HSPA systems overview

HSPA systems

Kari Aho
Senior Research Scientist
kari.aho@magister.fi

Disclaimer

 Effort has been put to make these slides as correct as
possible, however it is still suggested that reader confirms
the latest information from official sources like 3GPP specs
(http://www.3gpp.org/Specification-Numbering)
 Material represents the views and opinions of the author
and not necessarily the views of their employers
 Use/reproduction of this material is forbidden without a
permission from the author

2 © 2008 Magister Solutions Ltd

Readings related to the subject

 General readings
 WCDMA for UMTS – H. Holma, A. Toskala
 HSDPA/HSUPA for UMTS – H. Holma, A. Toskala
 3G Evolution - HSPA and LTE for Mobile Broadband - E.
Dahlman, S. Parkvall, J. Sköld and P. Beming,
 Network planning oriented
 Radio Network Planning and Optimisation for UMTS – J. Laiho,
A. Wacker, T. Novosad
 UMTS Radio Network Planning, Optimization and QoS
Management For Practical Engineering Tasks – J. Lempiäinen,
M. Manninen


Contents

 Introduction
 HSDPA
 HSUPA
 Continuous Packet Connectivity
 I-HSPA
 Conclusions


Introduction

5 © Magister Solutions Ltd

High Speed Packet Access (1/3)

 There were number of pushing forces to improve the packet data
capabilities of WCDMA even further, e.g.
 Growing interest towards rich calls, mobile-TV and music streaming in
the wireless domain
 Competitive technologies such as WIMAX
 High Speed Packet Access (HSPA) evolution introduced first
downlink counterpart of the evolution called High Speed Downlink
Packet Access (HSDPA) in Release 5
 Uplink evolution followed later in Release 6 by the name of High
Speed Uplink Packet Access (HSUPA)
 HSPA was originally designed for non-real time traffic with high
transmission rate requirements



 HSPA features/properties include e.g.
 Higher order modulation and coding
 Higher throughput and peak data rates
 In theory up to 5,8 Mbps in the uplink and 14 Mbps in the
downlink without Multiple Inputs and Multiple Outputs (MIMO)
 Multiple Inputs and Multiple Outputs (MIMO)
 Roughly speaking equals to additional transmitter and receiver
antennas
 Fast scheduling in the Node B
 Possibility to take advantage of channel conditions with lower latency



 Link adaptation in downlink
 Possibility to adjust the used modulation and coding scheme according
to be appropriate for current radio channel conditions
 Improved retransmission capabilities
 Newly introduced layer one retransmissions called as Hybrid Automatic
Repeat Request (HARQ) => reduced delay
 Radio Link Control (RLC) level retransmissions still possible
 Shorter frame sizes and thus Transmission Time Intervals (TTI)
 With HSDPA 2ms and with HSUPA 10ms and 2ms


WCDMA Background and Evolution
3GPP Rel 5 3GPP Rel 6 3GPP Rel 7
3GPP Rel -99 3GPP Rel 4 (HSDPA) (HSUPA) HSPA+ Further
12/99 03/01 03/02 2H/04 06/07 Releases, (LTE)

2000 2001 2002 2003 2004 2005 2006 2007

Europe
Europe HSDPA HSUPA
Japan (pre-
(commercial) (commercial) (commercial)
commercial)


Questions

 Why were the packet data capabilities of WCDMA improved
even further?
 For what kind of services was HSPA originally designed?


High Speed Downlink Packet Access
(HSDPA)

11 11 20082008 Magister Solutions Ltd
© © Magister Solutions Ltd

Introduction to HSDPA (1/2)

 In Release 99 there basically exists three different methods
for downlink packet data operation
 DCH,
 Forward Access Channel (FACH) and
 Downlink Shared Channel (DSCH)
 After the introduction of HSDPA in Release 5 some changes
to downlink packet data operations occurred
 New High Speed DSCH (HS-DSCH) channel was introduced
 DSCH was removed due to lack of interest for implementing it
in practical networks


Introduction to HSDPA (2/2)

 HSDPA Improvements for packet data performance both in
terms of capacity and practical bit rates are based on
 The use of link adaptation,
 Higher order modulation,
 Fast scheduling,
 Shorter frame size (or transmission time interval), and
 Physical layer retransmission
 HSDPA does not support DCH features like fast power
control or soft handover


HSDPA channels (1/2)

