As HSPA evolution continues to address the needs of changing user behavior, new techniques develop and become standardized. This article covers some of the more interesting techniques and concepts under study that will provide network operators with the flexibility, capacity and coverage needed to carry voice and data into the future, ensuring HSPA evolution and good user experience.

1. The communications technology journal since 1924 2013 • 9
HSPA evolution for future
mobile-broadband needs
August 28, 2013

2. HSPA evolution for future
mobile-broadband needs
As HSPA continues to evolve, addressing the needs of changing user behavior, new
techniques develop and become standardized. These techniques provide network operators
with the flexibility, capacity and coverage needed to carry voice and data into the future.
achievedbysecuring:
capacity–tohandlegrowingsmart-
phonetrafficcost-efficiently;
flexibility–tomanagethewiderangeof
trafficpatternsefficiently;and
coverage–toensuregoodvoiceandapp
userexperienceeverywhere.
Appcoverage
For smartphone applications, like
social networking and video stream-
ing, to function correctly, access to
the data network and a network that
can deliver a defined minimum lev-
el of performance is needed. The rela-
tionship between the performance
requirements (in terms of data speed
and response time) of an application
and the actual performance delivered
by the network for that user at their
location at a given time determines
howwelltheuserperceivestheperfor-
manceoftheapplication.
The term app coverage denotes the
level of network performance need-
ed to provide subscribers with a sat-
isfactory user experience for a given
application. In the past, the task of
dimensioning networks was simpler,
as calculations were based on deliv-
ering target levels of voice coverage
and providing a minimum data rate.
Today’s applications, however, have
widely varying performance require-
ments. As a result, dimensioning a
network has become a more dynam-
ic process and one that needs to take
these varying performance require-
mentsintoconsideration,forappsthat
arecurrentlypopularwithsubscribers.
Footprint
Illustrated in Figure 2, at the end
of 2012, 55 percent of the world’s
replacingvoice-centricfeaturephones.
For less than USD 100, consumers can
purchase highly capable WCDMA/
HSPA-enabledsmartphoneswithdual-
core processors and dual-band oper-
ation that support data rates up to
14.4Mbps.Thisprice-to-­sophistication
ratio has turned the smartphone into
an affordable mass-market product,
and has accelerated the increase in
smartphonesubscriptions–­estimated
to rise from 1.2 billion at the end of
2012to4.5billionby20181
.
Ericsson ConsumerLab studied
a group of people to assess how they
perceived network quality and what
issues they encountered when using
their smartphones. The study identi-
fiedtwokeyfactorsthatareessentialto
theperceivedvalueofasmartphone:a
fastandreliableconnectiontothedata
network,andgoodcoverage2
.
These findings highlight an impor-
tant goal for operators: to provide
all network users with high-speed
data services and good-quality voice
­services everywhere. This can be
NIKLAS JOHANSSON, LINDA BRUS, ERIK LARSSON, BILLY HOGAN AND PETER VON WRYCZA
BOX A Terms and abbreviations
CELL_FACH Cell forward access channel
CPC Continuous Packet Connectivity
DPCH Dedicated Physical Channel
EUL Enhanced Uplink
HS-DSCH High-Speed Downlink Shared
Channel
HSDPA High-speed Downlink
Packet Access
HSPA High-speed Packet Access
HSUPA High-speed Uplink Packet Access
LPN low-power node
M2M machine-to-machine
MBB mobile broadband
MIMO multiple-input multiple-output
ROT rise-over-thermal
SRB Signaling Radio Bearer
UL uplink
URA_PCH UTRAN registration area
paging channel
UTRAN Universal Terrestrial
Radio Access Network
WCDMA Wideband Code Division Multiple
Access
Mobile broadband (MBB),
providing high-speed internet
access from more or less
anywhere, is becoming a reality
for an increasing proportion of
the world’s population. There
are several factors fuelling the
need for high-performance
MBB networks, not the least,
the growing number of mobile
internet connections. As Figure 1
illustrates, global mobile
subscriptions (excluding M2M)
are predicted to grow to 9.1 billion
by the end of 2018. Nearly 80
percent of mobile subscriptions
will be MBB ones1
, indicating that
MBB will be the primary service
for most operators in the coming
years.
