Frequency-domain receiver design for doubly-selective channels

This work is devoted to the broadband wireless transmission techniques, which are serious candidates to be implemented in future broadband wireless and cellular systems, aiming at providing high and reliable data transmission and concomitantly high mobility. In order to cope with doubly-selective channels, receiver structures based on OFDM and SC-FDE block transmission techniques, are proposed, which allow cost-effective implementations, using FFT-based signal processing. The first subject to be addressed is the impact of the number of multipath components, and the diversity order, on the asymptotic performance of OFDM and SC-FDE, in uncoded and for different channel coding schemes. The obtained results show that the number of relevant separable multipath components is a key element that influences the performance of OFDM and SC-FDE schemes. Then, the improved estimation and detection performance of OFDM-based broadcasting systems, is introduced employing SFN (Single Frequency Network) operation. An initial coarse channel is obtained with resort to low-power training sequences estimation, and an iterative receiver with joint detection and channel estimation is presented. The achieved results have shown very good performance, close to that with perfect channel estimation. The next topic is related to SFN systems, devoting special attention to time-distortion effects inherent to these networks. Typically, the SFN broadcast wireless systems employ OFDM schemes to cope with severely time-dispersive channels. However, frequency errors, due to CFO, compromises the orthogonality between subcarriers. As an alternative approach, the possibility of using SC-FDE schemes (characterized by reduced envelope fluctuations and higher robustness to carrier frequency errors) is evaluated, and a technique, employing joint CFO estimation and compensation over the severe time-distortion effects, is proposed. Finally, broadband mobile wireless systems, in which the relative motion between the transmitter and receiver induces Doppler shift which is different or each propagation path, is considered, depending on the angle of incidence of that path in relation to the direction of travel. This represents a severe impairment in wireless digital communications systems, since that multipath propagation combined with the Doppler effects, lead to drastic and unpredictable fluctuations of the envelope of the received signal, severely affecting the detection performance. The channel variations due this effect are very difficult to estimate and compensate. In this work we propose a set of SC-FDE iterative receivers implementing efficient estimation and tracking techniques. The performance results show that the proposed receivers have very good performance, even in the presence of significant Doppler spread between the different groups of multipath components

Optical Time-Frequency Packing: Principles, Design, Implementation, and Experimental Demonstration

Time-frequency packing (TFP) transmission provides the highest achievable spectral efficiency with a constrained symbol alphabet and detector complexity. In this work, the application of the TFP technique to fiber-optic systems is investigated and experimentally demonstrated. The main theoretical aspects, design guidelines, and implementation issues are discussed, focusing on those aspects which are peculiar to TFP systems. In particular, adaptive compensation of propagation impairments, matched filtering, and maximum a posteriori probability detection are obtained by a combination of a butterfly equalizer and four 8-state parallel Bahl-Cocke-Jelinek-Raviv (BCJR) detectors. A novel algorithm that ensures adaptive equalization, channel estimation, and a proper distribution of tasks between the equalizer and BCJR detectors is proposed. A set of irregular low-density parity-check codes with different rates is designed to operate at low error rates and approach the spectral efficiency limit achievable by TFP at different signal-to-noise ratios. An experimental demonstration of the designed system is finally provided with five dual-polarization QPSK-modulated optical carriers, densely packed in a 100 GHz bandwidth, employing a recirculating loop to test the performance of the system at different transmission distances.Comment: This paper has been accepted for publication in the IEEE/OSA Journal of Lightwave Technolog

Radar System Characterization Extended to Hardware in the Loop Simulation for the Lab-Volt™ Training System

Modeling RADAR signals in software allows the testing of potential electronic counter measures and electronic counter counter measures without the associated RADAR hardware and test facilities. Performing a characterization process on a real world RADAR system reveals all imperfections within the system. The Lab-Volt™ RADAR system served as the characterized real world RADAR system. The characterization process consisted of measurements at selected front panel locations on the Lab-Volt™ transmitter module, antenna pedestal, receiver module, and dual channel sampler module. Due to the overwhelming influence of antenna parameters on a received signal, the characterization process also attempted to derive an antenna transfer function that described how the antenna filters a signal that is passed through it. The characterization process also determined the manner in which different adjustments influenced the signal. A MatLab simulation modeled the Lab-Volt™ system operating under ideal conditions. Comparing measurements from the characterization process and the MatLab simulation placed numerical values on the imperfections in the Lab-Volt™ system. Finally, integration of the Lab-Volt ™ system explored an elementary hardware-in-the-loop configuration

RAPID CLOCK RECOVERY ALGORITHMS FOR DIGITAL MAGNETIC RECORDING AND DATA COMMUNICATIONS

SIGLEAvailable from British Library Document Supply Centre-DSC:DXN024293 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

A Compact Radar Altimeter Satellite for Monitoring Global Climate Change

Altimetry has become the focus of global climate studies because it is the only tool available able to provide both mesoscale (100-500 kIn) and basin-scale (10,000 kIn) circulation information on a global, synoptic basis. . The Atlas-launched Navy Geosat mission proved the capability of the radar altimeter to measure the mesoscale ocean features. A lightsat compatible Geosat Follow-On Technology Model (GTM) altimeter, capable of Scout or Pegasus launch and with half the weight and power (63-lbs and 69-W) of the Geosat altimeter, was developed and built at JHU/APL. This altimeter demonstrated the feasibility of a compact satellite version of Geosat. The Navy is now procuring a series of compact altimeter satellites to support their tactical operations and to provide mesoscale data for global climate change monitoring. With the successful performance evaluation of GTM, APL now is pursuing the next step in exploring a compact altimeter mission to meet the needs of basin-scale global climate monitoring. A conceptual design, showing that the stringent centimeter precision measurement capability requirement can be met, includes a C-band channel for correcting for ionospheric effects. This improvement in performance will provide a basin-scale measurement capability in a compact satellite design that is a fraction of the weight and power of the Ariane launched TOPEX mission

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

NOSS/ALDCS analysis and system requirements definition

The results of system analyses and implementation studies of an advanced location and data collection system (ALDCS) , proposed for inclusion on the National Oceanic Satellite System (NOSS) spacecraft are reported. The system applies Doppler processing and radiofrequency interferometer position location technqiues both alone and in combination. Aspects analyzed include: the constraints imposed by random access to the system by platforms, the RF link parameters, geometric concepts of position and velocity estimation by the two techniques considered, and the effects of electrical measurement errors, spacecraft attitude errors, and geometric parameters on estimation accuracy. Hardware techniques and trade-offs for interferometric phase measurement, ambiguity resolution and calibration are considered. A combined Doppler-interferometer ALDCS intended to fulfill the NOSS data validation and oceanic research support mission is also described