Mobile Communication system has been on high rampage for high data transmission over wireless
medium with various challenges caused by the transmission Channel. OFDM is been discovered in recent years
to deal with this problems because of its ability to elegantly cope with multipath interference. This paper
investigates the performance of different modulation schemes using M-ary Phase Shift Keying (M-PSK) and Mary
Quadrature Amplitude Modulation (M-QAM) in information transmission with OFDM technique over Ideal
channel AWGN and worst channel Rayleigh Fading channel in terms of Bits Error Rate (BER). Analysis was
made for different types of modulation schemes BPSK, QPSK, 4-QAM and 16-QAM gray coded bit mapping.
Also, a feasibility of OFDM been used to combat multipath fading was analyzed with comparison between a
single carrier technique and OFDM multicarrier technique. Variation between SNR results with respect to BER
is plotted to show the trade off differences between the modulation schemes with the result showing that OFDM
allows data transmission with minimal error over fading channel than a Single Carrier
Implementation and Study of Universal Filtered Multi Carrier under Carrier Fr...Editor IJAIEM
Sathiyapriya N.S
PG Student, Dept. of ECE, Periyar Maniammai University Thanjavur, Tamilnadu, India
ABSTRACT
OFDM is a matured technology and applied in various wireless standards. However they are not suitable for Uplink and this
technology is replaced by SC FDMA in 4G standards. Similarly Universal Filtered Multicarrier Communication (UFMC) is
another suitable technology for Multi user Uplink and for applications like cognitive radio. UFMC is a new, non-orthogonal,
waveform designed by Alcatel Lucent Labs which provide a much more efficient way of enabling networks to serve both
broadband users and very narrowband “short data” devices such as any embedded sensor or M2M module. In UFMC the
filtering of waveform is done on a group of subcarriers. In OFDM it is done on the whole subcarriers together. This reduces
the side lobe levels, inters carrier interference (ICI) and requires reduced filter length. Moreover Internet-of-Things where
Machine-Machine communication and applications where very tight response in time requirements are needed, OFDM
miserably fails. We examine impact of carrier frequency offset on the performance of the proposed scheme and compare the
results performance of cyclic prefix based orthogonal frequency division multiplexing(CP-OFDM) system.-
Key words: ICI,CFO,OFDM,UFMC
Single Mode Optical Fiber in Rof System Using DWDMIJERA Editor
Performance analysis was carried out to find the effect of crosstalk in a WDM system. Firstly, analysis of BER
was carried out without crosstalk. Then analysis of BER with crosstalk was done. Using equation for crosstalk,
number of channels was plotted using matlab. System parameters were optimized for a particular crosstalk.
Objective of the thesis work
Performance Analysis is carried out to find the effect of crosstalk due to optical cross connect in a DWDM
system considering a WDM based optical cross connect (OXC). An analysis is carried out to find the amount of
crosstalk due to OXC. The bit error rate performance degradation due to crosstalk is evaluated for OXC
parameter and number of wavelengths per fiber. The optimum parameters such as optimum number of channels
and hops are determined.
techInvestigations with mode division multiplexed transmissionelelijjournal
This article presents proposed topology for mode division multiplexed link with SPDML and VCSEL, modulate electrical signal of 820nm wavelength. Transmission performance has been investigated for numerous modes, bit rates (2.5 to 10Gbps), transmission lengths of MMF (1 to 100km) and attenuation factor in conjunction with parabolic operational mode. Results illustrated successful performance up to nine modes in mode-division multiplexed transmission. Performance is improved at low data rates, illustrated higher OSNR with lower BER,-5dB attenuation factor. Though, at higher bit rate and longer
transmission length received OSNR is unsteady. It further inferred that transmission with large number of multiplexed modes result in degraded performance, augmented with minimization of mode coupling losses.Mode division multiplexed multimode optical communication can be a viable option for supplementary capacity augment in the preexisting and future fiber optic communication links.
Implementation and Study of Universal Filtered Multi Carrier under Carrier Fr...Editor IJAIEM
Sathiyapriya N.S
PG Student, Dept. of ECE, Periyar Maniammai University Thanjavur, Tamilnadu, India
ABSTRACT
OFDM is a matured technology and applied in various wireless standards. However they are not suitable for Uplink and this
technology is replaced by SC FDMA in 4G standards. Similarly Universal Filtered Multicarrier Communication (UFMC) is
another suitable technology for Multi user Uplink and for applications like cognitive radio. UFMC is a new, non-orthogonal,
waveform designed by Alcatel Lucent Labs which provide a much more efficient way of enabling networks to serve both
broadband users and very narrowband “short data” devices such as any embedded sensor or M2M module. In UFMC the
filtering of waveform is done on a group of subcarriers. In OFDM it is done on the whole subcarriers together. This reduces
the side lobe levels, inters carrier interference (ICI) and requires reduced filter length. Moreover Internet-of-Things where
Machine-Machine communication and applications where very tight response in time requirements are needed, OFDM
miserably fails. We examine impact of carrier frequency offset on the performance of the proposed scheme and compare the
results performance of cyclic prefix based orthogonal frequency division multiplexing(CP-OFDM) system.-
Key words: ICI,CFO,OFDM,UFMC
Single Mode Optical Fiber in Rof System Using DWDMIJERA Editor
Performance analysis was carried out to find the effect of crosstalk in a WDM system. Firstly, analysis of BER
was carried out without crosstalk. Then analysis of BER with crosstalk was done. Using equation for crosstalk,
number of channels was plotted using matlab. System parameters were optimized for a particular crosstalk.
Objective of the thesis work
Performance Analysis is carried out to find the effect of crosstalk due to optical cross connect in a DWDM
system considering a WDM based optical cross connect (OXC). An analysis is carried out to find the amount of
crosstalk due to OXC. The bit error rate performance degradation due to crosstalk is evaluated for OXC
parameter and number of wavelengths per fiber. The optimum parameters such as optimum number of channels
and hops are determined.
techInvestigations with mode division multiplexed transmissionelelijjournal
This article presents proposed topology for mode division multiplexed link with SPDML and VCSEL, modulate electrical signal of 820nm wavelength. Transmission performance has been investigated for numerous modes, bit rates (2.5 to 10Gbps), transmission lengths of MMF (1 to 100km) and attenuation factor in conjunction with parabolic operational mode. Results illustrated successful performance up to nine modes in mode-division multiplexed transmission. Performance is improved at low data rates, illustrated higher OSNR with lower BER,-5dB attenuation factor. Though, at higher bit rate and longer
transmission length received OSNR is unsteady. It further inferred that transmission with large number of multiplexed modes result in degraded performance, augmented with minimization of mode coupling losses.Mode division multiplexed multimode optical communication can be a viable option for supplementary capacity augment in the preexisting and future fiber optic communication links.
Pilot Decontamination over Time Frequency and Space Domains in Multi-Cell Ma...IJECEIAES
In this article, we show that Pilot contamination problem can be seen as a source separation problem using time, frequency, and space domains. Our method capitalizes on a nonunitary joint diagonalization of spatial quadratic time-frequency (STFD) signal representation to identify the desired and interfering users. We first compute the noise subspace from the STFD matrices selected appropriately. Secondly, we use the noise subspace obtained to estimate the Elevation (El) and the Azimuth (Az) angles for which the MUSIC cost function is maximized. Numerical simulations are provided to illustrate the effectiveness and the behavior of the proposed approach.
