PowerPoint GSM Fundamentals
Name the frequency spectrum used in GSM
Name the concept of frequency reused.
Name the two different cell types and understand why and when each would be used.
Internal Use
Chapter 2 GSM Network Components
Chapter 3 Terrestrial Interface
Chapter 5 Channels On Air Interface
Chapter 6 Radio Technologies
Internal Use
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95MHz spacing
GSM 900
GSM 900
Fdownlink (n) = Fuplink (n) + 45MHz
Where, 1 < n < 124
Fdownlink (n) = Fuplink (n) + 95MHz
Where, 512 < n < 885
-Bandwidth is from f1 to f2
-Clean signal can be obtained if only one user using this spectrum and the signal energy must higher than the noise floor.
Wanted signal
Internal Use
f1
f2
-Interference occur when two signal are transmitting at the same frequency spectrum.
-Signal with higher energy will win.
10dB
20dB
Adopt multiple access techniques
timeslots
Note: Max number of users can only support up to 8Ts x 124ARFCN=(992 users). [for GSM900]
Internal Use
However maintain the quality of service.
Why need Frequency Re-Use?
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k=4, C/I = 1.5(4)2 = 13.8 dB
Note: - GSM standard required C/I > 9 dB. That’s mean minimum number of reuse pattern is k=3.
Internal Use
Note: In practical C/I should be greater than 12 dB
dB
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for first tier KI = 6 (theoretically)
for first tier KI = 2 - 3
narrow beam antennas (e.g. 60º) better than wide beam antennas (e.g. 120º)
Ex.
3x4
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Where, S = sectorization
C/I = 1.5k2 x 3 = 4.5 K2
= 1.5x (4)2 x 3
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Chapter 2 GSM Network Components
Chapter 3 Terrestrial Interface
Chapter 5 Channels On Air Interface
Chapter 6 Radio Technologies
Internal Use
Draw the structure of GSM
Identify the functions of each component
Internal Use
– Mobile Equipment
– Subscriber Identity Module
Location Area Identity (LAI)
Subscriber Authentication Key (Ki)
it is optional.
The Trans-coder – TC and Sub multiplexer (SM)
BTS
BSC
TC/SM
BSS
MSC
Call Processing
Supplementary service information
Subscriber status (registered/deregistered)
*
IMEI
If NOT found, checked against Grey/Black List
If NOT found, checked against White List indications
If found, returns a Black or Grey List indicator
White List
Black List
Grey List
*
OMC/iManager M2000: OMC assigned specifically for GSM, CDMA & WCDMA NEs.
Internal Use
Chapter 2 GSM Network Components
Chapter 3 Terrestrial Interface
Chapter 5 Channels On Air Interface
Chapter 6 Radio Technologies
Internal Use
Upon completion this course, you will be able to:
Identify the protocols used on the terrestrial interfaces between the GSM system entities
Internal Use
Traffic
Traffic
SCCP
BSSAP
TUP Telephone User Part
ISUP ISDN User Part
MAP Mobile Application Part
BSSMAP BSS Management Application Part
DTAP Direct Transfer Application Part
Internal Use
Chapter 2 GSM Network Components
Chapter 3 Terrestrial Interface
Chapter 5 Channels On Air Interface
Chapter 6 Radio Technologies
Internal Use
Identify the system identification number
Identify the of mobile identification number
Identify the cell identification number
Internal Use
CCCountry Code.
NDCNational Destination Code.
For example: The NDC of China Mobile is 139138137136135.
LSP(locally significant part): is defined by Telecom operator.
For example: 86-139-00311
The format isCC+NDC+H0 H1 H2 H3 0000.
CCCountry Code.
NDCNational Destination Code.
For example: The NDC of China Mobile is 139138137136135.
H0H1H2H3 is defined by Telecom operator.
For example: 86-139-0666-0000.
The LAI is the international code for a location area.
MCCMobile Country CodeIt consists of 3 digits .
