Note that occasionally the phase shift is 180 degrees. To accommodate this situation, the transmitter output power amplifier must be linear over a wide dynamic range to prevent spectral splatter and therefore interference with adjacent frequency channels. That is, a second set of four possible phase states is utilized. If the current symbol is on the I or Q axis, the next symbol must be off the axes, and vice versa. QAM QAM takes advantage of the fact that the greater the number of symbols, the greater the efficiency of the system.
Occupied bandwidth is determined, mostly, by the symbol rate.
The number of symbols required for a given system is 2 n , where n is the number of bits per symbol.