This paper presents a comparative performance analysis of wireless orthogonal frequency division multiplexing (OFDM) system with the implementation of comb type pilot-based channel estimation algorithm over frequency selective multi-path fading channels. The Minimum Mean Square Error (MMSE) method is used for the estimation of channel at pilot frequencies. For the estimation of channel at data frequencies different interpolation techniques such as low-pass, linear, and second order interpolation are employed. The OFDM system simulation has been carried out with Matlab and the performance is analyzed in terms of bit error rate (BER) for various signal mapping (BPSK, QPSK, 4QAM, 16QAM, and 64QAM) and channel (Rayleigh and Rician) conditions. The impact of selecting number of channel taps on the BER performance is also investigated.
Classical Discrete-Time Fourier TransformBased Channel Estimation for MIMO-OF...IJCSEA Journal
In this document, we look at various time domain channel estimation methods with this constraint of null carriers at spectrumborders.We showin detail howto gauge the importance of the “border effect” depending on the number of null carriers, which may vary from one system to another. Thereby we assess the limit of the technique discussed when the number of null carriers is large. Finally the DFT with the truncated singular value decomposition (SVD) technique is proposed to completely eliminate the impact of the null subcarriers whatever their number. A technique for the determination of the truncation threshold for any MIMO-OFDM system is also proposed.
In this paper, we analyzed a numerical evaluation of the performance of MIMO radio systems in the LTE network environment. Downlink physical layer of the OFDM-MIMO based radio interface is considered for system model and a theoretical analysis of the bit error rate of the two space-time codes (SFBC 2×1 and FSTD 4×2 codes are adopted by the LTE norm as a function of the signal to noise ratio. Analytical expressions are given for transmission over a Rayleigh channel without spatial correlation which is then compared with Monte-Carlo simulations. Further evaluated channel capacity and simulation results show throughput almost reaches to the capacity limit.
Modified Whitening Rotation based Joint Semi-blind Channel and Data Estimatio...IDES Editor
In this paper, we propose a novel joint semi-blind
channel and data estimation technique based on Whitening
Rotation (WR) method for Rayleigh flat fading Multiple Input
Multiple output (MIMO) channel using different receiver
antennas combinations. Here we divide newly proposed
technique in three steps. In the first step, we use conventional
Whitening Rotation based semi-blind channel estimation
technique, where MIMO channel matrix H can be decomposed
as H=WQ H . Whitening matrix W can be estimated blindly
using second order statistical information of received data
and unitary rotation matrix Q can be estimated exclusively
using Orthogonal Pilot Maximum Likelihood (OPML)
algorithm. In the second step, data symbols can be estimated
using estimated channel H and received output data by
applying maximum likelihood data estimation method.
Finally in the third step, Q can be re-estimated as a Q new
using OPML algorithm by considering estimated blind data
symbols itself as a pilot symbols for more statistical
information of unitary matrix and perform final channel
estimation H final=W Q new H . Simulation results are presented
under 4-PSK data modulation scheme for two transmitters
and different combinations of receiver antennas to support
proposed novel technique and they demonstrate improved BER
performance compared to conventional WR based optimal
technique and Rotation Optimization Maximum Likelihood
(ROML) based suboptimal semi-blind channel estimation
technique.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
Classical Discrete-Time Fourier TransformBased Channel Estimation for MIMO-OF...IJCSEA Journal
In this document, we look at various time domain channel estimation methods with this constraint of null carriers at spectrumborders.We showin detail howto gauge the importance of the “border effect” depending on the number of null carriers, which may vary from one system to another. Thereby we assess the limit of the technique discussed when the number of null carriers is large. Finally the DFT with the truncated singular value decomposition (SVD) technique is proposed to completely eliminate the impact of the null subcarriers whatever their number. A technique for the determination of the truncation threshold for any MIMO-OFDM system is also proposed.
In this paper, we analyzed a numerical evaluation of the performance of MIMO radio systems in the LTE network environment. Downlink physical layer of the OFDM-MIMO based radio interface is considered for system model and a theoretical analysis of the bit error rate of the two space-time codes (SFBC 2×1 and FSTD 4×2 codes are adopted by the LTE norm as a function of the signal to noise ratio. Analytical expressions are given for transmission over a Rayleigh channel without spatial correlation which is then compared with Monte-Carlo simulations. Further evaluated channel capacity and simulation results show throughput almost reaches to the capacity limit.
Modified Whitening Rotation based Joint Semi-blind Channel and Data Estimatio...IDES Editor
In this paper, we propose a novel joint semi-blind
channel and data estimation technique based on Whitening
Rotation (WR) method for Rayleigh flat fading Multiple Input
Multiple output (MIMO) channel using different receiver
antennas combinations. Here we divide newly proposed
technique in three steps. In the first step, we use conventional
Whitening Rotation based semi-blind channel estimation
technique, where MIMO channel matrix H can be decomposed
as H=WQ H . Whitening matrix W can be estimated blindly
using second order statistical information of received data
and unitary rotation matrix Q can be estimated exclusively
using Orthogonal Pilot Maximum Likelihood (OPML)
algorithm. In the second step, data symbols can be estimated
using estimated channel H and received output data by
applying maximum likelihood data estimation method.