PAPR Reduction in OFDM using Active and Non-Active ChannelsIOSR Journals
Abstract : According to the request of advance communication field there should be high data rate in addition to both power efficiency and lower bit error rate. This request of high data rate can be achieved by the multi carrier modulation scheme using the OFDM technique. But the great drawback of the OFDM technique is its high peak to average power ratio (PAPR). High PAPR reduces OFDM signals by driving the analog amplifier to work in the nonlinear region, changing this way the signal and making the amplifier to consume more power. To reduce the PAPR methods exist which adjust or present new signals to battle large signal peaks. The methods which use data carrying channels are called active channel methods and which use redundant channel are called non active channel methods. This work deals with reduction of the PAPR of OFDM signal using both Active and Non Active Channels. Clipping technique has been applied to active channels and Tone reservation has been applied to Non Active Channels. By using both channels we can get considerable reduction in PAPR. Keywords:Orthogonal Frequency Division Multiplexing (OFDM), Peak to Average Power Ratio (PAPR), Power Amplifier (PA).
Mitigation of non-linear four-wave mixing phenomenon in a fully optical commu...TELKOMNIKA JOURNAL
This paper aims to point out the nonlinear phenomenon occurring in coarse/dense wavelength division multiplex (C/D-WDM) systems. This phenomenon has to betaken into account during the design of the optical network itself, as wavelengthsin the optical fiber are constantly densified. The paper points out the emergence of the non-linear four-wave mixing (FWM) phenomenonand how it relates to the dispersion in the optical fiber together with the transmit power. The output of the paper is a proposed design of the system that points to the improvement of the bit error rate (BER) with a suitable choice of dispersion and suitable transmission power.
Comparison of Various Waveform Contenders of 5G Wireless Communication Based ...ijtsrd
This paper presents an extensive and fair comparison among the most promising waveform contenders for the 5G air interface which includes- Filtered OFDM, Filter-bank multi carrier (FBMC), universal filtered multi-carrier (UFMC) has been compared with OFDM in terms of spectral efficiency and bit error rate using mat lab. The disadvantages of OFDM have been addressed and it has shown that (fofdm), (UFMC), (FBMC) could be a more effective solution. FBMC is a method for improving out of band (OOB) characteristics by filtering each subcarrier, it is also expected to improve the Inter-Carrier Interference (ICI) characteristics while UFMC is a method for improving OOB characteristics by filtering each block. Raksha Vishnoi | Saurabh Gaur | Ashish Verma"Comparison of Various Waveform Contenders of 5G Wireless Communication Based on OFDM" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-2 | Issue-4 , June 2018, URL: http://www.ijtsrd.com/papers/ijtsrd15637.pdf http://www.ijtsrd.com/engineering/electronics-and-communication-engineering/15637/comparison-of-various-waveform-contenders-of-5g-wireless-communication-based-on-ofdm/raksha-vishnoi
OFDM allows tightly packed carriers to convey information orthogonally and with high bandwidth efficiency
Objectives Description:
Concepts
Basic idea
Introduction to OFDM
Implementation
Advantages and Drawbacks.
FDMA
Wavelet Packet based Multicarrier Modulation for Cognitive UWB SystemsCSCJournals
Orthogonal frequency division multiplexing (OFDM) is a multi-carrier modulation (MCM) scheme where the sub carriers are orthogonal waves. The main advantages of OFDM are robustness against multi-path fading, frequency selective fading, narrowband interference, and efficient use of spectrum. Recently it is proved that MCM system optimization can be achieved by applying wavelet bases instead of conventional fourier bases. Wavelet packet based MCM (WPMCM) systems have overall the same capabilities as OFDM systems with some improved features. In this research the literature and analytic schemes of WPMCM system is addressed, a wavelet packet based cognitive ultra wideband (UWB) transceiver is proposed, and performance analysis of WPMCM in different wireless multipath channels is investigated. Simulation results show a significant enhancement in terms of BER, spectral efficiency and side-lobes suppression comparing to conventional OFDM.
Integrated DWDM and MIMO-OFDM System for 4G High Capacity Mobile Communicatio...CSCJournals
Dense wavelength-division multiplexing (DWDM) technique is a very promising data transmission technology for utilizing the capacity of the fiber. By DWDM, multiple signals (video, audio, data etc) staggered in wavelength domain can be multiplexed and transmitted down the same fiber. The Multiple-input multiple-output (MIMO) wireless technology in combination with orthogonal frequency division multiplexing (MIMO-OFDM) is an attractive air-interface solution for next-generation wireless local area networks (WLANs) and fourth-generation mobile cellular wireless systems. This article provides an overview of the integrated DWDM MIMO-OFDM technology and focuses on DWDM transmitter design with adequate dispersion compensation for high data rate of 10Gbps ,MIMO-OFDM system design, space-time coded signaling, receiver design and performance analysis in terms of bit error rate for Integrated system. The simulation is carried out using powerful software tools Optisystem and MATLAB . In this paper a 64 channel DWDM system is simulated for transmission of baseband NRZ signal over fiber. Each of the transmission is at bit rate of 10 Gbps leading to high data rate transmission of 640 Gbps.The resultant Bit Error Rate(BER) is in the range 10-12 for DWDM system which is given as input to MIMO-OFDM system..This system performance is analyzed in terms of BER with SNR for Rayleigh, and AWGN channels and BER of 10-4 is achieved at SNR of 10dbs
RECONFIGURABLE OPTICAL ADD AND DROP MULTIPLEXERS A REVIEWecijjournal
Optical multiplexing is the key function of a WDM network and reliable method for data transport networks. WDM networks configured as rings/mesh along with Optical Add-Drop Multiplexers supports added flexibility, simplicity and augment the spectral efficiency. Further enhancement achieved with Reconfigurable OADM architectures, growing briskly along with automatic network management, let the transport network to acclimatize with dynamically varying environment and flexibly respond to the transport network changes. It permits single or many wavelengths to be added and/or dropped from a
transport fiber without optical-to-electrical-to-optical domain translation. Presently ROADM technology
has revolutionized optical networking and an inseparable part of modern optical communication offering huge bandwidth for data transport at minimum expense. In this view the article presents comprehensive study for numerous generations of ROADM and their architecture and persistent development
Research Inventy : International Journal of Engineering and Scienceresearchinventy
Research Inventy : International Journal of Engineering and Science is published by the group of young academic and industrial researchers with 12 Issues per year. It is an online as well as print version open access journal that provides rapid publication (monthly) of articles in all areas of the subject such as: civil, mechanical, chemical, electronic and computer engineering as well as production and information technology. The Journal welcomes the submission of manuscripts that meet the general criteria of significance and scientific excellence. Papers will be published by rapid process within 20 days after acceptance and peer review process takes only 7 days. All articles published in Research Inventy will be peer-reviewed.
- Least Squares Estimation (Part III)
- Constrained Linear Least Squares
- Reduced Model
- Examples: Non-linear device modeling using least squares - Sinusoidal parameters estimation using least squares, Numerical solution of non-linear least squares
- Ill-conditioned measurement matrix
- Regularized least squares
- SVD-based model modification
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.
Pilot Decontamination over Time Frequency and Space Domains in Multi-Cell Ma...IJECEIAES
In this article, we show that Pilot contamination problem can be seen as a source separation problem using time, frequency, and space domains. Our method capitalizes on a nonunitary joint diagonalization of spatial quadratic time-frequency (STFD) signal representation to identify the desired and interfering users. We first compute the noise subspace from the STFD matrices selected appropriately. Secondly, we use the noise subspace obtained to estimate the Elevation (El) and the Azimuth (Az) angles for which the MUSIC cost function is maximized. Numerical simulations are provided to illustrate the effectiveness and the behavior of the proposed approach.
PAPR Reduction in OFDM using Active and Non-Active ChannelsIOSR Journals
Abstract : According to the request of advance communication field there should be high data rate in addition to both power efficiency and lower bit error rate. This request of high data rate can be achieved by the multi carrier modulation scheme using the OFDM technique. But the great drawback of the OFDM technique is its high peak to average power ratio (PAPR). High PAPR reduces OFDM signals by driving the analog amplifier to work in the nonlinear region, changing this way the signal and making the amplifier to consume more power. To reduce the PAPR methods exist which adjust or present new signals to battle large signal peaks. The methods which use data carrying channels are called active channel methods and which use redundant channel are called non active channel methods. This work deals with reduction of the PAPR of OFDM signal using both Active and Non Active Channels. Clipping technique has been applied to active channels and Tone reservation has been applied to Non Active Channels. By using both channels we can get considerable reduction in PAPR. Keywords:Orthogonal Frequency Division Multiplexing (OFDM), Peak to Average Power Ratio (PAPR), Power Amplifier (PA).
