Lyapunov-Guided Optimal Service Placement in Vehicular Edge Computing

Vehicular Edge Computing(VEC)brings the computational resources in close proximity to the service requestors and thus supports explosive computing demands from smart vehicles.However,the limited computing capability of VEC cannot simultaneously respond to large amounts of offloading requests,thus restricting the performance of VEC system.Besides,a mass of traffic data can incur tremendous pressure on the front-haul links between vehicles and the edge server.To strengthen the performance of VEC,in this paper we propose to place services beforehand at the edge server,e.g.,by deploying the services/tasks-oriented data(e.g.,related libraries and databases)in advance at the network edge,instead of downloading them from the remote data center or offloading them from vehicles during the runtime.In this paper,we formulate the service placement problem in VEC to minimize the average response latency for all requested services along the slotted timeline.Specifically,the time slot spanned optimization problem is converted into per-slot optimization problems based on the Lyapunov optimization.Then a greedy heuristic is introduced to the drift-plus-penalty-based algorithm for seeking the approximate solution.The simulation results reveal its advantages over others in terms of optimal values and our strategy can satisfy the long-term energy constraint.

Bats adjust temporal parameters of echolocation pulses but not those of communication calls in response to traffic noise

Many studies based on acute short-term noise exposure have demonstrated that animals can adjust their vocal­izations in response to ambient noise.However,the effects of chronic noise over a relatively long time scale of multiple days remain largely unclear.Bats rely mainly on acoustic signals for perception of environmental and social communication.Nearly all previous studies on noise-induced vocal adjustments have focused on echo­location pulse sounds.Relatively little is known regarding the effects of noise on social communication calls.Here,we examined the dynamic changes in the temporal parameters of echolocation and communication vocal­izations of Vespertilio sinensis when exposed to traffic noise over multiple days.We found that the bats start­ed to modify their echolocation vocalizations on the fourth day of noise exposure,with an increase of 42-91%in the total number of pulse sequences per day.Under noisy conditions,the number of pulses within a pulse se­quence decreased by an average of 17.2%,resulting in a significantly slower number of pulses/sequence(P<0.001).However,there was little change in the duration of a pulse sequence.These parameters were not signifi­cantly adjusted in most communication vocalizations under the noise condition(all P>0.05),except that the duration decreased and the number of syllables/sequences increased in 1 type of communicative vocalization(P<0.05).This study suggests that bats routinely adjust temporal parameters of echolocation but rarely of com­munication vocalizations in response to noise condition.