This document summarizes research on performance analysis of adaptive multi-user OFDM systems. It describes using adaptive modulation to maximize throughput by selecting modulation schemes on a per-subcarrier basis to maintain bit error rate while maximizing spectral efficiency. Adaptive user allocation is also analyzed to improve signal power by optimizing user-subcarrier combinations based on frequency selective fading differences between users. Simulation results show adaptive modulation providing 12-16dB SNR improvement over fixed modulation. Adaptive user allocation provides an additional 3-5dB average signal power gain. The document concludes these adaptive techniques allow OFDM systems to approach channel capacity limits given constraints of the radio channel, transmitter power and quality of service requirements.
COMPARISON OF BIT ERROR RATE PERFORMANCE OF VARIOUS DIGITAL MODULATION SCHEME...ijasa
Digital modulation increases information capacity, data security, and system availability while maintaining high communication quality. As a result, digital modulation techniques are in higher demand than analog modulation techniques due to their ability to transmit larger amounts of data. Amplitude Shift Keying (ASK), Frequency Shift Keying (FSK), Phase Shift Keying (PSK), Differential Phase Shift Keying (DPSK), and Quadrature Amplitude Modulation (QAM) are critical components of current communications systems development, particularly for broadband wireless communications. In this paper, the comparison of bit error rate performance of different modulation schemes (BPSK, QPSK, and16-QAM) and various equalization techniques such as constant modulus algorithm (CMA) and maximum likelihood sequence estimate (MLSE) for the AWGN and Rayleigh fading channels is analyzed using Simulink. BPSK outperforms QPSK and 16-QAM when compared to the other two digital modulation schemes. Among the three digital modulation schemes, BPSK is showing better performance as compared to QPSK and 16- QAM
Peak to Average Power Ratio (PAPR) Reduction in OFDM-OQAM Signalspaperpublications3
Abstract: The Orthogonal Frequency Division Multiplexing (OFDM) is a type of modulation that is being used for many of the latest wireless, telecommunication and broadcasting standards. OFDM is considered to be complicated than other signals but also it possess high data rate transmissions with relatively wide bandwidths. The major disadvantage included in OFDM signal is Peak-to-Average Power Ratio (PAPR) in higher level and Sensitive to Carrier offset. Hence there were found to be many reduction techniques for PAPR have been proposed where in need to reduction in high PAPR and carrier sensitivity still more to make it efficient for future optical domain standards. This paper not only makes the OFDM system advantageous but also suitable for fast data transmission and reduces the complication at receiver side, because all the transmitting data are cleared out of signal noise, interferences, etc. The technique which is going to get implemented for PAPR reduction is Optimized Iterative Clipping and Filtering (OICF).The OFDM is provided with the subcarrier of N=256 and the modulation of Offset Quadrature Amplitude Modulation (OQAM). The OQAM-OFDM provides the higher spectral efficiency and also the inter-symbol interference is avoided since not using Cyclic Prefix (CP) in OQAM-OFDM signal. The main reason for reducing PAPR is that to avoid non- linearity at the receiving end in high speed wireless communication.
COMPARISON OF BIT ERROR RATE PERFORMANCE OF VARIOUS DIGITAL MODULATION SCHEME...ijasa
Digital modulation increases information capacity, data security, and system availability while maintaining high communication quality. As a result, digital modulation techniques are in higher demand than analog modulation techniques due to their ability to transmit larger amounts of data. Amplitude Shift Keying (ASK), Frequency Shift Keying (FSK), Phase Shift Keying (PSK), Differential Phase Shift Keying (DPSK), and Quadrature Amplitude Modulation (QAM) are critical components of current communications systems development, particularly for broadband wireless communications. In this paper, the comparison of bit error rate performance of different modulation schemes (BPSK, QPSK, and16-QAM) and various equalization techniques such as constant modulus algorithm (CMA) and maximum likelihood sequence estimate (MLSE) for the AWGN and Rayleigh fading channels is analyzed using Simulink. BPSK outperforms QPSK and 16-QAM when compared to the other two digital modulation schemes. Among the three digital modulation schemes, BPSK is showing better performance as compared to QPSK and 16- QAM
Peak to Average Power Ratio (PAPR) Reduction in OFDM-OQAM Signalspaperpublications3
Abstract: The Orthogonal Frequency Division Multiplexing (OFDM) is a type of modulation that is being used for many of the latest wireless, telecommunication and broadcasting standards. OFDM is considered to be complicated than other signals but also it possess high data rate transmissions with relatively wide bandwidths. The major disadvantage included in OFDM signal is Peak-to-Average Power Ratio (PAPR) in higher level and Sensitive to Carrier offset. Hence there were found to be many reduction techniques for PAPR have been proposed where in need to reduction in high PAPR and carrier sensitivity still more to make it efficient for future optical domain standards. This paper not only makes the OFDM system advantageous but also suitable for fast data transmission and reduces the complication at receiver side, because all the transmitting data are cleared out of signal noise, interferences, etc. The technique which is going to get implemented for PAPR reduction is Optimized Iterative Clipping and Filtering (OICF).The OFDM is provided with the subcarrier of N=256 and the modulation of Offset Quadrature Amplitude Modulation (OQAM). The OQAM-OFDM provides the higher spectral efficiency and also the inter-symbol interference is avoided since not using Cyclic Prefix (CP) in OQAM-OFDM signal. The main reason for reducing PAPR is that to avoid non- linearity at the receiving end in high speed wireless communication.
