There is the classical way as suggested in the RDS specification or the alternative of symbolic modulation
The classical RDS encoder as shown in this diagram from the RDS Handbook is a complicated beast. A 57KHz oscilator is locked to the stereo pilot and a pre-formatted RDS data stream is assumed
The bit stream is differential encoded, then passed through a bi-phase generator using two clocks derived from the 57KHz carrier.
The resultant modulation is passed through a raised cosine filter to reduce the bandwidth occupied by the pulses thus minimising possible injection of the modulation into the normal stereo band.
Finally the shaped data modulates the 57KHz carrier to produce a DSB-SC (Double sideband suppressed carrier) signal that is added onto the stereo MPX.