Download - Cellular Wireless Networks

Cellular Wireless NetworksCellular Wireless Networks

Example of a Cellular Wireless Example of a Cellular Wireless NetworkNetwork

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1G Cellular Networks1G Cellular Networks

11stst generation cellular networks are generation cellular networks are purely analog cellular systems. purely analog cellular systems.

The transmission of data is sent via a The transmission of data is sent via a continuously variable signalcontinuously variable signal


22ndnd generation cellular networks refer generation cellular networks refer to digital cellular to digital cellular and PCand PC wireless wireless systems.systems.

voice and low speed data servicesvoice and low speed data services..They consist of digital traffic They consist of digital traffic

channels, perform encryption, error channels, perform encryption, error detection & correctiondetection & correction

Users share channels dynamicallyUsers share channels dynamically


33rdrd generation refers generation refers to the next to the next generation of wireless systems.generation of wireless systems.

This is digital with high speed data This is digital with high speed data transfertransfer

It is voice quality comparable with a It is voice quality comparable with a switched telephone network. switched telephone network.

Data transmission rates can be Data transmission rates can be asymmetric or symmetricalasymmetric or symmetrical

It provides support for circuit switched and It provides support for circuit switched and packet switched data servicespacket switched data services

Cellular OperationCellular Operation

Three basic devicesThree basic devices A mobile stationA mobile station A base transceiverA base transceiver A Mobile Telecommunications Switching A Mobile Telecommunications Switching

Office (MTSO)Office (MTSO)


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Cellular Network OrganizationCellular Network Organization

Base Station (BS)Base Station (BS) includes an antenna, a controller, and a number of includes an antenna, a controller, and a number of

receivers receivers

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

Two types of channels available between mobile unit Two types of channels available between mobile unit and BSand BS• Control channelsControl channels

• used to exchange information having to do with setting up and used to exchange information having to do with setting up and maintaining calls (out-band or in-band through stealing bits)maintaining calls (out-band or in-band through stealing bits)

• Traffic channelsTraffic channels• carry voice or data connection between userscarry voice or data connection between users


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

This network consists of: This network consists of: • Mobile station (MS): A device used for Mobile station (MS): A device used for

communication over the network. communication over the network. • Base station transceiver (BST): A Base station transceiver (BST): A

transmitter/receiver used to transmit/receive transmitter/receiver used to transmit/receive signals over the network. signals over the network.


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

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

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


Outgoing from mobile Outgoing from mobile input phone number and press send input phone number and press send mobile links to base transceiver via mobile links to base transceiver via

control channel control channel base to MTSO to PSTNbase to MTSO to PSTNMTSO routes connection back to mobile MTSO routes connection back to mobile

via voice channel via voice channel mobile shifts from control to voicemobile shifts from control to voice


Incoming to mobile Incoming to mobile call goes from PSTN to MTSO call goes from PSTN to MTSO on control channel, MTSO searches for on control channel, MTSO searches for

mobile by PAGING every active mobile mobile by PAGING every active mobile If found, MTSO rings it and establishes If found, MTSO rings it and establishes

voice channel connection voice channel connection uses transceiver with strongest signal uses transceiver with strongest signal

from mobilefrom mobile

Cellular Network Organization Cellular Network Organization (Cells)(Cells)

Cells use low powered transmitters. Cells use low powered transmitters. Each cell is allocated a band of Each cell is allocated a band of

frequencies, and is served by its own frequencies, and is served by its own antenna as well as a base station antenna as well as a base station consisting of a transmitter, receiver and consisting of a transmitter, receiver and control unit. control unit.

