The invention relates to a method of non-coherent decoding an encoded CPM signal received by a wireless receiver, and a CPM decoder implementing the method, wherein the signal is generated by a transmitter using a serial concatenation of an outer encoder, an interleaver and an M-ary CPM modulator, and may have a frequency-hopping RF carrier. In a preferred embodiment, the method includes iteratively decoding the received signal by first recursively finding a sub-set of dominant sequences of CPM symbols that maximize a path metric for one hop interval using a non-coherent CPM detector, determining on the basis of this sub-set a sequence of soft inner bits, decoding these soft inner bits with an outer decoder, and using extrinsic information for the soft inner bits provided by the outer decoder to iteratively update the sub-set of dominant sequences of CPM symbols in the inner CPM detector.

Iterative non-coherent cpm decoder

A family of spectrally efficient waveforms for serial concatenated continuous phase modulation in frequency hopping systems is presented, for the challenging case where there are multiple hops per interleaver duration. The proposed waveforms are designed for narrowband tactical communication systems and are shown to meet stringent spectral emission masks of -40 dBc at the band edges for terrestrial communications below 100 MHz whilst maintaining data rates up to 64 kbit/sec in a standard 25 kHz bandwidth. In addition, a design approach is outlined enabling near-constant envelope waveforms for a variety of user defined information rates. This ensures efficient use of energy by the transmitter power amplifier, and achieves good performance and spectral efficiency for both tactical data and low latency voice communications. Furthermore, simulation results based on channel measurements in the tactical VHF band allow for the evaluation of the overall system performance in typical multipath environments

Spectrally Efficient CPM Waveforms for Narrowband Tactical Communications in Frequency Hopped Networks

This paper presents novel receiver processing for wideband continuous phase modulation (CPM). It is shown that
a relatively simple basis function expansion can be used to reduce the receiver complexity for channel estimation
and equalisation of CPM signals. Simulation results show that, in general, only two orthogonal basis functions
are required in the receiver irrespective of the parameters for the transmitted CPM waveform. In addition, error
rate performance curves demonstrate a robust frequency domain equaliser for multipath channels when compared
to more traditional time domain techniques.

Equalisation for Continuous Phase Modulation using Basis Functions

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Medium access for narrowband wireless ad-hoc networks - requirements and initial approaches

Modern spectrally efficient continuous phase modulation (CPM) waveforms offer attractive properties for narrowband tactical communications operating in VHF/UHF 30-400MHz bands. These waveforms exhibit robustness to a significant amount of intersymbol interference, due to multipath propagation, when iterative receivers are used for demodulation and decoding. However, certain propagation characteristics encountered in mountainous or coastal terrains may represent exceptionally challenging multipath environments. In these scenarios, the use of simple types of channel equalisation schemes, with an iterative CPM receiver, is demonstrated to alleviate the detrimental impact of multipath propagation. The combined effect of equalisation and iterative demodulation and decoding is investigated as a method to operate under these conditions.

Equalisation and iterative reception for spectrally efficient CPM in multipath environments

An iterative symbol-by-symbol non-coherent detection scheme using serially concatenated continuous phase modulation for application in wireless, frequency hopping, military communication systems is presented. The scheme exploits an iterative tree search algorithm in the detector, to reduce the overall complexity of the receiver, whilst maintaining a BER performance within 0.5 dB compared to detectors employing exhaustive tree search techniques. In addition, simulation results show that the iterative detection scheme can readily be employed to enable reliable communications in the presence of signal jamming and/or interference in frequency hopping systems

P.J. Vigneron

Papers

A reduced complexity iterative non-coherent CPM detector for frequency hopped wireless military communication systems