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284 23-3128 Uen Rev B | June 2009
and performance of
HSPA and Mobile WiMAX
How the performance of HSPA and Mobile WiMAX compare, in theory and in practice.
1 Introduction 3
1.1 HSPA 4
1.2 Mobile WiMAX 5
2 Technical comparison 7
2.1 Similarities 7
2.2 Differences 11
2.3 Summary technical comparison 14
3 Performance characteristics 14
3.1 Peak data rates 15
3.2 Spectrum efﬁciency 16
3.3 Coverage 17
3.4 Real-life experience 19
4 Network architecture 21
4.1 WiMAX Forum and IEEE 22
4.2 Architecture comparison 23
4.3 System architecture evolution 24
4.4 Mobile WiMAX 24
5 Conclusion 25
6 Glossary 26
7 References 27
2 Technical overview and performance of HSPA and Mobile WiMAX Contents
The internet has had a dramatic impact on transmitter and receiver, effectively
our private and professional lives. And its multiplying the peak rate
importance continues to grow. To fully enjoy ✒ for improved QoS and low latency
the beneﬁts of the internet, however, users • dynamic scheduling, with end-user
need a broadband connection. In coming trafﬁc streams prioritized according to
years, millions of people will turn to wireless service agreements
technology for this experience. • short transmission time intervals (TTI),
A host of technologies are competing to allowing round-trip times to approach
deliver commercial mobile broadband that of wired equivalents (such as DSL)
services. By far the most successful of these ✒ for higher capacity
is high-speed packet access (HSPA), which • shared-channel transmission to make
has been commercially deployed by over 250 efﬁcient use of available time/
operators in more than 110 countries.1 HSPA frequency/codes and power resources
is a state-of-the-art technology that can • link adaptation to dynamically optimize
provide mobile and wireless broadband transmission parameters, depending on
services with unsurpassed performance and actual radio conditions
economies of scale to the vast majority of the • channel-dependent scheduling to
market. By 2010, when it is anticipated that assign radio resources to users with
the number of wireless broadband the most favorable radio conditions
connections will exceed 600 million, HSPA • hybrid automatic repeat request
will deliver more than 70 percent of all mobile (HARQ) to enable rapid retransmission
broadband connections. of missing data, and soft-combining
A good mobile broadband system must to signiﬁcantly improve performance
fulﬁll certain criteria, including high data rate, and robustness
high capacity, low cost per bit, low latency, ✒ for greater coverage
good quality of service (QoS), and good • advanced antenna systems and
coverage. Several techniques can be receivers to enhance the radio link and
used to meet these criteria in a wireless improve cell range.
Both HSPA and Mobile WiMAX employ
✒ for higher data rates (and capacity) most of these techniques, and their
• higher-order modulation schemes, such performance is broadly similar. However, they
as 16 and 64 quadrature amplitude differ in areas such as the duplex scheme
modulation (16QAM and 64QAM) (FDD versus TDD), frequency bands, multiple
• multiple-input, multiple-output (MIMO) access technology, and control channel
advanced antenna systems that rely on design, giving rise to differences mainly in
multiple antennas at both the uplink data rates and coverage.
Source: Global mobile Suppliers Association (GSA), March 2009
Technical overview and performance of HSPA and Mobile WiMAX Introduction 3
The Third Generation Partnership Project 14Mbps. These enhancements, which
(3GPP) is a collaboration that brings together commonly go under the denomination
several telecommunications standards bodies HSDPA (high-speed downlink packet access),
in the USA, Europe, Japan, South Korea and were a ﬁrst step in the evolution of WCDMA.
China. At present, 3GPP has more than 400 Although a great deal of trafﬁc is downlink-
member companies and institutions. The oriented, several applications also beneﬁt
3GPP deﬁnes GSM and WCDMA from an improved uplink. Examples include
speciﬁcations for a complete mobile system, the sending of large e-mail attachments,
including terminal aspects, radio access pictures, video clips and blogs. The key
networks, core networks, and parts of the enhancement in WCDMA 3GPP Release 6
service network. Standardization bodies in was a new transport channel in the uplink:
each world region have a mandate to take enhanced uplink (EUL), also sometimes
output from the 3GPP and publish it in their called HSUPA (high-speed uplink packet
region as formal standards. access). This enhancement improved
3GPP speciﬁcations are structured in throughput, reduced latency and increased
releases. Ordinarily, discussions of 3GPP capacity. EUL provides data rates of up
technologies refer to the functionality in one to 5.8Mbps.
or another release. It is worth noting that all The combination of HSDPA and EUL is
new releases are backward-compatible with called HSPA. To further boost the peak data
previous releases. rate and capacity, 3GPP Release 7
The development of the 3GPP technology introduced HSPA evolution (also called
track (GSM/WCDMA/HSPA) has been HSPA+), which supports MIMO, 64QAM in
spectacular. Over a period of 10 years, for the downlink, and 16QAM in the uplink. Rel 8
example, there has been a 1,000-fold support 2 ways to give downlink bitrates of
increase in supported data rates. Moreover, 42Mbps, one is the combination of 64QAM
the 3GPP technologies continue to evolve. and MIMO and the other way is by using dual
WCDMA 3GPP Release 99 provided data carriers with 64QAM modulation.
rates of 384Kbps for wide-area coverage. In future releases we will see both
Greater speed (data rates) and capacity combinations of dual carriers and MIMO
were soon required, however, (at lower and combinations of up to 4 carriers, both
production cost) as new services were these alternatives support up to 84Mbps
introduced and more people began to use and even higher bitrates are possible if
packet data services. combinations of MIMO and 4 carriers will
Among other things, WCDMA 3GPP be supported in the future.
