This document summarizes a study that compares different methods for estimating the power delay profile (PDP) in MIMO-OFDM systems. It proposes a new method for PDP estimation that aims to mitigate noise and improve accuracy with limited sample sizes. The key steps of the proposed method are: 1) estimating the channel impulse response from pilot subcarriers, 2) deriving samples from the estimated channel response to estimate the PDP, 3) mitigating residual noise in the estimate by detecting and averaging noise at zero taps, and 4) using the estimated PDP in an LMMSE channel estimator. Simulation results show that the proposed method approaches the performance of Wiener filtering and provides better SNR than using a constant PDP estimate
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.
Performance Analysis of MIMO-OFDM System Using QOSTBC Code Structure for M-PSKCSCJournals
MIMO-OFDM system has been currently recognized as one of the most competitive technology for 4G mobile wireless systems. MIMO-OFDM system can compensate for the lacks of MIMO systems and give play to the advantages of OFDM system. In this paper, a general Quasi orthogonal space time block code (QOSTBC) structure is proposed for multiple-input multiple-output–orthogonal frequency-division multiplexing (MIMO-OFDM) systems for 4X4 antenna configuration. The signal detection technology used in this paper for MIMO-OFDM system is Zero-Forcing Equalization (linear detection technique). In this paper the analysis of high level of modulations (i.e. M-PSK for different values of M) on MIMO-OFDM system is presented. Here AWGN and Rayleigh channels have been used for analysis purpose and their effect on BER for high data rates have been presented. The proposed MIMO-OFDM system with QOSTBC using 4X4 antenna configuration has better performance in terms of BER vs SNR than the other systems.
Reduction of Outage Probability in Fast Rayleigh Fading MIMO Channels Using OFDMIJERA Editor
Multiple-input multiple-output (MIMO) techniques are used in wireless communications for achieving high spectral efficiency; however, a fast fading spatial channel can increase the outage probability of a MIMO system if not taken care of. This paper investigates the use of orthogonal frequency division multiplexing (OFDM) modulation technique for a MIMO system operating in fast Rayleigh fading channels with the aim of eliminating outage probabilities in the MIMO systems. Simulation results show that the MIMO-OFDM system gives significant reduction in outage probabilities compared to the conventional MIMO system.
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.
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.
Performance Analysis of MIMO-OFDM System Using QOSTBC Code Structure for M-PSKCSCJournals
MIMO-OFDM system has been currently recognized as one of the most competitive technology for 4G mobile wireless systems. MIMO-OFDM system can compensate for the lacks of MIMO systems and give play to the advantages of OFDM system. In this paper, a general Quasi orthogonal space time block code (QOSTBC) structure is proposed for multiple-input multiple-output–orthogonal frequency-division multiplexing (MIMO-OFDM) systems for 4X4 antenna configuration. The signal detection technology used in this paper for MIMO-OFDM system is Zero-Forcing Equalization (linear detection technique). In this paper the analysis of high level of modulations (i.e. M-PSK for different values of M) on MIMO-OFDM system is presented. Here AWGN and Rayleigh channels have been used for analysis purpose and their effect on BER for high data rates have been presented. The proposed MIMO-OFDM system with QOSTBC using 4X4 antenna configuration has better performance in terms of BER vs SNR than the other systems.
Reduction of Outage Probability in Fast Rayleigh Fading MIMO Channels Using OFDMIJERA Editor
Multiple-input multiple-output (MIMO) techniques are used in wireless communications for achieving high spectral efficiency; however, a fast fading spatial channel can increase the outage probability of a MIMO system if not taken care of. This paper investigates the use of orthogonal frequency division multiplexing (OFDM) modulation technique for a MIMO system operating in fast Rayleigh fading channels with the aim of eliminating outage probabilities in the MIMO systems. Simulation results show that the MIMO-OFDM system gives significant reduction in outage probabilities compared to the conventional MIMO system.
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.
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.
