SIGNALS, SPECTRA, SIGNAL PROCESSING

Communication

From the word “commnicare” which means to share. it involves 2 parties - the sender and receiver. It takes many forms

Examples of Media

Guided or Wired such as coax, UTP, Twin-Lead, Fiber Optics, Wave Guide, and many more.

Unguided or Wireless such as antenna and other radiators

Communication System

It starts with tranducer, then transmitter, channel, to the receiver, and finally to Transducer.

Transducer

Any device that converts from one form to another (e.g sond to electrical)

Basebands

The band of frequencies occupied by the signal in a carrier system before it modulates the carrier frequency.

Voice Frequency

300 Hz to 3kHz

Hearing Frequency

20hz to 20kHz

Fidelity

Ability to replicate its input to its output

Signals

Physical quantity or variable and typically contains information about the behavior or nature of the phenomenon. It starts with information, data, then signal (something that the senses can sense), message, representation, then the meaning.

Analog Signal

Continuous signal in both time and amplitude. Electrical properties used are voltage, followed closely by frequency, current and charge

Digital Signal

Discrete (mathematically, finite and countavle infinite) in both time and signal

Sampling

Selecting values of an analog signal at a discrete time instant. First step when performing from analog to digital signal conversion

Advantages of Digital over Analog

Easier to store, Immune to Noise, Have error detection and correction, and Encryption can be added.

Disadvantage of Digital to Analog

Wider bandwidth and Complex Circuit

Quantization

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

Continuous-Time Signal

Classification of signal that is continuous and real in domain and range

Discrete-TIme Signal

Clasification of signal that often identifies as a sequence of numbers

Sampling Theorem

A bandwidth continuous time signal can be sampled and perfectly reconstructed from its sample if the waveform is sample over twice as the highest frequency component

Aliasing

Effect produced when a signal is imperfectly reconstructed from the sampled signal. it occurs when a signal is not sampled at a high enough frequency to create an accurate representation

Real and Complex

Classification of signal if it is purely real or signal has an imaginary part

Deterministic and Random

Classification of signal whose values are completely specified for any given amount of time or signals that take random values at any given time.

Even and Odd

Classification of signal if the signal have 1 flip or 2 flips

Period and Aperiodic

Classification of signals that tells if it is repeating or non-repeating (all random)

Energy

Classification of signal that has finite duration and ampitude

Power

Classification of signal which states that signal is not limited in time, non zero for infinite amount of time.

Causal

Classification of signal that describe signal that does not start before t=0

Anti-Causal

Classsification of signal that describe signal that ends at t=0

Non-Causal

Classification of signal that describes signal that starts before

Shifting

Signal manipulation where signal can be delayed or advanced

Reversal

Signal manipulation where signal is reversed in n value of t

Scaling

Signal manipulation where the is upscaling (expand k times) or downsampling (compress k times)

System

Physical device that performs an operation on a given signal

Memoryless

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

Invertible

If distinct inputs lead to distinct outputs or if an inverse system exist. 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 proceduces a bounded output. output of a stable system does not change reasonably. Else, unstable, even if one bounded input generates an unbounded output

Linearity

Either homogeneous or additive

Time in Variance

A shift in the inout signal results to an identical shift in the output signal