			Home About us Contact

Channel Estimation (channel + estimation)

Distribution by Scientific Domains

Engineering	100%

Selected Abstracts

Channel estimation and physical layer adaptation techniques for satellite networks exploiting adaptive coding and modulation

INTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 2 2008
Stefano Cioni
Abstract The exploitation of adaptive coding and modulation techniques for broadband multi-beam satellite communication networks operating at Ka-band and above has been shown to theoretically provide large system capacity gains. In this paper, the problem of how to accurately estimate the time-variant channel and how to adapt the physical layer taking into account the effects of estimator errors and (large) satellite propagation delays is analyzed, and practical solutions for both the forward and the reverse link are proposed. A novel pragmatic solution to the reverse link physical layer channel estimation in the presence of time-variant bursty interference has been devised. Physical layer adaptation algorithms jointly with design rules for hysteresis thresholds have been analytically derived. The imperfect physical layer channel estimation impact on the overall system capacity has been finally derived by means of an original semi-analytical approach. Through comprehensive system simulations for a realistic system study case, it is showed that the devised adaptation algorithms are able to successfully track critical Ka-band fading time series with a limited impact on the system capacity while satisfying the link outage probability requirement. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Channel estimation methods for preamble-based OFDM/OQAM modulations,

EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 7 2008
C. Lélé
In this paper, OFDM/OQAM is proposed as an alternative to conventional OFDM with cyclic prefix (CP) for transmission over multi-path fading channels. Two typical features of the OFDM/OQAM modulation are the absence of a guard interval (GI) and the fact that the orthogonality property only holds in the real field and for a distortion-free channel. Thus, the classical channel estimation (CE) methods used for OFDM cannot be directly applied to OFDM/OQAM. Therefore, we propose an analysis of the transmission of an OFDM/OQAM signal through a time-varying multi-path channel and we derive two new CE methods. The first proposed method only requires the use of pair of real pilots (POP). In a second method, named interference approximation method (IAM), we show how the imaginary interference can be used to improve the CE quality. Several preamble variants of the IAM are compared with respect to the resulting instantaneous power. Finally, the performance results obtained for the transmission of an OFDM/OQAM signal through an IEEE 802.22 channel using the POP method and three variants of IAM are compared to those obtained with CP-OFDM. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Joint data detection and estimation of time-varying multipath rayleigh fading channels in asynchronous DS-CDMA systems with long spreading sequences,

EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 2 2007
Pei Xiao
In this paper, we present a joint approach to data detection and channel estimation for the asynchronous direct-sequence code-division multiple access (DS-CDMA) systems employing orthogonal signaling formats and long scrambling codes. Our emphasis is placed on different channel estimation algorithms since the performance of a communication system depends largely on its ability to retrieve an accurate measurement of the underlying channel. We investigate channel estimation algorithms under different conditions. The estimated channel information is used to enable coherent data detection to combat the detrimental effect of the multiuser interference and the multipath propagation of the transmitted signal. In the considered multiuser detector, we mainly use interference cancellation techniques, which are suitable for long-code CDMA systems. Interference cancellation and channel estimation using soft estimates of the transmitted signal is also proposed in this paper. Different channel estimation schemes are evaluated and compared in terms of mean square error (MSE) of channel estimation and bit error rate (BER) performance. Based on our analysis and numerical results, some recommendations are made on how to choose appropriate channel estimators in practical systems. Copyright © 2006 AEIT [source]

On extrinsic information of good binary codes operating over Gaussian channels

EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 2 2007
M. Peleg
We show that the extrinsic information about the coded bits of any good (capacity achieving) binary code operating over a Gaussian channel is zero when the channel capacity is lower than the code rate and unity when capacity exceeds the code rate, that is, the extrinsic information transfer (EXIT) chart is a step function of the signal to noise ratio and independent of the code. It follows that, for a common class of iterative receivers where the error correcting decoder must operate at first iteration at rate above capacity (such as in turbo equalization, iterative channel estimation, parallel and serial concatenated coding and the like), classical good codes which achieve capacity over the Additive White Gaussian Noise Channel are not effective and should be replaced by different new ones. Copyright © 2006 AEIT. [source]