 The Release 99 based DCH is the key part of the system –
despite the introduction of HSDPA
 Release 5 HSDPA is always operated with the DCH
 DCH with HSDPA
 If the service is only for packet data, then at least the
signaling radio bearer (SRB) is carried on the DCH
 In case the service is circuit-switched then the service always
runs on the DCH
 With Release 6, signaling can also be carried without the DCH
 In Release 5, uplink user data always go on the DCH (when
HSDPA is active)


HSDPA channels (2/2)

 in Release 6 an alternative is provided by the Enhanced DCH
(E-DCH) with the introduction of high-speed uplink packet
access (HSUPA)
 User data is sent on High Speed Downlink Shared Channel
(HS-DSCH)
 Control information is sent on High Speed Common Control
Channel (HS-SCCH)
 HS-SCCH is sent two slot before HS-DSCH to inform the
scheduled UE of the transport format of the incoming
transmission on HS-DSCH


Questions

 Mention at least purpose to which Rel’99 DCH is used with
HSDPA
 What kind of handovers are supported with HSDPA?


Link Adaptation (1/3)

 UE informs the Node B regularly of its channel quality by
CQI messages (Channel Quality Indicator)



 Adaptive modulation and higher order modulation
(16/64QAM) with HSDPA
16
In sta n ta n e o u s E sN o [d B ]

14
12
10
8
6
4
2
0
Link
-2 adaptation
0 20 40 60 80 1 00 1 20 1 40 1 60
Tim e [n u m b e r o f TTIs ] adjusts the
1 6 Q A M 3 /4
mode within
1 6 Q A M 2 /4
few ms based
Q P S K 3 /4
on CQI
Q P S K 2 /4
Q P S K 1 /4



 More complex modulation schemes require more energy
per bit to be transmitted than simply going for transmission
with multiple parallel code channels, thus HSUPA benefits
more from using multiple codes as PC keeps the signal
levels quite good anyway


Fast Retransmissions (1/3)
Rel ‘99 HSPA

RNC
Retransmisson Packet
Packet

NodeB

RLC
ACK/NACK
Retransmisson
UE Layer 1
ACK/NACK

 Radio Link Control (RLC) layer ACK/NACKs also possible with HSPA



UE NodeB RNC

User data

(Re)transmission
RLC
RLC (N)ACK

MAC-d

MAC-hs

(Re)transmission
Layer1
HARQ (N)ACK



 Layer 1 signaling indicates the need of retransmission which leads to much
faster round trip time that with Rel ‘99
 Retransmission procedure with layer 1 retransmissions (HARQ) is done so
that decoder does not get rid of the received symbols if the transmission
fails but combines them with new transmissions
 Retransmissions can operate in two ways:
 Identical retransmissions (soft/chase combining)
 Non-identical retransmissions (incremental redundancy)


Questions

 What is CQI?
 What does link adaptation do?
 Which entity initiates RLC re-transmissions?
 Which entity initiates HARQ re-transmissions?


Downlink scheduling (1/5)

 NodeB has certain amount of users connected to it and it
needs to schedule the different users for transmission in
different fractions of time (Transmission Time Intervals)
 Certain fairness for scheduling time for each user should be
maintained
 Resources should be utilized in optimal manor
 There exists different ways that users can be scheduled in
downlink, e.g.
 Round Robin
 Proportional Fair



 Round Robin (RR)
 Simplest scheduling algorithms
 Assigns users in order i.e. handling all users without priority
 Positive sides
 Easy to implement
 Each user gets served equally
 Negative sides
 No channel conditions are taken into account and thus resources
might be wasted



 Proportional Fair (PF)
 Compromise-based scheduling algorithm
 Based upon maintaining a balance between two competing
interests
 Maximize network throughput i.e. users are served in good channel
conditions
 Allowing all users at least a minimal level of service



 PF assigning each users a scheduling priority that is inversely
proportional to its anticipated resource consumption
 High resource consumption => low priority



 In general priority metric for certain user can be defined as follows

d
priority = ,
r
 where instantaneous data rate, d, is obtained by consulting the
link adaptation algorithm and average throughput, r, of the user
is defined and/or updated as follows

(1 − a ) * rold + a * d , if user is served
r = ,
 (1 − a ) * rold , otherwise
−1
 where a is so called forgetting factor. Hence, a equals the
equivalent averaging period in a number of TTIs for the
exponential smoothing filter


Mobility with HSDPA (1/4)

 Handovers are roughly tradeoff between two issues
 When channel conditions are getting worse, handover to better
cell should be made so that packets won’t get lost due to poor
channel conditions
 However, each time when the handover is made, transmission
buffers in the Node B are flushed resulting to additional delays
from RLC level retransmission or disruption of service
 When regarding HSDPA, the user can be connected only to
one serving HSDPA Node B at the time
 Leading to hard handover when the handover between HSDPA
Node Bs is required in contrary to DCH soft handover



