OFDM is a digital multi-carrier modulation technique that encodes data over multiple carrier frequencies. It splits a high-rate data stream into multiple lower-rate streams that are transmitted simultaneously over separate subcarriers. The subcarriers are chosen so they are orthogonal to each other, allowing them to be packed closely together without interference. OFDM provides high spectral efficiency, resilience to radio interference and multipath distortion, and works well for broadband applications including wireless networks, digital television and audio broadcasting.
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HiperLAN2[3].The orthogonality of the subcarriers is no longer
maintained which results in ICI (Inter carrier Interference)[4]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 Due to this the orthogonality of the subcarriers is no
longer maintained which results in ICI (Inter carrier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.
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HiperLAN2[3].The orthogonality of the subcarriers is no longer
maintained which results in ICI (Inter carrier Interference)[4]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.
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
IOSR Journal of Electronics and Communication Engineering(IOSR-JECE) is an open access international journal that provides rapid publication (within a month) of articles in all areas of electronics and communication engineering and its applications. The journal welcomes publications of high quality papers on theoretical developments and practical applications in electronics and communication engineering. Original research papers, state-of-the-art reviews, and high quality technical notes are invited for publications.
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.
Performance Analysis of OFDM in Combating Multipath FadingIOSR Journals
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
Performance Analysis of OFDM in Combating Multipath FadingIOSR Journals
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
PAPR REDUCTION AND BIT ERROR RATE EVALUATION IN OFDM SYSTEM USING HYBRID TECH...pijans
Orthogonal frequency division multiplexing (OFDM) has become an important component of waveform
generation in wideband transmission. it's a superior technology for the high-speed rate of wired and
wireless communication systems. Currently, multiple-input multiple-output orthogonal frequency division
multiplexing (MIMO OFDM) systems are crucial wireless communication systems like 4G and 5G
networks & tactical communication. The OFDM has many advantages over other techniques like its high
capacity and immunity against multipath fading channels. However, one amongst the foremost drawbacks
of the OFDM system is that the high-peak-to-average power ratio (PAPR) that leads the system to provide
in-band distortion and out-of-band radiation and reduces its efficiency. This problem increases with a rise
within the number of transmit antennas. Therefore, it's highly desirable to cut back the PAPR of an OFDM
signal. For this, numerous techniques are proposed to beat the PAPR problem like i) Selective mapping
(SLM) ii) Partial transmit sequence (PTS), iii) Clipping, iv) Clipping and filtering. All of those are reduced
the PAPR by generating alternative subcarrier vector that are statistically independent OFDM symbols for
a given data frame and transmitting the symbol with rock bottom peak power. During this paper we also
proposed, some hybrid techniques. The hybrid techniques are the technique of clipping is employed in
conjunction with SLM and PTS to cut back computational complexity. And also the combination of SLM-
PTS to scale back PAPR. Simulations are acquainted with analyze the efficiency of the techniques used
which signifies OFDM to be providing much better PAPR reduction and a way better Bit Error Rate
(BER). it's shown in simulation results that the proposed scheme performs well reducing PAPR. But the
proposed scheme is more complex than the prevailing techniques.
PAPR REDUCTION AND BIT ERROR RATE EVALUATION IN OFDM SYSTEM USING HYBRID TECH...pijans
Orthogonal frequency division multiplexing (OFDM) has become an important component of waveform
generation in wideband transmission. it's a superior technology for the high-speed rate of wired and
wireless communication systems. Currently, multiple-input multiple-output orthogonal frequency division
multiplexing (MIMO OFDM) systems are crucial wireless communication systems like 4G and 5G
networks & tactical communication. The OFDM has many advantages over other techniques like its high
capacity and immunity against multipath fading channels. However, one amongst the foremost drawbacks
of the OFDM system is that the high-peak-to-average power ratio (PAPR) that leads the system to provide
in-band distortion and out-of-band radiation and reduces its efficiency. This problem increases with a rise
within the number of transmit antennas. Therefore, it's highly desirable to cut back the PAPR of an OFDM
signal. For this, numerous techniques are proposed to beat the PAPR problem like i) Selective mapping
(SLM) ii) Partial transmit sequence (PTS), iii) Clipping, iv) Clipping and filtering. All of those are reduced
the PAPR by generating alternative subcarrier vector that are statistically independent OFDM symbols for
a given data frame and transmitting the symbol with rock bottom peak power. During this paper we also
proposed, some hybrid techniques. The hybrid techniques are the technique of clipping is employed in
conjunction with SLM and PTS to cut back computational complexity. And also the combination of SLMPTS to scale back PAPR. Simulations are acquainted with analyze the efficiency of the techniques used
which signifies OFDM to be providing much better PAPR reduction and a way better Bit Error Rate
(BER). it's shown in simulation results that the proposed scheme performs well reducing PAPR. But the
proposed scheme is more complex than the prevailing techniques.
