CN102497251A - Adaptive modulation coding method in wireless MESH network - Google Patents

Abstract

The invention relates to an adaptive modulation coding method in a wireless MESH network. The method is characterized in that: the rate of the system is chosen according to the channel state of a physical layer and the data buffer queue length of a link layer; when the buffer queue length of the link layer is less than the rate which can be chosen by a channel, a minimum rate which is more than the buffer length is chosen to perform transmission; a new design variable is imported in a rate choosing mechanism simultaneously; two threshold values (Lthr, Uthr) are set in a queue; when the number of data packets in the queue is more than the Uthr, an excessive packet rate is reduced by increasing a transmission rate; when the number of data packets in the queue is less than the Lthr, a packet error rate is reduced by reducing the transmission rate; and the total throughput performance of the system is improved by compromising the excessive packet rate and the packet error rate.

Description

Adaptive modulation coding method in a kind of Wireless MESH net

Technical field

The present invention relates to adaptive modulation coding method in a kind of Wireless MESH net.

Background technology

Wireless Mesh netword has become the key technology of Radio Access Network of future generation, the emphasis that its capacity problem is studied especially owing to its many advantages.The main application of wireless Mesh netword is that node is closed through netted connection access network, from the relaying of gateway node far away through other node data are sent to gateway, so data flow occurs in mainly between gateway node and other node.This makes network traffics have the inhomogeneous characteristic that converges along the Mesh path to a certain extent, thereby the network throughput performance is impacted.

Adaptive modulation technology is a kind of layer technology of striding that can effectively increase network utilization; It is widely used; But traditional adaptive modulation technology is just selected transmission rate according to the channel status of physical layer, does not have well to unite the parameter of other layers, and this has limited its performance to a certain extent.

Summary of the invention

For avoiding the deficiency of above prior art, the present invention proposes adaptive modulation coding method in a kind of Wireless MESH net, unites the parameter of having considered physical layer and data link layer, can better improve network performance.

The object of the invention is realized through following technical scheme:

Adaptive Modulation and Coding new method in the Wireless MESH net, this method is:

1) definite Adaptive Modulation pattern of selecting;

2) obtain the buffering area queue length of link layer and the signal to noise ratio size of physical layer;

3) judge the speed that the Adaptive Modulation lower channel is selected according to the signal to noise ratio size of physical layer;

4) when speed that the buffering area queue length of link layer is selected less than channel, adopt and transmit greater than the minimum transmission rate of buffering area queue length, said minimum transmission rate does

The preliminary improvement transmission rate that obtains system is: $c^{\left(1\right)}(n,k)=\left\{\begin{array}{cc}R\left(n\right),& \mathrm{If\; c}\left(n\right)\≤k\\ R\left(\mathrm{\σ}\right),& \mathrm{If\; c}\left(n\right)>k\end{array}\right.;$ N is the concrete pattern of the Adaptive Modulation that adopted, and k is the buffering area queue length;

5) length to the buffering area formation is provided with two length threshold (L _Thr, U _Thr), the relation of judgement buffering area queue length and two length thresholds is as queue length＞U _ThrThe time, the transmission rate of raising system; As queue length＜L _ThrThe time, the transmission rate of reduction system; The improvement transmission rate that further obtains system does

The invention has the advantages that:

This self-adaptive modulation method of the present invention has been united the channel status of physical layer and the data buffer zone queue length of link layer system's speed has been selected., select to transmit during in the buffering area queue length greater than the minimum speed of buffer length less than the selectable speed of channel.In rate selection mechanism, introduce new design variable simultaneously.In formation, set 2 threshold value (L _Thr, U _Thr), the more (＞U of packet in formation _Thr) time reduce the bag rate of overflowing through improving transmission rate; The less (＜L of packet in formation _Thr) time reduce Packet Error Ratio through reducing transmission rate.Through overflowing the compromise of bag rate and Packet Error Ratio, the throughput performance that the raising system is total.

Description of drawings

Fig. 1: the inventive method flow chart;

Fig. 2: three node multihop network system models;

Fig. 3: the target Packet Error Ratio is 0.01 o'clock performance evaluation figure of the present invention;

Fig. 4: the target Packet Error Ratio is 0.001 o'clock performance evaluation figure of the present invention.

Embodiment

Fig. 1 is the inventive method flow chart, is elaborated in the face of adaptive modulation coding method in this Wireless MESH net of the present invention down.

Owing to when channel status is good, adopt Adaptive Modulation that system can two-forty be transmitted, but the Packet Error Ratio of system is raise.Therefore, select to transmit during in the buffering area queue length, so not only can not influence the data amount transmitted of system, can also reduce the Packet Error Ratio of network greater than the minimum speed of buffer length less than the selectable speed of channel, thus the raising network throughput.The system speed of setting up departments be c (n, k), the buffering area queue length is k, its rate selection mode can be expressed as:

$c(n,k)=\left\{\begin{array}{cc}R\left(n\right),& \mathrm{if\; c}\left(n\right)\≤k\\ R\left(\mathrm{\σ}\right),& \mathrm{if\; c}\left(n\right)>k\end{array}\right.---\left(1\right)$

Wherein,

is the minimum speed more than or equal to queue length.

