Data Sheet

AC4490
Datasheet
https://www.lairdconnect.com/
18
© Copyright 2022 Laird Connectivity
All Rights Reserved
Americas: [phone]
Europe: [phone]
Hong Kong: [phone]
8 SECURITY
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.
8.1.1 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.
8.1.2 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.
8.1.3 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.
8.1.4 AC4490 Security Features
As mentioned at the beginning of this section, the AC4490 uses FHSS technology. In addition, Laird has implemented three
levels of security in the AC4490. All three levels of security are associated with their own EEPROM parameter that can
programmed for permanent operation or be changed during system operation in volatile memory. The first two levels of
security must be configured to establish a network of transceivers and are defined as the Channel Number and System ID.
The Channel Number represents a specific hopping sequence and provides physical separation between collocated networks.
Thus, all transceivers in a network must be programmed to the same channel number. There are a total of 48 channel
numbers.
System ID is similar to a password character or network number and makes network eavesdropping more difficult. A receiving
radio does not go in range of or communicate with another radio on a different system ID. There are a total of 256 system ID
values.