Demosthenes Vouyioukas

Face detection and recognition of natural human emotion using Markov random fields

This paper presents an integrated system for emotion detection. In this research effort, we have taken into account the fact that emotions are most widely represented with eye and mouth expressions. The proposed system uses color images and it is consisted of three modules. The first module implements skin detection, using Markov random fields models for image segmentation and skin detection. A set of several colored images with human faces have been considered as the training set. A second module is responsible for eye and mouth detection and extraction. The specific module uses the HLV color space of the specified eye and mouth region. The third module detects the emotions pictured in the eyes and mouth, using edge detection and measuring the gradient of eyes’ and mouth’s region figure. The paper provides results from the system application, along with proposals for further research.

A Survey on Buffer-Aided Relay Selection

Relays receive and retransmit signals between one or more sources and one or more destinations. Cooperative relaying is a novel technique for wireless communications that increases throughput and extends the coverage of networks. The task of relay selection serves as a building block to realize cooperative relaying. Recently, relays with buffers have been incorporated into cooperative relaying providing extra degrees of freedom in selection, thus improving various performance metrics, such as outage probability, power reduction, and throughput, at the expense of tolerating an increase in packet delay. In this survey, we review and classify various buffer-aided relay selection policies and discuss their importance through applications. The classification is mainly based on the following aspects: 1) duplexing capabilities, 2) channel state information (CSI), 3) transmission strategies, 4) relay mode, and 5) performance metrics. Relay selection policies for enhanced physical-layer security and cognitive communications with reduced interference are also discussed. Then, a framework for modeling such algorithms is presented based on Markov Chain theory. In addition, performance evaluation is conducted for various buffer-aided relay selection algorithms. To provide a broad perspective on the role of buffer-aided relay selection, various issues relevant to fifth-generation (5G) networks are discussed. Finally, we draw conclusion and discuss current challenges, possible future directions, and emerging technologies.

Emergency m-Health Services through High-Speed 3G Systems: Simulation and Performance Evaluation

The present paper studies the prospective and the performance of a forthcoming high-speed third-generation (3G) networking technology called High Speed Packet Access (HSPA) for delivering emergency m-health applications. The joint transmission of voice, real-time video, medical data such as electrocardiogram, vital signals, heart sound and file transfer is performed for both uplink and downlink. Various scenarios are involved in terms of emergency situations in random locations, where no other system but 3G is available. The accomplishment of quality of service (QoS) is explored through a step-by-step improvement of HSPA systems parameters, incorporating admission and congestion control elements and the use of prioritization for m-health services. HSPA managed to meet the requirements for emergency m-health scenarios and adequately served the generated load.

A Buffer-Aided Successive Opportunistic Relay Selection Scheme With Power Adaptation and Inter-Relay Interference Cancellation for Cooperative Diversity Systems

In this paper, we present a relay selection scheme which combines the spectral efficiency of successive opportunistic relaying with the robustness of single-link relay selection. More specifically, we propose a scheme that minimizes the total energy expenditure per time slot under an inter-relay interference cancellation scheme. The new relay selection policy is analyzed in terms of outage probability and diversity by modeling the evolution of relay buffers as a Markov Chain. We construct the state transition matrix of the Markov Chain and obtain its stationary distribution, which in turn, yields the outage probability. The proposed scheme outperforms relevant state-of-the-art relay selection schemes in terms of throughput, diversity, energy efficiency and average delay, as demonstrated via representative numerical examples.

Buffer-aided successive opportunistic relaying with inter-relay interference cancellation

In this paper we consider a simple cooperative network consisting of a source, a destination and a cluster of decode-and-forward relays characterized by the half-duplex constraint. At each time-slot the source and (possibly) one of the relays transmit a packet to another relay and the destination, respectively. When the source and a relay transmit simultaneously, inter-relay interference is introduced at the receiving relay. In this work, with the aid of buffers at the relays, we mitigate the detrimental effect of inter-relay interference through either interference cancellation or mitigation. More specifically, we propose the min-power opportunistic relaying protocol that minimizes the total energy expenditure per time slot under an inter-relay interference cancellation scheme. The min-power relay-pair selection scheme, apart from minimizing the energy expenditure, also provides better throughput and lower outage probability than existing works in the literature. The performance of the proposed scheme is demonstrated via illustrative examples and simulations in terms of outage probability and average throughput.

