Embodiments of the invention provide a decoder for decoding a signal received through a transmission channel in a communication system, said signal comprising a vector of information symbols, said transmission channel being represented by a channel matrix, wherein the decoder comprises: an initial radius determination unit (307) configured to determine an initial radius; a symbol estimation unit (309) configured to iteratively determine a current radius to search a lattice point inside a current spherical region defined by said current radius, said current radius being initially set to said initial radius, said symbol estimation unit (309) being configured, for each lattice point found in said current spherical region, to store said lattice point in association with a metric, said symbol estimation unit (309) being further configured to update said current radius using a linear function, said linear function having a slope parameter strictly inferior to one, The decoder being configured to determine at least one estimate of said vector of information symbols from at least one of the lattice points found by the symbol estimation unit (309).