20080331 E3 ASMOFDMA WCNC LasVegas Slides2spectru (2)

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Advanced Spectrum Management in

Multicell OFDMA Networks enablingCognitive Radio Usage

F. Bernardo, J. Pérez-Romero, O. Sallent, R. Agustí

Radio Communications Group

Dept. of Signal Theory and Communications

Universitat Politècnica de Catalunya (Spain)



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Francisco Bernardo Álvarez WCNC 2008 Las Vegas, USA, 03/April/2008 2/24

Outline

Introduction

Proposed ASM Framework

Proposed DSA Algorithm

Simulation Model

Results

Conclusions

Future work





Outline

Introduction



Simulation Model

Results

Conclusions

Future work





Introduction (1/3)

Future wireless networks will demand flexible spectrumallocation policies that cope with the detected spectrumscarcity and its underutilization in current networks.

Advanced Spectrum Management (ASM) techniques optimizethe use of the spectrum in time and space.

Fixed Spectrum Allocation (FSA) (the classical policies)� eases spectrum management and controls the interference

between RATs� limits the flexibility of spectrum and leads to large pieces of the

spectrum wasted due to the time and space varying trafficdistribution.

Dynamic Spectrum Allocation (DSA)� improves the spectral efficiency while maintaining user¶s QoS.� permits to pool frequency resources and enable opportunistic

secondary use of the spectrum. Better usage of spectrum





Introduction (2/3)

OFDMA (Orthogonal Frequency Division Multiple Access) is thecandidate technology to have a flexible radio interface.

Resource Block (RB) is the minimum resource that could be allocatedto a user.

In frequency, the whole available bandwidth is divided into groups of adjacent subcarriers or chunks

Can be exploited by an ASM strategy to obtain high spectral efficiency.





Introduction (3/3)

Objectives of the paper:

Present a framework for ASM in a multicell

OFDMA system.

Propose a DSA algorithm to decide aproper chunk-to-cell assignment.

Show that ASM may improve system

performance and enables opportunistic

secondary usage of the spectrum.





Outline

Introduction



Simulation Model

Results

Conclusions

Future work





Proposed ASM Framework (1/3)

Inhomogeneous spatialtraffic distribution

There are spatial andtemporal variations of network conditions

Additionally, a spectrumbroker manages thespectrum transactionsbetween primary andsecondary markets






The proposed ASM framework for a single operator is divided into twodecision blocks:

Short-Term Scheduler (STS)

ASM Scheduler

Short-Term Scheduler

Located at the base station

low latencies and high speed channels Each RB of the time-frequency grid is given fairly to each user.� Proportional Fair Scheduler:

� R m,n(t) represents the instantaneous achievable rate that user m can get at

chunk n.� W m,n(t) is the window-averaged version of R m,n(t) as follows:

,*

,

( )( ) arg max

( )

m n

mm n

R t m t

W t

E

F

® ¾± ±! ¯ ¿

± ±° À

, , ,

1 1 Ö( ) (1- ) ( -1) ( -1)m n m n m n

W W

W t W t R t T T

!






ASM scheduler Decides the chunks to allocated to each cell by executing the DSA

algorithm. Located in a network node with the ability to control a set of cells. Adapts the system to traffic variations in time and space in the medium-

long term

Allows efficient spectrum usage





Outline

Introduction



Simulation Model

Results

Conclusions

Future work





Proposed Dynamic Spectrum

Allocation Algorithm (1/2)

It is run by the ASM scheduler

It is an heuristic algorithm divided into two steps

1. Computes the number of chunks to assign to a

given cell (N j)

2. Allocates the chunks to each cell taking into accountthe potential intercell interference and cell load

(costs matrix A)

max

min ,max 1,/

j th

j

U T N N f

W N L

¨ ¸¨ ¸�« »! © ¹© ¹¬ ¼© ¹© ¹� ½ª ºª º

0

ji

ij j i

i f i j

U U R A( i, j)otherwise

DU U

H

!®±̈ ¸¨ ¸! ¯ © ¹© ¹± © ¹© ¹

ª ºª º°





Proposed Dynamic Spectrum

Allocation algorithm (2/2)

n* ! �

jC (n)=

j; ! �

n j

j j

j j

Select i / i and i= {i}

C (n)=C (n) + A(i,j)

� * � ;

; ; �

n j| |=| |* ;

j= ! �

j

j j

n n

j

n*=arg m¡

n ¢

£

¤

= ¢ n*}

= ¢ j}C (n) = n=n+1

= = �

* * �

g

j

n

j

j

N = Maximum numb¥

r of ¦ hunks

n = ¦ hunk numb

¥ r

C = ¦ osts v

¥ ¦ tor for

¦ ¥

§ §

j (1xN) =

¨ ¥ t of

¦ ¥

§ §

s with¦ hunk n allo

¦ ated

= ̈ et of ¦ ells ¦ ompared with ¦ ell jA = Cost Matrix

=Set of ¦ hunks allo

¦ ated to

*

;

= ¦

ell j

Start

n=0

n=0

n=n+1

n=Nj

n=N

End

Yes

No

Yes

Yes

Yes

No

No

No

The second step,calculates per each basestation and chunk thepotential intercell

interference and assignthose chunks with lower cost

The DSA algorithm

assigns only thenecessary chunks per cellreducing intercellinterference.





Outline

Introduction



Simulation Model

Results

Conclusions

Future work





Simulation Model

19 Cells and 12 chunks

SINR per chunk taking

into account fast fading

Adaptive Coding andModulation per chunk

Heterogeneous spatial

traffic distribution

Spatial distribution of the users in the scenario.









Results (2/3)

The DSA algorithm

adapts the number of chunks to system load

Improves spectral efficiency

Maintains user¶s requirements

Average cellspectral efficiency

Dissatisfactionprobability

Average number of chunks per cell





Results (3/3)

Regional Spectrum Usage per cell for chunks 9 to 12 andfor FRF1 (a), FRF3 (b) , and DSA (c,d,e,f)

System average RSUFRF1 1

FRF3 0.67

DSA 30 users 0.17

DSA 100 users 0.19

DSA 200 users 0.28

DSA 300 users 0.45

DSA 400 users 0.55

Note that RSU(B)�[0,1].

RSU(B)=1 band B is completely used in a cell and/or in neighboring cells.

RSU(B)=0 the band is completely free.

Thus, the lower the RSU(B), the easier that band B can be released in a regionaround a given cell.





Outline

Introduction



Simulation Model

Results

Conclusions

Future work





Conclusions

An approach to an Advanced Spectrum Management (ASM)framework in a multicell OFDMA network has been given.

The proposed DSA algorithm improves overall system¶sspectral efficiency while maintains users¶ satisfaction.

Also it has been shown that DSA could release spectrumbands in large geographical areas so that this spectrum willnot be wasted and could be exploited by secondarycognitive users.

Dynamic reuse is very suitable for future wireless networks

because spectrum is a scarce and expensive resource thatwill be used in a more efficient way, satisfying primary users¶needs and making room for opportunistic secondary users.





Outline

Introduction



Simulation Model

Results

Conclusions

Future work





Future Work

Proposed algorithm nearly approximates the solution for thelong-term. Improve the algorithm to adapt also to smallvariations in the medium-term.

Develop heuristic algorithms that take into account users

positions in order to deploy different strategies for the userslocated at the center and edge part of the cell respectively

Theoretical formulation of the optimal allocation algorithm.

Practical implications of implementing DSA in a a realnetwork and complexity.

Users with heterogeneous preferences to rates.



Thank you

Questions?

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20080331 E3 ASMOFDMA WCNC LasVegas Slides2spectru (2)