Release 5 extended the speciﬁcation with a Long-term evolution (LTE), also speciﬁed in
new downlink transport channel, the high- 3GPP Release 8, introduces OFDM/OFDMA
speed downlink shared channel, which technology in the downlink and single-carrier
enhanced support for high-performance FDMA (SC-FDMA) in the uplink. LTE supports
packet-data applications. Compared with very high data rates – more than 300Mbps in
Release 99, the enhanced downlink gave a the downlink and 80Mbps in the uplink. In
considerable increase in capacity, which addition, it supports operation both in paired
translated into reduced production cost per and unpaired spectrum (FDD and TDD) using
bit. It also signiﬁcantly reduced latency and channel bandwidths of approximately 1.4MHz
provided downlink data rates of up to up to 20MHz.
4 Technical overview and performance of HSPA and Mobile WiMAX Introduction
Table 1: Progressive enhancements to 3GPP speciﬁcations
Version Released Info
Release 99 2000 Q1 Speciﬁed the ﬁrst UMTS 3G networks, incorporating a
WCDMA air interface
Release 4 2001 Q2 Added features, including an all-IP core network
Release 5 2002 Q1 Added IMS and HSDPA
Release 6 2004 Q4 Integrated operation with Wireless LAN networks,
added enhanced uplink, MBMS and enhancements to
IMS such as Push to Talk over Cellular (PoC)
Release 7 2007 Q4 Added downlink MIMO, reduced latency, improved QoS
and improvements to real-time applications like VoIP
Release 8 2009 Q1 Included E-UTRA (LTE) and the Evolved Packet Core
(SAE) architecture and further enhancements of HSPA
(MIMO with 64QAM modulation and dual carrier with
1.2 Mobile WiMAX
The IEEE 802.16 Working Group on access equipment that conforms to
broadband wireless access standards, IEEE 802.16 and the ETSI HiperMAN standard.
established by the IEEE Standards Board in The WiMAX Forum deﬁnes and conducts
1999, prepared the formal speciﬁcations for conformance and interoperability testing to
broadband wireless metropolitan area ensure that different vendor systems work
networks (WirelessMAN, the 802.16 family of seamlessly with each other. WiMAX
standards is the basis of Mobile WiMAX). certiﬁcation proﬁles specify characteristics
IEEE 802.16-2004 (also called 802.16d) such as spectrum band, duplexing and
provides support for non-line-of-sight (NLOS) channelization. Several proﬁles exist for Fixed
and indoor end-user terminals for ﬁxed and Mobile WiMAX.
wireless broadband. In 2005, the standard
was amended (IEEE 802.16e-2005 or There are currently two waves of
802.16e) to add support for data mobility. certiﬁcation planned for Mobile
IEEE 802.16e or Mobile WiMAX improves WiMAX equipment:
on the modulation schemes used in the ✒ Wave 1: Mobile WiMAX system proﬁle with
original (Fixed) WiMAX standard by single-input single-output (SISO) terminals
introducing scalable orthogonal frequency- for the 2.3GHz and 3.5GHz bands
division multiple access (SOFDMA ). ✒ Wave 2: Mobile WiMAX system proﬁle with
The system proﬁle in IEEE 802.16e-2005 is multiple-input multiple-output (MIMO)
not backward compatible with the Fixed terminals and beam-forming support for
WiMAX system proﬁle. the 2.6GHz band (sometimes referred to
The charter of the WiMAX Forum, which as the 2.5GHz band).
has more than 400 members, is to promote
and certify the compatibility and Because IEEE 802.16 standardization only
interoperability of broadband wireless covers basic connectivity up to the media
Technical overview and performance of HSPA and Mobile WiMAX Introduction 5
access (MAC) level, the WiMAX Forum also full IMS interworking, carrier-grade VoIP,
addresses network architecture issues for broadcast applications, such as mobile TV,
Mobile WiMAX networks. The ﬁrst network and over-the-air provisioning. While Mobile
architecture speciﬁcation (Release 1.0) WiMAX offers the promise of high-speed
focused on delivering a wireless internet wireless broadband services, it is still very
service with mobility. much in its infancy and real-life performance
Release 1.5 introduced support for has yet to be proved.
telecom-grade mobile services, supporting
Table 2: Evolution of WirelessMAN (802.16 family of standards)
Version Released Info
IEEE 802.16d 2004 Q2 Replaced all previous 802.16 speciﬁcations. Support for
IEEE 802.16-2004 non-line-of-sight operation
IEEE 802.16e 2005 Q4 Enhanced 802.16-2004 with support for data mobility
WiMAX Forum Network 2007 Q1 Networking speciﬁcations for ﬁxed, nomadic, portable
Architecture Speciﬁcation and mobile WiMAX systems. Release 1.0 covers
Release 1.0 internet applications and data mobility
WiMAX Forum Network 2008 Q3 Enhancements to the Release 1.0 speciﬁcation for
Architecture Speciﬁcation carrier-grade VoIP, location-based services, MBMS, full
Release 1.5 IMS interworking and over-the-air client provisioning
6 Technical overview and performance of HSPA and Mobile WiMAX Introduction
2 Technical comparison
HSPA and Mobile WiMAX technologies have mechanism, and operating frequency bands.
been designed for high-speed packet-data This chapter provides a high-level description
services. They feature similar technology of the similarities and differences between
enablers, including dynamic scheduling, link HSPA and Mobile WiMAX. Technical details
adaptation, HARQ with soft combining, of HSPA can be found in the 3GPP
multiple-level QoS, and advanced antenna speciﬁcations. Likewise, details of Mobile
systems. Notwithstanding, their performance WiMAX can be found in the IEEE 802.16e-
differs due to differences in the physical layer 2005 standard and the WiMAX Forum Mobile
signal format, duplex scheme, handover System Proﬁle.
