Digital Modulation RF Simulator

Chronological signal-flow view from bits to recovered samples, with BER and timing recovery kept as dedicated analysis pages.

1. Bit Sequence

Rectangular NRZ waveform. All time-domain charts below use the same aligned time axis model.

2. Bit Grouping and Ideal Bit-to-Symbol Conversion

Mandatory ideal mapping stage. This shows how input bits are grouped into modulation symbols and converted into the physical symbol state.

3. Ideal Modulated Signal

Clean modulation result with no practical impairments. Representation depends on modulation family, but the displayed waveform is the ideal signal corresponding to the mapped symbols.

4. TX Baseband / Symbol-domain View

Most meaningful pre-RF view for the selected family: I/Q for PSK and QAM, amplitude states for ASK/OOK, or tone-state sequence for FSK.

5. TX Passband RF Signal

Practical RF waveform at the transmitter output.

6. RX Signal

Signal after channel effects such as AWGN, delay, phase offset, and optional echo.

7. Downconverted / Recovered Baseband or Decision Variable

Recovered receive-domain representation used for symbol decisions.

8. Constellation / Decision Plot

PSK/QAM use I-Q points. ASK/OOK uses one-dimensional decision space. FSK uses tone-energy decision space instead of a fake constellation.

For PSK/QAM, this controls whether the full valid grid, the symbols actually used, TX samples, and RX samples are displayed.

9. Spectrum

FFT-based PSD approximation of TX and RX waveforms.

10. Dynamic Signal Chain Block Diagram

Family-specific processing chain. Click a block to jump to the related graph or analysis page.

BER vs Eb/N0

Monte Carlo style symbol-domain BER simulation for browser responsiveness, using the selected modulation and coherent/noncoherent decision logic appropriate to the family.

Timing Recovery View

Illustrates the effect of timing offset on the sampling phase and decoded symbols.

Explanations

This page explains what each graph represents, why it matters, and how to read it correctly.

1. Bit Sequence

This graph shows the raw binary input as a rectangular NRZ waveform. A level near 0 represents bit 0, and a level near 1 represents bit 1. The horizontal axis is time.

  • Use it to verify that the input sequence is what you expect.
  • It is the starting point of the whole signal chain.
  • Its timing should align with the later signal-flow plots.

2. Bit Grouping and Ideal Bit-to-Symbol Conversion

This graph shows how the input bits are grouped into symbols according to the selected modulation order. For example, 256-QAM uses 8 bits per symbol, QPSK uses 2 bits per symbol, and BPSK uses 1 bit per symbol.

  • For ASK, it shows amplitude states.
  • For FSK, it shows frequency-state selection.
  • For PSK and QAM, it shows ideal I and Q symbol values before channel impairments.

3. Ideal Modulated Signal

This is the clean waveform that would be transmitted if there were no impairments. It represents the ideal modulation result directly generated from the mapped symbols.

  • ASK and OOK vary mainly in amplitude.
  • FSK varies mainly in tone frequency.
  • PSK varies mainly in phase.
  • QAM varies in both I and Q, which produces amplitude and phase changes in passband.

4. TX Baseband / Symbol-domain View

This is the most meaningful pre-RF view of the selected modulation family.

  • PSK and QAM show I(t) and Q(t).
  • ASK and OOK show symbol amplitude states.
  • FSK shows tone-state evolution before practical receive processing.

5. TX Passband RF Signal

This graph shows the actual real-valued RF waveform sent by the transmitter. It is what you would think of as the carrier after modulation.

  • Its appearance changes with carrier frequency, symbol rate, and modulation family.
  • It is useful for seeing amplitude and phase continuity or abrupt symbol transitions.

6. RX Signal

This is the received signal after the selected channel effects are applied. Noise, delay, phase offset, and optional echo alter the transmitted waveform.

  • Use it to compare TX and RX visually.
  • More noise should make the RX waveform look more corrupted.
  • Delay shifts the waveform in time; echo can smear transitions.

7. Downconverted / Recovered Baseband or Decision Variable

This is the receive-domain signal used for symbol decisions after basic downconversion or detection.

  • For PSK and QAM, it shows recovered I and Q tracks.
  • For ASK and OOK, it shows a one-dimensional decision variable.
  • For FSK, it shows tone-correlation metrics used to decide which tone was most likely transmitted.

8. Constellation / Decision Plot

This is a symbol-space view of the modulation, but it is family dependent.

  • PSK and QAM use the I-Q plane.
  • The full ideal constellation grid shows every valid ideal point.
  • Ideal constellation used shows only the ideal points actually present in the current bit sequence.
  • Transmitted symbols are the symbol-domain points before channel corruption.
  • Received samples are the decision samples after channel and receive processing.
  • For FSK, the app uses tone-energy decision space instead of a fake IQ constellation.

9. Spectrum

This is an FFT-based approximation of the TX and RX spectra. It gives a frequency-domain view of how signal energy is distributed.

  • It helps compare bandwidth occupation across modulations.
  • Noise tends to raise the apparent floor.
  • Frequency spacing and symbol rate affect the spectrum shape.

BER vs Eb/N0

This graph estimates bit error rate by repeatedly transmitting, corrupting, demodulating, and comparing bits over a range of Eb/N0 values.

  • The horizontal axis is Eb/N0 in dB.
  • The vertical axis is BER on a logarithmic scale.
  • As Eb/N0 increases, BER should generally decrease.
  • Higher-order modulations usually need more Eb/N0 to reach the same BER.

Timing Recovery View

This graph shows how sampling timing affects symbol decisions. Correct sampling should occur near the most stable point of each symbol interval. Offset sampling can increase decision error.

  • The main timing waveform overlays correct and offset sampling instants.
  • The eye diagram folds many symbol intervals on top of each other.
  • A more open eye usually means easier and more reliable symbol sampling.

Bit / Symbol Mapping Table

The mapping table lists how each possible bit group is converted into its modulation state.

  • For high-order QAM, the table is paginated so the UI stays readable.
  • Use Next and Previous to browse large mappings such as 1024-QAM and 4096-QAM.
  • This table is useful to validate the exact bit-to-symbol conversion logic being used.

Dynamic Signal Chain Block Diagram

This block diagram summarizes the complete transmit and receive chain in a compact engineering view.

  • The main chain shows the chronological signal path from input bits to recovered bits.
  • Arrow labels represent signals or data moving between stages.
  • Variables inside each block are the parameters or internal quantities most relevant to that block.
  • When a stage has too many control variables, they appear in a connected side box.
  • The diagram changes depending on the selected modulation family, so QAM, PSK, FSK, and ASK/OOK show different internal processing logic.
  • Clicking blocks opens the corresponding chart or analysis tab.