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Next generation wireless systems are foreseen to adopt OFDM based transmission schemes. Unfortunately, conventional OFDM schemes suffer from the high mobility associated with next generation wireless systems, thus they need to be supported with enhanced techniques that alleviate the effects of the mobility. Among these, techniques for channel identification bear a particular importance. In this paper,...
Direct-conversion architectures suffer from the mismatch between the in-phase (I) and the quadrature-phase (Q) branches, commonly called I/Q imbalance. Even low I/Q imbalances imply poor performance of orthogonal frequency division multiplexing (OFDM) systems. In this paper, we propose a new algorithm that uses both training and data symbols in a decision-directed fashion to jointly estimate the channel...
Channel estimation plays an important role in wireless OFDM systems. This paper studies the channel order estimation problem, which aims to estimate the number of paths of wireless channels. We first introduce the traditional channel order estimation method based on minimum description length (MDL) criterion. We find that the traditional method do not perform well when the number of channel samples...
Time-interleaved (TI) analog-to-digital converters (ADCs) are a promising architecture for realizing the highspeed ADCs required to implement "mostly digital" receivers for emerging multiGigabit communication systems. Mismatch between the parallel ADCs comprising a TI-ADC is a fundamental performance bottleneck. While there exist mismatch correction techniques for generic applications of...
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 on-line Bayesian Cramer-Rao (BCRB) lower bound for the dynamic estimation of a time-varying multi-path Rayleigh channel in 4-QAM OFDM system is considered. In case of negligible channel variation within one symbol and delay related information, true BCRB for data-aided (DA) context, and two closed-form expressions for non-data aided (NDA) context are derived.
This paper provides three channel estimations including LS (least square) estimation, LMMSE (linear minimum mean square error) estimation and Lr-MMSE (low rank minimum mean square error) estimation utilized to the relay channel to approximate the optimal solution in OFDM system. The simulation results show that LMMSE estimation outperforms the other two estimations, but it is too complicated. The...
In OFDM-based systems, data symbols are usually transmitted together with pilots, which are used for channel estimation or prediction. More pilots in use can further improve the accuracy of channel estimation or prediction. However, this can also result in the efficiency loss of channel gain allocated for data transmission. In this paper, we investigate the joint pilot and data adaptation regarding...
This paper presents a nonlinear decision feedback channel estimation technique for Discrete Multi Tone (DMT) transmission in broadband indoor powerline communications (PLC). The estimation is carried out in a decision directed mode and the decisions are made using a modified self organizing map (SOM) classifier. The performance of the proposed method is evaluated through simulations over measured...
Some communication applications, like multimedia, deliver data of different importance classes allowing unequal error protection (UEP) levels. In this paper, a multiple-input multiple-output (MIMO) system using orthogonal frequency division multiplexing (OFDM) is considered with a new UEP bit-loading algorithm based on the non-UEP algorithm by Chow, Cioffi, and Bingham. In the proposed bit-loading...
This paper addresses adaptive channel estimation for time-varying mobile wireless channels with nonstationary statistics. We presents a reduced complexity adaptive channel estimator based on a set membership filtering approach known as the Optimal Bounding Ellipsoid (OBE) algorithm. To exploit time and frequency domain correlation properties of the channel in an efficient low-complexity way, we allow...
Effects of improved channel estimation are studied for a proposed IEEE 802.11n OFDM MIMO system. Three channel estimation methods are considered: maximum likelihood (ML), time-domain truncation (TDT) and model-based (MB). TDT and MB are particularly useful when the channel delay spread is short. For an MMSE receiver, MB shows a 1-2.5 dB improvement over ML on the packet error rate performance for...
In this paper, we consider a new channel probing scheme for opportunistic scheduling in the uplink of orthogonal frequency division multiplexing (OFDM)-based wireless systems. To reduce signaling overhead for the probing, we consider a two-step channel probing process; called pre-probing and mainprobing. Good subchannels are first estimated through the pre-probing process using a probing signal transmitted...
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