5 hspa evolution

Ericsson Review No. 1, 200832
HSPA Evolution – Boosting the
performance of mobile broadband access
Johan Bergman, Mårten Ericson, Dirk Gerstenberger, Bo Göransson, Janne Peisa and Stefan
Wager
Introduction
Today, 84% of all reported global cellular
subscribers make calls via radio access tech-
nology specified by the Third Generation
Partnership Project (3GPP). This signifies
that WCDMA is the predominant third-
generation (3G) radio network technology,
and as such, represents a substantial economy
of scale.
In addition, the recent introduction of
high-speed packet access (HSPA, 3GPP Re-
lease 6) has
significantly improved the performance
of packet data traffic in Ericsson products
– on the downlink (HSDPA) 14Mbps, and
uplink (E-UL), 1.4Mbps, giving users a
mobile broadband experience that is on
par with ADSL; and
given rise to large increases in packet data
traffic – packet data is now the principal
type of traffic in 3G networks.1-2
•
•
Ericsson continues to build on this success
by enabling operators who have deployed
WCDMA to boost their system performance
through software upgrades. The HSPA Evo-
lution specification (3GPP Releases 7 and 8)
introduces new features that support higher
data bit rates, lower latency, greater capacity,
better support for VoIP, and improved sup-
port for multicast services.1-2
Release 7 of the
specification introduces:
higher-order modulation (HOM);
multiple input, multiple output (MIMO);
continuous packet connectivity (CPC);
layer-2 enhancements;
enhanced CELL_FACH;
multicast/broadcast single-frequency net-
work (MBSFN); and
advanced receivers.
In addition, 3GPP is considering multi-
carrier operation, downlink-optimized
broadcast (DOB) and more advanced receiv-
ers for future releases of the specification.
•
•
•
•
•
•
•
These new concepts will yield substantial-
ly higher peak data bit rates as well as greater
spectral efficiency and voice-over-IP (VoIP)
capacity. In Release 8, for example, the peak
data bit rates will reach up to 42Mbps in the
downlink and 11Mbps in the uplink (per
5MHz carrier).
This article deals primarily with the fea-
tures 3GPP has added to HSPA in Releases
7 and 8 of the WCDMA specification.1-2
It
also touches on candidate techniques for
further evolving the specification in future
releases.
HSPA features and
performance
Higher-order modulation
The digital modulation scheme determines
how bits are mapped to the phase and am-
plitude of transmitted signals. Figure 1 de-
picts the constellation diagrams of a variety
of modulation schemes. Each consecutive
bit sequence is mapped to a modulation
symbol whose phase and amplitude cor-
respond to one of the constellation points.
The number of bits conveyed per modula-
tion symbol is as follows: 1 for BPSK, 2 for
QPSK, 4 for 16QAM, and 6 for 64QAM.
Therefore, higher modulation order means
greater achievable peak data bit rate for a
given symbol rate.
HSPA (3GPP Release 6) supports the
QPSK and 16QAM modulation schemes
in the downlink and the BPSK and QPSK
modulation schemes in the uplink. Release
7 introduces higher-order modulations that
increase the data bit rate. In the down-
link, it introduces 64QAM, increasing the
peak data bit rate by 50% from 14Mbps to
21Mbps. In the uplink, 16QAM doubles
the peak data bit rate from 5.7Mbps to
11Mbps.
Furthermore, the physical control channels
(HS-SCCH, HS-DPCCH, E-AGCH and
E-DPCCH) have been modified to support
signaling of the new modulation schemes;
larger transport block sizes; and
larger range for the channel quality indica-
tor (CQI).
Higher-order modulation enables users to
experience significantly higher data bit rates
under favorable radio-propagation condi-
tions. Careful cell planning is a prerequisite
for achieving these conditions. Table 1 sum-
marizes a number of HSPA features.
•
•
•
This article presents the main concepts of HSPA Evolution (high-speed
packet access evolution), which is currently being standardized by 3GPP
in Releases 7 and 8 of the WCDMA specification. The aim of HSPA Evolu-
tion is to further improve the performance of WCDMA systems through
higher peak rates, lower latency, greater capacity, increased battery
times, better support for VoIP, and improved multicast/broadcast capabili-
ties.
The authors briefly cover MIMO, higher-order modulation, protocol
optimizations, optimizations for VoIP, improved multicast/broadcast, and
advanced receivers. They also describe a variety of features (such as
multicarrier operation) that will boost performance even further in subse-
quent releases of the WCDMA specification.
TERMS AND ABBREVIATIONS
3GPP Third Generation Partnership
Project
ADSL Asymmetric digital subscriber line
BPSK Binary phase-shift keying
CPC Continuous packet connectivity
CQI Channel quality indicator
DOB Downlink-optimized broadcast
E-UL Enhanced uplink
FDD Frequency-division multiplexing
HARQ Hybrid automatic repeat request
HOM Higher-order modulation
HSPA High-speed packet access
(HSPDA + E-UL)
HSPDA High-speed packet downlink
access
MAC Media access control
MBSFN Multicast/broadcast single-
frequency network
MIMO Multiple input, multiple output
MMSE Minimum mean-squared error
PDU Packet data unit
QAM Quadrature amplitude modulation
QPSK Quadrature phase-shift keying
RLC Radio link control
RRC Radio resource control
RTT Roundtrip time
SDU Service data unit
TDD Time-division multiplexing
UE User equipment (terminal)
VoIP Voice over IP
WCDMA Wideband code-division multiple
access
Review108.indd 32Review108.indd 32 08-01-21 16.12.0908-01-21 16.12.09

