arXiv subjects

Taufik Abrão

Publications and source records attributed to Taufik Abrão.

45 records · Page 3Linked to original sources

arXiv2019

Hopfield Learning-based and Nonlinear Programming methods for Resource Allocation in OCDMA Networks

This paper proposes the deployment of the Hopfield's artificial neural network (H-NN) approach to optimally assign power in optical code division multiple access (OCDMA) systems. Figures of merit such as feasibility of solutions and complexity are compared with the classical power allocation methods found in the literature, such as Sequential Quadratic Programming (SQP) and Augmented Lagrangian Method (ALM). The analyzed methods are used to solve constrained nonlinear optimization problems in the context of resource allocation for optical networks, specially to deal with the energy efficiency (EE) in OCDMA networks. The promising performance-complexity tradeoff of the modified H-NN is demonstrated through numerical results performed in comparison with classic methods for general problems in nonlinear programming. The evaluation is carried out considering challenging OCDMA networks in which different levels of QoS were considered for large numbers of optical users.

eess.SY↗

arXiv2019

Massive MIMO for Internet of Things (IoT) Connectivity

Massive MIMO is considered to be one of the key technologies in the emerging 5G systems, but also a concept applicable to other wireless systems. Exploiting the large number of degrees of freedom (DoFs) of massive MIMO essential for achieving high spectral efficiency, high data rates and extreme spatial multiplexing of densely distributed users. On the one hand, the benefits of applying massive MIMO for broadband communication are well known and there has been a large body of research on designing communication schemes to support high rates. On the other hand, using massive MIMO for Internet-of-Things (IoT) is still a developing topic, as IoT connectivity has requirements and constraints that are significantly different from the broadband connections. In this paper we investigate the applicability of massive MIMO to IoT connectivity. Specifically, we treat the two generic types of IoT connections envisioned in 5G: massive machine-type communication (mMTC) and ultra-reliable low-latency communication (URLLC). This paper fills this important gap by identifying the opportunities and challenges in exploiting massive MIMO for IoT connectivity. We provide insights into the trade-offs that emerge when massive MIMO is applied to mMTC or URLLC and present a number of suitable communication schemes. The discussion continues to the questions of network slicing of the wireless resources and the use of massive MIMO to simultaneously support IoT connections with very heterogeneous requirements. The main conclusion is that massive MIMO can bring benefits to the scenarios with IoT connectivity, but it requires tight integration of the physical-layer techniques with the protocol design.

cs.IT↗

arXiv2018

Efficient Detection in Uniform Linear and Planar Arrays MIMO Systems under Spatial Correlated Channels

In this paper, the efficiency of various MIMO detectors was analyzed from the perspective of highly correlated channels, where MIMO systems have a lack of performance, besides in some cases an increasing complexity. Considering this hard, but {a useful} scenario, various MIMO detection schemes {were accurately evaluated concerning} complexity and bit error rate (BER) performance. Specifically, successive interference cancellation (SIC), lattice reduction (LR) and the combination of them were associated with conventional linear MIMO detection techniques. {To demonstrate effectiveness}, a wide range of the number of antennas and modulation formats have been considered aiming to verify the potential of such MIMO detection techniques according to their performance-complexity trade-off. We have also studied the correlation effect when both transmit and receiver sides are equipped with uniform linear array (ULA) and uniform planar array (UPA) antenna configurations. The performance of different detectors is carefully compared when both antenna array configurations are deployed {considering} a different number of antennas and modulation order, especially {under} near-massive MIMO condition. We have also discussed the relationship between the array factor (AF) and the BER performance of both {antenna array} structures.

eess.SP↗

arXiv2016

Energy efficient OFDMA networks maintaining statistical QoS guarantees for delay-sensitive traffic

An energy-efficient design is proposed under specific statistical quality-of-service (QoS) guarantees for delay-sensitive traffic in the downlink orthogonal frequency-division multiple-access (OFDMA) networks. This design is based on Wu's $\textit{effective capacity}$ (EC) concept [1], which characterizes the maximum throughput of a system subject to statistical delay-QoS requirements at the data-link layer. In the particular context considered, our main contributions consist of quantifying the $\textit{effective energy-efficiency}$ (EEE)-versus-EC tradeoff and characterizing the delay-sensitive traffic as a function of the QoS-exponent $θ$, which expresses the exponential decay rate of the delay-QoS violation probabilities. Upon exploiting the properties of fractional programming, the originally quasi-concave EEE optimization problem having a fractional form is transformed into a subtractive optimization problem by applying Dinkelbach's method. As a result, an iterative inner-outer loop based resource allocation algorithm is conceived for efficiently solving the transformed EEE optimization problem. Our simulation results demonstrate that the proposed scheme converges within a few Dinkelbach algorithm's iterations to the desired solution accuracy. Furthermore, the impact of the circuitry power, of the QoS-exponent and of the power amplifier inefficiency is characterized numerically. These results reveal that the optimally allocated power maximizing the EEE decays exponentially with respect to both the circuitry power and the QoS-exponent, whilst decaying linearly with respect to the power amplifier inefficiency.

