HARQ Aware Frequency Domain Packet Scheduler with Different Degrees of Fairness for the UTRAN lte

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HARQ Aware Frequency Domain Packet Scheduler

with Different Degrees of Fairness for the UTRAN

Long Term Evolution

A. Pokhariyal†, K. I. Pedersen‡, G. Monghal†, I. Z. Kovacs‡, C. Rosa‡, T. E. Kolding‡ and P. E. Mogensen†,‡

† Aalborg University, ‡ Nokia Networks — Aalborg, Denmark

Abstract— In this paper we evaluate the performance of

downlink channel dependent scheduling in time and frequency

domains. The investigation is based on the 3GPP UTRAN long

term evolution (LTE) parameters. A scheduler framework is

developed encompassing frequency domain packet scheduling,

HARQ management and inter-user fairness control. It is shown

that by dividing the packet scheduler into a time-domain and

a frequency-domain part the fairness between users can be

effectively controlled. Different algorithms are applied in each

scheduler part, and the combined performance is evaluated

in terms of cell throughput, coverage, and capacity. We show

that frequency-domain packet scheduling can provide a gain of

around 35% in both throughput and coverage over opportunistic

time-domain only scheduling. Furthermore, it is shown that by

using an equal throughput scheduler, coverage can be improved

by 100% at the expense of a 5% loss in average cell throughput

in comparison with the proportional fair scheduler.

I. INTRODUCTION

Orthogonal frequency division multiple access (OFDMA)

has been selected as the downlink access technology for

the 3GPP UTRAN long-term evolution (LTE) system [1]. It

provides scalability, simple equalization and facilitates ad-

vanced frequency-domain adaptation techniques. In this paper

we investigate the performance of various downlink packet

scheduling (PS) algorithms that are able to exploit available

multi-user diversity in both time and frequency domains. This

isoftenreferredtoasfrequency domain packet scheduling

(FDPS).

Recent FDPS studies [2], [3], [4] have shown signiﬁcant

potential over time-domain only scheduling. Focusing on the

LTE it was reported in [4] that FDPS can provide both cell

throughput and coverage gain of around 40%. However, in

[4] the impact of HARQ on the scheduling ﬂexibility was not

explicitly modeled and non-ideal serving cell selection was not

included. Further, we extend the study to include also methods

for controlling inter-user fairness. A two-layer scheduling

framework is developed consisting of a time-domain (TD)

scheduler followed by a frequency-domain (FD) scheduler.

We show that this approach can effectively encompass the

HARQ scheduling constraints as well as control the fairness

among users. We evaluate the performance of the scheduling

algorithms based on a detailed system model according to

the 3GPP evaluation criteria laid out in [1]. Performance is

reported in terms of average cell throughput, coverage and

capacity, in the 3GPP macro-cell outdoor scenario. Capacity

Fig. 1. Interaction between PS, LA & HARQ entities involved in dynamic

resource allocation.

is deﬁned as the number of users that can be supported at the

target coverage data rate.

The paper is organized as follows. Section II presents the

scheduler frame-work including detailed algorithm descrip-

tions as well as inner and outer loop link adaptation. Section III

presents the system model and the simulation assumptions,

while Section IV covers the simulation results and analysis.

Finally, the conclusions are presented in Section V.

II. TIME AND FREQUENCY DOMAIN PACKET SCHEDULER

The interaction between the main entities involved in

scheduling, i.e., packet scheduler, link adaptation (LA) and

HARQ manager is illustrated in Fig. 1. These entities are

located at the base station (eNode-B) in order to support

fast adaptation to radio channel conditions. The controlling

entity is the packet scheduler. The minimum resolution for

scheduling in the frequency domain is one physical resource

block (PRB), and its bandwidth is equal to 375 kHz [1]. 24

PRBs are available in 10 MHz bandwidth, each consisting of

25 neighboring sub-carriers. The packet scheduler can consult

link adaptation to obtain an estimate of the supported data rate

for certain users in the cell for different allocations of PRBs.

Link adaptation is based on the channel quality indication

(CQI) feedback from the users, as well as Ack/Nack’s from

past transmissions to ensure that the estimate of the supported

data rate corresponds to a certain block error rate (BLER)

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摘要：

HARQAwareFrequencyDomainPacketSchedulerwithDifferentDegreesofFairnessfortheUTRANLongTermEvolutionA.Pokhariyal†,K.I.Pedersen‡,G.Monghal†,I.Z.Kovacs‡,C.Rosa‡,T.E.Kolding‡andP.E.Mogensen†,‡†AalborgUniversity,‡NokiaNetworks—Aalborg,DenmarkAbstract—Inthispaperweevaluatetheperformanceofdownlinkchanneldepe...

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