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Cellular Wireless Networks

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Cellular Wireless Networks In GSM, there are five main functions: Transmission. Radio Resources management (RR). Mobility Management (MM). Communication Management (CM). – PowerPoint PPT presentation

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Title: Cellular Wireless Networks


1
Cellular Wireless Networks
2
Example of a Cellular Wireless Network
Picture http//www.scom.hud.ac.uk
3
1G Cellular Networks
  • 1st generation cellular networks are purely
    analog cellular systems.
  • The transmission of data is sent via a
    continuously variable signal

4
2G Cellular Networks
  • 2nd 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 correction
  • Users share channels dynamically

5
3G Cellular Networks
  • 3rd generation refers to the next generation of
    wireless systems.
  • This is digital with high speed data transfer
  • It is voice quality comparable with a switched
    telephone network.
  • Data transmission rates can be asymmetric or
    symmetrical
  • It provides support for circuit switched and
    packet switched data services

6
Cellular Operation
  • Three basic devices
  • A mobile station
  • A base transceiver
  • A Mobile Telecommunications Switching Office
    (MTSO)

7
Cellular Operation
Picture www.Xanthippi.ceid.upatras.gr
8
Cellular Network Organization
  • Base 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 BS
  • Control channels
  • used to exchange information having to do with
    setting up and maintaining calls (out-band or
    in-band through stealing bits)
  • Traffic channels
  • carry voice or data connection between users

9
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.

10
Cellular Operation
  • Mobile 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
  •  

11
Cellular Operation
  • Outgoing from mobile
  • input phone number and press send
  • mobile links to base transceiver via control
    channel
  • base to MTSO to PSTN
  • MTSO routes connection back to mobile via voice
    channel
  • mobile shifts from control to voice

12
Cellular Operation
  • Incoming 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

13
(No Transcript)
14
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.

15
Hexagon Reuse Clusters
16
Cellular Coverage Representation
17
Frequency Reuse
  • Each colour/letter uses the same frequency band

Picture netlab.cis.temple.edu/jmulik/teaching/85
50s03-slides/ 8550-Cellular-14.sxi.pdf
18
3-cell reuse pattern (i1,j1)
19
4-cell reuse pattern (i2,j0)
20
7-cell reuse pattern (i2,j1)
21
12-cell reuse pattern (i2,j2)
22
19-cell reuse pattern (i3,j2)
23
Relationship between Q and N
24
Factors limiting frequency reuse
  • Co-channel interference
  • Adjacent channel interference

25
Adjacent Channel Interference
Picture xanthippi.ceid.upatras.gr/courses/
mobi_net/Lecture1.ppt
  • Adjacent channel interference can be controlled
    with transmit and receive filters

26
Coping with increasing capacity
  • Adding new channels
  • Frequency borrowing
  • frequencies are taken from adjacent cells by
    congested cells

Picture www.its.bth.se/courses/etc019/handouts/
ch10_Cellular_wireless_netw.pdf
27
Coping with increasing capacity
  • Cell splitting
  • cells in areas of high usage can be split into
    smaller cells
  • Cell sectoring
  • cells are divided into a number of wedge-shaped
    sectors, each with their own set of channels
  • Microcells
  • antennas move to buildings, hills, and lamp posts

28
Cell Splitting
29
Site Configurations
30
Handoffs
  • Network 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.

31
Handoffs
  • This practice must preserve end-to-end
    connectivity in a dynamically reconfigured
    network topology.

32
Handoff Types (contd)
33
Avoiding handoff Umbrella cells
34
Encoding Modulation(1)
  • Amplitude Modulation
  • Frequency Modulation
  • Phase Modulation
  • are the three different methods of encoding
    binary information on a regular wave.

35
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).

36
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

37
Encoding Multiplexing(2)
  • Frequency Division Multiplexing involves a
    different frequency channel given to each user

38
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.

39
Differences between FDMA, TDMA, and CDMA.
40
Advantages of Code Division Multiplexing
  • better protection against interference
  • good security
  • signal difficult to jam

41
Disadvantages of Code Division Multiplexing
  • pseudo-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.

42
AnalogyMultiplexing
  • Lectures at a learning institute
  • Frequency Division takes place in different
    rooms
  • Time Division taking turns in a single room
  • Code Division lectures on different subjects.

43
Wired vs. Wireless
44
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.

45
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.

46
Advantages of wireless networks
  • Flexible
  • Cost is less (long term)
  • Mobile user choice
  • Accesses areas that wired networks cannot reach

47
Disadvantages of wireless networks
  • Compared to wired networks the data rates are
    slower
  • User location determines performance
  • Devices such as microwaves, cordless phones, etc
    may cause interference
  • Can be accessed by hackers from the outside

48
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).

