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Robustness of MIMO-OFDM Schemes for Future Digital TV to Carrier Frequency Offset  [PDF]
Youssef Nasser,Jean-Fran?ois Hélard,Matthieu Crussière
Computer Science , 2008,
Abstract: This paper investigates the impact of carrier frequency offset (CFO) on the performance of different MIMO-OFDM schemes with high spectral efficiency for next generation of terrestrial digital TV. We show that all studied MIMO-OFDM schemes are sensitive to CFO when it is greater than 1% of inter-carrier spacing. We show also that the Alamouti scheme is the most sensitive MIMO scheme to CFO
Outage Performance of Flexible OFDM Schemes in Packet-Switched Transmissions  [cached]
Romain Couillet,Mérouane Debbah
EURASIP Journal on Advances in Signal Processing , 2009, DOI: 10.1155/2009/698417
Abstract: α-OFDM, a generalization of the OFDM modulation, is proposed. This new modulation enhances the outage capacity performance of bursty communications. The α-OFDM scheme is easily implementable as it only requires an additional time symbol rotation after the IDFT stage and a subsequent phase rotation of the cyclic prefix. The physical effect of the induced rotation is to slide the DFT window over the frequency spectrum. When successively used with different angles α at the symbol rate, α-OFDM provides frequency diversity in block fading channels. Interestingly, simulation results show a substantial gain in terms of outage capacity and outage BER in comparison with classical OFDM modulation schemes. The framework is extended to multiantenna and multicellular OFDM-based standards. Practical simulations, in the context of 3GPP-LTE, called hereafter α-LTE, sustain our theoretical claims.
On the Influence of Carrier Frequency Offset and Sampling Frequency Offset in MIMO-OFDM Systems for Future Digital TV  [PDF]
Youssef Nasser,Jean-Fran?ois Hélard,Matthieu Crussière
Computer Science , 2008,
Abstract: This paper investigates the impact of carrier frequency offset (CFO) and sampling frequency offset (SFO) on the performance of different MIMO-OFDM schemes with high spectral efficiency for next generation of terrestrial digital TV. We analyze particularly orthogonal Alamouti scheme, and non-orthogonal (NO) schemes like VBLAST, linear dispersion (LD) code and Golden code. This analysis gives a global view on the best suitable MIMO-OFDM scheme with respect to CFO and SFO. We show that for high spectral efficiency, Alamouti is more sensitive to CFO and SFO. Moreover, we show that all studied MIMO-OFDM schemes are sensitive to CFO when it is greater than 1% of inter-carrier spacing. Their sensitivity due to SFO is less than that due to CFO.
An Efficient Inter Carrier Interference Cancellation Schemes for OFDM Systems  [PDF]
B. Sathish Kumar,K. R. Shankar Kumar,R. Radhakrishnan
Computer Science , 2010,
Abstract: Orthogonal Frequency Division Multiplexing (OFDM) has recently been used widely in wireless communication systems. OFDM is very effective in combating intersymbol interference and can achieve high data rate in frequency selective channel. For OFDM communication systems, the frequency offsets in mobile radio channels distort the orthogonality between subcarriers resulting in Inter Carrier Interference (ICI). ICI causes power leakage among subcarriers thus degrading the system performance. A wellknown problem of OFDM is its sensitivity to frequency offset between the transmitted and received carrier frequencies. There are two deleterious effects caused by frequency offset one is the reduction of signal amplitude in the output of the filters matched to each of the carriers and the second is introduction of ICI from the other carriers. This research work investigates three effective methods for combating the effects of ICI: 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 and bandwidth efficiency. Through simulations, it is shown that the three techniques are effective in mitigating the modulation schemes, the ML and EKF methods perform better than the SC method.
An Efficient Inter Carrier Interference Cancellation Schemes for OFDM Systems
B. Sathish Kumar,K. R. Shankar Kumar,R. Radhakrishnan
International Journal of Computer Science and Information Security , 2009,
Abstract: Orthogonal Frequency Division Multiplexing (OFDM) has recently been used widely in wireless communication systems. OFDM is very effective in combating inter-symbol interference and can achieve high data rate in frequency selective channel. For OFDM communication systems, the frequency offsets in mobile radio channels distort the orthogonality between subcarriers resulting in Inter Carrier Interference (ICI). ICI causes power leakage among subcarriers thus degrading the system performance. A well-known problem of OFDM is its sensitivity to frequency offset between the transmitted and received carrier frequencies. There are two deleterious effects caused by frequency offset one is the reduction of signal amplitude in the output of the filters matched to each of the carriers and the second is introduction of ICI from the other carriers. This research work investigates three effective methods for combating the effects of ICI: 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 and bandwidth efficiency. Through simulations, it is shown that the three techniques are effective in mitigating the modulation schemes, the ML and EKF methods perform better than the SC method.Keywords- Orthogonal frequency Division Multiplexing (OFDM); Inter Carrier Interference(ICI); Carrier to Interference Power Ratio (CIR);Self Cancellation(SC);Carrier Frequency Offset (CFO); Maximum Likelihood(ML); Extended Kalman Filtering(EKF).
