Browsing by Author "Jacob Mathecken, Pramod"

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Experiments on Self-interference Cancellation in Full-Duplex Wireless Communication Systems
(2017-05-08) Li, Boxiong
Sähkötekniikan korkeakoulu | Master's thesis
Full-duplex is one of the promising technologies in the next generation of mobile access networks (5G) and its main drawback is self-interference resulting from power leakage between transmit and receive antennas. In this thesis we conduct the implementation of self-interference cancellation in full duplex wireless communica- tion system. Firstly, we present literature review on frequency division multiplexing (OFDM) technology, including basic OFDM principle, peak-to-average power ratio (PAPR) and sensitivity to frequency offset problem. The synchronization part of OFDM system is also emphasized, especially on the method of compensating frequency offset. We also present the history of full-duplex and its opportunities and challenges. In addition, methods in different domain in order to cancel the self-interference (SI) are studied in this thesis. Secondly, we use software defined radio (SDR), which is built with open-source software development toolkit and hardware platform USRP N210, to implement the full-duplex system. We introduce in details how to build a basic module with SDR and create the self-interference cancellation module based on a digital domain cancellation method. This adaptive gradient based algorithm uses cross-correlation between received and transmitted signals to estimate the channel characteristics in order to cancel SI. We encounter a delay problem when samples going through different buffers and the range varies from few to thousand samples. To avoid using more than thousand taps filter in cancellation, orthogonal preamble symbols are assigned to different transmitters and detection of the coming interference signal is implemented to reduce the number of filter taps. Thirdly, we measure the SI cancellation performance and bit error rate after cancellation. We report the SI cancellation performance with different amount of filter tap as well as gradient step size. The best SI cancellation rate observed in the experiment is around -31dB when filter tap equals to six.
OFDM under Oscillator Phase Noise : Contributions to Analysis and Estimation Methods
(2016) Jacob Mathecken, Pramod
School of Electrical Engineering | Doctoral dissertation (article-based)
Most modern transmitters and receivers involve an analog front-end unit and a digital back-end unit. The digital back-end is responsible for information processing which involves thefollowing: redundancy removal from information; information representation; improvinginformation resilience; and information correction. The analog front-end is responsible forinformation transmission and reception. The information processing algorithms developedand implemented in the digital back-end assume a linear and noiseless analog front-end which,in reality, is not the case. This renders some of the information processing algorithms to be lesseffective in practice. The focus of this thesis is on orthogonal frequency-division multiplexing(OFDM) systems under the influence of oscillator phase noise. OFDM is an efficientinformation representation technique used in many communication systems. On the otherhand, phase noise is one type of undesired noise that occurs in the oscillator device used in theanalog front-end. It arises due to the imperfect task of frequency conversion, performed by theoscillator device, between baseband and radio frequency. This thesis contributes to the areas of analysis and estimation in OFDM systems under theinfluence of oscillator phase noise. With regard to analysis, this thesis contributes by derivingthe channel capacity assuming a Gaussian input alphabet. The aim here is to show bothquantitatively and qualitatively the degradation in performance of the OFDM system in thepresence of phase noise. The analysis is conducted for phase noise processes that occur in bothfree-running and phase-locked loop based oscillators and also extended to include the effect ofcarrier frequency offset. With regard to estimation, two new phase noise estimation algorithmsare proposed in this thesis. In particular, these algorithms restrict the search space to a specific subset, where the desired phase noise parameter of interest is shown to lie. For example, in the first estimation method, possible subspaces in which the desired phase noise spectral vector may lie are used in the estimation step. In the second method, the geometry of the desired phase noise spectral vector is used in the estimation step. Specifically, this geometry corresponds to a non-convex set described by a set of quadratic forms that involve permutation matrices. By restricting the search space to this set, the accuracy of phase noise estimation can be improved.
Performance analysis of OFDM with Wiener phase noise and frequency selective fading channel
(2010) Jacob Mathecken, Pramod
Elektroniikan, tietoliikenteen ja automaation tiedekunta | Master's thesis
This thesis studies the effect of Wiener phase noise on the performance of orthogonal frequency division multiplexing (OFDM) systems. The main performance metrics used in the analysis are capacity and signal-to-interference-plus-noise ratio (SINR). OFDM is a multi-carrier modulation technique in which data is transmitted in parallel streams using closely spaced (in frequency) orthogonal carriers. Phase noise is the random fluctuation in the phase of the oscillator signal used in the frequency translation between baseband and radio frequency. These fluctuations occur because of the inherent imperfections in the components that make up the oscillator. With respect to OFDM, phase noise destroys the orthogonality between the carriers and this causes interference between the parallel streams of data which results in degradation of the capacity and SINR. We derive closed-form analytical expressions of average capacity and average SINR and highlight the key parameters of the phase noise process and OFDM system that affect its behaviour. In comparison with previous works, a probability density function (PDF) based approach is used in arriving at these performance metrics. This approach necessitates the derivation of the PDF of a sum of gamma random variables. In earlier literature, this result is available for gamma variables that have a full-rank square-root normalized covariance matrix. We generalize the result for the rank-deficient case and apply this result to obtain the statistical expressions of capacity and SINR.