Introduction - Energy Harvesting Autonomous Sensor Systems - page 6

Application Layer
Transport Layer
Network Layer
Data Link Layer
Physical Layer
FIGURE 1.6
Sensor networks protocol stack. (From I.F. Akyildiz, W.L. Su, S. Yogesh, and C. Erdal, “A survey
on sensor networks,” IEEE Communications Magazine , vol. 40, no. 8, pp. 102-114, 2002 [4].)
then the WSN can be redesigned accordingly for lower power consumption.
To start the basic communication process, consists of sending data from the
source to the destination. Primarily, it is the case of two wireless sensor nodes
wanting to communicate with each other. The sensor node at source gener-
ates information, which is encoded and transmitted to the destination, and
the destination sensor node decodes the information for the user. This entire
process is logically partitioned into a definite sequence of events or actions,
and individual entities then form layers of a communication stack. The WSN
protocol stack [4] shown in Figure 1.6 consists of five network layers: phys-
ical (PHY) (lowest), data link, network, transport, and application (highest)
layers.
Starting from the lowest level, the PHY layer receives and transfers data
collected from the hardware. It is well known that long-distance wireless
communication can be expensive in terms of both energy and implementa-
tion complexity. While designing the PHY layer for WSNs, energy minimiza-
tion is considered significantly more important than the other factors, like
propagation and fading effects. Energy-efficient PHY layer solutions are cur-
rently being pursued by researchers to design for tiny, low-power, low-cost
transceiver, sensing, and processing units [6]. The next-higher layer is the data
link layer, which ensures reliable point-to-point and point-to-multipoint con-
nections for the multiplexing of data streams, data frame detection, medium
access, and error control in the WSN. The data link layer should be power
aware and at the same time minimize the collisions between neighbours'
signals because the environment is noisy and sensor nodes themselves are
highly mobile. This is also one of the layers in the WSN whereby power