International Journal of Engineering Trends and Technology (IJETT) - Volume4Issue4- April 2013
Diversity combining techniques using LPDC
coding in OFDM
Karamjeet Singh, Komal Arora
Department of Electronics Engineering
Lovely Professional University, Punjab
Department of Electronics Engineering
Lovely Professional University, Punjab
Abstract-For The Enhancement of BER In Communication
System We Use The Different Type of Channel coding.
LDPC(low density parity check) are the codes Which are
used in channel coding for the different enhancement in
the system performance. We are trying LDPC channel
coding with BPSK modulation scheme with MRC and
EGC at the receiver over Rayleigh fading channel. BER
Performance of System is analyzed with And without
LDPC channel coding.
Keywords- OFDM MIMO, Low density parity check,
Maximal ratio combining, Equal gain combining.
I. INTRODUCTION
Orthogonal
frequency-division multiplexing (OFDM) is
a method of encoding digital data on multiple carrier
frequencies. OFDM has developed into a popular scheme
for wideband digital communication, whether wireless or
over copper wires, used in applications such as digital
television and audio broadcasting, DSL broadband internet
access, wireless networks, and 4G mobile communications.[1]
In radio Communication, multiple-input and multiple-output,
or MIMO (commonly pronounced my-moh or me-moh), is the
use of multiple antennas at both the transmitter and receiver to
improve communication performance. Diversity is a powerful
communication receiver technique that provides wireless link
improvement at a relatively low cost. Diversity techniques are
used in wireless communications systems to primarily to
improve performance over a fading radio channel. Lowdensity parity check (LDPC) codes [1], are equipped with
very fats encoding and decoding algorithm which makes
them very useful for practical applications. The main
attraction of LDPC codes is that they approach the
Shannon limit of channel. There have been simulations that
perform within 0.04dB of the Shannon limit. The LDPC
codes are characterized by a sparse parity check matrix in
which the number of 1‟s is very less as compared to the
number of 0‟s [2]. LDPC codes have been proved to achieve
capacity on binary erasure channels (BEC). Unlike turbo
codes, they can be optimized for good bit-error rate
performance over a given channel and for a given code-rate
ISSN: 2231-5381
[3]. maximal-ratio combining (MRC) is a method of diversity
combining in which the signals from each channel are added
together. The gain of each channel is made proportional to the
rms signal level and inversely proportional to the mean
square noise level in that channel equal-gain combining
(EGC), which co-phases the signals on each branch and then
combines them with equal weighting. Performance of EGC
is quite close to that of MRC, typically exhibiting less
than 1 dB of power penalty.
II. LDPC RESEARCH
Satoshi Gounai et al. [4] find result that the SNR thresholds
of a regular LDPC codes and the irregular LDPC codes and
optimum degree distributions of the irregular LDPC codes
for SIMO systems with several diversity orders. Eric Villier
[5] drived the performance of optimum combining in the
presence of multiple equal power interferers and noise when
there is less no. of the interferers than the number of antenna
elements. We have Desired signal and interferers which use
flat Rayleigh fading and t h er e a r e propagation channels
which are independent. the probability density function
(PDF) of the output signal-to-interference-plus-noise ratio
(SINR), cumulative distribution function (CDF) of the SINR
and the bit-error rate (BER) of some binary modulations has
been derived using the rayleigh fading.
Kwok Hung Li et al.[6] drived that the Low-density paritycheck (LDPC) codes wh e n combined with Selection ratio
combining and Maximal ratio Combining gives better biterror rate (BER) performance then multipath fading
channels. We used the GA approach with the LDPC over the
i.i.d Nakagami-fading channels to find the BER.
Mackey et al. [7] proposed that the most powerful error
correcting codes LDPC is based on very sparse matrices that
gievs better results then the turbo codes. These resluts using
LDPC codes gives results close to Shannon capacity for
binary- symmetric channel and symmetric stationary ergodic
noise.
S. Sharma et al. [8] deined that LDPC codes have much
better gives much better performance in some cases than
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International Journal of Engineering Trends and Technology (IJETT) - Volume4Issue4- April 2013
turbo codes. These are easy to implement with iterative
decoding algorithm.. it is shown that LDPC codes with
optimum combining (LDPC-OC) system improves SINR
by 1.98 dB and 2.62 dB with 3 and 4 receive antennas
respectively in multipath fading channel in the presence of a
single interferer.
2003.
Vishwanatha R. Gowda et al. [9] calculated the Error
performance of selection diversity (SD) receiver with nonidentical fading channels, in which the fading statistics of
each branches are different. Bit-error rate (BER) results
are calculated from the cumulative distribution function
(CDF), which reduces the complexity and give simple BER
expressions..
[5] Eric Villier, “Performance Analysis of Optimum
Combining with Multiple Interferers in Flat Rayleigh
Fading”, IEEE Communication Letters, vol. 47, No. 10,
pp.1503-1510, 1999.
III. PROPOSED WORK
LDPC channel coding is used for the better results of BER
and SNR of the system. In this we have joined LDPC coding
with the BPSK modulation for the MRC diversity to improve
the BER of Rayleigh fading channel. We have calculated that
BER of OFDM is decreasing using LDPC coding techniques.
IV.CONCLUSION
Diversity Such as Maximal Ratio Combining and Equal Gain
Combining is important for the OFDM system performance in
wireless communication system. It reduces the effect of fading
and give better BER.
From the comparing study we have concluded that BER of
OFDM is decreasing using LDPC codes and Diversity
combining techniques over the faded channel .
[4] Satoshi Gounai and Tomoaki Ohtsuki, “Performance
Analysis of LDPC Code with Spatial Diversity,” IEEE
international conference on Vehicular Technology, pp 1-5,
2005.
[6] Kwok Hung Li , Kwok Hung Li and Kah Chan The,
“Performance Analysis of LDPC Codes with MaximumRatioCombining Cascaded
with
Selection Combining
overNakagami-Fading”,IEEETransactionsOnWireless
Communications, vol. PP, no. 99, pp.1-9, 2011.
[7] David J. C. MacKay, “Good Error-Correcting Codes
Based on Very Sparse Matrices”, IEEE Transactions of
information theory, vol. 45, no. 2, pp. 399-431,1999.
[8] Surbhi Sharma and Rakesh khanna “Analysis of
LDPC with optimum combining”, International Journal of
Electronics, vol.96, no.8, pp.803-811, 2009.
[9] Vishwanatha R. Gowda, Kwok H. Li and Kah C. The,
“Performance Study of Selection Diversity Systems with
Non-identical Fading Branches”, International Symposium
on Information Theory and its Applications, ISITA, pp. 1-5,
2008.
V. FUTURE WORK
By using the channel LDPC coding with diversity
combining
technique such as MRC/SC,
the
BER
performance of system is improved. This system is
implemented over the independent and identically distributed
Rayleigh channel fading. It can be further implement on the
correlated Rayleigh fading channel.
In this thesis, we have not used any t y p e o f
interference. W e u s e Only noise. So we can extend this
work over the interferers which may give equal power or
not.
REFERENCES
[1]
Theodore
S.Rappaport,
“Wireless
Communication:
nd
Principles and Practice”, 2 Edition, Prentice-Hall, India.
[2] David Tse and Pramod Viswanath, Fundamentals of
Wireless Communication, Cambridge University Press, 2005.
[3] Li Tang and Zhu Hongbo, “Analysis and Simulation of
Nakagami Fading Channel with MATLAB”, Asia-Pacific
Conference on Environmental Electromagnetic, pp. 490-494,
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