Browsing by Author "Atapattu, S"

Now showing 1 - 10 of 10

item: Article-Full-text
Eigenvalue-Based Detection of a Signal in Colored Noise: Finite and Asymptotic Analyses
(IEE, 2020) Chamain, LD; Dharmawansa, P; Atapattu, S; Tellambura, C
Signal detection in colored noise with an unknown covariance matrix has a myriad of applications in diverse scientific/engineering fields. The test statistic is the largest generalized eigenvalue (l.g.e.) of the whitened sample covariance matrix, which is constructed via m-dimensional p signal-plusnoise samples and m-dimensional n noise-only samples. A finite dimensional characterization of this statistic under the alternative hypothesis has hitherto been an open problem. We answer this problem by deriving cumulative distribution function (c.d.f.) of this l.g.e. via the powerful orthogonal polynomial approach, exploiting the deformed Jacobi unitary ensemble (JUE). Two special cases and an asymptotic version of the c.d.f. are also derived. With this new c.d.f., we comprehensively analyze the receiver operating characteristics (ROC) of the detector. Importantly, when the noise-only covariance matrix is nearly rank deficient (i.e., m = n), we show that (a) when m and p increase such that m/p is fixed, at each fixed signal-to-noise ratio (SNR), there exists an optimal ROC profile. We also establish a tight approximation of it; and (b) asymptotically, reliable signal detection is always possible if SNR scales with m.
item: SRC-Report
Energy efficiency improvement in cloud radio access networks (CRANs) using device centric caching policies
(2018) Samarasinghe, T; Hemachandra, K; Atapattu, S; Nuradha, T; Ranawaka, I
As the demand for wireless services is projected to double every year, wireless system designers are facing a major crisis to cater to this demand with the conventional cellular network architecture due to the scarcity of spectrum resources and high cost of energy consumption. Therefore, major architectural changes such as cloud radio access networks (CRANs) and device-to-device (D2D) communications have been proposed as potential solutions. The proposed research project is mainly focuses on improving the performance of the CRAN architecture. Firstly, we propose a spectrum selection scheme and a transmit power minimization scheme for a D2D network cross-laid with a CRAN. The D2D communications are allowed as an overlay to the CRAN as well as in the unlicensed industrial, scientific and medical radio (ISM) band. A link distance-based scheme is proposed and closed-form approximations are derived for the link distance thresholds to select the operating band of the D2D users. Furthermore, analytical expressions are derived to calculate the minimum required transmit power to achieve a guaranteed level of quality of service in each operating band. Secondly, a novel content caching strategy is proposed for a cache enabled D2D network where the user devices are allowed to communicate using millimeter wave (mmWave) D2D links (> 6 GHz) as well as conventional sub 6 GHz cellular links. The proposed content placement strategy maximizes the successful content delivery probability of a line-of-sight D2D link. Furthermore, a heuristic algorithm is proposed for efficient content delivery. The overall scheme improves the successful traffic offloading gain of the network compared to conventional cache-hit maximizing content placement and delivery strategies. Significant energy efficiency improvements can also be achieved in ultra-dense networks. Finally, we consider the physical layer security of an untrusted unmanned aerial vehicle (UAV) based D2D network, operating in full-duplex mode. A source-based jamming scheme is exploited for secure communication without utilizing any external jammers. Firstly, the optimal power allocation between the confidential signal and the jamming signal is derived to maximize the secrecy rate of each link between the source and the destination. Then, the best UAV selection scheme is proposed to maximize the overall secrecy rate of the network. The corresponding secrecy outage probability and the average secrecy rate of the network are analyzed based on the proposed UAV selection and the optimal power allocation schemes. Asymptotic results are also obtained to derive the achievable diversity order.
