1). Describe frequency modulation, amplitude modulation, phase-shift modulation,
ID: 3671270 • Letter: 1
Question
1). Describe frequency modulation, amplitude modulation, phase-shift modulation, and on-off keying.
2What are the components of a communiication channel?
3) What are the components of a communication protocol?
4) Describe simplex, half-duplex, and full-duplex transmission and compare them in terms of cost and effective data transfer rate
5)What’s a block check character? How is it computed and used?
6) What is character framing? Why is it generally not an issue in parallel data transmission?
How many bits are in an IP address? What is a TCP or UDP port? What is
a TCP or UDP socket?
Explanation / Answer
1)Frequency modulation:
Frequency modulation is widely used for FM radio broadcasting. It is also used in telemetry, radar, seismic prospecting, and monitoring newborns for seizures via EEG,two-way radio systems, music synthesis, magnetic tape-recording systems and some video-transmission systems. In radio transmission, an advantage of frequency modulation is that it has a larger signal-to-noise ratioand therefore rejects radio frequency interference better than an equal power amplitude modulation (AM) signal. For this reason, most music is broadcast over FM radio.
Frequency modulation has a close relationship with phase modulation; phase modulation is often used as an intermediate step to achieve frequency modulation. Mathematically both of these are considered a special case of quadrature amplitude modulation(QAM).
frequency modulation (FM) is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave. This contrasts with amplitude modulation, in which the amplitude of the carrier wave varies, while the frequency remains constant.
In analog frequency modulation, such as FM radio broadcasting of an audio signal representing voice or music, the instantaneousfrequency deviation, the difference between the frequency of the carrier and its center frequency, is proportional to the modulating signal.
Digital data can be encoded and transmitted via FM by shifting the carrier's frequency among a predefined set of frequencies representing digits - for example one frequency can represent a binary 1 and a second can represent binary 0. This modulation technique is known as frequency-shift keying (FSK). FSK is widely used in modems and fax modems, and can also be used to sendMorse code. Radioteletype also uses FSK.
Amplitude modulation:
Amplitude modulation (AM) is a method of impressing data onto an alternating-current (AC) carrier waveform.The highest frequency of the modulating data is normally less than 10 percent of the carrier frequency.The instantaneous amplitude(overall signal power) varies depending on the instantaneous amplitude of the modulating data.
In AM, the carrier itself does not fluctuate in amplitude. Instead,the modulating data appears in the form of signal components at frequencies slightly higher and lower than that of the carrier. These components are called sidebands.The lower sideband (LSB) appears at frequencies below the carrier frequency; the upper sideband (USB) appears at frequencies above the carrier frequency.The LSB and USB are essentially "mirror images" of each other in a graph of signal amplitude versus frequency, as shown in the illustration.The sideband power accounts for the variations in the overall amplitude of the signal.
When a carrier is amplitude-modulated with a pure sine wave, up to 1/3 (33percent) of the overall signal power is contained in the sidebands.The other 2/3 of the signal power is contained in the carrier, which does not contribute to the transfer of data.With a complex modulating signal such as voice, video, or music, the sidebands generally contain 20 to 25 percent of the overall signal power; thus the carrier consumes75 to 80 percent of the power.This makes AM an inefficient mode.If an attempt is made to increase the modulating data input amplitude beyond these limits, the signal will become distorted, and will occupy a much greater bandwidth than it should.This is called overmodulation, and can result in interference to signals on nearby frequencies.
Phase-shift modulation:
It is a modulation pattern that encodes information as variations in the instantaneous phase of a carrier wave.
Phase modulation is widely used for transmitting radio waves and is an integral part of many digital transmission coding schemes that underlie a wide range of technologies like WiFi, GSM and satellite television.
Phase modulation is closely related to frequency modulation (FM); it is often used as an intermediate step to achieve FM. Mathematically both phase and frequency modulation can be considered a special case of quadrature amplitude modulation (QAM).
PM is used for signal and waveform generation in digital synthesizers, such as the Yamaha DX7 to implement FM synthesis. A related type of sound synthesis called phase distortion is used in the Casio CZ synthesizers.
On-off keying:
On-off keying (OOK) denotes the simplest form of amplitude-shift keying (ASK) modulation that represents digital data as the presence or absence of a carrier wave. In its simplest form, the presence of a carrier for a specific duration represents a binaryone, while its absence for the same duration represents a binary zero. Some more sophisticated schemes vary these durations to convey additional information. It is analogous to unipolar encoding line code.
On-off keying is most commonly used to transmit Morse code over radio frequencies (referred to as CW (continuous wave) operation), although in principle any digital encoding scheme may be used. OOK has been used in the ISM bands to transfer data between computers, for example.
OOK is more spectrally efficient than frequency-shift keying, but more sensitive to noise when using a regenerative receiver or a poorly implemented superheterodyne receiver. For a given data rate,the bandwidth of a BPSK (Binary Phase Shift keying) signal and the bandwidth of OOK signal are equal.
In addition to RF carrier waves, OOK is also used in optical communication systems (e.g. IrDA).
In aviation, some possibly unmanned airports have equipment that let pilots key their VHF radio a number of times in order to request an Automatic Terminal Information Service broadcast, or turn on runway lights.