Finally in the third step, Q can be re-estimated as a Q new
using OPML algorithm by considering estimated blind data
symbols itself as a pilot symbols for more statistical
information of unitary matrix and perform final channel
estimation H final=W Q new H . Simulation results are presented
under 4-PSK data modulation scheme for two transmitters
and different combinations of receiver antennas to support
proposed novel technique and they demonstrate improved BER
performance compared to conventional WR based optimal
technique and Rotation Optimization Maximum Likelihood
(ROML) based suboptimal semi-blind channel estimation
technique.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
MIMO Channel Estimation Using the LS and MMSE AlgorithmIOSRJECE
Wireless Communication Technology has developed over the past few yearsfor other objectives.The Multiple InputMultiple Output (MIMO) is one of techniques that is used to enhancethe data rates, in which multiple antennas are employed both the transmitter and receiver. Multiple signals are transmitted from different antennas at the transmitter using the same frequency and separated space. Various channel estimation techniques are employed in order to judge the physical effects of the medium present. In this paper, we analyze and implementvarious estimation techniques for MIMO Systems such as Least Squares (LS), Minimum Mean Square Error (MMSE),these techniques are therefore compared to effectively estimate the channel in MIMO System. The results demonstrate that SNR required to support different values of bit error rate varies depending on different low correlation between the transmitting and the receiving antennas .In addition, it is illustrated that when the number of transmitter and receiver antennas increases, the performance of TBCE schemes significantly improves. The Same behavior isalso observed for MIMO system. Performance of both MMSE and LSestimation are the same for allkinds of modulation at small value of SNR but the more we increase the SNR value the more performance gap goes on increasing.
Performance evaluation of high mobility OFDM channel estimation techniques IJECEIAES
In wireless communication, Orthogonal Frequency Division Multiplexing (OFDM) has been adopted due to its robustness to multipath fading and high data rate transmissions. At the other hand, the performance of OFDM systems severely degraded due to multi-path fading and Doppler frequency shifts in mobile systems, which causes inter-carrier-interference (ICI). Thus, Estimation of channel parameters is required at the receiver using a pre designed estimator where pilot tones are inserted in each OFDM symbol. In this paper, a random pilot data are generated and inserted in each OFDM symbol at equally spaced locations. The performance test of Least Square (LS) and Linear Minimum Mean Square (LMMSE) estimation methods are proposed with Discrete Fourier Transform (DFT) based on both LS and LMMSE, where different ITU channel models are considered in order to compare their performance for data transmission in high mobile systems with different Doppler frequencies exceeds 200 Hz and minimal number of pilots.
This paper aims, a 3D-Pilot Aided Multi-Input Multi-Output Orthogonal Frequency Division Multiplexing (MIMO-OFDM) Channel Estimation (CE) for Digital Video Broadcasting -T2 (DVB-T2) for the 5 different proposed block and comb pilot patterns model and performed on different antenna configuration. The effects of multi-transceiver antenna on channel estimation are addressed with different pilot position in frequency, time and the vertical direction of spatial domain framing. This paper first focus on designing of 5-different proposed spatial correlated pilot pattern model with optimization of pilot overhead. Then it demonstrates the performance comparison of Least Square (LS) & Linear Minimum Mean Square Error (LMMSE), two linear channel estimators for 3D-Pilot Aided patterns on different antenna configurations in terms of Bit Error Rate. The simulation results are shown for Rayleigh fading noise channel environments. Also, 3x4 MIMO configuration is recommended as the most suitable configuration in this noise channel environments.
ESTIMATION OF CHANNEL IN OFDM WIRELESS CHANNEL USING LS AND MMSE TECHNIQUESIAEME Publication
In recent years with the increase in digital data communication, the need for high data rates with less information loss or distortion is being a continuous research area and new techniques are being invented in this area. Large amount of people are using the air interface for proper communication which also have a lot of drawbacks which include multipath fading, Inter symbol interference (ISI), Doppler shift etc..This paper is being presented on basis of channel estimation of wireless mobile OFDM channels using known pilot symbols.
General analytical framework for cooperative sensing and access trade-off opt...Polytechnique Montreal
In this paper, we investigate the joint cooperative spectrum sensing and access design problem for multi-channel cognitive radio networks. A general heterogeneous setting is considered where the probabilities that different channels are available, SNRs of the signals received at secondary users (SUs) due to transmissions from primary users (PUs) for different users and channels can be different. We assume a cooperative sensing strategy with a general a-out-of-b aggregation rule and design a synchronized MAC protocol so that SUs can exploit available channels. We analyze the sensing performance and the throughput achieved by the joint sensing and access design. Based on this analysis, we develop algorithms to find optimal parameters for the sensing and access protocols and to determine channel assignment for SUs to maximize the system throughput. Finally, numerical results are presented to verify the effectiveness of our design and demonstrate the relative performance of our proposed algorithms and the optimal ones.
International Journal of Engineering and Science Invention (IJESI)inventionjournals
International Journal of Engineering and Science Invention (IJESI) is an international journal intended for professionals and researchers in all fields of computer science and electronics. IJESI publishes research articles and reviews within the whole field Engineering Science and Technology, new teaching methods, assessment, validation and the impact of new technologies and it will continue to provide information on the latest trends and developments in this ever-expanding subject. The publications of papers are selected through double peer reviewed to ensure originality, relevance, and readability. The articles published in our journal can be accessed online.
IMPROVEMENT OF LTE DOWNLINK SYSTEM PERFORMANCES USING THE LAGRANGE POLYNOMIAL...IJCNCJournal
To achieve a high speed data rate, higher spectral efficiency, improved services and low latency the 3rd
generation partnership project designed LTE standard (Long Term Evolution).the LTE system employs
specific technical as well the technical HARQ, MIMO transmission, OFDM Access or estimation technical.
In this paper we focus our study on downlink LTE channel estimation and specially the interpolation which
is the basis of the estimation of the channel coefficients. Thus, we propose an adaptive method for polynomial interpolation based on Lagrange polynomial. We perform the Downlink LTE system MIMO transmission then compare the obtained results with linear, Sinus Cardinal and polynomial Newton Interpolations. The simulation results show that the Lagrange method outperforms system performance in term of Block Error Rate (BLER) , throughput and EVN(%)vs. Signal to Noise Ratio (SNR).
A Subspace Method for Blind Channel Estimation in CP-free OFDM SystemsCSCJournals
In this paper, a subspace method is proposed for blind channel estimation in orthogonal frequency-division multiplexing (OFDM) systems over time-dispersive channel. The proposed method does not require a cyclic prefix (CP) and thus leading to higher spectral efficiency. By exploiting the block Toeplitz structure of the channel matrix, the proposed blind estimation method performs satisfactorily with very few received OFDM blocks. Numerical simulations demonstrate the superior performance of the proposed algorithm over methods reported earlier in the literature.
