schedulinginumts-120923103839-phpapp01
TRANSCRIPT
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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:
www.cs.utwente.nl/~heijenk/