114 research outputs found
Widely-linear versus linear blind multiuser detection with subspace-based channel estimation: finite sample-size effects
No full textIn a recent paper [A. S. Cacciapuoti et al., “Finite-
Sample Performance Analysis of Widely Linear Multiuser
Receivers in DS-CDMA Systems, IEEE TRANSACTIONS ON SIGNAL PROCESSING, vol. 56, no. 4, pp. 1572–1588, Apr. 2008], we presented the finite-sample theoretical performance comparison between linear (L) and widely linear (WL) minimum output-energy (MOE) receivers for direct-sequence code-division multiple-access (DS-CDMA) systems, worked out under the assumption that the channel impulse response of the desired user is exactly known. The main scope of this paper is to extend such an analysis, taking into
account not only autocorrelation matrix (ACM) estimation effects, but also the accuracy of subspace-based blind channel estimation (CE). We aim to answer the two following questions: Which of the two estimation processes (ACM or CE) is the main source of degradation when implementing the receivers on the basis of a finite sample-size? Compared with the L-MOE one, is the finite-sample WL-MOE receiver with blind CE capable of achieving the performance gains predicted by the theory? To this goal, simple and easily interpretable formulas are developed for the signal-to-interference-
plus-noise ratio (SINR) at the output of the L- and WL-MOE
receivers with blind CE, when they are implemented using either the sample ACM or its eigendecomposition. In addition, the derived formulas, which are validated by simulations, allow one to recognize and discuss interesting tradeoffs between the main parameters of the DS-CDMA system
Mobility-Aware User Association for 5G mmWave Networks
No full textIn this paper, we design a mobility-aware user association strategy for millimeter-wave (mmW) networks to overcome the limitations of the conventional received power (RSS)-based association strategies in a mobile 5G scenario. More in detail, first the design of a mobility-aware strategy for user association in 5G mmW networks is posed as a constrained optimization problem. Then, it is showed that the proposed strategy exhibits several attractive features: a) it is able to track the dynamic changes in the network topology and in the channel conditions induced by the user mobility; b) it takes into account the distribution of the loads among the small base stations (sBSs), thus overcoming to associate an UE to an already congested sBS. This, in turn, affects positively the overall fairness of the network; c) it overcomes overly frequent handovers between sBSs, and thus the need of frequent re-association; d) it takes into account the peculiar aspects of the mmW communications, such as directionality, sensitivity to blockage, and NLoS propagation effects; and e) it is fully distributed, i.e., each mobile user associates to an sBS independently of each other, stemming from local information only. Furthermore, it is showed that the exhaustive search for the solution of the posed optimization problem is computationally unfeasible. Consequently, within this paper, an efficient algorithm exhibiting a polynomial-time complexity is proposed. Finally, the numerical results validate the benefits of adopting the proposed mobility-aware and fully distributed association rule. In particular, it is quantified the very significant performance enhancement of the proposed association with respect to the conventional RSS-based one
On the achievable throughput over TVWS sensor networks
No full textIn this letter, we study the throughput achievable by an unlicensed sensor network operating over TV white space spectrum in presence of coexistence interference. Through the letter, we first analytically derive the achievable throughput as a function of the channel ordering. Then, we show that the problem of deriving the maximum expected throughput through exhaustive search is computationally unfeasible. Finally, we derive a computational-efficient algorithm characterized by polynomial-time complexity to compute the channel set maximizing the expected throughput and, stemming from this, we derive a closed-form expression of the maximum expected throughput. Numerical simulations validate the theoretical analysis
Database access strategy for TV White Space cognitive radio networks
No full textVery recently, city administrations launched TV White Space wireless networks to enable the smart city paradigm. These initiatives leverage the possibility allowed by regulations of unlicensed access to the TV White Space spectrum. All theses rulings rely on a periodic access to a database service as the primary mechanism for the unlicensed users to determine the White Space availability. Nevertheless, the specifics of such a mechanism are yet to be determined. In this paper, we address this issue by designing a database access strategy that allows unlicensed users to: i) respect the requirements imposed by the existing rulings; ii) maximize the expected communication opportunities provided by the TV White Space through the on-demand database accesses. To this aim, we prove the database access problem can be modeled as a Markov Decision Process and we provide the closed-form expressions of the transition probabilities. The analytical results are finally validated through simulations
On the probabilistic deployment of smart grid networks in TV white space
No full textTo accommodate the rapidly increasing demand for wireless broadband communications in Smart Grid (SG) networks, research efforts are currently ongoing to enable the SG networks to utilize the TV spectrum according to the Cognitive Radio paradigm. To this aim, in this letter, we develop an analytical framework for the optimal deployment of multiple closely-located SG Neighborhood Area Networks (NANs) concurrently using the same TV spectrum. The objective is to derive the optimal values for both the number of NANs and their coverage. More specifically, regarding the number of NANs, we derive the optimal closed-form expression, i.e., the closed-form expression that assures the deployment of the maximum number of NANs in the considered region satisfying a given collision constraint on the transmissions of the NANs. Regarding the NAN coverage, we derive the optimal closed-form expression, i.e., the closed-form expression of the NAN transmission range that assures the maximum coverage of each NAN in the considered region satisfying the given collision constraint. All the theoretical results are derived by adopting a stochastic approach. Finally, numerical results validate the theoretical analysis
Optimal database access for TV white space
