Antijam Systems Research Articles

Study on LDPC Coded SFH System with Multi-Tone Interference

Low-Density Parity-Check code, for its admiring performance which is close to the Shannon limit, has attracted large attention in anti-jamming systems. In this paper, we studied the LDPC coded slow frequency-hopping (SFH) system and analyzed its performance with Multi-tone Interference (MTI). Three modulation schemes (BPSK, QPSK and 8PSK) are adopted in the system. Especially for 8PSK, we compared the performance of two different soft-decision demodulation schemes over additive white Gaussian noise (AWGN) channel. Also, the influences of code rate, code length, modulation scheme and jamming mode are analyzed and examined, respectively. Finally, some valuable guidelines for designing LDPC coded SFH system are proposed. Simulation results demonstrate that a desirable performance can be achieved with the appropriately designed LDPC in SFH system.

Broadcast anti-jamming systems

In a traditional anti-jamming system a transmitter who wants to send a signal to a single receiver spreads the signal power over a wide frequency spectrum with the aim of stopping a jammer from blocking the transmission. In this paper, we consider the case that there are multiple receivers and the transmitter wants to broadcast a message to all receivers such that colluding groups of receivers cannot jam the reception of any other receiver. We propose efficient coding methods that achieve this goal and link this problem to well-known problems in combinatorics. We also link a generalisation of this problem to the Key Distribution Pattern problem studied in combinatorial cryptography.

A perspective on the evolution of multiple access satellite communication

The evolution of communication satellites is reviewed, with an emphasis on multiple access by large populations of users employing mobile and personal terminals. It is argued that the basic problem of mutual interference rejection is most effectively solved by employing modern digital technology to implement spread-spectrum modulation systems based on military antijam communication systems which are inherently robust to interference. A perspective on the impact of this approach on future networks of low-Earth-orbit satellites is presented, along with concluding remarks on the well-established theoretical foundations of emerging satellite technologies. >

Performance of diversity combining techniques for DS/DPSK signaling over a pulsed jammed multipath-fading channel

The effectiveness of antenna and spread-spectrum diversity is evaluated for direct-sequence differential phase-shift-keyed signaling over a worst-case pulse-jammed multipath-fading channel. Two diversity combining techniques are proposed. One uses predetection selective combining followed by postdetection equal-gain combining, and the other uses only postdetection equal-gain combining. The use of coding with hard and soft decision decoding is also considered. It is shown that the proposed diversity techniques can provide a significant improvement in the performance of coded antijam systems operating over jammed multipath-fading channels. >

Performance of Adaptive Transmission for FH/MFSK Signaling Over Jammed Fading Channels

This paper gives an evaluation of the performance of adaptive signaling techniques for jammed fading channels. These techniques perform remarkably well for fading channels with AWGN. The performance of both uncoded and coded systems is examined in the presence of jamming. Adaptive signaling schemes are shown to offer little improvement for uncoded antijam systems. However, for coded antijam systems, they provide improvements in the performance and, in some cases, simplify the receiver implementation.

A comparison between frequency hopping and direct spread pn as antijam techniques

FREQUENCY Hopping (FH) and Direct Spread Pseudonoise (PN) are the signal processing techniques most often used to achieve an antijam capability. However, comparisons between the techniques in order to determine relative superiority have often been marred in the past by one-sided defenses of one technique or the other. In this paper, an unbiased and comprehensive comparison between the two techniques is presented. The comparison is based on the premise that neither technique is categorically superior, and compares the relative merit of the two techniques for each of a number of issues relevant to antijam systems. By noting both the important issues for a particular application and the relative performance of the two techniques for those important issues, support can be provided for the process of selecting the appropriate technique.

Theory of Spread-Spectrum Communications - A Tutorial

Spread-spectrum communications, with its inherent interference attenuation capability, has over the years become an increasingly popular technique for use in many different systems. Applications range from antijam systems, to code division multiple access systems, to systems designed to combat multipath. It is the intention of this paper to provide a tutorial treatment of the theory of spread-spectrum communications, including a discussion on the applications referred to above, on the properties of common spreading sequences, and on techniques that can be used for acquisition and tracking.

Coded Error Probability Evaluation for Antijam Communication Systems

Presents a general union-Chernoff bound on the bit error probability for coded communication systems and apply it to examples of antijam systems. The key feature of this bound is the decoupling of the coding aspects of the system from the remaining part of the communication system which includes jamming, suboptimum detectors, and arbitrary decoding metrics which may or may not use jammer state knowledge.

Performance Criteria for Spread Spectrum Communications

The criteria for antijam (AJ) and anti-intercept (AI) systems are described, in terms of the appropriate action taken by the jammer or interceptor. Avoiding pseudonoise (PN) sequences which can be partially or totally predicted is a foremost criteria, especially for AJ, and use of nonlinear feedforward logic (NFFL) with long-period linear maximal sequences appears attractive. A frequency-hopping (FH) system must anticipate a multitone jamming signal, and an error-control code is necessary. A novel method for generating a multitone signal using repeating maximal sequences is described. PN systems must anticipate a tone jammer, and now an errorcontrol code may be needed to assure that sporadic PN sequence correlation with the tone does not reduce the processing gain. Any AI system must anticipate that the interceptor may, if advantageous, integrate his decision energy over many communicator symbols (up to the message length). Now spreading both in frequency and in time may be valuable. Finally, the use of an automatic adaptive data rate is suggested to realize flexibly either AJ or AI objectives.