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.
In recent past the influence of Radar has played a significant part in various fields. Radar sensing is one of
the prime application by which velocity and distance of a moving target can be found out. A joint RadCom
system to serve both radar sensing and wireless communication is proposed which ensures better
performance in terms of spectral efficiency, extended detection range and cost effectiveness. Such systems
demand for a common waveform which is designed in this work that perfectly matches to the system
requirements. OFDM multi carrier technique is chosen to generate a common waveform. Applicability of
multiple antenna technique for direction of arrival estimation is also considered. MIMO-OFDM technique
has gained much interest in the field of communication which improves the signal to noise ratio and lowers
the bit error rate. On the other hand the usage of MIMO reflects in the form of interference between
signals. In order to overcome this effect beamforming technique is used. In addition to theoretical
explanations we have also simulated and discussed the results for the proposed RadCom system using
MATLAB simulation tool.
Performance Investigation of OFDM-FSO System under Diverse Weather Conditions...IJECEIAES
Free space optical (FSO) communication systems which are deployed for last mile access, being considered as a suitable alternative technology for optical fiber networks. It is one of the emerging technologies for broadband wireless connectivity which has also been receiving growing attention due to high data rate transmission capability with low installation cost and license free spectrum. However, the widespread use of FSO technology has been hampered by the randomly time varying characteristics of propagation path mainly due to atmospheric turbulence, sensitivity to diverse weather conditions and the nonlinear responsivity of laser diode. This paper presents the performance investigation of an OFDM-FSO system over atmospheric turbulence channels under diverse weather conditions of Bangladesh. The channel is modeled with gamma-gamma distribution using 16-QAM modulation format and 4×4 multiple transceiver FSO system. All possible challenges are imposed on the system performance such as atmospheric attenuation, turbulence, pointing error, geometric loss etc. The refractive index structure parameter and atmospheric attenuation coefficient for different weather conditions are calculated by using the data, collected from Bangladesh Meteorological Department. The acquired results can be fruitful for scheming, forecasting and assessing the OFDM-FSO system’s ability to transmit wireless services over turbulent FSO links under actual conditions of Bangladesh.
Performance analysis of round trip time in narrowband rf networks for remote ...ijcsit
Networks for remote wireless communications using narrow band radios modem &Routers ((RipEX unit)
,as a means of transmission to communicate between the loins broadcast sites TV/FM.
RTT delay measurement is influenced by different parameters of Narrowband RF Networks.
We illustrate, in this paper, how RTT varies (in remote wireless practical communications application)
versus distance, modulation, baud rates, number of hops and throughput, between source and destination.
Also, we will see how the Forward Error Correction (FEC) affect, in the same time, the RTT according the
factors cited above.
Wireless communication system with frequency selective channel OFDM modulatio...TELKOMNIKA JOURNAL
This paper introduces the design and implementation of a wireless communication system with MATLAB based on orthognal frequency division multiplexing technique (OFDM). The constructed system is consisting of transmitter, fading channel and receiver. At the transmitter, the transmitted signal first modulated with PSK modulation, and then multiplexed with OFDM technique to achieve a higher bit rates transmission. The signal was then transmitted through a frequency selective channel with 6 taps. In the receiver parity. The received faded signal processed to be de-multiplexed and de-modulated. Then, a frequency domain equalizer was adopted to remove the fading noise and the inter-symbol interference from the received signal that introduced due to the fading channel. In order to inspect the performance of the frequency equilizer, bit error rate for the overall system was calculated at the receiving point and to recover the original information signal. The simulation results of the designed system as well as the frequency equilizer showed a robustness against the frequency selective faded channel effects. The maximum obtained bit error rate was around 10-5, which means that original signal was effectively recovered.
Multicarrier modulation can be implemented by using Orthogonal Frequency Division Multiplexing (OFDM) to achieve utmost bandwidth exploitation and soaring alleviation attributes profile besides multipath fading. To support delay sensitive and band bandwidth demanding multimedia applications and internet services, MIMO in addition with other techniques can be used to achieve high capacity and reliability. To obtain high spatial rate by transmitting data on several antennas by using MIMO with OFDM results in reducing error recovery features and the equalization complexities arise by sending data on varying frequency levels. Three parameters frequency OFDM, Spatial (MIMO) and time (STC) can be used to achieve diversity in MIMO-OFDM. This technique is dynamic and well-known for services of wireless broadband access. MIMO if used with OFDM is highly beneficial for each scheme and provides high throughput. There are several space time block codes to exploit MIMO OFDM; one of the techniques is called Alamouti Codes. The paper investigates adaptive Alamouti Codes and their application in IEEE 802.11n.
In recent past the influence of Radar has played a significant part in various fields. Radar sensing is one of
the prime application by which velocity and distance of a moving target can be found out. A joint RadCom
system to serve both radar sensing and wireless communication is proposed which ensures better
performance in terms of spectral efficiency, extended detection range and cost effectiveness. Such systems
demand for a common waveform which is designed in this work that perfectly matches to the system
requirements. OFDM multi carrier technique is chosen to generate a common waveform. Applicability of
multiple antenna technique for direction of arrival estimation is also considered. MIMO-OFDM technique
has gained much interest in the field of communication which improves the signal to noise ratio and lowers
the bit error rate. On the other hand the usage of MIMO reflects in the form of interference between
signals. In order to overcome this effect beamforming technique is used. In addition to theoretical
explanations we have also simulated and discussed the results for the proposed RadCom system using
MATLAB simulation tool.
Performance Investigation of OFDM-FSO System under Diverse Weather Conditions...IJECEIAES
Free space optical (FSO) communication systems which are deployed for last mile access, being considered as a suitable alternative technology for optical fiber networks. It is one of the emerging technologies for broadband wireless connectivity which has also been receiving growing attention due to high data rate transmission capability with low installation cost and license free spectrum. However, the widespread use of FSO technology has been hampered by the randomly time varying characteristics of propagation path mainly due to atmospheric turbulence, sensitivity to diverse weather conditions and the nonlinear responsivity of laser diode. This paper presents the performance investigation of an OFDM-FSO system over atmospheric turbulence channels under diverse weather conditions of Bangladesh. The channel is modeled with gamma-gamma distribution using 16-QAM modulation format and 4×4 multiple transceiver FSO system. All possible challenges are imposed on the system performance such as atmospheric attenuation, turbulence, pointing error, geometric loss etc. The refractive index structure parameter and atmospheric attenuation coefficient for different weather conditions are calculated by using the data, collected from Bangladesh Meteorological Department. The acquired results can be fruitful for scheming, forecasting and assessing the OFDM-FSO system’s ability to transmit wireless services over turbulent FSO links under actual conditions of Bangladesh.
Performance analysis of round trip time in narrowband rf networks for remote ...ijcsit
Networks for remote wireless communications using narrow band radios modem &Routers ((RipEX unit)
,as a means of transmission to communicate between the loins broadcast sites TV/FM.
RTT delay measurement is influenced by different parameters of Narrowband RF Networks.
We illustrate, in this paper, how RTT varies (in remote wireless practical communications application)
versus distance, modulation, baud rates, number of hops and throughput, between source and destination.
