Managing packet collisions in scavenging-based ULP transmit-only indoor localization systems

Ultra-wideband (UWB) enabled wireless sensor networks (WSNs) are capable of identification, localization and recording of sensor readings. For reasons of cost, size and above all energy consumption constraints, scavenging-based ultra-lower-power (ULP) sensor nodes (SNs) are designed with only UWB transmitters. Transmit-only SNs are unaware of each other and broadcast data packets as soon as enough energy is harvested from the environment. The trade-off is that the resulting uncoordinated multiuser access causes packet collisions so that many SNs become undetectable. In this paper, we propose several techniques to control the transmit time of SNs. These techniques help to alleviate packet collisions and improve SNs detectability. They are evaluated and compared as a function of the network density (the number of SNs per m³). We determine the effective techniques for different network density. Results obtained from simulations indicate that by adding randomness in the transmissions while introducing pause time between two consecutive transmissions, all SNs can be identified up to quite a large network density (500 SNs/m³) in this scavenging-based transmit-only scenario.