Cellular Communications
description
Transcript of Cellular Communications
CELLULAR COMMUNICATIONSGSM/GPRS/EDGE
Groupe Speciale Mobile/Global System for Mobile
GSM Air Interface TDMA with FDD
200Khz channels with 200KHz guard bands GSM 900 has 124 carriers GMSK modulation, 270kbps per carrier Up to 8 users, 24.8kbps per user FEC reduces to 13kbps per user for voice
Physical Channel RF carrier divided into 8 slots, numbered
0..7 Timeslots carrying data
At most 8 traffic channels Control messages
At least 1 control channels More control (logical) channels Packed into RF carrier
Single Burst/Slot
Frame Structure
Trafficchannels
(TCH)
Signalingchannel
TCH/F: Full-rate Traffic ChannelTCH/H: Half-rate Traffic Channel
FCCH: Frequency correctionSCH: SynchronizationBCCH: Broadcast control
PCH: PagingAGCH: Access grantRACH: Random access
SDCCH: Stand-alone dedicated control
SACCH: Slow associated controlFACCH: Fast associated control
Two-way
Base-to-mobile
Two-way
Logical Channel List
BCH
CCCH
DCCH
Broadcast Control Channels
Common Control Channels
Dedicated Control Channels
Channel Coding
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What is a location area (LA)? A powered-on mobile is informed of an incoming
call by a paging message sent over the PAGCH channel of a cell
One extreme is to page every cell in the network for each call - a waste of radio bandwidth
Other extreme is to have a mobile send location updates at the cell level. Paging cut to 1 cell, but large number of location updating messages.
Hence, in GSM, cells are grouped into Location Areas – updates sent only when LA is changed; paging message sent to all cells in last known LA
International Mobile Station Equipment Identity (IMEI)
Type Approval Code (TAC): 6 decimal places, centrally assigned.
Final Assembly Code (FAC): 6 decimal places, assigned by the manufacturer.
Serial Number (SNR): 6 decimal places, assigned by the manufacturer.
Spare (SP): 1 decimal place.
International Mobile Subscriber Identity ( IMSI)
Mobile Country Code (MCC): 3 decimal places, internationally standardized.
Mobile Network Code (MNC): 2 decimal places, for unique identification of mobile network within the country.
Mobile Subscriber Identification Number (MSIN): Maximum 10 decimal places, identification number of the subscriber in the home mobile network.
Mobile Subscriber ISDN Number ( MSISDN):
Country Code (CC) : Up to 3 decimal places.
National Destination Code (NDC): Typically 2-3 decimal places.
Subscriber Number (SN): Maximum 10 decimal places.
SMS SMS allowed
Two way communications of the text messages Maximum character length of 160 characters
This can change though depending on the operator or the character set used
Character sets supported are ASCII + additional European characters Unicode
First Text Was sent in December 1992, to a Vodafone device
Sent by Neil Papworth, saying “Merry Christmas” Standard
Defined by ETSI and is known as “GSM 03.40”
SMS
SMS Continued The success is SMS was never planned for! It was only ever intended as the Pager replacement,
with limited use This will explain some of the design decisions made
SMS GSM
At a defined time interval in GSM all devices will listen to a transmission. This is when a Digital Control Channel (DCCH) packet of
information is being sent across the network. These DCCH packets are used to transfer essential information
into the devices. Information like a call is in coming Paging signals from the Base stations, to work out if a handover
is needed One of these packet formats is called SMS point to point
messaging, Paging, access control channel (SPACH) This message type can be used to carry a text message.
Advantage of this method is a text message can still be delivered during a phone conversation.
SMS
SMS Packet format All data is transferred in a single DCCH SPACH
packet
SCA Service Centre Address
MR Message Reference PID Protocol Identifier
PDU Type Protocol Data Unit Type
DA Destination Address DCS Data Coding Scheme
VP Validity Period UDL User Data Length UD User Data
GPRS: General Packet Radio Service
GSM data CSD: circuit switched data Max 14kbps Similar to voice call Inefficient usage of spectrum
GPRS packet-based service Upgrade of infrastructure GGSN is a gateway to outside world SGSN is a gateway within the network
GPRS architecture
GPRS handset classes Class A
Class A terminals have 2 transceivers which allow them to send / receive data and voice at thesame time. This class of device takes full advantage of GPRS and GSM. You can be taking a call and receiving data all at the same time.
Class B
Class B devices can send / receive data or voice but not both at the same time. Generally if you are using GPRS and you receive a voice call you will get an option to answer the call or carry on.
Class CThis device only allows one means of connectivity. An example would be a GPRS data card in a laptop.
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Packet switched Upgrades the modulation scheme
From GMSK to 8-PSK Maximum speed ~59 Kb/sec per time slot, ~473.6 Kb/sec for all 8 time
slots Variable data rate – depending on the channel conditions
Defines several different classes of service and mobile terminals
Enhanced Data GSM Environment (EDGE)
EDGE enabled data mobile
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Practically achievable data rates
Theoretical rates are constrained by mobile power and processing capabilities
Most mobiles support less than the maximum allowed by standardPractically achievable
data rates
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Migration:1. High speed circuits
switched data (HSCSD)
2. Packet switched data (GPRS,EDGE)
3. Integrated packet services – possibly under different access scheme (UMTS)
GSM Migration Towards 3G
G SM 2+9.6 Kb/sec
H S C S D64 K b/sec
G P R S114 Kb /sec
E D G E384 K b/sec
U M TS2M b/sec
1999 1Q2000
2Q2000
3Q2001
4Q2002
T im eline
D ata R ate
H S C S D - H igh S peed C ircu it S witched D ataG P R S - G ene ra l P acke t R adio S ystemED G E - Enhanced D ata G SM Environm entU M T S - U niversa l M o bile Te lephone Se rvice