No full textIn TV White Space, the unlicensed users are required to periodically access a database to acquire information on the spectrum usage of the licensed users. In addition, the unlicensed users can access the database on-demand, whenever they believe convenient, to update the spectrum availability information. In this paper, we design the optimal database access strategy, i.e., the strategy allowing the unlicensed users to jointly: (1) maximize the expected overall communication opportunities through on-demand accesses; and (2) respect the regulatory specifications. To this aim, we develop a stochastic analytical framework that allows us to account for: (1) the PU activity dynamics; (2) the quality dynamics among the different channels; and (3) the overhead induced by the database access. Specifically, at first, we prove that the database access problem can be modeled as a Markov decision process, and we show that it cannot be solved through brute-force search. Then, we prove that the optimal strategy exhibits a threshold structure, and we exploit this threshold property to design an algorithm able to efficiently compute the optimal strategy. The analytical results are finally validated through simulations
On the misbehavior of constant modulus equalizers for improper modulations
No full textIn this letter, the constant-modulus (CM) cost function is analyzed under the general assumptions that improper modulation schemes of practical interest are employed and the baseband equivalent of the channel impulse response is complex-valued. This study allows one to determine a broad family of undesired minima of the CM cost function, which do not lead to perfect symbol recovery in the absence of noise. The results developed herein generalize and subsume as a particular case existing studies of the CM cost function, which exclusively consider real-valued binary modulations
Spectrum Sensing in small-scale networks: Dealing with multiple mobile PUs
No full textThe emerging applications of the small-scale primary-user (PU) paradigm require Cognitive Radio (CR) networks to explicitly support the mobility of a multitude of PUs, concurrently using the same spectrum band. In this paper, the effects of multiple mobile PUs on the spectrum sensing functionality are analyzed to jointly maximize the sensing efficiency and the sensing accuracy. To this aim, as first, a new mathematical model (the aggregate PU model) is proposed to effectively describe the cumulative effects of multiple mobile PUs on the spectrum sensing functionality. Then, stemming from this model, closed-form expressions for the sensing time and the transmission time that jointly maximize the sensing efficiency and the sensing accuracy are derived. Through the derived closed-form expressions, the following fundamental questions are answered: (i) How long can a CR user transmit without interfering with the multiple mobile PUs? (ii) How long must a CR user observe a targeted spectrum band to reliably detect multiple mobile PUs? All the theoretical results are derived by adopting a general mobility model for the multiple mobile PUs. The analytical results are finally validated through simulations
Receiver design for a bionic nervous system: Modeling the dendritic processing power
No full textIntrabody nanonetworks for nervous system monitoring are envisioned as a key application of the Internet of Nano-Things (IoNT) paradigm, with the aim of developing radically new medical diagnosis and treatment techniques. Indeed, very recently, bionic devices have been implanted inside a living human brain as innovative treatment for drug-resistant epilepsy. In this context, this paper proposes a systems-theoretic communication model to capture the actual behavior of biological neurons. Specifically, biological neurons exhibit physical extension due to their projections called dendrites, which propagate the electrochemical stimulation received via synapses to the soma. Experimental evidences show that the dendrites exhibit two main features: 1) the compartmentalization at the level of the dendritic branches of the neuronal processes and 2) the location-dependent preference for different frequencies. Stemming from these experimental evidences, we propose to model the dendritic tree as a spatiotemporal filter bank, where each filter models the behavior in both space and time of a dendritic branch. Each filter is fully characterized along with the overall neuronal response. Furthermore, sufficient conditions on the incoming stimulus for inducing a null-neuronal response are derived. The conducted theoretical analysis shows that: 1) the neuronal information is encoded in the stimulus temporal pattern, i.e., it is possible to select the neuron to affect by changing the stimulus frequency content; in this sense, the communication among neurons is frequency-selective and 2) the spatial distribution of the dendrites affects the neuronal response; in this sense, the communication among neurons is spatial-selective. The theoretical analysis is validated through a real neuron morphology
Distributed design for fair coexistence in TVWS
No full textVery recently, regulatory bodies worldwide started to approve the opportunistic access of unlicensed networks to the TVWS spectrum. Hence, in the near future, multiple heterogeneous and independently-operated unlicensed networks will coexist within the same geographical area over shared TVWS. Nevertheless, the coexistence among heterogeneous unlicensed networks over TVWS represents an open problem, and innovative solutions for handling the coexistence interference are needed to fully unleash the TVWS potentials. Hence, in this paper, we design a coexistence strategy for TVWS scenarios with the following attractive features: i) fully distributed, i.e., it avoids the need of centralized interference management; ii) over-the-air communications free, i.e., it avoids the need of direct communications among the heterogeneous networks; iii) adaptive to the time- and space-dynamics of the coexistence interference; iv) selfless, i.e., it allows a fair TVWS spectrum sharing by accounting for the communication demands of each unlicensed network. These attractive features are obtained by designing a coexistence strategy based on a system of multi-dimensional ordinary differential equations, and by incorporating the tradeoff between selfish bandwidth maximization and fair spectrum allocation within the system dynamics. Performance evaluation is conducted through numerical simulations, and the results confirm the attractive features of the proposed coexistence strategy
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