1. A method of determining a current receiver state of a Global Navigation Satellite System (GNSS) receiver, the method comprising: 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, and each correlation grid including a plurality of correlation values computed from a respective one of the positioning signals; applying a distortion function to the plurality of correlation values in each of the correlation grids to produce a plurality of converted correlation values, wherein each of the correlation grids is modified according to a signal strength of the respective received positioning signals; estimating a probability distribution of the current receiver state from the plurality of converted correlation values; and determining a maximum likelihood estimate of the current receiver state from the estimated probability distribution.