8PSK’s Explained

[bigevil69]

Here is a brief, layman’s explanation of 8PSK.
We are speaking of digital modulation of signals today, rather than the analog signals of the past, but the concept is equally applied.
There are many means to modulate a signal to transmit data today. Amplitude Modulation and Frequency Modulation are the most familiar to us all (i.e. AM radio and FM radio).
In AM radio (amplitude modulation) you understand that there is a carrier wave that is transmitted with a constant frequency. But, that carrier wave’s amplitude is increased or decreased by an external signal, the data signal. The receiver detects these variations in the carrier’s amplitude.
The receiver does not care about the carrier signal itself, only the changes in its amplitude. So, it basically only identifies the amplitude changes and strips that information away from the carrier wave and tosses the carrier aside. Only the signal that created the variations in the carrier’s amplitude remains and that is the data information. If there is no change in the amplitude of the carrier, we get a digital “zero” if it does change, we detect a digital “one”.
If we strip all this information from the carrier wave, we will end up with a stream of data which can be processed and converted back into the original information (audio or video).
In FM radio, the carrier wave has a fixed amplitude, but the data information readjusts or modulates the frequency of the wave. If the frequency doesn’t change, the receiver reads this as a digital “zero” and if it changes, it reads it as a digital “one”. So the receiver strips the information or data signal from the carrier wave by analyzing the changes in the carrier’s frequency.
Now we can discuss PSK, or Phase Shift Keying. This is a little harder to visualize, but the overall principle (theory) is the same.
In PSK, you have a constant amplitude and constant frequency carrier wave, but the data information modulates the “phase” of the signal. If the phase of the signal is suddenly altered (modulated) by the data signal, the receiver will detect this as a digital “one”. If it does not change, it detects it as a digital “zero”. So you get an idea that the same process is occurring here as with AM and FM modulation.
Here is where the advantage begins to come into play. If you have one carrier, of a set frequency and set amplitude (a sine wave), you can modulate its phase to produce 1’s and 0’s (BPSK or Binary Phase Shift Keying).
If you add a second carrier with the same frequency and same amplitude, but transmit it so many degrees offset from the first carrier (now as a cosine wave), then you can put more data on the same radio frequency band. One wave carries some information and the second wave carries additional information.
Now your receiver can extract “00″, “01″, “10″ or “11″ from the data in the same instant, as opposed to just a “0″ or a “1″. This would be QPSK (Quadrature Phase Shift Keying). Quadrature PSK is also referred to as 4PSK, which seems more logical and makes it easier to compare to the next step up, 8PSK.
Now, if we add a third carrier wave, with the same frequency and amplitude as the first two, but so many degrees out from the first two, we can transmit and receive three bits of data or 000, 001, 010, 011, 100, 101, 110, 111 during the same instant! This would be 8PSK modulation.
I am sure you are seeing the advantage here. The data is being transmitted at the same time, within the same bandwidth, but you are transmitting more data simultaneously. Therefore, there is more data (more information) to work with immediately, which means more accuracy and a better quality picture (and sound).
There is also 16PSK signals! HOTDOG!
Just to add a summary:
BPSK or binary PSK is 1 and 0 (binary = two packets)
QPSK or 4PSK is 00, 01, 10, 11 (quadrature = four packets)
8PSK is 000, 001, 010, 011, 100, 101, 110, 111 (eight packets)
16PSK is 0000, 0001, 0010, 0011, 0100, 0101, 0110, 0111, 1000, 1001, 1010, 1011, 1100, 1101, 1110, 1111 (16 packets)
Many people ask if they can use a Coolsat 5K to view the 8PSK signals. The answer is no, of course. The reason should be obvious. Even though QPSK and 8PSK are similar in theory, they are still just as different as AM and FM radio. The receiver’s tuner (or tuner MODULE) has to be designed specifically to detect, decode and process these signals.