Ericsson Review No. 1, 2008 33
Multiple input, multiple output
One can increase the data bit rate by trans-
mitting multiple transport blocks in paral-
lel using multiple antennas to a single user.
This technique is often termed MIMO with
spatial multiplexing (as opposed to trans-
mit/receive diversity, where a single trans-
port block is sent or received by multiple
antennas). The receiver uses channel proper-
ties and knowledge of the coding scheme to
separate the data streams. Note: A prerequi-
site for MIMO is the standardization of the
multilayer transmission scheme.
For HSDPA, 3GPP chose a MIMO scheme
that is based on precoded and rank-adaptive
multi-codeword transmission. This means
that
each layer (substream) carries separate
transport blocks; and
the number of parallel streams can be
adapted to the current channel conditions
(rank adaptation).
Separate encoding facilitates the use of suc-
cessive interference cancellation receivers,
which are anticipated to boost performance
compared with linear receivers (for example,
MMSE-based receivers).
Before data is transmitted, the modulated
and spread signal is spatially weighted (pre-
coded) or, in other words, the data streams
are transmitted over separate transmit an-
tennas using different transmission weights.
The preferred weights are estimated by the
user equipment (UE) and fed back to the
network together with the channel quality
indicator. The main benefit of precoding is
that both power amplifiers are loaded even
when a single transport block is transmitted.
When two streams are transmitted, each
stream contains the same channelization
codes. Figure 2 shows the MIMO transmit-
ter chain.
To incorporate MIMO into Release 7,
3GPP has updated the uplink and downlink
physical control channels (HS-SCCH and
HS-DPCCH) to accommodate information
about precoder weights, the transport for-
mat, and hybrid automatic repeat request
(HARQ) parameters per stream.
In Release 7, MIMO is defined for trans-
mitting up to two streams. In this case, each
stream can use QPSK or 16QAM, extending
the peak data bit rate of HSDPA to approxi-
mately 28Mbps. In Release 8, each stream
can use 64QAM, which extends the peak
data bit rate to 42Mbps (Figure 3).
HARQ acknowledges each stream sepa-
rately and independently. Undetected blocks
•
•
TABLE 1. HSPA FEATURES
Feature Explanation
Higher-order modulation Using more bits per symbol raises the peak
data bit rate by 50% in the downlink and 100%
in the uplink.
Multiple input, multiple output Employing two transmitter antennas at Node-B
and at least two receiver antennas at the UE
has the potential to increase the peak data bit
rate by 100%.
Multicarrier By using N 5MHz carriers, one can increase
the data rate can N-fold.
Continuous packet connectivity (CPC) CPC improves the physical layer signaling,
resulting in lower latency, greater capacity, and
better battery time.
Layer-2 enhancements To match the higher bit rates provided by the
physical layer, layer 2 has been optimized to
support higher peak data bit rates and greater
coverage.
Enhanced CELL_FACH Improved support for background traffic and
faster switching to continuous transmission
state.
MBMS single-frequency network, downlink-
optimized broadcast
Transmitting the same waveform from mul-
tiple cells puts the broadcast capabilities of
WCDMA on par with, for example, DVB-H.
Figure 1
Constellation diagrams of modulation schemes.

