Chapter 2
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Example of simple transmission is TV and Radio.
Example of Half-Duplex is Walkie-Talkie.
Example of Full-Duplex is Mobile phone.
An analog signal is any for which the time-varying feature of the signal is a representation of some other time-varying quantity
A digital signal is a signal that is being used to represent data as a sequence of discrete values; at any given time it can only take on, at most, one of a finite number of values
3 main factors of the signal are : magnitude , frequency , phase.
baud rate formula : s(t) = m(t) cos(2*phi*f(t)+teta(t)).
To lower the probability of interruption , we have to be closer to the access point to be faster , because the smaller the difference, the easier it will be for interruptions to occur.
lightspeed = frequency x wavelength(lamda).
modulation : take original signal to a carrier.
demodulation : take original signal from carrier
carrier is like a transportation and carrier is always an analog signal.
All of those modulation are analog signals.
4 steps for digital signal to anaolog signal
Sampling
Quantization
Magnitude
PCM Encoding
Encoding
Self Clocking: to put clocking information into signal , so we don't have to match the clocking from the sender and receiver.
TD is a legacy multiplexing technology still providing the backbone of most National fixed line Telephony networks in Europe, providing the 2m/bit voice and signalling ports on Narrow band Telephone exchanges such as the DMS100. Each E1 or 2m/bit TDM port provides either 30 or 31 speech timeslots in the case of CCITT7 signalling systems and 30 voice channels for customer connected Q931, DASS2, DPNSS, V5 and CASS signalling systems.
For the brief explanation :
FDM : example for TV Station , it can be divided into sub-channel and can be used by different people.
TDM : Who get it first who used it first.
CDM : the orthogonal signal encoded with different ways so they don't disturb each other.
Message switching is a network switching technique in which data is routed in its entirety from the source node to the destination node, one hope at a time. During message routing, every intermediate switch in the network stores the whole message. If the entire network's resources are engaged or the network becomes blocked, the message-switched network stores and delays the message until ample resources become available for effective transmission of the message.
DSL stands for Digital Subscriber Line. Users get a high speed bandwidth connection from a phone wall jack on an existing telephone network. DSL works within the frequencies that the telephone doesn’t so you can use the Internet while making phone calls.
Amplitude modulation (AM) is a technique used in electronic communication, most commonly for transmitting messages with a . In amplitude modulation, the (signal strength) of the carrier wave is varied in proportion to that of the message signal, such as an . This technique contrasts with , in which either the frequency of the is varied as in , or its , as in .
Frequency modulation (FM) is the encoding of in a by varying the of the wave. The technology is used in , , , and .
Phase modulation (PM) is a pattern for conditioning communication signals for . It encodes a message signal as variations in the of a . Phase modulation is one of the two principal forms of , together with .
The ISM radio bands are of the reserved internationally for industrial, scientific and medical (ISM) purposes, excluding applications in . Examples of applications for the use of (RF) energy in these bands include , , and medical machines. The powerful emissions of these devices can create and disrupt using the same , so these devices are limited to certain bands of frequencies. In general, communications equipment operating in ISM bands must tolerate any interference generated by ISM applications, and users have no regulatory protection from ISM device operation in these bands.
Power over Ethernet, or PoE, describes any of several or systems that pass along with data on cabling. This allows a single cable to provide both data connection and electric power to devices such as (WAPs), , and .
A modulator-demodulator, or simply a modem, is a device that converts data from a digital format, intended for communication directly between devices with specialized wiring, into one suitable for a such as telephone lines or radio. A modem one or more signals to encode for transmission, and signals to decode the transmitted information. The goal is to produce a that can be transmitted easily and decoded reliably to reproduce the original digital data.
In and , multiplexing (sometimes contracted to muxing) is a method by which multiple analog or digital signals are combined into one signal over a . The aim is to share a scarce resource.
Frequency-division multiplexing (FDM): The spectrum of each input signal is shifted to a distinct frequency range.
