Removing non-stationary noise in spectrum sensing using matrix factorization

Spectrum sensing is key to many applications like dynamicspectrum access (DSA) systems or telecom regulators who need to measure utilization of frequency bands. The International Telecommunication Union (ITU) recommends a 10 dB threshold above the noise to decide whether a channel is occupied or not. However, radio frequency (RF) receiver front-ends are non-ideal. This means that the obtained data is distorted with noise and imperfections from the analog front-end. As part of the front-end the automatic gain control (AGC) circuitry mainly affects the sensing performance as strong adjacent signals lift the noise level. To enhance the performance of spectrum sensing significantly we focus in this article on techniques to remove the noise caused by the AGC from the sensing data. In order to do this we have applied matrix factorization techniques, i.e., SVD (singular value decomposition) and NMF (non-negative matrix factorization), which enables signal space analysis. In addition, we use live measurement results to verify the performance and to remove the effects of the AGC from the sensing data using above mentioned techniques, i.e., applied on block-wise available spectrum data. In this article it is shown that the occupancy in the industrial, scientific and medical (ISM) band, obtained by using energy detection (ITU recommended threshold), can be an overestimation of spectrum usage by 60%

Моделирование двух частотного акустического тракта для прибора диагностики гайморита

В данной ВКР проводилось изучение методов диагностики гайморита, применения ультразвука в медицине, метода конечных элементов, двухчастотного метода для компенсации погрешности измерения ультразвукового локатора. Кроме того, построены многослойные модели в программной пакете COMSOL, проведены предварительные расчеты распространения упругой волны в различных средах, имеющих различную геометрическую форму на разработанной модели, обработаны принятые сигналы для определения начала прихода эхо-сигнала, разработана структурная схема прибора, а также рассчитаны необходимые элементы для его реализации.In this diplom were studied methods for diagnosing sinusitis, ultrasound in medicine purpose, the finite element method, and the two-frequency method to compensate the measurement error of ultrasonic locators. In addition, multilayer models were built in the COMSOL software package, preliminary calculations of the propagation of an elastic wave in various media with different geometric shapes, received signals were processed to determine the recieve moment of the echo signal, a structural diagram of the device was developed, and the necessary elements were calculated

Моделирование двух частотного акустического тракта для прибора диагностики гайморита

В данной ВКР проводилось изучение методов диагностики гайморита, применения ультразвука в медицине, метода конечных элементов, двухчастотного метода для компенсации погрешности измерения ультразвукового локатора. Кроме того, построены многослойные модели в программной пакете COMSOL, проведены предварительные расчеты распространения упругой волны в различных средах, имеющих различную геометрическую форму на разработанной модели, обработаны принятые сигналы для определения начала прихода эхо-сигнала, разработана структурная схема прибора, а также рассчитаны необходимые элементы для его реализации.In this diplom were studied methods for diagnosing sinusitis, ultrasound in medicine purpose, the finite element method, and the two-frequency method to compensate the measurement error of ultrasonic locators. In addition, multilayer models were built in the COMSOL software package, preliminary calculations of the propagation of an elastic wave in various media with different geometric shapes, received signals were processed to determine the recieve moment of the echo signal, a structural diagram of the device was developed, and the necessary elements were calculated

New OFDM schemes based on orthogonal transforms for mobile communications systems :

PhD ThesisIn this thesis, two new orthogonal frequency division multiplexing (OFDM) systems are presented. The first scheme proposes a new OFDM system transceiver based on the C-transform, which is termed C-OFDM. Over multipath channels, the C-OFDM achieves 10 dB signal-to-noise ratio (SNR) gain at 10−4 bit-error-rate (BER), in comparison to the OFDM that based on the is discrete cosine transform (DCT-OFDM) and the conventional OFDM schemes. It also reduces the peak-to-average power ratio (PAPR) of the OFDM signal by about 1 dB and in some cases up to 3 dB. In the second scheme, a new fast, orthogonal X-transform is produced. The proposed X-transform is then used in a new OFDM named X-OFDM to greatly reduce the complexity, the PAPR and the BER. The proposed scheme achieves around 15 dB SNR gain in comparison to the conventional OFDM at 10−4 BER and reduces the average PAPR (over 105 OFDM symbol) by about 6 dB for N =1024 subcarriers. Furthermore, in this study, the X-transform is utilized to produce a new Alamouti space-time OFDM (ST-OFDM). The proposed ST-X-OFDM scheme reduces the transmitter complexity and achieves important SNR gain over the conventional ST-OFDM systems. The BER performance of the proposed schemes in the presence of solid-state power amplifiers (SSPAs) is also investigated analytically and by simulation. It shows that the X-OFDM is resilient to the SSPAs nonlinear distortion whereas the C-OFDM may lead to BER impairment in the presence of the SSPA. Furthermore, a coding technique to mitigate the sensitivity of the COFDM scheme to the SSPA is also proposed in this study. In this research, mathematical models for the proposed C-OFDM, XOFDM and ST-X-OFDM, which tightly match the simulation results over a diverse range of transmission scenarios and mapping schemes, are also derived. In addition, the BER performance of the proposed COFDM and X-OFDM schemes in the presence of the carrier frequency offset (CFO), with and without frequency synchronization algorithm, are also investigated. The proposed C-OFDM and X-OFDM schemes are more sensitive to the CFO than the conventional schemes. However, when frequency synchronization algorithm is used, both the proposed schemes retain their significant BER improvement in comparison to the conventional schemes.Ministry of Higher Education and Scientific Research (MOHSR), Iraq and to the Iraqi cultural attach- London for supporting me financially during my study in England