DARP: Distance-Aware Relay Placement in WiMAX Mesh Networks

Weiyi Zhang*, Shi Bai*, Guoliang Xue§, Jian Tang†, Chonggang Wang‡

* Department of Computer Science, North Dakota State University, Fargo§ Department of Computer Science and Engineering, Arizona State University, Tempe

† Department of Electrical Engineering and Computer Science, Syracuse University, Syracuse‡ NEC Laboratories America, Princeton, USA

IEEE INFOCOM 2011

Outline

• Introduction

• Motivation & Problem

• Observation & Goals

• System Model

• Solution for DARP: Distance-Aware Relay station Placement– LORC-MIS // lower tier

– LORC-HS // lower tier

– MUST // upper tier

• Simulation

• Conclusion

Introduction

• The emerging WiMAX technology is the 4G standard for– high-speed (up to 75Mbps)

– long-range communications

BSSS

SS

SS

Introduction

• IEEE 802.16j enhances IEEE 802.16e by the concept of mesh networks– Base Station (BS)

– Relay Station (RS)

– Subscriber Station (SS)

BS

RS

SSRS

SS

SS

• WiMAX 802.16j Relay Station– eliminate coverage hole

– Range extension

Introduction

InternetCoverageExtension

Coverage Hole

Mobile Access

BuildingPenetration

SS

RS

BS

RS

RS

RS

SS

• n Subscriber Stations (SS)– different user data rate requests

• Problem:– finding where to place a minimum number of relay nodes

– to satisfy the certain performance requests

Motivation

SS BSSS

SS

SS

SS

Observation – distance aware

• Signal to noise ratio (SNR) at receiver– SNRr = Pr / N0

– Pr : power level at the receiver

– N0 : noise power is normally a constant

SS user data rate requests: 35 Mbps

Observation – distance aware

• Two-ray ground path loss model– Pr = Pt Gt Gr Ht

2 Hr2 d -

– Pt : Transmission power (constant)

– Gt / Gr : gains of transmitter/receiver antenna (constant)

– Ht /Hr : heights of transmitter/receiver antenna (constant)

– d : Euclidean distance between transmitter and receiver : attenuation factor (constant : 2~4)

SS SS

higher data rate request lower data rate request

Goals

• Given a WiMAX mesh network– One BS

– A set of SSs, S = {s1, s2, …, Sn}

– A set of distance requirements for the SSs, D = {d1, d2, …, dn}

SS

BS

SS

Goals

• Solve the distance-aware relay placement (DARP) problem by a minimum number of RSs– Providing feasible coverage for each SS

• covered by at least one RS or BS

– Each placed RS has enough data rate to relay traffic for each SS or another RS

SSSS

BS

25 Mbps

RS

25 Mbps

System Model

• A WiMAX mesh network– n SSs, S = {s1, s2, …, Sn}

• Distance requirements D = {d1, d2, …, dn}

• No routing and traffic relay capabilities

– BS, is aware of the location and distance requirement of each SS

SS

BS

SS

Solution for DARP problem

• Two-tiered relay model

SS

SS

BS

RS

lower tier

upper tier

LORC-MISLORC-HS

MUST

LORC-MIS

• LORC-MIS– LOwer-tier Relay Coverage –

Maximal Independent Set based approximation solution

SS

SS

lower tier

LORC-MIS

• First consider the SS with the smallest distance requirement– Highest user data rate requirement

12

34

5C4

C5

C3

C1 C2

d2

d1

d3

d4d5

LORC-MIS

• Construct a regular hexagon with 7 possible positions

S2 d2

A2H

23d 23d

F2H C

2H

B2H

E2H D

2H

3d

d

LORC-MIS

• Choose the point which covers most SSs

A2H

F2H

E2H

D2H

C2H

B2H

A5H B

5H

C5H

D5HE

5H

F5H

S2

S5

S1

S4 S3

• LORC-HS– LOwer-tier Relay Coverage –

Hitting Set based approximation solution

LORC-HS

SS

SS

lower tier

LORC-HS

• Find the Minimum hitting set– to cover all SSs // {p0, p2}

– admits PTAS [18]

s2s1

s3

p3p1

p0

p7p6

p2

p4 p5s0

S0={p0, p1}S1={p0, p1 , p2 , p3 , p4 , p5 , p7}S2={p2, p3 , p4 , p5 , p6}S3={p2, p4 , p5 , p6 , p7}

[18] N. Mustafa and S. Ray, PTAS for geometric hitting set problems via local search, SCG’09, pp. 17-22.

MUST

• Minimum Upper-tier Steiner Tree

upper tier

BS

RS

MUST

• The “MUST” ensures data rate for each individual SS or RS

RS3

RS1

RS2

BS

A B

C

15

15

1516

18

18

MUST

• Construct a complete graph

• Assign edge weight w– Number of RSs

RS1 RS2

BS

d1=10

w=3

d2=5

10

20 21

16

5

w=4

w=3

min

( , )( , ) 1

i j

i j

e x xw x x

d

min min 5ii Sd d

MUST

• Minimum spanning tree

min

( , )( , ) 1

i j

i j

e x xw x x

d

min min 5ii Sd d

RS1 RS2

BS

d1=5

w=3

d2=5

20

16

w=3

MUST

• Place RSs on edges

RS1 RS2

BS

d1=5

w=3

d2=5

20

16

w=3

5

4

5

5

5

4 4 4

Simulation Setup

• SSs are uniformly distributed in a square playing ground– 20002000

– 30003000

• Distance requirements randomly distributed in [100,150]

• BS is deployed at the center of the field

• All figures illustrate the average of 10 test runs for various scenarios

Simulation

Simulation – lower-tier relay coverage

Simulation – upper-tier relay connectivity

Simulation

Simulation

Conclusion

• This paper studies the Distance-Aware Relay Placement (DARP) problem– Multi-hop relay placement

– Relay coverage

– Relay connectivity

TheENDThanks for your attention !