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LTE & WiMAX- A Tale of Two Technologies
his paper aims to highlight the possible convergence path between LTE , WiMAX . LTE is the new kid on the
block, the talk of the town ever since its inception. It has been tipped as the future for data and voice
communication. LTE holds a lot of performance for the Telco operators worldwide in terms of catering for
the ever increasing consumer demands for high data rates on the move along with the native voice
communications. Therefore there is a great need to upgrade the current deployed networks to LTE. In an
increasingly interconnected world, consumers demand high-speed communication, ease of access and flexibility.
Digital convergence is revolutionizing the way data is delivered and consumed, however the challenges are to track
evolving consumer demands and meet the expectations for faster and more sophisticated digitization capabilities.
While WiMAX enjoys slight edge over relatively new LTE commercially, but the adoption of LTE will
surpass WiMAX sometime at the end of 2012. It is largely due to LTE is backward compatible with existing GSM
and HSPA networks, enabling mobile operators deploying LTE to continue to provide a seamless service across LTE
and existing deployed networks. Presently LTE and WiMAX exist independently; however, the union of these
technologies is expected to allow operators the flexibility to deploy multi-mode networks, enabling them to take
advantage of the relative strengths of each technology while downplaying its weakness. The technology used for
LTE is similar to that chosen for WiMAX even though they have both evolved from two different standards, i.e.
3GPP and IEEE802.16 respectively.The WiMAX/LTE network decision will be less complex if multimode devices are
available.The Broadband wireless market has been divided into the two main groups of wireless operators: the
established mobile operators with or without 3G spectrum and the new entrants, mainly greenfield operators and
other fixed line operators. The WiMAX Forum and 3GPP have been pursuing two separate avenues to reach the
same market mobile broadband.
WiMAX was for greenfield players or operators with TDD spectrum that did not need backward-
compatibility with legacy cellular technologies
supported by LTE. On the other hand, LTE was
developed by mobile operators along withtheir vendors with little likelihood they
would embrace a new disruptive standard. LTE
had never been appealing to WiMAX
operators as an FDD-only technology at least
not until TD-LTE appeared. There is plenty of
TDD spectrums available, and in most cases it
is cheaper and under-utilized. Even 3G licenses
frequently have TDD allocations and upcoming
2.5 GHz auctions in most cases contemplate
TDD bands. In response to these trends, the
WiMAX forum initiated the WiMAX 2.0upgrade that offers most of the same features
as LTE-Advanced while providing backward
compatibility to WiMAX 1.0. WiMAX 2.0.
T
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Mobile Industry Technologies
As a technical point of view, mobile networks today are split into three main families with many different flavors,
and are usually based on where they originated from and from what industry there were emerging from
(Telecommunications versus PCs):
GSM (Global System for Mobile Communications) is the most popular standard for mobile telephony systems in
the world. GSM is used by over 3 billion people across 212 countries and territories, representing 80% of the global
mobile market uses (The GSM Association, 2009).
IS-95 (Interim Standard 95), which represents 15% of the global market, has been originally from the US and Asia
(outside Japan). The standard is more widely known under its latest release as CDMA and CDMA200 and has a
long-term plan to merge with the GSM technology at the LTE (Long Term Evolution) stage.
WiMAX (Worldwide Interoperability for Microwave Access) represents only 5% of the global market. The WiMAX
(IEEE 802.16 standard) comes
from IEEE family of protocols and
extendsthe wireless access fromthe Local Area Network (typically
based on the IEEE
802.11standard) to Metropolitan
Area Networks (MAN) and Wide
Area Networks (WAN). Ituses a
new physical layer radio access
technology called OFDMA
(OrthogonalFrequency Division
Multiple Access) for uplink and
downlink. While the initial
versions802.16-2004 focused onfixed and nomadic access, the
later version 802.16-2005, an
amendment to 802.16-2004
include many new features and
functionalities needed to support
enhanced QoS and high mobility
broadband services at speeds
greater than 120 Km/h. The
802.16-2004 is also called
802.16d and is referred to as fixed WiMAX while the 802.16-2005 is referred to as 802.16e or Mobile WiMAX. The
Mobile WiMAX uses an all IP backbone with uplink and downlink peak data rate capabilities of upto 75 Mbpsdepending on the antenna configuration and modulation, practicable to 10 Mbps within a 6 miles (10 Km) radius.
