Electronic Communications

Electronic Communications

• Electronic communications involves the transmission, reception, and processing of information using electronic circuits.
• Information is defined as knowledge or intelligence that is communicated between two or more points.

Digital Modulation

• Digital modulation is the transmission of digitally modulated analog signals (carriers) between two or more points in a communications system.
• Digital modulation is sometimes called digital radio because it can be propagated through Earth’s atmosphere and used in wireless communications systems.

Types of Digital Modulation

• Amplitude Shift Keying (ASK): the amplitude of the carrier is varied proportional to the information signal.
• Frequency Shift Keying (FSK): the frequency of the carrier is varied proportional to the information signal.
• Phase Shift Keying (PSK): the phase of the carrier is varied proportional to the information signal.
• Quadrature Amplitude Modulation (QAM): both the amplitude and the phase are varied proportional to the information signal.

Information Theory

• Information theory is a highly theoretical study of the efficient use of bandwidth to propagate information through electronic communications systems.
• Information capacity is a measure of how much information can be propagated through a communications system and is a function of bandwidth and transmission time.

Digital Symbols

• The most basic digital symbol used to represent information is the binary digit, or bit.
• Bit rate is the number of bits transmitted during one second and is expressed in bits per second (bps).
• M-ary is a term that represents a digit that corresponds to the number of conditions, levels, or combinations possible for a given number of binary variables.

Baud and Bit Rate

• Baud is a unit of transmission rate, modulation rate, or symbol rate, and is often used interchangeably with symbols per second.
• Baud is not the same as bit rate, as the baud of a data communications system may be less than the bit rate.
• In binary systems, baud and bits per second are equal, but in higher-level systems, bps is always greater than baud.

Minimum Nyquist Bandwidth

• The minimum theoretical bandwidth necessary to propagate a signal is called the minimum Nyquist bandwidth or minimum Nyquist frequency.
• fb = 2 B, where fb is the bit rate in bps and B is the ideal Nyquist bandwidth.

Amplitude-Shift Keying (ASK)

• Amplitude-Shift Keying (ASK) is the simplest digital modulation technique.
• In ASK, a binary information signal directly modulates the amplitude of an analog carrier.
• ASK is sometimes called digital amplitude modulation (DAM) or on-off keying (OOK).