Nonlinear Mitigation for Two Carrier Transmission
B3G/4G Workshop Seoul 2006
International Workshop for B3G/4G Satellite Communications
INSTITUTE FOR TELECOMMUNICATIONS RESEARCH
November 2006
Nonlinear Mitigation for Two Carrier Transmission
B3G/4G Workshop Seoul 2006
Presentation Overview

Joint research between ITR from University of South
Australia and ETRI, South Korea

Project description and problem statement

TWTA characterisation

Iterative ISI cancellation process for two carriers

Summary of performance results
INSTITUTE FOR TELECOMMUNICATIONS RESEARCH
November 2006
Nonlinear Mitigation for Two Carrier Transmission
B3G/4G Workshop Seoul 2006
Regenerative Satellite Model
INSTITUTE FOR TELECOMMUNICATIONS RESEARCH
November 2006
Nonlinear Mitigation for Two Carrier Transmission
B3G/4G Workshop Seoul 2006
Satellite Transmission Model
INSTITUTE FOR TELECOMMUNICATIONS RESEARCH
November 2006
Nonlinear Mitigation for Two Carrier Transmission
B3G/4G Workshop Seoul 2006
Transmission Model Summary

Multiple uplink TDMA channels

Regenerative satellite model, including onboard switch

Two high rate TDM downlink carriers per transponder

Mitigation technique has knowledge of both data streams and
nonlinear characteristics of the TWTA

Investigate an optimum mitigation technique
INSTITUTE FOR TELECOMMUNICATIONS RESEARCH
November 2006
Nonlinear Mitigation for Two Carrier Transmission
B3G/4G Workshop Seoul 2006
Measured TWTA Characteristics
AM/AM Characteristic
INSTITUTE FOR TELECOMMUNICATIONS RESEARCH
AM/PM Characteristic
November 2006
Nonlinear Mitigation for Two Carrier Transmission
B3G/4G Workshop Seoul 2006
TWTA AM/AM and AM/PM Functions
Fit a piecewise polynomial to the characteristics with the following
constraints:
• Both AM/AM and AM/PM pass through the origin
• Extension of the curves past the measured data
• No discontinuities at breakpoints and first derivative continuous
• AM/AM polynomial contains only odd coefficients
• AM/PM polynomial contains only even coefficients
 2.05r  1.85r 3  1.05r 5  0.25r 7 ;
r  1.0

Ar    3.0r 3  58.92r 5  635.8r 7 ;
1.0  r  1.188
1.1639  0.14751r ;
r  1.188

 105r 2  180r 4  228r 6  176r 8  71r10  11r12 ; r  1.3
 r   
r  1.3
  17.64  19.75r;
INSTITUTE FOR TELECOMMUNICATIONS RESEARCH
November 2006
Nonlinear Mitigation for Two Carrier Transmission
B3G/4G Workshop Seoul 2006
Polynomial Approximations
TWTA AM/AM
INSTITUTE FOR TELECOMMUNICATIONS RESEARCH
TWTA AM/PM
November 2006
Nonlinear Mitigation for Two Carrier Transmission
B3G/4G Workshop Seoul 2006
Simulation Scenarios
Three models for the nonlinearity are considered for comparison purposes:
•Original nonlinear characteristics
•Clipped nonlinear characteristics
•Ideal linearised model
Clipped Nonlinear:
3
5
7

2
.
05
r

1
.
85
r

1
.
05
r

0
.
25
r
; r  1.0

Ar   
r  1.0
1.0;
2
4
6
8
10
12


105
r

180
r

228
r

176
r

71
r

11
r
; r  1.0
r   
r  1.0
 36.34;
INSTITUTE FOR TELECOMMUNICATIONS RESEARCH
November 2006
Nonlinear Mitigation for Two Carrier Transmission
B3G/4G Workshop Seoul 2006
Three Simulation Scenarios
Ideal Linearised:
r;
r   
A

1.0;
r  1.0
r  1.0
r   0
INSTITUTE FOR TELECOMMUNICATIONS RESEARCH
November 2006
Nonlinear Mitigation for Two Carrier Transmission
B3G/4G Workshop Seoul 2006
Iterative ISI Cancellation
for each block of 8196 symbols
for each of 10 iterations
construct the transmitted two carrier signal
simulate the nonlinear distortion
for each of the two carriers
determine the ISI, , for each received symbol
subtract  from each transmitted symbol
end for
end for
end for
where  = 0.1
INSTITUTE FOR TELECOMMUNICATIONS RESEARCH
November 2006
Nonlinear Mitigation for Two Carrier Transmission
B3G/4G Workshop Seoul 2006
Total Degradation

Overall performance through the nonlinear amplifier
 Output power
 Output distortion components
DdB  OdB  dB


Assume two QPSK carriers of the same bandwidth and
same power level
Performance results are for uncoded at a BER of 10-1
which loosely corresponds to error free transmission for
rate ½ QPSK turbo coded systems
INSTITUTE FOR TELECOMMUNICATIONS RESEARCH
November 2006
Nonlinear Mitigation for Two Carrier Transmission
B3G/4G Workshop Seoul 2006
Performance Results
INSTITUTE FOR TELECOMMUNICATIONS RESEARCH
November 2006
Nonlinear Mitigation for Two Carrier Transmission
B3G/4G Workshop Seoul 2006
Conclusions




Mitigation technique for the combined nonlinearity and
memory
Iterative predistortion technique using data
predistortion
Better results and less complexity than signal
predistortion
Can be extended to OFDM systems
INSTITUTE FOR TELECOMMUNICATIONS RESEARCH
November 2006