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In this paper we propose a scheme with a dedicated relay node for an OFDM-based system. We consider an antenna array at the base station and a single antenna at both the user terminal and the relay node. The relay-assisted protocol considered is equalize-and-forward. The proposed scheme requires the computation of parameters which depend on unknown variables at the destination and we show that under...
This paper studies the problem of pilot-aided joint carrier frequency offset (CFO) and channel estimation using a Bayesian approach in multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) transmissions over time- and frequency-selective (doubly selective) channels. Unlike the joint CFO and channel impulse response (CIR) estimation over block-fading channels, the...
A crucial parameter required for adaptive transmission in orthogonal frequency division multiplexing (OFDM) systems is the signal-to-noise ratio (SNR). In this paper, certain modifications to previously proposed preamble-based SNR estimator for wireless OFDM systems are suggested in order to improve estimation performance. Proposed modifications, related to DFT interpolation, are based on the adaptive...
In future wireless communication systems like LTE, wide bandwidths for the transmission of high data rates result in frequency selective mobile radio channels. If data transmission takes place at high mobile speeds the mobile radio channel becomes also time selective. In this paper we propose for the estimation of such double selective channels a modification to the well known complex exponential...
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...
This paper tackles the problem of fast varying channel estimation in LTE systems. Particular attention is given to downlink transmission where OFDMA is used as the multiple access technique for the air interface. In OFDMA, fast variation of the channel results in significant inter-carrier interference (ICI) which cannot be mitigated with conventional estimation and equalization techniques. In this...
This paper presents a new blind symbol timing offset (STO) estimation scheme for wireless orthogonal frequency division multiplexing (OFDM) systems with constant modulus constellation. In the proposed scheme, the STO estimation is performed by minimizing the power difference between either adjacent or consecutive subcarriers, which basically depends on the assumptions made on the channel conditions...
In this paper, we consider design optimization of low-density parity-check (LDPC) coded multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems for high data rate wireless transmission. First, starting from the maximum-likelihood (ML) principle, we devise a novel expectation-maximization (EM)-based scheme for joint estimation of carrier frequency-offset (CFO)...
It is well known that precoding techniques in multiuser multiple-input multiple-output (MU-MIMO) communication systems improve the whole data throughput since they allow for spatial multiplexing of different users. However, these techniques require a precise knowledge of the channel information at the transmitter. In most of the current systems, transmitter can not estimate the channel so feedback...
A new scheme for Doppler estimation and data detection for OFDM underwater acoustic communications is derived in this paper. We design the OFDM symbol as a concatenation of two sub-blocks. The first one is shorter and carries out few data with few subcarriers whereas the second one contains both informative and pilot symbols. The first sub-block serves to estimate the Doppler scaling factor while...
We demonstrate the first digital laser-phase-noise (PN) mitigation approach for DDO-OFDM which applies a simple Wiener filter for adaptively estimating the statistical-unknown PN. The PN tolerance, in terms of the achievable fibre length, is about tripled with this PN mitigation technique.
A new method for frequency synchronization based upon Zero-Intermediate Frequency (zero-IF) receiver and characteristics of the received signal's power spectrum for MC-DS-CDMA-Uplink system is proposed in this paper. The variance for Carrier Frequency Offset (CFO) estimators of MC-DS-CDMA-Uplink is compared with that of an OFDM system to estimate the CFO. Our study and results show that the MC-DS-CDMA...
A channel estimation scheme for a multi-input multi-output orthogonal frequency division multiplexing (MIMO-OFDM) system was presented. The scheme makes use of the pilots to estimate the channel impulse response based on least square criteria. To improve the estimation performance, a neural network approach was applied to track the varying of the channel, which using a variable step-size RLS. The...
With only second-order statistical information, subspace based blind channel estimation has received considerable attention. To make subspace based blind channel estimation methods feasible, signal redundancy is necessary, which is usually acquired by time-domain oversampling or using multiple receive antennas. In this paper, a new perspective, frequency-domain oversampling, is taken to develop a...
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...
In this paper, a new improved CFO tracking algorithm for OFDM systems is proposed. It is based on the fact that energy on virtual subcarriers could be quadratic or trigonometric with CFO estimation errors when it's small, so the CFO can be estimated by coarse search and interpolation. Simulation results suggest that performance of the proposed method is equivalent with enumeration method while the...
MIMO OFDM is a promising technique for the future wireless communications. However, the performance of MIMO OFDM systems is very sensitive to carrier frequency offset (CFO) which introduces inter-carrier-interference (ICI). Therefore, frequency synchronization is a critical problem in MIMO OFDM systems. In this paper, we study the problem of frequency synchronization in MIMO OFDM systems and propose...
A self-cancellation scheme is proposed to cope with the sample frequency offset (SFO) problem in OFDM systems in the presence of a carrier frequency offset (CFO). Making use of the symmetry between the phase shifts caused by SFO and the subcarrier index, we put the same constellation symbol on symmetrical subcarriers, and combine the pairs at the receiver coherently. In this way, the SFO effects are...
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...
In this paper, a novel low complexity integer frequency offset estimation algorithm is derived for broadcast type orthogonal frequency division multiplexing (OFDM) systems. Different from conventional algorithm, the power detection technique and signed bits of subcarriers are exploited, so the algorithm complexity is lowered greatly. Simulation results have demonstrated the robust performance of the...
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