11th Class Computer Science Notes Chapter 6 (Wireless Communications)

Short Questions and long question class 11th computer science notes chapter number 6 (Wireless Communications) the best and only one notes.

Q.2 Give short answers to the following questions.

i. What is Radio Transceiver?

A radio transceiver is a device which comprises both a transmitter and a receiver which is combined and share common circuitry or a single device. It can perform both functions simultaneously so, it is a full duplex device. The cable to which it is connected provides separate pathways for sending and receiving the data.

ii. What is ‘Hotspot’?

A Hotspot is a wireless LAN node that provides internet connection access from a given location. For example, business travellers with a WIFI device (a laptop or mobile) can look up for a local hotspot, contact it and get connected through its network to reach the internet and their own company remotely with a secure connection.

iii. What does IEEE stand for?

IEEE stands for Institute of Electrical and Electronics Engineer.
It is an organization composes of engineers, scientists and students. All LAN standards are provided by IEEE

iv. What is meant by line of sight communication?

Line of Sight (LoS) is a type of propagation that can transmit and receive data only where transmit and receive stations are in view of each other without any sort of an obstacle between them. Some of the examples of LoS are FM radio, microwave and satellite transmission.


v. Differentiate between short distance and long distance wireless communication.

The difference between short and long distance wireless communication is as follows:

Headings                              Short distanceLong distance
Used forShort distance wireless communication is used for transferring information within few metersLong distance wireless communication is used for transferring information over thousands or millions of kilometers.
Technologies                                          Information is transferred through Wi-Fi, Wi-Max, Bluetooth and infrared.Information is transferred through cellular and satellite communication.
Pass through obstaclesThe waves of short distance communication cannot pass through obstaclesThe waves of long distance communication can pass through obstacles
Data transfer rateHigh data transfer rateLow data transfer rate

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vi. What is Global Positioning System (GPS)?

GPS stands for Global Positioning System (GPS) is a satellite-based system that is used to locate positions anywhere on the earth.  This system is operated by US Department of Defense (DoD). GPS provides continuous (24 hours / day), real-time, 3-dimensional positioning, navigation and timing worldwide.
The GPS system consists of 24 satellites. Any person with a GPS receiver can access the system and it can be used for any application that requires location coordinates.

vii. What is Wireless Markup Language?

Wireless Markup Language (WML) is a XML based markup language designed to describe content and format for presenting data on limited bandwidth devices such as cellular phones and pagers. It provides a tool to make web pages accessible from handheld, wireless devices.

viii. What   is Wireless Application Protocol?

Wireless Application Protocol commonly known as WAP is used to enable the access of internet in the mobile phones or PDAs. WAP is an international standard for the devices that use the wireless communications. Use of internet is necessary today but we cannot have access to our personal computers all the time to connect to the internet especially when we on the way and we want to check out email. In the situations like this WAP comes in handy. If we are carrying WAP enabled mobile phone or PDA, then we can use WAP services on that i.e. web surfing, after configuring WAP setting from our concerned wireless carrier.
For the full use of WAP in our device, we need certain applications. First thing is WAP browser, which is used to access different websites. Second is instant messenger for chatting like Skype, YAHOO etc. All these applications are by default enable in all devices now a days.


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ix. Write short note on Web Protocol Stack?

A web service implementation depends on technologies often organized in a layered stack. The implementation itself defines a standard protocol for each technology layer, each layer depending on the layers appearing in the stack.
A web service protocol stack is an evolving set of protocols used to define, discover and implement web services.
The protocol stack consists of four layers:
1.      Transport protocol
2.      Messaging protocol
3.      Description protocol
4.      Discovery protocol

Extensive Questions for class 11 computer science Notes KPK

i. What are the advantages and disadvantages of wireless networks?

Wireless networks are used as an alternative to cable and fiber optic networks. The aim of wireless technology is to remove the expensive and huge cables used for connectivity. Wireless networks have various advantages and disadvantages. Some of them are as follows:

Advantages of wireless networks:

The advantages of wireless networks are as follows:

  • Efficiency: It increased the efficiency of data communications. It provides the facility to transfer information at a ster speed.
  • Manageability: Users can connect to different wireless networks without changing their physical connection.
  • Security: Wireless networks provide better security protections. Its traffic can be blocked or can be filtered.
  • Cost: Wireless networks are cost-effective. These are easier to install than cables.
  • Mobility: By using wireless networks, we are not bound with any location. We can use it anywhere by accessing it from a ptop computer or mobile device.
  • Expandability: Expanding wireless networks is much easier. We can easily add new computers or devices in our network with existing equipment contrary to the wired network, requiring new equipment and cables to grow the network.
  • Last mile data delivery: Wireless connection is very suitable for places where cables are unable or difficult to reach.

