  Geographic routing provides relatively good performance at a much lower
overhead than conventional routing protocols such as AODV. However, the
performance of these protocols is impacted by physical voids, and localization
errors. Accordingly, virtual coordinate systems (VCS) were proposed as an
alternative approach that is resilient to localization errors and that
naturally routes around physical voids. However, we show that VCS is vulnerable
to different forms of the void problem and the performance of greedy routing on
VCS is worse than that of geographic forwarding. We show that these anomalies
are due to the integral nature of VCS, which causes quantization noise in the
estimate of connectivity and node location. We propose an aligned virtual
coordinate system (AVCS) on which the greedy routing success can be
significantly improved. With our approach, and for the first time, we show that
greedy routing on VCS out-performs that on physical coordinate systems even in
the absence of localization errors. We compare AVCS against some of the most
popular geographical routing protocols both on physical coordinate system and
the virtual coordinate systems and show that AVCS significantly improves
performance over the best known solutions.
