Catálogo de publicaciones - libros

Recently, the 802.11e Working Group (WG) has proposed the Hybrid Coordination Function (HCF), which has a HCF Controlled Channel Access (HCCA) and an Enhanced Distributed Coordination Access (EDCA), in order to provide QoS in WLANs.

In this paper an innovative HCCA-based algorithm, which will be referred to as Power Save Feedback Based Dynamic Scheduler (PS FBDS) providing bounded delays while ensuring energy saving, has been developed. The performance of PS FBDS has been extensively investigated using ns-2 simulations; results show that the proposed algorithm is able to provide a good trade-off between QoS and power saving at both low and high network loads.

We investigate the energy-saving potential of transport protocols. We focus on the system-related aspect of energy. Do we have to damage or enhance system fairness in order to provide energy efficiency? We depart from defining protocol potential; we compare different transmission strategies and protocol mechanisms; and we report our results on the impact of each mechanism on system energy. We highlight our conclusion that protocol fairness appears to be a key factor for system energy efficiency.

Cooperative relaying recently has emerged as a means of providing gains from spatial diversity to devices in a distributed manner. A cooperative relaying system deploying Alamouti’s space-time coding (STC) design is investigated in this paper. According to amplify-and-forward (AF) and decode-and-forward (DF) modes, two TDMA-based cooperative transmission schemes are presented. Considering resource utilization efficiency, adaptive power allocation (PA) algorithms are proposed to adjust the power of each hop based on different channel conditions. Most importantly, the PA results also can be used to decide whether or not to relay, which recovers the loss of spectral efficiency due to the orthogonal transmission to a great extent. Numerical results indicate that the cooperative system with adaptive PA significantly outperforms the direct transmission system. Compared with the uniform power allocation (UPA), the proposed PA algorithm with power constraint of 1W can provide (52, 54)% capacity gains at most for Scheme (I, II), respectively.

The needs for run-time data storage in modern wired and wireless network applications are increasing. Additionally, the nature of these applications is very dynamic, resulting in heavy reliance to dynamic memory allocation. The most significant problem in dynamic memory allocation is fragmentation, which can cause the system to run out of memory and crash, if it is left unchecked. The available dynamic memory allocation solutions are provided by the real time Operating Systems used in embedded or general-purpose systems. These state-of-the-art dynamic memory allocators are designed to satisfy the run-time memory requests of a wide range of applications. Contrary to most applications, network applications need to allocate too many different memory sizes (e.g. hundreds different sizes for packets) and have an extremely dynamic allocation and de-allocation behavior (e.g. unpredictable web-browsing activity). Therefore, the performance and the de-fragmentation efficiency of these allocators is limited. In this paper, we analyze all the important issues of fragmentation and the ways to reduce it in network applications, while keeping the performance of the dynamic memory allocator unaffected or even improving it. We propose highly customized dynamic memory allocators, which can be configured for specific network needs. We assess the effectiveness of the proposed approach in two representative real-life case studies of wired and wireless network applications. Finally, we show very significant reduction in memory fragmentation and increase in performance compared to state-of-the-art dynamic memory allocators utilized by real-time Operating Systems.