A COMPARATIVE PERFORMANCE STUDY OF OFDM SYSTEM WITH THE IMPLEMENTATION OF COM...ijcsa
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.
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.
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 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.
Performance analysis of DWT based OFDM over FFT based OFDM and implementing o...VLSICS Design
Growth in technology has led to unprecedented demand for high speed architectures for complex signal processing applications. In 4G wireless communication systems, bandwidth is a precious commodity, and service providers are continuously met with the challenge of accommodating more users with in a limited allocated bandwidth. To increase data rate of wireless medium with higher performance, OFDM (orthogonal frequency division multiplexing) is used. Recently DWT (Discrete wavelet transforms) is adopted in place of FFT (Fast Fourier transform) for frequency translation. Modulation schemes such as 16-QAM, 32-QAM, 64-QAM and 128-QAM (Quadrature amplitude modulation) have been used in the developed OFDM system for both DWT and FFT based model. In this paper we propose a DWT-IDWT based OFDM transmitter and receiver that achieve better performance in terms SNR and BER for AWGN channel. It proves all the wavelet families better over the IFFT-FFT implementation. The OFDM model is developed using Simulink, various test cases have been considered to verify its performance. The DWTOFDM using Lifting Scheme architecture is implemented on FPGA optimizing hardware, speed & cost. The wavelet filter used for this is Daubechies (9, 7) with N=2. The RTL code is written in Verilog-HDL and simulated in Modelsim. The design is then synthesized in Xilinx and implemented on Virtex5 FPGA board and the results were validated using ChipScope.
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.
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).
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.
Hardware Implementation of OFDM system to reduce PAPR using Selective Level M...IOSR Journals
Abstract : OFDM is a modulation as well as multiplexing technique which is widely used in various high speed mobile and wireless communication systems because of its capacity of ensuring high level robustness against interference. In this paper the design and implementation of OFDM system along with SLM implementation to reduce PAPR[6]is illustrated and a detailed simulation of the OFDM system with 16-QAM. OFDM transceiver is implemented using FPGA Spartan6 kit. The hardware results show a detailed study of RTL schematics and Test Bench. In this paper, the software simulation results show 2dB reduction in the peaks. Keywords - Field Programmable Gate Array, Matlab Simulink, Orthogonal Frequency Division Multiplexing , Peak-to-Average Power Ratio, Selective level Mapping and Xilinx
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.
A SEMI BLIND CHANNEL ESTIMATION METHOD BASED ON HYBRID NEURAL NETWORKS FOR UP...ijwmn
The paper describes how to improve channel estimation in Single Carrier Frequency Division Multiple
Access (SC-FDMA) system, using a Hybrid Artificial Neural Networks (HANN). The 3rd Generation
Partnership Project (3GPP) standards for uplink Long Term Evolution Advanced (LTE-A) uses pilot based
channel estimation technique. This kind of channel estimation method suffers from a considerable loss
ofbitrate due to pilot insertion; all data frame sent contains reference signal. The HANN converts data
aided channel estimator to semi blind channel estimator. To increase convergence speed, HANN uses some
channel propagation Fuzzy Rules to initialize Neural Network parameters before learning instead of a
random initialization, so its learning phase ismore rapidly compared to classic ANN.HANN allows more
bandwidth efficient and less complexity. Simulation results show that HANN has better computational
efficiency than the Minimum Mean Square Error (MMSE) estimator and has faster convergence than
classic Neural Networks estimators.
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.
A COMPARATIVE PERFORMANCE STUDY OF OFDM SYSTEM WITH THE IMPLEMENTATION OF COM...ijcsa
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.
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.
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 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.
