On-chip cross-talk analysis for multiple RF front ends of a wireless gigabit LAN system

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2004.Includes bibliographical references (leaves 169-173).In the Wireless-Gigabit-Local-Area-Network (WiGLAN) project, we proposes a system architecture that adopts multiple antennas [1, 2, 3, 4] to control the trade-off between data rate and transmission quality [5, 6] through Space-Time Coding (STC) [7, 8, 9] and Orthogonal Frequency Division Multiplexing (OFDM). However, along the multiple RF front-ends, there are multiple nodes that signal cross-talk can occur. Such signal cross-talk occurring on a silicon chip becomes more and more significant as the integration level and operating radio frequency rise, seriously degrading the system performance, the data rate and transmission quality. Most of the literature about on-chip crosstalk suppression have been focusing on adopting various process-technology techniques, such as using guard ring structures to separate the parallel RF front ends or inserting a ground plane to shield the cross-talk. In this study, we will take a different approach. We will investigate the effects of on-chip cross-talk upon the operations of the coding and modulation schemes adopted in the WiGLAN system and explore methods, other than those mentioned, to counteract them.by Jie De Jacky Liang.S.M

Minimization of Interchannel Interference E ects in Nyquist-WDM Systems

ABSTRACT: The need of increasing the capacity of current deployed optical networks to perform terabits transmissions has been driven to the development of superchannel systems, (principally based on Nyquist-WDM) to be carried out in flexible grid or gridless scenarios. Nevertheless, one of the main issues to be mitigated in these systems is the interchannel interference (ICI), whose effect is intensified when the spectral channel spacing is reduced (for further spectral efficiency increment). In this thesis, we present a study of the ICI effects in Nyquist-WDM systems by means of BER calculation as a function of several system parameters such as: frequency channel spacing, roll-off factor of the digital pulse-shaping filter, laser's linewidth, transmission distance, mark probability of the pseudo-random bit sequence, optical-to-signal noise ratio, among others. Besides, two methods enabling ICI mitigation are proposed: on one hand, a method based on FEC-coded sequence distribution among optical carriers for applications of multiple carriers (superchannels) as a single entity, and on the other hand, a method to perform nonsymmetrical demodulation (NSD) based on the k-means algorithm enabling time-varying distortions mitigation. In contradiction of techniques for ICI mitigation in recent art, these proposals avoid the use of multiple-input multiple-output equalizers or training sequences. Specifically, for NSD approach, information of adjacent channels is not required

Wavelet-based multi-carrier code division multiple access systems

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Iterative receivers and multichannel equalisation for time division multiple access systems

The thesis introduces receiver algorithms improving the performance of TDMA mobile radio systems. Particularly, we consider receivers utilising side information, which can be obtained from the error control coding or by having a priori knowledge of interference sources. Iterative methods can be applied in the former case and interference suppression techniques in the latter. Convolutional coding adds redundant information into the signal and thereby protects messages transmitted over a radio channel. In the coded systems the receiver is usually comprised of separate channel estimation, detection and channel decoding tasks due to complexity restrictions. This suboptimal solution suffers from performance degradation compared to the optimal solution achieved by optimising the joint probability of information bits, transmitted symbols and channel impulse response. Conventional receiver utilises estimated channel state information in the detection and detected symbols in the channel decoding to finally obtain information bits. However, the channel decoder provides also extrinsic information on the bit probabilities, which is independent of the received information at the equaliser input. Therefore it is beneficial to re-perform channel estimation and detection using this new extrinsic information together with the original input signal. We apply iterative receiver techniques mainly to Enhanced General Packet Radio System (EGPRS) using GMSK modulation for iterative channel estimation and 8-PSK modulation for iterative detection scheme. Typical gain for iterative detection is around 2 dB and for iterative channel estimation around 1 dB. Furthermore, we suggest two iteration rounds as a reasonable complexity/performance trade-off. To obtain further complexity reduction we introduce the soft trellis decoding technique that reduces the decoder complexity significantly in the iterative schemes. Cochannel interference (CCI) originates from the nearby cells that are reusing the same transmission frequency. In this thesis we consider CCI suppression by joint detection (JD) technique, which detects simultaneously desired and interfering signals. Because of the complexity limitations we only consider JD for two binary modulated signals. Therefore it is important to find the dominant interfering signal (DI) to achieve the best performance. In the presence of one strong DI, the JD provides major improvement in the receiver performance. The JD requires joint channel estimation (JCE) for the two signals. However, the JCE makes the implementation of the JD more difficult, since it requires synchronised network and unique training sequences with low cross-correlation for the two signals.reviewe

