Advanced Communication : Communication Network | Electronic Engineering

By Neha Pathak|Updated : July 7th, 2021

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Brief about Paging Systems

  • Paging systems vary widely in their complexity and coverage area.
  • Simple paging systems cover a limited range of 2 km to 5 km. They are confined to within individual buildings.
  • Wide area paging system can provide worldwide coverage. They consist of a network of telephone lines, many base station transmitters and large radio towers that simultaneously broadcast a page from each base station which is called simulcasting. Simulcast transmitters maybe located within the same service area or in different countries or cities.
  • Paging systems require a large transmitter power and low data rates for maximum coverage from each base station.
  • The diagram of a wide area paging system is as shown.

Cellular Telephone Systems

A cellular telephone system provides a wireless connection to the PSTN (Public Switched Telephone Network) for any user within the radio range of the system. Cellular systems accommodate a large number of users over a large geographic area within a limited frequency spectrum.

Cellular radio systems provide high quality service that is often comparable to that of the landline telephone system.

The coverage of each base station is limited to a small geographic area called a Cell so that the same radio channels may be reused by another base station located some distance away.

The technique called Handoff enables a call to proceed uninterrupted when the user moves from one cell to another.

The cellular system consists of Mobile stations, base stations and a mobile switching centre (MSC) also called the Mobile telephone Switching Office (MTSO),It is responsible for connecting all mobiles to the PSTN in a cellular system.

The towers represent base stations which provide radio access between mobile users and the MSC.

Comparison of common mobile radio systems

Service

Coverage Range

Required Infrastructure

Complexity

Hardware cost

Carrier Frequency

Functionality

TV remote Control

Low

Low

Low

Low

Infra-red

Receiver

Garage Door opener

Low

Low

Low

Low

< 100 MHz

Receiver

Paging system

High

High

High

High

<1 GHz

Transmitter

Cordless Phone

Low

Low

Low

Moderate

< 100 MHz

Transceiver

Cellular phone

High

High

High

High

< 1 GHz

Transceiver

 

 

 

 

 

 

 

First-Generation Analog Cellular Telephone:

  • First generation cellular and cordless telephone networks are based on analog circuit switching technology. The first 1G mobile phone was introduced in the USA 1980. FDMA was the multiple access technique used and worked mainly in the 800-900 MHz frequency binds. The 1G mobile phone had only voice facility.
  • Examples of 1G systems are AMPS (Advanced mobile. tone service) and TACS (total access communication systems)
  • The limitations of 1 G are:
  • Supports Speech only
  • Low traffic capacity
  • Unreliable handover
  • Long call setup time
  • Frequent call drops
  • Inefficient bandwidth usage
  • Poor battery life
  • Poor voice quality
  • Large size of handset
  • Allowed users to make voice calls within a country only

First generation wireless systems provide analog speech and inefficient low-rate data transmission between the base -station and the mobile user. The speech signals are usually digitized using a standard TDM format for transmission between the base station and the MSC and are always digitized for distribution from the MSC to the PSTN.

  Second-generation wireless telephone networks

  • First-generation cellular telephone systems were designed primarily for a limited customer base, such as business customers and a limited number of affluent residential customers. The problems inherent with these cellular telephones were poor battery performance and channel unavailability. Improved batteries were also needed to reduce the size and cost of mobile units, especially those that were designed to be handheld. Weak signal strengths resulted in poor performance and a high rate of falsely initiated handoffs (false handoffs).
  • It was determined that improved battery performance and higher signal quality were possible only by employing digital technologies.

Second-generation wireless telephone networks

  • The architecture employed in second generation networks have reduced the computational burden on the MSC.
  • GSM for example uses a base station controller (BSC) which allowed the data interface between the BSC and MSC to be standardized.

This allows carriers to use different manufacturers for MSC and BSC components.

  • All Second generation systems use digital voice coding and digital modulation. The systems employ dedicated control channels within the air interface for simultaneously exchanging voice and control information between the subscriber, the base station and the MSC while the call is in progress.
  • Second generation networks also provide dedicated voice and signaling trunks between MSCs and between each MSC and the PSTN.
  • The first generation systems were designed primarily for voice whereas the second generation systems are specifically designed to provide paging, Fax and high data rate internet access.
  • The network controlling structure is more distributed in second generation networks since mobile stations assume greater control functions.
  • The handoff process is more mobile controlled and is known as Mobile assisted handoff (MAHO). The mobile units perform additional functions of received power reporting, adjacent base station scanning, data encoding and encryption.