Mitigation of non-linear four-wave mixing phenomenon in a fully optical commu...TELKOMNIKA JOURNAL
This paper aims to point out the nonlinear phenomenon occurring in coarse/dense wavelength division multiplex (C/D-WDM) systems. This phenomenon has to betaken into account during the design of the optical network itself, as wavelengthsin the optical fiber are constantly densified. The paper points out the emergence of the non-linear four-wave mixing (FWM) phenomenonand how it relates to the dispersion in the optical fiber together with the transmit power. The output of the paper is a proposed design of the system that points to the improvement of the bit error rate (BER) with a suitable choice of dispersion and suitable transmission power.
Comparison of Various Waveform Contenders of 5G Wireless Communication Based ...ijtsrd
This paper presents an extensive and fair comparison among the most promising waveform contenders for the 5G air interface which includes- Filtered OFDM, Filter-bank multi carrier (FBMC), universal filtered multi-carrier (UFMC) has been compared with OFDM in terms of spectral efficiency and bit error rate using mat lab. The disadvantages of OFDM have been addressed and it has shown that (fofdm), (UFMC), (FBMC) could be a more effective solution. FBMC is a method for improving out of band (OOB) characteristics by filtering each subcarrier, it is also expected to improve the Inter-Carrier Interference (ICI) characteristics while UFMC is a method for improving OOB characteristics by filtering each block. Raksha Vishnoi | Saurabh Gaur | Ashish Verma"Comparison of Various Waveform Contenders of 5G Wireless Communication Based on OFDM" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-2 | Issue-4 , June 2018, URL: http://www.ijtsrd.com/papers/ijtsrd15637.pdf http://www.ijtsrd.com/engineering/electronics-and-communication-engineering/15637/comparison-of-various-waveform-contenders-of-5g-wireless-communication-based-on-ofdm/raksha-vishnoi
OFDM allows tightly packed carriers to convey information orthogonally and with high bandwidth efficiency
Objectives Description:
Concepts
Basic idea
Introduction to OFDM
Implementation
Advantages and Drawbacks.
FDMA
Wavelet Packet based Multicarrier Modulation for Cognitive UWB SystemsCSCJournals
Orthogonal frequency division multiplexing (OFDM) is a multi-carrier modulation (MCM) scheme where the sub carriers are orthogonal waves. The main advantages of OFDM are robustness against multi-path fading, frequency selective fading, narrowband interference, and efficient use of spectrum. Recently it is proved that MCM system optimization can be achieved by applying wavelet bases instead of conventional fourier bases. Wavelet packet based MCM (WPMCM) systems have overall the same capabilities as OFDM systems with some improved features. In this research the literature and analytic schemes of WPMCM system is addressed, a wavelet packet based cognitive ultra wideband (UWB) transceiver is proposed, and performance analysis of WPMCM in different wireless multipath channels is investigated. Simulation results show a significant enhancement in terms of BER, spectral efficiency and side-lobes suppression comparing to conventional OFDM.
Integrated DWDM and MIMO-OFDM System for 4G High Capacity Mobile Communicatio...CSCJournals
Dense wavelength-division multiplexing (DWDM) technique is a very promising data transmission technology for utilizing the capacity of the fiber. By DWDM, multiple signals (video, audio, data etc) staggered in wavelength domain can be multiplexed and transmitted down the same fiber. The Multiple-input multiple-output (MIMO) wireless technology in combination with orthogonal frequency division multiplexing (MIMO-OFDM) is an attractive air-interface solution for next-generation wireless local area networks (WLANs) and fourth-generation mobile cellular wireless systems. This article provides an overview of the integrated DWDM MIMO-OFDM technology and focuses on DWDM transmitter design with adequate dispersion compensation for high data rate of 10Gbps ,MIMO-OFDM system design, space-time coded signaling, receiver design and performance analysis in terms of bit error rate for Integrated system. The simulation is carried out using powerful software tools Optisystem and MATLAB . In this paper a 64 channel DWDM system is simulated for transmission of baseband NRZ signal over fiber. Each of the transmission is at bit rate of 10 Gbps leading to high data rate transmission of 640 Gbps.The resultant Bit Error Rate(BER) is in the range 10-12 for DWDM system which is given as input to MIMO-OFDM system..This system performance is analyzed in terms of BER with SNR for Rayleigh, and AWGN channels and BER of 10-4 is achieved at SNR of 10dbs
RECONFIGURABLE OPTICAL ADD AND DROP MULTIPLEXERS A REVIEWecijjournal
Optical multiplexing is the key function of a WDM network and reliable method for data transport networks. WDM networks configured as rings/mesh along with Optical Add-Drop Multiplexers supports added flexibility, simplicity and augment the spectral efficiency. Further enhancement achieved with Reconfigurable OADM architectures, growing briskly along with automatic network management, let the transport network to acclimatize with dynamically varying environment and flexibly respond to the transport network changes. It permits single or many wavelengths to be added and/or dropped from a
transport fiber without optical-to-electrical-to-optical domain translation. Presently ROADM technology
has revolutionized optical networking and an inseparable part of modern optical communication offering huge bandwidth for data transport at minimum expense. In this view the article presents comprehensive study for numerous generations of ROADM and their architecture and persistent development
Research Inventy : International Journal of Engineering and Scienceresearchinventy
Research Inventy : International Journal of Engineering and Science is published by the group of young academic and industrial researchers with 12 Issues per year. It is an online as well as print version open access journal that provides rapid publication (monthly) of articles in all areas of the subject such as: civil, mechanical, chemical, electronic and computer engineering as well as production and information technology. The Journal welcomes the submission of manuscripts that meet the general criteria of significance and scientific excellence. Papers will be published by rapid process within 20 days after acceptance and peer review process takes only 7 days. All articles published in Research Inventy will be peer-reviewed.
- Least Squares Estimation (Part III)
- Constrained Linear Least Squares
- Reduced Model
- Examples: Non-linear device modeling using least squares - Sinusoidal parameters estimation using least squares, Numerical solution of non-linear least squares
- Ill-conditioned measurement matrix
- Regularized least squares
- SVD-based model modification
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.
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).
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.
Peak to Average Ratio PAPR Reduction Technique in OFDM MIMO System A Reviewijtsrd
Orthogonal Frequency Division Multiplexing OFDM is an new method for fourth generation wireless communication. MIMO OFDM has become a promising candidate for high performance 4G and 5G broadband wireless communications. However, one main of MIMO OFDM is the high peak to average power ratio PAPR of the transmitter’s output signal on different antennas. In this paper, we present a new noble SLM PAPR reduction techniques such as selective mapping technique and Partial transmit sequence techniques and shows which of these PAPR reduction techniques are more effective to reduce PAPR in OFDM MIMO. Er. Sukhjinder Singh | Dr. Hitanshu Kumar | Dr. Arashdeep Singh "Peak to Average Ratio (PAPR) Reduction Technique in OFDM-MIMO System- A Review" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-6 | Issue-3 , April 2022, URL: https://www.ijtsrd.com/papers/ijtsrd49719.pdf Paper URL: https://www.ijtsrd.com/engineering/electronics-and-communication-engineering/49719/peak-to-average-ratio-papr-reduction-technique-in-ofdmmimo-system-a-review/er-sukhjinder-singh
Orthogonal frequency-division multiplexing (OFDM)
[1] is a method of encoding digital data on multiple carrier
frequencies. OFDM[1] has developed into a popular scheme
for wideband digital communication, whether wireless or
over copper wires, used in applications such as digital television
and audio broadcasting, DSL Internet access, wireless networks,
powerline networks, and 4G mobile communications. In the
Several wireless standards such as IEEE 802.11a[2] and
HiperLAN2[3].The orthogonality of the subcarriers is no longer
maintained which results in ICI (Inter carrier Interference)[4]
.ICI reduction techniques achieve a better SNR and BER in
OFDM at zero phase noise variance . This technique will use a
large number of closely spaced orthogonal subcarriers to avoid
phase noise. It provides high data rates with sufficient robustness
to radio channel damages. A major problem in OFDM is carrier
frequency offset error between the transmitted and received
signals. Due to this the orthogonality of the subcarriers is no
longer maintained which results in ICI (Inter carrier
Interference). In this paper, we used the ICI self-cancellation
technique and reduced the ICI and improved the BER and SNR
we are also calculate the SNR=15db and 20db at different phase
noise variance.
