oalib
Search Results: 1 - 10 of 100 matches for " "
All listed articles are free for downloading (OA Articles)
Page 1 /100
Display every page Item
Alamouti OFDM/OQAM systems with time reversal technique  [PDF]
Ilhem Blel,Ridha Bouallegue
Mathematics , 2015,
Abstract: Orthogonal Frequency Division Multiplexing with Offset Quadrature Amplitude Modulation (OFDM/OQAM) is a multicarrier modulation scheme that can be considered as an alternative to the conventional Orthogonal Frequency Division Multiplexing (OFDM) with Cyclic Prefix (CP) for transmission over multipath fading channels. In this paper, we investigate the combination of the OFDM/OQAM with Alamouti system with Time Reversal (TR) technique. TR can be viewed as a precoding scheme which can be combined with OFDM/OQAM and easily carried out in a Multiple Input Single Output (MISO) context such as Alamouti system. We present the simulation results of the performance of OFDM/OQAM system in SISO case compared with the conventional CP-OFDM system and the performance of the combination Alamouti OFDM/OQAM with TR compared to Alamouti CP-OFDM. The performance is derived by computing the Bit Error Rate (BER) as a function of the transmit signal-to-noise ratio (SNR).
MIMO-OFDM for 4G Wireless Systems  [PDF]
Dr. Jayakumari.J
International Journal of Engineering Science and Technology , 2010,
Abstract: Orthogonal frequency division multiplexing (OFDM) is a popular method for high data rate wireless transmission. OFDM may be combined with antenna arrays at the transmitter and receiver to increase the diversity gain and/or to enhance the system capacity on time-variant and frequency-selective channels, resulting in a multiple-input multiple-output (MIMO) configuration. As a promising technology for future broadband communication, MIMO –OFDM has gained more and more interests in recent years. In this paper, the performance of MIMO-OFDM system employing Quadrature Amplitude Modulation (QAM) is analysed. Simulation results show that this is a promising technique for next generation wireless systems.
Analysis of Link Adaptation Algorithms Using Coding Scheme for OFDM Systems Under Frequency Selective Fading Environment  [PDF]
Sandeep Singh,Neetu Sood
International Journal of Computer and Electrical Engineering , 2013, DOI: 10.7763/ijcee.2013.v5.686
Abstract: Orthogonal frequency division multiplexing (OFDM) is a robust technique utilized in wireless communication systems affected by frequency selectivity. In combination with multiple antennas at the transmitter and receiver as well as adaptive loading algorithms, OFDM proves to be robust against frequency selectivity. This paper presents OFDM with link adaptation algorithms applied to Multi-Input Multi-output (MIMO) systems. In this paper we apply an optimization discrete bit loading algorithm and power allocation for each subcarrier assuming instantaneous channel state information is known at both the transmitter and receiver. To improve the BER performance of wireless systems, coding techniques such as gray code and trellis coded modulation (TCM) are employed at the transmitter.
Doppler Shift Impact On The MIMO OFDM System In Vehicular Channel Condition  [cached]
Samarendra Nath Sur,Rabindranath Bera
International Journal of Information Technology and Computer Science , 2012,
Abstract: Vehicle-to-vehicle (V2V) communication systems will play an important role in intelligent transportation systems (ITS). But in high mobility road condition, orthogonal frequency division multiplexing (OFDM) is very sensitive to Doppler shift. In this scenario multiple input and multiple output (MIMO) system combined with OFDM, make MIMO -OFDM techniques very attractive and productive for vehicle-to-vehicle communications. This paper deals with the bit error rate (BER) performance analysis of MIMO-OFDM system in high way road condition which is modeled based on the Nakagami fading characteristic. The system performance is analyzed with the change in m value of Nakagami channel and also with the variation in the modulation schemes.
Time-Frequency Based Channel Estimation for High-Mobility OFDM Systems–Part I: MIMO Case  [cached]
Erol Önen,Aydın Akan,Luis F. Chaparro
EURASIP Journal on Advances in Signal Processing , 2010, DOI: 10.1155/2010/549197
Abstract: Multiple-input multiple-output (MIMO) systems hold the potential to drastically improve the spectral efficiency and link reliability in future wireless communications systems. A particularly promising candidate for next-generation fixed and mobile wireless systems is the combination of MIMO technology with Orthogonal Frequency Division Multiplexing (OFDM). OFDM has become the standard method because of its advantages over single carrier modulation schemes on multipath, frequency selective fading channels. Doppler frequency shifts are expected in fast-moving environments, causing the channel to vary in time, that degrades the performance of OFDM systems. In this paper, we present a time-varying channel modeling and estimation method based on the Discrete Evolutionary Transform to obtain a complete characterization of MIMO-OFDM channels. Performance of the proposed method is evaluated and compared on different levels of channel noise and Doppler frequency shifts.
Time-Frequency Based Channel Estimation for High-Mobility OFDM Systems–Part I: MIMO Case  [cached]
?nen Erol,Akan Ayd?n,Chaparro LuisF
EURASIP Journal on Advances in Signal Processing , 2010,
Abstract: Multiple-input multiple-output (MIMO) systems hold the potential to drastically improve the spectral efficiency and link reliability in future wireless communications systems. A particularly promising candidate for next-generation fixed and mobile wireless systems is the combination of MIMO technology with Orthogonal Frequency Division Multiplexing (OFDM). OFDM has become the standard method because of its advantages over single carrier modulation schemes on multipath, frequency selective fading channels. Doppler frequency shifts are expected in fast-moving environments, causing the channel to vary in time, that degrades the performance of OFDM systems. In this paper, we present a time-varying channel modeling and estimation method based on the Discrete Evolutionary Transform to obtain a complete characterization of MIMO-OFDM channels. Performance of the proposed method is evaluated and compared on different levels of channel noise and Doppler frequency shifts.