2.1.1 Dynamic scheduling
Traditional circuit-switched telephone channels, radio links often experience
systems set up connections as dedicated ﬂuctuations in signal strength. It is thus
links for an entire session. This approach more effective to schedule the base station
wastes communication resources for packet and terminal to communicate only when
data because the dedicated link is tied up radio conditions are good. HSPA and
even during idle periods. For high-speed Mobile WiMAX systems use channel-
packet-data systems with bursty trafﬁc, it dependent scheduling techniques
makes better sense to allocate radio (Figure 1) to make efﬁcient and effective
resources only during active periods. use of packet-data resources.
Given the volatile nature of wireless
Scheduling: determines which end user to transmit to, at a given moment
Channel-dependent Scheduling: transmit at fading peaks
Figure 1: Channel-dependent scheduling
Technical overview and performance of HSPA and Mobile WiMAX Technical comparison 7
2.1.2 Link adaptation
When a mobile device is scheduled for HSPA and Mobile WiMAX support dynamic
transmission, the quality of its radio link will selection between QPSK, 16QAM and
vary in time. The modulation scheme and 64QAM modulation schemes, as well as of
channel-coding rate used for a scheduled link the channel-coding rate, where the lowest
can be adapted to minimize errors under a coding rate without repetition is 1/2 for
variety of radio conditions. Link adaptation Mobile WiMAX and 1/3 (additional coding
(Figure 2) enables full utilization of channel gain) for HSPA. Overall, HSPA has ﬁner
capacity for each communication link in the granularity of modulation and coding formats
wireless environment and so maximizes the than Mobile WiMAX.
throughput of scheduling-based systems.
Adjust transmission parameters and match instantaneous channel conditions
Figure 2: Link adaptation
8 Technical overview and performance of HSPA and Mobile WiMAX Technical comparison
2.1.3 H-ARQ with soft combining
Because of delays in channel quality feedback, On the uplink, H-ARQ with soft combining
link adaptation may suffer from errors also reduces transmission power and
incurred between time instances of reporting improves system capacity, thanks to lower
and scheduling. Hybrid acknowledgement interference and more stable power control.
request (H-ARQ) with soft combining on the In HSPA, incremental redundancy is used for
downlink and uplink quickly corrects these extra coding gain of the lower coding rate
error packets without having to rely on that goes along with the retransmission. In
higher-layer automatic repeat request (ARQ). Mobile WiMAX, only Chase combining is
H-ARQ with soft combining is an effective available for energy gain; the coding rate is
remedy to link adaptation errors and reduces not adjusted after retransmission.
retransmission delays that are vital for higher-
Figure 3: Hybrid acknowledgement request (H-ARQ) with soft combining
2.1.4 Multilevel QoS
HSPA and Mobile WiMAX support multiple mechanisms deﬁned for different QoS levels
QoS levels. In HSPA, QoS levels are divided in the uplink: unsolicited grant service (UGS),
into four categories: conversational, extended real-time polling service (ertPS),
streaming, interactive, and background. In real-time polling service (rtPS), non-real-time
Mobile WiMAX, there are ﬁve scheduling polling service (nrtPS), and best-effort.
Technical overview and performance of HSPA and Mobile WiMAX Technical comparison 9
2.1.5 Advanced antenna technologies
Advanced multiple antenna technologies instantaneous downlink channel conditions.
improve the performance and capability of Therefore, in addition to diversity, WCDMA
modern mobile communication systems closed-loop transmit diversity allows for
(Figure 4). In general, they rely on the use beam-forming gains.
of multiple transmit and receiver antennas WCDMA open-loop and closed-loop
to achieve: transmit diversity are also available for HSPA.
✒ diversity against fading on the In addition, 2x2 spatial multiplexing (in HSPA
radio channel Release 7) effectively doubles downlink peak
✒ beam-forming, to improve the radio link data rates.
signal-to-noise/interference ratio The Mobile WiMAX system proﬁle
✒ spatial multiplexing, often referred to as speciﬁes two types of multi-antenna
multiple-input multiple-output (MIMO) transmission schemes:
antenna processing, to increase the ✒ transmit diversity using the Alamouti
peak data rates and make more efﬁcient space-time code (STC), which is similar to
use of high radio-link signal-to-noise/ WCDMA/HSPA open-loop transmit
interference ratios. diversity; and
✒ spatial multiplexing (MIMO).
WCDMA supports two multi-antenna
transmission schemes: open-loop transmit Mobile WiMAX also supports beam-forming,
diversity, and closed-loop transmit diversity. which is enabled by uplink sounding. By
WCDMA open-loop transmit diversity uses taking advantage of TDD channel reciprocity,
modiﬁed Alamouti coding and can be applied the spatial characteristics measured at the
to dedicated as well as common channels. base station can be used to form downlink
Open-loop transmit diversity guards against beams. In practice, however, performance is
radio-channel fading. WCDMA closed-loop limited by the asymmetry of interference and
transmit diversity allows for adjustment of different antenna settings at the terminal and
transmission phase and amplitude, based on base station.
