The document provides an overview of GSM (Global System for Mobile Communications), detailing its history, features, types, network components, and structure. It describes how GSM is employed for mobile communication using digital technology, emphasizing its noise robustness, flexibility, and security. Additionally, the document elaborates on the communication process, network management systems, and AT commands for GSM modules in microcontroller applications.

1. Communication PIC-Microcontroller Lab
Course by JAOM Center, Feb. 2013
GSM Module
Instructor:
Mohsen Sarakbi

2. GSM Definition
 Short for Global System for Mobile Communications
 One of the leading digital cellular systems.
 GSM was first introduced in 1991 and as of the end of 1997;
GSM service was available in more than 100 countries and
has become the de standard in Europe and Asia.
 GSM uses narrowband TDMA, which allows eight
simultaneous calls on the same radio frequency.

3. GSM Types
 Three types of GSM differ according to the frequency band used
in each one and the number of ARFCNs;
1. GSM: Use frequencies between 890-915 MHz UL and 935-960
DL (Band of 25 MHz) with 124 ARFCNs.
2. EGSM: Use frequencies between 880-915 MHz UL and 925-
960 DL (Band of 35 MHz) with 174 ARFCNs.
3. DCS1800: Use frequencies between 1710-1785 MHz UL and
1805-1880 MHz DL (Band of 75 MHz) with 374 ARFCNs
 Where ARFCN (Absolute Radio Frequency Channel Number) is
a pair of frequencies, one to transmit (Up Link) and one to receive
(Down Link).

4. GSM Features
 Compatibility that we can use the same mobile to make calls in several
countries.
 Noise Robust such that digital GSM is better than analog because it
suffer from noise therefore using digital will reduce the noise
interference.
 Flexibility and increased capacity due to equipment is smaller in size.
 Security and confidentiality such that GSM offers increase defense
against eavesdropping
 Flexible handovers in using GSM than by using analog systems.
 Enhanced range services such that the services available are speech
services including Telephony and emergency calls, Data services
including Short Message Service (SMS), cell Broadcast and
supplementary services which charge extra including number
identification, call Baring, call forwarding and call completion.

5. GSM Network Components

6. GSM Network Components
 Mobile Station (MS)
o Mobile equipment (ME). Every ME has a unique identity number
called International Mobile Equipment Identity (IMEI), it enables
stolen mobile to be detected.
o Subscriber Identity Module (SIM)
 Base Station System (BSS)
It is linked to MS using air interface and contains the following
components:
o Base Transceiver System (BTS) which provides air interface
connection to MS, it support one cell or more.
o Base Station Controller (BSC) used to control one or more BTS,
conveys information to/from BTS and connects terrestrial circuits
and air interface.

7. GSM Network Components
 Network Switching System (NSS)
It contains the function of the GSM Network as well as subscriber and Mobility Management (MM)
database. It includes:
o Mobile Station Centre (MSC) used as a call switcher exchange for mobile originated or terminated
subscriber traffic.
o Home Location Register (HLR) which adds information including subscriber ID (IMSI and MSISDN),
o Visitor Location Register (VLR) creates a temporary local data base copied from the HLR for
subscribers who are active in the area it covers avoiding the need to constantly refer back to the HLR
(Roaming).
 Operational and Maintenance System (OMS)
A central network entity that controls and monitors other entities, including the QoS provided by the
network. It is divided into two parts:
o Network Management Centre (NMC) which provides global network management responsible for
operation and maintenance at net level. Its function also includes:
 Oversees Alarms
o Operational and Maintenance Center (OMC) which provides regional network management and
should support events and alarms, faults, performance configuration and security.
 Monitors network service quality

8. GSM Cell Structure
Macro-cells(3 to 35 km)
Micro-cells(0,1 to 1 km)

9. Cell Mode Layout
 Omni-directional cell
 Adopt omni-directional antenna， O
 the overall directional
propagation characteristic is the
same.
 Directional cell
 In general, cell with multi-sector
is in common use. Every
directional cell adopts directional
antenna.

10. Terrestrial Interfaces
 2M bit/s trunks (E1):
o Each 2M bit/s link provides 32*64 kbps timeslot. These
timeslot carry: Speech or Data
 155Mbit/s STM1
o 63xE1s
 Ethernet:
o Max Ethernet frame size 1500Byte

11. PDH & SDH
PDH: Plesiochronous Digital Hierarchy
Plesio: near, Chronos: time
E1 = 2.048 Mb/s
SDH: Synchronized Digital Hierarchy
Synchronized, Standard
STM1= 155 Mb/s

12. PDH, E1
HumanVoice: 4000 Hz
Sampling Rate: 8000 Hz (2 x 4000)
8 bits/sample
8000 x 8 = 64 kbit/s = E0
64 kbit/s x 32 = 2.048Mbit/s = E1
0 16 31

13. PDH, E1

14. PDH, E1
Problems with PDH:
 Synchronization
 Limited network management (Alarms, …)
 Limited capacity growth (Data Rate)
 Difficulty in adding or dropping a line

15. SDH, STM1
Advantage of SDH:
 Synchronization
 High transmission rates
 Simple add & drop
 Reliability

16. SDH Frame

17. PDH to SDH

18. Air Interface
 Phase modulation is easy to implement for digital signals and
provide good noise tolerance when applied to digital it is
known as (PSK).
 PSK require a wide BW for transmission because abrupt
phase changes produce high frequency components, Gaussian
PSK (GPSK) reduces the addition of high frequency
components, therefore reducing the BW required.
 Such that GMSK filters the signal through a Gaussian filter,
rounding the corners of the signal, the result signal is used to
phase shift the carrier signal.

