cellular wireless networks

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Cellular Wireless Networks. Example of a Cellular Wireless Network. Picture: http://www.scom.hud.ac.uk. 1G Cellular Networks. 1 st generation cellular networks are purely analog cellular systems. The transmission of data is sent via a continuously variable signal. 2G Cellular Networks. - PowerPoint PPT Presentation


  • Cellular Wireless Networks

  • Example of a Cellular Wireless NetworkPicture: http://www.scom.hud.ac.uk

  • 1G Cellular Networks1st generation cellular networks are purely analog cellular systems. The transmission of data is sent via a continuously variable signal

  • 2G Cellular Networks2nd generation cellular networks refer to digital cellular and PC wireless systems. voice and low speed data services.They consist of digital traffic channels, perform encryption, error detection & correctionUsers share channels dynamically

  • 3G Cellular Networks3rd generation refers to the next generation of wireless systems.This is digital with high speed data transferIt is voice quality comparable with a switched telephone network. Data transmission rates can be asymmetric or symmetricalIt provides support for circuit switched and packet switched data services

  • Cellular OperationThree basic devicesA mobile stationA base transceiverA Mobile Telecommunications Switching Office (MTSO)

  • Cellular OperationPicture: www.Xanthippi.ceid.upatras.gr

  • Cellular Network OrganizationBase Station (BS)includes an antenna, a controller, and a number of receivers

    Mobile Telecommunications Switching Office (MTSO)connects calls between mobile units

    Two types of channels available between mobile unit and BSControl channelsused to exchange information having to do with setting up and maintaining calls (out-band or in-band through stealing bits)

    Traffic channelscarry voice or data connection between users

  • Cellular Operation Public Land Mobile Network (PLMN) refers to a cellular network that has land and radio based sections.

    This network consists of: Mobile station (MS): A device used for communication over the network. Base station transceiver (BST): A transmitter/receiver used to transmit/receive signals over the network.

  • Cellular OperationMobile switching center (MSC): Sets up and maintains calls made over the network.

    Base station controller (BSC): Communication between a group of BSTs and a single MSC is controlled by the BSC

    Public switched telephone network (PSTN): Section of the network that is land based

  • Cellular OperationOutgoing from mobile input phone number and press send mobile links to base transceiver via control channel base to MTSO to PSTNMTSO routes connection back to mobile via voice channel mobile shifts from control to voice

  • Cellular OperationIncoming to mobile call goes from PSTN to MTSO on control channel, MTSO searches for mobile by PAGING every active mobile If found, MTSO rings it and establishes voice channel connection uses transceiver with strongest signal from mobile

  • Cellular Network Organization (Cells)Cells use low powered transmitters. Each cell is allocated a band of frequencies, and is served by its own antenna as well as a base station consisting of a transmitter, receiver and control unit.

  • Hexagon Reuse Clusters

  • Cellular Coverage Representation

  • Frequency Reuse

    Each colour/letter uses the same frequency bandPicture: netlab.cis.temple.edu/~jmulik/teaching/8550s03-slides/ 8550-Cellular-14.sxi.pdf

  • 3-cell reuse pattern (i=1,j=1)

  • 4-cell reuse pattern (i=2,j=0)

  • 7-cell reuse pattern (i=2,j=1)

  • 12-cell reuse pattern (i=2,j=2)

  • 19-cell reuse pattern (i=3,j=2)

  • Relationship between Q and N

  • Factors limiting frequency reuseCo-channel interference

    Adjacent channel interference

  • Adjacent Channel InterferenceAdjacent channel interference can be controlled with transmit and receive filters Picture: xanthippi.ceid.upatras.gr/courses/ mobi_net/Lecture1.ppt

  • Coping with increasing capacityAdding new channelsFrequency borrowingfrequencies are taken from adjacent cells by congested cells

    Picture: www.its.bth.se/courses/etc019/handouts/ ch10_Cellular_wireless_netw.pdf

  • Coping with increasing capacityCell splittingcells in areas of high usage can be split into smaller cellsCell sectoringcells are divided into a number of wedge-shaped sectors, each with their own set of channelsMicrocellsantennas move to buildings, hills, and lamp posts

  • Cell Splitting

  • Site Configurations

  • HandoffsNetwork protocols must refresh and renew paths as a mobile station host moves between cells. Handoffs are the function of one cell handing over the communication link between itself and a mobile station as the mobile station moves out of the boundary of its region into the boundary of an adjacent cell.