Figure 4: Overview of different antenna transmission schemes
10 Technical overview and performance of HSPA and Mobile WiMAX Technical comparison
2.2.1 Physical signal format
The main differences between Mobile WiMAX uplink multiple accesses, Mobile WiMAX
and HSPA in the physical layer are in the base stations must ﬁne tune the frequency
signal format. Mobile WiMAX is based on errors of each terminal within tolerable
orthogonal frequency domain multiplexing ranges, and minimize the total interference
(OFDM), whereas HSPA is a direct-sequence level by means of power control.
spread-spectrum system. One of the most In addition, OFDM signals have a relatively
important features of OFDM is its robustness large peak-to-average power ratio (PAPR),
to multipath propagation. The key enabler of which means that for a given average power,
this feature is the use of narrowband tones in the power ampliﬁer must be able to handle
combination with a cyclic preﬁx. The cyclic very high power peaks without distorting the
preﬁx serves two purposes: it provides a transmitted signal.
guard time against inter-symbol interference, HSPA uses CDM code aggregation
and it ensures that the multipath channel only (orthogonal Walsh code) to offer a high-speed
imposes a scalar distortion on each tone, downlink channel, and direct-sequence code-
making equalization simple and effective. division multiple access (CDMA) for the
When properly synchronized and protected uplink. While this method is less sensitive to
by cyclic preﬁx, tones of an OFDM signal Doppler spread, the loss of orthogonality in
remain mutually orthogonal even after going time-dispersive channels creates intra-cell
through multipath channels. The interference that limits the use of high-order
disadvantage of using cyclic preﬁx is modulation. Generalized RAKE receivers
increased overhead, which effectively can alleviate interference through advanced
reduces bandwidth efﬁciency. signal processing on the receiver side
The ability of an OFDM signal to maintain at the moderate cost of additional
orthogonality under multipath conditions receiver complexity.
gives an intra-cell interference-free system When compared with OFDM signals, the
that is well suited to high-speed data HSPA uplink signals have lower PAPR—
transmission. Notwithstanding, inter-tone which implies a less complex power ampliﬁer.
interference arises (degrading performance) Alternatively, for a given complexity, a
when there are large Doppler spreads in higher average power can be used, giving
OFDM. When OFDM signals are used for greater coverage.
2.2.2 Duplex scheme
One other difference between HSPA and channels, one for the uplink and one for
Mobile WiMAX is the duplex scheme. HSPA the downlink).
is an FDD technology, with uplink and The Mobile WiMAX system proﬁle, as
downlink transmission taking place in currently deﬁned in the WiMAX Forum, is a
separate frequency channels (usually denoted TDD technology with just one frequency
as 2x5MHz to indicate two separate 5MHz channel (10MHz for example) that is shared in
Technical overview and performance of HSPA and Mobile WiMAX Technical comparison 11
Figure 5: Overview of FDD and TDD
the time domain between the uplink and The interference scenarios are different
downlink. The ratio between the uplink and between FDD and TDD systems (Figure 6).
downlink deﬁnes how the frequency channel FDD systems use a frequency duplex gap
is shared. A 2:1 ratio means the channel is between the uplink and the downlink to
used two-thirds of the time for the downlink prevent interference between transmissions.
and one-third of the time for the uplink TDD systems use a guard time between the
(Figure 5). uplink and downlink.
The IEEE 802.16 speciﬁcation allows for When building a TDD network, one must
FDD operation, but to date, the Mobile deal with a variety of interference scenarios:
WiMAX system proﬁle solely stipulates TDD. ✒ Interference within a network –
TDD has the ﬂexibility of changing the interference between base stations and
downlink-to-uplink ratio to accommodate a between terminals. All the base stations
variety of trafﬁc asymmetries, although in must be fully time-synchronized with each
practice the ratio needs to be ﬁxed system- other (for example, using a GPS receiver at
wide (unless guard bands are used to limit each base station).
interference effects). In addition, TDD ✒ Between a network and an adjacent
systems with a large downlink-to-uplink ratio, TDD network – two or more TDD
have a link budget penalty as the uplink networks using the same frequency band
average power is reduced for a given in the same geographical area. To avoid
peak power. interference, synchronization must be
Figure 6: Overview of interference scenarios for FDD and TDD systems
12 Technical overview and performance of HSPA and Mobile WiMAX Technical comparison
coordinated between neighboring can only be resolved using suitable
networks, or guard bands must be used. guard bands.
This scenario might occur at national or ✒ Duty cycle uplink/downlink settings in
state borders, especially where only local the TDD network relative to adjacent
licenses have been issued. networks—in addition to synchronization
✒ Between a network and a spectrum- in time, when setting the uplink/downlink
adjacent TDD network—one TDD ratio in a TDD network, the ratio within the
network uses adjacent frequencies, giving network and with neighboring networks
rise to base station to base station must be coordinated, to avoid all the
interference if the base stations from the interference cases mentioned above.
different networks are in close proximity. Alternatively, guard bands can be used.
The uplink to one base station can suffer
interference from out of band leakage from Stringent requirements from existing
another base station. This interference can satellite services in speciﬁc bands make it
be reduced by synchronizing the difﬁcult to deploy TDD technologies in these
networks, or by using guard bands. frequencies. The tougher coexistence
✒ FDD and TDD spectrum borders—an environment for TDD puts heavy requirements
FDD network uses frequencies adjacent to on the RF ﬁlters, which are just as complex as
the TDD network, giving rise to base the duplex ﬁlter requirements for FDD.
station to base station interference if the The 3GPP speciﬁcation covers FDD and
base stations from the different networks TDD, but there have not been any major
are in close proximity. This interference deployments of TDD-based cellular systems.
