This document summarizes a research paper that analyzes the performance of different pilot-based channel estimation schemes for OFDM systems using QPSK and 16-QAM modulation over Rayleigh fading channels with Doppler frequency shifts. It compares block-type pilot arrangement, which inserts pilots into all subcarriers periodically, to comb-type arrangement, which inserts pilots into each symbol and requires interpolation. It evaluates channel estimation algorithms like LS, LMMSE, SVD for block pilots and linear, quadratic, and cubic spline interpolation for comb pilots. The goal is to analyze how bit error rate is affected by Doppler shifts. Simulations are conducted in MATLAB to compare the schemes.
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
This document proposes an OFDM receiver capable of estimating and correcting the subcarrier dependent Doppler shifting on a symbol-by-symbol basis for highly mobile underwater acoustic networks. It presents a receiver structure that estimates the Doppler rate for each OFDM symbol based on the recovered data from the previous symbol, allowing for compensation of changing Doppler rates. Two algorithms are developed for the symbol-by-symbol Doppler rate estimation: one ad-hoc and one based on the marginal maximum likelihood principle. Simulation results show the receiver design performs well for a source accelerating at 0.29 m/s^2.
This document summarizes design issues in OFDM systems. It discusses the OFDM modem block diagram and signal description. It then focuses on key receiver design issues like time and frequency synchronization through techniques like frequency offset correction, carrier phase tracking, and channel equalization. It also addresses signal dynamic range issues and how they are handled in standards like IEEE 802.11a/g. The document provides illustrations of effects of different impairments and solutions used in practical OFDM systems.
OFDM is a digital multi-carrier modulation technique that divides the available spectrum into multiple orthogonal subcarriers. It allows high spectral efficiency by spacing the carriers to maintain orthogonality even when their spectra overlap. The document provides an intuitive explanation of OFDM using analogies like a shower head vs faucet and multiple smaller trucks vs one large truck. It explains how OFDM provides resistance to interference by spreading data across orthogonal subcarriers rather than a single carrier. The key concept of orthogonality allows the subcarriers to overlap without interference by ensuring the area under one subcarrier's frequency multiplied by another is always zero.
This document summarizes a research paper that investigates reducing peak-to-average power ratio (PAPR) in an MC-CDMA system using partial transmit sequence (PTS) technique with a suboptimal combination algorithm. The paper simulates a downlink MC-CDMA system with BPSK and QPSK modulation under varying system parameters like number of users and phase sequences. Results show the complementary cumulative distribution function (CCDF) of PAPR for the original and PTS-processed signals. Using PTS with 4, 8, or 16 phase sequences provides 1dB, 2dB, and 4.2dB of PAPR reduction respectively compared to the original signal for a 8-user BPSK modulated MC-CD
What is the main difference between single carrier and ofdm yahoo! answersen_maruf78
Single carrier (SC) transmission has a lower peak-to-average power ratio than orthogonal frequency-division multiplexing (OFDM). SC frequency-division multiple access (SC-FDMA) divides the frequency band into subsets, assigning each user a different subset, whereas OFDM divides data into multiple parallel streams and assigns each stream a unique subcarrier. Both SC-FDMA and OFDM use guard intervals and fast Fourier transforms to combat interference, but SC-FDMA applies these on the transmitter side while OFDM applies them on the receiver side. SC-FDMA has a lower peak-to-average power ratio than OFDM, making it more suitable for applications with power constraints like uplink mobile communications.
Popular Interview Wireless Question with AnswerVARUN KUMAR
Favourable propagation refers to the orthogonality among vector-valued wireless channels that can maximize total system throughput. It occurs when the interference terms in the channel capacity equation, which involve the product of different channel coefficients, approach zero. Time division duplexing (TDD) is more complex than frequency division duplexing (FDD) due to hardware mismatches across base stations and user equipment for uplink and downlink channels. Channel reciprocity can be achieved through FDD if the uplink and downlink carrier frequencies are nearly equal, but not if they are significantly different.
This document provides an overview of channel estimation strategies used in orthogonal frequency division multiplexing (OFDM) systems. It describes the basic types of channel estimation methods: block-type pilot channel estimation and comb-type pilot channel estimation. For block-type estimation, pilots are inserted into all subcarriers of OFDM symbols periodically. This allows estimation of the channel conditions between pilot symbols. Estimation can be done with least squares (LS), minimum mean-square error (MMSE), or modified MMSE. For comb-type estimation, pilots are inserted into certain subcarriers of each symbol, requiring interpolation to estimate data subcarriers. The document compares the implementation complexity and performance of different estimation methods.
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
This document proposes an OFDM receiver capable of estimating and correcting the subcarrier dependent Doppler shifting on a symbol-by-symbol basis for highly mobile underwater acoustic networks. It presents a receiver structure that estimates the Doppler rate for each OFDM symbol based on the recovered data from the previous symbol, allowing for compensation of changing Doppler rates. Two algorithms are developed for the symbol-by-symbol Doppler rate estimation: one ad-hoc and one based on the marginal maximum likelihood principle. Simulation results show the receiver design performs well for a source accelerating at 0.29 m/s^2.
This document summarizes design issues in OFDM systems. It discusses the OFDM modem block diagram and signal description. It then focuses on key receiver design issues like time and frequency synchronization through techniques like frequency offset correction, carrier phase tracking, and channel equalization. It also addresses signal dynamic range issues and how they are handled in standards like IEEE 802.11a/g. The document provides illustrations of effects of different impairments and solutions used in practical OFDM systems.
OFDM is a digital multi-carrier modulation technique that divides the available spectrum into multiple orthogonal subcarriers. It allows high spectral efficiency by spacing the carriers to maintain orthogonality even when their spectra overlap. The document provides an intuitive explanation of OFDM using analogies like a shower head vs faucet and multiple smaller trucks vs one large truck. It explains how OFDM provides resistance to interference by spreading data across orthogonal subcarriers rather than a single carrier. The key concept of orthogonality allows the subcarriers to overlap without interference by ensuring the area under one subcarrier's frequency multiplied by another is always zero.
This document summarizes a research paper that investigates reducing peak-to-average power ratio (PAPR) in an MC-CDMA system using partial transmit sequence (PTS) technique with a suboptimal combination algorithm. The paper simulates a downlink MC-CDMA system with BPSK and QPSK modulation under varying system parameters like number of users and phase sequences. Results show the complementary cumulative distribution function (CCDF) of PAPR for the original and PTS-processed signals. Using PTS with 4, 8, or 16 phase sequences provides 1dB, 2dB, and 4.2dB of PAPR reduction respectively compared to the original signal for a 8-user BPSK modulated MC-CD
What is the main difference between single carrier and ofdm yahoo! answersen_maruf78
Single carrier (SC) transmission has a lower peak-to-average power ratio than orthogonal frequency-division multiplexing (OFDM). SC frequency-division multiple access (SC-FDMA) divides the frequency band into subsets, assigning each user a different subset, whereas OFDM divides data into multiple parallel streams and assigns each stream a unique subcarrier. Both SC-FDMA and OFDM use guard intervals and fast Fourier transforms to combat interference, but SC-FDMA applies these on the transmitter side while OFDM applies them on the receiver side. SC-FDMA has a lower peak-to-average power ratio than OFDM, making it more suitable for applications with power constraints like uplink mobile communications.
Popular Interview Wireless Question with AnswerVARUN KUMAR
Favourable propagation refers to the orthogonality among vector-valued wireless channels that can maximize total system throughput. It occurs when the interference terms in the channel capacity equation, which involve the product of different channel coefficients, approach zero. Time division duplexing (TDD) is more complex than frequency division duplexing (FDD) due to hardware mismatches across base stations and user equipment for uplink and downlink channels. Channel reciprocity can be achieved through FDD if the uplink and downlink carrier frequencies are nearly equal, but not if they are significantly different.
This document provides an overview of channel estimation strategies used in orthogonal frequency division multiplexing (OFDM) systems. It describes the basic types of channel estimation methods: block-type pilot channel estimation and comb-type pilot channel estimation. For block-type estimation, pilots are inserted into all subcarriers of OFDM symbols periodically. This allows estimation of the channel conditions between pilot symbols. Estimation can be done with least squares (LS), minimum mean-square error (MMSE), or modified MMSE. For comb-type estimation, pilots are inserted into certain subcarriers of each symbol, requiring interpolation to estimate data subcarriers. The document compares the implementation complexity and performance of different estimation methods.
