26 research outputs found
Cache-Aided Non-Orthogonal Multiple Access for 5G-Enabled Vehicular Networks
The increasing demand for rich multimedia services and the emergence of the
Internet-of-Things (IoT) pose challenging requirements for the next generation
vehicular networks. Such challenges are largely related to high spectral
efficiency and low latency requirements in the context of massive content
delivery and increased connectivity. In this respect, caching and
non-orthogonal multiple access (NOMA) paradigms have been recently proposed as
potential solutions to effectively address some of these key challenges. In the
present contribution, we introduce cache-aided NOMA as an enabling technology
for vehicular networks. In this context, we first consider the full file
caching case, where each vehicle caches and requests entire files using the
NOMA principle. Without loss of generality, we consider a two-user vehicular
network communication scenario under double Nakagami fading conditions and
propose an optimum power allocation policy. To this end, an optimization
problem that maximizes the overall probability of successful decoding of files
at each vehicle is formulated and solved. Furthermore, we consider the case of
split file caching, where each file is divided into two parts. A joint power
allocation optimization problem is formulated, where power allocation across
vehicles and cached split files is investigated. The offered analytic results
are corroborated by extensive results from computer simulations and interesting
insights are developed. Indicatively, it is shown that the proposed
caching-aided NOMA outperforms the conventional NOMA technique.Comment: Accepted for publication in IEEE Transactions on Vehicular Technolog
Opportunistic Ambient Backscatter Communication in RF-Powered Cognitive Radio Networks
In the present contribution, we propose a novel opportunistic ambient
backscatter communication (ABC) framework for radio frequency (RF)-powered
cognitive radio (CR) networks. This framework considers opportunistic spectrum
sensing integrated with ABC and harvest-then-transmit (HTT) operation
strategies. Novel analytic expressions are derived for the average throughput,
the average energy consumption and the energy efficiency in the considered set
up. These expressions are represented in closed-form and have a tractable
algebraic representation which renders them convenient to handle both
analytically and numerically. In addition, we formulate an optimization problem
to maximize the energy efficiency of the CR system operating in mixed ABC
and HTT modes, for a given set of constraints including primary
interference and imperfect spectrum sensing constraints. Capitalizing on this,
we determine the optimal set of parameters which in turn comprise the optimal
detection threshold, the optimal degree of trade-off between the CR system
operating in the ABC and HTT modes and the optimal data transmission
time. Extensive results from respective computer simulations are also presented
for corroborating the corresponding analytic results and to demonstrate the
performance gain of the proposed model in terms of energy efficiency
Energy efficiency analysis of collaborative compressive sensing scheme in cognitive radio networks
In this paper, we investigate the energy efficiency of conventional collaborative compressive sensing (CCCS) scheme, focusing on balancing the tradeoff between energy efficiency and detection accuracy in cognitive radio environment. In particular, we derive the achievable throughput, energy consumption and energy efficiency of the CCCS scheme, and then formulate an optimization problem to determine the optimal values of parameters which maximize the energy efficiency of the CCCS scheme. The maximization of energy efficiency is proposed as a multi-variable, non-convex optimization problem, and we provide approximations to reduce it to a convex optimization problem. We highlight that errors due to these approximations are negligible. Subsequently, we analytically characterize the tradeoff between dimensionality reduction and collaborative sensing performance of the CCCS scheme, i.e., the implicit tradeoff between energy saving and detection accuracy. It is shown that the resulting loss due to compression can be recovered through collaboration, which improves the overall energy efficiency of the system
Near-Optimal Detection Thresholds for Bayesian Spectrum Sensing Under Fading
This paper considers the problem of energy-based, Bayesian spectrum sensing in cognitive radios under various fading environments. Under the well-known central limit theorem based model for energy detection, we derive analytically tractable expressions for near-optimal detection thresholds that minimize the probability of error under lognormal, Nakagami-m, and Weibull fading. For the Suzuki fading case, a generalized gamma approximation is provided, which saves on the computation of an integral. In each case, the accuracy of the theoretical expressions as compared to the optimal thresholds are illustrated through simulations
Multi-dimensional Goodness-of-Fit Tests for Spectrum Sensing Based on Stochastic Distances
In this paper, we study two multi-dimensional Goodness-of-Fit tests for spectrum sensing in cognitive radios. The multi-dimensional scenario refers to multiple CR nodes, each with multiple antennas, that record multiple observations from multiple primary users for spectrum sensing. These tests, viz., the Interpoint Distance (ID) based test and the h, f distance based tests are constructed based on the properties of stochastic distances. The ID test is studied in detail for a single CR node case, and a possible extension to handle multiple nodes is discussed. On the other hand, the h, f test is applicable in a multi-node setup. A robustness feature of the KL distance based test is discussed, which has connections with Middleton's class A model. Through Monte-Carlo simulations, the proposed tests are shown to outperform the existing techniques such as the eigenvalue ratio based test, John's test, and the sphericity test, in several scenarios
Three-User Cooperative Dual-Stage Non-Orthogonal Multiple Access for Power Line Communications
We present a cooperative, dual-stage (DS) non-orthogonal multiple access (NOMA) scheme for power line communication (PLC) systems, where three PLC modems are served in two time slots. The network consists of a source (S) modem, two relay (R) modems and a destination (D) modem. In each of the two time slots, S communicates with one R using NOMA, and the other R communicates with D using the decode-and-forward technique. We consider both scenarios where a direct link may or may not exist between S and D. We derive expressions for the approximate average sum rate and overall outage probability of the network. Next, we formulate an optimization problem to find the optimal power allocation coefficients at S, such that the sum rate is maximized. We establish the accuracy of our approximations using Monte Carlo simulations. Furthermore, we show that our scheme outperforms the two-user single-stage and the DS schemes, and the three-user NOMA scheme proposed in the earlier literature, in terms of sum rate and outage probability