2.2.3 Handover mechanism
HSPA supports soft handover in the uplink, Hard handover is used for intra-frequency
which yields macro-combining gain and handover and intersystem handover to GSM.
improves the link budget (by 1.5dB on The Mobile WiMAX system proﬁle includes
average). It also helps increase network only hard handover.
capacity by reducing intra-cell interference.
2.2.4 Operating frequency bands
HSPA currently supports frequency bands Several frequency bands are under
ranging from 800MHz to 2,600MHz, including discussion for Mobile WiMAX, but current
most current 2G operating bands in Europe, certiﬁcation proﬁles only cover the 2.3GHz,
Africa, the Americas and Asia-Paciﬁc. The 2.6GHz and 3.3–3.8GHz frequency bands. At
most common bands for HSPA are 2.1GHz, present, there are only a few deployments of
deployed worldwide, and the 850MHz band Mobile WiMAX, mainly in the 2.3GHz and
deployed in the Americas, Australia, New 2.6GHz bands.
Zealand, and parts of Asia. Approximately 90 percent of all spectrum
allocations worldwide are FDD.
Technical overview and performance of HSPA and Mobile WiMAX Technical comparison 13
2.3 Summary technical comparison
Table 3 summarizes the technical similarities and differences between HSPA and Mobile WiMAX.
Table 3.Technical comparison of HSPA and Mobile WiMAX
HSPA Mobile WiMAX
Physical signal format DL code aggregation, OFDMA for both DL and UL
Hybrid ARQ with soft Adaptive IR + Chase Chase combining
Multi-level QoS √ √
Link adaptation QPSK, 16QAM, 64QAM QPSK, 16QAM, 64QAM
Lowest code rate: 1/3 Lowest code rate: 1/2
Duplex scheme FDD TDD
Frequency bands 850MHz to 2,600MHz 2.3GHz, 2.6GHz and 3.4–3.8GHz
Handover Hard handover, Hard handover
Frequency reuse one √ √
Advance antenna • Closed- and open-loop • Open-loop transmit diversity
technologies transmit diversity • Spatial multiplexing
• Spatial multiplexing • Beam forming
• Beam forming
14 Technical overview and performance of HSPA and Mobile WiMAX Technical comparison
3 Performance characteristics
Vital characteristics of system performance which might give a misleading picture – the
are data rates, delay, spectrum efﬁciency and discourse covers a set of HSPA and Mobile
coverage. For end users, these WiMAX releases, to enable a fair comparison.
characteristics determine which services can Because many features are common to both
be offered. For operators, they deﬁne number system families – including antenna (MIMO)
of users and base station coverage area, concepts, modulation and channel coding –
which directly inﬂuences the cost of operating performance is similar in many respects.
the system. There are some differences, however, such as
This chapter presents the performance the duplex scheme, frequency bands,
characteristics of HSPA and Mobile WiMAX in multiple-access technology and design of the
terms of peak data rates, spectrum efﬁciency control channel, which give rise to
and coverage. Rather than cover just one differences, for example, in uplink bit rates
version (or release) of each system family – and coverage.
3.1 Peak data rates
The peak data rate indicates the bit rate a data rates, measured above the MAC layer,
user in good radio conditions can reach when for a set of system concepts. Early releases
the channel is not shared with other users. of HSPA (Release 6) and Mobile WiMAX
Figure 7 shows the downlink and uplink peak Wave 1 achieve comparable peak rates.
Figure 7: Peak data rates for a set of HSPA releases and WiMAX waves. For WiMAX, the TDD symmetry is expressed in
terms of number of downlink and uplink slots for data (that is, 28:15). The use of multistream MIMO is indicated by a factor
in front of the modulation scheme.
Technical overview and performance of HSPA and Mobile WiMAX Performance characteristics 15
Mobile WiMAX uses higher-level modulation same modulation formats (64QAM and
(64QAM in the downlink and 16QAM in uplink) 16QAM) and comparable MIMO schemes
than HSPA release 6, which uses 16QAM in (two streams in the downlink) are used, but
the downlink and QPSK in the uplink. HSPA HSPA has less overhead. Release 8 also
Release 7 introduces 64QAM and two-stream supports downlink transmission using 2
MIMO in the downlink (but not for carriers with 64QAM, which gives the same
simultaneous use) and offers comparable peak rate as MIMO + 64QAM.
performance to Mobile WiMAX Wave 2. The Mobile WiMAX may use TDD asymmetries
peak data rate of HSPA Release 8 betters that to increase downlink peak data rates at the
of Mobile WiMAX Wave 2. In this case, the expense of reduced uplink peak data rates.
3.2 Spectrum efﬁciency
Spectrum efﬁciency measures the maximum trafﬁc load per user, spectral efﬁciency can
total amount of data that can be carried by a be used to determine the number of users a
cell per unit of time, normalized with the cell can support (Figure 8).
occupied system bandwidth. For any given
Figure 8. Spectrum efﬁciency comparisons (Note that absolute spectrum efﬁciency values vary with models and
assumptions—the above values should only be used for relative comparisons).
