OFDM and OFDMA Signal in Frequency Domain

By Vikas Bagwe -
OFDM and OFDMA Signal in Frequency Domain

The sub-carriers are divided into several types
  • Data Sub-carriers
    • - Use QPSK, 16-QAM, 64-QAM modulation to transport data bits 
  • Pilot Sub-carriers
    • - Data-free symbols used to maintain optimal operation of the receiver 
  • Guard Sub-carriers
    • - Off, no power is generated at these frequencies 
  • DC Sub-carrier
    • - Off to support direct-conversion receivers 
Sub-carrier Spacing (1/T) is the reciprocal of the modulation symbol time (T)

OFDM - All sub-carriers belong to a single user for some period of time. Multiple users are accommodated at different times.
OFDMA - Users share the sub-carriers with a bandwidth dependent on the data service in use.
Each color represents a different user.




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