NarrowBand Waveforms (NBWF) are often used in VHF or UHF tactical communications. For these kinds of waveforms, low latency and robust data rates result in short codeword lengths that are challenging in terms of channel coding. Usually, serially concatenated convolutional code and continuous phase modulation (CC-CPM) schemes are considered in the context of NBWF. When evaluating the achievable rates, CC-CPM schemes show a 1 to 4 dB maximum margin. In this paper, we investigate on two new sparse graph-based channel coding strategies, trying to reduce this degradation for the achievable rate. Some implementation issues with short codeword lengths are also addressed. To this end, we first consider a serially concatenated CPM scheme where the outer code is an optimized Low-Density Parity-Check code (LDPC) based on some recently introduced methods for this kind of applications. The optimized LDPC scheme exhibits a good bit error rate when binary CPMs are used. This new design comes with lower computational complexity and greater flexibility. Second, in order to avoid the cubersome of iterative detection and decoding, we investigate on recently introduced precoded CPM that can achieve near optimal performance, referred to us as Pragmatic CPM (P-CPM). For this kind of precoded CPM schemes, we will show that associated EXIT chart curves have the flat property. It means that, to achieve good performance, P-CPM can be used with standard capacity approaching codes like LDPC Accumulate Repeat Jagged Accumulate (ARJA) or Turbo Codes without the need for iterative decoding. Bit error rate simulations confirm that P-CPM is a reliable alternative NBWF scheme compatible with versatile modern channel codes. As P-CPM is non-iterative, implementation is made easier. In additive white Gaussian noise, both schemes are found practical.

FASTNET is the latest tactical VHF radio from THALES. It offers multiple waveforms in frequency hopping, including a new (time multiplex based) waveform called GE-OMUX. Multipath situations had been identified and synchronization multipath related changes had been designed for the previous radio generation for Switzerland. Realistic propagation channels are required for the development and testing of a robust communication systems. Thus, Channel sounding in the 30-88 MHz band has been performed in Switzerland (in Jura and the Alps) and has confirmed the existence of challenging multipath propagation with delay spread up to 80 μs. This results in a dual problem : InterSymbol Interference (ISI) up to 3 modulated symbols in 25 kHz channel bandwidth and potential problems in hop synchronization strategy. In this article, a highly sensitive multipath detection channel sounder is first introduced. Then, an analysis of the measured channel impulse responses is provided. A method to extract propagation parameters from previous measurements is also described. A realistic and reproducible channel model has been developed and injected into a waveform test environment. FASTNET signal processing has been successfully tested on this test environment. The results were confirmed with dedicated field trials in Switzerland, both for the legacy Combat Net Radio (CNR) mode and the multi-services GEOMUX modes. It shows significant range improvements due to the equalization and synchronization design.