16 Technical overview and performance of HSPA and Mobile WiMAX Performance characteristics
The spectrum efﬁciency ﬁgures have been RAKE receivers (indicated by the dotted line
evaluated using models, assumptions and in Figure 8). However, with more advanced
methodology aligned with 3GPP standards receivers, such as G-RAKE with receive
(in this case, a system with 19 three-sector diversity, HSPA has substantially better
sites, placed on a regular grid with 500m spectrum efﬁciency – a comparison of HSPA
inter-site distance). “Full-buffer” type users Release 6 with advanced receivers shows
are uniformly distributed. The selected that HSPA has greater spectrum efﬁciency.
propagation models (which model spatial HSPA Release 7 is modeled with two-stream
correlation between antennas to enable MIMO in the downlink and 16QAM in the
accurate MIMO evaluations) simulate an uplink. Mobile WiMAX Wave 2 performance is
urban environment. comparable to HSPA Release 7.
System models, such as antenna solutions HSPA Release 8 shows better spectrum
and output powers, have been aligned with efﬁciency than Mobile WiMAX Wave 2.
the capabilities of the studied systems. These results are similar to those presented
Similar assumptions have been made for all by 3G Americas. The ﬁgures for Mobile
systems, with the aim of achieving fair WiMAX are somewhat lower than those
comparisons. Note: the ﬁgures should only presented by WiMAX Forum, probably
be used for comparative purposes and not as because of differences in modeling. The
absolute values. WiMAX Forum does not present results for
The spectrum efﬁciency achieved by HSPA HSPA Release 7 or 8. Its results for HSPA
Release 6 is dependent on receiver type. Release 6 are similar to those presented here
Mobile WiMAX Wave 1 has better spectrum and assume simple receivers.
efﬁciency than HSPA Release 6 with basic
Coverage is a crucial metric of performance, speciﬁc case. Relative comparisons of link
because it determines the number of sites budgets for different system concepts are
needed to deploy a complete network, and informative and easy to make. HSPA and
the data rate available at a given distance in a Mobile WiMAX have distinctive
given deployment. A common way of characteristics that affect the link budget,
measuring coverage is to use link budgets, including output power, duplex method
which provide an estimate of the maximum and frequency band—especially on the
path loss the system can sustain between the uplink, which is typically the limiting link.
base station and terminal. Figure 9 summarizes the impact of
Accurate absolute link budgets depend on these characteristics.
several factors and are best simulated for a
Technical overview and performance of HSPA and Mobile WiMAX Performance characteristics 17
Figure 9: HSPA typically has 6-10dB greater coverage than Mobile WiMAX
Using typical terminal power classes, the operating at about 2.0GHz, the path loss
maximum output power of Mobile WiMAX increases by a factor of (2.6/2.0)2 = 1.7,
terminals (23dBm) is 1dB lower for than for or 2.3dB. At 3.5GHz the corresponding
HSPA (24dBm). This constitutes a difference ﬁgure is 4.9dB.
of 1dB in the link budget. One reason for this Apart from these differences, soft handover
disparity is the difference in uplink modulation in HSPA improves coverage, and lower
and multiple access methods. overhead improves sensitivity.
With TDD, if the link is used only half the In summary, although Mobile WiMAX and
time for a given average data rate, then the HSPA are based on similar techniques, the
transmission data rate must be twice as high. link budget of Mobile WiMAX can be as much
If the link is used one-quarter of the time, as 6dB lower than that of HSPA. In a
then the transmission data rate must be four coverage-limited network, this translates into
times as high. Radio links to terminals at the the need for 2.2 times as many sites. This
cell border are typically power-limited. This ﬁgure is derived on the basis of d3.5
means that the achievable bit rate is propagation (which is typical in urban and
proportional to the transmitted power but suburban areas). In this case, a 6dB increase
insensitive to channel bandwidth. To in path loss (a factor of four) corresponds to a
compensate for this loss, the terminal must distance coverage loss of a factor of 41/3.5 =
have better path loss—by a factor 2 (3dB) or 1.5, or an area coverage loss of a factor of
4 (6dB) for activity factors of 50 percent and 1.52 = 2.2. In rural areas, which have lower
25 percent, respectively. path loss exponents, the differences are
Deploying Mobile WiMAX in higher even larger.
frequency bands than are typically used for For coverage-driven deployment, Mobile
HSPA will result in additional loss in the link WiMAX at 2.6GHz would need approximately
budget. Path loss is proportional to the 2.3 to 3.4 times as many sites than HSPA at
square of the frequency. Given Mobile WiMAX 2.1GHz. Even compared with HSPA at 2.6
operating in the 2.6GHz band, HSPA GHz, Mobile WiMAX increases the site count
operating in the 2.1GHz band, and the uplink by approximately 1.7 to 2.5 times.
18 Technical overview and performance of HSPA and Mobile WiMAX Performance characteristics
3.4 Real-life experience
HSDPA became commercially available in Better still, the ﬁrst terminals to support 15
2005 and has since been rolled out for codes and 64QAM modulation are now
commercial operation in networks around becoming available. Initial tests show that
the world. these terminals can support average bit rates
Initially, user terminals were limited to ﬁve of more than 10Mbps.
codes and 16QAM modulation, giving a HSPA is a mature technology which offers
theoretical maximum data rate of 3.6Mbps. mobile broadband services that rival the
Feedback from live networks shows that the performance of ﬁxed broadband networks
actual rates are close to the theoretical (such as ADSL and cable). Load calculations
simulations (Figure 10). in an HSPA network show that with a 10GB
Many user terminals now support 10 codes monthly “bit bucket,” operators can deliver
and have a theoretical maximum data rate of a commercially viable ﬂat-rate mobile
7.2Mbps (Figure 11). In commercial networks broadband service to every subscriber
these terminals give impressive results with in the network.
user data rates of up to 6Mbps.
