A method of wireless communication includes transmitting, from a first communication device to a second communication device, an indication of N regions in a resource grid defined by transmission resources in a frequency domain and/or time resources in a time domain and communicating the reference signal between the first communication device and the second communication device according to the density information. Here, each of the N regions has a corresponding resource density indicative of a density of time-frequency resources configured for reference signal transmissions and N is an integer greater than 1.