PARO: Conserving power in wireless ad-hoc networks

Introduction

A reduction in the power consumption increases the operational lifetime of network enabled devices. Especially for small computing and communication devices with built-in or attached radios reducing the transmission power may extend operational lifetime.

What is PARO?

PARO is a power-aware routing technique for wireless ad hoc networks where all nodes are located within the maximum transmission range of each other.

PARO uses a packet forwarding technique where immediate nodes can elect to become redirectors on behalf of source-destination pairs.

As the required transmission power to communicate between any source and destination node is not proportional to the distance of them adding multiple intermediate redirectors may result in an overall lower power consumption compared to the direct communication.

PARO in comparison to other MANET routing techniques

PARO's approach is in direct contrast to existing MANET routing protocols:

• MANET protocols try to minimize the amount of hops therefore wasting power

• MANET routing protocols are not suitable for discovering optimal power-aware routes in wireless ad hoc networks

PARO Model

Here the PARO Model is beeing described including the link assumption, the way PARO calculates the cost of transmission power as well as the operation of the PARO protocol.

Link Assumptions

• radios need to be capable of dynamically adjusting transmission power

• Assumption: transmission power needed to transmit between nodes A and B is somewhat similar to transmission power between B and A

• Requirement: interference-free Media Access Control (MAC) found in frequency band radios such as Channel Sense Multiple Access (CSMA)

• Every data packet successfully received is acknowledged at the link layer

• Nodes in the network are capable of overhearing any transmission by other nodes as long as the received signal to noise ratio (SNR) is above a certain minimum value

Cost Function

Assuming a network with several static nodes:

• A node keeps its transmitter “on” to transmit one data packet to another node for L/C seconds
  • L: size of transmitted frame in bits
  • C: raw speed of wireless channel in bits/s

• Receiver node keeps transmitter “on” to acknowledge a successful data transmission for a combined period of l/C seconds
  • l: size of the acknowledgment frame including layer 2 headers

Cost function for transmitting Q packets between a given source-destination pair along the best route then is:

$P_{k}=R_{k}+Q\cdot \sum _{i=0}^{N_{k}}={\frac {T_{i,i+1}\cdot L+T_{i+1,i}\cdot l}{C}}$

• $T_{i,j}$ : minimum transmission power at node i such that the receiver node j along route k is still able to receive the packet correctly

• $N_{k}$ : number of times a data packet is forwarded along route k including the source node

Protocol Operations

• Before transmitting a packet, a node updates its packet header to indicate the power required to transmit

• Nodes capable of overhearing source and destination can compute whether packet forwarding can reduce transmission power in comparison to direct exchange

• In that case an intermediate node may elect to become a redirector and send a route-redirect message to the source and destination