Aside from the issues presented by the other comments, the core block doing work here is gr_gsm which is a GSM demodulator (FSK). 4G/LTE is not FSK so you are g

Aside from the issues presented by the other comments, the core block doing work here is gr_gsm which is a GSM demodulator (FSK). 4G/LTE is not FSK so you are going to have to find a different solution for 4G.