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.
Successful interference cancellation with Blind Equalization method for MC-CD...IJTET Journal
Abstract— The increasing demand for wireless services has created the need for cost effective transmission techniques that can exploit scarce spectral resources efficiently. Inorder to achieve the high data rates needed to meet the quality of service requirements of future multimedia applications, MC-CDMA has been considered as good air-interface candidate, especially for the downlink. However, the user capacity of MC-CDMA system is essentially limited by interference. This interference can be mitigated by employing precoding techniques, IB-DFE based receivers and other efficient interference suppression techniques. In the proposed system, combined Iterative IA precoding at the transmitter with IB-DFE based processing at the receiver is suggested for MC-CDMA systems. The matrices for this nonlinear space-frequency equalizer are obtained by minimizing the overall MSE of all data streams at each subcarrier.
Blind Channel Shortening for MIMO-OFDM System Using Zero Padding and Eigen De...ijsrd.com
This paper deals with multiple-input multiple-output (MIMO) broadband wireless communication systems, employing orthogonal frequency-division multiplexing (OFDM). In order to exploit the benefits of OFDM in highly frequency-selective channels, without any significant increase in receiver complexity, a channel shortening prefilter is inserted at the receiver. The main aim of inserting channel shorteners is to shorten the channel so that the main energy of the composite channel is concentrated within a duration smaller than the guard interval inserted while transmission. Thus by including channel shortening equalizers at the receiver the inter symbol interference or the inter block interference can be suppressed. The new approach proposed in this thesis is zero padding approach with Eigen decomposition approach. The advantages of the proposed approaches include immunity to delay spread, resistance to frequency selective fading and simple equalization. This shortening design is a blind one, i.e., a priori knowledge of the MIMO channel impulse response to be shortened is not required, and can be carried out in closed-form.
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
IOSR Journal of Electronics and Communication Engineering(IOSR-JECE) is an open access international journal that provides rapid publication (within a month) of articles in all areas of electronics and communication engineering and its applications. The journal welcomes publications of high quality papers on theoretical developments and practical applications in electronics and communication engineering. Original research papers, state-of-the-art reviews, and high quality technical notes are invited for publications.
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.
Performance Analysis of OFDM in Combating Multipath FadingIOSR Journals
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
Performance Analysis of OFDM in Combating Multipath FadingIOSR Journals
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
PAPR REDUCTION AND BIT ERROR RATE EVALUATION IN OFDM SYSTEM USING HYBRID TECH...pijans
Orthogonal frequency division multiplexing (OFDM) has become an important component of waveform
generation in wideband transmission. it's a superior technology for the high-speed rate of wired and
wireless communication systems. Currently, multiple-input multiple-output orthogonal frequency division
multiplexing (MIMO OFDM) systems are crucial wireless communication systems like 4G and 5G
networks & tactical communication. The OFDM has many advantages over other techniques like its high
capacity and immunity against multipath fading channels. However, one amongst the foremost drawbacks
of the OFDM system is that the high-peak-to-average power ratio (PAPR) that leads the system to provide
in-band distortion and out-of-band radiation and reduces its efficiency. This problem increases with a rise
within the number of transmit antennas. Therefore, it's highly desirable to cut back the PAPR of an OFDM
signal. For this, numerous techniques are proposed to beat the PAPR problem like i) Selective mapping
(SLM) ii) Partial transmit sequence (PTS), iii) Clipping, iv) Clipping and filtering. All of those are reduced
the PAPR by generating alternative subcarrier vector that are statistically independent OFDM symbols for
a given data frame and transmitting the symbol with rock bottom peak power. During this paper we also
proposed, some hybrid techniques. The hybrid techniques are the technique of clipping is employed in
conjunction with SLM and PTS to cut back computational complexity. And also the combination of SLM-
PTS to scale back PAPR. Simulations are acquainted with analyze the efficiency of the techniques used
which signifies OFDM to be providing much better PAPR reduction and a way better Bit Error Rate
(BER). it's shown in simulation results that the proposed scheme performs well reducing PAPR. But the
proposed scheme is more complex than the prevailing techniques.
