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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...
As an alternative to the OFDM transceiver, single carrier frequency domain equalization (SC FDE) based transceiver has received much attention because of its simple implementation and low peak to average power ratio (PAPR). In this paper, a minimum mean square error (MMSE) FDE for single carrier block transmission is presented to effectively equalize the channels with high frequency selectivity such...
The Fourth generation (4G) wireless networks are expected to afford high data rate transmission of multimedia services such as wireless video, wireless Internet access and mobile computing. Orthogonal frequency division multiplexing (OFDM) is an effective technique for the future 4G communications because of its great immunity to impulse noise and intersymbol interference. Ultra wide band (UWB) wireless...
The bit error rate performance of orthogonal frequency division multiplexing (OFDM) systems is severely degraded in the presence of phase noise. The effect of phase noise on an OFDM signal has been studied in the literature. The OFDM signal sub-carriers are distorted due to phase noise in two ways. First is the constant phase shift of all the sub-carriers, and second is the inter-carrier interference...
In this paper we propose a blind estimation of fading coefficients without using the pilot symbols in QAM-OFDM systems subjected to carrier frequency offset (CFO), where the phases of the fading coefficients are within ±7r/4. First, under a frequency selective fading channel, the inter-carrier interference (ICI) due to CFO is formulated in the framework of independent component analysis (ICA). Then...
Orthogonal Frequency Division Multi-plexing (OFDM) is a significant technology to provide a high-rate wireless transmissions. In this paper, a scheme called as a step size delta - least mean square (SSD-LMS) is used for phase error cancellation. The results show that SSD-LMS algorithm can provide a rapid convergence with a low steady-state fluctuation error than that with the conventional LMS algorithm.
OFDM (Orthogonal Frequency Division Multiplexing) has been chosen as the air interface technique for LTE (Long Term Evolution) standard. Furthermore, CA (Carrier Aggregation) is defined by 3GPP (the 3rd Generation Partnership Project) to support wide-bandwidth transmission. However, OFDM system is sensitive to synchronization errors generated by multipath delay, Doppler shift and oscillator instability...
Base on the results of FFT in OFDM demodulation, one new single frequency interference estimation scheme is proposed, which can estimate accurately the parameters of single frequency interference by analyzing two spectrum lines having higher energy than others. The complexity of the scheme is very low and its accuracy is much higher than that of the conventional scheme which using only single spectra...
The performance of an OFDM system can be strongly degraded by the presence of random phase noise. In the proposed compensation scheme, we jointly estimate channel and phase noise and data. This estimation consists of three stages. In the first stage, phase noise, channel and transmitted data are initially estimated by using of linear interpolation method. In the second stage, with Linear Least Square...
This paper addresses the effect of timing synchronization errors for two different multicarrier techniques CPOFDM and FBMC. Such errors degrade the performance of the reference receiver by causing multi user interference. This interference occurs when the signals from different transmitters arrive at a given receiver with arbitrary timing misalignments, leading to the destruction of orthogonality...
New channel estimation technique is proposed for multiband orthogonal frequency division multiplexing (MB-OFDM) ultra-wideband (UWB) systems. Several steps have been carried out to achieve this purpose. In first step, refined least square (LS) channel estimation is found out by using subspace-based narrowband interference (NBI) estimation method with prilimonary LS channel. In second step, low rank...
We discuss a novel pilot design for multi-user channel estimation in the OFDM uplink with localized block-type pilot placement. Due to this placement, multiple users' channels interfere with each other. By analyzing the properties of this multi-user interference, a criterium of choosing an appropriate DFT phase shift in frequency domain is derived. With this optimized shift, the multi-user interference...
Abstract - A new inter-cell interference aware channel estimation technique for OFDM systems is presented. In the proposed algorithm, user equipment (UE) jointly detects the channel weights of the communication links associated with the serving and the interfering cells. Performance benefits of the proposed method are demonstrated by considering the OFDMA downlink as defined in 3GPP Long Term Evolution...
Applying multiple-input multiple-output (MIMO) techniques to orthogonal frequency division multiplexing (OFDM) systems promise to achieve high spectral efficiency. However, similar to single antenna OFDM systems, phase noise drastically degrades the performance of such systems. In this paper, we investigate the influence of phase noise in MIMO-OFDM wireless systems and propose a new algorithm for...
This paper deals with the problem of channel estimation for multiple-input multiple-output/orthogonal frequency-division multiplexing (MIMO/OFDM) systems based on superimposed training (ST). Channel coefficients are firstly estimated by judicious designing superimposed pilot sequences across different users. Then, we analyze the channel estimation performance and derive a closed-form expression for...
The multi-access orthogonal frequency division multiplexing (OFDMA) technology has drawn a lot of attention in next generation wireless mobile communications. It is well-known that carrier frequency offsets in OFDMA systems can destroy the orthogonality among subcarriers and produce intercarrier interference (ICI) and multiuser interference (MUI). In our previous works, we proposed a common carrier...
We prove that discrete Fourier basis channel model is optimal for least squares estimation of channel coefficients used for low-complexity equalization of OFDM transmission over doubly selective channels. We show that regardless of channel statistics, the channel model order is determined by the number of coefficients used in the equalization. Our theoretical findings are numerically validated by...
The paper presents an investigation into methods for maximizing the spectral Efficiency of Orthogonal Frequency Division Multiplexing (OFDM) systems. As part of this, an investigation of detrimental effects on OFDM is presented, the use of pilots between carriers, Clipping Distortion, Additive Complex Noise (ACN) on modulation QPSK rate, on multi path Synchronization error, using estimation results...
In this paper, location estimation algorithms for cellular communications systems employing orthogonal frequency division multiplexing (OFDM) are investigated. To determine the location of a mobile station, usually time difference of arrival (TDOA) measurements are performed with at least three base stations using pilot symbols included in the signal streams. With these TDOAs then the location is...
When pulsed interference is mitigated by means of pulse blanking, interference is reduced significantly. However, at the same time certain fractions of the useful orthogonal frequency-division multiplexing (OFDM) signal are erased. Consequently, only moderate improvements are achieved with pulse blanking. When representing the pulse blanking operation as multiplication with a rectangular window exhibiting...
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