TRANSMITTED-REFERENCE SCATTER COMMUNICATIONS. VOLUME II - APPENDIXES.
Spilker, J. J., Jr., Luby, D. D., L. Schuchman · Defense Technical Information Center (DTIC) · 1966
The use of transmitted reference signals for information transmission over channels having time or frequency dispersion has been discussed recently by several authors. In the transmitted reference system, one transmits a reference carrier signal, Sr, over a random or unknown channel and a modulated version, Sm, of that reference carrier over a similar (ideally identical) channel. The basic objective here, is to have the reference carrier received at the channel output, Yr, serve as an exact reference, or pilot tone, for the received modulated carrier, Ym. An implicit or explicit assumption is usually made that the reference and modulated carriers are offset from one another in frequency and/or time in order that they can be separated at the receiver. If the received reference and modulated carriers occupy nonoverlapping time-frequency space, or otherwise orthogonal spaces B-8, they can be separated perfectly at the receiver. Thus, the reference and modulated carriers do not, in fact, sound identical channels. The objective of this note is to determine, for several example channels, how much the correspondence between reference and modulated carriers is degraded by an arbitrary offset in time-frequency (T-F) space. The amount of this time-frequency offset is shown to determine the effective signal energy of the transmitted signals. (Author)