Design of Microstrip UWB Bandpass Filter using open-circuited resonatorsIJERD Editor
A compact band pass filter with a fractional bandwidth of 59% is designed for Ultra Wide Band (UWB) applications using a microstrip structure consisting of open circuit resonators. Transmission zeros are utilized at the passband edges to enhance the signal selectivity. The filter is characterized by sharp roll-off characteristics due to the presence of transmission zeros. The insertion loss and return loss are found to be 0.1dB and -15dB respectively. This filter has a measured 3-dB passband of (3 to 5.5) GHz, with a compact size of (13.2 x 9.7) mm. The filter offers desirable performance for the lower-band frequency of a UWB system and exhibits low insertion loss. As the structure comprises of only transmission line sections and no coupling gap, the filter is made easy for fabrication. This UWB BPF is useful to alleviate the strong WLAN signals interference to UWB receivers. To illustrate the concept, band pass filter was designed using Agilent® ADS software and simulated results are obtained.
Comparison of Three Different Cancellation Schemes for Orthogonal Frequency D...ijtsrd
Orthogonal Frequency Division Multiplexing OFDM is an exceptional case of Frequency Division Multiplexing. The dilemma of OFDM is its sensitivity to frequency offset between the transmitted and received carrier frequencies. This frequency offset establishes Inter Carrier Interference ICI Cancellation in the OFDM symbol. ICI reduction methods have been had by OFDM. This research considers three ICI self cancellation SC , maximum likelihood ML estimation, and extended Kalman filter EKF method. These three methods are compared in terms of bit error rate performance, bandwidth efficiency, and computational complexity. For high values of the frequency offset and for higher order modulation schemes, the SC method does not as well as the ML and EKF methods. Simulation results using MATLAB software. Ma Khin Saw | Aye Aye Khine ""Comparison of Three Different Cancellation Schemes for Orthogonal Frequency Division Multiplexing (OFDM) System"" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-3 | Issue-4 , June 2019, URL: https://www.ijtsrd.com/papers/ijtsrd25182.pdf
Paper URL: https://www.ijtsrd.com/engineering/electronics-and-communication-engineering/25182/comparison-of-three-different-cancellation-schemes-for-orthogonal-frequency-division-multiplexing-ofdm-system/ma-khin-saw
A 3 – 14 GHZ LOW NOISE AMPLIFIER FOR ULTRA WIDE BAND APPLICATIONSVLSICS Design
This paper presents an ultra wide band (UWB) low noise amplifier (LNA) with very high gain, better input matching, low noise figure, better linearity and low power consumption. A dual source degenerated resistive current reuse is used as an input stage and a cascode stage with shunt-series peaking is used to enhance the bandwidth and reverse isolation. The proposed LNA achieves a peak power gain of 20.92 dB at 9 GHz while achieving a gain greater than 20.3 dB over 3 – 14 GHz bandwidth. The achieved noise figure is in the range of 3.72 – 4.78 dB, while the input matching and the output matching are kept below – 9 dB and –10 dB respectively. The reverse isolation is below –52 dB throughout the entire band. This LNA ensures better linearity with an IIP3 of 4 dBm at 9 GHz with very low power consumption of 5.876 mW at 1 V supply.
Ber performance of ofdm with discrete wavelet transform for time dispersive c...eSAT Publishing House
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology
The peer-reviewed International Journal of Engineering Inventions (IJEI) is started with a mission to encourage contribution to research in Science and Technology. Encourage and motivate researchers in challenging areas of Sciences and Technology.
Transmission system used for optical fibers Jay Baria
In this presentation I have explained various types of transmission system used for optical transmission and also described about the budget method that has to be followed while selecting an source for optical fibers and also about the factors that should be consider while selecting an source.
This paper presents the design and performance comparison of a two stage
operational amplifier topology using CMOS and BiCMOS technology. This conventional op
amp circuit was designed by using RF model of BSIM3V3 in 0.6 μm CMOS technology and
0.35 μm BiCMOS technology. Both the op amp circuits were designed and simulated,
analyzed and performance parameters are compared. The performance parameters such as
gain, phase margin, CMRR, PSRR, power consumption etc achieved are compared. Finally,
we conclude the suitability of CMOS technology over BiCMOS technology for low power
RF design.
A review paper on the papr analysis of orthogonal frequency division multiple...ijmnct
OFDM (Orthogonal Frequency Division Multiplexing) has been raised a new modulation technique. Due
to its advantages in multipath fading channel e.g. robust against ISI, ICI and some other advantages like
best QoS for multiple users, efficient usage of bandwidth it is suggested to be the modulation technique for
next generation 4G networks e.g. LTE. But along with all its advantages there are some disadvantages also
e.g. High PAPR (Peak to Average Power Ratio) at the transmitter end and BER (Bit Error Rate) at the
receiving end. Since OFDM is only used in the downlink of 4G networks. To reduce the problems of OFDM
some techniques e.g. SLM, PTS, Clipping, Coding, & Pre-coding etc are suggested but none of them is
reduce the PAPR and BER to an acceptable value. This Paper will discuss some techniques of PAPR &
BER reduction, and their advantages and disadvantages in detail.
Performance Analysis of Post Compensated Long Haul High Speed Coherent Optica...Yayah Zakaria
This paper addresses the performance analysis of OFDM transmission system based on coherent detection over high speed long haul optical links with high spectral efficiency modulation formats such as Quadrature Amplitude Modulation (QAM) as a mapping method prior to the OFDM multicarrier representation. Post compensation is used to compensate for
phase noise effects. Coherent detection for signal transmitted at bit rate of 40 Gbps is successfully achieved up to distance of 3200km. Performance is analyzed in terms of Symbol Error Rate and Error Vector Magnitude by varying Optical Signal to Noise Ratio (OSNR) and varying the length of the fiber i.e transmission distance. Transmission performance is also observed through constellation diagrams at different transmission distances and
different OSNRs.
