1 Network-Coding based Scheduling And Routing Schemes for Serivce- Oriented Wireless Mesh Networks Jian-Liang Pan Nguyen Thi Mai Phuong Yu-Chen Chang Tai

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Network-Coding based Scheduling And Routing Schemes for Serivce-Oriented Wireless Mesh Networks

Jian-Liang PanNguyen Thi Mai Phuong

Yu-Chen ChangTai Yang WuTai Long Chen

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Talk Outline

Introduction & Background

- Wireless Mesh Networks Mesh vs. Ad-Hoc Networks Wireless Network Coding Routing Strategies Link Scheduling & Channel Assignment Performance Evaluation

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Wireless Mesh Networks WMN - Wireless Mesh

Network: Ad-hoc network with a

core which has limited mobility

Mesh Router: A wireless base station

with limited or no mobility Infrastructure of the

network Mesh Clients:

A wireless node which is fully mobile, may also act as a router in some WMNs

Image: Indigo Systems – WMN for Environmental Monitoring

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Hybrid WMN

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Overview

Wireless routers

Gateways

Printers, servers

Mobile clients

Stationary clients

Intra-mesh wireless links

Stationary client access

Mobile client access

Internet access links

Node Types Link Types

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Gateways

Multiple interfaces (wired & wireless)

Mobility Stationary (e.g. rooftop) –

most common case Mobile (e.g., airplane,

busses/subway)

Serve as (multi-hop) “access points” to user nodes

Relatively few are needed, (can be expensive)

GW

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Wireless Router At least one wireless interface.

Mobility

Stationary (e.g. rooftop) Mobile (e.g., airplane,

busses/subway). Provide coverage (acts as a

mini-cell-tower).

Do not originate/terminate data flows

Many needed for wide areas, hence, cost can be an issue.

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Users

• Typically one interface.

• Mobility

– Stationary

– Mobile

• Connected to the mesh network through wireless routers (or directly to gateways)

• The only sources/destinations for data traffic flows in the network.

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User – Wireless Router Links• Wired

– Bus (PCI, PCMCIA, USB)– Ethernet, Firewire, etc.

• Wireless– 802.11x– Bluetooth– Proprietary

• Point-to-Point or Point-to-Multipoint

• If properly designed is not a bottleneck.

• If different from router-to-router links we’ll call them access links

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Router to Router Links

• Wireless– 802.11x– Proprietary

• Usually multipoint to multipoint– Sometimes a collection

of point to point• Often the bottleneck• If different from router-to-

user links we’ll call them backbone links

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Gateway to Internet Links• Wired

– Ethernet, TV Cable, Power Lines

• Wireless– 802.16– Proprietary

• Point to Point or Point-to-Multipoint

• We’ll call them backhaul links

• If properly designed, not the bottleneck

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How it Works

• User-Internet Data Flows– In most applications the

main data flows

• User-User Data Flows– In most applications a

small percentage of data flows

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Mesh vs. Ad-Hoc NetworksAd-Hoc Networks Wireless Mesh Networks

Multihop Nodes are wireless,

possibly mobile

May rely on infrastructure

Most traffic is user-to-user

Multihop Nodes are wireless,

some mobile, some fixed

It relies on infrastructure

Most traffic is user-to-gateway

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Abstract One of critical problem :

improve the network throughput

- Channel assignment problem Key technology: Network Coding Step1:

analyze the throughput improvement obtained by wireless network coding schemes in wireless mesh networks.

Step2:

develop a heuristic joint link scheduling, channel assignment, routing algorithm

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Wireless Network Coding

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Network coding is a particular in – network data processing technique that exploits the characteristics of the wireless medium (in particular, the broadcast communication channel) in order to increase the capacity or the throughput of the network

(Network Information Flow – Rudolf Ahlswede, Ning Cai, Shou – Yen Robert Li, Senior Member, IEEE, and Raymond W.Yeung, Senior Member, IEEE)

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Let G=(V,E) be a graph (G is the set of nodes of a point – to – point communication, E is the set of edges) with source s and sinks t1,t2, …tL.

R=[Rij,(i,j) E], Rij is the capacity of an edge (i,j) E. h is the rate of information source F=[Fij,(i,j) E] is a flow in G from s to tl (l=1,…L) if for

all (i,j) E : and for all i V except s and tl:

RijFij 0

Eiii Ejij

ijii FF),'(:' ),(:

'

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F is a max-flow from s to tl in G if F is a flow from s to tl whose value is greater than equal to any other flow from s to tl

Max – Flow Min – Cut theorem:

Let G = (V,E) be a graph with source s and sinks t1,…,tL, and the capacity of an edge (i,j) be denoted by Rij. (R,h,G) is admissible if and only if the values of a max – flow from s to tl are greater than or equal to h

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A total of 9 bits are sent (network coding) If network coding is not allowed, at least one more bit

has to be sent

=> Saving 10% bandwidth

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Using the scheme in fig.8(b), if 2 bits are sent in each edge, then 4 bits can be multicast to all the sinks

If network coding is not allowed: Let B = {b1,…,bk} be the set of bits to be multicast to all the

sinks.

