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Lecture #11Lecture #11: Cellular : Cellular Radio. Satellite Radio. Satellite

Communications.Communications.C o n t e n t s C o n t e n t s Cellular RadioCellular Radio

– Evolution of wireless and mobile Evolution of wireless and mobile communicationscommunications

– Cellular mobile systemsCellular mobile systems

Communication SatellitesCommunication Satellites– Geosynchronous satellitesGeosynchronous satellites

– Low-orbit satellitesLow-orbit satellites

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Mobile Telecommunication Mobile Telecommunication Services Services

Extension of the traditional telephone Extension of the traditional telephone

and data services, includingand data services, including– satellite pagingsatellite paging

– cordless phonescordless phones

– cellular phonescellular phones

– mobile data applications mobile data applications

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Paging SystemsPaging Systems Non-interactive Non-interactive unidirectionalunidirectional transmission transmission of short of short

messages from [conventional] telephone to one or more messages from [conventional] telephone to one or more

subscribers based on subscribers based on

– small receiving device portable by the subscriber orsmall receiving device portable by the subscriber or

– computer plug-in device for receiving of arbitrary long computer plug-in device for receiving of arbitrary long

messagesmessages AddressingAddressing is based on unique number like the phone is based on unique number like the phone

systemsystem Calls Calls are made to the service company and the messages are made to the service company and the messages

are transmitted locally by antenna or to remote client via are transmitted locally by antenna or to remote client via

satellite.satellite. Possibility for broad- and multi-castingPossibility for broad- and multi-casting Narrow bandwidth (because of the small buffer of the Narrow bandwidth (because of the small buffer of the

receiving device); transmission band is in the diapason receiving device); transmission band is in the diapason

930-932 MHz.930-932 MHz.

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Cordless PhonesCordless Phones Two-part cordless extension of standard Two-part cordless extension of standard

telephone, including base station and portable telephone, including base station and portable

telephone connected by bi-directional radio line telephone connected by bi-directional radio line Preset frequency or user-selectable frequency or Preset frequency or user-selectable frequency or

frequency hops on predefined channels to avoid frequency hops on predefined channels to avoid

interference with other devices and for privacyinterference with other devices and for privacy Analog or digital (newer standard) codingAnalog or digital (newer standard) coding Range under 1km (usually wider range is under Range under 1km (usually wider range is under

different regulation)different regulation) Some new versions support roaming between Some new versions support roaming between

the base stationsthe base stations

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Mobil PhonesMobil Phones evolutionevolution Single channelSingle channel push-to-talk systems push-to-talk systems IMTSIMTS (Improved Mobile Telephone System): (Improved Mobile Telephone System):

– bi-directional bi-directional analoganalog transmission on two-frequencies- transmission on two-frequencies-channel; channel;

– up to 23 channels in system in the 150-450MHz band up to 23 channels in system in the 150-450MHz band and up to 23 simultaneous conversations; and up to 23 simultaneous conversations;

– powerful 200W transmitter covering up to 100km area;powerful 200W transmitter covering up to 100km area;

– long distance between adjacent transmitters, separation long distance between adjacent transmitters, separation by uncovered zone to avoid interference.by uncovered zone to avoid interference.

Cellular telephone systemsCellular telephone systems::– small areas of the region (“small areas of the region (“cellscells”) use subset of ”) use subset of

frequency channels so that the same channels can be frequency channels so that the same channels can be reused in one or several near-by but not adjacent cellsreused in one or several near-by but not adjacent cells

– Analog systems: AMPS (Advanced Mobile phone System) Analog systems: AMPS (Advanced Mobile phone System)

– Digital systems: GSMDigital systems: GSM

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Not to be mixed with the ATM cell!

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Analog Cellular Analog Cellular Telephone SystemsTelephone Systems

Small retransmission cells with low-power Small retransmission cells with low-power

transceiver (radio transmitter+receiver); low-power transceiver (radio transmitter+receiver); low-power

telephones (05.-3W depends on usage: hand-set, telephones (05.-3W depends on usage: hand-set,

car-set).car-set).

Channel adjacency scheme that allocates two equal Channel adjacency scheme that allocates two equal

sets of channels distanced by two cell’s dimensions.sets of channels distanced by two cell’s dimensions.

Cell size can be reduced by reducing the Cell size can be reduced by reducing the

transmitting power and congesting the transceivers transmitting power and congesting the transceivers

in the area. The result is higher frequency reuse i.e. in the area. The result is higher frequency reuse i.e.

higher number of service users. higher number of service users.

