http://en.wikibooks.org/wiki/Signals_and_Systems/Time_Domain_Analysis
http://web.eecs.umich.edu/~fessler/course/451/l/pdf/c2.pdf
http://www.ece.jhu.edu/~cooper/courses/214/signalsandsystemsnotes.pdf
http://www3.nd.edu/~mhaenggi/ee344-04/overview.html
http://en.wikipedia.org/wiki/LTI_system_theory
http://maxim.ece.illinois.edu/teaching/fall08/lec3.pdf
http://www.ee.ucr.edu/~yhua/ee141/lecture2.pdf
http://web.eecs.umich.edu/~aey/eecs206/lectures/lti2.pdf
http://www.engineering.uiowa.edu/~systems/Exams/review.pdf
http://tintoretto.ucsd.edu/jorge/teaching/mae143a/lectures/3timedomainanalysis.pdf
http://www.cis.hut.fi/Opinnot/T-61.140/Luennot/Ch2.pdf
http://www.eecg.toronto.edu/~ahouse/mirror/engi7824/course_notes_7824_part7.pdf