An access node of a communication system comprises a plurality of transmitters adapted for communication with at least one receiver. The access node is operative to simultaneously estimate channel coefficients between multiple ones of the transmitters and the receiver, and to utilize the estimated channel coefficients to control at least one data signal sent by at least one of the multiple transmitters to the receiver. In the process of simultaneously estimating the channel coefficients, the access node transmits a plurality of distinct probing signals generated based on respective ones of a plurality of different frequency expansions. For example, each of the distinct probing signals may be generated based on a distinct combination of a common probing sequence and a selected one of the plurality of different frequency expansions.