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.
Orthogonal Frequency Division Multiplexing, OFDM uses a large number of narrow sub-carriers for multi-carrier transmission to overcome the effect of multi path fading problem. LTE uses OFDM for the downlink, from base station to terminal to transmit the data over many narrow band careers of 180 KHz each instead of spreading one signal over the complete 5MHz career bandwidth. OFDM meets the LTE requirement for spectrum flexibility and enables cost-efficient solutions for very wide carriers with high peak rates.
The primary advantage of OFDM over single-carrier schemes is its ability to cope with severe channel conditions. Channel equalization is simplified. The low symbol rate makes the use of a guard interval between symbols affordable, making it possible to eliminate inter symbol interference (ISI).
This document discusses channel estimation techniques in OFDM systems. It compares LS and MMSE estimation methods. It also describes simulating an OFDM transmission in Matlab to analyze how the bit error ratio is affected by changing the signal-to-noise ratio and multipath effects. The key steps of the simulation are outlined, including OFDM transmission, channel estimation using LS and MMSE, and calculating the bit error ratio to compare performance of the estimation techniques.
LTE Physical Layer Transmission Mode Selection Over MIMO Scattering ChannelsIllaKolani1
Although LTE networks systems profits from recent advanced transmission techniques as MIMO systems, it encounters particularly two mains challenges:
MIMO channel Modeling or MIMO channel estimation .
An Optimal Dynamic MIMO transmission modes switching following the variation of MIMO Channel.
This Thesis proposes a channel model taking into account the motion of the UE first and after use this model to design an optimal transmission mode selection for 4G networks
A Peak to Average Power Ratio (PAPR) Reduction in OFDM SystemsIRJET Journal
This document discusses peak-to-average power ratio (PAPR) reduction techniques for orthogonal frequency division multiplexing (OFDM) systems. It begins with an introduction to OFDM and the problem of high PAPR values in OFDM signals. It then describes the clipping and filtering method and parabolic peak cancellation method for PAPR reduction. It analyzes these techniques by evaluating complementary cumulative distribution function (CCDF) curves and bit error rate (BER) with the goal of minimizing PAPR while maintaining acceptable BER. Power amplifier nonlinearity is also discussed as a key factor affected by high PAPR OFDM signals.
Performance and Analysis of OFDM Signal Using Matlab SimulinkIJMER
Multi-carrier modulation is an attractive technique for fourth generation .OFDM is based on
multicarrier modulation technique. In OFDM system the bit stream is divided into many different sub
channels. An efficient and distortionless scheme for peak power reduction in OFDM is proposed. In this
paper, a set of mapping where the actual transmit signal is selected. From this set of signal reduced
PAPR. Simulation results are shown. The lowest PAPR is compared with conventional work. It is also
compared BER to SNR and best result is achieved.
This document discusses the effects of time offset (TO) and carrier frequency offset (CFO) on orthogonal frequency division multiplexing (OFDM) systems and proposes interference cancellation techniques. It introduces the OFDM system model and how CFO causes loss of orthogonality between subcarriers, resulting in inter-carrier interference (ICI) that degrades performance. The paper proposes an ICI reduction scheme using self-cancellation and evaluates its performance compared to standard OFDM. It also discusses using space-time block coding (STBC) with OFDM to improve performance by reducing bit error rate (BER) under different signal-to-noise ratios. Simulation results show STBC effectively mitigates the effects of inter-
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
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.
PAPR REDUCTION OF OFDM SIGNAL BY USING COMBINED HADAMARD AND MODIFIED MEU-LAW...IJCNCJournal
Orthogonal frequency division multiplexing (OFDM) is a technique which gives high quality of service (QOS) to the users by mitigating the fading signals as well as high data rates in multimedia services. However, the peak-to-average power ratio (PAPR) is a technical challenge that reduces the efficiency of RF power amplifiers. In this paper, we propose the combined Hadamard transform and modified meu-law companding transform method in order to lessen the effects of the peak-to-average power ratio of the
OFDM signal. Simulation results show that the proposed scheme reduces PAPR compared to other companding techniques as well as the Hadamard transform technique when used on its own.
1. The document analyzes the effect of signal distortion techniques for PAPR reduction like clipping and peak windowing on the bit error rate (BER) performance of turbo and low density parity check (LDPC) coded orthogonal frequency division multiplexing (OFDM) systems.
2. It implements an OFDM system based on IEEE 802.11a standards with turbo and LDPC error correcting codes over additive white Gaussian noise (AWGN) and exponentially decaying Rayleigh fade channels.
3. The results show that LDPC-COFDM performs better than turbo-COFDM in both channels, even with clipping applied. However, turbo-COFDM is better with peak windowing due to
Comparative Analysis of Distortive and Non-Distortive Techniques for PAPR Red...IDES Editor
OFDM is a popular and widely accepted modulation
and multiplexing technique in the area of wireless
communication. IEEE 802.15, a wireless specification defined
for WPAN is an emerging wireless technology for short range
multimedia applications. Two general categories of 802.15
are the low rate 802.15.4 (ZigBee) and high rate 802.15.3
(UWB). In their physical (PHY) layer design, OFDM is a
competing technique due to the various advantages it renders
in the practical wireless media. OFDM has been a popular
technique for many years and adopted as the core technique
in a number of wireless standards. It makes the system more
immune to interference like InterSymbol Interference (ISI)
and InterCarrier Interference (ICI) and dispersive effects of
the channel. It is also a spectrally efficient scheme since the
spectra of the signal are overlapping in nature. Despite these
advantages OFDM suffers from a serious problem of high
Peak to Average Power. This limits the system’s capabilities
and increases the complexity. This paper compares the signal
distortion technique of Amplitude Clipping and the
distortionless technique of SLM for Peak to Average Power
reduction
1) OFDM uses multiple carriers to transmit data in parallel. It can be described mathematically using the Fourier transform which relates events in the time and frequency domains.
2) At the transmitter, the signal is defined in the frequency domain using a discrete Fourier transform and generated using the inverse discrete Fourier transform. This allows the carriers to be orthogonal.
3) A guard interval is added between symbols to prevent intersymbol interference from multipath distortion. This increases the symbol duration and provides timing tolerance at the receiver.
This document discusses various channel estimation techniques for OFDM systems. It describes pilot structures like block, comb and lattice types and how they are suited for different channel conditions. It also explains training symbol based channel estimation techniques like LS and MMSE. DFT-based channel estimation aims to improve performance by eliminating noise outside the channel delay. Decision directed channel estimation updates the channel coefficients without pilots by using detected signal feedback.
Performance analysis of Multiband - OFDM systems using LDPC coder in pulsed -...IDES Editor
In this paper, a combined approach where low density
parity check (LDPC) codes are used to reduce the complexity
and power consumption of pulsed orthogonal frequencydivision
multiplexing (pulsed-OFDM) ultra-wideband (UWB)
systems is described. The proposed system uses LDPC codes
to achieve higher code rates without using convolution
encoding and puncturing thereby reducing the complexity and
power consumption of pulsed-OFDM system. The LDPCpulsed-
OFDM system achieves channel capacity with different
code rates and has good performance in different channel
fading scenarios. The pulsed OFDM system is used where
pulsed signals could spread the frequency spectrum of the
OFDM signal. The performance of LDPC-pulsed-OFDM
system for wireless personal area networks (WPAN) is
analyzed for different UWB indoor propagation channels (CM3
and CM4) provided by the IEEE 802.15.3a Standard activity
committee. To establish this, a design of LDPC-pulsed-OFDM
system using the digital video broadcasting-satellite-second
generation (DVB-S2) standard and provide the simulation
results for the different code rates supported by LDPC codes
is presented.
This document summarizes a student project on OFDM transmitters and receivers. It includes an introduction to OFDM that describes its use of orthogonal subcarriers. It also compares single carrier modulation to multi-carrier modulation using OFDM. The document outlines the basic OFDM transmitter and receiver block diagrams. It discusses the constellation mapper, IFFT block, cyclic prefix, and design approaches for these blocks. Simulation results are presented comparing transmitted and received signals. BER performance is evaluated for different modulation schemes like QPSK and QAM. The document concludes that OFDM provides high bandwidth efficiency and overcomes interference through the IFFT and cyclic prefix.
