kind of sub-clustering type M2M network.

Background technology

When MTC device a certain intra-zone administration too much and the same period more intensively access network time, network just can face overload and possible MTC communication amount is increased sharply, and the congestion overload of network inevitably causes loss or even the service disruption of unnecessary time delay, packet.For the network congestion overload in M2M communication, the underaction of existing ACB strategy own, is difficult to effectively reduce collision probability and not readily passes through adjustment relevant parameter realizing trading off between various performance when number of users to be accessed increases further; In addition ACB strategy be only applicable to those can to time delay insensitive equipment access in reality the existence of delay sensitive equipment just make the application of ACB strategy receive limitation.Meanwhile, although EAB strategy considers time delay sensitive type equipment, but not realizing grouping to pilot resources causes two class users to share fixing pilot resources, it is unfair that this processing mode inevitably causes low priority user to access, in view of the above problems, need to dynamically arrange pilot tone subregion ratio to the M2M network under cluster structured using time delay sensitivity as standard, maximize the access rate of MTC device with this, but prior art does not relate to the technology of this respect.

Summary of the invention

The object of the invention is to the shortcoming overcoming above-mentioned prior art, provide the access overload controlling method of RAN layer in a kind of sub-clustering type M2M network, this control method can effectively improve MTC device access rate.

For achieving the above object, in sub-clustering type M2M network of the present invention, the access overload controlling method of RAN layer comprises the following steps:

1) according to the time delay sensitivity preset, each MTC device in base station is divided into time delay sensitive type equipment and time delay insensitive equipment;

2) base station obtains the number of users of current time slots application access, obtain MTC device access successfully total maximum time corresponding pilot tone subregion compare β ^*, then according to MTC device access successfully total maximum time corresponding pilot tone subregion compare β ^*obtain and distribute to the pilot resources number of time delay sensitive type equipment and distribute to the pilot resources number of time delay insensitive equipment;

3) time delay sensitive type equipment adopts ACB mechanism access user according to the pilot resources number distributed, and time delay insensitive equipment adopts ACB mechanism access user according to the pilot resources number distributed.

Step 2) in obtain MTC device access successfully total maximum time corresponding pilot tone subregion compare β ^*concrete steps be:

If A _sfor the time delay sensitive type number of devices of current time slots, A _nfor the time delay insensitive number of devices of current time slots, A _ifor the MTC device sum of current time slots, then there is A _s+ A _n=A _i; If M _sfor distributing to the pilot resources number of time delay sensitive type equipment, M _nfor distributing to the pilot resources number of time delay insensitive equipment, c is the sum of pilot resources, and β is the pilot tone subregion ratio of current time slots, then have

$\mathrm{\β}=\frac{M_s}{M_n}---\left(1\right)$

M _s+M _n＝c (2)

Obtained by formula (1) and formula (2):

$\left\{\begin{array}{c}{M}_s=\frac{\mathrm{c\β}}{1+\mathrm{\β}}\\ M_n=\frac{c}{1+\mathrm{\β}}\end{array}\right.---\left(3\right)$

Each MTC device accesses successful probability P _s=e ^-N/P, wherein, N is the MTC device quantity of current time slots application, and P is the patterns available number of resources of current time slots application, then the successful total S of MTC device access _nfor:

$S_N=A_s{f}_s\×e^{-\frac{A_s{f}_s}{M_s}}+A_n{f}_n\×e^{-\frac{A_n{f}_n}{M_n}}---\left(4\right)$

Wherein, f _sfor the restriction factor of time delay sensitive type equipment under ACB mechanism, f _nfor the restriction factor of time delay insensitive equipment under ACB mechanism, formula (3) is brought in formula (4) and obtains

$S_N=A_s{f}_s\×e^{-\frac{A_s{f}_s(1+\mathrm{\β})}{\mathrm{c\β}}}+A_n{f}_n\×e^{-\frac{A_n{f}_n(1+\mathrm{\β})}{c}}---\left(5\right)$

Then set up according to formula (5) and solve the Mathematical Modeling that maximum MTC device accesses successfully sum:

