A method of relocating a mobile sink in a wireless sensor network, the wireless sensor network comprising sensors for transmitting sensor data and the mobile sink, the method including: selecting candidate sink locations by identifying the centre of gravity of the sensors within reception range of the sink and selecting locations surrounding the centre of gravity; finding the suitability of each candidate sink location by: physically positioning the sink at each candidate sink location and receiving transmissions from the sensors within range of that location, the sensors within range of that candidate sink location sending a reference signal to assist the sink in estimating a channel between the sensor and the potential sink; and using a calculation based on the reference signal received from those sensors at that candidate sink location to determine a transmission rate achievable from each sensor by estimating the channel and by taking into account sensor data transmitted to the sink by the sensors, producing as a result a total transmission rate for the sensors within its range indicating the suitability of the candidate sink location for communication with a plurality of the sensors; comparing the result for each candidate sink location to determine the most suitable candidate sink location; and locating the mobile sink at said most suitable candidate sink location by physically positioning the mobile sink. selecting candidate sink locations by identifying the centre of gravity of the sensors within reception range of the sink and selecting locations surrounding the centre of gravity; finding the suitability of each candidate sink location by: physically positioning the sink at each candidate sink location and receiving transmissions from the sensors within range of that location, the sensors within range of that candidate sink location sending a reference signal to assist the sink in estimating a channel between the sensor and the potential sink; and using a calculation based on the reference signal received from those sensors at that candidate sink location to determine a transmission rate achievable from each sensor by estimating the channel and by taking into account sensor data transmitted to the sink by the sensors, producing as a result a total transmission rate for the sensors within its range indicating the suitability of the candidate sink location for communication with a plurality of the sensors; physically positioning the sink at each candidate sink location and receiving transmissions from the sensors within range of that location, the sensors within range of that candidate sink location sending a reference signal to assist the sink in estimating a channel between the sensor and the potential sink; and using a calculation based on the reference signal received from those sensors at that candidate sink location to determine a transmission rate achievable from each sensor by estimating the channel and by taking into account sensor data transmitted to the sink by the sensors, producing as a result a total transmission rate for the sensors within its range indicating the suitability of the candidate sink location for communication with a plurality of the sensors; comparing the result for each candidate sink location to determine the most suitable candidate sink location; and locating the mobile sink at said most suitable candidate sink location by physically positioning the mobile sink.