This paper provides a high-level comparison between LTE and WiMAX. The focus is on two primary areas: System Architecture and Physical Layer. The System Architecture describes the different functional elements in LTE and WiMAX and attempts to map similar functionality (such as mobility, security, access-gateway). We also compare and contrast the various aspects (such as transmission modes, duplexing types) of the physical layer.

1. Comparison of LTE and WiMAX
by Rajesh S. Pazhyannur
Abstract
This article provides a high-level compari-
son between LTE and WiMAX. The focus
of paper is on two primary areas: System
Architecture and Physical Layer. The Sys-
tem Architecture describes the different
functional elements in LTE and WiMAX and
attempts to map similar functionality (such
as mobility, security, access-gateway). We
also compare and contrast the various
aspects (such as transmission modes,
duplexing types) of the physical layer.
Introduction Figure 16 - Evolution of LTE
LTE (Long Term Evolution) and WiMAX
(Worldwide Interoperability for Microwave
Access) are expected to be primary tech-
nologies for mobile broadband wireless
for the next 10 years. As with most emerg-
ing and competing technologies, there is
considerable effort by the correspond- Figure 17 - Evolution of Mobile WiMax
ing technology advocates to frame the
discussion as LTE versus WiMAX with the
end result of declaring one technology as
LTE Evolution support for EV-DO Rev C has waned and
The first generation of cellular systems it has now become clear that the GPP2
the “winner”. We take a different approach
were based on analog standards and radio interface evolution has effectively
in this paper. We frame the discussion,
introduced in the mid-80s. These quickly ceased, allowing a single cellular technol-
rather, in terms of similarities and differ-
led to a second generation of digital cel- ogy —LTE.
ences across various technology/technical
lular standards that made use of digital
factors. This is motivated by the fact that 1) As shown in Figure 16, the GPP and
modulation and signal processing. The
technological factors only partially contrib- GPP2 cellular technology offerings have
second generation also led to a technol-
ute to determining winners, and in some evolved and GPP2 operators are now
ogy fragmentation. At one point many
cases play a small role and 2) technical dif- switching camps and backing a single
competing standards existed, however
ferences are not universally advantageous. specification based on LTE.
what remains now are two main branches:
The goal of the paper is to primarily focus
referred to as GSM and CDMA branches WiMAX Evolution
on technical/technology aspects as com-
or alternately referred as the GPP and WiMAX evolved almost independently
pared to business and strategic aspects.
GPP2 branches. (GPP and GPP2 are (and in parallel) to the cellular standards
The article is organized as follows.Firstly, the standardization bodies responsible for mentioned earlier. In the late 0s, IEEE
we describe the evolution of LTE and technical specifications.) These branches started a working group to create an air-
WiMAX as well as provide the primary remained separate as they migrated to G interface for point to multipoint broadband
motivations. A system-level comparison of systems focusing on more efficient voice wireless standard. The working group lev-
LTE and WIMAX focusing on system-archi- transport as well providing data-services. eraged DOCSIS (data over cable service
tecture and protocol stacks for the control LTE originated in the GPP standards or- interface specification) standard heavily
and user traffic is provided and the air ganization, and a competing specification especially in the definition of the MAC
interfaces for LTE and WiMAX described. (EV-DO Rev C) started in the GPP2 body layers. The original standard was modified
as the next evolutionary step. However, the into 802.16d in 2004 introducing OFDM as
IP NGN ARCHITECTURE THOUGHT LEADERSHIP JOURNAL - Q1 FY2010

2. Technology Highlights
• Mobile Data Network: The primary
UMTS (aka WCDMA) CDMA, Spread Spectrum, 5 MHz spectrum usage of both networks is to provide
Circuit Voice and Packet Data (up to 84 Kbps) a data-centric network as compared
Deployed since 200 to voice-centric network of 2G and G
HSDPA (High Speed CDMA, Spread Spectrum, 5 MHz systems. This aspect is highlighted by
Downlink Packet Downlink Only; Data Only the absence of any provisions to carry
Access) Multiple Codes per Subscriber any circuit-type service. The networks
Up to 16 QAM, Peak Rates of 14.4 Mbps do support voice, but in the form of
Deployed since 2005 packetized VoIP service.
