CN102724706B - Two-stage frame aggregation method - Google Patents

Abstract

The invention discloses a two-stage frame aggregation method which comprises the following steps that a media access control (MAC) level two-dimensional Markov chain model is established, and the free probability of a network, data sending successful probability and data collision probability in the network as well as the length of an MAC level time slot which corresponds to the state of the network are obtained; the length Lth of an A-MSDU frame which enables the saturation throughput S of the network to be the highest is obtained; the upper limit Llimit of the length of the A-MSDU frame which meets a time delay requirement Dmax is obtained; the length Lth of the A-MSDU frame and the upper limit Llimit of the length of the A-MSDU frame (whichever is smaller) is selected as the length LA-MSDU of the final A-MSDU frame; and the A-MSDU frame is determined according to the length LA-MSDU of the A-MSDU frame, and two-stage frame aggregation is realized. The problems of throughput performance reduction and data time delay control are solved by automatically adjusting the length of the A-MSDU frame.

Description

A kind of two-stage frame aggregation method

Technical field

The invention belongs to MAC Layer in Wireless field, particularly a kind of two-stage frame aggregation method.

Background technology

Along with the rapid growth of radio communication service amount, need to improve the throughput of WLAN (wireless local area network) to adapt to user's request.IEEE 802.11n standard is by adopting multiple-input and multiple-output (MIMO) technology and OFDM (OFDM) technology greatly to improve the physical layer transmission speed of WLAN (wireless local area network).Along with the lifting of physical layer rate, the inefficiencies of traditional mac-layer protocol becomes the principal element that restriction throughput performance of WLAN increases.In traditional MAC Layer in Wireless agreement, each packet all needs to add MAC layer head, and packet all adopts independent access channel and the mode confirmed is separately transmitted, and has brought a large amount of room and time expenses, causes MAC layer inefficiency.In order to promote MAC layer efficiency, IEEE 802.11n standard has proposed mac layer frame polymerization technique.

Mac layer frame polymerization technique, by a plurality of packets being polymerized to a long data frame, makes a plurality of packets share MAC layer head or physical layer header, has reduced the ratio of accessing cost for data.Techniques of frame aggregation makes a plurality of packets access channel simultaneously and at receiving terminal, a plurality of packets be carried out to integral body and confirm, has reduced the time overhead that channel access and data validation process are brought.Compare with traditional MAC layer, adopt the MAC layer of techniques of frame aggregation more efficient, can make network throughput obtain greatly and improve.

In IEEE 802.11n standard, stipulate, MAC layer can be realized the polymerization of MAC layer service data cell, three kinds of frame aggregation mechanism of the polymerization of mac-layer protocol data cell and two-stage frame aggregation.

MAC layer service data cell polymerization (Aggregate-MAC Service Data Unit, A-MSDU) is polymerized to A-MSDU frame by a plurality of MSDU.The subframe of A-MSDU frame is comprised of subframe head, MSDU and padding data, and wherein subframe head comprises destination address (DA), source address (sa) and MSDU length (Length) three parts.By for A-MSDU frame adds MAC layer head and frame check sequence (FCS), can further form mac-layer protocol data cell (MPDU).Therefore owing to only existing a FCS to detect aggregate frame, as long as some subframes are subject to channel effect and produce error code in A-MSDU frame, receiving terminal just can think that aggregate frame makes mistakes, and requires transmitting terminal to retransmit all subframes.So when channel bit error rate is higher, the throughput performance of A-MSDU mechanism can sharply worsen.

Mac-layer protocol data cell polymerization (Aggregate-MAC Protocol Data Unit, A-MPDU) becomes A-MPDU frame by a plurality of MPDU polymerizations.The subframe of A-MPDU frame is by separator (Delimiter), and MPDU and padding data form.Because each MPDU all comprises MAC layer head and FCS, so receiving terminal can detect respectively the subframe of A-MPDU, only requires that transmitting terminal resends the subframe that produces error code, so the error-resilient performance of A-MPDU is better than A-MSDU.Compare with A-MSDU, A-MPDU need to be that each MSDU adds MAC layer head and FCS, when MSDU hour, the accessing cost for data that frame aggregation brings increases with the ratio of the valid data that MSDU carries, and causes A-MPDU decrease in efficiency.According to IEEE 802.11n agreement, A-MPDU can comprise at most 64 subframes, and for the scene that has a large amount of short MSDU to exist, the data volume that A-MPDU once sends is limited, less to the lifting of network throughput, decrease in efficiency.

