Abstract
The rapid proliferation of Internet of Things (IoT) systems, encompassing a wide range of devices and sensors with limited battery life, has highlighted the critical need for energy-efficient solutions to extend the operational lifespan of these battery-powered devices. One effective strategy for reducing energy consumption is minimizing the number and size of retransmitted packets in case of communication errors. Among the potential solutions, Incremental Redundancy Hybrid Automatic Repeat reQuest (IR-HARQ) communication schemes have emerged as particularly compelling options by adopting the best aspects of error control, namely, automatic repetition and variable redundancy. This work addresses the challenge by developing a simulator capable of executing and analysing several (H)ARQ schemes using different channel models, such as the Additive White Gaussian Noise (AWGN) and Gilbert-Elliott (GE) models. The primary objective is to compare their performance across multiple metrics, enabling a thorough evaluation of their capabilities. The results indicate that IR-HARQ outperforms alternative methods, especially in the presence of burst errors. Furthermore, its potential for further adaptation and enhancement opens up new ways for optimizing energy consumption and extending the lifespan of battery-powered IoT devices.

Abstract
Communications in high-speed wireless mobile networks have to deal with large varying transmission and service requirement conditions, often needing complex radio modulatians and concatenated error control functions. For the latter, it is usual to implement Forward Error Correction and Automatic Repeat reQuest (ARQ) mechanisms in, respectively, the Physical (PHY) and the Data Link Control (DLC) layers. Even so, the communication requirements of medium/high quality real-time services may be hard to meet under hostile transmission conditions. In this paper an analysis on some improvements over current ARQ error control schemes is presented, envisaging more efficient communications in high-speed wireless LANs. It will be shown that high performance ARQ schemes can be used at the DLC layer of wireless LANs by carrying critical control information in more robust physical modes. performance comparisons for current and proposed ARQ schemes, and some protocol implementation aspects, are the main focuses of analysis.

Abstract
When accessing and interacting with regular electronic devices or informatics systems, users frequently depend on the sight sense because the information is, consistently, presented in a visual format, despite the feasibility to use additional formats, such as audio. It also happens that the access to the information systems is triggered by the action of the users, hence requiring an awareness of the surrounding environment. These two facts lead to an exclusion of a considerable number of citizens, such as the visually impaired ones, from a fair access to the so-called Information Society. The development of automatic user-aware Interactive Voice Response (IVR) systems can be an interesting solution to this issue, particularly, if the communications are done in a private manner and a low-cost implementation is achieved. In a reply to this challenge, it was formulated a pervasive user detection and communication concept, based on Bluetooth technology and Linux software modules, allowing improved interaction between the personal area information systems and the mobile user devices. To demonstrate the validity of the concept, it was developed a personal area IVR system, based on Linux, being the interaction with the users made by means of the Bluetooth technology.

Abstract
This paper focuses on improved error control schemes for highspeed wireless digital communications. The main objective is a better quality support for real-time services, such as video, when using wireless mobile digital networks. In view of that, and besides the schemes already standardized, a novel error control mechanism is proposed. This new mechanism relies mainly in the use of Hybrid Automatic Repeat reQuest (HARQ) error control schemes and differentiated error robustness transmission modes. In this sense, when implementing this new technique, some of the capabilities offered by modem Wireless Local Area Networks (WLANs) are significantly better utilized. To make the performance analysis of the proposed error control mechanism, and corresponding comparison with existing systems, it was developed a system simulation environment, together with other computational tools. Analysis for diverse radio channel conditions, from AWGN modeling to Gilbert-Elliot modeling, has been done and some examples are subsequently presented. The simulation results show that this new strategy greatly improves the performance of real-time services, fulfilling the requirement of limited delays and enabling higher data rates.

Abstract
The provision of real time services through a Packet Switched Network, requires the adoption of end-to-end synchronization methods. Several of these methods, are compared and a specific hardware solution is discussed. Results obtained through a specially designed Simulation Programme are included, for several network time delay jitter distributions and synchronization methods. These results are used to evaluate systems and design parameters.