Clifford Hessel

High Performance Waveform, MIL-STD-188-181b and MIL-STD-188-184: their differences, similarities and applications

This paper explains the relationships between MIL-STD-188-181b, MIL-STD-188-184, High Performance Waveform modulation and High Performance Waveform protocol. We discuss the important features of each of these items, their similarities and differences, and how these various pieces do and do not work together. The paper discusses these issues with regard to non-DAMA satellite communications since, at the time of this writing, 181b and 184 are not officially part of DAMA.

Performance of trellis coded M-ary 1RC CPM with linear receiver and pre-coding

1RC continuous phase modulation (CPM) has a constant envelope and good spectral containment. It can thus be effectively used over highly non-linear bandlimited channels for high data rates. In this paper the performance of trellis coded 4, 8 and 16 ary 1RC CPM in additive white Gaussian noise (AWGN) channel is investigated. A linear receiver followed by a Viterbi (1989) decoder matched to the trellis code is used for the detection of the waveform. The IF filter is optimized for all the three different waveforms so as to minimize the combined effect of intersymbol interference (ISI) and noise at the sampling instant. In order to use a coherent linear receiver we propose to pre-code the transmitted signal so that the information is in the received phase and not in the phase difference between the two consecutive phase samples. BER performance results for these waveforms are presented.

Using retransmission information in a black side data link layer

In the current MIL-STD-188-184 [184], the data link layer is hosted on the RED side of the communications security (COMSEC). This constrains the set of solutions available to the link layer. This paper analyses the possible benefits of moving the link layer to the black side of COMSEC in increasing throughput for a given channel. The benefits of waveform switching, retransmission combining and ARQ protection of crypto synch are discussed in terms of throughput performance. Formulas for throughput are presented in terms of the signal to noise density ratio and the bit error probability function of the chosen modulation on coherent channels. Performance differences between BLACK side combining and the red side combining of 184 are discussed. Based on results given, the recommendation is made that MIL-STD-188-184A (184 A) allow for the eventual migration of the data link layer to the black side of the COMSEC engine. A proposal is made to use the new MIL-STD-188-181B (181B) preamble to allow this migration to begin now without sacrificing interoperability with older equipment.

Application of post-distortion angular equalizer on continuous phase modulated (CPM) waveform

CPM waveforms which are utilized in both MIL-STD-188-181B (181B) and high performance waveform SATCOM operation undergo appreciable distortion due to the effects of the bandlimiting and hard-limiting satellite transponder. In this application, the traditional LMS equalizer can remove some of the intersymbol interference, but at the higher symbol rates, the modem performance is still far off from the same bit error rate achieved in an environment which only contains additive white Gaussian noise. Observation of the SATCOM channel has shown that the CPM waveform is predictable, distorted in phase during symbol transitions. Large phase transitions incur a larger, proportional amount of distortion when compared to smaller phase transitions. A characterization of the phase error as a function of all the possible clockwise and counterclockwise adjacent phase transitions for the CPM phase constellation illuminates this proportion property of the distortion caused by the intersymbol interference. Once this error is characterized for all the symbols, it can be removed via complex multiplication. This method has been shown to outperform the traditional LMS equalizer in this application especially when considering the noise enhancement inherent in the LMS equalizer implementation. This paper documents the simulation comparison of the LMS equalizer and the new non-linear equalizer approach along with actual radio bit error rate curves.

The effects of phase constraint approaches on the spectrum of shaped M-PSK waveforms

As coded modulation techniques become prevalent in the industry, higher order signaling constellations will be used more often. The need to contain bandwidth and constant envelope simultaneously in these waveforms often requires that transitions between signal states occur around the unit circle over a period of time. The length of the path around the unit circle has effects on the bandwidth of the signal. Approaches to minimizing these transition paths are explored and their effects on signal bandwidth are presented.