$\left\{\begin{array}{ccc}\underset{\mathrm{\β}}{\max }& \{A_s{f}_s\·e^{-\frac{A_s{f}_s}{c}(1+\frac{1}{\mathrm{\β}})}+A_n{f}_n\·e^{-\frac{A_n{f}_n(1+\mathrm{\β})}{c}}\},A_s{f}_s\∈\left(\mathrm{0,1}\right]& \\ \underset{A_s{f}_s{e}^{-\frac{A_s{f}_s}{c}(1+\frac{1}{\mathrm{\β}})}\≥1}{\max }& \{A_s{f}_s\·e^{-\frac{A_s{f}_s}{c}(1+\frac{1}{\mathrm{\β}})}+A_n{f}_n\·e^{-\frac{A_n{f}_n(1+\mathrm{\β})}{c}}\},A_s{f}_s\∈\left(\mathrm{1,3}\right)& \\ \underset{A_s{f}_s{e}^{-\frac{A_s{f}_s}{c}(1+\frac{1}{\mathrm{\β}})}\≥2}{\max }& \{A_s{f}_s\·e^{-\frac{A_s{f}_s}{c}(1+\frac{1}{\mathrm{\β}})}+A_n{f}_n\·e^{-\frac{A_n{f}_n(1+\mathrm{\β})}{c}}\},A_s{f}_s\∈[3,+\∞)& \end{array}\right.---\left(6\right)$

Set up target function, then according to target function solve formula (6) MTC device access successful total maximum time corresponding pilot tone subregion compare β ^*.

The process setting up target function is:

Differentiate is carried out to formula (5) equal sign both sides, and is 0 by the result after differentiate, then have

$\frac{A_s^2{f}_s^2}{c{\mathrm{\β}}^2}{\×e}^{-\frac{A_s{f}_s(1+\mathrm{\β})}{\mathrm{c\β}}}-\frac{A_n^2{f}_n^2}{c}\×e^{-\frac{A_n{f}_n(1+\mathrm{\β})}{c}}\≡0---\left(7\right)$

Abbreviation is carried out to formula (7) and obtains target function:

$\frac{A_s{f}_s}{c}(1+\frac{1}{\mathrm{\β}})-\frac{A_n{f}_n}{c}(1+\mathrm{\β})+2\log \mathrm{\β}=\log \left(\frac{A_s^2{f}_s^2}{A_n^2{f}_n^2}\right)---\left(8\right)$

Work as A _sf _s∈ (0,1] time, then according to target function adopt Newton iterative solve formula (6), obtain MTC device access successful total maximum time corresponding pilot tone subregion compare β ^*.

Work as A _sf _stime ∈ (1,3), formula (6) can be expressed as the optimization problem under inequality constraints, and the detailed process solving formula (6) is:

Determine the feasible zone D of optimization problem ₁:

$D_1=\left\{\mathrm{\β}\right|\mathrm{\β}\≥\frac{A_s{f}_s}{c*\log \left(A_s{f}_s\right)-A_s{f}_s}\}---\left(9\right)$

Due to feasible zone D ₁internal object function monotone decreasing, therefore when β gets boundary value, target function gets maximum, namely

${\mathrm{\β}}^{*}=\frac{A_s{f}_s}{c*\log \left(A_s{f}_s\right)-A_s{f}_s}---\left(10\right).$

Work as A _sf _s∈ [3 ,+∞) time, formula (6) can be expressed as the optimization problem under inequality constraints, and the detailed process solving formula (6) is:

Determine the feasible zone D of optimization problem ₂:

$D_2=\left\{\mathrm{\β}\right|\mathrm{\β}\≥\frac{A_s{f}_s}{\text{c*log}(A_s{f}_s/2)-A_s{f}_s}\}---\left(11\right)$

Due to feasible zone D ₂internal object function monotone decreasing, therefore when β gets boundary value, target function gets maximum, namely

${\mathrm{\β}}^{*}=\frac{A_s{f}_s}{\text{c*log}(A_s{f}_s/2)-A_s{f}_s}---\left(12\right).$

The present invention has following beneficial effect:

In sub-clustering type M2M network of the present invention, the access overload controlling method of RAN layer is when accessing each MTC device, first according to the time delay sensitivity preset, each MTC device in base station is divided into time delay sensitive type equipment and time delay insensitive equipment, obtain again MTC device access successfully total maximum time corresponding pilot tone subregion ratio, then according to MTC device access successfully total maximum time corresponding pilot tone subregion than obtaining the pilot resources number distributing to time delay sensitive type equipment and time delay insensitive equipment, time delay sensitive type equipment and time delay insensitive equipment adopt ACB mechanism access user according to distributing to respective pilot resources number, thus effective raising MTC device access rate, make total access successful user number maximum, reasonable in design, simple to operate, practicality is extremely strong.