  • HandoffsThis practice must preserve end-to-end connectivity in a dynamically reconfigured network topology.

  • Handoff Types (contd)

  • Avoiding handoff: Umbrella cells

  • Encoding: Modulation(1)Amplitude ModulationFrequency Modulation Phase Modulationare the three different methods of encoding binary information on a regular wave.

  • Encoding: Modulation(2)When using digital signals the methods are known as Amplitude Shift Keying (ASK), Frequency Shift Keying (FSK), and Phase Shift Keying (PSK).

  • Encoding: Multiplexing(1)Multiplexing allows many mobile users to use cellular radio transmission schemes at the same time. The different schemes are:Frequency Division Multiplexing Time Division Multiplexing Code Division Multiplexing

  • Encoding: Multiplexing(2)Frequency Division Multiplexing involves a different frequency channel given to each user

  • Encoding: Multiplexing(3)Time Division Multiplexing involves a channel with a given number of time slots (per millisecond) where each user is assigned certain time interval. Code Division Multiplexing gives each user a code for differentiation purposes. The receiver picks out each channel from the noise using the code. Wide frequency band is used. Does not contain single frequencies or time slots.

  • Differences between FDMA, TDMA, and CDMA.

  • Advantages of Code Division Multiplexing better protection against interferencegood securitysignal difficult to jam

  • Disadvantages of Code Division Multiplexingpseudo-random code sequences generated by the transmitters and receivers are not always random fast power control system needed so that strong signals dont overpower weaker signals.

  • Analogy:MultiplexingLectures at a learning institute: Frequency Division: takes place in different roomsTime Division: taking turns in a single roomCode Division: lectures on different subjects.

  • Wired vs. Wireless

  • Wired vs. Wireless (1)A problem with wireless networks is that anyone with a wireless network card is able to access this network and is potentially harmful since they are able to corrupt and steal important files. These networks transmit data over an area such that the network signals may penetrate physical areas such as walls.

  • Wired vs. Wireless (1)Although this problem is relevant to a wired network also, it exists to a greater degree in a wireless network.With regard to wired networks, the electromagnetic waves that are given off from the current traveling through the network cables.

  • Advantages of wireless networks FlexibleCost is less (long term)Mobile user choiceAccesses areas that wired networks cannot reach

  • Disadvantages of wireless networks Compared to wired networks the data rates are slowerUser location determines performanceDevices such as microwaves, cordless phones, etc may cause interferenceCan be accessed by hackers from the outside

  • Wired Equivalent Privacy Algorithm (WEP) (1)Wireless networks may include additional security elements, which are not supported in wired networks. For eg. The use of security algorithms such as WEP (Wired Equivalent Privacy Algorithm), that uses an encryption algorithm which deals with unauthorized access to the network (eavesdropping).

  • WEP (2)WEP is a implemented such that a block of plaintext (input text) is bitwise XORed with an equal length random key sequence. A random number generator is used on the initialization vector and the secret key and outputs a key sequence of random of octets.An integrity check value is produced to protect against data modification.The key sequence combined with plaintext combined with the integrity check value gives the enciphered message. The integrity check value and the ciphertext is the combination of the output.

  • Block CiphersAnother security algorithm is Block Ciphers which is the most common of the encryption techniques. The Block Cipher consists of: Data Encryption Standard (DES)Triple Data Encryption (TDEA)Advanced Encryption Standard (AES).

  • The GSM NetworkThe Global System for Mobile communications.-most widely used digital cellular communications system

  • The GSM NetworkPicture: http://www.alphaorg.com/cellular/

  • Mobile StationMobile equipment or terminal3 types: fixed, portable, handheld

    Subscriber Identity Module (SIM).

  • The Base Station Subsystem (BSS)The Base Station Subsystem connects the Mobile Station and the Network and Switching Subsystem. It is responsible for transmission and reception and can be divided into two parts:

    The Base Transceiver Station (BTS) or Base Station. The Base Station Controller (BSC).

  • The Base Transceiver Station (BTS)The BTS corresponds to the transceivers and antennas used in each cell of the network. It is usually placed in the center of a cell. The size of a cell defines the transmitting power. A BTS can have up to 16 transceivers. It all depends on the densi

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