Methods, systems, and devices for wireless communications are described in which control information is transmitted using a single carrier (SC) waveform in time domain blocks without a cyclic prefix (CP). A base station may configure a user equipment (UE) for control information transmissions using a SC waveform without CPs in time domain blocks, and may activate the SC waveform without CPs in time domain blocks based on one or more parameters. The control information may be non-uniformly segmented across two or more time domain blocks or two or more portions of a time domain block. A reference signal, such as a demodulation reference signal, may be transmitted in the time domain blocks, where the reference signals may be distributed evenly or unevenly across the time domain blocks.