PAPR REDUCTION AND BIT ERROR RATE EVALUATION IN OFDM SYSTEM USING HYBRID TECH...pijans
Orthogonal frequency division multiplexing (OFDM) has become an important component of waveform
generation in wideband transmission. it's a superior technology for the high-speed rate of wired and
wireless communication systems. Currently, multiple-input multiple-output orthogonal frequency division
multiplexing (MIMO OFDM) systems are crucial wireless communication systems like 4G and 5G
networks & tactical communication. The OFDM has many advantages over other techniques like its high
capacity and immunity against multipath fading channels. However, one amongst the foremost drawbacks
of the OFDM system is that the high-peak-to-average power ratio (PAPR) that leads the system to provide
in-band distortion and out-of-band radiation and reduces its efficiency. This problem increases with a rise
within the number of transmit antennas. Therefore, it's highly desirable to cut back the PAPR of an OFDM
signal. For this, numerous techniques are proposed to beat the PAPR problem like i) Selective mapping
(SLM) ii) Partial transmit sequence (PTS), iii) Clipping, iv) Clipping and filtering. All of those are reduced
the PAPR by generating alternative subcarrier vector that are statistically independent OFDM symbols for
a given data frame and transmitting the symbol with rock bottom peak power. During this paper we also
proposed, some hybrid techniques. The hybrid techniques are the technique of clipping is employed in
conjunction with SLM and PTS to cut back computational complexity. And also the combination of SLMPTS to scale back PAPR. Simulations are acquainted with analyze the efficiency of the techniques used
which signifies OFDM to be providing much better PAPR reduction and a way better Bit Error Rate
(BER). it's shown in simulation results that the proposed scheme performs well reducing PAPR. But the
proposed scheme is more complex than the prevailing techniques.
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.
Successful interference cancellation with Blind Equalization method for MC-CD...IJTET Journal
Abstract— The increasing demand for wireless services has created the need for cost effective transmission techniques that can exploit scarce spectral resources efficiently. Inorder to achieve the high data rates needed to meet the quality of service requirements of future multimedia applications, MC-CDMA has been considered as good air-interface candidate, especially for the downlink. However, the user capacity of MC-CDMA system is essentially limited by interference. This interference can be mitigated by employing precoding techniques, IB-DFE based receivers and other efficient interference suppression techniques. In the proposed system, combined Iterative IA precoding at the transmitter with IB-DFE based processing at the receiver is suggested for MC-CDMA systems. The matrices for this nonlinear space-frequency equalizer are obtained by minimizing the overall MSE of all data streams at each subcarrier.
Blind Channel Shortening for MIMO-OFDM System Using Zero Padding and Eigen De...ijsrd.com
This paper deals with multiple-input multiple-output (MIMO) broadband wireless communication systems, employing orthogonal frequency-division multiplexing (OFDM). In order to exploit the benefits of OFDM in highly frequency-selective channels, without any significant increase in receiver complexity, a channel shortening prefilter is inserted at the receiver. The main aim of inserting channel shorteners is to shorten the channel so that the main energy of the composite channel is concentrated within a duration smaller than the guard interval inserted while transmission. Thus by including channel shortening equalizers at the receiver the inter symbol interference or the inter block interference can be suppressed. The new approach proposed in this thesis is zero padding approach with Eigen decomposition approach. The advantages of the proposed approaches include immunity to delay spread, resistance to frequency selective fading and simple equalization. This shortening design is a blind one, i.e., a priori knowledge of the MIMO channel impulse response to be shortened is not required, and can be carried out in closed-form.
Unit 8 - Information and Communication Technology (Paper I).pdfThiyagu K
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Instructions for Submissions thorugh G- Classroom.pptxJheel Barad
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Honest Reviews of Tim Han LMA Course Program.pptxtimhan337
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Introduction to AI for Nonprofits with Tapp NetworkTechSoup
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How to Make a Field invisible in Odoo 17Celine George
It is possible to hide or invisible some fields in odoo. Commonly using “invisible” attribute in the field definition to invisible the fields. This slide will show how to make a field invisible in odoo 17.
