Research On Optimal Deployment Of Wireless Charger Under Co-frequency Interference

Wireless charging technology is considered as a promising solution to address the energy limitation problem for wireless sensor networks(WSNs).Using multiple fixed chargers to remotely charge WSNs is a feasible way in many harsh terrains where using mobile chargers is infeasible.Obviously,the chargers with diverse frequencies will occupy too much channel resources of WSNs.If the chargers have the same radio frequency,the charging efficiency with multiple chargers may not simply be the sum of that with single charger due to the radio interference,which may significantly increase the charging power at some sensor nodes while seriously decrease the charging power at other nodes because of the particularity of deployment location.For this,we manufacture several wireless charger with exactly same frequency and verify this phenomenon by conducting experiments.On this basis,this paper will focus on the following question: in consideration of less channel resources unique-frequency charges occupied,to charge a given WSN,can unique-frequency chargers be comparable to diverse-frequency chargers?In view of this problem,this paper will start from two aspects.On the one hand,given threshold of radio power at sensor nodes,whether the number of unique-frequency chargers can be close to that of diverse-frequency chargers.On the other hand,given the charger number,whether the minimum radio power provided by unique-frequency chargers on the sensor node can be close to that with same number of diverse-frequency chargers.Then,we give the mathematical modeling of the problem respectively for the above two research ideas,and prove that these two kinds of problems are NP-hard.On this basis,the paper designs the corresponding greedy algorithm respectively for these two kinds of problems and proves that the upper bound of the algorithm performance of the first problem.At the end of the paper,a large number of simulation experiments are carried out.The simulation results show that: i)given threshold of radio power at sensor nodes,the number of unique-frequency chargers required is no more than 1.1 times of that of diverse-frequency chargers in most cases;and ii)given the charger number,the minimum radio power provided by unique-frequency chargers can be up to 80% of that with diverse-frequency chargers in most cases.It can be seen that unique-frequency chargers can achieve similar charging performance with diverse-frequency chargers in most cases with occupying only one channel.Finally,after appropriate placement of the unique-frequency chargers,we find it needless to further schedule these chargers to improve the minimum charging power that they provide.