The earliest iterations of WiMAX was approved with the TDMA TDD and FDD with line of sight (LOS) propagation
across the 10 to 66 GHz frequency range which was later expanded to include operation in the 2 to 11 GHz range
with non line of sight (NLOS) capability using the robust OFDMA PHY layer with sub-channelization allowing
dynamic allocation of time and frequency resources to multiple users. The 802.16m (Mobile WiMAX Release 2)
Task-force is currently working on the next-generation systems with an aim for optimizations for improved
interworking and coexistence with other access technologies such as 3G cellular systems, WiFi and Bluetooth and
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enhance the peak rates to 4G standards set by theITU under IMT-Advanced umbrella which calls for data rates of
100 Mbps for high mobility and 1 Gbps for fixed/nomadic wireless access.
LTE (Long Term Evolution) LTE, on the other hand evolves from the Third-generation technology which is based on
WCDMA and defines the long term evolution of the 3GPP UMTS/HSPA cellular technology. The specifications of
these efforts are formally known as the evolved UMTS terrestrial radio access (E-UTRA) and evolved UMTS
terrestrial radio access network (E-UTRAN), commonly referred to by the 3GPP project LTE. The first version of LTE
is documented in Release
8 of the 3GPP
specifications. It defines a
new physical layer radio
access technology based
on Orthogonal Frequency
Division Multiple Access
(OFDMA) for the downlink,
similar in concept to the
PHY layer of Mobile
WiMAX, and uses SC-
FDMA (single Carrier
Frequency Division
Multiple Access) for the
uplink. LTE supports high
performance mobile
access functional upto
350Km/h with 500Km/h
under consideration. Peak
data rates range from 100
to 326.4Mbps on the
downlink and 50 to 86.4
Mbps on the uplink
depending on the antenna
configuration and modulation depth. The LTE also targets to achieve the data rates set by the 4G IMT-Advanced
standard. The development of LTE interface is linked closely with the 3GPP system architecture evolution (SAE)
which defines the overall system architecture and Evolved Packet Core (EPC). The LTE aims to provide an all IP
backbone with reduction in cost per bit, better service provisioning, flexibility in use of new and existing frequency
bands, simple network architecture with open interfaces, and lower power consumption. The next step in this
development line was the introduction of HSPA, a 3Gtechnology capable of delivering theoretical data rates up to
14Mbps. The data rate was improved even further with the introduction of HSPA+ that increased the data rates
over the two link directions; the uplink and the downlink. This technology is considered the big step towards LTE. Itcan be considered as a revolutionary development along the line, since it departed from the split circuit packet
switch network by introducing, for the first time, an all-IP architecture as an option for the voice and data services.
In addition, HSPA+ integrated the MIMO technology as a major part of its PHY layer, paving the way for its
integration in LTE. A similar line of evolution was followed by the 3GPP2. It has progressively evolved IS-95 form a
mere voice services network into the Evolution Data Optimized (EVDO) Rev B, a network that efficiently supports
both data and voice services and at various mobility levels.
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To enable possible deployment around the world, supporting as many regulatory requirements as possible, LTE is
developed for a number of
frequency bands, ranging from
800 MHz up to 3.5 GHz. The
available bandwidths are also
flexible starting with 1.4 MHz upto 20 MHz. LTE is developed to
support both the time division
duplex technology (TDD) as well
as frequency division duplex
(FDD). Since LTE provides high
spectral efficiency, supports high
data rates and implements
flexible access architecture, it is
proven to become a success
amongst operators as well as
customers.
Some Key Features of LTE Evolution
WCDMA HSPAHSPA+ LTE
(UMTS) HSDPA / HSUPA
Max downlink speed384 k 14 M 28 M 100M
bps
Max uplink speed128 k 5.7 M 11 M 50 M
bps
Latency
150 ms 100 ms 50ms (max) ~10 msround trip time
approx
3GPP releases Rel 99/4 Rel 5 / 6 Rel 7 Rel 8
Approx years of initial roll out2003 / 4
2005 / 6 HSDPA2008 / 9 2009 / 10
2007 / 8 HSUPA
Access methodology CDMA CDMA CDMA OFDMA / SC-FDMA
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Are WiMAX and LTE really moving towards convergence?
WiMAX and LTE are expected to converge on
several levels as they have many common
characteristics and deliver similar performances. In
addition, several stakeholders are taking steps to
accelerate this union. Initially, these and otherwireless networks will converge in devices on a
service level through multi-mode device integration,
which are expected to be much simpler and more
effective in supporting seamless handoff of sessions.