For example: The MCC of China is "460"
MNCMobile Network CodeIt consists of 2 digits .
For example: The MNC of China Mobile is "00"
LAC Location Area CodeIt is a two bytes BCD code(hex).
The value 0000 and FFFF is invalid.
For example: 460-00-0011
The CGI is a unique international identification for a cell
The format is LAI+CI
LAI: Location Area Identification
CICell Identity. This code uses two bytes BCD code(hex) to identify the radio cells within an LAI.
For example : 460-00-0011-0001
BSIC
NCCPLMN network color code. It comprises 3 bit. It allows various neighboring PLMNs to be distinguished.
BCCBTS color code. It comprises 3 bit. It allows distinction
between different radio frequency channels using the same frequency in neighboring cells.
BSICBase Station Identification Color Code)
NCC
BCC
BSIC
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CC Country Code. For example: The CC of China is "86".
NDCNational Destination Code. For example: The NDC of China Telecom is 139, 138, 137, 136, 135.
SN Subscriber Number. Format:H0 H1 H2 H3 ABCD
Example: 86-139-0666-1234
For example: The MCC of China is "460"
MNCMobile Network CodeIt consists of 2 digits .
For example: The MNC of China Telecom is "00"
MSINMobile Subscriber Identification Number. H1H2H3 S ABCDEF
For example: 666-9777001
NMSINational Mobile Subscriber IdentificationMNC and MSIN form it together.
For Example of IMSI : 460-00-666-9777001
Not more than 15 digits
3 digits
2 digits
The TMSI is assigned only after successful subscriber authentication.
The VLR controls the allocation of new TMSI numbers and notifies them to the HLR.
TMSI is used to ensure that the identity of the mobile subscriber on the air interface is kept secret.
The TMSI consists of 4 bytes( 8 HEX numbers) and determined by the telecom operator.
TMSI
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IMEI
TACType approval code. It is administered by the type approval center.
FACFinal assembly code.It is administered by the manufacturer.
SNRSerial number.It is issued by the manufacturer of the MS.
SPNot used.
TAC
FAC
SNR
SP
IMEI
Chapter 2 GSM Network Components
Chapter 3 Terrestrial Interface
Chapter 5 Channels On Air Interface
Chapter 6 Radio Technologies
Internal Use
Understand the structure of multi frames
Name the 4 most commonly used channel combinations
Identify the types of physical channels and logical channels
Internal Use
*
The physical channel is the medium over which the information is carried
The logical channels consist of the information carried over the physical channel
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slot is called a “burst”
Physical and Logical Channels
Burst (148 bits)
3bit
142bit
3bit
8.25bit
Frequency correction burst (FCH): Used in frequency synchronization between MS and BTS
3bit
64 synchronous bits
Synchronous burst (SCH): Used in timing synchronization between MS and BTS
Internal Use
Tail bit
Tail bit
Guard interval
Dummy burst (BCH): Used in transmission of filling frames by BTS at timeslots when there is no information delivered
3bit
Frame stealing flag
Normal burst (TCH): Used to carry the information of the traffic channel and the control channel.
Internal Use
Broadcast control channel
TCH/9.6 Data Channel 9.6kb/s
TCH/4.8 Data Channel 4.8kb/s
TCH/2.4 Data Channel 2.4Kb/s
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The information carried on the BCCH is monitored by the mobile periodically when it is switched on and not in a call
BCCH:Broadcast Control Channel
CCH
CCCH
RACH
uplink
CBCH
downlink
PCH/AGCH
downlink
The CCCH is responsible for transferring control information between all mobiles and the BTS.
RACH: Random Access Control Channel
PCH: Paging Channel
CBCH:Cell Broadcast Channel
CCH
DCCH
SDCCH
FACCH
SACCH
DCCH is assigned to a single mobile connection for call setup or for measurement and handover purpose.
