Exploring the hot-carrier effect on the wireless transceivers

Phase noise can be regarded as the most severe cause of performance degradation in the wireless communication systems. The hot-carriers (HCs), found in the CMOS synchronization circuits, are the high-energy charge carriers that degrade the MOSFET devices’ performance by increasing the threshold voltage required to operate the MOSFETs. The HC effect manifests itself as the phase noise whose level increases with the continued MOSFET operation and such increases result in the performance degradation of the voltage-controlled oscillator (VCO) built on the MOSFETs. The HC effect is particularly evident in the short-channel MOSFET devices. In this dissertation, we analyze the wireless transceiver performances in the presence of the synchronization errors induced by the HC effect, for both single-carrier and multi-carrier communication systems. We derive the relationship between the corresponding system performances and the HC effect in terms of a crucial parameter, the MOSFET threshold voltage. We employ a new phase noise model for the wireless systems influenced by the HC effect, which is based on a new precise phase noise mask function. In addition, we analyze the impact of the phase noise arising from the HC effect on the single-carrier wireless systems in terms of the BER and the signal-to-interference-plus-noise ratio (SINR). We derive the exact BER expression and show the SINR degradation for the QPSK systems that suffer from the phase noise. We apply Monte Carlo simulations to verify our analysis. To study the HC effect thoroughly, we simplify the BER expression as a new asymptotical analysis as the signal-to-noise ratio approaches to infinity and obtain the lower bound of the achievable BER for the single-carrier wireless systems. For multi-carrier systems, we focus our discussions on the orthogonal frequency division multiplexing (OFDM) systems. According to our simulations, we show that the bit-error-rate (BER) evaluation for OFDM using our new phase noise model in the presence of the HCs can be very different up to three orders-of-magnitude from the existing models disregarding the HCs. We have also found that the ICI self-cancellation coding is very effective for combating the phase noise in the OFDM systems

BER Analysis of OFDM Systems Impaired by Phase Noise in Frequency-Selective Rayleigh Fading Channels

[[abstract]]In this paper, we study the effect of finite-power, phase-locked-loop (PLL) based phase noise on the bit-error-rate (BER) of orthogonal frequency division multiplexing (OFDM) systems in frequency-selective Rayleigh fading channels. Based on the conditional Gaussian approximation technique, we derive the BER formulas for BPSK and 16-QAM modulated OFDM signals impaired by phase noise in frequency-selective Rayleigh fading channels. Simulation results not only validate the accuracy of our analysis but also show the dependency of BERs on the shapes of phase noise spectra.[[conferencetype]]國際[[conferencedate]]20081130~20081204[[booktype]]電子版[[iscallforpapers]]Y[[conferencelocation]]New Orleans, U.S.A

Multi-antenna OFDM systems in the presence of phase noise and doubly-selective fading

Orthogonal frequency division multiplexing (OFDM), which has been very attractive for future high rate wireless communications, is very robust to channel multipath fading effect while providing high transmission data rate with high spectral efficiency. Multiple antennas can be combined with OFDM to increase diversity gain and to improve spectral efficiency through spatial multiplexing and space-time coding (STC). This dissertation focuses on performance analysis and detection schemes of multi-antenna OFDM systems in the presence of phase noise and doubly-selective fading where channel is both time-selective and frequency-selective. In space-time coded OFDM (ST-OFDM), channel time variations cause not only intercarrier interference (ICI) among different subcarriers in one OFDM symbol, but also intertransmit-antenna interference (ITAI). We quantify the impact of time-selective fading on the performance of quasi-orthogonal ST-OFDM systems by deriving, via an analytical approach, the expressions of carrier-to-interference ratio (CIR) and signal-to-interference-plus-noise ratio (SINR). We also evaluate the performance of five different detection schemes and show that all these schemes suffer from an irreducible error floor. Multiple-input multiple-output (MIMO) antennas combined with OFDM are very attractive for high-data-rate communications. However, MIMO-OFDM systems are very vulnerable to time-selective fading. We apply frequency-domain correlative coding in MIMO-OFDM systems over doubly-selective fading channels and derive the analytical expression of CIR to demonstrate the effectiveness of correlative coding in mitigating ICI. When applied in fast fading channels, common ST-OFDM receivers usually suffer from an irreducible error floor. We apply frequency-domain correlative coding combined with a modified decision-feedback (DF) detection scheme with low complexity to effectively suppress the error floor of quasi-orthogonal ST-OFDM over fast fading channels. Similar to single-antenna OFDM, MIMO-OFDM suffers from significant performance degradation due to phase noise and time-selective fading. After characterizing the common phase error (CPE) caused by phase noise and ICI caused by phase noise as well as time-selective fading, we derive a minimum mean-squared error (MMSE)- based scheme to mitigate the effect of both phase noise and Doppler frequency shift. We also evaluate and compare the performance of various detection schemes combined with the proposed CPE mitigation scheme. Throughout the dissertation, theoretical performance analysis is always presented along with corroborating simulations.Keywords: OFDM, space-time coding, doubly-selective, MIMO, phase nois

OFDM under Oscillator Phase Noise : Contributions to Analysis and Estimation Methods

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

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