This document provides an overview of OFDM (Orthogonal Frequency Division Multiplexing) including:
1. The basic principles of OFDM including modulation using IDFT and demodulation using DFT.
2. How a cyclic prefix is used to mitigate multipath interference.
3. A block diagram of a basic OFDM system showing key components like mapping, IFFT/FFT, insertion of cyclic prefix, and demapping.
4. Examples of OFDM parameters used in standards like IEEE 802.11a.
This document summarizes research on reducing peak-to-average power ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) systems. It discusses using a companding technique with Gaussian distribution to compress the signal before transmission and decompress it upon reception. The key aspects covered are: applying a compander and decompander with Gaussian distribution parameters at the transmitter and receiver; how the central limit theorem allows the sum of subcarriers to approximate a Gaussian distribution for large numbers; and how this technique reduces PAPR by increasing average power while keeping peak power the same. Performance is analyzed by simulating PAPR and bit error rate with and without companding under different parameters.
This document summarizes a research paper that investigates the effect of different orthogonal frequency division multiplexing (OFDM) transmission modes on the performance of carrier frequency offset (CFO) estimation using a cyclic prefix-based synchronization technique. Five transmission modes are tested (0.25K, 0.5K, 1K, 2K, 4K) by developing an OFDM system simulation in MATLAB. The results show that synchronization performance, as measured by mean squared error of CFO estimation, improves with increasing transmission mode/IFFT size but requires more estimation time. Larger transmission modes provide better frequency synchronization.
Performance Analysis of M-ary Optical CDMA in Presence of Chromatic DispersionIDES Editor
The performance of M-ary optical code division
multiple access (OCDMA) is analytically investigated in
presence of chromatic dispersion. The study is carried out for
single mode dispersion shifted and non dispersion shifted
fibers. Walsh code is used as user address. The p-i-n
photodetector is used for optoelectronic conversion process.
In our proposed model 16 different symbols are modulated
with different intensity levels and detected by direct detection
technique. The numerical results show that, the reconstruction
of the transmitted symbol is strongly dependent on the received
symbols magnitude which is reduced by fiber length and
symbol rate. It is found that the proposed OCDMA system
shows better performance when dispersion shifted fiber is
used as a communication medium.
The document analyzes friction stir welding tools with various threaded pin profiles. Three tool pin profiles are modeled in CATIA and analyzed using ANSYS: cylindrical, frustum, and conical pins with threads. The stress distributions and displacement vectors in the pins are obtained for different rotational speeds and temperatures. The results show that the cylindrical pin profile experiences the lowest stress levels and displacement compared to the other profiles. Increasing rotational speed does not significantly affect the stress, while higher temperatures generally increase stress across all pin profiles. The cylindrical pin profile is determined to be preferable for withstanding loads during friction stir welding.
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
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.
Orthogonal Frequency Division Multiplexing, OFDM uses a large number of narrow sub-carriers for multi-carrier transmission to overcome the effect of multi path fading problem. LTE uses OFDM for the downlink, from base station to terminal to transmit the data over many narrow band careers of 180 KHz each instead of spreading one signal over the complete 5MHz career bandwidth. OFDM meets the LTE requirement for spectrum flexibility and enables cost-efficient solutions for very wide carriers with high peak rates.
The primary advantage of OFDM over single-carrier schemes is its ability to cope with severe channel conditions. Channel equalization is simplified. The low symbol rate makes the use of a guard interval between symbols affordable, making it possible to eliminate inter symbol interference (ISI).
This document discusses channel estimation techniques in OFDM systems. It compares LS and MMSE estimation methods. It also describes simulating an OFDM transmission in Matlab to analyze how the bit error ratio is affected by changing the signal-to-noise ratio and multipath effects. The key steps of the simulation are outlined, including OFDM transmission, channel estimation using LS and MMSE, and calculating the bit error ratio to compare performance of the estimation techniques.
LTE Physical Layer Transmission Mode Selection Over MIMO Scattering ChannelsIllaKolani1
Although LTE networks systems profits from recent advanced transmission techniques as MIMO systems, it encounters particularly two mains challenges:
MIMO channel Modeling or MIMO channel estimation .
An Optimal Dynamic MIMO transmission modes switching following the variation of MIMO Channel.
This Thesis proposes a channel model taking into account the motion of the UE first and after use this model to design an optimal transmission mode selection for 4G networks
A Peak to Average Power Ratio (PAPR) Reduction in OFDM SystemsIRJET Journal
This document discusses peak-to-average power ratio (PAPR) reduction techniques for orthogonal frequency division multiplexing (OFDM) systems. It begins with an introduction to OFDM and the problem of high PAPR values in OFDM signals. It then describes the clipping and filtering method and parabolic peak cancellation method for PAPR reduction. It analyzes these techniques by evaluating complementary cumulative distribution function (CCDF) curves and bit error rate (BER) with the goal of minimizing PAPR while maintaining acceptable BER. Power amplifier nonlinearity is also discussed as a key factor affected by high PAPR OFDM signals.
Performance and Analysis of OFDM Signal Using Matlab SimulinkIJMER
Multi-carrier modulation is an attractive technique for fourth generation .OFDM is based on
multicarrier modulation technique. In OFDM system the bit stream is divided into many different sub
channels. An efficient and distortionless scheme for peak power reduction in OFDM is proposed. In this
paper, a set of mapping where the actual transmit signal is selected. From this set of signal reduced
PAPR. Simulation results are shown. The lowest PAPR is compared with conventional work. It is also
compared BER to SNR and best result is achieved.
This document discusses the effects of time offset (TO) and carrier frequency offset (CFO) on orthogonal frequency division multiplexing (OFDM) systems and proposes interference cancellation techniques. It introduces the OFDM system model and how CFO causes loss of orthogonality between subcarriers, resulting in inter-carrier interference (ICI) that degrades performance. The paper proposes an ICI reduction scheme using self-cancellation and evaluates its performance compared to standard OFDM. It also discusses using space-time block coding (STBC) with OFDM to improve performance by reducing bit error rate (BER) under different signal-to-noise ratios. Simulation results show STBC effectively mitigates the effects of inter-
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
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.
PAPR REDUCTION OF OFDM SIGNAL BY USING COMBINED HADAMARD AND MODIFIED MEU-LAW...IJCNCJournal
Orthogonal frequency division multiplexing (OFDM) is a technique which gives high quality of service (QOS) to the users by mitigating the fading signals as well as high data rates in multimedia services. However, the peak-to-average power ratio (PAPR) is a technical challenge that reduces the efficiency of RF power amplifiers. In this paper, we propose the combined Hadamard transform and modified meu-law companding transform method in order to lessen the effects of the peak-to-average power ratio of the
OFDM signal. Simulation results show that the proposed scheme reduces PAPR compared to other companding techniques as well as the Hadamard transform technique when used on its own.
1. The document analyzes the effect of signal distortion techniques for PAPR reduction like clipping and peak windowing on the bit error rate (BER) performance of turbo and low density parity check (LDPC) coded orthogonal frequency division multiplexing (OFDM) systems.
2. It implements an OFDM system based on IEEE 802.11a standards with turbo and LDPC error correcting codes over additive white Gaussian noise (AWGN) and exponentially decaying Rayleigh fade channels.
3. The results show that LDPC-COFDM performs better than turbo-COFDM in both channels, even with clipping applied. However, turbo-COFDM is better with peak windowing due to
Comparative Analysis of Distortive and Non-Distortive Techniques for PAPR Red...IDES Editor
OFDM is a popular and widely accepted modulation
and multiplexing technique in the area of wireless
communication. IEEE 802.15, a wireless specification defined
for WPAN is an emerging wireless technology for short range
multimedia applications. Two general categories of 802.15
are the low rate 802.15.4 (ZigBee) and high rate 802.15.3
(UWB). In their physical (PHY) layer design, OFDM is a
competing technique due to the various advantages it renders
in the practical wireless media. OFDM has been a popular
technique for many years and adopted as the core technique
in a number of wireless standards. It makes the system more
immune to interference like InterSymbol Interference (ISI)
and InterCarrier Interference (ICI) and dispersive effects of
the channel. It is also a spectrally efficient scheme since the
spectra of the signal are overlapping in nature. Despite these
advantages OFDM suffers from a serious problem of high
Peak to Average Power. This limits the system’s capabilities
and increases the complexity. This paper compares the signal
distortion technique of Amplitude Clipping and the
distortionless technique of SLM for Peak to Average Power
reduction
1) OFDM uses multiple carriers to transmit data in parallel. It can be described mathematically using the Fourier transform which relates events in the time and frequency domains.
