International Journal of Engineering Trends and Technology (IJETT) - Volume4Issue5- May 2013
Wimax Technology Performance Enhancement Using Phy Layer with
Turbo Coding
*Shaik Avaes Mohsin,**Kilaru Kalyan, # Suresh Angadi
*(Department of Electronics & communication, KLUniversity, Vaddeswaram ,AP,India
**(Department of Electronics & communication, KLUniversity, Vaddeswaram ,AP,India
# Associate Professor(Department of Electronics & communication, KLUniversity, Vaddeswaram ,AP,India
I. ABSTRACT
We introduce a paper on IEEE 802.16d / e PHY layer
adapted by WiMax forum contains multiple
specifications, making the standard flexible and
adaptable to different frequency ranges. The PHY
layer specifies a number of mandatory features and
some optional functions must be performed to
provide a reliable end-to-end connection has to offer.
The primary issue in the implementation of PHY
layer is robust performance in multipath fading
environments. In this paper, the performance of
WiMAX PHY layer with turbo coding mechanisms
were investigated and compared with existing
mechanisms. The results obtained show that turbo
coding offers lower BER, and improve the
performance of the PHY layer in the cell (multi-path)
environments.
Keywords: WiMax, IEEE 802.16 PHY layer, Turbo
coder
II. INTRODUCTION
Worldwide Interoperability for Microwave Access
(WiMAX) is an emerging global broadband wireless
system based on the IEEE 802.16 standard. WiMAX
is a new OFDM-based technology and promises high
data rate services with broad coverage (10-66 GHz
frequency range (line of sight) and 2 -11 GHz (Non
Line of Sight)) and to develop large user densities
with a variety Quality of Service (QoS) requirements
[1, 2]. WiMAX can provide broadband wireless
access (BWA) up to 30 miles (50 km) for fixed
station and 3 to 10 miles (5-15 km) for mobile
stations with theoretical data rates between 1.5 and
75 Mbps per channel. The 802.16e standard is an
amendment to 802.16d standard and adds important
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new specifications for complete mobility vehicle
speed is increased to the QoS (below 6 GHz NLOS
operation). The WiMAX standard air interface
contains the definition of both the medium access
control (MAC) and physical (PHY) layers for the
subscriber station and the base station, while access
to the network operability is defined by the WiMAX
Forum, an organization comprising entrepreneurs and
component and equipment manufacturers.
The IEEE 802.16 standard supports multiple physical
specifications that increase the flexibility of the PHY
layer and the system designers to tailor their system
based on their needs. The PHY specifies some
mandatory functions are performed by the system
with a number of optional features to provide a
reliable end-to-end connection. WiMax PHY layer
makes use of OFDM (Orthogonal Frequency
Division Multiplexing) and Orthogonal Frequency
Division Multiple Access (OFDMA) for fixed (256 point FFT) and mobile communications (128 bits to
2048 point FFT). This adaptation provides higher
data rate transmissions with reduced Inter Symbol
Interference (ISI) in non-line-of-sight or multipath
environments. Scalable OFDMA (SOFDMA) was
also introduced in IEEE 802.16e to support scalable
channel bandwidths 1.5-20 MHz with a guaranteed
bandwidth of up to 15 Mbps. To the demands of
higher spectral efficiency and higher data rate
applications in both fixed and mobile environments,
the IEEE 802.16 standard provides powerful tools
known as to support a variety of applications and
environments higher QoS. Mechanisms PHY lowlevel flexibility and efficiency One of the important
mechanisms is a combination of modulation scheme
with forward error correction codes (FEC). Which is
a high transmission rate provided by a high order
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International Journal of Engineering Trends and Technology (IJETT) - Volume4Issue5- May 2013
modulation scheme but it makes more susceptibility
to interference. FEC builds redundancy into the
transmission by repeating some of the information
bits, so pieces that are missing or error can be
corrected at the receiving end and helps to reduce by
cutting down the transmission latency. Without error
correction, FEC would require all the frames to be
transmitted, resulting in delays and lower quality of
service. There are three basic types of forward error
correction codes are block codes (Reed Solomon
codes), convolutional codes and turbo codes. The
Reed-Solomon Convolutional Code (RS-CC) are
mandatory schemes in IEEE 802.16 PHY layer
standard, while Convolutional Turbo Code (CTC)
and Block Turbo Code (BTC) are both optional and
basically meant for mobile environments. In this
paper, the behavior of the IEEE 802.16 standardsbased PHY layer for WiMax system is analyzed with
and without Turbo codes for mobile environments.
