Patent ID: 8117522

Claim:
A sphere decoder for simultaneously detecting a plurality of symbols from a signal received through a communication channel, the sphere decoder comprising: an initial estimation unit for obtaining an initial estimate of a transmitted symbol vector from the received signal; an initial radius setting unit for calculating a Euclidean distance between a lattice vector corresponding to the initial estimate of the symbol vector and the received signal, and for setting the Euclidean distance as an initial radius; an initial radius reduction unit for further reducing the initial radius before the lattice vectors are searched by the lattice search unit; a lattice search unit for searching a set of candidate lattice vectors included inside a hypersphere with the initial radius, centered at a received signal vector; and a maximum likelihood estimate determination unit for selecting a lattice vector having a minimum Euclidean distance from the set of candidate lattice vectors, wherein the initial radius reduction unit: a) selects one dimension; b) searches all candidate lattice vectors except for a current estimate in the selected dimension, and obtains the corresponding minimum Euclidean distance and a lattice vector corresponding to the minimum Euclidean distance; c) compares the minimum Euclidean distance and a current initial radius; d) updates the current initial radius by the Euclidean distance and updates a current lattice point estimate by a lattice point estimate corresponding to the updated initial radius when the minimum Euclidean distance is smaller than the current initial radius; and e) repeatedly performs b) to d) by changing the dimension according to a particular order.