Advanced HF Communications for Remote Sensors in Antarctica

The Antarctica is a continent mainly devoted to science with a big amount of sensors located in remote places for biological and geophysical purposes. The data from these sensors need to be sent either to the Antarctic stations or directly to the home country. For the last 15 years, La Salle has been working in the application of HF communications (3–30 MHz) with ionospheric reflection for data collection of remote sensors in Antarctica. We have developed and tested the several types of modulations, the frame structure, the radio-modem, and the antennas for two different scenarios. First, a long-range transequatorial (approximately 12,800 km) and low-power communication system is used as an alternative to satellites, which are often not visible from the poles. This distance is covered with a minimum of four hops with oblique incidence in the ionosphere. Second, a low-power system using near vertical incidence skywave (NVIS) communications provides coverage in a surface of approximately 200–250 km radius, a coverage much longer than any other systems operating in either the VHF or UHF band without the need of line of sight

Military Radio Communications Research in Australia

An overview of recent research by the Australian Defence Science and Technology Organisation in the field of military radio communications is presented. A philosophy for improving digital radio system performance over complex, variable channels is outlined. A key breakthrough, called PDF-directed adaptive radio, which can provide substantially greater throughput over HF channels whilst minimising bit-error rate and delay, is described. Simulation results for fast adaptive Schemes applied to both serial-tone and parallel-tone HF modems are presented and shown to significantly out-perform fixed rate modems and modems employing hybrid automatic-repeat-request schemes. A new detector scheme is discussed which has superior performance to conventional detectors for digital traffic in the presence of inter-symbol interference and impulsive noise

New Adaptive Data Transmission Scheme Over HF Radio

Acceptable Bit Error rate can be maintained by adapting some of the design parameters such as modulation, symbol rate, constellation size, and transmit power according to the channel state.<br />An estimate of HF propagation effects can be used to design an adaptive data transmission system over HF link. The proposed system combines the well known Automatic Link Establishment (ALE) together with variable rate transmission system. The standard ALE is modified to suite the required goal of selecting the best carrier frequency (channel) for a given transmission. This is based on measuring SINAD (Signal plus Noise plus Distortion to Noise plus Distortion), RSL (Received Signal Level), multipath phase distortion and BER (Bit Error Rate) for each channel in the frequency list. Channel condition evaluation is done by two arrangements. In the first an FFT analysis is used where a pilot signal is transmitted over the channel, while the data itself is used in the second arrangement. Passive channel assessment is used to avoid bad channels hence limiting the frequency pool size to be used in the point to point communication and the time required for scanning and linking. An exchange of channel information between the transmitting and receiving stations is considered to select the modulation scheme for transmission. Mainly MPSK and MFSK are considered with different levels giving different data rate according to the channel condition. The results of the computer simulation have shown that when transmitting at a fixed channel symbol rate of 1200 symbol/sec, the information rate ranges from 2400 bps using 4FSK up to 3600 bps using 8PSK for SNR ranges from 11dB up to 26dB.<br /

M-ary Chirp Modulation for Data Transmission

M-ary chirp modulations, both discontinuous- and continuous-phase, for M-ary data transmission are proposed and examined for their error rate performances in additive, white, Gaussian noise (AWGN) channel. These chirp modulated signals are described and illustrated as a function of time and modulation parameters. M-ary chirp modula­ tion with discontinuous phase is first proposed and then the M-ary Continuous Phase Chirp Modulation (MCPCM) is considered. General descriptions of these modula­ tion systems are given and properties of signals representing these modulations are given and illustrated. Optimum algorithms for detection of these signals in AWGN are derived and structures of optimum receivers are identified. Using the minimum Euclidean distance criterion in signal-space; upper bounds on Signal-to-Noise Ratio (SNR) gain relative to Multiple Phase Shift Keying (MPSK) are established for 2-. *4-, and 8-ary MCPCM systems. It is observed that the maximum likelihood coherent and non-coherent receivers for MCPCM are non-linear and require multiple-symbol observations. Since symbol error probability performance analyses of these receivers are too complex to perform, union upper bounds on their performances are derived and illustrated as a function of SNR, number of observation symbols, and modulation parameters for MCPCM. Optimum 2-, 4-, and 8-ary modulation schemes that mini­ mize union upper bound on symbol error rates have been determined and illustrated. Our results show that 2-, 4-, and 8-ary optimum coherent MCPCM systems, with 5-symbol observation length, offer 1.6 dB, 3.6 dB, and 8 dB improvements relative to 2-ary, 4-ary, and 8-ary PSK systems, respectively. Also, it is shown that opti­ mum 2-ary and 4-ary non-coherent MCPCM systems can outperform 2-ary and 4-ary coherent PSK systems, respectively

Application of statistical decision theory to the detection of radiotelegraph signals

Imperial Users onl