Abstract
Recently, the IEEE 802.11 a standard was published as an amendment to the original IEEE 802.11 standard. This amendment is intended to provide differentiated levels of QoS to the supported applications. The 802.11e amendment incorporates an. additional coordination function called Hybrid Coordination. Fraction. (HCF) that uses both a contention-based channel access method, called the Enhanced Distributed Channel Access (EDCA) and a controlled channel access, referred to as the HCF Controlled Channel Access (HCCA). Under the EDCA mechanism, it is a common assumption to consider the highest access category (voice) adequate to support real-time communication. In this paper, we analyze the timing behavior of the EDCA function, when it is used to support real-tune traffic. Basically, we assess the behavior of the voice category in open communication environments (i.e., a communication environment subject to eternal disturbances) when this access category is used to transfer small sized packets, generated in periodic intervals. We show that the transmission opportunity (TXOP) mechanism included in. the IEEE 802.11e amendment improves the system throughput, for the case of message streams with small packet sizes. However, the impact of external disturbances upon the transfer of real-tune messages is highly relevant. For instance, the average access delay for the real-time messages is more than one order of magnitude larger when. the external disturbance increases the network load from just 10% to 30%. Furthermore, both the number of packet losses anal the average size of the MAC queues forecast an. unacceptable number of deadline losses for the real-time message streams, even for intermediate load cases.

Abstract
In this paper, a new Traffic Separation mechanism (TSm) is proposed for CSMA-based networks. The TSm mechanism is intended to be used as an underlying traffic separation mechanism, able to prioritize traffic in CSMA-based networks. It allows the coexistence of standard CSMA (non-modified) stations with TSm (modified) stations in the same communication domain. When a station implementing the TSm mechanism has a high-priority message to transfer, it will impose its transfer prior to any message from standard CSMA stations. This behavior guarantees the highest transmitting probability to the TSm-enabled station in open communication environments. Therefore, the TSm approach can be used as an underlying mechanism to build real-time communication systems upon CSMA-based networks. The behavior of the TSm mechanism was assessed by simulation in the case of a relevant CSMA-based network (IEEE 802.11). The simulation analysis shows that the TSm mechanism guarantees values for both the throughput and the average access delay that significantly improve the results obtained for standard IEEE 802.11 stations.

Abstract
In this paper, we propose the VOA algorithm (Variable Offset Algorithm) to deal with the optimization of communication efficiency in dense WSN s with star topologies. The use of the VOA algorithm has been assessed by means of an experimental setup. The results highlight that the use of the VOA algorithm, implemented as a light middleware at the application layer, clearly enhances the communication efficiency in a WSN with star topology. © 2010 IEEE.

Abstract
In this paper, a new traffic separation mechanism is proposed for IEEE 802.11e networks. Such Traffic Separation Mechanism (TSm) allows the coexistence of CSMA standard stations with modified (real-time) stations in the same network domain. A station implementing the proposed TSm scheme has the same operating behavior as a standard IEEE 802.11e network station, except in what concerns the evaluation of the backoff delay. For the case of stations implementing the TSm scheme, whenever they have traffic to transfer, they eventually impose its transfer prior to the transfer of any other message with lower priority. This behavior guarantees the highest transmitting probability to the TSm stations in an open communication environment, where multiple IEEE 802.11e standard stations may coexist with a subset of TSm-enabled real-time stations.

Abstract
Wireless Sensor Networks (WSNs) based on the Long-Range radio modulation (LoRa) can use the LoRaWAN protocol as the medium access layer. However, this protocol only supports a single-hop star topology. As a consequence, devices can not use retransmissions along the network to extend their coverage area or to circumvent signal attenuation with distance, obstacles or interference from other radio sources. This paper proposes a multi-hop LoRaWAN wide-scale WSN based on a scheduled cluster-tree topology. This methodology can expand the spatial coverage of the network, decrease collisions, and improve overall network performance. A multi-hop cluster-tree topology eliminates the need for adjustments of LoRa radio parameters as an attempt to expand the single-hop coverage limitation. Simulation results show that the scheduled cluster-tree topology can scale the network coverage and significantly improve communication and energy consumption performances.

Abstract
The use of cooperative diversity techniques and network coding concepts are promising solutions to improve the communication reliability in industrial Wireless Sensor Networks (WSNs). In this paper, we propose the NetCoDer scheme to address this problem, whose design is based in these concepts. The effectiveness of the NetCoDer scheme is evaluated through both an experimental setup with real WSN nodes and a simulation assessment, comparing its performance against state-of-the-art TDMA-based retransmission techniques.