Performance analysis of DWT based OFDM over FFT based OFDM and implementing o...VLSICS Design
Growth in technology has led to unprecedented demand for high speed architectures for complex signal processing applications. In 4G wireless communication systems, bandwidth is a precious commodity, and service providers are continuously met with the challenge of accommodating more users with in a limited allocated bandwidth. To increase data rate of wireless medium with higher performance, OFDM (orthogonal frequency division multiplexing) is used. Recently DWT (Discrete wavelet transforms) is adopted in place of FFT (Fast Fourier transform) for frequency translation. Modulation schemes such as 16-QAM, 32-QAM, 64-QAM and 128-QAM (Quadrature amplitude modulation) have been used in the developed OFDM system for both DWT and FFT based model. In this paper we propose a DWT-IDWT based OFDM transmitter and receiver that achieve better performance in terms SNR and BER for AWGN channel. It proves all the wavelet families better over the IFFT-FFT implementation. The OFDM model is developed using Simulink, various test cases have been considered to verify its performance. The DWTOFDM using Lifting Scheme architecture is implemented on FPGA optimizing hardware, speed & cost. The wavelet filter used for this is Daubechies (9, 7) with N=2. The RTL code is written in Verilog-HDL and simulated in Modelsim. The design is then synthesized in Xilinx and implemented on Virtex5 FPGA board and the results were validated using ChipScope.
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.
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).
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.
Hardware Implementation of OFDM system to reduce PAPR using Selective Level M...IOSR Journals
Abstract : OFDM is a modulation as well as multiplexing technique which is widely used in various high speed mobile and wireless communication systems because of its capacity of ensuring high level robustness against interference. In this paper the design and implementation of OFDM system along with SLM implementation to reduce PAPR[6]is illustrated and a detailed simulation of the OFDM system with 16-QAM. OFDM transceiver is implemented using FPGA Spartan6 kit. The hardware results show a detailed study of RTL schematics and Test Bench. In this paper, the software simulation results show 2dB reduction in the peaks. Keywords - Field Programmable Gate Array, Matlab Simulink, Orthogonal Frequency Division Multiplexing , Peak-to-Average Power Ratio, Selective level Mapping and Xilinx
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.
A SEMI BLIND CHANNEL ESTIMATION METHOD BASED ON HYBRID NEURAL NETWORKS FOR UP...ijwmn
The paper describes how to improve channel estimation in Single Carrier Frequency Division Multiple
Access (SC-FDMA) system, using a Hybrid Artificial Neural Networks (HANN). The 3rd Generation
Partnership Project (3GPP) standards for uplink Long Term Evolution Advanced (LTE-A) uses pilot based
channel estimation technique. This kind of channel estimation method suffers from a considerable loss
ofbitrate due to pilot insertion; all data frame sent contains reference signal. The HANN converts data
aided channel estimator to semi blind channel estimator. To increase convergence speed, HANN uses some
channel propagation Fuzzy Rules to initialize Neural Network parameters before learning instead of a
random initialization, so its learning phase ismore rapidly compared to classic ANN.HANN allows more
bandwidth efficient and less complexity. Simulation results show that HANN has better computational
efficiency than the Minimum Mean Square Error (MMSE) estimator and has faster convergence than
classic Neural Networks estimators.
Comparative performance analysis of different modulation techniques for papr ...IJCNCJournal
One of the most important multi-carrier tran
smission techniques used in the latest wireless com
munication
arena is known as Orthogonal Frequency Division Mul
tiplexing (OFDM). It has several characteristics
such as providing greater immunity to multipath fad
ing & impulse noise, eliminating Inter Symbol
Interference (ISI) & Inter Carrier Interference (IC
I) using a guard interval known as Cyclic Prefix (C
P). A
regular difficulty of OFDM signal is high peak to a
verage power ratio (PAPR) which is defined as the r
atio
of the peak power to the average power of OFDM Sign
al. An improved design of amplitude clipping &
filtering technique of us previously reduced signif
icant amount of PAPR with slightly increase bit err
or rate
(BER) compare to an existing method in case of Quad
rature Phase Shift Keying (QPSK) & Quadrature
Amplitude Modulation (QAM). This paper investigates
a comparative performance analysis of the differen
t
higher order modulation techniques on that design.