SDCCH: Standalone Dedicated Control Channel
ACCH: Associated Control Channel
FACCH:Fast Associated Control Channel
Search for synchronous pulse
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UA: Unnumbered acknowledgement response
TCH combination – TCH8/FACCH + SACCH
0 10 20 30 40 50
S C C .. F S C C .. F S C C ..
Uplink
0 10 20 30 40 50
F = FCCH (Frequency)
S = SCH (Sync.)
C = CCCH (Common)
Uplink
D6
Downlink
D3
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A2
A3
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D0
D1
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D2
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D3
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A2
A3
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D0
D1
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R
Uplink
A = SACCH/4 (Associated) I = Idle
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25
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This is used to transmit a Traffic Channel Combination (TCH/ SACCH/FACCH). The FACCH is not showed in the diagram as it does not receive its own time allocation. The FACCH steals a time period from the TCH is required.
The 13th frame is used by the SACCH which carriers link control information to and from the mobile and BTS.
The 26th frame is idle.
Downlink
Uplink
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IDLE
SACCH
IDLE
SACCH
Chapter 2 GSM Network Components
Chapter 3 Terrestrial Interface
Chapter 5 Channels On Air Interface
Chapter 6 Radio Technologies
Internal Use
Objectives
On completion of this section you will be able to know about the following radio technologies :
GMSK Modulation Techniques
Modulation Techniques
– phase modulation can be implemented easily for digital signals, this is the method which is used for the GSM air interfaces. Phase Modulation is known as Phase Shift Keying when applied to digital signals
Amplitude Modulation (AM)
Frequency Modulation (FM)
Phase Modulation (PM)
Gaussian
TA
Note: Max TA = 2t = 1/2*3.7μs/bit*63bit*C=35km,
Not Applicable to RACH Bursts.
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TX
RX
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Internal Use
8W
0.8W
5W
Both Uplink and Downlink power settings can be controlled independently and individually.
10.unknown
VAD & DTX
Encoding the speech silences at a rate of 500 bit/s rather than the full 13Kb/s.
If the mobile does not transmit during ‘silence’ there is a reduction in the overall power output requirement
Without DTX
With DTX
Comfort Noise
DTX: Discontinuous Transmission
Only transmit SID frames
The transcoder at the RX terminal produces comfortable noise based on SID background noise.
Improvement on the C/I ratio.
VAD: Voice Activity Detection
Implemented in the transcoder.
Note: DTX is not used on a BCCH carrier and measurements must based no Sub value.
Internal Use
DRX
DRX allows the mobile station to effectively “switch off” during times when reception is deemed unnecessary.
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P
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BCCH
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Diversity
When diversity is implemented two antennas are situated at the receiver. These antennas are placed several wavelengths apart to ensure minimum correlation between the two receive paths.
The two signals are then combined, this ensures that a low signal strength is less likely to occur.
Compare or
add signals
Resultant Signal
Frequency Hopping
Synthesizer Hopping:each timeslot on a given transceiver can transmit at a different frequency
Baseband Hopping: each transceiver stays at the same frequency and the data is switched to the appropriate transceiver.
Each time the BTS or mobile transmits a burst, it does so on a different RF carrier frequency.
time
frequency
Chapter 2 GSM Network Components
Chapter 3 Terrestrial Interface
Chapter 5 Channels On Air Interface
Chapter 6 Radio Technologies
Internal Use
Objectives
On completion of this section you will be able to know :
State the future development of digital cellular mobile system
Internal Use
*
GSM will stay in the Lead, all professional Market Forecasts say
GSM users world wide in millions
GSM User World Wide
GSM Network Components
Radio Technologies
CM
MM
RR
LAPDm
SigL1
L3
L2
L1
MS
RR
BTSM
LAPDm
SigL1
LAPD
SigL1
LAPD
SigL1
BTSM
RR
SCCP
MTP
BSSMAP
CM
MM
BSSMAP
SCCP
MTP
MSC
BSC
BTS