Interim 2.5 G -generation wireless telephone networks

  • The need for increased throughput data rates in data transfer such as web browsing and email led to the evolution of 2.5 G which is between 2G and 3G.
  • The mobile technology using GPRS (General Packet Radio Service) has been termed as 2.5 G.
  • The 2.5 G was started in 1998 with added GPRS and enhanced data rates for GSM evolution (EDGE). In addition to the Hypertext transfer protocol (HTTP) it supports the Wireless Access Protocol (WAP) through which web pages can be viewed on the small screen of a mobile phone or 'a handheld device which led to the development of mobile commerce (m-comment).
  • 2.5 G is packet switched and can use some of the existing infrastructures of GSM and CDMA (Code division multiple access) networks.

  Third-generation wireless telephone networks

  • The aim of third generation wireless networks is to provide a single set of standards that can meet a wide range of wireless applications and provide universal access throughout the world.
  • In 3 G networks the distinctions between cordless telephones and cellular telephones disappear and a universal personal communicator or personal handset provides access to a variety of voice, data and video communication services.
  • Third generation systems use the Broadband ISDN to provide access to information networks such as the Internet and other private and public databases.
  • 3 G networks carry all types of information like voice, data and video.
  • They operate in densely populated and sparsely populated areas.
  • They serve both stationary users and vehicular users travelling at high speeds.
  • Packet radio communication is used in the 3 G networks
  • Personal communication System (PCS) , International Mobile Telecommunication (IMT-2000) and Universal Mobile telecommunication System(UMTS) are examples of 3G wireless networks. UMTS is also known as W-CDMA (Wideband CDMA)
  • 3G technology has added multimedia facilities to 2.5 G phones.
  • 3 G operates in the 1710-2170 MHz band
  • In short 3G is the next generation of wireless network technology that provides high speed bandwidth (high data transfer rates) to handheld devices. The high data transfer rates will allow 3G networks to offer multimedia services combining voice and data.
  • Main characteristics of 3 G networks include
  • Always-on connectivity. 3G networks use IP connectivity, which is packet based.
  • Multi-media services with streaming audio and video.
  • Email with full-fledged attachments such as PowerPoint files.
  • Instant messaging with video/audio clips.
  • Fast downloads of large files such as faxes and PowerPoint files.
  • Access to corporate applications.
  • Applications include Mobile TV, Video on demand, Video conferencing, Telemedicine, Location based services.

   Fourth-generation wireless telephone networks

  • 4th-generation networks emerged as a data-optimized technology with the promise of speed improvements up to 10-fold over existing 3G technologies.
  • It is basically the extension in the 3G technology with more bandwidth and services offers in the 3G.
  • The expectation for the 4G technology is basically the high quality audio/video streaming over end to end Internet Protocol. The transmission rates of 4G will be upto 20Mbps higher than that of 3G.
  • The first two commercially available technologies billed as 4G were the WiMAX standard and the LTE standard. LTE - Advanced is the newest version of LTE.
  • One of the main ways in which 4G differed technologically from 3G was in its elimination of circuit switching, instead employing an all-IP network. 4G utilizes packet switching over internet, LAN or WAN networks via VoIP.
  • 4G technology is meant to provide what is known as "ultra-broadband" access for mobile devices. It is set to deliver 100 Mbps to a roaming mobile device and up to 1 Gbps to a stationary device.
  • 4G will bring the perfect real world wireless inter networking called WWWW: World Wide Wireless Web.
  • 4 G allows for video conferencing, streaming picture perfect video for telemetric applications
  • OFDMA multi-carrier transmission methods, frequency-domain equalization (FDE) methods, MIMO (Multiple Input Multiple Output) and Turbo Code techniques are used in 4 G networks.
  • Peak data rates for 4G networks must be close to 100 megabit per second for a user on a highly mobile network and 1 gigabit per second for a user with local wireless access or a nomadic connection.
  • True 4G must also be able to offer smooth handovers across differing networks without data loss and provide high quality of service for next-gen media.

Wireless Local Area Network (WLAN)

  • A wireless local area network (WLAN) is a wireless distribution method for two or more devices that use high-frequency radio waves or spread spectrum and often include an access point to the Internet. A WLAN allows users to move around the coverage area, often a home or small office, while maintaining a network connection.
  • The FCC has allocated 300 MHz of unlicensed spectrum in the ISM bands of 5.1 GHz and 5.8 GHz range for supporting private computer connections by WLAN. The IEEE 802.11 WLAN standard is the popular standard for the use of internet and wireless communication.