This report discusses the planning Associate in
nursing the implementation of an OFDM system
in several information module schemes like MQPSK,
M-QAM. First, a short introduction is
provided by explaining the background and the
specification of the project. Then the report deals
with the system model, every block of the OFDM
system is represented (IFFT, FFT, Cyclic prefix,
modulation / reception, Channel estimation, bit
error rate). System design is analyzed. The
transmission techniques, further because the
system parameters for transmission and reception
are explained well. Finally, the results are
provided.
Abstract: The growing demand on wireless communication service has created the necessity to support higher data rates for multimedia services. .As next generation wireless communication networks are expected to provide broadband multimedia services such as voice, web browsing, video conferencing etc. For high data rate achievement one must enhance the capacity of the wireless communication system. The capacity of a communication system can be enhanced by using OFDM system. OFDM is commonly used for communication system due to its high transmission rate and robustness against multipath fading So as to enhance the capacity of fading channels the OFDM system are combined to form hybrid system. Capacity is the measure of maximum information that can be transmitted reliably over a channel. This paper review on different channel capacity enhancement techniques used in OFDM system is SVD (Singular Value Decomposition), water Filling algorithm.
A Hybrid PAPR Reduction Scheme for OFDM System ijmnct
Orthogonal frequency division multiplexing (OFDM) i
s considered as most efficient technique for future
wireless communication systems due to its higher sp
ectral bandwidth efficiency, robustness to frequenc
y
selective fading channels, etc. However, the succes
sful implementation of the OFDM system necessitates
several difficulties. The biggest disadvantage to w
ork with OFDM system is its high peak-to-average po
wer
ratio PAPR leadsto severe inter carrier interferenc
e, out-of-band radiation, and poor bit error rate
performance due to the nonlinearity of the high pow
er amplifier. In this paper, a novel hybrid techniq
ue is
proposed to reduce PAPR further and comparison has
been done with conventional techniques as well.
Simulated results are presentedconfirm theoretical
results.MATLAB 7.5 is used to simulate the results
for system parametersconsidered.
BER Analysis of OFDM Systems with Varying Frequency Offset Factor over AWGN a...rahulmonikasharma
The progressively escalating demand for tremendously high rate data transmission over wireless mediums needsresourcefulconcord of electromagnetic resources considering restrictions like power incorporation, spectrum proficiency, robustness in disparity to multipath propagation and implementation complication. Orthogonal frequency division multiplexing (OFDM) is a favorable approach for upcoming generation wireless communication systems. However its susceptibility to the frequency offset triggered by frequency difference between local oscillator of transmitter and receiver or due to Doppler shift results to Inter Carrier Interference. This delinquent of ICI results inworsening performance of the wireless systems as bit error rate increaseswith increase in value of frequency offset. In this paper simulation results aredemonstratedfor analyzing the effect of varying frequency offset factor on system’s error rate performance.
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.
HYBRID LS-LMMSE CHANNEL ESTIMATION Technique for LTE Downlink Systemsijngnjournal
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H04654853
1. IOSR Journal of Engineering (IOSRJEN) www.iosrjen.org
ISSN (e): 2250-3021, ISSN (p): 2278-8719
Vol. 04, Issue 06 (June. 2014), ||V5|| PP 48-53
International organization of Scientific Research 48 | P a g e
Performance comparison of power delay profile Estimation for
MIMO OFDM
Manisha K. Ahirrao, Beena R. Ballal ,Shraddha Panbude
Electronics and Telecommunication Department Vidyalankar Institute Of Technology
Wadala, Dadar (w), Mumbai, India
Abstract: - A multiple-input multiple-output (MIMO) communication system combined with the orthogonal
frequency division multiplexing (OFDM) modulation technique can achieve reliable high data rate transmission
over broadband wireless channels. In linear minimum mean square error channel (MSE) estimation for
multicarrier system, it is necessary to know channel correlation function. Hence estimation of noise variance
using null carrier and power delay profile can be used to approximation which can be described in two
parameters like; mean delay and root mean square (RMS) delay spread. The approximate power delay profile is
used to generate LMMSE coefficient for subcarrier channel estimation. In this paper the estimation of channel at
pilot frequencies with Minimum Mean Square (MMSE) estimation algorithms is carried out through Mat lab
simulation. The performance of MIMO OFDM is evaluated on the basis of Mean Square Error (MSE)
level.Simulation results shows the performance of MSE for estimated PDP and Constant PDP for varying
number of samples and for SNR. The performance of LMMSE channel estimation using the proposed PDP
estimate approaches to that of Wiener filtering while in the other case, the estimated PDP gives less SNR than
constant PDP.