Also, we will see how the Forward Error Correction (FEC) affect, in the same time, the RTT according the
factors cited above.
Wireless communication system with frequency selective channel OFDM modulatio...TELKOMNIKA JOURNAL
This paper introduces the design and implementation of a wireless communication system with MATLAB based on orthognal frequency division multiplexing technique (OFDM). The constructed system is consisting of transmitter, fading channel and receiver. At the transmitter, the transmitted signal first modulated with PSK modulation, and then multiplexed with OFDM technique to achieve a higher bit rates transmission. The signal was then transmitted through a frequency selective channel with 6 taps. In the receiver parity. The received faded signal processed to be de-multiplexed and de-modulated. Then, a frequency domain equalizer was adopted to remove the fading noise and the inter-symbol interference from the received signal that introduced due to the fading channel. In order to inspect the performance of the frequency equilizer, bit error rate for the overall system was calculated at the receiving point and to recover the original information signal. The simulation results of the designed system as well as the frequency equilizer showed a robustness against the frequency selective faded channel effects. The maximum obtained bit error rate was around 10-5, which means that original signal was effectively recovered.
Multicarrier modulation can be implemented by using Orthogonal Frequency Division Multiplexing (OFDM) to achieve utmost bandwidth exploitation and soaring alleviation attributes profile besides multipath fading. To support delay sensitive and band bandwidth demanding multimedia applications and internet services, MIMO in addition with other techniques can be used to achieve high capacity and reliability. To obtain high spatial rate by transmitting data on several antennas by using MIMO with OFDM results in reducing error recovery features and the equalization complexities arise by sending data on varying frequency levels. Three parameters frequency OFDM, Spatial (MIMO) and time (STC) can be used to achieve diversity in MIMO-OFDM. This technique is dynamic and well-known for services of wireless broadband access. MIMO if used with OFDM is highly beneficial for each scheme and provides high throughput. There are several space time block codes to exploit MIMO OFDM; one of the techniques is called Alamouti Codes. The paper investigates adaptive Alamouti Codes and their application in IEEE 802.11n.
ESTIMATION AND COMPENSATION OF INTER CARRIER INTERFERENCE IN WIMAX PHYSICAL L...ijngnjournal
WiMAX is Wireless Interoperability for Microwave Access has emerged as a promising solution for transmission of higher data rates for fixed and mobile applications. IEEE 802.16d and e are the standards proposed by WiMAX group for fixed and mobile. As the wireless channel have so many limitation Such as Multipath, Doppler spread, Delay spread and Line Of Sight (LOS)/Non Line Of Sight (NLOS) components. To attain higher data rates the Multi Carrier System with Multiple Input and Multiple Output (MIMO) is incorporated in the WiMAX. The Orthogonal Frequency Division Multiplexing (OFDM) is a multi carrier technique used with the WiMAX systems. In OFDM the available spectrum is split into numerous narrow band channels of dissimilar frequencies to achieve high data rate in a multi path fading environment. And all these sub carriers are considered to be orthogonal to each other. As the number of sub carriers is increased there is no guarantee of sustained orthogonality, i.e. at some point the carriers are not
independent to each other, and hence where the orthogonality can be loosed which leads to interference and also owing to the synchronization between transmitter and receiver local oscillator, it causes interference known as Inter Carrier Interference (ICI). The systems uses MIMO-OFDM will suffer with the effects of ICI and Carrier Frequency Offset (CFO) “ε”. However these affect the power leakage in the midst of sub carriers, consequently degrading the system performance. In this paper a new approach is proposed in order to reduce the ICI caused in WiMAX and improve the system performance. In this scheme at the transmitter side the modulated data and a few predefined pilot symbols are mapped onto the non
neighboring sub carriers with weighting coefficients of +1 and -1. With the aid of pilot symbols the frequency offset is exactly estimated by using Maximum Likelihood Estimation (MLE) and hence can be minimized. At demodulation stage the received signals are linearly combined along with their weighted
coefficients and pilot symbols, called as Pilot Aided Self Cancellation Method (PASCS). And also to realize the various wireless environments the simulations are carried out on Stanford University Interim (SUI) channels. The simulation results shows that by incorporating this method into WiMAX systems it performs better when the Line Of Sight (LOS) component is present in the transmission and also it improves the Bit Error Rate (BER) and Carrier to Interference Ratio (CIR). The CIR can be improved 20 dB. In this paper the effectiveness of PASCS scheme is compared with the Self Cancellation Method (SCM). It provides accurate estimation of frequency offset and when residual CFO is less significant the ICI can be diminished successfully.
Performance Analysis of 802.lln MIMO OFDM TransceiverIJERA Editor
The increasing demand on real time application to achieve high throughput, reliable wireless system and network capacity for fourth generation wireless local area networks is to combine MIMO wireless technology with OFDM. Orthogonal Frequency Division Multiplexing (OFDM), which offers reliable high bit rate wireless system with reasonable low complexity. OFDM does provide large data rates with sufficient robustness to radio channel impairments. OFDM is a combination of modulation and multiplexing and are able to maximize spectral efficiency without causing adjacent channel interference. This paper first focuses on 802.11n standard, MIMO-OFDM system. This paper further reviews different work done on implementation of MIMO-OFDM transceiver for 802.11n standard.
Analysis of a framework implementation of the transceiver performances for in...IJECEIAES
The greatest advantages of optical fibers are the possibility of extending data rate transmission and propagation distances. Being a multicarrier technique, the orthogonal frequency division multiplexing (OFDM) can be applicable in hybrid optical-wireless systems design owing to its best spectral efficiency for the interferences of radio frequency (RF) and minor multipath distortion. An optical OFDM-RoF-based wireless local area network (W-LAN) system has been studied and evaluated in this work. The outline for integrating an optical technology and wireless in a single system was provided with the existence of OFDM-RoF technology and the microstrip patch antenna; these were applied in the Optisystem communication tool. The design of the proposed OFDM-RoF system is aimed at supporting mm-wave services and multi-standard operations. The proposed system can operate on different RF bands using different modulation schemes like 4.16 and 64QAM that may be associated to OFDM and multidata rates up to 5 Gbps. The results demonstrate the robustness of the integrated optical wireless link in propagating OFDM-RoF-based WLAN signals across optical fibers.
IMPLEMENTATION OF LINEAR DETECTION TECHNIQUES TO OVERCOME CHANNEL EFFECTS IN ...IJCI JOURNAL
Spatial diversity technique enables improvement in quality and reliability of wireless link. Antenna
diversity along with understanding effects of channel on transmitted signal and methods to overcome the
channel impairment plays an important role in wireless communication where sharing of channel occurs
between users. In this paper single input single output system (SISO) is compared with multiple input
multiple output system (MIMO) in terms of bit error rate performance. Bit error rate performance is also
evaluated for MIMO with least squares (LS) and Minimum mean square error (MMSE) linear detection.
Further analysis and simulation is done to understand the effect of channel imperfections on BER.
