A burst may include a three-bit tail sequence derived from a four-bit Enhanced General Packet Radio Service (EGPRS)-2 tail sequence. A legacy wireless transmit/receive unit (WTRU) may be multiplexed onto an Orthogonal Sub-channel (OSC) resource, and may receive a burst including four-bit Quadrature Phase Shift Keying (QPSK)-type tail sequences that decode to legacy three-bit Gaussian Minimum Shift Keying (GMSK)-type or 8PSK-type tail sequences. The legacy WTRU processes the tail sequences, unaware that the burst was received on an OSC sub-channel or that the tail sequences were encoded as QPSK-type tail sequences. An OSC QPSK tail sequence may be chosen such that it corresponds to the legacy GMSK tail sequence format when decoded on an OSC sub-channel, but also so that a power-versus-time mask, power constraint, or other criteria on the other MUROS sub-channel may be optimized. Different tail sequences may be used in OSC bursts, depending upon whether the WTRUs multiplexed onto a timeslot are legacy WTRUs or include OSC-specific features.