• AN ALTERNATE PROPOSAL FOR ARTM CPM

      Rice, Michael; Perrins, Erik; Brigham Young University (International Foundation for Telemetering, 2004-10)
      Since the Advanced Range Telemetry (ARTM) program first proposed the use of multi-h continuous phase modulation (ARTM CPM), there has been much work done to characterize the performance of this waveform. The ideal performance of ARTM CPM is well understood and has been shown to be close to that of PCM/FM and the Tier I modulations (FQPSK-B and SOQPSK). In practice, however, ARTM CPM is very sensitive to phase noise at the receiver and also requires very long synchronization times. These difficulties can be addressed with additional link margin. In this paper we propose an alternate set of modulation indexes which are approximately 2 dB superior in performance with respect to the original set (we use minimum distance concepts to characterize the performance of each set). Brief consideration is also given to frequency pulses other than the existing raised cosine (RC) pulse. We also characterize the effect these new parameters have on the signal spectrum. This 2 dB gain gives ARTM CPM some of the system flexibility currently enjoyed by PCM/FM and the Tier I modulations. One such option is to realize this 2 dB gain using low-complexity coherent detection schemes, which we demonstrate; we also show a noncoherent detection scheme that performs within 2 dB of optimum (or in other words, it has the same performance as the existing coherent detector for ARTM CPM). This is significant since noncoherent detection avoids some of the synchronization burdens that have plagued ARTM CPM thus far.
    • COMPARISON OF ALAMOUTI AND DIFFERENTIAL SPACE-TIME CODES FOR AERONAUTICAL TELEMETRY DUAL-ANTENNA TRANSMIT DIVERSITY

      Jensen, Michael A.; Rice, Michael D.; Anderson, Adam L.; Brigham Young University (International Foundation for Telemetering, 2004-10)
      The placement of two antennas on an air vehicle is one possible practice for overcoming signal obstruction created by vehicle maneuvering during air-to-ground transmission. Unfortunately, for vehicle attitudes where both antennas have a clear path to the receiving station, this practice also leads to self-interference nulls, resulting in dramatic degradation in the average signal integrity. This paper discusses application of unitary space-time codes such as the Alamouti transmit diversity scheme and unitary differential space-time codes to overcome the self-interference effect observed in such systems.
    • A COMPARISON OF MMSE AND CMA EQUALIZATION TECHNIQUES FOR ARTM TIER-1 WAVEFORMS

      Rice, Michael; Satorius, Ed; Brigham Young University; Jet Propulsion Laboratory (International Foundation for Telemetering, 2004-10)
      The performance of two adaptive equalization techniques applicable to ARTM Tier-1 waveforms over a frequency selective multipath channel is summarized. Adaptive equalization based on the constant modulus algorithm (CMA) and the decision-directed minimum mean squared error (DF-MMSE) concept are shown to be effective in reducing the bit error rate in the presence of frequency selective multipath interference. The performance of the DF-MMSE equalizer is slightly better than the CMA equalizer. Implementation trade-offs between the two types of equalizers are also discussed.
    • ORTHOGONAL DUAL-ANTENNA TRANSMIT DIVERSITY FOR SOQPSK IN AERONAUTICAL TELEMETRY CHANNELS

      Jensen, Michael A.; Rice, Michael D.; Nelson, Thomas; Anderson, Adam L.; Brigham Young University (International Foundation for Telemetering, 2004-10)
      Transmit diversity schemes such as the Alamouti space-time code have been shown to be viable candidates to enable robust dual-antenna transmission from maneuvering air vehicles. However, due to the complicated structure of shaped offset quadrature phase shift keying (SOQPSK) modulation, the Alamouti approach has not been applicable to SOQPSK systems. This paper develops a precoding and detection algorithm which allows implementation of dual-antenna Alamouti signaling for SOQPSK modulation. Performance simulations demonstrate the performance of the scheme for a realistic flight scenario.
    • Performance Analysis of FQPSK and SOQPSK in Aeronautical Telemetry Frequency Selective Multipath Channel

      Rice, Michael; Dang, Xiaoyu; Brigham Young University (International Foundation for Telemetering, 2004-10)
      The impact of frequency selective multipath fading on the bit error rate performance of ARTM Tier-1 waveforms (FQPSK and SOQPSK) is derived and analyzed. In the presence of a strong specular reflection with relative magnitude |Γ1|, the ARTM Tier-1 waveforms suffer a loss in performance of (1 - |Γ1)^(-4√(|Γ1|)) for |Γ1| < 0:5 and a relatively high error floor at approximately 10^(-2) for |Γ1| ≥ 0.5. The ARTM Tier-1 waveforms possess twice the spectral efficiency of PCM/FM, but exhibit a greater loss and higher error floors than PCM/FM for the same multipath conditions and signal-to-noise ratio.
    • SPACE-TIME CODED SOQPSK IN THE PRESENCE OF DIFFERENTIAL DELAYS

      Rice, Michael; Nelson, Tom; Brigham Young University (International Foundation for Telemetering, 2004-10)
      This paper presents a method of detecting the Tier I modulation SOQPSK when it is used in a space-time coded (STC) system in which there is a non-negligible differential delay between the received signals. Space-time codes are useful to eliminate data dropouts which occur on aeronautical telemetry channels in which transmit diversity is employed. The proposed detection algorithm employs a trellis to detect the data while accounting for the offset between the in-phase and quadrature-phase components of the signals as well as the differential delay. The performance of the system is simulated and presented and it is shown that the STC eliminates the BER floor which results from the data dropouts.
    • SURVEY OF DETECTION METHODS FOR ARTM CPM

      Perrins, Erik; Rice, Michael; Brigham Young University (International Foundation for Telemetering, 2004-10)
      The ARTM Tier-2 waveform, called “ARTM CPM” in IRIG 106-04, has almost three times the spectral efficiency of PCM/FM and approximately the same detection efficiency. The improved spectral efficiency comes at the price of computational complexity in the receiver. The optimum receiver requires 128 real-valued matched filters and keeps track of the waveform state with a trellis of 512 states and 2048 branches. Various complexity reducing techniques are applied and the resulting loss in detection efficiency is quantified. It is shown that the full 512-state trellis is not required to achieve the desired detection efficiency: two different 32-state configurations were found to perform within one tenth of a dB of optimal. Noncoherent techniques are also evaluated. It is shown that the required complexity can be quite large to achieve a respectable detection efficiency. One noncoherent technique performed within 1.9 dB of the optimal with only 64 states, which is significant when considering the additional complexity savings of not having to track the carrier phase.