Disadvantages of wireless networks:
Some of the disadvantages of wireless networks are as follows:

  • Security: Wireless networks have a big problem with security. Wireless transmission is more vulnerable to attack by unauthorized users.
  • Coverage: At some places consistency of its service is difficult. Users might face problems of signals strength.
  •  Speed: Sometimes its speed gets slower because of signals dropping problem.
  •  Cost: Usually wireless networks are inexpensive but sometimes they are more costly to install than wired networks.
  • Interference: Wireless signals often face interference from the signals of other electronic devices.
  • Throughput: At some places, their throughput is affected by electromagnetic interference.
  • Network backbones: These are not suitable for network backbones due to the limitation of data transfer rates.

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ii. Explain different types of short distance communications technologies.

Short distance communication technologies:
The technologies used to transfer wireless signals at short distances are called short distance communication technologies.
The stations of sender and receivers are in few meters or kilometers. These devices include:

  • Wi-Fi
  • WiMax
  • Bluetooth
  • Infrared

Wi-Fi stands for Wireless Fidelity. It is a wireless networking technology that uses access point or router to broadcast a signal. It uses IEEE 802.11 wireless standards developed by the Institute of Electrical and Electronic Engineering (IEEE).
If the desktop computer or laptop does not have wireless, it requires a wireless adapter to connect to the wireless network to create hotspots. Wireless adapter translates data sent into a radio signal. This same signal will be transmitted via antenna to a decoder known as router. Once decoded, the data will be sent to the internet through a wired Ethernet connection.
Wi-Fi technology uses radio waves to provide network connectivity. It is compatible with almost every operating system, game device and advanced printer.

WiMax stands for Windows Interoperability for Microsoft Access. WiMax is a standard technology for providing internet access and multimedia services to at very high speed. It uses IP addresses for wireless broadband and provides similar working as of Wi-Fi. It provides coverage to cellular networks as like Wi-Fi.  
WiMax uses IEEE 802.16 standard for communication. It provides broadband wireless access in the range of 30 miles or 50 Km for fixed stations and 3-10 miles or 5-15 Km for mobile stations.
It provides wireless data transmission by various transmission methods like portable or fully mobile internet access via point to point multipoint links. Speed of WiMax technology is 72 megabits per seconds.

Bluetooth is a low power microwave wireless link technology. It has high speed. It is designed to connect portable equipment like phones, laptops, PDAs etc. It does not require line of sight positioning like infrared to connect devices.  
Bluetooth is known for providing connectivity between non network devices like laptops, mobile phones, telephones, fax machines, PCs, Printer, GPS receivers, digital photo camera and video game controllers. Its data transfer speed which is documented is 1Mbps but in real use it is much lower than this.
It can transmit wireless signals in the range of 30 feet (10 meters). Bluetooth is also called piconet or PAN. Piconets contain a minimum of two and a maximum of eight Bluetooth peer devices.

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Infrared is a wireless technology used for device communication over short ranges. It requires line of sight, has a short range and is unable to penetrate walls. These are its major limitations. Infrared transceivers are quite cheap and serve as a short range communication solutions.
Its data transfer rate is very low and communication interception is difficult. Infrared data association device communication is usually exchanged on one to one basis. So, the data transfer through infrared is normally unencrypted. Some applications of infrared are as follows:

  • It is used in car locking system for automatic locking and unlocking of car doors.
  • Modern computers use infrared enabled mouse, keyboards and printers.
  • Infrared enabled home burglar alarm is used for home security systems.
  • Remote control systems of various home appliances like TV, AC and also Toys etc. uses infrared technology.

iii. Describe long distance communications technologies in detail.

