Are other phones in same location getting good signal? Check your mobile network settings and make sure it's set correctly. If phone came with a SIM card, you may need to contact your carrier. If not, get a new SIM to see if signal improves. There may be tower work/upgrade going on close to you as well. Next time it happens, put the phone in airplane mode for about 10 seconds then turn airplane mode off. No need to keep restarting. See customer support for more technical help.
