1,721,214 research outputs found
Space-time code design for MIMO detection based on Kullback-Leibler divergence
No full textThe focus of the paper is on the design of space-time codes for a general multiple-input, multiple-output detection problem, when multiple observations are available at the receiver. The figure of merit used for optimization purposes is the convex combination of the Kullback-Leibler divergences between the densities of the observations under the two hypotheses, and different system constraints are considered. This approach permits to control the average sample number (i.e., the time for taking a decision) in a sequential probability ratio test and to asymptotically minimize the probability of miss in a likelihood ratio test: the solutions offer an interesting insight in the optimal transmit policies, encapsulated in the rank of the code matrix, which rules the amount of diversity to be generated, as well as in the power allocation policy along the active eigenmodes. A study of the region of achievable divergence pairs, whose availability permits optimization of a wide range of merit figures, is also undertaken. A set of numerical results is finally given, in order to analyze and discuss the performance and validate the theoretical results
Performance analysis for the improved linear multiuser detectors in BPSK-modulated DS-CDMA systems
No full textRecently, a new class of linear multiuser receivers for direct-sequence code-division multiple-access (CDMA) systems employing binary phase-shift keying modulation has been introduced. Unlike classical decorrelating and minimum mean-square error linear multiuser detectors, the new receivers exploit the information contained in the pseudo-autocorrelation of the observables, and are, thus, capable of achieving much better performance. We present new results on the performance analysis of this class of new receivers. In particular, with reference to a CDMA system with deterministic spreading codes, we show that the new receivers outperform the classical ones in terms of both error probability and near-far resistance. With regard, instead, to CDMA systems with random spreading, we compute the average system near-far resistance, showing that the new receivers can accommodate twice the number of users accommodated by the classical linear multiuser receivers
Sequential along-track integration for early detection of moving targets
No full textThis paper concerns the joint multiframe sequential target detection and track estimation in early-warning radar surveillance systems. The rationale for applying sequential procedures in such a scenario is that they promise a sensitivity increase of the sensor or, alternatively, a reduction in the time needed to take a decision. Unlike previous works on sequential radar detection, the attention is not restricted to stationary targets, namely position changes during the illumination period are allowed. Starting from previous sequential rules, different truncated sequential strategies are proposed and assessed: they are aimed at orienting the sensor resources towards either the detection or the track estimation or the position estimation. Bounds on the performances of the proposed procedures in terms of the system parameters are derived and computational complexity is examined. Also, numerical experiments are provided to elicit the interplay between sensor-target parameters and system performances, and to quantify the gain with respect to other fixed-sample-size procedures
A New Look at the Radar Detection Problem
No full textIn a typical radar system, the same hypothesis testing problem is periodically repeated to constantly monitor the scene: this results in a fundamental tradeoff between integration time and scan rate. In this paper, we propose a novel design criterion for radar systems, which carefully balances the contrasting requirements for a large probability of detection, a small probability of false alarm, and a short scan time. In particular, our goal is to maximize the detection rate, defined as the average number of detections per unit of time, under a constraint on the false alarm rate, defined as the average number of false alarms per unit of time. Some examples modeling situations commonly encountered in the radar applications are presented to illustrate the effects of this design philosophy
Widely linear reception strategies for layered space-time wireless communications
No full textA new class of receivers based on widely linear data processing has been recently proposed for data detection in communication systems affected by improper complex noise. In this paper, it is shown that this detection strategy may be applied to wireless communication systems employing multiple transmit and receive antennas and adopting a noncircular modulation. Improved versions of the linear decorrelating and minimum mean square error (mmse) receivers, and of the nonlinear nulling and cancellation (V-BLAST) receiver are, thus, developed and analyzed. In particular, we show that the improved receivers outperform the conventional ones both in terms of the error probability and of the capacity to cope with the power disparities that the fading channel may induce on the data streams transmitted by different antennas. Moreover, the improved receivers exhibit satisfactory performance also in systems with a number of transmit antennas exceeding the number of receive antennas. Finally, we also consider the situation in which the propagation channel is not perfectly known to the receiver, and show that the performance of the improved receivers is less sensitive to the channel estimation errors than the conventional receivers
A novel dynamic programming algorithm for track-before-detect in radar systems
No full textIn this paper we present a novel procedure for multi-frame detection in radar systems. The proposed architecture consists of a pre-processing stage, which extracts a set of candidate alarms (or plots) from the raw data measurements (e.g., this can be the Detector and Plot-Extractor of common radar systems), and a track-before-detect (TBD) processor, which jointly elaborates observations from multiple scans (or frames) and confirms reliable plots. A computationally efficient dynamic programming algorithm for the TBD processor is derived, which does not require a discretization of the state space and operates directly on the input plot-lists. Finally, a simple algorithm to solve possible data association problems arising at the track-formation step is given, and a thorough complexity and performance analysis is provided, showing that large detection gains with respect to the standard radar processing are achievable with negligible complexity increase
A heuristic algorithm for track-before-detect with thresholded observations in radar systems
No full textWe consider here the two-stage, multi-frame detection architecture proposed in in the context of radar systems, wherein the Detector and Plot Extractor provides a list of candidate detections (or plots) on a scan-by-scan basis to a Track-before-detect (TBD) Processor, which correlates data over multiple scans before taking the final decision as to the target presence. We propose a heuristic algorithm to implement the TBD processor, and we show that its computational complexity is smaller than that of the algorithm proposed in . Numerical examples demonstrate that the detection and estimation performance obtained with the new algorithm is almost coincident with that obtained with the algorithm in
Blind multiantenna receivers for dispersive DS/CDMA channels with no channel-state information
No full textThe problem of blind multiuser detection for a DS-CDMA system employing multiple transmit and receive antennae over a fading dispersive channel is considered. Relying upon a well known signal representation, we develop a new family of linear receivers adapted to account for MIMO channels. Linear receivers share the key property of substantial immunity to co-channel interference, without requiring any prior knowledge on the signals to be decoded, except for the spreading sequence. The performance assessment, conducted through semianalytical methods - whenever possible - and validated through Monte Carlo counting techniques, shows that the newly proposed receivers perform pretty close to their non-blind counterparts, which rely on prior knowledge of the spreading codes, symbol timings and channel impulse responses for all of the active users
Generalized Deterministic-Random Tradeoff of Integrated Sensing and Communications: The Sensing-Optimal Operating Point
No full textIntegrated sensing and communications (ISAC) has been
recognized as a key component in the envisioned 6G communication
systems. Understanding the fundamental performance
tradeoff between sensing and communication functionalities
is essential for designing practical cost-efficient
ISAC systems. In this paper, we aim for augmenting the
current understanding of the deterministic-random tradeoff
(DRT) between sensing and communication, by analyzing the
sensing-optimal operating point of the fundamental capacitydistortion
region. We show that the DRT exists for generic
sensing performance metrics that are in general not convex/
concave in the ISAC waveform. Especially, we elaborate
on a representative non-convex performance metric, namely
the detection probability for target detection tasks
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