Cell keeps updating on nrf9160

Question

Hello, 
 We are doing some network quality tests on LTE-M with PSM off and notice loss on UDP between 0% to sometimes 15% on simple udp messages sent every 10 seconds from the server to a client running on thingy91. 
 We noticed that when higher loss occurs we get more events of LTE_LC_EVT_CELL_UPDATE. The cell keeps changing between few cells in the area, their description according to cellmapper.net is attached. 
 Questions: 1. Is it possible that cell changing can induce loss on packets coming from server to client? Something like the packet is kept on the cell until the DRX passes and device checks every 1.28 s, but if device changes cell then packet is lost? 
 2. Is there any way to make the device stop searching? 
 
 Thanks

user111520 · Accepted Answer

Hello! 
 From my understanding, the nRF9160 will only actively search for cells if the current cell signal is weak: 
 To save energy, nRF9160 does not search and measure neighboring cells for mobility purposes if the level and quality of the serving cell signal are above the thresholds defined by the network. 
 So I believe the reason your device keeps switching cells is because it is unable to find a signal it is satisfied with, and this threshold seems to be set by the network, not the device. 
 Also, yes I do believe it is likely that packet loss can happen on a cell change. 
 If it is very important for your application that every packet reaches the device, have you considered using TCP rather than UDP? 
 Best regards, 
 Einar