2) At the transmitter, the signal is defined in the frequency domain using a discrete Fourier transform and generated using the inverse discrete Fourier transform. This allows the carriers to be orthogonal.
3) A guard interval is added between symbols to prevent intersymbol interference from multipath distortion. This increases the symbol duration and provides timing tolerance at the receiver.
This document discusses various channel estimation techniques for OFDM systems. It describes pilot structures like block, comb and lattice types and how they are suited for different channel conditions. It also explains training symbol based channel estimation techniques like LS and MMSE. DFT-based channel estimation aims to improve performance by eliminating noise outside the channel delay. Decision directed channel estimation updates the channel coefficients without pilots by using detected signal feedback.
Performance analysis of Multiband - OFDM systems using LDPC coder in pulsed -...IDES Editor
In this paper, a combined approach where low density
parity check (LDPC) codes are used to reduce the complexity
and power consumption of pulsed orthogonal frequencydivision
multiplexing (pulsed-OFDM) ultra-wideband (UWB)
systems is described. The proposed system uses LDPC codes
to achieve higher code rates without using convolution
encoding and puncturing thereby reducing the complexity and
power consumption of pulsed-OFDM system. The LDPCpulsed-
OFDM system achieves channel capacity with different
code rates and has good performance in different channel
fading scenarios. The pulsed OFDM system is used where
pulsed signals could spread the frequency spectrum of the
OFDM signal. The performance of LDPC-pulsed-OFDM
system for wireless personal area networks (WPAN) is
analyzed for different UWB indoor propagation channels (CM3
and CM4) provided by the IEEE 802.15.3a Standard activity
committee. To establish this, a design of LDPC-pulsed-OFDM
system using the digital video broadcasting-satellite-second
generation (DVB-S2) standard and provide the simulation
results for the different code rates supported by LDPC codes
is presented.
This document summarizes a student project on OFDM transmitters and receivers. It includes an introduction to OFDM that describes its use of orthogonal subcarriers. It also compares single carrier modulation to multi-carrier modulation using OFDM. The document outlines the basic OFDM transmitter and receiver block diagrams. It discusses the constellation mapper, IFFT block, cyclic prefix, and design approaches for these blocks. Simulation results are presented comparing transmitted and received signals. BER performance is evaluated for different modulation schemes like QPSK and QAM. The document concludes that OFDM provides high bandwidth efficiency and overcomes interference through the IFFT and cyclic prefix.
This document provides an overview of OFDM (Orthogonal Frequency Division Multiplexing) including:
1. The basic principles of OFDM including modulation using IDFT and demodulation using DFT.
2. How a cyclic prefix is used to mitigate multipath interference.
3. A block diagram of a basic OFDM system showing key components like mapping, IFFT/FFT, insertion of cyclic prefix, and demapping.
4. Examples of OFDM parameters used in standards like IEEE 802.11a.
This document summarizes research on reducing peak-to-average power ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) systems. It discusses using a companding technique with Gaussian distribution to compress the signal before transmission and decompress it upon reception. The key aspects covered are: applying a compander and decompander with Gaussian distribution parameters at the transmitter and receiver; how the central limit theorem allows the sum of subcarriers to approximate a Gaussian distribution for large numbers; and how this technique reduces PAPR by increasing average power while keeping peak power the same. Performance is analyzed by simulating PAPR and bit error rate with and without companding under different parameters.
This document summarizes a research paper that investigates the effect of different orthogonal frequency division multiplexing (OFDM) transmission modes on the performance of carrier frequency offset (CFO) estimation using a cyclic prefix-based synchronization technique. Five transmission modes are tested (0.25K, 0.5K, 1K, 2K, 4K) by developing an OFDM system simulation in MATLAB. The results show that synchronization performance, as measured by mean squared error of CFO estimation, improves with increasing transmission mode/IFFT size but requires more estimation time. Larger transmission modes provide better frequency synchronization.
Performance Analysis of M-ary Optical CDMA in Presence of Chromatic DispersionIDES Editor
The performance of M-ary optical code division
multiple access (OCDMA) is analytically investigated in
presence of chromatic dispersion. The study is carried out for
single mode dispersion shifted and non dispersion shifted
fibers. Walsh code is used as user address. The p-i-n
photodetector is used for optoelectronic conversion process.
In our proposed model 16 different symbols are modulated
with different intensity levels and detected by direct detection
technique. The numerical results show that, the reconstruction
of the transmitted symbol is strongly dependent on the received
symbols magnitude which is reduced by fiber length and
symbol rate. It is found that the proposed OCDMA system
shows better performance when dispersion shifted fiber is
used as a communication medium.
The document analyzes friction stir welding tools with various threaded pin profiles. Three tool pin profiles are modeled in CATIA and analyzed using ANSYS: cylindrical, frustum, and conical pins with threads. The stress distributions and displacement vectors in the pins are obtained for different rotational speeds and temperatures. The results show that the cylindrical pin profile experiences the lowest stress levels and displacement compared to the other profiles. Increasing rotational speed does not significantly affect the stress, while higher temperatures generally increase stress across all pin profiles. The cylindrical pin profile is determined to be preferable for withstanding loads during friction stir welding.
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
El documento presenta una serie de fotos de la ciudad de San Petersburgo, Rusia. Muestra lugares históricos como el Palacio de Invierno, el Hermitage, la Catedral de Kazán, el Palacio Peterhof y otros. También incluye detalles arquitectónicos de estos lugares así como escenas de la vida diaria en San Petersburgo.
Este documento presenta un relato ficticio sobre un grupo de jóvenes que salen de fiesta y terminan en una playa con tres chicas. Describe su comportamiento agresivo y misógino, y sugiere que planean agredir sexualmente a una de las chicas que está intoxicada.
Este documento trata sobre los caudales ecológicos en la cuenca del río Tajo en España. Se discuten los métodos hidrológicos y biológicos utilizados para determinar los caudales ecológicos, incluido el cálculo de medias móviles de caudales y el uso de curvas de hábitat preferido frente a caudal. También se analiza el proceso de concertación para establecer los caudales ecológicos y se proporciona una lista de masas de agua estratégicas en la cuenca.
El documento presenta las propuestas de AICI Argentina para los próximos 2 años. Propone capacitación continua a través de certificaciones internacionales y talleres, fomentar el networking entre profesionales de Sudamérica y España, y establecer alianzas estratégicas con otros capítulos. También busca posicionar a AICI como referente profesional, promover la ética y el voluntariado, y expandir la marca a través de la participación de los miembros.
Este documento apresenta a Lei 11.340/2006, conhecida como Lei Maria da Penha, que cria mecanismos para coibir a violência doméstica e familiar contra a mulher no Brasil. A lei define violência doméstica, estabelece formas de violência como física, psicológica, sexual, patrimonial e moral. Também trata de assistência à mulher em situação de violência, medidas de prevenção e integração de ações entre poderes para enfrentar o problema.
"Más allá del desarrollo sostenible: agua y límites de crecimiento" es el título de la ponencia del profesor Leandro del Moral en el VII Congreso Ibérico de la FNCA en Talavera de la Reina.
El documento presenta una breve introducción a los componentes electrónicos, incluyendo resistencias, que se oponen al paso de corriente eléctrica de acuerdo a la ley de Ohm, condensadores que almacenan energía eléctrica, y alternadores y dinamos que generan corriente eléctrica.
Actividad comunitaria veredas Carpintero y Porvenirjairnet5
Las mujeres ahorradoras de la vereda Carpintero organizaron un evento de bingo y celebración del Día de los Niños con el apoyo de la Junta de Acción Comunal y la Alcaldía Municipal para recaudar fondos y celebrar a la comunidad.
iTunes es un reproductor de medios desarrollado por Apple para reproducir, organizar y sincronizar iPods, iPhones, iPads y comprar música. Es compatible con sistemas operativos Mac OS X y Windows y permite a los usuarios organizar su música, editar archivos, grabar CD, comprar música en línea y crear listas de reproducción inteligentes.
O documento apresenta um exercício de percepção visual que pede para os alunos observarem uma ilustração por alguns instantes e depois responderem a perguntas sobre os detalhes da imagem com SIM ou NÃO. O objetivo é treinar a percepção dos alunos.
