Analogue And Digital Signalling Computer Science Essay

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Analogue signal is any continuous signal for which the time varying feature (variable) of the signal is a representation of some other time varying quantity, i.e. analogous to another time varying signal. It differs from a digital signal in that small fluctuations in the signal are meaningful.

(ii) Digital signal

Digital signals are non-continuous, they change in individual steps. They consist of pulses or digits with discrete levels or values. The value of each pulse is constant, but there is an abrupt change from one digit to the next. Digital signals have two amplitude levels called nodes. The value of which are specified as one of two possibilities such as 1 or 0, HIGH or LOW, TRUE or FALSE and so on. In reality, the values are anywhere within specific ranges and we define values within a given range.

Different types of transmission media

(i)Coaxial cable

Coaxial cable, or coax, is an electrical cable with an inner conductor surrounded by a insulating layer typically of a flexible material with a high dielectric constant, all of which are surrounded by a conductive layer (typically of fine woven wire for flexibility, or of a thin metallic foil), and finally covered with a thin insulating layer on the outside.

The advantages of a coaxial cable are that it has a greater bandwidth, great channel capability and lower error rates. On the other hand, it is costly due to the high installation costs and constant upgrading is required.

(ii)Optical fibre

An optical fiber is a glass or plastic fiber that carries light along its length.

How does it work?

Transmitter - Produces and encodes the light signals

Optical fiber - Conducts the light signals over a distance

Optical regenerator - May be necessary to boost the light signal (for long distances)

Optical receiver - Receives and decodes the light signals

The light in a fiber-optic cable travels through the core (hallway) by constantly bouncing from the cladding (mirror-lined walls), a principle called total internal reflection. Because the cladding does not absorb any light from the core, the light wave can travel great distances.

Diagram of total internal reflection in an optical fibre

Advantages of optical fibre

Less expensive - Several miles of optical cable can be made cheaper than equivalent lengths of copper wire. This saves your provider (cable TV, Internet) and you money.

Thinner - Optical fibers can be drawn to smaller diameters than copper wire.

Higher carrying capacity - Because optical fibers are thinner than copper wires, more fibers can be bundled into a given-diameter cable than copper wires. This allows more phone lines to go over the same cable or more channels to come through the cable into your cable TV box.

(iii)Wireless links

Bluetooth is one of the examples of

Wireless links. Wireless links are used because there

is no need for a wired connection and it enables a lot

of devices to be connected at once. Wireless is

needed because a lot of devices can be connected at

once and they can be portable.

Task 2

An analogue-to-digital interfacing conversion: an input selector receiving at least one analogue signal and selectively outputting the at least one analogue signal based on a plurality of clock signals; an analogue-to-digital converter converting the at least one analogue signal output from the selector to at least one digital signal; a plurality of registers; and an output selector receiving each digital signal output from the analogue-to-digital converter and selectively routing the digital signal to one of the plurality of registers based on the plurality of clock signals, wherein the input selector includes at least one first logic controlled gate, each first logic controlled gate receiving one of the at least one analogue signal and selectively outputting the received analogue signal to the analogue-to-digital converter based on the plurality of clock signals.

Level shifting:

A communication system including at least one controller for enabling a plurality of radio systems to communicate over a packet network, each radio system communicating one of at least two different radio signals transmitted using different radio-protocols, the communication system comprising: a plurality of gateways adapted to communicate over an IP link using a generic IP data packet protocol having a component for storing audio signals and a component for storing radio control signals; for each radio signal of the at least two radio signals: at least one gateway of the plurality of gateways converting audio and control protocol signals in the radio protocols to and from audio and control components of the generic IP data packet protocol for at least one radio system that communicates using the radio signal; and where in the component of the generic IP data packet protocol for storing radio control signals is configured to store at least one event selected from a group consisting of: activating a transmitter in a radio station; releasing a transmitter in a radio station; tuning a transmitter in a radio station to a specific RF channel; switching a receiver in a radio station to a specific RF channel; and monitoring the carrier status of a radio station.

In the component of the generic IP data packet protocol for storing radio control signals is configured to store at least one events selected from a group consisting of: sending a data packet to a specific subscriber unit via a radio station; receiving a data packet from a specific subscriber unit via a radio station; and sending a paging alert tone to a specific subscriber unit via a radio station.

Task 3

Digital to analogue

In electronics, a digital-to-analogue converter (DAC or D-to-A) is a device for converting a digital (usually binary) code to an analogue signal (current, voltage or electric charge).An analog-to-digital converter (ADC) performs the reverse operation. A DAC converts an abstract finite-precision number (usually a fixed-point binary number) into a concrete physical quantity (e.g., a voltage or a pressure). In particular, DACs are often used to convert finite-precision time series data to a continually-varying physical signal. A typical DAC converts the abstract numbers into a concrete sequence of impulses that are then processed by a reconstruction filter using some form of interpolation to fill in data between the impulses. Other DAC methods (e.g., methods based on Delta-sigma modulation) produce a pulse-density modulated signal that can then be filtered in a similar way to produce a smoothly-varying signal.

Serial Input/parallel output

A serial-in/parallel-out shift register is similar to the serial-in/ serial-out shift register in that it shifts data into internal storage elements and shifts data out at the serial-out, data-out, and pin. It is different in that it makes all the internal stages available as outputs. Therefore, a serial-in/parallel-out shift register converts data from serial format to parallel format. If four data bits are shifted in by four clock pulses via a single wire at data-in, below, the data becomes available simultaneously on the four Outputs after the fourth clock pulse.

Parallel input/serial output

Where there is a need for serial-to-parallel conversion, there is also a need for parallel-to-serial conversion. The parallel-in, serial-out register (or parallel-to-serial shift register, or shift-out register), however, is a bit more complex than its counterpart. Since each flip-flop in the register must be able to accept data from either a serial or a parallel source, a small two-input multiplexer is required in front of each input. An extra input line selects between serial and parallel input signals, and as usual the flip-flops are loaded in accordance with a common clock signal.