The paper presents two mechanisms for designing an on-demand, reliable and efficient collection protocol for Wireless Sensor Networks. The former is the Bidirectional Link Quality Estimation, which ...allows nodes to easily and quickly compute the quality of a link between a pair of nodes. The latter, Hierarchical Range Sectoring, organizes sensors in different sectors based on their location within the network. Based on this organization, nodes from each sector are coordinated to transmit in specific periods of time to reduce the hidden terminal problem. To evaluate these two mechanisms, a protocol called HBCP (Hierarchical-Based Collection Protocol), that implements both mechanisms, has been implemented in TinyOS 2.1, and evaluated in a testbed using TelosB motes. The results show that the HBCP protocol is able to achieve a very high reliability, especially in large networks and in scenarios with bottlenecks.
This paper offers an overview of the Commons for Europe (C4EU) project and the role of Bottom-up Broadband (BuB) in developing the information society. BuB is characterized by the fact that the ...beneficiaries of the networks actively participate in the planning, deployment and maintenance tasks. For the beneficiaries, this represent a paradigm shift from a consumer-only position to an active-participant position. We summarize a representative set of the BuB pilot proposals that have been considered in the context of the C4EU project. A selection of these proposals will be executed and carefully documented to define good practices in BuB deployments. The documentation will include project templates, work plans, case studies, replicable success models and regulatory guidelines. The overall goal of the project is to assess the validity of the BuB model to effectively and efficiently complement exiting traditional deployments in satisfying the networking and technological needs of the European citizens and organizations.
A novel flow admission control mechanism for infrastructure IEEE 802.11e EDCA-based WLANs is presented. The proposed admission control works jointly with a tuning algorithm which decides the most ...suitable configuration of the MAC parameters each time a new flow arrives or leaves the system. It is designed to work in heterogeneous scenarios with both elastic and real-time flows, so it aims to: i) guarantee the QoS requirements for real-time flows (like VoIP) and ii) maximize the best-effort throughput (such as TCP web browsing or P2P transfers). Results, compared with the use of the DCF (distributed coordination function) and EDCA (enhanced distributed channel access) with static parameters, show a clear improvement on the overall HotSpot performance. Our mechanism provides better QoS, uplink versus downlink fairness and a more efficient use of the transmission resources.
Carrier Sense Multiple Access with Enhanced Collision Avoidance (CSMA/ECA) is a distributed MAC protocol that allows collision-free access to the medium in WLAN. The only difference between CSMA/ECA ...and the well-known CSMA/CA is that the former uses a deterministic backoff after successful transmissions. Collision-free operation is reached after a transient state during which some collisions may occur. This article shows that the duration of the transient state can be shortened by appropriately setting the contention parameters. Standard absorbing Markov Chain theory can be used to describe the behaviour of the system in the transient state and to predict the expected number of slots to reach the collision-free operation. The article also introduces CSMA/E2CA, in which a deterministic backoff is used two consecutive times after a successful transmission. CSMA/E2CA converges quicker to collision-free operation and delivers higher performance than CSMA/CA in harsh wireless scenarios with high frame error rates. To achieve collision-free operations when the number of contenders is large, it may be necessary to dynamically adjust the contention parameter. The last part of the article suggests an approach for such parameter adjustment which is validated by simulation results.
In this paper we study the impact of rate changes at the physical layer on VoIP flows in multi-rate IEEE 802.11-based environments. We determine how the network's rate changes affect the QoS of the ...active flows, and how these effects can be quantified and corrected using a mixture of RTCP and MAC layer information. We propose a decision mechanism that, upon hints of QoS degradation, triggers the transmission of RTCP packets to collect QoS feedback as perceived by the application, together with MAC layer information on the network's state. Subsequently, the VoIP flow parameters are changed, by adapting their codecs and choosing a more appropriate codec combination for the new conditions. Our results show a significant increase in network usage, without a significant QoS loss for the active flows in the cell.
The LWT-MAC protocol extends the normal operation of B-MAC by taking advantage of the local synchronization that can be achieved after each packet transmission. Sensor nodes wake up at the end of ...each successful transmission to send or receive messages eliminating the need for the long preamble transmission. Current LPL analytical models are extremely simple as they do not consider the energy waste due to collisions. In this work, a detailed analytical model of the LWT-MAC protocol, which considers the energy waste of collisions and overhearing for both saturated and unsaturated conditions, is presented. Results show a reduction of the energy consumption as the traffic increases and an improvement, in terms of throughput and delay, compared to B-MAC. Additionally, a performance evaluation is presented in which some key network parameters (check interval, traffic load and the number of sensor nodes) are modified in order to analyze the behavior of the studied LWT-MAC protocol.
Dynamic Channel Bonding (DCB) allows for the dynamic selection and use of multiple contiguous basic channels in Wireless Local Area Networks (WLANs). A WLAN operating under DCB can enjoy a larger ...bandwidth, when available, and therefore achieve a higher throughput. However, the use of larger bandwidths also increases the contention with adjacent WLANs, which can result in longer delays in accessing the channel and consequently, a lower throughput. In this paper, a scenario consisting of multiple WLANs using DCB and operating within carrier-sensing range of one another is considered. An analytical framework for evaluating the performance of such networks is presented. The analysis is carried out using a Markov chain model that characterizes the interactions between adjacent WLANs with overlapping channels. An algorithm is proposed for systematically constructing the Markov chain corresponding to any given scenario. The analytical model is then used to highlight and explain the key properties that differentiate DCB networks of WLANs from those operating on a single shared channel. Furthermore, the analysis is applied to networks of IEEE 802.11ac WLANs operating under DCB-which do not fully comply with some of the simplifying assumptions in our analysis-to show that the analytical model can give accurate results in more realistic scenarios.
This paper presents a joint VoIP / IEEE 802.11 model for ad-hoc networks. The model calculates the average number of collisions and the average packet delay. It is used to predict the impact of ...different configuration parameters (codec, packetization interval and datarate) in the performance of the network. The simulations validate the results obtained from the model and, additionally, expose that the distribution of the VoIP packet generation times of the different stations also modifies the average packet delay.
GSM/GPRS networks have been designed to carry both voice and data traffic. Our aims are to study the behaviour of the GPRS mechanisms (RLC/MAC layer and radio resource scheduler) when the application ...layer carries packetized voice, and determine if the quality of service provided by the network is suitable for the VoIP service. The paper includes a discussion about the voice source model, an analysis of the effects in capacity of a GPRS carrier when feed with VoIP packets, measurements of statistical parameters of the voice traffic stream and a discussion of the influence in the quality of the service.
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