Dear P. Prakasam,

The constellation of the M-ASK is one dimensional, where the amplitude of the carrier is assigned M values corresponding to the M states of modulated carrier signal. Where as the QAM has two dimensional constellation such that every constellation point  has an I component and  a Q component. since the two components are perpendicular to each other it is called quadrature. This means that QAM is a specific form of a combined amplitude and phase modulation.

Expressed in mathematical form:

M-ASK

v= Vim sin wc t    with i having M-values,

M-QAM

The I compoment

I(i,j)= Iim sin (wct +phi j) and

Q(i,j)= Qi cos (wct+ phj)  , where M= ixj,

Wish you success

QAM conveys two analog message signals, or two digital bit streams, by changing (modulating) the amplitudes of two carrier waves, using the amplitude-shift keying (ASK) digital modulation scheme or amplitude modulation (AM) analog modulation scheme.

The two carrier waves, usually sinusoids, are out of phase with each other by 90° and are thus called quadrature carriers or quadrature components

M-ASK-Amplitude-shift keying (ASK) is a form of amplitude modulation that represents digital data as variations in the amplitude of a carrier wave. In an ASK system, the binary symbol 1 is represented by transmitting a fixed-amplitude carrier wave and fixed frequency for a bit duration of T seconds.

An M-ary transmission is a type of digital modulation where instead of transmitting one bit at a time, two or more bits are transmitted simultaneously.\

So ASK with multiple m-ask more than 1 bit is used to represent a signal .

I am wondering what is the shape of I/Q on constellation diagram  if I use M-ASK modulation

Dear Murtadha,

welcome,

The signals in the costellation diagram has two components, an I component and a Q-component such that S=(I,Q).  The M-ASK has an I component only such that S= I, for binary I= -I1, I1, for 4ASK I=I1,I2,-I1,-I2 ,... etc.

So it appears as points on the I axis with symmetry around I=0.

Best wishes