| 475051. |
- Katselis, Dimitrios
(författare)
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On Estimating the Number of Co-Channel Interferers in MIMO Cellular Systems
- 2011
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Ingår i: IEEE Signal Processing Letters. - 1070-9908 .- 1558-2361. ; 18:6, s. 379-382
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Tidskriftsartikel (refereegranskat)abstract
- Two crucial tasks arising in current wireless packet networks are those of link adaptation and power control. It has been recently shown that large performance gains can be attained if proper algorithms for the aforementioned tasks are employed. These algorithms require the estimation of interference power. To this end, an intermediate step is the estimation of the number of active co-channel interferers. This letter aims at determining such an estimate without resorting to traditional training sequences.
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| 475052. |
- Katselis, D., et al.
(författare)
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On experiment design for single carrier and multicarrier systems
- 2015
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Ingår i: 2015 European Control Conference, ECC 2015. - : Institute of Electrical and Electronics Engineers (IEEE). - 9783952426937 ; , s. 1772-1777
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Konferensbidrag (refereegranskat)abstract
- In this paper, the problem of experiment design in single input single output (SISO) single carrier (SC) systems under a deterministic channel assumption is investigated and several connections with optimal preamble designs in multicarrier (MC) systems are established. In the context of SC systems, we derive optimal input sequences for the least-squares (LS) channel estimator under an input energy constraint. We then establish certain connections to optimal input designs for LS frequency domain channel estimation in MC systems. These connections reflect similarities between SC and MC systems both quantitative, i.e., in the achievable mean square error (MSE) performance, as well as qualitative, i.e., in the actual optimal input sequences. Simulations are provided to support the derived results.
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| 475053. |
- Katselis, Dimitrios, et al.
(författare)
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On OFDM/OQAM receivers
- 2012
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Ingår i: 2012 Proceedings Of The 20th European Signal Processing Conference (EUSIPCO). - : IEEE Computer Society. - 9781467310680 ; , s. 2566-2570
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Konferensbidrag (refereegranskat)abstract
- In OFDM/OQAM systems, the presence of the intrinsic interference effect, caused by the lack of complex field orthogonality of the pulses employed, challenges the symbol detection task at the receiver. In this paper, the problem of equalization in such a system is studied, through the comparative analysis of three approaches to zero forcing equalization: (a) the classical receiver, which operates directly on the received signal at each subcarrier without any additional processing, (b) the dispersive receiver, forming sufficient statistics for the symbol decision, and (c) an alternative approach, which aims at completely eliminating intrinsic interference before deciding the symbols. The receivers are formulated and analyzed under the common assumptions for the OFDM/OQAM input/output model. The classical receiver is then shown to perform similarly with the other two for relatively short channels, while it outperforms them when the channel dispersion is large with respect to the number of subcarriers. Through these results, the sensitivity of the detection performance of alternative receivers to the validity of the input/output model is revealed and assessed.
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| 475054. |
- Katselis, Dimitrios, et al.
(författare)
-
On Preamble-Based Channel Estimation in OFDM/OQAM Systems
- 2011
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Ingår i: Proceedings of the 19th European Signal Processing Conference (EUSIPCO 2011). - : European Association for Signal and Image Processing. ; , s. 1618-1622
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Konferensbidrag (refereegranskat)abstract
- In this paper, the problem of preamble-based channel estimation in OFDM offset QAM (OFDM/OQAM) systems under a deterministic channel assumption is studied. Recent results indicate that full (all tones carrying pilot symbols) preambles with equal pilot symbols are locally optimal, in the sense that they yield a local minimum of the mean square error (MSE) performance metric of the estimated channel frequency response (CFR), subject to a total training energy constraint. We study the problem of finding the globally optimal full preamble. We show that under a channel constancy assumption, the global optimum coincides with the full preamble of equal symbols. The same result holds even if the channel constancy assumption is removed. Numerical simulations are presented to support the derived results.
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| 475055. |
- Katselis, Dimitrios, et al.
(författare)
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On secret key generation through multipath for wireless networks
- 2013
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Ingår i: 2013 IEEE International Symposium on Signal Processing and Information Technology (ISSPIT). - : IEEE Computer Society. ; , s. 148-153
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Konferensbidrag (refereegranskat)abstract
- The complexity of cryptographic key management and the wireless medium salient features motivated a number of works that generate secret keys. Simply put, two nodes can estimate their wireless channel and derive common information to generate a key that other nodes cannot obtain. A gamut of methods, each drawing this information in a different manner, has been proposed. In this landscape, this paper contributes a few findings. First, we propose a method that renders channel impulse response magnitude samples roughly uniform, thus facilitating their quantization and agreement on the derived secret keys. We provide a characterization of the probability of successful agreement for this method, which could be useful for other related methods. Moreover, we consider the cost of the key agreement and we propose a trade-off to increase the probability of success while increasing local processing. With an appropriate configuration, a significant reduction in protocol rounds, and thus communication overhead, for key agreement can be achieved. Through simulations, we validate our approximation of the probability of success and demonstrate the reduced communication overhead.
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| 475056. |
- Katselis, Dimitrios, et al.
