HSDPA/HSUPA Packet Scheduling
JARNO NIEMELÄ
jarno.niemela@tut.fi
21.03.2005
Outline
Principles of packet scheduling in WCDMA /
HSDPA Rel’05
Performance analysis of HSDPA PS for NRT
services [1]
Scheduling in E-DCH/HSUPA (NRT services) [2]
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Packet scheduling in WCDMA/HSDPA Rel’05
NodeB controlled packet scheduling (fast).
MULTIUSER DIVERSITY
(Selection diversity)
TIME SHARED ALLOCATION
OF HS-DSCH
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Sensitivity of throuhgput for channel quality
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Task of packet scheduler
To schedule interactive and background services
(NRT) for users.
To allocate radio resources efficienctly for a cell
such that cell capacity will be maximized while
fulfilling the QoS requirements according to
certain policy.
To monitor allocation of NRT services and system
loading.
To perform load control actions.
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Input parameters for packet scheduler
 Resource allocation
 HS-PDSCH and HS-SCCH powers
 HS-PDSCH codes
 Number of HS-SCCHs
 Downlink channel quality measurements
 CQI reports
 Power measurements on associated DPCH
 HARQ acknowledgements
 QoS parameters
 QoS attributes
 Scheduling priority indicator (SPI)
 Guarantee bit rate
 Miscellaneous
 Amount of buffered data
 Mobile capabilities
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Fairness
Selection of scheduling approach is always a tradeoff between the fairness and maximum cell
throughput.
C/I scheduling maximizes the system capacity
with the cost of lack of fairness.
Fair resources scheduling distributes equally the
radio resources (codes, power and allocation time).
Not completely fair.
Fair throughput tries to provide the same
throughput for all users.
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Packet scheduling algorithms
Slow scheduling methods (Blind)
 Average C/I
 Round robin
 Fair throughput
~100 ms scheduling
period
Does not consider instantaneous radio conditions
Fast scheduling methods (Advanced/opportunistic)
 Maximum C/I
 Proportional fair
 Fast fair throughput
Per TTI basis
(2ms)
Utilizes temporary changes of radio conditions
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Slow scheduling methods
Average C/I (Avg. C/I)
 Priorities users with the highest average C/I (~100 ms period)
 Fast fading averaged out
Round Robin (RR)
 Cyclic order used without considering channel conditions
 Blind method
 Simple and allocates radio resources evenly between the
users (=high fairness)
Fair Throughput (FTH)
 No instantaneous channel information utilized
 Priorities users with lowest average throughput
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Fast scheduling methods (1/2)
 Maximum C/I (Max. C/I)
 Serves in every TTI (transmission time interval) the user with the
best radio conditions with the largest supportable bit rate.
 High cell throughput, low fairness.
 Proportional fair (PF)
 Serves the user with largest relative channel quality:
Ri  t  Instantaneous supported data rate
Pi 

i  t 
Average served throughput
where Pi(t) denotes the user priority.
 User’s with relatively good channel conditions are served.
Available information of CQI and previous transmissions is
utilized.
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Fast scheduling methods (2/2)
Fast fair throughput (FFTH)
 Aims at providing a fair throughput distribution among all
the users in the cell, while still taking advantage of the fast
fading variations

 
Ri  t   max j Ri (t )
Pi 

i  t  
Ri (t )



where Ri (t ) is the average supportable data rate of a user i
and max j Ri (t ) is a constant that indicates the maximum
average supportable data from all j users.
 
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Summary
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Multi-user diversity
Fast allocation (2ms TTI) of radio resources 
Users with good radio conditions served  Multiuser diversity (selection diversity)
Increases the system/
cell throughput
The gain naturally
depends on the dynamics
of fast fading (short term
variations)
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Throughput vs. Es/N0
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Gain of multi-user diversity
Diversity order =
number of scheduled
users
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Performance analysis of PS in HSDPA
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User throughput distribution
2 Mbps load for slow
and 3 Mbps load for
fast scheduling
algorithms
Pedestrian A channel
(3 km/h)
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Average user throughput
CELL EDGE ---------------------------------- CLOSE TO BS
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Efficiency of resource utilization
Fast scheduling is able to use more efficiently
higher MCSs.
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Link utilization
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Performance of Max C/I and PF under high load
Provisioning of fairness
in high load starts to
be problem with
Max C/I
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Cell throughputs (1/2)
 With minimum user throughput guarantees (< 64 kbps)
PEDESTRIAN A (3 km/h)
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VEHICULAR A (3 km/h)
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Cell throughputs (2/2)
PEDESTRIAN A (3 km/h)
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Summary table of cell throughputs with
minimum user throughput guarantees
@ 5 % OUTAGE LEVEL
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Conclusions from PS methods for HSDPA
Selection of PS algorithm important for HSDPA
capacity maximization and QoS provisioning.
Multi-user diversity gain for 10-15 users 100 % in
PedA and 50 % in VehA channels (over RR).
Max C/I maximizes the cell throughput (with
degraded QoS provisioning)
Proportional fair scheduler seems to provide a
trade-off between QoS and cell throughput (time
dispersion of the channel still a great problem.
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Fast packet scheduling for E-DCH/HSUPA
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UL PS in REL’99
RNC –based packet scheduling
 Upgrading based on capacity requests
 Downgrading based on inactivity timer
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PS approaches for Node B scheduling (1/2)
Blind data rate detection (BRD)
 Instantaneous (TTI=10ms) data rate observed by Node B and
compared to maximum allowed. This information is
thereafter used for resource allocation according to UE´s
actual needs.
 PS algorithm based on resource utilization factor (RUF)
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PS approaches for Node B scheduling (2/2)
 Time Division Multiplexing (TDM)
 Fast allocation (TTI=2ms) based on same approach as in
HSDPA.
 Easier to keep resource utilization closer to the planned one.
 Exploitation of instantaneous channel conditions.
 Requires uplink syncronization
1) Utilization of USTS (uplink synchronous transmittion scheme) [5]
2) Synchronization achieved through DL frames. Would require guard
intervals together with using the information provided by RTT.
 To support SHO, only one Node B is allowed to perform
scheduling decisions.
 Allocation strategies (RRFT, maximized transmit power
efficincy (MTPE), PFT)
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Performance analysis (macrocellular)
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Performance analysis (macrocellular)
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Performance analysis (microcellular)
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Performance analysis (microcellular)
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Performance analysis
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Conclusions from PS for E-DCH/HSUPA
Node B PS based on BRD is able to provide 3040% capacity gain over RNC based PS (TVM)
Intuitively, channel-dependent methods are able to
provide better performance
Uplink synchronisation provides capacity gain of
20%.
Extra signalling load might reduce the capacity
gains in some extent.
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Main references
1. Pablo José Ameigeiras Gutiérrez, “Packet Scheduling
and Quality of Service in HSDPA”, Ph. D. Thesis,
Aalborg University, Denmark, October 2003.
2. José Outes Carnero, “Uplink capacity enhancements
in WCDMA,” Ph. D. Thesis, Aalborg University,
Denmark, March 2004.
3. H. Holma, A. Toskala (ed.), “WCDMA for UMTS,”
3rd ed., John Wiley & Sons, Ltd., 2004.
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Accessory references
4. J. Laiho, A. Wacker, T. Novosad, “Radio Network
Planning and Optimisation for UMTS,” John
Wiley & Sons, Ltd., 2002.
5. 3GPP, “Study report of Uplink Synchronous
Transmission Scheme (USTS),” TR 25.854, Ver
5.00, Rel. 5., December 2001.
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