[AusNOG] Mobile Data Capacity - Where's the bottleneck?

[John Edwards]

It's complicated

Ignoring channel aggregation (CA), the maximum amount of spectrum available
to an LTE endpoint is 20Mhz, which is shared with everyone in the same
sector. The amount of spectrum might be as small as 1.5Mhz

If you have say an iPhone X with 2x2 MIMO, and can stand close enough to
the base station to achieve 2 spatial streams with 256 QAM modulation, then
perhaps you can get 150-170 Mbps of total throughput. The base station
might have 3 sectors each with 4 bands, which could easily overwhelm a
1Gbps backhaul with 12 of these ideal iPhone users.

But in reality, if you share that spectrum with just 1 long distance
handset who can only achieve a single spatial stream at QPSK modulation
then perhaps they will get 5mbps of bandwidth, and cut your iPhone's speed
to half. So now a gigabit backhaul is more than adequate even though the
number of users has doubled.

Add in an inverse square law to the distance a handset is from the tower,
and it's also apparent that the majority of users will be the "long
distance" type.

Telcos need to get an average of about 200 users on a sector to break even
on building and operating the tower, each of them contending for the same
spectrum.

Now imagine each of those 200 users with no data cap to regulate their
usage and you can quickly see how it can come undone due to sharing of
spectrum.

Then consider that the spectrum can't simply be re-used at each site - or
it will interfere with an adjacent site. It's an art and a science to
design physical networks that manage this interference across cities.

John





On Mon, 23 Mar 2020 at 13:32, Roy Adams <roy at racs.com.au> wrote:

> +1 needed for clarification also.
> Philippines carriers are a mess.
>
> Just to add to the mix, the provider I use has 10+ APN's, and on any given
> day, 1 or 2 of the APN's will be consistently faster than the other 8.
>
> So Backhaul, Spectrum, APN are the factors where I cannot figure the
> slowness.
> Industrial 4G/LTE router with Cat6 aggregation, and 3 or 4 out of 5 bars
> signal
>
> Kindly,
>
> ROY ADAMS* | *P 07 3040 5010  | Web: http://www.racs.com.au/ | Wiki:
> https://ex.racs.com.au:444/ | eMail: mailto:roy at racs.com.au
> <roy at racs.com.au>
> Please never upgrade to the latest Windows 10 - You don’t need the hassle,
> and I don’t need the work.
> More seriously, the 6 months older Windows 10 releases are typically FAR
> MORE stable - a simple RACS script can fix this - just ask :)
> If you think it's expensive to hire a professional to do the job, wait
> until you hire an amateur - Red Adair.
> Life is a journey through a series of adventures... Live them, love them,
> hate them, but never give up on your dreams, desires, and goals.
> Have you been good today? .ಠ_ಠ
>
>
> On Mon, 23 Mar 2020 at 12:42, Troy Kelly <troy at troykelly.com> wrote:
>
>> I understand that this isn't directly related to shifting packets - but
>> it's come up in discussions a few times, and I feel like my understanding
>> of things is wrong - if somebody has a few minutes for a diversion to their
>> day - I'd love some clarity.
>>
>> If a mobile carrier was to remove data caps, there would obviously be
>> increased demand on the network. One of the arguments against removing data
>> caps is that there is "not enough spectrum" available - and this there
>> would be a massive speed impact for all users of the cell/tower.
>>
>> My understanding was that the tower slowdowns were typically related to a
>> lack of backhaul - but the argument I am seeing is that it is spectrum
>> related.
>>
>> Thanks in advance for any clarity you can share.
>>
>> Troy
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