Accompanying drawing explanation

Fig. 1 is typical M2M system architecture diagram;

Fig. 2 is MTC device random access procedure figure;

Fig. 3 is scenario-frame design drawing;

Fig. 4 (a) is for the access probability of success is with the change curve of relation between two groups of restriction factors;

Fig. 4 (b) is for average access delay is with the change curve of relation between two groups of restriction factors;

Fig. 5 is the correlation curve figure accessing the probability of success under different restriction factor;

Fig. 6 is the correlation curve figure of average access delay under different restriction factor;

Fig. 7 is the correlation curve figure of collision probability under different restriction factor;

Fig. 8 is the correlation curve figure that under different restriction factor, two class users access the probability of success;

Fig. 9 is the correlation curve figure of the average access delay of two class users under different restriction factor;

Figure 10 is the correlation curve figure of two class user collision probabilities under different restriction factor.

Embodiment

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

With reference to figure 1, concrete being described below of typical M2M system architecture diagram:

Consider typical M2M SNA, comprise LTE-A base station, MTC device, gateway node and the interface between gateway and base station, wherein, LTE-A base station comprises macro station, Picocell base station, Femtocell base station and via node, and the pilot resources of user and the issue of various control information and storage are distributed in the regulation and control of primary responsibility the whole network, the base station of Serving cell, each equipment place wants elder generation and corresponding gateway node (GW) to communicate simultaneously, and gateway node contacts the serving BS of community, two equipment places as a via node; Between gateway and base station, then need interface S1 transmission of information, under this deployment scenario, realize direct communication each other by LTE-A base station between MTC device and connect.

With reference to figure 2, the access procedure of MTC device mainly completes in RACH channel, here configuration and the operational circumstances of RACH channel might as well be provided, RACH channel is made up of some RA time slots that can be used for transmitting access request, the length of RA time slot depends on the value of Configuration Index, point out in agreement, the every 5ms configuration of RACH is meaned once when Configuration Index value is 6, namely every 5ms just has 64 orthogonal guide frequency resources available, wherein, 54 accesses that can be used for based on collision, remain 10 then for collisionless access is reserved.Be that a time slot is as pilot resources configuration cycle using 5ms, MTC device goes competition 54 can supply the pilot resources utilized at each time slot, and in current time slots, the equipment of each application access must complete four step random access procedures between base station and equipment and just can complete this access request.Four handshake procedures of Stochastic accessing (RA) are as follows:

Msgl: the MTC device of application access sends pilot resources information to base station

Msg2: base station is by the MTC device transmission RA feedback information of PDSCH channel to correspondence

(connection request) information that Msg3:MTC equipment sends to base station " request connects "

Msg4: base station sends " Conflict solving " (contention resolution) information to MTC device

With reference to figure 3, in sub-clustering type M2M network of the present invention, the access overload controlling method of RAN layer comprises the following steps:

1) according to the time delay sensitivity preset, each MTC device in base station is divided into time delay sensitive type equipment and time delay insensitive equipment;

2) base station obtains the number of users of current time slots application access, obtain MTC device access successfully total maximum time corresponding pilot tone subregion compare β ^*, then according to MTC device access successfully total maximum time corresponding pilot tone subregion compare β ^*obtain and distribute to the pilot resources number of time delay sensitive type equipment and distribute to the pilot resources number of time delay insensitive equipment;

3) time delay sensitive type equipment adopts ACB mechanism access user according to the pilot resources number distributed, and time delay insensitive equipment adopts ACB mechanism access user according to the pilot resources number distributed.

