Reliable and real time communication in industrial wireless mesh networks
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Reliable and Real-time Communication in Industrial Wireless Mesh Networks. Speaker : Chih-Ching Chen Advisor : Dr. Ho-Ting Wu 2014/10/21. Outline. Introduction Wireless Mesh Network Reliable Graph Routing Definitions Algorithms Conclusions References. Introduction.

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Reliable and Real-time Communication in Industrial Wireless Mesh Networks

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Reliable and real time communication in industrial wireless mesh networks

Reliable and Real-time Communication in Industrial Wireless Mesh Networks

Speaker : Chih-Ching Chen

Advisor : Dr. Ho-Ting Wu

2014/10/21


Outline

Outline

  • Introduction

  • Wireless Mesh Network

  • Reliable Graph Routing

    • Definitions

    • Algorithms

  • Conclusions

  • References


Introduction

Introduction

Wireless Mesh Network具有與傳統有線網路截然不同的特性,包括隨時可能改變的網路型態、沒有方向或範圍限制的移動等,因此,它需要一種新的路由協定(Routing Protocol)來替這些Node(節點)找出彼此聯繫的路徑。

在無線網路的環境中,時常會因為距離和雜訊的影響下而導致資料無法成功傳送,為了確保資料傳送的成功率上升,這裡敘述如何建立 reliable graphrouting。


Wireless mesh network 1 2

Wireless Mesh Network(1/2)

Wireless MeshNetwork是一種完全無線、可任意移動的網路架構,不需要基地台,所有Node可以任意地進行連結,且每個Node同時具有Router(路由器)的功能。


Wireless mesh network 2 2

Wireless Mesh Network (2/2)

在Wireless Mesh Network網路架構中,當其中一個Node發生問題,其他與它相連的Node會自動找到其他的Node代替,也就是說,Wireless Mesh Network不會因為一個Node無法發揮作用,就導致該Node以下的全部Node都跟著失去作用,而使用者可視情況需要隨時新增或移除一個Node,非常方便。

同時每個Node都必須擁有動態的Routing能力,讓每個裝置在接收訊息的時候,都能判斷這個訊息是“接收這個訊息”或是“傳給下一個Node”,訊息也就是利用這樣的方式傳送到目的地。


Reliable graph routing

Reliable Graph Routing

為了增加傳送的資料可以到達目的地的成功率,這裡定義一些關於 Reliable Graph Routing 的概念。


Source routing

Source Routing

Figure 1 - Source routing

來源裝置到目的裝置在傳送資料之前先決定一條繞送方式,之後傳送資料只能依照此路徑傳送,

如Figure 1。


Graph routing

Graph Routing

Figure 2 – Graph routing

來源裝置到目的裝置能夠在傳送資料的過程中,選擇繞送的方式,如Figure 2。


Network topology

Network Topology

Figure 3 – Network topology

以下(Figure 3)是一網路拓樸


Uplink graph

Uplink Graph

Figure 4 – Uplink graph

每個裝置都有到Gateway的路徑,如Figure 4。


Broadcast graph

Broadcast Graph

Figure 5 – Broadcast graph

從Gateway到每個裝置的路徑,如Figure 5。


Downlink graph

Downlink Graph

Figure 6 – Downlink graph

從Gateway到其中一個裝置的路徑,如Figure 6所示,實線為Gateway到裝置4,虛線為Gateway到裝置3。


Notations

Notations

G(V, E): original network topology (Figure 3)

GU(VU, EU): uplink graph (Figure 4)

GB(VB, EB): broadcast graph (Figure 5)

GV(VV, EV): downlink graph (Figure 6)

δi-: device i有多少 incoming degree

δi+: device i有多少 outgoing degree


Reliability requirements and reliable graphs definition 1

Reliability Requirements and Reliable Graphs – Definition 1

Definition 1: 一有向圖 G(V, E)的所有節點v必須滿足 (k, m)-reliability 且 δv-≧k, δv+≧m。

若k = 0, δv-則沒有限制

若m = 0, δv+則沒有限制


Reliability requirements and reliable graphs definition 2

Reliability Requirements and Reliable Graphs – Definition 2

Definition 2: 從有向圖G(V, E)找到一有向無環圖GB(VB, EB)(其中 VB= V, EB為E的子集合),此圖符合 (2, 0)-reliability 則是一 reliable broadcast graph,其中Gateway和AP不在此限制。


