Optimum transmitter/receiver design for a narrowband overlay in noncoordinated subscriber lines

Transmitter/receiver optimization for a generic narrowband overlay communication scenario is addressed. The overlay and existing legacy systems are assumed to occupy the same frequency bands for spectral efficiency, thus introducing cochannel interference; however, the new and legacy systems are assumed to be noncooperative, as is appropriate for some pragmatic scenarios. A composite figure of merit is used consisting of a weighted sum of the mean-squared error (MSE) of the (new) overlay system plus the excess MSE in the legacy system caused by the introduction of the overlay system. Necessary conditions on the transmitter and receiver that jointly optimize the above metric are derived. The effects of varying key parameters such as the loop length (range) and transmitter power are investigated via computational examples.