1. manasa066@gmail.com
BRAHMAIAH COLLEGE OF ENGINEERING
A Paper presentation on…
Wi-max
By
D.ANUSHA
R.MANASA
III B.Tech-II SEMISTER.
ROLL: 092M1A0406
BCEN Engineering College
NH-5,N.R. palem,SPSR
NELLORE (Dist.). 524366
Mobile no:+91- 9989741124
III B.Tech-II SEMISTER.
ROLL: 092M1A0424
BCEN Engineering College
NH-5,N.R. palem,SPSR
NELLORE (Dist.). 524366
Mobile no:+91-9440637769
e-mail : manasa066@gmail.com
e-mail: anushadevireddyece@gmail.com,
1

2. “WiMAX”
-
Emerging wireless technology
ABSTRACT
New and increasingly advanced data services are driving up wireless
traffic, which is being further boosted by growth in voice applications in advanced
market segments as the migration from fixed to mobile voice continues. This is already
putting pressure on some networks and may be leading to difficulties in maintaining
acceptable levels of service to subscribers.
For the past few decades the lower band width applications are growing
but the
growth of broad band
additional features in physical layer
data applications is slow. Hence we
and MAC layer and the benefits of
require technology which helps in the
each feature.
growth of the broad band data
This paper focuses on
applications. WiMAX is such a
technology which helps in point-tomultipoint broadband wireless access
with out the need of direct line of
sight connectivity with base station.
the major technical comparisons (like
QOS and coverage) between WiMAX
and
other
technologies.
It
also
explains about the ability of the
WiMAX to provide efficient service
This
paper
explains
about the WiMAX technology, its
in multipath environment.

3. broadband connectivity without the
need for Direct line-of-sight with a
base station.
III.What is wimax?
WiMAX
is
an
acronym that stands for “Worldwide
II. Introduction:
Interoperability
group number 16 of IEEE 802,
decades, low-bandwidth applications
specializing
such as downloading ring tones and
email
point-to-multipoint
known as WiMAX. There are at least
but the growth of broadband data
as
in
broadband wireless access. It also is
SMS are experiencing sharp growth,
such
Microwave
Access”. IEEE 802.16 is working
For the past couple
applications
for
four 802.16 standards: 802.16, 802.16a,
and
802.16-2004 (802.16), and 802.16e.
downloading/ uploading files with a
WiMAX
laptop computer or PDA has been
slow. The demand for broadband
conflict
access
complements it.
continues
to
escalate
with
WiFi
does
but
not
actually
WiMAX is a
worldwide and lower-bandwidth wire
wireless metropolitan area network
line methods have failed to satisfy the
(MAN) technology that will connect
need for higher bandwidth integrated
IEEE 802.11 (WiFi) hotspots to the
data and voice services. WiMAX is
Internet
radio technology that promises two-
extension to cable and DSL for last
way
several
km broadband access. IEEE 802.16
megabits per second with ranges of
provides up to 50 km of linear
several miles. It is believed that the
service
technology
DSL
connectivity without a direct line of
(Digital Subscriber Line) and cable
sight to a base station. The technology
broadband services because it offers
also provides shared data rates up to
similar speeds but is less expensive to
70 Mbit/s.
Internet
access
can
at
challenge
set up. The intention for WiMAX is to
Mobile
provide
a
wireless
area range and allows user’s
The portable version of
provide fixed, nomadic, portable and,
eventually,
and
WiMAX,
wireless
3
IEEE
802.16
utilizes

4. Orthogonal
Frequency
Division
Multiplexing
Access
(OFDM/OFDMA)
where
the
spectrum is divided into many subcarriers. Each sub-carrier then uses
QPSK or QAM for modulation.
WiMAX standard relies mainly on
spectrum in the 2 to 11 GHz range.
The WiMAX specification improves
upon many of the limitations of the
WiFi standard by providing increased
bandwidth and stronger encryption
In
reviewing
the
standard, the technical details and
For years, the wildly
features that differentiate WiMAX
successful 802.11 x or WiFi wireless
certified equipment from WiFi or
LAN technology has been used in
other
BWA applications. When the WLAN
technologies
can
best
be
illustrated by focusing on the two
technology was examined closely, it
layers addressed in the standard, the
was evident that the overall design
physical (PHY) and the media access
and feature set available was not well
control (MAC) layer design.
suited for outdoor Broadband wireless
access (BWA) applications. WiMAX
III. a) WIMAX PHY Layer:
is suited for both indoor and outdoor
BWA; hence it solves the major
The first version of the
problem.
802.16 standard released addressed
Line-of-Sight (LOS) environments at
high frequency bands operating in the
10-66
GHz
range,
whereas
the
recently adopted amendment,
the
802.16a standard, is designed for
systems operating in bands between 2
GHz and 11 GHz. The significant
difference
between
these
two
frequency bands lies in the ability to
4