Keywords: - Channel estimation, Power delay profile, Mean Square Error, MIMO, OFDM.
I. INTRODUCTION
Orthogonal frequency division multiplexing (OFDM) is a multi-carrier transmission technology in
wireless environment, and can also be seen as a multi-carrier digital modulation or multi-carrier digital
multiplexing technology [9]. The basic idea of OFDM is to divide available bandwidth into N narrow sub-
channel at equidistant frequencies.[8]. A large number of orthogonal sub-carriers are used to transmit
information. OFDM system has high utilization of frequency spectrum and satisfactory capability of reducing
multi-path inference. So, OFDM has been considered as one of the core technologies of 4th generation (4G)
wireless communication system in the future Orthogonal Frequency Division Multiplexing. [1]
A single stream of data is split into parallel streams each of which is coded and modulated on to a
subcarrier, a term commonly used in OFDM systems.OFDM is a multicarrier system uses discrete Fourier
Transform/Fast Fourier Transform (DFT/FFT), sin(x)/x spectra for subcarriers .Available bandwidth is divided
into very many narrow bands, Data is transmitted in parallel on these bands. In OFDM each subcarrier has a
different frequency, Frequencies chosen so that an integral number of cycles in a symbol period, Signals are
mathematically orthogonal and Data is carried by varying the phase or amplitude of each subcarrier. Orthogonal
frequency division multiplexing (OFDM) transmission scheme is another type of a multichannel system, which
employs multiple subcarriers, it does not use individual band limited filters and oscillators for each sub channel
and furthermore, the spectra of subcarriers are overlapped for bandwidth efficiency, The multiple orthogonal
subcarrier signals, which are overlapped in spectrum, can be produced by generalizing the single-carrier In
practice, discrete Fourier transform (DFT) and inverse DFT (IDFT) processes are useful for implementing these
orthogonal signals. DFT and IDFT can be implemented efficiently by using fast Fourier transform (FFT) and
inverse fast Fourier transform (IFFT), respectively.
Single carrier system Signal representing each bit uses the entire available spectrum. In multicarrier system
available spectrum divided into many narrow bands data is divided into parallel data streams each transmitted
on a separate band
II. PILOT BASED OFDM MODEL
2. Performance comparison of power delay profile Estimation for MIMO OFDM
International organization of Scientific Research 49 | P a g e
I/P data
O/P data
Fig 1: Pilot based OFDM system model.
Channel estimation plays a very important role in OFDM system .Many related algorithms have been
presented these years, which can be generally separated into two methods, pilot-based channel estimation and
blind channel estimation. In paper [4] the present channel estimation methods generally can be divided into two
kinds: One is based on blind channel estimation which does not use pilots. Other is based on the pilots
Blind channel estimation
pilot-based channel estimation is a practical and an effective method[1]. Blind channel estimation, this
uses statistical information of the received signals.Blind channel estimation methods avoid the use of pilots and
have higher spectral efficiency. However, they often suffer from high computation complexity and low
convergence speed since they often need a large amount of receiving data to obtain some statistical information
such as cyclo stationarity induced by the cyclic prefix. Therefore, blind channel estimation methods are not
suitable for applications with fast varying fading channels. And most practical communication systems such as
World Interoperability for Microwave Access (WIMAX) system adopt pilot assisted channel estimation.