III.DESCRIPTION
Physical (PHY) Layer Model Description The
primary function of WiMAX PHY is the actual
physical transport of data. To reach the various QoS
requirements PHY supports various mechanisms with
features maximum performance for high data rate
transmission (both fixed and mobile environments)
and high spectral efficiency such as:
Frequency Division Duplex (FDD) and Time
Division Duplex (TDD): Provides flexible bandwidth
allocation.
OFDM / OFDMA: OFDM technique is an efficient
bandwidth multicarrier technique which divides the
system bandwidth into orthogonal sub-channels, each
taking only a narrow bandwidth and a separate carrier
is assigned to each. By means of guard interval and
cyclic prefix, an OFDM system also provides for a
good resistance to multipath fading.
Adaptive PHY profile: Provides ability to Radio Link
Control (RLC) switch to a more robust and efficient
PHY technology (burst profile, including the UL
(Uplink) or DL (downlink), Modulation Type,
Forward Error Correction (FEC, preamble length,
waiting time), adaptive antenna systems and preOFDM systems. depending on channel conditions.
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Adaptive Modulation and Coding: WiMax
supports link adaptation techniques known conditions
as adaptive modulation and coding modulation
scheme which changes depending on channel. Using
adaptive modulation scheme, WiMax system can
switch to the highest order modulation depending on
the channel conditions. AMC technique helps reduce
the time selective fading, the range can be. Higher
modulation scheme used
Forward Error Correction (FEC): It is achieved by
using convolutional codes (correct independent bit
errors) and Reed-Solomon codes (correct burst errors
at the byte level) to the extra coding gain that the
additional amount of SNR that would be required in
order to provide measurement provide the same BER
performance for an uncoded message signal in the
same channel conditions. The RS coder is
particularly useful for OFDM compounds in the
presence of multipath while the puncture
functionality CC made concatenated codes rate
compatible in accordance with specification
summarizes several combinations of modulation and
coding rates, which can be assigned to each
subscriber (both UL and DL), defined selective by
the PHY layer.
Supports Optional: Apart from the mandatory
regulations mentioned above several optional carriers
are also included in the PHY layer standard. These
include: channel coding schemes such as block turbo
codes, convolutional turbo codes and low density
parity check (LDPC) to increase the coverage and / or
strengthen both transmit and receive diversity
performance in fading environments through spatial
diversity capacity, codes for increasing the capacity
of the system, hybrid ARQ that an effective hybrid of
FEC and ARQ to improve reliability, a signaling
structure that the use of adaptive antenna system
(AAS) is switching the transmission of DL and UL
burst with directed beams, each directed for the BS;
advanced OFDM systems (MC-CDMA) to support
multi-user diversity.
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International Journal of Engineering Trends and Technology (IJETT) - Volume4Issue5- May 2013
Table: Different modulation and coding rates
Conventional Turbo Encoder in IEEE 802.16e2005 standard
Turbo Coding in IEEE 802.16 standard
Turbo codes may be supplied as an optional channel
coding scheme in the IEEE 802.16 standard. Turbo
codes are convolutional codes, in principle, joined
together in series or in parallel are well-known as a
convolutional turbo codes (CTC). The IEEE 802.16
uses duo binary turbo codes in which a pair of bits
used for the coding of both the normal and
interleaved coding iterations with a component
recursive encoder constraint length 4.
In the duo binary turbo codes two consecutive bits of
the coded bit sequence at the same time the encoder
are sent with two generating polynomials, 1 + D2 +
D3 + D3 1 and two parity bits. For two consecutive
bits are used as simultaneous inputs, this encoder has
four possible state transitions compared with two
possible transitions to a binary turbo encoder. Duo
binary turbo codes have better convergence larger
minimum distances and less sensitivity to puncturing.
The output of the native 1/3 coding rate encoder is
first separated into six blocks (A, B, Y1, Y2, W1 and
W2) in which A and B contain the system bits, Y1
and W1 contains the parity bits of the encoded
sequence in the natural order , and Y2 and W2
include the parity bits of the interleaved sequence.
independently interleaved and the sub-blocks
containing the parity bits are punctured (delete some
parity bits after encoding) to achieve the goal. code
rate The sub block interleaver consists of two phases:
(1) The first stage of the interleaver flips bits in the
alternate symbol.2 The second phase of the sub block
interleaver permutates the positions of the symbols.
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Look Up Table for CRSC Coder
IV.MODELING AND SIMULATION
The PHY layer model is developed based on the
standard documents MATLABTM R2007a. The
basic system model is developed and analyzed further
investigated with the introduction of Turbo Coder as
below.
