11-04-2012, 04:50 PM
Power Control in Ad-Hoc Networks: Theory, Architecture, Algorithm and Implementation of the COMPOWProtocol
compow_ewc_2002_IMPPPPP.pdf (Size: 237.77 KB / Downloads: 26)
INTRODUCTION
Transmit power control is important in wireless ad hoc
networks for at least two reasons: (i) It can impact on
battery life, and (ii) It can impact on the traffic carrying
capacity of the network.
For the first point, note that there is no need for N1 in
Figure 1 to broadcast at 30mW to send a packet to the
neighboring N2, since N2 is within range even at 1mW.
Thus it can save on battery power. For the second point,
suppose that in the same figure, N3 also wishes to broadcast
a packet at the same time to N4 at 1mW.
BIDIRECTIONAL LINKS ARE GOOD
We begin by arguing that it is good to have bidirectional
links. First note that the wireless medium is inherently
lossy due to obstructions, shadowing, multipath
effects, fading, etc., in addition to interference from other
nodes. So, even on a single hop, a packet can never be
assumed to have been successfully received by a neighbor
unless the neighbor acknowledges it.
COMMON POWER AND BIDIRECTIONALITY
How can bidirectional links be ensured? The simplest
approach, assuming nodes are homogeneous, is for nodes
to transmit at the same power. Since all physical paths
taken by radio waves from a node
. Note that this does
not require a spherical region for the range, that is, equal
range in all directions.
COMMON POWER ASYMPTOTICALLY OPTIMIZES
NETWORK CAPACITY
The question that naturally arises is: How much of
a network’s potential traffic carrying capacity is sacrificed
by insisting that all nodes operate at a common
power level, rather than selecting an optimum power for
each node for each outgoing link? The answer is “not
much,” as the number of nodes is increased.
CONCLUDING REMARKS
We have provided a conceptualization of the power
control problem in ad hoc networks, given theoretical arguments
in support of a common power level, produced
a minimalist architectural design, and finally completely
implemented the COMPOW protocol. Our power control
protocol guarantees bidirectionality of links and connectivity
of the network, asymptotically maximizes the
traffic carrying capacity, provides power aware routes, reduces
MAC contention, and can be used with any proactive
routing protocol. To the best of our knowledge, it
is the only power control scheme which has been implemented
and tested on a real wireless test-bed.