1. A method comprising: receiving a photoplethysmograph (PPG) signal; processing, with processing equipment, the PPG signal to generate at least one respiration information signal; generating, with the processing equipment, an autocorrelation sequence based on the at least one respiration information signal; identifying, with the processing equipment, a respiration peak of the autocorrelation sequence; generating, with the processing equipment, a composite peak based on the respiration peak and at least one previous respiration peak; and calculating, with the processing equipment, respiration information based at least in part on the composite peak.