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Stupid question: Aredn mesh fails but cell phones get thru trees and hills

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wa2ise's picture
Stupid question: Aredn mesh fails but cell phones get thru trees and hills
I have a stupid question.  In NNJ we have lots of trouble setting up links because of the rolling hills and trees around my QTH.  900MHz and 2.4GHz.  But cell phones use frequencies between and around these, and cellphones seem to get thru.  Maybe the modulation schemes are much different?  Echo correction that copes with tons of reflections? 

AE6XE's picture

"The LTE standard covers a range of many different bands, each of which is designated by both a frequency and a band number. In North America, 700, 750, 800, 850, 1900, 1700/2100 (AWS), 2300 (WCS) 2500 and 2600 MHz (Rogers CommunicationsBell Canada)".

There are more and lower bands to get through the trees.     LTE uses OFDM (same as AREDN) for the downlink and has many channel width options.  Another factor is the density of cell coverage sites.  The density keeps increasing--they're everywhere.

Joe AE6XE  
This can be a very

This can be a very fascinating subject, part of this is technological and part of it is investment. We as HAM's can learn from this, some of it we can pickup and some we can't. I'm going to give a number of items below, but first it should be known I'm not a cellular service technician, the below information is based on discussions with techs, rf site managers and reading cellular service literature from manufactures which may be biased info. Any corrections to the below appreciated.

First off some definitions:
Cellular Service Provider --- A company that provides cellular services (AT&T, T-Mobile, Verizon, etc)
CELL - An area of coverage for one transmitter/receiver combo.
Handset - A  phone, or other device that uses the Cellular Service Provider network (phone or data modem)

Some differneces between us:

Output Power Cellular Service Providers are often putting out in excess of 100w at the cell transmitter location. This is an order of magnitude higher than most mesh nodes are transmitting (2^7 tims more power.) Even handsets will put out up to 2 watts (depends on model and what country the handset is used in)

RX from Handset to Cell Transmitter:
These can be filtered to just a single RF channel, and a preamps can be added here.

Frequency Control:
This is a big one, the cellular band is licensed to a single company on each frequency used. This means its a "clean" band controlled by the cellular service provider.

Cellular Service Providers analyzer the RF for each cell,  RF is controlled to avoid co-cell interference.  Cellular Service Providers will take every action to ensure each cell is interference free, both from 3rd parties and from their own systems which includes changing the frequency used at adjacent cell sites (or even far away) to avoid two cell's causing issues.

Cell Size and Pattern: Cellular Service Providers adjust their RF pattern as needed for each cell.  Along this line a number of cellular service antenna manufactures actually make antennas that have electric motors in them that can be adjusted remotely from a command center. I'm not sure how often they do this, but its interesting seeing these antennas available for sale to Cellular Service Providers.  These sites can be made to be very wide to a direction with very few handsets and in a direction that is excessively populated (say everyone went to the fairgrounds) they could be tuned during the fair to have multiple beams aim that direction temporally.

Signal Bandwidth: This depends a lot on what one is doing. Audio for example doesn't need a significant amount of bandwidth to send the audio. 100KHz (I'm not sure actual width for a cellular signal) can be more than enough to send audio, and this can cut through easier than a 5MHz wide signal can.  Of course high speed data can take significantly wide bandwidth. I will note that the average handset data of for example requesting a website is a very small upload from the handset to the cell transmitter, with a large response from the cell transmitter to the handset (the low power link sends less data than the high power cell transmitter does so the wide bandwidth signal is less of an issue because of higher TX power)

The list can keep going on and on, but this is just an entry starter guide to the differences.

Joe's comments on bands and density are also significantly relevant.

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