Considerations for automatic link establishment in HF radio systems

The US Navy has all but ceased to use high frequency (HF) radio for long-haul ship-shore communications. Satellite systems have rightfully assumed this role, but the antiquated nature of the Navy HF system has soured planners on even considering HF for supplementary uses or other roles. In an attempt to dispel this undeserved reputation and gain operating experience for application of automation to new shipboard HF systems, an HF radio communications system incorporating automatic link establishment (ALE), single-tone serial modems and 500-watt transceivers was deployed on USS TARAWA (LHA-1) and to serving Navy shore communications stations during her recent deployment to the Indian Ocean and Persian Gulf. The authors describe the use of this system for bidirectional 600 baud message traffic. This is the first application of the combination of MIL-STD-188-141A ALE and MIL-STD-188-100A single tone serial modem technology in a US Navy operational environment. The ALE radio system was used to automatically test and select the best channel from among several assigned frequencies and establish a link between ship and shore. Accumulated message traffic was then passed over the single-tone serial modem to the distant end. Technical details of the installation and operational techniques are presented along with a discussion of how automation greatly reduced the level of skill and experience needed to successfully operate this HF system. Test results are presented which illustrate the success enjoyed in maintaining communications over paths which had long been considered unworkable with existing shipboard HF equipment and techniques. The potential for application of automated HF to short-range over-the-horizon (OTH) communication needs for littoral warfare is also discussed. >

The author describes an attempt to use HF automatic link establishment (ALE) radio equipment as a ship-shore sounder in the Mediterranean Sea. The method selected as potentially most effective for HF channel selection purposes was a state-of-the-art HF ALE radio system. This system consists of fully automatic microprocessor-controlled HF radio transceivers incorporating the ALE control protocols and waveform specified in MIL-STD-188-141A. The primary result of the test was that the use of the HF ALE radio system as a sounder to support VFCT (voice frequency carrier telegraph) HF terminations provided no operating advantage in the Mediterranean operating areas. It is concluded that, in spite of the inability to find a ready solution for HF communications in the Mediterranean, this was a very successful test. The ALE radio system performance data obtained provides a first real-world glimpse at how MIL-STD-188-141A might serve the navy in future automated HF communications system. >

Knowledge of the state of the upper atmosphere, and in particular its ionospheric part, is very important in several applications affected by space weather, especially the communications and navigation systems that rely on radio transmission. To better classify the ionosphere and forecast its disturbances over Europe, a data collection endeavour called the European Digital Upper Atmosphere Server (DIAS) was initiated in 2004 by a consortium formed around several European ionospheric stations that transmit in real-time ionospheric parameters automatically scaled. The DIAS project is a collaborative venture of eight institutions funded by the European Commission eContent Programme. The project seeks to improve access to digital information collected by public European institutes and to expand its use. The main objective of the DIAS project is to develop a pan-European digital data collection describing the state of the upper atmosphere, based on real-time information and historical data collections provided by most of the operating ionospheric stations in Europe. Various groups of users require data specifying upper atmospheric conditions over Europe for nowcasting and forecasting purposes. The DIAS system is designed to distribute such information. The successful operation of DIAS is based on the effective use of observational data in operational applications through the development of new added-value ionospheric products and services that best fit the needs of the market. DIAS is a unique European system, and its continuous operation will efficiently support radio propagation services with the most reliable information. DIAS began providing services to users in August 2006. The Need for Accurate Ionospheric Products Radio frequency communications and satellite positioning and navigation systems are applications most affected by ionospheric disturbances. Such disturbances can cause drastic and large-scale changes in the usable ranges of high frequency (HF) or below HF bands affecting standard ground-to-ground and submarine communication systems. The characteristics of an ionospheric propagation channel, whether it is HF or transionospheric frequencies, are highly variable on timescales ranging from a few seconds to the 11-year solar cycle. Even during its quietest periods, the Sun produces electromagnetic radiation and solar wind, both of which can affect a variety of geomagnetic and ionospheric phenomena, which in turn affect radio waves propagating through the ionosphere. Hence day-to-day and hour-to-hour changes in propagation channel characteristics can occur.

