Showing papers presented at "Theory of Cryptography Conference in 1994"

A new error control scheme for high speed networks

Abstract: Many network applications require interprocess communication (IPC) services that are not supported by assisting transport protocol mechanisms. Large bandwidth-delay products of high-speed networks also make the existing control mechanisms such as those for flow and error control less efficient. Especially, new error control schemes that can provide variable degrees of error recovery according to the applications requirements are needed. The authors present the design, evaluation results, and implementation of a new error control scheme that addresses the error control requirement. The results show that the proposed error control scheme allows effective control of trade-off between the amount of error an application can tolerate and the amount of delay it suffers. >

Sensitivity loss of real-time DFT-based frequency excision with direct sequence spread-spectrum communication

Abstract: The capacity of direct sequence spread-spectrum modulation to reject narrow-band interference can be significantly improved by eliminating narrowband energy at the receiver (frequency excision) using algorithms that operate on the real time discrete Fourier transform of the received signal (RT-DFT-Based). These algorithms have the potential to adapt very quickly to a change in interference spectrum and eliminate multiple interferers, but to do this the decision of which frequency bins to excise must be made based on a very short observation time. Under these circumstances, the number of bins excised can be much larger than the number of bins containing narrow-band interference. The receive signal strength loss due to "over-excision" can be very significant and limits receive sensitivity. This paper shows theoretical over-excision losses of several heuristic algorithms. The sensitivity loss due to time weighting (or windowing) is presented for variable overlap and several different windows. These theoretical results are confirmed with simulation results and can be used to project sensitivity of PN spread spectrum systems that are located in a band that is also used by narrow-band systems. >

A multivariate rank sum test for network simulation validation

Abstract: A primary goal of any verification and validation process should be to enhance both the correctness of a simulation and the confidence placed in its results. One challenge is to develop a process that is at the same time feasible and compatible with an organization's needs, and can be applied to both existing simulations as well as new ones. Multivariate methods can be used to test the hypothesis of agreement between simulated predictions and empirical observations. This paper describes a statistical test useful for the validation of simulations of battlefield communications networks. The method employs a multivariate nonparametric rank sum test with the aid of a computer-intensive randomization procedure to assess the significance of the defined test statistic. For illustrative purposes, the validation procedure is applied to a simulation that was developed to duplicate a configuration tested, in which "messages" were passed over a communications network using the combination of the Tactical Fire Direction System (TACFIRE) protocol and Single-Channel Ground and Airborne Radio System (SINCGARS) Combat Net Radios (CNR). The purpose of this research is to strengthen the link between experimentation and simulation, both of which should be utilized in evaluating communications systems' measures of performance (MOP). >

Implementation of the single cycle detector using the signal processing workstation

Abstract: Detection of unknown signals is often accomplished using energy detection devices, such as the wideband, or total power, radiometer. While this is an effective approach for stationary signals and background noise, much attention has lately focused on the use of other detection methods, such as time-frequency analysis and spectral correlation. This paper investigates the simulation of a single cycle detector, which provides some immunity to the effects of interference and non-stationary noise backgrounds, through the exploitation of the cyclostationary properties of most communications signals. Comparisons of the single cycle detector and the radiometer are made through the use of receiver operating characteristics curves, obtained through simulations using COMDISCO's signal processing workstation (SPW). >

Soldier's radio: innovative communication and networking technologies for the individual warrior

Abstract: Research at InterDigital Communications Corp. on a distributed control wireless broadband-code division multiple access (B-CDMA) mobile multimedia cellular network (MMC-NET) using an asynchronous transfer mode (ATM) cell based architecture and connected to various backbone networks, such as ATM/SONET, is discussed. The main objective of the MMC-NET architecture is to provide secure, seamless, theater-wide, multimedia communications. Some attributes of this wireless B-CDMA based MMC-NET are: mobility, multimedia capabilities, distributed control, B-CDMA, security, scalability, interoperability, reconfigurability, LPI/LPJ, ability to work as part of the global grid system and capable in being incorporated into the synthetic theater of war (STW) mobile defense simulation internet (DSI). The design specifications of the network along with its interface to ATM/SONETs are based on the OSI model. Some system characteristics and strategies in meeting the above objectives are discussed. >