Iterative channel estimation and data detection in frequency-selective fading MIMO channels,

EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 5 2004
Maja Lon
Signals transmitted through multiple-input multiple-output (MIMO) wireless channels suffer from multiple-access interference (MAI), multipath propagation and additive noise. Iterative multiuser receiver algorithms mitigate these signal impairments, while offering a good tradeoff between performance and complexity. The receiver presented in this paper performs channel estimation, multiuser detection and decoding in an iterative manner. The estimation of the frequency selective, block-fading channel is initiated with the pilot symbols. In subsequent iterations, soft decisions of all the data symbols are used in an appropriate way to improve the channel estimates. This approach leads to significant improvement of the overall receiver performance, compared to other schemes. The bit-error-rate (BER) performance of the receiver is evaluated by simulations for different parameter setups. Copyright © 2004 AEI. [source]

Load-Adaptive MUI/ISI-Resilient Generalized Multi-Carrier CDMA with Linear and DF Receivers

EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 6 2000
Georgios B. Giannakis
A plethora of single-carrier and multi-carrier (MC) CDMA systems have been proposed recently to mitigate intersymbol interference (ISI) and eliminate multiuser interference (MUI). We present a unifying all-digital Generalized Multicanier CDMA framework which enables us to describe existing CDMA schemes and to highlight thorny problems associated with them. To improve the bit error rate (BER) performance of existing schemes, we design block FIR transmitters and decision feedback (DF) receivers based on an inner-code/outer-code principle, which guarantees MUI/ISI-elimination regardless of the frequency-selective physical channel. The flexibility of our framework allows further BER enhancements by taking into account the load in the system (number of active users), while blind channel estimation results in bandwidth savings. Simulations illustrate the superiority of our framework over competing MC CDMA alternatives especially in the presence of uplink multipath channels. [source]

A Hybrid Interference Cancellation Scheme for Multiuser Systems in Multipath Fading Channels

EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 2 2000
Ann-Louise Johansson
A new hybrid interference cancellation (IC) scheme is proposed for the uplink of multirate direct-sequence code division multiple access (DS-CDMA) systems communicating over mobile radio channels. The hybrid IC scheme includes both non-decision directed and decision directed IC, together with a modified RAKE combiner to utilize the diversity in a frequency-selective channel. The performance is evaluated via computer simulations for the two multiple data rate schemes, mixed modulation and multicode, in a multipath environment. Both known channel parameters and channel estimation using pilot symbols are considered. The results show that rnulticode or a combination of multicode and mixed modulation are preferable when handling multirate system and the loss in performance compared to the single-user bound is small. [source]

Performance of multi level-turbo coding with neural network-based channel estimation over WSSUS MIMO channels

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 3 2009
Ersin Gose
Abstract This paper presents the performance of the transmit diversity-multi level turbo codes (TD-MLTC) over the multiple-input,multiple-output (MIMO) channels based on the wide sense stationary uncorrelated scattering (WSSUS). The multi level-turbo code (ML-TC) system contains more than one turbo encoder/decoder block in its structure. At the transmitter side, the ML-TC uses the group partitioning technique that partitions a signal set into several levels and encodes each level separately by a proper component of the encoder to improve error performance. The binary input sequence is passed through the MLTC encoder and mapped to 4-PSK and then fed into the transmit diversity scheme for high data transmission over wireless fading channels. At the receiver side, distorted multi-path signals are received by multiple receiver antennae. WSSUS MIMO channel parameters are estimated by using an artificial neural network and an iterative combiner. Input sequence of the first level of the MLTC encoder is estimated at the first level of MLTC decoder. Subsequently, the other input sequences are computed by using the estimated input bit streams of the previous levels. 4-PSK two-level turbo codes are simulated for 2Tx,1Rx and 2Tx,2Rx antenna configurations over WSSUS MIMO channels. Here, TD-MLTC and its efficient implementations are discussed and simulation results are given. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Kalman filter-based channel estimation and ICI suppression for high-mobility OFDM systems