Let the set of bits sent in the edge (s,i) be Bi, where |Bi| = 2,

i = 1, 2, 3

B = Bi Bj for any

We have:

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31 ji

BBBBBBBB )()()( 2313213


Therefore:

k 3 or if network coding is not allowed, only 3 bits can be multicast to all sinks (if 2 bits are sent in each edge)

=> Throughput of network can be increased by one-third using a very simple network code

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k

BBBBB

BBB

BBBk

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||||||||

||||

|)(|

21213

213

213


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Butterfly Network

When two or more signal transmission path of partial overlap ， Encoded to improve the signal transmission rate of the technology can be called 「 common path coding 」

Each arrow indicates assumed to send a signal ， the signal value is 0 or 1 ， A point given by the two signals x and y ， should be sent to the B point and C point.

Let M points x and y send a representative to the similarities and differences of the signal ， when the B point to receive this signal and x, can be solved y; Similarly, C-point can also be solved x.

Graph signal x y ⊕ ， x y is ⊕called 「 binary sum 」， it not only represents a coded form, is also a mathematical "linear" code.

Oct. 23, 2007 28

Use network coding ， the encoding method has three restrictions:

1. Each encoded packet must be the linear independence.

2. The node after the packet encoded into the nodes need to encode packets with each other linearly independent .

3. Enter the node will be re-encoded packets and transmitted.

Linear Network Coding

P1 ， P2 ， ‧ ‧ ‧ ‧ ‧ ‧ Pn the packets for the node Se = {e1, e2, e3 en} is coded coefficients‧ ‧ ‧ ‧ ‧ ‧

Figure (2), (3) is linear combination of matrix encoding.

Linear Network Decoding

The coefficient matrix is converted into an anti-matrix, the re-encoded packet multiplied by the value of the packet can be restored.

Network coding of fault tolerance

反矩陣的算法 ( 一 ) : 高斯消去法

步驟 : ( 步驟 1) 將單位矩陣 In連接於所給矩陣 A 之後

[A In] ( 步驟 2) 利用高斯消去法將步驟 1 中的 A 矩陣化成單位矩

陣 In

求 A-1的教學範例 : 求出矩陣 A 的反矩陣，

反矩陣的算法 ( 二 )

伴隨矩陣 (adj A)

餘因子 (cofactor) Aij:

伴隨矩陣 (adj A) 的算法

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Routing Strategies

Two types ： Shortest single-path routing

Optimized single-path routing

Shortest single-path routing

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● In particular, single-path routing can be obtained by

Dijkstra’s algorithm.

Dijkstra’s Algorithm

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Initial


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Finish

Optimized single-path routing

Select the path that provides the maximum flow in the

multipath routing for each session and following two

steps ：

Solve the LP with multipath routing. For each session, we

select the path that achieves the highest flow.

Input these obtained optimized single-path routes for each

session to the LP and re-solve the LP.

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Link Scheduling

Let Ts (Ts ≥ 1) be this period of time in the unit of time

slots. Thus, we can update the channel assignment every

Ts time slots.

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Channel Assignment

Note that the problem of optimal channel assignments is NP-hard.

Therefore design a heuristic greedy algorithm to obtain the schedule, which approximates the optimal solution derived by the LP.

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Channel Assignment (Cont.)

The NC links combinations with larger unassigned flows

have higher priority to select the channels.

After going through all the NC traffic and all the links for

the unicast traffic, we check if there are still unassigned

flows. If so, we move on to the next Ts time slots and

repeat the scheduling process until all unassigned flows

become zero.

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PERFORMANCE EVALUATION

We solve the linear program to obtain the theoretically optimized network throughputs and the corresponding flows for the non-NC scheme , conventional NC scheme, NC3 scheme, and NC5 scheme.

multipath routing can significantly increase the network throughput gain as compared to single-path routing.

NC5 and NC3 can increase network throughput by 24 and18 percent

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The network throughput gain of wireless NC schemes over over the non-NC scheme in the random graph network with 34 nodes the non-NC scheme in the random graph network with 34 nodes.

The impact of routing strategies on network throughput.

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The performance impact of multichannel and multiradio in the random graph network where there are 20 unicast sessions.

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CONCLUSIONS

the analog NC scheme increases by 24 and 34 percent on average as compared to the conventional NC scheme and non-NC scheme, respectively.

We modeled the throughput gains of both the

conventional NC and analog NC schemes over

the traditional non-NC scheme in multichannel

multiradio wireless mesh networks.

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Thank you!

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Documents

1 Network-Coding based Scheduling And Routing Schemes for Serivce- Oriented Wireless Mesh Networks Jian-Liang Pan Nguyen Thi Mai Phuong Yu-Chen Chang Tai