19. TDMA Frame

20. TDMA, FDMA & CDMA

21. Channels on Air Interface
The digital air interface has two channel types:
 Physical:
o The medium over which the information is carried and represent by
the 8 timeslots occupy the ARFCN for exactly one eighth of the time.
o The 8-timeslots sequence is called TDMA Frame
 Logical:
o The information carried along the physical channel. GSM logical
channels consist of Traffic Channels (TCHs) and Control Channels
(CCHs).

22. Logical Channels
 Traffic Channels (TCHs):
o The traffic channel consists of speech and data.
o Control channels associated to the traffic channels are:
o Slow Associated Control Channel (SACCH) used by the MS for reporting
signal strength and quality measurements.
o Fast Associated Control Channel (FACCH) used when rapid signaling is
required between MS and BTS, example handover
 Control Channels (CCHs), and fall into 3 groups:
o Broadcast Control Channel BCCH
o Common Control Channel CCCH
o Dedicated Control Channel DCCH

23. Logical Channels

24. Outgoing Call
1, MS sends dialed number to BSS
2, BSS sends dialed number to MSC
3,4 MSC checks VLR if MS is allowed
the requested service. If so, MSC asks
BSS to allocate resources for call.
4, MSC routes the call to GMSC
6, GMSC routes the call to local
exchange of called user
7,8 Answer back
9,10 Answer back(ring back) tone is
routed from called user to MS via
GMSC,MSC,BSS
http://spvp.zesoi.fer.hr/predavanja/extra/GSMdemo.swf

25. Incoming Call
1. Calling a GSM subscribers
2. Forwarding call to GSMC
3. Signal Setup to HLR
4. 5. Request MSRN from VLR
6. Forward responsible MSC to
GMSC
7. Forward Call to current
MSC
8. 9. Get current status of MS
10.11. Paging of MS
12.13. MS answers
14.15. Security checks
16.17. Set up connection
http://spvp.zesoi.fer.hr/predavanja/extra/GSMdemo.swf

26. Data Rate Evolution

27. Data Rate Evolution
 2G  3G
 GSM: Data rate: 9.6 Kbps  WCDMA(Wide band CDMA)
 RSS: Data rate : 0.348 – 2.0
 2.5G Mbps
 GPRS (General Packet Radio  HSPA: Data rate: 7.2 Mbps
service): Data rate: 14.4 - 115.2
Kbps  3.5G (3G+)
 HSPA+: Data rate: 21 – 42 Mbps
 2.75G
 EDGE (Enhanced data rate  4G
for GSM Evolution): Data
 LTE (Long Term Evaluation): Data
rate: 547.2 Kbps
rate: 100 Mbps

28. GSM Module
 Any GSM module is using the normal GSM network
 GSM modules can be communicated to PIC-microcontroller
using normal serial USART protocol
 Communication is being done using regular GSM modem AT
Commands.

29. AT Commands
Call control
Command Description
ATA Answer command
ATD Dial command
ATH Hang up call
ATL Monitor speaker loudness
ATM Monitor speaker mode
ATO Go on-line
ATP Set pulse dial as default
ATT Set tone dial as default
AT+CSTA Select type of address
AT+CRC Cellular result codes
http://www.expertcore.org/viewtopic.php?f=18&t=3549

30. AT Commands
MS Text mode
Command Description
AT+CSMS Select message service
AT+CPMS Preferred message storage
AT+CMGF Message format
AT+CSCA Service centre address
AT+CSMP Set text mode parameters
AT+CSDH Show text mode parameters
AT+CSCB Select cell broadcast message types
AT+CSAS Save settings
AT+CRES Restore settings
AT+CNMI New message indications to TE
AT+CMGL List messages
AT+CMGR Read message
AT+CMGS Send message
AT+CMSS Send message from storage
AT+CMGW Write message to memory
AT+CMGD Delete message

31. AT Commands, Calls
Command CHECK COM Positive Response
AT<CR><LV> OK
Command DIAL Positive Response
ATD<number><CR><LV> OK
Command ANSWER Positive Response
ATA<CR><LV> After RING, OK
Command end Positive Response
ATH<CR><LV> OK
Parameters
<CR> = ASCII character 13
<LV> = ASCII character 10

32. AT Commands, SMS
Command SET Positive Response
AT+CMGF=<mode><CR><LV> <mode>: 0 = PDU Mode, 1 = Text Mode
OK
Command DELETE Positive Response
AT+CMGD=<index><CR><LV> <index>: Index number of the message
, OK
Command SEND Response
AT+CMGS=<number><CR><LV><message><CTRL-Z> +CMGS:<mr> OK
Parameters
<CR> = ASCII character 13
<LV> = ASCII character 10
<CTRL-Z> = ASCII character 26
<mr> = Message Reference

33. Lab
 SMS – Call to MS
 Use PIC project