1. GLOBAL SYSTEM FOR MOBILE COMMUNICATION
Welcome to VT TECHNOLOGIES name of module which we are going to discus is GSM
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2. Digital Radio Technology
GSM 1800 (DCS1800)
Receive (uplink) MHz
Transmit (downlink) MHz
Absolute Radio Frequency Channels
PCS 1900:-
Receive (uplink) MHz
Transmit (downlink) MHz
299 Absolute Radio Frequency Channels (ARFCN)
ARFCN stands for Absolute radio frequency carrier number.
Every ARFCN i.e. each channel is having bandwidth of 200 KHz.
Each carrier is shared by 8 subscriber using 8 TDMA timeslots.

3. ADVANTAGES OF GSM
GSM uses radio frequencies efficiently, and due to the digital radio path.
The average quality of speech achieved is better than in analogue cellular systems. Data transmission is supported throughout the GSM system.
Speech is encrypted and subscriber information security is Guaranteed.

4. ADVANTAGES OF GSM
Due to the ISDN compatibility, new services are offered compared to the analogue systems
International roaming is technically possible within all countries using the GSM system
The large market increases competition and lowers the prices both for investments and usage.

5. FEATURES OF GSM

6. Improved Security and Confidentiality
GSM offers high speech and data confidentiality.
Both the Mobile Equipment (ME) and Mobile Subscriber are identified.
GSM offers high speech and data confidentiality.
Both the Mobile Equipment (ME) and Mobile Subscriber are identified.
In Mobile Equipment (ME):-
ME has a unique number coded into it when it is manufactured. This can be checked against a database every time the mobile makes a call to validate the actual equipment.
In Subscriber authentication :-
Subscriber authentication can be performed by the system to check if a subscriber is a valid subscriber or not.
GSM also offers the capability to encrypt all signalling over the air interface.

7. There are many frequency bands in GSM.
In Punjab, following GSM bands used:-

8. GSM 900
Use radio frequencies between MHz for receive and between MHz for transmit.
RF carriers are spaced every 200 kHz, allowing a total of 124 carriers for use.
An RF carrier is a pair of radio frequencies, one used in each direction.
Transmit and receive frequencies are always separated by 45 MHz

9. GSM 1800/DCS1800 FREQUENCIES
Use radio frequencies between MHz for receive and between MHz for transmit
RF carriers are spaced every 200 kHz, allowing a total of 373 carriers.
Transmit and receive frequencies are always separated by 95MHz.

10. DIFFERENCE BETWEEN GSM 900 AND GSM 1800
Characteristics
P-GSM 900
GSM 1800
Frequency Band
Uplink
Downlink
MHz
MHz
MHz MHz
Wavelength
~ 33 cm
~ 17 cm
Bandwidth
25 MHz
75 MHz
Duplex Distance
45 MHz
95 MHz
Carrier Separation
200kHz
200 kHz
Radio Channels(Total bandwidth/carrier bandwidth)
125
375
Transmission Rate
270 kbps
Now we are going to discuss the differences between GSM-900 and GSM-1800
First one is the Frequency Band.
These are the main differences between both of them.
For GSM-900
MHz(Uplink) is the uplink frequency
MHz(Downlink) is the downlink frequency
For GSM 1800
MHz is the uplink frequency.
MHz is the downlink frequency.
Where Uplink frequency is defined as the frequency band used from MS(Mobile station) to BTS.
And Down link frequency is defined as the frequency band used from BTS to MS.
2nd one is the wavelength.
In GSM-900 wavelength is ~ 33 cm
In GSM-1800 wavelength is ~ 17 cm
3rd one is the bandwidth.
In GSM-900 total spectrum bandwidth is 25MHz.
And in GSM-1800 bandwidth is 75MHz.
Where the bandwidth is the difference between the Upper and lower band of frequencies.
4th one is the Duplex distance
In GSM-900 duplex distance is 45MHz.
In GSM-1800 duplex distance is 95MHz.
Where duplex distance is the frequency difference between the uplink and the downlink frequencies.
5th one is the carrier seperation
In GSM-900 and GSM-1800 the carrier separation is same i.e. 200KHz
It is comes out to be as follows:-
6th one is the radio channels
In GSM-900 the total no of channels are 125.
And in GSM-1800 the total no. channels are 375.
But we left last channel for guard band we use 124 from GSM-900 and GSM-1800.
Last one is Transmission rate
In GSM-900 and GSM-1800 transmission rate is upto 270kbps

