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Multiple Input Multiple Output (MIMO) adds a new dimension, the spatial one, to be optimized in Cognitive Radio (CR) by offering service simultaneously to more than one user. In this paper, statistical optimization techniques are applied to assess the performance of the Quality of Experience (QoE) in CR systems, where each user has different demands. A Multiuser scenario is considered where the transmitter can accomplish either a random or an opportunistic scheduling approach. Closed form expressions are derived for different scenarios and obtained for three QoE indicators in the system. The performance of primary and secondary users in such scenarios are mathematically formulated and compared their results to computer simulations.Index Terms-Quality of experience, multiuser MIMO, cognitive radio.

Accurate representation of the physical layer is instrumental for a sound design and optimization of Medium Access Control (MAC) protocols for cooperative wireless networks. However, the vast majority of MAC protocols are designed and analyzed by considering simplified physical layer and channel models, which often lead to too optimistic performance predictions. In particular, even though many experimental activities have showcased the important role played by shadow-fading, most protocols are designed and evaluated by taking into account only the transmission distance (circular coverage model) or only the fast-fading. Motivated by the proved unsuitability of these models, the contribution of this paper is threefold: i) we provide important considerations on how to adequately include the effect of shadowing into the design of MAC protocols for cooperative networks; ii) we provide an analytical framework to determine the subset of active relays in order to meet a given Quality-of-Service (QoS) requirement; and iii) we study, through analysis and simulation, the performance of a promising MAC protocol for cooperative networks, which is called Persistent Relay Carrier Sensing Multiple Access (PRCSMA), by explicitly taking into account the effect of shadowing. Our study shows that shadowing can dramatically change system and protocol performance.

-The fact that the IEEE 802.15.4 MAC does not fully satisfy the strict wireless body sensor network (BSN) requirements in healthcare systems highlights the need for the design of new scalable MAC solutions, which guarantee low-power consumption to all specific sorts of body sensors and traffic loads. While taking the challenging healthcare requirements into account, this article aims at the study of energy consumption in BSN scenarios. For that purpose, the IEEE 802.15.4 MAC limitations are first examined and other potential MAC layer alternatives further explored. Our intent is to introduce energy-aware radio activation polices into a highperformance distributed queuing medium access control (DQ MAC) protocol and evaluate its energy-saving achievements, as a function of the network load. To do so, a fundamental energy-efficiency theoretical analysis for DQ MAC protocols is hereby for the first time provided. By means of computer simulations, its performance is validated using IEEE 802.15.4 MAC system parameters. The achieved outcome shows that the proposed DQ MAC scheme outperforms IEEE 802.15.4 MAC energy efficiency in all possible BSN scenarios.

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