Method and arrangement in a base station for selecting a transmission parameter. The selected transmission parameter is used when sending a signal over a radio channel to a user equipment in a wireless communication network. The radio channel is allocated bandwidth for signalling. The method comprises the step of obtaining an estimation of the signal quality of the radio channel. Also, the allocation to the radio channel. Further yet, the method may comprise the step of calculating a signal quality margin, which signal quality margin is based on the bandwidth size. Still further, the method comprises the step of selecting the transmission parameter based on the estimated signal quality of the radio channel and the calculated signal quality margin.