Frequency Hopping Spread Spectrum Technique Research Articles

Photonics based frequency hopping spread spectrum system for secure terahertz communications.

Terahertz (THz) spectrum (100 GHz-10 THz) is considered the next frontier in the design of high-speed wireless communication systems. While the high-power THz sources have commercially become available, it increases the possibility of developing THz jammers to disrupt the THz communication link. Therefore, the development of novel anti-jamming solutions is the need of the hour. In this work, we present the photonics-based THz communication system and demonstrate the frequency hopping spread spectrum (FHSS) technique which acts against the single/multi-tone jamming attack in the frequency window of 110 GHz-170 GHz. By tuning the output wavelength of the distributed feedback lasers, the THz carrier frequencies are swept back and forth within the scanning window. The frequency tuning range was measured for different scanning rates of the laser which decreases rapidly with the increase in the scanning rate. Next, we demonstrate the THz FHSS technique in a real-time communication system by transmitting a 6 Gbps NRZ signal in both wireless and THz-fiber-based links within the link distance of 1.75 m. We experimentally found that the measured bit error rate in the THz FHSS system is the time average of the measured BER for individual carrier frequencies within the hopping frequency window. By combining with the forward error correction codes and by using the tunable filter in the receiver, we believe that the proposed technique will offer a novel and compact solution against the single/multi-tone jammer for high-bit rate THz communications.

Prenos u proširenom spektru - frekvencijsko skakanje - istorija, principi i primena

Introduction/purpose: The frequency hopping spread spectrum (FH-SS) technique assumes the carrier generated by the syntesizer to hop from frequency to frequency over a wide bandwidth, according to a pseudonoise code sequence defined by the code sequence generator. The article presents the history, principles and applications of the FH-SS technique. Both military and commercial applications are discussed. Methods: This article presents an overview of data from the technical literature, with appropriate comments. Results: After presenting the history and principles of the FH-SS technique, the article summarizes its use with examples of military and commercial applications. The importance of using FH-SS in the described applications is highlighted. Conclusion: The FH-SS technique has been successfully implemented in many military and commercial technologies due to its high protection against interference, making communication difficult for reconnaissance and eavesdropping, and its ability to provide code division multiple access.

Interference Rejection in FH/BFSK System Using Blind Source Separation

This paper introduces a new approach based on blind source separation (BSS) to mit igate intentional interference in BFSK d igital co mmun ication systems using frequency hopping spread spectrum technique. The use of BSS is possible thanks to adopting an adequate selection block to distinguish between the useful signal and other undesirable signals, hence, circu mvent the problem of amb iguity of permutation. An analytical calculation of the probability of error to predict the performance is done. The simulat ion results showed the effectiveness of this approach, whatever the level of the JSR and without using the fast frequency hopping alternative or error-correcting codes.

Conducted Emission Reduction by Frequency Hopping Spread Spectrum Techniques

Spreading the switching frequency of a DC–DC converter is a cost effective method for reducing conducted emission. In this paper the main objective is to implement spread spectrum techniques in a digitally controlled DC–DC converter and to reduce conducted emission by modulation. To vary the switching frequency the spectrum can be spread across a band of frequencies and thus reducing the peak amplitude at individual frequencies. Here we introduce two methods Bifrequency technique and spread spectrum techniques. The effect of these techniques in ripple current and output ripple will be analyzed. The analysis is carried out on a digital DC–DC converter which has a PID based control device.

One Tooth, Two Tooth, Green Tooth, Bluetooth, Part I

One Tooth, Two Tooth, Green Tooth, Bluetooth, Part I

An effective defensive node against jamming attacks in sensor networks

AbstractJamming is defined as the act of intentionally directing electromagnetic energy towards a communication system to disrupt or prevent signal transmission. In the context of wireless sensor networks (WSNs), jamming is the type of attack which interferes with the radio frequencies used by sensor nodes and may be viewed as a special case of denial of service (DoS) attacks. Herein, we outline the possible jamming attacks a WSN may encounter. The main contribution of this paper is the outline of the design specifications of a prototype node ‘Ares’ that effectively defends jamming attacks. Our focus is on frequency hopping spread spectrum (FHSS) and direct sequence spread spectrum (DSSS), two of the most effective countermeasures against jamming. The main novel aspect of Ares is that it uses a hybrid FHSS–DSSS approach to defend jamming attacks. We suggest the use of a specific FHSS technique in 5 GHz band with 51 frequency channels wherein the channel sequence is generated using a key (which derives from a secret word), known only to the sink and the sensor nodes, as a seed. Each channel uses DSSS modulation with 16‐bit pseudo noise (PN) code. The PN code derives from the same key used for FHSS channel generation. The pre‐eminence of our method against alternative anti‐jamming techniques is demonstrated through extensive simulation tests. Copyright © 2008 John Wiley & Sons, Ltd.

Low cost architecture of direct conversion digital receiver

The paper presents a low-cost architecture for a direct conversion digital receiver that uses six-port technology. An experimental prototype has been constructed and tested. Analogue carrier recovery and decision circuits are investigated as a means to provide future system integration and high data rate capacity. The designed receiver is operated at an ISM frequency of 2.45 GHz and uses a QPSK modulation format. Results on data rate limitations are given for QPSK signals up to 52 Mb/s. Test results related to adjacent channel, co-channel and CW interferences are presented for a data rate of 40 Mb/s. Phase offset between carrier and reference signals, along with carrier frequency deviation performances, are also presented for a rate of 40 Mb/s. A frequency hopping spread spectrum technique is discussed on the basis of the proposed architecture.

Frequency adaptation efficiency of spread spectrum communications under narrowband interference

We investigate a new possibility of frequency adaptation for spread spectrum communication systems. A special index is introduced to characterize the adaptation gain referring to the nonadaptive case. An existence of frequency band limit is developed for the allocated frequency band for possible frequency maneuver. The investigation method can be adapted both to direct sequence and frequency hopping spread spectrum techniques. In the paper only the narrowband interference case is treated

Using frequency hopping spread spectrum technique to combat multipath interference in a multiaccessing environment

The purpose of this paper is to conduct performance analysis for a frequency-hopped spread spectrum multiaccess network which is subject to the threat of multipath interference. Baseband modulation is done through frequency shift keying and signal detection is accomplished by a noncoherent type receiver. The quality of a signal is affected by the channel noise, multiuser interference, and multipath interference. Performance analysis is conducted on the basis of bit error rate. Due to the sophistication of the system exact analysis is not feasible. The accuracy of approximation is checked against simulations. One major discovery Is that when signal-to-noise ratio is low, multipath interference on the contrary may help to enhance the quality of the signal. Another discovery is that when signal-to-noise ratio is high enough, multipath/multiuser interference becomes the bottleneck of performance. The effect of channel noise can be eliminated by maintaining a large signal-to-noise ratio while spread spectrum technique is employed to reduce the effect of multipath/multiuser interference.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Applications of Frequency Hopping Spread Spectrum Techniques: An Overview

Frequency hopping spread spectrum techniques have been successfully implemented in many space systems and avionics systems for multiple access communications, protection against jamming and interfe...