Hexagon Reuse ClustersHexagon Reuse Clusters

Cellular Coverage Cellular Coverage RepresentationRepresentation

Frequency ReuseFrequency Reuse

Each Each colour/letter colour/letter uses the same uses the same frequency frequency bandband

Picture: netlab.cis.temple.edu/~jmulik/teaching/8550s03-slides/ 8550-Cellular-14.sxi.pdf

33-cell reuse pattern-cell reuse pattern (i=1,j=1) (i=1,j=1)

4-cell reuse pattern4-cell reuse pattern (i=2,j=0) (i=2,j=0)

77-cell reuse pattern-cell reuse pattern (i=2,j=1) (i=2,j=1)

12-cell12-cell reuse pattern reuse pattern (i=2,j=2)(i=2,j=2)

19-cell reuse pattern 19-cell reuse pattern (i=3,j=2)(i=3,j=2)

Relationship between Relationship between Q Q and and NN

Factors limiting frequency Factors limiting frequency reusereuse

Co-channel interference Co-channel interference

Adjacent channel interference Adjacent channel interference

Adjacent Channel InterferenceAdjacent Channel Interference

Adjacent channel interference can be controlled with transmit Adjacent channel interference can be controlled with transmit and receive filters and receive filters

Picture: xanthippi.ceid.upatras.gr/courses/ mobi_net/Lecture1.ppt

Coping with increasing Coping with increasing capacitycapacity

Adding new channelsAdding new channels Frequency borrowingFrequency borrowing

frequencies are taken from adjacent cells by frequencies are taken from adjacent cells by congested cellscongested cells

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

Coping with increasing Coping with increasing capacitycapacity

Cell splittingCell splitting cells in areas of high usage can be split cells in areas of high usage can be split

into smaller cellsinto smaller cells Cell sectoringCell sectoring

cells are divided into a number of cells are divided into a number of wedge-shaped sectors, each with their wedge-shaped sectors, each with their own set of channelsown set of channels

MicrocellsMicrocellsantennas move to buildings, hills, and antennas move to buildings, hills, and

lamp posts lamp posts

Cell SplittingCell Splitting

Site Configurations Site Configurations

HandoffsHandoffs

Network protocols must refresh and Network protocols must refresh and renew paths as a mobile station host renew paths as a mobile station host moves between cells. moves between cells.

Handoffs are the function of one cell Handoffs are the function of one cell handing over the communication link handing over the communication link between itself and a mobile station between itself and a mobile station as the mobile station moves out of as the mobile station moves out of the boundary of its region into the the boundary of its region into the boundary of an adjacent cell.boundary of an adjacent cell.

HandoffsHandoffs

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

Handoff Types (cont’d)Handoff Types (cont’d)

Avoiding handoff: Umbrella Avoiding handoff: Umbrella cellscells

Encoding: Encoding: Modulation(1)Modulation(1)

Amplitude ModulationAmplitude ModulationFrequency ModulationFrequency Modulation Phase ModulationPhase Modulation

are the three different methods of are the three different methods of encoding binary information on a regular encoding binary information on a regular wave.wave.

Encoding: Encoding: Modulation(2)Modulation(2)

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

Encoding: Encoding: Multiplexing(1)Multiplexing(1)

Multiplexing allows many mobile users to Multiplexing allows many mobile users to use cellular radio transmission schemes use cellular radio transmission schemes at the same time. The different at the same time. The different schemes are:schemes are:

Frequency Division MultiplexingFrequency Division Multiplexing Time Division MultiplexingTime Division Multiplexing Code Division MultiplexingCode Division Multiplexing


Frequency Division MultiplexingFrequency Division Multiplexing involves a involves a different frequency channel given to each userdifferent frequency channel given to each user


Time Division MultiplexingTime Division Multiplexing involves a involves a channel with a given number of time slots channel with a given number of time slots (per millisecond) where each user is (per millisecond) where each user is assigned certain time interval. assigned certain time interval.

Code Division MultiplexingCode Division Multiplexing gives each gives each user a “code” for differentiation purposes. user a “code” for differentiation purposes. The receiver picks out each channel from The receiver picks out each channel from the “noise” using the code. Wide the “noise” using the code. Wide frequency band is used. Does not contain frequency band is used. Does not contain single frequencies or time slots. single frequencies or time slots.

