• Analysis of Communication Rates in the Proximity of Near-Earth Asteroids

      Nelson, Evan; Creusere, Charles D.; Critz, Thomas; Butcher, Eric; New Mexico State University (International Foundation for Telemetering, 2013-10)
      In this paper we analyze fundamental local-area communication issues related to proximity operations around near-earth asteroids. We are motivated by NASA's plan to send robotic spacecraft to numerous such asteroids in the coming years in preparation for an eventual manned mission. We consider here the case where multiple probes are deposited on the surface of an asteroid and must communicate the data they collect to each other and to earth by using the orbiting `mothership' as a relay. With respect to this scenario, we statistically analyze the ability of surface probes in various locations to communicate with the mothership as well as their abilities to network with one another. For the purposes of this analysis, we assume the simplest possible communications scenario: a surface probe can communicate with the mothership only when it has an unobstructed line of sight. At the frequencies of interest here, line of sight is a necessary condition but it is obviously not sufficient - the end-to-end link margins of our communications system must be high enough to support the desired/required data rates. The work presented in this paper extends our previous research in which we only analyzed the visibility of the locations on the surface of the asteroid. Here, we consider how visibility affects the required communications bandwidth and buffer sizes for both surface-to-spacecraft and surface-to-surface scenarios.
    • Design and Development of a Digital Signal Processing System that Responds Automatically to an Audio Trigger Event

      Borah, Deva K.; Chavez, Rudy; Favela, Frank; Ontiveros, Adrian; Smith, Matthew; Wallace, Matthew; New Mexico State University (International Foundation for Telemetering, 2013-10)
      This paper presents the development of a signal processing system that responds automatically to an audio trigger event. The audio trigger event, for example, can be a gun shot, and the system's response is to fire back at the source. The proposed system uses microcontrollers to digitally process audio signals coming from the audio trigger. Once the event is detected, the location of that source relative to the base location is estimated and retaliatory measures are automatically activated by the system. In our study, gunshot sounds are replaced by recorded audio tones and the retaliatory mechanism consists of a Nerf dart being fired toward the sound source. Sound localization is achieved via time stamping the digitized microphone signals. With an array of microphones, angular components as well as radial components can be determined. Servo motors are used to control the turret type mechanism for firing back Nerf darts to the source. The project has potentials for both lethal and non-lethal responses to a firearm discharge. The work is based on a 2013 senior undergraduate capstone project.
    • Full-Waveform LIDAR Recovery at Sub-Nyquist Rates

      Creusere, Charles D.; Castorena, Juan; New Mexico State University (International Foundation for Telemetering, 2013-10)
      Third generation LIDAR full-waveform (FW) based systems collect 1D FW signals of the echoes generated by laser pulses of wide bandwidth reflected at the intercepted objects to construct depth profiles along each pulse path. By emitting a series of pulses towards a scene using a predefined scanning patter, a 3D image containing spatial-depth information can be constructed. Unfortunately, acquisition of a high number of wide bandwidth pulses is necessary to achieve high depth and spatial resolutions of the scene. This implies the collection of massive amounts of data which generate problems for the storage, processing and transmission of the FW signal set. In this research, we explore the recovery of individual continuous-time FW signals at sub-Nyquist rates. The key step to achieve this is to exploit the sparsity in FW signals. Doing this allows one to sub-sample and recover FW signals at rates much lower than that implied by Shannon's theorem. Here, we describe the theoretical framework supporting recovery and present the reader with examples using real LIDAR data.
    • Pulse Position Modulation using BICM-ID for FSO Channels

      Borah, Deva K.; Kumar, Kuldeep; New Mexico State University (International Foundation for Telemetering, 2013-10)
      We investigate pulse position modulation (PPM) and multipulse PPM (MPPM) for free space op- tical channels using bit interleaved coded modulation with iterative decoding. Data bits are first encoded by using a non recursive convolutional code and the coded bits after an interleaver are modulated before transmission. Iterative decoding is performed at the receiver. Optimized mapping is designed for MPPM. A genetic algorithm is used to find the optimized mapping for MPPM. Our simulation results show that a significant improvement in the error performance can be achieved by using optimized mapping and iterative decoding at the receiver.
    • Relay Selection for Multiple Source Communications and Localization

      Borah, Deva K.; Perez-Ramirez, Javier; New Mexico State University (International Foundation for Telemetering, 2013-10)
      Relay selection for optimal communication as well as multiple source localization is studied. We consider the use of dual-role nodes that can work both as relays and also as anchors. The dual-role nodes and multiple sources are placed at fixed locations in a two-dimensional space. Each dual-role node estimates its distance to all the sources within its radius of action. Dual-role selection is then obtained considering all the measured distances and the total SNR of all sources-to-destination channels for optimal communication and multiple source localization. Bit error rate performance as well as mean squared error of the proposed optimal dual-role node selection scheme are presented.