Figure 10: HSPA performance measured in a live commercial network
Technical overview and performance of HSPA and Mobile WiMAX Performance characteristics 19
Figure 11: HSPA performance measured on a commercial system using a terminal that supports up to 7.2Mbps
20 Technical overview and performance of HSPA and Mobile WiMAX Performance characteristics
4 Network architecture
The 3GPP is a collaboration between several with HSPA, 3GPP Release 7 enhanced the
telecommunications standards bodies. It reference architecture (Figure 12) with a 3G
handles GSM and WCDMA standardization direct tunnel that optimizes the delivery of
for the complete mobile system, including mobile and wireless broadband services.
terminal aspects, radio access networks, Compared with 3GPP Release 6 and earlier
core networks, and parts of the architectures, the direct tunnel architecture
service network. provides a direct data path from the RNC to
The air interface, as well as the network, is the GGSN, increasing topological ﬂexibility
progressively being improved with every and improving latency.
advance in the 3GPP speciﬁcation. In step
Figure 12: Overview of the 3GPP reference architecture
Technical overview and performance of HSPA and Mobile WiMAX Network architecture 21
4.1 WiMAX Forum and IEEE
Figure 13: Mobile WiMAX network architecture
The IEEE 802.16 standard covers the air • Split management of radio resources,
interface (IEEE 802.16e) and basic with a radio resource agent in the base
connectivity up to the media access (MAC) station and a radio resource controller
level. The WiMAX Forum deﬁned the network in the ASN-GW.
architecture speciﬁcations for WiMAX • Open interfaces for Proﬁle A: R1, R6,
networks (Figure 13). The ﬁrst speciﬁcation R4, and R3.
(Release 1.0) focuses on delivering internet ✒ Proﬁle B:
services with mobility. At present, the network • ASN solution where the base station
architecture deﬁnes three RAN proﬁles and ASN-GW functions are
(Proﬁle A, Proﬁle B, Proﬁle C), each with a implemented on a single platform.
different functional allocation: • Open interfaces Proﬁle B: R4 and R3.
✒ Proﬁle A: ✒ Proﬁle C:
• ASN model with base station and ASN • Similar to Proﬁle A except that radio
gateway (ASN-GW) implemented on resource management is not split but is
separate platforms, interacting through located entirely in the base station.
the R6 interface.
22 Technical overview and performance of HSPA and Mobile WiMAX Network architecture
4.2 Architecture comparison
Figure 14 compares the Mobile WiMAX However, using IP tunneling protocols to
architecture with the 3GPP Release 7 meet the need for wireless mobility requires a
architecture for mobile broadband services. lot of functionality in areas such as bearer
The target requirements are broadly similar in management, QoS, charging, radio access
terms of functional allocations and architecture. type information, and more. From the outset,
However, the selection of protocols in each GTP was tailored to support this functionality.
standards organization has been inﬂuenced by This differs from the approach of the WiMAX
the chosen technology. 3GPP builds on GTP Forum, which has instead extended the
and DIAMETER, which provide optimized inter- baseline IETF protocols to include wireless-
working with legacy GSM terminals and speciﬁc functionality and to deploy multiple
common anchoring in the GGSN for dual-mode protocols in parallel over the same interface.
GSM/WCDMA/HSPA terminals. In addition, At a high level, RADIUS and DIAMETER
GTP provides an efﬁcient way of handling QoS look similar. Both were developed by IETF,
and of creating binding to radio bearers. The and DIAMETER is an evolved version of
WiMAX Forum, by contrast, has gone with RADIUS. DIAMETER is widely used within
Mobile IP and RADIUS; it also supports PMIP IMS speciﬁcations and provides functionality
and CMIP for both IPV4 and IPV6. beyond RADIUS, mainly in the area of carrier-
A comparison of Mobile IP and GTP reveals grade performance. This translates into
several similarities in terms of functionality. For functionality, such as standardized
instance, the protocols solve the same types of application packages (instead of vendor-
problems in areas such as session speciﬁc attributes), reliable transport
management, user plane tunnel setup for IPv4 layer, bidirectional communication, and
and IPv6 payload, and multiple packet sessions heartbeat mechanisms.
Figure 14: HSPA and Mobile WiMAX network architectures
Technical overview and performance of HSPA and Mobile WiMAX Network architecture 23
4.3 System Architecture Evolution
The system architecture evolution (SAE), The mobility management entity (MME), an
speciﬁed together with LTE, is the next step evolution of the SGSN server, has been
in the 3GPP architecture evolution. It will speciﬁed for 3G Direct Tunnel functionality in
deliver a ﬂattened network architecture 3GPP Release 7. In all likelihood many
with simpliﬁed QoS, for the delivery of IP implementations will co-locate the MME with
services (Figure 15). the SGSN.
SAE is an evolution of 3GPP Release 7, The SAE-GW node will include evolved
with support for 3GPP LTE and non-3GPP GGSN functionalities including IP networking
access technologies, as well as current 2G interfaces and end-user IP point of presence,
and 3G access technologies. shallow and deep packet inspection, as well
The architecture splits packet core control as real-time charging, policy control, and
and user plane functionality into separate mobility to non-3GPP accesses using mobile
nodes. Moreover, it further optimizes the IP. What is more, operators who evolve their
HSPA architecture for mobile broadband networks to LTE/SAE from GSM/WCDMA/
services with two nodes (eNodeB and SAE HSPA will enjoy full backward compatibility
gateway, SAE-GW) in the user plane for the with legacy networks.
main use cases.