It is believed that both WiMAX and LTE will co-exist
in certain regions, and that operators will use
WiMAX for one set of applications and LTE for
another. Some of the similarities can be seen below
These commonalities and developments make the merger of WiMAX and LTE a certainty in the near
future. As the rollout of LTE begins, base stations, handsets, and CPE equipment will be built using baseband and
RF devices that support WiMAX and LTE. LTE and WiMAX provide comparable performance,because they both use
an Internet Protocol (IP) core and an Orthogonal Frequency Division Multiple Access(OFDMA) air interface as theircore technologies. However, in commercial networks in most countries, WiMAX has reached a more mature state
that will take a few years for LTE to match.
Overlaying a LTE network to complement existing WiMAX networks will allow bundling of services and
dual-mode devices. This will help increase an operators subscriber base. Achieving this is not difficult because:
1. An LTE overlay on WiMAX would not require additional towers.2. The wired network infrastructure is mostly common between systems and network management, back-office
accounting, operations and billing.
3. Other functions will also be common (operator dependent).The 3 major factors that have made operators realize a possible convergence to LTE are Firstly, the growing
support for a TDD-version of LTE, known as time-division LTE (TD-LTE), has created a more direct competitor to
WiMAX. Interest in TD-LTE originated in China, but it has spread worldwide, with many mobile operators attracted
by the opportunities for international roaming and for using much less expensive TDD spectrum to boost capacity
in their domestic markets. Further demand for TD-LTE is driven by WiMAX operators who have started to take a
more active role in the TD-LTE standardization process. In the US, for instance, Clearwire has asked the Third
Generation Partnership Project (3GPP) to create a TD-LTE profile for the 2.5 GHz band it uses for its WiMAX rollout.
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Second, vendors have introduced platforms that support multiple air interfaces through software upgrades, and
they plan to expand the selection of affordable multimode devices. The cost and complexity of migrating to a new
air interface has dropped, making it more attractive for WiMAX operators to switch to LTE or to support both
WiMAX and LTE.
Third, with a larger market size and commitment from most tier-one mobile operators, a powerful LTE ecosystem
is rapidly building, with a wider choice of subscriber devices and competitive equipment prices. The table belowshows a comparison of LTE and WiMAX
WIMAX LTE
IP-based technology with OFDMA modulation used in the
uplink and downlink.
IP-based technology with OFDMA modulation in the
downlink and Single Carrier Frequency Division Multiple
Access (SC-FDMA) in the uplink.
WiMAX networks operated by 559 operators covering more
than 620 million people in 147 countries and supporting a
rapidly growing subscriber base.
Few commercial networks for FDD LTE with a limited
number of subscribers, and none for TD-LTE to date
Commercial FDD LTE deployments are expected to
increase in early 2012.
Only TDD supported, in the 2.3 GHz, 2.5 GHz, and 3.5 GHz
bands. Additional bands might be added in the future.
Supports both TDD and FDD. TD-LTE frequencies range
from 1800 MHz to 2.6 GHz (with possible inclusion of the
3.5 GHz band in the future). LTE FDD bands range from700 MHz to 2.6 GHz.
Less complex solution for regional/rural operators who
dont need roaming with 3GPP networks.
Larger market share in the long term, with better
opportunities for international and domestic roaming
Standardization driven by vendors, operators, and
greenfield players at the Institute of Electrical and
Electronics Engineers (IEEE) and the WiMAX Forum.
3GPP standardization process led by mobile operators and top
vendors.
WiMAX Forum certification program supports
interoperability across vendors, but smaller market size
results in more limited choice of devices.
Powerful ecosystem with strong vendor and operator support
to ensure affordability and choice among devices.
The next version of WiMAXWiMAX 2, based on IEEE
802.16mis expected to be commercially available by end
2012.
Legacy support for Global System for Mobile
Communications (GSM), and High Speed Packet Access
(HSPA) gives LTE potential access to 4.6 billion mobile
subscribers. LTE Advanced is the next version of LTE; the
standard is still being developed.
Supports fixed, nomadic, and mobile usage scenarios. Developed with mobility in mind, but could support fixed
usage scenarios.
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Hard realities of WiMAX-to-LTE conversion
Current subscriber base
Cost to convert a subscriber is high. Declaration of intent to convert may imply to customers that the current
network is obsolete.
