AC4490 Hardware Integration Guide
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S
ECURITY
The AC4490 product family utilizes a Frequency Hopping Spread Spectrum (FHSS) technology which provides
the foundation for secure digital wireless communications. This section describes how spread spectrum
technology works and explains how an OEM can enable specific security features available in the AC4490.
Spread Spectrum History
Spread Spectrum dates back to World War II when a German scientist was granted a patent on a simple
frequency hopping continuous wave (CW) system. The allies also experimented with Spread Spectrum in
World War II. These early research and development efforts tried to provide countermeasures for radar,
navigation beacons, and communications. The U. S. military has used SS signals over satellites for at least 25
years.
How Spread Spectrum Works
SS radio communications has long been a favorite technology of the military because it resists jamming and is
difficult to intercept. This very same technology is now being widely used in the commercial, industrial, and
consumer markets.
The reason for this is because SS signals are distributed over a wide range of frequencies and then collected
onto their original frequency at the receiver, making them so inconspicuous as to be transparent. Just as they
are unlikely to be intercepted by a military opponent, they are also unlikely to interfere with other signals
intended for business and consumer users – even signals transmitted on the same frequencies.
Spread signals are intentionally made to be a much wider band than the information they are carrying and
they use special pseudo-noise codes to make them more noise-like. It is this characteristic that makes SS
signals difficult to detect, intercept, and demodulate. SS signals are hard to detect on narrowband equipment
because the signal's energy is spread over a much wider bandwidth. Further, SS signals are harder to jam
(interfere with) than narrowband signals and have a much lower probability to be intercepted, which is why
the military has used Spread Spectrum for so many years.
The spread of energy over a wide band makes SS signals less likely to interfere with narrowband
communications. Narrowband communications, conversely, cause little to no interference to SS systems
because the receiver effectively integrates the signal over a wide bandwidth to recover it.
Besides being hard to intercept and jam, spread spectrum signals are hard to exploit or imitate. Signal
exploitation is the ability of a non-network member to listen to and use information from the network
without being a valid network member or participant. Imitation is the act of falsely or maliciously introducing
false traffic or messages into a network.
SS signals are also more secure than narrowband radio communications. Thus SS signals can have any degree
of desired message privacy. Messages can also be encrypted to any level of desired secrecy. The very nature
of SS allows military or intelligence levels of privacy and security with minimal complexity. While these
characteristics may not be important to everyday business or consumer needs, they are important to
understand.
Frequency Hopping Spread Spectrum
A FHSS radio does what its name implies: it “hops” from frequency to frequency over a wide band. The
specific order in which frequencies are occupied is a function of a code sequence, and the rate of hopping
from one frequency to another is a function of the information rate.