Pilot channel estimation
Pilot-based channel estimation estimates the channel information by obtaining the impulse response from all sub
carriers by pilot. [1]
Pilot based channel estimation is based on the transmission of symbols that are known to receiver so
called pilot symbols[4]. The pilot symbols are inserted into data stream and transmitted over mobile channel, at
receiver pilot symbols are analyzed in order to obtain channel estimate which is utilized for equalization .As the
characteristic of mobile channel is varying with time and frequency in order to obtain estimate which provides
information about time and frequency domain channel variation, pilot symbol need to be transmitted
periodically in time and spread over whole bandwidth which is provided for data transmission. For the pilot-
aided channel estimation methods, there are two classical pilot patterns, which are the block-type pattern and the
comb-type pattern. The block-type refers to that the pilots are inserted into all the subcarriers of one OFDM
symbol with a certain period i.e. symbols are transmitted periodically, and all subcarriers are used as pilots.[2]
The block-type can be adopted in slow fading channel, that is, the channel is stationary within a certain period of
OFDM symbols. The comb-type refers to that the pilots are inserted at some specific subcarriers in each OFDM
symbol. The comb-type is preferable in fast varying fading channels [7], that is, the channel varies over two
adjacent OFDM symbols but remains stationary within one OFDM symbol. The comb-type pilot arrangement-
based channel estimation has been shown as more applicable since it can track fast varying fading channels,
compared with the block-type one.
Mapping S/P Pilot insertion IFFT Add cyclic prefix
De mapping Pilot extraction
Remove cyclic
prefix
Channel
estimation
Chanel
AWGN
P/S
S/PFFTP/S
3. Performance comparison of power delay profile Estimation for MIMO OFDM
International organization of Scientific Research 50 | P a g e
III. SYSTEM MODEL
The system under consideration is a MIMO-OFDM system with 𝑃 transmits and 𝑄 receive antennas, and 𝐾 total
subcarriers [3].Suppose that the MIMO-OFDM system with the specified antennas transmits 𝐾 𝑑 subcarriers at
the central spectrum assigned for data and pilots, in order to control interferences with other systems. Let [𝑘 𝑝,
𝑛 𝑝] be the pilot subcarrier for the 𝑝 th transmit antenna at the 𝑛 𝑝 th OFDM symbol, which is a QPSK modulated
signal
Fig : 2 Pilot symbol arrangement in a block of OFDM system [3]
We assume that the pilot subcarriers are distributed over a time and frequency grid as in Fig. 2, to
preserve the orthogonality of pilots among different transmits antennas. At the 𝑛 𝑝 th OFDM symbol, the number
of pilot subcarriers is defined as 𝐾𝑝=𝑝. The pilot inserted OFDM symbol is transmitted over the wireless
channel after performing an inverse fast Fourier transform (IFFT) and adding a CP. It is assumed that the length
of CP, 𝐿 𝑔, is longer than the channel maximum delay, 𝐿𝑐ℎ, making the channel matrix circulate (𝐿𝑐ℎ ≤ 𝐿 𝑔). At the
receiver, after perfect synchronization, the removal of CP, and FFT operation, the received pilot symbol for the
𝑞 th receive antenna can be represented as, yq[np] = diag Xp Fphp,q + nq (1)[3]
where hp,q =[hp,q[np ,0],hp,q[np , 1], … ….,hp,q[npLch ],0,….,0]T