UNDERWATER COMMUNICATIONS WITH ACOUSTIC STEGANOGRAPHY: RECOVERY ANALYSIS AND MODELING

In the modern warfare environment, communication is a cornerstone of combat competence. However, the increasing threat of communications-denied environments highlights the need for communications systems with low probability of intercept and detection. This is doubly true in the subsurface environment, where communications and sonar systems can reveal the tactical location of platforms and capabilities, subverting their covert mission set. A steganographic communication scheme that leverages existing technologies and unexpected data carriers is a feasible means of increasing assurance of communications, even in denied environments. This research works toward a covert communication system by determining and comparing novel symbol recovery schemes to extract data from a signal transmitted under a steganographic technique and interfered with by a simulated underwater acoustic channel. We apply techniques for reliably extracting imperceptible information from unremarkable acoustic events robust to the variability of the hostile operating environment. The system is evaluated based on performance metrics, such as transmission rate and bit error rate, and we show that our scheme is sufficient to conduct covert communications through acoustic transmissions, though we do not solve the problems of synchronization or equalization.Lieutenant, United States NavyApproved for public release. Distribution is unlimited

The transmission of digitally-coded-speech signals by means of random access discrete address systems

Imperial Users onl

Simulation of a multicarrier demultiplexer

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1997.Includes bibliographical references (p. 166-167).by Michael A. Saginaw.M.Eng

Digital transmission systems operating over high frequency radio channels

Imperial Users onl

Compensation of Laser Phase Noise Using DSP in Multichannel Fiber-Optic Communications

One of the main impairments that limit the throughput of fiber-optic communication systems is laser phase noise, where the phase of the laser output drifts with time. This impairment can be highly correlated across channels that share lasers in multichannel fiber-optic systems based on, e.g., wavelength-division multiplexing using frequency combs or space-division multiplexing. In this thesis, potential improvements in the system tolerance to laser phase noise that are obtained through the use of joint-channel digital signal processing are investigated. To accomplish this, a simple multichannel phase-noise model is proposed, in which the phase noise is arbitrarily correlated across the channels. Using this model, high-performance pilot-aided phase-noise compensation and data-detection algorithms are designed for multichannel fiber-optic systems using Bayesian-inference frameworks. Through Monte Carlo simulations of coded transmission in the presence of moderate laser phase noise, it is shown that joint-channel processing can yield close to a 1 dB improvement in power efficiency. It is further shown that the algorithms are highly dependent on the positions of pilots across time and channels. Hence, the problem of identifying effective pilot distributions is studied.The proposed phase-noise model and algorithms are validated using experimental data based on uncoded space-division multiplexed transmission through a weakly-coupled, homogeneous, single-mode, 3-core fiber. It is found that the performance improvements predicted by simulations based on the model are reasonably close to the experimental results. Moreover, joint-channel processing is found to increase the maximum tolerable transmission distance by up to 10% for practical pilot rates.Various phenomena decorrelate the laser phase noise between channels in multichannel transmission, reducing the potency of schemes that exploit this correlation. One such phenomenon is intercore skew, where the spatial channels experience different propagation velocities. The effect of intercore skew on the performance of joint-core phase-noise compensation is studied. Assuming that the channels are aligned in the receiver, joint-core processing is found to be beneficial in the presence of skew if the linewidth of the local oscillator is lower than the light-source laser linewidth.In the case that the laser phase noise is completely uncorrelated across channels in multichannel transmission, it is shown that the system performance can be improved by applying transmitter-side multidimensional signal rotations. This is found by numerically optimizing rotations of four-dimensional signals that are transmitted through two channels. Structured four-dimensional rotations based on Hadamard matrices are found to be near-optimal. Moreover, in the case of high signal-to-noise ratios and high signal dimensionalities, Hadamard-based rotations are found to increase the achievable information rate by up to 0.25 bits per complex symbol for transmission of higher-order modulations