A network node, wireless device, base station, user equipment and corresponding methods are provided. The network node includes processing circuitry configured to: select a first set and second set of reference signal resources in a subframe and aggregate the first set and second set of reference signal resources in the subframe to form a code division multiplexing, CDM, aggregation configuration. The first set and second set of reference signal resources in the subframe satisfy a temporal criterion such that any two resource elements in the first set and second set of reference signal resources have up to a maximum time separation of six OFDM symbols. The first set and second set of reference signal resources in the subframe satisfy a frequency criterion such that any two resource elements in the first set and second set of reference signal resources have up to a maximum frequency separation of six subcarriers.