The third diversity axis
devourer's long-range single-stream video link already exploits two physical-layer
diversity axes:
- frequency — single-adapter per-packet hopping (
docs/frequency-hopping.md),
which doubles as a frequency-diversity interleaver for the outer FEC;
- code — the fused cross-layer FEC stack (
docs/fused-fec.md): sub-block
integrity salvage, an MDS outer code, soft-decision inner decode, and
per-temporal-layer unequal error protection.
The spatial axis is unexploited. Because a single-stream video link never
stacks spatial streams, the extra RF chains (1 idle on a 2T2R part, up to 3 on a
4T4R 8814) sit unused. Turning them into diversity/robustness rather than
throughput is almost pure upside for this use case: it is USB-free (one
stream in, one stream out — no MIMO-multiplexing bandwidth hit), and it composes
multiplicatively with the frequency and code axes already in place.
The single hard constraint (from docs/frequency-hopping.md): there is one LO
per chip, so the chains share one centre frequency — they give spatial
diversity within a channel, orthogonal to (not a substitute for) the frequency
diversity that hopping provides.
Why this matters
- RX MRC across a 4T4R chip's chains is a ~10·log₁₀(N) dB SNR win from a
single ground adapter — partially replacing wfb-ng's multi-adapter diversity
array, in-chip, at zero USB cost.
- TX diversity (CSD / STBC) attacks the deep fades that push corruption
into the frame-wide regime where sub-block salvage fails — so spatial diversity
improves the precondition of the whole fused-FEC stack, not just its input.
- Chain count is a new lever for the energy-minimizing adaptive link
(docs/adaptive-link.md), which today has no spatial knob: a convex
PA-power-saved vs chain-baseline-added tradeoff with an optimal N per range,
and a per-layer spatial UEP knob alongside modulation and FEC.
Approach
Research/design track — simulators, measurement harnesses, and conceptual docs
first (the way the frequency and code axes were developed), hardware validation
following. Each activity is a separate tracked issue.
Roadmap
Foundations
Core diversity techniques
Cross-layer composition
Speculative
Sequencing
#128, #129 (foundations) → #130, #131 (feedback-free wins) → #132 →
#133 (the strongest cross-layer link) → #134, #135, #136 (composition) →
#137 (go/no-go, gated on the rest).
Current-state anchors
- CSD is chip-validated; STBC lives in the radiotap path but on-air STBC is
unresolved; 4-path RF is supported for the 8814.
The third diversity axis
devourer's long-range single-stream video link already exploits two physical-layer
diversity axes:
docs/frequency-hopping.md),which doubles as a frequency-diversity interleaver for the outer FEC;
docs/fused-fec.md): sub-blockintegrity salvage, an MDS outer code, soft-decision inner decode, and
per-temporal-layer unequal error protection.
The spatial axis is unexploited. Because a single-stream video link never
stacks spatial streams, the extra RF chains (1 idle on a 2T2R part, up to 3 on a
4T4R 8814) sit unused. Turning them into diversity/robustness rather than
throughput is almost pure upside for this use case: it is USB-free (one
stream in, one stream out — no MIMO-multiplexing bandwidth hit), and it composes
multiplicatively with the frequency and code axes already in place.
The single hard constraint (from
docs/frequency-hopping.md): there is one LOper chip, so the chains share one centre frequency — they give spatial
diversity within a channel, orthogonal to (not a substitute for) the frequency
diversity that hopping provides.
Why this matters
single ground adapter — partially replacing wfb-ng's multi-adapter diversity
array, in-chip, at zero USB cost.
into the frame-wide regime where sub-block salvage fails — so spatial diversity
improves the precondition of the whole fused-FEC stack, not just its input.
(
docs/adaptive-link.md), which today has no spatial knob: a convexPA-power-saved vs chain-baseline-added tradeoff with an optimal N per range,
and a per-layer spatial UEP knob alongside modulation and FEC.
Approach
Research/design track — simulators, measurement harnesses, and conceptual docs
first (the way the frequency and code axes were developed), hardware validation
following. Each activity is a separate tracked issue.
Roadmap
Foundations
Core diversity techniques
Cross-layer composition
Speculative
Sequencing
#128, #129(foundations) →#130, #131(feedback-free wins) →#132→#133(the strongest cross-layer link) →#134, #135, #136(composition) →#137(go/no-go, gated on the rest).Current-state anchors
unresolved; 4-path RF is supported for the 8814.