Performance Analysis of MIMO-LTE for MQAM over Fading ChannelsIOSRJECE
LTE (Long Term Evolution) is a 3GPP (Third Generation Partnership Project) wireless standards which uses the standard OFDMA (Orthogonal Frequency Division Multiple Access) modulation, MU-MIMO (Multiuser Multiple Input Multiple Output) technology and different multipath fading models. LTE uses the spectrum more efficiently to deliver high speed data. This paper characterizes the downlink performance of LTE. The MIMO technology which provides high data rate applications to the users made a breakthrough in wireless communication and is defined in the LTE standard. The performance is characterized in terms of BER (Bit Error Rate). In this paper the LTE system is modelled and simulated using MATLAB and the BER for 2×2 and 4×4 MIMO-LTE using 16QAM and 64QAM modulation schemes for Rayleigh fading environment are obtained against different SNR values.
Rapid developments in modern wireless communication permit the trade of spectrum scarcity. Higher data rate and wider bandwidth emerge the development in growing demand of wireless communication system. The innovative solution for the spectrum scarcity is cognitive radio (CR). Cognitive radio is the significant technology used to utilize the spectrum effectively. The important aspect of CR is sensing the spectrum band and detects the presence or absence of the primary user in the licensed band. Moreover, another serious issue in next generation (5G) wireless communication is to decide the less complex 5G waveform candidate for achieving higher data rate, low latency and better spectral efficiency. Universal filtered multi-carrier (UFMC) is one of the noticeable waveform candidates for 5G and its applications. In this article, we investigate the spectrum sensing methods in multi-carrier transmission for cognitive radio network applications. Especially, we integrate the sensing algorithm into UFMC transceiver to analyze the spectral efficiency, higher data rates and system complexity. Through the simulation results, we prove that the UFMC based cognitive radio applications outperform the existing Orthogonal Frequency Division Multiplexing (OFDM) based CR applications.
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.
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
Improvement of MFSK -BER Performance Using MIMO Technology on Multipath Non L...theijes
Digital communications has evolved rapidly with a lot of success. The new trend seems to be the reinvention of already existing and even discredited or discarded theories or in this case, channels. Extensive research into optimizing or enhancing already existing schemes is still gaining momentum with practical results for all to experience and utilize. This paper describes the design and BER performance of an M-ary frequency shift keyed (FSK) signaling and demodulation scheme improved by MIMO antenna technology for wireless communications. MFSK and MIMO systems were briefly reviewed including AWGN, Non LOS fading and an important factor employed to estimate the performance of digital transmission. The research was performed using MATLAB for simulation and evaluation of the BER
A simulation study of wi max based communication system using deliberately cl...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
A simulation study of wi max based communication system using deliberately cl...eSAT Journals
Abstract WiMAX is a highly sophisticated technology in the broadband wireless access communication system. Scalable Orthogonal Frequency Division Multiple Access (OFDMA) is a key technology behind mobile WiMAX and it is also expected to play a key role in 3GPP Long Term Evolution (LTE) standards. Designers and OEMs have to concentrate on flexibility, scalability and stability of the overall Orthogonal Frequency Division Multiplexing (OFDM) system along with its proper data processing and channeling process to achieve high performance and competitiveness. In this paper, the performance of a strictly band limited OFDM signal is examined using deliberate clipping method, one of the simplest signal distortion based way to reduce high Peak to Average Power Ratio (PAPR) and its effect on the resultant Bit Error Rate (BER) against Signal to Noise Ratio (SNR) performance. A simulation program using MATLAB software was developed to investigate performance of OFDM signal by optimization of different parameters such values of FFT size, Cyclic Prefix co-efficient (CPC) and The Voltage Clipping Ratio (VCR). The simulation results show that with the increment of VCR at optimized parameter values of FFT size and CP, the performance of BER vs SNR improves compared to the results found without clipping. Keywords: WiMAX, PAPR, OFDM, CPC, Voltage Clipping Ratio, Deliberately Clipped
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
Performance Analysis of Ultra Wideband Communication SystemEditor IJMTER
Ultra-Wideband (UWB) is a radio transmission scheme that uses extremely low power
pulses of radio energy spread across a wide spectrum of frequencies. UWB has several advantages
over conventional continuous wave radio communications including potential support for high data
rates, robustness to multipath interference and fading. The paper covers Ultra Wide-Band
technology. General description, Challenges, various modulation schemes such as OOK, PAM,
PPM, and BPSK under specified Ultra Wide Band regimes: low Power spectral density, large
spreading ratio and a highly dispersive channel. The capacity and BER performance of a single user
ultra wideband communication is investigated for various modulation schemes and coded, uncoded
methods also simulated. Fading channel like Ricean and Rayleigh are compared. Channelized digital
receiver concept is discussed.
Massive MIMO Channel Calibration in TDD Wireless NetworksXiao-an Wang
Massive MIMO in TDD wireless networks depends crucially on channel reciprocity, which can be established by calibration. Existing calibration approaches, however, have been proven to be impractical for deployment in 5G NR and 802.11. This presentation introduces terminal-assisted calibration, which is shown to overcome the drawbacks of existing approaches and to enable various massive MIMO modes in 5G NR and 802.11.
ESTIMATION AND COMPENSATION OF INTER CARRIER INTERFERENCE IN WIMAX PHYSICAL L...ijngnjournal
WiMAX is Wireless Interoperability for Microwave Access has emerged as a promising solution for transmission of higher data rates for fixed and mobile applications. IEEE 802.16d and e are the standards proposed by WiMAX group for fixed and mobile. As the wireless channel have so many limitation Such as Multipath, Doppler spread, Delay spread and Line Of Sight (LOS)/Non Line Of Sight (NLOS) components. To attain higher data rates the Multi Carrier System with Multiple Input and Multiple Output (MIMO) is incorporated in the WiMAX. The Orthogonal Frequency Division Multiplexing (OFDM) is a multi carrier technique used with the WiMAX systems. In OFDM the available spectrum is split into numerous narrow band channels of dissimilar frequencies to achieve high data rate in a multi path fading environment. And all these sub carriers are considered to be orthogonal to each other. As the number of sub carriers is increased there is no guarantee of sustained orthogonality, i.e. at some point the carriers are not
independent to each other, and hence where the orthogonality can be loosed which leads to interference and also owing to the synchronization between transmitter and receiver local oscillator, it causes interference known as Inter Carrier Interference (ICI). The systems uses MIMO-OFDM will suffer with the effects of ICI and Carrier Frequency Offset (CFO) “ε”. However these affect the power leakage in the midst of sub carriers, consequently degrading the system performance. In this paper a new approach is proposed in order to reduce the ICI caused in WiMAX and improve the system performance. In this scheme at the transmitter side the modulated data and a few predefined pilot symbols are mapped onto the non
neighboring sub carriers with weighting coefficients of +1 and -1. With the aid of pilot symbols the frequency offset is exactly estimated by using Maximum Likelihood Estimation (MLE) and hence can be minimized. At demodulation stage the received signals are linearly combined along with their weighted
coefficients and pilot symbols, called as Pilot Aided Self Cancellation Method (PASCS). And also to realize the various wireless environments the simulations are carried out on Stanford University Interim (SUI) channels. The simulation results shows that by incorporating this method into WiMAX systems it performs better when the Line Of Sight (LOS) component is present in the transmission and also it improves the Bit Error Rate (BER) and Carrier to Interference Ratio (CIR). The CIR can be improved 20 dB. In this paper the effectiveness of PASCS scheme is compared with the Self Cancellation Method (SCM). It provides accurate estimation of frequency offset and when residual CFO is less significant the ICI can be diminished successfully.
