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Wireless Communication Basics

Which is a characteristic of NFC, used in transit IC cards and contactless smartphone payments?

  1. AIt uses radio waves in the 2.4 GHz band and can communicate with devices several tens of meters away
  2. BThe card has a built-in battery and uses its power to emit strong radio waves
  3. CIt uses 13.56 MHz electromagnetic induction with a range of a few centimeters to about 10 cm, and the card runs on power received from the reader's magnetic field
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Answer: C. It uses 13.56 MHz electromagnetic induction with a range of a few centimeters to about 10 cm, and the card runs on power received from the reader's magnetic field

NFC is short-range wireless communication using electromagnetic induction by a 13.56 MHz magnetic field. The coil in the card receives power from the magnetic field produced by the reader, so the card needs no battery. The range is short, a few centimeters to about 10 cm, so cards are hard to read unintentionally from a distance and are used with a "tap" action. FeliCa, used in Japanese transit IC cards and elsewhere, also uses the same 13.56 MHz.

  • A. These are characteristics of wireless LAN and Bluetooth.
  • B. NFC cards have no battery and receive power from the reader's magnetic field.
  • C. Correct. It communicates at close range by 13.56 MHz electromagnetic induction.
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More Wireless Communication Basics questions

  1. Which is the minimum number of satellites a GNSS (global navigation satellite system) receiver such as GPS needs to determine its three-dimensional position while also solving for its own clock error?
  2. In a radio receiver, which circuit is placed right after the antenna and amplifies the weak received signal while adding as little of its own noise as possible?
  3. In a receiver, which circuit multiplies the received signal by the signal of the local oscillator (LO) to produce a signal at the difference (or sum) of their frequencies, thereby converting frequency?
  4. A superheterodyne receiver receives a 900 MHz signal by setting its local oscillator (LO) to 800 MHz and converting to a 100 MHz intermediate frequency (IF). Which is the image frequency that would also be converted to the same 100 MHz IF?
  5. Which describes a direct-conversion receiver, which sets the local oscillator (LO) to the same frequency as the received signal and converts directly to baseband without an intermediate frequency, compared with a superheterodyne receiver?