Long distance communication technologies:
The technologies that use wireless communication at long distances are as follows:
a. Cellular communication
b. Global Positioning System (GPS)

a. Cellular communication:
Cellular systems are widely used today and cellular technology needs to offer very efficient use of the available frequency spectrum. Billions of mobile phones are using cellular technology today. Cellular technology provides connectivity even at the places where wired networks are unreachable.
The area of cellular network is divided into cells and multiple low power transmitters are used to specify the cell. Each cell is served by its own antenna. A band of frequencies is allocated to cell base station where transmitters, receivers, and control unit are situated. Other cells contain different range of frequencies to avoid interference but the cells at quite distant places can use frequency band. This is called frequency reuse which is the heart of cellular communication.
In early FM radio technology, there was no concept of frequency re-use and a large area was covered by an antenna mounted on a tall tower. There was no concept of frequency reuse and also there was no interference then but it limits the user capacity.
Frequency reuse concept in cellular communication has increased the user capacity and interference of signals is also avoided in it.

Characteristics of cellular networks:

  • Thousands of cells which cellular network contains have a coverage area of 500m to 35 km radius.
  • Cellular networks are comprised of several accesses and a single core network.
  • Millions of subscribers are served through these networks.
  • It was designed for speech telephony but nowadays it is also used for data transmission.
  • GSM and CDMA are its examples.

b. Global Positioning System (GPS):
GPS systems are extremely useful and can be found in almost any industry sector. It is made up of 24 satellites placed into orbit by the US Department of Dense (DoD). They can be used to map forests, help farmers harvest their fields and navigate airplanes on the ground or in the air. GPS systems are used in military applications and by emergency crews to locate people in need of assistance. GPS technologies are often working in many areas that we do not normally consider.
Global positioning system applications generally fall into 5 major categories:

  1. Location – determining a position
  2. Navigation – getting from one location to another
  3. Tracking – monitoring object or personal movement
  4. Mapping – creating maps of the world
  5. Timing – bringing precise timing to the world

Some of the applications that GPS systems are currently being used for around the world include

  •  Mining
  •  Aviation
  • Surveying
  • Agriculture
  • Marine
  • Recreation
  • Military

These days doctors, scientists, farmers, soldiers, pilots, hikers, delivery drivers, sailors, fishermen, dispatchers, athletes, and people from many other walks of life are using GPS systems in ways that make their work more productive, safer, and easier.

GPS Segment:
GPS has three segments:

  • Space segment: It consists of 24 operating satellites, transmits one-way signals and provides current GPS satellite position and time.
  • Control segment: This segment consists of a global network of ground facilities that are used for tracking GPS satellites, monitoring their transmissions, perform their analysis and send commands and data to the constellation.
  • User segment: The user segment consists of GPS receiver equipment which is used for receiving signals from the GPS satellites and for using transmitted information to calculate the user’s three-dimensional position and time.

iv. Explain different classifications of Satellite Systems.

Satellite systems are classified into three types according to their orbits:

1. Geostationary Earth Orbit (GEO)
2. Medium Earth Orbit (MEO)
3. Low Earth

1. Geostationary Earth Orbit (GEO):
GEO is a circular orbit 35,786 kilometers above the Earth equator and it follows the direction of the Earth’s rotation. An object in such an orbit has an orbital period equal to the Earth’s rotational period and thus appears motionless at a fixed position in the sky, to ground observers.
Its orbital speed is based on the distance of the planet and because of this only one orbit can be geostationary. This orbit is at 22,000 miles from the surface of the earth. One geostationary orbit cannot cover the whole earth. It is line of sight connected with a number of stations but the earth rotation keeps most of the stations out of sight. Minimum of three satellites situated at equal distances from each other in GEO can cover the whole earth to provide global transmission. These three satellites are 120o from each other in geosynchronous orbit around the equator.

2. Medium Earth Orbit (MEO):
MEO satellite is an orbit within the range from a few hundred miles to a few thousand miles above the earth surface. These satellites are lower than geostationary satellites and higher than lower earth orbit satellites. MEO is used in telecommunications.
MEO satellites complete their orbit in about two to 12 hours. MEO’s are mainly used in GPS and travel in constant speed.  MEO satellites are closer to the earth that’s why earth based transmitters with relatively low power and small size antennas can also able to access the system.


3. Low Earth Orbit (LEO):
LEO is satellite system used in telecommunication. It has orbit between 400 and 1,000 miles above the earth’s surface. They are used mainly for data communication such as email, video conferencing and paging. They move at extremely high speeds and are not fixes in space in relation to the earth.
LEO telecommunication systems provide undeveloped countries with the ability to acquire satellite telephone service in areas where cellular communication is not possible.

v. What are the Requirements of a bile Communication System?