HSUPA (High Speed CDMA, Spread Spectrum, 5 MHz • Improve Spectral Efficiency: Given the
Uplink Packet Access) Uplink Only; Data Only scarcity of licensed spectrum, improv-
Multiple Codes per Subscriber ing efficiency is a major impetus for
Up to 16 QAM, Peak Rates of 4.5 Mbps both networks. The main technologies
Deployed since 2007 to enable higher efficiency are to move
towards higher modulation schemes
HSPA+(Evolved High CDMA, Spread Spectrum, 5 MHz
(like 64 QAM), smart antenna tech-
Speed Packet Access) Up to 64 QAM, MIMO. Peak Rates (DL,UL): 42, 11
niques (MIMO, Beam Forming, etc) and
Mbps
OFDM.
Likely to be deployed in 200-2010
LTE Scaleable OFDM on downlink, Single Carrier • Spectrum Flexibility: Unlike previous
FDMA on uplink networks which operated on a fixed
Variable Spectrum Width from to 20 MHz width spectrum (5 MHz for WCDMA
Up to 64 QAM, MIMO, Spatial Multiplexing(SM), and 1.25 MHz for CDMA-DO), both net-
Beamforming works allow scaleability from 1.25 MHz
Likely to be deployed between 2010-2012 up to 20 MHz.
WiMAX Scaleable OFDM on downlink and uplink • Higher Peak Data Rates: Both networks
Variable Spectrum Width from 1.25 to 10 MHz attempt to improve the peak data rate
Up to 64 QAM, MIMO, Spatial Multiplexing, Beam- on the downlink and uplink so that high
forming data rate services such as high-defi-
Mobile WiMAX deployed since 2008 nition video can be transmitted over
Table 1: Technology Summary broadband wireless links. Specifically,
the goal is to increase the peak rates
from range of (-10) Mbps to (50-100)
the transmission scheme. This standard Looking forward, the 802.16e standard is Mbps.
was targeted at fixed applications and is
sometimes referred to as fixed WiMAX.
evolving to 802.16m which focuses on en-
hancements to air-interface specifications. • Lower Infrastructure Costs: Traditional
cellular networks comprise a combina-
This evolution is shown in Figure 17.
In 2005, 802.16d was further enhanced tion of TDM and packet infrastructure
to provide support for mobility as well as Technology Summary partly because of the need to carry
provide a scalable OFDM transmission As seen from Table 1, the main differences circuit voice. LTE and WiMAX networks
system. This standard is known as 802.16e between the G technologies and 4G simplify the network considerably, mi-
and also as mobile WiMAX. (It should be technologies such as LTE/WiMAX are the grating towards an all-IP infrastructure
noted that products based on 802.16d different transmission schemes (OFDM relying on IP network for transporting
and 802.16e exist in the marketplace and compared to CDMA) and much higher data and control messages. Addition-
both are classified as WiMAX products peak rates. ally, both networks embody a design
leading to some ambiguity about which principle of “flattening” the architecture
Motivation for LTE and WiMAX
specific standard is supported—802.16d wherein the system eliminates a cen-
The primary motivations for both LTE and
or 802.16e.) tralized base station controller (or Radio
WiMAX are similar and can be stated as::
Network Controller (RNC)) in favor of
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3. distributing the functionality to Base
Stations and Access Gateways.
System-Level
Comparison
Architecture
Figure 18 provides a simplified view of
the LTE and WiMAX architecture (not all
nodes and interfaces are shown, only the
main elements involved in user and control
plane traffic).
We first compare the main functional ele-
ment below.
• eNodeB and BS: Functionally speaking,
the LTE and WiMAX BS are quite similar.
