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OFDM transmitter

Short answer

The OFDM transmitter codes, maps bits to QAM symbols, and assigns N symbols to orthogonal subcarriers spaced by 1/Ts. An IFFT generates the time-domain symbol, a cyclic prefix longer than delay spread is added, then DAC and up-conversion produce the RF signal. This replaces many oscillators.

Explain OFDM transmitter in brief.

The OFDM transmitter divides a high-rate data stream into N low-rate streams and places them on N orthogonal subcarriers (spacing Δf = 1/T_s) using an IFFT, then adds a cyclic prefix to fight multipath.

bits->[FEC +]->[QAM  ]->[S/P]->[IFFT ]->[P/S]
      [intlv]  [map  ]          [N-pt ]    |
                                            v
RF <-[Up-conv + PA]<-[DAC]<-[Add cyclic prefix]
  1. Coding and interleaving – add error-correction redundancy and spread bits across subcarriers.
  2. Symbol mapping – map bits to QPSK/16-QAM/64-QAM symbols X_k.
  3. Serial-to-parallel – N symbols assigned to N subcarriers; pilots inserted.
  4. IFFT – x(n) = (1/N) Σ X_k e^(j2πkn/N) modulates all subcarriers at once into one time-domain OFDM symbol.
  5. Parallel-to-serial and cyclic prefix – the last few samples are copied to the front; CP longer than the delay spread prevents ISI.
  6. DAC, up-conversion and power amplifier – produce the RF signal.

The IFFT replaces a bank of N oscillators, making OFDM cheap to implement in Wi-Fi, LTE and DVB-T.

✓ Answer checked by Claude Opus 5.5 (high effort)

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