Communication

• “Communicare” which means to share

• it involves two parties (sender, receiver)

• it takes many forms

Types of Media

1. Guided or Wired

• Coax, UTP, Twin-Lead

• Fiber Optics

• Wave Guide

2. Unguided/Wireless

• Antenna, radiators

Communication System

1. Transducer (change of effect, sound to electrical) - any device that converts from one form to another.

2. Transmitter

3. Channel

4. Receiver

5. Transducer

Basebands

• the band of frequencies including guard bands, assigned to a channel.

• Voice frequencies - 300Hz to 3kHz

• Hearing frequencies - 20 Hz to 20kHz

Fidelity

• abilityt to replicate its input to its output

Signals

• Physical quantity or variable, and typical it contains information about the behavior or nature of the phenomenon.

• Starts with Information, then data, then converted into signal (something we can hear, smell, see, feel, taste), then the message, representation, and meaning.

Analog Signal

• Continuous signals in both time and amplitude. Electrical prperties used are voltage, followed closely by frequency current, and charge.

Digital Signal

• discrete (mahematically, finite and countable infinite) in both time and signal.

Advantages of Digital over Analog

1. Easier to store.

2. Immune to noise.

3. Have error detection and correction.

4. Encryption can be added.

Disadvantages of Digital to Analog

1. Wider bandwidth

2. Complex Circuit.

Sampling

• Selecting values of an analog signal at a discrete time instant.

• First step when performing from analog to digital signal conversion

Sampling Theorem

• a bandwidth continuous time signal can be sampled and perfectly reconstructed from its sample if the waveform is sample over twise as the highest frequency component.

Quantization

• number of bits used to store each intensity defies the accuracy of the digital signals

Aliasing

• effect produced when a signal is imperfectly reconstructed frm the sampled signal. It occurs when a signal is not sampled at a high enough frequency to create an accurate representation.

Classifications of Signal

1. Continuous-Time (continuous and real in domain and range) and Discrete-Time (often identifies as a sequence of numbers)

2. Real (signal is purely real) and Complex (signal has an imaginary part).

3. Deterministic (signal whose vaues are completely specified for any given time) and Random (signals that take random values at any given time, like white noise).

4. Even (divisible by 2 with 0 as a reminder, only having one flip) and odd (divisible by 2 with remainder not equal to 0, signal is flipped 2 times).

5. Period and Aperiodic (non repeating, all randoms are aperiodic).

6. Energy (finite duration, finite amplitude) and Power (not limited in time, non zero for infinite amount of time).

7. Causal (signal that does not start before t=0), Anti-causal (signal that ends at t=0), and Non-causal (sarts before t=0 and coontinues after t=0)

Signal manipulation

1. Shifting - delay: shift to the right, advance: shift to the left

2. Reversal

3. Scaling - upsampling: expand k time, downsampling: compress k ties

System

• physical device that performs an operation on a given signal.

Memoryless

• if the input y[n] at every value of n depends on the input x[n] at the same value of n. Else, with memory with delay or advance.

Invertible

• if distinct inouts lead to distinct outputs or if an inverse system exists. Else, non-invertible

Causal

• output does not depend on future input. Else, non-causal if output depends on future input.

Stable

• if and only if every bounded input produces a bouned output. Output of a stable system does not change unreasonably Else, unstable even if one bounded input generates an unbounded output.

Linear-time variant system

1. Linearity

• Homogeneous

• Additive

2. Time in Variance

• a shift in the input signal results to an indentical shift in the output signal