11. GSM Network Components
In above shown figure different various components of GSM are shown. We will discuss all these network components in detail one by one

12. The Mobile Station (MS)
This consists of the mobile equipment and SIM.
Firstly the MS i.e. the mobile station is shown in slide.
Mobile Station is the gadget used by a GSM subscriber. Mobile Station provides the user the GSM communication services for Voice and Data. GSM Mobile Phones are made according to GSM standards. Each and every Phone produced in the world by any manufacturer complies to GSM standards. Any make Mobile Phone can be used on any GSM Network. GSM phone cannot be used, until it is activated by the Service Provider. This activation is done by providing a SIM card to the user.
SIM card is plugged inside the MS. This SIM card has an identification which is unique to the SIM card. MS also has other identification which is its unique IMEI number. IMEI number is also stored in a central database called EIR .This will be discussed in detail later.

13. The Base Station System (BSS)
This is the part of the network which provides the radio interconnection from the MS to the land-based switching equipment.

14. MOBILE STATION (MS) The Mobile Equipment (ME):-
The ME is the hardware used by the subscriber to access the network.
The hardware has an identity number associated with it, which is unique for that particular device and permanently stored in it & called the International Mobile Equipment Identity (IMEI)
Mobile Equipment may be purchased from any store but the SIM must be obtained from the GSM network provider. Without the SIM inserted, the ME will only be able to make emergency calls.

15. MOBILE EQUIPMENT (ME) Types of Mobile Equipment :- Vehicle Mounted
Portable Mobile Unit
Hand portable Unit
Vehicle Mounted:-
These devices are mounted in a vehicle and the antenna is physically mounted on the outside of the vehicle
Portable Mobile Unit:-
This equipment can be handheld when in operation, but the antenna is not connected to the handset of the unit.
Handportable Unit
This equipment comprises of a small telephone handset not much bigger than a calculator. The antenna is be connected to the handset.

16. Subscriber Identity Module (SIM)
The SIM contains several pieces of information:
Mobile Station International Services Digital Network (MSISDN)
International Mobile Subscriber Identity (IMSI)
Temporary Mobile Subscriber Identity (TMSI)
Subscriber Authentication Key
The SIM as mentioned previously is a “smart card” which plugs into the ME.
International Mobile Subscriber Identity (IMSI):-
This number identifies the MS subscriber. It is only transmitted over the air during initialization.
Temporary Mobile Subscriber Identity (TMSI):-
This number identifies the subscriber, it is periodically changed by the system
management to protect the subscriber from being identified by someone attempting to monitor the radio interface.
Subscriber Authentication Key (Ki):-
This is used to authenticate the SIM card.
Mobile Station International Services Digital Network (MSISDN):-
This is the telephone number of the mobile subscriber. It is comprised of a country code, a network code and a subscriber number.
All these identities stored in SIM will discuss in detail later.

17. BASE STATION SYSTEM(BSS)
The BSS consists of three major hardware components:-
The Base Transceiver Station – BTS
The Base Station Controller – BSC
The Transcoder
The BSS comprises one or more Base Transceiver Stations (BTSs), each containing the radio components that communicate with MSs in a given area, and a Base Site Controller (BSC) which supports call processing functions and the interfaces to the MSC.

18. BASE TRANSCEIVER STATION (BTS)
It is the interface between the MS and the MSC.
Comprises the radio equipment such as transceivers and antennas which are needed to serve each cell in the network.
The BSS is the fixed end of the radio interface that provides control and radio coverage functions for one or more cells and their associated MSs.
The BTS contains the RF components that provide the air interface for a particular cell. This is the part of the GSM network which communicates with the MS. The antenna is included as part of the BTS.

