Xiaoxiang-4 (TY-4 Tianyi-4) Operational 43669 2019-08-07 draft Beacon 435925000 GMSK 9600 T1 435925000 435925000 9k6 GMSK T2 2409000000 2409000000 5Mbps OFDM T3 5659000000 5839000000 5Mbps OFDM