1. A method of receiving data transmitted in a MIMO system, wherein the data is transmitted from a transmitter over a MIMO channel as a transmit vector comprising a plurality of values, the method comprising: receiving the data as a receive vector comprising a plurality of values, the data being received over the MIMO channel at a receiver in which the MIMO channel is represented as a combination of a unitary matrix and a triangular matrix, wherein there is a relationship linking: (i) a function of the unitary matrix and the receive vector, and (ii) a multiplication of the triangular matrix and the transmit vector; determining a set of candidate vectors for representing the transmit vector by: for each of a plurality of constellation points, setting a particular value of a corresponding candidate vector to that constellation point and using the relationship to map the other values of the candidate vector to ones of the constellation points, thereby determining the set of candidate vectors in which the particular value within the respective candidate vectors is set to be the respective ones of the constellation points; and using the set of candidate vectors at the receiver to determine soft bits representing the plurality of values of the transmit vector.