GMSK with GSM
Transcript of GMSK with GSM
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
Architecture Diagram :
MS: Mobile equipment
Handset + SIM +
SIM:Subscriber Identification Module
Base Transceiver Station:
Time and frequency synchronizing
Decoding, decrypting
Uplink channel measurements
Base station Controller :
Connect between the mobile and the MSC.
Time and frequency synchronization
Power management
BSS consists of three element
BTS ( Base transceiver station)
BSC ( Base station controller )
TC ( Tran coder)
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 )
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.
EIR : Data base used to store mobile identity
Help us blocking calls from stolen MS
AUC is a database connected to the HLR
Function is to authenticate the subscribers attempting to use a network.
AUC:
MSK modulation 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.
MSK: Minimum shifting keying .
MSK gives us half cycle sinusoidal wave for a symbol
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
GMSK:
Spectral density of MSK and GMSK signals
Signal using MSK modulation
Voltage control oscillator
GMSK generator
Generating GMSK using a Gaussian filter and VCO
GMSK BIT ERROR RATE Bit error probability for GMSK is
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
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
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