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

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

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 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)

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

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

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

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

Figure 3 – Network topology

以下(Figure 3)是一網路拓樸


Uplink Graph

Figure 4 – Uplink graph

每個裝置都有到Gateway的路徑,如Figure 4。


Broadcast Graph

Figure 5 – Broadcast graph

從Gateway到每個裝置的路徑,如Figure 5。


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

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

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

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

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

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

  • 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

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

Figure 8 - Percentage of reliable nodes

Figure 7 –

Success ratio vs. Edge success probability


Constructing Reliable Broadcast Graph - Algorithm

G

A

A

1

3

2

4

5


Constructing Reliable Uplink Graph - Algorithm

G

A

A

1

3

2

4

5


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

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

G

A

A

Gu1

Gu2

u1

1

3

2

u1

u1

u2

u2

u2

4

5

v

v

v

C1

C2

C3


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

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


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