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

An Assessment of Indoor Geolocation Systems

Currently there is a need to design, develop, and deploy autonomous and portable indoor geolocation systems to fulfil the needs of military, civilian, governmental and commercial customers where GPS and GLONASS signals are not available due to the limitations of both GPS and GLONASS signal structure designs. The goal of this dissertation is (1) to introduce geolocation systems; (2) to classify the state of the art geolocation systems; (3) to identify the issues with the state of the art indoor geolocation systems; and (4) to propose and assess four WPI indoor geolocation systems. It is assessed that the current GPS and GLONASS signal structures are inadequate to overcome two main design concerns; namely, (1) the near-far effect and (2) the multipath effect. We propose four WPI indoor geolocation systems as an alternative solution to near-far and multipath effects. The WPI indoor geolocation systems are (1) a DSSS/CDMA indoor geolocation system, (2) a DSSS/CDMA/FDMA indoor geolocation system, (3) a DSSS/OFDM/CDMA/FDMA indoor geolocation system, and (4) an OFDM/FDMA indoor geolocation system. Each system is researched, discussed, and analyzed based on its principle of operation, its transmitter, the indoor channel, and its receiver design and issues associated with obtaining an observable to achieve indoor navigation. Our assessment of these systems concludes the following. First, a DSSS/CDMA indoor geolocation system is inadequate to neither overcome the near-far effect not mitigate cross-channel interference due to the multipath. Second, a DSSS/CDMA/FDMA indoor geolocation system is a potential candidate for indoor positioning, with data rate up to 3.2 KBPS, pseudorange error, less than to 2 m and phase error less than 5 mm. Third, a DSSS/OFDM/CDMA/FDMA indoor geolocation system is a potential candidate to achieve similar or better navigation accuracy than a DSSS/CDMA indoor geolocation system and data rate up to 5 MBPS. Fourth, an OFDM/FDMA indoor geolocation system is another potential candidate with a totally different signal structure than the pervious three WPI indoor geolocation systems, but with similar pseudorange error performance

Adaptive PN code synchronisation in DS-CDMA systems

Spread Spectrum (SS) communication, initially designed for military applications, is now the basis for many of today's advanced communications systems such as Code Division Multiple Access (CDMA), Global Positioning System (GPS), Wireless Local Loop (WLL) , etc. For effective communication to take place in systems using SS modulation, the Pseudo-random Noise (PN) code used at the receiver to despread the received signal must be identical and be synchronised with the PN code that was used to spread the signal at the transmitter. Synchronisation is done in two steps: coarse synchronisation or acquisition, and fine synchronisation or tracking. Acquisition involves obtaining a coarse estimate of the phase shift between the transmitted PN code and that at the receiver so that the received PN code will be aligned or synchronised with the locally generated PN code. After acquisition, tracldng is now done which involves maintaining the alignment of the two PN codes. This thesis presents results of the research calTied out on a proposed adaptive PN code acquisition circuit designed to improve the synchronisation process in Direct Sequence CDMA (DS-CDMA) systems. The acquisition circuit is implemented using a Matched Filter (MF) for the correlation operation and the threshold setting device is an adaptive processor known as the Cell Averaging Constant False Alarm Rate (CA-CFAR) processor. It is a double dwell acquisition circuit where the second dwell is implemented by Post Detection Integration (PDI). Depending on the application, PDI can be used to mitigate the effect of frequency offset in non-coherent detectors and/or in the implementation of multiple dwell acquisition systems. Equations relating the performance measures - the probability of false alarm (Pra ), the probability of detection (P d) and the mean acquisition time (E {Tacq}) - of the circuit are deri ved. Monte Carlo simulation was used for the independent validation of the theoretical results obtained, and the strong agreement between these results shows the accuracy of the derived equations for the proposed circuit. Due to the combination of PDI and CA-CFAR processor in the implementation of the circuit, results obtained show that it can provide a good measure of robustness to frequency offset and noise power variations in mobile environment, consequently leading to improved acquisition time performance. The complete synchronisation circuit is realised by using this circuit in conjunction with a conventional code tracking circuit. Therefore, a study of a Non-coherent Delay-Locked Loop (NDLL) code tracking circuit is also calTied out.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Proceedings of the Third International Mobile Satellite Conference (IMSC 1993)

Satellite-based mobile communications systems provide voice and data communications to users over a vast geographic area. The users may communicate via mobile or hand-held terminals, which may also provide access to terrestrial cellular communications services. While the first and second International Mobile Satellite Conferences (IMSC) mostly concentrated on technical advances, this Third IMSC also focuses on the increasing worldwide commercial activities in Mobile Satellite Services. Because of the large service areas provided by such systems, it is important to consider political and regulatory issues in addition to technical and user requirements issues. Topics covered include: the direct broadcast of audio programming from satellites; spacecraft technology; regulatory and policy considerations; advanced system concepts and analysis; propagation; and user requirements and applications

Adaptive PN code synchronisation in DS-CDMA systems.

