Efficient modified viterbi decoder
AssigneeHarris Corporation
InventorsClifford Hessel, Prabodh Varshney
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Abstract
A decoder for Trellis encoded modulated signals. The decoder utilizes a modified Viterbi algorithm. The algorithm includes the use of two look-up tables. The look-up tables contain information regarding the current symbol, previous symbol and previous to previous symbol which can bring the trellis to the given state. The symbol information contained within these tables is indexed into the appropriate branch metric values and the path metric for the Viterbi algorithm is computed. The tables can be used effectively with the branch metric in either polar or rectangular form.
Claims16
A method of decoding a TCM signal using a Viterbi decoder comprising the steps of:
- generating a first table indexed by a plurality of trellis states, each state having a current symbol and a previous symbol in the trellis necessary to bring the trellis to such state;
- generating a second table indexed by a plurality of trellis states, each state having a current symbol, a previous symbol, and a symbol previous to the previous symbol in the trellis necessary to bring the trellis to such state;
- and,
- calculating the path metric for the received TCM signal by indexing the values of the first and second tables into branch metric equations to thereby decode the received TCM signal.
In a method for decoding a TCM signal using a Viterbi decoder the improvement comprising the use of lookup tables to reduce the computational complexity of the algorithm, wherein the TCM signal includes LSBs and MSBs and the improvement further comprises removing the effects of the LSBs prior to making a decision on the MSBs.
A method for decoding a trellis encoded modulated signal in a radio frequency receiver comprising the steps of:
- (a) generating a data table wherein the step of generating a data table comprises the steps of:
- generating a first table indexed by a plurality of trellis states, each state having a current symbol and a previous symbol in the trellis necessary to bring the trellis to the state;
- and generating a second table indexed by a plurality of trellis states, each state having a current symbol, a previous symbol, and a symbol previous to the previous symbol in the trellis necessary to bring the trellis to the state;
- (b) storing the data table in the receiver:
- (c) indexing the symbol information into the results of a branch metric computation of a Viterbi algorithm wherein the algorithm is resident in a field programmable gate array in the receiver;
- and
- (d) computing the path metric for the Viterbi algorithm to thereby decode the signal.
A receiver for a trellis modulated signal comprising:
- a decoder comprising:
- a field programmable gate array, wherein a Viterbi algorithm is resident on said array;
- a ROM, wherein said ROM includes look-up tables that contain information regarding a current symbol, a previous symbol and a previous to previous symbol necessary to bring the trellis to a given state.
Dependencies are inferred from the claim text.