An inherent non-observability of the thermal noise power level is circumvented by estimating an upper limit of the thermal noise power level by time evaluations. An instantaneous total received wideband power is measured in a receiver. Preferably, also an instantaneous sum of powers of all links used in the same cell is provided. A quantity (P′), preferably the difference between the instantaneous total received wideband power and the instantaneous sum of powers of all links used in the same cell, is followed (110) during a time period (TLag). A minimum value (PMIN) of that quantity is then used as an estimate of the thermal noise power level upper limit. Preferably, the time period is configured as a sliding window. An improved determination of noise rise can then be calculated and used for controlling traffic within the cell.