1. A method of determining crosstalk for at least one first line in a communication system having a plurality of second lines, the method comprising: obtaining at least one pilot matrix representing a sequence of pilot signals; transmitting pilot signals across the plurality of second lines in accordance with the at least one pilot matrix; obtaining measurement vectors for the at least one first line on a plurality of subcarriers, in response to the transmitted pilot signals; determining a weighted vector, the weighted vector being a weighted combination of the measurement vectors; and determining a crosstalk coupling vector based on the determined weighted vector.