Both handle the traffic to/from the
subscriber device. This involves per-
forming the function of Radio Resource Figure 18 - LTE and WiMAX System Architecture
Management on the control plane,
in terms of authentication, setting up
connections, allocating resources and
the packet network. Both systems use
an IP tunnel to route user plane traffic to
• MME/S-GW and ASN-GW: Function-
ally speaking, the combined functions
performing functions like packet trans- an access gateway. There are sig- of MME and S-GW match closely to
missions, MAC, H-ARQ and link-adapta- nificant differences in the air interface those performed by the ASN-GW. This
tion on the user-plane. In addition, the standards that are described next. element (in LTE and WiMAX) provides
base stations provide an interface into mobility between BS, security func-
tions, QoS functions, idle state (paging)
management. LTE defines a functional
element, the MME, for handling control
plane traffic and another element for
handling the user plane traffic called
the Serving Gateway. WiMAX (at least in
Profile C) does not separate the control
and user plane handling into separate
elements. The control and user plane
traffic both are carried by the ASN-
GW. The protocols used between the
gateways and the BS’ differ between
LTE and WiMAX as well. LTE uses GTP
(GPRS Tunneling Protocol) for the S1u
and S1-AP/SCTP for S1c interface, while
WiMAX uses GRE/UDP as the tunnel-
ing protocol and UDP for control plane
transport. The specific control mes-
sages transferred differ as well and are
defined by corresponding specifica-
tions: S1 for LTE and R6 for WiMAX. A
function unique to MME and S-GW is
to interface with legacy G networks
IP NGN ARCHITECTURE THOUGHT LEADERSHIP JOURNAL - Q1 FY2010

4. (omitted from Figure ). GPP has
defined interfaces from the MME and
S-GW to connect to WCDMA systems
as well as CDMA-1X and EV-DO sys-
tems. The WiMAX forum is expected
to define corresponding interfaces
between WiMAX and G systems in
future releases.
• PDN-GW and HA: Functionally speak-
ing, the PDN-GW and HA are similar.
Both provide mobility between the
Access Gateways (S-GW for LTE and
ASN-GW for WiMAX). In WiMAX R1.0,
the defined protocol for the R inter-
face is Mobile IPv4 (MIPv4), and in most
instances, the ASN-GW performs Proxy
MIP (PMIP). LTE defines two alterna-
tives for the S5 interface: One is based Figure 19 - LTE and WiMAX User Plane Protocol Stacks
on GTP (GPRS Tunneling Protocol)
and the other is based on Proxy MIPv6
(PMIPv6). PMIPv6 is being defined as
an option for WiMAX R1.5.
Other Architectural Considerations
All IP (Packet-only) Systems: As shown
in Figure 18, LTE and WiMAX are packet-
only systems. There are no defined inter-
faces to circuit switched systems. More-
over, all RAN and Core Network systems
are IP based.
Inter BS interface: LTE and WiMAX define
interfaces to optionally route traffic related
to handover between BS’ directly eliminat- Figure 20 - LTE and WiMAX Control Plane Protocol Stacks
ing the need to go through a core network
element. This is referred to as the R8
interface in WiMAX and X2 interface in LTE. Protocol Stacks control stacks for the subscriber. One stack
This interface can improve the latency in The user and control plane stacks further is for RRM messages and is between the
handovers between BS as well reduce the illustrate the similarities and differences UE and eNB. The other stack is for security,
control and user plane traffic traversing the between LTE and WiMAX and are given in idle state management, QoS negotiation,
access gateways. Figure 1 and Figure 20 respectively. As etc and is between the UE and the MME
shown in Figure 1 the key difference is (and known as Non-Access Stratum (NAS)
Multiple forms of Mobility: LTE and WiMAX
that the interface between base-site and layer). In comparison, the subscriber sta-
define multiple forms of mobility: across
access-gateway uses GTP and S5 uses ei- tion (SS) never communicates directly with
BS’ connected to the same Access Gate-
ther PMIPv6 or GTP in LTE, while in WiMAX the ASN-GW. The 802.16e layer defines
way (R8 or R6 relay in WiMAX), across BS’
the corresponding protocols are GRE and procedures between the SS and the
connected to different Access Gateway
PMIPv4. BS (shown as MAC in Figure 5) while the
(R4 in WiMAX).
WiMAX Forum defines the procedures
As shown in Figure 20, the key difference
between the BS and the ASN-GW (shown
in the control plane is that LTE defines two
as R6 in Figure 20).