2)Communication is a two way process. It is a chain of events that can be broken into six phases:
1. Source 2. Message 3. Channel 4. Receiver 5. Effect 6. Feed back
1. Source : “Sender of message who determine the point, message, material and channel of message.” The source is the originator of the idea or the message. It is also known as sender or encoder who may be an individual or group. He chooses such symbols to express the message so that the receiver may understand and it reacts with the desired response. He decides which symbols best convey his message and which sending mechanism to choose among the available written and oral media.
2. Message : “When a person express his ideas thinking and emotions in the form of words so that the meaningful words become message for the other person” A message is the conversion of conceived idea into symbols. It may consist of both verbal symbol and non-verbal symbol. Whenever you compose a message, you need to consider what content to include, how the receiver will interpret and how it may affect your relationship. For instance, for thanking some one the word “Thanks you” is suitable but not for the excuse
. 3. Channel : “Medium, channel way which is used for sending message, it may be printed words, electronic mail, sound etc.” Inter relationship between the sender and the receiver and the urgency of message are the major determiners of the medium used for the message. The other factors are number of receivers, cost, and amount of information and effectiveness of the channel. The channel may be print media such as newspaper, brochure, hand bill or the electronic media like T.V, Radio and internet etc. selection of channel depends upon the message.
4. Receiver : “A person who receives the message and takes decision in the form of feed back is known as receiver.” The receiver is the person for whom the message is intended. It is the single most important element in the communication process. Any neglect on this part of receiver many senders the communication ineffective. Actually message receiver is your sender or listener, also known as “Decoder”. Many of your messages have more than one decoder (receiver).
5. Effect : Effect is the change in the behavior of the receiver occurring in response to the message receiver. The receiver may ignore the message or store the information received, or act according to the wishes of the sender.
6. Feed Back: “Feed back action or decision taken by receiver after receiving the message. It can be oral or a written message, an action or simply silence.” Feed back is the response that sender gets from the receiver. It may be positive or negative. At times the receiver misunderstands the subject or symbols as all of us do not have identical experiences with the subject or symbols by the sender. If the receiver incorrectly perceives our message, we may say it as miscommunication.
3)A communications protocol includes message content, which is composed of data and command content, message transmission, which is composed of media, which is composed of bit encoding and transmission, channel organization, which is composed of simplex/half-duplex/duplex modes, parallel/serial transmission, and channel sharing, and coordination, which includes clock synchronization, error detection and correction. In order for communications to take place, there must be message content to communicate, which includes the data to be communicated as well as command content, which includes instructions such as device control, addressing, and routing as well as information about the size, content, and format of the data. Message transmission takes place over media, where bits are transmitted via sine waves, where variations in amplitude and frequency of the wave encode the true/false values of the bits.
4)Simplex is one direction. A good example would be your keyboard to your CPU. The CPU never needs to send characters to the keyboard but the keyboard always sends characters to the CPU. In many cases, Computers almost always send characters to printers, but printers usually never send characters to computers (there are exceptions, some printers do talk back). Simplex requires only one lane (in the case of serial).
Half-Duplex is like the dreaded "one lane" road you may have run into at construction sites. Only one direction will be allowed through at a time. Railroads have to deal with this scenario more often since it's cheaper to lay a single track. A dispatcher will hold a train up at one end of the single track until a train going the other direction goes through. The only example I could think of for Half-Duplex is actually a Parallel interface. Even though parallel is eight lanes, data travels through the lanes in the same direction at the same time but never in both directions at the same time. The IEEE-1284 allows printers to send messages to the computer. The printer cannot send these messages while the computer is sending characters but when the computer stops sending characters, then the printer can send messages back. It's kind of like some roads that head into downtown. In the morning, they're one way roads, allowing traffic to go into downtown. In the evening their one way roads, allowing traffic to head out of downtown. The only advantage that Half-Duplex would have is the single lane or single track is cheaper then the double lane or double track.
Full-Duplex is like the ordinary two-lane highway. In some cases, where traffic is heavy enough, a railroad will decide to lay a double track to allow trains to pass in both directions. In communications, this is most common with networking. Our fiber optic hubs have two connectors on each port, one for each lane of a two-lane roadway. Full-Duplex fiber is two cables bundled or tied together to form the two-lane roadway. In 100Base-TX, the two lanes are housed in the same jacket. RS232 was also designed to handle Full-Duplex but some of our short haul modems and converters give the user the option to go Half-Duplex or Simplex to reduce the number of conductors needed to connect between them.
5)In telecommunications, a block check character (BCC) is a characteradded to a transmission block to facilitate error detection. In longitudinal redundancy checking and cyclic redundancy checking, block check characters are computed for, and added to, each message blocktransmitted.
6)Character refers to the total number of bits used to transmit a character. This includes the length of the coded character and the number and type of overhead bits required for transmitting it. A common character-framing scheme calls for a start bit, seven data bits, an odd-parity bit, and a stop bit. An additional bit is often added to the frame for error-checking purposes.
The two most common versions of IP in use today are Internet Protocol version 4 (IPv4) and Internet Protocol version 6 (IPv6). Both IPv4 and IPv6 addresses come from finite pools of numbers. For IPv4, this pool is 32-bits (232) in size and contains 4,294,967,296 IPv4 addresses
Transport layer protocols, such as the Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP), specify a source and destination port number in their segment headers. A port number is a 16-bit unsigned integer, thus ranging from 0 to 65535.
To manage the connection between application layer network protocols,TCP and UDP use ports and sockets. TCP and UDP operate at the host-to-host layer in the IP communication model and provide host-to-host communication services for the application layer protocol.
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