El documento resume un dictamen preliminar sobre el Anteproyecto de Plan Hidrológico Nacional presentado al Consejo Nacional del Agua en septiembre de 2000. Señala que el plan tiene un enfoque estructuralista anticuado y poco equilibrado, con un énfasis excesivo en la regulación de aguas superficiales y un olvido de las aguas subterráneas. También indica que el plan carece de transparencia sobre los regadíos con aguas subterráneas y que los déficits hídricos propuestos pare
Geólogos del Mundo está buscando contratar a un técnico de proyecto para trabajar en un proyecto de fortalecimiento de capacidades locales para la gestión del riesgo de desastres en El Salvador. El proyecto tiene como objetivo mejorar la calidad de vida de la población a través de una mejor gestión del riesgo de desastres a nivel municipal. El técnico de proyecto será responsable de la ejecución técnica del proyecto, incluyendo la recopilación de información sobre amenazas, la construcción de un sistema
Este documento resume las biografías de tres personas muy influyentes: Bill Gates, Warren Buffett y Carlos Slim. Detalla los orígenes humildes de Gates y cómo co-fundó Microsoft después de crear uno de los primeros lenguajes de programación para computadoras personales. Explica cómo Buffett se convirtió en uno de los inversionistas más exitosos a través de su enfoque value investing. También resume la vida de Slim y cómo construyó un imperio de telecomunicaciones en México.
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
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
Performance evaluation on the basis of bit error rate for different order of ...ijmnct
This document summarizes research evaluating the bit error rate (BER) for different modulation orders and subchannel lengths in an orthogonal frequency division multiplexing (OFDM) system. The research considers QPSK, 8-QAM, and 16-QAM modulation with 256, 512, and 4096 subchannels. Simulation results in MATLAB show that:
1) For 256 subchannels, QPSK modulation has the lowest BER across signal-to-noise ratio (SNR) values from 0-27dB.
2) BER increases with higher modulation orders (from QPSK to 16-QAM) for a given subchannel length.
3) The research provides a comparative analysis of BER performance in an OFDM system
Performance Analysis of MIMO-OFDM System Using QOSTBC Code Structure for M-PSKCSCJournals
This document discusses performance analysis of MIMO-OFDM systems using QOSTBC coding for M-PSK modulation. It proposes a QOSTBC code structure for a 4x4 antenna configuration MIMO-OFDM system. It analyzes the performance of the system in AWGN and Rayleigh channels by evaluating BER versus SNR for different M-PSK modulation schemes and antenna configurations. The proposed MIMO-OFDM system with 4x4 QOSTBC coding is shown to have better performance than other systems in terms of lower BER for a given SNR.
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.
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
Ofdm-cpm Ber Performance and FOBP Under IEEE802.16 ScenarioCSCJournals
This document discusses the performance of OFDM-CPM (orthogonal frequency division multiplexing-continuous phase modulation) under IEEE 802.16 scenarios. It shows that OFDM-CPM can exploit frequency diversity in multipath channels unlike conventional OFDM. Simulation results over multipath Stanford University Interim channel models show that OFDM-CPM with an MMSE equalizer outperforms Rayleigh fading channels by exploiting multipath diversity. The document also compares the spectral properties and bit error rate performance of OFDM-CPM to conventional OFDM.
This document reviews the OFDM-IDMA technique and its implementations. It begins with introductions to OFDM and OFDM-IDMA. OFDM-IDMA uses interleaving instead of spreading sequences to distinguish users, avoiding bandwidth expansion without coding gain. The document then summarizes various implementations of OFDM-IDMA using discrete wavelet transform, MIMO systems, and implementations on FPGA. It also discusses implementations using finite Radon transform and discrete wavelet transform. Finally, it proposes future work on implementing OFDM-IDMA using Radon transform and performing comparative analysis of wavelet, FFT, and Radon-based OFDM-IDMA systems over AWGN and Rayleigh fading channels.
Reduction of Outage Probability in Fast Rayleigh Fading MIMO Channels Using OFDMIJERA Editor
1) The document presents research on reducing outage probabilities in MIMO systems operating in fast fading channels using OFDM modulation.
2) Simulation results show that a MIMO-OFDM system provides significant reduction in outage probabilities compared to a conventional MIMO system without OFDM. For example, with a 2x2 antenna configuration and SNR threshold of 5dB, MIMO-OFDM had a 41.38% lower outage probability than MIMO alone.
3) The outage probability is also reduced as the number of antennas increases for a MIMO-OFDM system. For instance, with a transmitted SNR of 10dB, configurations with 2x3, 3x3 and 4x4 antennas had outage probabilities of
Design Ofdm System And Remove Nonlinear Distortion In OFDM Signal At Transmit...Rupesh Sharma
although OFDM seems to be a solution to keep up with
the demand of increasing data rates, it has some drawbacks.
Sensitivity to high PAPR is the most significant of these
drawbacks. The main objective of this paper was to investigate
and document the effects of PAPR on the performance of OFDM
based digital communications under different channel conditions.
A step-by-step approach was adopted in order to achieve the
objective of this paper. The first step is to provide a basic
background on the principles of OFDM. The reasons for the
PAPR and a theoretical analysis of these effects on OFDM
systems are documented. The OFDM system has a high peak-toaverage
power ratio (PAPR) that can cause unwanted saturation
in the power amplifiers, leading to in-band distortion and out-ofband
radiation. To be able to observe the system behavior, the
simulation results for different channel models are presented in
graphical form. Next, the simulation results obtained in this work
are compared to the simulation results reported in related studies
Peak-to-Average Power Ratio Reduction in NC-OFDM based Cognitive Radio.CSCJournals
This document summarizes a research paper that proposes a technique for reducing peak-to-average power ratio (PAPR) in non-contiguous band spectrum of orthogonal frequency division multiplexing (OFDM) based cognitive radio systems. The proposed system uses repeated clipping and filtering at the transmitter to reduce PAPR. Simulation results show that higher order modulation schemes like 16-QAM achieve better PAPR reduction compared to lower order schemes like BPSK and QPSK. Bit error rate performance evaluations indicate higher signal-to-noise ratios are needed to achieve the same error rates when using PAPR reduction techniques.
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.
The document discusses Coherent Optical OFDM (CO-OFDM) and analyzes its performance at different data rates such as 1Gbps, 20Gbps, and 100Gbps. 4QAM-OFDM signals are generated and transmitted through 250km of fiber. The results show that distortions in the OFDM spectrum and QAM constellations increase as the data rate increases, due to nonlinearities in the fiber. CO-OFDM has advantages over other modulation formats as it provides both coherent detection and OFDM modulation, but its performance is affected by fiber nonlinearities at high data rates due to its high peak-to-average power ratio.
CS Based Channel Estimation for OFDM Systems under Long Delay Channels Using ...IJERA Editor
Orthogonal frequency division multiplexing (OFDM) is a technique which are used in the next-generation wireless communication. Channel estimation in the OFDM technique is one of the big challenges, ever since high-resolution channel estimation can significantly improve the equalization at the receiver and consequently enhance the communication performances. Channel computation using superimposed pilot sequences is also a fully new area, idea for using superimposed pilot sequences has been proposed by various authors for different applications. In this paper, we are introduced a high accurate, low complexity compressive sensing (CS) based channel estimation namely Auxiliary information based Subspace Pursuit (ASP) in TFT-OFDM systems. ASP based channel estimation in TFT-OFDM system is based on two steps. First is, by exploiting the signal structure of recently proposed TDM-OFDM scheme, the supporting channel information is obtained. Second is, we propose the supporting information based subspace pursuit (SP) algorithm to use a very small amount of frequency domain pilots embedded in the OFDM block used for the exact channel estimation. Moreover, the obtained auxiliary channel information is adopted to reduce the complexity of the conventional SP algorithm. Simulation results demonstrate a important reduction of the number of pilots relative to least-squares channel estimation and supporting high-order modulations like 256 QAM.