Wherein, when the time delay sensitivity of MTC device is more than or equal to default time delay sensitivity, then this MTC device is time delay sensitive type equipment, and when the time delay sensitivity of MTC device is less than default time delay sensitivity, then this MTC device is time delay insensitive equipment;

Step 2) in obtain MTC device access successfully total maximum time corresponding pilot tone subregion compare β ^*concrete steps be:

If A _sfor the time delay sensitive type number of devices of current time slots, A _nfor the time delay insensitive number of devices of current time slots, A _ifor the MTC device sum of current time slots, then there is A _s+ A _n=A _i; If M _sfor distributing to the pilot resources number of time delay sensitive type equipment, M _nfor distributing to the pilot resources number of time delay insensitive equipment, c is the sum of pilot resources, and β is the pilot tone subregion ratio of current time slots, then have

$\mathrm{\β}=\frac{M_s}{M_n}---\left(1\right)$

M _s+M _n＝c (2)

Obtained by formula (1) and formula (2):

$\left\{\begin{array}{c}{M}_s=\frac{\mathrm{c\β}}{1+\mathrm{\β}}\\ M_n=\frac{c}{1+\mathrm{\β}}\end{array}\right.---\left(3\right)$

Each MTC device accesses successful probability P _s=e ^-N/P, wherein, N is the MTC device quantity of current time slots application, and P is the patterns available number of resources of current time slots application, then the successful total S of MTC device access _nfor:

$S_N=A_s{f}_s\×e^{-\frac{A_s{f}_s}{M_s}}+A_n{f}_n\×e^{-\frac{A_n{f}_n}{M_n}}---\left(4\right)$

Wherein, f _sfor the restriction factor of time delay sensitive type equipment under ACB mechanism, f _nfor the restriction factor of time delay insensitive equipment under ACB mechanism, formula (3) is brought in formula (4) and obtains

$S_N=A_s{f}_s\×e^{-\frac{A_s{f}_s(1+\mathrm{\β})}{\mathrm{c\β}}}+A_n{f}_n\×e^{-\frac{A_n{f}_n(1+\mathrm{\β})}{c}}---\left(5\right)$

Then set up according to formula (5) and solve the Mathematical Modeling that maximum MTC device accesses successfully sum:

$\left\{\begin{array}{ccc}\underset{\mathrm{\β}}{\max }& \{A_s{f}_s\·e^{-\frac{A_s{f}_s}{c}(1+\frac{1}{\mathrm{\β}})}+A_n{f}_n\·e^{-\frac{A_n{f}_n(1+\mathrm{\β})}{c}}\},A_s{f}_s\∈\left(\mathrm{0,1}\right]& \\ \underset{A_s{f}_s{e}^{-\frac{A_s{f}_s}{c}(1+\frac{1}{\mathrm{\β}})}\≥1}{\max }& \{A_s{f}_s\·e^{-\frac{A_s{f}_s}{c}(1+\frac{1}{\mathrm{\β}})}+A_n{f}_n\·e^{-\frac{A_n{f}_n(1+\mathrm{\β})}{c}}\},A_s{f}_s\∈\left(\mathrm{1,3}\right)& \\ \underset{A_s{f}_s{e}^{-\frac{A_s{f}_s}{c}(1+\frac{1}{\mathrm{\β}})}\≥2}{\max }& \{A_s{f}_s\·e^{-\frac{A_s{f}_s}{c}(1+\frac{1}{\mathrm{\β}})}+A_n{f}_n\·e^{-\frac{A_n{f}_n(1+\mathrm{\β})}{c}}\},A_s{f}_s\∈[3,+\∞)& \end{array}\right.---\left(6\right)$

Set up target function, then according to target function solve formula (6) MTC device access successful total maximum time corresponding pilot tone subregion compare β ^*.

The process setting up target function is:

Differentiate is carried out to formula (5) equal sign both sides, and is 0 by the result after differentiate, then have

$\frac{A_s^2{f}_s^2}{c{\mathrm{\β}}^2}{\×e}^{-\frac{A_s{f}_s(1+\mathrm{\β})}{\mathrm{c\β}}}-\frac{A_n^2{f}_n^2}{c}\×e^{-\frac{A_n{f}_n(1+\mathrm{\β})}{c}}\≡0---\left(7\right)$

Abbreviation is carried out to formula (7) and obtains target function:

$\frac{A_s{f}_s}{c}(1+\frac{1}{\mathrm{\β}})-\frac{A_n{f}_n}{c}(1+\mathrm{\β})+2\log \mathrm{\β}=\log \left(\frac{A_s^2{f}_s^2}{A_n^2{f}_n^2}\right)---\left(8\right)$

Work as A _sf _s∈ (0,1] time, then according to target function adopt Newton iterative solve formula (6), obtain MTC device access successful total maximum time corresponding pilot tone subregion compare β ^*.