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.
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.
DISCRETE COSINETRANSFORM-II FOR REDUCTION IN PEAK TO AVERAGE POWER RATIO OF O...ijwmn
Orthogonal frequency Division multiplexing (OFDM) is the most familiar word in telecommunication
and wireless communication systems as it provides enhanced spectral efficiency than Frequency division
multiplexing (FDM).Although it is sustaining an orthogonal relation betweencarriers but high peak to
average power ratio (PAPR) is one of the main disadvantages of OFDM system.Various PAPR reduction
techniques have been used, including techniques based on companding. Incompanding, -Law
companding has potential to reduce the PAPR of OFDMsignals. -Law Companding technique
preserves the dynamic range of samples at low amplitudes.A new method named as precoding which is
having less complexity compared to the other power reduction techniques is proposed to reduce PAPR.
This paper put forward combination of two existing techniques namely -Law Companding Transform
and Discrete Cosine Transform-II precoding technique. The simulation results show that, the proposed
combinedscheme gives better result for PAPR Reduction and results in no distortion.
Investigation and Analysis of SNR Estimation in OFDM systemIOSR Journals
Estimation of signal to noise ratio (SNR) of received signal and to transmit the signal effectively for
the modern communication system. The performance of existing non-data-aided (NDA) SNR estimation methods
are substantially degraded for high level modulation scheme such as M-ary amplitude and phase shift keying
(APSK) or quadrature amplitude modulation (QAM).In this paper SNR estimation proposed method which uses
zero point auto-correlation of received signal per block and auto/cross- correlation of decision feedback signal
in orthogonal frequency division multiplexing (OFDM) system. Proposed method can be studied into two types;
Type 1 can estimate SNR by zero point auto-correlation of decision feedback signal based on the second
moment property. Type 2 uses both zero point auto-correlation and cross-correlation based on the fourth
moment property. In block-by-block reception of OFDM system, these two SNR estimation methods can be
possible for the practical implementation due to correlation based the estimation method and they show more
stable estimation performance than the earlier SNR estimation methods.
Channel Estimation Techniques in MIMO-OFDM LTE SystemsCauses and Effects of C...IJERA Editor
There is an increasing demand for high data transmission rates with the evolution of the very large scale integration (VLSI) technology. The multiple input multiple output-orthogonal frequency division multiplexing (MIMO-OFDM) systems are used to fulfill these requirements because of their unique properties such as high spectral efficiency, high data rate and resistance towards multipath propagation. MIMO-OFDM systems are finding their applications in the modern wireless communication systems like IEEE 802.11n, 4G and LTE. They also offer reliable communication with the increased coverage area. The bottleneck to the MIMO-OFDM systems is the estimation of the channel state information (CSI). This can be estimated with the help of any one of the Training Based, Semiblind and Blind Channel estimation algorithms. This paper presents various channel estimation algorithms, optimization techniques and their effective utilization in MIMO-OFDM for modern wireless LTE systems.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
Performance 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.
Simulation Study and Performance Comparison of OFDM System with QPSK and BPSKpaperpublications3
Abstract: FDMA, TDMA and CDMA are the well-known multiplexing techniques used in wireless communication systems. While working with the wireless systems using these techniques various problems are encountered especially when a typical transmitted signal arrives at the receiver using various paths of different lengths. Since multiple versions of the signal interfere with each other, it becomes difficult to extract the original information. The use of orthogonal frequency division multiplexing (OFDM) technique provides better solution for the above mentioned problem. OFDM technique distributes the data over a large number of carriers that are spaced apart at precise frequencies. This spacing provides the "orthogonality", which prevents the demodulator from seeing frequencies other than their own. The benefits of OFDM are high spectral efficiency, resiliency of RF interference, and lower multi-path distortion. OFDM is a powerful modulation technique that is capable of high data rate and is able to eliminate ISI. Using MATLAB, simulation of OFDM was done with different modulation techniques using different transform techniques. The digital modulation schemes such as BPSK and QPSK were selected to assess the performance of the designed OFDM system.
One of vital parts of the mobile wireless channel is channel estimation significantly
improve the performance of the system, especially for 4G LTE and 5G systems. The
main goal of this project is to test the time-variant channel estimation using F-OFDM
model. It investigates the Mean Square Error (MSE), the Least Squares (LS) method
and compares performance of OFDM and F-OFDM using BER vs SNR.
Techniques for Improving BER and SNR in MIMO Antenna for Optimum PerformanceIJMTST Journal
The use of multiple antennas for diversity, including MIMO (Multiple Input Multiple Output) is one of the most promising wireless technologies for broadband communication applications. This antenna system is a vital study in today’s wireless communication system especially when the signal propagates through some corrupted environments. In our paper new techniques of improving bit error ratio and signal to noise ratio are discussed. Inter symbol interference is a major limitation of wireless communications. It degrades the performance significantly if the delay spread is comparable or higher than the symbol duration. To remove ISI, equalization needs to be included at the receiver end. This paper discusses the merits of the MIMO system and the techniques used for improving BER performance and SNR. In MIMO wireless communication, an equalizer is used to recover a signal that suffers from Inter symbol Interference (ISI) and the BER characteristics is improved and a good SNR can be obtained. Different equalization techniques are discussed in this paper.
Optimal Channel and Relay Assignment in Ofdmbased Multi-Relay Multi-Pair Two-...ijcnes
Efficient utilization of radio resources in wireless networks is crucial and has been investigated extensively. This letter considers a wireless relay network where multiple user pairs conduct bidirectional communications via multiple relays based on orthogonal frequency-division multiplexing (OFDM) transmission. The joint optimization of channel and relay assignment, including subcarrier pairing, subcarrier allocation as well as relay selection, for total throughput maximization is formulated as a combinatorial optimization problem. Using a graph theoretical approach, we solve the problem optimally in polynomial time by transforming it into a maximum weighted bipartite matching (MWBM) problem. Simulation studies are carried out to evaluate the network total throughput versus transmit power per node and the number of relay nodes
Similar to Performance Analysis of OFDM in Combating Multipath Fading (20)
Welcome to WIPAC Monthly the magazine brought to you by the LinkedIn Group Water Industry Process Automation & Control.
In this month's edition, along with this month's industry news to celebrate the 13 years since the group was created we have articles including
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CFD Simulation of By-pass Flow in a HRSG module by R&R Consult.pptxR&R Consult
CFD analysis is incredibly effective at solving mysteries and improving the performance of complex systems!
Here's a great example: At a large natural gas-fired power plant, where they use waste heat to generate steam and energy, they were puzzled that their boiler wasn't producing as much steam as expected.
R&R and Tetra Engineering Group Inc. were asked to solve the issue with reduced steam production.
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Based on our results, Tetra Engineering installed covering plates to reduce the bypass flow. This improved the boiler's performance and increased electricity production.
It is always satisfying when we can help solve complex challenges like this. Do your systems also need a check-up or optimization? Give us a call!
