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Scheduling in the UMTS enhanced uplink

Camilo Orejuela Mesa & Geert HeijenkUniversity of Twente

Neill Whillans, Frank Brouwer & Sonia Heemstra de GrootTwente Institute for Wireless and Mobile Communications (WMC)

Cost 290, TD(06)052

September 29, 2006

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Problem Statement

An important new technique for the UMTSenhanced uplink, as defined in 3GPP

Release 6 , is fast packet scheduling.

How do different schedulers for the enhanceduplink compare?

What is the suitability of our current ns2-

based simulator, for evaluating these

schedulers?

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Outline

UMTS Enhanced Uplink Enhanced Uplink Schedulers

Simulation Conclusions & Future Work

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UMTS Architecture

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Enhanced Uplink

High Speed Uplink Packet Access (HSUPA) Defined for 3GPP R6

(HSDPA already in R5)

Main features increases throughput (5.76 Mbps)

reduces latency

Main new tecniques used: Hybrid Automatic Retransmission Request

(HARQ)

Fast Packet Scheduling(No higher order modulation)

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Fast Packet Scheduling

Based at the NodeB

reduces the delay

allows faster reaction than when residing at the RNC

controls the received power which is distributed among all

the users in the cell.

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Scheduling Signalling

Uplink:

Happy bit:

A single bit field indicates

whether the UE could

use more resources ornot.

Total E-DCH buffer

status

Highest priority logicalchannel ID

UE power headroom

Used transmit power?

Downlink:

Relative Grants:

up, down or hold,

indicating the UE to step

up, step down or hold theindex of its allowed TFC

Absolute Grants:

allows the NodeB

scheduler to directlyadjust the resources of

UEs under its control in

one single command

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2 extreme scheduling schemes

Users perform uplink

transmissions in parallel,with a low rate, so thatthe noise rise level at theNodeB does not exceed

the establishedthreshold.

Only one or a set of UEs

are allowed to transmit ata given time so that thenoise rise level at theNodeB does not exceed

the establishedthreshold.

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Scheduling Procedure

UE requests resources (bit rate)

NodeB determines allowed rates for UEs,based on scheduling scheme (see next slides)Condition:

UEs must meet their required BLER total received power below threshold (noise rise target)

NodeB sends grant (allowed rate) to UE

UE sends at granted rate Or at lower rate if max power reached, lower grant fromother nodeB, or not enough data

Delay from request to sending typically a few TTI (we

assume 7, i.e. 14 ms)

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UE 1

UE 2

UE 3

UE 4

Rate

P

P

P

P

UE 1

UE 2

UE 3

UE 4

Rate

TTI Time

Schedulers (1/2)

Rate Scheduling:

Try to grant to allactive UEs,assigning them

low rates.

Round RobinScheduling:Try to grant to afew UEs with themaximum rate.

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P P P P

UE 1

UE 2

UE 3

UE 4

Rate

RateP

P

P

UE 1

UE 2

UE 3

UE 4

TTI

P

time

Schedulers (2/2)

Uplink CQI:

Always selects the

UE with best UCQI

and grants it with the

maximum rate.

Rate Estimation:

Estimate the ratecapabilities of the

UEs to assign a rate.

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Simulator

Ns2-based

Detailed implementation of HARQ and fastscheduling

Single cell(fixed other-to-own cell interference ratio)

Link-level included by means of AVI:

(Actual Value Interface:look-up tables for Eb/N0 BLER)

Path loss and shadowing based on position

Multi-path fading precalculated

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BLER 0 .1

N o is e Ris e Ta r g e t 6 d B

TTI d u r a t io n 2 m s - 1 0 m s

Ma x UE t r a n s m is s io n p o we r 2 6 d Bm (-4 d B)

UE s p e e d 3 Km p h

C e ll r a d iu s 1 .5 Km

N u m b e r o f UEs 2 4

Tr a ffic r a t e p e r b u r s t 2 5 0 Kb p s

Bu r s t p e r io d 5 s e c

Id le p e r io d 5 s e c

Simulation Parameters

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Mean StdRate scheduling -3.59 2.5

Round Robin -5.46 3.05

Rate Est im at ion -5.36 3.04UCQI -9.58 7.1

0

200

400

600

800

1000

1200

1400

1600

1800

Ratescheduling

RoudRobin

Rate EstimSch

UCQI

Thro

ugput(Kbps

)

Average Cell

Throughput (kbps)

Total Transmitted

Power (dB)

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Mean StdRate scheduling 0.36 0.22

Round Robin 0.22 0.16

Rate Est im at ion 0.21 0.14UCQUI 0.16 1.72MAC MAC

RLC RLC

PHY PHY

UE NodeB

t1 t2

delay=t2-t1

Delay (sec)

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Conclusions & Future Work

Fast packet scheduling for the UMTS enhanced

uplink can benefit from:

Scheduling few users at the same time with high bit rates.

Using the channel condition as a scheduling parameter to

take advantage of the rapid reaction to channel variations. Estimating the maximum rate that the UEs are able to

support

To reliably compare and quantify the performance ofschedulers, a multi-cell simulator is a necessity

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More info:

geert.heijenk@utwente.nl

www.cs.utwente.nl/~heijenk/