A method performed by a location server for assisting a mobile device to perform positioning measurements on positioning signals periodically transmitted by at least some of a plurality of cells in a wireless communication network, wherein one of the plurality of cells is a serving cell for the mobile device, the method comprising: determining an estimated position of the mobile device; determining a first set of candidate cells of the plurality of cells in the wireless communication network based on the estimated position of the mobile device; for each candidate cell that transmits a positioning signal at a different frequency to the serving cell, setting an expected interference of the respective positioning signal for that candidate cell to a default level; for each candidate cell that transmits a positioning signal at a same transmit frequency as the serving cell, estimating an expected interference of the respective positioning signal for that candidate cell, comprising: determining whether a serving power level of the serving cell is known; if the power level of the serving cell is not known, estimating an expected interference for the candidate cell at multiple serving power levels associated with various locations within the serving cell; if the serving power level of the serving cell is known, setting the expected interference level for the candidate cell to below a serving power level of the serving cell; selecting a subset of cells from the first set of candidate cells based on the estimated expected interference; generating assistance data that identifies the selected subset of cells; and sending the generated assistance data to the mobile device. determining an estimated position of the mobile device; determining a first set of candidate cells of the plurality of cells in the wireless communication network based on the estimated position of the mobile device; for each candidate cell that transmits a positioning signal at a different frequency to the serving cell, setting an expected interference of the respective positioning signal for that candidate cell to a default level; for each candidate cell that transmits a positioning signal at a same transmit frequency as the serving cell, estimating an expected interference of the respective positioning signal for that candidate cell, comprising: determining whether a serving power level of the serving cell is known; if the power level of the serving cell is not known, estimating an expected interference for the candidate cell at multiple serving power levels associated with various locations within the serving cell; if the serving power level of the serving cell is known, setting the expected interference level for the candidate cell to below a serving power level of the serving cell; determining whether a serving power level of the serving cell is known; if the power level of the serving cell is not known, estimating an expected interference for the candidate cell at multiple serving power levels associated with various locations within the serving cell; if the serving power level of the serving cell is known, setting the expected interference level for the candidate cell to below a serving power level of the serving cell; selecting a subset of cells from the first set of candidate cells based on the estimated expected interference; generating assistance data that identifies the selected subset of cells; and sending the generated assistance data to the mobile device.