Wireless Communication

Chapter: Analog and Digital Transmission
Section: Multi-Carrier Modulation, OFDM, Effect of Doppler

Effect of Doppler for OFDM and Synchronous MC-CDMA

Contributed by Jean-Paul Linnartz and Haibing Yang

The OFDM receiver structure allows relatively straightforward signal processing to combat channel delay spreads. However, mobile reception leads to disadvantageous channel conditions, with both (frequency) dispersion and rapid variations of the channel with time. Doppler spread and the corresponding time variations are known to corrupt the orthogonality of the OFDM subcarrier waveforms. In such case, Intercarrier Interference (ICI) occurs because signal components from one subcarrier cause interference to neighboring subcarriers.

This spreadsheet allows you to interactively experiment with the effect of mobility. The channel model is Rayleigh fading with a U-shaped spectrum.

InterCarrier Interference for
OFDM in a Rayleigh fading channel

Input parameters:

Carrier frequency
MHz
Speed
m/s
Frame size
(excluding guard time)
subcarriers
Symbol rate
Number of 64-QAM symbols per second
ksymbol/sec
Es/N0
Energy per subcarrier over spectral power density of the AWGN. Used for SER calculation.
dB
 
 
fsub
Subcarrier spacing.
Hz
fDoppler
Doppler spread.
Hz

Results for Intercarrier Interference

P0
Local mean of wanted signal component.
dB = ( )
P1
Variance of first-order ICI, i.e., from neighboring subcarriers.
dB = ( )
P2
Variance of second-order ICI.
dB = ( )
P3
Variance of third-order ICI.
dB = ( )
P0 / SUM Pi
Signal-to-ICI ratio
dB = ( )

Results for SER

 
OFDM
MC-CDMA
BPSK uncoded
QPSK uncoded
16-QAM uncoded
64-QAM uncoded

 

Matlab code

The program ser.m calculates the symbol error rate. It calls func.m and summ.m in the numercial analysis. Ser.m generates a curve, see the jpg image.

 

 



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