Equipment
Will current RAN vendors solution support dual operation? (No = expensive) Some vendors RAN equipment
will support both WiMAX and LTE concurrently in the same base station, which can reduce the cost of running dual
networks but even these have restrictions about how this can be done. Motorola is one of the vendors claiming it
can support both WiMAX and LTE in the same base station with the LTE channel turned on as overlay to the
WiMAX channel. Of course a new card on the rack or a new rack can also be installed but everything that involves a
visit to the site will be expensive. Another challenge is whether the base station has enough processing power to
support two channels, as there may not be enough spectrum to run two parallel networks.
How long will it take to fully convert subscriber base to new devices? (Quick = expensive)
The core architecture of each standard is significantly different, requiring the concurrent operation of two core
networks until subscribers are completely migrated. There is a small percentage of the core network that is
suitable in both networks, such as the AAA and packet router, but mostly the carrier will buy separate core
equipment for WiMAX and for LTE. In the case of a migration, 80% of the core infrastructure would have to be
duplicated, the biggest expense being to replace the WiMAX ASN gateway with the LTE equivalent.
Spectrum
Concurrent networks require double the spectrum, albeit mitigated somewhat by variable channel sizes and
novel spectrum reuse techniques available in both standards
TDD and FDD are not compatible in adjacent spectrum, so most WiMAX carriers will be forced to deploy TD-LTE.
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TOP WIMAX OPERATORS WORLDWIDE
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IEEE 802.16 FAMILY
Standard Description Status
802.16-2001 Fixed Broadband Wireless Access (1066 GHz) Superseded
802.16.2-2001 Recommended practice for coexistence Superseded
802.16c-2002 System profiles for 1066 GHz Superseded
802.16a-2003 Physical layer and MAC definitions for 211 GHz Superseded
P802.16bLicense-exempt frequencies
(Project withdrawn)Withdrawn
P802.16dMaintenance and System profiles for 211 GHz
(Project merged into 802.16-2004)Merged
802.16-2004Air Interface for Fixed Broadband Wireless Access System
(rollup of 802.16-2001, 802.16a, 802.16c and P802.16d)Superseded
P802.16.2aCoexistence with 211 GHz and 23.543.5 GHz
(Project merged into 802.16.2-2004)Merged
802.16.2-2004Recommended practice for coexistence
(Maintenance and rollup of 802.16.2-2001 and P802.16.2a)Current
802.16f-2005 Management Information Base (MIB) for 802.16-2004 Superseded
802.16-2004/Cor 1-
2005
Corrections for fixed operations
(co-published with 802.16e-2005)Superseded
802.16e-2005 Mobile Broadband Wireless Access System Superseded
802.16k-2007Bridging of 802.16
(an amendment to IEEE 802.1D)Current
802.16g-2007 Management Plane Procedures and Services Superseded
P802.16iMobile Management Information Base
(Project merged into 802.16-2009)
Merged
802.16-2009
Air Interface for Fixed and Mobile Broadband Wireless Access System
(rollup of 802.16-2004, 802.16-2004/Cor 1, 802.16e, 802.16f, 802.16g and
P802.16i)
Current
802.16j-2009 Multihop relay Current
802.16h-2010 Improved Coexistence Mechanisms for License-Exempt Operation Current
802.16m-2011
Advanced Air Interface with data rates of 100 Mbit/s mobile and 1 Gbit/s
fixed.
Also known as Mobile WiMAX Release 2 or WirelessMAN-Advanced.
Aiming at fulfilling the ITU-R IMT-Advanced requirements on 4G systems.
Current
P802.16n Higher Reliability Networks In Progress
P802.16p Enhancements to Support Machine-to-Machine Applications In Progress
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EVOLUTION PATH TO LTE FOR DIFFERENT OPERATORS AND TECHNOLOGIES
1) 3GPP operator examples
GSM(2G) GPRS(2.5g) EDGE(2.75g) WCDMA UMTS (3G) HSDPA (3.5g) HSUPA (3.75g) HSPA+
(3.95g) LTE (4G)
2) 3GPP2 operator examples
CDMA1x CDMA2000 EVDO Rev O EVDO Rev A EVDO Rev B(Wimax)(HSPA/HSPA+) LTE
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3) TD-LTE specific operator examples
2G TD/SCDMA TD-LTE