(FDM) is inherently an analog technology. FDM achieves the combining of several signals into one medium by sending signals in several distinct frequency ranges over a single medium. In FDM the signals are electrical signals. One of the most common applications for FDM is traditional radio and television broadcasting from terrestrial, mobile or satellite stations, or cable television. Only one cable reaches a customer's residential area, but the service provider can send multiple television channels or signals simultaneously over that cable to all subscribers without interference. Receivers must tune to the appropriate frequency (channel) to access the desired signal.
A variant technology, called (WDM) is used in .
Time-division multiplexing (TDM).
(TDM) is a digital (or in rare cases, analog) technology which uses time, instead of space or frequency, to separate the different data streams. TDM involves sequencing groups of a few bits or bytes from each individual input stream, one after the other, and in such a way that they can be associated with the appropriate receiver. If done sufficiently quickly, the receiving devices will not detect that some of the circuit time was used to serve another logical communication path.
Consider an application requiring four terminals at an airport to reach a central computer. Each terminal communicated at 2400 , so rather than acquire four individual circuits to carry such a low-speed transmission, the airline has installed a pair of multiplexers. A pair of 9600 baud modems and one dedicated analog communications circuit from the airport ticket desk back to the airline data center are also installed. Some (e.g. ) use TDM in of multiple transactions onto the same .
and communication methods are similar to time-division multiplexing in that multiple data streams are separated by time on the same medium, but because the signals have separate origins instead of being combined into a single signal, are best viewed as , rather than a form of multiplexing.
(CDM), (CDMA) or is a class of techniques where several channels simultaneously share the same , and this spectral bandwidth is much higher than the bit rate or . One form is frequency hopping, another is direct sequence spread spectrum. In the latter case, each channel transmits its bits as a coded channel-specific sequence of pulses called chips. Number of chips per bit, or chips per symbol, is the . This coded transmission typically is accomplished by transmitting a unique time-dependent series of short pulses, which are placed within chip times within the larger bit time. All channels, each with a different code, can be transmitted on the same fiber or radio channel or other medium, and asynchronously demultiplexed. Advantages over conventional techniques are that variable bandwidth is possible (just as in ), that the wide bandwidth allows poor signal-to-noise ratio according to , and that multi-path propagation in wireless communication can be combated by .
A significant application of CDMA is the (GPS).
Telephony is the field of technology involving the development, application, and deployment of services for the purpose of electronic transmission of voice, fax, or data, between distant parties. The history of telephony is intimately linked to the invention and development of the .
The public switched telephone network (PSTN) provides and services for public . The PSTN is the aggregate of the world's circuit-switched networks that are operated by national, regional, or local operators. These consist of , , links, , , and , all interconnected by which allow most telephones to communicate with each other.
Originally a network of fixed-line telephone systems, the PSTN is now almost entirely digital in its and includes and other networks, as well as fixed telephones.
Circuit switching is a method of implementing a in which two establish a dedicated () through the network before the nodes may communicate. The circuit guarantees the full bandwidth of the channel and remains connected for the duration of the . The circuit functions as if the nodes were physically connected as with an . Circuit switching originated in analog where the network created a dedicated circuit between two telephones for the duration of a . It contrasts with and used in modern digital networks in which the between switching centers carry data between many different nodes in the form of without dedicated circuits.
In , packet switching is a method of grouping that is transmitted over a digital into . Packets are made of a and a . Data in the header is used by networking hardware to direct the packet to its destination, where the payload is extracted and used by . Packet switching is the primary basis for data communications in worldwide.
Asymmetric digital subscriber line (ADSL) is a type of (DSL) technology, a data communications technology that enables faster data transmission over than a conventional can provide. ADSL differs from the less common (SDSL). In ADSL, and are said to be asymmetric, meaning greater toward the customer premises () than the reverse (). Providers usually market ADSL as an service primarily for content from the Internet, but not for serving content accessed by others.
The term Base station is used in the context of , and other and in . In surveying, it is a at a known position, while in wireless communications it is a connecting a number of other devices to one another and/or to a wider area. In mobile telephony, it provides the connection between and the wider . In a , it is a transceiver acting as a for in the network, possibly connecting them to a/another and/or the . In traditional wireless communications, it can refer to the hub of a fleet such as a or fleet, the base of a network as used by and or a .
