Methods, systems, and devices for wireless communications are described. In some systems (e.g., non-orthogonal multiple access (NOMA) systems), a base station may serve a large number of user equipments (UEs) on the uplink. To improve detectability for these uplink transmissions (e.g., if reference signals are not available for the transmissions), the UEs may implement parallel transmissions of preambles with uplink data. A UE may split the uplink data into one or more data layers, and may select one or more preamble layers to transmit superposed with the data layers. These preambles may be sequences known to both the UE and the base station to aid in detectability. The UE may assign different signature sequences to each of these layers based on cross-correlation values (e.g., assigning sequences with higher cross-correlation values to the data layers for improved detectability), and may scramble the layers into a single shared signal for transmission.