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Wireless Communication Basics

In 64QAM, which is the number of bits that can be sent per symbol?

  1. A6 bits
  2. B8 bits
  3. C64 bits
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Answer: A. 6 bits

In M-ary modulation, each symbol sends one of M possible signal points, so the number of bits it carries is log₂ M. 64QAM has 64 signal points, so it carries log₂ 64 = 6 bits. The 64 points form a grid with 8 levels on each of the in-phase (I) and quadrature (Q) axes. Similarly, 16QAM carries 4 bits and 256QAM carries 8 bits.

  • A. Correct. 2⁶ = 64, so it is 6 bits.
  • B. This is the number of levels (8) on one of the I or Q axes. 256QAM is the scheme that sends 8 bits per symbol.
  • C. This is the number of signal points itself. The number of bits is the base-2 logarithm of the number of points.
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More Wireless Communication Basics questions

  1. With 16QAM at a symbol rate of 5 M symbols per second (5 Mbaud), which is the bit rate?
  2. Which is a general property when the modulation is changed from 16QAM to 256QAM at the same symbol rate?
  3. For a channel with a bandwidth of 20 MHz and an S/N (signal-to-noise ratio) of 30 dB, which is closest to the channel capacity (the theoretical upper limit on the error-free transmission rate) given by Shannon's theorem?
  4. Which describes OFDM (orthogonal frequency-division multiplexing)?
  5. In OFDM, which is the main purpose of the cyclic prefix (CP), formed by copying part of the end of each symbol to its beginning?