Per-SVC-layer spatial UEP: the third protection axis (#136)#146
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UEP already runs on MCS (svc_tx.h ladder) and FEC rate (svc_uep_fec.py). The spatial axis is also already in the ladder — its default flies critical/base with LDPC+STBC and leaves enhancement single-stream — but was never quantified as an axis until #132 measured the STBC gain (~2-3 dB coding + diversity). This adds the sim that shows the three knobs compound. - tools/precoder/svc_spatial_uep_sim.py (+ pytest): analytical per-layer delivery (soft FER around the MCS threshold, STBC shifting it down by the measured coding gain, RS repair budget via binomial), an SNR-sweep staircase, and --no-stbc for an A/B of the spatial axis. - docs/fused-fec.md: "The third axis: per-layer spatial diversity". Result: the staircase holds on three knobs — enhancement (T2/T1) sheds first, base/critical hold deepest, and the spatial knob extends critical/base survival SNR by the STBC coding gain (~2.5 dB) on top of MCS and FEC. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
josephnef
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enhancement
This was referenced Jul 2, 2026
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Summary
The third UEP axis — per-layer spatial diversity (#136). Unequal error
protection already runs on MCS (
svc_tx.hladder) and FEC rate(
svc_uep_fec.py). The spatial axis is also already in the ladder — its defaultflies the critical/base layers with
LDPC/STBCand leaves enhancementsingle-stream — but it was a flag, not a measured axis, until #132 quantified the
STBC gain (~2–3 dB coding + diversity that widens under motion). This adds the sim
showing the three knobs compound.
Model
Analytical (no codec dependency): each layer's per-frame PHY delivery is a soft
FER transition around its MCS threshold, shifted down by the STBC coding gain when
enabled; the layer's RS block survives if per-symbol losses stay within its repair
budget (binomial). Sweeping link SNR down produces the per-layer staircase.
Result
Default ladder (critical MCS0/STBC ov1.0, T0 MCS1/STBC ov0.75, T1 MCS4 ov0.5,
T2 MCS7 ov0.25) survival SNR:
Enhancement (T2/T1) sheds first; base/critical hold deepest; the spatial knob
buys the critical/base layers ~2.5 dB more survival on top of MCS and FEC.
Contents
tools/precoder/svc_spatial_uep_sim.py(+ pytest): staircase sweep,--no-stbcA/B,
--self-test.docs/fused-fec.md: "The third axis: per-layer spatial diversity".Testing
--self-testgreen; 6 pytest pass. Pure-Python, consistent with the sibling sims.🤖 Generated with Claude Code