Paraphrasing

1.1.3 Energy management

Energy management is the process of managing the sources and consumers of energy in a node or in the network. Energy is controlling the lifetime of ad hoc network. Shaping the energy discharge pattern of node’s battery to enhance the battery life; finding routes that result in minimum total energy consumption in the network; using distributed scheduling schemes to improve battery life; and handing the processor and interface devices to minimize power consumption are some of the functions of energy management. Energy management can be classified into the following categories:

Transmission power management: the power consumed by the radio frequency (RF) module of a mobile node is determined by several factors such as the state of operation, the transmission power, and technology used for the RF circuitry. The state of operation refers to transmit, receive and sleep modes of operation. The transmission power is determined by the reachability requirement of the network, the routing protocol, and the MAC protocol.

The RF hardware design should ensure minimum power consumption in all the three states of operation. Going to the sleep mode when not transmitting or receiving can be done by additional hardware that can wake up on reception of control signal. Power conservation responsibility lies across the data link layer network, transport, and application layers. By designing a data link layer protocol that reduces unnecessary retransmissions, by preventing collisions, by switching to standby mode or sleep mode whenever possible, and by reducing the transmit/ receive switching, power management can be performed at the data link layer.

Battery energy management: the battery management is aimed at extending the battery life of node by taking advantage of its chemical properties, discharge patterns, and by the selection of battery from a set of batteries that is available for redundancy. Recent studies showed that pulsed discharge of a battery gives longer life than continuous discharge. Controlling the charging rate and discharging rate of the battery is important in avoiding early charging to maximum charge or full discharge below the minimum threshold. This can be achieved by means of embedded charge controllers in the battery pack. Also, the protocols at the data link layer and network layer can be designed to make use of the discharge models. Monitoring of the battery for voltage levels, remaining capacity, and temperature so that proactive actions can be taken is required.

Processor power management: the clock speed and the number of instructions executed per unit time are some of the processor parameters that affect power consumption. The CPU can be put into different power saving modes during low processing load conditions. The CPU power can be completely turned off if the machine is idle for a long time. In such cases, interrupts can be used to turn on CPU upon detection of user interaction or other events.

Devices power management: intelligent device management can reduce power consumption of a mobile node significantly. This can be done by the operating system (OS) by selectively powering down interface devices that are not used or by putting devices into different power-saving modes, depending on their usage. Advanced power management features built into the operating system and application software for managing devices effectively are required.