can thus be retransmitted independently be-
tween the two streams.
Multicarrier operation
Multicarrier operation is a candidate for a
future 3GPP release of the WCDMA speci-
fication. Operators with access to multiple
adjacent paired frequency bands can make
efficient use of spectrum by operating HSPA
on multiple adjacent 5MHz carriers in a co-
ordinated way. Control channel structures,
for instance, need not be fully replicated in
all carriers. By having only one anchor car-
rier, for example, one can have more power
for HSPA in the other carriers. Therefore, if
it is impractical to deploy 2x2 MIMO, opera-
tors might consider multicarrier operation on
two carriers as an alternative way of reach-
ing downlink peak data bit rates of 42Mbps.
On the other hand, however, the operation of
two carriers in combination with 2x2 MIMO
and 64QAM will yield peak data bit rates of
up to 84Mbps without requiring 4x4 MIMO
antenna systems. What is more, four carriers
can support 4x42Mbps.
Layer-2 enhancements
The downlink peak data bit rate using ac-
knowledged-mode radio link control (RLC)
is limited by the size of the RLC protocol
data unit (PDU), RLC roundtrip time (RTT),
and the size of the RLC window.
A large RLC PDU size is needed to sustain
the peak data bit rates obtained in the down-
link with MIMO and 64QAM modulation.
Therefore, to make efficient use of large
PDU sizes, and to generally enhance the
performance of the layer-2 protocol, Release
7 adopts flexible RLC sizes, media access
control (MAC) segmentation, and improved
MAC multiplexing for downlink transmis-
sion. As a consequence, the transmitter may
freely select the size of the RLC PDU.
The ability to segment the RLC has been
preserved, and in general the network can
segment RLC service data units (SDU) into
PDUs, which facilitates more efficient trans-
mission and retransmission over the air inter-
face. The ability of the transmitter to flexibly
select the size of RLC PDUs helps reduce
level-2 protocol overhead by reducing RLC
header overhead and padding. In addition,
the use of larger PDUs means that UEs need
not process as many of them.
In the downlink, the RLC protocol is
originated in the radio network controller
(RNC), whereas the MAC-hs is terminated
in the Node-B. If, due to changing radio con-
Figure 3
Ninetieth percentile throughput in Pedestrian A-channel for higher-order modulation and
multiple input/multiple output (MIMO).
Figure 2
The MIMO transmitter chain.