is an 𝐿 𝑔×1 CIR vector at the 𝑝 th transmit
antenna and 𝑞 th receive antenna. [3]
IV. PROPOSED METHOD FOR PDP ESTIMATION:
The proposed method is as follows:
From (1), the CIR at the (𝑝, 𝑞)th antenna port can be estimated approximately using the regularized least squares
(RLS) channel estimation with a fixed length of 𝐿 𝑔 as h,R,p,q= (Fp
H
Fp+∈ ILg )−1
Fp
H
diag(Xp)H
yq[np]
≜ WRLS ,pyq np , (2)[3]
Where 𝜖 =0.001 is a small regularization parameter, and I 𝐿𝑔 is the 𝐿𝑔×𝐿𝑔 identity matrix. To derive the PDP
from the estimated CIR in (2), the ensemble average of h,R, hH is given by
E{hR,p,qhR,p,q
H
}=WRhh WH
+ σn
2
WRLS ,pWRLS ,p
H
(3)[3]
Where Rhh =E{hp,qhp,q
H
}and W=(Fp
H
Fp+∈ IL,g)−1
Fp
H
Fp
Rℎℎ, represent the PDP of multipath channel within the length of 𝐿 𝑔, Unfortunately, Rℎℎ is distorted by W, which
is an ill-conditioned matrix due to the presence of F 𝐻 F 𝑝. Thus, instead of calculating W−1, we investigate the
method for eliminating the spectral leakage of W. The covariance matrix of the estimated CIR is defined as
Rhh = WRℎℎW 𝐻 which can be expressed as
Rhh = W diag
Lg−1
l=0
(plul)WH
(4)[3]
Where u𝑙 is a unit vector with the 𝑙 th entry being one and otherwise zeros. Let Ph and t𝑙 be the 𝐿 𝑔×1 vectors
defined as Ph= (Rh) and t𝑙=𝐷 𝑔 ( W𝑑𝑖𝑎𝑔(u𝑙)W𝐻 ) , respectively, where 𝐷𝑔(A) is the column vector containing
all the diagonal elements of A. Then, the relation in (4) is simplified as
Ph = p0t0+p1t1+⋯ . +pLg−1tLg−1 ≜TPh (5)[3]
where T=[t0, t1, ..., t𝐿𝑔−1] is defined as a distortion matrix by W.. In addition, the distortion matrix is a well-
conditioned matrix. Hence, the distortion of W can be eliminated as
ph=T−1
Ph = E {gp,q[np]}- σn
2
w (6)[3]
where gp,q [np]=T−1𝐷𝑔 (h 𝑅, 𝑝,𝑞 h 𝐻 𝑅, 𝑝,𝑞 ) is defined as the received sample vector for estimating PDP at the (𝑝,
𝑞)th antenna port on the 𝑛𝑝th OFDM symbol, and w= T−1(W𝑅𝐿𝑆,𝑝WRLS ,p
H
).
4. Performance comparison of power delay profile Estimation for MIMO OFDM
International organization of Scientific Research 51 | P a g e
PDP Estimation in MIMO-OFDM Systems
The received sample vector in (6) can be expressed as
gp,q[np]= 𝐷𝑔(hp,qhp,q
H
) + np,q + ep,q (7)[3]
where np,q= T−1
𝐷 𝑔(W 𝑅𝐿𝑆, 𝑝n 𝑞nq
H
WRLS ,p
H
) and
ep,q = 2 𝑅e {T−1
(Whp,qnq
H
WRLS ,p
H
)}. Here, 𝑅e{a} denotes the real part of a. We assume that np,q is an effective
noise by AWGN. Then, the sample average of gp,q[np] is given by
< 𝑔p,q[np]>N ≜
1
N
gp,q[np]Q
q=1
p
p=1
|Tp |
np =1 (8)[3]
= Dg hp,qhp,q
H
+ np,q N + ep,q N
Where 𝑁 ≜ ∣𝒯𝑝∣𝑃𝑄 represents the total number of samples for PDP estimation. ∣𝒯𝑝∣ is the number of pilot
symbols at the 𝑘𝑝 th subcarrier in a time slot. When is sufficiently large, the PDP can be perfectly estimated,
since Dg hp,qhp,q
H
N →Ph, np,q N →σn
2
w, and ep,q N → 0. However, it is difficult for a receiver of
practical MIMO-OFDM systems to obtain such a large number of samples. With an insufficient number of
samples, the PDP can be approximated as Ph ͌Dg hp,qhp,q
H
N
To improve the accuracy of PDP estimation with insufficient we mitigate the effective noise as follows
< 𝑔p,q[np]>N ‒ σn
2
w = Dg hp,qhp,q
H
+ ZN, (9)[3]
where ZN ≜ ep,q N + np,q N ‒ σn
2
w is defined as a residual noise vector, in which each entry has a zero-
mean. Then, the error of PDP estimation with 𝑁 samples can be calculated as
eN = ( Dg hp,qhp,q
H