IRJET- Orthogonal Frequency Division Multiplexing (OFDM) based Uplink Multipl...IRJET Journal
This document discusses Orthogonal Frequency Division Multiplexing (OFDM) for uplink transmission over different channel conditions. It begins by introducing OFDM and how it splits data across multiple narrowband carriers to mitigate intersymbol interference. It then discusses using QPSK modulation with OFDM. Next, it analyzes OFDM performance over additive white Gaussian noise (AWGN) channels and different fading channels like Rayleigh and Rician fading. It finds that BER decreases with increasing SNR in AWGN channels, and the amount of fading impacts BER in fading channels. Simulation results using MATLAB show the effect of different channels on OFDM signals.
Design and Fabrication of a Two Axis Parabolic Solar Dish CollectorIJERA Editor
The work consists of the design of the chain drive system and the fabrication of the two axis parabolic solar dish.
It is a model study of the two axis parabolic dish which worked by the automatic circuit that was developed. Ready
made parabolic solar dish is taken and fabricated. The circular iron ring provides the two axis motion of the dish.
A compound chain drive system was developed for the smooth movement of the dish. An electromechanical
system which tracks the sun on both axes and which is controlled via a programmable logic control (PLC) was
designed and implemented. In this a theoretical study was done. A C program was made which gave the required
result for the graphical representation of the recorded radiation. Programmable Logic Controls (PLC) was used
instead of photo sensors, which are widely used for tracking the sun. The azimuthal angle of the sun from sunrise
to sunset times was calculated for each day of the year at 23.59 Lat & 72.38Longitude in the Northern hemisphere,
the location of the city Mehsana. According to this azimuth angle, the required analog signal was taken from the
PLC analog module and sent to the power window motor, which controlled the position of the panel to ensure that
the rays fall vertically on the panel. After the mechanical control of the system was started, the performance
measurements of the solar panel were carried out. The values obtained from the measurements were compared and
the necessary evaluations were conducted.
Analysis of Peak to Average Power Ratio Reduction Techniques in Sfbc Ofdm SystemIOSR Journals
This document summarizes techniques to reduce peak-to-average power ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) systems. It analyzes applying selected mapping (SLM) and clipping with differential scaling techniques to space frequency block coded (SFBC) OFDM systems. SLM generates alternative representations of OFDM symbols by rotating frames with different phase sequences and selects the one with minimum PAPR. Clipping clips signal amplitudes above a threshold and differential scaling scales different amplitude ranges differently to reduce PAPR without degrading bit error rate. Simulation results show SLM and clipping with scaling effectively reduce PAPR.
This document discusses the bit error rate (BER) performance of orthogonal frequency division multiplexing (OFDM) in cognitive radio networks over Rayleigh fading channels. It analyzes the signal to noise ratio of OFDM and proposes two pulse shaping approaches, improved sinc power pulses and raised cosine filters, to reduce inter-carrier interference and minimize BER. Simulation results using MATLAB show that applying these inter-carrier interference cancellation schemes can improve BER performance.
COMPARISON OF BER AND NUMBER OF ERRORS WITH DIFFERENT MODULATION TECHNIQUES I...Sukhvinder Singh Malik
This paper provides analysis of BER and Number of Errors for MIMO-OFDM wireless communication system by using different modulation techniques. Wireless designers constantly seek to improve the spectrum efficiency/capacity, coverage of wireless networks, and link reliability. So the performances of the wireless communication systems can be enhanced by using multiple transmit and receive antennas, which is generally referred to as the MIMO technique. Here analysis will be carried out for an OFDM wireless communication system using different modulation techniques and considering the effect and the wireless channel like AWGN, fading. Performance results will be evaluated numerically and graphically using the plots of BER versus SNR and plots of number of errors versus SNR.
1) The document presents channel estimation methods for MIMO-OFDM systems using QPSK modulation.
2) It compares the performance of least squares (LS), minimum mean square error (MMSE) and discrete Fourier transform (DFT) based channel estimation techniques.
3) The analysis finds that applying DFT to the estimated channel power improves the performance of the channel estimators.
1. Sanjay Kumar Khadagade, Poornima Raikwar / International Journal of Engineering Research
and Applications (IJERA) ISSN: 2248-9622 www.ijera.com
Vol. 3, Issue 1, January -February 2013, pp.784-792
Performance of OFDM QPSK, 16-QAM System using Pilot-Based
Channel Estimation in presence of Doppler Frequency Shift over
Rayleigh Fading Channel
Sanjay Kumar Khadagade#1, Poornima Raikwar *2
# *
(Electronic and Communication, RGPV, Bhopal (M.P.) India)
Abstract—
With the rapid growth of digital
communication in recent year the need for high Pilot-based channel estimation estimates the channel
speed data transmission is increased, OFDM is a information by obtaining the impulse response from
promising solution for achieving high data rates in all sub-carriers by pilot. Compared with blind
mobile environment, due to its resistance to ISI channel estimation, which uses statistical information
and ICI, which are the common problems found of the received signals, pilot-based channel
in high speed data communication. In this paper, estimation is a practical and an effective method.
the performance of different pilot based channel The pilot based channel estimation can be
estimation schemes for OFDM with QPSK and 16 performed by either inserting pilot tones into all of
QAM over Rayleigh fading channel are the subcarriers of OFDM symbols with a specific
investigated. In the block type pilot arrangement, period or inserting pilot tones into each OFDM
the performance of channel estimation is analyzed symbol. The first one, block type pilot channel
with three different algorithms: LS, LMMSE and estimation, has been developed under the assumption
SVD algorithm. In comb type pilot arrangement, of slow fading channel. Even with decision feedback
the paper introduces three method of equalizer, this assumes that the channel transfer
interpolation: linear interpolation, second order function is not changing very rapidly. The estimation
interpolation and cubic spline interpolation for of the channel for this block-type pilot arrangement
channel estimation. Here in this paper, it is our can be based on Least Square (LS) or Minimum
goal to show the way through which the Bit Error Mean-Square-Error (MMSE). The MMSE estimate
Rate (BER) result varies due to Doppler has been shown to give 10–15 dB gain in signal-to-
frequency shift. The analysis has been carried out noise ratio (SNR) for the same mean square error of
with simulation studies under MATLAB channel estimation over LS estimate [2]. In [3], a
environment. low-rank approximation is applied to linear MMSE
Keywords- BER, Doppler Frequency, OFDM, Pilot by using the frequency correlation of the channel to
Carrier. eliminate the major drawback of MMSE, which is
complexity. The later, the comb-type pilot channel
I. INTRODUCTION estimation has been introduced to satisfy the need for
For high-volume and high-speed wireless equalizing when the channel changes even in one
mobile communication systems, Orthogonal OFDM block. The comb-type pilot channel
Frequency Division Multiplexing (OFDM) is a estimation consists of algorithms to estimate the
promising modulation scheme, and will play an channel at pilot frequencies and to interpolate the
increasingly important role in the future development channel. MMSE has been shown to perform much
of wireless mobile communication network due to its better than LS. In [4], the complexity of MMSE is
high data rate transmission capability with high reduced by deriving an optimal low-rank estimator
bandwidth efficiency and its robustness to multi-path with singular-value decomposition (SVD).
delay and no Inter Symbol Interference (ISI). It has The interpolation of the channel for comb-
been used in wireless LAN standards such as type based channel estimation can depend on linear
American IEEE802.11a and the European equivalent interpolation, second order interpolation and spline
HIPERLAN/2 and in multimedia wireless services cubic interpolation. In [4], second-order interpolation
such as Japanese Multimedia Mobile Access has been shown to perform better than the linear
Communications. interpolation. In [5], cubic spline interpolation has
When the mobile station is doing communication been proven to give lower BER compared to second
in motion, the frequency of the received signal will order interpolation.
change. In multipath conditions, each multipath wave In this paper, our aim is to compare the
has a frequency shift, called Doppler spread. The performance of all of the above schemes by applying
shift of the mobile received signal frequency caused 16QAM (16 Quadrature Amplitude Modulation),
by the movement is called Doppler frequency shift, QPSK (Quadrature Phase Shift Keying), as
and it is proportional to the speed of mobile users. modulation schemes with multipath Rayleigh fading
and Doppler frequency shift channels with Additive
784 | P a g e
2. Sanjay Kumar Khadagade, Poornima Raikwar / International Journal of Engineering Research
and Applications (IJERA) ISSN: 2248-9622 www.ijera.com
Vol. 3, Issue 1, January -February 2013, pp.784-792
White Gaussian Noise (AWGN) as channel models. where w n is AWGN and h n is the
In Section II, the description of the OFDM
transceiver based on pilot channel estimation, channel impulse response. The channel response
channel modal and QPSK, 16QAM is given. In h n can be represented by [5]:
Section III, the estimation of the channel based on
block-type pilot arrangement is discussed. In Section r 1
IV, the estimation of the channel at pilot frequencies
h n hi e j 2 / N f DiTn 𝛿 ( ʎ-τi),
is presented. In Section VI, the simulation
i 0
environment and results are described. Section VI
concludes the paper. 0 n N 1 (4)
where r is the total number of propagation paths, hi
th
II. SYSTEM MODEL is the complex impulse response of the i path, f Di
th
In this section we cover the basic of OFDM is the i path Doppler frequency shift, ʎ is delay
system block diagram and working. And see the spread index, T is the sample period and τi is the
modulation method and channel that use in our
simulation. i th path delay normalized by the sampling time. At
the receiver, after passing to discrete domain through
A. OFDM Block Diagram A/D and low pass filter, guard time is removed:
The OFDM system based on pilot channel y f n for N g n N 1
y n y f n Ng
estimation is given in Fig. 1.
