Citation
Abstract
A class of receivers called “conditionally nulling receivers” is defined for quantum noise limited optical communications. These receivers have the ability to decide at each moment in time whether or not to coherently combine a predetermined local oscillator field with the received optical field, prior to performing an energy measurement (photodetection) on the combined field. Conditionally nulling receivers are applicable to pulse position modulation (PPM) and related modulation schemes, which have the property that, at each moment in time, the transmitted signal is in one of only two states, ON or OFF. The local oscillator field which may or may not be added by the receiver is an exact replica of the negative of the received ON field; hence, the receiver can exactly null the ON signal if the ON signal is present and the receiver chooses to use the local field. An ideal conditionally nulling receiver achieves very nearly the same error probability (within a multiplicative factor varying from I to 2.15) as the optimum quantum measurement for quantum noise limited detection of M-ary PPM signals, In contrast, other known receiving methods, such as direct, heterodyne, and homodyne detection, are exponentially suboptimum. The performance of receivers which are only approximately conditionally nulling receivers, due to imperfect nulling, is also investigated for the quantum limited PPM detection problem. Imperfect nulling is assumed to be caused by a phase discrepancy between the received ON field and the local nulling field. The performance of the imperfect conditionally nulling receiver is found to degrade rapidly to that o fa direct detection receiver in the presence of nonzero phase error.
Details
- Volume
- 42-72
- Published
- February 15, 1983
- Pages
- 30–42
- File Size
- 914.5 KB