 Even though there is only one serving HS-DSCH cell, the
associated DCH itself can be in soft(er) handover and
maintain the active set as in Rel’99

Node B,
Serving HSDPA
DCH

DCH Node B,
Part of DCH active set
HS-SCCH

UE
DCH/HSDPA
DCH



 HSDPA handover procedure includes following steps
 Serving HS-DSCH cell change procedure is initiated when a
link in (DCH) active set becomes higher in strength and stays
stronger for certain period of time, referred as time-to-trigger
 If the condition mentioned above is met then the
measurement report is sent from the UE to the Node B, which
forwards it to the RNC
 If e.g. the admission control requirements are met the RNC
can then give the consent for the UE to make the handover by
sending so called Signaling Radio Bearer (SRB)
(re)configuration message



 In the case of intra Node B handover, the HARQ processes
(transmissions) and Node B buffers can be maintained and
thus there is only minimal interruption in data flow
 However, with inter Node B handover i.e. between Node Bs,
the Node B packet buffers are flushed including all unfinished
HARQ processes which are belonging to the UE that is handed
off


Questions

 How does Round Robin allocate resources for the users?
 How intra- and inter-Node B handovers differ from each
other?


High Speed Uplink Packet Access
(HSUPA)


Introduction to HSUPA (1/2)

 Roughly three years later when HSDPA was introduced
uplink counterpart of the high speed packet access
evolution was introduced in Release 6
 In 3GPP original name was not HSUPA but Enhanced Dedicated
Channel (E-DCH)
 The obvious choices for uplink evolution was to investigate the
techniques used for HSDPA and, if possible, adopt them for the
uplink as well
 Improvements in HSUPA when compared to Rel’99
 Layer 1 Hybrid ARQ (HARQ) i.e. fast retransmissions
 Node B based scheduling


Introduction to HSUPA (2/2)

 Easier multicode transmissions
 Shorter frame size, 10ms mandatory for all HSUPA capable
devices and 2 ms as optional feature
 HSUPA is not a standalone feature, but requires many of
the basic features of the WCDMA Rel’99
 Cell selection and synchronization,
 random access,
 basic power control loop functions,
 basic mobility procedures (soft handover), etc.


HSUPA channels (1/4)

 New uplink transport channel - Enhanced Dedicated
Channel (E-DCH)
 Supports key HSUPA features such as HARQ, fast scheduling
etc.
 Unlike HS-DSCH (HSDPA) E-DCH is not a shared channel, but
a dedicated channel (*)
 Similarly to DCH, E-DCH is also mapped to physical control
and data channels
 The user data is carried on the enhanced dedicated physical data
channel (E-DPDCH) while new control information is on the E-
DPCCH

(*)Dedicated channel means that each UE has its own data path to the Node B that is
continuous and independent from the DCHs and E-DCHs of other UEs



 From the Release 99 DCH, the dedicated physical control
channel (DPCCH) is unchanged and the need for the
DPDCH depends on possible uplink services mapped to the
DCH
 DPCCH is used e.g. for fast power control
 New channels for scheduling control
 E-DCH absolute grant channel (E-AGCH) - absolute scheduling
value
 E-DCH relative grant channel (E-RGCH) - relative step
up/down scheduling commands



 New channel for retransmission control, carries information
in the downlink direction on whether a particular base
station has received the uplink packet correctly or not
 E-DCH HARQ indicator channel (E-HICH)



DPCCH
NodeB
E-DPCCH

E-DPDCH

E-RGGH
UE
E-AGCH

E-HICH


Questions

 What new features on top of multicodes and shorter frame
sizes do HSUPA offer?
 Is DCH part of the HSUPA?


Uplink scheduling (1/5)

 With HSDPA all the cell power can be directed to a single
user for a short period of time
 Very high peak data rates achievable for certain UE and all the
others can be left with a zero data rate
 However, in the next time instant another UE can be served
and so on
 With HSUPA HSDPA type of scheduling is not possible
 HSUPA is a many-to-one scheduling
 The uplink transmission power resources are divided to
separate devices (UEs) which can be used only for their
purposes and not shared as with HSDPA



 The shared resource of the uplink is the uplink noise rise(*), or
the total received power seen in the Node B receiver
 Typically, one UE is unable to consume that resource alone
completely and it is very beneficial for the scheduler to know at
each time instant how much of that resource each UE will consume
and to try to maintain the interference level experienced close to
the maximum
 Thus, HSUPA scheduling could be referred as very fast DCH
scheduling

