Oppcast: Exploiting Spatial and Channel Diversity for Robust Data Collection in Urban Environments.

ZigBee shares the 2.4 GHz ISM band with a number of wireless technologies like WiFi, Bluetooth, and common household appliances like a microwave and a cordless phone to name a few. Due to the large-scale penetration of these technologies in urban environments, ZigBee communication suffers from severe cross-technology interference (CTI). Data collection in the presence of such highly dynamic CTI is quite challenging. Our work first examines the different deployment environments under the influence of planned and unplanned CTI and later proposes Oppcast, a robust and energy-efficient data collection protocol that carefully exploits a combination of spatial and channel diversity to eliminate the need for performing expensive channel estimation in advance. Our extensive evaluation in both a large-scale testbed (Academic Institution) and various urban environments (Carpark, Residential Complex, Shopping Mall and Cafeteria) shows that Oppcast is not only robust to CTI with reliability consistently maintained above 98.55%, but is also up to 2.4 times more energy efficient than the state-of-the-art data collection protocols. The rationale behind Oppcast exhibiting high robustness in highly dynamic environments is a significant increase in the number of communication opportunities it gets by exploiting multiple routes over multiple channels towards the destination.