International Telemetering Conference Proceedings / October 26-29, 1998 / Town & Country Resort Hotel and Convention Center, San Diego, California / The recent proliferation of Low Earth Orbiting (LEO) science, earth resources, and global communication satellites requires a significant number of ground stations for support. A network of satellite tracking ground stations with the ability to support multiple users and communicate with multiple satellites requires a robust scheduling and conflict resolution system. This paper describes an automated scheduling implementation for managing such a commercial, multi-user, multiple satellite, ground station network.

This thesis describes the analysis, design, simulation, evaluation and implementation of an optimized network protocol and its software system for 'little LEO' satellite networks to support an efficient digital store and forward (S&F) global data deliyery service. Many protocols have been proposed for 'little LEO' satellite S&F communication net""orks. These protocols fall into two categories. One category is the protocols which have been implemented in the real world, such as MSG2 and P ACSA T. These protocols were designed under constrained conditions and concentrated more on real world implementation. Another category is the protocols which are still proposals, such as LAMSLM, LAMS-DLC, variable-length information frame-type random access scheme and so on. These protocols were designed under some idealized conditions and concentrated only on some aspects. All these protocols are evaluated on their capability to handle the dominating problems in a typical LEO satellite S&F communication system, such as message addressing, multiple access control, multiplexing, and error control. Some problems in the design of these protocols are identified from real world statistics and others by simulation or analysis. To solve the problems, an optimized network layer protocol (called LEONET) is developed. LEONET provides an optimized and integrated solution to the dominating problems in 'little LEO' satellite S&F networks. Several improvements over previous protocols have been achieved in LEONET. On the up-link, LEONET defines a ne"" multiple access control protocol which allocates the number of reservation time slots according to dynamic network requirements, and therefore reduces collisions and leaves more up-link resource to upload messages. On the down-link, LEONET adopts a new message addressing and multiplexing mechanism which eliminates the directory downloading and can dO\\lnload more messages. The message uploading and downloading are scheduled by a novel routing optimization algorithm which can further improve the network performance. Simulation models are built for both pervious protocol and proposed protocols to evaluate their performance. It shows that LEONET can better use the 'little LEO' satellite network resource and provide much better performance, especially when the offered load is heavy orland the user population is large. An object-oriented software model for the proposed protocol is built. A software system of the proposed protocol is generated from the model and verified by OPNET.

No description available.

No description available.

Thesis (M.S. in Electrical Engineering and Electrical Engineer) Naval Postgraduate School, June 1997. / Thesis advisors, Randy L. Borchardt, Rudlof Panholzer. Includes bibliographical references (p. 99). Also available online.

New payload concepts of low cost earth stations for future mobile satellite communications can only be realised by using dedicated on-board processing satellites. The satellite uplink and downlink are optimised by the use of FDMA/SCPC for uplink and TDM on the down link. This scheme allows mobile transmitters to transmit a narrow band, low power signal, resulting in smaller dishes and HPAs with lower output power. On the uplink, there are hundreds of FDM channels to be demodulated on-board. The most promising approach is the use of all-digital multicarrier demodulators (MCDs), where analogue and digital hardware are efficiently shared amongst the channels and digital signal processing is used at an early stage to take advantage of VLSI technology. A MCD consists of a channeliser for separation of FDM channels followed by individual demodulators for each channel. The major research areas in MCD's are efficient implementation of channelisers and the optimal demodulation algorithms for the demodulator. This thesis is focused on the demodulator part of an MCD using OQPSK modulation which haye received attention recently due to its spectral advantages in non-linear mobile satellite channels. Most of the research carried out on the OQPSK modulation has been addressed to its spectral performance under satellite channel non-linearities, but little attention has been paid to efficient receiver designs. The most important requirements of the demodulator in a mobile environment is fast acquisition with minimum overhead. This over-head includes long preambles in data frames to aid the acquisition of the carrier and the symbol timing recovery loops. In this thesis, research on preambleless all-digital demodulators for OQPSK has been carried out. The performance of the most suitable OQPSK synchronisation algorithms have been evaluated using extensive computer simulations. These algorithms have been selected after a comprehensive survey of digital synchronisation techniques. It is shown how these algorithms are related to the maximum likelihood (ML) principle and these algorithms are classified according to their technique of parameter extraction from the likelihood function. The synchronisation problems associated with OQPSK are pointed out with possible solutions. On the basis of the performance results of individual synchronisers, various demodulation algorithms for OQPSK have been developed for fixed, mobile and deep space applications. The DSP implementation of the all- digital OQPSK demodulator developed for the MCD for mobile applications is described in detail and its performance compared with simulation results.

