International Journal of Engineering Trends and Technology- Volume4Issue4- 2013
Analysis of Different Error Detection Schemes
over OFDM Signal
Ajay Siwach
Sunil Malhotra
Student, M.Tech (ECE)
Department of ECE
Lovely Professional University,
Phagwara, Punjab, India.
Student, M.Tech (ECE)
Department of ECE
Lovely Professional University,
Phagwara, Punjab, India.
Abstract—
A High speed communication is the basic
requirement for any network. But such kind of networks
always suffers from the problem noise and the internal
interference. These problems can destroy or alter the
communication data. The data reliability is the main
concentration in such communication network. To get the
integrity and reliability in such high speed network number of
error detection and correction approaches are present. The
effect of these approaches also change according to the
capacity and the SNR ratio. This paper is about the analysis of
different error correction schemes over the high speed OFDM
networks so that the error rate can be reduced. In this work, a
efficient scheme is suggested to reduce the error rate over the
OFDM signal while transferring the video data.
Ravi Shankar
Asstt. Professor, ECE
Department of ECE
Lovely Professional University,
Phagwara, Punjab, India.
spectrum resulting in performance egradation. If no
measure is taken to reduce the high PAPR, MIMO-OFDM
system could face serious restriction for practical
applications.
Keywords-OFDM, Error Detection, Video Transmission, SNR
I.
INTRODUCTION
Orthogonal frequency division multiplexing (OFDM) is a
multicarrier modulation MCM) technique which seems to be
an attractive candidate for fourth generation (4G) wireless
communication systems. OFDM offer high spectral
efficiency, immune to the multipath elay, low inter-symbol
interference (ISI), immunity to frequency selective fading
and high power efficiency. Due to these merits OFDM is
chosen as high data rate communication systems such as
Digital Video Broadcasting (DVB) and based mobile
worldwide interoperability for microwave access (mobile
Wi-MAX). However OFDM system suffers from serious
problem of high PAPR. In OFDM system output is
superposition of multiple sub-carriers. In this case some
instantaneous power output might increase greatly and
become far higher than the mean power of system. To
transmit signals with such high PAPR, it requires power
amplifiers with very high power scope. These kinds of
amplifiers are very expensive and have low efficiency-cost.
If the peak power is too high, it could be out of the scope of
the linear power amplifier. This gives rise to non-linear
distortion which changes the superposition of the signal
Figure 1:Block Diagram of OFDM System
Here, Figure 1 is showing the basic model of OFDM
system. OFDM has been chosen for several current and
future communications systems all over the world. It is
well-suited for systems in which the channel characteristics
make it difficult to maintain adequate communications link
performance. Asynchronous digital subscriber line (ADSL)
provides a method of delivering high speed data over the
phone line. The system uses OFDM techniques, calling their
variation discrete multi-tone (DMT). European digital
television is based on the DVB-T (digital video broadcast terrestrial) standard that uses either 2048 (2K) or 8192 (8K)
subcarriers within a standard 8 MHz TV channel. The
system specifications and coding were specifically designed
to allow multipoint repeater signaling that creates cochannel
signals.
The next generation of radio broadcast may also
make use of OFDM techniques. In the U.S., the system
under consideration will initially “co-exist” in the same
frequency slot as the current analog broadcast. OFDM
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International Journal of Engineering Trends and Technology- Volume4Issue4- 2013
allows the system designers to shape the digital spectrum by
disabling the subcarriers that correspond to the current
analog spectrum during the co-existence period. After the
co-existence period the subcarriers can be enabled and the
subsequent data rate increased. Various high-speed wireless
networking standards in the 5 GHz frequency region employ
OFDM modulation. The U.S. IEEE 802.11a and European
ETSI Hiperlan/2 standards utilize similar physical layer
structures with 64-carrier OFDM and modulation ranging
from BPSK to 64-QAM per subcarrier. Various data rates
from 6 to 54 Mbps are possible. OFDM works well in home
and office environments for handling wall reflections and
movement within the structure.
II.
