TEMPEST Communications

Notes on engineering design for meeting CRYPTO-TEMPEST requirements in electronic equipment


Jamproof is like waterproof: it works to a certain depth of jam

The need for jamproof radio is primarily its error-correction/detection capability, its data-integrity against spurious interference-interruptions, its data-rate maintenance [and sequentiality currency], secondarily its survivability under duress of prolonged intense interference from concurrent transmissions or 'jam', and thirdly its stealth low-detectability - and thusly in summary, its convenient readiness for the occasions. Any case where mathematically precise information must be transmitted, jamproof suffices: geo/spatial-coordinates, flight-paths, machine-telemetry, security-confirmations, computer-programs, database-indices, ... operational coordination ... generally digitized-parameters, and special applications in strong radio-noise environments.

As the Earth community becomes increasingly internationally intertwined, meaning globally self-entwined, the occasions will arise for proof-of-technology - in the customer-safety business market, for example, the jumbo-jet travel industry, both in normal operation with multi-lingual consistency requirements, and the under-duress situtations of reduced flight-envelope margins. Likewise as we develop space-exploration, we'll need secure unambiguous communications of scientific requirements and discoveries.

Digital communications presently consists of digital or digitized data transmitted by R-F Radio-Frequency e-m electro-magnetic emissions from antenna wires and horns. Eventually we'll advance to UHF neutrino communications. [We need 'only' determine the shape of the UHF neutrino: most likely the unipolar-end-transmissions of ordinary electronic UHF antenna wires - optimized for UHF neutrino generation preference: the regular antenna emits RF transversal-wave 'photon's from its broadside; the end emits point-symmetric RF longitudinal-wave 'neutrino's inefficiently - and therefor inefficiently detected end-on, as is the case of NDE Neutrino Detection Equipments of higher energies, 7MeV, as from supernovae, whereas UHF 'neutrino's are about 7meV, micro]

Jamproof communications tends generally to include mathematically code-encrypted digital-data, and [frequency] spread-spectrum antenna transmission techniques: CDMA Code-Division Multiple-Access and frequency-hopped MFSK Multiple-Frequency-Shift-Keying, FH-MFSK - in either case the transmitted signal takes-up manifold orders [thousands or millions times] more bandwidth [spectrum] than is needed for the signal-data itself:

Both techniques utilize power efficiently by transmitting constant-amplitude signals - this also helps in jam-rejection signal-processing. Military applications go one step further to [stealth] hide the signal by sending only what might be interpreted received as background noise-level, were it not decrypted - the amount of signal-energy added to the spread-spectrum space is kept to one usual-valued-energy sample per any point within that space: whence FH is military-preferred over CDMA [which has broader instantaneous distribution].

Both CDMA and FH-MFSK are useful for multi-channel [overlap] communications: CDMA codes can be chosen orthogonally to deliberately minimize cross-channel interference, while maintaining general jamproofing. FH-MFSK likewise can be programmed to hop away from other channels within the same spread-spectrum. And both are intrinsically transmission-encrypted. [FH-MFSK can also be programmed for multiple channels taking interleaved alternate hops - this helps the acquisition algorithm by allowing it longer dwell on each time-base, and so resolving fractional time-bases directly, rather than retrying each fractional offset - this can also facilitate cross-communications between near-vicinity transceivers: but high-switching rates between receiver and transmitter are not common technology yet, and the military environment requires separate transmit and receive bands to avert sabotage-opportunities in altered force-terminal equipments]

Jam is any noise not distinguished by the designated receiver of the desired signal, to the extent that it is not: background radiation [including SNR SuperNovae Remnants and radio-stars, even our daytime sun and solar-flares], untuned sources [even power-plant arcking] and unscheduled test sources [similarly formatted decoys for military stealth], signal-synchronization hand-over between satellite/cells operations-servers, multi-path reflections [on other planes, metal-structured buildings, long wire fences, rain-soaked hillside salted ore-deposits, etc.] contribute to various strategy requirements. The most troublesome is the reflection jam, as it is most-like the desired original signal - indeed it is but a delayed copy which may be further modulated by the multi-path mechanism: it may be far stronger that the original [as the curvature of a cattle/sheep barb-wire fence strung along a hill-top may focus directed lobes of reflected signal energy] and it may change signal-carrier-phase, and it may drop-out altogether ... because it is delayed it may drag the receiver off the desired original synchronization, far enough to where there is no original [synchronization] - then the drop-out bereaves the receiver altogether.

The spread-spectrum signal is acquired by testing each possible time-and-frequency base, from slightly ahead and scanning back to slightly behind - and usually with the full code-modulation detected [attempted] to maximize jam-rejection at the lowest signal-to-noise expectancy [where it must yet acquire per specification]. Because CDMA is finely time-decimated, and FH-MFSK is finely frequency-decimated, it is operationally preferrable to stage the acquisition bandwidth [and reception] from LDR Low-Data-Rate [of simple 'telnet'like signalling capacity] thence to finely-adjusted MDR and HDR Medium- and High-Data-Rates [capable of speech and images, even video]. But the longer temporal dwell of the LDR synchronization also allows more of that dragging delaying reflection jam, and increases subsequent fine-tuning acquisition processing - the dwell must be shortened as soon as acquired - MDR and LDR must acquired to [also] hop faster-still - and sought well-outside the initial LDR synchronization. [CDMA is already finely time-decimated, but typically not by millions of code bases, and not as narrowly tuned against noise]

Grand-Admiral Petry
'Majestic Service in a Solar System'
Nuclear Emergency Management

© 1997 GrandAdmiralPetry@Lanthus.net