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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...
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...
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...
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...
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...
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 long-term variation of the channel leads to changing the delay spread during the transmission time. This variation degrades the performance of conventional orthogonal frequency division multiplexing (OFDM) systems that use fixed length of the guard interval by introducing inter-symbol-interference (ISI) in highly frequency selective scenarios (high delay spread) or causes needless loss of capacity...
This paper is concerned with a simple in-phase and quadrature-phase (IQ) imbalance compensation scheme using a single pilot symbol in orthogonal frequency division multiplexing (OFDM) systems. The proposed scheme can estimate the IQ imbalance factors with pilot subcarriers of an OFDM symbol while existing method requires more OFDM symbols. Also, the proposed method is computationally efficient and...
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