What are the advantages of FHSS?
FHSS offers four main advantages over a fixed-frequency transmission: FHSS signals are highly resistant to narrowband interference because the signal hops to a different frequency band. Signals are difficult to intercept if the frequency-hopping pattern is not known.
Why is the FHSS signal so resistant to interference?
FHSS signals are highly resistant to narrowband interference because the signal hops to a different frequency band. Signals are difficult to intercept if the frequency-hopping pattern is not known. Jamming is also difficult if the pattern is unknown; the signal can be jammed only for a single hopping period if the spreading sequence is unknown.
What is the difference between FHSS and DSS?
In the US, FCC part 15 on unlicensed spread spectrum systems in the 902–928 MHz and 2.4 GHz bands permits more power than is allowed for non-spread-spectrum systems. Both FHSS and direct-sequence spread-spectrum (DSSS) systems can transmit at 1 watt, a thousand-fold increase from the 1 milliwatt limit on non-spread-spectrum systems.
What is FHSS transmission?
FHSS transmissions can share a frequency band with many types of conventional transmissions with minimal mutual interference. FHSS signals add minimal interference to narrowband communications, and vice versa.
What is FHSS in radio?
Frequency-hopping spread spectrum ( FHSS) is a method of transmitting radio signals by rapidly changing the carrier frequency among many distinct frequencies occupying a large spectral band. The changes are controlled by a code known to both transmitter and receiver. FHSS is used to avoid interference, to prevent eavesdropping, and to enable code-division multiple access (CDMA) communications.
What band is FHSS?
In the US, since the Federal Communications Commission (FCC) amended rules to allow FHSS systems in the unregulated 2.4 GHz band, many consumer devices in that band have employed various FHSS modes. eFCC CFR 47 part 15.247 covers the regulations in the US for 902–928 MHz, 2400–2483.5 MHz, and 5725–5850 MHz bands, and the requirements for frequency hopping
What is adaptive frequency hopping?
Adaptive frequency-hopping spread spectrum ( AFH) as used in Bluetooth improves resistance to radio frequency interference by avoiding crowded frequencies in the hopping sequence. This sort of adaptive transmission is easier to implement with FHSS than with DSSS .
What was the secret communication system?
Patent 2,292,387 for their "Secret Communications System" an early version of frequency hopping using a piano-roll to change among 88 frequencies to make radio-guided torpedoes harder for enemies to detect or to jam, it was rejected by the US Navy then seized as 'alien property' in 1942 (Lamarr was Austrian) but filed away with no record of a working device being produced. Lamarr and Antheil's idea was rediscovered in the 1950s during patent searches when private companies were independently developing direct-sequence Code Division Multiple Access, a non-frequency-hopping form of spread-spectrum, and has been cited numerous times since. In 1957, engineers at Sylvania Electronic Systems Division adopted the patented concept, combined with the recently invented transistor. In 1962, the US Navy finally utilised the technology during the Cuban Missile Crisis; Lamarr and Antheil's patent had since expired.
Why is FHSS signal resistant to interference?
FHSS offers three main advantages over a fixed-frequency transmission: FHSS signals are highly resistant to narrowband interference because the signal hops to a different frequency band.
How many watts can a FHSS transmit?
Both FHSS and direct-sequence spread-spectrum (DSSS) systems can transmit at 1 watt, a thousand-fold increase from the 1 milliwatt limit on non-spread-spectrum systems. The Federal Communications Commission (FCC) also prescribes a minimum number of frequency channels and a maximum dwell time for each channel.
What is FHSS in radio?
In FHSS, the transmitter hops between available narrowband frequencies within a specified broad channel in a pseudo-random sequence known to both sender and receiver.
Why is FHSS used?
Because no channel is used for long and the odds of any other transmitter being on the same channel at the same time are low, FHSS is often used as a method to allow multiple transmitter and receiver pairs to operate in the same space on the same broad channel at the same time.
How is frequency-hopping spread spectrum regulated?
Governments regulate the broadcast spectrum and often dictate some aspects of spread- spectrum communications.
What are the variations of FHSS?
Additional spread spectrum techniques and variations of FHSS are commonly used today. A few examples follow.
Why is FHSS important?
FHSS is useful to counter eavesdropping, as well as to obstruct the frequency jamming of telecommunications and to enable code-division multiple access communications. It can also minimize the effects of unintentional interference.
What is chirp modulation?
Chirp modulation is another form of frequency hopping that simply scans all available frequencies in consecutive order.
What band is FHSS?
In the 2000s, the U.S. Federal Communications Commission ( FCC) allowed FHSS systems to operate in the unregulated 2.4 gigahertz band in order to support the use of FHSS in 802.11b, 802.11g and 802.11n Wi-Fi deployments.