Work done in cooperation with James Malloy and David Moelling from Tetra Engineering.
More examples of our work https://www.r-r-consult.dk/en/cases-en/
Cosmetic shop management system project report.pdfKamal Acharya
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Data file handling has been effectively used in the program.
The automated cosmetic shop management system should deal with the automation of general workflow and administration process of the shop. The main processes of the system focus on customer's request where the system is able to search the most appropriate products and deliver it to the customers. It should help the employees to quickly identify the list of cosmetic product that have reached the minimum quantity and also keep a track of expired date for each cosmetic product. It should help the employees to find the rack number in which the product is placed.It is also Faster and more efficient way.
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Hierarchical Digital Twin of a Naval Power SystemKerry Sado
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Final project report on grocery store management system..pdfKamal Acharya
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Performance Analysis of OFDM in Combating Multipath Fading
1. IOSR Journal of Electronics and Communication Engineering (IOSR-JECE)
e-ISSN: 2278-2834,p- ISSN: 2278-8735.Volume 6, Issue 2 (May. - Jun. 2013), PP 99-107
www.iosrjournals.org
www.iosrjournals.org 99 | Page
Performance Analysis of OFDM in Combating Multipath Fading
Adewuyi O.S1
, Lawal W.2
, Ogunti E.O.3
Department of Electrical/Electronic Engineering, Federal university of Technology Akure, Ondo State Nigeria
Department of Electrical/Electronic Engineering, Rufus Giwa Polytechnics Owo, Ondo State, Nigeria
Department of Electrical/Electronic Engineering, Federal university of Technology Akure, Ondo State
NigeriaThanks
Abstract: Mobile Communication system has been on high rampage for high data transmission over wireless
medium with various challenges caused by the transmission Channel. OFDM is been discovered in recent years
to deal with this problems because of its ability to elegantly cope with multipath interference. This paper
investigates the performance of different modulation schemes using M-ary Phase Shift Keying (M-PSK) and M-
ary Quadrature Amplitude Modulation (M-QAM) in information transmission with OFDM technique over Ideal
channel AWGN and worst channel Rayleigh Fading channel in terms of Bits Error Rate (BER). Analysis was
made for different types of modulation schemes BPSK, QPSK, 4-QAM and 16-QAM gray coded bit mapping.
Also, a feasibility of OFDM been used to combat multipath fading was analyzed with comparison between a
single carrier technique and OFDM multicarrier technique. Variation between SNR results with respect to BER
is plotted to show the trade off differences between the modulation schemes with the result showing that OFDM
allows data transmission with minimal error over fading channel than a Single Carrier.
Keywords: OFDM, Single Carrier, AWGN, Rayleigh fading, BER, M-ary PSK, M-ary QAM
I. Introduction
The concept of OFDM in term of parallel data transmission and frequency division multiplexing was
first developed in the 50s [1, 2] and introduced in some papers in the mid 60s [3]. Although the idea of
OFDM started back in 1966, it has never been widely utilized until the last decade when it “becomes the
modem of choice in wireless applications” [4]. OFDM can be seen as either a modulation technique or a
multiplexing technique allowing high speeds at wireless communications; its hierarchy corresponds to the
physical and medium access layer. OFDM as a multicarrier technique is used to increase the robustness
against frequency selective fading or narrowband interference.
In a single carrier system, a single fade or interfere can cause the entire link to fail, but in OFDM
multicarrier system, only a small percentage of the subcarriers will be affected. Data to be transmitted in OFDM
is typically in the form of a serial data stream and since OFDM transmits data as a set of parallel low bandwidth
(100Hz – 50 kHz), hence a serial to parallel conversion is needed to divide the serial data into parallel sub
carriers. OFDM provides high bandwidth efficiency because the subcarriers are orthogonal to each other. This
made the carrier to be independent of each other even though their spectral overlap. The frequency spacing
between the sub carriers is made to be the reciprocal of the useful symbol.
An important component in OFDM that makes its subcarrier to each other is Discrete Fourier
Transform (DFT) which is been replaced by Inverse Fast Fourier Transform (IFFT) because IFFT is cost
effective to implement. IFFT converts the symbols in frequency domain to time domain at the transmitter while
Fast Fourier Transform (FFT) is been used at the receiver to convert back from time domain to frequency
domain. High data rate systems are achieved by using a large number of carriers. Other components a basic
OFDM system will contain are modulation scheme a QAM or PSK modulator or demodulator, a serial to
parallel converter and a parallel to serial converter.
However, since OFDM has proved to be very effective in mitigating adverse multipath effects of a
broadband wireless channel, counteracting the frequency selectivity of multipath channels by multiplexing
information on different orthogonal carriers, it now becomes the underlying technology for various new
applications such as digital audio broadcast (DAB) () and for Digital Video Broadcast (DVB) in Europe and
Australia. Other areas of OFDM applications are wireless LAN (802.11a&g, 802.16a&b, Wimax and Hiper
LAN-2), broadband wireless (MMDS, LMDS), xDSL, and home networking.
Modulation schemes in OFDM are used to cover data rates for various needs. Modulation mapping rate
are dynamically adapted based on channel condition to increase the system performance in terms of Bit Error
Rate (BER). Gray bit mapping is been used in different modulation schemes for the bit constellation of the
transmitted bits to be rearranged thereby making every adjacent bits differ by one bit.
This paper now presents the average Bit Error Rate for different modulation schemes trying to see which
is the best modulation scheme to use under an idea AWGN and worst channel Rayleigh fading channel using
2. Performance Analysis of OFDM in Combating Multipath Fading
www.iosrjournals.org 100 | Page
some forward error corrections such as Concatenated Reed Solomon and Convolutional Encoder with General
interleaver.
The paper is divided into sections; section II will discuss OFDM system, Propagation Characteristics of
Mobile Radio Channels, and mathematical model. In section III, simulations and results are presented. Finally,
conclusion is sdrawn in the last section of this paper.
OFDM
The next generation of wireless communication, that is 4G has adopted OFDM as their physical layer
because OFDM efficiently utilize multiple performance for 4G [M. Nakagami, 1960].The growing demand for
modulated carriers tightly together reducing the required bandwidth but keeping the modulated signals
orthogonal so that they do not interfere with each other. OFDM that is highly efficient technique shows
favorable properties such as robustness to channel fading and inter symbol interference (ISI) and is immune to
noise. OFDM system is capable of mitigating a frequency selective fading channel to a set of parallel flat fading.
Orthogonal Frequency Division Multiplexing (OFDM) is a multicarrier transmission technique, many
carriers, each one being modulated by a low rate data stream share the transmission bandwidth. OFDM is
similar to FDMA in that the multiple user access is achieved by subdividing the available bandwidth into
multiple channels that are then allocated to users. However, OFDM uses the spectrum much more efficiently by
spacing the channels much closer together. This is achieved by making all the carriers orthogonal to one
another, preventing interference between the closely spaced carriers.
Unlike the conventional multicarrier communication scheme in which spectrum of each subcarrier is
non-overlapping and band, pass filtering is used to extract the frequency of interest, in OFDM the frequency
spacing between subcarriers is selected such that the subcarriers are mathematically orthogonal to each other‟s.
The spectra of subcarriers overlap each other but individual subcarrier can be extracted by baseband processing.
This overlapping property makes OFDM more spectral efficient than the conventional multicarrier
communication scheme.
Figure 1: Concept of OFDM Signal: Orthogonal Multicarrier Technique versus Conventional Multicarrier
Techniques.
Orthogonality of OFDM
The main concept in OFDM is Orthogonality of the subcarriers. Since the carriers are all sine and
cosine waves, area under one period of a sine or cosine wave is Zero. Taking a sine wave of frequency m and
multiplying it by a sinusoid (sine/cosine) of a frequency n, where m and n are integers, the integral or the area
under this product is given by:
𝑓 𝑡 = 𝑠𝑖𝑛𝑚𝜔𝑡 ∗ 𝑠𝑖𝑛𝑛𝜔𝑡 (1)
By the simple trigonometry relationship, this is equal to a sum of two sinusoids of frequencies (m-n)
and (m+n) given as:
=
1
2
cos 𝑚 − 𝑛 −
1
2
(2)
Equation (2) shows that the two frequencies components are sinusoids; hence integrating them over
one period gives zero:
1
2
cos 𝑚 − 𝑛 𝜔𝑡 −
1
2
cos 𝑚 + 𝑛 𝜔𝑡 (
2𝜋
0
2𝜋
0
3)
= 0 − 0
3. Performance Analysis of OFDM in Combating Multipath Fading
www.iosrjournals.org 101 | Page
Therefore, it can be concluded that when a sinusoid of a frequency n is multiplied by sinusoid of
frequency m/n, the area under the product is zero. Integral for all integer n and m, sinm𝓍, cosm𝓍, cosn𝓍, sinn𝓍,
are all orthogonal to each other. These frequencies are called harmonics.
In a simple way it can be put that, two periodic signals are orthogonal when the integral of their
product, over one period, is equal to zero. This is true of certain sinusoids as illustrated in the equations below:
Continuous Time
cos 2𝜋𝑛𝑓𝑜 𝑡 𝑐𝑜𝑠 2𝜋𝑚𝑓𝑜 𝑡 𝑑𝑡 = 0 𝑛 ≠ 𝑚 (4)
𝜏
0
Discrete Time
𝑐𝑜𝑠
2𝜋𝑘𝑛
𝑁
𝑐𝑜𝑠
2𝜋𝑘𝑚
𝑁
𝑁−1
0 = 0 𝑛 ≠ 𝑚 (5)
The carriers of an OFDM are sinusoids that meet this requirement because each one is a multiple of
frequency. Each one has an integer number of cycles in the fundamental period. If the dot product of two
deterministic signals is equal to zero, these signals are said to be orthogonal to each other.
1.3 Mathematical Model of OFDM System.
The basic idea of OFDM is to divide the available spectrum into several sub channels (subcarriers) by
making all sub channels narrowband, they experience almost flat fading, which makes equalization very simple
or may not require equalization. To obtain a high spectral efficiency the frequency response of the sub-channels
are overlapping and orthogonal, hence the name OFDM. This orthogonality can be completely maintained, even
though the signal passes through a time dispersive channel, by introducing a cyclic prefix [6]. There are several
versions of OFDM, [7, 8, 9] but this research focus on systems using such a cyclic prefix [10]. A cyclic prefix
is a copy of the last part of the OFDM symbol, which is presented to the transmitted symbol. This makes the
transmitted signal periodic, which plays a decisive role in avoiding intersymbol and intercarrier interference [7].
Starting with the waveforms used in the transmitter and proceeding all the way to the receiver, the
description goes thus:
Transmitter
Assuming an OFDM system with N subcarriers, a bandwidth of Q Hz and symbol length of T seconds,
of which Tcp seconds is the length of the cyclic prefix, the transmitter uses the following waveforms:
𝜙𝜅 𝑡
=
1
𝑇 − 𝑇𝑐𝑝
𝑒 𝑗2𝜋 𝑘(𝑡−𝑇 𝑐𝑝 ) if t ϵ 0 T𝑁
𝜔
0 𝑜𝑡𝑒𝑟𝑤𝑖𝑠𝑒
(6)
Where 𝑇 =
𝑁
𝑊
+ 𝑇𝑐𝑝. Note that ∅𝑡 (𝑡) = ∅ 𝑘 𝑡 +
𝑁
𝑊
, where T is within the cyclic prefix 0, 𝑇𝑐𝑝 since ∅ 𝑘 (𝑡)
is the rectangular pulse modulated on the carrier frequency
𝐾𝑊
𝑁
, the common interpretation of OFDM is that it
uses N subcarriers, each carrying a low-bit rate. Now the transmitted baseband signal for OFDM symbol
number l is:
𝑠𝑡 𝑡
= 𝑥 𝑘
𝑁−1
𝑘=0
, ℓ∅ 𝑘 𝑡−ℓ𝑇
(7)
Where 𝑥0, ℓ, 𝑥1, ℓ … … … … 𝑥 𝑁−1 are complex symbols from the set of signal constellation points. When an
infinite sequence of OFDM symbols is transmitted, the output from the transmitter is a juxtaposition of
individual OFDM symbols:
𝑠 𝑡 = 𝑠ℓ 𝑡 = 𝑥 𝑘,ℓ∅ 𝑘
𝑡 − ℓ𝑇
𝑁−1
𝑘=0
+∞
ℓ=−∞
∞
ℓ=−∞
(8)
Physical Channel
An assumption that the support of possibly time variant impulse response g(𝜏;t) of the physical channel
is restricted to the interval 𝜏 ∈ [0, 𝑇𝑐𝑝 ] i.e to the length of the cyclic prefix. The received signal becomes:
𝑟 𝑡 = 𝑔 𝜏, 𝑡 ∗ 𝑠 𝑡 + 𝑛 𝑡 = 𝑔 𝜏; 𝑡 𝑠 𝑡 − 𝜏 𝑑𝜏 + ṅ 𝑡 (9)
𝑇𝑐𝑝
0
Where ṅ 𝑡 is additive white, complex Gaussian channel noise.
Receiver
In an OFDM receiver, a filter bank is matched to the last part [𝑇𝑐𝑝 , 𝑇] of the transmitter waveforms
∅ 𝑘 𝑡 , 𝑖. 𝑒
4. Performance Analysis of OFDM in Combating Multipath Fading
www.iosrjournals.org 102 | Page
𝜓 𝑘 𝑡
=
𝜙∗
𝑇 − 𝑡 𝑖𝑓 𝑡 𝜖 [0, 𝑇 − 𝑇𝑐𝑝 ]
0 𝑜𝑡𝑒𝑟𝑤𝑖𝑠𝑒
(10)
From the equation above, it is been observed that the cyclic prefix is removed at the receiver. Since the
cyclic prefix contains all ISI from the previous symbol, the sampled output from the reciver filter bank contains
no ISI. Therefore, the time index when calculating the sampled output at the kth matched filter.
When we consider equations, we arrive at
𝑦 𝑘 = ( 𝑔(𝜏; 𝑡) 𝑥 𝑘′∅ 𝑘′(𝑡 − 𝜏)]𝑑𝜏 ∅ 𝑘
∗
(𝑡) 𝑑𝑡 + ℏ 𝑇 − 𝑡 ∅ 𝑘
∗
(𝑡) 𝑑𝑡
𝑇
𝑇𝑐𝑝
𝑁−1
𝑘′=0
𝑇𝑐𝑝
0
𝑇
𝑇𝑐𝑝
(11)
Considering the channel to be fixed over the OFDM symbol interval is denoted by which gives
𝑦 𝑘 = 𝑥 𝑘′
𝑁−1
𝑘′=0
( 𝑔 𝜏
𝑇𝑐𝑝
0
𝑇
𝑇𝑐𝑝
∅ 𝑘′(𝑡 − 𝜏)]𝑑𝜏 ∅ 𝑘
∗
(𝑡) 𝑑𝑡 + ℏ 𝑇 − 𝑡 ∅ 𝑘
∗
𝑡 𝑑𝑡
𝑇
𝑇𝑐𝑝
(12)
The integration intervals are and which implies that
and the inner integral can be written as:
( 𝑔 𝜏
𝑇𝑐𝑝
0
𝑇
𝑇𝑐𝑝
∅ 𝑘′(𝑡 − 𝜏)]𝑑𝜏 = 𝑔 𝜏
𝑇𝑐𝑝
0
𝑒 𝑗2𝜋𝑘′ 𝑡−𝜏−𝑇𝑐𝑝
𝑊
𝑁
𝑇 − 𝑇𝑐𝑝
𝑑𝜏 =
𝑒 𝑗2𝜋𝑘′ 𝑡−𝜏−𝑇𝑐𝑝
𝑊
𝑁
𝑇 − 𝑇𝑐𝑝
𝑔 𝜏
𝑇𝑐𝑝
0
𝑒−𝑗2𝜋𝑘
′
𝑊
𝑁
𝑑𝜏 ,
𝑇𝑐𝑝 < 𝑡
< 𝑇 (13)
The latter part of this expression is the sampled frequency response of the channel at frequency
at the th subcarrier frequency:
𝑘′ = 𝐺 𝑘′ 𝑊
𝑁
= 𝑔 𝜏
𝑇𝑐𝑝
0
𝑒−𝑗2𝜋𝑘
′
𝑊
𝑁
𝑑𝜏 ,
(14)
Where is the fourier transform of Using this notation the output from the reciver filter bank can be
smplified to
𝑦 𝑘 = 𝑥 𝑘′
𝑁−1
𝑘′=0
𝑒 𝑗2𝜋𝑘′ 𝑡−𝑇𝑐𝑝
𝑊
𝑁
𝑇 − 𝑇𝑐𝑝
𝑘′ ∅ 𝑘
∗
𝑡 𝑑𝑡 + ℏ
𝑇
𝑇𝑐𝑝
𝑇
𝑇𝑐𝑝
𝑇 − 𝑡 𝑘′ ∅ 𝑘
∗
𝑡 𝑑𝑡
= 𝑥 𝑘′
𝑁−1
𝑘′=0
𝑘′ ∅ 𝑘′ 𝑡
𝑇
𝑇𝑐𝑝
∅ 𝑘
∗
𝑡 𝑑𝑡 + 𝑛 𝑘 (15)
Where
Since the transmitter filters are orthogonal,
∅ 𝑘′ 𝑡
𝑇
𝑇𝑐𝑝
∅ 𝑘
∗
𝑡 𝑑𝑡 =
𝑒 𝑗2𝜋𝑘′ 𝑡−𝑇𝑐𝑝
𝑊
𝑁
𝑇 − 𝑇𝑐𝑝
𝑇
𝑇𝑐𝑝
𝑒−𝑗2𝜋𝑘′ 𝑡−𝑇𝑐𝑝
𝑊
𝑁
𝑇 − 𝑇𝑐𝑝
𝑑𝑡 = 𝛿 𝑘 − 𝑘′
(16)
Where is the Kronecker delta function (Oppenheim and Schafer, 1989), equation (15) can be simplified to
obtain
𝑦 𝑘 = 𝑘 𝑥 𝑘 + 𝑛 𝑘 (17)
Where is the additive white Gaussian noise (AWGN).
The benefit of cyclic prefix is to avoid ISI since it acts as a guard interval and ICI because it maintains
the orthogonality of the sub carriers.
Discrete-time model
In discrete time model, as compared to continuous time model, an inverse DFT (IDFT) and a DFT
respectively replace the modulation and demodulation, and the channel is a discrete time convolution. The
cyclic prefix operates in the same fashion and the calculations can be performed in essentially the same way.
The main difference is that all integrals are replaced by sums. From the receiver‟s point of view, the use of a
cyclic prefix longer than the channel will transform the linear convolution in the channel to a cyclic convolution.
Denoting cyclic convolution by‟ ‟ the whole OFDM system can be written as:
=
(18)
5. Performance Analysis of OFDM in Combating Multipath Fading
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Where contains N received data points, the N transmitted constellation points, the impulse
response of the channel (padded with zero to obtain a length of N), and the channel noise. Since the channel
noise is assumed white and Gaussian, the term = DFT ( ) represents the uncorrelated Gaussian noise.
Further, we use that the DFT of two cyclically convolved signals is equivalent to the product of their individual
DFTs. Denoting element-by-element multiplication by (.), the above expression can be written
(19)
Where DFT ( ) is the frequency response of the channel. Thus, we have obtained the same
type of parallel Gaussian channels as for the continuous-time model. The only difference is the channel
attenuations are given by the N point DFT of the discrete time channel, instead of the sampled frequency
response as in Equation (17).
1.4 Propagation Characteristics of Mobile Radio Channels
Channel Fading Techniques
The physical medium between the transmitter and receiver is known as channel. Radio channel is the
link between the transmitter and the receiver that carries information bearing signal in the form of
electromagnetic waves. Scatters (local to the receiver) and reflectors (local to the transmitter) commonly
characterize the radio channel. Small-scale fading, or simply fading, is used to describe the rapid fluctuations of
the amplitude of a radio signal over a short period or travel distance, so that large-scale path loss effects may be
ignored.
This channel results in random delay (random phase shift) with total a factor. Channels may be three types as
tabulated below
Type Descriptions Example
Simplex One way only FM radio, television
Half duplex Two way, only one at a
time
Police Radio
Full duplex Two way, both at the same
time
Mobile systems
Table1.Types of Channels with examples.
Attenuation
Attenuation can be described as the drop in the signal power when signal is been transmitted from one
point to another. Transmission path length, obstructions in the signal path, and multipath effects are the major
factors causing attenuation. Any objects, which obstruct the line of sight signal from the transmitter to the
receiver, can cause attenuation. The most important environmental attenuation factor generally caused by
buildings and hills is Shadowing. Shadowing of the signal can occur whenever there is an obstruction between
the transmitter and receiver, especially in heavily built up areas with much building shadows.
Diffraction is the bending of a radio signal towards a solid obstruction. Radio signals diffract off the
boundaries of obstruction, thus preventing total shadowing of the signals behind hills and buildings. Hills can
cause a large problem due to the large shadow they produce. However, the amount of diffraction is dependent
on the radio frequency used, with low frequencies diffracting more than high frequency signals. Hence, for
adequate signal strength, Ultra High Frequencies (UHF), and microwave signals require line of sight. More so,
to overcome the problem of shadowing, transmitters are usually elevated as high as possible to minimize the
number of obstruction. The typical amounts of variation in attenuation due to shadowing are shown in the table
2 below [11].
Description Typical Attenuation due to Shadowing
Heavy built-up urban
center
20dB variation from street to street
Sub-urban area (fewer
large buildings)
10dB greater signal power then built-up urban
center
Open rural area 20dB greater signal power then sub-areas
Terrain irregularities and
tree foliage
3-12dB signal power variation.
Table 2: Typical Attenuation in Radio Channel [11]
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Multipath Effects.
In mobile communications, the signal is degraded by terrestrial multipath fading in the lower
atmosphere known as troposphere [12].This troposphere is between altitude of 0 and 70 km and consists of
many objects such as buildings, mountains, trees, moving cars, sign posts at the ground surface and natural
phenomena like temperature, humidity, rainfall, etc at above the ground surface. These artificial and natural
phenomena obstruct the transmitted signal, hindered the signal to reflect, refract, diffract and scatter, and move
in different paths called multipath propagation causing the received signal to be degraded. The different paths
add up constructively when the received signal paths are in phase and destructively under unfavourable phase
conditions. The effects of terrestrial multipath propagation are signal fading, delay spread which is very
dominant in urban environment leading to intersymbol interference (ISI) distortion, and lastly the doppler spread
which occurs when there is relative motion in terrestrial environment. Therefore, these result in signal
fluctuation at the receiver [13]. In wireless channel, the medium is the free space. In this case, there is no
specified or particular path for signal transmission. The transmitted signal may be reflected from many things
like hills, trees, etc before being received at the destined receiver. This can give rise to multiple transmission
paths up to the receiver. The relative phase of the multiple reflected signals causes destructive or constructive
interference at the receiver. This is normally experienced for very short distances (typically at half of the
wavelength distances), thus is given the term - fast fading. This variation can vary from10 to 30dB [over short
distances [14].