(*)ratio between the total power received from all of the UEs at the base station and
the thermal noise



 Two different scheduling schemes are defined for HSUPA
traffic
 Scheduled transmissions controlled by Node B which might not
guarantee high enough minimum bit rate. In addition each
request requires time consuming signaling
 Non-scheduled transmissions (NST) controlled by radio
network controller (RNC) which defines a minimum data rate
at which the UE can transmit without any previous request.
This reduces signaling overhead and consequently processing
delays



 Scheduled transmissions
 The scheduler measures the noise level and decides whether
 Additional traffic can be allocated
 Should some users have smaller data rates
 The scheduler also monitors the uplink feedback
 Transmitted on E-DPCCH in every TTI
 Referred as happy bits
 Tells which users could transmit at a higher data rate both from
the buffer status and the transmission power availability point of
view



 Depending on possible user priorities given from the RNC, the
scheduler chooses a particular user or users for data rate
adjustment
 The respective relative or absolute rate commands are then send
on the E-RGCH or E-AGCH
 UE in soft handover receives only relative hold/down
commands from other than serving HSUPA Node B


Questions

 What is the shared resource in the uplink if power is in the
downlink?
 What kind of scheduling possibilities HSUPA offer?


Multicodes with HSUPA (1/2)

 Even though Rel’99 DCH supports in theory multicode
transmissions in practice only E-DCH can support multicode
transmissions and thus higher bitrates
 In theory DCH can use 6xSF4 leading to 5.4 Mbps
 E-DCH can in practice support 2xSF2 + 2xSF4 leading to 5.4
Mbps
 The reason why DCH does not support multicodes is that
the DCH is controlled by RNC and thus DCH is rather slowly
controllable


Multicodes with HSUPA (2/2)

 If the UE could send with fully utilizing multicodes in some
time instant this might not be the case later and UE might end
up in power outage and thus wouldn’t be able to use its
allocation
 With RNC control reallocation of resources is slow => resources
wasted
 Also, HSUPA with HARQ increases the possibility to operate
with higher BLER target which leads to lower power
requirement for corresponding data rate


Mobility with HSUPA (1/2)

 HSUPA supports the soft(er) handover procedure similar to
WCDMA Rel’99
 The HARQ operation in HSUPA soft handover situation is
done in following manor
 If any Node B part of the active set sends an ACK, then the
information given to the Medium Access Control (MAC) layer is
that an ACK has been received and the MAC layer will consider
the transmission successful


Mobility with HSUPA (2/2)
Packet
reordering RNC

Correctly
NodeB
received
Layer 1 packet
ACK/NACK Data
NodeB

UE
Layer 1
ACK/NACK


Questions

 Why does not DCH support multicodes in practice?
 If UE is in a two-way soft handover how does the HARQ
operate?


Continuous Packet Connectivity
(CPC)


Continuous Packet Connectivity (1/5)

 Continuous Packet Connectivity (CPC) was released in
Release 7
 Designed to improve the performance of delay critical small
bit rate services like VoIP
 Eliminates the need for continuous transmission and
reception when data is not exchanged. Can be categorized
into three feature
 UL discontinuous transmission
 DL discontinuous transmission
 HS-SCCH less for HSDPA VoIP



 Benefits
 Connected inactive HSPA users need less resources and create
less interference => more users can be connected
 UE power savings => increased talk time (VoIP)
 UTRAN resources are saved


9 9 D C H w it h 2 0 - m s T T12 .2 k b p s D C H
I
(Re l 9 , C S v o ic e )
’9

32 k b p s E -D CH
- D C H w it h 10 - m s T T I
(Re l , p h a s e 1, Vo I P )
’6

16 0 k b p s E - D C H

- D C H w it h 2 - m s T T I
Po w e r o f f s e t
Re l 6 , p h a s e 2 , Vo I P )
-

16 0 k b p s E - D C H
E - D C H w it h 2 m s T T I PO
a n d U L D P C C H g a t in g
(Re l 7 , Vo I P )
-

= D P D C H (D C H ) / E - D P D C H (E - D C H )
= D PCCH



 DL discontinuous transmission or Discontinuous Reception
(DRx) cycles allow an idle UE to power off the radio
receiver for a predefined period
 Period after the UE wakes up again is called as DRx cycle
 When UE wakes up it listens predefined time for incoming
transmissions and if it successfully decodes a new transmission
during that time it starts timer for staying active certain period
of time
No
m e as u r e m e n
On Duration DRX Period
UE shall monitor
t s done or
PDCCH d at a
r e c e iv e d