Impactofaffordablesmartphones
To a large extent, the rapid growth
of MBB can be attributed to the wide-
spread availability of low-cost MBB-
capable smartphones, which are
2
ERICSSON REVIEW • AUGUST 28, 2013
Smarter networks

3. population was covered by WCDMA/
HSPA, a figure that is set to rise to 85
percent by the end of 20181
. Today,
many developed markets are nearing
the 100 percent population coverage
mark3
. This widespread deployment,
togetherwithsupportforthebroadest
rangeofdevices,makesWCDMA/HSPA
the primary radio-access technology
to handle the bulk of MBB and smart-
phonetrafficforyearstocome.
Since its initial release, the 3GPP
WCDMA standard has, and continues
to,evolveextensively.Today,WCDMA/
HSPA is a best-in-class voice solution
withexceptionalvoiceaccessibilityand
retainability. It offers high call reten-
tionaswellasbeinganexcellentaccess
technologyforMBB,asitdelivershigh
data rates and high cell-edge through-
put – all of which enable good user
experienceacrosstheentirenetwork.
ThecontinuedevolutionofWCDMA/
HSPAinReleases11and12includessev-
eral key features that aim to increase
network flexibility and capacity to
meet growing smartphone traffic and
securevoiceandappcoverage.
Evolutionoftrafficpatterns
Applications have varying demands
and behaviors when it comes to when
and how much data they transmit.
Some apps transmit a large amount
of data continuously for substantial
periods of time and some transmit
small packets at intervals that can
range from a few seconds to minutes
orevenlonger.Applicationshavevary-
ing demands, typically sending lots of
data in bursts, interspersed with peri-
ods of inactivity when they send little
ornodataatall.
Rapid handling of individual user
requests, enabled by high instanta-
neous data rates, improves overall net-
work performance as control-channel
overhead is reduced and capacity for
other traffic becomes available soon-
er. So, if a network can fulfill requests
speedily, all users will experience the
benefits of reduced latency and faster
round-triptimes.
Web browsing on a smartphone is a
classicexampleofaburstyapplication,
bothforuplinkanddownlinkcommu-
nication.Whenasmartphonerequests
the components of a web page from
the network (in the uplink) they are
transferredinbursts(inthedownlink),
andthedeviceacknowledgesreceiptof
the content (in the uplink). As a result,
uplink and downlink performance
becomes tightly connected and there-
fore better uplink performance has a
positive effect on downlink data rates
aswellasoverallsystemthroughput.
Forwebbrowsing,theinstantaneous
downlinkspeedformobileusersneeds
tobemuchhigheronaveragethanthe
uplinkspeed.However,thenumberof
services requiring higher data rates in
the uplink, such as video calling and
cloud synching of smartphone data, is
ontherise.
As user behavior changes, traffic-­
volumepatternsalsochange,andmea-
surements show it is becoming more
commonforuplinklevelstobeon
FIGURE 1 Mobile and MBB subscriptions (2009-2018)1
Mobile subscriptions
Mobile broadband
2009 2010 2011 2012 2013 2014 2015 2016 2017 2018
0
2,000
1,000
3,000
4,000
6,000
5,000
8,000
7,000
9,000
10,000
Subscriptions/lines (million)
FIGURE 2 Population coverage by technology (2012-2018)
100
80
60
40
20
2012 2018 2012 2018 2012 2018
0
%populationcoverage
(Source: Ericsson1
)
85%
90%
~55%
85%
~10%
~60%
GSM/EDGE WCDMA/HSPA LTE
3
ERICSSON REVIEW • AUGUST 28, 2013

4. par with downlink levels, and in
some cases even outweigh the down-
link traffic. Consequently, continuing
to develop data rates to secure uplink-
heavyservicesiskeytoimprovingover-
alluserperformance.
Highperformancenetworks
Thestandardapproachusedtocreatea
high-performance network with wide
coverage and high capacity is to first
improve the macro layer, then ­densify
it by deploying additional macro base
stations, and finally add low power
nodes (LPNs) in strategic places, such
astraffichotspots,thatcanoffloadthe
­macronetwork.
