An apparatus for estimating the location of a remote node, the apparatus comprising: an antenna array comprising a plurality of elements in a fixed spatial arrangement, at least one element being a transmitting element configured to transmit a first wireless signal to the remote node, and at least two elements being receiving elements configured to receive a second wireless signal transmitted by the remote node in response to the first wireless signal, wherein the first wireless signal is used to measure a first time of arrival between the apparatus and the remote node and the second wireless signal is used to measure a second time of arrival between the remote node and the apparatus; and a signal processing unit connected to the antenna array, the signal processing unit being configured to: estimate a plurality of round trip distances using the first time of arrival and second time of arrival based on the first and second wireless signals, each round trip distance being from the transmitting element to the remote node and back to the receiving element; and estimate the location of the remote node using the round trip distance estimates; wherein each receiving element is configured to measure the phase of the second wireless signal relative to a common reference phase, and the signal processing unit is configured to estimate the location of the remote node using the phase measurements as well as the round trip distance estimates. an antenna array comprising a plurality of elements in a fixed spatial arrangement, at least one element being a transmitting element configured to transmit a first wireless signal to the remote node, and at least two elements being receiving elements configured to receive a second wireless signal transmitted by the remote node in response to the first wireless signal, wherein the first wireless signal is used to measure a first time of arrival between the apparatus and the remote node and the second wireless signal is used to measure a second time of arrival between the remote node and the apparatus; and a signal processing unit connected to the antenna array, the signal processing unit being configured to: estimate a plurality of round trip distances using the first time of arrival and second time of arrival based on the first and second wireless signals, each round trip distance being from the transmitting element to the remote node and back to the receiving element; and estimate the location of the remote node using the round trip distance estimates; wherein each receiving element is configured to measure the phase of the second wireless signal relative to a common reference phase, and the signal processing unit is configured to estimate the location of the remote node using the phase measurements as well as the round trip distance estimates. estimate a plurality of round trip distances using the first time of arrival and second time of arrival based on the first and second wireless signals, each round trip distance being from the transmitting element to the remote node and back to the receiving element; and estimate the location of the remote node using the round trip distance estimates; wherein each receiving element is configured to measure the phase of the second wireless signal relative to a common reference phase, and the signal processing unit is configured to estimate the location of the remote node using the phase measurements as well as the round trip distance estimates.