19. MOBILE SWICTHING CENTRE(MSC)
For call-switching.
Purpose is the same as that of any telephone exchange.
Mobile switching centre is used:-
For call-switching.
Purpose is the same as that of any telephone exchange.

20. The frequency ranges of GSM 900 and GSM 1800 are indicated:-
Note that the Uplink refers to a signal flow from Mobile Station (MS) to Base Transceiver Station (BTS) and the downlink refers to a signal flow from Base Transceiver Station (BTS) to Mobile Station (MS)

21. Frequency Division Multiple Access (FDMA)
Refers to the fact that each Base Transceiver Station is allocated different radio frequency channels.
Subscriber can operate at the same time but are separated according to frequency.
The FDMA method is employed by using multiple carrier frequencies, 124 in GSM 900 and 374 in GSM 1800.

22. CHANNEL CONCEPT Physical channel
Each timeslot on a carrier is referred to as a physical channel. Per carrier there are 8 physical channels.
Logical channel
Variety of information is transmitted between the MS and BTS. There are different logical channels depending on the information sent.
The logical channels are of two types
Traffic channel
Control channel

23. LOGICAL CHANNELS
Above we have shown the different types of logical channels in diagram.

24. BROADCAST CONTROL CHANNELS
(GROUP-1)
BROADCAST CONTROL CHANNELS
Downlink only
The Broadcast Control Channel is transmitted by the BTS at all times.
Base Stations can use several TRXs but there is always only one TRX which can carry Common Channels.
Above different types of broadcast control channels as shown in figure i.e. broadcast channel, synchronization channel and frequency channel.
The information distributed over the broadcast channels helps the MS to orient themselves in the mobile radio network.
All above channels are downlink i.e. from BTS to MS . Also these channel are point to multipoint. For example as in Radio broadcast each user receives the same information from the network.
Let’s look at things in a more practical way: a subscriber switches on his mobile phone and receives a call. This simple act of switching on
the phone involves the following steps:
The mobile scans all the radio frequencies and measures them
It selects the frequency with the best quality and tunes to it.
With the help of a synchronization signal in a TDMA frame, the mobile synchronizes itself to the network.

25. Carries the following information
BCCH( Broadcast Channel )
Downlink only.
Informed about the system configuration parameters.
Also known as beacon.
Carries the following information
Location Area Identity (LAI).
List of neighboring cells which should be monitored by the MS.
List of frequencies used in the cell.
Cell identity
CBCH description(Will discuss CBCH in detail later)
Using this system parameter MS can choose the best cell to attached to.
The BCCH contains detailed network and cell specific information such as:
Channel combination:-
There are a total of twelve logical channels. All the logical channels except Traffic Channels are mapped into Timeslot 0 or Timeslot 1 of the
broadcasting TRX. Channel combination informs the mobile station about the mapping method used in the particular cell.
2. Frequencies:-
Used in the particular cell (To which the MS is latched) presently i.e. cell id and neighboring cells.
3. Paging groups:-
To prevent a mobile from listening to all the paging channels for a paging message, the paging channels are divided in such a way that only a group of mobile stations listen to a particular paging channel. These are particular paging channel. These are referred to as paging groups.
4. Information on surrounding cells:-
A mobile station has to know what are the cells surrounding the present cell and what frequencies are being broadcast on them. This is necessary if, for example, the user initiates a conversation in the current cell, and then decides to move on. The mobile station has to measure the signal strength and quality of the surrounding cells and report this information to the base station controller.

26. SCH( Synchronization Channel )
Downlink only
Allows the mobile to synchronize its own frequency to that of the transmitting base site.
Carries information for frame synchronization. Contains TDMA frame number and BSIC.
As mentioned above SCH contains the Base Station Identity Code (BSIC) and TDMA frame number.
The BSIC is needed to identify that the frequency strength being measured by the mobile station is coming from a particular base station. In some cases, a distant base station broadcasting the same frequency can also be detected by the mobile station.
The TDMA frame number is required for speech encryption.