Performance of Multiple symbol representation with clipping scheme for PAPR r...ijsrd.com
OFDM is one of the multicarrier modulation technique used in various communication systems. The major problem one faces while implementing this system is the high peak to average power .For an efficient OFDM system this PAPR should be low. In this paper a hybrid PAPR (peak to average power ratio) reduction technique for the OFDM (orthogonal frequency division multiplexing) signal which combines a multiple symbol representations method with a signal clipping method is proposed. In multiple symbol representations alternative signaling points are used to represent one symbol and PAPR is further reduced with the clipping scheme. The performance of the hybrid scheme is compared with the partial transmit sequence which is one of the other PAPR reduction scheme. In partial transmit sequence the input data is divided in to disjoint blocks transformed in to time domain sequence and rotated by phase factors. Theoretical analysis and simulation results validate that the proposed scheme has the ability to provide large PAPR reduction, low bit error rate. Performance analysis is also done with the partial transmit sequence scheme.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
Design and Optimal Configuration of Full-Duplex MAC Protocol for Cognitive Ra...Polytechnique Montreal
In this paper, we propose an adaptive medium access control (MAC) protocol for
full-duplex (FD) cognitive radio networks in which FD secondary users (SUs) perform channel contention
followed by concurrent spectrum sensing and transmission, and transmission only with maximum power
in two different stages (called the FD sensing and transmission stages, respectively) in each contention
and access cycle. The proposed FD cognitive MAC (FDC-MAC) protocol does not require synchronization
among SUs, and it efciently utilizes the spectrum and mitigates the self-interference in the FD transceiver.
We develop a mathematical model to analyze the throughput performance of the FDC-MAC protocol, where
both half-duplex (HD) transmission and FD transmission modes are considered in the transmission stage.
Then, we study the FDC-MAC conguration optimization through adaptively controlling the spectrum
sensing duration and transmit power level in the FD sensing stage.We prove that there exists optimal sensing
time and transmit power to achieve the maximum throughput, and we develop an algorithm to congure
the proposed FDC-MAC protocol. Extensive numerical results are presented to illustrate the optimal
FDC-MAC conguration and the impacts of protocol parameters and the self-interference cancellation
quality on the throughput performance. Moreover, we demonstrate the signicant throughput gains of the
FDC-MAC protocol with respect to the existing HD MAC and single-stage FD MAC protocols
International Journal of Modern Engineering Research (IJMER) is Peer reviewed, online Journal. It serves as an international archival forum of scholarly research related to engineering and science education.
MIMO Channel Estimation Using the LS and MMSE AlgorithmIOSRJECE
Wireless Communication Technology has developed over the past few yearsfor other objectives.The Multiple InputMultiple Output (MIMO) is one of techniques that is used to enhancethe data rates, in which multiple antennas are employed both the transmitter and receiver. Multiple signals are transmitted from different antennas at the transmitter using the same frequency and separated space. Various channel estimation techniques are employed in order to judge the physical effects of the medium present. In this paper, we analyze and implementvarious estimation techniques for MIMO Systems such as Least Squares (LS), Minimum Mean Square Error (MMSE),these techniques are therefore compared to effectively estimate the channel in MIMO System. The results demonstrate that SNR required to support different values of bit error rate varies depending on different low correlation between the transmitting and the receiving antennas .In addition, it is illustrated that when the number of transmitter and receiver antennas increases, the performance of TBCE schemes significantly improves. The Same behavior isalso observed for MIMO system. Performance of both MMSE and LSestimation are the same for allkinds of modulation at small value of SNR but the more we increase the SNR value the more performance gap goes on increasing.
Performance evaluation of high mobility OFDM channel estimation techniques IJECEIAES
In wireless communication, Orthogonal Frequency Division Multiplexing (OFDM) has been adopted due to its robustness to multipath fading and high data rate transmissions. At the other hand, the performance of OFDM systems severely degraded due to multi-path fading and Doppler frequency shifts in mobile systems, which causes inter-carrier-interference (ICI). Thus, Estimation of channel parameters is required at the receiver using a pre designed estimator where pilot tones are inserted in each OFDM symbol. In this paper, a random pilot data are generated and inserted in each OFDM symbol at equally spaced locations. The performance test of Least Square (LS) and Linear Minimum Mean Square (LMMSE) estimation methods are proposed with Discrete Fourier Transform (DFT) based on both LS and LMMSE, where different ITU channel models are considered in order to compare their performance for data transmission in high mobile systems with different Doppler frequencies exceeds 200 Hz and minimal number of pilots.
This paper aims, a 3D-Pilot Aided Multi-Input Multi-Output Orthogonal Frequency Division Multiplexing (MIMO-OFDM) Channel Estimation (CE) for Digital Video Broadcasting -T2 (DVB-T2) for the 5 different proposed block and comb pilot patterns model and performed on different antenna configuration. The effects of multi-transceiver antenna on channel estimation are addressed with different pilot position in frequency, time and the vertical direction of spatial domain framing. This paper first focus on designing of 5-different proposed spatial correlated pilot pattern model with optimization of pilot overhead. Then it demonstrates the performance comparison of Least Square (LS) & Linear Minimum Mean Square Error (LMMSE), two linear channel estimators for 3D-Pilot Aided patterns on different antenna configurations in terms of Bit Error Rate. The simulation results are shown for Rayleigh fading noise channel environments. Also, 3x4 MIMO configuration is recommended as the most suitable configuration in this noise channel environments.
ESTIMATION OF CHANNEL IN OFDM WIRELESS CHANNEL USING LS AND MMSE TECHNIQUESIAEME Publication
In recent years with the increase in digital data communication, the need for high data rates with less information loss or distortion is being a continuous research area and new techniques are being invented in this area. Large amount of people are using the air interface for proper communication which also have a lot of drawbacks which include multipath fading, Inter symbol interference (ISI), Doppler shift etc..This paper is being presented on basis of channel estimation of wireless mobile OFDM channels using known pilot symbols.