June 3, 2024 Anti-Semitism Letter Sent to MIT President Kornbluth and MIT Cor...Levi Shapiro
Letter from the Congress of the United States regarding Anti-Semitism sent June 3rd to MIT President Sally Kornbluth, MIT Corp Chair, Mark Gorenberg
Dear Dr. Kornbluth and Mr. Gorenberg,
The US House of Representatives is deeply concerned by ongoing and pervasive acts of antisemitic
harassment and intimidation at the Massachusetts Institute of Technology (MIT). Failing to act decisively to ensure a safe learning environment for all students would be a grave dereliction of your responsibilities as President of MIT and Chair of the MIT Corporation.
This Congress will not stand idly by and allow an environment hostile to Jewish students to persist. The House believes that your institution is in violation of Title VI of the Civil Rights Act, and the inability or
unwillingness to rectify this violation through action requires accountability.
Postsecondary education is a unique opportunity for students to learn and have their ideas and beliefs challenged. However, universities receiving hundreds of millions of federal funds annually have denied
students that opportunity and have been hijacked to become venues for the promotion of terrorism, antisemitic harassment and intimidation, unlawful encampments, and in some cases, assaults and riots.
The House of Representatives will not countenance the use of federal funds to indoctrinate students into hateful, antisemitic, anti-American supporters of terrorism. Investigations into campus antisemitism by the Committee on Education and the Workforce and the Committee on Ways and Means have been expanded into a Congress-wide probe across all relevant jurisdictions to address this national crisis. The undersigned Committees will conduct oversight into the use of federal funds at MIT and its learning environment under authorities granted to each Committee.
• The Committee on Education and the Workforce has been investigating your institution since December 7, 2023. The Committee has broad jurisdiction over postsecondary education, including its compliance with Title VI of the Civil Rights Act, campus safety concerns over disruptions to the learning environment, and the awarding of federal student aid under the Higher Education Act.
• The Committee on Oversight and Accountability is investigating the sources of funding and other support flowing to groups espousing pro-Hamas propaganda and engaged in antisemitic harassment and intimidation of students. The Committee on Oversight and Accountability is the principal oversight committee of the US House of Representatives and has broad authority to investigate “any matter” at “any time” under House Rule X.
• The Committee on Ways and Means has been investigating several universities since November 15, 2023, when the Committee held a hearing entitled From Ivory Towers to Dark Corners: Investigating the Nexus Between Antisemitism, Tax-Exempt Universities, and Terror Financing. The Committee followed the hearing with letters to those institutions on January 10, 202
The Roman Empire A Historical Colossus.pdfkaushalkr1407
The Roman Empire, a vast and enduring power, stands as one of history's most remarkable civilizations, leaving an indelible imprint on the world. It emerged from the Roman Republic, transitioning into an imperial powerhouse under the leadership of Augustus Caesar in 27 BCE. This transformation marked the beginning of an era defined by unprecedented territorial expansion, architectural marvels, and profound cultural influence.
The empire's roots lie in the city of Rome, founded, according to legend, by Romulus in 753 BCE. Over centuries, Rome evolved from a small settlement to a formidable republic, characterized by a complex political system with elected officials and checks on power. However, internal strife, class conflicts, and military ambitions paved the way for the end of the Republic. Julius Caesar’s dictatorship and subsequent assassination in 44 BCE created a power vacuum, leading to a civil war. Octavian, later Augustus, emerged victorious, heralding the Roman Empire’s birth.
Under Augustus, the empire experienced the Pax Romana, a 200-year period of relative peace and stability. Augustus reformed the military, established efficient administrative systems, and initiated grand construction projects. The empire's borders expanded, encompassing territories from Britain to Egypt and from Spain to the Euphrates. Roman legions, renowned for their discipline and engineering prowess, secured and maintained these vast territories, building roads, fortifications, and cities that facilitated control and integration.
The Roman Empire’s society was hierarchical, with a rigid class system. At the top were the patricians, wealthy elites who held significant political power. Below them were the plebeians, free citizens with limited political influence, and the vast numbers of slaves who formed the backbone of the economy. The family unit was central, governed by the paterfamilias, the male head who held absolute authority.
Culturally, the Romans were eclectic, absorbing and adapting elements from the civilizations they encountered, particularly the Greeks. Roman art, literature, and philosophy reflected this synthesis, creating a rich cultural tapestry. Latin, the Roman language, became the lingua franca of the Western world, influencing numerous modern languages.