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5. Remarks Remarks
Scalable Band- LTE: 1.4,, 5, 10, 15, 20 MHz Duplexing Mode LTE is primarily for FDD (though TDD is defined).
width WiMAX: 1.25, 5, 10 MHz WiMAX is primarily for TDD (though FDD is being considered)
Downlink OFDMA Frequency Bands LTE: 700, 1700, 100, 2100, 2500, 2600
Transmission
WiMAX: 200, 2500 and 500
MIMO 2x2 (STBC and SM)
Uplink Transmission LTE: SC-FDMA
Table 2: Air Interface Similarities
WiMAX: Uplink Transmission is OFDMA
Frame Duration and LTE: 1 msec frame; subcarrier frequency :15KHz
SubCarrier Frequncy WiMAX: 5 msec frame; subcarrier frequency : 10KHz
Table : Air Interface Differences
Air Interface
Similarities • Duplexing Mode: WiMAX is currently FDD is a natural choice for cellular
Table 2 provides the key similarities be- defined as a TDD system (though there operators and partly explains the
tween LTE and WiMAX air Interface. are plans to define a FDD system in a preference shown by existing cellular
future release). LTE has a defined TDD
• Scalable Bandwidth: G technolo- and FDD specifications, though most
operators to migrate towards LTE.
gies were designed to operate in a deployments are expected to be FDD. • Frequency Bands: The frequency
fixed bandwidth. For example, WCDMA bands that LTE and WiMAX are ex-
FDD uses “paired” spectrum (one for
bandwidth is 5 MHz. Unlike G, LTE and pected to be deployed are quite differ-
uplink and other for downlink). TDD
WiMAX are defined over a wide range ent. This is also related to the fact that
on the other hand requires contigu-
of bandwidth ranging from 1.5 to 20 cellular operators are expecting to use
ous spectrum. Cellular/G systems
MHz. This allows the operators (service existing frequency bands for LTE usage
are FDD and cellular operators have
providers) deployment flexibility based in the future. See Figure 6 for more
unused (or in-use) paired spectrum that
on spectrum availability and capacity/ details.
can be utilized for LTE. One of the key
coverage needs. benefits of TDD is the reciprocal nature LTE is specified over a large number
• Downlink Transmission: LTE and of the channel, facilitating the use of
beamforming techniques to provide
of spectrum bands owned by cellular
WiMAX deploy OFDM for downlink provided throughout the world.
improved edge of cell performance as
transmission. The transmission is
divided into time intervals (frames) and well as stabilizing multipath in wide area • Uplink Transmission: WiMAX deploys
OFDMA in uplink and downlink direc-
the spectrum is divided into a number MIMO deployments. Another techni-
tions. LTE deploys OFDMA on the
of subcarriers. Downlink Resources are cal aspect of TDD and FDD systems
downlink but SC-FDMA (Single Carrier-
managed by a scheduler at the Base is the synchronization requirement.
Frequency Division Multiple Access) on
Station that determines the number of TDD systems have to be synchronized
the uplink. The choice of SC-FDMA is
subcarriers and time intervals for each to ensure non-interference of uplink
motivated by reducing the PAPR (Peak
user on the downlink and uplink. and downlink burst across different
to Average Power Ratio) on the uplink.
BS’. FDD systems do not require this
• MIMO: LTE and WiMAX allow for MIMO form of synchronization. A typical way
PAPR ratio has a direct impact on the
options comprising STBC (Space Time requirements of the power amplifier
of implementation of achieving the
Block Coding) or SM (Spatial Multiplex- and resulting battery life. (OFDM trans-
synchronization is by using an accurate
ing). WiMAX Release 1.0 defines 2 x missions consist of multiple subcarriers
GPS receiver than can provide a pulse
2 MIMO (and higher MIMO are being leading to a relatively larger PAPR than
at 1 PPS (Pulse per second). In low-
developed for future release). The LTE those for a single-carrier.)
end base stations such as Pico Base
specification allows up to 4 x 4 MIMO. Stations and Femto Base Stations, the SC-FDMA provides a 1-2 dB PAPR
Differences additional GPS receiver cost becomes advantage over OFDMA that in turn
Table provides the key similarities be- an important consideration while in improves battery life of subscriber
tween LTE and WiMAX air Interface. A little indoor Femto Base stations, the non- devices (SC-FDMA would increase re-
more detail is provided on these below availability of GPS signals becomes an ceiver complexity at the BS compared
additional issue. to OFDMA receiver). This improve-
IP NGN ARCHITECTURE THOUGHT LEADERSHIP JOURNAL - Q1 FY2010

6. these elements are considerably
different (motivated partly by the
existing protocols in G systems
and to facilitate backward compat-
ibility with already deployed G
systems).
