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This Defense Intelligence Reference Document was prepared by the Defense Intelligence Agency under its Advanced Aerospace Weapon System Applications (AAWSA) program, is dated 6 April 2010 and is part of a series of advanced technology reports produced in FY 2009. It reviews proposed laboratory generators and detectors of high-frequency gravitational waves for communications. It favors an infrared-excited molecules transmitter and the Li-Baker detector, estimating about 1.9 million bits per second over 7,000 km through the Earth. It also discusses timing standards and interplanetary navigation uses.
UNCLASSIFIED/ ,SFIHl 8FFHil.tzk Wili &HkY Signal to noise ratios (SNR's) at the transmitter and at the receiver must be calculated to support a communications link design. i GW Sour Signal Noise Noise i EMtoGW/ Conversion Noise Predicted SNR Components at the Transmitter GW Xmit Signal ' EM Source Noise Link Loss 1/R2 Loss EM Receiver Noise Predicted SNR Components at the Receiver GW Signal Rcv'ed Figure 16. Conceptual SNR Fill Factors: Signal and Noise Components GW Antenna & Receiver Noise GWtoEM ~ Conversion Noise In the receiver all these same noise sources are duplicated in reverse, as shown on the right had side of Figure 16. Referring power now to the input, there will be a received power, and the created by the receiver that was not created at the transmitter, also GW to EM conversion noise, and EM receiver noise of the same types as received propagated transmit noise. Added to this will be GW noise admitted or outlined for transmitters. When all these noise components are referred the input of the receiver, the total NEP, which is the RSS of all the noise components, must be less than the signal present at the input of the receiver to qualify as a useful link. A few comments are in order regarding the "Q-factor" of the receiver. One way to increase Q is to narrow bandwidth. However, this has limited value. At some point, shrinking the bandwidth will shrink the signal received as quickly as the noise received, and some receiver noise components remain constant, resulting in a net drop in SNR. Another way to increase Q is to arbitrary increase sample times of the signal. This technique will, relatively speaking, shrink receiver end noise components as referred to the input of the receiver, but it will not have any impact of the noise generated at the transmitter. Therefore in this case the SNR will approach a constant. However, both of these approaches for improving sensitivity will have an adverse effect on the information capacity of the channel, which is important for a communication application. 3.1.2 Link Budget Considerations Now consider the signal side of the communication challenge. The central question is, How do we close the link? That is, how much signal is necessary at the input of a communication channel to have a useful signal at the other end? These questions may be answered, qualitatively in this case, by considering the terms of the expression in 23 UNCLASSIFIED/ /F&lil 8FFI&I.«1k W&liii Ollk¥
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Report, from the dia collection. The PDF is mirrored here; the original link is above. 57 pages are in the text index: search them above, or from the library's search.