I. Introduction
With the proliferation of various kinds of sensor-rich mobile devices (such as smartphones, wearable devices, and intelligent vehicles), mobile crowdsensing (MCS) [1], [2], [3] has rapidly emerged as a widely popular paradigm for sensory data collection regarding various kinds of objects in practice. Among others, location-based MCS has greatly benefited many real-world applications, such as road monitoring, smart transportation, and environmental monitoring [1], [4], [5], [6], [7]. For example, MCS allows harnessing of mobile devices to collect measurements in a target area for environment-related objects such as air quality, temperature, and noise pollution [5], [6], [7], [8]. In practical deployment of such location-based MCS applications, however, it is quite common that there exist in the target area blank regions whose sensory data are missing, due to various factors like the budget limit of the MCS application campaigners (commonly referred to as requesters), the large area size, or the scarcity of participants in the target area [6], [7], [9].