Resource Allocation Algorithms in OFDMA

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Resource Allocation Algorithms in

OFDMA

Wafa BEN HASSEN

Equity optimization problems


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Agenda

Introduction

Max- Min fairness

Proportional fairness

Hard fairness

Conclusion

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Introduction

` In order to perform the resource allocation, fairnessparameter is an advisable criteria to enforce a fairerbehavior of the OFDMA system.

` Fairness parameter reduces the monopolization of resources by set of users that experience good channelgain. Hence, users with low channel gain may not receivedata due to lack of resources.

` Several different optimization criteria are presented toenforce a fairer behavior of the system such as, max-min,proportional and hard fairness problem.

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Fairness Algorithm

Max- Min fairness : maximizing the minimum data rate among user

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Problem formulation:


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Max- Min fairness

Wonjong Rhee & John M. Cioffi.Increase in capacity of multiuser OFDM system using dynamic subchannel allocation. (2000)

2- Assign to each user each bestchannel gain

- If there are subcarriers not

yet assigned to users. The user k

ith the first lo est rate receivesits best subcarrier from the

remaining subcarriers

1- Initizialisation

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Max-Min fairnessRomano Fantacci DaniaMarabissi, Daniele archi and Alessandro Biagioni.

Adaptive subcarrier allocation algorithms in wireless ofdma systems (2008)

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Maximize the minimum value among all users:


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Max-Min fairness

1- Initizialisation

2-assign to each user a

slot within the frequenciesin which the user has thebest channel conditions.

3- the user with the lowest

amount of capacity is selectedand a slot is allocated to him.

he selection of the user with

the lowest capacity allows to

obtain an approximately equal

distribution of capacity

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Drawbacks:

In the case of multiple users with a multi-services

requirements ( specially in the 4G).

he users with the best channel conditions obtain a

lower number of resources with respect to the users with

the worst channel conditions, who need a lot of slots to

achieve the same amount of capacity, so, the channel

capacity is not fully exploited.

Max-Min fairness

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Fairness Algorithm

Proportional fairness :

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Z. Shen I. C.Wong, B. L. Evans, and J. G. Andrews.A low complexity algorithm for proportional resource allocation in ofdma systems (2004)

Step 2 : Assign the subcarriers to each user in a way that ensures rough proportionality

Step 3 : Assign the total power for user k to maximize the capacity while enforcing the

proportionality.

Step 4: Assign the powers for each user's subcarriers subject to his total power

constraint using the waterfilling algorithm

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Step 2 :

2- Assign to each user each best

channel gain

1- Initizialisation

Assign the subcarriers to each user in a way that ensures rough proportionality

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4- Assign the remaining subcarriersto the best users for them, wherein

each user can get at most oneunassigned subcarrier. his is to

prevent the user with the best

gains to get the rest of the

subcarriers

Step 2 : Assign the subcarriers to each user in a way that ensures rough proportionality

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the slot allocation for which the capacity values assigned to the users are proportional tothe maximum capacity values:

Romano Fantacci DaniaMarabissi, Daniele archi and Alessandro Biagioni.Adaptive subcarrier allocation algorithms in wireless ofdma systems(2008)

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1- Initizialisation

2-assign to each user a

slot within the frequenciesin which the user has thebest channel conditions.

3- the selected user is the one

who has the minimum ratiobetween the temporary valueof capacity and the value of

the maximum obtainable

capacity.

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Fairness Algorithm

Hard fairness :

his formulation corresponds to the minimum sum power problem.Each user transmits at his own desired rate careless to the actual channel realization.

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Conclusion

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he (4G) is characterized by:Multiuser diversity

Multiservice

Fast channel variation

Capability to support mobility

Proportional fairness seems to be the most powerful

criterion to enforce the equity among users in the case of

4G.

Documents

Resource Allocation Algorithms in OFDMA