Differences between FDMA, TDMA, and CDMA.

Advantages of Advantages of Code Division Code Division MultiplexingMultiplexing

better protection against better protection against interferenceinterference

good securitygood securitysignal difficult to jamsignal difficult to jam

Disadvantages of Disadvantages of Code Division Code Division MultiplexingMultiplexing

pseudo-random code sequences pseudo-random code sequences generated by the transmitters and generated by the transmitters and receivers are not always randomreceivers are not always random

fast power control system needed so fast power control system needed so that strong signals don’t overpower that strong signals don’t overpower weaker signals.weaker signals.

AnalogyAnalogy::MultiplexingMultiplexing

Lectures at a learning institute:Lectures at a learning institute: Frequency Division: Frequency Division: takes place in takes place in

different roomsdifferent roomsTime Division: Time Division: taking turns in a taking turns in a

single roomsingle roomCode Division: Code Division: lectures on different lectures on different

subjects.subjects.

Wired vs. WirelessWired vs. Wireless

Wired vs. WirelessWired vs. Wireless (1) (1)

A problem with wireless networks is that A problem with wireless networks is that anyone with a wireless network card is anyone with a wireless network card is able to access this network and is able to access this network and is potentially harmful since they are able potentially harmful since they are able to corrupt and steal important files. to corrupt and steal important files.

These networks transmit data over an These networks transmit data over an area such that the network signals may area such that the network signals may penetrate physical areas such as walls. penetrate physical areas such as walls.

Wired vs. WirelessWired vs. Wireless (1) (1)

Although this problem is relevant to a Although this problem is relevant to a wired network also, it exists to a wired network also, it exists to a greater degree in a wireless network.greater degree in a wireless network.

With regard to wired networks, the With regard to wired networks, the electromagnetic waves that are electromagnetic waves that are given off from the current traveling given off from the current traveling through the network cables. through the network cables.

Advantages of wireless Advantages of wireless networksnetworks

FlexibleFlexibleCost is less (long term)Cost is less (long term)Mobile user choiceMobile user choiceAccesses areas that wired networks Accesses areas that wired networks

cannot reachcannot reach

Disadvantages of wireless Disadvantages of wireless networksnetworks

Compared to wired networks the data Compared to wired networks the data rates are slowerrates are slower

User location determines performanceUser location determines performanceDevices such as microwaves, cordless Devices such as microwaves, cordless

phones, etc may cause interferencephones, etc may cause interferenceCan be accessed by hackers from the Can be accessed by hackers from the

outsideoutside

Wired Equivalent Privacy Wired Equivalent Privacy Algorithm (WEP) (1)Algorithm (WEP) (1)

Wireless networks may include Wireless networks may include additional security elements, which additional security elements, which are not supported in wired networks. are not supported in wired networks.

For eg. The use of security algorithms For eg. The use of security algorithms such as WEP (Wired Equivalent such as WEP (Wired Equivalent Privacy Algorithm), that uses an Privacy Algorithm), that uses an encryption algorithm which deals encryption algorithm which deals with unauthorized access to the with unauthorized access to the network (eavesdropping).network (eavesdropping).

WEP (2)WEP (2)WEP is a implemented such that a block of WEP is a implemented such that a block of

plaintext (input text) is bitwise XORed with plaintext (input text) is bitwise XORed with an equal length random key sequence. A an equal length random key sequence. A random number generator is used on the random number generator is used on the initialization vector and the secret key and initialization vector and the secret key and outputs a key sequence of random of octets.outputs a key sequence of random of octets.

An integrity check value is produced to An integrity check value is produced to protect against data modification.protect against data modification.

The key sequence combined with plaintext The key sequence combined with plaintext combined with the integrity check value combined with the integrity check value gives the enciphered message. The integrity gives the enciphered message. The integrity check value and the ciphertext is the check value and the ciphertext is the combination of the output.combination of the output.