Performance Analysis of 802.lln MIMO OFDM TransceiverIJERA Editor
The increasing demand on real time application to achieve high throughput, reliable wireless system and network capacity for fourth generation wireless local area networks is to combine MIMO wireless technology with OFDM. Orthogonal Frequency Division Multiplexing (OFDM), which offers reliable high bit rate wireless system with reasonable low complexity. OFDM does provide large data rates with sufficient robustness to radio channel impairments. OFDM is a combination of modulation and multiplexing and are able to maximize spectral efficiency without causing adjacent channel interference. This paper first focuses on 802.11n standard, MIMO-OFDM system. This paper further reviews different work done on implementation of MIMO-OFDM transceiver for 802.11n standard.
Analysis of a framework implementation of the transceiver performances for in...IJECEIAES
The greatest advantages of optical fibers are the possibility of extending data rate transmission and propagation distances. Being a multicarrier technique, the orthogonal frequency division multiplexing (OFDM) can be applicable in hybrid optical-wireless systems design owing to its best spectral efficiency for the interferences of radio frequency (RF) and minor multipath distortion. An optical OFDM-RoF-based wireless local area network (W-LAN) system has been studied and evaluated in this work. The outline for integrating an optical technology and wireless in a single system was provided with the existence of OFDM-RoF technology and the microstrip patch antenna; these were applied in the Optisystem communication tool. The design of the proposed OFDM-RoF system is aimed at supporting mm-wave services and multi-standard operations. The proposed system can operate on different RF bands using different modulation schemes like 4.16 and 64QAM that may be associated to OFDM and multidata rates up to 5 Gbps. The results demonstrate the robustness of the integrated optical wireless link in propagating OFDM-RoF-based WLAN signals across optical fibers.
IMPLEMENTATION OF LINEAR DETECTION TECHNIQUES TO OVERCOME CHANNEL EFFECTS IN ...IJCI JOURNAL
Spatial diversity technique enables improvement in quality and reliability of wireless link. Antenna
diversity along with understanding effects of channel on transmitted signal and methods to overcome the
channel impairment plays an important role in wireless communication where sharing of channel occurs
between users. In this paper single input single output system (SISO) is compared with multiple input
multiple output system (MIMO) in terms of bit error rate performance. Bit error rate performance is also
evaluated for MIMO with least squares (LS) and Minimum mean square error (MMSE) linear detection.
Further analysis and simulation is done to understand the effect of channel imperfections on BER.
Performance Analysis of MIMO-LTE for MQAM over Fading ChannelsIOSRJECE
LTE (Long Term Evolution) is a 3GPP (Third Generation Partnership Project) wireless standards which uses the standard OFDMA (Orthogonal Frequency Division Multiple Access) modulation, MU-MIMO (Multiuser Multiple Input Multiple Output) technology and different multipath fading models. LTE uses the spectrum more efficiently to deliver high speed data. This paper characterizes the downlink performance of LTE. The MIMO technology which provides high data rate applications to the users made a breakthrough in wireless communication and is defined in the LTE standard. The performance is characterized in terms of BER (Bit Error Rate). In this paper the LTE system is modelled and simulated using MATLAB and the BER for 2×2 and 4×4 MIMO-LTE using 16QAM and 64QAM modulation schemes for Rayleigh fading environment are obtained against different SNR values.
Rapid developments in modern wireless communication permit the trade of spectrum scarcity. Higher data rate and wider bandwidth emerge the development in growing demand of wireless communication system. The innovative solution for the spectrum scarcity is cognitive radio (CR). Cognitive radio is the significant technology used to utilize the spectrum effectively. The important aspect of CR is sensing the spectrum band and detects the presence or absence of the primary user in the licensed band. Moreover, another serious issue in next generation (5G) wireless communication is to decide the less complex 5G waveform candidate for achieving higher data rate, low latency and better spectral efficiency. Universal filtered multi-carrier (UFMC) is one of the noticeable waveform candidates for 5G and its applications. In this article, we investigate the spectrum sensing methods in multi-carrier transmission for cognitive radio network applications. Especially, we integrate the sensing algorithm into UFMC transceiver to analyze the spectral efficiency, higher data rates and system complexity. Through the simulation results, we prove that the UFMC based cognitive radio applications outperform the existing Orthogonal Frequency Division Multiplexing (OFDM) based CR applications.
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.
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
Improvement of MFSK -BER Performance Using MIMO Technology on Multipath Non L...theijes
Digital communications has evolved rapidly with a lot of success. The new trend seems to be the reinvention of already existing and even discredited or discarded theories or in this case, channels. Extensive research into optimizing or enhancing already existing schemes is still gaining momentum with practical results for all to experience and utilize. This paper describes the design and BER performance of an M-ary frequency shift keyed (FSK) signaling and demodulation scheme improved by MIMO antenna technology for wireless communications. MFSK and MIMO systems were briefly reviewed including AWGN, Non LOS fading and an important factor employed to estimate the performance of digital transmission. The research was performed using MATLAB for simulation and evaluation of the BER
A simulation study of wi max based communication system using deliberately cl...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
A simulation study of wi max based communication system using deliberately cl...eSAT Journals
Abstract WiMAX is a highly sophisticated technology in the broadband wireless access communication system. Scalable Orthogonal Frequency Division Multiple Access (OFDMA) is a key technology behind mobile WiMAX and it is also expected to play a key role in 3GPP Long Term Evolution (LTE) standards. Designers and OEMs have to concentrate on flexibility, scalability and stability of the overall Orthogonal Frequency Division Multiplexing (OFDM) system along with its proper data processing and channeling process to achieve high performance and competitiveness. In this paper, the performance of a strictly band limited OFDM signal is examined using deliberate clipping method, one of the simplest signal distortion based way to reduce high Peak to Average Power Ratio (PAPR) and its effect on the resultant Bit Error Rate (BER) against Signal to Noise Ratio (SNR) performance. A simulation program using MATLAB software was developed to investigate performance of OFDM signal by optimization of different parameters such values of FFT size, Cyclic Prefix co-efficient (CPC) and The Voltage Clipping Ratio (VCR). The simulation results show that with the increment of VCR at optimized parameter values of FFT size and CP, the performance of BER vs SNR improves compared to the results found without clipping. Keywords: WiMAX, PAPR, OFDM, CPC, Voltage Clipping Ratio, Deliberately Clipped
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
Performance Analysis of Ultra Wideband Communication SystemEditor IJMTER
Ultra-Wideband (UWB) is a radio transmission scheme that uses extremely low power
pulses of radio energy spread across a wide spectrum of frequencies. UWB has several advantages
over conventional continuous wave radio communications including potential support for high data
rates, robustness to multipath interference and fading. The paper covers Ultra Wide-Band
technology. General description, Challenges, various modulation schemes such as OOK, PAM,
PPM, and BPSK under specified Ultra Wide Band regimes: low Power spectral density, large
spreading ratio and a highly dispersive channel. The capacity and BER performance of a single user
ultra wideband communication is investigated for various modulation schemes and coded, uncoded
methods also simulated. Fading channel like Ricean and Rayleigh are compared. Channelized digital
receiver concept is discussed.
