The modulator receives the bits from the encryption unit, see GSM 05.01 [1], and produces an RF signal. The filtering of the Radio Frequency (RF) signal necessary to obtain the spectral purity is not defined, neither are the tolerances associated with the theoretical filter requirements specified. These are contained in GSM 05.05 [4].
DS/EN 300959 V6.1.1:2003 history
2003DS/EN 300959 V8.1.2:2003 Digital cellular telecommunications system (Phase 2+); Modulation (GSM 05.04 version 8.1.2 Release 1999)
2003DS/EN 300959 V7.1.1:2003 Digital cellular telecommunications system (Phase 2+); Modulation (GSM 05.04 version 7.1.1 Release 1998)
2003DS/EN 300959 V6.1.1:2003 Digital cellular telecommunications system (Phase 2+); Modulation (GSM 05.04 version 6.1.1 Release 1997)