Spread Spectrum (SS) communication, initially designed for military applications, isnow the basis for many of today's advanced communications systems such as CodeDivision Multiple Access (CDMA), Global Positioning System (GPS), Wireless LocalLoop (WLL) , etc. For effective communication to take place in systems using SSmodulation, the Pseudo-random Noise (PN) code used at the receiver to despread thereceived signal must be identical and be synchronised with the PN code that was used tospread the signal at the transmitter. Synchronisation is done in two steps: coarsesynchronisation or acquisition, and fine synchronisation or tracking. Acquisitioninvolves obtaining a coarse estimate of the phase shift between the transmitted PN codeand that at the receiver so that the received PN code will be aligned or synchronisedwith the locally generated PN code. After acquisition, tracldng is now done whichinvolves maintaining the alignment of the two PN codes.This thesis presents results of the research calTied out on a proposed adaptive PN codeacquisition circuit designed to improve the synchronisation process in Direct SequenceCDMA (DS-CDMA) systems. The acquisition circuit is implemented using a MatchedFilter (MF) for the correlation operation and the threshold setting device is an adaptiveprocessor known as the Cell Averaging Constant False Alarm Rate (CA-CFAR)processor. It is a double dwell acquisition circuit where the second dwell isimplemented by Post Detection Integration (PDI). Depending on the application, PDIcan be used to mitigate the effect of frequency offset in non-coherent detectors and/or inthe implementation of multiple dwell acquisition systems. Equations relating theperformance measures - the probability of false alarm (Pra ), the probability of detection (P d) and the mean acquisition time (E {Tacq}) - of the circuit are deri ved. Monte Carlosimulation was used for the independent validation of the theoretical results obtained,and the strong agreement between these results shows the accuracy of the derivedequations for the proposed circuit. Due to the combination of PDI and CA-CFARprocessor in the implementation of the circuit, results obtained show that it can providea good measure of robustness to frequency offset and noise power variations in mobileenvironment, consequently leading to improved acquisition time performance. Thecomplete synchronisation circuit is realised by using this circuit in conjunction with aconventional code tracking circuit. Therefore, a study of a Non-coherent Delay-LockedLoop (NDLL) code tracking circuit is also calTied out

Proceedings of the Mobile Satellite Conference

A satellite-based mobile communications system provides voice and data communications to mobile users over a vast geographic area. The technical and service characteristics of mobile satellite systems (MSSs) are presented and form an in-depth view of the current MSS status at the system and subsystem levels. Major emphasis is placed on developments, current and future, in the following critical MSS technology areas: vehicle antennas, networking, modulation and coding, speech compression, channel characterization, space segment technology and MSS experiments. Also, the mobile satellite communications needs of government agencies are addressed, as is the MSS potential to fulfill them

TDRSS telecommunications system, PN code analysis

The pseudo noise (PN) codes required to support the TDRSS telecommunications services are analyzed and the impact of alternate coding techniques on the user transponder equipment, the TDRSS equipment, and all factors that contribute to the acquisition and performance of these telecommunication services is assessed. Possible alternatives to the currently proposed hybrid FH/direct sequence acquisition procedures are considered and compared relative to acquisition time, implementation complexity, operational reliability, and cost. The hybrid FH/direct sequence technique is analyzed and rejected in favor of a recommended approach which minimizes acquisition time and user transponder complexity while maximizing probability of acquisition and overall link reliability

Shuttle Communications and Tracking Systems Modeling and TDRSS Link Simulations Studies

An analytical simulation package (LinCsim) which allows the analytical verification of data transmission performance through TDRSS satellites was modified. The work involved the modeling of the user transponder, TDRS, TDRS ground terminal, and link dynamics for forward and return links based on the TDRSS performance specifications (4) and the critical design reviews. The scope of this effort has recently been expanded to include the effects of radio frequency interference (RFI) on the bit error rate (BER) performance of the S-band return links. The RFI environment and the modified TDRSS satellite and ground station hardware are being modeled in accordance with their description in the applicable documents

UWB communication systems acquisition at symbol rate sampling for IEEE standard channel models

For ultra-wideband (UWB) communications, acquisition is challenging. The reason is from the ultra short pulse shape and ultra dense multipath interference. Ultra short pulse indicates the acquisition region is very narrow. Sampling is another challenge for UWB design due to the need for ultra high speed analog-to digital converter.A sub-optimum and under-sampling scheme using pilot codes as transmitted reference is proposed here for acquisition. The sampling rate for the receiver is at the symbol rate. A new architecture, the reference aided matched filter is studied in this project. The reference aided matched filter method avoids using complex rake receiver to estimate channel parameters and high sampling rate for interpolation. A limited number of matched filters are used as a filter bank to search for the strongest path. Timing offset for acquisition is then estimated and passed to an advanced verification algorithm. For optimum performance of acquisition, the adaptive post detection integration is proposed to solve the problem from dense inter-symbol interference during the acquisition. A low-complex early-late gate tracking loop is one element of the adaptive post detection integration. This tracking scheme assists in improving acquisition accuracy. The proposed scheme is evaluated using Matlab Simulink simulations in term of mean acquisition time, system performance and false alarm. Simulation results show proposed algorithm is very effective in ultra dense multipath channels. This research proves reference aided acquisition with tracking loop is promising in UWB application