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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. 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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  1. Reliable and Real-time Communication in Industrial Wireless Mesh Networks Speaker : Chih-Ching Chen Advisor : Dr. Ho-Ting Wu 2014/10/21

  2. Outline • Introduction • Wireless Mesh Network • Reliable Graph Routing • Definitions • Algorithms • Conclusions • References

  3. 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。

  4. 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。

  5. 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。

  6. 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。

  7. 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。

  8. 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。

  9. Network Topology Figure 3 – Network topology 以下(Figure 3)是一網路拓樸

  10. Uplink Graph Figure 4 – Uplink graph 每個裝置都有到Gateway的路徑，如Figure 4。

  11. Broadcast Graph Figure 5 – Broadcast graph 從Gateway到每個裝置的路徑，如Figure 5。

  12. 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。

  13. 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

  14. 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

  15. 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。

  16. 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。

  17. 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

  18. 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。

  19. 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

  20. Difficulties in Achieving Completely Reliable Graphs Figure 8 - Percentage of reliable nodes Figure 7 – Success ratio vs. Edge success probability

  21. Constructing Reliable Broadcast Graph - Algorithm G A A 1 3 2 4 5

  22. Constructing Reliable Uplink Graph - Algorithm G A A 1 3 2 4 5

  23. 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。

  24. Constructing Scalable Reliable Downlink Graph- constraints Gu1 Gu2 u1 u1 u1 u2 u2 u2 v v v C1 C2 C3

  25. Constructing Scalable Reliable Downlink Graph - Algorithm

  26. 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

  27. 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。

  28. 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

  29. Thanks for listening

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