item: Article-Full-text
Energy-efficiency fairness of interference multi-relay networks for multi-User communication
(IEEE, 2021) Ding, M; Atapattu, S; Weeraddana, C; Evans, J
We investigate a single-antenna multi-user multi-relay interference network, where multiple source nodes simultaneously communicate with their respective destination nodes via half-duplex decode-and-forward relays. To ensure fairness among users, we consider a power allocation strategy to maximize the worst-case energy efficiency (EE) of all users for a fixed relay assignment. The resulting optimization problem turns out to be non-convex. Different from those in the literature, our method here is an iterative algorithm where two geometric programs (GPs) are solved in each iteration, one producing an upper-bound to the solution of the original problem and the other providing a feasible lower-bound. Moreover, the upper-bound GP approaches the original problem asymptotically. Our algorithm also works for the problem arising in the non-interfering (orthogonal) transmission, which was previously solved as a fractional program. Numerical results reveal that non-orthogonal transmission outperforms orthogonal transmission in terms of the worst-case EE at low and medium signal-to-noise ratios.
item: Article-Full-text
Exact outage analysis of multiple-user downlink with MIMO matched-filter precoding
(Institute of Electrical and Electronics Engineers, 2017) Atapattu, S; Dharmawansa, P; Tellambura, C; Evans, J
Here, we address the problem of outage characterization of a single-cell multiple-user multiple-inputmultiple- output (MU-MIMO) network with matched-filter precoding at the base-station (BS). In particular, we derive an exact expression for the outage probability of any user. This expression is valid for an arbitrary number of BS antennas and mobile users. Since the expression contains an infinite sum, a tight truncation error bound has been derived to facilitate precise numerical evaluations. Furthermore, asymptotic expressions are provided for high BS transmit power and massive MIMO scenarios.
item: Conference-Full-text
Federated learning for improved automatic modulation classification: data heterogeneity and low SNR accuracy
(IEEE, 2023-12-09) Siriwardana, GK; Jayawardhana, HD; Bandara, WU; Atapattu, S; Herath, VR; Abeysooriya, R; Adikariwattage, V; Hemachandra, K
This research introduces novel federated learning (FL)-based methods, namely FedAvgAMC, FedPerAMC, and FedAvgAMCAug, to enhance automatic modulation classification (AMC) in communication systems. By addressing data heterogeneity, incorporating higher-order modulation schemes, and exploring personalized models for clients, these methods overcome challenges associated with centralized learning and data leakage. Simulation results demonstrate significant improvements in accuracy, particularly at low and moderate signal-to-noise ratios (SNRs). FedAvgAMCAug, a privacy-preserving method, achieves superior performance, outperforming CentAMC by 18% in accuracy at an SNR of 5 dB and consistently surpassing existing learning techniques across all clients and SNR values. This research highlights the potential of federated learning to enhance AMC accuracy in real-world scenarios, paving the way for future optimizations and exploration of techniques to address data uncertainty for even more robust performance.
item: Article-Full-text
Multi-user relay selection for full-duplex radio
(IEEE, 2019) Atapattu, S; Dharmawansa, P; Di Renzo, M
Abstract—This paper investigates a user-fairness relay selection (RS) problem for decode-and-forward (DF) full-duplex (FD) relay networks where multiple users cooperate with multiple relays in each coherence time. We consider two residual self-interference (RSI) models with or without direct links. We propose a suboptimal relay selection (SRS) scheme which requires only the instantaneous channel state information (CSI) of source-to-relay and relay-to-destination links. To evaluate performance, the outage probability of SRS is derived for different scenarios depending on RSI models and the availability of direct links. To further investigate, asymptotic expressions are derived for the high transmit power regime. For comparison purposes, i) the average throughputs of FD and half-duplex (HD) modes are derived; ii) non-orthogonal transmission is considered and its performance is discussed with approximations; and iii) the impact of imperfect CSI is investigated with the aid of analysis. While simulation results are provided to verify the analytical results, they reveal interesting fundamental trends. It turns out that a significant throughput degradation occurs with FD mode over HD mode when self-interference is fully proportional to the transmit power. Since all users can communicate in the same coherence time with FD mode, these joint RS schemes are useful for user-fairness low-latency applications.
