1. A method of determining a current receiver state of a Global Navigation Satellite System (GNSS) receiver, the method comprising the steps of: receiving positioning signals from a plurality of satellites; generating a plurality of correlation grids from the received positioning signals, each correlation grid associated with a respective one of the plurality of satellites; estimating a probability distribution of the current receiver state from the plurality of correlation grids; and determining a maximum likelihood estimate of the current receiver state from the estimated probability distribution.