LITERATURE SURVEY
A work is presented by the author on Optimized channel
codign for digital transmission over the channel. In this
proposed approach, the author defined anew class of non
linear block codes, which are designed for the parametric
source encoding for audio and videos. The new code is not
optimized for the minimizing the bit error rate but it
maximize the signal to noise ratio. The decoding process is
based on the bit error correction and parametric
estimation[1]. The another work Is done in same area by
using the combination of source coding with decoder side
information and channel. In this work Author show an
alternative scheme for the quadratic-Gaussian case, which
merges source and channel coding. This scheme achieves
the optimal performance by a applying
modulo-lattice modulation to the analog source[2]. Guy
Keshet also focus on the concept of source encoding from
the receiver side. The author defined the casual and non
casual side information and associated capacity formula.
The main stress of author is about the channel capacity and
the encoding schemes for the communication system[3].
The another work is done by Juyul Lee for the linear
precoding and broadcasting by using the concepts of zero
forcing and block diagnolization transmission. It defines the
spatial transmission by using the concept of multiplexing
gain. The defined work gives the better SNR ratio and
weighted sum rate maximization. Weighted sum rate
maximization is also considered in this work to improve the
throughput over the channel[5]. Amir Bennatan has shows a
simple and novel approach for the binary and Gaussian
channel. The author defined the superposition coding for
achieving the better capacity with random component codes
and the maximum likelihood decoding. The author also
gives the practical implementation of work along with
results. The proposed framework is simple and effective
under defined constraints[6].
Daniel J. Costello proposed a work to improve the channel
capacity with the implementation of hamming codes. The
author focus on the performance and the complexity
measures. The author defined an algebraic block codes to
implement the presented approach[7]. The variable length
coding is suggested by Stark C. Draper to perform the erfect
noiseless feedback to improve the communication
reliability. The author defined a robust approach for
feedback link over the discrete memory less channel. The
reliability is achieved using positive capacity feedback
channel[8]. Daniel Costello defined a work on Error
Control Coding. This wok includes the encoding scheme for
satellite communication, data transmission, file transmission
etc. It also defines some historical and current
communicatin channel over which the communication can
be performed efficiently and accurately[9]. Nihar Jindal
defined a work to peform the channel encoding over the
broadcast channels like TDMA and MIMO. The author
define the sum rate capacity approach for the multiple
antenna for the broadcast channel. The author also defined
the bounds of the presented work[10]. Same author
presented another approach for the capacity analysis and
encoding process for the multiuser channel. It includes the
broadcast over the multiple channels. In his work the author
defined the duality between the communication channel.
This duality result is applicable to additive Gaussian noise
and fading channels for several different notions of fading
channel capacity, including ergodic capacity, outage
capacity, and minimum rate capacity[11].
Yingda Chen performed a work,” Wireless Diversity
through Network Coding”. This paper investigates the
diversity gain offered by implementing network coding over
wireless communication links. The network coding
algorithm is applied to both a wireless network containing a
distributed antenna system (DAS) as well as one that
supports user cooperation between users. The results show
that DAS with network coding leads to better diversity
performance, at a lower hardware cost and higher spectral
efficiency. In the case of user cooperation, network coding
yields additional diversity, especially when there are
multiple network users[12]. Zukang Shen performed a
work,” Sum Capacity of Multiuser MIMO Broadcast
Channels with Block Diagonalization”. The sum capacity of
a Gaussian broadcast MIMO channel can be achieved with
Dirty Paper Coding (DPC). Deploying DPC in real-time
systems is, however, impractical. Block Diagonalization
(BD) is an alternative precoding technique for downlink
multiuser MIMO systems, which can eliminate interuser
interference at each receiver, at the expense of suboptimal
sum capacity vs. DPC. In this paper, Author study the sum
capacity loss of BD for a fixed channel. Author show that 1)
if the user channels are orthogonal to each other, then BD
achieves the complete sum capacity; and 2) if the user
channels lie in a common row vector space, then the gain of
DPC over BD can be bounded by the minimum of the
number of transmit and receive antennas and the number of
users. Author also compare the ergodic sum capacity of
DPC with that of BD in a Rayleigh fading channel.