Two-stage frame aggregation mechanism is the cascade to A-MSDU and A-MPDU mechanism, as shown in Figure 1.In the frame aggregation of the two poles of the earth, first the MSDU that arrives MAC layer is polymerized to longer A-MSDU frame, for forming MPDU after A-MSDU frame interpolation MAC head and FCS, and then form physics layer service data cell (PSDU) by A-MPDU mechanism polymerization MPDU.By using two-stage techniques of frame aggregation, wireless site can once send more data.Compare with A-MPDU with A-MSDU, in there is the scene that a large amount of short MSDU or physical layer rate are higher, two-stage frame aggregation can make WLAN (wireless local area network) obtain higher throughput.

In realizing process of the present invention, in discovery prior art, at least there is following shortcoming and defect in inventor:

The throughput performance of existing two-stage frame aggregation method is subject to channel bit error rate impact, cannot make network throughput arrive maximum; And existing two-stage frame aggregation method does not have time delay controlling mechanism, when business has delay requirement, can not guarantee the service quality of business.

Summary of the invention

The invention provides a kind of two-stage frame aggregation method, this method makes two-stage frame aggregation mechanism automatically regulate A-MSDU frame length according to channel bit error rate and service delay requirement, has solved the problem of throughput performance decline and control data delay, described below:

A two-stage frame aggregation method, said method comprising the steps of:

(1) set up MAC layer two dimension Markov chain model, obtain the idle probability P of network _idle, data send probability of success P in network _swith in network, there is data collision probability P _c, and the length T of the MAC layer time slot corresponding with above-mentioned network state _idle, T _sand T _c;

(2) obtain and make network saturation throughput S reach peaked A-MSDU frame length L _th;

(3) obtain and meet delay requirement D _maxa-MSDU frame length upper limit L _limit;

(4) choose described A-MSDU frame length L _thwith A-MSDU frame length upper limit L _limitin smaller as final A-MSDU frame length L _a-MSDU;

(5) according to described A-MSDU frame length L _a-MSDU, determine A-MSDU frame, realize two-stage frame aggregation.

The described MAC of foundation layer two dimension Markov chain model specifically comprises:

1) set up the two-dimentional Markov chain that represents MAC layer state;

2) determine the single step state transition probability of described two-dimentional Markov chain;

3) by described single step state transition probability, calculate and send data probability τ;

4), according to described transmission data probability τ, obtain the idle probability P of described network _idle, data send probability of success P in described network _swith in described network, there is data collision probability P _c;

5) calculate the length T of described MAC layer time slot under heterogeneous networks state _idle, T _sand T _c.

Described obtaining makes network saturation throughput S reach peaked A-MSDU frame length L _thbe specially:

1) calculate the valid data amount E[payload that in a time slot, network sends];

2) calculate the average duration E[slot of MAC layer time slot];

3) by described valid data amount E[payload] and described average duration E[slot] determine and to make described network saturation throughput S reach peaked A-MSDU frame length L _th.

Described obtaining meets delay requirement D _maxa-MSDU frame length upper limit L _limitbe specially:

1) calculated data sends successful probability q after experience retransmits for k time _k;

2) determine the QoS parameter Q of business;

3) determine and satisfy condition minimum j value;

4) the maximum j rank time delay D of data estimator _{j, max};

5) determine described A-MSDU frame length upper limit L _limit.

The beneficial effect of technical scheme provided by the invention is: the present invention has provided under error code channel, the maximum j rank time delay D of data _{j, max}computational methods; For different service delays, require D _maxrequire Q with QoS, two-stage frame aggregation mechanism can regulate A-MSDU frame length automatically, thereby controls data delay, guarantees that data delay, within claimed range, has guaranteed the service quality of business; The present invention adapts to changeable wireless channel environment, makes two-stage frame aggregation mechanism regulate A-MSDU frame length according to the variation of channel bit error rate, has guaranteed the throughput performance of network; By the method for mathematical modeling, realize the adjusting of A-MSDU frame length in two-stage frame aggregation, accurate during fructufy.

Accompanying drawing explanation

Fig. 1 is realization flow figure and the frame structure of two-stage frame aggregation provided by the invention;

Fig. 2 is the flow chart of a kind of two-stage frame aggregation method provided by the invention;

Fig. 3 is the flow chart that makes network saturation throughput reach peaked A-MSDU frame length that obtains provided by the invention;

Fig. 4 is the flow chart that obtains the A-MSDU frame length upper limit that meets given delay requirement provided by the invention;

Fig. 5 is the schematic diagram that A-MSDU frame length provided by the invention changes with channel bit error rate;

Fig. 6 is that the network throughput Performance Ratio of this method and fixedly frame length two-stage frame aggregation, A-MPDU frame aggregation is compared with schematic diagram.

