1. A method of determining a position estimate of a mobile device with respect to a user, comprising: receiving signals from at least one motion sensor in the mobile device; analyzing the signals from the at least one motion sensor in the mobile device to generate a plurality of proposed positions with respect to the user with associated likelihoods; receiving signals from at least one light sensor in the mobile device; processing the signals from the at least one light sensor in the mobile device to produce a list of candidate positions; eliminating at least one of the plurality of proposed positions using the list of candidate positions; and determining the position estimate for the mobile device with respect to the user based on remaining proposed positions and associated likelihoods.