Block CiphersBlock Ciphers

Another security algorithm is Block Ciphers Another security algorithm is Block Ciphers which is the most common of the which is the most common of the encryption techniques. The Block Cipher encryption techniques. The Block Cipher consists of:consists of:

Data Encryption Standard (DES)Data Encryption Standard (DES)

Triple Data Encryption (TDEA)Triple Data Encryption (TDEA)

Advanced Encryption Standard (AES).Advanced Encryption Standard (AES).

The GSM NetworkThe GSM Network

TheThe G Globallobal S System for ystem for MMobile obile communications.-most widely used communications.-most widely used digital cellular communications digital cellular communications systemsystem

The GSM NetworkThe GSM Network

Picture: http://www.alphaorg.com/cellular/Picture: http://www.alphaorg.com/cellular/

Mobile StationMobile Station

Mobile equipment or terminalMobile equipment or terminal3 types: fixed, portable, handheld3 types: fixed, portable, handheld

Subscriber Identity Module Subscriber Identity Module (SIM).(SIM).

The Base Station Subsystem The Base Station Subsystem (BSS)(BSS)

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

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

The Base Station Controller (BSC). The Base Station Controller (BSC).

The Base Transceiver Station The Base Transceiver Station (BTS)(BTS)

The BTS corresponds to the The BTS corresponds to the transceivers and antennas used in transceivers and antennas used in each cell of the network. It is usually each cell of the network. It is usually placed in the center of a cell. The placed in the center of a cell. The size of a cell defines the transmitting size of a cell defines the transmitting power. A BTS can have up to 16 power. A BTS can have up to 16 transceivers. It all depends on the transceivers. It all depends on the density of users in the cell.density of users in the cell.

The Base Station Controller The Base Station Controller (BSC) (BSC)

The BSC controls a group of BTS. The BSC controls a group of BTS. A BSC is primarily responsible for A BSC is primarily responsible for

handovers, frequency hopping, handovers, frequency hopping, exchange functions and control of exchange functions and control of the frequency power levels of the the frequency power levels of the BTSs. BTSs.

The Network and Switching The Network and Switching Subsystem (NSS) Subsystem (NSS)

Its main role is to manage the Its main role is to manage the communications between the mobile communications between the mobile users and other users, such as users and other users, such as mobile users, ISDN users, landline mobile users, ISDN users, landline users, etc. users, etc.

It also has databases that store It also has databases that store information about the subscribers information about the subscribers and to manage their mobility. and to manage their mobility.

The different components of the NSS The different components of the NSS are described below. are described below.

The Mobile services Switching The Mobile services Switching Center (MSC) Center (MSC)

Central component of the NSS. Central component of the NSS. It performs switching functions and It performs switching functions and

also provides connection to other also provides connection to other networks. networks.

The Gateway Mobile services The Gateway Mobile services Switching Center (GMSC) Switching Center (GMSC)

A gateway is a node that A gateway is a node that interconnects two networks. interconnects two networks.

The GMSC is the interface between The GMSC is the interface between the mobile cellular network and the the mobile cellular network and the Public Switched Telephone Network Public Switched Telephone Network (PSTN). (PSTN).

It is responsible for routing calls from It is responsible for routing calls from the fixed network towards a GSM the fixed network towards a GSM user.user.

Home Location Register Home Location Register (HLR) (HLR)

The HLR is an important database as it The HLR is an important database as it stores information about the subscribers stores information about the subscribers belonging to the covering area of a MSC. belonging to the covering area of a MSC.

It stores the current location of these It stores the current location of these subscribers and the services to which they subscribers and the services to which they have access. have access.

The location of the subscriber corresponds The location of the subscriber corresponds to the SS7 address of the Visitor Location to the SS7 address of the Visitor Location Register (VLR) associated to the terminal. Register (VLR) associated to the terminal.