General analytical framework for cooperative sensing and access trade-off opt...Polytechnique Montreal
In this paper, we investigate the joint cooperative spectrum sensing and access design problem for multi-channel cognitive radio networks. A general heterogeneous setting is considered where the probabilities that different channels are available, SNRs of the signals received at secondary users (SUs) due to transmissions from primary users (PUs) for different users and channels can be different. We assume a cooperative sensing strategy with a general a-out-of-b aggregation rule and design a synchronized MAC protocol so that SUs can exploit available channels. We analyze the sensing performance and the throughput achieved by the joint sensing and access design. Based on this analysis, we develop algorithms to find optimal parameters for the sensing and access protocols and to determine channel assignment for SUs to maximize the system throughput. Finally, numerical results are presented to verify the effectiveness of our design and demonstrate the relative performance of our proposed algorithms and the optimal ones.
International Journal of Engineering and Science Invention (IJESI)inventionjournals
International Journal of Engineering and Science Invention (IJESI) is an international journal intended for professionals and researchers in all fields of computer science and electronics. IJESI publishes research articles and reviews within the whole field Engineering Science and Technology, new teaching methods, assessment, validation and the impact of new technologies and it will continue to provide information on the latest trends and developments in this ever-expanding subject. The publications of papers are selected through double peer reviewed to ensure originality, relevance, and readability. The articles published in our journal can be accessed online.
IMPROVEMENT OF LTE DOWNLINK SYSTEM PERFORMANCES USING THE LAGRANGE POLYNOMIAL...IJCNCJournal
To achieve a high speed data rate, higher spectral efficiency, improved services and low latency the 3rd
generation partnership project designed LTE standard (Long Term Evolution).the LTE system employs
specific technical as well the technical HARQ, MIMO transmission, OFDM Access or estimation technical.
In this paper we focus our study on downlink LTE channel estimation and specially the interpolation which
is the basis of the estimation of the channel coefficients. Thus, we propose an adaptive method for polynomial interpolation based on Lagrange polynomial. We perform the Downlink LTE system MIMO transmission then compare the obtained results with linear, Sinus Cardinal and polynomial Newton Interpolations. The simulation results show that the Lagrange method outperforms system performance in term of Block Error Rate (BLER) , throughput and EVN(%)vs. Signal to Noise Ratio (SNR).
A Subspace Method for Blind Channel Estimation in CP-free OFDM SystemsCSCJournals
In this paper, a subspace method is proposed for blind channel estimation in orthogonal frequency-division multiplexing (OFDM) systems over time-dispersive channel. The proposed method does not require a cyclic prefix (CP) and thus leading to higher spectral efficiency. By exploiting the block Toeplitz structure of the channel matrix, the proposed blind estimation method performs satisfactorily with very few received OFDM blocks. Numerical simulations demonstrate the superior performance of the proposed algorithm over methods reported earlier in the literature.
Performance of Multiple symbol representation with clipping scheme for PAPR r...ijsrd.com
OFDM is one of the multicarrier modulation technique used in various communication systems. The major problem one faces while implementing this system is the high peak to average power .For an efficient OFDM system this PAPR should be low. In this paper a hybrid PAPR (peak to average power ratio) reduction technique for the OFDM (orthogonal frequency division multiplexing) signal which combines a multiple symbol representations method with a signal clipping method is proposed. In multiple symbol representations alternative signaling points are used to represent one symbol and PAPR is further reduced with the clipping scheme. The performance of the hybrid scheme is compared with the partial transmit sequence which is one of the other PAPR reduction scheme. In partial transmit sequence the input data is divided in to disjoint blocks transformed in to time domain sequence and rotated by phase factors. Theoretical analysis and simulation results validate that the proposed scheme has the ability to provide large PAPR reduction, low bit error rate. Performance analysis is also done with the partial transmit sequence scheme.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
Design and Optimal Configuration of Full-Duplex MAC Protocol for Cognitive Ra...Polytechnique Montreal
In this paper, we propose an adaptive medium access control (MAC) protocol for
full-duplex (FD) cognitive radio networks in which FD secondary users (SUs) perform channel contention
followed by concurrent spectrum sensing and transmission, and transmission only with maximum power
in two different stages (called the FD sensing and transmission stages, respectively) in each contention
and access cycle. The proposed FD cognitive MAC (FDC-MAC) protocol does not require synchronization
among SUs, and it efciently utilizes the spectrum and mitigates the self-interference in the FD transceiver.
We develop a mathematical model to analyze the throughput performance of the FDC-MAC protocol, where
both half-duplex (HD) transmission and FD transmission modes are considered in the transmission stage.
Then, we study the FDC-MAC conguration optimization through adaptively controlling the spectrum
sensing duration and transmit power level in the FD sensing stage.We prove that there exists optimal sensing
time and transmit power to achieve the maximum throughput, and we develop an algorithm to congure
the proposed FDC-MAC protocol. Extensive numerical results are presented to illustrate the optimal
FDC-MAC conguration and the impacts of protocol parameters and the self-interference cancellation
quality on the throughput performance. Moreover, we demonstrate the signicant throughput gains of the
FDC-MAC protocol with respect to the existing HD MAC and single-stage FD MAC protocols
International Journal of Modern Engineering Research (IJMER) is Peer reviewed, online Journal. It serves as an international archival forum of scholarly research related to engineering and science education.
An Efficient Performance of Mimo - Ofdm Based Cognitieve Radio System for Arr...IOSR Journals
Abstract: The wireless channel is central within this context, thus estimating the channel is the key to make CR operational, taking in consideration that the transmission-reception technology is available. In this thesis, we design a MIMO system using OFDM modulation technology to transmit and receive two signals over the mobile wireless channel. First formulate the pilot design as a new optimization problem. We use MIMO concept to enhance system capacity and robustness of the wireless transmission. In Multi-Input Multi-Output (MIMO) based cognitive radio (CR) systems, with the increasing demand for data rate and reliability in Wireless communicationsand devices, several issues become very important like bandwidth efficiency, quality of service and radio coverage. In this new scheme, adaptive arrays are group-selected in the spatial domain. Simulation shows that the proposed system can get significant performance improvements over the conventional array based OFDM systems over frequency-selective multipath fading channels with cognitive radio (CR) system. Keywords: Cognitive radios, MIMO, OFDM, and Joint transmit and receive group selected arrays.
