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A New Opportunistic Scheduling Approach for OFDMA-based WiMAX Networks
Abstract- Scheduler is one of the main components in WiMAX
networks to ensure efficiency use of radio resources. In this paper
we will be presenting a review for some of scheduler algorithms
for OFDMA based WiMAX networks, MaxSNR scheduler,
Proportional Fair (PF) scheduler, Round Robin (RR) algorithm
and a novel scheduling algorithm MORRA. The MORRA
algorithm takes into account both channel conditions and
fairness in terms of subcarriers number between all users in each
time slot. We present simulation results in two scenarios to
achieve the best evaluation of the scheduler performance.
MORRA outperforms MaxSNR, PF and RR algorithms.
Keywords-WiMAX; OFDMA; Opportunistic Scheduling;
MORRA; Throughput, Fairness.
I. INTRODUCTION
Orthogonal Frequency Division Multiplexing (OFDM) is
widely implemented in most recent wireless systems like
802.11a/g or 802.16 and has clearly emerged for future
broadband wireless multimedia networks (4G systems).[1,2]
The OFDM technique alone is not sufficient to achieve the
diverse requirements encountered in wireless networks of the
new generations. This modulation technique must be married
with algorithms for efficient resource allocations called
"schedulers". These algorithms must allow us to benefit of the
flexibility and the performance offered by OFDM so that they
can significantly increase the throughput while providing a
high equity.
As a result, a new class of algorithms (schedulers)
emerged to address this problem: opportunistic schedulers.
These resource allocation algorithms effectively use
information on the states of the links, SNRs (Signal-to-Noise
Ratio) indicators related to each couple "subcarrier; user ", it is
to take into account the CSI (Channel State Information) or
CQI (Channel Quality Indicator) [3, 4].
The primary function of CSIs is to adapt the modulation
function of the attenuation experienced on each link to get the
best throughput while respecting the target BER (Bit Error
Rate) [5,6], knowing that for a given SNR, each modulation
(MDP-2, M-QAM ...) offers a different throughput and BER
[7].
978-1-4799-608S-9/1S/$31.00©201S IEEE
Mohamed Ouwais KABAOU
RU MACS, ENIG, Gabes University
Gabes, Tunisia
[email protected]
When a subcarrier has a strong mitigation for a given
mobile (user), "links state" for this couple "subcarrier; user" is
identified as" degraded" via the CSIs and therefore the
throughput of the transmission in question will be low.
Conversely if another user for this frequency undergoes little
attenuation, the rate associated with the couple "subcarrier;
user "will be higher this time.
The highlight of opportunistic scheduler is twofold: on the
one hand they are able to adjust the flow of each transmission
to the radio conditions through the CSIs (thus limiting the
degradation of network performance) and also to take
advantage of the frequency diversity and multi-user to allocate
radio resources to users who have the conditions of
transmission / receiving the most favorable (a good signal /
noise ratio, a good CSI), thus optimizing the overall system
throughput [7].
The new scheduling approach proposed in this paper is
based on Round Robin algorithm, called MORRA, which
intent to accommodate maximum real-time traffic while still
sustaining fairness and maximizing system throughput in
downlink OFDMA systems.
The rest of this paper is organized as follows. In Section II,
we describe conventional scheduler algorithms. In section III
we describe the investigated system model. Section IV
contains our proposed scheme. Simulation results are
presented in Section V. Finally, we draw conclusion in Section
VI.
II. CONVENTIONAL SCHEDULER ALGORITHMS
One of the most conventional scheduling algorithms for
High Speed Packet (HSPA) are: MaxSNR, Proportional Fair
and Round Robin.
A. MaxSNR Scheduler
All the users are classified with their respective SNR
Values in MaxSNR Scheduling [8].
For every scheduling event and depending on the service
requirements and availability of resources, the user with the
highest SNR value is selected and allocated a number of time
cy
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A New Opportunistic Scheduling Approach for OFDMA-based WiMAX Networks
Abstract- Scheduler is one of the main components in WiMAX
networks to ensure efficiency use of radio resources. In this paper
we will be presenting a review for some of scheduler algorithms
for OFDMA based WiMAX networks, MaxSNR scheduler,
Proportional Fair (PF) scheduler, Round Robin (RR) algorithm
and a novel scheduling algorithm MORRA. The MORRA
algorithm takes into account both channel conditions and
fairness in terms of subcarriers number between all users in each
time slot. We present simulation results in two scenarios to
achieve the best evaluation of the scheduler performance.
MORRA outperforms MaxSNR, PF and RR algorithms.
Keywords-WiMAX; OFDMA; Opportunistic Scheduling;
MORRA; Throughput, Fairness.
I. INTRODUCTION
Orthogonal Frequency Division Multiplexing (OFDM) is
widely implemented in most recent wireless systems like
802.11a/g or 802.16 and has clearly emerged for future
broadband wireless multimedia networks (4G systems).[1,2]
The OFDM technique alone is not sufficient to achieve the
diverse requirements encountered in wireless networks of the
new generations. This modulation technique must be married
with algorithms for efficient resource allocations called
"schedulers". These algorithms must allow us to benefit of the
flexibility and the performance offered by OFDM so that they
can significantly increase the throughput while providing a
high equity.
As a result, a new class of algorithms (schedulers)
emerged to address this problem: opportunistic schedulers.
These resource allocation algorithms effectively use
information on the states of the links, SNRs (Signal-to-Noise
Ratio) indicators related to each couple "subcarrier; user ", it is
to take into account the CSI (Channel State Information) or
CQI (Channel Quality Indicator) [3, 4].
The primary function of CSIs is to adapt the modulation
function of the attenuation experienced on each link to get the
best throughput while respecting the target BER (Bit Error
Rate) [5,6], knowing that for a given SNR, each modulation
(MDP-2, M-QAM ...) offers a different throughput and BER
[7].
978-1-4799-608S-9/1S/$31.00©201S IEEE
Mohamed Ouwais KABAOU
RU MACS, ENIG, Gabes University
Gabes, Tunisia
[email protected]
When a subcarrier has a strong mitigation for a given
mobile (user), "links state" for this couple "subcarrier; user" is
identified as" degraded" via the CSIs and therefore the
throughput of the transmission in question will be low.
Conversely if another user for this frequency undergoes little
attenuation, the rate associated with the couple "subcarrier;
user "will be higher this time.
The highlight of opportunistic scheduler is twofold: on the
one hand they are able to adjust the flow of each transmission
to the radio conditions through the CSIs (thus limiting the
degradation of network performance) and also to take
advantage of the frequency diversity and multi-user to allocate
radio resources to users who have the conditions of
transmission / receiving the most favorable (a good signal /
noise ratio, a good CSI), thus optimizing the overall system
throughput [7].
The new scheduling approach proposed in this paper is
based on Round Robin algorithm, called MORRA, which
intent to accommodate maximum real-time traffic while still
sustaining fairness and maximizing system throughput in
downlink OFDMA systems.
The rest of this paper is organized as follows. In Section II,
we describe conventional scheduler algorithms. In section III
we describe the investigated system model. Section IV
contains our proposed scheme. Simulation results are
presented in Section V. Finally, we draw conclusion in Section
VI.
II. CONVENTIONAL SCHEDULER ALGORITHMS
One of the most conventional scheduling algorithms for
High Speed Packet (HSPA) are: MaxSNR, Proportional Fair
and Round Robin.
A. MaxSNR Scheduler
All the users are classified with their respective SNR
Values in MaxSNR Scheduling [8].
For every scheduling event and depending on the service
requirements and availability of resources, the user with the
highest SNR value is selected and allocated a number of time
cy
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