Visitor Location Register Visitor Location Register (VLR) (VLR)

The VLR contains information from a The VLR contains information from a subscriber's HLR. subscriber's HLR.

It is necessary for the provision of It is necessary for the provision of subscribed services to visiting users. subscribed services to visiting users.

When a subscriber enters the covering area When a subscriber enters the covering area of a new MSC, the VLR associated to this of a new MSC, the VLR associated to this MSC will request information about the new MSC will request information about the new subscriber to its corresponding HLR. subscriber to its corresponding HLR.

The VLR will then have enough information The VLR will then have enough information to assure the subscribed services without to assure the subscribed services without needing to confirm with the HLR each time needing to confirm with the HLR each time a communication is established. a communication is established.

The Authentication Center The Authentication Center (AuC) (AuC)

The AuC register provides the The AuC register provides the parameters needed for parameters needed for authentication and encryption authentication and encryption functions. functions.

These parameters help verify the These parameters help verify the user's identity. user's identity.

The Equipment Identity Register The Equipment Identity Register (EIR) (EIR)

The EIR is also used for security The EIR is also used for security purposes. It is a register containing purposes. It is a register containing information about the mobile equipment. information about the mobile equipment.

It particularly contains a list of all valid It particularly contains a list of all valid terminals. terminals.

A terminal is identified by its A terminal is identified by its International Mobile Equipment Identity International Mobile Equipment Identity (IMEI). (IMEI).

The EIR uses this to forbid calls from The EIR uses this to forbid calls from stolen or unauthorized terminals.stolen or unauthorized terminals.

The GSM Interworking Unit The GSM Interworking Unit (GIWU) (GIWU)

The GIWU corresponds to an The GIWU corresponds to an interface to various networks for data interface to various networks for data communications. communications.

During these communications, the During these communications, the transmission of speech and data can transmission of speech and data can be alternated. be alternated.

The Operation and Support The Operation and Support Subsystem (OSS) Subsystem (OSS)

The OSS is connected to the different The OSS is connected to the different components of the NSS and BSC in components of the NSS and BSC in order to control and monitor the GSM order to control and monitor the GSM system. system.

It also takes care of controlling the It also takes care of controlling the traffic load of the BSS.traffic load of the BSS.

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

Maintenance Maintenance

GSMGSMGSM uses an intriguing method to GSM uses an intriguing method to

send data. By simply sending send data. By simply sending computer data as it would send voice computer data as it would send voice data, GSM allows every phone to be data, GSM allows every phone to be "data enabled." "data enabled."

Since the GSM network is already a Since the GSM network is already a packet network of sorts because of its packet network of sorts because of its frequency hopping, it requires no frequency hopping, it requires no additional hardware to support data. additional hardware to support data.

GSM allows data rates in multiples of GSM allows data rates in multiples of 300 bits per second, up to 64 kilobits 300 bits per second, up to 64 kilobits per second.per second.

Advantages of Cellular Advantages of Cellular NetworksNetworks

Cellular networks use "small" cells with low Cellular networks use "small" cells with low powered transceivers instead of one large powered transceivers instead of one large area with a high powered transceiver.area with a high powered transceiver.

Using cellular networks increases overall Using cellular networks increases overall call handling capacity.call handling capacity.

Avoids central point of failure.Avoids central point of failure. Allows dynamic distribution of capacity Allows dynamic distribution of capacity

based on demand.based on demand. Less interference with other wireless Less interference with other wireless

communications communications

Conclusion (1)Conclusion (1)

Mobile phone contracts provide a Mobile phone contracts provide a useful and relatively cheap service. useful and relatively cheap service.

Cellular radio network infrastructures Cellular radio network infrastructures are growing at a tremendous rate.are growing at a tremendous rate.

Cellular networks are becoming high Cellular networks are becoming high speed data networks. speed data networks.

Conclusion (2)Conclusion (2)

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

Download - Cellular Wireless Networks

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