reliable and real-time communication in industrial wireless mesh networks
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
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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
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Outline
Introduction Wireless Mesh Network Reliable Graph Routing
Definitions Algorithms
Conclusions References
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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 graph routing 。
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Wireless Mesh Network (1/2)
Wireless Mesh Network 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。
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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。
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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。
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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 。
Figure 1 - Source routing
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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 。
Figure 2 – Graph routing
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Network Topology
以下 (Figure 3) 是一網路拓樸
Figure 3 – Network topology
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Uplink Graph
每個裝置都有到 Gateway 的路徑,如 Figure 4 。
Figure 4 – Uplink graph
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Broadcast Graph
從 Gateway 到每個裝置的路徑,如 Figure 5 。
Figure 5 – Broadcast graph
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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 。
Figure 6 – Downlink graph
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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
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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
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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。
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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。
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Reliability Requirements and Reliable Graphs – Property 1
Property 1: GB 和 GU 都不會少於兩個AP 。
Proof: 假設只有一個 AP
v
AP
u
AP
u
v
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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 。
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Reliability Requirements and Reliable Graphs – Property 2
Property 2: GV(VV, EV) 至少包含一條有向環路。
Proof: 假設裝置 v 鄰近 AP
A1
G
A2
v
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Difficulties in Achieving Completely Reliable Graphs
Figure 7 – Success ratio vs. Edge success probability
Figure 8 - Percentage of reliable nodes
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Constructing Reliable Broadcast Graph - Algorithm
G
A A
1 2 3
4 5
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Constructing Reliable Uplink Graph - Algorithm
G
A A
1 2 3
4 5
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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 。
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Constructing Scalable Reliable Downlink Graph - constraints
u1 u2
v
C1
u1
u2
v
Gu2
C2
v
u1
u2
Gu1
C3
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Constructing Scalable Reliable Downlink Graph - Algorithm
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Constructing Scalable Reliable Downlink Graph
G
A A
1 2 3
4 5
u1 u2
v
C1u1
u2
v
Gu2
C2
v
u1
u2
Gu1
C3
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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。
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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
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Thanks for listening