N ‒ Ph) + ZN (10)[3]
Since [Ph]i ≥ 0 for all 𝑖, the PDP can initially be estimated as
Pinit =
1
N
Sp,q
|Q|
q=1
|P|
p=1
|Tp|
np=1 [Np] (11)[3]
where Sp,q [Np] is the sample vector of proposed PDP estimator with the 𝑙 th entry
Sp,q
l
[Np] =
gp,q
l
Np − σn
2
w~1
if gp,q
l
Np > σn
2
w~1
0 otherwise
(12)[3]
where gp,q
l
Np = [gp,q[Np] ]l and w~1
= [w] To mitigate the detrimental effect of residual noise ZN, the
proposed scheme estimates the average of residual noise at the zero-taps of Ph. At the l th entry of, pinit the zero-
tap can be detected as
tz
l
=
1 if pinit < βth
0 otherwise
(13)[3]
where βth =
1
Lg
pinit
l|Lg−1|
Lg =1 is defined as a threshold value for the zero-tap detection. Then, the average of
residual noise at the zero-taps can be estimated as
nRavg =
1
Nz
pinit
l|Lg−1|
l=0 tz
l
(14)[3]
where Nz=
Lg−1
l=0 tl
𝑡𝑙 represents the total number of detected zero-taps. With the mitigation of residual noise,
the 𝑙th tap of the PDP estimate, Ph, can be expressed as
ph
l
=
pinit −
l
nRavg if pinit
l
> nRavg
0 therwise
(15)[3]
Then, the estimated PDP in (15) can be used to obtain the frequency-domain channel correlation in the LMMSE
channel estimator.
V. SIMULATION RESULTS
We consider a MIMO-OFDM system. The system bandwidth is 5 MHz with 301 subcarriers for
transmitting data information and pilots at 2-𝐺𝐻𝑧 carrier frequency. Number of pilots are 12. One frame consist
of 14 OFDM symbols . The MIMO-OFDM system utilizes two transmit and one receive antennas (𝑃=2, Q=1).
The length of CP is 40 (𝐿𝑔=40). One important parameter of the channel is the power delay profile which
represents the average power (also called multipath intensity profile) associated with a given multipath delay.
[6] For all simulations, the channel estimator is based on results.In fig 3.1 and in fig 3.2 we calculated effect of
Mean square Error over variable number of samples for estimated PDP and for constant PDP respectively. The
performance of proposed scheme is better than the constant power delay profile. In fig 3.3 we plotted MSE for
given SNR range. The performance of two PDPs constant and estimated is observed.
5. Performance comparison of power delay profile Estimation for MIMO OFDM
International organization of Scientific Research 52 | P a g e
Fig :3.1 Performance of MSE with number of samples 500
Fig :3.2 Performance of MSE with number of samples1000
Fig :3.3 Performance of MSE with SNR
VI. CONCLUSION
In this paper, we propose to evaluate the performance of LMMSE estimation techniques for the
systems under the effect of the number of samples for estimated PDP and for constant PDP. The transmitted
signals are quadrature phase-shift keying (QPSK) modulated. The cyclic prefix inserted at the beginning of each
OFDM symbol is usually equal to or longer than the channel length in order to suppress ICI and ISI [5].
Simulation results show that in the case where the number of samples is increased the performance of constant
PDP remains constant than the estimated PDP. MSE of the proposed scheme improves the MSE performance
with an increase in the number of samples for PDP estimation. Simulation results show that the performance of
LMMSE channel estimation using the proposed PDP estimate approaches that of Wiener filtering. [3]In the
other case, the estimated PDP gives less SNR than constant PDP.