• Detection of Scattered Optical Fields with Focal Plane Ring Detectors

      Vilnrotter, Victor A.; Hughes Aircraft Company (International Foundation for Telemetering, 1977-10)
      It is demonstrated that when communicating through scattering channels order-ofmagnitude improvement in system performance is possible by employing focal-plane processing techniques to recover some of the scattered radiation. Maximum a-posteriori and suboptimal system structures are derived and their performance evaluated. System sensitivity to the errors in the optimal weighting functions is discussed.
    • Self-Steering Arrays

      Kummer, W. H.; Hughes Aircraft Company (International Foundation for Telemetering, 1977-10)
      Self-steering arrays using complete receiver-transmitter-signal processing systems to direct the beam of an antenna automatically have been developed. These systems offer an alternative to mechanically gimballed systems for satellite communication applications. The operation of such systems using either a pilot signal or a phased lock loop technique for self-steering is described. Also described is an engineering model built for satellite-to-earth communications which incorporates these techniques. Additionally, other systems now in breadboard configurations are mentioned briefly. A summary of power requirements for a projected 25-module system has been included to indicate the feasibility of larger systems. Test results for the engineering model have proved satisfactory, and show that these systems can definitely be valuable in applications similar to the tracking and data relay satellite system (TDRSS) described here.
    • Some Operational Considerations in Deploying Anti-Jam Communications

      Goldman, Herbert B.; Hughes Aircraft Company (International Foundation for Telemetering, 1977-10)
      Operational and deployment considerations are described to enhance the performance of jam resistant communications. The potential different ground propagation characteristics of spread spectrum and CW type waveforms are used to the advantage of the communication system. Emphasis is placed on the use of tactical relay to continuously optimize against the jammer. Tactics such as spoofing are described as a technique in confusing the intelligent jammer. The objective of this paper is to illustrate how anti-jam communications with nominal AJ performance improvement can effectively be employed in a ground environment. These include the brute force and the so-called intelligent or sophisticated jammer. For many years the utilization of anti-jam communications has been stifled in anticipation or the optimum solution against the optimum jammer. When evaluating a "one on one" scenario where the jammer is dedicated to jamming a specific link there is an unending subset of tradeoffs of optimum techniques to consider. However, when the jammer is trying to disrupt communications along a broad geographical axes. the techniques of jamming and communicating should be based on more general operating conditions. The ground communications environment in the presence of ground-based jamming presents the greatest opportunity for improving performance as a function of propagation anomalies and the use of relay. Airborne terminals within line of sight of the jammer have the most severe jamming environment. Ground based terminals generally will have an advantage of terrain against the ground based jammer. Those links that exhibit poor communications margin should always have the option of an alternate route in a jamming environment. The alternative to an alternate route is to provide excessive performance margins for worst case analysis. Unfortunately there is a significant cost factor associated with this latter approach. An important element of the scenario is the concept of position location. The use of position location and reporting equipment enables the apriori determination of appropriate links by different classes of users. As an example an aircraft can maneuver close to a ground terminal for communications to utilize the advantage of range ratio. This can be done in the worst case of a close Air Support Mission where the FO must provide voice or digital data to direct a strike at several mobile targets. At high altitudes the AC may be jammed but at low altitude the link may be viable. At low altitudes the aircraft A-G link will be constrained to a small geographic area and must therefore know which area to cover. The use of GPS can also be enhanced at low altitudes against the ground based jammer if acquisition of the GPS signal can be speeded up. The use of a digital matched filter (DMF) for CA code acquisition can provide this capability.