International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org, editorijaiem@gmail.com
Volume 2, Issue 6, June 2013
ISSN 2319 - 4847
Channel Estimation Algorithms in OFDM, A
Review
Navdeep Bansal1 Sukhjeet Singh 2 Pardeep Kumar Jindal 3
1
ECE Department, GTBKIET Chhapianwali
ECE Department, GTBKIET Chhapianwali
3
ECE Department GGSCET Talwandi Sabo
2
Abstract
Main objectives of this paper is to review the work already done related to channel estimation in OFDM (Orthogonal
Frequency Division Multiplexing) using QAM (Quadrature Amplitude multiplexing) & PSK (Phase Shift Keying) modulation
techniques used in OFDM for wireless communications. To estimate the channels three algorithms are used i.e. LS, LMMSE &
Modified MMSE. These three algorithms have basically played key role in channel estimation.
Keywords: OFDM, PSK, QAM
1. INTRODUCTION
In this paper we will review the work done by the different research fellows and professors related to Channel
Estimation by using different techniques.
Chi-Hsiao Yih1In this paper, we study the effects of channel estimation error on the bit-error-rate (BER) of orthogonal
frequency division multiplexing (OFDM) systems in frequency-selective slowly fading channels of Rayleigh fading.
Due to the additive white Gaussian noise (AWGN) and the inter-carrier interference (ICI) caused by the residual carrier
frequency offset (CFO), the channel estimation based on the training symbols is not perfect. The author characterized
the performance degradation resulting from imperfect channel state information (CSI) by deriving the BER formulas
for BPSK, QPSK, 16-QAM, and 64-QAM modulation schemes. The derived BER formulas contain no numerical
integrals and can be evaluated easily and accurately. Simulation results validate the correctness of our theoretical
analysis.The results given in this paper are:
Fig 1: Effect of channel estimation error on
the BER of BPSK modulated OFDM signals
in multipath Rayleigh fading channels.
Fig 3:Effect of channel estimation error on the
BER QAM of 16-QAMmodulated OFDM signals
in multipath channels Rayleigh fading channels
Volume 2, Issue 6, June 2013
Fig 2: Effect of channel estimation error on the
BER of QPSK modulated OFDM signals in
multipath Rayleigh fading channels.
Fig 4: Effect of Channel estimation error on
the BER of 64-modulated OFDM signals in
multipath Rayleigh fading
Page 290
International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org, editorijaiem@gmail.com
Volume 2, Issue 6, June 2013
ISSN 2319 - 4847
Fig 5: BER performance of BPSK, QPSK, 16QAM, 64- QAM modulated OFDM signals with
different numbers of training symbols.
Fig 6: BER performance of BPSK and 16QAM modulated.
OFDM signal with three different training sequences. We investigated the effects of channel estimation error on the
BER performance of OFDM systems in multipath fading channels. For BPSK, QPSK, 16-QAM, and 64- QAM
modulated OFDM signals, we derived the BER formula characterizing the performance degradation due to imperfect
channel estimation. Computer simulations were conducted to verify the accuracy of our theoretical analyses. The BER
analysis can be extended to frequency selective Rician fading channels by generalizing the Lemma 1 to the case of
nonzero mean complex-valued Gaussian random variables. From the BER expression, we learn the BER depends on
the patterns of training sequences. The design of optimal training sequence in the sense of minimizing the average
BER subject to the PAPR constraint is left for future studies
Sajjad Ahmed Ghauri, Sheraz Alam, M. Farhan Sohail, Asad Ali, Faizan Saleem7 During the last few years, the
development in digital communication are rapidly increasing to meet the ever increasing demand of high data rates.
OFDM has an edge over other frequency multiplexing techniques by using highly densely packed carriers which helps
in achieving higher data rates using similar channels. In this paper author discussed the channel estimation in OFDM
and its implementation in MATLAB using pilot based block type channel estimation techniques by using LS and
MMSE algorithms. This paper includes the comparisons of OFDM using BPSK and QPSK on different channels,
followed by designing the LS and MMSE estimators on MATLAB. In the end, the results of different simulations are
compared to conclude that LS algorithm gives less complexity but MMSE algorithm provides comparatively better
results. Results are based on simulation parameters:
Table No. 1
Parameters
Specifications
FFT Size
64
No. of Subcarriers
52
Cyclic Prefix
16
No. of OFDM symbols
100
Constellation
BPSK/QPSK
Channel Model
AQWGN, FNS,
Multipath
No. of taps/multipath
8
Fig 7: Comparison of BER for BPSK in
AWGN/FNS/Rayleigh channel
Volume 2, Issue 6, June 2013
Fig: 8 : Comparison of BER for QPSK in
AWGN/FNS/Rayleigh
Page 291
International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org, editorijaiem@gmail.com
Volume 2, Issue 6, June 2013
ISSN 2319 - 4847
Fig 9: Comparison of BER of QPSK for different
no of taps
Fig 10: BER for MMSE/LS Estimator based receiver for 3taps
Channel Estimation Parameters:
Table No.2
Parameters
No. of Subcarriers
No. of OFDM Symbols
Channel
K
γm
Constellation
Specifications
64
100
Slow fading
0……..N-1
Value of Taps
BPSK
The paper highlights the channel estimation technique based on pilot aided block type training symbols using LS and
MMSE algorithm. The Channel estimation is one of the fundamental issues of OFDM system design. The transmitted
signal under goes many effects such reflection, refraction and diffraction. Also due to the mobility, the channel
response can change rapidly over
time. At the receiver these channel effects must be canceled to recover the original signal. The BER of AWGN channel
is approximately 10-4which is better than Rayleigh fading and flat fading channel at SNR=10dB using BPSK & QPSK
on different number of taps. The MMSE is compared with LS and the MMSE performs better than the LS using 3 taps
where the performance metric is mean square and symbol error rate.
