Abstract
This chapter cover the following topics: • the focus and application of the wireless sensor network; • the implications of the radio system; • the test bed implementation of the proposed low cost wireless sensors networks; • the wireless link power budget, coding and data recovering; • performance metrics of the wireless sensors networks; • cost analysis versus other technologies (wired and emerging wireless).
TopImplications Of The Radio-Frequency System
Normally, in the majority of the wireless sensors network applications, the total power consumption of a wireless node has a low or negligible contribution due to the electronics of control and processing, when compared with those from the radio-frequency (RF) system. The simple matter of fact that the available technologies present increased low-power features, it is not synonymous of a total power consumption relief. This is justified due to the fact the RF transceiver to be the bloc with the highest power consumption (Enz et al., 2005). The usage under low periods of time or low-duty cycles is a key to save power in wireless nodes. As depicted in Figure 1, the duty-cycle is defined by the ratio duty-cycle = Tu/Tf, where Tu [s] is the working time of the network for a total life time, Tf [s] and must be low. This paradigm is useful and it corresponds to what happens in a real wireless sensor network, where the nodes work in a peaked based transmission (Mateu et al., 2007).
Key Terms in this Chapter
Radio: Electronic system used to transmit and receive RF signals;
Radio-Frequency (RF): Frequencies used to transmit data across the air;
RF Transceiver: The same as radio;
Wireless Sensors Network: A network comprising wireless nodes, whose principal function is to acquire physical measures and send them wirelessly towards a base station. Also, these nodes can work as relays to other nodes or directly to the base station, and it must possess the ability to temporarily store its acquired data and the data to be forwarded;
PIC: A family of microcontrollers from Microchip Inc;
Error: A change (toggle) in the bit value due to channel impairments (noise, interferences, multipath, among others).
Frame: Set composed of bits (unities of binary information) arranged in a logic sequence;