27. FCCH( Frequency Correction Channel )
Downlink only.
This is transmitted frequently on the BCCH timeslot and allows the mobile to synchronize its own frequency to that of the transmitting base site.
As mentioned above to communicate with the BTS the mobile station must tune to the BTS.
FCCH bursts consist of all "0"s which are transmitted as a pure sine wave. This acts like a flag for the mobile stations which enables them to find the TRX among several TRXs, which contains the Broadcast transmission. The MS scans for this signal after it has been switched on since it has no information as to which frequency to use.

28. CBCH( Cell Broadcast Channel )
Downlink only.
Used for short message service messages.
This channel is used for transmission generally accessible information in a cell, which can be polled by Mobile station.

29. CCCH(COMMAN CONTROL CHANNEL)
(GROUP-2)
CCCH(COMMAN CONTROL CHANNEL)
Point to point connection.
Responsible for transferring control information between all mobiles and the BTS.
Above shown channel are second set of logical channels. They are used to set up a point to point connection. These channels only operate in one direction of transmission, either uplink or downlink direction.

30. RACH(Random Access Channel)
Uplink only
Used by the mobile station for requesting a channel for a connection.
This channel is used when the mobile initiates a call or responds to a page.
Above mentioned channel is used by the MS to request the radio resources for call initiation. For example subscriber wants to make a call then its requires the RACH CHANNEL for requesting the network that he/she wants to make a call.

31. PCH(Paging Channel) Downlink only
The PCH is a downlink channel which is broadcast by all the BTSs of a Location Area in the case of a mobile terminated call.
As mentioned above paging channel is used in case of incoming call. Whenever any MS receive a call from the network it will receive the paging broadcasted by the BTS.
Note that paging is a kind of alert messages broadcasted by the group of subscriber when MS want to receives a call.

32. AGCH (Access Grant Control Channel)
Downlink only
Used by the BTS to assign a dedicated control channel to a MS in response to an access message received on the Random Access Channel.
It is used to assign a mobile a Stand-alone Dedicated Control Channel (SDCCH).This means in response to RACH this channel us assigned The MS will move to the dedicated channel in order to proceed with either a call setup, response to a paging message, Location Area Update or Short Message Service.

33. DCCH(DEDICATED CONTROL CHANNEL)
(GROUP-3)
DCCH(DEDICATED CONTROL CHANNEL)
Full duplex point to point.
Used to carry signaling between the BTS and a certain mobile station.
Above mentioned group of channels are used for call set-up, sending measurement reports and handover. They are all bi-directional and point to point channels. There are three dedicated control channels described in next coming slides.

34. Stand-Alone Dedicated Control Channel
(SDCCH)
The SDCCH is used:-
For System signaling i.e.
call set- up
Timing advance
Authentication
location update
assignment of traffic channels and transmission of short messages.
Above mentioned channel is duplex, point to point channel.
Carries all signaling between the BTS and the mobile station when no TCH is allotted.

35. Slow Associated Control Channel(SACCH)
An SACCH is associated with each SDCCH and Traffic Channel (TCH).
Used for:-
Measurement reports
Power control time alignment.
Timing advance information
SACCH is duplex channel.
Timing advance is a term used to define the distance between MS and BTS(to which currently MS is latched).
1 timing advance(TA)=1/2 KM from BTS
2 timing advance(TA) = 1 KM from BTS and so on
Note that the SACCH is only used for non-urgent procedures.

36. Fast Associated Control Channel(FACCH)
The FACCH is used:-
Carry handover information
Required for call set-up and release.
When Subscriber moves from one point to another its required that subscriber MS must latch to new BTS without call being disconnected.
Also When a handover is required. It is mapped onto a TCH, and it replaces 20 ms of speech and therefore it is said to work in "stealing" mode.

37. THE END THANKS REGARDS VT TECHNOLOGIES FOR ANY QUERY CONTACT US
CONTACT PERSON: HARISH VERMA,VIPIN DAHIYA
CONTACT NUM: ,