  This paper describes Census, a protocol for data aggregation and statistical
counting in MANETs. Census operates by circulating a set of tokens in the
network using biased random walks such that each node is visited by at least
one token. The protocol is structure-free so as to avoid high messaging
overhead for maintaining structure in the presence of node mobility. It biases
the random walks of tokens so as to achieve fast cover time; the bias involves
short albeit multi-hop gradients that guide the tokens towards hitherto
unvisited nodes. Census thus achieves a cover time of O(N/k) and message
overhead of O(Nlog(N)/k) where N is the number of nodes and k the number of
tokens in the network. Notably, it enjoys scalability and robustness, which we
demonstrate via simulations in networks ranging from 100 to 4000 nodes under
different network densities and mobility models.