International Journal of Engineering Research and DevelopmentIJERD Editor
Electrical, Electronics and Computer Engineering,
Information Engineering and Technology,
Mechanical, Industrial and Manufacturing Engineering,
Automation and Mechatronics Engineering,
Material and Chemical Engineering,
Civil and Architecture Engineering,
Biotechnology and Bio Engineering,
Environmental Engineering,
Petroleum and Mining Engineering,
Marine and Agriculture engineering,
Aerospace Engineering.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
NEW BER ANALYSIS OF OFDM SYSTEM OVER NAKAGAMI-n (RICE) FADING CHANNELijcseit
Modern wireless communication systems support high speed multimedia services. These services require
high data rates with acceptable error rates. Orthogonal Frequency Division Multiplexing (OFDM) is a
capable candidate to solve this problem. In this paper, a new expression for the BER of OFDM system has
been derived over Nakagami–n (Rice) fading channels using characteristics function (CHF) approach. The
exact probability density function of first order of Nakagami-n (Rice) random vector is used to derive the
expression for the error rates of OFDM system. The BER derivation of Rician fading channel is slightly
more complex compared to the Nakagami–m distribution because the PDF of the Rician RV contains an
explicit term of a modified Bessel function of first kind. Earlier, this problem was solved by replacing the
Bessel function with its infinite series and exponential integral representation. Here we propose an integral
expression to remove the complexity of the expression.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
Performance evaluation on the basis of bit error rate for different order of ...ijmnct
Today, we have required to accommodate a large number of users under a single base station. This can be
possible only if we have some flexibility over the spectrum. Previously we have lots of multiplexing methods
to accommodate large number of signals in time and frequency domain. But now we have required to
accommodate a large number of users in the same bandwidth, without any fading over the received signal.
So, orthogonality can be maintained over the frequency response. This technology is now more popular in
the mobile communication domain, called Orthogonal Frequency Division Multiplexing (OFDM). Actually
user data can be converted into the parallel form and then they are modulated using digital modulation
techniques. Finally, they have followed by OFDM Modulator and cyclic prefix can be inserted into the
OFDM symbols. Here, I have worked on the measurement of Bit error rate for different modulation
techniques in OFDM technology. It has been considered that subchannel size is not constant. According to
that I have concluded the overall idea regarding the performance under OFDM technology.
Indexed-channel estimation under frequency and time-selective fading channels...IJECEIAES
Index modulation (IM) techniques have been employed in different communication systems to improve bandwidth efficiency by carrying additional information bits. In high-mobility communication systems and under both time-selective and frequency-selective fading channels with Doppler spread, channel variations can be tracked by employing pilot-aided channel estimation with minimum mean-squared error estimation. However, inserting pilot symbols among information symbols reduces the system's spectral efficiency in pilot-aided channel estimation schemes. We propose pilot-aided channel estimation with zero-pilot symbols and an energy detection scheme to tackle this issue. Part of the information bit-stream is conveyed by the indices of zero-pilot symbols leading to an increase in the system's spectral efficiency. We used an energy detector at the receiver to detect the transmitted zero-pilot symbols. This paper examines the impacts of diversity order on the zero-pilot symbol detection error probability and the mean-squared of error estimation. The impacts of pilot symbols number and the zero-pilot symbol number on the mean-squared error of the minimum mean-squared error (MMSE) estimator and the system error performance are also investigated in this paper.
Study of the VariousChannel Estimation Schemes in Wireless Mimo-Ofdm Networkstheijes
The Multiple Input Multiple Output Orthogonal Frequency Division Multiplexing system is used widely use.so it
is essential to understand the data transmission in such system. As the characteristics of the transmission
channel always changing with time, it is necessary to know the channel and channel estimation schemes in
wireless networks. The channel estimation schemes are required to make the channels according to required
parameters for the data transmission. Several channel estimation schemes are available and can be used with
different algorithms. In this paper various channel estimation schemes were discussed and their performance in
fading channel.
Hybrid Low Complex near Optimal Detector for Spatial Modulation IJECEIAES
In our previous work maximum throughput in multi stream MIMO is analyzed by overcoming the inter antenna interference. To mitigate the Inter antenna interference spatial modulation can be used. Spatial Modulation (SM) aided MIMO systems are the emerging MIMO systems which are low complex and energy efficient. These systems additionally use spatial dimensions for transmitting information. In this paper a low complex detector based on matched filter is proposed for spatial modulation to achieve near maximum likelihood performance while avoiding exhaustive ML search since MF based detector exhibits a considerable reduced complexity since activated transmitting antenna and modulated amplitude phase modulation constellation are estimated separately. Simulation results show the performance of the proposed method with optimal ML detector, MRC and conventional matched filter methods.
On Channel Estimation of OFDM-BPSK and -QPSK over Nakagami-m Fading ChannelsCSCJournals
This paper evaluates the performance of OFDM - BPSK & -QPSK based system with and without channel estimation over Nakagami-m fading channels. Nakagami-m variants are generated by decomposition of Nakagami random variable into orthogonal random variables with Gaussian distribution envelopes. Performance of OFDM system in Nakagami channel has been reported here. The results yield the optimum value of m based on BER and SNR. Using this optimum value of m, Channel estimation over flat fading has been reported here. It has been depicted clearly from simulated graphs that channel estimation has further reduced the BER. However, threshold value of m has played a vital role during channel estimation.
