Microwave Transmission System

Microwave Spectrum:

Range is approximately 1 GHz to 40 GHz

Total of all usable frequencies under 1 GHz gives a reference on the capacity of in the microwave range
Components of a Microwave System:

1) Digital Modem.

2) Radio Frequency (RF) Unit.

3) Antenna.
Digital Modem:

The digital modem modulates the information signal.

(intermediate frequency or IF)

RF Unit:

IF is fed to the RF unit which is mounted as close physically to the antenna as possible.

(direct connect is optimal)

Waveguides:
Waveguides are hollow channels of low-loss material used to direct the signal from the RF unit to the antenna.  

Advantages & Applications

Advantages of GSM:

1. Capacity increases.
2. Reduced RF transmission power and longer battery life.
3. International roaming capability.
4. Better security against fraud (through terminal validation and user authentication).
5. Encryption capability for information security and privacy.
6. Compatibility with ISDN,leading to wider range of services.

GSM Applications:
   1. Mobile telephony.

   2. GSM-R.

   3. Telemetry System:

- Fleet management.

- Automatic meter reading.

- Toll Collection.

- Remote control and fault reporting of DG sets.

   4. Value Added Services. 

Characteristics of GSM Standard

1. Fully digital system using 900,1800 MHz frequency band.
2. TDMA over radio carriers(200 KHz carrier spacing.
3. 8 full rate or 16 half rate TDMA channels per carrier.
4. User/terminal authentication for fraud control.
5. Encryption of speech and data transmission over the radio path.
6. Full international roaming capability.
7. Low speed data services (upto 9.6 Kb/s).
8. Compatibility with ISDN.
9. Support of Short Message Service (SMS).

Authentication & Encryption

Handovers & Security

Handovers:

Between 1 and 2 – Inter BTS / Intra BSC.

Between 1 and 3 – Inter BSC/ Intra MSC.

Between 1 and 4 – Inter MSC

 

Security in GSM:

On air interface, GSM uses encryption and TMSI instead of IMSI.

SIM is provided 4-8 digit PIN to validate the ownership of SIM.3 algorithms are specified :

- A3 algorithm for authentication
- A5 algorithm for encryption
- A8 algorithm for key generation

 

Call Routing

Call Originating from MS.
Call Termination to MS.

 

Logical Channels