The binary information is first grouped and n 0,1, 2....., N 1
mapped according to the modulation in “signal (5)
mapper.” After inserting pilots either to all sub-
carriers with a specific period or uniformly between Then y n is sent to DFT block for the following
the information data sequence, IDFT block is used to operation:
transform the data sequence of length N X k
into time domain signal x n with the following
equation:
x n IDFT x k , n 1,2,..., N 1
N 1
X k e
j 2 kn / N
(1)
k 0
Where N is the DFT length. We used inverse fast
Fourier transform/fast Fourier transform (IFFT/ FFT)
in place of IDFT/DFT to reduce computation
complexity. Following IDFT block, guard time,
which is chosen to be larger than the expected delay
spread, is inserted to prevent ISI. This guard time
includes the cyclically extended part of OFDM
symbol in order to eliminate inter-carrier interference Fig.1. OFDM system for simulation
(ICI). The resultant OFDM symbol is given as [1].
follows: Y k DFT y n k 0,1, 2....., N 1.
N 1
x N n ,
n N g , N g 1,..., 1
1
y n e
j 2 kn / N
x f n
. (6)
N
x n ,
n 0
n 0,1,......, N 1 Assuming there is no ISI shows the relation of the
(2) resulting Y k to H k = DFT h n , I k
Where N g is the length of the guard interval. The
that is ICI because of Doppler frequency and
transmitted signal x f n will pass through the w k DFT w n , with the following
frequency selective time varying fading channel with equation [4]:
additive noise. The received signal is given by:
Y k X k H k I k W k , k 0,1...., N 1
y f n x f n h n w n (3)
(7)
where
785 | P a g e
3. Sanjay Kumar Khadagade, Poornima Raikwar / International Journal of Engineering Research
and Applications (IJERA) ISSN: 2248-9622 www.ijera.com
Vol. 3, Issue 1, January -February 2013, pp.784-792
sin f DiT
r 1 j f DiT
H k hi e f DiT j 2 i / N k
e ,
i 0
r 1 N 1
hi X K 1 e j 2 f DiT k K j 2 i / N K
I k e .
i 0 K 0, N 1 e j 2 / N f DiT k K
K k
Following DFT block, the pilot signals are
extracted and the estimated channel He k for the
data sub-channels is obtained in channel estimation
block. Then the transmitted data is estimated by:
Y k
Xe , k 0,1,,...., N 1 (8)
He k
Fig.2. Block type Pilot and Comb type pilot
Then the binary information data is obtained back in arrangement[2].
“signal demapper” block.
Emin means the energy of symbol with
B. M-ary PSK and 16QAM Modulation in OFDM
model minimum amplitude. ai , bi i 1, 2,....M 1 are a
The general analytic expression for M-ary PSK pair of independent integer numbers that could be
waveform is: determined by constellation.
si t A cos wct i t ; i 0,1, 2,..., M 1 C. Pilot arrangement
(14) The pilot channel estimation methods are based on
2 Es 2 m the pilot channel and pilot symbol. However, due to
Where A , , two-dimensional time-frequency structure of OFDM
Ts M system, pilot symbol assisted modulation (PSAM) is
m 0,1, 2,..., M 1 more flexible [6]. The fading channel of the OFDM
system can be viewed as a 2D lattice in a time-
The parameter E s is symbol energy, Ts is symbol frequency plane, because signal is transmitted in the
time duration, and 0 t T . For BPSK modulation, fixed position. And the 2D sampling should satisfy
𝑀=2, and for QPSK modulation 𝑀=4, and the the Nyquist sampling theorem in order to eliminate
modulation data signal shifts the phase of the the distortion. So the minimum limit of pilot symbols
inserted is decided by Nyquist theorem. From
waveform, si t . The BPSK bandwidth efficiency Nyquist theorem, the interval of time domain N t and
is 1 bit/Hz, while QPSK bandwidth efficiency is 2
bits/Hz. frequency domain N f should satisfy [7]
16-QAM is a one type of M-ary QAM, where f m .T .N t 1/ 2 , and
M = 16. In 16-QAM modulation scheme we can send
(k = log2M = log216 = 4) 4 bit information per max .w f .N f 1/ 2
symbol. The general analytic expression for M-ary
Where w f is bandwidth of sub-carrier, T is period of
QAM waveform is:
signal, τmax is the maximum multipath time delay and
si t Emin ai cos 2 fct Emin bi sin 2 fct
fm is the maximum Doppler shift.
The two basic channel estimations in OFDM
(15) systems, block-type pilot and comb-type pilot, are
illustrated in Fig.2. In the block-type pilot channel
estimation, we inserting pilot tones into all
subcarriers of OFDM symbols with a specific period
in time and in comb-type pilot channel estimation, we
inserting pilot tones into certain subcarriers of each
OFDM symbol, where the interpolation is needed to
estimate the conditions of date subcarriers.
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and Applications (IJERA) ISSN: 2248-9622 www.ijera.com
Vol. 3, Issue 1, January -February 2013, pp.784-792
Y Y 0 Y 1 .......Y N 1
D. Channel Model T
In simulation, we take three OFDM channel model:
W W 0 W 1 ......W N 1
AWGN channel, Rayleigh fading channel and T
Doppler spread channel model. In a multipath
environment, it is reasonably intuitive to visualize
that an impulse transmitted from the transmitter will
reach the receiver as a train of pulses. When there are
large numbers of paths, applying Central Limit
Theorem, each path can be modeled as circularly
complex Gaussian random variable with time as the
variable. This model is called Rayleigh fading
channel model in Fig.3. A circularly symmetric
complex Gaussian random variable is of the form,
Z X jY (9)
where real and imaginary parts are zero mean
independent and identically distributed Gaussian
random variables. For a circularly symmetric
complex Gaussian random variable 𝑍, Fig. 3 Rayleigh channel model.
𝑍 which has a probability density,
E z E ei Z ei E z
(10)
H H 0 H 1 .......H N 1 DFTN h
T
The statistics of a circularly symmetric complex
Gaussian random variable is completely specified by
WN WN
0 N 1
the variance, E z Now, the magnitude
2 2 00
z2 F
z 2
p z 3 e 2 z0 (11) N 10 N 1 N 1
WN
WN
is called a Rayleigh random variable. This model
called Rayleigh fading channel model, is reasonable 1 j 2 n / N k
and WN
nk
for an environment where there are large number e .
reflectors. The channel impulse response (CIR) of N
Rayleigh multipath channel could be expressed as, If the time domain channel vector h is Gaussian
L 1 and uncorrelated with the channel noise W , the
h t , uk e jk t k (12) frequency domain MMSE estimate of h is given by
k 0
[3]:
where L is the number of multipath, τk is delay of the
j H MMSE FRhY RYY1Y (17)
kth path, u k e k is gain coefficient, respectively. For
where
Doppler spread channel CIR is given by,
RhY E hY Rhh F H X H
h t ue j e j 2 fDt (13)
RYY E YY XFRhh F H X H 2 I N (18)
III. CHANNEL ESTIMATION BASED ON are the cross covariance matrix between h and Y and
BLOCK –TYPE PILOT ARRANGEMENT
the auto covariance matrix of Y. Rhh is the auto-
In block-type pilot based channel estimation,
covariance matrix of h and σ2 represent the noise
.
