Technology for a base station operable to transmit downlink reference signals to user equipments (UEs) is disclosed. The base station can identify a UE to receive a set of pre-configured downlink reference signals from the base station. The set of pre-configured downlink reference signals can include a set of pre-configured pilot symbols in accordance with a defined reference signal transmission pattern that is characterized by a first pilot symbol spacing parameter (Nt) in a subcarrier time domain and a second pilot symbol spacing parameter (Nf) in a subcarrier frequency domain. The base station can transmit to the UE the set of pre-configured downlink reference signals in accordance with the defined reference signal transmission pattern. The UE can be configured to detect the set of pre-configured downlink reference signals and perform a channel estimation based on the set of pre-configured downlink reference signals.