The application of the automatic link establishment (ALE) procedures of MIL-STD-188-141A, combined with improved signal processing technology found in advanced modems, provides the basic elements to create adaptive high frequency (HF) radio networks. Dynamic changes in ionospheric conditions and noise fluctuations make the HF network a hostile one, where links between nodes are subject to frequent failure. The addition of adaptive routing and information management enhances network robustness in this environment. This suggests the use of a distributed routing algorithm in which convergence to the shortest path is of primary concern. However, routing decisions derived from such distributed processes exhibit an inherent uncertainty due to the randomness of link failures and the latency of network performance information. The authors describe predictions of a computer simulation of a wide area HF radio network that invokes ALE procedures, adaptive routing, and information management protocols. Aspects include the impact of modem interleaver delay time, encryption synchronization delay, management overhead, and message handling on throughput and network latency. Recommendations are presented with respect to the application of statistical neural processing to improve network management in this environment. >

The SoDark cipher is used to protect transmitted frames in the second and third generation automatic link establishment (ALE) standards for high frequency (HF) radios. The cipher is primarily meant to prevent unauthorized linking and attacks on the availability of HF radio networks. This paper represents the first known security analysis of the cipher used by the second generation ALE protocol—the de facto world standard—and presents a related-tweak attack on the full eight round version of the algorithm. Under certain conditions, collisions of intermediate states several rounds into the cipher can be detected from the ciphertext with high probability. This enables testing against the intermediate states using only parts of the key. The best attack is a chosen-ciphertext attack which can recover the secret key in about an hour with 100% probability, using 29 chosen ciphertexts.

Traditionally, high frequency (HF) communications have been difficult to manage efficiently, mainly due to the variable nature of the propagating conditions. An automatic radio control system (ARCS) consisting of automatic channel selection (ACS), automatic link establishment (ALE), and automatic link maintenance (ALM) will provide an automated system which will alleviate operator workload and improve communications availability at HF. Effective network management is fundamental to such a system. Computer modelling and simulation is a powerful method for testing the suitability of parameter values and how they affect the operation of a communications systems. Various networks can be simulated highlighting the shortcomings and also the positive aspects of each configuration. This paper describes the current status and capabilities of a computer based ARCS network simulation designed to be used as an aid to developing the ARCS specification. It also presents some initial results.

Accomplishment of basic services implementation with specific quality is one of the main challenges of the command and communication systems for modern maritime safety and defense. The specificity of the marine environment imposes the use of narrowband HF (High Frequency) and VHF (Very High Frequency) radio communication devices which are capable to implement IP transmission. This paper presents the requirements for the HF and VHF radio systems according to the IP protocol requirements. At the beginning basic properties of narrowband HF and VHF waveforms in context of their operational scenarios has been described. Then results of experimental research (implementation of narrowband services — voice and data) has been presented. Finally further research directions with contribution of the authors, in NATO working groups related to the development of NBWF (Narrowband Waveform) for coalition communication has been presented.

There has been a re-newed interest for frequency adaptive HF systems due to the reliable and fully automatic cost-effective voice link and message transfer they can provide. An important requirement for general market acceptance is the existence of a standardised platform, though. This is available in the form of the U.S. MIL-STD-188-141A/FED-STD-1045A standard, popularly referred to as the Automatic Link Establishment (ALE) standard. However, as can be seen from the build-up of other information transfer system (e.g. the Intemet), it is difficult to estimate the sufficient throughput capacity needed to be provided. When store-and-forward type traffic, such as e-mail, became a regular means of communication the overall traffic load broke (and still does) every capacity increase plan made. Therefore it is important to take such (expandability) effects into account when designing automated HF networks. This paper proposes a synchronous scanning scheme which would still enable full compatibility with the current (asynchronously scanning) ALE standard. The proposed scheme makes it possible to use more frequencies which can be dynamically exchanged, thus providing increased resilience to interference and varying propagation conditions. The proposed scheme ought also to be comparably easy to implement since it does not impose any higher performance or implementation requirements than the asynchronous scheme. In fact, a network may consist of both asynchronous stations and synchronous stations.

It is difficult to recognize Automatic Link Establishment (ALE) behaviors of a short-wave radio station, if we do not acquire the radio station's communication protocol standard. A method is proposed to recognize different ALE behaviors by using an improved unidimensional DenseNet. In this work, we directly recognize ALE signals in physical layer without the radio station's communication protocol standard. Hence, we can avoid difficulties in demodulation, decryption and so on. Actually, the original DenseNet is used extensively in the field of computer vision, so the original DenseNet is firstly adapted for the unidimensional input. And then, two parallel dense blocks are used in our improved unidimensional DenseNet, which could improve the capability of network to extract ALE signals' deep features. The experimental results show that the proposed method is able to recognize different ALE behaviors of a short-wave radio station. And improved DenseNet has better recognition performance than simple DenseNet. The simple DenseNet only contains one dense block. Finally, the results of comparison experiments also show that some classic networks have worse performance in ALE behaviors recognition, such as LeNet-5, ResNet-34, and DenseNet-121.

