Matlab Generate Gnss WaveformSAFE

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---
name: matlab-generate-gnss-waveform
description: >
  Generate GNSS baseband waveforms (GPS, Galileo, NavIC) with physically
  realistic or user-specified channel impairments using the Satellite
  Communications Toolbox. Use when generating GPS L1 C/A, L1C, L2C, L5,
  Galileo E1, E1C, E5a, E5b, E5, or NavIC L5, S, L1 signals. Covers
  gpsWaveformGenerator, galileoWaveformGenerator, satelliteScenario,
  Doppler/delay from orbital dynamics or custom values, navigation data
  encoding with ephemeris, and RINEX integration.
  Triggers on: GPS waveform, Galileo waveform, NavIC waveform, GNSS signal,
  satellite scenario, GNSS simulation, receiver test signal, baseband GNSS,
  L-band satellite signal, navigation signal generation.
license: https://www.mathworks.com/content/dam/mathworks/license/pmrl/license.md
compatibility: ">=R2026a"
metadata:
  author: MathWorks
  version: "1.0"
---

# Generate GNSS Waveform

Generate multi-satellite GNSS baseband waveforms with properly encoded
navigation data. Channel impairments (Doppler, delay, noise) can come from
a realistic satellite scenario OR from user-specified custom values.
Supports GPS, Galileo, and NavIC constellations. The waveform carries real
ephemeris so a receiver can decode it for position estimation.

## When to Use

- Generating GNSS baseband signals (GPS, Galileo, or NavIC) for receiver testing
- Simulating multi-satellite channels with Doppler and delay from orbital dynamics
- Testing with specific Doppler/delay/SNR values (custom channel mode)
- Building end-to-end GNSS receiver simulations that need decodable nav data

## When NOT to Use

- Signal acquisition, tracking loops, nav decoding, or position estimation
- BeiDou/GLONASS (not supported) or SDR hardware transmission

## Prerequisites: Helper Files

Copy helper files from MathWorks examples into your project folder.
See `references/helper-files.md` for the full list of source examples
and files to copy per constellation (GPS, Galileo, NavIC).

## Workflow

The pipeline has 6 steps (0-5). Step 0 determines signal type, channel
mode, and data source. The channel mode decides whether Steps 2-3 are needed.

```
Step 0: Determine signal type + channel mode + data source + nav data intent
Step 1: Configure waveform generator
         ├── Scenario mode → Step 2 (satellite scenario) + Step 3 (compute channel from physics)
         └── Custom mode   → Step 3c (user provides Doppler/delay/SNR directly)
Step 4: Encode navigation data (both modes)
Step 5: Generate waveform with channel (both modes)
```

### Step 0: Determine signal type, channel mode, and data source

**If the user's prompt does not clearly specify the signal type**, ask:

> What GNSS waveform would you like to generate?
>
> **GPS:** L1 C/A, L1C, L2C, L5
> **Galileo:** E1, E1C (pilot only), E5a, E5b, E5 (wideband)
> **NavIC:** L5, S, L1
>
> Also, how should channel impairments (Doppler shift, propagation delay,
> noise) be applied?
>
> **(a) Scenario-driven** — I compute realistic values from a satellite
> scenario. You provide a receiver location (lat/lon) and I handle the
> orbital dynamics.
>
> **(b) Custom values** — You provide Doppler (Hz), delay (s), and/or
> SNR (dB) per satellite. Useful for controlled testing or when you already
> have your own channel model.

**Detection heuristics:** Location/city/lat-lon → Scenario. Specific
Doppler/delay/SNR numbers → Custom. "Stress test" or "extreme" → Custom.
No cues → Ask. If signal type is clear but mode ambiguous, ask only
about mode.

#### Data source selection

**Available:** `gpsAlmanac.txt` (always on path), RINEX `.rnx` files
(Nav Toolbox). **Require setup:** `galileoAlmanac.xml` (copy from
example), fresh almanac (download from USCG NAVCEN).

**Decision rules:**
1. User provides RINEX → use for both scenario AND nav data.
2. No RINEX → use bundled almanac (`gpsAlmanac.txt` or `galileoAlmanac.xml`).
3. Current-epoch needed → offer fresh almanac download (requires internet).
4. RINEX requested but no Nav Toolbox → fall back to almanac or parse
   manually (see `references/rinex-integration.md`).

**All bundled files are from a fixed past epoch.** This is fine for receiver
algorithm testing (orbital geometry is still valid) but does not represent
today's actual sky. The agent MUST communicate which file and epoch is being
used.

#### Navigation data intent

Navigation data can be:
- **Real ephemeris** (from almanac/RINEX) — required for end-to-end receiver
  testing where position estimation must work
- **Random/dummy bits** — valid for signal-level testing (acquisition,
  tracking, modulation quality) where nav decode is not the goal

If user's intent is unclear, ask:
> Do you need the waveform to carry real navigation data (for position
> estimation), or are dummy bits fine (for signal-level testing)?

#### STOP — Present choices before generating

**Before writing or executing ANY code**, print a standalone configuration
summary stating: signal type, center frequency, sample rate, duration,
data source + epoch, start time, and nav data type. This MUST appear as
visible text BEFORE any code block — not buried in comments or post-run
summaries. In interactive mode, wait for user confirmation.

### Step 1: Configure waveform generator (constellation-specific)

**GPS:**
```matlab
sampleRate = 5e6;
wavegenobj = gpsWaveformGenerator(SampleRate=sampleRate);
wavegenobj.SignalType = "legacy";  % L1 C/A
navDataType = "LNAV";
centerFrequency = 1575.42e6;
stepTime = wavegenobj.BitDuration;
```
**Verify:** `stepTime` should be 0.02 (20 ms) for L1 C/A, 0.01 for L1C/L5.

**Galileo:**
```matlab
sampleRate = 25e6;  % Use 60e6 for E5 wideband
wavegenobj = galileoWaveformGenerator(SampleRate=sampleRate);
wavegenobj.SignalType = "E1";  % or "E1C","E5a","E5b","E5"
centerFrequency = 1575.42e6;  % E5 uses 1191.795e6
stepTime = wavegenobj.BitDuration;
```
**Verify:** `stepTime` should be 0.004 (4 ms) for E1/E1C/E5b, 0.02 for E5a/E5.

**E5 has critical pitfalls** — nav data must be 

SAFEgrade B · trust 89/100 Nothing in the source contradicts what it says it does. Grade A is reserved for packages that have also passed the behavioural sandbox.

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