[Make-wifi-fast] Re: [Bloat] Re: [Codel] [Rpm] Re: Re: [Cake] "Fi-Wi is a new forwarding plane for wireless" - Bob McMahon

[bob.mcmahon@umbernetworks.com]

> you may be able to make a dent in the AP use of airtime, but how are 
> you going to coordinate the wifi devices you are talking to that are 
> using so much of it, and doing most of the hidden transmitter stomping 
> on each other? you can do channel allocation and lower the AP power to 
> reduce (and if you can use DFS channels almost eliminate) the APs 
> stepping on each other, but doesn't solve the mobile device 
> coordination.
> 

David,

The first answer is RRH density.

With many RRHs distributed through the building, each RRH serves a 
smaller number of STAs in a smaller physical area. STAs associated to 
the same RRH are much more likely to hear each other, so the hidden-node 
precondition becomes less common by construction. Hidden node requires 
two STAs that cannot hear each other but share the same AP. Shrink the 
cell and the geometry works in your favor before any other mechanism is 
applied.

After that, the toolkit splits into three categories.

For all devices, regardless of 802.11 generation, the concentrator can 
use building-wide PHY visibility to manage association, channel, power, 
EDCA policy, and protection windows across RRHs. A conventional AP can 
only do this locally. Fi-Wi can coordinate those choices across the 
building.

That includes coordinated use of standard protection mechanisms, per-RRH 
EDCA parameters, transmit-power control to reduce interference radius, 
and TCP ACK pacing to limit uplink window growth without requiring STA 
cooperation.

For devices with L4S-aware transport, the concentrator can mark ECN 
based on WLAN service time as well as WAN behavior. That gives the 
sender a congestion signal tied to the radio bottleneck, not just the 
internet edge. Legacy devices do not get that benefit, but L4S-capable 
senders can react directly.

For 802.11ax and later clients, uplink OFDMA, trigger-based access, 
MU-RTS, and TWT give the infrastructure more explicit control over 
uplink timing and resource allocation. That does not make every client a 
proprietary scheduled endpoint, but it moves cooperative clients much 
closer to scheduled uplink behavior.

There is also a compounding effect from receive quality. Distributed 
receive combining across multiple RRHs improves uplink SNR, which drives 
higher MCS. Higher MCS shortens each TXOP. Shorter TXOPs return the 
medium faster, reducing collision exposure for other STAs. Lower PER 
from better SNR eliminates retransmissions, which are pure airtime 
waste. And once phase coherency is established across RRHs, more spatial 
streams can be driven to the same STA, multiplying throughput per TXOP 
without consuming more airtime. The net effect is that the total airtime 
required to serve a given load shrinks, which directly reduces 
contention pressure on legacy devices. The uplink problem gets easier 
not just from coordination mechanisms but from making each transmission 
more efficient.

The honest answer is that legacy hidden-node behavior is mitigated, not 
eliminated. The architectural advantage is that Fi-Wi applies all of 
these mechanisms from one concentrator with building-wide PHY visibility 
and a shared cost function. Conventional APs apply them locally, 
independently, and through vendor-specific firmware.

Bob