A Novel Diversity Receiver Structure for Severe Fading and Frequency Offset Conditions

This paper presents a novel diversity receiver of MPSK signal in fading channel in the presence of the carrier frequency offset. As a part of this receiver, a new algorithm for the estimation of the combining coefficients (ECC algorithm) is introduced. Having in mind that the QPSK modulation is one of the most used modulation formats in many wireless communication standards (LTE, WiFi, WiMax), the performance of the proposed receiver is analyzed in more detail for the QPSK modulation. In the presence of Rayleigh fading, representing the most severe fading condition, this algorithm shows significantly better performance comparing to the same receiver structure that uses conventional constant modulus algorithm (CMA1 or CMA2). The proposed diversity receiver structure with ECC algorithm operates within a wide carrier frequency offset range with a very small variation of the performance. For this reason, it can be applied in 4G mobile communication systems

Novi pristup rešavanju problema frekvencijskog ofseta kod sistema sa ortogonalnim frekvencijskim multipleksom

In this dissertation, principles of orthogonal frequency division multiplex (OFDM), a method of encoding digital data on multiple carrier frequencies, are given. After theoretical basics of wireless channel and discrete adaptive filters, advantages and disadvantages of this kind of transfer are presented. Also, basic blocks of classical OFDM system are described, with comments on how behavior and implementation of each of them can be improved. OFDM systems with MDPSK modulation and differential detection in receiver are considered. Performances for different values of modulation levels and different OFDM parameter values are analyzed, in accordance with existing standards and OFDM systems that do not belong to certain standard classification. For this purpose, a modular simulation environment is developed, in which a universal model of the OFDM system with possibility of all OFDM parameters adjustment and wireless channel parameters is possible. The main OFDM system disadvantage is frequency offset sensitivity, which destroys subcarrier orthogonality and produces intercarrier interference. Hence, frequency offset is the main factor which limits the subcarrier bandwidth and increase of system bitrate. In order to resolve frequency offset problem, we analyze OFDM receivers with different configuration and complexity. Proposed receivers are designed by modifying existing differential detection algorithms, such as double differential detection, multisymbol differential detection and decision differential detection algorithm. The new approach to the frequency offset problem solving in system with orthogonal frequency division multiplex is based on adaptive transversal filter application. We proposed optimal OFDM receivers with good performance in wide frequency offset range in the Rician and Rayleigh fading channel. Proposed receivers significantly improve the quality of the received signal and can be applied in modern wireless telecommunication systems

Design and analysis of a high-rate acoustic link for underwater video transmission

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 2004.Includes bibliographical references (leaves 74-75).A high bit rate acoustic link for underwater video transmission is examined. Currently, encoding standards support video transmission at bit rates as low as 64 kbps. While this rate is still above the limit of commercially available acoustic modems, prototype acoustic modems based on phase coherent modulation/detection have demonstrated successful transmission at 30 kbps over a deep water channel. The key to bridging the remaining gap between the bit-rate needed for video transmission and that supported by the acoustic channel lies in two approaches: use of efficient image/video compression algorithms and use of high-level bandwidth-efficient modulation methods. An experimental system, based on discrete cosine transform (DCT) and Huffman entropy coding for image compression, and variable rate M-ary quadrature amplitude modulation (QAM) was implemented. Phase-coherent equalization is accomplished by joint operation of a decision feedback equalizer (DFE) and a second order phase locked loop (PLL). System performance is demonstrated experimentally, using transmission rate of 25000 symbols/sec at a carrier frequency of 75 kHz over a 10 m vertical path.(cont.) Excellent results were obtained, thus demonstrating bit rates as high as 150 kbps, which are sufficient for real-time transmission of compressed video. As an alternative to conventional QAM signaling, whose high-level constellations are sensitive to phase distortions induced by the channel, M-ary differential amplitude and phase shift keying (DAPSK) was used. DAPSK does not require explicit carrier phase synchronization at the receiver, but instead relies on simple differentially coherent detection. Receiver processing includes a linear equalizer whose coefficients are adjusted using a modified linear least square (LMS) algorithm. Simulation results confirm good performance of the differentially coherent equalization scheme employed.by Konstantinos Pelekanakis.S.M

MSAT-X: A technical introduction and status report

A technical introduction and status report for the Mobile Satellite Experiment (MSAT-X) program is presented. The concepts of a Mobile Satellite System (MSS) and its unique challenges are introduced. MSAT-X's role and objectives are delineated with focus on its achievements. An outline of MSS design philosophy is followed by a presentation and analysis of the MSAT-X results, which are cast in a broader context of an MSS. The current phase of MSAT-X has focused notably on the ground segment of MSS. The accomplishments in the four critical technology areas of vehicle antennas, modem and mobile terminal design, speech coding, and networking are presented. A concise evolutionary trace is incorporated in each area to elucidate the rationale leading to the current design choices. The findings in the area of propagation channel modeling are also summarized and their impact on system design discussed. To facilitate the assessment of the MSAT-X results, technology and subsystem recommendations are also included and integrated with a quantitative first-generation MSS design

Proceedings of the Second International Mobile Satellite Conference (IMSC 1990)

Presented here are the proceedings of the Second International Mobile Satellite Conference (IMSC), held June 17-20, 1990 in Ottawa, Canada. Topics covered include future mobile satellite communications concepts, aeronautical applications, modulation and coding, propagation and experimental systems, mobile terminal equipment, network architecture and control, regulatory and policy considerations, vehicle antennas, and speech compression

Physical Layer Watermarking of Binary Phase-shift Keyed Signals Using Standard Gnu Radio Blocks

This thesis discussed the development, implementation, simulation, and testing of a physical layer watermarking method. The method was to use pre-existing GNU Radio building blocks. The main goal of the project was to implement a watermarking method using GNU Radio with the USRP software radios which could also be implemented using standard communications hardware so implementation on SDR systems as well as pre-existing communications systems was possible. Simulations of the physical layer watermarking system were created using a Monte Carlo method. The generation of a probability distribution of phase difference error was appropriate to analyze the expected performance of the DPSK watermarking system developed. Testing was performed in a realistic office environment where interference in the tested frequency band was common. A stationary receiver gathered data from a transmitter at various locations and power levels. The bit error rate of the gathered data was determined to analyze performance. While the testing in a real world environment had a limited range of valid analysis due to limited sampling time and interference, the results were comparable with the simulations. Testing and simulations showed the proposed physical layer watermarking method has the potential to compete with the performance of other authentication focused watermarking methods. In addition, the proposed method could be used to provide a separate, possible secretive, data channel under certain circumstances. An important benefit of the proposed watermarking method is its ability to be implemented in many SDR or traditional communication systems with no hardware modifications.School of Electrical & Computer Engineerin