ditions, the RLC PDUs are too large to be
transmitted over the air interface with a rea-
sonable number of HARQ retransmissions,
then they must be segmented. Accordingly,
Release 7 introduces a new MAC protocol,
MAC-ehs, which supports flexible RLC PDU
sizes and the segmentation of RLC PDUs. In
addition, the MAC multiplexing capabilities
have been improved so that RLC PDUs that
carry signaling or data from different radio
access bearers can now be multiplexed into a
single MAC-ehs PDU.
In Release 8, the enhancements made to
the downlink protocol will be applied to the
uplink protocol. Support for flexible RLC
PDU sizes improves uplink coverage and
helps reduce processing and level-2 over-
head.
Continuous packet connectivity
The activity level of packet data users var-
ies considerably over time. Even so, from an
end-user point of view, in order to avoid the
delays associated with state transitions, it
might be advantageous to remain in a state
with a dedicated connection (CELL_DCH)
even when temporarily inactive.
3GPP has worked to make the dedicated
connection state for packet data users more
efficient in Release 7. The result of these ef-
forts is commonly referred to as continuous
packet connectivity (CPC). CPC consists of
two main features called UE DTX/DRX
and HS-SCCH-less operation.
UE DTX/DRX
UE DTX (discontinuous transmission from
the UE) allows UEs to switch off continuous
transmission of the dedicated physical control
channel (DPCCH) when there is no informa-
tion to transmit in the uplink. When this
is the case, only a minimum of transmission
is needed to maintain synchronization and
control power. Two immediate benefits of
switching off transmission are reduced bat-
tery consumption and reduced interference,
which increases uplink capacity (in terms of
number of users).
By the same token, UE DRX (discontinu-
ous reception at the UE) allows UEs to switch
off their receivers when there is nothing to be
received in the downlink. This technique can
be exploited to further reduce battery con-
sumption. The UEs need only periodically
check to see if they should to wake up from
their “micro sleep” mode.
In Release 7, UE DTX/DRX can be de-
ployed even during very short periods of in-
activity between the packets of a VoIP call.
HS-SCCH-less operation
When many small packets (typically VoIP
packets) are transported in the downlink, the
overhead from the downlink control channel,
HS-SCCH, becomes significant. Release 7
introduces HS-SCCH-less operation, which
reduces this overhead by removing the HS-
SCCH transmission completely for the first
HARQ transmission. HS-SCCH-less opera-
tion relies on blind decoding of up to four
different formats of the downlink data chan-
nel, HS-DSCH, in the UE to eliminate the
need for HS-SCCH transmission. In sum-
mary, the concept increases capacity in the
downlink by reducing code usage as well as
interference from control signaling. Figure 4
shows the relative increase in VoIP capacity
compared with 3GPP Release 6.
Simulations show that the CPC concept in
Release 7 boosts capacity for VoIP by around
40% in the uplink and 10% in the downlink.
The addition of advanced receivers boosts ca-
pacity even further.7
Enhanced CELL_FACH
HSPA is becoming a replacement to ADSL
for connecting PCs to the internet. This
change in behavior has an impact on traf-
Figure 4
Relative increase in VoIP capacity.