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 10 2008
Prerana Gupta
Abstract The use of orthogonal frequency division multiplexing (OFDM) in frequency-selective fading environments has been well explored. However, OFDM is more prone to time-selective fading compared with single-carrier systems. Rapid time variations destroy the subcarrier orthogonality and introduce inter-carrier interference (ICI). Besides this, obtaining reliable channel estimates for receiver equalization is a non-trivial task in rapidly fading systems. Our work addresses the problem of channel estimation and ICI suppression by viewing the system as a state-space model. The Kalman filter is employed to estimate the channel; this is followed by a time-domain ICI mitigation filter that maximizes the signal-to-interference plus noise ratio (SINR) at the receiver. This method is seen to provide good estimation performance apart from significant SINR gain with low training overhead. Suitable bounds on the performance of the system are described; bit error rate (BER) performance over a time-invariant Rayleigh fading channel serves as the lower bound, whereas BER performance over a doubly selective system with ICI as the dominant impairment provides the upper bound. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Closed-form expression for the BER of m-QAM-OFDM systems over time- and frequency-selective wireless channels

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 8 2006
F. Castells
Abstract The broadcast DVB-T system is an m-QAM-OFDM communication system that includes pilot-symbol-assisted modulation (PSAM) in order to enhance channel estimation at the receiver. This characteristic makes DVB-T suitable for a mobile reception, over time- and frequency-selective wireless channels. In this work, a closed-form expression for the BER as a function of the transmission system, channel model and the channel estimation strategy employed at the receiver is derived. In addition, adjacent channel interference due to Doppler effects is also considered. The results are focused on the DVB-T system under different scenarios. The channel estimation at the receiver has been shown to be very critical, and the impact of channel estimation errors on the BER is analysed in detail. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Channel estimation and physical layer adaptation techniques for satellite networks exploiting adaptive coding and modulation

Iterative interference cancellation and channel estimation in multibeam satellite systems

INTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 3 2007
J. P. Millerioux
Abstract This paper deals with the use of non-linear multiuser detection techniques to mitigate co-channel interference on the reverse link of multibeam satellite systems. These techniques allow more capacity efficient frequency reuse strategies than classical ones, as they make possible to cope with lower C/I. The considered system takes as a starting point the DVB-RCS standard, with the use of convolutional coding, and the use of the Ka-band. We propose different iterative interference cancellation schemes, which operate at the beamformer outputs, and which use information from decoders. The proposed receivers assume an initial single-user synchronization step: frame synchronization and timing recovery, and then perform channel estimation: beamformer coefficients; signal carrier phases and signal amplitudes. In a first step, these receivers are evaluated by simulation in terms of bit error rate and of channel estimation error on two interference configurations. For one of these receivers, sensitivity to imperfect timing recovery and to low-frequency offsets from user terminals is evaluated. In a second step, since the receiver performances highly depend on the interference configuration, we propose an approach to evaluate performances on a multibeam coverage (by taking into account the variability of interference configurations on the coverage). This method is used to compare different receivers on an example based on a coverage designed on a digital focal array feed reflector antenna. Copyright © 2007 John Wiley & Sons, Ltd. [source]

A low complexity partially adaptive CDMA receiver for downlink mobile satellite communications

INTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 1 2003
Gau-Joe Lin
Abstract A novel CDMA receiver with enhanced interference suppression is proposed for pilot symbols assisted mobile satellite systems in the presence of frequency offset. The design of the receiver involves the following procedure. First, adaptive correlators are constructed at different fingers, based on the scheme of generalized sidelobe canceller (GSC), to collect the multipath signals and suppress multi-access interference (MAI). In particular, a partially adaptive (PA) realization of the GSC correlators is proposed based on the Krylov subspace technique, leading to an efficient algorithm without the need of complicated matrix computations. Second, pilot symbols assisted frequency offset estimation, channel estimation and RAKE combining give the estimate of signal symbols. Finally, further performance enhancement is achieved by an iterative scheme in which the signal is reconstructed and subtracted from the GSC correlators input, leading to faster convergence of the receiver. The proposed low complexity PA receiver is suitable or the downlink of mobile satellite CDMA systems, and shown to outperform the conventional fully adaptive MMSE receiver by using a small number of pilot symbols. Copyright © 2003 John Wiley & Sons, Ltd. [source]