Su, Han
(2017)
Wide band TX Leakage
Cancellation for FDD Transceivers.
PhD thesis, National University of Ireland Maynooth.
Abstract
Frequency division duplex (FDD) is the most widely used full duplex technique for
modern wireless communication systems. A device called a duplexer is needed in
order to separate the transmitter (TX) and the receiver (RX) signals. To avoid RX
being saturated and desensitized, the isolation between the TX and RX ports of the
duplexer needs to be as large as possible. However, such a duplexer is less desirable
for a base station due to its bulky size, high cost and design challenges. Relaxing
the isolation performance requirement of the duplexer allows TX signal to appear
in the RX path. Such a signal is known as TX leakage and consists of in-band and
out-of-band portions. Due to the fact that the in-band leakage can’t be filtered out
with conventional filtering techniques, an active cancellation system is required.
This thesis will present a novel wide band TX leakage cancellation approach along
with two new modelling techniques. The cancellation system is based on the analog
finite impulse response (FIR) filter structure and consists of several cancellation
paths (also known as taps). In each of the taps, there is an attenuator, phase shifter
and delay line. These components are utilized to recondition the reference signal
which is the replica of the output signal of the high power amplifier (PA) in the
TX path. The output of the cancellation system (the cancellation signal) in theory
should have the same amplitudes, but 180� phase offsets from the leakage signal
within the band of interest. By combining the cancellation signal and the leakage,
the latter can thus be suppressed. The two novel modelling techniques, named as
the modified adaptive delay filter using direct cross-correlation (MADF-DC) and
the modified compressed sampling matching pursuit (MCoSaMP) are proposed in
this thesis. The two algorithms are developed from the classic adaptive delay filter
(C-ADF) and the classic compressed sampling matching pursuit (C-CoSaMP), respectively.
These modelling techniques can provide the optimization of not only the
amplitudes and phase, but the delays. They are designed for the cancellation system
in order to achieve wide band cancellation with the minimum hardware resources.
The evaluation of the cancellation system was carried out utilizing a test bench,
which represented a typical base station. Experimental results show that greater
than 15 dB of cancellation has been achieved for 35 MHz bandwidth at the carrier
frequency of 897.5 MHz using four taps. In contrast, such result is about 7 dB
less than the simulated cancellation performance. The reasons of such performance
degradation have been analysed and will be presented in this thesis.
vii
| Item Type: |
Thesis
(PhD)
|
| Keywords: |
Wide band TX Leakage; Cancellation; FDD Transceivers; |
| Academic Unit: |
Faculty of Science and Engineering > Electronic Engineering |
| Item ID: |
8773 |
| Depositing User: |
IR eTheses
|
| Date Deposited: |
07 Sep 2017 15:36 |
| URI: |
|
| Use Licence: |
This item is available under a Creative Commons Attribution Non Commercial Share Alike Licence (CC BY-NC-SA). Details of this licence are available
here |
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