1. A method of channel estimation and detection at a receiver, comprising the steps, carried out for each of sample instants, of: receiving over a communication channel a digital sample which is dependent on one or more of the most recently transmitted data symbols of a series of transmitted data symbols, expanding each of a first number k of stored first vectors, each representing a different possible received sequence of a second number n of data symbols by means of n components, into a third number m of second vectors by adding for each of possible second vectors a further component representing a respective combination of data symbols which could be received at that sample instant and selecting as the m second vectors those of the possible vectors which represent the data-symbol sequences most likely to have been received as derived from the received sample and one of a fourth number j of stored predictions of the channel for the current sample instant, determining costs, of a type where a lower cost is indicative of a higher likelihood that sequences are correct, associated with each respective second vector, selecting that combination of data symbols represented by one component of a second vector having a relatively low cost as the detected data symbol, selecting k second vectors with relatively low costs, and storing the selected vectors and their associated costs, and forming and storing j new predictions of the channel for the next sample instant, the new predictions representing the attenuation and phase change introduced into the signal by the channel, each prediction using the current sample, and a respective one of the j stored predictions of the channel for the current sample instant.