1. Wireless Networking Radio frequency constraints Current standards
Current limitations
11/7/2018
George Cybenko, ENGS 112

2. Atmospheric Propagation of RF
400km
250km
220km
200km
150km
90km
50km F2 F2 F1 E D F1 E D
Height above ground
EARTH
Electron Density
Layers in the ionosphere
11/7/2018
George Cybenko, ENGS 112

3. Refraction of Radiowaves
30 MHz F2
20 MHz F1
30 MHz E
20 MHz D
10 MHz
EARTH
11/7/2018
George Cybenko, ENGS 112

4. Resulting Classes of RF Waves
Space Wave
MHz
Sky Wave
3-30 MHz
Communications
satellite
> 3GHz
Ground Wave
kHz
11/7/2018
George Cybenko, ENGS 112

5. Interior Path Loss Function
(Frequency dependent) d
Powertransmitted - Powerreceived = Lp = L + 10n log10 (d) +lognorm(v)
Experimentally and statistically determined - n is signal decay exponent,
L is path loss at d=1m, lognorm is log-normal distribution with variance v.
11/7/2018
George Cybenko, ENGS 112

6. Ambient Noise and Absorption
Power required for constant
signal/(ambient noise)
Power for constant
received signal power
Power required
Sweet Spot
1GHz GHz
Frequency
11/7/2018
George Cybenko, ENGS 112

7. Digital bps vs Analog Hz
Digital bandwidth of B bits per second can be encoded
into an analog signal of roughly B Hertz.
The B Hz signal is attached to a C Hz carrier resulting
in a signal that lives in the interval [C,C+B] Hz.
Example: GHz can carry 50 Mbps.
11/7/2018
George Cybenko, ENGS 112

8. Current Standards Cellular Digital Packet Data (CDPD)
19.2 kbps extension of cellular telephone network
Wireless LAN’s
1-2 Mbps using 2.4 GHz ISM (Industrial, Scientific
Medical) band. Range meters. IEEE
standard in place. Products by Lucent, Digital, etc.
$100+ PCMCIA radio transceiver. > $1000 for base.
Wireless WAN’s
Metricom Richocet technology (US only) kbps
with a range of about 1 km.
11/7/2018
George Cybenko, ENGS 112

9. Architecture Access point (base station) Multihop not implemented
Handoffs between
access points in the same
subnet - else need mobile IP
Wired network
11/7/2018
George Cybenko, ENGS 112

10. Satellite Communications Upswing
Name Speed Cost Receiver Start Date Satellites
Planet kbps $3/min Notebook Now 5 GEO’s
ICO Globalcom 64kbps $1.50/min Dual-mode MEO’s
(Inmarsat)
Iridium 2.4kpbs $3/min Handset LEO’s
(Motorola)
Globalstar 9.6kbps <$1/min Dual-mode GEO’s
Cyberstar 6mbps ?? Home dish GEO’s
(Loral)
Odyssey 9.6kbps $0.95/min Handset MEO’s
(TRW) kbps $0.65/min Dish
Teledesic mbps $100’s Dish LEO’s
(Gates/McCaw) /month
11/7/2018
George Cybenko, ENGS 112

11. Glossary LEO’s - Low Earth Orbit about 1,000 kms above earth
MEO’s - Medium Earth Orbit about 10,000 kms
GEO’s - Geostationary/Geosynchronous Earth Orbit
about 36,000 kms
Dual-mode handset supports both satellite and cellular
communications.
11/7/2018
George Cybenko, ENGS 112

12. Cellular Technology Frequencies used in cell phones have limited
spatial propagation - this is good....we can reuse them.
But adjacent “cells” cannot use the same frequencies if the
phones are frequency multiplexed
So must multiplex based on space as well.
Cells of
different
colors use
frequencies.
is a cell
in which
certain
frequencies
are allowed
to be used.
11/7/2018
George Cybenko, ENGS 112

13. Frequency Division Multiple Access (FDMA)
Time
User A
User B
User C
Within a “cell” users are
allocated a single frequency.
11/7/2018
George Cybenko, ENGS 112

14. Time Division Multiple Access (TDMA)
Freq 1
Time
User A
User B
User C
Within a “cell” users are
allocated time slots within
a single frequency.
11/7/2018
George Cybenko, ENGS 112

15. Code Division Multiple Access (CDMA)
Freq 1
Freq 2
Freq 3
Time
User A
User B
User C
Within a “cell” users are
allocated different frequencies
at different times.
11/7/2018
George Cybenko, ENGS 112

16. Different Multiple Access Concepts
TDMA - examples??
FDMA - examples??
CDMA - examples??
SDMA - examples??
11/7/2018
George Cybenko, ENGS 112

17. Implications for Wireless Networking
Mobile users will experience varying delivered bandwidth.
Connections will be intermittent, unreliable.
Spatial multiplexing (cellular architecture) is required.
Bandwidth will be a precious resource.
Battery technology is very important.
Antenna size and type is a factor.
Security - eavesdropping, jamming.
11/7/2018
George Cybenko, ENGS 112