Figure 15: Overview of the SAE architecture
4.4 Mobile WiMAX
Details of the network architecture evolution functionality, such as policy management and
for Mobile WiMAX beyond Release 1.0, IMS support, prepaid support, emergency
approved in March 2007, is described in services, and roaming.
Release 1.5, which includes enhanced
24 Technical overview and performance of HSPA and Mobile WiMAX Network architecture
Given that HSPA and Mobile WiMAX employ factors help ensure nationwide coverage
many of the same techniques, their for voice (GSM/WCDMA) and data
performance is comparable in many areas. (HSPA/EDGE).
However, key differences in areas such as Thanks to its heritage, HSPA gives
duplex mode (FDD versus TDD), frequency operators a single network for multiple
bands, multiple access technology, and services with a sound business case built on
control channel design give rise to differences revenues from voice, SMS, MMS, roaming,
in uplink bit rates and coverage. and mobile broadband.
While the peak data rates, spectral HSPA offers an ecosystem of unrivalled
efﬁciency and network architecture of HSPA breadth and depth as well as unmatched
Evolution and Mobile WiMAX are similar, economies of scale that beneﬁt all players in
HSPA offers better coverage. In short, Mobile the ecosystem, which currently serves more
WiMAX does not offer any technology than 2 billion subscribers.
advantage over HSPA. Operator choices of technology today will
What is more, HSPA is a proven mobile inﬂuence operations for many years to come.
broadband technology deployed in more than The good news in this context is that 3GSM
250 commercial networks. It is built on the technologies are future-proof in terms of initial
ﬁrm foundations of the 3GPP family, offering investment, economies of scale, and the
users the broadband speeds they want and ability to extend and continuously enhance
the carrier-grade voice services they expect. the solution.
HSPA can be built out using existing GSM Compared with other alternatives, HSPA is
radio network sites and is a software upgrade the clear and undisputed choice for mobile
of installed WCDMA networks. When used broadband services.
together with dual-mode terminals, these
Technical overview and performance of HSPA and Mobile WiMAX Conclusion 25
AAA authentication, authorization and accounting
ASN access service network
BS base station
CDMA code division multiple access
CSCF Call Session Control Function
DSL digital subscriber line
EDGE Enhanced Data rates for Global Evolution
FA/HA Foreign Agent/Home Agent
FDD frequency division duplexing
GGSN gateway GPRS support node
GPRS General Packet Radio Service
GSM Global System for Mobile communications
G-RAKE receiver generalized RAKE receiver
HSPA High Speed Packet Access – an extension of WCDMA to provide high
bandwidth and enhanced support for interactive, background, and
HSS Home Subscriber Server
IEEE Institute of Electrical and Electronics Engineers
IMS IP Multimedia Subsystem
IPR intellectual property rights
ITU International Telecommunication Union
MAC Media Access Control
MIMO multiple input, multiple output
MME mobility management entity
OFDM orthogonal frequency division multiplexing – a digital encoding and
modulation technology used by 802.16-based systems (including WiMAX)
as the air interface
PCRF Policy Charging Rule Function
PDG packet data gateway
RAKE receiver a radio receiver designed to counter the effects of multipath fading
RX receiving antennas
SAE-GW system architecture evolution gateway
SGSN serving GPRS support node
TDD time division duplexing
TTG tunnel termination gateway
TX transmitting antennas
WAG wireless access gateway
WCDMA Wideband Code Division Multiple Access – a wideband spread-spectrum
3G mobile telecommunication air interface
WiMAX Worldwide Interoperability for Microwave Access – a standards-based
technology that enables the delivery of last mile wireless broadband
access as an alternative to cable and DSL
VoIP Voice over IP technology enables users to transmit voice calls via the
internet using packet-linked routes; also known as IP telephony.
3G Third-generation radio technology for mobile networks, telephones
and other devices. Narrowband digital radio is the second generation
3GPP Third Generation Partnership Project, a collaboration agreement that brings together
a number of telecommunications standards bodies
3G LTE/SAE 3G Long Term Evolution/System Architecture Evolution
26 Technical overview and performance of HSPA and Mobile WiMAX Glossary
 3GPP. October 2006. TR 25.814, Physical layer aspect for evolved Universal Terrestrial
Radio Access (UTRA). Available at: http://www.3gpp.org/ftp/Specs/html-info/25814.htm
[Accessed 8 December 2008].
 3G Americas. September 2006. Mobile Broadband: EDGE, HSPA and LTE.
Available at: http://www.3gamericas.org/documents/2006_Rysavy_Data_Paper_
FINAL_09.15.06.pdf [Accessed 8 December 2008].
 3rd Generation Partnership Project (3GPP). http://www.3gpp.org/ [Accessed 8
 WiMAX Forum, http://www.wimaxforum.org/ [Accessed 8 December 2008].
 IEEE-SA. June 2004. IEEE 802.16-2004 Air Interface for Fixed Broadband Wireless
Access Systems. Part 3: Radio Conformance Tests (RCT)for 10–66 GHz
WirelessMAN-SC™ Air Interface. Available at:
Accessed 8 December 2008].
 IEEE-SA. February 2006. IEEE 802.16e-2005 Air Interface for Fixed and Mobile
Broadband Wireless Access Systems. Part 16: Air Interface for Fixed and Mobile
Broadband Wireless Access Systems. Available at:
http://standards.ieee.org/getieee802/download/802.16e-2005.pdf [Accessed 8
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