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5G NR DMRS-Based OFDM Simulator


 

User Input

+---------------------------+

| # Subcarriers (Nsc)       |

| # OFDM Symbols (Nsym)     |

| DMRS length (Ldmrs)       |

| # Channel taps            |

| Noise std deviation       |

+---------------------------+

              |

              v

Generate DMRS Pilot Sequence

+---------------------------+

| QPSK symbols of length Ldmrs

| e.g., [1+j, -1+j, ...]

+---------------------------+

              |

              v

Frequency-Domain Mapping

+---------------------------+

| Zero-pad DMRS to all Nsc   <-- Pilot insertion

| DMRS on first Ldmrs, rest 0

| X[k] = [DMRS, 0, 0, ..., 0]

+---------------------------+

              |

              v

OFDM Modulation (IFFT)

+---------------------------+

| Time-domain OFDM symbol

| Each subcarrier → sinusoid

+---------------------------+

              |

              v

Add Cyclic Prefix (CP)

+---------------------------+

| Prepend CP to symbol

| Prevents ISI in multipath

+---------------------------+

              |

              v

Transmit Through Channel

+---------------------------+

| Frequency-selective multipath

| Complex channel taps (amplitude + phase)

| Add AWGN noise

+---------------------------+

              |

              v

Receiver

+---------------------------+

| Remove CP

| Apply FFT → Frequency-domain received symbols

| Y[k] = FFT(received symbol)

+---------------------------+

              |

              v

Channel Estimation Using DMRS

+---------------------------+

| For DMRS subcarriers only:

| H_hat[k] = Y[k] / X[k]

| Gives per-subcarrier complex channel

+---------------------------+

              |

              v

Optional: Interpolation to non-pilot subcarriers

              |

              v

Plots & Visualization

+---------------------------+

| Time-domain: Tx & Rx signals

| Frequency-domain: Rx FFT magnitude

| Channel estimate: |H_hat[k]|

+---------------------------+




5G NR DMRS-Based OFDM Simulator (QPSK)

5G NR DMRS-Based OFDM Simulation Workflow

  1. User Input: Set number of subcarriers, OFDM symbols, DMRS length, channel taps, and noise level.
  2. DMRS Generation: Create a QPSK pilot sequence for channel estimation.
  3. Frequency-Domain Mapping: Insert DMRS pilots into subcarriers; zero-pad remaining subcarriers.
  4. OFDM Modulation: Apply IFFT to produce time-domain symbols, then add cyclic prefix (CP).
  5. Channel Transmission: Pass the signal through multipath channel taps and add AWGN noise.
  6. Receiver Processing: Remove CP and perform FFT to recover frequency-domain symbols.
  7. Channel Estimation: Estimate per-subcarrier complex gain using DMRS: Ĥ[k] = Y[k] / X[k].
  8. Visualization: Plot transmitted and received signals, correlation magnitude, and estimated channel.

Note: Current demo transmits only DMRS pilots (no data) for simplicity. Adding data symbols enables a full PHY-level simulation.

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