Embodiment

For making the object, technical solutions and advantages of the present invention clearer, below in conjunction with accompanying drawing, embodiment of the present invention is described further in detail.

In WLAN (wireless local area network), wireless channel changes very fast, and network throughput performance is subject to the real-time Control of Bit Error Rate of channel, and the frame aggregation mechanism of existing fixedly frame length and fixedly number of sub-frames can not be made adjustment with channel variation, causes the decline of network throughput performance.For the stronger business of the real-time that has delay requirement, for guaranteeing service quality, data delay must be within claimed range, and current techniques of frame aggregation does not have time delay controlling mechanism.For the problems referred to above, the embodiment of the present invention has proposed a kind of two-stage frame aggregation method, consider channel bit error rate and service delay requirement, dynamic adjustments A-MSDU frame length, guarantee to promote when data delay is within claimed range the throughput performance of network, referring to Fig. 1, Fig. 2, Fig. 3, Fig. 4, Fig. 5 and Fig. 6, described below:

101: set up MAC layer two dimension Markov chain model, obtain the idle probability P of network _idle, data send probability of success P in network _swith in network, there is data collision probability P _c, and the length T of the MAC layer time slot corresponding with above-mentioned network state _idle, T _sand T _c;

Wherein, MAC layer two dimension Markov chain model, is to adopting the mathematical modeling of the MAC layer of distributed coordination function (DCF) competitive channel.Distributed coordination function must be chosen competition window (CW) to realize competitive channel before requiring website to send data.Contention window can constantly reduce after choosing, and is decreased at 0 o'clock, and website starts to send data.Contention window size determines by binary exponential backoff algorithm, and binary exponential backoff algorithm comprises: the competition window of website is at [0, W _i] in choose at random, 0≤i≤m wherein; W _iinitial value W ₀be set to CW _min; When the every experience primary collision of data need to retransmit, the expansion of the span of CW is twice, i.e. W _i=2 ⁱw ₀; W _iincrease to maximum CW _maxafter no longer increase, CW _max=2 ^m' CW _min, m' is maximum back-off stage; After transfer of data success, W _iagain be set to CW _min; Surpass after the maximum retransmission m of IEEE 802.11n standard regulation, data are dropped, W _iagain be set to CW _min.

Wherein, the concrete modeling flow process of MAC layer two dimension Markov chain model is as follows:

1) set up the two-dimentional Markov chain that represents MAC layer state;

With { s (t), b (t) }, represent two-dimentional Markov chain, wherein s (t) represents that website is in the random process of t number of retransmissions constantly, and b (t) represents the t random process of contention window size constantly.The steady-state distribution of two dimension Markov chain is as shown in Equation (1):

$b_{i,k}=\underset{t\→\∞}{\lim }P\{s\left(t\right)=i,b\left(t\right)=k\},i\∈[0,m],k\∈[0,W_i-1]---\left(1\right)$

P represents probability.

2) determine the single step state transition probability of two-dimentional Markov chain;

If p is data collision probability, as shown in Equation (2), shifting science and technology in four directions probability represents respectively one-step transition probability: the probability that competition window reduces; Data send successfully, W _ibe set to W ₀probability; Data bump, W _i-1be set to W _iprobability; After m rear transmission success of data re-transmission or the m time collision, be dropped W _ibe set to W ₀probability.

$\left\{\begin{array}{cc}P\{i,k|i,k+1\}=1& k\∈[0,W_i-2],i\∈[0,m]\\ P\{0,k|i,0\}=(1-p)/W_0& k\∈[0,W_0-1],i\∈[0,m-1]\\ P\{i,k|i-\mathrm{1,0}\}=p/W_i& k\∈[0,W_i-1],i\∈[1,m]\\ P\{0,k|m,0\}=1/W_0& k\∈[0,W_0-1]\end{array}\right.---\left(2\right)$

3) calculate and send data probability τ;

According to formula (2) and normalizing condition, website be can try to achieve and the probability τ of data and the numerical solution of data collision Probability p in a time slot, sent.Normalizing condition as shown in Equation (3).

