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Energous Disrupted: WattUp Interferes With Wi-Fi Signals, WattUp Mini Approval Too Late


WattUp interferes with Wi-Fi transmissions.

WattUp charging will completely block a Wi-Fi signal for the device being charged.

WattUp will cause problems and reduction in Wi-Fi data rates for surrounding devices.

FCC approval for WattUp Mini comes too late to generate revenue in 2016.

In my previous article, I analyzed the Energous (NASDAQ:WATT) beam forming technology and the challenges that Energous faces in obtaining FCC approval for its high power wireless charging technology. Specifically, I concluded that it is not possible to obtain 4W power delivered over a distance of six feet within the established safety rules governing the electromagnetic radiation. I also pointed out that the high power WattUp transmitter would potentially interfere with Wi-Fi signals and be in effect a "jammer" that blocks the wireless communication.

The article prompted Energous management to hold an emergency conference call to "provide a company update and address misinformation about the company's technology and direction." During the call, Energous CTO Michael Leabman dismissed my concern regarding interference. According to Leabman, Energous will use frequencies at the edge of the ISM band thus avoiding the interference problems.

In this article, I will take a closer look at the interference issues. I show that a high-power WattUp array would effectively block a Wi-Fi signal that operates in the same ISM frequency band. Moreover, even the low power WattUp Mini will interfere with Wi-Fi transmissions. Next, I will analyze the impact of recent FCC approval for WattUp Mini. Finally, I will update the company's cash burn situation.

Basics of interference

To understand interference, think about pressing two adjacent piano keys simultaneously: Normally, you will hear two tones, but if one of the keys is broken and really quiet, you will hear only the loud note. The quiet note, still audible alone, will be drowned by the interfering strong note.

Same happens in communication systems. The signal from a Wi-Fi base station is very weak by the time it arrives to the receiving Wi-Fi enabled mobile device. If there's a strong signal nearby, it will drown the Wi-Fi signal. In fact, the mobile device receiving the Wi-Fi transmission has to be quiet while receiving the transmission. A Wi-Fi device cannot transmit and receive at the same time. The situation is comparable to listening your friend whisper: You can hear your friend unless you shout at the same time. To avoid this issue, the Wi-Fi standard uses time division duplexing meaning the base station and mobile device take turns in transmitting and receiving.

Problems arise when there are other systems nearby, for example, another Wi-Fi base station or even a weak transmitter such as a Bluetooth device. These signals are not time-synchronized and may cause interference:

"Microwave ovens operating within 10 feet or so of an access point or radio-equipped user will generally just cause 802.11b performance to drop. Bluetooth enabled devices, such as laptops and PDAs, also will cause performance degradations if operating in close proximately to 802.11 stations, especially if the 802.11 station is relatively far (i.e., low signal levels) from the station that it's communicating with."

This happens even though a Bluetooth transmitter transmits only 2.5 mW (about 100 times less than WattUp Mini transmitter).

WattUp transmitter operation frequency is 5.86 GHz. This is just outside the Wi-Fi operation band as shown on Figure 1. According to Energous CTO Michael Leabman, placing the WattUp frequency on the ISM channel edge avoids the interference problems. Unfortunately, this is not correct. I will show that placing a WattUp signal outside Wi-Fi channels reduces but does not eliminate the interference issues.

Figure 1. WattUp signal relative to Wi-Fi channels.

To estimate the impact of WattUp transmitters on Wi-Fi, we have two rules of thumb: