gsm_networks cu presentation
TRANSCRIPT
-
8/2/2019 GSM_Networks CU Presentation
1/34
GSM Cellular System And GPRS
Technology
By
Seyhun Barbaros YABACI Ersin ADALDecember 2010
-
8/2/2019 GSM_Networks CU Presentation
2/34
Cellular Systems - Background
1G - First Generation NMT(Nordic Mobile Telephone) ,AMPS(Advanced Mobile Phone System)TACS (Total
Access Communications System)
Narrow Band Analog Systems,
Voice Services, no handover.
Now Obsolote
2G - Second Generation GSM, CDMA ONE, CDMA2000, PDC
%80 of Currently users are GSM users.
Digital, Coded Voice, Voice and Additional Services, SMS.
FDMA , TDMA, CDMA
3G - Third Generation
WCDMA UMTS, CDMA2000(1xEVDO) Voice, Video, Streaming, Data services
Wideband, WCDMA FDD and TDD
4G Fourth Generation
LTE, OFDMA, all IP system, Wideband.
-
8/2/2019 GSM_Networks CU Presentation
3/34
GSM Definition
GSM: Global System for Mobile Communication
A Narrow Band Digital Cellular System.
Standardized by ETSI(European Telecommunications
Standards Institute), www.etsi
.org
3GPP TS 45.005 - GSM/EDGE Radio Access Network; Radio
transmission and reception
3GPP TS 45.001 - Physical layer on the radio path; Generaldescription
http://www.etsi.org/http://www.etsi.org/http://www.etsi.org/http://www.etsi.org/http://www.etsi.org/http://www.etsi.org/ -
8/2/2019 GSM_Networks CU Presentation
4/34
GSM-UMTS Network Architecture
-
8/2/2019 GSM_Networks CU Presentation
5/34
Base Station System
The Base Station Controller (BSC)
Manages BSS operations as an intelligent point. Provides Mobile station connection handlingand Radio NW management.
Transcoding and Rate adaptation.
BTS transmission management and remote control.Base Transceiver Station (BTS)
Consisted of one or more GSM cells, performs radio releated functions, mamaged by BSC.
Has radio and transmission interfaces
MS (Mobile Station)
Consists of Mobile Terminal and SIM(Subsiscriber identitiy module). Mobile terminal providesradio access functions via air interface. SIM stores IMSI number that used for authenticationprocesses..
-
8/2/2019 GSM_Networks CU Presentation
6/34
Switching System Mobile Services Switching Centre (MSC): Setup, routing and
supervision of calls to and from mobile subscribers. Performs
suthentication processes.
Visitor Location Register (VLR): Contains non-permanent
information about the mobile subscribers in its location area.
Gateway Mobile Services Switching Centre (GMSC): Routes
incoming calls from other networks to the MSC.
Home Location Register (HLR): HLR holds information of all
subscribers of its PLMN. (Such as IMSI and location of
subscribers)
Authentication Center (AUC): Provides authentication and
encryption parameters for subscriber verification and call
confidientality.
Equipment Identity Register (EIR): Checks the mobile
equipment IMEI and prevents barred equpment usage.
Serving GPRS Support Node (SGSN): Center of packet switched
operations , performs similar functions as MSC for GPRS.
Gateway GPRS Support Node (GGSN):Gateway point to other
packet switching networks, functions as similar to GMSC.
-
8/2/2019 GSM_Networks CU Presentation
7/34
GSM Frequeny Bands
GSM is a narrow band, full duplex system.
Downlink: BTS transmit MS receive.
Uplink: MS transmit BTS receive.
-
8/2/2019 GSM_Networks CU Presentation
8/34
ARFCN
Fixed designation of ARFCN
Dynamically mapped ARFCN
Absolute Radio-Frequency Channel Number : A code that
specifies a pair of physical radio carriers and channels used fortransmission and reception on the air interface.
-
8/2/2019 GSM_Networks CU Presentation
9/34
P-GSM , DCS-1800
Duplex Distance: 45 Mhz , 95 Mhz
Carrier Seperation: 200 KHz
For GSM 900 , 124 channels
For GSM 1800 , channels
GSM bands in Trkiye
-
8/2/2019 GSM_Networks CU Presentation
10/34
FDMA and TDMA GSM system uses two radio access methods for air interface, these two system
combined to achieve better spectrum efficiency.
FDMA (Frequency division multiple access): For FDMA system frequency banddivided to number of channels by seperation distance 200 Khz.
TDMA (Time division multiple access): A TDMA frame consists of 8 Time Slot. Eachtime slot corresponds to a physical channel. Logical channels of GSM mappedon these physical channels.
The Modulation type of GSM is GMSK(Gaussian minimum-shift keying). GMSK is a
continuous-phase frequency-shift keying modulation scheme. This modulation
type sends one bit per symbol.
-
8/2/2019 GSM_Networks CU Presentation
11/34
Logical channels
GSM LOGICAL CHANNELS
Control Channels
Broadcast Channels(BCH)
FCCH SCH BCCH
Common Control Channels(CCCH)
PCH RACH AGCH
Dedicated Channels (DCH)
SDCCH SACH FACH
TrafficChannels
TCH
FULLRATE HALFRATE
Uplink
Uplink -Downlink
Downlink
FCCH : Frequency Correction Channel
SCH: Synchronization Channel
BCCH: Broadcast Control Channel
PCH: Paging Channel
RACH: Random Access Channel
AGCH: Access Grant Channel
SDCCH: Stand Alone Dedicated Control Channel
SACCH: Slow Associated Control Channel
FACCH: Fast Associated Control Channel
-
8/2/2019 GSM_Networks CU Presentation
12/34
Mapping of Logical Channels Onto
Physical Channels Several logical channels can share the same physical channel or Time Slot.
On TS 0 (on one carrier per cell, the BCCH-carrier) the broadcast channels
and the common control channels are multiplexed.
Dedicated control channels and traffic channels mapped onto TS 1 to TS 7.
1 TDMA frame = 8 Time Slot = 4,615 ms
-
8/2/2019 GSM_Networks CU Presentation
13/34
Registering The Mobile Network
GSM network consists of many neighbor cells that creates continious air interface. In order to
communicate to the network, a mobile station must choose best serving cell in its location.
1. When a MS powered on, it firstly measures the BCCH carriers signal strengths of its
PLMN(Public Land Mobile Network) cells. If it can measure more than one allowed BCCH
carriers, makes a decision on basically measured signal strengths to camp on a cell.
2. MS receives system information from BCCH carrier than registers itself to the GSM network.
3. MS request an SDCCH channel via RACH. Then sends an IMSI attach message via SDCCH to
the VLR.
4. VLR analyzes IMSI and changes its flag on database to attached. Then sends a message to
MS that attaching process completed.
-
8/2/2019 GSM_Networks CU Presentation
14/34
Call setup Mechanism Calls From MS
1. Dedicated Channel Request from MS via RACH channel.2. Getting dedicated channel information from AGCH channel.
3. MS service(call) request via SDCCH channel
4. Authentication performed
5. Ciphering may be initiated
6. MSC recevies setup message from MS
7. A PCM TS allocated between MSC and BSC. BSC assigns a TCH for call. Traffic
control system sets up to connection to target subscriber.8. The ringing tone sent to MS.
9. When subscriber B answers, network sends a connect message to the MS, MS
completes the call setup
-
8/2/2019 GSM_Networks CU Presentation
15/34
Call setup Mechanism Calls to MS
1. When a call is made from another network(i.e PSTN) the exchange analysis the
number, the call routed to the GMSC in the PLMN .2. GMSC finds the HLR that MSISDN (Mobile Subscriber Integrated Services Digital
Network Number) registered in and gets the MSC/VLR information which called
MS registered. HLR finds out IMSI( International Mobile Subscriber Identity)
number of MS via MSISDN.
3. By rquest of HLR, VLR generates a roaming number , this number forwarded to
GMSC via HLR.
4. GMSC routes the call to appropriate MSC.5. MSC sends a paging message to BSC, and BSC pages for location area of called MS.
6. BSC sends paging message to BTS of appropriate location area.
7. BTS sends paging message via air interface with IMSI or TIMSI of mobile.
8. MS detects its identity on paging message and sends a request for SDCCH channel
allocation. MSC starts authentication and ciphering process.
9. BSC orders to BTS activate TCH and release the SDCCH. MS ordered to tune in TCH
channel . A ringing tone created in MSC and sent to calling number.
-
8/2/2019 GSM_Networks CU Presentation
16/34
Cellular System
GSM network consists of many neighbour cells that creates continious air interface.
Each cell has its coverage area and users can change their serving cell both in active and
idle mode.
-
8/2/2019 GSM_Networks CU Presentation
17/34
SEYHN1
SEYHN2
SEYHN3
ELEKT1
ELEKT2
ELEKT3
INDOR1
BARBA1
BARBA2
BARBA3
BARBA4
YABAC1
YABAC2
YABAC3
AHMET1
AHMET2
AHMET3
KEREM1
KEREM2
KEREM3
EMIR1EMIR2
ERSIN1
ERSIN2
ERSIN3
Cellular System Example Locations , Urban Areas
-
8/2/2019 GSM_Networks CU Presentation
18/34
ADATA1
ADATA2
ADATA3
GEKOY1
GEKOY2
GEKOY3
CAMDA1
CAMDA2
CAMDA3
KARTA1
KARTA2
KARTA3
KARTA4
TUZLA1
TUZLA2
TUZLA3
TUZCA1
TUZCA2
YOLKS1
YOLKS2
YOLKS3
CELMI1
CELMI2
CELMI3
Cellular System Example Locations , Rural Areas
-
8/2/2019 GSM_Networks CU Presentation
19/34
Frequency Planning - Reuse of Available
Frequencies
Since the capacity of a single cell is limited by available number of frequencies,the needing coverage area divided to many cells. Each cell uses a different set of
frequencies of its neighbours to prevent interference.
-
8/2/2019 GSM_Networks CU Presentation
20/34
1,3,5,7,9,11
22,24,28,16
2,4,6,18,22
10,12,14,16
18,22,24,28,30
2,4,6,8
INDOR1
BARBA1
BARBA2
BARBA3
BARBA4
3,5,7,9,11
2,4,6,8,10
10,12,14,,32
AHMET1
AHMET2
AHMET3
KEREM1
KEREM2
KEREM3
EMIR1EMIR2
ERSIN1
ERSIN2
ERSIN3
Frequency Planning Example
-
8/2/2019 GSM_Networks CU Presentation
21/34
Traffic Dimensioning
Cellular system capacity depends on;
Number of available channels
Target Grade of Service (GOS = Blocking Probability) level of Subcribers
Traffic expressed in Erlang;
E= h , where=Call arrival rate, h=Average call duration.
Erlang B formula gives;
How many traffic can be handled for desired GOS(Blocking Probability), for
available traffic channels.
Assuming an average subscriber creates 0,050 Erlang traffic, a cell with 4 traffic
channel at GOS 0.2 , can serve 1/0,050= 20 subscriber.
Erlang B Table
-
8/2/2019 GSM_Networks CU Presentation
22/34
Handover
In a cellular system the ongoing calls of the moving users must be carried between theneighbour cells to ensure the communication continuity. This process called handover.
The handover decision is a result of locating algorithm and given by network and
specifically on BSC. The signal strength measurements of serving and neighbor cells andnetwork parameter settings are used as inputs for locating algorithm.
The reasons that produces handover decision;
Decreasing field strength of the serving cell prior to neighbouring cell/cells.
Decreasing signal quality of serving cell.
Exceeding allowed timing advance limits for serving cell.
Parameter settings that favoured another cell.
-
8/2/2019 GSM_Networks CU Presentation
23/34
TEMS Output example
-
8/2/2019 GSM_Networks CU Presentation
24/34
GPRS(General Packet Radio Service) GSM is actually designed for carrying simultaneous duplex speech data, it is
based on the circuit switched system. GPRS is an extenison of GSM
architecture. To carry data packets on air interface we have to reserve some traffic channels
for this purpose. This data channels called PDCHs (packet data channels).
Packet data is coded in radio blocks which consists of four consecutive radioburst. A Radio block includes 456 bits. The number of information bits isdepend on Coding Schema(CS-1 to CS-4).
At the limit values, coding of GPRS System can carry maximum 20 kbit/s foreach time slot. But these are theoratical values, heavily depended upon radioconditions. To achieve more data rate, GSM terminals(e.g. MS) can use morethan one time slot at the same time.
-
8/2/2019 GSM_Networks CU Presentation
25/34
EGPRS (Enhanced GPRS)
To achieve higher data rates in same TS and frequency limitations, there is another
technology in GSM named EDGE. The main improvement on EDGE is modulation
scheme. Edge uses 8 PSK modulation, which allows transmitting 3 bits per symbol
versus 1 bit of the GMSK.
Coding Scheme Modulation Method Max data rate MCS family Max Data rate(Kbps)
MCS-9 8 PSK 59.2 A 236.8
MCS-8 8 PSK 54.4 A 217.6
MCS-7 8 PSK 44.8 B 179.2
MCS-6 8 PSK 29.6 A 118.4
MCS-5 8 PSK 22.4 B 89.6
MCS-4 GMSK 17.6 C 70.4
MCS-3 GMSK 14.8 A 59.2
MCS-2 GMSK 11.2 B 44.8
MCS-1 GMSK 8.8 C 35.2
-
8/2/2019 GSM_Networks CU Presentation
26/34
Antennas
-
8/2/2019 GSM_Networks CU Presentation
27/34
In order to restrain the serving area or provide better signal strength for highly
located antennas, antenna tilting is used.
Antennas can be tilted electrically or mechanically. Electrical tilting is more
effective and does not degenerates antenna pattern.
Antenna Downtilting
-
8/2/2019 GSM_Networks CU Presentation
28/34
To reduce the negative effect of fading dips and improve the receiver
performance pair of antennas used at receiver side. This is called diversity. Thereis two types of diversity used in GSM.
Space Diversity; Vertically polarized antennas placed in 12-18 (wavelength)
Polarization Diversity; Cross polarized antennas used. No space seperation
used.
Antenna Diversity
-
8/2/2019 GSM_Networks CU Presentation
29/34
Base Station Examples
-
8/2/2019 GSM_Networks CU Presentation
30/34
Base Station Examples
-
8/2/2019 GSM_Networks CU Presentation
31/34
Base Station Examples
-
8/2/2019 GSM_Networks CU Presentation
32/34
Base Station Examples
-
8/2/2019 GSM_Networks CU Presentation
33/34
Suggested Reference Books
HEINE G. , 1998, GSM Networks, Protocols, Terminology and
Implementation, Artech House
MISHRA A. R. , 2004, Cellular Network Planning and
Optimization, John Wiley & Sons Ltd
HALONEN T. , ROMERO J. And MELERO J. , 2003, GSM, GPRS
and EDGE performance, John Wiley & Sons Ltd.
-
8/2/2019 GSM_Networks CU Presentation
34/34
Thanks