Simulations show that BD can achieve a significant part of
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International Journal of Engineering Trends and Technology- Volume4Issue4- 2013
the total throughput of DPC. An upper bound on the ergodic
sum capacity gain of DPC over BD is derived, which can be
evaluated with a few numerical integrations. With this
bound, Author can easily estimate how far away BD is from
being optimal in terms of ergodic sum capacity, which is
useful in directing practical system designs[13]. Mahesh R
Patel performed a work,” New Channel Coding Technique
to Achieve The Ultimate Shannon Limit”. After Shannon’ s
1948 channel coding theorem, many contributions have led
to significant improvements in performance versus
complexity for practical applications, particularly on the
additive white Gaussian noise channel (AWGN). This paper
exhibits the new channel coding technique and its
simulation results, which can achieve near ultimate Shannon
limit error correction performance with moderate decoding
complexity[14].
III
ERROR DETECTION SCHEMES
Several schemes exist to achieve error detection. The
general idea is to add some redundancy, i.e., some extra
data, to a message, that enables detection of any errors in the
delivered message. Most such error-detection schemes are
systematic: the transmitter sends the original data bits, and
attaches a fixed number of check bits, which are derived
from the data bits by some deterministic algorithm. The
receiver applies the same algorithm to the received data bits
and compares its output to the received check bits; if the
values do not match, an error has occurred at some point
during the transmission. In a system that uses a "nonsystematic" code, such as some raptor codes, the original
message is transformed into an encoded message that has at
least as many bits as the original message.
In general, any hash function may be used to compute the
redundancy. However, some functions are of particularly
widespread use, due to their simplicity, or their suitability of
detecting certain kinds of errors, such as the cyclic
redundancy check's performance in detecting burst errors.
Other mechanisms of adding redundancy are repetition
schemes and error-correcting codes. Repetition schemes are
rather inefficient but very simple to implement. Errorcorrecting codes can provide strict guarantees on the
number of errors that can be detected.
A)
Repetition schemes
Variations on this scheme exist. Given a stream of data that
is to be sent, the data is broken up into blocks of bits, and in
sending, each block is sent some predetermined number of
times. For example, if we want to send "1011", we may
repeat this block three times each.
Suppose we send "1011 1011 1011", and this is received as
"1010 1011 1011". As one group is not the same as the other
two, we can determine that an error has occurred. This
scheme is not very efficient, and can be susceptible to
problems if the error occurs in exactly the same place for
each group (e.g. "1010 1010 1010" in the example above
will be detected as correct in this scheme). The scheme
however is extremely simple, and is in fact used in some
transmissions of numbers stations
B)
Parity schemes
A simple parity bit is an error detection mechanism that can
only detect an odd number of errors. The stream of data is
broken up into blocks of bits, and the number of 1 bits is
counted. Then, a "parity bit" is set (or cleared) if the number
of one bits is odd (or even). (This scheme is called even
parity; odd parity can also be used.) If the tested blocks
overlap, then the parity bits can be used to isolate the error,
and even correct it if the error affects a single bit: this is the
principle behind the Hamming code.
There is a limitation to parity schemes. A parity bit is only
guaranteed to detect an odd number of bit errors (one, three,
five, and so on). If an even number of bits (two, four, six
and so on) are flipped, the parity bit appears to be correct,
even though the data is corrupt.
Extension and variations on the parity bit mechanism are
horizontal redundancy checks, vertical redundancy checks
and "double", "dual" or "diagonal" parity (used in RAIDDP).
C)
Checksums
A checksum of a message is a modular arithmetic sum of
message code words of a fixed word length (e.g., byte
values). The sum is often negated by means of a one'scomplement prior to transmission as the redundancy
information in order to detect errors resulting in all-zero
messages.
Checksum schemes include parity bits, check digits, and
longitudinal redundancy check. Some checksum schemes,
such as the Luhn algorithm and the Verhoeff algorithm, are
specifically designed to detect errors commonly introduced
by humans in writing down or remembering identification
numbers.
D)
Cyclic redundancy checks
The cyclic redundancy check (CRC) considers a block of
data as the coefficients to a polynomial over a finite field,
and then divides by a fixed, predetermined polynomial. The
remainder of the division serves as the redundancy for the
message. CRCs have favorable properties in that they are
specifically suited for detecting burst errors. They are easily
implemented in hardware, and are widely used in various
protocols.
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IV
CONCLUSION
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In this presented work, we have defined an effective
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ACKNOWLEDGMENT
I wish to convey warmest thanks to my supervisor Mr. Ravi
Shankar for his support and encouragement. I also thank Mr
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