Each step addresses specific perfor-
mance targets and applies to different
population densities, from urban to
rural – as illustrated in Figure 3. The
evolution of WCDMA/HSPA includes a
number of features that target macro
layer improvement and how deploy-
ments where LPNs have been added
canbeenhanced.
Improvingtheuplink
Featuresinthe3GPPspecificationhave
recentlyachievedsubstantialimprove-
ment of uplink capabilities. Features
such as uplink multi-carrier, higher-
order modulation with MIMO, EUL
in CELL_FACH state, and Continuous
Packet Connectivity (CPC) have multi-
plied the peak rate (up to 34Mbps per
carrierinRelease11)andincreasedthe
number of simultaneous users a net-
workcansupportalmostfivefold.
Given the high uplink capabilities
already supported by the standard,
thenextdevelopment(Release12)will
enable and extend the use of these
capabilities to as many network users
aspossible.
Themaximumalloweduplinkinter-
ference level in a cell, also known as
maximum rise-over-thermal (ROT),
is a highly important quantifier in
WCDMAnetworks.Thisisbecausethe
maximum allowed interference level
has a direct impact on the peak data
ratesthatthecellcandeliver.
Typically, macro cells are dimen-
sioned with an average ROT of around
7dB, which enables UL data rates of
5.7Mbps (supported by most commer-
cial smartphones), and secures voice
and data coverage for cell-edge users.
FIGURE 3 Where to improve, densify and add
Improve
Densify
Add
Improve
Densify
Improve
Dense
urban
Urban Suburban Rural
Area traffic density
FIGURE 4 Relationship between maximum interference and peak rate
UL ROT
Rate
Y
X
Y = Maximum interference
handled by the network
X = Maximum uplink data
rate that can be achieved
Legend
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ERICSSON REVIEW • AUGUST 28, 2013
Smarter networks

5. High data rates, such as 11Mbps (avail-
ablesincerelease7)and34Mbps(avail-
ablesincerelease11)requireROTlevels
greaterthan10dBand20dBrespective-
ly.Figure 4illustratestherelationship
betweenROTandpeakdatarate.
The maximum uplink interference
level permissible is determined by a
number of factors including the den-
sity of the network, the capability of
thenetworktohandleinterference(for
example with advanced techniques
suchasInterferenceSuppression),and
the capabilities of the devices in the
network,includingbothsmartphones
andlegacyfeaturephones.
The Lean Carrier solution, intro-
duced in Release 12, is an additional
capability that helps operators meet
the needs of high-data-rate users. This
multi-carrier solution is built on the
Release 9 HSUPA dual-carrier one that
is currently being implemented in
commercial smartphones. The dual-
carrier solution allows two carriers,
primaryandsecondary,tobeassigned
to a user. By doing this, the traffic gen-
eratedbytheusercanbeallocatedina
flexible way between the two carriers,
while at the same time doubling the
maximumpeakrateachievable.
TheLeanCarriersolutionoptimizes
thesecondarycarrierforfastandflexi-
blehandlingofmultiplehigh-data-rate
users, through more efficient grant-
ingandlowercostperbit.Thesolution
is designed to support multiple bursty
data users in a cell transmitting at the
highestpeakrateswithoutcausingany
uplinkinterferenceamongthemselves
ortolegacyusers.Tomaximizeenergy
efficiency, the Lean Carrier solution
should cost nothing in system or ter-
minal resources on the secondary car-
rieruntiltheuserstartstosenddata.
LeanCarriercanbeflexiblydeployed
accordingtotheneedsofthenetwork.
For example, the maximum ROT on a
user’s secondary (lean) carrier can be
configured to support any available
uplink peak data rate, while the maxi-
mum ROT on a user’s primary carrier
can be configured to secure cell-edge
coverage for signaling, random access
andlegacy(voice)users.
Rateadaptationisanothertechnolo-
gyunderstudythatresultsinincreased
network capacity for some common
traffic scenarios, such as areas where
subscribers are a mix of high and
low-rate users or areas where there
are only high-rate users. High
uplinkdataratesrequiremorepow-
er. Maintaining a fixed data rate at
thedesiredqualitytargetinanenvi-
ronment where interference lev-
els vary greatly can result in large
fluctuations in received power. To
avoidsuchfluctuations,theconcept
of rate adaptation can be applied.
