linearModulation
As shown in title: what's the difference between linear modulation and non-linear modulation scheme?
I can not find the formal definition of this.
And there is a different determination for the FSK modulation (linear and non-linear).
FSK is linear and can be classified using likely-hood ratio function
While the GMSK is non-linear according to the searched results, however I don't know why.
Thanks for any help.
A signal that is phase-shift modulated with some continuous signal f will have the same waveform as one which is frequency-shift modulated with the derivative of f. Likewise, a signal that is frequency-modulated by some signal f will have the same waveform as one which is phase-modulated by the integral of f. Note that in some cases, it may not be practical to take the integral or derivative of f, so some signals can only be meaningfully represent phase modulation and others may only meaningfully represent frequency modulation.
Even though the waveforms of a frequency-modulated signal and phase-shift-modulated signal may look similar, however, there's often another important distinction. Phase-shift modulated signals are often modulated relative to some other reference signal. In some cases, the reference may be a signal sent on another wire. In other cases, the reference may be a signal which was sent at an earlier time on the same wire. In NTSC video, for example, every scan line starts with a few cycles of a 3.579545Mhz reference sine wave. Colors later in the line will be encoded by waves that have a certain phase relationship to that reference wave. Yellow, for example, will be represented by a wave whose phase matches the reference; blue will be represented by a wave 180 degrees out of phase. Red and green are represented by waves +/- 90 degrees out of phase. Note that all solid colors are be represented by the same frequency; the only difference between them is the phase relative to the reference wave.
I am pretty sure that the IR carrier is just on-off keyed with the output of an UART.
It's 8-bit asynchronous serial, probably at 38400 baud, with a single stop bit. There are 6 bytes of data in a transmission. It can't be 7-bit serial with a parity bit, as the last bit matches up with neiter odd nor even parity.
The data being transmitted is
01101111 00111011 11000010 10000000 01101000 00010010 AKA 6F 3B C2 80 68 12
No idea what it means. I would have to know what specific device is being reverse-engineered to proceed further. The endianess might be different from what you expect and there is probably either an an error correcting code or a checksum.
Best Answer
According to this source:
Digital modulation techniques are classified as linear if:
The only other "linearity"-reference I could find was in the same course slides:
For Frequency Modulation, the relationship between received power and quality is non-linear (Rapid increase in quality for an increase in received power).
For Amplitude Modulation there is a linear relationship between the received signal quality and received signal power.
But I am not totally convinced that this is at the basis of the definition (I'm also not totally unconvinced).
IMHO, I think they started out calling the AM scheme linear, as \$AM(a\cdot V_{in}) = a\cdot AM(V_{in})\$, and then they started playing with the phase ((Q)PSK) and just labeled it as linear as well, while it isn't strictly true.
[EDIT] I also found this which seems to support my last remark.