Completely satisfied Birthday Hedy Lamarr – Wi-Fi Visionary

Excessive Networks and I wish to want a cheerful 108th birthday to well-known expertise pioneer and actress Hedy Lamarr. If it had not been for Hedy Lamarr, we in all probability wouldn’t be utilizing Wi-Fi, Bluetooth, and different RF applied sciences that we take with no consideration in our on a regular basis lives. Hedy Lamar was born on November ninth, 1914 in Vienna. She was a well-known actress who starred in lots of Austrian, German, and Czech movies earlier than she fled Europe in 1937 and immigrated to america. Her profitable movie profession continued in Hollywood.

You would possibly say, “Critically, a Hollywood actress invented Wi-Fi?” The reply can be that Hedy Lamar was a lot greater than an actress, she was an inventor and expertise innovator.

Determine 1 – Know-how Pioneer – Hedy Lamarr

Frequency-hopping unfold spectrum (FHSS) radio expertise was initially patented on August 11, 1942, by actress Hedy Kiesler Markey (Hedy Lamarr) and composer George Antheil. It was initially designed to be a radio steering system for torpedoes, a objective for which it was by no means used. The thought of unfold spectrum was forward of its time. Throughout World Warfare II, Lamarr discovered that RF-controlled torpedoes of the United Sates Navy, may simply be jammed by the enemy and veered off-course. This made it harder to sink the enemy’s ships. So, Hedy Lamarr brilliantly got here up with the thought of a frequency-hopping RF steering system that might be very exhausting to jam. Along with George Antheil, they created a RF transmitter gadget that emulated player-piano capabilities… and frequency hopping was born. They filed a patent in 1942, nevertheless, the US authorities instantly labeled the expertise. FHSS was not utilized in time for World Warfare II.

Determine 2 – US Patent for Frequency-Hopping

It was not till 1957 that additional improvement on unfold spectrum occurred, and in 1962 frequency-hopping (FHSS) was used for the primary time between the US ships on the blockade of Cuba throughout the Cuban Missile Disaster. FHSS was declassified within the Nineteen Seventies. Sadly, neither inventor made any cash from their patent as a result of it expired earlier than the expertise was developed.

So, what does this need to do with Wi-Fi? What you might not know is that almost all of early Wi-Fi deployments used frequency-hopping expertise. Frequency-hopping unfold spectrum (FHSS) was one of many unique applied sciences outlined for RF communications utilizing the two.4 GHz ISM band for legacy Wi-Fi radios. The vast majority of legacy frequency-hopping Wi-Fi radios have been manufactured between 1997 and 1999.

Typically, the way in which FHSS works is that it transmits information through the use of a small frequency service area, then hops to a different small frequency service area and transmits information, then to a different frequency, and so forth, as illustrated in Determine 3. Extra particularly, FHSS transmits information through the use of a selected frequency for a set time period, often called the dwell time. When the dwell time expires, the system adjustments to a different frequency and begins to transmit on that frequency during the dwell time. Every time the dwell time is reached, the system adjustments to a different frequency and continues to transmit.

Determine 3 – Frequency-Hopping

FHSS radios use a predefined hopping sequence (additionally referred to as a hopping sample or hopping set) comprising a sequence of small service frequencies, or hops. As a substitute of transmitting on one set channel or finite frequency area, an FHSS radio transmits on a sequence of subchannels referred to as hops. Every time the hop sequence is accomplished, it’s repeated. Determine 3 exhibits a make-believe hopping sequence that consists of 5 hops.

The unique IEEE 802.11 normal mandated that every hop be 1 MHz in dimension. These particular person hops have been then organized in predefined sequences. In North America and most of Europe, the hopping sequences contained no less than 75 hops however not more than 79 hops. Different international locations had totally different necessities; for instance, France used 35 hops, whereas Spain and Japan used 23 hops in a sequence. For profitable transmissions to happen, all FHSS transmitters and receivers should be synchronized on the identical service hop on the identical time. Hopping sequences that may very well be configured on an FHSS entry level, and the hopping sequence info was delivered to shopper stations by way of an 802.11 beacon administration body.

Dwell time is an outlined period of time that the FHSS system transmits on a selected frequency earlier than it switches to the subsequent frequency within the hop set. The native regulatory physique sometimes limits the quantity of dwell time. For instance, the FCC specified a most dwell time of 400 milliseconds (ms) per service frequency throughout any 30-second time period. Typical dwell occasions are round 100 ms to 200 ms. The unique IEEE 802.11 normal specified {that a} hopping sequence encompass no less than 75 frequencies, 1 MHz extensive. As a result of the usual specified a most bandwidth of 79 MHz, the utmost variety of hops doable for a hop set can be 79. With an FHSS hop sequence consisting of 75 hops and a dwell time of 400 ms, it might take about 30 seconds to finish the hop sequence. After the hop sequence is full, it’s repeated. As a result of Wi-Fi FHSS transmissions leap inside a frequency vary of 79 MHz, a

narrowband sign or noise would disrupt solely a small vary of frequencies and would produce solely a minimal quantity of throughput loss. Reducing the dwell time can additional scale back the impact of interference. Conversely, as a result of the radio is transmitting information throughout the dwell time, the longer the dwell time, the better the throughput.

Hop time will not be a specified time period however relatively a measurement of the period of time it takes for the transmitter to vary from one frequency to a different. Hop time is often a reasonably small quantity, typically about 200 to 300 microseconds (μs). With typical dwell occasions of 100 to 200 milliseconds (ms), hop occasions of 200 to 300 μs are insignificant. Insignificant or not, the hop time is basically wasted time, or overhead, and is similar whatever the dwell time. The longer the dwell time, the much less typically the transmitter has to waste time hopping to a different frequency, leading to better throughput. If the dwell time is shorter, the transmitter has to hop extra ceaselessly, thus reducing throughput.

We not use frequency hopping for Wi-Fi, and we now have moved on to different RF applied sciences corresponding to orthogonal frequency-division a number of entry (OFDMA). Nevertheless, we use frequency-hopping for our Bluetooth units and different radio transmitters. Unnecessary, to say, had it not been for Hedy Lamarr, we’d not have Wi-Fi or Bluetooth!

If you need to be taught extra concerning the attention-grabbing historical past of frequency-hopping, search the Web for Lamarr and Antheil. Even higher, I extremely advocate you’re taking the time to observe an impressive movie documentary “Bombshell – the Hedy Lamarr Story”. It is a nice documentary concerning the fascinating lifetime of Hedy Lamarr.

It ought to be famous that, as with all applied sciences, nice minds fairly often suppose alike, but totally different paths typically result in innovation. For instance, Ellison Purington filed a patent utility in September 1940, a 12 months earlier than Lamarr and Antheil utilized for his or her patent. He proposed “wobbling” the frequency of a radio sign to scale back interference from different transmitters. I extremely advocate an American Scientist article, “Random Paths to Frequency Hopping” by Tony Rothman, which particulars contributions from many different researchers and scientists.


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