The present disclosure relates to an access point (2) and to a sensor station (4) and methods performed therein. The access point (2) is adapted to communicate with the sensor station (4) and vice versa, over a communication channel using a contention based channel access. The access point (2) monitors (110) the traffic of the communication channel and estimates a congestion level of the communication channel. Information indicating the congestion level is incorporated (125) into a synchronization frame (200; 300) which is transmitted (140) to the sensor station (4). The sensor station (4) uses the congestion information when it selects which modulation and coding scheme it should use when sending data to the access point.