OFDM channel estimation symbols are transmitted
E W k
2
periodically, in which all sub-carriers are used as variance The LS estimate is
pilots. If the channel is constant during the block,
there will be no channel estimation error since the represented by:
pilots are sent at all carriers. The estimation can be H LS X 1Y , (20)
performed by using either LS or MMSE [2], [3]. If
which minimizes Y XFh Y XFh .
H
ISI is eliminated by the guard interval, we write (7)
in matrix notation: Since LS estimate is susceptible to noise and ICI,
Y XFh W (16) MMSE is proposed while compromising complexity.
where Since MMSE includes the matrix inversion at each
X diag X 0 , X 1 ,.....X N 1 iteration, the simplified linear MMSE estimator is
suggested in [8]. In this simplified version, the
inverse is only need to be calculated once. In [4], the
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5. Sanjay Kumar Khadagade, Poornima Raikwar / International Journal of Engineering Research
and Applications (IJERA) ISSN: 2248-9622 www.ijera.com
Vol. 3, Issue 1, January -February 2013, pp.784-792
complexity is further reduced with a low-rank 0 H
approximation by using singular value decomposition. H SVD U p U H LS . (24)
Assuming the same signal constellation on all 0 0
tones and equal probability on all constellation points where p is the upper left p * p corner of .
we get,
A block diagram of the rank-p estimator in (24) is
1
E X X E
H
2
I shown in
Fig. 3, where the LS-estimator is calculated from y
| X k |
by multiplying by X 1 .
and average Signal to Noise Ratio (SNR) is
SNR E | X k |2 / N , the term N X H X
2 1
2
IV. CHANNEL ESTIMATION BASED ON
is the COMB-TYPE PILOT ARRANGEMENT
In Comb-type pilot based channel estimation, an
approximated by I , where efficient interpolation technique is necessary in order
SNR to estimate
E | X k | 2
. (21)
1 2
E | |
Xk
β is a constant which depends only on the signal
constellation for QPSK and 16-QAM. Then the
modified MMSE estimator in terms of Linear-MMSE
is given by:
1
H LMMSE RHH RHH I H LS . (22)
SNR
Since LS estimate is susceptible to noise and ICI, Fig.4 Block diagram of the rank-p channel estimator
MMSE is proposed while compromising complexity. [3].
Since MMSE includes the matrix inversion at each
iteration, the simplified linear MMSE estimator is channel at data sub-carriers by using the channel
suggested in [8]. In this simplified version, the information at pilot sub-carriers. Let N p pilot
inverse is only need to be calculated once. In [4], the
complexity is further reduced with a low-rank signals are uniformly inserted into X k according
approximation by using SVD. to the following equation:
The optimal rank reduction of the estimator in
(22), using the SVD, is obtained by exclusion of base
X k X mL l (25)
vectors corresponding to the smallest singular values xp m ,
l 0
[9]. We denote the SVD of the channel correlation
matrix: inf .data
l 1,......L 1
Rhh U U H (23) where L = number of carriers / N p and xp m is
where U is a matrix with orthonormal columns th
the m pilot carrier value. we define
u0 , u1 ,......u N 1 and is a diagonal matrix,
containing the singular values ʎ0 ʎ1 ≥ …… ʎN-1
H p k , k 0,1,....N p as the frequency
0 , on its diagonal. This allows the estimator in(22) response of the channel at pilot sub-carriers. The
to be written: estimate
of the channel at pilot sub-carriers based on LS
H SVD U U H H LS ,
estimation is given by:
where is a diagonal matrix containing the values
Yp
He k 0,1,...., N p 1 (26)
𝛿 k = ʎk / (ʎk + ), k 0,1,....., N 1. Xp
SNR
on its diagonal. The best rank – p approximation of where Ye k and X e k are output and input at
the estimator in (22) then becomes th
the k pilot sub carrier respectively.
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and Applications (IJERA) ISSN: 2248-9622 www.ijera.com
Vol. 3, Issue 1, January -February 2013, pp.784-792
The linear interpolation method is shown to
perform better than the piecewise-constant B. Simulation Results
interpolation in [9]. The channel estimation To analyze and compare the performances of
at the data-carrier k , mL < k < (m + 1)L , different channel estimation schemes for QPSK and
using linear interpolation is given by: 16QAM modulation in OFDM over Rayleigh fading
He k He mL l , 0 l L channel, we perform simulation using MATLAB.
Fig. 5 shows the BER performance of Block -
H p m 1 H p m
l type pilot based channel estimation in OFDM system
under 16QAM and QPSK modulation, we could find
L (27)
LMMSE with SVD rank p=16,20 have better
H p m performance over LS estimator. 16 QAM shows
The second-order interpolation is shown to worse performance. However, the bandwidth
fit better than linear interpolation [4]. The efficiency, 16QAM is more feasible in practice.
channel estimated by second-order
interpolation is given by: TABLE I:
SIMULATION PARAMETRES
He k He mL l Parameters Specification
Channel Bandwidth 1MHz
c1H p m 1 c0 H p m c1H p m 1 Number of Sub- 128
Carriers
(28)
IFFT/FFT size 128 bin points
1 Pilot Ratio 1/8
c1 , Guard Type Cyclic Extension
2
l Cyclic Prefix Length 16 Samples
where c0 1 1 , . Number of Multipath 5
N
c 1 .
Multipath Delays 0, 2e-6, 4e-6, 8e-6,
12e-6
1
2 Sub-Carrie Frequency 7.8125KHz
The cubic spline interpolation is shown to fit Spacing
better than second-order interpolation [4]. The SNR 40 dB
channel estimated by cubic spline interpola
H e k 1 H e m 1 0 H e m 1
Fig.6 shows that, the cubic spline interpolation
L1 H p m 1 L 0 H p m
' ' estimator has better performance than linear and
second order interpolation, when we used 16 QAM
(29) modulation. From Fig. 7 we can say that after
where H p m is the first order derivative of
'
performing MATLAB simulation with Block-type
pilot based channel estimation for QPSK modulation
H p m , in presence of Doppler spread, LS and LMMSE has
3 L l 2 L l
better performance over LMMSE (SVD) rank p=5.
2 3
1
L2 L3
and .
3l 2 2l 3
0 L2 L3
V. SIMULATION
A. System parameters for simulation
OFDM system parameters used in the simulation are
indicated in Table I: We assume to have perfect
synchronization since the aim is to observe channel
estimation performance. Moreover, we have chosen
the guard interval to be greater than the maximum
delay spread in order to avoid inter-symbol
interference. Simulations are carried out for different
sig SNR ratios and for different Doppler spreads.
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and Applications (IJERA) ISSN: 2248-9622 www.ijera.com
Vol. 3, Issue 1, January -February 2013, pp.784-792
Fig. 5. Comparison of QPSK and 16QAM under Fig. 7 Comparison of Block type under QPSK
Block type pilot(Doppler frequency = 40Hz) modulation(SNR=40db)
Fig. 6 Comparison of comb type under 16QAM
modulation(SNR=40db)
As seen in Fig. 8 the performances of BER for QPSK,
we can say that cubic spline interpolation has better Fig. 8 Comparison of comb type under QPSK
results over linear and second order interpolation, but modulation(SNR=40db)
cubic spline interpolation give fluctuating BER.
From Fig. 9 we see that, when we used interpolation
technique in place of block –type estimator we get
opposite results from Fig. 7, means for Comb –type
pilot estimator LS and LMMSE has worse
performances.
790 | P a g e
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and Applications (IJERA) ISSN: 2248-9622 www.ijera.com
Vol. 3, Issue 1, January -February 2013, pp.784-792
Fig. 9 Comparison of comb type under QPSK Fig. 11 Comparison of comb type under 16QAM
modulation(SNR=40db) modulation (Doppler frequency=80Hz)
VI. CONCLUSION
Finally in this paper, we conclude that, in
presence of Doppler frequency shift the performance
of OFDM system degrade. For higher Doppler spread,
BER increase, the reason is the existence of severe
ICI caused by Doppler shift. The simulation results
shows that, Comb-type pilot based channel
estimation with cubic spline interpolation for QPSK
and16QAM performs the best as compared to linear
and second order interpolation. For Block –type pilot
based channel estimation with LS and LMMSE
estimator gives better performance as compared to
LMMSE (SVD) rank p=5.
But when we used Block-type pilot for interpolation
estimator, linear and second order interpolation
perform better.
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