1. Error control coding for wireless communication technologies
Instructor: Prof. Dr. János LEVENDOVSZKY
EU-USA Atlantis Programme
FIT & Budapest University of Technology and Economics

2. Raised cosine

3. Raised cosine in time domain

5. BER vs. SNR in QPSK

8. Characterization of the wireless channel
Transmitter
shadowing
Receiver
Receiver
Mutipath propagation
wavelength
Received Power (PRX)
0 dB
-50 dB
Path loss
Larg-scal fading
-100 dB
Small-scale fading
Distance (d)
1km
2km
TÁMOP – /2/A/KMR 8

9. Multipath propagation
ISI !!
Consequences of fading:
Error probability is dominated by the probabilty of being in a fading dip.
Deterministic modeling of channel at each point is very difficult.
Statistical modeling of system behavior.
QoS (e.g.: BER)
TÁMOP – /2/A/KMR 9
TÁMOP – /2/A/KMR 9

10. Channel modeling: single-path propagation
Radio channel
Ideal propagation (only attenuation)
Tx and Rx antenna gains
Example: Compute the attenuation of a radio link r=10km, G_T and G_R both 20 db, f=450 MHz

11. Channel modeling: two-path propagation
Direct and reflected
h_T
h_R

12. Impact on BER
Selective fading is one of the most dominant effects which impairs the quality of radio communication !

13. Multipath propagation
Severe distortions in the frequency characteristics which results in bad quality radio communication (very high Bit Error Rate).

14. The noise
Thermal noise: electronic noise generated by the thermal agitation of the charged carriers (usually the electrons) inside an electrical conductor at equilibrium. The power spectral density of thermal noise depends on the environment temperature Te that antenna „sees”. (Note: white power spectral density, gaussian p.d.f.)
Man-made noise:
Spurious emmision: electric devices have it (e.g car ignitions), it is not necessarily Gaussian-distributed, but in theory it is assumed Gaussian anyway.
Coexistence of other wireless systems: wireless communication systems operate at same time in unlicensed bands (eg.: 2.45-GHz ISM band).
Receiver noise: the amplifiers and mixers in the RX are noisy, and thus increase the total noise power.

15. Man-made noise TÁMOP – 4.1.2-08/2/A/KMR-2009-0006 15 2018.12.06..

16. Modeling the thermal noise
Noise energy density
kB=1.38x10-23 J/K is Boltzmann constant. It is usually assumed that the environmental temperature is isotropically 300K, therefore N0 = -174 dBm/Hz.
White Gaussian Noise (WGN) in “radio domain” f N0
TÁMOP – /2/A/KMR 16
TÁMOP – /2/A/KMR 16

17. The noise power
The noise power: PN = N0 B where B is the bandwidth in Hz,
using logarithmic units: PN[dBm] = lg( B )
Hw: Calculate the SNR of a 10km radio link assuming single-path propagation power at the frequency 450 MHz in the frequency band 100kHz assuming 1mW Tx power!

18. Statistical description
Sample from the noise process:

19. Statistical description cont’
Samples from the noise process:

20. Characterization of the radio channel – summary
Attenuation
AWGN
Single path propagation model
Full characterization with SNR
H(f)
AWGN
Multi-path propagation model
Attenuation
Full characterization with impulse response and SNR

21. Summary Challenges of wireless communication technologies
Resources vs. algorithms in order to cope with the energy and spectral constraints
Modeling the source
Modeling the radio channel (propagation models, linear distortion, noise)

22. Thank you for your attention !