1. Chapter 2: Digital Modulation
Introduction
Electronic communications
 is the transmission, reception and the processing of the information with the use of electronic circuits
Information
knowledge or intelligence that is communicated ( transmitted or received )
Digital modulation
the transmittal of digitally modulated analog signals (carrier) between two points or more
Digital radio
 Relatively high-frequency analog carriers modulated by relatively low-frequency digital signals (can be carried by free space)

2. If the information signal is digital and the amplitude (V) is varied proportional to the information signal
amplitude shift keying (ASK)
If the information signal is digital and the phase of the carrier is varied proportional to the information signal
phase shift keying (PSK)
If the information signal is digital and the frequency (f) is varied proportional to the information signal
frequency shift keying (FSK)

3. Digital modulation is good for the use in both cable and wireless system such as
Low-speed voice band data communication modem
High-speed data transmission system such as DSL (digital subscriber line)
Digital microwave and satellite communication systems
Cellular telephone Personal communications systems (PCS)

4. Information theory  study the efficient use of bandwidth to propagate information through electronic communication systems
Information capacity
 represent the number of independent symbols (usually binary digit or bit) that can be carried through a system in a given unit of time (bit rate  bps)
Hartley’s Law
Shannon limit for information capacity

5. Amplitude-shift keying (ASK)
 the binary information signal directly modulates the amplitude of an analog carrier
 there are only two output amplitudes possible
 mathematically written as

6. Frequency-shift keying (FSK)
 mathematically written as
 when the binary input change logic from 1 to logic 0, the output frequency change from a mark (fm) to a space frequency (fs) as shown in picture

7. Continuous-Phase Frequency-Shift Keying (CP-FSK)
is normal binary FSK except the mark and space frequencies are synchronized (synchronous does not have to be equal, but there is a precise time relationship between the two frequency )
 with CP-FSK, the mark and space frequencies are selected such that they are separated from the center frequency by an exact multiple of one-half the bit rate (fm and fs =n*(fb/2))
in discontinuity FSK, when the input changes, there is an abrupt phase discontinuity in analog signal. So, the demodulator has trouble following the shift frequency causing error
CP-FSK has better bit-error performance but expensive to implement

8. Binary Phase-Shift Keying
two phases are for carrier. One phase represents logic 1 and the other represents logic 0
 the phase of the output carrier shifts between two angles that are separated by 180 degree
Quadrature –Amplitude Modulation (QAM)
is a form of digital modulation similar to PSK but digital information is contained in both the amplitude and phase of the transmitted carrier