Above-mentioned improvement has mainly reduced the Packet Error Ratio of system; Therefore under the big situation of Packet Error Ratio, this method can effectively improve systematic function, but at Packet Error Ratio hour; The bag rate of overflowing plays a decisive role to packet loss; Improvement is little to the influence of systematic function, therefore considers on this preliminary improved basis, once more rate selection mechanism to be improved.Introduce new design variable, obtain optimal transmission rate, make network throughput maximum.

On above-mentioned improved basis, in rate selection mechanism, introduce new design variable.Pooled buffers queue length and channel selection modes are set 2 threshold value (L in formation _Thr, U _Thr), the more (＞U of packet in formation _Thr) time reduce the bag rate of overflowing through improving transmission rate; The less (＜L of packet in formation _Thr) time reduce Packet Error Ratio through reducing transmission rate.Through overflowing the compromise of bag rate and Packet Error Ratio, the throughput performance that the raising system is total.Based on above-mentioned principle, can the rate selection mechanism table be shown:

Be the correctness of checking the invention described above, the present invention verified as follows:

(1) as shown in Figure 2, the multihop network to three nodes carries out modeling earlier:

To the performance of Wireless Mesh network multi-hop, we consider the multihop network of one three node, and like Fig. 2, node A, B have data to be sent to base station BS, and Node B is served as the via node of node A.The tentation data bag is regular length, and the number of data packets that in the unit interval, arrives node A and Node B all obeys the Possion distribution, and its parameter is respectively λ _AAnd λ _B, suppose that simultaneously the buffer length of node A and Node B is respectively K _AAnd K _B, and Node B does not add the two kinds of packets of treating of differentiation.

(2) jump network to three and carry out performance evaluation, obtain the expression formula of network throughput:

Be the total throughput performance of phase-split network, at first should obtain the inlet flow situation of Node B.We adopt a kind of new layer multi-hop queuing model of striding, and the output stream that calculates A earlier distributes, and the output stream according to node A distributes again, and the inlet flow that obtains Node B distributes, thereby can further go to find the solution the throughput performance that the base station is located with the method for queueing theory.

When the inlet flow distribution obedience parameter of node A was the Poisson distribution of λ A, the steady-state distribution of its output flow was P, and the output speed average is:

$E\left\{{\mathrm{\μ}}_A\right\}=\underset{n=0}{\overset{c_N}{\mathrm{\Σ}}}\mathrm{n\; P}({\mathrm{\μ}}_A=n)---\left(3\right)$

Because being input to the packet of Node B is by constituting jointly from the packet of node A and the packet of Node B itself.The bag arrival rate of supposing Node B itself is λ _B, the packet that therefore in time slot t, arrives Node B adds up to

It distributes as follows:

$P({\mathrm{\Θ}}_i^B=a)=\underset{i=0}{\overset{a}{\mathrm{\Σ}}}\frac{{\mathrm{\λ}}_B^i{e}^{-{\mathrm{\λ}}_B}}{i!}P({\mathrm{\μ}}_A=a-i)---\left(4\right)$

After obtaining inlet flow that B orders and distributing, can analyze and obtain multihop network packet loss performance (comprise overflow and miss the two kinds of situation of wrapping) and throughput performance:

ξ＝1-(1-P _d)(1-P ₀) (5)

η＝E{Θ _B}(1-ξ)＝(λ _B+E{u _A})·(1-ξ)

Simulation result such as Fig. 3 and 4, as can be seen from the figure, the adaptive modulation technology that the present invention proposes can effectively improve the throughput performance of network.

Should be appreciated that the above detailed description of technical scheme of the present invention being carried out by preferred embodiment is schematic and nonrestrictive.Those of ordinary skill in the art is reading on the basis of specification of the present invention and can make amendment to the technical scheme that each embodiment put down in writing, and perhaps part technical characterictic wherein is equal to replacement; And these are revised or replacement, do not make the spirit and the scope of the essence disengaging various embodiments of the present invention technical scheme of relevant art scheme.

Claims (1)

1. Adaptive Modulation and Coding new method in the Wireless MESH net is characterized in that, this method is:

1) definite Adaptive Modulation pattern of selecting;

2) obtain the buffering area queue length of link layer and the signal to noise ratio size of physical layer;

3) judge the speed that the Adaptive Modulation lower channel is selected according to the signal to noise ratio size of physical layer;

4) when speed that the buffering area queue length of link layer is selected less than channel, adopt and transmit greater than the minimum transmission rate of buffering area queue length, said minimum transmission rate does

The preliminary improvement transmission rate that obtains system is: $c^{\left(1\right)}(n,k)=\left\{\begin{array}{cc}R\left(n\right),& \mathrm{If\; c}\left(n\right)\≤k\\ R\left(\mathrm{\σ}\right),& \mathrm{If\; c}\left(n\right)>k\end{array}\right.;$ N is the concrete pattern of the Adaptive Modulation that adopted, and k is the buffering area queue length;

5) length to the buffering area formation is provided with two length threshold (L _Thr, U _Thr), the relation of judgement buffering area queue length and two length thresholds is as queue length＞U _ThrThe time, the transmission rate of raising system; As queue length＜L _ThrThe time, the transmission rate of reduction system; The improvement transmission rate that further obtains system does

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