MOBILE COMMUNICATION
STANDARDS By
Pradip Paudyal
GSM (GLOBAL SYSTEM FOR MOBILE)
2 G, digital standard
Wide range of services through the use of ISDN
GSM Services and Features
Teleservices: standard mobile telephony
Data services: Packet switched traffic; Computer
to computer communication
GSM SERVICES AND FEATURES
User Services are categorized as:
Telephone Services: emergency calling, facsimile,
videotext and teletext.
Barrier Services/ Data Services: Limited to layer
1, 2, 3 of OSI model, support packet switched
protocol, data rates from 300bps to 9.6 Kbps.
GSM SERVICES AND FEATURES
Supplementary ISDN Services: digital in nature
Call diversion
Caller identification
Closed user group
Short massaging services
SMS call broadcast
GSM SERVICES AND FEATURES
Features
Subscriber Identity Module; Memory devices
stores the information such as subscriber identity
number, network, country, privacy keys .
On the air privacy: Cryptography key known only
for carrier and changes with time for the user;
GSM SYSTEM ARCHITECTURE
GSM SYSTEM ARCHITECTURE CONT..
BSS (Base Station Subsystem)
Also known as radio subsystem, provides and
manages radio interface for transmission path.
Contains many BS, BSC and MS
NSS (Network Switching Subsystem)
Manage switching function of the system
Allow the MSC to communicate with other
network such as PSTN and ISDN.
GSM SYSTEM ARCHITECTURE CONT…
NSS handles the switching of GSM call between
external networks and BSCs
NSS is responsible for managing and providing
access to databases.
MSC control the traffic among BSCs
GSM SYSTEM ARCHITECTURE CONT…
Contains three databases called;
Home Location Register (HLR):
Contains subscriber information and location information of user.
Each subscriber is assigned a unique IMSI (International Mobile Subscriber Identity) number to identify the each home user.
Visitor Location Register (VLR):
Temporary store the IMSI and customer information for each roaming subscriber who is visiting particular coverage area of MSC.
VLR are linked between several adjoining MSCs in particular geographical region.
GSM SYSTEM ARCHITECTURE CONT…
Authentication Center (AuC):
Strongly protected database which handles the
authentication and encryption keys for every
single subscriber in HLR and VLR.
Contains a register called EIR (Equipment
Identity Register).
GSM SYSTEM ARCHITECTURE CONT…
OSS (Operation Support Subsystem)
Support the operation and maintenance of GSM
Allows the system engineer to monitor, diagnose
and troubleshoot of all aspect of GSM system.
Support one or more OMC (Operation and
Maintenance Center)
GSM SYSTEM ARCHITECTURE CONT…
Three main function of OSS are:
To maintain all telecommunication hardware
and network operation with a particular market.
Manage all charging and billing procedure
Manage all mobile equipment in the system
INTERFACES USED IN GSM
INTERFACES USED IN GSM CONT…
Interface which connect BTS and BSC called Abis
interface.
Abis interface carries traffic and maintenance
data.
BSCs are physically connected through
dedicated/leased line or microwave link to the
MSC
A interface uses an SS7 protocol
A interface allows service provider to use base
station and switching equipment made by
different manufacturer.
GSM RADIO SUBSYSTEM
Use two band of 25 MHz.
890-915 MHz band is used for reverse link.
935-960 MHz band is used for forward link.
It use FDD, TDMA and FHMA.
Available band is divided in to 200 KHz sub-
channel called ARFCN (Absolute Radio
Frequency Channel Number)
ARFCN denotes forward and reverse channel
pairs which are separated by 45 MHz and shared
by 8 time slots.
0.3 GMSK Modulation
GSM RADIO SUBSYSTEM
GSM FRAME STRUCTURE
GSM RADIO SUBSYSTEM
SIGNAL PROCESSING
Several successive operations have to be
performed to convert a speech signal into a radio
signal and back.
SIGNAL PROCESSING
The following operations take place on the
transmitting side:
• Source coding: Converts the analogue speech
signal into a digital equivalent.
• Channel coding: Adds extra bits to the data flow.
This way redundancy is introduced into the data
flow, increasing its rate by adding information
calculated from the source data, in order to allow
detection or even correction of bit errors that
might be introduced during transmission.
SIGNAL PROCESSING
• Interleaving:
Changes sequence of data stream
Reduces loss sequential data (Burst Error →
Random Error)
Improves ability to reconstruct original data
1 2 3 4 5 6 7 8 9 10 11 12
13 14 15 16 17 18 19 20 21 22 23 24
25 26 27 28 29 30 31 32 33 34 35 36
37 38 39 40 41 42 43 44 45 46 47 48
49 50 51 52 53 54 55 56 57 58 59 60
Data Input
Data
Output
Block Interleaver Input Data : 1, 2, 3, 4, . . . . . . 59, 60
Block Interleaver Output Data : 1, 13, 25, 37, . . . . . . 48, 60
SIGNAL PROCESSING
• Ciphering: Modifies the contents of these blocks through a secret code known only by the mobile station and the base station.
