Frequency Domain Packet Scheduling Under Fractional Load for the UTRAN LTE Downlink

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Frequency Domain Packet Scheduling Under

Fractional Load for the UTRAN LTE Downlink

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

† Aalborg University, ‡ Nokia Networks — Aalborg, Denmark

Abstract— In this paper we investigate the performance of

frequency domain packet scheduling (FDPS) under fractional

load (FL), based on the UTRAN Long Term Evolution downlink.

Under FL, the packet scheduler does not need to transmit on

entire system bandwidth due to lack of trafﬁc in the network,

which leads to an improvement in the user experienced SINR.

System-level simulations show that the proportional fair sched-

uler tries to optimize resource allocation by avoiding transmission

on frequencies that are experiencing severe interference. As an

example, FDPS can provide a gain of 4 dB in SINR over the

round-robin scheduler, when the load is equal to 25%. The

observed interference control is achieved without any centralized

management. Further, FDPS under FL can provide an effective

trade-off between cell throughput and coverage. The FDPS

performance is dependent on the ability of link adaptation to

track variations in interference. This ability is reduced when the

frequency usage pattern is changing rapidly over time.

I. INTRODUCTION

The downlink radio access of the 3GPP UTRAN long term

evolution (LTE) will be based on the orthogonal frequency

division multiple access (OFDMA) scheme. The guidelines for

the Physical layer design are described in [1]. As LTE sup-

ports frequency-domain adaptation techniques in downlink we

will investigate the performance of frequency domain packet

scheduling (FDPS), which refers to fast channel dependent

scheduling in both time and frequency domains. Previous

FDPS studies [2], [3], [4] indicate that it has signiﬁcant

potential over time-domain only scheduling, e.g. in [4] it is

reported that FDPS can provide a gain of around 40% in cell

throughput. The main drawbacks of FDPS are high scheduler

complexity and increased signaling overhead in the uplink as

well as in the downlink. Previous FDPS studies are based on

the full load scenario.

As OFDMA can provide intra-cell orthogonality by means

of the cyclic preﬁx, the main source of interference in down-

link is inter-cell interference (ICI) [5]. It can severely limit the

throughput of users near the cell edge, in a reuse 1 network

with continuous coverage. When the network is experiencing

a lack of trafﬁc, the packet scheduler optimizes resource

allocation by transmitting only on a portion of the system

bandwidth. This leads to a reduction in ICI and thereby an

improvement in SINR, which can be particularly useful to

cell-edge users as their data rate can be improved. The focus

of this study is the investigation of FDPS under the fractional

load (FL) scenario.

We assume that there is no co-ordination between the

entities responsible for resource allocation in the neighboring

cells. The analysis is based on a detailed LTE system-level

Fig. 1. Interaction between PS, LA, and the HARQ manager entities of the

eNode-B that are responsible for dynamic resource allocation.

model, developed according to the guidelines given in [1]. The

important scheduling related functions such as link adaptation

(LA) and HARQ have been modeled explicitly. Further, as

the FDPS performance is sensitive to the accuracy of channel

quality indication (CQI) reports, realistic assumptions for

achievable CQI accuracy and reporting frequency have been

used [4].

The paper is organized as follows: Section II describes the

interaction between the different functional entities involved

in packet scheduling. It also covers the description of the LA

functionality and the FDPS algorithm. Section III provides

details on the system-model as well as describes the modeling

of FL. Section IV covers the results and analysis, while the

conclusions are summarized in Section V.

II. PACKET SCHEDULING FRAMEWORK

Fig. 1 illustrates the interaction between the different entities

involved in packet scheduling (PS), which are located at

the base station (eNode-B) in order to facilitate fast channel

dependent scheduling [6]. Following LTE naming convention

the basic time-frequency resource available for data transmis-

sion is denoted as the physical resource block (PRB). The

PRB consists of a ﬁxed number of adjacent OFDM sub-

carriers and represents the minimum scheduling resolution in

the frequency domain [1]. The PS is the controlling entity in

the overall scheduling process. It can consult the LA module

to obtain an estimate of the supported data rate for certain

users in the cell, for different allocations of PRBs. LA utilizes

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摘要：

FrequencyDomainPacketSchedulingUnderFractionalLoadfortheUTRANLTEDownlinkA.Pokhariyal†,G.Monghal†,K.I.Pedersen‡,P.E.Mogensen†,‡,I.Z.Kovacs‡,C.Rosa‡andT.E.Kolding‡†AalborgUniversity,‡NokiaNetworks—Aalborg,DenmarkAbstract—Inthispaperweinvestigatetheperformanceoffrequencydomainpacketscheduling(FDPS)unde...

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