Fading Statistics in Radio Channel
In communications systems, fading occurs due to the multipath propagation. As a result, signals
reaching the receiver from several different paths that may have different lengths corresponding to different time
delays and gains. Time delay causes additional phase shifts to the main signal component. Therefore, the signal
reaching the receiver is the sum of some copies of the original signal with different delays and gains. With this
explanation, the channel impulse response can be modelled as described in [15] with the equation given below:
𝑐 𝑡 = 𝛼 𝑘 𝛿(𝑡 −𝐾−1
𝐾=0
𝜏𝑘) (20)
Where:
𝛼 𝑘 = Complex path gain
𝑘 = Number of paths
𝜏 𝑘 = Path delay
Fading can be classified into two different scales:
Small Scale fading: small-scale fading happens in very short time duration, is caused by reflectors, and scatters
that change the amplitude, phase and angle of the arriving signal. Rayleigh distribution and Rician distribution
are often used to define small scale fading.
Large Scale fading: Large-scale fading is due to shadowing and the mobile station should move over a large
distance to overcome the effects of shadowing. Log-normal distribution is often used to define large-scale
fading.
Fast Fading
In a fast fading channel, the rate of change of the channel is higher than the signal symbol period and
hence the channel changes over one period. In other words, the channel coherence time 𝑇𝑐 , is smaller than the
symbol period𝑇𝑠. 𝑇𝑐 is related to the Doppler spread,𝑓𝑑 , as:
𝑇𝑐=0.423/𝑓𝑑 (21)
From this relation it is clear that a high Doppler spread results in a smaller channel coherence time. The
coherence time of 0.423ms corresponding to a 𝑓𝑑 of 1 kHz is clear.
1.4.6 Slow Fading
As the name suggests, in a slow fading channel, the channel coherence time is larger than the symbol
period and hence the channel remains approximately static over a symbol or multiple symbols. From the above
equation it is clear that slow fading is usually expected with low Doppler spread values; i.e. with slower moving
obstacles and receiver/transmitter. Multipath delay spread based and Doppler spread based fades are completely
independent of each other and hence is quite possible to have a flat, fast fading channel or a flat, slow fading
channel; and so on.
7. Performance Analysis of OFDM in Combating Multipath Fading
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Additive White Gaussian Noise
Zero-mean white Gaussian Noise (WGN) has the same power spectral density AWGN (f) for all
frequencies. The adjective „white‟ is used in the sense that white light contains equal amounts of all frequencies
within the visible band of electromagnetic radiation. The autocorrelation function of WGN is given by the
inverse Fourier transform of the noise power spectral density GWGN (f): The autocorrelation function RaWGN
(t) is zero for t 0. This means that any two different samples of WGN, no matter how close together in time
they are taken, are uncorrelated. The noise signal WGN (t) is totally decorrelated from its time-shifted version
for any t 0.
Fig 2. Signal with AWGN Noise
The amplitude of „integrated‟ (bandwidth) WGN has a Gaussian probability density distribution P
(WGNi).Noise exists in all communications systems operating over an analog physical channel, such as radio.
The main sources are thermal background noise, electrical noise in the receiver amplifiers, & inter-cellular
interference.
Rayleigh Fading Distribution
Rayleigh distributions are defined for fading of a channel when all the received signals are reflected
signals and there is no dominant component. The Rayleigh distribution has a Probability Density Functions
(PDF) given as: [18].
𝑝 𝑟 =
𝑟
𝜎2 exp −
𝑟2
2𝜎2 (0 ≤ 𝑟)
0 (𝑟 ≤ 0)
(22)
Where 𝜎 is the Root Mean Square (RMS) value of voltage in a received signal and 𝜎2
is the time-
average power of the received signal. The Cumulative Distribution Function (CDF) is defined to specify the
probability that the received signal does not exceed a specific threshold R. The CDF is given by [16]
𝑃 𝑅 = 𝑃 𝑟 ≤ 𝑅 = 𝑝 𝑟 𝑑𝑟 = 1 − exp −
𝑅2
2𝜎2 (23)
𝑅
0
The Rayleigh distribution is commonly used to describe the statistical time varying nature of the
received signal power. It describes the probability of the signal level being received due to fading.
The central limit theorem will give the channel the statistical characteristics of a Rayleigh Distribution.
Fig. 3: Rayleigh distribution
8. Performance Analysis of OFDM in Combating Multipath Fading
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II. Simulation Results And Discurssion
In this paper, analysis of the performance of different modulation schemes with gray coded bit mapping
over AWGN and Rayleigh fading Channel with OFDM technique is performed using MATLAB SIMULINK.
The diagram below shows the typical block diagram of an OFDM system.
Fig 4: The OFDM Model block diagram.
1. Required Bandwidth 20 MHz
2. Sampling Frequency 20 MHz
3. Carrier Modulation Used BPSK, QPSK, 4QAM, 16QAM.
4. Number of FFT size (𝑁𝑓𝑓𝑡 ) 256
5. Number of data subcarrier (𝑁𝑆𝐷) 200
6. Number of pilot subcarrier (𝑁𝑆𝑃) 28
Table 3 the Simulation Parameters for OFDM Transceiver
Fig 5: Single Carrier Modulation Schemes over Multipath Rayleigh Fading Channel.
Fig 6: Single Carrier Modulation Schemes over AWGN Channel.
0 5 10 15 20 25 30 35 40
10
-4
10
-3
10
-2
10
-1
10
0
EbNo [dB]
BER
BPSK
QPSK
4QAM
16QAM
0 5 10 15 20 25 30 35 40
10
-4
10
-3
10
-2
10
-1
10
0
EbNo [dB]
BER
BPSK
QPSK
4QAM
16QAM
9. Performance Analysis of OFDM in Combating Multipath Fading
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Fig 7: BER versus SNR Curve for OFDM technique in Multipath Rayleigh fading Channel with different
modulation Schemes.
Fig 5 and Fig 7 above show the effect of multipath fading channel on data transmission and the
feasibility of using OFDM Schemes to combat the effect of fading. A single fade or interferer in a single carrier
system of fig 5 can cause the entire link to fail hence not making the graph to converge due to much attenuation
and loss of transmitted bits that occur at the multipath channel. Hence, the BER is high in a Single Carrier
System. Fig 6 shows Single carrier converges easily over the AWGN Channel because it is an idea Channel with
noise and no delay spread. This establishes the fact that OFDM is used in combating frequency selective fading
channel and not AWGN.
However, the effect of Multipath Rayleigh Fading channel to the performance of the OFDM system for
four modulation techniques namely BPSK, QPSK, 4-QAM and 16-QAM are shown in the figure 6. It can be
observed from the above figure that, to achieve a BER of 10-5
, the OFDM model system with BPSK modulation
needs at least a SNR of 20dB, the OFDM system when using QPSK modulation needs at least 34dB, the OFDM
system with 4-QAM modulation needs at least SNR around 32dB and the OFDM system for 16-QAM
modulation needs at least SNR around 38dB.
III. Conclusion
Analysis was made on a Single Carrier technique and OFDM multicarrier technique. It has been shown
that OFDM allows data transmission with minimal error over fading channel than a Single Carrier. In addition,
performances of different modulation scheme for BPSK, QPSK, 4-QAM, and 16-QAM has been analyzed. It
can be deduced hence that in a channel with high interference, a small modulation scheme like BPSK is
favourable since it requires a low signal to noise ratio (SNR) in the receiver but with low data rate. However, in
an interference free channel, a larger constellation modulation scheme (16-QAM) is more beneficial due to the
higher bit rate.
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0 5 10 15 20 25 30 35 40
10
-4
10
-3
10
-2
10
-1
10
0
EbNo [dB]
BER
OFDM-BPSK
OFDM-QPSK
OFDM-4QAM
OFDM-16QAM