Work as A _sf _stime ∈ (1,3), formula (6) can be expressed as the optimization problem under inequality constraints, and the detailed process solving formula (6) is:

Determine the feasible zone D of optimization problem ₁:

$D_1=\left\{\mathrm{\β}\right|\mathrm{\β}\≥\frac{A_s{f}_s}{c*\log \left(A_s{f}_s\right)-A_s{f}_s}\}---\left(9\right)$

Due to feasible zone D ₁internal object function monotone decreasing, therefore when β gets boundary value, target function gets maximum, namely

${\mathrm{\β}}^{*}=\frac{A_s{f}_s}{c*\log \left(A_s{f}_s\right)-A_s{f}_s}---\left(10\right).$

Work as A _sf _s∈ [3 ,+∞) time, formula (6) can be expressed as the optimization problem under inequality constraints, and the detailed process solving formula (6) is:

Determine the feasible zone D of optimization problem ₂:

$D_2=\left\{\mathrm{\β}\right|\mathrm{\β}\≥\frac{A_s{f}_s}{\text{c*log}(A_s{f}_s/2)-A_s{f}_s}\}---\left(11\right)$

Due to feasible zone D ₂internal object function monotone decreasing, therefore when β gets boundary value, target function gets maximum, namely

${\mathrm{\β}}^{*}=\frac{A_s{f}_s}{\text{c*log}(A_s{f}_s/2)-A_s{f}_s}---\left(12\right).$

According to the realization mechanism of ACB strategy, first need to design the parameter of two in ACB mechanism (restriction factor and binding hours) respectively, because design focal point of the present invention is dynamic conditioning pilot tone subregion ratio, so now make following hypothesis in order to reduction procedure:

The binding hours of time delay sensitive type equipment is equal with the binding hours of time delay insensitive equipment, i.e. T _s=T _n; When being limited, the back off time of time delay sensitive type equipment and time delay insensitive equipment is as follows:

For the non-sensitive user of time delay, back off time is:

$T_{\mathrm{barred}}=(0.7+\frac{0.6\·\mathrm{rand}}{\mathrm{ac}\_\mathrm{barringfactor}})\×\mathrm{ac}\_\mathrm{barringtime}---\left(13\right)$

For latency sensitive user, back off time is:

T _barred＝(0.7+0.6·rand)*ac_barringtime (14)

And two bunches of equipment adopt the relation between the restriction factor of ACB mechanism to be set to linear relationship: f _n=p+qf _s, wherein f _s∈ (0,1), the value of p and q will make f _n∈ (0,1); Fig. 4 (a) and 4 (b) are the access probability of success and the average access delay change curve with relation between two groups of restriction factors respectively, according to the integrated survey accessing the probability of success and average access delay two indices, we select following relation:

$f_n=0.6+\frac{1}{3}{f}_s---\left(15\right)$

In sum, main realization mechanism of the present invention is the pilot tone subregion ratio of attempt by each time slot of Dynamic controlling, to optimize the equipment access situation of each time slot; The essence of this algorithm be by RACH resource Dynamic Separation ability in cluster structured to realize the control to RAN overload in M2M communication.

Emulation experiment

With reference to figure 5, emulate in the LTE community of a 5MHz, 30000 MTC device are evenly distributed in community, and collision indicating device is set to 5ms, only accesses situation to user in 10s and consider in emulation.The quantitative proportion of the quantity of delay sensitive equipment and the non-sensitive equipment of time delay is set to 1: 9.In addition, for the parameter of two in ACB strategy, in emulation, delay sensitive equipment is the same with the binding hours of the non-sensitive equipment of time delay, meet (15) formula between restriction factor, and the random-backoff time of the equipment of respective cluster after restriction factor " restriction " meets (13) and (14) formula respectively.Under above-mentioned simulating scenes, Zong Fig. 5 show the access probability of success with the change curve of restriction factor and depict traditional ACB algorithm with algorithm proposed access rate compare.Can find out, when restriction factor changes between 0.2-0.8, along with restriction factor increases, the corresponding increase of access rate, and when restriction factor value is 0.9, access rate reduces, this is because major part user all can not obtain chance access under ACB mechanism by " restriction " when restriction factor is larger, this causes a large number of users collide and access rate is declined to some extent unavoidably.Meanwhile, the present invention compares traditional ACB mechanism and has higher access rate, and reason is that this programme realizes always accessing optimum by selecting optimum pilot tone subregion ratio.

