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Time varying channel breaks the orthogonality between the subcarriers of Orthogonal Frequency Domain Multiplexing (OFDM). This introduces Intercarrier Interference (ICI). One of the ways to mitigate ICI is to first estimate the channel and then equalize it. In this paper we propose to estimate the channel using Discrete Proplate Spheroidal Sequences (DPS) using pilot carriers interleaved with data...
Adaptive Bit Loading (ABL) in Multiple-Input Multiple-Output Orthogonal Frequency-Division Multiplexing (MIMO-OFDM) is most likely used for achieving the desired Bit Error Rate (BER) performance in wireless systems. In this paper, we discuss some of the bit loading algorithms, compare them with respect to their BER performance, and present an effective concise Adaptive Grouped Loading (AGL) algorithm...
An efficient frequency offset estimation and compensation method is proposed for LTE uplink system. In the proposed method, the current instantaneous frequency offset estimation combines with the last frequency offset estimation to get the current frequency offset estimation by Altering. According to the frequency offset estimation, data is compensated in inter-symbols and intra-symbols. The simulation...
In this paper, we propose a simple in-service delay time estimation method and two adaptive transmission schemes, that is, adaptive GI length transmission scheme and adaptive modulation transmission scheme, based on the estimation method for broadband vehicular OFDM transmissions. The simple in-service delay time estimation method uses the characteristic that the symmetry of received signal point...
This paper presents a hardware-efficient autocorrelation scheme for the synchronization of MIMO-OFDM based wireless local area network (WLAN) systems, such as IEEE 802.11n. Carrier frequency offset (CFO) estimation for the frequency synchronization requires high complexity autocorrelation operations of many training symbols. In order to reduce the hardware complexity of the MIMO-OFDM synchronization,...
To improve the overall performance of time-domain synchronous (TDS) orthogonal frequency division multiplexing (OFDM) systems, novel iterative decoding and channel estimation algorithm with Nordstrom-Robinson (NR) code is proposed in this paper. Compared to the non-iterative case, the system performance can be significantly improved by the proposed iterative algorithm at the cost of a little complexity...
Sampling clock offset (SCO) could lead to a phase rotation and the Inter-Carrier Interferences (ICI), thus introduce an unacceptable BER in OFDM system. To estimate SCO, conventional methods rely on a known synchronization symbol or pilot symbols, which inevitably trim down the spectral efficiency of OFDM systems and are not available in non-cooperative communications. A novel blind estimation algorithm...
In orthogonal frequency division multiplexing (OFDM) system, synchronization and channel estimation are two important issues under the wireless fading channel in broadband wireless communication. The timing and frequency offset will affect the accuracy of channel estimation. These issues are studied in this paper, and a frequency selective fading channel under the OFDM system model is set up. This...
The classical channel estimation method in TDS-OFDM is carried out based on the PN sequence in the GI which suffers from the intersymbol interference of the previous OFDM data symbols. This paper presents a novel data-aided channel estimation method to refine the initial channel estimation obtained from PN sequence. The data symbols are rebuilt based on the log-likelihood ratio (LLR) from the output...
The existed preamble structure for orthogonal frequency division multiplex/offset QAM (OFDM/OQAM) system requires two zero-value guard symbols to guarantee ISI and ICI avoidance (equivalent to 3/2 complex value symbols in OFDM with cyclic prefix system), which leads to OFDM/OQAM system with low spectrum efficiency. In this paper, we shorten the preamble with 1 zero-value guard symbol to improve the...
This paper introduces a novel algorithm for jointly estimating carrier frequency offset and I/Q imbalance for OFDM systems. The new algorithm is a closed form solution to obtain the frequency offset and I/Q imbalance parameters in the absence of noise. In the presence of noise, the proposed algorithm uses the least squares algorithm to accurately estimate the parameters. The proposed algorithm is...
This paper presents a technique for maintaining good broadband transmission quality in the face of impulsive noise in OFDM-PLC systems. The proposed technique is based on adding one zero between two signal samples in order to estimate the noise power in every transmitted signal sample. Simulation results of complete PLC system highlight good improvement in BER and correction ability performances for...
In this paper, we study the joint estimation of I/Q imbalance, CFO and channel response for OFDM systems. Using two repeated OFDM blocks for training, we propose a new method to solve the joint estimation problem. The implementation complexity is low. Simulation results show that the proposed method has a good performance and its BER is very close to the ideal case where all the parameters are known...
In this paper we investigate channel estimation in the context of the OFDM-based HomePlug AV system using the OPERA power-line channel models. In particular, the proposed channel estimation exploits the sounding procedure available in HomePlug AV, by averaging the estimates of the channel collected during several received frames. To allow the channel estimation to properly work also in the case of...
An Ultra-Wideband (UWB) channel exhibits frequency dependent delay characteristics in different bands of transmission. In [6] we studied and quantified the differences of delay parameters over frequency bands 3.1-4.6 GHz in several UWB channel models (CM). Based on this observation, we proposed an adaptive timing synchronization scheme (ATS) which estimates and maintains the timing delays of each...
OFDM has recently been applied widely in wireless communication system due its high data rate transmission capability with high bandwidth efficiency. The channel estimation is playing key role for wireless communication system. In this paper, we present the improved scheme of LS based channel estimation technique using block type pilot arrangement for varying different values of channel impulse responses...
In orthogonal frequency division multiplexing (OFDM) systems, time- and frequency-selective (or doubly-selective) fading leads to the loss of subcarrier orthogonality and the occurrence of inter-carrier interference (ICI), which increases an irreducible error floor in proportional to the normalized Doppler frequency offset. Channel estimation (CE) in rapidly time-varying multi-path scenarios is critical...
The previously proposed first-order perturbation-based algorithm and linear constrained least mean square (LMS) based algorithm for channel matrix singular value decomposition (SVD) in multiple - input multiple - output (MIMO) orthogonal frequency division multiplexing (OFDM) systems are evaluated and compared in this paper from orthogonality, signal to noise plus interference ratio (SINR) and bit...
The transmission of Discrete Fourier Transform Spread Orthogonal Frequency Division Multiplexing (DFT-SOFDM) [4] through a time-selective fading channel with a significant amount of Doppler spread suffers from severe performance degradation. A shift in frequency caused by such channel leads to a loss of orthogonality between users. In this paper, we propose a DFT-SOFDM scheme augmented by MIMO and...
It is well known that Carrier frequency offset (CFO) is a performance limiting factor in orthogonal frequency division multiplexing (OFDM) systems. In this paper, we present maximum-likelihood estimators (MLE) for the CFO in OFDM systems in static and time-varying channels and evaluate the Cramer-Rao lower bounds (CRLB) for both cases. In addition, we examine the effect of power amplifiers' (PA) nonlinearity,...
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