High-rate users are assigned with a
fixedreceived-powerbudget,andas
interferencelevelschange,bitrates
areadaptedtomaintainthedesired
quality target, while not exceeding
theallowedpowerbudget.Inshort,
as illustrated in Figure 5, the bit
rate is adapted to received power,
andnotthepowertotherate.
Limitingfluctuationsinreceived
power for high-rate users is good
for overall system capacity because
these high-rate users can transmit
more efficiently, and other users in
thesystem,includinglow-rateones
such as voice users, consume less
powerwhenpowerlevelsarestable
andpredictable.
Maintaining a device in connect-
ed mode for as long as possible is
anothertechniquethatcanbeused
to improve performance of the
uplink.
Smartphone users want to be
able to rapidly access the network
from a state of inactivity. Maintaining
a device in a connected-mode state,
such as CELL_FACH or URA_PCH, for
aslongaspossibleisonewayofachiev-
ing this – access to the network from
these states is much faster than from
the IDLE state. In recent releases, con-
nectedmodehasbeenmademoreeffi-
cientfromabatteryandresourcepoint
ofviewthroughtheintroductionoffea-
turessuchasCPC,fractionalDPCHand
SRB on HS-DSCH. As a consequence it
is now feasible to maintain inactive
devicesinthesestatesforlonger.
As the number of smartphone
users increases, networks need flexi-
ble mechanisms to maintain high sys-
tem throughput, even during periods
of extremely heavy load. Allowing the
networktocontrolthenumberofcon-
currently active users, as well as the
number of random accesses, is one
suchmechanism.
Improvements that enable high
throughput under heavy load, and
allowuserstobenefitfromlowerlaten-
cy in connected mode, while enabling
service-differentiated admission deci-
sions and control over the number of
simultaneous users, have been pro-
posedforRelease12.
Expandingvoiceandappcoverage
Good coverage is crucial for positive
smartphone user experience and cus-
tomerloyalty2
,whichforoperators
FIGURE 5 Rate adaptation results in predictable interference levels
Baseline: Fixed rate
variable power
Received power
DATA
Control
DATA
Control
Time
Rate adaptation: Fixed
received power and
variable rate
5
ERICSSON REVIEW • AUGUST 28, 2013

6. lower-rate speech codecs, where-
as, four-way receiver diversity and
advanced antennas can improve cov-
erageforbothvoiceanddata.
Uplinktransmitdiversitywasintro-
duced in Release 11. This feature sup-
ports terminals with two antennas to
increase the reliability and coverage
of uplink transmissions and decrease
overall interference in the system. It
works by allowing the device to use
both antennas for transmission in
an efficient way using beamforming.
Figure 6 illustrates how the radio
transmission becomes focused in a
given direction, resulting in a reduc-
tionininterferencebetweenthedevice
and other nodes, and improving over-
all­systemperformance.
An additional mode within uplink
transmitdiversityisantennaselection.
Here, the antenna with the best radio
propagation conditions is chosen for
transmission. This is useful, for exam-
ple, when one antenna is obstructed
by the user’s hand. Uplink transmit
diversity increases the coverage of all
uplink traffic for voice calls and data
transmissions.
With Release 11, multi-flow HSDPA
transmissions are supported. This
allows two separate nodes to transmit
to the same terminal, improving per-
formanceforusersatthecelledgeand
resultinginbetterappcoverage.
In Release 12, simultaneous app
data and voice call transmissions will
become more efficient, and the time
it takes to switch transmission time
interval from 10ms to 2ms is consid-
erably shorter. These improvements
increasebothvoiceandappcoverage.
Enhancingsmall-celldeployments
The addition of small cells through
deploying LPNs in a macro network –
resulting in a heterogeneous network
–isastrategicwaytoimprovecapacity,
dataratesandcoverageinurbanareas.