Bit error rate analysis of miso system in rayleigh fading channeleSAT Publishing House
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology
Performance Improvement for Hybrid L-band Remote Erbium Doped Fiber Amplifier...IJECEIAES
We have demonstrated the performance improvement of L-band hybrid remote Erbium-doped fiber amplifier by introducing a phase modulator to suppress the stimulated Brilloiun scattering (SBS) effect in the transmission. The transmission gain has improved by 12.65dB while the noise figure has reduced by 47.1dB when 0dBm signal power is generated at 1590.05nm wavelength. Furthermore, the optical signal-to-noise ratio has improved from 7.81dB to 29.72dB when the signal power is varied from -30dBm to 0dBm. By implementing a phase modulator to the input signal somehow able to produce better performance regarding gain, noise figure and optical signalto-noise ratio, especially at the higher signal power as the gain, has been transferred to the Stokes signal and the amplified signal.
A compact fourth order multi-fold hairpin line microstrip bandpass filter at ...eSAT Publishing House
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology
Design of Microstrip UWB Bandpass Filter using open-circuited resonatorsIJERD Editor
A compact band pass filter with a fractional bandwidth of 59% is designed for Ultra Wide Band (UWB) applications using a microstrip structure consisting of open circuit resonators. Transmission zeros are utilized at the passband edges to enhance the signal selectivity. The filter is characterized by sharp roll-off characteristics due to the presence of transmission zeros. The insertion loss and return loss are found to be 0.1dB and -15dB respectively. This filter has a measured 3-dB passband of (3 to 5.5) GHz, with a compact size of (13.2 x 9.7) mm. The filter offers desirable performance for the lower-band frequency of a UWB system and exhibits low insertion loss. As the structure comprises of only transmission line sections and no coupling gap, the filter is made easy for fabrication. This UWB BPF is useful to alleviate the strong WLAN signals interference to UWB receivers. To illustrate the concept, band pass filter was designed using Agilent® ADS software and simulated results are obtained.
Comparison of Three Different Cancellation Schemes for Orthogonal Frequency D...ijtsrd
Orthogonal Frequency Division Multiplexing OFDM is an exceptional case of Frequency Division Multiplexing. The dilemma of OFDM is its sensitivity to frequency offset between the transmitted and received carrier frequencies. This frequency offset establishes Inter Carrier Interference ICI Cancellation in the OFDM symbol. ICI reduction methods have been had by OFDM. This research considers three ICI self cancellation SC , maximum likelihood ML estimation, and extended Kalman filter EKF method. These three methods are compared in terms of bit error rate performance, bandwidth efficiency, and computational complexity. For high values of the frequency offset and for higher order modulation schemes, the SC method does not as well as the ML and EKF methods. Simulation results using MATLAB software. Ma Khin Saw | Aye Aye Khine ""Comparison of Three Different Cancellation Schemes for Orthogonal Frequency Division Multiplexing (OFDM) System"" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-3 | Issue-4 , June 2019, URL: https://www.ijtsrd.com/papers/ijtsrd25182.pdf
Paper URL: https://www.ijtsrd.com/engineering/electronics-and-communication-engineering/25182/comparison-of-three-different-cancellation-schemes-for-orthogonal-frequency-division-multiplexing-ofdm-system/ma-khin-saw
A 3 – 14 GHZ LOW NOISE AMPLIFIER FOR ULTRA WIDE BAND APPLICATIONSVLSICS Design
This paper presents an ultra wide band (UWB) low noise amplifier (LNA) with very high gain, better input matching, low noise figure, better linearity and low power consumption. A dual source degenerated resistive current reuse is used as an input stage and a cascode stage with shunt-series peaking is used to enhance the bandwidth and reverse isolation. The proposed LNA achieves a peak power gain of 20.92 dB at 9 GHz while achieving a gain greater than 20.3 dB over 3 – 14 GHz bandwidth. The achieved noise figure is in the range of 3.72 – 4.78 dB, while the input matching and the output matching are kept below – 9 dB and –10 dB respectively. The reverse isolation is below –52 dB throughout the entire band. This LNA ensures better linearity with an IIP3 of 4 dBm at 9 GHz with very low power consumption of 5.876 mW at 1 V supply.
Ber performance of ofdm with discrete wavelet transform for time dispersive c...eSAT Publishing House
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology
The peer-reviewed International Journal of Engineering Inventions (IJEI) is started with a mission to encourage contribution to research in Science and Technology. Encourage and motivate researchers in challenging areas of Sciences and Technology.
Transmission system used for optical fibers Jay Baria
In this presentation I have explained various types of transmission system used for optical transmission and also described about the budget method that has to be followed while selecting an source for optical fibers and also about the factors that should be consider while selecting an source.
This paper presents the design and performance comparison of a two stage
operational amplifier topology using CMOS and BiCMOS technology. This conventional op
amp circuit was designed by using RF model of BSIM3V3 in 0.6 μm CMOS technology and
0.35 μm BiCMOS technology. Both the op amp circuits were designed and simulated,
analyzed and performance parameters are compared. The performance parameters such as
gain, phase margin, CMRR, PSRR, power consumption etc achieved are compared. Finally,
we conclude the suitability of CMOS technology over BiCMOS technology for low power
RF design.
A review paper on the papr analysis of orthogonal frequency division multiple...ijmnct
OFDM (Orthogonal Frequency Division Multiplexing) has been raised a new modulation technique. Due
to its advantages in multipath fading channel e.g. robust against ISI, ICI and some other advantages like
best QoS for multiple users, efficient usage of bandwidth it is suggested to be the modulation technique for
next generation 4G networks e.g. LTE. But along with all its advantages there are some disadvantages also
e.g. High PAPR (Peak to Average Power Ratio) at the transmitter end and BER (Bit Error Rate) at the
receiving end. Since OFDM is only used in the downlink of 4G networks. To reduce the problems of OFDM
some techniques e.g. SLM, PTS, Clipping, Coding, & Pre-coding etc are suggested but none of them is
reduce the PAPR and BER to an acceptable value. This Paper will discuss some techniques of PAPR &
BER reduction, and their advantages and disadvantages in detail.
