Method of rapidly controlling the frequency of a coherent radio receiver and apparatus for carrying out the method

DETAILED DESCRIPTION I claim: 1.
A method for controlling the frequency of a radio receiver wherein a channel subjected to interference is used to receive signal sequences including at least one synchronizing sequence and at least one data sequence, comprising the signal processing steps of: converting a received signal sequence to a baseband signal; sampling the baseband signal to obtain a plurality of signal points in a signal plan; correlating said synchronization sequence with a known synchronization sequence to thereby generate a plurality of adaptation signals; adapting a Viterbi algorithm having a desired number of states chosen according to prevailing interference conditions of the channel based on at least the adaptation signals, the number of adaptation signals corresponding to the number of states in the Viterbi algorithm; analyzing the signal points in the data sequence in a Viterbi analyzer according to said Viterbi algorithm to determine a bit sequence of the data sequence; fanning out a signal corresponding to one of the signal points at a particular time to obtain branch signal points, each of the branch signal points corresponding to a respective state of the Viterbi algorithm; phase shifting the branch signal point of each respective state through an angle associated with that respective state to obtain a respective corrected signal point; comparing the corrected signal point for each of the respective states with the adaptation signal corresponding with the respective state, said adaptation signal having signal points corresponding to the number of possible state transitions in the Viterbi algorithm; calculating distances and angular deviations between the corrected signal point and the signal points of the adaptation signal for each state; selecting a state transition based on the result of said step of calculating distances for each state; selecting one of said angular deviations, corresponding to said selected state transition, for each state separately; introducing the selected angular deviation into a control loop filter wherein a control loop filter algorithm determines a phase correction signal for each state; and phase shifting, based on the phase correction signals, the next incoming signal point in the data sequence or the adaptation signal separately for each state