• Burst formatting: Adds synchronization and equalization information to the ciphered data. Part of this is the addition of a training sequence.
• Modulation: Transforms the binary signal into an analogue signal at the right frequency. Thereby the signal can be transmitted as radio waves.
The receiver side performs the reverse operations as follows:
• Demodulation: Transforms the radio signal received at the antenna into a binary signal.
SIGNAL PROCESSING
• Deciphering: Modifies the bits by reversing the ciphering code.
• De-interleaving: Puts the bits of the different bursts back in order to rebuild the original code words.
• Channel decoding: Tries to reconstruct the source information from the output of the demodulator, using the added coding bits to detect or correct possible errors, caused between the coding and the decoding.
• Source decoding: Converts the digitally decoded source information into an analogue signal to produce the speech.
GSM CHANNELS
Channels
Traffic Channels (TCH): may be full rate or half rate
When transmitted at full rate user data is contained within one time slot per frame; but for half rate same time slot but in alternative frame
Full rate TCH
Full Rate Speech Channel (TCH/FS): 13 Kbps from the source and after channel coding 22.8 Kbps.
Full Rate Data Channel for 9600 Bps
Full Rate Data Channel for 4800 Bps
Full Rate Data Channel for 2400 Bps
Half rate TCH
Half Rate Speech Channel: 6.5 Kbps from the speech coder and after channel coding 11.4 Kbps
Full Rate Data Channel for 4800 Bps
Full Rate Data Channel for 2400 Bps
GSM CONTROL CHANNEL
Control Channels:
For signaling and synchronization commands
Broadcast Channel (BCH)
Forward link and in TS0 of certain frame
Broadcast Control Channel (BCCH): Used to
broadcast certain information such as cell and
network identity, operating characteristics of cell, list
of channel that are currently being used
Frequency Correction Channel (FCCH): TS0 on
every 10 frames, frequency synchronization of user to
system
Synchronization Channel (SCH): to identify
serving base station
GSM CONTROL CHANNEL
Common Control Channel (CCCH): If
channel is not used by BCH or if idle
Paging Channel (PCH): Provides paging signal
from BS to MS, transmits IMSI number of user along
with request for acknowledgement from the mobile
unit on RACH, to broadcast text message e.g. SMS
Random Access Channel (RACH): Reverse link
channel, to ACK page from PCH and to originate
mobile call. (slotted ALOHA )
Access Grant Channel (AGCH): used by BS to
provide forward link communication to mobile and
carries data which instruct mobile to operate on
particular channel.
GSM CONTROL CHANNEL
Dedicated Control Channel (DCCH)
Stand Alone Dedicated Control Channel (SDCCH):
carries the signaling data just before TCH assignment by
BS, to remain in connection when BS and MSC verify the
subscriber unit and allocate resource for mobile. E.g.
temporary channel
Slow Associated Control Channel (SACCH):
Associated with TCH/SDCCH, on forward link used to send
slow (13th frame)but regularly changing control
information e.g. transmit power level and timing, on
reverse link received signal strength and quality of TCH
and BCH strength from neighboring cell.
Fast Associated Control Channel (FACCH): Carries
urgent message e.g. hand-off request, by stealing time slot
from TCH.
EXAMPLE OF GSM CALL
First MS must be synchronize with near by BS as it monitors BCH.
By receiving FCCH (frequency Correction Channel), BCCH (Broadcast Control Channel) and SCH (Synchronization Channel) message the subscriber would be locked on system and appropriate BCH.
First user dial the number and press send button
MS will transmit a burst of RACH (Random Access Channel) data using same ARFCN as locked with BS.
BS responds with AGCH; which assign a new channel for SDCCH (Stand-alone Dedicated Control Channel ) connection.
Once tuned to SDCCH, MS waits for SACCH (Slow Associated Control Channel) which gives power level and timing command.
EXAMPLE OF GSM CALL
Then MS is able to transmit normal burst
message.
SDCCH send message between MS and BS;
making care of validation and authentication.
After few second MS is commanded by BS via
SDCCH to retune to a new ARFCN and new TS
for TCH assignment.
Then speech data is transferred on forward and
reverse link.