Performance Analysis of Post Compensated Long Haul High Speed Coherent Optica...Yayah Zakaria
This paper addresses the performance analysis of OFDM transmission system based on coherent detection over high speed long haul optical links with high spectral efficiency modulation formats such as Quadrature Amplitude Modulation (QAM) as a mapping method prior to the OFDM multicarrier representation. Post compensation is used to compensate for
phase noise effects. Coherent detection for signal transmitted at bit rate of 40 Gbps is successfully achieved up to distance of 3200km. Performance is analyzed in terms of Symbol Error Rate and Error Vector Magnitude by varying Optical Signal to Noise Ratio (OSNR) and varying the length of the fiber i.e transmission distance. Transmission performance is also observed through constellation diagrams at different transmission distances and
different OSNRs.
Bit error rate analysis of miso system in rayleigh fading channeleSAT Publishing House
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology
Performance Improvement for Hybrid L-band Remote Erbium Doped Fiber Amplifier...IJECEIAES
We have demonstrated the performance improvement of L-band hybrid remote Erbium-doped fiber amplifier by introducing a phase modulator to suppress the stimulated Brilloiun scattering (SBS) effect in the transmission. The transmission gain has improved by 12.65dB while the noise figure has reduced by 47.1dB when 0dBm signal power is generated at 1590.05nm wavelength. Furthermore, the optical signal-to-noise ratio has improved from 7.81dB to 29.72dB when the signal power is varied from -30dBm to 0dBm. By implementing a phase modulator to the input signal somehow able to produce better performance regarding gain, noise figure and optical signalto-noise ratio, especially at the higher signal power as the gain, has been transferred to the Stokes signal and the amplified signal.
A compact fourth order multi-fold hairpin line microstrip bandpass filter at ...eSAT Publishing House
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology
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.
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.
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
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.
An Adaptive Approach to Switching Coded Modulation in OFDM System Under AWGN ...ijsrd.com
In this paper we have studied the OFDM for different Quadrature amplitude modulation technique (QAM) The scatter plot and their output signal to noise ratio, dependent bit error rate variation is analyzed for every type of modulation in OFDM. After observing the BER for each SNR in the system, switching threshold range has been prepared and now system is ready to face the Adaptive coded modulation (ACM).The results shows the switching of modulation technique.
Improving The Performance Of Multiuser OFDM Wireless System With UWB ChannelIJTET Journal
The multi user OFDM system can be used to produce a highly flexible and effective communication
system. In the existing multi user OFDM system, resource allocation to each user is the major problem. Also the existing
multi user OFDM system uses frequency diversity technique that requires sparse bandwidth and multiple receivers
improving the complexity. In order to increase the system performance, the proposed system allows multiple user data to
be multiplexed together to form a single OFDM symbol where the resources are allocated equally to all users. The
proposed multiuser OFDM system achieves double the capacity and better performance in terms of Signal-to-Noise Ratio
and Bit Error Rate of a single user OFDM system and the UWB channel is used to securely transmit the data through the
channel. Also, the proposed system reduces the receiver complexity by using polarization diversity to receive the
multipath components for multiple users.
An Efficient Data Communication Using Conventional CodesIJERA Editor
The BER performance of conventional FFT-OFDM system is compared with DWT-OFDM system and DCT-OFDM system in an AWGN environment and Saleh-Valenzuela (SV) channel model at 60 GHz. Several wavelets such as Haar, Daubechies, Symlet, biorthogonal are considered. The BER is calculated for signaling format BPSK and the performance is analyzed at 60 GHz. Simulation results show that DCT based scheme yields the lowest average bit error rate. While out of all wavelet mother used Haar and Daubechies wavelet based scheme yields lower BER than FFT-OFDM for an AWGN channel. But it may include the implementation of forward error correction techniques such as convolution codes. An efficient channel estimation algorithm may be included for performance evaluation of DCT-OFDM and DWT- OFDM working at 60 GHz band. We introduce the Interfacing Techniques for Accessing data transfer data delivery. By using our approach we are increasing the efficiency of the data communication.
The several assets for high-speed data transmission over wireless uses the Orthogonal Frequency Division
Multiplexing (OFDM) as it is a multicarrier transmission scheme. A large number of narrow bandwidth carriers is
therefore adopted by the OFDM. Individually for an OFDM, each subcarrier is attenuated under the frequency-selective
and fast fading channel, therefore the resulting gain is high attenuation which leads to poor performance of all OFDM
subcarriers if the same fixed transmission scheme are used. Thus the main goal of the indicated paper is to grab an
understanding of the inequality between fixed & adaptive modulations schemes as the introduction of the adaptive
modulation. The need for the above system is to make use of the speaker's voice to check their character and control
approach to administrations, for example, voice dialing data administrations, voice send, and security control for secret
data. The performance of paperwork basically states that implementation of adaptive modulation is done into blocks of
adjacent subcarriers which is the result of dividing whole subcarriers. Therefore the equivalent modulation scheme which
is the calculation of average instantaneous signal to noise (SNR) is exercised to entire subcarriers of the equal block. The
OFDM system average bit error rate (BER) performance is observed here under fixed modulation and adaptive
modulation, and these modulation techniques are recorded by accepting the different inverse fast Fourier transforms
(IFFT) size and uncomplicated adaptive Quadrature amplitude modulation (QAM) strategy. The simulation in MATLAB
shows the results as the performance of fixed modulation is inferior to that of the BER performance of OFDM system
using adaptive modulation. The prospective adaptive modulation and coding Technique uses OFDM to manage the fixed
BER under changing the channel.