Bluetooth Technology

  • Bluetooth is a short-range wireless communication technology that allows devices such as mobile phones, computers, and peripherals to transmit data or voice wirelessly over a short distance. The purpose of Bluetooth is to replace the cables that normally connect devices, while still keeping the communications between them secure. The devices can communicate within a nominal range of 10m.
  • The "Bluetooth" name is taken from a 10th-century Danish king named Harald Bluetooth, who was said to unite disparate, warring regional `actions Like its namesake, Bluetooth technology brings together a broad range of devices across many different industries through a unifying communication standard.
  • Bluetooth operates in the 2.4 GHz ISM band
  • It uses the frequency hopping spread spectrum technique.
  • The standard followed is IEEE 802.15
  • The modulation used is Gaussian FSK (GFSK).
  • Data transfer rate of 1 Mbps.
  • Useful for data transfer between two devices that are near to each other in low bandwidth situations.
  • Connection and exchange of information between mobile phones, laptops, PCs, GPS receivers, printers, digital cameras, video game consoles etc is made possible.

Comparison of Circuit switching and Packet switching

Circuit Switching

  • First generation cellular systems provide connection-oriented services for each voice user by a technique called circuit switching.
  • A physical radio channel is switched in to use for two-way traffic between the mobile user and the MSC, and the PSTN dedicates a voice circuit between the MSC and the end-user.
  • Circuit switching establishes a dedicated connection between the base and mobile, and a dedicated frill duplex phone line between the MSC and the PSTN for the entire duration of a call.
  • Wireless data networks are not well supported by circuit switching, due to their short, bursty transmissions which are often followed by periods of inactivity.
  • Circuit switching is best suited for dedicated voice-only traffic, or for instances where data is continuously sent over long periods of time.

Packet Switching

  • Packet switching (also called virtual switching) is the most common technique used to implement connectionless services
  • It allows a large number of data users to remain virtually connected to the same physical channel in the network.
  • Call set-up procedures are not needed to dedicate specific circuits when a particular user needs to send data.
  • Packet switching breaks each message into smaller units for transmission and recovery and adds a certain amount of control information to each packet (fig below).
  • It provides excellent channel efficiency for bursty data transmissions of short length.
  • The channel is utilized only when sending or receiving bursts of information which is useful in cases of limited bandwidth.

OSI MODEL

  • OSI consists of seven layers, and each layer performs a particular network function.
  • OSI model was developed by the International Organization for Standardization (ISO) in 1984, and it is now considered as an architectural model for the inter-computer communications.
  • OSI model divides the whole task into seven smaller and manageable tasks. Each layer is assigned a particular task.
  • Each layer is self-contained, so that task assigned to each layer can be performed independently.

byjusexamprep

Physical Layer: It is responsible for transmitting bits from one node to another node.

Data link layer: It is responsible for node to node delivery within the LAN and the systems will be identified by the MAC address. It checks for physical transmission errors and packages bits into data frames. The data link layer encompasses two sub-layers of its own:

  1. Media Access Control (MAC) layer- It is responsible for controlling how device in a network gain access to medium and permits to transmit data.
  2. Logical link control layer- This layer is responsible for identity and encapsulating network-layer protocols and allows you to find the error.

Network layer: It is responsible for source to destination delivery and the system will be identified by IP Address. It is responsible for receiving frames from the data link layer and delivering them to their intended destinations among based on the addresses contained inside the frame.

Transport layer: It is responsible for process to process or end to end delivery and the system will be identified by port address. It regulates the size, sequencing, and ultimately the transfer of data between systems and hosts. One of the most common examples of the transport layer is TCP or the Transmission Control Protocol.

It determines how much data should be sent where and at what rate. This layer builds on the message which are received from the application layer. It helps ensure that data units are delivered error-free and in sequence.

Transport layer helps you to control the reliability of a link through flow control, error control, and segmentation.

The transport layer also offers an acknowledgment of the successful data transmission and sends the next data in case no errors occurred. TCP is the best-known example of the transport layer.

Session layer: It is used to establish, maintain and synchronizes the interaction between communicating devices. Session Layer controls the dialogues between computers. It helps in establishing the starting and terminating connections between the local and remote application.

Presentation layer: It is mainly concerned with the syntax and semantics of the information exchanged between the two systems. Because of this, it at times also called the syntax layer.  It also helps in handling the data compression and data encryption.

Application layer: It serves as a window for users and application processes to access network service. The application layer identifies communication partners, resource availability, and synchronizes communication.

 

          

 

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