$1=\underset{i=0}{\overset{m}{\mathrm{\Σ}}}\underset{k=0}{\overset{W_i-1}{\mathrm{\Σ}}}{b}_{i,k}=\underset{i=0}{\overset{m}{\mathrm{\Σ}}}{b}_{i,0}\underset{k=0}{\overset{W_i-1}{\mathrm{\Σ}}}\frac{W_i-k}{W_i}---\left(3\right)$

4) according to sending data probability τ, make n represent wireless site quantity in WLAN (wireless local area network), obtain the idle probability P of network _idle, data send probability of success P in network _swith in network, there is data collision probability P _c;

Wherein, P _idle=(1-τ) ⁿ; P _s=n τ (1-τ) ^n-1; P _c=1-(1-τ) ⁿ-n τ (1-τ) ^n-1.

5) calculate MAC layer slot length T under heterogeneous networks state _idle, T _sand T _c.

When MAC layer adopts RTS/CTS pattern to send data:

(i) MAC layer slot length T when network is idle _idle=σ, σ is the system time gap that physical layer determines;

(ii) MAC layer slot length T when data send successfully _s=DIFS+3SIFS+T _rTS+ T _cTS+ T _data+ T _bA+ 4 δ;

(iii) MAC layer slot length T when data bump _c=DIFS+SIFS+T _rTS+ T _cTS+ 2 δ.

Wherein, DIFS and SIFS are respectively DCF frame period and the short frame period of IEEE 802.11n standard regulation, T _rTS, T _cTSand T _bAbe respectively the transmission time of RTS frame, CTS frame and BlockACK frame, T _datafor the transmission time of Frame (aggregate frame), δ represents the spatial time delay of data.

102: obtain and make network saturation throughput S reach peaked A-MSDU frame length L _th;

Wherein, by two-dimentional Markov chain model parameters obtained, can further be tried to achieve the computing formula of network saturation throughput S, to formula differentiate, can obtain making S to reach peaked A-MSDU frame length L _th, referring to Fig. 3,

Idiographic flow is as follows:

1) calculate the valid data amount E[payload that in a time slot, network sends];

The quantity N of the A-MSDU frame wherein, comprising in aggregate frame _a-MSDU, A-MSDU frame length L _a-MSDUwith channel bit error rate P _bcan obtain E[payload] computing formula, as shown in Equation (4), η means the constant of A-MSDU polymerization expense and MSDU length ratio, L _{mAC_H}for MAC layer head length.

E[payload]=8ηL _A-MSDU(1-P _b)^(8L _A-MSDU+8L _{MAC_H})N _A-MSDUP _s (4)

2) calculate the average duration E[slot of MAC layer time slot];

The average duration of MAC layer time slot can be calculated by formula (5):

E[slot]=T _idleP _idle+T _cP _c+T _sP _s (5)

3) by valid data amount E[payload] and average duration E[slot] determine and make network saturation throughput S reach peaked A-MSDU frame length L _th.

$S=\frac{E\left[\mathrm{payload}\right]}{E\left[\mathrm{slot}\right]}$ (6)

$=\frac{8\mathrm{\η}{L}_{A-\mathrm{MSDU}}(1-P_b)^({8L}_{A-\mathrm{MSDU}}+{8L}_{\mathrm{MAC}\_H})N_{A-\mathrm{MSDU}}{P}_s}{T_{\mathrm{idle}}{P}_{\mathrm{idle}}+T_c{P}_c+T_s{P}_s}$

Wherein, in the computing formula of network saturation throughput, N _a-MSDUaccording to IEEE 802.11n standard, be made as 64, error rate P _bcan be obtained by channel feedback mechanism, so only have A-MSDU frame length L in formula (6) _a-MSDUfor unknown quantity, can be by obtain making S to reach peaked A-MSDU frame length L to the mode of saturation throughput formula differentiate _th, i.e. L _thmeet S'(L _a-MSDU)=0.

103: obtain and meet delay requirement D _maxa-MSDU frame length upper limit L _limit;

According to two-dimentional Markov chain model parameter, obtain the maximum j rank time delay D of data _{j, max}, and then require D according to given service delay _max, utilize condition D _{j, max}≤ D _maxobtain the upper limit L of A-MSDU frame length _limit.

1) calculated data sends probability of success q after experience retransmits for k time _k, as shown in Equation (7).

