  Geographical routing protocols have several desirable features for use in ad
hoc and sensor networks but are susceptible to voids and localization errors.
Virtual coordinate systems are an alternative solution to geographically based
routing protocols that works by overlaying a coordinate system on the sensors
relative to well chosen reference points. VC is resilient to localization
errors; however, we show that it is vulnerable to different forms of the void
problem and have no viable complementary approach to overcome them.
Specifically, we show that there are instances when packets reach nodes with no
viable next hop nodes in the forwarding set. In addition, it is possible for
nodes with the same coordinates to arise at different points in the network in
the presence of voids. This paper identifies and analyzes these problems. It
also compares several existing routing protocols based on Virtual Coordinate
systems. Finally, it presents a new routing algorithm that uses backtracking to
overcome voids to achieve high connectivity in the greedy phase, higher overall
path quality and more resilience to localization errors. We show these
properties using extensive simulation analysis.
