Non-coherent sequence estimation receiver for digital modulations

A non-coherent reception process of information symbol sequences obtained through phase and/or amplitude digital modulation of a carrier, transmitted on a communication channel affected by additive white gaussian noise, based on a use of the Viterbi algorithm applied to a trellis whose branches represent possible transitions among states defined by possible sub-sequences of information symbols of finite length, through which algorithm, each symbol interval, paths are selected on the trellis such that a cumulative path metric of transition metrics is maximum, said path metric being indicative of the likelihood degree existing among the symbols of the path associated with the same path metric and a sequence of transmitted symbols, wherein each of said transition metrics (λn(s)) is calculated through the following steps:

• a) non-coherent base band conversion of a received signal, subsequent filtering of the converted signal (r(t)) through a filter (FRIC) matched to a transmitted pulse and sampling at symbol frequency of the filtered signal, to obtain a sequence of complex samples ({xn});
• b) identification of a maximizing function corresponding to a known expression for maximum likelihood sequence estimation of a non-coherent receiver, as an expression of a general metric associated with said sequence of complex samples ({xn});
• c) expression of a partial metric, obtained by considering said general metric up to a current n-th sample of said sequence of complex samples ({xn});
• d) expression of an incremental metric, of unlimited memory, obtained from the difference between the expression of said partial metric at a current signalling interval and at an immediately preceding interval;
• e) truncation of the length of said unlimited memory at N-1 samples of said sequence of complex samples {xn} preceding the current sample, obtaining the analytical expression of said transition metrics (λn(s)) of said trellis, built on the basis of all the possible symbol subsequences having length N;
• f) calculation of said general metric through recurrent updating of said partial metric.

A non-coherent receiver of sequences of coded symbols ({cn}) obtained by amplitude and/or phase digital modulation of a carrier, transmitted on a communication channel affected by additive white gaussian noise, including:

• a non-coherent converter base band converting a received signal, followed by a filter (FRIC) matched to transmission pulse, followed in turn by a sampler (CAMP) sampling at symbol frequency, which obtains a sequence of complex samples {xn};
• a phase reconstruction memory (SHF1) in which N-1 samples (xn−1, . . . , xn−N+1) of said sequence of complex samples {xn} preceding a current sample (xn) are stored;
• a calculator calculating transition metrics (λn(s)) of a trellis sequential diagram, or trellis, whose branches represent possible transitions among states defined by possible subsequences of information symbols of finite length;
• a Viterbi processor adapted to select paths on the trellis such that a cumulative path metric of transition metrics is maximum, said path metric indicating the likelihood level existing among symbols ({{tilde over (c)}k}) of a relevant path and a sequence of transmitted symbols, wherein said calculator is subdivided into a plurality of identical sub-calculators, each being adapted to calculate a relevant transition metric (λn(s)), including:
• a memory for N code symbols ({tilde over (c)}n−1, . . . , {tilde over (c)}n−N+1) univocally associated with a relevant branch of the trellis;
• a phase reference constructor controlled by said N-1 samples (xn−1, . . . , xn−N+1) stored in said phase reconstruction memory (SHF1) and by N-1 said code symbols ({tilde over (c)}n−1, . . . , {tilde over (c)}n−N+1) corresponding to said samples;
• a first multiplier adapted to multiply said current sample (xn) by the conjugate of a code symbol ({tilde over (c)}n) corresponding to said current sample;
• a second multiplier adapted to multiply the result from said first multiplier by the conjugate of a reconstructed phase reference;
• an extraction unit extracting the real part of the result from said second multiplier;
• a modulus calculator calculating the modulus of said constructed phase reference;
• a normalizer dividing said real part by said modulus;
• a first adder adding the quotient result from said normalizer with the square modulus, changed in sign and divided by two, of said code symbol ({tilde over (c)}n) corresponding to said current sample (xn), to obtain a relevant transition metric (λn(s)).

A non-coherent receiver of symbol sequence ({an}), obtained by impressing M phase discrete values to a carrier transmitted on a communication channel affected by white gaussian noise, including:

• a non-coherent converter base band converting a received signal, followed by a filter (FRIC) matched to a transmission pulse, followed in turn by a sampler (CAMP) sampling at symbol frequency, that obtains a sequence of complex samples {xn};
• a phase reconstruction memory (SHF1) where N-1 samples (xn−1, . . . , xn−N+1) of said sequence of complex samples {xn} preceding a current sample (xn) are stored;
• a calculator calculating transition metrics (λn(s)) of a trellis whose branches represent possible transitions among states defined by possible subsequences of information symbols ({cn}) of finite length;
• a Viterbi processor adapted to select paths on the trellis such that a cumulative path metric of transition metrics is maximum, said path metric indicating the likelihood degree existing among the symbols ({{tilde over (c)}n}) of a relevant path and transmitted information symbols ({cn}), wherein said calculator of the transition metrics (λn(s)) is subdivided into a plurality of identical sub-calculators, each calculating a relevant transition metric (λn(s)), including:
• a memory for N code symbols ({tilde over (c)}n−1, . . . , {tilde over (c)}n−N+1) univocally associated with a relevant branch of the trellis;
• a phase reference constructor controlled by said N-1 samples (xn−1, . . . , xn−N+1) stored in said phase reconstruction memory (SHF1) and by N-1 said code symbols ({tilde over (c)}n−1, . . . , {tilde over (c)}n−N+1) corresponding to said samplers;
• a first multiplier multiplying said current sample (xn) by the conjugate of a code symbol ({tilde over (c)}n) corresponding to said current sample;
• a second multiplier multiplying the value resulting from said first multiplier by the conjugate of a constructed phase reference;
• an extractor extracting the real part of the value resulting from said second multiplier, obtaining the relevant transition metric (λn(s)).