Massive MIMO Channel Calibration in TDD Wireless NetworksXiao-an Wang
Massive MIMO in TDD wireless networks depends crucially on channel reciprocity, which can be established by calibration. Existing calibration approaches, however, have been proven to be impractical for deployment in 5G NR and 802.11. This presentation introduces terminal-assisted calibration, which is shown to overcome the drawbacks of existing approaches and to enable various massive MIMO modes in 5G NR and 802.11.
This MATLAB section of source code covers MATLAB based projects.
Download free source code viz. FIR,IIR,scrambler,interleaver,FFT,convolution,correlation,interpolation,decimation,CRC,impairments,data type conversions and more.
RS encoder,convolutional encoder,viterbi decoder,OFDM,OFDMA,MIMO is also covered.WiMAX,WLAN,LTE source codes are also provided.
An Investigation of Self-Interference Reduction Strategy in Correlated SM-OFD...Rosdiadee Nordin
R. Nordin, M. Ismail, "An Investigation of Self-Interference Reduction Strategy in Correlated SM-OFDMA Systems", Proceedings of 17th Asia-Pasific Conference on Communications. APCC 2011, Oct. 2011
Dynamic subcarrier allocation with ESINR metric in correlated SM-OFDMARosdiadee Nordin
R. Nordin, S. Armour, J.P. McGeehan, “Dynamic subcarrier allocation with ESINR metric in correlated SM-OFDMA”, Proceedings of 2010 6th Conference on Wireless Advanced (WiAD), pp.1-5, June 2010
Averzs technologies chennai mobile 9500068577_profile_matlab_image processing...AverzsRamesh
AVERZS TECHNOLOGIES ... IEEE RESEARCH AND DEVELOPMENT PROJECT FOR M.E., M. Tech., B.E., B. Tech., MCA., and Ph.D in MATLAB, NS2, EMBEDDED SYSTEMS, VLSI, ADS, JAVA, DOTNET, CADENCE, ANDROID...
CONTACT ADDRESS
Averzs Technologies, No.468/324, T2, Reshma Tower,
MKN Road, Alandur-600 016, Phone:044-4558 9227
Mobile:9500068577, 9500048577,Mail:info@averzs.com
Web:www.averzs.com,Near St.Thomas Mount Railway Station
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.
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.
Orthogonal frequency-division multiplexing (OFDM)
[1] is a method of encoding digital data on multiple carrier
frequencies. OFDM[1] has developed into a popular scheme
for wideband digital communication, whether wireless or
over copper wires, used in applications such as digital television
and audio broadcasting, DSL Internet access, wireless networks,
powerline networks, and 4G mobile communications. In the
Several wireless standards such as IEEE 802.11a[2] and
HiperLAN2[3].The orthogonality of the subcarriers is no longer
maintained which results in ICI (Inter carrier Interference)[4]
.ICI reduction techniques achieve a better SNR and BER in
OFDM at zero phase noise variance . This technique will use a
large number of closely spaced orthogonal subcarriers to avoid
phase noise. It provides high data rates with sufficient robustness
to radio channel damages. A major problem in OFDM is carrier
frequency offset error between the transmitted and received
signals. Due to this the orthogonality of the subcarriers is no
longer maintained which results in ICI (Inter carrier
Interference). In this paper, we used the ICI self-cancellation
technique and reduced the ICI and improved the BER and SNR
we are also calculate the SNR=15db and 20db at different phase
noise variance.
Abstract: The growing demand on wireless communication service has created the necessity to support higher data rates for multimedia services. .As next generation wireless communication networks are expected to provide broadband multimedia services such as voice, web browsing, video conferencing etc. For high data rate achievement one must enhance the capacity of the wireless communication system. The capacity of a communication system can be enhanced by using OFDM system. OFDM is commonly used for communication system due to its high transmission rate and robustness against multipath fading So as to enhance the capacity of fading channels the OFDM system are combined to form hybrid system. Capacity is the measure of maximum information that can be transmitted reliably over a channel. This paper review on different channel capacity enhancement techniques used in OFDM system is SVD (Singular Value Decomposition), water Filling algorithm.
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.
VLSI Implementation of OFDM Transceiver for 802.11n systemsIJERA Editor
Orthogonal Frequency Division Multiplexing (OFDM) is the most widely used modulation technique for wireless communication network. In this paper, 4 x 4 spatially multiplexed MIMO OFDM transceiver is designed using 1/2 encoder and 64 bit FFT. The implementation has been carried out in hardware using Field Programmable Gate Array (FPGA). Both the transmitter and the receiver are implemented on a single FPGA board with the channel being a wired one. The FPGA board used is Diligent Atlys Xilinx Spartan 6. We have analysed the effect of Bit Error Rate and Data rate with respect to Signal to Noise ratio.
Index modulation is one of the promising techniques for future communications systems due to many improvement over the classical orthogonal frequency division multiplexing systems such as single RF chain, increased throughput for the same modulation order, achieved tradeoff between the efficiencies of the power and the spectral, and elimination of inter-channel interference. Many forms of index modulation researches exist where symbols are conveyed in antennas, subcarriers, time slots, and the space-time matrix. Spatial modulation is one member of index modulation family where symbols are conveyed in activating transmit/receive antennas. In this paper, a modification to a standard multiple input single output scheme by integrating spatial modulation using simplified mathematical procedure is achieved. In the transmitter side, data and activation symbols are distributed simultaneously using mathematical module and floor functions. At the receiver, a simplified maximum likelihood detector is used to obtain transmitted pair of symbols. To verify this, MATLAB simulink is used to simulate a downlink system where spatial modulation is applied to a base station. Results for different transmit antenna number and modulation order are obtained in the form of bit error rate versus signal to noise ratio.
HYPERSPECTRAL IMAGERY CLASSIFICATION USING TECHNOLOGIES OF COMPUTATIONAL INTE...IAEME Publication
Texture information is exploited for classification of HSI (Hyperspectral Imagery) at high spatial resolution. For this purpose, framework employs to LBP (Local Binary Pattern) to extract local image features such as edges, corners & spots. After the extraction of LBP feature two levels of fusions are applied along with Gabor feature & spectral feature, i.e. Feature level fusion & Decision level fusion. In Feature level fusion multiple features are concurred before pattern classification. While in decision level fusion, it works on probability output of each individual classification pipeline combines the distinct decisions into final one. Decision level fusion consists of either hard fusion, soft fusion method. In hard fusion we consider majority part & in soft fusion linear logarithmic opinion pool at probability level (LOGP). In addition to this, extreme learning machine (ELM) classifier is included which is more efficient than support vector machine (SVM), used to provide probability classification output. It has simple structure with one hidden layer & one linear output layer. ELM trained much faster than SVM.
