16-05-2013, 03:47 PM
Adaptive PF Scheduling Algorithm in LTE Cellular System
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Abstract
The traditional proportional fair scheduling algorithm
can only provide users with limited fairness while the channel is
changing. To solve this problem and enhance the fairness
between users, an adaptive proportional fair scheduling
algorithm for LTE (Long term Evolution) system is proposed. It
adjusts the scheduling priority according to individual user’s
channel condition. The proposed algorithm provides a good
trade-off between capacity and fairness, and the simulation
results show the validity.
INTRODUCTION
Long Term Evolution (LTE) was proposed in 3GPP recent
years to meet the demand of future communication. The targets
of LTE concern significantly increased instantaneous peak data
rates, decreased latency, higher average spectrum efficiency
and the cell edge users’ throughput efficiency [1]. Orthogonal
Frequency Division Multiplexing (OFDM) and Multiple Input
Multiple Output (MIMO) are used as the basic transmission
scheme of LTE, which can achieve relatively high system
capacity and provide relative high data rate. But without a good
scheduler and good scheduling algorithm, it can not meet the
requirement of system performance [2]. Packet scheduling
algorithm is the main component to control the system
performance in terms of fairness and throughput.
TRADITIONAL PF SCHEDULING ALGORITHM
There are three basic packet scheduling algorithms:
Maximum Carrier to Interference (Max C/I) scheduling
algorithm, Round Robin (RR) scheduling algorithm and
Proportional Fair (PF) scheduling algorithm. Max C/I chooses
the users with the best channel gain, it results in the maximum
system throughput. RR chooses users in turn, and gives users
the equal scheduling probability without priority. RR
scheduling algorithm results in the lowest throughput but the
highest fairness.
SIMULATION RESULTS
This section presents simulation results to validate the
performance of the proposed method. We compare our
adaptive PF scheduling algorithm with the traditional PF
scheduling algorithm in an LTE based system simulation
platform. In LTE cellular system, subcarriers are grouped into
resource blocks (RBs) of 12 adjacent subcarriers with an
intersubcarrier spacing of 15 kHz. The smallest resource unit
that a scheduler can assign to a user is a scheduling block (SB),
which consists of two consecutive RBs, spanning a subframe
time duration of 1 millisecond [11].
CONCLUSION
In this paper, we propose an adaptive proportional fair
scheduling algorithm, which adjusts the scheduling priority
according to individual user’s channel condition. This method
gives more scheduling probability to the users who are under
poor channel condition for a long period of time, and avoids
the users whose channel conditions are favorable occupying
too much resource. It enhances the fairness with a limited
degradation of whole system throughput.