Security architecture for tactical/strategic interoperability

Abstract: The technology and market forces have influenced the way we view the world of tactical and strategic communications. Our view of secure communications has always seen the strategic world as unique from the mobile platforms of the tactical world. Interoperability of such systems has always been a goal but has never become a reality. This has changed as a result of the Gulf War. In the Gulf War operation, the demand far an interoperable mix of tactical and strategic resources revealed significant weaknesses. Today, with such concepts as Global Grid and Command Control Communications Computers and Intelligence for the Warrior (C4IFIW), it has grown into a requirement where anyone, any place, at any time can talk to anybody. This expanded view of interoperability coupled with the fact that new communication products are introduced every twelve to eighteen months has forced us to look at providing security for the diverse products and networks in a new way. This paper describes a high level architectural methodology for developing future tactical to strategic interoperability while addressing security concerns. >

Throughput of a FHMA system for variable rate coding and interference estimates

Abstract: Frequency hopped multiple access (FHMA) systems are sed to provide a secure link in military communication systems. The author considers a decentralized FHMA packet communication system in which a collection transmitter-receiver pairs share a common channel. One criterion to measure the performance of a FHMA system effectively is the average normalized throughput. The optimum average normalized throughput of the system is a function of both the number of users simultaneously supported and the information rate of each user. This information rate is determined by the error correction code employed in the system. Intuitively, as the number of users increases the throughput will increase; however, the multi-user interference will require additional error protection, thereby lowering the information rate. For a given number of simultaneous users, there is an optimum code rate which maximizes throughput. The authors investigate the average normalized throughput performance of a FHMA system for several cases. There are two extreme cases: The case in which number of users in the system is unknown, but the probability is modeled as a random distribution, and the case in which the number of users is exactly known. The more interesting and practical case is the situation in which imperfect estimates of the number of active users are available. These estimates could be generated by monitoring a few frequency slots at any given time. The authors investigate the performance of the FHMA and the choice of optimal code rate for a variety this case. Reed-Solomon codes are considered. >

A framework for reliability modeling of electronics

Abstract: A physics-of-failure approach and the associated CADMP (computer aided design of microelectronic packages) software assist cost effective MCM (multichip module) designs scientific consideration of reliability during the design phase; evaluation of new materials, structures, and technologies; assessment of packages designed by different manufacturers; development of science-based tests, screens, and derating methods. The tools can also be used to assess reliability, of single chip package designs, including plastic encapsulated microcircuits (PEMs). The development and validation process for CADMP software continues. At present, the software is being exercised by over forty government and industry organizations, and feedback is being used to ready the software for commercialization. >

A narrowband/wideband packet radio system

Abstract: By transmitting packet headers on a narrowband channel, followed by packet data on a wideband channel, one can gain several advantages over using either narrowband or wideband techniques exclusively. All network nodes can easily obtain channel traffic loading and destination information by examining only the narrowband headers. Wideband synchronization is facilitated by using the end of the header transmission as a time index for wideband signal acquisition. Long signature sequences minimize the probability that two or more wideband packets will be transmitted with their sequences aligned, while avoiding the requirement that each receiver search for several different sequences as in a transmitter-oriented protocol. A common signature sequence facilitates packet broadcasting. Finally, flow control can be implemented by monitoring the CSMA narrowband channel and insuring that the network offered rate remains below the saturation point. >

A distributed routing algorithm for multihop packet radio networks with uni- and bi-directional links

Abstract: In multihop packet radio networks (PRNs) the nodes are not all within direct radio range of each other; to be able to forward the packets to their final destination the nodes must have enough knowledge about the network topology. This information is usually represented in the form of routing and distance tables. On a packet radio network the connectivity among the nodes can change due to several causes such as node or link failures and the presence of mobile nodes which can join or leave the network. This dynamic nature of the network topology requires that the tables at each node be continuously and accurately updated to avoid unnecessary delays or incorrect packet forwarding. The manner in which the packets are forwarded in the method proposed here is called incremental source routing, i.e. each node keeps a routing table which indicates the next hop (a node address) for each network final destination. Each packet is then delivered incrementally by the decisions made by each node in the path from source to destination. >