Typically, the deployment of LPNs is
beneficialinhotspotswheredatausage
is heavy, to bridge coverage holes cre-
ated by complex radio environments,
andinsomespecificdeploymentssuch
asin-buildingsolutions.
Figure 7 shows the performance
gains in a heterogeneous-network
deployment (described in Box B).
Offloading to small cells not only
FIGURE 7 System-level gains – for scenario described in Box B
1W
5W
0
50
Average Cell edge
100
150
200
250
300
User throughput gain (percent)
BOX B
The system
The scenario
shown in
Figure 7 is for
bursty traffic.
Four LPNs have
been added
to each macro
base station in
the network,
and 50 percent
of the users are
located in traffic
hotspots. The
transmission
power for the
macro base
station was
20W, and 1W and
5W LPNs were
deployed.
LPNs were
deployed
randomly and
no LPN range
expansion was
used. Gains are
given relative
to a macro-only
deployment.
Offloading was
32 percent for
1W LPNs and 41
percent for 5W
LPNs, where
offloading is a
measure of the
percentage of
traffic served by
the LPN.
FIGURE 6 Release 11 uplink transmit diversity beamforming
translatesintosecuringvoicecoverage
and delivering data-service coverage
that meets the needs of current and
futureapps.
There are several ways to improve
coverage for voice and data. One way
is to use lower frequency bands, and
refarmingthe900MHzspectrumfrom
GSM, for example, provides a consid-
erable coverage improvement when
compared to 2GHz bands. Voice cover-
agecanbesignificantlyextendedwith
6
ERICSSON REVIEW • AUGUST 28, 2013
Smarter networks

7. 1. Ericsson Mobility Report, June 2013, available at:
http://www.ericsson.com/res/docs/2013/ericsson-mobility-report-june-2013.pdf
2. Ericsson ConsumerLab report, January 2013, Smartphone usage experience –
the importance of network quality and its impact on user satisfaction, available
at: http://www.ericsson.com/news/130115-ericsson-consumerlab-report-
network-quality-is-central-to-positive-smartphone-user-experiences-and-
customer-loyalty_244129229_c
3. International Communications Market Report 2011, Ofcom, available at: http://
stakeholders.ofcom.org.uk/binaries/research/cmr/cmr11/icmr/ICMR2011.pdf
References
FIGURE 8 LPN deployment scenarios
LPN LPN
LPN
Macro
LPNs deployed as separate cells
on the same carrier
RNC
LPN LPN
LPN
Macro
LPNs deployed as part of a combined cell
on the same carrier
RNC
7
ERICSSON REVIEW • AUGUST 28, 2013
provides increased capacity for han-
dlingsmartphonetraffic,italsoresults
inenhancedappcoverage.
To maximize spectrum usage, the
traditional macro base stations and
LPNs share the same frequency, either
with separate or shared cell identi-
ties. These deployments, illustrated in
Figure 8, are referred to as separate
cellandcombinedcell.
It is possible to operate both sepa-
rate and combined-cell deployments
based on functionality already imple-
mentedinthe3GPPstandard,andsuch
deployments have been shown to pro-
videsubstantialperformancebenefits
overmacro-onlydeployments.
Today, combined cells tend to be
deployed in specific scenarios, such as
railroad,highwayandin-buildingenvi-
ronments. Separate-cell deployments,
on the other hand, are more generic
andprovideacapacityincreaseinmore
commonscenarios.
In 3GPP Release 12, small-cell range
expansion techniques and control
channel improvements are being
introduced to enable further offload-
ing of the macro network. Mobility
performance enhancements for users
moving at high speeds through small
cell deployments are also being inves-
tigatedby3GPP.
When a macro cell in a combined-
celldeploymentiscomplementedwith
additionalLPNsclosetousers,thedata
rateandnetworkcapacityisimproved.
By allowing the network to reuse the
same spreading codes in different
parts of the combined cell, the cell’s
capacity can be further increased – a
techniquebeingstudiedinRelease12.
Andasthereisnofundamentaluplink/
downlink imbalance in a combined
cell, mobility signaling is robust, sig-
naling load is reduced, and network
managementissimplified.
