LAUSR

We analyze the performance of direct detection receivers with low-order bandpass filtering in terms of achievable rates. Such analysis is of interest in the context of millimeter-wave wireless systems as well as wired and wireless optical links, where low power and low cost are considered to be key requirements. By using a bandpass filter with asymmetric passband transfer function of low order ( $1/f$ roll-off rate) prior to the intensity detection device (a diode or photodiode), we show that the ideal Shannon data rate attainable with coherent receivers can still be asymptotically approached with simple filtering and direct detection. We also discuss practical aspects that partially limit this remarkable behavior, and show that gains are still possible compared with conventional direct detection.