Practical Integer-Forcing Linear Receivers: from OFDM Signal Architecture to WARP Experimental Validation
Ionita, Corina I
Doctor of Philosophy
This thesis presents the first practical implementation of the integer-forcing (IF) linear receiver. Instead of treating interference as noise, the IF linear receiver decodes linear combinations of all transmitted signals. In theory, this promising approach has been shown to improve the overall performance of wireless networks by using the interference in a constructive way. However, in practice, little is known about the actual performance of IF linear receivers, because they pose significant practical challenges. In this work, I introduce solutions to the practical challenges of IF linear receivers and I implement and test these solutions in an experimental environment. First, I identify the transmitter's coded and uncoded signal architectures which enable the use of IF linear receivers in practical orthogonal frequency-division multiplexing (OFDM) systems. Also, I develop the receiver's signal architecture and derive the corresponding probability density functions of the received linear combinations of messages. Secondly, I use the Wireless Open Access Research Platform (WARP) and the WARPlab 802.11 OFDM framework to build the IF linear receiver for a 2x2 Multiple Input Multiple Output (MIMO) wireless network. This work validates in a practical wireless network the theoretical symbol error rate and code error rate improvements of the IF linear receiver. For the uncoded framework, I show that the IF linear receiver performs arbitrarily close to the optimal maximum likelihood (ML) receiver and always better than conventional linear receivers, (the zero-forcing (ZF) and the minimum-mean square error (MMSE) linear receivers). Furthermore, when combined with typical LDPC codes, the performance gap between the IF and ZF linear receiver increases drastically. Third, I also propose new ways of reducing the complexity of the IF linear receiver. This complexity reduction introduces some performance loss. However, I show through experimental results that, even with this decrease in performance the IF linear receiver still outperforms conventional ones. Together, these contributions demonstrate that IF linear receivers can be indeed applied in practical Wi-Fi networks and can lead to significant performance improvements.