 Abstract—This paper describes a simulation architecture developed to address the need in the defence and aerospace industry for a rapid prototyping capability to test new and existing network protocols and systems where analytical methods no longer suffice. In particular, the simulator introduced here allows study of High Frequency (HF) radio networks and other unorthodox systems that cannot be easily modelled using existing communications network simulators. This paper describes the architecture and gives an example use case - modelling an HF System using the 2G Automatic Link Establishment (ALE) linking protocol under a variety of conditions; exploring the effects of changing the number of nodes in the network, and of altering the input data rate to the system. The network performance was analysed under a wide range of combinations of conditions, and it was found that increasing the number of nodes in these networks causes specific latency increases and an overall throughput decrease, both in the unidirectional and bidirectional case, although it is better tolerated in the unidirectional case. Increasing the input data rate causes an overall throughput increase up to a threshold point, after which it saturates and then decreases as data remains unsent, due to the physical limits of the system (including networking overhead) being surpassed. This simulator, known as CommNetSim has been developed for use in evaluating the technical capabilities of, and business cases for, real-world applications to be developed by Thales UK. Index Terms—Communication networks, discrete event simulation, high frequency radio, modelling, simulation.

The author explains the various features and capabilities within the PropMan system that enable quick and comprehensive personal computer (PC)/laptop HF frequency-management analysis and tradeoffs. The evolving propagation resource manager PropMan provides a comprehensive, quick, and user-friendly process for making HF channel allocations. It is noted that PropMan can encompass the expertise necessary to eliminate many of the blatant errors typical of HF misuse. This expertise can be applied at two levels: frequency assignments and in-the-field operator support. Applying PropMan to the communications mission to generate an ALE (automatic link establishment) scan list and using ALE automation significantly enhance HF communications and facilitate effective utilization of frequency assets. >

The manually operated high frequency radio requires operators with extensive training, knowledge, and experience. The resurgence of interest in HF radio has led to increased automation of the operator functions, thus allowing operation by personnel with only a minimum of training. Although the automatic link establishment (ALE) system provides the basic system automation, there are a number of additional automation functions being developed. The future adaptive radios will be devices that can sense their communication environment and automatically adapt to enhance their communications links as well as mitigate against detractors. >

Their have been major advances in the field of automatic and adaptive radio communication systems. Advances in such diverse areas as frequency management, automatic link establishment, modem technology, networking protocols and message handling systems have led to the possibility of separating the user from the radio. They have led to the concept of HF as a transparent subnetwork within a wider communications infrastructure, and they have led to the idea of radical new approaches to the allocation and utilisation of the HF band itself. A system that consolidates many of these advances is under development for the Swedish armed forces. The contract was awarded by the Swedish Defence Material Administration (Forsvarets Materielverk) to GEC-Marconi after an extensive evaluation of the proposed solution involving computer simulations and on-air trials over an 18 month period. This paper describes some of the key concepts of the system and outlines the main elements involved in its implementation.

The HF radio band is very important for military operations, enabling communications beyond line-of-sight. To deal with the variability of the Ionosphere, several technologies have emerged in the last years, like automatic Link Quality Analysis (LQA), Automatic Link Establishment (ALE) and Data Rate Change (DRC) algorithms. In this paper, two DRC algorithms are assessed — namely, Trinder and RapidM — and improved versions of these algorithms are proposed: Avoiding Cut-Off State (ACOS) and Bit Error Optimization (BEO). The first proposal reduces the occurrences of link cut-offs (corresponding to bit error rates higher than 10−3); the second proposal, besides increasing the link availability, eliminates data rate oscillations. When compared to the original versions of the algorithms, both proposals showed significant improvements in all of the considered link assessment metrics, either when evaluated in a simulation environment, or in real field propagation tests.

A novel scheme to deploy a point-to-multipoint optical wireless communication network is proposed. The master node provides hemispherical field-of-view (FOV) acquisition via a fisheye lens to achieve the automatic establishment of optical links with user nodes. We present an effective distortion-correcting algorithm based on two-ary piecewise bicubic spline interpolation to correct the large optical distortions of the fisheye lens. Using this algorithm, the angles of the incident beams are accurately calculated according to the laser spot position on the CCD (charge-coupled device) sensor with the maximum error of 0.027 deg. In addition, the strong background radiation from such an ultrawide FOV also leads to significant degradation of the angle detection accuracy under the condition of weak received optical power. A Voigt anomalous dispersion optical filter with ultra-narrow-pass bandwidth is adopted to resist the background radiation. The numerical simulation results show that the total angle detection error caused by the optical distortion and the background radiation is within 0.06 deg. Considering the extra gimbal pointing error and the angle-of-arrival fluctuations due to atmospheric turbulence, the pointing error of the master node is less than 0.079 deg, which meets the high-accuracy requirement of pointing for the automatic optical link establishment.