• A DECOUPLED APPROACH TO COMPENSATION FOR NONLINEARITY AND INTERSYMBOL INTERFERENCE

      Lyman, Raphael J.; Wang, Qingsong; New Mexico State University (International Foundation for Telemetering, 2002-10)
      To achieve good efficiency in a space-based radio transmitter, its final amplifier must be operated near the saturation point, in its nonlinear region. Because of strict band limitations, this nonlinear operation is combined with the problem of intersymbol interference. Normally, these problems are addressed using a combination of equalization and power back-off, resulting in reduced power efficiency. Many proposed receiver-based methods, such as Volterra equalization, attempt to compensate for the nonlinearity and ISI in a single block before the detector, allowing higher efficiency operation, but introducing a great deal of complexity. We propose a receiver-based method in which the two effects are dealt with in separate blocks, an equalizer and a linearizer, resulting in considerable simplification. We go further and place the detector before the linearizer, achieving improved performance by eliminating the errors introduced by the linearizer. Simulation results compare favorably with the performance of a linear AWGN channel.
    • NETWORKING SATELLITE GROUND STATIONS USING LABVIEW

      Mauldin, Kendall; New Mexico State University (International Foundation for Telemetering, 2002-10)
      A multi-platform network design that is automated, bi-directional, capable of store and forward operations, and low-bandwidth has been developed to connect multiple satellite ground stations together in real-time. The LabVIEW programming language has been used to develop both the server and client aspects of this network. Future plans for this project include implementing a fully operational ground network using the described concepts, and using this network for real-time satellite operations. This paper describes the design requirements, RF and ground-based network configuration, software implementation, and operational testing of the ground network.
    • OBJECT DETECTION AND LOCALIZATION IN THE WAVELET DOMAIN

      Kandadai, Srivatsan; New Mexico State University (International Foundation for Telemetering, 2002-10)
      We are interested in the problem of detecting and localizing objects in the compressed domain. The practical uses of this research are video surveillance, queries over digital library archives and teleconferencing. Most image operations, such as object recognition, are formulated as sequences of operations in the image domain. Such methods need direct access to pixel information as a starting point, but pixel information is not directly available in a compressed image stream. The standards that have emerged for still-image and video compression each contain steps that are commonly found in compression algorithms, like linear transformations, coefficient quantization, run-length coding and entropy coding. Coders like JPEG 2000 and SPHIT are built around the wavelet transform. Thus as a step toward detection and localization of objects embedded in the compressed bit stream we consider here the problem of localizing and detection in the wavelet domain.
    • PERFORMANCE STUDY OF ENHANCED FQPSK AND CONSTRAINED ENVELOPE MODULATION TECHNIQUES

      Borah, Deva K.; Horan, Stephen; New Mexico State University (International Foundation for Telemetering, 2002-10)
      This paper investigates the spectral properties and the bit error rate (BER) performance of enhanced FQPSK (EFQPSK) and constrained envelope modulation (CEM) techniques. Both the techniques are found to provide good spectral efficiencies. The EFQPSK signals are found to generate spectral lines for unbalanced data. An analytical spectral study for the spectral lines is presented. While the performance of CEM techniques has been presented in [6] for an ideal nonlinear amplifier, we present results for more realistic amplifiers with AM/AM and AM/PM effects. It is shown that such an amplifier generates spectral regrowth and a predistorter is required to reduce the adverse effects. A BER performance study with/without channel coding is also presented for the two techniques.
    • USING MDP FOR TELEMETRY DATA TRANSFERS

      Chakraborti, Anirban; New Mexico State University (International Foundation for Telemetering, 2002-10)
      The current challenge has been to develop and adapt commercial Internet protocols for usage in space communications. Commercialized solutions, rather than Customized ones are cheaper, have low turnaround time and offer higher flexibility in deployment and operation. The focus of the study was to modify and develop UDP/IP based protocols commonly used in commercial Internet for reliable data transfers in space environment. Multicast Dissemination Protocol was designed by Naval Research Laboratory to provide reliable multicast data and file transfer delivery on the top of general UDP/IP platform. It is very suited for bulk data transfer over the Internet. We have extended its usage in space channels and evaluated it as a solution to meet key challenges in space communications like high bit error rates and asymmetric channels. We have also tried to optimize the performance of the protocol in the terms of throughput, reliability, integrity and security of data. The evaluation test were carried on our Space to Ground Link Simulator which uses PPP to model point to point satellite links and correspond to low capacity systems as found in small satellite systems.