Today, more than 8 billion devices are connected around the world, including medical devices, wearables, vehicles, and smart household and city technologies. Those devices are vulnerable to hacker attacks that locate, intercept, and overwrite the data, jamming signals. One method to protect the data is frequency hopping, which sends each data packet, containing thousands of individual bits, on a random, unique radio frequency (RF) channel, so hackers can't pin down any given packet. Hopping large packets, however, is just slow enough that hackers can still execute an attack.

The transmitter frequency hops data bits ultrafast to prevent signal jamming on wireless devices. The transmitter's design features bulk acoustic wave resonators (side boxes) that rapidly switch between radio frequency channels, sending data bits with each hop. A channel generator (top box) each microsecond selects the random channels to send bits. Two transmitters work in alternating paths (center boxes), so one receives channel selection while the other sends data to ensure ultrafast speeds. (MIT)

A transmitter was developed that frequency hops each individual 1 or 0 bit of a data packet every microsecond, which is fast enough to thwart hackers. The transmitter leverages frequency-agile devices called bulk acoustic wave (BAW) resonators, and rapidly switches between a range of RF channels, sending information for a data bit with each hop. In addition, a channel generator was incorporated that, each microsecond, selects the random channel to send each bit. A wireless protocol — different from the protocol used today — was developed to support the ultrafast frequency hopping.

The transmitter could help secure medical devices, such as insulin pumps and pacemakers, that could be attacked using selective jamming in which a hacker intercepts and corrupts data packets transmitting from a single device, but leaves all other nearby devices unscathed. Such targeted attacks are difficult to identify, as they're often mistaken for a poor wireless link and are difficult to combat with current packet-level frequency-hopping transmitters. With frequency hopping, a transmitter sends data on various channels, based on a predetermined sequence shared with the receiver. Packet-level frequency hopping sends one data packet at a time, on a single 1-megahertz channel, across a range of 80 channels. A packet takes about 612 microseconds for BLE-type transmitters to send on that channel. But attackers can locate the channel during the first 1 microsecond and then jam the packet.

To build the ultrafast frequency-hopping method, the researchers first replaced a crystal oscillator — which vibrates to create an electrical signal — with an oscillator based on a BAW resonator. The BAW resonators only cover about 4 to 5 megahertz of frequency channels, falling far short of the 80-megahertz range available in the 2.4-gigahertz band designated for wireless communication. Components were incorporated that divide an input frequency into multiple frequencies. An additional mixer component combines the divided frequencies with the BAW's radio frequencies to create a host of new radio frequencies that can span about 80 channels.

Most of the current vulnerability to signal jamming stems from the fact that transmitters hop slowly and dwell on a channel for several consecutive bits. Bit-level frequency hopping makes it very hard to detect and selectively jam the wireless link.

For more information, contact Abby Abazorius at This email address is being protected from spambots. You need JavaScript enabled to view it.; 617-253-2709.


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This article first appeared in the September, 2018 issue of Tech Briefs Magazine.

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