Many long-distance communication systems use a continuously oscillating electromagnetic

wave called a carrier. The system makes small changes to the carrier

that represent information being sent. We use the term modulation to refer

to changes made in a carrier according to the information being sent. Conceptually,

modulation takes two inputs, a carrier and a signal, and generates a

modulated carrier as output. So in essence, a sender must change one of the

fundamental characteristics of the wave in order to encode information onto the

carrier wave.

Typically modulation techniques allows analogue information to be directly

encoded on the carrier signal, however for the purposes of digital representation

of data to be encoded on a carrier, a zero (0) or one (1) must be encoded

onto the carrier.

With analogue modulation, a continuum of possible values can thus be

modulated on the carrier, but digital encoding has a fixed set of values that can

be encoded per signal change. For example, if amplitude modulation is used

to encode a zero or a 1, in the simplest case, a full amplitude can correspond

to a logical 1 and a significantly smaller amplitude can correspond to a logical 0.

From the discussion above it is clear that if digital data is modulated on a

carrier, only one bit can typically be encoded per signal change of the carrier

wave.

a) Is there an encoding scheme that allow for more than one bit to be encoded

per signal change of the carrier wave? [2]

b) Motivate the answer you provided above (in a) with a brief discussion and

remember to provide subject related diagrams and clear naming of aspects

that will substantiate your discussion [15]