$q_k=p^k\frac{1-p}{1-p^{m+1}},(0\≤k\≤m)---\left(7\right)$

2) determine the QoS parameter Q of business;

Parameter Q (0<Q≤1) represents that the requirement of this business is: the ratio that the data of time delay within maximum delay requires account for data total amount must not be less than Q, and Q value can be set according to the quality of service requirement of business.

3) determine and satisfy condition minimum j value;

Condition physical significance be to experience j time and be less than retransmitting the ratio that the data of transmission success afterwards account for all transmission success data for j time and be greater than Q.

4) the maximum j rank time delay D of data estimator _{j, max};

D _{j, max}refer to after data experience retransmits for j time and send the maximum delay that successfully caused, as shown in Equation (8).

$D_{j,\max }=\frac{[(W_j-1)+\underset{i=0}{\overset{j-1}{\mathrm{\&Sigma;}}}\frac{W_i-1}{2}]E^{\&prime;}\left[\mathrm{slot}\right]+j{T}_c+T_s}{(1-P_b)^[8(L_{A-\mathrm{MSDU}}+L_{\mathrm{MAC}\_H})}---\left(8\right)$

Wherein, E'[slot] average slot length while representing to remain n-1 website competitive channel in network, computational methods and E[slot] computational methods identical, need be by parameter P _idle, P _sand P _cn in computing formula is set to n-1.

5) determine A-MSDU frame length upper limit L _limit.

Maximum j rank time delay that can primary data by formula (8) is greater than the maximum j-1 rank time delay of data, i.e. D _{j-1, max}<D _{j, max}.So require D at given service delay _maxsituation under, known in conjunction with above-mentioned steps, as long as guarantee D _{j, max}≤ D _maxjust can guarantee to meet the data of delay requirement and the ratio of data total amount is greater than Q, guarantee to meet the quality of service requirement of business.Due to D _{j, max}computing formula in only have L _a-MSDUfor unknown quantity, so utilize D _{j, max}≤ D _maxcan determine the upper limit L of A-MSDU frame length _limit.

104: choose A-MSDU frame length L _thwith A-MSDU frame length upper limit L _limitin smaller as final A-MSDU frame length L _a-MSDU;

Wherein, gained frame length L in contrast step 102 _thwith gained frame length L in step 103 _limit, select wherein smaller as final A-MSDU frame length L _a-MSDU.Work as L _th≤ L _limittime, adopt L _thas A-MSDU frame length, can make the throughput of network reach maximum, data delay also meets the demands simultaneously.Work as L _th>L _limittime, should adopt L _limitas A-MSDU frame length, guarantee that data delay meets the demands, at this moment the throughput of network is the accessible maximum of throughput under this delay requirement.

105: according to A-MSDU frame length L _a-MSDU, determine A-MSDU frame, realize two-stage frame aggregation.

Wherein, the concrete operations of this step are conventionally known to one of skill in the art, and the embodiment of the present invention does not repeat at this.

Through the calculating of above-mentioned steps, just can obtain the length of A-MSDU frame in two-stage frame aggregation.The gained A-MSDU frame length result that to be the embodiment of the present invention automatically adjust according to channel bit error rate and service delay, this A-MSDU frame length, when guaranteeing that data delay meets the demands, makes network throughput reach maximum.Performance for checking this method, adopts following network scenarios as embodiment, the method to be tested:

1) WLAN (wireless local area network) is distributed in the region of 50m*50m;

2) in WLAN (wireless local area network), have 20 wireless sites and a central access point, wireless site adopts mode and the central access point of competition to communicate, and each wireless site is all within the communication coverage of other wireless sites;

3) business datum that wireless site sends is permanent bit rate (CBR) data flow, and data package size is 100Byte, and business maximum delay requires D _maxbe 100 μ s, QoS parameter Q is set to 0.9;

4) MAC layer adopts two-stage frame aggregation mechanism, is operated in RTS/CTS pattern, and MAC layer parameter arranges according to IEEE 802.11n standard, and DIFS is set to 89 μ s, and SIFS is set to 16 μ s, and system time gap σ length is 9 μ s, and maximum retransmission m is set to 7;

5) WLAN (wireless local area network) physical layer rate is 1Gbps;

6) channel bit error rate is 10 ^-6to 10 ^-3between change.