High Throughput of WiMAX MIMO OFDM Including Adaptive Modulation and Coding  [PDF]
Hadj Zerrouki,Mohamed Feham
Computer Science , 2010,
Abstract: WiMAX technology is based on the IEEE 802.16 specification of which IEEE 802.16-2004 and 802.16e amendment are Physical (PHY) layer specifications. IEEE 802.16-2004 currently supports several multiple-antenna options including Space-Time Codes (STC), Multiple-Input Multiple-Output (MIMO) antenna systems and Adaptive Antenna Systems (AAS). The most recent WiMAX standard (802.16e) supports broadband applications to mobile terminals and laptops. Using Adaptive Modulation and Coding (AMC) we analyze the performance of OFDM physical layer in WiMAX based on the simulation results of Bit Error Rate (BER), and data throughput. The performance analysis of OFDM PHY is done. In this paper, an extension to the basic SISO mode, a number of 2 by 2 MIMO extensions are analysed under different combinations of digital modulation (QPSK, 16QAM and 64QAM) and Convolutional Code (CC) with half, two-third and three quarter rated codes. The intent of this paper is to provide an idea of the benefits of multiple antenna systems over single antenna systems in WiMAX type deployments.
Study Of Transmission Characteristics Of 2x2 Mimo System for OFDM Multiplexing and Bpsk Modulation With ZF Equalizer And MMSE Receivers  [PDF]
Bhagya. R,,A. G. Ananth
International Journal of Soft Computing & Engineering , 2012,
Abstract: A detailed analysis of 2×2 MIMO (Multiple Input Multiple Output) combined with OFDM (Orthogonal Frequency Division Multiplexing) transmission system and BPSK modulation has been carried out. The BER performance of the system has been determined for Additive white Gaussian Noise (AWGN) presuming Flat fading Rayleigh channel. On the receiver side linear equalization techniques such as Zero Force Equalizer (ZF) and Minimum Mean Square Error (MMSE) detectors were employed for studying the BER performance. The simulation results show that for BER of ~10-4, the SNR required are ~34 dB for ZF equalizer and ~31dB for MMSE equalizer. The simulation results indicate that the MMSE equalizer shows better performance ~3 dB over the ZF equalizer. Further comparison of the 2X2 MIMO performance of OFDM with STBC multiplexing indicates comparable BER performances. The simulation results are presented and discussed in the paper.
Single-Carrier Modulation for Large-Scale Antenna Systems  [PDF]
Yinsheng Liu,Geoffrey Ye Li,Zhenhui Tan,Deli Qiao
Mathematics , 2015,
Abstract: \emph{Large-scale antenna} (LSA) has gained a lot of attention due to its great potential to significantly improve system throughput. In most existing works on LSA systems, \emph{orthogonal frequency division multiplexing} (OFDM) is presumed to deal with frequency selectivity of wireless channels. Although LSA-OFDM is a natural evolution from \emph{multiple-input multiple-output} OFDM (MIMO-OFDM), several drawbacks of LSA-OFDM are inevitable. In this paper, we investigate \emph{single-carrier} (SC) modulation for LSA systems (LSA-SC). In LSA-SC, the multipath propagation can be suppressed using antenna array when the antenna number is large enough and the channels at different antennas are independent. In that case, the transmit symbol can be recovered by directly sampling the received waveform if the waveform in SC modulation is designed to satisfy the Nyquist condition. In practical systems, however, the antenna number is always finite and the channels at different antennas may be also correlated when placing hundreds of antennas in a small area. Therefore, we will analyze the performance of LSA-SC in such practical environments.
Analytical Performance Evaluation of Space Time Coded MIMO OFDM Systems Impaired by Fading and Timing Jitter  [cached]
Md. Rubaiyat H. Mondal,Satya P. Majumder
Journal of Communications , 2009, DOI: 10.4304/jcm.4.6.380-387
Abstract: An analytical approach is presented to determine the impact of time selective fading, timing jitter and additive white Gaussian noise (AWGN) on the bit error rate (BER) performance of an orthogonal frequencydivision multiplexing (OFDM) system with differential quaternary phase-shift keying (DQPSK), differential phase-shift keying (DPSK) and quaternary phase-shift keying (QPSK) modulation. The expression for the conditional BER conditioned on a given timing error and fading, is derived and the average BER is evaluated. The BER performance results are evaluated for different values of fading and jitter. The performance of the OFDM system in Rayleigh and Rician fading channels is also compared. Analytical approach is also developed to evaluate the BER performance of a quasi-orthogonal- space-time block coded OFDM system having multiple transmitting and single receiving antennas. The analysis is extended for a multiple-input multiple-output (MIMO)-OFDM system using the “selection method” for combining multiple receiving antennas, which offers significant improvement in the system performance. The effects of increase in number of OFDM subcarriers and increase in Doppler frequency are also investigated.
Page 1 /100
Display every page Item


Home
Copyright © 2008-2017 Open Access Library. All rights reserved.