• On Overlapped Fast Fourier Transforms

      Harris, Fred; San Diego State University; Naval Ocean Systems Center (International Foundation for Telemetering, 1978-11)
      Many signal processing applications require the averaging of transforms taken over partitioned sets of data. We show that the required overlap for the partitions is window dependent and that is varies from 50% to 75% depending upon the sidelobe levels of the window.
    • On the Combined Performance of Joint Access Control/Modulation/Coding Schemes

      Rubin, Izhak; University of California, Los Angeles (International Foundation for Telemetering, 1978-11)
      The combined performance of a multi-access communication channel under joint access control/modulation/coding procedures is examined. The multi-access channel serves as a shared information transmission medium in a data communication network, such as a satellite, computer or terrestrial radio communication network. The performance of the underlying modulation/coding scheme is expressed in terms of the corresponding bit-error probability vs. signal-to-noise ratio curve. The computational cutoff error rate is also used as a proper performance measure characterizing the joint modulation/coding scheme. The performance of the underlying access-control algorithm is described by the message-delay vs. network-throughput curve. Integrating these performance functions, the combined performance of the joint access-control/modulation/coding procedure is derived. In particular, under proper bandwidth and power limitations, one can then evaluate the total amount of information that can be transmitted through the channel, in a reliable and timely fashion, at prescribed bit-error-probability and message-delay values, under various communication link, transceiver, repeater and antenna conditions.
    • Optical Antennas

      Kraemer, Arthur R.; Jones, Robert W.; GTE Sylvania Incorporated (International Foundation for Telemetering, 1978-11)
      Optical communication systems have the capability to transmit very high data rates (1-Gbps) over long distances. One primary reason is the narrow beamwidths achievable with optical antennas having diameters of less than 30 cm. This paper discusses how the Gaussian beam patterns of the laser sources are modified as they are transmitted through physically realizable optical antennas. Measurements taken on an optical antenna developed for spaceborne operation are presented and compared with theoretical predictions. Optical receiver antennas are also discussed stressing the differences between direct and heterodyne detection. Finally, consideration is given to the privacy and jamming resistance of optical communication systems using these small optical antennas.
    • Optical Fiber Thermosensor

      Ishikawa, S.; Doi, K.; Hamatsuki, T.; Nonaka, S.; Nippon Electric Co., Ltd. (International Foundation for Telemetering, 1978-11)
      An optical fiber thermosensor with bimetal has been newly developed for telemetering temperature readings at an electrically noisy place and high voltage point. Thermosensor measuring accuracy was less than 0.5 degree in the 10 to 50°C range. The device has proved to be practical and reliable.
    • Optimum Quantization for Minimum Distortion

      Caprio, James R.; Westin, Nancy; Esposito, John; Comptek Research, Inc.; State University of N.Y. at Buffalo (International Foundation for Telemetering, 1978-11)
      This paper treats the problem of optimal selection of data quantization levels for minimum error. No assumptions are made regarding the underlying statistics of the process to be quantized. A finite precursor sample of the data is analyzed to infer the underlying distribution. Selection of optimum quantization levels can then be related to the generation of an optimum histogram for the data record. The optimum histogram is obtained by a dynamic programming approach for both least mean square error and minimum Chebychev error criteria. Transmitted data can then be quantized according to levels specified by the histogram. The process can be repeated periodically either with a new data sample, if the underlying process is nonstationary, or performed on the accumulated record in the stationary case.
    • Packet Telemetry: A Possible Standard Protocol for Spacecraft Data Handling

      Greenberg, Edward; Hooke, Adrian J.; NASA Jet Propulsion Laboratory (International Foundation for Telemetering, 1978-11)
      Packetized telemetry-handling offers an opportunity to standardize major portions of the spacecraft-to-ground interface for future NASA missions. An end-to-end packet transport protocol is proposed which enables delivery of telemetry data from a remote space sensor to a ground-based user with virtually no project-unique intermediate processing. This paper reviews the possibility of creating a single telemetry format standard for both deep-space and near-earth missions. The proposed standard addresses the greatest NASA problem of the coming decade - cost - by allowing telemetry streams from many inflight spacecraft to be handled on the ground by common, simple, multimission processing elements.
    • Performance Evaluation for Shuttle/TDRSS Links Using Analytical Simulation

