Wireless Sensor Networks : Technology, Protocols, and Applications

274 OPERATING SYSTEMS FOR WIRELESS SENSOR NETWORKS
The basic function of WSNs is to collect information and to support certain
applications specific to the task of WSN deployment. Commercially available
sensor nodes are categorized into four groups [10.13]:
1. Specialized sensing platforms such as the Spec [10.13] node designed at the
University of California–Berkeley. This sensor node has a single chip with
low-power low-cost, operation.
2. Generic sensing platforms such as Berkeley motes [10.1]. This node can
perform generic sensing tasks.
3. High-bandwidth sensing platforms such as iMote [10.13]. This node can
handle sensed data flow with high bandwidth.
4. Gateway platforms such as Stargate [10.13]. This node can be used as a sink
and can connect low-level senor nodes directly to the Internet.
The differences in the sensor types above are in the function of the sensor, frequency
of the microprocessor, memory size, and transceiver bandwidth. Although
these nodes have different characteristics, their basic hardware components are the
same: a physical sensor, a microprocessor or microcontroller, a memory, a radio
transceiver, and a battery. Therefore, these hardware components should be organized
in a way that makes them work correctly and effectively without a conflict
in support of the specific applications for which they are designed. Each sensor
node needs an operating system (OS) that can control the hardware, provide
hardware abstraction to application software, and fill in the gap between applications
and the underlying hardware.
The traditional OS is system software that operates between application software
and hardware and is often designed for workstations and PCs with plenty of
resources. This is usually not the case with sensor nodes in WSNs. There are
also embedded operating systems such as VxWorks [10.21] and WinCE [10.22],
none of which is specially designed for data-centric WSNs with constrained
resources. Sensors usually have a slow processor and small memory, different
from most current systems. In this chapter, parameters that should be kept in
mind in the process of OS design for WSN nodes are considered.
10.2 OPERATING SYSTEM DESIGN ISSUES
Traditional operating systems [10.17,10.20] are system software, including
programs that manage computing resources, control peripheral devices, and provide
software abstraction to the application software. Traditional OS functions are therefore
to manage processes, memory, CPU time, file system, and devices. This is
often implemented in a modular and layered fashion, including a lower layer of
kernels and a higher layer of system libraries. Traditional OSs are not suitable
for wireless sensor networks because WSNs have constrained resources and diverse
data-centric applications, in addition to a variable topology. WSNs need a new type