BT
The required baseband bandwidth, and hence the RF bandwidth requirement of a CML GMSK IC in a system is principally determined by two factors: the data rate and the system filter's response.
The response characteristic with respect to an applied data rate is referred to as the system BT (bandwidth - data rate factor. The BT factor is the ratio of the -3dB point of the filter (-3dBf0) and the applied data rate.