Telemetry: enhancing tactical network management

Abstract: A prototype was developed to process telemetry messages from tactical transmission assemblages in a digital group multiplexer (DGM) network and present status information to the nodal network manager. A data orderwire (DOW) system continuously forwards telemetry data from each DGM assemblage within the network. The DOW system is readily available for use, yet there is no capability at an Army tactical communications node to monitor the telemetry data within the DOW. Telemetry messages contain status information, including subcomponent alarms, for each DGM assemblage in the transmission network. This paper details the design approach for a telemetry processing prototype as well as background information on the DOW system. The telemetry processing prototype runs within a graphical user interface on a 486 personal computer (PC) that interfaces with the nodal communications system control element (CSCE) at each tactical communications node. The nodal CSCE contains the equipment which terminates the DOW. From a central location, the prototype can simultaneously monitor alarms from all DGM assemblages within a node's portion of the overall transmission network. Ongoing enhancements will extend the usefulness of telemetry data throughout the entire network, allowing the Army to project technical expertise in support of signal force projection. >

Probabilistic contention based forwarding in multihop packet radio networks

Abstract: The forward echelon battle area (FEBA) presents specific challenges for the use of packet radio in forward area communications. The FEBA is highly dynamic due to mobility of friendly and opposing forces, the uncertainty of battle action, severe and rapidly changing electromagnetic environment (EME) and rapidly varying communications load. These characteristics create challenges for communications systems that are to provide resilient, reliable, and survivable communications in this difficult environment. Packet radio is being proposed as a technology that can meet the communications challenges of the forward echelon battle area. Use of packet radio in forward area communications demands that the packet protocols automatically adapt to arbitrary and unforeseen multihop network topologies and unpredictable traffic conditions. An automatically adaptive forwarding protocol for multihop packet radio systems is presented. This forwarding protocol is compared to classic incremental-source forwarding. Performance figures developed using a detailed simulation are presented. >

Performance comparison of slotted and unslotted DS/SSMA networks

Abstract: Throughput and delay for both slotted and unslotted direct-sequence spread-spectrum multiple-access (DS/SSMA) packet radio networks are compared. In both systems, each user employs a newly chosen random signature sequence for each bit in a transmitted packet. Accurate packet success probabilities for both systems are computed using an improved Gaussian approximation technique. Average throughput and delay results are obtained for varying levels of block error correction. The slotted system is shown to have better performance than the unslotted system in all cases. >

Comparison of performance measures for intercept detectors

Abstract: The performance of intercept detectors is generally analyzed using the Neyman-Pearson criterion, which evaluates the probability of detection, P/sub d/, as a function of input signal-to-noise ratio (SNR) at a particular probability of false alarm, P/sub fa/. While the Neyman-Pearson criterion closely represents typical system requirements, it is often difficult to evaluate, and obscures important effects in tradeoff analyses. Consequently other performance measures, such as output SNR or the deflection, are often used instead. While the output SNR is useful for evaluating and optimizing a particular detector class, it may be inappropriate when applied to different detector classes. This paper examines the output SNR and probability of detection, for three intercept detectors: the radiometer, the chip rate detector, and the carrier harmonic detector (frequency doubler). The analysis makes the following assumptions: a direct-sequence pseudo-noise spread spectrum signal of interest additive stationary white Gaussian-distributed noise background with fixed known power (i.e., no noise power uncertainty) known power spectral density of the signal of interest input SNR much less than unity observation time much greater than the chip duration. The analysis highlights the danger of blindly evaluating detector performance solely by output SNR. Specific examples are identified in which the radiometer's performance, using the Neyman-Pearson criterion, is inferior to that of the cyclostationary feature detectors operating at equal output SNR for the decision variable. >

Serial and parallel demodulation trade-offs for QBL-MSK

Abstract: The authors discuss quasi bandlimited MSK. Analytical and simulated BER performance results for both carrier phase and bit synchronization timing errors were determined for serial and parallel demodulation. For a nonlimited modulated signal and ideal demodulator (no carrier phase or timing error), a BER degradation of 0.41 dB with respect to MSK performance is achieved for both serial and parallel demodulators with the sub-optimum data filter. A limited modulation signal increases the BER degradation by no more than 0.2 dB for both demodulator architectures. Serial demodulation is shown to be less sensitive to carrier phase error, while parallel demodulation offers less sensitivity to timing error. For both carrier phase and timing errors, the serial demodulator will provide less BER degradation than the parallel, if the timing error is kept small. Serial demodulation using average zero crossing bit synchronization is shown to provide either the same or less than a 0.1 dB increase in BER degradation as compared to that obtained with maximum eye opening synchronization. This result is significant, since average zero crossing synchronization is easily implemented in hardware. >