A successive opportunistic relaying protocol with inter-relay interference mitigation

In this work, we present a successive opportunistic relaying protocol with an inter-relay interference (IRI) mitigation scheme, in a quasi-static environment with Rayleigh fading. In order to recover the half duplex loss of the transmission, we adopt a successive relaying (SR) strategy, coupled with reactive relay selection considering the Signal to Noise Ratio (SNR) and the Signal to Interference plus Noise Ratio (SINR) of each hop, after every source transmission. The main degrading factor in this scheme is the IRI introduced by the best relay, which is selected to forward the previous frame, while the rest of the relays are receiving the current source frame. Trying to cancel the effect of IRI, we employ interference cancelation (IC) to subtract the interference signal depending on the capacity of the interference channel.

Performance Evaluation of an Enhanced Uplink 3.5G System for Mobile Healthcare Applications

The present paper studies the prospective and the performance of a forthcoming high-speed third generation (3.5G) networking technology, called enhanced uplink, for delivering mobile health (m-health) applications. The performance of 3.5G networks is a critical factor for successful development of m-health services perceived by end users. In this paper, we propose a methodology for performance assessment based on the joint uplink transmission of voice, real-time video, biological data (such as electrocardiogram, vital signals, and heart sounds), and healthcare records file transfer. Various scenarios were concerned in terms of real-time, nonreal-time, and emergency applications in random locations, where no other system but 3.5G is available. The accomplishment of quality of service (QoS) was explored through a step-by-step improvement of enhanced uplink systems parameters, attributing the network system for the best performance in the context of the desired m-health services.

Joint relay-pair selection for buffer-aided successive opportunistic relaying

In this work, we propose a buffer-aided successive opportunistic relay scheme where each time a relay-pair is selected with the target of rate maximization. Due to overlapping transmissions by the source and the relay which transmits to the destination, inter-relay interference arises. The efficient mitigation of inter-relay interference either through cancellation or avoidance, requires increased channel state information. Thus, in order to reduce the implementation complexity induced by centralized selection, distributed switch-and-stay combining is combined with buffer-aided successive opportunistic relaying. In this way, by applying a rate threshold we can avoid increased relay-pair switching and channel state information acquisition. The efficiency of the proposed scheme is demonstrated through simulations and comparisons with other state-of-the-art relay selection policies.

A Survey on Beamforming Techniques for Wireless MIMO Relay Networks

One of the major challenges the mobile broadband community faces is the exponential increase in mobile data traffic, even more so, for cell-edge users. Thus, in a multitier network, the demand for high-speed and interference-free transmission and reception is inevitable. Beamforming (BF) is an advanced technology that offers a significantly improved solution to reduce the interference levels and improve the system capacity. Accordingly, the establishment of relays in mobile data networks has emerged spectral efficiency enhancements and cell capacity gains from an overall system perspective. This paper provides a comprehensive survey focused on the performance of adopted beamforming technique on MIMO relay networks that is expected to overcome crucial obstacles in terms of capacity and interference. The main objective is to point out the state-of-the-art research activity on BF techniques in MIMO relay networks, under various network performance challenges. Thereby, it focuses on recently developed procedures for interference modeling and mitigation, BF channel modeling, channel estimation and feedback, complexity and power consumption, adaptive BF for multiuser relaying, degrees of freedom, diversity issues, and spectral efficiency, in cooperative and opportunistic systems. Different network topologies have been considered and categorized, pertaining the challenges of BF implementation in MIMO relay networks.

Modeling Buffer-Aided Relay Selection in Networks With Direct Transmission Capability

We consider a wireless relay network that consists of a source, half-duplex decode-and-forward buffer-aided relays and a destination. While the majority of previous works on relay selection assume no direct transmission between source and destination in such a setting, we lift this assumption and propose a link selection policy that exploits both the buffering ability and the opportunity for successful reception of a packet directly from the source. The proposed relay selection scheme incorporates the instantaneous strength of the wireless links and adapts the relay selection decision based on the strongest available link. The evolution of the network as a whole is modeled by means of a Markov chain and thus, the outage probability is associated with the steady state of the Markov chain. It is deduced that even if the link between the source and the destination is in principle a very unreliable link, it is always beneficial for the source to multicast a packet to both the relay with the strongest available link and the destination.