      Lindsey, William C.; Braun, Walter R.; LinCom Corporation (International Foundation for Telemetering, 1978-11)
      An analytical simulation package has been developed by LinCom Corporation for analytical verification of bit error rate and tracking services performance for both S- and K-band Shuttle user service through the Tracking and Data Relay Satellite System (TDRSS). The purpose of this effort was to provide a tool to assess overall system performance as well as the sensitivity to key subsystem parameters and to ensure compatibility of TDRSS and Shuttle transponder performance specifications. The evaluation is based on analytical simulation, i.e., a combination of simulation techniques and analytical performance evaluation. This allows the use of a more realistic signal format than is possible with a purely analytical approach and maintains the advantage of short computation time. The Shuttle forward and return link models and the main features of the simulation are described. Sample results of the computer runs are provided for current power budgets and system design parameters.
    • Performance Evaluation of Communication Channels by Computer Simulation

      Poza, H. B.; TRW Defense and Space Systems Group (International Foundation for Telemetering, 1978-11)
      A computer simulation model capable of aiding in the design and predicting the performance of complex end-to-end communication systems is described in this paper. The model is used to choose the optimal modulation scheme under certain communication channel constraints, define the signal distortion characteristics introduced by realizable channel components and select the demodulator/bit synchronizer designs for minimization of bit error rate. A parameter sensitivity analysis is conducted to demonstrate the usefulness of the model in evaluating the effect of different signal distortion phenomena on overall link performance.
    • Performance Evaluation of Step Stare Sensor for Space-Based Air Vehicle Detection

      Ho, C. Q.; Rockwell International (International Foundation for Telemetering, 1978-11)
      Detection of aircraft by a space-based infrared sensor is a demanding task using near-term technology. To achieve sufficient sensitivity, background noise suppression is required because of the relatively weak target signal. Background noise suppression techniques, first order, second order, and higher order temporal differencing, spatial and temporal differencing, are analyzed and compared. Background noise due to both background drift and system vibration effects are calculated. Pixel-to-Pixel offset-induced background noise leakage is also evaluated.
    • Performance of Bandlimited and Hardlimited PSK Signals

      Rey, R. D.; TRW Defense and Space Systems Group (International Foundation for Telemetering, 1978-11)
      Transmission of a signal through a channel, such as a satellite communication channel, results in distortion of the signal due to bandlimiting in the individual channels and hardlimiting. The purpose of this paper is to study the effects that channel distortion due to filtering and hardlimiting have on the performance of BPSK and QPSK. The results will be used to determine the maximum bit rate which can be transmitted through a channel having a particular bandwidth with a specified limit in degradation of performance.
    • Performances of Regenerative and Nonregenerative Satellite Repeaters with MPSK Signalling

      Woo, K. T.; California Institute of Technology (International Foundation for Telemetering, 1978-11)
      Linear (translation), hard-limited, and demod/remod types of satellite repeaters are considered in this paper. Both uncoded and coded multiple phase shift keyed (MPSK) signals are assumed to be transmitted through these repeaters. Relative performances of these repeaters in the presence of uplink and downlink noises are then compared quantitively. Probabilities of bit errors and the computational cutoff rates are computed for 2, 4, and 8 phases PSK signals, with uplink and downlink SNR's as parameters.
    • Phase Referencing for MA Demultiplexing in the TDRSS

      Gagliardi, R. M.; University of Southern California (International Foundation for Telemetering, 1978-11)
      The TDRSS performance is based, to a large extent, on the ability to maintain phase coherency between user, satellite, and ground segment. This is especially true for the MA return subsystem, which uses coherent referencing for multiplexing and demultiplexing between the TDRS and ground processor. Phase noise appearing on these referencing waveforms destroy the phase coherency, and will degrade the overall MA return operation. In this paper the manner in which this phase referencing is achieved is described. In addition, the results of a preliminary study to distinguish the key MA return phase noise sources, and the manner in which each will ultimately influence performance, is presented. The results show that the return phase noise effects can be separated into "coherent" and "noncoherent" contributions, and each must be separately evaluated. The effect of the various tracking loop bandwidths throughout the link is shown, and the manner in which the specific phase noise spectra are eventually filtered is developed.
    • The Power of Desarguesian Sets

      Wu, W. W.; Communications Satellite Corporation (International Foundation for Telemetering, 1978-11)
      A Desarguesian set is a planar Euclidean geometry difference set which can be used to derive new cyclic block codes, convolutional self-orthogonal codes, and random multiple access codes. This paper discusses the usefulness of these codes and presents the step-by-step procedure for the purpose of constructing such sets. Comparisons are also made with planar projective geometry sets in which two types of existing codes were obtained.
    • Processing Satellites

