Joint Scheduling and Power Control for Wireless Ad Hoc Networks

Advisor: 王瑞騰Student: 黃軍翰

Introduction Infrastructure Wireless Networks

Wired Network

Access Point Access Point

Introduction Ad Hoc Wireless Networks

Abstract In this paper,we introduce a cross-layer design frame

work to the multiple access problem in contention-based wireless ad hoc networks.

The motivation for this study is twofold, limiting multiuser interference to increase single-hop

throughput and reducing power consumption to prolong battery life.

We focus on next neighbor transmissions where nodes are required to send information packets to their respective receivers subject to a constraint on the signal-to interference-and-noise ratio.

ASSUMPTIONS AND DEFINITIONS Consider a wireless ad hoc network consisting of n

nodes. Each node is supported by an omni-directional ante

nna. Each node knows the geographical location of all ot

her nodes Routing is not considered in this study.

The effect of users’ mobility is not considered in this study.

ASSUMPTIONS AND DEFINITIONS Assume that all nodes share the same frequency band,

and time is divided into equal size slots that are grouped into frames

The slot duration is assumed to be larger than the packet duration by an interval called a “guard band.”

In this study, we assume that the frame lengthis fixed throughout system operation.

Each node generates information packets of fixed length, destined to all other nodes, according to a Poisson distribution with aggregate rate λ packets/second.

ASSUMPTIONS AND DEFINITIONS We assume that each generated packet is

intended for a single neighbor only We assume a maximum power level, denoted

PMAX, that a node can use for transmission. assume that the transmission range of any

node is limited (typically circular) and beyond that range no interference

The power decay law is assumed to be inversely proportional to the fourth order of the distance between the transmitter and the receiver.

ASSUMPTIONS AND DEFINITIONS

We assume the existence of a separate feedback channel that enables receivers to send their SINR measurements to their respective transmitters in a contention-free manner

We assume the existence of a central controller responsible for executing the scheduling algorithms

Define the average slot throughout as the long-run average of the percentage of packets successfully received by single-hop neighbors in each time slot.

Algorithm Description The proposed algorithm determines the admissible set

of users that can safely transmit in the current slot without disrupting each other’s transmission. Accordingly, the objective is twofold

1. determine the set of users who can attempt transmission simultaneously in a given slot

2. specify the set of powers needed in order to satisfy SINR constraints at their respective receivers.

Algorithm Description Definition 1: In TDMA wireless ad hoc networks, a transmissio

n scenario is valid iff it satisfies the following three conditions.1. A node is not allowed to transmit and receive si

multaneously.2. A node cannot receive from more than one neig

hbor at the same time.3. A node receiving from a neighbor should be spa

tially separated from any other transmitter by at least a distance D.

5

4

3

2

1

6

7

i

j

k

x

dkx<dkj , D=dkx

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1

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dkx<dkj , D=dkx

i

j

k

x

Algorithm Description Definition 2: A transmission scenario involving

m links is admissible iff there is a set of transmission powers,pij≧0 ,which solves the following minimization problem:

s.t

minij

ijPm links

P

ijSINR ij links

DISTRIBUTED POWER CONTROL(TDMA Wireless Ad Hoc Networks)

max( 1) min , ( )( )i ii

P N P P NSINR N

Where

Pi power transmitted by node to its receiver

SINRi signal-to-interference-and-noise ratio at BS

N iteration number.

Algorithm DescriptionGiven a

transmission scenario in slot i

Is this scenario Valid?

Search for the optimum valid subset of users

Run the Distributed Power Control algorithm for this

valid scenario

Is the Valid scenario

Admissible

Nodes use the obtained set of powers to send

their packets

Go to next slot i = i+1

Search for the optimum

admissible subset of users

Scheduling Policies It is evident from the proposed algorithm that the

objective is to pack the maximum number of transmissions that can be successfully detected at their respective receivers in each slot.

The scheduling algorithm is responsible for solving two optimization problems, namely “valid scenario optimization” and “admissible scenario optimization”

Scheduling Policies valid scenario optimization

s.t.

INV:invalid transmission scenario admissible scenario optimization

s.t.

INA:vaild,yet inadmissable transmission scenario

max

SS

S INV

S is a valid scenario

max

Z

Z

ZZ

INA

is a admissible scenario

5

4

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1

6

7

Node 1 2 3 4 5 6 7

7 7 2 3 6 7 4

Node 1 2 3 4 5 6 7

7 7 2 3 6 7 47 0 2 3 6 0 0

7 0 2 0 6 0 0

0 7 0 3 6 0 0

Node 1 2 3 4 5 6 7

7 7 2 3 6 7 4

7 0 2 0 6 0 0~3

0 7 0 3 6 0 0~3

0 0 2 0 6 0 4~3

7 0 0 3 6 0 0~3

0 0 2 0 6 0 4~3

0 0 2 0 0 7 0~2

0 0 2 0 6 0 4~3

5

4

3

2

1

6

7

Node 1 2 3 4 5 6 7

7 0 2 0 6 0 0

dkx<dkj

Node 1 2 3 4 5 6 7

7 0 0 0 0 0 0

5

4

3

2

1

6

7

Node 1 2 3 4 5 6 7

0 7 0 3 6 0 0

dkx<dkj

Node 1 2 3 4 5 6 7

0 7 0 0 0 0 0

5

4

3

2

1

6

7

Node 1 2 3 4 5 6 7

0 0 2 0 6 0 4

dkx<dkj

Node 1 2 3 4 5 6 7

0 0 0 0 6 0 4

Node 1 2 3 4 5 6 7

7 7 2 3 6 7 4

7 0 2 0 6 0 0~3

0 7 0 3 6 0 0~3

0 0 2 0 6 0 4~3

7 0 0 3 6 0 0~3

0 0 2 0 6 0 4~3

0 0 2 0 0 7 0~2

0 0 2 0 6 0 4~3

Node 1 2 3 4 5 6 7

7 7 2 3 6 7 4

7 0 0 0 0 0 0~1

0 7 0 0 0 0 0~1

0 0 0 0 6 0 4~2

7 0 0 0 0 0 0~1

0 0 0 0 6 0 4~2

0 0 2 0 0 0 0~1

0 0 0 0 6 0 4~2

5

4

3

2

1

6

7

Simulation Parameters

Number of nodes(n) 7

Slot Duration 2 msec

Frame Length 3 slots

Packet Inter-Arrival Time(1/λ) 6,7,..20 msec

SINR Threshold(β) 5

Noise Variance(σ2) 3.5

Maximum Power (Pmax) 100

Maximum Number of Iterations 30

Simulation

Simulation

Simulation

Simulation

Simulation

Simulation

Simulation

References [1] L. Williams, “Technology advances from small unit operations sit

uation awareness system development,” IEEE Personal Commun. Mag.pp. 30–33, Feb. 2001

[2] M. Mauve, J.Widmer, and H. Hartenstein, “A survey on position-based routing in mobile ad hoc networks,” IEEE Networks, pp. 30–39,Nov./Dec. 2001.

[3] Tamer Elbatt,Anthony Ephremides,”Joint Scheduling and Power Control for Wireless Ad Hoc Networks” IEEE Trans. Commun,vol.3no.1,January 2004

[4] S. Ulukus and R. Yates, “Stochastic power control for cellular radio systems,”IEEE Trans. Commun., vol. 46, pp. 784–798, June 1998.