49
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.

50
Block Ciphers
  • Another 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).

51
The GSM Network
  • The Global System for Mobile communications.-most
    widely used digital cellular communications
    system

52
The GSM Network
Picture http//www.alphaorg.com/cellular/
53
Mobile Station
  • Mobile equipment or terminal
  • 3 types fixed, portable, handheld
  • Subscriber Identity Module (SIM).

54
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).

55
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 density of users in the cell.

56
The Base Station Controller (BSC)
  • The BSC controls a group of BTS.
  • A BSC is primarily responsible for handovers,
    frequency hopping, exchange functions and control
    of the frequency power levels of the BTSs.

57
The Network and Switching Subsystem (NSS)
  • Its main role is to manage the communications
    between the mobile users and other users, such as
    mobile users, ISDN users, landline users, etc.
  • It also has databases that store information
    about the subscribers and to manage their
    mobility.
  • The different components of the NSS are described
    below.

58
The Mobile services Switching Center (MSC)
  • Central component of the NSS.
  • It performs switching functions and also provides
    connection to other networks.

59
The Gateway Mobile services Switching Center
(GMSC)
  • A gateway is a node that interconnects two
    networks.
  • The GMSC is the interface between the mobile
    cellular network and the Public Switched
    Telephone Network (PSTN).
  • It is responsible for routing calls from the
    fixed network towards a GSM user.

60
Home Location Register (HLR)
  • The HLR is an important database as it stores
    information about the subscribers belonging to
    the covering area of a MSC.
  • It stores the current location of these
    subscribers and the services to which they have
    access.
  • The location of the subscriber corresponds to the
    SS7 address of the Visitor Location Register
    (VLR) associated to the terminal.

61
Visitor Location Register (VLR)
  • The VLR contains information from a subscriber's
    HLR.
  • It is necessary for the provision of subscribed
    services to visiting users.
  • When a subscriber enters the covering area of a
    new MSC, the VLR associated to this MSC will
    request information about the new subscriber to
    its corresponding HLR.
  • The VLR will then have enough information to
    assure the subscribed services without needing to
    confirm with the HLR each time a communication is
    established.

62
The Authentication Center (AuC)
  • The AuC register provides the parameters needed
    for authentication and encryption functions.
  • These parameters help verify the user's identity.

63
The Equipment Identity Register (EIR)
  • The EIR is also used for security purposes. It is
    a register containing information about the
    mobile equipment.
  • It particularly contains a list of all valid
    terminals.
  • A terminal is identified by its International
    Mobile Equipment Identity (IMEI).
  • The EIR uses this to forbid calls from stolen or
    unauthorized terminals.

64
The GSM Interworking Unit (GIWU)
  • The GIWU corresponds to an interface to various
    networks for data communications.
  • During these communications, the transmission of
    speech and data can be alternated.

65
The Operation and Support Subsystem (OSS)
  • The OSS is connected to the different components
    of the NSS and BSC in order to control and
    monitor the GSM system.
  • It also takes care of controlling the traffic
    load of the BSS.

66
  • In GSM, there are five main functions
  • Transmission.
  • Radio Resources management (RR).
  • Mobility Management (MM).
  • Communication Management (CM).
  • Operation, Administration and Maintenance

67
GSM
  • GSM uses an intriguing method to send data. By
    simply sending computer data as it would send
    voice data, GSM allows every phone to be "data
    enabled."
  • Since the GSM network is already a packet network
    of sorts because of its frequency hopping, it
    requires no additional hardware to support data.
  • GSM allows data rates in multiples of 300 bits
    per second, up to 64 kilobits per second.

68
Advantages of Cellular Networks
  • Cellular networks use "small" cells with low
    powered transceivers instead of one large area
    with a high powered transceiver.
  • Using cellular networks increases overall call
    handling capacity.
  • Avoids central point of failure.
  • Allows dynamic distribution of capacity based on
    demand.
  • Less interference with other wireless
    communications

69
Conclusion (1)
  • Mobile phone contracts provide a useful and
    relatively cheap service.
  • Cellular radio network infrastructures are
    growing at a tremendous rate.
  • Cellular networks are becoming high speed data
    networks.

70
Conclusion (2)
  • Speeding up the development of mobile
    communication technologies is the focus of the
    industry. The ideal communication system where
    both voice and data services can be delivered
    regardless of location, network, or terminal.
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