(författare)
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On the end-performance metric estimator selection
- 2015
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Ingår i: Automatica. - : Elsevier BV. - 0005-1098 .- 1873-2836. ; 58, s. 22-27
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Tidskriftsartikel (refereegranskat)abstract
- It is well known that appropriately biasing an estimator can potentially lead to a lower mean square error (MSE) than the achievable MSE within the class of unbiased estimators. Nevertheless, the choice of an appropriate bias is generally unclear and only recently there have been attempts to systematize such a selection. These systematic approaches aim at introducing MSE bounds that are lower than the unbiased Cramer-Rao bound (CRB) for all values of the unknown parameters and at choosing biased estimators that beat the standard maximum-likelihood (ML) and/or least squares (LS) estimators in the finite sample case. In this paper, we take these approaches one step further and investigate the same problem from the aspect of an end-performance metric different than the classical MSE. This study is motivated by recent advances in the area of system identification indicating that the optimal experiment design Should be done by taking into account the end-performance metric of interest and not by quantifying a quadratic distance of the unknown model from the true one.
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| 475057. |
- Katselis, Dimitrios, et al.
(författare)
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OOK/DS-CDMA bit error probability over Rayleigh fading channels
- 2013
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Ingår i: Communications (ICC), 2013 IEEE International Conference on. - : IEEE conference proceedings. - 9781467331227 ; , s. 5619-5624
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Konferensbidrag (refereegranskat)abstract
- A major constraint in deployments of resource-limited networks is the energy consumption related to the battery lifetime of the network nodes. To this end, power efficient digital modulation techniques such as On-Off keying (OOK) are highly attractive. In this paper, a novel complete probabilistic description of the Direct Sequence - Coded Division Multiple Access (DS-CDMA) system with random signatures employing OOK modulation is presented. The system scenario considers simultaneously transmitting nodes in Rayleigh fading conditions. Numerical simulations are provided to support the derived results.
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| 475058. |
- Katselis, Dimitrios, et al.
(författare)
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Robust Experiment Design for System Identification via Semi-Infinite Programming Techniques
- 2012
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Ingår i: Proceedings of the 16th IFAC Symposium on System Identification (SYSID 2012). - 9783902823069 ; , s. 680-685
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Konferensbidrag (refereegranskat)abstract
- Robust optimal experiment design for dynamic system identification is cast as a minmax optimization problem, which is infinite-dimensional. If the input spectrum is discretized (either by considering a Riemmann approximation, or by restricting it to the span of a finite dimensional linear space), this problem falls within the class of semi-infinite convex programs. One approach to this optimization problem of infinite constraints is the so called "scenario approach", which is based on a probabilistic description of the uncertainty to deliver a finite program that attempts to approximate the optimal solution with a prescribed probability. In this paper, we propose as an alternative an exchange algorithm based on some recent advances in the field of semi-infinite programming to tackle the same problem. This method is compared with the scenario approach both from the aspects of accuracy and computational efficiency. Furthermore, the comparison includes the MATLAB semi-infinite solver fseminf to provide a general palette of methods approximating the robust optimal design problem.
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| 475059. |
- Katselis, Dimitrios
(författare)
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Some Preamble Design Aspects in CP-OFDM Systems
- 2012
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Ingår i: IEEE Communications Letters. - 1089-7798 .- 1558-2558. ; 16:3, s. 356-359
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Tidskriftsartikel (refereegranskat)abstract
- A fundamental problem in training-based channel estimation for various communication systems is the preamble design. Two crucial aspects in such a design are the achievable mean square error (MSE) and the corresponding peak-to-average power ratio (PAPR). In this letter, preamble-based least squares (LS) channel estimation in CP-OFDM systems is considered. Ignoring the PAPR aspect, several MSE-optimal preambles and a necessary condition for their existence are presented. To this end, a training energy constraint, containing also the energy spent to the cyclic prefix (CP), is imposed. This constraint differs from the usual training energy constraints in the existing literature, which ignore the CP energy during training. These preambles contribute in the completion of existing results concerning MSE-optimal preambles in CP-OFDM systems. However, since high PAPR is an issue concerning these optimal designs, we show how these MSE-optimal preambles can be combined with the usual Zadoff-Chu (ZC) sequences to enlarge the class of PAPR-optimal preambles that achieve good MSE performance at the same time.
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| 475060. |
- Katselis, Dimitrios, et al.
(författare)
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Training sequence design for MIMO channels: an application-oriented approach
- 2013
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Ingår i: EURASIP Journal on Wireless Communications and Networking. - : Springer Science and Business Media LLC. - 1687-1472 .- 1687-1499. ; 2013, s. 245-
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, the problem of training optimization for estimating a multiple-input multiple-output (MIMO) flat fading channel in the presence of spatially and temporally correlated Gaussian noise is studied in an application-oriented setup. So far, the problem of MIMO channel estimation has mostly been treated within the context of minimizing the mean square error (MSE) of the channel estimate subject to various constraints, such as an upper bound on the available training energy. We introduce a more general framework for the task of training sequence design in MIMO systems, which can treat not only the minimization of channel estimator's MSE but also the optimization of a final performance metric of interest related to the use of the channel estimate in the communication system. First, we show that the proposed framework can be used to minimize the training energy budget subject to a quality constraint on the MSE of the channel estimator. A deterministic version of the 'dual' problem is also provided. We then focus on four specific applications, where the training sequence can be optimized with respect to the classical channel estimation MSE, a weighted channel estimation MSE and the MSE of the equalization error due to the use of an equalizer at the receiver or an appropriate linear precoder at the transmitter. In this way, the intended use of the channel estimate is explicitly accounted for. The superiority of the proposed designs over existing methods is demonstrated via numerical simulations.
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