  Location-based services in a wireless network require nodes to know their
locations accurately. Conventional solutions rely on contention-based medium
access, where only one node can successfully transmit at any time in any
neighborhood. In this paper, a novel, complete, distributed ranging and
localization solution is proposed, which let all nodes in the network broadcast
their location estimates and measure distances to all neighbors simultaneously.
An on-off signaling is designed to overcome the physical half-duplex
constraint. In each iteration, all nodes transmit simultaneously, each
broadcasting codewords describing the current location estimate. From the
superposed signals from all neighbors, each node decodes their neighbors'
locations and also estimates their distances using the signal strengths. The
node then broadcasts its improved location estimates in the subsequent
iteration. Simulations demonstrate accurate localization throughout a large
network over a few thousand symbol intervals, suggesting much higher efficiency
than conventional schemes based on ALOHA or CSMA.