VHF forward area battlefield internet simulation

Abstract: A simulation of the forward area battlefield (FAB) Internet communication system using SINCGARS SIP (system improvement program) and ITT's battlefield enhanced MIL-STD-188-220 protocol has been performed. The preliminary results are promising in meeting the future requirements of a digitized battlefield. It shows that by using a horizontal net architecture, adjacent platoons belonging to different companies can share an up-to-date situation awareness database and still have the capacity to handle normal mixed voice and data communications. >

Detection of multiple access low-probability-of-intercept networks

Abstract: Increased demands for highly connective, yet covert, communications in the tactical battlefield have fueled the development of so-called multiple access low-probability-of-intercept (MALPI) networks. Although there have been a number of research efforts regarding the design of MALPI networks, detectability analyses are typically carried out for a single network transmitter, rather than for the network at large. In this paper, we present a slightly different approach to analyzing the detectability of a MALPI network. It is assumed that the interceptor knows the basic parameters of the waveforms used (i.e., total bandwidth, number of channels, frequency hop rate, etc.). However, in the network detection scenario, we assume that the detection of any transmission(s) within the network by an unauthorised listener effectively compromises the network. What distinguishes this approach from conventional link intercept analysis is that the detection decision is based on reception of signal energy from multiple sources. Frequency hop code division multiple access (FH-CDMA) is considered. >

High-speed frequency synthesizer for spread spectrum communication systems

Abstract: A high-speed direct digital frequency synthesizer has been designed for ultra-fast frequency-hopped spread spectrum applications. It is called the low-latency residue synthesizer (LLRS) and exhibits frequency switching times which are reduced by more than 50% below previously published designs. The switching speed advantage is made possible by the use of the residue number system and one-hot encoding of phase information. Pipeline lengths in the phase accumulator and other circuitry are thereby reduced significantly. >

Multiple-packet forwarding protocols for frequency-hop packet radio networks

Abstract: Reliable data distribution within spread-spectrum packet radio networks requires high performance from the network protocols. The high variability of the qualities of the links and the unique characteristics of frequency-hop spread-spectrum signaling impose special requirements for network protocols that are to be employed in frequency-hop packet radio networks. These features can be exploited in the forwarding protocols by allowing multiple packets to be included in each forwarding attempt. The use of multiple-packet transmissions exploits the capture property of frequency-hop signaling, and it reduces the overhead required for acknowledgments. In general, a potential tradeoff arises because the use of multiple-packet transmissions increases the throughput, but it can also increase the delay. In certain situations, however, the delay is decreased with the use of multiple-packet transmissions, or at least the increase in delay is not too great. Two new transmission protocols that employ multiple-packet transmissions are described, and their performance is evaluated. >

Wideband frequency selective limiter

Abstract: A novel technique for narrowband/broadband frequency selective limiting in direct sequence-spread spectrum (DS-SS) communications is presented. This technique relies on setting the magnitude response of the received signal Fourier transform to a predetermined function while leaving the phase response unchanged. When the Fourier transform magnitude response of the signal is made constant over the entire signal spectrum, this nonlinear processor will operate as a whitening filter. The processor is particularly attractive in environments where many interferers of different powers coexist in the same frequency band with the desired signal (e.g. wideband HF communications). The only requirement imposed by the processor is that the desired signal must be broadband relative to the interferer(s). This requirement is in general fulfilled by a wide class of communication and radar signals such as DS-SS, hybrid FK/DS-SS, and WB-FM (chirp radar signals). >

Adaptive FSK decoding with an artificial neural network

Abstract: We describe an empirical study of the capability of an artificial neural network (ANN) to decode a frequency shift key (FSK) signal. An algorithm for generating a minimal, yet comprehensive ANN training data set is discussed. The FSK signal is over sampled. The samples are presented to the ANN as a window in time. The window is one symbol wide. After initial training, white Gaussian noise is added to the samples and the ANN's ability to generalize is tested. We then conduct additional training, using the noisy data, to test the ANN's ability to adaptively recover. Simulation results are reported. >

