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Wireless Communication Basics

Which multiple-access scheme lets several users use the same frequency at the same time and distinguishes their signals by a different code for each user?

  1. AFDMA
  2. BTDMA
  3. CCDMA
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Answer: C. CDMA

FDMA (frequency-division multiple access) assigns each user a different frequency, and TDMA (time-division multiple access) divides the same frequency into short time frames (slots) and assigns each user a different time. CDMA (code-division multiple access) uses a different spreading code for each user, and the receiver separates signals sent at the same time on the same frequency by their codes. CDMA was used in third-generation (3G) mobile phones, and from 4G onward OFDMA, based on OFDM, has mainly been used.

  • A. This assigns a different frequency to each user.
  • B. This assigns a different time (slot) to each user.
  • C. Correct. Signals at the same frequency and time are separated by their codes.
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