[LibreQoS] On FiWi

rjmcmahon rjmcmahon at rjmcmahon.com
Tue Mar 14 00:27:23 EDT 2023

To change the topic - curious to thoughts on FiWi.

Imagine a world with no copper cable called FiWi (Fiber,VCSEL/CMOS 
Radios, Antennas) and which is point to point inside a building 
connected to virtualized APs fiber hops away. Each remote radio head 
(RRH) would consume 5W or less and only when active. No need for things 
like zigbee, or meshes, or threads as each radio has a fiber connection 
via Corning's actifi or equivalent. Eliminate the AP/Client power 
imbalance. Plastics also can house smoke or other sensors.

Some reminders from Paul Baran in 1994 (and from David Reed)

o) Shorter range rf transceivers connected to fiber could produce a 
significant improvement - - tremendous improvement, really.
o) a mixture of terrestrial links plus shorter range radio links has the 
effect of increasing by orders and orders of magnitude the amount of 
frequency spectrum that can be made available.
o) By authorizing high power to support a few users to reach slightly 
longer distances we deprive ourselves of the opportunity to serve the 
o) Communications systems can be built with 10dB ratio
o) Digital transmission when properly done allows a small signal to 
noise ratio to be used successfully to retrieve an error free signal.
o) And, never forget, any transmission capacity not used is wasted 
forever, like water over the dam. Not using such techniques represent 
lost opportunity.

And on waveguides:

o) "Fiber transmission loss is ~0.5dB/km for single mode fiber, 
independent of modulation"
o) “Copper cables and PCB traces are very frequency dependent.  At 
100Gb/s, the loss is in dB/inch."
o) "Free space: the power density of the radio waves decreases with the 
square of distance from the transmitting antenna due to spreading of the 
electromagnetic energy in space according to the inverse square law"

The sunk costs & long-lived parts of FiWi are the fiber and the CPE 
plastics & antennas, as CMOS radios+ & fiber/laser, e.g. VCSEL could be 
pluggable, allowing for field upgrades. Just like swapping out SFP in a 
data center.

This approach basically drives out WiFi latency by eliminating shared 
queues and increases capacity by orders of magnitude by leveraging 10dB 
in the spatial dimension, all of which is achieved by a physical design. 
Just place enough RRHs as needed (similar to a pop up sprinkler in an 
irrigation system.)

Start and build this for an MDU and the value of the building improves. 
Sadly, there seems no way to capture that value other than over long 
term use. It doesn't matter whether the leader of the HOA tries to 
capture the value or if a last mile provider tries. The value remains 
sunk or hidden with nothing on the asset side of the balance sheet. 
We've got a CAPEX spend that has to be made up via "OPEX returns" over 

But the asset is there.

How do we do this?


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