item: Article-Full-text
Performance analysis of a two-tile reconfigurable intelligent surface assisted 2 × 2 MIMO system
(IEEE, 2021) Dharmawansa, P; Atapattu, S; Di Renzo, M
We consider a two–tile reconfigurable intelligent surface (RIS) assisted wireless network with a two-antenna transmitter and receiver over Rayleigh fading. We show that the average received signal-to-noise-ratio (SNR) optimal combining and transmission vectors are given by the left and right singular spaces of the RIS-receiver and transmit-RIS channel matrices, respectively. Moreover, the optimal phases at the two tiles of the RIS are determined by the phases of the elements of the latter spaces. To further study the effect of phase compensation, we statistically characterize the average SNR of all possible combinations of transmission and combining directions pertaining to the latter singular spaces by deriving novel expressions for the outage probability and throughput of each of those modes. Furthermore, for comparison, we derive the corresponding expressions in the absence of RIS. Our results show an approximate SNR improvement of 2 dB due to the phase compensation at the RIS.
item: Article-Full-text
Physical layer security for intelligent reflecting surface assisted two-way communications
(IEEE, 2021) Wijewardena, M; Samarasinghe, T; Hemachandra, KT; Atapattu, S; Evans, JS
This letter investigates the exploitation of an intelligent reflecting surface (IRS) to communicate securely in a two-way network consisting of an untrusted user. In particular, the transmit powers and the phase shift at each element of the IRS are optimized to maximize the sum-secrecy rate, such that the IRS-reflected and non-IRS-reflected signals are added destructively at the untrusted user. The proposed iterative algorithm converges rapidly to a feasible solution of high accuracy with a few iterations. Numerical results demonstrate sum-secrecy rate gains up to 120% compared to naive or partially optimized schemes.
item: Conference-Full-text
Quadcopter disturbance estimation using different learning methods
(IEEE, 2021-07) Atapattu, S; De Silva, O; Mann, G; Gosine, R; Adhikariwatte, W; Rathnayake, M; Hemachandra, K
Precise modeling of quadcopter dynamics is challenging due to the complex nature of its construction, aerodynamic effects, friction at rotors, and wind effects involved. In general analysis, these unmodeled dynamics are kept as external disturbances to the system. Machine learning techniques can effectively be used to estimate or predict the unknown kinetic effects in the quadcopter dynamical model. This paper attempts to compare the effectiveness of two popular machine learning techniques in modeling vehicle dynamics, namely neural networks (NN) and Gaussian process regression (GPR). The dynamic model of the quadcopter is expressed as a combination of a known nominal model and the unknown term, which was learned separately using the two methods. The performance of these two approaches is evaluated using a dataset collected by manually flying the AscTec Hummingbird quadcopter under an OptiTrack motion capture system. The learning process has been performed off-line, and a performance comparison between NN and GPR is discussed in the paper.
item: Article-Full-text
Reconfigurable Intelligent Surface Assisted Two-Way Communications: Performance Analysis and Optimization
(IEEE, 2020) Atapattu, S; Fan, R; Dharmawansa, P; Wang, G; Evans, J; Tsiftsis, TA
In this paper, we investigate the two-way communication between two users assisted by a reconfigurable intelligent surface (RIS). The scheme that two users communicate simultaneously over Rayleigh fading channels is considered. The channels between the two users and RIS can either be reciprocal or non-reciprocal. For reciprocal channels, we determine the optimal phases at the RIS to maximize the signal-to-interference-plus-noise ratio (SINR). We then derive exact closed-form expressions for the outage probability and spectral efficiency for single-element RIS. By capitalizing the insights obtained from the single-element analysis, we introduce a gamma approximation to model the product of Rayleigh random variables which is useful for the evaluation of the performance metrics in multiple-element RIS. Asymptotic analysis shows that the outage decreases at (log(ρ)/ρ) L rate where L is the number of elements, whereas the spectral efficiency increases at log(ρ) rate at large average SINR p. For non-reciprocal channels, the minimum user SINR is targeted to be maximized. For single-element RIS, closed-form solution is derived whereas for multiple-element RIS the problem turns out to be non-convex. The latter one is solved through semidefinite programming relaxation and a proposed greedy-iterative method, which can achieve higher performance and lower computational complexity, respectively.