The increase in demand for channel capacity and the limitations in satellite power and frequency spectrum is leading to requirements for advanced multiple beam antenna systems with frequency reuse. The concept of the Olympus satellite evolved from the fact that new technologies and methods are to be explored for future satellites. The role of Olympus can be seen in both the development of earth station networks and at the same time the satellite requirements for the future satellites. It is a step between advanced transparent repeaters and the future intelligent satellite with on-board processing. A review of commercial and experimental satellites employed in the European region is given in the thesis. The services offered by these satellites and the access methods used are discussed with particular emphasis on business services. The new research work reported was done on the experiments related to the Olympus SS-TDMA payload. First a survey of commercial TDMA systems was performed and their capabilities discussed in detail for the SS-TDMA experimental application. The Olympus payload description and link budget analysis was performed in order to identify the size of the earth station required for these networks. The performance of the satellite link was simulated using BOSS software package together with some earlier simulation using the TOPSIM software package. The methods of BER estimation used are investigated and various results compared. These simulations covered most aspects of the RF (degradation due to TWTA non-linearity, fading, carrier spacing, co-channel interference) and some aspects of the baseband circuits. These simulation results have been compared with the experimental results and were found to be in close agreement. Thus giving confidence in the simulation methods used. In SS-TDMA the problem of acquisition and synchronisation is very important. In this respect the design of the acquisition and synchronisation unit (ASU) is discussed in detail. The resulting ASU was interfaced with the reference station of the commercial TDMA system for the first phase of the SS-TDMA experiments. Finally we present results of various network control methods for the SS-TDMA network, including the buffer requirement for the on-board clock control with the sidereal day clock correction. The ASU design, its interface to the reference TDMA terminal and successful operation with the reference station in acquiring and synchronising with the satellite switch provided the real time operation of the SS-TDMA scheme. The operation was conducted experimentally using the BTRL (British Telecom Research Labs) experimental earth station at Martlesham both in the "reference station loopback" and "reference station and traffic station" configuration via the the SS-TDMA switch. Full details of the experiments and comparison with systems simulations are presented in the thesis.

Most contemporary modems provide a bit-oriented service at the physical layer of the OSI reference model. They do not provide any specific support for packet data transmission. A novel Hop-Aligned Slow Frequency Hopping (HA-SFH) concept is proposed to provide a packet traffic service in a Partial Band Jamming (PBJ) environment. Frequently, SFH is used together with deep interleaving and powerful Forward Error Correction (FEC) to combat PBJ. The proposed HA-SFH exploits the error control mechanism of the link layer packet protocol and reduces the data redundancy by using a low gain FEC, it results in a more bandwidth efficient system. The HA-SFH and deep interleaving SFH (DI-SFH) performance were analysed and compared by using a series of simulations and experiments employing a network simulator and hardware such as Viterbi decoders and a channel noise simulator, etc. The results are presented in terms of throughput and average frame delay, which are more meaningful qualities than BER for packet traffic. It shows concrete results that HA-SFH performs 2 times better than DI-SFH in terms of throughput under PBJ. This thesis also discusses a wide range of technical issues involving the implementation of HA-SFH such as the coding level required, protocol enhancement, networking traffic, adaptive FEC, channel state estimation, etc. It also explores an adaptive code rate system called the Smart Codec (SmCodec), which can be integrated into HA-SFH. The further development of the SmCodec also makes it a suitable system for use in commercial PSK modems to combat the effect of channel fading (eg. from rain). A new channel state estimation technique is also proposed. It estimates the channel state from the block error rate and the required estimation time is as low as 2 seconds for the most required range of E_b/N_o at a 64 kbps link (the estimation time decreases when the link speed increases).

International Telemetering Conference Proceedings / October 28-31, 1996 / Town and Country Hotel and Convention Center, San Diego, California / An operational concept for how a Demand Access Multiple Assignment (DAMA) system could be configured for the NASA Space network is examined. Unique aspects of this concept definition are the use of the Multiple Access system within the Space Network to define an order wire channel that continuously scans the Low Earth Orbit space for potential users and the use of advanced digital signal processing technology to look for the Doppler-shifted carrier signal from the requesting satellite. After the reception of the signal, validation and processing of the request is completed. This paper outlines the concept and the ways in which the system could work.

International Telemetering Conference Proceedings / October 30-November 02, 1995 / Riviera Hotel, Las Vegas, Nevada / Satellite transmission systems have proven themselves very effective in a variety of applications. One such application is the transmission of telemetry (TM) data and associated information in a near real-time environment. This paper describes the satellite data relay system currently utilized by the Telemetry Data Center at Patuxent River, Maryland and the corresponding remote receiving site, and discusses the performance of this system.