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Communication PIC-Microcontroller Lab
     Course by JAOM Center, Feb. 2013




    GSM Module




           Instructor:
          Mohsen Sarakbi
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.
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).
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.
GSM Network Components
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.
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
GSM Cell Structure

Macro-cells(3 to 35 km)
Micro-cells(0,1 to 1 km)
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.
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
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
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
PDH, E1
PDH, E1

Problems with PDH:
   Synchronization
   Limited network management (Alarms, …)
   Limited capacity growth (Data Rate)
   Difficulty in adding or dropping a line
SDH, STM1

Advantage of SDH:
   Synchronization
   High transmission rates
   Simple add & drop
   Reliability
SDH Frame
PDH to SDH
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.
TDMA Frame
TDMA, FDMA & CDMA
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).
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
Logical Channels
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
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
Data Rate Evolution
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
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.
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
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
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
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
Lab

 SMS – Call to MS


 Use PIC project
GSM Module

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GSM Module

  • 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.
  • 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
  • 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
  • 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.
  • 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
  • 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
  • 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