Analysis of Simulation Parameters of Pulse Shaping FIR Filter for WCDMAijsrd.com
The application of signal processing techniques to wireless communications is an emerging area that has recently achieved dramatic improvement in results and holds the potential for even greater results in the future as an increasing number of researchers from the signal process and communications areas participate in this expanding field. From an industrial viewpoint also, the advanced signal processing technology cannot only dramatically increase the wireless system capacity but can also improve the communication quality including the reduction of all types of interference. The present paper deals with simulation model of square root raised cosine pulse shaping filter for WCDMA with different parameters of the filter at 5Mhz.The present paper deals with study of Simulation Parameters (Number of Bits, Number of Errors) of Pulse Shaping FIR Filter at different value of group delay(2,4,6,8) to the calculate BER for WCDMA.
Reduction of Frequency offset Using Joint Clock for OFDM Based Cellular Syste...IJRST Journal
This project addresses the problem of clock synchronization between a base station (BS) and a mobile station (MS). A conventional technique for clock synchronization is that the MS clock is derived from the downlink signal originated from a base station. In cellular systems, a base station and mobile stations need to be synchronized before data exchange. Since the base station clock reference is more accurate, a mobile station typically derives its clock reference from the base station. But the carrier frequency offset due to Doppler shift may have harmful effects on the local clock derivation. This project proposes a joint clock and frequency synchronization technique between a base station and a mobile station, which is effective even with Doppler shift. We derive the joint estimation algorithm by analyzing the phase and the amplitude distortion caused by the sampling frequency offset and the carrier frequency offset. Simulation results showing the effectiveness of the proposed algorithm will also be presented.
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.
Designing and Performance Evaluation of 64 QAM OFDM SystemIOSR Journals
Abstract (11Bold) : — In this report, the performance analysis of 64 QAM-OFDM wireless communication
systems affected by AWGN in terms of Symbol Error Rate and Throughput is addressed. 64 QAM (64 ary
Quadrature Amplitude Modulation) is the one of the effective digital modulation technique as it is more power
efficient for larger values of M(64). The MATLAB script based model of the 64 QAM-OFDM system with
normal AWGN channel and Rayleigh fading channel has been made for study error performance and
throughput under different channel conditions. This simulated model maximizes the system throughput in the
presence of narrowband interference, while guaranteeing a SER below a predefined threshold. The SER
calculation is accomplished by means of modelling the decision variable at the receiver as a particular case of
quadratic form D in complex Gaussian random variables. Lastly comparative study of SER performance of 64
QAM-OFDM simulated & 64 QAM-OFDM theoretical under AWGN channel has been given. Also
performance of the system is given in terms of throughput (received bits/ofm symbol) is given in a plot for
different SNR. Keywords (11Bold) –64 QAM, BPSK, OFDM, PDF, SNR.
Designing and Performance Evaluation of 64 QAM OFDM SystemIOSR Journals
In this report, the performance analysis of 64 QAM-OFDM wireless communication
systems affected by AWGN in terms of Symbol Error Rate and Throughput is addressed. 64 QAM (64 ary
Quadrature Amplitude Modulation) is the one of the effective digital modulation technique as it is more power
efficient for larger values of M(64). The MATLAB script based model of the 64 QAM-OFDM system with
normal AWGN channel and Rayleigh fading channel has been made for study error performance and
throughput under different channel conditions. This simulated model maximizes the system throughput in the
presence of narrowband interference, while guaranteeing a SER below a predefined threshold. The SER
calculation is accomplished by means of modelling the decision variable at the receiver as a particular case of
quadratic form D in complex Gaussian random variables. Lastly comparative study of SER performance of 64
QAM-OFDM simulated & 64 QAM-OFDM theoretical under AWGN channel has been given. Also
performance of the system is given in terms of throughput (received bits/ofm symbol) is given in a plot for
different SNR
Improving quality of service using ofdm technique for 4 th generation networkeSAT Journals
Abstract The migration to 4G networks will bring a new level of expectation to wireless communications. As after digital wireless revolution made mobile phones available for everyone, the higher speeds and packet delivery of 4G networks will make high quality multimedia available everywhere. The key to achieving this higher level of service delivery is a new air interface, OFDM, which is in turn enabled by the high level of performance. OFDM provides a robust signal that requires relatively little power yet uses bandwidth very efficiently. Carriers will benefit from greater flexibility by using OFDM, since in the same spectrum they will be able to offer more channels, including higher ‘bandwidth channels, with more types of services. Currently these systems are still being defined and prototyped. Achieving higher data rates requires OFDM systems to make more efficient use of the bandwidth than CDMA systems. One method of achieving this higher efficiency is through the use of higher order modulation. In this paper we have compared two digital modulation techniques 32QAM and 64QAM used for digital transmission of data. Our main objective to develop this configuration is to compare the performance of each modulation techniques. Comparison is done by Bit Error Rate analysis of both modulation techniques. We have developed existing configurations and improved them with high quality senders and receivers using MATLAB technology. In this paper we have also considered how OFDM can improve the real time video streaming over the wireless network. We have considered the problem of multiuser video streaming over OFDM. OFDM is a multi carrier modulation. The growing interest in Multicarrier Transmission by researchers and product developers motivated us to propose this topic for a special issue of Wireless Video transmission and Communications. Index Terms: QAM’ Quadrature Amplitude Modulation, OFDM' Orthogonal Frequency Division Multiplexing, QoS’ Quality of service
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IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology.