COMPARING VARIOUS CHANNEL ESTIMATION TECHNIQUES FOR OFDM SYSTEMS USING MATLABijwmn
This paper compares the performance of various channel estimation techniques for OFDM systems over quasi-static channels using MATLab. It compares the performance of five channel estimation techniques, these are: decision directed (DD), linear interpolation, second-order interpolation, discrete Fourier transform (DFT) interpolation, minimum mean square error (MMSE) interpolation. The performance is evaluated in terms of two widely-used performance measures, namely, bit-error rate (BER) and the mean square error (MSE) for different levels of signal-to-noise ratio (SNR). The OFDM model is explained and implemented using MATLab to run different simulations. The simulation results demonstrate that the DD channel estimation provides the lowest BER and MSE as compared to interpolation techniques, at the cost of extra processing delay and comparatively sensitive to channel variations between OFDM symbols. Also, the MMSE interpolation outperforms all other interpolation techniques.
Implementation of 8x8 MIMO OFDM systems for higher order modulation using QOS...ijsrd.com
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A COMPARATIVE PERFORMANCE STUDY OF OFDM SYSTEM WITH THE IMPLEMENTATION OF COMB PILOT-BASED MMSE CHANNEL ESTIMATION
1. International Journal on Computational Sciences & Applications (IJCSA) Vol.3, No.6, December 2013
A COMPARATIVE PERFORMANCE STUDY OF OFDM
SYSTEM WITH THE IMPLEMENTATION OF COMB
PILOT-BASED MMSE CHANNEL ESTIMATION
A. Z. M. Touhidul Islam
Department of Information and Communication Engineering
University of Rajshahi, Rajshai-6205, Bangladesh
ABSTRACT
This paper presents a comparative performance analysis of wireless orthogonal frequency division
multiplexing (OFDM) system with the implementation of comb type pilot-based channel estimation
algorithm over frequency selective multi-path fading channels. The Minimum Mean Square Error (MMSE)
method is used for the estimation of channel at pilot frequencies. For the estimation of channel at data
frequencies different interpolation techniques such as low-pass, linear, and second order interpolation are
employed. The OFDM system simulation has been carried out with Matlab and the performance is
analyzed in terms of bit error rate (BER) for various signal mapping (BPSK, QPSK, 4QAM, 16QAM, and
64QAM) and channel (Rayleigh and Rician) conditions. The impact of selecting number of channel taps on
the BER performance is also investigated.
KEYWORDS
OFDM, Multipath fading channels, Comb Pilot, MMSE estimation, Interpolation, Signal mapping.
1. INTRODUCTION
Orthogonal frequency division multiplexing (OFDM) is a parallel transmission technique and is
widely used in wireless communication systems because of its high rate transmission capability
and robustness against multipath fading, high spectral efficiency and so on [1]. However, as the
radio channel is frequency selective and time-variant, the channel transfer function in OFDM
systems looks unequal in both the time and frequency domains. Thus a dynamic estimation of the
channel is necessary before demodulating the OFDM signals for the coherent detection of the
information symbols.
Two basic training-based one dimensional (1D) channel estimation techniques can be adopted in
OFDM system are block type and comb type pilot-based channel estimation. In block type pilot
arrangement, the pilot signal is allocated to particular OFDM block and sent periodically in time
domain. Instead, in comb type pilot arrangement, the pilot signals are uniformly distributed
within each OFDM block. The comb pilot-based channel estimation consists of algorithms to
estimate the channel at pilot frequencies and to interpolate the channel at data frequencies. The
estimation of channel at pilot frequencies can be based on least square (LS), minimum mean
square error (MMSE) or least mean square (LMS) method, while different interpolation
techniques can be incorporated for the channel estimation at data frequencies [2, 3].
The aim of this paper is to evaluate the bit error rate (BER) performance of OFDM
communication system with the implementation of comb type pilot-based MMSE channel
DOI:10.5121/ijcsa.2013.3605
45
2. International Journal on Computational Sciences & Applications (IJCSA) Vol.3, No.6, December 2013
estimation algorithms and to compare the system performance for signal mapping with different
digital modulation schemes over Rayleigh and Rician multi-path fading channels. In addition, the
impact of selecting number of channel taps and different interpolation techniques such as lowpass, linear, and second order interpolation on the system performance are also examined. The
organization of the paper is as follows. Relevant studies of pilot-based channel estimation in
OFDM systems are discussed in Section 2. Section 3 describes a model of OFDM system used for
the implementation. Comb type pilot-based channel estimation algorithm is briefly explained in
Section 4. In section 5, simulation results are displayed in graphical form, analyzed and
compared. Conclusions of the present work are given in Section 6.
2. RELATED WORKS
In earlier studies the performance of different pilot-based channel estimation techniques both in
the time and frequency domains for wireless OFDM communication systems were investigated
[4-6]. The authors in [7] reviewed block type and comb type pilot-based channel estimation and
revealed that comb-type pilot based channel estimation with low-pass interpolation performs the
best among all channel estimation algorithms. Cai and Giannakis [8] studied the OFDM system
performance with M-PSK digital modulation over Raleigh frequency fading channel and
optimized the number of pilot symbols, the placement of pilot symbols and the power allocation
between pilot and information symbols.
In [9-11], OFDM channel estimation with MMSE estimator was investigated. The authors in [10]
shown that among the MMSE and ZF equalizers, the BER performance of MIMO OFDM system
is better for MMSE equalizer. Pramano and Triyono [12] found that the performance of MIMO
system is better than SISO system and the MMSE estimator produced better performance than
low complexity LS estimator. In another study [13], it was concluded that block type pilot-based
channel estimation is better for slow fading channel while comb type pilot-based channel
estimation shows better performance in fast fading environment.
3. OFDM SYSTEM DESCRIPTION
Figure 1 shows a typical block diagram of OFDM communication system with comb type pilotbased MMSE channel estimation. The binary data (information) from the input are first grouped
and mapped into multi-amplitude and multi-phase signals according to the type of modulation
(BPSK, QPSK, 4QAM, 16QAM, and 64QAM) used at the signal mapper. After serial to parallel
conversion of the modulated data, comb type pilots are inserted uniformly between the
information data sequence. The IFFT block is used for transforming and multiplexing the
complex data sequence into time domain signal. Following the IFFT block, a cyclic prefix is
added to avoid possible inter-symbol interference (ISI) in OFDM systems. After the parallel to
serial conversion, the signal is transmitted through a frequency selective multi-path Rayleigh or
Rician fading channel.
