Essay Wireless Technology

5281 Words Sep 26th, 2012 22 Pages
IEEE 802.15.4: a wireless communication technology for large-scale ubiquitous computing applications
Anis Koubâa, Mario Alves, Eduardo Tovar
PP-HURRAY! Research Group, Polytechnic Institute of Porto Rua Dr. Antonio Bernardino de Almeida, 431, 4200-072 Porto, PORTUGAL {akoubaa, emt}@dei.isep.ipp.pt, mjf@isep.ipp.pt

Abstract. Wireless Sensor Networks (WSNs) have been attracting increasing interest for supporting a new generation of ubiquitous computing systems with great potential for many applications such as surveillance, environmental monitoring, health care monitoring or home automation. However, the communication paradigms in WSNs differ from the ones associated to traditional wireless networks, triggering the need for new
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Additionally, the IEEE 802.15.4 protocol may also provide timeliness guarantees by using the Guaranteed-Time Slot (GTS) mechanism, which is quite attractive for time-sensitive WSNs. In fact, when operating in beacon-enabled mode, i.e. beacon frames are transmitted periodically by a central node called the PAN Coordinator for synchronizing the network, the IEEE 802.15.4 protocol allows the allocation/deallocation of GTSs in a superframe for applications with real-time constraints. Hence, the GTS mechanism provides a minimum service guarantee for the corresponding nodes, thus enabling the prediction of the worst-case performance for each node's application. In this paper, we describe the most important features of the IEEE 802.15.4 protocol that are relevant for WSNs and we discuss the ability of this protocol to fulfill the different requirements of WSNs and to resolve inherent paradoxes involving power-efficiency and timeliness guarantees.

2. Overview of the IEEE 802.15.4 protocol

2.1. Physical Layer (PHY) IEEE 802.15.4 offers three operational frequency bands: 2.4 GHz, 915 MHz and 868 MHz. There is a single channel between 868 and 868.6 MHz, 10 channels between 902 and 928 MHz, and 16 channels between 2.4 and 2.4835 GHz. The data rates are 250 kbps at 2.4 GHz, 40 kbps at 915 MHZ and 20 kbps at 868 MHz. Lower frequencies are more suitable for longer transmission ranges due to lower propagation losses. However, the advantage of high data
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