□ Fiber optics is converging with other digital communications fields – cellular, satellite, digital subscriber line, etc. □ But techniques from existing fields are of limited help ▪ our carrier linewidth is much higher, 10-4 baud rate ▪ our impairments are of long duration, >100 symbols ▪ our data rate is much higher, 100Gb/s □ We must develop our own algorithms □ Existing field of estimation theory says how to develop algorithms ▪ best possible estimate is the optimal estimate ▪ other ad hoc estimate may be good enough, or not ▪ must compare ad hoc estimate with optimal estimate to find out how good it is