Fig. 6 is the correlation curve figure of system average access delay under different restriction factor.Can find out, along with increasing progressively of restriction factor, average access delay constantly reduces, and the average access delay of user obtained under traversal restriction factor is all in below 4s, and this also illustrates another superiority of the present invention.Meanwhile, the present invention more traditional ACB mechanism significantly reduces in average access delay.

Fig. 7 show mean collisional probability with the change curve of restriction factor and give traditional ACB algorithm with institute proposes algorithm collision rate contrast, be not difficult discovery, the collision rate of this programme increases with the increase of restriction factor.Meanwhile, the present invention's more traditional ACB mechanism collision rate slightly improves, although collision rate improves, this is in the tolerance that systematic function promotes.

Under Fig. 8-10 discusses different restriction factor respectively, two class users are accessing the correlation curve figure in the probability of success, average access delay and mean collisional probability three.On the one hand, for sensitive equipment, from Fig. 8 and Fig. 9, compared with ACB mechanism, its access probability of success remains basically stable compared with ACB algorithm with average access delay, and Figure 10 shows that the collision rate of sensitive users significantly declines; On the other hand, for non-sensitive user, known by Fig. 8 and Fig. 9, than ACB strategy, its access probability of success greatly promotes and change with restriction factor is not obvious, and its average access delay significantly declines, in addition, Figure 10 also shows that the collision rate of non-sensitive user raises to some extent, and this is in the tolerance of other two performance boosts.

Claims (6)

1. an access overload controlling method for RAN layer in sub-clustering type M2M network, is characterized in that, comprise the following steps:

1) according to the time delay sensitivity preset, each MTC device in base station is divided into time delay sensitive type equipment and time delay insensitive equipment;

2) base station obtains the number of users of current time slots application access, obtain MTC device access successfully total maximum time corresponding pilot tone subregion compare β ^*, then according to MTC device access successfully total maximum time corresponding pilot tone subregion compare β ^*obtain and distribute to the pilot resources number of time delay sensitive type equipment and distribute to the pilot resources number of time delay insensitive equipment;

3) time delay sensitive type equipment adopts ACB mechanism access user according to the pilot resources number distributed, and time delay insensitive equipment adopts ACB mechanism access user according to the pilot resources number distributed.

2. the access overload controlling method of RAN layer in sub-clustering type M2M network according to claim 1, is characterized in that, step 2) in obtain MTC device access successfully total maximum time corresponding pilot tone subregion compare β ^*concrete steps be:

If A _sfor the time delay sensitive type number of devices of current time slots, A _nfor the time delay insensitive number of devices of current time slots, A _ifor the MTC device sum of current time slots, then there is A _s+ A _n=A _i; If M _sfor distributing to the pilot resources number of time delay sensitive type equipment, M _nfor distributing to the pilot resources number of time delay insensitive equipment, c is the sum of pilot resources, and β is the pilot tone subregion ratio of current time slots, then have

$\mathrm{\β}=\frac{M_s}{M_n}---\left(1\right)$

M _s+M _n＝c (2)

Obtained by formula (1) and formula (2):

$\left\{\begin{array}{c}{M}_s=\frac{\mathrm{c\β}}{1+\mathrm{\β}}\\ M_n=\frac{c}{1+\mathrm{\β}}\end{array}\right.---\left(3\right)$

Each MTC device accesses successful probability P _s=e ^-N/P, wherein, N is the MTC device quantity of current time slots application, and P is the patterns available number of resources of current time slots application, then the successful total S of MTC device access _nfor:

$S_N=A_s{f}_s\×e^{-\frac{A_s{f}_s}{M_s}}+A_n{f}_n\×e^{-\frac{A_n{f}_n}{M_n}}---\left(4\right)$

Wherein, f _sfor the restriction factor of time delay sensitive type equipment under ACB mechanism, f _nfor the restriction factor of time delay insensitive equipment under ACB mechanism, formula (3) is brought in formula (4) and obtains

$S_N=A_s{f}_s\×e^{-\frac{A_s{f}_s(1+\mathrm{\β})}{\mathrm{c\β}}}+A_n{f}_n\×e^{-\frac{A_n{f}_n(1+\mathrm{\β})}{c}}---\left(5\right)$

Then set up according to formula (5) and solve the Mathematical Modeling that maximum MTC device accesses successfully sum:

$\left\{\begin{array}{c}\underset{\mathrm{\β}}{\max }\{A_s{f}_s\·e^{-\frac{A_s{f}_s}{c}(1+\frac{1}{\mathrm{\β}})}+A_n{f}_n\·e^{-\frac{A_n{f}_n(1+\mathrm{\β})}{c}}\},A_s{f}_s\∈\left(\mathrm{0,1}\right]\\ \underset{A_s{f}_s{e}^{-\frac{A_s{f}_s}{c}(1+\frac{1}{\mathrm{\β}})}\≥1}{\max }\{A_s{f}_s\·e^{-\frac{A_s{f}_s}{c}(1+\frac{1}{\mathrm{\β}})}+A_n{f}_n\·e^{-\frac{A_n{f}_n(1+\mathrm{\β})}{c}}\},A_s{f}_s\∈\left(\mathrm{1,3}\right)\\ \underset{A_s{f}_s{e}^{-\frac{A_s{f}_s}{c}(1+\frac{1}{\mathrm{\β}})}\≥2}{\max }\{A_s{f}_s\·e^{-\frac{A_s{f}_s}{c}(1+\frac{1}{\mathrm{\β}})}+A_n{f}_n\·e^{-\frac{A_n{f}_n(1+\mathrm{\β})}{c}}\},A_s{f}_s\∈[3,+\∞)\end{array}\right.---\left(6\right)$

Set up target function, then according to target function solve formula (6) MTC device access successful total maximum time corresponding pilot tone subregion compare β ^*.

3. the access overload controlling method of RAN layer in sub-clustering type M2M network according to claim 2, it is characterized in that, the process setting up target function is:

Differentiate is carried out to formula (5) equal sign both sides, and is 0 by the result after differentiate, then have

$\frac{A_s^2{f}_s^2}{c{\mathrm{\β}}^2}\×e^{-\frac{A_s{f}_s(1+\mathrm{\β})}{\mathrm{c\β}}}-\frac{A_n^2{f}_n^2}{c}\×e^{-\frac{A_n{f}_n(1+\mathrm{\β})}{c}}\≡0---\left(7\right)$

Abbreviation is carried out to formula (7) and obtains target function:

$\frac{A_s{f}_s}{c}(1+\frac{1}{\mathrm{\β}})-\frac{A_n{f}_n}{c}(1+\mathrm{\β})+2\log \mathrm{\β}=\log \left(\frac{A_s^2{f}_s^2}{A_n^2{f}_n^2}\right)---\left(8\right)$

4. the access overload controlling method of RAN layer in sub-clustering type M2M network according to claim 3, is characterized in that, work as A _sf _s∈ (0,1] time, then according to target function adopt Newton iterative solve formula (6), obtain MTC device access successful total maximum time corresponding pilot tone subregion compare β ^*.

5. the access overload controlling method of RAN layer in sub-clustering type M2M network according to claim 3, is characterized in that, work as A _sf _stime ∈ (1,3), formula (6) can be expressed as the optimization problem under inequality constraints, and the detailed process solving formula (6) is:

Determine the feasible zone D of optimization problem ₁:

$D_1=\left\{\mathrm{\β}\right|\mathrm{\β}\≥\frac{A_s{f}_s}{c*\log \left(A_s{f}_s\right)-A_s{f}_s}\}---\left(9\right)$

Due to feasible zone D ₁internal object function monotone decreasing, therefore when β gets boundary value, target function gets maximum, namely

${\mathrm{\β}}^{*}=\frac{A_s{f}_s}{c*\log \left(A_s{f}_s\right)-A_s{f}_s}---\left(10\right).$

6. the access overload controlling method of RAN layer in sub-clustering type M2M network according to claim 3, is characterized in that, work as A _sf _s∈ [3 ,+∞) time, formula (6) can be expressed as the optimization problem under inequality constraints, and the detailed process solving formula (6) is:

Determine the feasible zone D of optimization problem ₂:

$D_2=\left\{\mathrm{\β}\right|\mathrm{\β}\≥\frac{A_s{f}_s}{c*\log (A_s{f}_s/2)-A_s{f}_s}\}---\left(11\right)$

Due to feasible zone D ₂internal object function monotone decreasing, therefore when β gets boundary value, target function gets maximum, namely

${\mathrm{\β}}^{*}=\frac{A_s{f}_s}{c*\log (A_s{f}_s/2)-A_s{f}_s}---\left(12\right).$