HF to wireline modem conversion

Abstract: The advent of personal communication systems (PCS) will provide global connectivity over commercial communication networks. Small, inexpensive, low-power terminals that are becoming available support this connectivity, provided that the user is reasonably close to a base station. Similar efforts are underway to provide extended connectivity to military users. The problems here are somewhat different because the communications often need to be end-to-end secure and because there often is no fixed infrastructure (base stations). The paper describes the design of an HF to wireline modem converter that plays the role of a radio-wireline interface (RWI). The RWI acts as a gateway between tactical communications equipment (for example, MINTERM) and strategic (STU III). >

A generalized frequency correction technique for multiple access satellite communication networks

Abstract: The frequency correction mechanism used within each earth terminal will typically control both transmit and tuned receiver frequencies, the latter being the center of the frequency window over which a receiving terminal searches for a signal. This frequency correction is sometimes referred to as frequency tracking because the controlled corrections are updated periodically to track changes in the contributing sources of these offsets. The technique presented generalizes one previously studied by Chandler (see IEEE Tactical Communications Conference (TCC-90) Proceedings, p.369-379, April 1990). It can be applied to time division multiple access (TDMA) networks where the measured receive frequencies of specific burst signals are used to adjust both the transmitter frequency and the tuned receiver frequency for signals that are later transmitted or received. The primary objectives of this study are to demonstrate that the technique of the previous study can be generalized by applying it successively to multiple signal types, to demonstrate that the procedure for optimizing the frequency correction factors of the previous study can be used for each of the multiple components or signal types of the generalized technique, and to illustrate by examples the performance improvement achieved by using the generalized technique with multiple signal types as opposed to the single-component technique based on one signal type. >

Performance of direct-sequence spread-spectrum in a multipath fading environment with error control coding

Abstract: The performance of a coherent communication system using direct-sequence spread-spectrum in specular multipath fading is analyzed in terms of average probability of error. Approximations to such are based on the characteristic-function method. The probability mass function of the correlation receiver output is also derived with this approach. Numerical results on the error probability are presented for various multipath environments with channel coding. >

Spread spectrum technology for the command post on the move

Abstract: Discusses the operating conditions for broadband CDMA cellular systems as they may be used for mobile command posts The authors conclude that the mobile command post will permit communication of voice and data with no performance degradation as compared to a fixed command post >

Rain outage modeling for tactical applications

Abstract: The rain propagation-reliability forecasting method provided improves the planning of tactical communications networks by including expected rain-fall in the planning process Forecasting has stimulated new approaches to network planning and management Calendar-month performance engineering of SHF links in network planning has been made possible by the rain propagation-reliability forecasting method >

Communications reliability of tactical wideband radio systems

Abstract: Describes the efforts of the US Army's Communications Electronics Command (CECOM) in the areas of realistic communications-channel modeling, realtime simulation of on-the-move tactical communications, and a high capacity digital radio communications performance model. The paper concludes with an illustration of using the digital radio performance model to determine maximum link lengths telecomm. >

Achieving open interoperability in tactical remoted systems with COTS technology

Abstract: Interoperability between systems is increasingly important within the military community. Traditionally, many tactical systems have been implemented as self-contained entities, incapable or minimally capable of interoperation with systems of different versions, vendors, and military branches. This has certainly been true of remoted signals intelligence (SIGINT) systems. Custom protocols and architectures, unique to each system, have frequently been justified as necessary to meet operations requirements. The real-time sharing of resources or data between systems has not been feasible. This approach is costly and inflexible. This paper describes the approach taken by SRI International (SRI) to address this problem. Our goal was to define an interoperability architecture for remoted SIGINT systems; this architecture must be open and based on international standards and commercially available products. Key to our architecture is the use at the application layer of the ISO 9506 Manufacturing Message Specification (MMS) protocol standard for the control of remote devices. We validated our approach by implementing a demonstration system consisting primarily of commercial off-the-shelf (COTS) hardware and software products, within a testbed environment. The results of this effort have shown that open, interoperable systems can be developed with commercial technology, thereby reducing implementation effort and cost. The structure of this paper is as follows. First, we present an example of the problem of interoperability in tactical remoted systems, and specifically within tactical airborne SIGINT systems; we then present our method for solving this problem through the use of open COTS technology; and finally, we summarize the lessons learned from taking this approach. >