At the receiver, after serial to parallel conversion of the received signal, the cyclic prefix is
removed first and then fed to an FFT block for de-multiplexing the multi-carrier signals.
Following the FFT block, the pilot signals are extracted from the demultiplexed samples. The
channel estimation at pilot subcarriers is performed by MMSE while the estimation of channel at
data subcarriers is achieved by different interpolation techniques. After signal demodulation at the
signal demapper, the information binary data is reconstructed at the receiver output.
4. COMB PILOT-BASED CHANNEL ESTIMATION
Comb type pilot-based channel estimation is suitable for fast-fading channel where the channel
condition changes between adjacent OFDM symbols. The comb type pilot arrangement is shown
in Fig. 2 in which the pilot signals are uniformly distributed within each OFDM block. In comb
46
3. International Journal on Computational Sciences & Applications (IJCSA) Vol.3, No.6, December 2013
type channel estimation, after extracting the pilot signals from the received signal, the channel
transfer function is estimated from the received pilot signals and the known pilot signals. The
channel responses of data subcarriers can be estimated with the interpolation of the neighboring
pilot channel responses.
Fig. 1 OFDM system block diagram with Comb pilot-based
MMSE channel estimation.
Pilot
Frequency (Sub Carriers)
Data
Time (OFDM Symbols)
Fig. 2 Comb type pilot arrangement.
Comb type pilot-based channel estimation can be based on least square (LS), minimum mean
square error (MMSE) or least mean square (LMS) method. Here only MMSE channel estimator is
employed for the estimation of channel at pilot subcarriers because of its superior performance as
compared to LS estimator. Pilot signal estimation and channel interpolation algorithms are
discussed in the following subsections.
47
4. International Journal on Computational Sciences & Applications (IJCSA) Vol.3, No.6, December 2013
4.1 Channel estimation at Comb pilot subcarriers by MMSE
Suppose Npi comb pilot signals X pi n, where n 0,1,, N pi 1 , are uniformly added into
X(m) data signals. If the OFDM signal modulated on the m-th subcarrier, X(m) can be expressed
as
X m X nLs i
(1)
X n , i 0
pi
Information data , i 1, 2,, Ls 1
Here the total N subcarriers are divided into Npi groups, each with
Ls N / N pi adjacent
subcarriers. The least squares (LS) estimate of pilot signal is given by [3, 4]
ˆ
H pi, LS X pi1Ypi
where
(2)
H pi H pi 0 H pi 1H pi N pi 1
T
(3)
is the channel frequency response at pilot subcarriers,
Ypi Ypi 0Ypi 1Ypi N pi 1
T
(4)
is the vector of the received pilot signals. It can also be expressed as
Ypi X pi. H pi I pi Wpi
(5)
X pi 0
0
where X pi
,
0
X pi N pi 1
Ipi is the ICI vector and Wpi is the Gaussian noise vector at pilot subcarriers.
The
ˆ
H pi, LS can also be expressed as H pi, LS H pi, LS 0 H pi, LS 1H pi, LS N pi 1T .
The estimate of pilot signals based on minimum mean square error (MMSE) is given by [4],
ˆ
ˆ
H pi, MMSE RH pi H pi, LS RH1pi H pi, LS H pi, LS
(6)
2
H
RH pi H pi RH pi H pi n X pi X pi
ˆ
H
1 1
pi, LS
,
2
ˆ
where H pi, LS is the LS estimate of H pi , n is the noise variance of Wpi , and the
covariance matrices are defined by,
.
H
H
RH pi H pi E H pi H pi , RH pi H pi, LS E H pi H pi, LS , and
H
RH pi, LS H pi, LS E H pi, LS H pi, LS
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5. International Journal on Computational Sciences & Applications (IJCSA) Vol.3, No.6, December 2013
4.2 Channel estimation at data subcarriers by Interpolation
A highly efficient interpolation technique is necessary for the estimation of channel at data
subcarriers using the channel information at pilot subcarriers. Three interpolation techniques:
low-pass, linear and second order interpolations are employed for the present study. In low-pass
interpolation, at first zeros are added to the original sequence. Then a low-pass finite impulse
response (FIR) filter is applied to pass the original data sequence without any change and to
interpolate between such that it can minimize the mean square error (MSE) between the
interpolated points and their ideal values.
In linear interpolation, two successive pilot subcarriers that are located in between the pilots are
used to determine the channel response for data subcarriers. It is implemented with the usage of
digital filtering technique. The estimated channel response for data subcarriers m,
nLs m n 1 Ls is given as [4],
ˆ
ˆ
H m H nLs i
(7)
The second order interpolation is implemented by a linear time-invariant FIR filter. The estimated
channel response is expressed by [4],
ˆ
ˆ
H m H nLs i
ˆ
ˆ
ˆ
D1H pi n 1 D0 H pi n D1H pi n 1
where
D1
1
2
, D0 1 1, D1
(8)
1
2
, i N .
5. SIMULATION RESULTS AND DISCUSSION
The simulation of OFDM system in Fig. 1 has been performed using Matlab 7.5 programming
language. The parameters used for the simulation are listed in Table 1. The graphical
representation of simulation results are shown in Figures 3 to 7. The Doppler frequency and
number of channel taps are considered as 80 Hz and 20, respectively.
