Failure mode: good SNR, bad packets

OFDM links can show high SNR but still fail CRC due to synchronization errors. The critical trio:

• Frame timing offset
• Carrier frequency offset (CFO)
• Residual phase tracking

Recommended sync chain

1. Detect preamble via correlation peak.
2. Coarse CFO from repeated short preamble structure.
3. FFT window alignment from long preamble timing metric.
4. Fine CFO from pilot phase slope.
5. Per-symbol common phase error correction.

Approximate coarse CFO estimate from repeated segments: f_hat = (Fs / (2*pi*L)) * angle(sum_{n=0}^{L-1} r[n+L] * conj(r[n])) where L is the repetition length.

Hardware mapping notes

• Correlators map well to pipelined MAC trees.
• Angle extraction can use CORDIC.
• Keep phase unwrap logic deterministic between symbols.
• Pilot smoothing improves jitter but increases loop lag.

Debugging checklist

• Inspect constellation before and after CFO correction.
• Plot pilot phase over subcarrier index and time.
• Verify FFT window drift under multipath and Doppler.

In real deployments, synchronization robustness is usually a bigger differentiator than peak demod speed.