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1. IOSR Journal of Electronics and Communication Engineering (IOSR-JECE)
e-ISSN: 2278-2834,p- ISSN: 2278-8735.Volume 10, Issue 2, Ver.1 (Mar - Apr.2015), PP 86-91
www.iosrjournals.org
DOI: 10.9790/2834-10218691 www.iosrjournals.org 86 | Page
Performance Analysis of Adaptive Multi User OFDM
1
k,vanisree , 2
V,Arun Associate, 3
Y,Smruthi Assistant
1Prof ECE Depatment , ACE College of Engg Ghateskar Hyderabad
2Prof ECE Department MLRIT College of Engg ,Michal Hyderabad
3Prof ECE Depatment , ACE College of Engg Ghateskar Hyderabad
Abstract: The demand for high-speed mobile wireless communications is rapidly growing. OFDM technology
promises to be a key technique for achieving the high data capacity and spectral efficiency requirements for
wireless communication systems of the near future. In our proposed method Adaptive modulation techniques is
used for maximizing the data throughput of subcarriers allocated to a user. It measures the SNR of each
subcarrier in the transmission, then selecting a modulation scheme that will maximize the spectral efficiency,
while maintaining an acceptable BER. This technique has been used in Asymmetric Digital Subscriber Line
(ADSL) to maximize the system throughput.In addition Adaptive user allocation improves signal power of 3-5
dB. Also in the first techniques Crest Factor (CF)is reduced by using OFDM pilot symbols ,in the second
techniques reduces the CF of data carrying symbols, by including additional subcarriers
Keywords: OFDM ,SNR, Spectral efficiency, throughput, BER,CF
I. Introduction:
This paper presents an investigation into methods for maximizing the spectral efficiency of Orthogonal
Frequency Division Multiplexing (OFDM) systems. As part of this, an investigation of detrimental effects on
OFDM is presented, showing the effect of: band pass filtering, the use of a raised cosine guard period, clipping
distortion, Additive White Gaussian Noise (AWGN) on modulation BER rate, time synchronization error, and
frequency offset errors. An investigation of two adaptive techniques is also presented. These techniques utilize
knowledge obtained by dynamically tracking the radio channel response, to optimize the user frequency, and
subcarrier modulation. Adaptive modulation independently optimizes the modulation scheme applied to each
subcarrier so that the spectral efficiency is maximized, while maintaining a target Bit Error Rate (BER).For a
fading channel, adaptive modulation results in an improvement of 12 - 16 dB in the Signal to Noise Ratio (SNR)
required to maintain a given BER, as compared with fixed modulation. Adaptive user allocation exploits the
difference in frequency selective fading between users, to optimise user subcarrier allocation. In a multipath
environment the fading experienced on each subcarrier varies from user to user, thus by utilizing user/subcarrier
combinations that suffer the least fading, the overall performance is maximized. Adaptive user allocation results
in an additional average signal power improvement of 3 - 5 dB.
In addition, two techniques are presented for reducing the Crest Factor (peak to average power ratio
of the RF signal envelope) of OFDM signals. The first technique is a phasing scheme for OFDM pilot symbols,
which uses genetic algorithms to optimize the phase angle of each subcarrier. This technique achieves a lower
CF than any previously published techniques, obtaining a CF as low as 0.65 dB, which is 2 dB lower than
commonly used techniques. The second technique reduces the CF of data carrying symbols, by including
additional subcarriers that are optimized in amplitude and phase to cancel out the peaks in the overall OFDM
symbol. This was found to produce a net improvement of 4 dB to the worst-case symbol CF.
II. System Model:
Adaptive modulation is a powerful technique for maximizing the data throughput of subcarriers
allocated to a user. Adaptive modulation involves measuring the SNR of each subcarrier in the transmission,
then selecting a modulation scheme that will maximize the spectral efficiency, while maintaining an acceptable
BER. This technique has been used in Asymmetric Digital Subscriber Line (ADSL) to maximize the system
throughput. ADSL uses OFDM transmission over copper telephone cables. The channel frequency response of
copper cables is relatively constant and so reallocation of the modulation scheme does not need to be performed
very often, as a result the benefit greatly out ways the overhead required for measuring of the channel response.
Using adaptive modulation in a wireless environment is much more difficult as the channel response and SNR
can change very rapidly, requiring frequent updates to track these changes
2. Performance Analysis of Adaptive Multi User OFDM
DOI: 10.9790/2834-10218691 www.iosrjournals.org 87 | Page
Fig1: block diagram of basic OFDM transceiver
Sets of functions are orthogonal to each other if they match the conditions in equation 1. If any two
different functions within the set are multiplied, and integrated over a symbol period, the result is zero, for
orthogonal functions. Another way of thinking of this is that if we look at a matched receiver for one of the
Orthogonal functions, a subcarrier in the case of OFDM, and then the receiver will only see the result for that
function. The results from all other functions in the set integrate to zero, and thus have no effect.
These subcarriers are orthogonal to each other because when we multiply the waveforms of any two
subcarriers and integrate over the symbol period the result is zero. Multiplying the two sine waves together is
the same as mixing these subcarriers. This results in sum and difference frequency components, which will
always be integer subcarrier frequencies, as the frequency of the two mixing subcarriers has integer number of
cycles. Since the system is linear we can integrate the result by taking the integral of each frequency component
separately then combining the results by adding the two sub-integrals. The two frequency components after the
mixing have an integer number of cycles over the period and so the sub-integral of each component will be zero,
as the integral of a sinusoid over an entire period is zero. Both the sub-integrals are zeros and so the resulting
addition of the two will also be zero, thus we have established that the frequency components are orthogonal to
each other.
III. Subcarrier Modulation:
Once each subcarrier has been allocated bits for transmission, they are mapped using a modulation
scheme to a subcarrier amplitude and phase, which is represented by a complex In-phase and Quadrature-phase
(IQ) vector. Figure2 shows an example of subcarrier modulation mapping. This example shows 16-QAM, which
maps 4 bits for each symbol. Each combination of the 4 bits of data corresponds to a unique IQ vector, shown as
a dot on the figure. A large number of modulation schemes are available allowing the number of bits transmitted
per carrier per symbol to be varied In the receiver, mapping the received IQ vector back to the data word
performs subcarrier demodulation.