fic load and network characteristics. PCs
run a range of applications that communi-
cate in the background without the need for
end-user interaction. Among other things,
background traffic consists of keep-alive
messages, probes for software updates, and
presence signaling. To efficiently support this
traffic, the 3GPP has worked to enhance the
CELL_FACH state in Releases 7 and 8.
In Release 7, HSDPA has been activated
for users in CELL_FACH. In the downlink,
UEs monitor the HSDPA control channels
to detect scheduling information for their
own specific identities (H-RNTI). The lack
of a dedicated uplink channel means that
the specification (Release 7) does not support
continuous transmission of the channel qual-
ity indicator (CQI) or HARQ feedback. As
a consequence, 3GPP has modified link ad-
aptation and HARQ. The solution has been
to employ HARQ repetitions and to base
link adaptation on measurements of radio
resource control (RRC).
In Release 8, the uplink is improved by
activating E-DCH in CELL_FACH. Trans-
mission begins by ramping up power on a
random preamble as is done in Rel-99. After
having detected the preamble, the Node-B
assigns the UE to a common E-DCH con-
figuration (managed by Node-B). Contention
on the common E-DCH is resolved by means
of UE identities in the E-DCH transmis-
sion. A given UE can efficiently be moved to
CELL_DCH for continuous transmission.
The enhanced CELL_FACH attempts to
have the same layer-2 header format as that
of the CELL_DCH described above. This
way, data transmissions can continue with-
out interruption, even when switching be-
tween CELL_FACH and CELL_DCH. This
enhancement significantly improves user
perception of performance compared with
Release 6, which suspends data transmission
for channel switching.
MBSFN, downlink-optimized broadcast
Release 7 has further optimized MBMS to
boost transmission efficiency beyond what
could be achieved with multicell MBMS
transmission in Release 6.8
The solution,
multicast/broadcast single-frequency net-
work (MBSFN) operation, calls for simulta-
neous transmission of the exact same wave-
form from multiple cells. This way, the UE
receiver perceives the multiple MBSFN cells
as one large cell (Figure 5). Also, instead of
inter-cell interference from neighboring cell
transmissions, the UE experiences construc-
tive superposition of the signals transmitted
from multiple MBSFN cells. What is more,
advanced UE receiver techniques such as
G-RAKE eliminate intra-cell interference
by resolving the time difference of multipath
propagation. The result is highly efficient
radio broadcast transmission derived from
WCDMA technology.
A critical enhancement that eliminates
inter-cell interference is the use of a common
scrambling code on downlink carriers re-
served for MBSFN transmission. In this case,
3GPP did not have to modify the standard
because synchronized network operation for
FDD was included in Release 99.
Broadcast data is transmitted using the
same logical and physical channel structures
as for MBMS – that is, MTCH, FACH and
S-CCPCH, along with control channels such
as MICH and MSCH. MBSFN improves
power efficiency so much that the limiting
factor in the radio downlink is no longer
power but rather codes. For this reason, to
make full use of all available radio resources,
16QAM modulation has been introduced
for MBSFN FACH. And to further enhance
channel estimation in the mobile receiver,
Release 7 introduces support for a time-
multiplexed pilot that uses the synchroniza-
tion channel (SCH). To significantly reduce
battery consumption in UEs, one may even
multiplex services per transmission time in-
terval (TTI).
3GPP proposes to take MBSFN operation
one step further, by introducing the down-
link-optimized broadcast (DOB) concept as
a special mode of 3.84Mbps time-division
duplex (TDD) operation in unpaired bands
of spectrum.
The principles and radio solutions for
DOB are identical to those for MBSFN
FDD, which means radio performance is
identical. It also means that WCDMA opera-
tors with access to unpaired spectrum have
highly attractive options for migrating their
networks. The impact of DOB on UEs and
Node-Bs is minor thanks to maximum com-
monality between WCDMA MBMS and
MBSFN. DOB is thus a promising option
for deploying MBSFN in unpaired bands of
spectrum.
Advanced receivers
Receiver structures in UEs and Node-Bs
are constantly being improved as products
evolve and more complex features are added
to HSPA. The result is improved system
performance and higher user data bit rates.
This trend is reflected in constantly chang-
ing UE receiver requirements in 3GPP:
advanced UE receiver requirements were
introduced in Releases 6 and 7, reflecting
the use of
UE receive antenna diversity (UE receiver
type-1);
linear equalizers, such as G-RAKE (UE
receiver type-2); and
linear equalizers in combination with
UE receive antenna diversity, such as
G-RAKE2 (UE receiver type-3, suitable
for example, for MIMO).
Release 8 will introduce requirements for
even advanced receivers (type-3 G-RAKE2)
with additional support for interference can-
cellation (UE receiver type-3i).
•
•
•
Figure 5
Mobile TV broadcast with MBSFN.