ABOUT IS-95 CDMA
IS-95 is specified as:
Reverse Link: 824-849 MHz
Forward Link: 869-894 MHz
Forward and reverse is separated by 45 MHz
Maximum user data rate is 9.6 Kbps
Forward IS-95B Channel Structure
Pilot Channel (Walsh Code 0)
- The Pilot is “structural beacon” which does not contain a
character stream
- Allows Mobile to Acquire the System
- Reference Signal for System Acquiring, Timing, Coherent
Modulation
- Provides Mobile with Signal Strength Comparison during
handoffs
- Transmitted Constantly
- Non-Modulated Spread Spectrum Signal (Transmit Short PN
Code)
- Has Unique PN Offset(512) for each Cell or Sector
- Approximately 20% of radiated BTS power is in the pilot
Forward IS-95B Channel Structure
Sync Channel (Walsh Code 32)
- Used by Mobile to Synchronize with System
- Carries a data stream of system identification and
Parameter information used by MS during system
acquisition
- Pilot PN Offset
- System Time
- Long PN Code
- System ID
-Network ID
- Paging Channel Data Rate
- Tx at 1200 bps
Forward IS-95B Channel Structure
Paging Channel (Walsh Code 1 up to 7)
- Used by Base Station to :
-Page Mobile Information
-Transmit Overhead
-MS Control
-Assign Mobile to Traffic Channel
- Provides Mobile with:
-System parameter Message
- Neighbor List Message
-Access Parameter Message
-CDMA Channel List Message
- Tx at 9600 or 4800 bps
Forward IS-95B Channel Structure
Reverse IS-95B Channel Structure
Access Channel
- Used by Mobiles not yet in a call to transmit :
-Registration Requests
-Call Setup Requests
-Page Responses
-Order Responses
- other Signaling information
- Be really just a public Long Code Offset unique to the BTS Sector
- Be Paired to Paging Channel (Each Paging Channel can have up
32 access channels)
- Tx at 4800 bps, 20ms frame length
Reverse IS-95B Channel Structure
Reverse IS-95B Channel Structure
Traffic Channel - Be used by individual users during their actual calls to transmit traffic to the BTS
- Be really just a user-specific public or private Long Code Mask
- there are many reverse Traffic channels as there are CDMA phones in the world
- 64-ary Orthogonal Modulator : For Non-coherent detection
- Data Burst Randomizer : For Power Control and Variable Rate Transmission
SUMMARY OF POWER CONTROL
All types of power control work together to minimizes power
consumption at the mobile stations and BS, and increases the overall
capacity of the system
FER FER
Mobile BTS BSC
Signal Strength
Measurement
Setpoint
or
Adjust Fwd.
power
Reverse Outer
Loop Power
Control
Reverse Closed Loop
Power Control
Forward Link Power Control
Reverse Open Loop
Power Control
FORWARD QUICK POWER CONTROL
Received the Frame
Quality Information
from the Forward Link
Eb/Nt>Eb/No?
Outer-loop
Algorithm
Up Power
Control Bit
Down Power
Control Bit
Puncture to
Power Control
Subchannel
Power Control
Command
Measurement
Power Control
Command
Measurement
Demodulate and
measure Eb/Nt
Outer Loop Correction
Closed-loop Control
Mobile Station
Base Station
Eb/No
No
Yes
DECT DECT (Digital European Cordless Telephone)
standardized by ETSI (ETS 300.175-x) for cordless telephones
standard describes air interface between base-station and mobile phone
DECT has been renamed for international marketing reasons into „Digital Enhanced Cordless Telecommunication“
Characteristics frequency: 1880-1990 MHz
channels: 120 full duplex
duplex mechanism: TDD (Time Division Duplex) with 10 ms frame length
multiplexing scheme: FDMA with 10 carrier frequencies, TDMA with 2x 12 slots
modulation: digital, Gaussian Minimum Shift Key (GMSK)
power: 10 mW average (max. 250 mW)
range: ca 50 m in buildings, 300 m open space
DECT SYSTEM ARCHITECTURE REFERENCE
MODEL
global
network
local
network
local
network
FT
FT
PT PA
PT PA
VDB
HDB
D1
D2
D3 D4
PA - Portable Application
PT - Portable radio
Transmission
FT - Fixed radio
Transmission
HDB - Home Data Base
VDB - Visitor Data Base
physical layer
medium access control
data link
control
data link
control
network
layer
OSI layer 1
OSI layer 2
OSI layer 3
U-Plane C-Plane signaling,
interworking
application
processes
DECT REFERENCE MODEL
close to the OSI
reference model
management plane
over all layers
several services in
C(ontrol)- and U(ser)-
plane
man
agem
en
t
DECT LAYERS I Physical layer
modulation/demodulation
generation of the physical channel structure with a guaranteed throughput
controlling of radio transmission
channel assignment on request of the MAC layer
detection of incoming signals
sender/receiver synchronization
collecting status information for the management plane
MAC layer
maintaining basic services, activating/deactivating physical channels
multiplexing of logical channels
e.g., C: signaling, I: user data, P: paging, Q: broadcast
segmentation/reassembly
error control/error correction
DECT LAYERS II
Data link control layer
creation and keeping up reliable connections between
the mobile terminal and basestation
two DLC protocols for the control plane (C-Plane)
several services specified for the user plane (U-Plane)
null-service: offers unmodified MAC services
frame relay: simple packet transmission
frame switching: time-bounded packet transmission
error correcting transmission: uses FEC, for delay critical,
time-bounded services
bandwidth adaptive transmission
„Escape“ service: for further enhancements of the standard
DECT LAYERS III
Network layer
similar to ISDN (Q.931) and GSM (04.08)
offers services to request, check, reserve, control, and release resources at the basestation and mobile terminal
resources necessary for a wireless connection
necessary for the connection of the DECT system to the fixed network
main tasks call control: setup, release, negotiation, control
call independent services: call forwarding, accounting, call redirecting
mobility management: identity management, authentication, management of the location register
DECT: For detailed Ref: T.S.R
Thank You……………………..????????????????