GMSK with GSM

2. GSM
 What ?
 GSM: Global System for Mobile Communications.
 Formerly: Group Special Mobile
 When ?
 1982: GSM created to set standard.
 1988: Industrial development started.
 1991: First system deployed.
 Why ?
 Higher digital voice quality.
 Low cost alternatives for making calls and sms

3. Architecture Diagram :

4. MS:
 Mobile equipment
 Handset + SIM +
SIM:
Subscriber Identification Module

5. BSS consists of three element
 BTS ( Base transceiver station)
 BSC ( Base station controller )
 TC ( Tran coder)
Base station Controller :
 Time and frequency synchronizing
 Decoding, decrypting
 Uplink channel measurements
Base Transceiver Station:
 Connect between the mobile and the MSC.
 Time and frequency synchronization
 Power management

6. Network Switching Subsystem (NSS)
NSS typically consists of following
elements
 MSC (Mobile switching center)
 HLR (Home location register )
 VLR ( visitor location register )
 AUC (Authentication center )
 EIR ( Equipment identity register)
 GMSC ( Gate way mobile switching
center )

7. HLR:
Function
1. Subscriber identity
2. Subscriber supplementary services
3. Subscriber location information
4. Subscriber authentication information
VLR :
 It is a temporary database .
 Stores only information of subscriber those are in that
MSC.
 Every MSC has its own VLR
 When a subscriber roams into a new MSC service area, the
VLR connected to that MSC requests information about
the subscriber from the subscriber's HLR.

8. EIR :
 Data base used to store mobile identity
 Help us blocking calls from stolen MS
AUC:
 AUC is a database connected to the HLR
 Function is to authenticate the subscribers
attempting to use a network.

9. MSKmodulation is one type of FSK modulation, but it
occupies even less bandwidth than FSK modulation so the
bandwidth is interrupted by very little noise. The fact that
noise is low means that it has a high carrier-to-noise ratio
and good receiver sensitivity which gives it a long range
with stable communication. The modulation index of sub-carrier
MSK modulation is MSK modulation, so it’s m =
0.5.
 GMSK modulation is based on MSK, which is itself a form
of continuous-phase frequency-shift keying. One of the
problems with standard forms of PSK is that sidebands
extend out from the carrier. To overcome this, MSK
and its derivative GMSK can be used.

10. MSK:
 Minimum shifting keying .
 MSK gives us half cycle sinusoidal wave for a symbol

12. GMSK:
 Gaussian Minimum Shift Keying.
 Continuous phase digital frequency modulation
 Modulation index h=1/2
 Gaussian Frequency Shaping Filter
 GMSK = MSK + Gaussian filter
 Characterized by the value of BT
 T = bit duration
 B = 3dB Bandwidth of the shaping filter
 BT = 0.3 for GSM Bandwidth Time
 BT = 0.5 for DECT (Digital Enhanced Cordless Telecommunications)
 Data rate: 270.8 kbps

13. Signal using MSK modulation
Spectral density of MSK and GMSK signals

14. GMSK generator
Voltage control oscillator
Generating GMSK using a Gaussian filter and VCO

15. GMSK BIT ERROR RATE
 Bit error probability for GMSK is

16. GMSK PROPERTIES
 Improved spectral efficiency.
 Power Spectral Density.
 Reduced main lobe over MSK
 Requires more power to transmit data than many
comparable modulation schemes.
 Self synchronizing capability
 Constant envelope over entire B.W
 Good BER performance

17. APPLICATION
 Most widely used in the Global System for Mobile
Communications (GSM).
 Used for CDPD (cellular digital packet data)overlay
network.
 Used for GPRS system

18. ADVANTAGES DISADVANTAGES
 High spectral efficiency.
 Reducing sideband power.
 Excellent power efficiency
due to constant envelope.
 Good choice for voice
modulation.
 Higher power level than
QPSK.
 Requiring more complex
channel equalization
algorithms such as an
adaptive equalizer at the
receiver.
 Inter symbol interference