DRX Cycle



 HS-SCCH-less HSDPA operation in downlink
 Initial transmission of small (VoIP) packets can be sent without
High Speed Secondary Control Channel (HS-SCCH)
 Eliminates the control channel overhead from small packets
sent over HSDPA
 Retransmissions are sent with HS-SCCH pointing to the initial
transmission


VoIP performance with and without
CPC
 In general major performance enhancements visible if circuit switched
voice over WCDMA and VoIP over HSPA Rel 7 is compared
 With Rel 99 CS voice capacity 60-70 users/cell
 With Rel 7 VoIP capacity goes beyond 120 users/cell

H. Holma, M. Kuusela, E. Malkamäki, K. Ranta-aho, C. Tao:
“VoIP over HSPA with 3GPP Release 7”, PIMRC, 2006.


Internet HSPA
(I-HSPA)


I-HSPA (1/3)

 Internet-HSPA (I-HSPA) aims to provide competitive mobile
internet access with much more simpler network
architecture than it is in normal WCDMA systems
 Deployable with existing WCDMA base stations
 Utilizes standard 3GPP terminals
 Simplified architecture brings many benefits such as
 Cost-efficient broadband wireless access
 Improves the delay performance
 Transmission savings
 Enables flat rating for the end user
 Works anywhere (compared to WLAN or WIMAX)


I-HSPA (2/3)

NodeB /
E-NodeB SGSN

RNC GGSN
UE
Internet
/
Intranet

I-HSPA


I-HSPA (3/3)
Re l a s e
e
99 ~2 0 0
m s R ou n d t r i p t i me of 3 2 - B y t e p a c k et
200
18 0 HS D PA
<10 0 m s
16 0
HS U PA Internet
14 0 ~5 0 Iu + core
12 0 ms RNC
I -HS PA Iub
10 0
~2 5 Node B
80 ms AI
60 UE
40
20
0
T o d ay HS D P A HS D P A+ HS U P A I - HS D P A+
I - HS U P A


Conclusions


Conclusions (1/2)

 High Speed Packet Access evolution for WCDMA was
introduced in Release 5 and 6 for downlink and uplink,
respectively
 HSPA offers much higher peak data rates, reaching in
theory up to 14 Mbps in the downlink and 5,4 Mbps in the
uplink, in addition to reduced delays
 Key technologies with HSPA are
 Fast Layer 1 retransmissions i.e. HARQ
 Node B scheduling
 Shorter frame size (2ms in DL and 2/10ms UL)
 Higher order modulation and coding along with link adaptation
in downlink
 Real support for multicodes in the uplink


Conclusions (2/2)

 HSPA improved also the performance of delay critical low
bit rate services like VoIP even though it was not originally
designed for it
 Continuous Packet Connectivity (CPC) enhancements
introduced in Release 7 improved VoIP performance even
more
 I-HSPA was introduced to provide competitive internet
access solution
 High data rates with low delay
 Reduced costs => flat rate could be possible
 Femtocells were introduced to improve the mobile
convergence and performance in small offices or at home,
for instance


HSPA vs DCH (basic WCDMA)
Feature DCH HSUPA HSDPA

Variable spreading factor Yes Yes No

Multicode transmission Yes Yes Yes
(No in practice)

Fast power control Yes Yes No

Soft handover Yes Yes No
(associated DCH only)

Adaptive modulation No No Yes

BTS based scheduling No Yes Yes

Fast L1 HARQ No Yes Yes


HSPA Peak Data Rates
Downlink HSDPA Uplink HSUPA
 Theoretical up to 14.4 Mbps  Theoretical up to 5.76 Mbps
 Initial capability 1.8 – 3.6 Mbps  Initial capability 1.46 Mbps
M ax M ax
# of c od M od u l a t i on
es # of c od es T T I
dat a r at e dat a r at e
5 cod e s Q PS K 1.8 M b p s 2 ms
2 x SF4 1.4 6 M b p s
10 m s
5 cod e s 16 - Q AM 3 .6 M b p s 2 x SF2 10 m s 2 .0 M b p s

10 c o d e s 16 - Q AM 7 .2 M b p s 2 x SF2 2 ms 2 .9 M b p s

15 c o d e s 16 - Q AM 10 .1 M b p s 2 x SF2 +
2 ms 5 .7 6 M b p s
2 x SF4
15 c o d e s 16 - Q AM 14 .4 M b p s


Thank you!
kari.aho@magister.fi


HSPA systems overview

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