Roman architecture and engineering achievements were monumental. They perfected the arch, vault, and dome, constructing enduring structures like the Colosseum, Pantheon, and aqueducts. These engineering marvels not only showcased Roman ingenuity but also served practical purposes, from public entertainment to water supply.
2. 2
Introduction about OFDM.
What is OFDM.
OFDM Mechanism.
Variation of OFDM.
Different Types of
Multiplexing.
Applications of OFDM.
Advantages and Drawbacks
Conclusion.
3. In telecommunications, orthogonal
frequency-division multiplexing (OFDM)
is a method of encoding digital data on
multiple carrier frequencies.
OFDM is a modulation technique for
transmitting large amounts of digital
data over a radio wave.
4. OFDM technology was first conceived of in the
1960s and 1970s during research into
minimizing interference among channels near
each other in frequency, and
To achieve clean data transmission in situations
prone to interference and signal corruption when
more conventional modulation schemes are
used.
5. *Orthogonality:
The “orthogonal” part of the OFDM name
indicates that there is a precise
mathematical relationship between the
frequencies of the carriers in the system
Wireless, The OFDM modulation scheme
offers many advantages for broadband
wireless transport. -It supports high data
rates
6. 6
It is a special kind of FDM
The spacing between carriers are such
that they are orthogonal to one another
Therefore no need of guard band
between carriers.
One example makes the thing clear
7. 7
Vector space
• A, B and C vectors in space
are orthogonal to each other
• A.B=B.C=C.A=0
• (A+B+C).A=(mod A)^2
• (A+B+C).B=(mod B)^2
• (A+B+C).C=(mod C)^2
A
B
C
8. The use of the IFFT in OFDM- By the use of
the Inverse Fast Fourier Transform (IFFT)
algorithm. It can be better because it allows
precise control
9. Certain types of broadband access through POTS
(plain old telephone service) copper wiring
Power line communication (PLC)
Multimedia over Coax Alliance (MoCA) home
networking
Some digital radio systems
Some digital TV systems
Some mobile TV systems
OFDM is used in Wi-Fi, DSL internet
access, 4Gwireless communications, and digital
televisionand radio broadcast services.
10. 10
Main idea: split data stream into N parallel streams of
reduced data rate and transmit each on a separate
subcarrier.
When the subcarriers have appropriate spacing to satisfy
orthogonality, their spectra will overlap. OFDM
modulation is equivalent to the IDFT:
11. Orthogonal frequency division multiplexing (OFDM) is a
technique, method or scheme for digital multi-carrier
modulation using many closely spaced subcarriers - a
previously modulated signal modulated into another signal of
higher frequency and bandwidth.
Each of these subcarriers contains numbers of parallel data
streams or channels and is modulated conventionally at a
low symbol rate; these are groups of bits of data related to
(but not the same as) gross bitrate, which is expressed in
bits/second.
12. 12
Method of Digital Communication that breaks a large bandwidth into
small subcarriers using the Inverse Fast Fourier Transform (IFFT).
Removes Intersymbol Interference (ISI) by having subcarrier
frequency be integer multiples of the symbol rate.
By dividing total bandwidth into independent subchannels, multiple
access is achieved by distributing subchannels between users.
Allows for higher data rates by allocating power and subchannels to
users through Adaptive Modulation.
13. 13
Parallel Data Streams
The available frequency spectrum is
divided into several sub-channels
low-rate bit stream is transmitted
over one sub-channel by modulating
a sub-carrier using a standard
modelation scheme, for example 4-
QAM
Multiple Carriers are combined
through the Fourier Series
• Computed by Inverse Fast
Fourier transform
4-QAM modulation
15. 15
OFDM Transmitter :
An OFDM carrier signal is the sum of a number of orthogonal sub-carriers,
with base band data on each sub-carrier being independently modulated
commonly using some type of quadrature amplitude modulation (QAM) or
phase-shift keying (PSK).
16. 16
OFDM Receiver:
The receiver picks up the signal r(t), which is then quadrature-
mixed down to baseband using cosine and sine waves at the
carrier frequency. This returns N parallel streams, each of
which is converted to a binary stream using an appropriate
symbol detector. These streams are then re-combined into a
serial stream, , which is an estimate of the original binary
stream at the transmitter.