In summary, heterogeneous net-
worksareessentialforhandlinggrow-
ing smartphone traffic because they
supportflexibledeploymentstrategies,
increase the capacity of a given HSPA
network,andextendvoiceandappcov-
erage. The improvements standard-
izedinRelease12willfurtherenhance
theseproperties.
Conclusions
WCDMA/HSPA will be the main
technology providing MBB for
many years to come. Operators want
WCDMA/HSPA networks that can
guarantee excellent user experience
throughout the whole network cover-
age area for all types of current and
future mobile devices. The prerequi-
sitesfornetworksare:
capacity–tohandlegrowingsmart-
phonetrafficcost-efficiently;
flexibility–tomanagethewiderangeof
trafficpatternsefficiently;and
coverage–toensuregoodvoiceandapp
userexperienceeverywhere.
HSPA evolution, through the capabili-
tiesalreadyavailablein3GPPandthose
under study in 3GPP Release 12, aims
to fulfill these prerequisites. There
are several ways to improve voice and
app coverage. Enhancements to the
uplink improve the ability to quick-
ly and efficiently serve bursty traf-
fic – improving user experience and
increasing smartphone capacity.
Small-cellimprovementswillincrease
networkcapacityforsmartphonetraf-
fic and further improve voice and app
coverage.
With all of these enhancements,
WCDMA/HSPA, already the dominant
MBB and best-in-class voice technolo-
gy,hasastrongevolutionpathtomeet
the future demands presented by the
growth of MBB and highly capable
smartphonesglobally.

8. Telefonaktiebolaget LM Ericsson
SE-164 83 Stockholm, Sweden
Phone: + 46 10 719 0000
Fax: +46 8 522 915 99
284 23-3201 | Uen
ISSN 0014-0171
© Ericsson AB 2013
Niklas Johansson
is a senior researcher at
Ericsson Research. He
joined Ericsson after
receiving his M.Sc. in
engineering physics and B.Sc. in
business studies from Uppsala
University in 2008. Since joining
Ericsson, he has been involved in
developing advanced receiver
algorithms and multi-antenna
transmission concepts. Currently, he is
project manager for the Ericsson
Research project that is developing
concepts and features for 3GPP
Release 12.
Peter von Wrycza
is a senior researcher at
Ericsson Research, where
he works with the
development and
standardization of HSPA. He received
an M.Sc. (summa cum laude) in
electrical engineering from the Royal
Institute of Technology (KTH),
Stockholm, Sweden, in 2005, and was
an electrical engineering graduate
student at Stanford University,
Stanford, CA, in 2003-2005. In 2010,
he received a Ph.D. in
telecommunications from KTH.
Erik Larsson
joined Ericsson in 2005.
Since then has held
various positions at
Ericsson Research,
working with baseband algorithm
design and concept development for
HSPA. Today, he is a system engineer
in the Technical Management group in
the Product Development Unit
WCDMA and Multi-Standard RAN and
works with concept development and
standardization of HSPA. He holds an
M.Sc. in engineering physics (1999)
and a Ph.D. in signal processing
(2004), both from Uppsala University,
Sweden.
Billy Hogan
joined Ericsson in 1995
and works in the Technical
Management group in the
Product Development
Unit WCDMA and Multi-Standard RAN.
He is a senior specialist in the area of
enhanced uplink for HSPA. He works
with the system design and
performance of EUL features and
algorithms in the RAN product, and
with the strategic evolution of EUL to
meet future needs. He is currently
team leader of the EUL Enhancements
team for 3GPP release 12. He holds a
B.E. in electronic engineering from the
National University of Ireland, Galway,
and an M.Eng in electronic engineering
from Dublin City University, Ireland.
Linda Brus
joined Ericsson in 2008.
Since then, she has been
working with system
simulations, performance
evaluations, and developing algorithms
for WCDMA RAN. Today, she is a
system engineer in the Technical
Management group in the Product
Development Unit WCDMA and Multi-
Standard RAN, working with concept
development for the RAN product and
HSPA evolution. She holds a Ph.D. in
electrical engineering, specializing in
automatic control (2008) from
Uppsala University, Sweden.
8
ERICSSON REVIEW • AUGUST 28, 2013
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