Conclusion
HSPA Evolution (3GPP Releases 7 and
8) enables operators to prolong the life of
past investments by further improving the
performance of WCDMA systems. In par-
ticular, HSPA Evolution introduces several
new features that support higher data bit
rates, reduce latency, increase capacity, and
improve support for VoIP and multicast ser-
vices:
Higher-order modulation. In the down-
link, the introduction of 64QAM in-
creases the peak data bit rate to as much
as 21Mbps. Likewise, the introduction of
16QAM in the uplink increases the peak
data bit rate to 11Mbps.
Multiple input, multiple output (MIMO).
In Release 7, MIMO is defined for trans-
mitting up to two streams. In this case,
each stream can use QPSK or 16QAM, ex-
tending the peak data bit rate of HSDPA
to approximately 28Mbps. In Release 8,
each stream can use 64QAM, which ex-
tends the peak data bit rate to 42Mbps.
Continuous packet connectivity (CPC).
Simulations show that the CPC concept
in Release 7 boosts capacity for VoIP by
around 40% in the uplink and 10% in the
downlink.
Layer-2 enhancements. Release 7 introduc-
es a new MAC protocol, MAC-ehs, which
supports flexible RLC PDU sizes and the
segmentation of RLC PDUs. In addition,
the MAC multiplexing capabilities have
been improved so that RLC PDUs which
carry signaling or data from different ra-
•
•
•
•
dio access bearers can now be multiplexed
into a single MAC-ehs PDU. In Release 8,
the enhancements made to the downlink
protocol will be applied to the uplink pro-
tocol. Support for flexible RLC PDU sizes
improves uplink coverage and helps reduce
processing and level-2 overhead.
Enhanced CELL_FACH. In Release 7,
HSDPA has been activated for users in
CELL_FACH. In Release 8, the uplink
is improved by activating E-DCH in
CELL_FACH. This enhancement signifi-
cantly improves user perception of perfor-
mance compared with Release 6, which
must suspend data transmission for chan-
nel switching.
Multicast/broadcast single-frequency net-
work (MBSFN). MBSFN calls for simul-
taneous transmission of the exact same
waveform from multiple cells. This way,
the UE receiver perceives the multiple
MBSFN cells as one large cell.
Downlink-optimized broadcast (DOB).
3GPP proposes to take MBSFN opera-
tion one step further, by introducing DOB
as a special mode of 3.84Mbps time-
division duplex (TDD) operation in un-
paired bands of spectrum.
Advanced receivers. Receiver structures
in UEs and Node-Bs are constantly be-
ing improved as products evolve and more
complex features are added to HSPA. The
result is improved system performance and
higher user data bit rates.
For future releases of the specification, 3GPP
is considering multicarrier operation and
even more advanced receivers.
•
•
•
•
REFERENCES
Third Generation Partnership Project, http://www.3gpp.org
Dahlman, E., Parkvall, S., Sköld, J. and Beming, P.: 3G Evolution, HSPA and LTE for Mobile
Broadband. Academic Press
Peisa, J., Wager, S., Sågfors, M., Torsner, J., Göransson, B., Fulghum, T., Cozzo, C. and Grant,
S.: High Speed Packet Access Evolution – Concept and Technologies. Proceedings of the
IEEE VTC Spring 2007
Göransson, B., Cairns, D., Wang, Y.-P. E., Cozzo, C., Fulghum, T. andGrant, S.: Evolution of
WCDMA High Speed Access and Broadcast Services. SPAWC 2007, Helsinki, Finland
Derksen, J., Jansen, R., Maijala, M. and Westerberg, E.: HSDPA performance and evolution.
Ericsson Review, Vol 83(2006):3, pp 117-120
Peisa, J., Ekström, H., Hannu, H. and Parkvall, S.: End-to-End Performance of WCDMA
Enhanced Uplink. VTC Spring 2005
Murai, H. et. al.: System Performance for WCDMA Up-Link Interference Cancellation –
Simulated Results and Field Measurements Properties. WPMC’03 Osaka, Japan
Bakhuizen, M. and Horn, U.: Mobile Broadcast/Multicast in Mobile Networks. Ericsson Review,
Vol. 82(2005): 1 pp. 6-13
1.
2.
3.
4.
5.
6.
7.
8.

5 hspa evolution

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Viewers also liked

Viewers also liked (7)

Similar to 5 hspa evolution

Similar to 5 hspa evolution (20)

Recently uploaded

Recently uploaded (20)

5 hspa evolution