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OFDMA

By Vikas Bagwe
OFDMA
TDD Frame Structure


OFDMA is two-dimensional with users sharing in both the time and frequency domains.
This allows scheduling and optimum use of finite spectrum.


Each user is assigned a burst area that has dimensions of sub-channels and symbols.


Key Elements
  • Preamble is broadcast for one symbol period and allows the user devices to acquire the system and synchronize. A known PN code is transmitted.
  • FCH reports the length of the DL-Map.
  • DL-Map contains bandwidth allocation for users and location of the UL-Map.
  • UL-Map contains bandwidth allocation of the UL for the next frame.
  • Both maps contain burst data regions, modulation, and coding type for the user.
  • Allocated regions in UL are available for random access, CQI, and ACKs.
  • Transmit Recieve Transition Gap (TTG) and Receiver Transmit Transition Gap (RTG) are guard times between the transmit and receiver portions of the frame.
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