• Air Interface Efficiency: This is
often a highly debated and con-
tentious matter. The fact that both
technologies use OFDMA and
MIMO would lead to comparable
spectral efficiency up to first order
of approximation. However, design
choices about protocol overheads,
control channel overheads, would
determine the resulting efficiency.
Figure 21 - Frequency Bands for LTE and WiMAX Initial comparisons indicate that
LTE efficiency is slightly better
ment is available to users at the edge and Intel) plan to provide LTE and WiMAX than WiMAX Release 1.0, (see []
of the cell, e.g., in order to increase the equipment. Recently, some of the leading below) but author believes that this
up-link coverage or throughput in such vendors announced that they are scaling improvement would disappear with
scenarios. the investments in WiMaX. In most cases, modifications in WiMaX Release 1.5
and IEEE 802.16m.
• Frame Duration: LTE uses a frame of
the equipment vendors intend to leverage
1 msec while WiMAX uses a frame of
the commonality in their product devel-
opment. This may indicate that both may
• Likely Deployments: LTE and
5 msec. The shorter duration leads to WiMAX have unique advantages
successfully co-exist in a manner similar that will ultimately determine where
more complex implementation in the
to co-existence of GSM and CDMA for the they will be deployed. For example,
form of larger processors, etc. However,
last 10-15 years. LTE appears to be clear choice for
this reduces end-end latency and can
lead to improved H-ARQ (Hybrid ARQ) In closing, we suggest the following key operators with FDD spectrum as
performance, faster channel quality takeaways: well as operators with existing G
(GSM) deployments. WiMAX ap-
feedback channel.
• Similar Technology but different imple- pears to be the clear choice for op-
Summary mentations: LTE and WiMAX have de-
ployed similar air interface technology
erators with TDD spectrum as well
In this paper, we outlined the key similari- operators with frequency in the 2.5
(OFDMA, MIMO) but have considerably GHz and .5 GHz band and opera-
ties and differences between the tech-
different implementations (such as FDD tors with little or no legacy cellular
nologies. The ultimate success of either
versus TDD, 1 msec versus 5 msec deployments (mostly in emerging
technology (as measured by number
frames, etc). These design choices markets).
of worldwide deployments, number of
have been made for a variety reasons
subscribers, total revenue, etc) will be
and the relative merits of these are
determined by a combination of tech-
hotly contested by proponents of the
nology and business factors. Given the
LTE and WiMAX communities. From a
relatively similar technology (for example,
systems architecture standpoint they
OFDM) and design choices, the business
deploy similar functional decomposi-
factors will play a bigger role in determin-
tion (such as separating radio resource
ing the success of LTE and WiMAX. Most
management from IP management and
of the major equipment vendors (such
locating RRM in the BS and IP manage-
as Cisco, Nokia-Siemens, etc) with a few
ment in an access gateway). However,
notable exceptions (such as Ericsson,
the specific protocols used between
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Cisco Systems, Inc. Cisco Systems (USA) Pte. Ltd. Cisco Systems International BV
San Jose, CA Singapore Amsterdam, The Netherlands
Cisco has more than 200 offices worldwide. Addresses, phone numbers, and fax numbers are listed on the Cisco Website at www.cisco.com/go/offices.
CCDE, CCENT, CCSI, Cisco Eos, Cisco HealthPresence, the Cisco logo, Cisco Lumin, Cisco Nexus, Cisco Nurse Connect, Cisco Stackpower, Cisco StadiumVision, Cisco TelePresence, Cisco WebEx, DCE, and Welcome to
the Human Network are trademarks; Changing the Way We Work, Live, Play, and Learn and Cisco Store are service marks; and Access Registrar, Aironet, AsyncOS, Bringing the Meeting To You, Catalyst, CCDA, CCDP, CCIE,
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