Reliability requirements and reliable graphs definition 3

Reliability Requirements and Reliable Graphs – Definition 3

Definition 3:從有向圖G(V, E)找到一有向無環圖GU(VU, EU)(其中 VU= V, EU為E的子集合),此圖符合 (0, 2)-reliability 則是一 reliable broadcast graph,其中Gateway和AP不在此限制。


Reliability requirements and reliable graphs property 1

Reliability Requirements and Reliable Graphs – Property 1

AP

AP

u

u

v

v

Property1: GB和 GU都不會少於兩個AP。

Proof: 假設只有一個AP


Reliability requirements and reliable graphs definition 4

Reliability Requirements and Reliable Graphs – Definition 4

  • Definition 4:從有向圖G(V, E)找到一圖GV(VV, EV)(其中 VV為V的子集合, EV為E的子集合)。

    • 其中節點v是唯一的目的端,Gateway是唯一的來源端

    • 每一個中繼節點必須符合 (0, 2)-reliability

    • 環路的長度必須為2,並且在環路中的節點要有一條方向往節點v

  • 符合以上三項條件則是一 reliable download graph。


Reliability requirements and reliable graphs property 2

Reliability Requirements and Reliable Graphs – Property 2

G

A1

A2

v

Property 2: GV(VV, EV) 至少包含一條有向環路。

Proof: 假設裝置v鄰近AP


Difficulties in achieving completely reliable graphs

Difficulties in Achieving Completely Reliable Graphs

Figure 8 - Percentage of reliable nodes

Figure 7 –

Success ratio vs. Edge success probability


Constructing reliable broadcast graph algorithm

Constructing Reliable Broadcast Graph - Algorithm

G

A

A

1

3

2

4

5


Constructing reliable uplink graph algorithm

Constructing Reliable Uplink Graph - Algorithm

G

A

A

1

3

2

4

5


Constructing scalable reliable downlink graph

Constructing Scalable Reliable Downlink Graph

為什麼不是“Constructing Reliable Downlink Graph”?

因為有n個裝置要從G(V, E)找到n個GV(VV, EV) 會造成網路上不必要的配置開銷,並且考慮到裝置v的前一跳的節點若已經建立了自己的 reliable downlink graph,為何不將此 graph “reuse”則能減少網路上的配置開銷,還能夠建立裝置v的reliable downlink graph。


Constructing scalable reliable downlink graph constraints

Constructing Scalable Reliable Downlink Graph- constraints

Gu1

Gu2

u1

u1

u1

u2

u2

u2

v

v

v

C1

C2

C3


Constructing scalable reliable downlink graph algorithm

Constructing Scalable Reliable Downlink Graph - Algorithm


Constructing scalable reliable downlink graph1

Constructing Scalable Reliable Downlink Graph

G

A

A

Gu1

Gu2

u1

1

3

2

u1

u1

u2

u2

u2

4

5

v

v

v

C1

C2

C3


Conclusions

Conclusions

以上說明的這些演算法可以找到比較可靠的繞送方式,但對於比較邊緣裝置的可靠度較低,甚至只有一條連結可以連接,對此裝置的Packet delivery ratio (PDR)會比其他裝置還要低。

當底層使用TDMA的架構進行傳輸,在此並未詳細說明時槽的規劃。

假設在時槽規劃上,勢必會浪費一些時槽,但可以確保PDR會有所上升。


References

References

Song Han, Xiuming Zhu, Aloysius K. Mok, Deji Chen, Mark Nixon, “Reliable and Real-time Communication in Industrial Wireless Mesh Networks,” Real-Time and Embedded Technology and Applications Symposium (RTAS), 2011 17th IEEE, pp. 3-12, April 2011.

WirelessHART, 2010 International Electrotechnical Commission, IEC 62591.

無線網狀網路http://www.gss.com.tw/index.php/focus/eis/76-eis43/476-wireless-mesh-network


Thanks for listening

Thanks for listening


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