A controller for a wireless sensor, wherein the wireless sensor is for embedding in a biomass. The controller is configured to receive at least one biomass characteristic associated with the wireless sensor； determine two or more location estimate representations for said wireless sensor using at least properties of wireless communication between the wireless sensor and one or more wireless units； and determine an enhanced location estimate for said wireless sensor by combining at least two of said two or more location estimate representations. The controller is configured to perform at least one of the determinations using said at least one biomass characteristic. Location determination may be repeated on a periodic basis or in response to movement, change in a biometric characteristic (eg temperature, moisture etc) or change in the received signal strength. Enables more accurate location in a heterogeneous transmission medium.