      Omura, Kim; University of California, Los Angeles (International Foundation for Telemetering, 1978-11)
      With few exceptions, satellite communications systems today employ conventional nonprocessing satellites that are often referred to as "bent pipes in the sky." These satellites merely act as nonlinear (TWT) amplifiers that transmit on the downlink the same signals plus noise (frequency shifted) that it receives on the uplink. It is now clear that the "micro-processor revolution" will impact on satellite technology and result in a new generation of communication satellites with various on-board digital processing. The orbiting experimental military satellites Les-8/9 are the first-of the new generation of processing satellites. Many more such satellites are now being considered with increasingly complex digital processing on the satellites. For military applications these on-board processing capabilities are listed below in increasing order of complexity.
    • Pulse to Pulse Encoding in Optical Communications

      Prati, G.; Gagliardi, R.; University of Pisa; University of Southern California (International Foundation for Telemetering, 1978-11)
      Optical pulsing of a laser beam provides a convenient manner for transmitting digital information, and such procedures have led to well-accepted classes of pulse amplitude and pulse position modulation formats. However the excessive pulse dispersion and background light bursts that characterize several optical channels severely limit performance and achievable data rates. One procedure for combating these effects is to encode data over a multiple of pulse frames, and decode sequences of pulses rather than each pulse individually. In the paper pulse to pulse encoding and decoding of an optical beam is examined, considering both photodector gain effects and receiver thermal noise. Theoretical performance results are presented, and the relation between this type of decoding and "tree searching" is developed.
    • Quantization for Signal Detection and Representation

      Kassam, Saleem A.; University of Pennsylvania (International Foundation for Telemetering, 1978-11)
      For digital representation of analog data the minimum mean-squared-error criterion is commonly used as a criterion for the basis of optimum quantizer design. In this paper we show that in some situations measures other than the minimum mean-squared-error may be more appropriate. For the signal representation problem, it is shown that the mean-absolute-error criterion has theoretical justification, as again for some signal detection problems it is shown that the mean-squared-error criterion is not the most appropriate criterion.
    • Quasi-Optimal Decoding of Linear Block Codes Using Soft Decision Detection

      Greene, Edward P.; NASA/Goddard Space Flight Center (International Foundation for Telemetering, 1978-11)
      A simple but effective decoding procedure, applicable to any (n,k) linear block code with symbols from GF(q), is described. The technique involves a transformation of the parity check equations which focuses the code's correction power on the soft symbol set while still retaining the capability to correct one symbol error from outside this set. The soft symbol set is defined to be the n-k least reliably detected code symbol positions whose parity check rowspaces are linearly independent. The process generates a number of error vector screening candidates, each a solution to the parity check equations, and the maximum-likelihood candidate is accepted. If P(opt) and P(qopt) are the decoder error rates for the optimal and quasi-optimal decoders respectively, then P(opt) < P(qopt) < P(opt) + P(se) where P(se) is the probability that the actual error vector is not included in the screening candidate set. Since P(se) can be shown to approach zero for a wide range of codes and operating conditions, the performance of this decoder can be quasi-optimal in these cases.
    • A Rate Distortion Surface for Images

      Jones, Richard A.; University of Arkansas (International Foundation for Telemetering, 1978-11)
      In this paper the concept of a rate distortion surface is introduced. A signal class is considered such that the source can be viewed as a composite source that consists of a finite number of subsources. Also, it is demonstrated that the overall transmission requirement can be treated as different but connected transmission requirements. The connection arises through an intermediate fidelity criterion. It is shown that the rate distortion bound for a composite source is a convex surface with a unique minimum for any specified signal to noise ratio. It is further demonstrated that the locus of these minima, projected onto a composite source information rate-composite source average distortion plane, is the rate distortion curve for the composite source.
    • The Role of Microprocessor-Based Terminals in Computer Interpretation of ECG's: Engineering Considerations

      Ewing, Richard; Comp-U-Med, Inc. (International Foundation for Telemetering, 1978-11)
      This paper presents a case history of the selection and application of a microprocessor for a low cost phone-coupled computer electrocardiograph terminal. All phases of the project will be covered, from the ingredients which went into the decision to employ a microprocessor, through processor selection, design, program and manufacture.
    • The Role of Microprocessor-based Terminals in Computer Interpretation of ECG's: The View of Management

      Stuckelman, Robert; Comp-U-Med, Inc. (International Foundation for Telemetering, 1978-11)
      This paper discusses management considerations in the utilization of microcomputers in a new product design. Topics to be discussed include cost considerations in applying a new technology; dealing with development costs; and cost effectiveness of microprocessor utilization.