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Mobile Phone CellMobile Phone Cell CellCell consists of a base station that includes consists of a base station that includes

computer controlled transceiver (with antenna) computer controlled transceiver (with antenna) and connection to MTSO (Mobile Telephone and connection to MTSO (Mobile Telephone Switching Office) or MSC (Mobile Switching Switching Office) or MSC (Mobile Switching Center) Center)

MTSOMTSO is connected to one or more end offices of is connected to one or more end offices of the telephone system and also to other MTSOthe telephone system and also to other MTSO

Hierarchy of MTSO - packet switching networkHierarchy of MTSO - packet switching network

Intercell transfer of the mobile telephone based Intercell transfer of the mobile telephone based on the detection of the phone location by its on the detection of the phone location by its signal strength signal strength

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Mobile Phone ChannelsMobile Phone Channels In AMPS - 832 full duplex channels separated by their In AMPS - 832 full duplex channels separated by their

frequency (i.e. FDM) as follows:frequency (i.e. FDM) as follows:– 832 * 30kHz simplex transmission channels (total bandwidth 832 * 30kHz simplex transmission channels (total bandwidth

25MHz) in the range 82425MHz) in the range 824849MHz 849MHz – 832 * 30kHz simplex receiving channels (total bandwidth 832 * 30kHz simplex receiving channels (total bandwidth

25MHz) in the range 86925MHz) in the range 869894MHz894MHz Signal distortions: absorption and reflectionSignal distortions: absorption and reflection Those 832 channels are separated among the cells - Those 832 channels are separated among the cells -

usually ~50 channels/cell usually ~50 channels/cell ~17 (but ~17 (but 21) different 21) different kind of cells are to be allocated according some pattern kind of cells are to be allocated according some pattern for maximal distance between the similar cellsfor maximal distance between the similar cells

Channel typesChannel types– Control Control (station to mobile) system management (AMPS: 21 (station to mobile) system management (AMPS: 21

reserved control channels hardwired in each telephone PROM)reserved control channels hardwired in each telephone PROM)– PagingPaging (station to mobile) incoming calls (station to mobile) incoming calls – AccessAccess (bidirectional) outcoming calls and channel (bidirectional) outcoming calls and channel

assignmentassignment– DataData (bidirectional) conversation, fax, data exchange (bidirectional) conversation, fax, data exchange

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Mobile Phone CallsMobile Phone Calls Mobile Mobile phone numbersphone numbers are 34b addresses written in are 34b addresses written in

PROM:PROM:– 10b - 3 decimal digits for area code (10b - 3 decimal digits for area code (: not ASCII but binary : not ASCII but binary

coding! 10b binary code ranges 0 coding! 10b binary code ranges 0 (1K-1), 3 positions of decimal (1K-1), 3 positions of decimal code range 0 code range 0 999) 999)

– 24b - 7 decimal digits for subscriber # (24b code 0 24b - 7 decimal digits for subscriber # (24b code 0 16M-1; 7 16M-1; 7 decimal digits code 0 decimal digits code 0 9 999 999 ) 9 999 999 )

– control information is transmitted in digital form although the control information is transmitted in digital form although the voice channels are analogvoice channels are analog

Switching the phone on proceeds as follows:Switching the phone on proceeds as follows: scanning of the 24 control channels for nearest base stationscanning of the 24 control channels for nearest base station accepting the numbers of paging and access channelsaccepting the numbers of paging and access channels MTSO records the new customer and informs the originating MTSO records the new customer and informs the originating

(home) MTSo for his current location(home) MTSo for his current location periodical reregistration periodical reregistration

Call to another phone #: the request to the base station Call to another phone #: the request to the base station is send via one of the is send via one of the access channelsaccess channels

Call from another phone is received on Call from another phone is received on paging channelpaging channel which is scanned periodically by the telephone for which is scanned periodically by the telephone for message addressed to its numbermessage addressed to its number

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Digital Cellular Digital Cellular TelephonyTelephony

Digital coding makes cellular transmission more Digital coding makes cellular transmission more

secure against direct taping and gives more secure against direct taping and gives more

possibilities for encryption, computer and data possibilities for encryption, computer and data

services, etc.services, etc.

Standards:Standards:

– AMPSAMPS digital upgrade are IS-54/135. The 30kHz AMPS digital upgrade are IS-54/135. The 30kHz AMPS

channel packs 48.6 kb/S shared between 3 active users - channel packs 48.6 kb/S shared between 3 active users -

i.e. 13 kb/S for each useri.e. 13 kb/S for each user

– GSMGSM (Global System for Mobile communications) uses the (Global System for Mobile communications) uses the

10 MHz frequency bandwidth round 1.8 GHz. It is divided 10 MHz frequency bandwidth round 1.8 GHz. It is divided

into 50 200kHz-band channels - FDM. For each of those into 50 200kHz-band channels - FDM. For each of those

channels multiple user processes are multiplexed -TDMchannels multiple user processes are multiplexed -TDM

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Personal Personal Communication Communication

ServicesServices PCS/PCNPCS/PCN (Personal Communication (Personal Communication

{Services|Network}) world-wide {Services|Network}) world-wide mobile telephone with data-mobile telephone with data-transfer capabilities and global transfer capabilities and global addressing systemaddressing system

TechnologyTechnology: dense set of : dense set of cells, cells, that allows low-powered portable that allows low-powered portable and autonomous user devices and autonomous user devices (phones, etc.) (phones, etc.)

