Mondelinge geschiedenis in België en de (de-)constructie van collectieve herinnering

Wouters Nico, Aerts Koen. Mondelinge geschiedenis in Belgie en de (de-)constructie van collectieve herinnering. In: Revue belge de philologie et d'histoire, tome 92, fasc. 2, 2014. Histoire médiévale, moderne et contemporaine Middeleeuwse, moderne en hedendaagse geschiedenis. pp. 503-511

Lower bounds on the estimation performance in low complexity quantize-and-forward cooperative systems

Cooperative communication can effectively mitigate the effects of multipath propagation fading by using relay channels to provide spatial diversity. A relaying scheme suitable for half-duplex devices is the quantize-and-forward (QF) protocol, in which the information received from the source is quantized at the relay before being forwarded to the destination. In this contribution, the Cramer-Rao bound (CRB) is obtained for the case where all channel parameters in a QF system are estimated at the destination. The CRB is a lower bound (LB) on the mean square estimation error (MSEE) of an unbiased estimate and can thus be used to benchmark practical estimation algorithms. Additionally, the modified Cramer-Rao bound (MCRB) is also presented, which is a looser but computationally less complex bound. An importance sampling technique is developed to speed up the computation of the MCRBs, and the MSEE performance of a practical estimation algorithm is compared with the (M)CRBs. We point out that the parameters of the source-destination and relay-destination channels can be accurately estimated but that inevitably the source-relay channel estimate is poor when the instantaneous SNR on the relay-destination channel is low; however, in this case, the decoder performance is not affected by the inaccurate source-relay channel estimate

The Cramer-Rao Bound for channel estimation in block fading amplify-and-forward relaying networks

In this paper, we express the Cramer-Rao Bound (CRB) for channel coefficient and noise variance estimation at the destination of an Amplify-and- Forward (AF) based cooperative system, in terms of the a posteriori expectation of the codewords. An algorithm based on factor graphs can be applied in order to calculate this expectation. As the computation of the CRB is rather intensive, the modified CRB (MCRB), which is a looser bound, is derived in closed form. It can be shown that the MCRB coincides with the CRB in the high signal-to-noise ratio (SNR) limit and to that end the CRB/MCRB ratio is simulated in case of uncoded and convolutional encoded transmission

Low-complexity a posteriori probability approximation in EM-based channel estimation for trellis-coded systems

When estimating channel parameters in linearly modulated communication systems, the iterative expectation-maximization (EM) algorithm can be used to exploit the signal energy associated with the unknown data symbols. It turns out that the channel estimation requires at each EM iteration the a posteriori probabilities (APPs) of these data symbols, resulting in a high computational complexity when channel coding is present. In this paper, we present a new approximation of the APPs of trellis-coded symbols, which is less complex and requires less memory than alternatives from literature. By means of computer simulations, we show that the Viterbi decoder that uses the EM channel estimate resulting from this APP approximation experiences a negligible degradation in frame error rate (FER) performance, as compared to using the exact APPs in the channel estimation process

A novel quantize-and-forward cooperative system : channel parameter estimation techniques

The Quantize and Forward cooperative communication protocol improves the reliability of data transmission by allowing a relay to forward to the destination a quantized version of the signal received from the source. In prior studies of the Quantize and Forward protocol, all channel parameters are assumed to be perfectly known at the destination, while in reality these need to be estimated. This paper proposes a novel Quantize and Forward protocol in which the relay compensates for the rotation on the source-relay channel using a crude channel estimate, before quantizing the phase of the received M-PSK data symbols. Therefore, as far as the source-relay channel is concerned, only an SNR estimate is needed at the destination. Further, the destination applies the EM algorithm to improve the estimates of the source-destination and relay-destination channel coefficients. The resulting performance is shown to be close to that of a system with known channel parameters

EM based channel estimation in an amplify-and-forward relaying network

Cooperative communication offers a way to obtain spatial diversity in a wireless network without increasing hardware demands. The different cooperation protocols proposed in the literature [1] are often studied under the assumption that all channel state information is available at the destination. In a practical scenario, channel estimates need to be derived from the broadcasted signals. In this paper, we study the Amplify-and-Forward protocol and use the expectation-maximization (EM) algorithm to obtain the channel estimates in an iterative way. Our results show that the performance of the system that knows the channels can be approached at the cost of an increased computational complexity. In case a small constellation is used, a low complexity approximation is proposed with a similar performance

EM based channel estimation in an amplify-and-forward relaying network

Cooperative communication offers a way to obtain spatial diversity in a wireless network without increasing hardware demands. The different cooperation protocols proposed in the literature [1] are often studied under the assumption that all channel state information is available at the destination. In a practical scenario, channel estimates need to be derived from the broadcasted signals. In this paper, we study the Amplify-and-Forward protocol and use the expectation-maximization (EM) algorithm to obtain the channel estimates in an iterative way. Our results show that the performance of the system that knows the channels can be approached at the cost of an increased computational complexity. In case a small constellation is used, a low complexity approximation is proposed with a similar performance

Mondelinge geschiedenis en geheugenstudie: slotbedenkingen

Wouters Nico, Aerts Koen. Mondelinge geschiedenis en geheugenstudie: slotbedenkingen. In: Revue belge de philologie et d'histoire, tome 92, fasc. 2, 2014. Histoire médiévale, moderne et contemporaine Middeleeuwse, moderne en hedendaagse geschiedenis. pp. 689-698

SAGE-based estimation algorithms for time-varying channels in amplify-and-forward cooperative networks

Cooperative communication is a technique that achieves spatial diversity by exploiting the presence of other nodes in the network. Most analyses of such networks are conducted under the simplifying assumption of perfect channel knowledge. In this paper we focus on the popular Amplify-and-forward (AF) cooperative protocol. We propose several SAGE-based iterative algorithms with different complexities for estimating the channel gain and noise variance in the case of time-varying channels. Computer simulations are provided to evaluate their performance over Rice-fading channels. We point out a low-complexity estimation algorithm yielding an error performance that (for Rayleigh fading) is only about 0.5 dB worse than in the case of perfect estimation, while outperforming a pilot-based estimation algorithm by about 1.5 dB

Low-complexity quantize-and-forward cooperative communication using two-way relaying

Cooperative communication is used as an effective measure against fading in wireless communication systems. In a classical one-way cooperative system, the relay needs as many orthogonal channels as the number of terminal it assists, yielding a poor spectral efficiency. Efficiency is improved in two-way relaying systems, where a relay simultaneously assists two terminals using only one timeslot. In the current contribution, a two-way quantize-and-forward (QF) protocol is presented. Because of the coarse quantization, the proposed protocol has a low complexity at the relay and can be used with half-duplex devices, making it very suitable for low-complexity applications like sensor networks. Additionally, channel parameter estimation is discussed. By estimating all channel parameters at the destination terminals, relay complexity is kept low. Using Monte Carlo simulations, it is shown that the proposed QF protocol achieves a good frame error rate (FER) performance as compared to two-way amplify-and-forward (AF) and one-way relaying systems. It is further shown that, using the proposed estimation algorithm, the FER degradation arising from the channel parameter estimation is negligible when compared to an (unrealistic) system in which all parameters are assumed to be known