The aim of this paper is to determine the viability of Indoor Optical Wireless Communication System. This paper introduces Visible Light Communication along with its merits, demerits and applications. Then the main characteristics of VLC system are described, around which the project is designed. Multiple Input-Multiple Output (MIMO) technique is used in the project in order to enhance the data rate of transmission. Instead of using a system of only one LED and one APD, which transmits only one bit at a time, a system of 4 LEDs and 4 APDs is introduced, which increases the data rates by 300% from the previous case. We observe the signal, noise, SNR, BER etc. across the room dimension. Finally, in the last chapter we summarize our results on the basis of MATLAB simulations and propose some modifications to this model that can be implemented in future.
Event Management System Vb Net Project Report.pdfKamal Acharya
In present era, the scopes of information technology growing with a very fast .We do not see any are untouched from this industry. The scope of information technology has become wider includes: Business and industry. Household Business, Communication, Education, Entertainment, Science, Medicine, Engineering, Distance Learning, Weather Forecasting. Carrier Searching and so on.
My project named “Event Management System” is software that store and maintained all events coordinated in college. It also helpful to print related reports. My project will help to record the events coordinated by faculties with their Name, Event subject, date & details in an efficient & effective ways.
In my system we have to make a system by which a user can record all events coordinated by a particular faculty. In our proposed system some more featured are added which differs it from the existing system such as security.
Forklift Classes Overview by Intella PartsIntella Parts
Discover the different forklift classes and their specific applications. Learn how to choose the right forklift for your needs to ensure safety, efficiency, and compliance in your operations.
For more technical information, visit our website https://intellaparts.com
TECHNICAL TRAINING MANUAL GENERAL FAMILIARIZATION COURSEDuvanRamosGarzon1
AIRCRAFT GENERAL
The Single Aisle is the most advanced family aircraft in service today, with fly-by-wire flight controls.
The A318, A319, A320 and A321 are twin-engine subsonic medium range aircraft.
The family offers a choice of engines
Welcome to WIPAC Monthly the magazine brought to you by the LinkedIn Group Water Industry Process Automation & Control.
In this month's edition, along with this month's industry news to celebrate the 13 years since the group was created we have articles including
A case study of the used of Advanced Process Control at the Wastewater Treatment works at Lleida in Spain
A look back on an article on smart wastewater networks in order to see how the industry has measured up in the interim around the adoption of Digital Transformation in the Water Industry.
Democratizing Fuzzing at Scale by Abhishek Aryaabh.arya
Presented at NUS: Fuzzing and Software Security Summer School 2024
This keynote talks about the democratization of fuzzing at scale, highlighting the collaboration between open source communities, academia, and industry to advance the field of fuzzing. It delves into the history of fuzzing, the development of scalable fuzzing platforms, and the empowerment of community-driven research. The talk will further discuss recent advancements leveraging AI/ML and offer insights into the future evolution of the fuzzing landscape.
Automobile Management System Project Report.pdfKamal Acharya
The proposed project is developed to manage the automobile in the automobile dealer company. The main module in this project is login, automobile management, customer management, sales, complaints and reports. The first module is the login. The automobile showroom owner should login to the project for usage. The username and password are verified and if it is correct, next form opens. If the username and password are not correct, it shows the error message.
When a customer search for a automobile, if the automobile is available, they will be taken to a page that shows the details of the automobile including automobile name, automobile ID, quantity, price etc. “Automobile Management System” is useful for maintaining automobiles, customers effectively and hence helps for establishing good relation between customer and automobile organization. It contains various customized modules for effectively maintaining automobiles and stock information accurately and safely.
When the automobile is sold to the customer, stock will be reduced automatically. When a new purchase is made, stock will be increased automatically. While selecting automobiles for sale, the proposed software will automatically check for total number of available stock of that particular item, if the total stock of that particular item is less than 5, software will notify the user to purchase the particular item.
Also when the user tries to sale items which are not in stock, the system will prompt the user that the stock is not enough. Customers of this system can search for a automobile; can purchase a automobile easily by selecting fast. On the other hand the stock of automobiles can be maintained perfectly by the automobile shop manager overcoming the drawbacks of existing system.
Channel Estimation Techniques in MIMO-OFDM LTE SystemsCauses and Effects of Change Orders on Construction Projects in Kuwait
1. P. Venkateswarlu Int. Journal of Engineering Research and Applications www.ijera.com
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Channel Estimation Techniques in MIMO-OFDM LTE Systems P. Venkateswarlu*, R. Nagendra** *(M.Tceh Student, Department of Electronics and Communication Engineering, Sree Vidyanikethan Engineering college, Tirupati. ** (Assistant Professor, Department of Electronics and Communication Engineering, Sree Vidyanikethan Engineering college, Tirupati. ABSTRACT 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. Keywords - Spectral Efficiency, OFDM, MIMO-OFDM systems, Channel Estimation, Channel State information, Pilot Carriers, subspace approach, LTE.
I. INTRODUCTION
There is an increasing demand for the high data rates with effective utilization of available limited spectrum. To satisfy these requirements Multiple Input Multiple Output-Orthogonal Frequency Division Multiplexing (OFDM-OFDM) techniques have been adopted. MIMO technology is one of the major attracting techniques in wireless communications because; it offers significant increases in data throughput and coverage without additional bandwidth or transmitter power. It also provides high spectral efficiency and link reliability. Because of these properties, MIMO is an important part of modern wireless communication standards such as IEEE 802.11n (Wi-Fi), 4G, 3GPPLTE, WiMAX and HSPA+.
In Mobile communication systems prior to transmit the information certain characteristics of the radio waves are changed in accordance with the information bits. At the receiving end the information bits are retrieved accurately, if the channel characteristics are known. The channel may vary instantaneously because of the propagating medium, which leads to the signal degradation. The Channel State information (CSI) provides the known channel properties for a wireless link. It provides the effects of fading and scattering on a signal propagating through the medium. Normally the CSI estimated at the receiver fed back to the transmitter. If it is not estimated accurately at the receiver, leads to system degradation. It can be estimated by using different channel estimation algorithms. This estimation can be done with a set of well known sequence of unique bits for a particular transmitter and the same can be repeated in every transmission burst. Thus the channel estimator estimates the channel impulse response for each burst separately from the well known transmitted bits and corresponding received samples. This paper describes the fundamentals of MIMO-OFDM system and study of various channel estimation techniques and their performance. This paper organized as follows. Section II provides the over view of OFDM, the next section provides a description of the MIMO-OFDM system model. The section IV presents the various channel estimation algorithms for MIMO-OFDM LTE systems. Finally, the conclusion is specified in section V.