Requirements of the mobile communication system:

Different components work together to provide mobile service to subscribers. These components are as follows:

  1. Public Switched Telephone Network (PSTN)
  2. Mobile Telephone Switching Office (MSTO)
  3. Cell site with an antenna system
  4. Mobile Subscriber Unit (MSU)
  5. Mobile Station
  6. Base Station Subsystem
  7. Network and Switching Subsystem
  8. Operation subsystem
  9. Public Switched Telephone Network (PSTN)

PSTN connects telephone and other communication devices on worldwide basis. It is made up of local networks, the exchange area network and long haul networks.

2. Mobile Telephone Switching Office (MTSO):
MTSO is a central office for mobile switching. It contains the mobile switching center (MSC), field monitoring and relay stations. All these are used for switching calls from cell sites to PSTN. MSC controls the whole system operation in analog cellular networks.

3. Cell Site:
Cell site is the physical equipment that provides coverage within a cell. Some hardware equipment is located at cell site which includes power sources, interface equipment, radio frequency transmitters and receivers and antenna systems.

4. Mobile Subscribers Unit (MSU):
MSU consists of a control unit and a transceiver. Transceiver is used to transmit and receive radio transmissions to and from a cell site.

5. Mobile Station (MS):
MS includes mobile equipment and SIM (Subscriber Identity Module ). The SIM is a chip card used to store all information of subscriber. When SIM is inserted in mobile equipment, the information is checked and then call is delivered to mobile station. Mobile equipment in which SIM is inserted is not related to caller number that is used to identify caller. So, any kind of mobile equipment is used to insert SIM.

6. Base Station Subsystem (BSS):
BSS is used to connect MS and NSS through radio interface. BSS contains base transceiver station (BTS) which is located at antenna site and a base station controller (BSC). Speech encoding and decoding is carried out by rate adaptation unit for transmitting data.

7. Network and Switching Subsystem (NSS):
NSS consists of Mobile Services Switching Center (MSC), Home Location Register (HLR) and the Visitor Location Register (VLR). The MSC deals with call setup to and from mobile users.
The HLR is a database which contains subscriber information (e.g. current location). The VLR contains administrative information that is related to mobile current location.

8. Operation Subsystem (OSS)
OSS consists of three areas:

  • Network operation and maintenance functions
  • Subscription management ( includes charging and billing)
  • Mobile equipment management.

vi. Give important features and limitations of Mobile Communication System.

Features of mobile communication system:
Mobile communication technology provides number of features. Some of them are as follows:

  • It provides mobility. Aspects of mobility are:
    • User mobility: User can communicate wirelessly and can contact anyone from anywhere and anytime.
    • Device portability: Devices can connect to the each other and with network any time and from anywhere.
  • It has more capacity than single large transmitters because frequencies are reused here.
  • Mobile devices use less power.
  • Than can cover large area of coverage than a single terrestrial transmitter as more cell towers can be added and are not limited by the horizon.
  • To reuse frequencies is the key characteristic of a mobile network. It increases both coverage and capacity of mobile network.
  • It provides the facility of hand over or handoff. It means that mobile device can connect from network station to another during an ongoing call or data session.
  • It provides roaming services all around the world in fastest way to communicate with each other. It plays vital role in business, emergencies and management.
  • The cost of messaging and talking is very low.
  • Mobile devices provide services of MMS, GPRS and WAP for effective communication.
  • Mobile communication system uses GSM (Global System for Mobile Communication). GSM is a standard for improved spectrum efficiency, international roaming, low cost mobile sets and base stations, high quality speech, compatibility with integrated Services Digital Network (ISDN) and other telephone company services.
  • GSM is expanded to GPRS (General Packet Radio Services) and EDGE (Enhanced Data rate for GSM Evolution of EGPRS) which provides improved data communication and higher data rates.

Limitations of mobile communication:
Mobile communications have some limitations also. These are:

  • Mobile internet access is slower than direct cable communications. Mobile communication technologies GPRS and EDGE are available in the range of commercial cell phone towers. For high speed wireless internet wireless LAN’s can be used which are inexpensive but have limited range.
  • Security issues are severe with mobile systems. It is much easier to locate or trap mobile calls than wired calls.
  • Mobile devices mostly rely on battery power. These batteries are often expensive to use.
  • Mobile signals are badly inferred by weather, terrain and range of nearest signal point. Also signal reception at some places like tunnels, buildings and rural areas is poor.
  • Use of mobile devices is dangerous while driving. Cell phones may also interfere sensitive medical devices. Signals of cell phone may also cause health problems.
  • Use of small keyboards and screens is difficult

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