Fig. 5 is under above-mentioned network scenarios, adopts this method gained A-MSDU frame length with the variation of channel bit error rate.At channel bit error rate, be 10 ^-5time, A-MSDU frame length curve has a flex point.When channel bit error rate is greater than 10 ^-5time, A-MSDU frame length is mainly subject to channel bit error rate restriction, adopts gained frame length can make the throughput of network reach maximum, guarantees that data delay meets business need simultaneously.When channel bit error rate is less than 10 ^-5time, channel conditions is better, frame aggregation mechanism is reduced by the impact of the error rate, A-MSDU frame length is mainly subject to the constraint of service delay, adopt gained frame length to guarantee that data delay is no more than the delay requirement of business, and network throughput is now the maximum that under this delay requirement, throughput can reach.

Fig. 6 is under above-mentioned network scenarios, the throughput performance contrast of this method and fixedly frame length two-stage frame aggregation mechanism and A-MPDU mechanism.As shown in the figure, when channel bit error rate is lower, the throughput performance of this method and fixedly frame length two-stage frame aggregation is all greatly better than A-MPDU.Along with the rising of channel bit error rate, fixedly the throughput performance of frame length two-stage frame aggregation sharply declines, when the error rate surpasses 10 ^-4time, its throughput is lower than A-MPDU.When channel bit error rate is higher, the throughput performance of this method is better than fixedly frame length two-stage frame aggregation mechanism.This method can keep good throughput performance when channel bit error rate changes.

In sum, the embodiment of the present invention provides a kind of two-stage frame aggregation method, and this method has provided under error code channel, the maximum j rank time delay D of data _{j, max}computational methods; For different service delays, require D _maxrequire Q with QoS, two-stage frame aggregation mechanism can regulate A-MSDU frame length automatically, thereby controls data delay, guarantees that data delay, within claimed range, has guaranteed the service quality of business; This method adapts to changeable wireless channel environment, makes two-stage frame aggregation mechanism regulate A-MSDU frame length according to the variation of channel bit error rate, has guaranteed the throughput performance of network; By the method for mathematical modeling, realize the adjusting of A-MSDU frame length in two-stage frame aggregation, accurate during fructufy.

It will be appreciated by those skilled in the art that accompanying drawing is the schematic diagram of a preferred embodiment, the invention described above embodiment sequence number, just to describing, does not represent the quality of embodiment.

The foregoing is only preferred embodiment of the present invention, in order to limit the present invention, within the spirit and principles in the present invention not all, any modification of doing, be equal to replacement, improvement etc., within all should being included in protection scope of the present invention.

Claims (2)

1. a two-stage frame aggregation method, is characterized in that, said method comprising the steps of:

(1) set up MAC layer two dimension Markov chain model, obtain the idle probability P of network _idle, data send probability of success P in network _swith in network, there is data collision probability P _c, and the length T of the MAC layer time slot corresponding with above-mentioned network state _idle, T _sand T _c;

(2) obtain and make network saturation throughput S reach peaked A-MSDU frame length L _th;

(3) obtain and meet delay requirement D _maxa-MSDU frame length upper limit L _limit;

(4) choose described A-MSDU frame length L _thwith A-MSDU frame length upper limit L _limitin smaller as final A-MSDU frame length L _a-MSDU;

(5) according to described A-MSDU frame length L _a-MSDU, determine A-MSDU frame, realize two-stage frame aggregation;

Wherein, the described MAC of foundation layer two dimension Markov chain model specifically comprises:

1) set up the two-dimentional Markov chain that represents MAC layer state;

2) determine the single step state transition probability of described two-dimentional Markov chain;

3) by described single step state transition probability, calculate and send data probability τ;

4), according to described transmission data probability τ, obtain the idle probability P of described network _idle, data send probability of success P in described network _swith in described network, there is data collision probability P _c;

5) calculate the length T of described MAC layer time slot under heterogeneous networks state _idle, T _sand T _c;

Wherein, described in, obtain and make network saturation throughput S reach peaked A-MSDU frame length L _thbe specially:

1) calculate the valid data amount E[payload that in a time slot, network sends];

2) calculate the average duration E[slot of MAC layer time slot];

3) by described valid data amount E[payload] and described average duration E[slot] determine and to make described network saturation throughput S reach peaked A-MSDU frame length L _th.

2. a kind of two-stage frame aggregation method according to claim 1, is characterized in that, described in obtain and meet delay requirement D _maxa-MSDU frame length upper limit L _limitbe specially:

1) calculated data sends successful probability q after experience retransmits for k time _k;

2) determine the QoS parameter Q of business;

3) determine and satisfy condition minimum j value;

4) the maximum j rank time delay D of data estimator _{j, max};

5) determine described A-MSDU frame length upper limit L _limit.