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International Journal of Engineering Trends and Technology (IJETT) - Volume4Issue5- May 2013
Schematic Turbo Encoded WiMax PHY Layer
Model Developed in Matlab 2007a
BER performance of Turbo Coded WiMax system in
AWGN Channel and ITU Vehicular channel for
mobile user for QPSK ¾ System
V.RESULTS AND ANALYSIS
The performance of the turbo-encoded PHY layer of
WiMax system for a variety of modulation
techniques with varying channel conditions is
measured in Bit Error Rate (BER) curves. A
comparative performance analysis with FEC encoder
based WiMAX PHY layer is also performed. Figure
4 compares the performance of the turbo coded
WiMax PHY layer in AWGN channel of QPSK,
QPSK ½ and ¾ system. The result obtained is
consistent with the higher modulation scheme offer
better performance at high values of SNR while
lower order schemes perform better for lower SNRs.
BER performance of Turbo Coded WiMax system in
AWGN channel for QPSK QPSK ½ and ¾ System.
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shows the performance of turbo-encoded for a mobile
user in a QPSK ¾ system. It should be noted that the
mobile user is a BER higher than a fixed performance
is encountered for the account of the multipath fading
environment by a mobile user. compares the
performance of the turbo-encoded WiMax system
and FEC encoded WiMax system for a mobile user.
An improvement of ~ 5 dB is observed with the
introduction of Turbo coding in the PHY layer of the
WiMax system. Thus it is deduced that the
introduction of turbo coding in the WiMax PHY
layer reduces the BER and therefore improves
performance in multipath fading environments.
BER performance of Turbo Coded System WiMax
WiMax and FEC coded system in the ITU Vehicular
A channel for QPSK ¾ System.
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International Journal of Engineering Trends and Technology (IJETT) - Volume4Issue5- May 2013
Performance Improvement by Turbo Encoder for
WiMax QPSK ¾ System
[3]
[4]
[5]
[6]
[7]
[8]
[9]
However, the amplification was observed at the
expense of longer delays in the processing of the
signals resulting from the increased complexity of the
system, and can be overcome with improved turbo
encoder designs.
INTRODUCTION TO WIRELESS COMMUNICATION
AND TELEPHONE SYSTEMS(2ND EDITION) BY
LAWRENCE HARTE
http://howstuffworks.com
Operating System Concepts by Abraham Silberschatz, Peter
B. Galvin and Greg Gagne
A. Bomber, “Wireless Power Transmission: An Obscure
History, Possibly a Bright Future”.
http://www.wimax.com/.
http://www.bsnl.co.in/opencms/bsnl/BSNL/faq/faqans_wim
ax1.html.
http://www.networkworld.com/topics/wimax-lte.html.
VIII.BIOGRAPHY
VI. CONCLUSIONS
The performance of IEEE 802.16d / e, on the basis of
PHY layer is examined by the implementation of the
various important aspects in mobile environments.
The studies are also carried out with the
implementation of the optional function of turbo
coding in the PHY layer of the WiMax system. The
results obtained show that the performance of WiMax
system can be optimized at a lower BER of 10.2 at 3
dB SNR with the introduction of turbo coding in
multipath fading environments. Our paper focuses on
improving WiMAX PHY layer performance for a
mobile user with the introduction of turbo coder in
the PHY layer of the system. The turbo coded OFDM
PHY layer is found to the OFDM PHY layer FEC
based surpass the limitation of increased delay
through better memory states and system complexity
of the decoder. The improved interleaver design and
memory efficient decoding algorithms may be further
involved in order to overcome the delays.
*Shaik Avaes Mohsin was born in 1992 in
Guntur District. He is currently pursing
B.Tech from K L University. He is
interested in Telecommunication and VLSI
Email: mohsinavaes@gmail.com
**Kilaru Kalyan was born in 1992 in
Guntur District. He is currently pursing
B.Tech from K L University. He is
interested in Telecommunication and
Embedded Systems.
Email: 005kvs@gmail.com
#Suresh Angadi is presently working as a
Asst.Professor in K L University. He
received his B.Tech degree in electronics
and communication in G.V.P College of
Engineering, vizag, 2007 and completed
M.Tech in Maulana Azad National Institute
of Technology (MACT) in 2009, Bhopal.
He has published SEVEN international
journals of repute.
Email: Suresh.a@kluniversity.in
Corresponndence author:
Shaik.Avaes Mohsin
VII.REFERENCES
mohsinavaes@gmail.com
[1]
[2]
ph.no:9490604786
http://en.wikipedia.org/wiki/wimax_ technology
http://www.webopedia.com/TERM/S/wimax_technology.ht
ml
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