17. The IEEE 802.16e/ WiMax use OFDMA as
Multiple access technique
• Bandwidth options 1.25, 5, 10, or 20 MHz
• Entire bandwidth divided into 128, 512, 1024 or
2048 sub carriers
• 20 MHz bandwidth with 2048 sub carriers has 9.8
KHz spacing between sub carriers
20. 20
FDM frequency division multiplexing
(FDM) is a technology that transmits multiple signals simultaneously over a
single transmission path.
TDM (synchronous)
Time-division multiplexing (TDM) is a method of putting multiple data
streams in a single signal by separating the signal into many segments,
each having a very short duration.
Wavelength-Division Multiplexing (WDM)
technology which multiplexes multiple optical carrier signals on a single
optical fibre by using different wavelengths (colours) of laser light to carry
different signals.
21. 21
Digital Video Broadcasting
Digital Audio Broadcasting
ADSL
Wireless LANs
OFDMA -Multiple Access.
22. OFDM is used for wideband digital communication,
which is commonly used for digital television and audio
broadcasting (radio) as well as broadband Internet
access and wireless networking.
OFDM is very similar to FDM (frequency division
multiplexing) but with technology purposely
emphasizing the minimization of crosstalk or signal
interference from other nearby signal carrying
communication mediums.
OFDM uses many narrow band signals as opposed to
a signal modulated at a high symbol rate and a large
bandwidth.
23. Allows carriers to overlap (no guard band), resulting in
lesser wasted bandwidth without any Inter Carrier
Interference (ICI)
High data rate distributed over multiple carriers resulting
in lower symbol rate (more immune to ISI)
Permits higher data rate as compared to FDM
Increased security and bandwidth efficiency possible
using CDMA – OFDM (MC-CDMA)
Simple guard intervals make the system more robust to
multipath effects.
24. 24
OFDM is spectrally efficient
• IFFT/FFT operation ensures that sub-carriers do not interfere
with each other.
OFDM has an inherent robustness against narrowband interference.
• Narrowband interference will affect at most a couple
of subchannels.
• Information from the affected subchannels can be
erased and recovered via the forward error
correction (FEC) codes.
Equalization is very simple compared to Single-Carrier systems
25. 25
OFDM has excellent robustness in multi-path environments.
• Cyclic prefix preserves orthogonality between sub-
carriers.
• Cyclic prefix allows the receiver to capture multi-
path energy more efficiently.
Ability to comply with world-wide regulations:
• Bands and tones can be dynamically turned on/off
to comply with changing regulations.
Coexistence with current and future systems:
• Bands and tones can be dynamically turned on/off
for enhanced coexistence with the other devices.
26. 26
Multi-user Diversity
• broadband signals experience frequency
selective fading
• OFDMA allows different users to transmit over
different portions of the broadband spectrum
(traffic channel)
• Different users perceive different channel
qualities, a deep faded channel for one user
may still be favorable to others
29. Receiver Simplicity
• It eliminates the intra-cell interference avoiding
CDMA type of multi-user detection
• Orthogonality of code destroyed by selective
fading
• Only FFT processor is required
Bit Error Rate performance is better only in Fading
environment
30. Peak to average power
ratio (PAPR)
avg
P
t
x
PAPR
2
)
(
The large amplitude variation increases in-band noise and increases the
BER when the signal has to go through amplifier nonlinearities.
31. 31
Synchronization
• Tight Synchronization between users are required
for FFT in receiver
• Pilot signals are used for synchronizations
Co-channel interference
• Dealing with this is more complex in OFDM than in CDMA
• Dynamic channel allocation with advanced
coordination among adjacent base stations
32. 32
High sensitivity inter-channel interference, ICI
OFDM is sensitive to frequency, clock and phase offset
The OFDM time-domain signal has a relatively large peak-to-average
ratio
• tends to reduce the power efficiency of the RF amplifier
• non-linear amplification destroys the orthogonality of the OFDM
signal and introduced out-of-band radiation
33. 33
OFDM and Adaptive Modulation allow for increased
performance in a time-varying channel
Complicated communications system between three
software applications on two different processors
Root-finding and Linear methods handle allocations with
clear tradeoffs.
34. 34
Future works
• Peak-to-average power reduction in OFDM
• Timing and Frequency Synchronization
• Efficient digital signal processing Implementation of OFDM
• Multiple input/Multiple output (MIMO) OFDM
Conclusion
• Different variations of OFDMA are proposed
and have different pros and cons