International Workshop for B3G/4G Satellite Communications

INSTITUTE FOR TELECOMMUNICATIONS RESEARCH

B3G/4G Workshop Seoul 2006B3G/4G Workshop Seoul 2006

November 2006November 2006

Nonlinear Mitigation for Two Carrier TransmissionNonlinear Mitigation for Two Carrier Transmission

International Workshop for B3G/4G Satellite Communications





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





Regenerative Satellite Model





Satellite Transmission Model





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





Measured TWTA Characteristics

AM/AM Characteristic AM/PM Characteristic





TWTA AM/AM and AM/PM Functions

Fit a piecewise polynomial to the characteristics with the following Fit a piecewise polynomial to the characteristics with the following constraints:constraints:

• Both AM/AM and AM/PM pass through the originBoth AM/AM and AM/PM pass through the origin• Extension of the curves past the measured dataExtension of the curves past the measured data• No discontinuities at breakpoints and first derivative continuousNo discontinuities at breakpoints and first derivative continuous• AM/AM polynomial contains only odd coefficientsAM/AM polynomial contains only odd coefficients• AM/PM polynomial contains only even coefficientsAM/PM polynomial contains only even coefficients

188.1;14751.01639.1

188.10.1;8.63592.580.3

0.1;25.005.185.105.2753

753

rr

rrrr

rrrrr

rA

3.1;75.1964.17

3.1;1171176228180105 12108642

rr

rrrrrrrr





Polynomial Approximations

TWTA AM/AMTWTA AM/AM TWTA AM/PMTWTA AM/PM





Simulation Scenarios

Three models for the nonlinearity are considered for comparison purposes:Three models for the nonlinearity are considered for comparison purposes:

•Original nonlinear characteristicsOriginal nonlinear characteristics

•Clipped nonlinear characteristicsClipped nonlinear characteristics

•Ideal linearised modelIdeal linearised model

0.1;34.36

0.1;1171176228180105 12108642

r

rrrrrrrr

0.1;0.1

0.1;25.005.185.105.2 753

r

rrrrrrA

Clipped Nonlinear:Clipped Nonlinear:





Three Simulation Scenarios

0.1;0.1

0.1;

r

rrrA

Ideal Linearised:Ideal Linearised:

0r





Iterative ISI Cancellationfor 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 forwhere = 0.1





Total Degradation Overall performance through the nonlinear amplifier

Output power Output distortion components

dBdBOdBD

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





Performance Results





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

Documents

International Workshop for B3G/4G Satellite Communications