G. Vongas

Switchable-rate quasi-cyclic low-density parity-check codes for internet protocol over high-frequency systems

A switchable-rate quasi-cyclic low-density parity-check (QC-LDPC) coding scheme has been proposed for integration within the legacy and next-generation high-frequency internet protocol (HF-IP) systems. The novelty in this work is based upon using a class of switchable-rate short-block-length ( lt;;1500 bits) QC-LDPC codes for the HF fading channel modelled by the ITU-R F.1487 for all latitudes and conditions. The QC-LDPC codes are constructed using a switchable-rate approach based on finite fields which provides the ability to switch among three rates to combat varying channel conditions using a single encoder/decoder structure. The proposed structure enables low-complexity implementation of the low-density parity-check encoder/decoder for use within the existing data link (DL) layer of the standardisation agreement (STANAG) 5066 profile. The performance of the proposed scheme has been evaluated comprehensively for all the HF channel conditions and latitudes. A comparison between the proposed and the current coding scheme in HF-IP systems (based on convolutional coding) shows an improvement in error-rate performance.

Adaptive communication system design for HF/VHF multiple-mechanism propagation paths

The authors describe the nature of multiple-mechanism propagation paths (MMPPs) in the HF/low-VHF frequency range from 2 to 200 MHz. The design of systems to exploit such paths is then considered; channel encoding/decoding and real-time channel evaluation aspects are emphasized. Finally, the overall architectural framework for an MMPP radio system, currently under development, is presented.<<ETX>>

Adaptive DSP-based MFSK modems for HF aeromobile channels

An adaptive digital-signal-processing (DSP)-based MFSK modem using the PICCOLO modulation scheme has been developed, primarily as a research platform for the investigation of adaptive HF radio modems. The authors describe several important design features of the implementation, including a novel data-derived synchronization scheme. The modem exhibits a far greater degree of responsiveness to both user requirements and channel state than previous implementations. Of particular interest are the efficient memory shadowing technique used in the tone synthesis, the ability to vary the number of samples/symbol, the frequency offset correction method, and the modulation-derived synchronization (MDS) embedded synchronization technique which eliminates the need for any specific synchronization overheads. The use of the model in a semiorthogonal MFSK mode is also discussed.<<ETX>>