II. ORTHOGONAL FREQUENCY DIVISION MULTIPLEXING
2.1 OVERVIEW OF OFDM
Orthogonal Frequency-Division Multiplexing (OFDM) is a type of Frequency Division Multiplexing (FDM) method which can be used as a digital multi-carrier modulation technique. The unique property of the OFDM is orthogonality among the subcarriers, which are obtained by splitting the carrier into closely spaced orthogonal subcarriers or channels. This property ensures the reduction in Inter Carrier Interference (ICI) to a larger extent. Hence the design of the transmitter and the receiver
RESEARCH ARTICLE OPEN ACCESS
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becomes easier compared to the FDM method, which requires a separate filter bank for each subcarrier. It is quite simple to insert guard intervals between the OFDM symbols if the symbol duration is high. Therefore the Inter Symbol Interference (ISI) can be eliminated effectively without using pulse shaping filter. In OFDM the large data stream to be transmitted is divided into parallel data streams. These data streams are fed to the orthogonal carriers at lower rate. Each subcarrier is modulated by using any one of the digital modulation schemes such as Binary Phase Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK) and Quadrature Amplitude Modulation (QAM). The data rate for each channel is low compared to the conventional data rate for a single-carrier modulation. However the overall data rate is superior or comparable to the single-carrier modulation. Hence this scheme finds it’s applications in most of the modern wireless broadcasting systems namely 802.11n (WIFI), WiMaX, LTE and Ultra Wide Band (UWB) systems.
2.2 MATHEMATICAL FORMULATION OF OFDM
If symbols to be transmitted are Xk, k=0,1,..,N-1. The OFDM symbols are placed at a frequency spacing of fs, to keep orthogonality among the subcarriers. Where fs=1/ (NTs) Ts= sampling interval The OFDM signal transmitted through Kth subcarrier is given by
푥푛= Xk푒 푗2휋푛푘 푁 푁−1 푘=0
III. MIMO-OFDM SYSTEM
In MIMO systems multiple antennas are used at both ends of the transmitter and receiver. Usage of MIMO-OFDM systems in modern wireless communication systems provides increased system capacity and coverage with robustness against multipath fading. Because of the unique properties of the MIMO and OFDM systems, these systems are used in high-speed wireless communication systems. A simple MIMO-OFDM system with P transmit antennas and Q receive antennas is shown in Fig. 1. MIMO can be sub-divided into three main parts pre-coding, spatial multiplexing and diversity coding respectively. Precoding is one of the multi-stream beamforming techniques employed at the transmitter. In this method same type of signals are transmitted with weighted gains from each of the transmitting antennas in order to maximize the input signal power received at the receiver. It also reduces the multipath fading effect but, it requires CSI at the transmitter. Spatial multiplexing requires antenna configuration of the MIMO system. In this, a high data rate signal is split into a number of low data rate signals and each stream is transmitted using different antennas operating at the same frequency. At the receiver these signal arrive with different spatial signatures and it can easily separate these data stream into parallel channel. The spatial multiplexing technique increases the signal to noise ratio (SNR) and the system capacity. It can be used with or without the knowledge about the CSI at the transmitter. Diversity coding is used to improve the signal received at the receiver without knowing the CSI. In this technique the single data stream is transmitted by using space-time coding with full or near orthogonality from each transmitting antenna. Diversity coding exploits the independent fading in multiple antenna links to improve the signal power. Spatial multiplexing techniques make the design of the receivers very complex. Therefore it is usually combined with Orthogonal Frequency-Division Multiplexing (OFDM) to combat the problems created by multi-path fading.
Figure1 MIMO-OFDM system model
3.1 MATHEMATICAL DESCRIPTION
A simple MIMO system can be modeled as y=H x + n -------- (3) Where x and y are the transmit vector and receive vectors, H and n are the channel matrix and the noise vectors respectively.
3.2 CHANNEL ESTIMATION
In a wireless communication link, channel state information (CSI) provides the known channel properties of the link. The CSI should be estimated at the receiver and usually fed back to the transmitter. Therefore, the transmitter and receiver can have different CSI. The Channel State information may be instantaneous or statistical. In Instantaneous CSI, the current channel conditions are known, which can be viewed by knowing the impulse response of the transmitted sequence. But Statistical CSI contains the statistical characteristics such as fading distribution, channel gain, spatial correlation etc. The CSI acquisition is practically limited by how fast the channel conditions are changing. In fast fading systems statistical CSI is reasonable where channel
-------- (2)
-------- (1)
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conditions vary with a period less than the symbol time. But, in slow fading systems instantaneous CSI can be estimated with reasonable accuracy. So channel estimation technique is introduced to improve accuracy of the received signal. The radio channels in mobile communication systems are usually multipath fading channels, which are causing inter symbol interference (ISI) in the received signal. To remove ISI from the signal, several detection algorithms are used at the receiver side. These detectors should have the knowledge on channel impulse response (CIR) which can be provided by separate channel estimator.
3.3 CLASSIFICATION OF CHANNEL ESTIMATION TECHNIQUES
Basic classification of channel estimation algorithm is shown in Fig 2. They are training based, blind channel estimation and semi-blind channel estimation. The training based channel estimation can be carried out by either block type pilots or comb type pilots along with the data symbols. In block type pilot estimation, one specific symbol full of pilot subcarriers is transmitted periodically as in Fig 3(a). This estimation is suitable for slow fading channels. But, in comb type pilot estimation pilot tones are inserted into each OFDM symbol with a specific period of frequency bins as shown in Fig. 3(b). This type of channel estimation is very much suitable where the changes even in one OFDM block. The blind channel estimation is carried out by evaluating the statistical information of the channel and particular properties of the transmitted signals. This blind channel estimation has no overhead loss and it is only suitable for slowly time-varying channels. But in training based channel estimation, training symbols or pilot tones that are known to the receiver, are multiplexed along with the data stream for channel estimation. The Semi-blind channel estimation algorithm is a hybrid combination of blind channel estimation and training based channel estimation which utilizes pilot carriers and other natural constraints to perform channel estimation.
Figure 2 Classification of channel estimation algorithms
Figure 3(a) Block Type Pilot
Figure 3(b) Comb Type Pilot
IV. CHANNEL ESTIMATION ALGORITHMS FOR MIMO-OFDM LTE SYSTEMS
4.1 TRAINING BASED CHANNEL ESTIMATION TECHNIQUES
Various channel estimation and optimization techniques are proposed [1]-[5], [10] and [11].
W Hardjawana, R Li, B Vucetic and Y Li in [1] proposed a novel pilot- aided iterative receiver with joint ICI cancellation and decoding algorithm, based on pilot symbols and iterative soft-estimate of data symbols. The channel can be estimated using time- domain interpolation and least square (LS) methods. Soft-estimate for data symbols are obtained by a maximum-a-posterior (MAP) decoder and improved subsequently using iterative process.
In [2] an Iterative channel estimation and inter carrier interference (ICI) cancellation method for highly mobile users in long-term evolution (LTE) systems is proposed. This algorithm estimates the wireless channel by using pilot symbols, estimates of the data symbols, and Doppler spread information at the receiver. The channel estimates are obtained by employing a least-square (LS) method, a simplified parallel interference cancellation (PIC) scheme coupled with decision statistical combining (DSC) are used to cancel the ICI and to improve data symbol detection.
In [3] MM Rana and MK Hosain proposed a normalized least mean (NLMS) square and recursive least squares (RLS) adaptive channel estimator for MIMO-OFDM systems. These channel estimation
Channel Estimation
Training based estimation
LS, ML, MSE
Algorithms
Blind channel estimation
STBC, OSTBC Algorithms
Semiblindchannel estimation
Linear prediction, Sparse semiblind
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(CE) methods uses adaptive estimator which are able to update parameters of the estimator continuously, so that the knowledge of channel and noise statistics are not necessary. This NLMS/RLS CE algorithm requires knowledge of the received signal only. The simulation results show that the RLS CE algorithm provides faster convergence rate and good performance compared to NLMS CE method.