5. support Non-Line -of-Sight (NLOS)
of the PHY layer features of the IEEE
operation in the lower frequencies,
802.16a standard.
something that is not possible in
higher
bands.
Consequently,
the
802.16a amendment to the standard
opened up the opportunity for major
changes
to
the
PHY
layer
specifications specifically to address
the needs of the 2-11 GHz bands. This
is achieved through the introduction
of three new PHY-layer specifications
(a new Single Carrier PHY, a 256
point FFT OFDM PHY, and a 2048
point FFT OFDMA PHY);
Some of the other
PHY layer features of 802.16a that are
instrumental in giving this technology
the
power
to
deliver
robust
performance in a broad range of
channel environments are; flexible
channel
widths,
adaptive
burst
profiles, forward error correction with
concatenated
Reed-Solomon
and
convolutional encoding, optional AAS
(advanced
antenna
systems)
improve
range/capacity,
to
DFS
(dynamic frequency selection)-which
helps in minimizing interference, and
STC (space-time coding) to enhance
performance in fading environments
through spatial diversity. Table 1
gives a high level overview of some
5

6. b) IEEE 802.16a MAC Layer:The
802.16a standard uses a slotted TDMA
protocol scheduled by the base station to
allocate capacity to subscribers in a
point-to-multipoint network topology. By
tarting with a TDMA approach with
intelligent scheduling, WiMAX systems
will be able to deliver not only high
speed data with SLAs, but latency
sensitive services such as voice and
video or database access are also
supported. The standard delivers QoS
beyond mere prioritization, a technique
that is very limited in effectiveness as
traffic load and the number of
subscriber’s increases. The MAC layer in
6

7. WiMAX certified systems has also been
designed to address the harsh physical
layer environment where interference,
fast fading and other phenomena are
prevalent in outdoor operation.
802.11 MAC was never designed for
and is incapable of supporting.
a) Coverage:
IV.WiMAX Scalability:
The BWA standard is
At the PHY layer the
designed for optimal performance in
standard supports flexible RF channel
bandwidths
and
reuse
of
all types of propagation environments,
these
including LOS, near LOS and NLOS
channels (frequency reuse) as a way to
environments, and delivers reliable
increase cell capacity as the network
robust performance even in cases
grows. The standard also specifies
where extreme link pathologies have
support for automatic transmit power
control
and
measurements
layer
tools
channel
been introduced. The robust OFDM
quality
waveform
as additional PHY
to
support
planning/deployment
and
spectrum
cell
efficient
single
STC,
(mesh
Advanced
networks)
and
antenna
diversity)
can
be
employed to improve coverage even
further. These advanced techniques
can also be used to increase spectral
CSMA/CA foundation of 802.11,
efficiency,
basically a wireless Ethernet protocol,
capacity,
reuse,
and
average and peak throughput per RF
scales about as well as does Ethernet.
channel. In addition, not all OFDM is
That is to say - poorly. Just as in an
the same. The OFDM designed for
Ethernet LAN, more users results in a
BWA has in it the ability to support
geometric reduction of throughput, so
MAC
channel.
antenna techniques (beam-forming,
In the MAC layer, the
CSMA/CA
RF
topologies
through
number of subscribers grows.
the
spectral
kilometers with up to 70 Mbps in a
sectorization and cell splitting as the
does
high
efficiency over ranges from 2 to 40
spectrum use. Operators can reallocate
supports
longer range transmissions and the
for
multi-path or reflections encountered.
WLANs. In contrast the MAC layer in
In contrast, WLANs and 802.11
the 802.16 standard has been designed
systems have at their core either a
to scale from one up to 100's of users
basic CDMA approach or use OFDM
within one RF channel, a feat the
with a much different design, and
7

8. have as a requirement low power
implementation will never be able to
consumption
deliver the QoS of a BWA, 802.16
limiting
the
range.
OFDM in the WLAN was created
systems.
with the vision of the systems
covering tens and maybe a few
V. ROLE OF ‘OFDMA’ IN
hundreds of meters versus 802.16
which is designed for higher power
MULTIPATH
and an OFDM approach that supports
ENIRONMENT:
deployments in the tens of kilometers.
b) Quality of service:
The
802.16a
MAC
relies on a Grant/Request protocol for
access to the medium and it supports
differentiated service The protocol
employs TDM data streams on the DL
(downlink) and TDMA on the UL
(uplink),
with
the
hooks
for a
Technologies
centralized scheduler to support delay-
using
sensitive services like voice and
DSSS (802.11b, CDMA) and other
video. By assuring collision-free data
wide band technologies are very
access to the channel, the 16a MAC
susceptible to multipath fading, since
improves total system throughput and
the delay time can easily exceed the
bandwidth efficiency, in comparison
symbol duration, which causes the
with
access
symbols to completely overlap (ISI).
CSMA-CA
The use of several parallel sub-
protocol used in WLANs. The 16a
carriers for OFDMA enables much
MAC also assures bounded delay on
longer symbol duration, which makes
the data. The TDM/TDMA access
the signal more robust to multipath
technique also ensures easier support
time dispersion
contention-based
techniques
like
the
for multicast and broadcast services.
a). Multipath: Frequency Selective
With a CSMA/CA approach at its
core,
WLANs
in
their
Fading
current
8

