1. Chapter 9 – Mobile systems and networks
Mobile Network Model

2. Chapter 9 – Mobile systems and networks
Waveforms

3. Chapter 9 – Mobile systems and networks
How radio works:
Paths setup between vibrating electromagnetic energy (waves) transmitting and receiving antennas
Frequency – 3000 Hz – 300,000,000,000 Hz (300 GHz)
Mobile radio systems – 300 MHz – 3 GHz
Radio systems have to deal with loss/attenuation
Free space loss
Blocking – buildings, walls, etc. – worse at higher frequencies
Reflection – strength of reflection depends on degree of absorption by obstacle
Rain fade – water droplets and fog cause scattering and loss
Multi-path – waves reaching receiver via different paths – times and strengths different than transmitted
Interference

4. Chapter 9 – Mobile systems and networks

5. Chapter 9 – Mobile systems and networks
RF engineers design network to deal with loss/attenuation (link budget)
Continually optimizing network
Mobile radio frequency bands
450 MHz, 900 MHz, 1.8 GHz, 1.9 GHz, 2 GHz, 2.1 GHz
700 MHz
Biggest asset
Engineering and planning to use efficiently
Large scale mobile networks start in 1970s – analog AMPS
Evolution/2nd generation (2G) – 1990’s
TDMA, CDPD, CDMA, GSM 3G
4G/LTE 5G

6. Chapter 9 – Mobile systems and networks
Cellular design

7. Chapter 9 – Mobile systems and networks
Mobile system architecture
3 sectors – Alpha, Beta, Gamma

8. Chapter 9 – Mobile systems and networks
Mobile systems access
Frequency-division multiple access (FDMA)
The allocated frequency band is divided into a set of frequency blocks with the transmit and receive blocks separated (Frequency Division Duplex – FDD). Handsets are assigned frequency bands for access.
Time-division multiple access (TDMA)
Frequencies are split into transmit and receive and shared across a set of time slots. Handsets are assigned time slots for access.
Example figure next page

9. Chapter 9 – Mobile systems and networks

10. Chapter 9 – Mobile systems and networks
Code-division multiple access (CDMA)
Channels are separated by the application of a different code
Send and receive channels/frequencies are split as in FDD
Orthogonal frequency division multiple access (OFDMA)
Traffic carried over subcarriers of the frequency block
Global Systems for Mobile (GSM)
Developed in Europe to allow seamless roaming between European countries
Adopted worldwide
2nd generation 2G system
900 MHz, 1800 MHz, 1900 MHz
Auto handoff, roaming
13kb/s vs 64kb/s voice channels

11. Chapter 9 – Mobile systems and networks

12. Chapter 9 – Mobile systems and networks
GSM system
BTS – Antenna and RF link to handsets/devices
BSC – radio unit cabled to BTS/landline or microwave backhaul connections back to MSC
MSC – main switching center/central office
IWF/EC – connections to PSTN and other carriers (echo cancelling)
SMSC – text
HLR – database of system users
VLR – database of non system users (roaming)
Operations/Management system – translations, routing, features, alarms, billing, traffic, etc.

13. Chapter 9 – Mobile systems and networks
GSM system
Call routing between systems

14. Chapter 9 – Mobile systems and networks
GSM system
Call handoff between cell sites

15. Chapter 9 – Mobile systems and networks
Mobile systems evolution
2G – 3G

16. Chapter 9 – Mobile systems and networks
Mobile systems evolution (4G – LTE)

17. Chapter 9 – Mobile systems and networks
Mobile systems evolution

18. Chapter 9 – Mobile systems and networks
Managing capacity and coverage
Wi-Fi offload 5G

19. Chapter 9 – Mobile systems and networks
The wireless world