  Each node in a wireless multi-hop network can adjust the power level at which
it transmits and thus change the topology of the network to save energy by
choosing the neighbors with which it directly communicates. Many previous
algorithms for distributed topology control have assumed an ability at each
node to deduce some location-based information such as the direction and the
distance of its neighbor nodes with respect to itself. Such a deduction of
location-based information, however, cannot be relied upon in real environments
where the path loss exponents vary greatly leading to significant errors in
distance estimates. Also, multipath effects may result in different signal
paths with different loss characteristics, and none of these paths may be
line-of-sight, making it difficult to estimate the direction of a neighboring
node. In this paper, we present Step Topology Control (STC), a simple
distributed topology control algorithm which reduces energy consumption while
preserving the connectivity of a heterogeneous sensor network without use of
any location-based information. We show that the STC algorithm achieves the
same or better order of communication and computational complexity when
compared to other known algorithms that also preserve connectivity without the
use of location-based information. We also present a detailed simulation-based
comparative analysis of the energy savings and interference reduction achieved
by the algorithms. The results show that, in spite of not incurring a higher
communication or computational complexity, the STC algorithm performs better
than other algorithms in uniform wireless environments and especially better
when path loss characteristics are non-uniform.
