On the practicability of full-duplex relaying in OFDM systems
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Sähkötekniikan korkeakoulu |
Master's thesis
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Authors
Date
2011
Department
Major/Subject
Signaalinkäsittelytekniikka
Mcode
S-88
Degree programme
Language
en
Pages
[4] + 62 s.
Series
Abstract
A full-duplex relay is spectrally more efficient than a half-duplex relay because it uses the full band of available frequencies to receive and transmit signals simultaneously. However, the loop interference arriving at the receiver of the relay due to its own transmission is a major hindrance that must be overcome before the idea of full-duplex relaying can be put to practice. The simple technique of subtractive cancellation alone, in theory, could eliminate the loop interference completely from the received signal. In practice, however, the nonidealities inherent in the actual components within the relay transceivers create less than ideal conditions for the cancellation to work perfectly. This thesis studies the effect of such nonidealities on the performance of a single-input-single-output (SISO) full-duplex relay. The primary focus is on formulating an analytical framework that helps evaluate the feasibility of such a relay. The outcome illustrates that a number of factors determine whether the idea of a full-duplex relay with subtractive loop interference cancellation can be implemented in practice. As expected, it is necessary to have an analogy to-digital converter (ADC) with a large dynamic range at the receiver to ensure that the incoming can be digitized with sufficient accuracy. Another important requirement is to have an excellent transmitter with a very small error vector magnitude (EVM) because the contribution of the unknown random error in the transmitted signal to the loop interference cannot be cancelled no matter how accurately the incoming signal is digitized. Moreover, the physical design of the relay must, by itself, be able to provide a certain amount of natural isolation between the transmitting and receiving antennas; otherwise, the part of the loop interference resulting from the transmitter error alone can be sufficient to drown the useful signal beyond recovery.Description
Supervisor
Wichman, RistoThesis advisor
Riihonen, TaneliKeywords
full-duplex relay, loop interference cancellation, transceiver non-idealities, analog-to-digital conversion, quantization, dynamic range, error vector magnitude, OFDM