Jan-Jaap van de Beek, Ove Edfors, Magnus Sandell, Sarah Kate Wilson and Per Ola B.rjesson4 The use of
multi-amplitude signaling schemes in wireless OFDM systems requires the tracking of the fading RF
channel. This paper includes channel estimation based on time-domain channel statistics. Using a basic
m o d e l fo r a slowly fading channel, author explained the MMSE and LS estimators and a method
for modifications compromising between complexity and performance. The SER for a 16-QAM
system is
presented by means of simulation results. Depending upon estimator complexity, in the LS estimator 4
dB SNR can be gained.
Table No: 3
Estimator
MMSE
LS
Modified
MMSE
Modified LS
Volume 2, Issue 6, June 2013
Notation
MMSE
LS
MMSE-0
MMSE-5
MMSE-10
LS-0
LS-5
LS-10
Taps Used
0-63
0-63
0-4
0-9, 59-63
0-14, 54-63
0-4
0-9, 59-63
0-14, 54-63
Size Q’
64X64
NA
5X5
15X15
25X25
5X5
15X15
25X25
Page 292
International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org, editorijaiem@gmail.com
Volume 2, Issue 6, June 2013
ISSN 2319 - 4847
Fig 11: Mean Square Error for three modified
MMSE Estimators
Fig 13: Symbol Error Rate for three modified
MMSE Estimators
Fig 12: Mean Square Error for three LS Estimators
Fig 14: Symbol Error Rate for LS Estimators
Fig 15: Comparision between three modified MMSE & LS Estimator.
The Estimators in this study can be used to efficiently estimate the channel in an OFDM system given a certain
knowledge about the channel statistics. The MMSE estimators assume a priori knowledge of noise variance and
channel covariance. Moreover its complexity is large compared to LS estimators. For high SNRs the LSE estimators are
both simple and adequate. However for the
Low SNRs the presented modifications of MMSE and LS estimators will allow compromise between estimator
complexity and performance. For 16-QAM, signaling constellation, up to 4 dB gain in SNR over the LS estimator was
obtained, depending upon estimator complexity. Even relatively low complex modified estimator, however, perform
significantly better than the LS estimator for a range of SNR.
REFERENCES:
[1] Chi-Hsiao Yih, “Effects of Channel Estimation Error in the Presence of CFO on OFDM BER in FrequencySelective Rayleigh Fading Channels,” JOURNAL OF COMMUNICATIONS, VOL. 3, NO. 3, JULY 2008
[2] J. Torrance and L, Hanzo, Multicarrier Modulation for Data Transmission: An idea whose time has come IEEE
comun. Magazine, pp.5-14, May 1990.
[3] J.V. de Beek, O. Edfors, M. Sandell, S.K.Wilson and P.O Borjesson, “On Channel Estimation In OFDM”
Vehicular Technology Conference, vol. 2 pp. 815-819, Chicago, USA, September 1995
[4] Jan-Jaap van de Beek, Ove Edfors, Magnus Sandell, Sarah Kate Wilson and Per Ola B.rjesson” On Channel
Estimation In OFDM Systems”, In Proceedings of Vehicular Technology Conference (VTC Ô95), vol. 2, pp. 815819, Chicago, USA, September 1995.
[5] K. Fazel and G. Fettwis, “Performance of an Efficient Parallel Data Transmission System,” IEEE Trans. Commun.
Tech., pp. 805-813, December1967.
[6] M. Okada, S. Hara and N. Morinaga, “Bit Error Performances of Orthogonal Multicarrier modulation radio
transmission schemes.” IEICE Trans. Commun, Vol.E76-B, pp. 113-119, Fed. 1993
Volume 2, Issue 6, June 2013
Page 293
International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org, editorijaiem@gmail.com
Volume 2, Issue 6, June 2013
ISSN 2319 - 4847
[7] Sajjad Ahmed Ghauri, Sheraz Alam, M. Farhan Sohail, Asad Ali, Faizan Saleem, i m p l e m e n t a t i o n o f
O F D M a n d c h a n n e l e s t i m a t i o n u s i n g L S a n d M M S E E s t i m a t o r s . International Journal of
Computer and Electronics Research [Volume 2, Issue 1, February 2013].
[8] Sinem Coleri, Mustafa Ergen, AnujPuri, and Ahmad Bahai, “Channel Estimation Techniques Based on Pilot
Arrangement in OFDM Systems,” IEEE transactions on Broadcasting, Vol. 48, No. 3, September 2002.
[9] Sinem Coleri, Mustafa Ergen, Anuj Puri, and Ahmad Bahai “Channel Estimation Techniques Based on
PilotArrangement in OFDM Systems” IEEE TRANSACTIONS ON BROADCASTING, VOL. 48, NO. 3,
SEPTEMBER 2002.
[10] Yuping Zhao, Aiping Huang, “A novel channel estimation method for OFDM mobile communication systems
based on pilot signals and transform-domain processing ,” IEEE VTC , Vol. 3, May 1997
AUTHOR
Navdeep Bansal received B.Tech Degree in Electronics & Communication from Adesh Institute
of Engineering & Technology, Faridkot in 2007.He is pursuing M.Tech Degree from Guru Teg
Bhadur Khalsa Institute of Engineering & Technology (Regional Center) in under Punjab
Technical University, Jalandhar.I am on my thesis work.
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