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Satellite Satellite CommunicationsCommunications

Communication satellites act as signal reflectors Communication satellites act as signal reflectors or repeaters (reflection + amplification). They or repeaters (reflection + amplification). They contain several transponders which:contain several transponders which:– scan signals in given frequency bandscan signals in given frequency band– amplifies and retransmit the signals in at another amplifies and retransmit the signals in at another

frequency that not interfere the incoming signalfrequency that not interfere the incoming signal FunctionsFunctions::

– overcome the terrestrial curve for straight overcome the terrestrial curve for straight transmitted unguided media (e.g. microwave)transmitted unguided media (e.g. microwave)

– broadcasting a signal over wide areabroadcasting a signal over wide area– focusing the signal in a narrow surface spotfocusing the signal in a narrow surface spot

TypesTypes::– geosynchronous satellitesgeosynchronous satellites– low-orbit satelliteslow-orbit satellites

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Geosynchronous Geosynchronous SatellitesSatellites

Satellite rotates around the Earth with a 24-Satellite rotates around the Earth with a 24-hour period i.e. synchronously to given surface hour period i.e. synchronously to given surface point on a constant height of 36000 kmpoint on a constant height of 36000 km

Interference limitations: Interference limitations: up to 2up to 200 angle angle between adjacent satellitesbetween adjacent satellites and the Earth and the Earth center - up to 180 satellite orbit slots. Number center - up to 180 satellite orbit slots. Number of geosynchronous satellite may be bigger of geosynchronous satellite may be bigger because of the frequency separationbecause of the frequency separation

3 bind available for public communications:3 bind available for public communications: One or more spot beams of the satellite cover One or more spot beams of the satellite cover

the entire visible area or smaller elliptic areas the entire visible area or smaller elliptic areas that correspond to the national territories - that correspond to the national territories - depending on the number of transponders and depending on the number of transponders and equipment featuresequipment features

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The Geosynchronous The Geosynchronous SatelliteSatellite

Number of transponders vary between Number of transponders vary between

10 and 20 and their single bandwidth is 10 and 20 and their single bandwidth is

around 50MHz i.e. around 50MHz i.e. – more than 50Mb/S data path (depending more than 50Mb/S data path (depending

on modulation) or on modulation) or

– 800*64kb/S voice channels.800*64kb/S voice channels.

Frequency band is split between the Frequency band is split between the

transponders statically or dynamically transponders statically or dynamically

(FDM) and the channels are congested (FDM) and the channels are congested

by TDMby TDM

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Surface EquipmentSurface Equipment

System of low-power System of low-power VSATVSAT (Very Small (Very Small

Aperture Terminals) - low uplink rate (19.2 Aperture Terminals) - low uplink rate (19.2

kb/S) because of the weak transmitter; kb/S) because of the weak transmitter;

high down-link rate (512 kb/S) high down-link rate (512 kb/S)

Hub Hub - powerful transceiver with huge - powerful transceiver with huge

antenna retransmits inter-terminal antenna retransmits inter-terminal

communications. Thus all communication communications. Thus all communication

passes through the hub like in the passes through the hub like in the

networks of star-topology.networks of star-topology.

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Geosynchronous Geosynchronous Satellites Satellites

CommunicationCommunication Features:Features:

– relatively big delays for signal traveling to relatively big delays for signal traveling to and from the remote satellite - 270mS and and from the remote satellite - 270mS and 540mS for VSAT-via-Hub communication540mS for VSAT-via-Hub communication

– effective broadcastingeffective broadcasting– security measuressecurity measures– surface distance insensitive surface distance insensitive

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Low-Orbit SatelliteLow-Orbit Satellite Communication use of chains similar satellites that Communication use of chains similar satellites that

are ordered in spinning necklace. The data transfer are ordered in spinning necklace. The data transfer function in regard to given surface object is switched function in regard to given surface object is switched between the consecutively appearing satellites between the consecutively appearing satellites

Motorola Iridium projectMotorola Iridium project - 66 satellites chain in 6 - 66 satellites chain in 6 necklaces (~ 33° latitude angle) ; the necklaces (~ 33° latitude angle) ; the satellites have a mean of 24 beam spots (i.e. satellites have a mean of 24 beam spots (i.e. transponders) separated by the frequency; transponders) separated by the frequency; frequency reuse in 2-3 cells distance. 1628 moving frequency reuse in 2-3 cells distance. 1628 moving cells serve mobile clients by 1,6 GHz full-duplex cells serve mobile clients by 1,6 GHz full-duplex channels ; support by intersatellite channels ; support by intersatellite communications communications

## SATSAT spots(cells)/spots(cells)/ totaltotal channels/channels/ totaltotal

SATSAT cellscells cellcell channelschannels

6666 24(av.)24(av.) 16281628 174174 283 272283 272

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