Table 1. Simulation Parameters
Parameter
Number of Sub-carrier
Pilot Ratio
Pilot-to-Data Power Ratio
IFFT, FFT Size
Guard Type
Cyclic Prefix (C.P.) Length
Constellation
Channel Model
Number of Channel Taps
Doppler Frequency
Specification
256
1/8
2
256
Cyclic Extension
32
BPSK, QPSK, 4QAM, 16QAM, 64QAM
Rayleigh, Racian
20
80 Hz
The BER performance of the simulated wireless OFDM system over Rayleigh multipath fading
channel without and with the employment of comb type pilot-based channel estimation (LS and
MMSE) is shown in Fig. 3. The input binary data were BPSK modulated and the channel
49
6. International Journal on Computational Sciences & Applications (IJCSA) Vol.3, No.6, December 2013
estimation at data subcarriers was obtained by low-pass interpolation. It is seen that without using
any channel estimation algorithm, the bit error rate at the receiver is very high. However, with the
employment of MMSE channel estimation, the OFDM system performance has greatly improved
which results from the decrease of the amplitude and phase distortion of the transmitted signal
because of multipath fading. In Fig. 3, comb pilot-based, low complexity, LS channel estimation
is also incorporated for the comparison. It is clear that the MMSE channel estimator gives better
BER performance than the LS estimator in data transmission over the Rayleigh channel. Similar
results were observed in [12, 14] in studying the performance of channel estimation methods for
SISO and MIMO OFDM system.
0
10
-1
BER
10
-2
10
No Channel Estimation
With LS
With MMSE
-3
10
0
4
8
12
16
20
SNR(dB)
Fig. 3 BER performance of OFDM system without and with comb
pilot-based channel estimation (LS and MMSE).
0
10
Low-Pass
Second Order
Linear
-1
BER
10
-2
10
-3
10
0
4
8
12
16
20
SNR(dB)
Fig.4 Performance of different interpolation techniques used in Comb
pilot-based channel estimation of OFDM system
Fig. 4 depicts the impact of various channel interpolation techniques on the performance of
OFDM system. The simulation is performed under BPSK signal mapping over Rayleigh fading
50
7. International Journal on Computational Sciences & Applications (IJCSA) Vol.3, No.6, December 2013
channel. The performance of different interpolation techniques used in comb pilot-based MMSE
channel estimation follows the sequence of best to the worst as low-pass, second order and linear.
This result is consistent with earlier studies [9, 13].
The BER comparison of OFDM system with MMSE-interpolation-based comb type channel
estimation for different number of channel taps is shown in Fig. 5. Low-pass interpolation and
BPSK modulation were used for the system simulation over Rayleigh fading channel. The result
shows that the system performance is increased when we choose the number of channel taps per
multipath less than the CP length, whereas the performance getting worse if the number of
channel taps exceed the CP length. As we increase the number of taps, the transmitted signal go
under high degradation because of the increase of the number of times it would be reflected by
the multipath channel taps and, thus, the system performance degrades [15].
Fig. 6 demonstrates the BER performance of OFDM system with comb pilot-based MMSE
channel estimation over Rayleigh fading channel for BPSK, QPSK, 4QAM, 16QAM and 64QAM
signal mapping. Low-pass interpolation was used to estimate channel frequency response (CFR)
at data frequencies. Number of channel taps was chosen as 20. As seen the OFDM system
outperforms at BPSK modulation [10, 11] and the performance degrades with increasing the order
of the modulation over Rayleigh channel. The worst performance is observed at 64QAM
modulation. For a typical SNR of 8 dB, the BER values for BPSK and 64-QAM modulations are
0.032 and 1.141, respectively. Accordingly, the system performance is improved by 15.5 dB with
the use of BPSK modulation.
0
10
Taps: 10
Taps: 20
Taps: 40
Taps: 60
-1
BER
10
-2
10
-3
10
0
4
8
12
16
20
SNR(dB)
Fig.5 BER comparison of OFDM system with MMSE-interpolation-based
channel estimation for different number of channel taps.
The BER performance of OFDM system with comb pilot-based MMSE channel estimation over
Rician fading channel for BPSK, QPSK, 4QAM, 16QAM and 64QAM digital modulations are
shown in Fig. 7. Channel taps was selected as 20 per multipath and low-pass interpolation was
used for the estimation of channel at data frequencies. It is evident that the system provides better
error rate performance with BPSK [10] than other modulations used over Rician channel. The
OFDM system performance with BPSK is improved by 6.9 dB as compared to 64QAM at the
SNR of 8 dB.
51
8. International Journal on Computational Sciences & Applications (IJCSA) Vol.3, No.6, December 2013
0
10
-1
BER
10
-2
BPSK
QPSK
4QAM
16QAM
64QAM
10
-3
10
0
4
8
12
16
20
SNR(dB)
Fig.6 Performance of OFDM system with comb pilot-based channel estimation
for different signal mapping over Rayleigh fading channel.
0
10
-1
BER
10
-2
10
BPSK
QPSK
4QAM
16QAM
64QAM
-3
10
0
4
8
12
16
20
SNR(dB)
Fig. 7 Performance of OFDM system with comb pilot-based channel estimation
for different signal mapping over Rician fading channel.
Comparing the BER performance of OFDM system with comb pilot-based MMSE channel
estimation over Rayleigh and Rician multipath fading channels in Figs. 6 and 7, respectively, it is
observable that the system performance over Rician channel is somewhat better than that over the
Rayleigh channel environment [16]. For a typical SNR of 10 dB, the BER values for BPSK
modulation over Rayleigh and Rician channels are 0.032 and 0.0165, respectively, which
indicates that the system performance in Racian fading channel is improved by 2.88 dB.
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9. International Journal on Computational Sciences & Applications (IJCSA) Vol.3, No.6, December 2013
6. CONCLUSIONS
In this paper, the BER performance of wireless OFDM system with the implementation of comb
pilot-based channel estimation is examined for different signal mapping over multi-path Rayleigh
and Rician fading channels. In channel estimation, the MMSE method is used for the estimation
of channel at pilot subcarriers while different interpolation techniques are employed to estimate
the channel at data subcarriers. From the present simulation based comparative study it can be
concluded that the deployment of BPSK modulated OFDM system with MMSE and low-pass
interpolation-based comb type channel estimation achieves good error rate performance in data
transmission over all multipath fading environments involved.
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