[olug] [OT] How does upload work in White Space Broadband

[Sam Tetherow]

It should operate like traditional fixed wireless networking. While we 
are still waiting on the rules to be released the preliminary numbers 
being thrown out are 4 watts fixed and 100mw mobile, which means that 
mobile will be more for personal area networking.

There is some confusion though, as what has been talked about is 
strictly point to point applications and not point to multipoint which 
would mean backhaul or dedicated links per customer in an ISP environment.

We should see some rules in the coming weeks and months which will 
layout what the parameters are for the white space and we will have a 
better idea as to how it can be utilized.

As to your question of upload/download that is a function of two things 
in a radio environment.

The first is effective radiated power (EIRP) which basically says how 
'loud' a radio can broadcast, if both ends of the link can have the same 
EIRP then there is no physical difference between upload and download. 
In the case of point to multipoint there can be different rules for the 
AP and the client side equipment. This means that traffic going from the 
AP to the client can have different physical limitations due to beam 
width, power or even frequency (in the case of cell phones) than 
communications going from the client to AP.

In the case of unlicensed 2.4GHz ISM (802.11b/g/n) for instance the AP 
can only have 36dBi of radiated power where as the client can have 
48dBi. The reasoning is that the client will behave like a point to 
point link and have a concentrated beam toward the AP where as the AP is 
broadcasting in a general direction (or omnidirection) and hence it 
should not radiate as much power.

The second thing that will effect upload/download bandwidth is the 
transport protocol used. If the protocol is not a polling protocol then 
you run into the problem of the hidden node, you can think of this like 
older hub architecture in a wired environment where collisions will 
cause loss of available bandwidth. Hidden node occurs when more than one 
client is talking to the AP at the same time. Each client can see the AP 
and the AP sees each client, but each client does not see the other. So 
if the AP is transmitting data to the client there isn't a problem since 
the AP sees all clients and knows when they are not sending and each 
client sees the AP and knows not to send when it is sending. This means 
efficient use of bandwidth for downloading. However if client A is 
sending to the AP and client B has something to send he does not see A 
and sends over the top of him causing a collision in which case the AP 
will tell both to backoff and send again. This is why uploading on a 
PtMP wireless network is less efficient than downloading.

However if the radios are using a polling mechanism then the AP polls 
each client asking if they have something to send and the client doesn't 
send unless asked. This means that uploading and downloading can now be 
interchangable in a PtMP environment. Motorola, Trango and Alvarion all 
use proprietary polling mechanism in wireless environments to achieve 
better bandwidth utilization.

So to answer your question about upload capabilities in TVWS, it depends 
both on the rules that will come down from the FCC and on the equipment 
manufacturers.

Sorry that ended up being so long winded.

Sam Tetherow
Sandhills Wireless


Rob Townley wrote:
> We all need better ways for internet access, especially for uploading /
> webserving.  So i was intrigued that the FCC has opened the White Space
> areas between digital tv channels for public use.  i could see how this
> would offer high download speeds, but what about uploading?   Will it be
> exactly like traditional satellite/dialup hybrids where the phone line is
> used for uploads?
>
> If it is IEEE 802.22, then i would think it is duplex communication, but
> haven't found any solid evidence yet.
>
> If there is some way for each home to have a distinct up/down channel, how
> far away can a rancher broadcast uploads back to a TV tower receiver when he
> only has a 100mWatts.
>
> So will it be one-way internet broadcasts.  A set of podcasts determined by
> the provider.
>
> Since the Public Service Commissioners get $75,000, we should ask them.
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