Influence of frequency offset on the reception of OFDM/QPSK signal using MBDD algorithm  [PDF]
B. Dimitrijevi?,S. Sto?ovi?,N. Milo?evi?,Z. Nikoli?
Telfor Journal , 2011,
Abstract: In this paper we present the basic characteristics of Orthogonal Frequency Division Multiplex (OFDM) systems with quadrature phase shift keying (QPSK) modulation and multi-bit differential detection (MBDD). In the simulation environment designed for this purpose, we analyze the effects of frequency offset on the performances of OFDM digital communications. We also analyze the influence of OFDM system parameters on system performances for various values of frequency offset, number of bits for multi-bit detection and the number of subcarriers. We have shown the advantages and disadvantages of using MBDD in the OFDM systems.
Improving OFDM/DQPSK System Performance in the Conditions of Frequency Offset Existence  [PDF]
Z. B. Nikoli?,B. R. Dimitrijevi?,N. D. Milo?evi?,S. N. Sto?ovi?
Telfor Journal , 2010,
Abstract: The basic characteristics of Orthogonal Frequency Division Multiplex (OFDM) systems with DQPSK modulation and channel estimation with an adaptive transversal filter and LMS algorithm are analyzed and presented in this paper. In the simulation environment designed for this purpose, we analyzed the effects of frequency offset on the performance of OFDM digital communications and presented the method for improving system performance in the presence of frequency offset. We analyzed the influence of OFDM system parameters on system’s performance for various values of frequency offsets, filter lengths and the number of subcarriers. Finally, we compared the result with the one for a perfectly synchronized OFDM/DQPSK system with differential and coherent demodulation.
Carrier Frequency Offset and Phase Noise Recovery in Correlated MIMO-OFDM Systems  [cached]
Yong Yi,Haifang Jian,Zhi Fang,Yin Shi
Journal of Networks , 2010, DOI: 10.4304/jnw.5.4.492-499
Abstract: Many works have addressed the effect of CFO (Carrier Frequency Offset) and residual CFO (Phase Noise) on the performance of OFDM system, but few has been done to analysis the MIMO- (Multiple Input-Multiple Output) OFDM situation. In this paper, we provide an exact analysis of MIMO-OFDM performance in the presence of CFO and phase noise. A new CFO estimation method based on training sequences is proposed. The new method uses vector operation to calculate the fine frequency offset; it also reduces the noise energy and improves the signal-to-noise in the CFO estimation process. Since multiple antennas estimate the CFO, the MRC (Maximum Ratio Combining) technique is used. In this paper, adaptive phase noise mitigation (PNM) algorithm is also proposed. This method uses the pilots which insert in the data payload to track the rotation of channel response caused by residual CFO. For lower deviation, low pass filter is employed to the decision of sub-carrier after demodulation. Correlated MIMO channel TGn model is used to evaluate the performance of the proposed algorithm. With the maximum CFO (40ppm) requirement specified by the 802.11n Draft4.0 standard, simulation results show that the degradation is limited to within 3dB for the TGn channel model D and E in various modulations coding scheme (MCS) in 802.11n Draft 8.0. The results also show that the Bit Error Rate and Packet Error Rate can satisfy the requirement of the 802.11n Draft8.0
Low-Complexity Blind Symbol Timing Offset Estimation in OFDM Systems  [cached]
Tiejun Lv,Jie Chen,Hua Li
EURASIP Journal on Advances in Signal Processing , 2005, DOI: 10.1155/asp.2005.532
Abstract: A low-complexity blind timing algorithm is proposed to estimate timing offset in OFDM systems when multiple symbols are received (the timing offset estimation is independent of the frequency offset one). Though the maximum-likelihood estimation (MLE) using two or three symbols is good in offset estimation, its performance can be significantly improved by including more symbols in our previous work. However, timing offset estimation requires exhaustive search and a priori knowledge of the probability distribution of the received data. The method we propose utilizes the second-order statistics embedded in a cyclic prefix. An information vector (IVR) with the same length as the cyclic prefix is formed based on an autocorrelation matrix (AM). The modulus of elements in the IVR is first quantized based on a threshold that is defined by the variance of OFDM symbols. The timing offset is then estimated based on the binary sequence of the IVR. Because the exhaustive search used in the MLE can be avoided, computational complexity is significantly reduced. In practice, the proposed scheme can be used as a coarse synchronization estimation that can rapidly provide a rough and contractible estimation range, which serves as the basis for a fine estimation like the MLE. The proposed estimator will be proved theoretically to be asymptotically unbiased and mean-squared consistent. Simulations and comparisons will be provided in the paper to illustrate the advantages of our design.
Effects and Estimation Techniques of Symbol Time Offset and Carrier Frequency Offset in OFDM System: Simulation and Analysis
Sandeep Kaur,,Dr. Charanjit Singh,,Dr. Amandeep Singh Sappal
International Journal of Electronics and Computer Science Engineering , 2012,
Abstract: Orthogonal frequency division multiplexing system is multichannel system that provides high rate and high quality wireless communication services, but system performance is degraded by two factors, one is the symbol timing offset (STO) and other is the carrier frequency offset (CFO) caused by Doppler frequency shift. Several approaches have been proposed to estimate time and frequency offset. Most frequency and timing estimation methods use the periodic nature of the time domain signal by using a cyclic prefix or by designing the training symbol having repeated parts. In this paper, the effects of STO and CFO in OFDM system have been studied. Also, the estimation techniques to handle the STO and CFO problems in OFDM system by using cyclic prefix and training symbol has been analyzed.
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