The performance of LS and LMMSE channel estimation techniques for LTE Downlink Systems is analyzed in [4]. Here a 2x2 LTE Downlink system is considered, the estimator’s performance is evaluated in terms of Mean Square Error (MSE) and Bit Error Rate (BER). This method concentrates on the channel length parameter in comparison with the cyclic prefix (CP) inserted at the beginning of each OFDM symbol, which is usually equal to or longer than the channel length in order to suppress ICI and ISI. However, the CP length can be shorter than the channel length because of channel behavior. The simulation results show that the LMMSE outperforms the LSE, when the CP length is smaller than the channel length. In the other case, LMMSE continue its performance only for low SNR values and begins to lose its performance for higher SNR values. On the other hand, LS shows better performance than LMMSE in this range of SNR values.
In [5] Channel estimation algorithms and their implementations for mobile receivers are considered. The 3GPP long term evolution (LTE) based pilot structure is used as a benchmark in a MIMO-OFDM receiver. The decision directed (DD) space- alternating generalized expectation-maximization (SAGE) algorithm is used to improve the performance from that of the pilot symbol based least-squares (LS) channel estimator. The performance is improved with high user velocities, where the pilot symbol density is not sufficient. Minimum mean square error (MMSE) filtering is also used in estimating the channel in between pilot symbols. The pilot overhead can be reduced to a third of the LTE pilot overhead with DD channel estimation, obtaining a ten percent increase in data throughput and spectral efficiency.
In order to reduce complexity and take advantage of “null” sub-carriers, MMSE based iterative channel estimation algorithm is proposed in [10]. A compensation process is proposed to simplify the traditional iterative MMSE channel estimator. After this iterative compensated MMSE channel estimation in frequency domain, a simple “linear interpolation” in time domain is performed to obtain channel estimates over all OFDM symbols. Simulation results show that the IC-MMSE channel estimation algorithm has good performances which approach the performance with perfect channel state information in both SIMO and MIMO transmission modes.
In [11], an improved DCT based channel estimation with very low complexity is proposed and evaluated in IEEE802.11n and 3GPP/LTE MIMO- OFDM systems. The whole DCT window is divided into R small overlapping blocks where the length of these blocks is a power of 2. The performance is improved because the noise component is averaged on a larger number of subcarriers.
4.2 BLIND CHANNEL ESTIMATION TECHNIQUES
Most of the existing blind and semi blind methods for MIMO OFDM channel estimation, except for several algorithms that are proposed for orthogonal space–time-coded systems are based on the second-order statistics of a long vector, whose size is equal to or larger than the number of sub carriers
Enhancement of a blind channel estimator based on a subspace approach in a MIMO OFDM for a high mobility scenario is proposed in [6]. The simulations results have demonstrated the effectiveness of the approach for a 16 QAM modulation scheme and had been evaluated in term of bit error rate BER and mean square error MSE versus the signal to noise ratio SNR
4.3 SEMIBLIND CHANNEL ESTIMATION TECHNIQUES
The Semiblind channel estimation algorithms, exploit the second-order stationary statistics, correlative coding, and other properties, normally have better spectral efficiency With a small number of training symbols. These methods have been proposed to estimate the channel ambiguity matrix in MIMO- OFDM systems [7], [8].
An optimized channel estimation algorithm for Multipath MIMO-OFDM Systems has been proposed in [9]. This method has a better estimation performance than the compressive sampling matching pursuit sparse channel estimation method (CoSaMP-SCE). Furthermore, the proposed method does not need to use the sparsity information, while the CoSaMP-SCE requires it.
V. CONCLUSION
In this paper, the basic concepts of Orthogonal Frequency Division Multiplexing (OFDM), Multiple Input Multiple Output (MIMO) systems are addressed. The various channel estimation techniques such as training based, blind channel, semi-blind channel based algorithms are discussed. Also different optimization techniques, such as Decision- Directed Channel Estimation Implementation for Spectral Efficiency Improvement in Mobile MIMO- OFDM, Adaptive Channel Estimation Techniques for
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MIMO-OFDM Systems are reviewed for training based channel estimation algorithms. REFERENCES
[1] W Hardjawana, R Li, B Vucetic and Y Li, "A New Iterative Channel Estimation for High Mobility MIMO-OFDM Systems," IEEE Trans. Vehicular Technology Conference, pp. 1-5, 2010.
[2] N Aboutorab,W Hardjawana,B Vucetic, "A New Iterative Doppler-Assisted Channel Estimation Joint With Parallel ICI Cancellation for High-Mobility MIMO- OFDM Systems," IEEE Transactions on Vehicular Technology, VOL. 61, pp. 1577 - 1589, 2012.
[3] MM Rana, MK Hosain, "Adaptive Channel Estimation Techniques for MIMO-OFDM Systems," International Journal of Advanced Computer Science and Applications, Vol. 1, No.6, pp. 134-138, 2010.
[4] A Khlifi and R Bouallegue, "Performance Analysis of LS and LMMSE Channel Estimation Techniques for LTE Downlink Systems," International Journal of Wireless & Mobile Networks, Vol. 3, No. 5, pp. 141- 149, 2011.
[5] J Ketonen, M Juntti, J Ylioinas and J R. Cavallaro, “Decision-Directed Channel Estimation Implementation for Spectral Efficiency Improvement in Mobile MIMO- OFDM,” Springer Science, DOI 10.1007/s11265-013-0833-4, 2013.
[6] A Zaier and R Bouallègue, "Blind Channel Estimation Enhancement for MIMO- OFDM Systems under High Mobility Conditions," International Journal of Wireless & Mobile Networks (IJWMN) Vol. 4, No. 1, pp. 207- 214, February 2012.
[7] Y. Zeng, W. H. Lam, and T. S. Ng, “Semi blind channel estimation and equalization for MIMO space–time coded OFDM,” IEEE Trans. Circuits Syst. I: Reg. Papers, vol. 53, no. 2, pp. 463–474, Feb. 2006
[8] J. Kim and J. Lim, “Subspace-based iterative Semiblind channel estimation for MIMO- OFDM considering residual error,” IEEE Trans. Veh. Technol., vol. 58, no. 8, pp. 4660–4665, Oct. 2009.
[9] N Wang, G Gui, Z Zhang, T Tang and J Jiang, "A Novel Sparse Channel Estimation Method for Multipath MIMO-OFDM Systems," IEEE Vehicular Technology Conference, DOI. 10.1109/ VETECF. 2011.6093014, pp. 1-5, 2011.
[10] Y Liu and S Sezginer, "Iterative Compensated MMSE Channel Estimation in LTE Systems," IEEE International
Conference on Communications, DOI. 10.1109/ ICC. 2012. 6363977, pp. 4862 - 4866, 2012.
[11] M Diallo, R Rabineau, L Cariou, and M Hélard. "On Improved DCT Based Channel Estimation with Very Low Complexity for MIMO-OFDM Systems," In VTC spring. 2009.