Dear Sam,
You ask me to explain "how ONE receiver with a bad signal will somehow indicate to the transmitter the data rate needs to be changed?"
I can’t because that's not how it works. The satellite doesn't vary from its "pre-set" parameters, just as you said.
The receiver doesn't tell the satellite to slow down the data rate. The data rate slows down in the reception processing due to low and compromised signal. The slow down occurs
in your receiver according to the quality of your received signal.
But herein lies the understanding, and is the whole point. Let me try again to break it down using the same article you questioned.
First, a "communications channel" in wireless transmission is composed of three basic parts: the transmitter, the sent signal, and the receiver.
This article is talking about WIRELESS transmission. The SNR and BER that are discussed are being measured
at the receiving end; at your receiver. (Remember the Rf front end?) And
, as stated:
In general, the higher the SNR, the fewer the errors in the channel transmission; or simply stated, as the SNR increases, the BER decreases. Conversely, as the SNR decreases, the BER will increase, at which point the communications channel typically reduces the data rate…
Asset Tracking in Industrial Settings?A Review of Wireless Technologies Part 1: The Basics | Sensors Magazine
So, as SNR decreases, BER increases, and the
rate of data transfer reduces, or slows. The rate of data transfer is also called the bit rate. As SNR goes down, so does the bit rate.
Errors that occur in the signal stream of a data communications channel reduce the rate of data transfer
on the receiving end. On the transmitting end the sending rate doesn't change. It is the receiving rate that is variable in our case.
Low SNR causes reduced data rates. The rate of digital data transfer is called the bit rate. When the bit rate slows we call it lower bit rate. Faster bit rate is called higher bit rate.
The article follows up with an example of what happens to a channel with poor SNR.
For example, as a 5.8 GHz signal's SNR is degraded, the channel will tend to remain operational, albeit at a reduced data rate.
The channel will TEND to remain
operational but it will operate at a
lower bit rate (reduced data rate).And further the article says:
"Notice that as the SNR decreases, there is a graceful degradation, or roll-off, in channel performance." (Graceful degradation means that it is no longer "all-or-nothing" but instead there is continued operation as the quality degrades with the SNR. Prior to 2005 it WAS all-or-nothing. Since MPEG2 and especially MPEG4, things have changed and no one has bothered to tell us.)
And we understand the relationship of digital picture quality as it relates to bit rate, which is:
Higher bit rate = higher quality, and lower bit rate = lower quality
Since lower SNR causes lower bit rate in digital systems, and since
Lower bit rate causes lower picture quality, then
Lower SNR causes lower picture quality.
The fact that this (slow data) is happening
at your receiver is why so many people are seeing different quality of the same content sent from Dish (or any provider). The biggest difference in picture quality, as reported by Dish customers, is caused by the difference in the attention to detail of the installation.
While there are some artifacts that are in the signal being sent, the signal is affected by atmospheric and other noise influences along the way. Once the signal arrives at the dish, system performance and picture quality are then affected by:
Signal strength at the dish (Signal power)
vs.
Noise generated by the quality of installation (Noise power)
The ratio of signal power to noise power is called the signal-to-noise ratio (SNR).
The best way to lessen noise sources is to keep the manageable ones (connections, wiring, grounding) to a minimum by carefully following instructions during installation.
The best way to overcome noise sources is to
maximize signal reception at the dish.
In a digital system, the whole idea is to preserve signal integrity throughout the COMPLETE signal path to achieve the desired performance.
