No description available.

Wireless networks are less reliable than wired networks because channels are “exposed” to the surrounding environment that is susceptible to interference and noise. To minimize losses of data due to collisions, wireless networks need a mechanism to regulate the access on the transmission medium. Medium Access Control (MAC) protocols control access to the shared communication medium so that it can be used efficiently. In this thesis, we first describe the collision-controlled Dual Prohibition Multiple Access (DPMA) protocol [45]. The main mechanisms implemented in DPMA, such as binary dual prohibition, power control, interference control, and support for differentiated services (DiffServ), are presented in detail. We conducted a thorough simulation study on DPMA protocol from several aspects. First, we conduct simulations to observe the effects of binary competition number (BCN), unit slot length and safe margin on the performance of DPMA. Secondly, the DiffServ capability of DPMA is demonstrated through simulation results. Finally, we compare the DPMA protocol with the CSMA/CA protocol and find that DPMA with optimal configuration has better performance than CSMA/CA under both low and high network density. / Thesis (Master, Electrical & Computer Engineering) -- Queen's University, 2007-09-28 16:25:02.515

In the last few years Wireless Sensor Networks (WSNs) have become an interesting field of research mainly due to the challenges and constraints of their design and the broad range of potential applications they can provide. One of the most important constraints is the limited energy resources of the sensor nodes that directly influences the design of the Medium Access Control (MAC) layer, as it is the responsible of controlling the transceiver that is the most consuming component of a sensor node. In this thesis the limitations of preamble sampling, one of the most well-known MAC protocols for WSNs, have been studied. Moreover, a new approach, called Low power listening with Wake up after Transmissions MAC (LWT-MAC), has been designed with the goal to overcome preamble sampling limitations while maintaining its reduced energy consumption and simplicity. The performance results obtained have shown that the LWT-MAC protocol is able to significantly improve the performance of WSNs. / Les xarxes de sensors sense fils han esdevingut una interessant àrea de recerca degut als reptes que presenta el seu disseny i a la gran quantitat d’aplicacions potencials que poden proporcionar. Un dels principals problemes d’aquestes xarxes és la limitació en els recursos energètics dels nodes sensors, cosa que afecta directament al disseny del nivell Medium Access Control (MAC), degut a què és el responsable de controlar la ràdio, el component de major consum energètic d’un node sensor. En aquesta tesi s’estudien les limitacions d'un dels protocols MAC per xarxes de sensors més conegut: preamble sampling. A més, s’ha dissenyat un nou protocol, anomenat Low power listening with Wake up after Transmissions MAC (LWT-MAC), amb l’objectiu de reduir les limitacions de preamble sampling però mantenint el seu baix consum energètic i la seva simplicitat. Els resultats obtinguts mostren que el protocol LWT-MAC és capaç de millorar de forma significativa el rendiment de la xarxa.

The work focuses on introduction to the topic of wireless sensor networks and brings readers the various aspects of problem solving in these networks. Work is closely focused on the energy performance when communicating between devices on a network and discusses the causes of excessive energy consumption. It also addresses the mechanisms for saving energy and is also engaged today protocols that its contribution to proposing solutions to problems. The author had also proposes an adapted protocol, based on lessons learned from previous theoretical sources.