9. This type of fading
affects
certain
VI.
frequencies
Modulation and Coding (AMC):
of
a
OFDMA
with
Adaptive
transmission and can result in deep
fading at certain frequencies. One
reason this occurs is because of the
wide band nature of the signals. When
a signal is reflected off a surface,
different frequencies will reflect in
different ways. In Figure below, both
CDMA (left) and OFDMA (right)
experience selective fading near the
center of the band. With optimal
channel coding and interleaving, these
errors can be corrected. CDMA tries
to overcome this by spreading the
signal out and then equalizing the
whole signal. OFDMA is therefore
much more resilient to frequency
Both
selective fading when compared to
(HSDPA)
and
CDMA.
Quadrature
Phase
W-CDMA
OFDM
utilize
Shift
Keying
(QPSK) and Quadrature Amplitude
Modulation (QAM). It should be
noted here that for WCDMA, AMC is
only used on the downlink, since the
uplink still relies on WCDMA which
uses QPSK but not QAM. Modulation
and coding rates can be changed to
achieve higher throughput, but higher
order modulation will require better
Signal
to
illustrates
Noise
Ratio.
Figure
how
higher
order
modulations like QAM 64 are used
closer to the base station, while lower
9

10. order modulations like QPSK are used
In Figure below, you
to extend the range of the base
can see how sub-channels could be
station
results
chosen depending on the received
conducted for one of the 3GPP
signal strength. The sub-channels on
Working Groups [2], show that while
which
OFDM
the
significant fading are avoided and
maximum throughput of 9.6 Mbps
power is concentrated on channels
(16QAM), WCDMA does not exceed
with better channel conditions. The
3 Mbps. From these results, it appears
signals on the top indicate the
that even higher discrepancy may be
received signal strength, while the
found
higher
bottom part of the figure indicates
modulation and code rates to yield
which sub-carriers are then chosen for
even higher throughput for OFDM.
each signal.
.
is
Performance
able
when
to
achieve
utilizing
the
user
Adaptive Modulation and
Coding
(AMC)
With
OFDMA,
choose
sub
client
give
OFDMA
channels
based
further advantages since the flexibility
locations
with
to change the modulation for specific
eliminating the impact of deep fades.
sub-channels allows you to optimize
CDMA-based technologies utilize the
at
same frequency band regardless of
the
frequency
level.
Another
alternative would be to assign those
could
the
multipath
may
device
experiencing
a
environment
in
is
where the user is.
sub channels to a different user who
may have better channel conditions
for that particular sub-channel. This
could allow users to concentrate
transmit power on specific subchannels, resulting in improvements
to the uplink budget and providing
greater range. This technique is
known as Space Division Multiple
Access (SDMA).
10
on
the
geographical
potential
of

11. VII.ADVANCED
TECHNIQUES:
RADIO
a) Transmit and receive diversity
schemes:
Transmit and Receive
Diversity schemes are used to take
advantage of multipath and reflected
signals
that
occur
in
Adaptive
NLOS
antenna
environments. By utilizing multiple
systems (AAS) are an optional part of
antennas (transmit and/or receive),
the 802.16 standard. AAS equipped
fading, interference and path loss can
base stations can create beams that
be reduced. The OFDMA transmit
can be steered, focusing the transmit
diversity option uses space time
energy to achieve greater range as
coding.
diversity,
shown in the figure. When receiving,
techniques such as maximum ratio
they can focus in the particular
combining (MRC) take advantage of
direction of the receiver. This helps
two separate receive paths.
eliminate unwanted interference from
For
receive
other locations.
VIII. Conclusion:
Thus WiMAX systems
for portable/nomadic use will have
better
performance,
interference
rejection, multipath tolerance, high
data quality of service support (data
oriented MAC, symmetric link) and
lower future equipment costs i.e., low
chipset
complexity,
high
spectral
efficiencies. And hence WiMAX can
complement existing and emerging
3G mobile and wireline networks, and
b) Smart Antenna Technology:
play a significant role in helping
11

12. •
service provides deliver converged
service offerings
V.Poornima,
III/IV B-tech,
E.C.E,
IX. BIBLIOGRAPHY:
L.B.R.College of Engineering ,
MYLAVARAM.
 Understanding “WiMAX”- Joe
E-MAIL ADDRESS:
Laslo & Michael gartenberg
v_poornima06@yahoo.co.in
 www.intel.com/ebusiness/pdf/w
ireless/intel
Residential Address:
 www.intel.com/netcomms/techn
P.Tabitha Priyadarshini,
ologies/wimax
D/o P.Venkata Ratnam,
 P. S. Henry, “Wi-Fi: What’s
Door no- 21-171,
next?” IEEE Communications
Santhinagar, Main road,
Magazine
Tiruvuru. – 521235 (Krishna dst.)
 WWW.WiMaxeed.COM.
 WiMAX Handbook –Frank
PHONE: 9848783201
ohrtman
College Address:
L.B.R College of Engineering ,
L.B.R.nagar,
MYLAVAM.
AUTHORS :
•
P.Tabitha Priyadarshini,
III/IV B-tech,
E.C.E,
L.B.R. College of Engineering,
MYLAVARAM.
E-MAIL ADDRESS:
p_tabitha86@yahoo.co.in
12
(Krishna dst. A.P)