Fig2: Example Of Id Modulation Constellation
During transmission, noise and distortion becomes added to the signal due to thermal noise, signal
power reduction and imperfect channel equalization. Each of the IQ points is blurred in location due to the
channel noise. For each received IQ vector the receiver has to estimate the most likely original transmission
vector. This is achieved by finding the transmission vector that is closest to the received vector. Errors occur
3. Performance Analysis of Adaptive Multi User OFDM
DOI: 10.9790/2834-10218691 www.iosrjournals.org 88 | Page
when the noise exceeds half the spacing between the transmission IQ points, making it cross over a decision
boundary.
3.1 Frequency To Time Domain Conversion
After the subcarrier modulation stage each of the data subcarriers is set to an amplitude and phase
based on the data being sent and the modulation scheme; all unused subcarriers are set to zero. This sets up the
OFDM signal in the frequency domain. An IFFT is then used to convert this signal to the time domain, allowing
it to be transmitted. In the
frequency domain, before applying the IFFT, each of the discrete samples of the IFFT corresponds to an
individual subcarrier. Most of the subcarriers are modulated with data. The outer subcarriers are unmodulated
and set to zero amplitude. These zero subcarriers provide a frequency guard band before the nyquist frequency
and effectively act as an interpolation of the signal and allows for a realistic roll off in the analog anti-aliasing
reconstruction filters.
IV. Proposed Methodology:
OFDM has been used successfully in several broadcast systems, namely DAB and DVB, and for point-
to-point communications. However, its application in multiuser two-way communication systems has been
limited. Only recently has it been applied to Wireless LAN applications, with the development of HiperLAN2
and IEEE 802.11a .OFDM is a good contender for the RF interface in 4th generation mobile systems, however
not much work has been done to date in addressing the issues of applying.
OFDM in large scale multiuser applications. Multiuser OFDM provides a very Flexible RF interface
allowing users to be allocated using Frequency Division Multiplexing (FDM), by Time Division Multiplexing
(TDM) or a hybrid of FDM/TDM. In addition to this, the multicarrier nature of OFDM allows the radio channel
to be characterized and monitored quickly and easily, presenting numerous opportunities for optimising the
overall system performance, such as:
• Allocating user subcarriers so as to minimize Signal to Interference Ratio
• (SIR) in cellular systems.
• Allocate subcarriers to minimize the effects of frequency selective fading.
• Dynamically allocate the modulation scheme on an individual subcarrier
• basis to match the current channel conditions.
• Dynamically change the bandwidth of each user based on the link quality.
This allows the bandwidth of weak users to be reduced so that their energy spectral density remains sufficiently
high to maintain communications
4.1 Peer-To-Peer Networking
Most current WLAN systems, such as networks using the IEEE 802.11b standard (11Mbps DSSS), use
peer-to-peer networking. This allows computers to communicate directly to each other. Computers on this type
of network, typically connect to the rest of the world via a single computer connected via a wired Internet
connection.
This computer effectively acts as a virtual base station, as all external data traffic is
routed through it. This type of networking is simple to set up and doesn’t require any special hardware for the
virtual base station. One problem with peer-to-peer networking is that some of the stations can become hidden
from each other due to shadowing or distance, preventing communication. This problem can be overcome with
various methods of multiple hopping of data packets, but this can cause system complexity to be greatly
increased, especially if stations are mobile.
Fig3: Peer-To-Peer Networking
4. Performance Analysis of Adaptive Multi User OFDM
DOI: 10.9790/2834-10218691 www.iosrjournals.org 89 | Page
Peer-to-peer networking requires that all stations can communicate with each other. As a result most systems
use half duplex communications and transmit and receive at the same frequency.
4. 1 Adaptive Modulation
Adaptive modulation is a powerful technique for maximizing the data throughput of subcarriers
allocated to a user. Adaptive modulation involves measuring the SNR of each subcarrier in the transmission,
then selecting a modulation scheme that will maximize the spectral efficiency, while maintaining an acceptable
BER. This technique has been used in Asymmetric Digital Subscriber Line (ADSL) [86], [87],[88], to maximize
the system throughput. ADSL uses OFDM transmission over copper telephone cables. The channel frequency
response of copper cables is relatively constant and so reallocation of the modulation scheme does not need to
be performed very often, as a result the benefit greatly out ways the overhead required for measuring of the
channel response. Using adaptive modulation in a wireless environment is much more difficult as the channel
response and SNR can change very rapidly, requiring frequent updates to track these changes. Most OFDM
systems use a fixed modulation scheme over all subcarriers for simplicity. However each subcarrier in a
multiuser OFDM system can potentially have a different modulation scheme depending on the channel
conditions. Any coherent or differential, phase or amplitude modulation scheme can be used including BPSK,
QPSK, 8-PSK, 16-QAM, 64-QAM, etc, each providing a trade off between spectral efficiency and the bit error
rate. The spectral efficiency can be maximized by choosing the highest modulation scheme that will give an
acceptable Bit Error Rate (BER). In a multipath radio channel, frequency selective fading can result in large
variations in the received power of each subcarrier. For a channel with no direct signal path this variation can be
as much as 30 dB in the received power resulting in a similar variation in the SNR. In addition to this,
interference from neighboring cells can cause the SNR to vary significantly over the system bandwidth. To cope
with this large variation in SNR over the system subcarriers, it is possible to adaptively allocate the subcarrier
modulation scheme, so that the spectral efficiency is maximized while maintaining an acceptable BER.
