Building a mesh network from scratch is a complex process. Anyone wanting to deploy a mesh network should conform to the ZigBee specification.
Regardless of the network top-logy, ZigBee/802.15.4 networks have three basic types of nodes: controller nodes, full function (FFD) nodes, and reduced function (RFD) nodes, each of which minimally has a radio, a microcontroller, 802.15.4 MAC and a network layer. Different types of nodes have different processing, memory and power consumption requirements.
Controller and full function nodes, such as those in gateway servers or electrical equipment, are usually hard wired to a power source, so power consumption, per se , is not an issue. Reduced function nodes, on the other hand, are connected to sensors and switches and are usually battery powered.
Battery-powered nodes should have a very long battery life. If possible the battery should outlast the industrial control equipment itself because many of these battery powered end-nodes will be in hard to reach places that will make replacing their batteries very difficult and expensive.
The ZigBee standard actually mandates a 2-year battery life for battery-powered nodes. However, where battery life is concerned, longer is always better. Imagine how annoying (not to mention expensive) it would be to replace all the sensors and servo controllers embedded in a flow control system.
The importance of Sleep Mode Power Consumption Several factors affect power consumption, including the supply voltages of the radio and microcontroller, the active current drawn by the radio and microcontroller, the clock frequency at which the controller operates, the number of external components required in the system (particularly power amplifiers), and the code size, in as much as it affects the MCU clock frequency.
Radios and controllers are available with supply voltages that range from 1.8 to 3.6 volts. Lower is better, but be sure to verify the supply voltage specifications. Some vendors claim 1.8 volt operation, but actually require 2.2 volts to write to flash memory.
Atmel offers the only radios and controllers with "true" 1.8 volt operation. This ability to operate at 1.8 V actually allows the battery to last about 20% longer than it would with a 2 V supply voltage.
Radios draw different amounts of current during transmit and receive. ZigBee radios are available with transmit current consumption of 17 mA to 38 mA, and receive current consumption of 15 mA to 36 mA. Again, lower is obviously better.
However, in the case of radios, transmit power and receive sensitivity have an indirect effect on current consumption. If the radio's transmit power or receive sensitivity is too weak, power-hungry power amplifiers must be added to the design to beef up the signal. These external components can add up to 50 mA to node power consumption.