cs.IT↗

arXiv2014

BER Analysis of Multi-Cellular MIMO Systems with Increasing Number of BS Antennas

In this work, salient characteristics of a wireless communication system deploying a great number of antennas in the base station (BS), namely Massive MIMO system, are investigated. In particular, we found a simple and meaningful relationship that corroborates a fundamental assumption in recent related works: according the number of BS antennas $N$ grows, the product of the small-scale fading channel matrix with its conjugate transpose tends to a scaled identity, with a variability measure inversely proportional to $N$. Furthermore, analysis of the Massive MIMO system downlink is carried out from a bit-error-rate (BER) performance viewpoint, including some realistic adverse effects, such as interference from neighboring cells, channel estimation errors due to background thermal noise, and pilot contamination, which was recently shown to be the only impairment that remains in the MIMO multicell system with infinite number of BS antennas. Our numerical result findings show that, in the same way as with the sum capacity, the pilot contamination also limits the BER performance of a noncooperative multi-cell MIMO system with infinite number of BS antennas.

cs.NI↗

arXiv2012

Energy and Spectral Efficiencies Trade-off with Filter Optimization in Multiple Access Interference-Aware

This work analyzes the optimized deployment of two resources scarcely available in mobile multiple access systems, i.e., spectrum and energy, as well as the impact of filter optimization in the system performance. Taking in perspective the two conflicting metrics, throughput maximization and power consumption minimization, the distributed energy efficiency (EE) cost function is formulated. Furthermore, the best energy-spectral efficiencies (EE-SE) trade-off is achieved when each node allocates exactly the power necessary to attain the best SINR response, which guarantees the maximal EE. To demonstrate the validity of our analysis, two low-complexity energy-spectral efficient algorithms, based on distributed instantaneous SINR level are developed, and the impact of single and multiuser detection filters on the EE-SE trade-off is analyzed.

math.OC↗

arXiv2012

Error-Correcting Codes for Reliable Communications in Microgravity Platforms

The PAANDA experiment was conceived to characterize the acceleration ambient of a rocket launched microgravity platform, specially the microgravity phase. The recorded data was transmitted to ground stations, leading to loss of telemetry information sent during the reentry period. Traditionally, an error-correcting code for this channel consists of a block code with very large block size to protect against long periods of data loss. Instead, we propose the use of digital fountain codes along with conventional Reed-Solomon block codes to protect against long and short burst error periods, respectively. Aiming to use this approach for a second version of PAANDA to prevent data corruption, we propose a model for the communication channel based on information extracted from Cumã II's telemetry data, and simulate the performance of our proposed error-correcting code under this channel model. Simulation results show that nearly all telemetry data can be recovered, including data from the reentry period.

cs.IT↗

arXiv2010

Power-Rate Allocation in DS/CDMA Based on Discretized Verhulst Equilibrium

This paper proposes to extend the discrete Verhulst power equilibrium approach, previously suggested in [1], to the power-rate optimal allocation problem. Multirate users associated to different types of traffic are aggregated to distinct user' classes, with the assurance of minimum rate allocation per user and QoS. Herein, Verhulst power allocation algorithm was adapted to the single-input-single-output DS/CDMA jointly power-rate control problem. The analysis was carried out taking into account the convergence time, quality of solution, in terms of the normalized squared error (NSE), when compared with the analytical solution based on interference matrix inverse, and computational complexity. Numerical results demonstrate the validity of the proposed resource allocation methodology.

cs.CE↗

arXiv2010

Input Parameters Optimization in Swarm DS-CDMA Multiuser Detectors

In this paper, the uplink direct sequence code division multiple access (DS-CDMA) multiuser detection problem (MuD) is studied into heuristic perspective, named particle swarm optimization (PSO). Regarding different system improvements for future technologies, such as high-order modulation and diversity exploitation, a complete parameter optimization procedure for the PSO applied to MuD problem is provided, which represents the major contribution of this paper. Furthermore, the performance of the PSO-MuD is briefly analyzed via Monte-Carlo simulations. Simulation results show that, after convergence, the performance reached by the PSO-MuD is much better than the conventional detector, and somewhat close to the single user bound (SuB). Rayleigh flat channel is initially considered, but the results are further extend to diversity (time and spatial) channels.

cs.AI↗