William N. Furman

The Secure Communication Interoperability Protocol (SCIP) over a VHF/UHF radio channel

The secure communication interoperability protocol (SCIP) is a newly emerging application layer interoperability standard that is being developed for secure voice and data communication between international coalition partners. It was designed to operate independently of the characteristics of underlying media layers. This paper will present the results of an investigation into the performance of the SCIP point to multi-point protocol over a VHF radio narrowband channel and the SCIP point to point protocol over a VHF wideband channel. An ldquoover the airrdquo field demonstration using the Harris AN/PRC-117G multiband Manpack was designed and is described. Voice quality performance data was gathered over a range of radio configurations and channel conditions. Performance data is presented along with discussion and recommendations on future work.

Waveform and RF power amplifier interdependencies in battery-powered tactical radio applications

This paper will examine the subtle interdependencies of physical layer waveforms and RF power amplifiers when applied to a battery-powered tactical radio system. Traditional physical layer analysis usually compares the signal-to-noise ratio (SNR) required to achieve a desired bit error rate (BER) but does not consider how the peak-power to average-power ratio (PAPR) of the waveform will affect the design and performance of the power amplifier. This paper will address both the BER performance of physical layer waveforms and the class/efficiency/power constraints of power amplifiers for use in a battery-powered tactical environment.

Channel Quality Variation as a Design Consideration for Wireless Data Link Protocols

The data link protocol HDL+, which has been proposed for incorporation into NATO STANAG 4538, employs an innovative combination of Type II Hybrid-ARQ techniques with real-time adaptation of signal constellation and code rate to achieve high throughput performance under a wide variety of channel conditions. The ionospheric HF channels for which HDL+ was designed exhibit important variations in channel quality (SNR, fading and multipath chcracteristics) at a variety of time scales from seconds to minutes. It appears plausible that the design characteristics of the HDL+ protocol couldprove especially valuable in coping with time-varying channel quality over these time scales. In this paper, we ¿ Present and discuss a model of channel quality variation and a way of incorporating it into an ionospheric channel simulator suitable for performance characterization of HF communications waveforms andprotocols ¿ Provide overviews of HDL+ and of the STANAG 5066 data link protocol, a widely-used protocol based on conventional (not hybrid) ARQ techniques ¿ Present and discuss comparative performance data for the HDL+ and STANAG 5066 protocols obtained under test conditions including channel quality variation.

An active squelch technique for HF communication systems

A reliable squelch feature has long been a difficult goal in the low signal to noise ratio and high interference environments typical of HF links. Many passive techniques have been attempted and implemented. These passive techniques range from simple power measurement to elaborate neural network based speech detection systems. All of these approaches suffer from a decrease in reliability as channel conditions degrade due to the presence of noise and interference. However, it is under these degraded channel conditions where a reliable squelch function is most desirable to reduce operator fatigue. In addition, a reliable squelch function can be useful in the implementation of HF/HF or HF/VHF automated re-transmission systems, or as the basis for a robust field radio wakeup feature. This paper will discuss the design and implementation of an HF squelch system based on a burst serial tone waveform that operates in low signal to noise ratio and high narrowband and impulsive interference environments. The paper will present our initial design goals, an implementation overview, and final system performance. Performance data, including the rate of false unsquelch occurrences and the probability of missed unsquelch in various channel conditions will also be presented.

Evaluation and optimization of data link protocols for HF data communication systems

The authors discuss channel behavior based on measured signal and noise variations. A simulation model is presented which replicates the observed variations. The results of applying the simulation model to three different data link protocols, including a new fast automatic link establishment (ALE) technique are discussed.<<ETX>>

HF data link protocol RF simulator performance based on STANAG 4538 and STANAG 4539

STANAG 4538 (S4538) defines a pair of ARQ protocols that provide error free data transfer between HF terminals or nodes. These protocols utilize a form of code combining to automatically adapt to the conditions of the HF channel. The achievable throughput of these data link protocols is limited by the choice of the underlying waveform. STANAG 4539 (S4539) defines a set of high data rate HF modem waveforms that provide on-air data rates up to 12,800 bps. The data link protocols developed by Harris Corporation and discussed in this paper, HDL+, apply the code combining concepts to the higher capacity data waveforms of S4539. HDL+ is currently being considered by the NATO HF radio ad hoc working group as an enhancement to S4538. The paper begins with an overview of the current definition of HDL+ highlighting several waveform level improvements that provide better throughput and lower latency than existing standard approaches, when channel conditions allow. The paper continues by presenting throughput performance measured on the AN/PRC-150C HF tactical radio using a hardware RF channel simulator setup comparing HDL+ with the data link protocol defined in S4538. The paper also presents comparison data of IP message load versus message delivered for a simple mesh network using the same RF simulator setup.

Image compression and transmission for HF radio systems

This paper presents a novel image compression technique coupled with three HF transmission schemes. The image compression scheme is based on a phase dispersion technique originally developed for the design of pulse compression radar waveforms. The technique forms the basis for a lossless, invertible transform that converts sub-band coefficients to an intermediate domain. This image compression scheme generates significance map bits, which must be transferred across the HF link error free (hard bits) as well as magnitude vectors, which can sustain some degree of received errors (soft bits). The paper gives a brief overview of the image compression scheme followed by a discussion of three transmission schemes. The first transmission scheme investigated is the forward transmission HF modem. In this technique an HF modem is utilized set at an appropriate on-air data rate for the current HF channel conditions. This is a one way broadcast technique with no feedback from the destination. The second transmission scheme investigated is an automatic repeat request (ARQ) technique. This technique utilizes requests from the destination to resend data packets received in error and guarantees error free transmission of the image data. The third transmission scheme examined is a hybrid scheme, which couples an ARQ technique for the error free delivery of the hard bits with a forward transmission HF modem to provide good protection for the soft bits.

An enhanced prediction error filter design for hopped direct sequence spread spectrum (DSSS) receivers

Prediction error filter (PEF) design for narrowband interference (NBI) excision is examined for a hopped direct-sequence spread-spectrum system. The PEF is obtained by application of the Levinson Durbin algorithm (LDA). Several enhancements are utilized: unbiased autocorrelation estimation and normalization. LDA modification, and PEF weight normalization. The resulting composite technique provides a high-performance excision algorithm.<<ETX>>