4.2 Limitations Of Adaptive Modulation:
There are several limitations with adaptive modulation. Overhead information needs to be transferred,
as both the transmitter and receiver must know what modulation is currently being used. Also as the mobility of
the remote station is increased, the adaptive modulation process requires regular updates, further increasing the
overhead. There is a trade off between power control and adaptive modulation. If a remote station has a good
channel path the transmitted power can be maintained and a high modulation scheme used (i.e. 64-QAM), or the
power can be reduced and the modulation scheme reduced accordingly (i.e. QPSK). Distortion, frequency error
and the maximum allowable power variation between users limit the maximum modulation scheme that can be
used. The received power for neighboring subcarriers must have no more than 20 - 30 dB variation at the base
station, as large variations can result in strong signals swamping weaker subcarriers. Inter-modulation distortion
results from any non-linear components in the transmission, and causes a higher noise floor in the transmission
band, limiting the maximum SNR to typically 30 - 60 dB. Frequency errors in the transmission due to
synchronization errors and Doppler shift result in a loss of orthogonality between the subcarriers. A frequency
offset of only 1 - 2 % of the subcarrier spacing results in the effective SNR being limited to 20 dB . The limited
SNR restricts the maximum spectral efficiency to approximately 5 - 10 b/s/Hz.
V. Simulation Results:
5.1 Simulated Results Each User Having Fixed Transmision Power
Results shown in (a) and (c) are for each user having a fixed transmission power. The transmitter
power in (b) and (d) were set so that the average received power would result in an average SNR of 20 dB
Fig 5.1 (a) and (b) show the frequency allocations for each of the users. Each user is shown as a different colour
5. Performance Analysis of Adaptive Multi User OFDM
DOI: 10.9790/2834-10218691 www.iosrjournals.org 90 | Page
Fig 5.2 (c) and (d) show the modulation scheme used at each frequency. This simulation assumed perfect
channel knowledge for each user.
5.2 Simulated Adaptive User Allocation
Fig 5.3 (a) and (b) show the SNR for each user
Fig 5.4 (c) and (d) shows the bandwidth allocated to each user
Fig 5.5 (e) and (f) shows the resulting data rate for each user
Fig 5.6 (g) and (h) showing the overall system data rate.
VI. Conclusion
This thesis has presented an investigation into the application of OFDM in multiuser systems, and has
focused on techniques for improving the system spectral efficiency.
Most current communication systems operate at a very low spectral efficiency,resulting in under
utilisation of the radio spectrum. Future systems will have to improve the spectral efficiency to achieve the
capacities required. This thesis has investigated techniques that exploit the flexibility of OFDM to maintain a
maximum spectral efficiency, by matching the system parameters, such as subcarrier modulation and frequency,
based on current conditions of the radio channel. The aim of this work is for the communication system to
6. Performance Analysis of Adaptive Multi User OFDM
DOI: 10.9790/2834-10218691 www.iosrjournals.org 91 | Page
approach the maximum theoretical channel capacity given the constraints of the radio channel, transmitter
power and quality of service.
The application of adaptive modulation was investigated and found to provide an effective means to
mitigate the effects of fading. Adaptive modulation greatly decreases the BER, with it requiring 12 - 16 dB less
SNR to achieve the same BER as compared with a fixed modulation system. In addition to this, it allows the
data rate of the system to improve when the channel SNR is high. When using coherent QAM, every 3 dB
improvement in SNR allows the spectral efficiency of the system to improve by 1 b/s/Hz.
References:
[1]. K. W. Richard, “UMTS overview”, IEE Electronics and CommunicationEngineering Journal, Vol. 12, No. 3, June 2000, pp. 93 -
100
[2]. Ermanno Berruto, Giovanni Colombo, Pantelis Monogioudis, Antonella Napolitano, Kyriacos Sabatakakis, “Architectural Aspects
for the Evolution of Mobile Communications Toward UMTS”, IEEE Journal on Selected Areas in Communications, Vol. 15, No. 8,
October 1997,pp. 1477 - 1487
[3]. Erik Dahlman, Björn Gudmundson, Mats Nilsson, Johan Sköld, “UMTS/IMT-2000 Based on Wideband CDMA”, IEEE
Communications Magazine, September 1998, pp. 70 - 80
[4]. Fumiyuki Adachi, Mamoru Sawahasi, Hirohito Suda, “Wideband DS-CDMA for Next-Generation Mobile Communications
Systems”, IEEE Communications Magazine, September 1998, pp. 56 - 69
[5]. M. Fattouche, “Method and Apparatus for Multiple Access between Transceivers in Wireless Communications using OFDM spread
spectrum”, U.S. Patent 5,282,222, Filed Mar. 31, 1992, Issued Jan. 25, 1994
[6]. T. Williams, R. Prodan, “Multiple User Access Method Using OFDM”, U. S. Patent 5,815,488, Filed Sep. 28, 1995, Issued Sep. 29,
1998
[7]. L. Cimini, J. Chuang, N. Sollenberger, “Advanced Cellular Internet Service (ACIS)”, IEEE Communications Magazine, Oct. 1998,
pp. 150 – 159
[8]. Minh T. Le, Louis Thibault, “Performance Evaluation of COFDM for Digital Audio Broadcasting Part II: Effects of HPA
Nonlinearities”, IEEE Transactions on Broadcasting, Vol. 44, No. 2, June 1998, pp. 165 – 171
[9]. S. Merchán, A. García Armada, J. L. García, “OFDM Performance in Amplifier Nonlinearity”, IEEE Transactions on Broadcasting,
Vol. 44, No. 1, March 1998, pp. 106 - 113
[10]. Qun Shi, “OFDM in Bandpass Nonlinearity”, IEEE Transactions on Consumer Electronics, Vol. 42, No. 3, August 1996, pp. 253 -
258