Spread Spectrum Communication Technique Research Articles

Low-power DSSS transmitter and its VLSI implementation

An interesting area of application in wireless data communication is direct-sequence spread spectrum (DSSS). Spread spectrum communication techniques make the signals more robust against interference and jamming. These are based on a concept that narrowband signal is scrambled before transmission in such a way that the signals occupy a much larger part of the radio frequency spectrum. As the digital and the analogue system components are required on the same substrate in today’s mixed-signal chips, the DSSS transmitter system is proposed to be implemented in field-programmable gate array (FPGA)–based platforms and application-specific integrated circuits (ASICs). With a low-power very large-scale integration (VLSI) architecture, sophisticated processing of wide-bandwidth DSSS systems can be exploited in FPGAs/ASICs. In this article, binary pseudo-noise (PN) sequences are generated using a low-power linear feedback shift register (LFSR) in order to spread transmit signals extensively. The proposed low-power design of LFSR and DSSS transmitter with implementation results is illustrated in this paper. Dynamic power dissipation of the proposed DSSS transmitter is reduced up to 15% and 15.6% when compared to the conventional LFSR and the Gold code–based systems respectively. The proposed hardware is implemented in 180-nm technology and operates at 15.36-MHz frequency.

Invalidating Idealized BGP Security Proposals and Countermeasures

Border Gateway Protocol (BGP) is vulnerable to routing attacks because of the lack of inherent verification mechanism. Several secure BGP schemes have been proposed to prevent routing attacks by leveraging cryptographic verification of BGP routing updates. In this paper, we present a new type of attacks, called TIGER, which aims to invalidate the “proven” security of these secure BGP schemes and allow ASes to announce forged routes even under full deployment of any existing secure BGP proposal. By launching TIGER attacks, malicious ASes can easily generate and announce forged routes which can be successfully verified by the existing secure BGP schemes. Furthermore, TIGER attacks can evade existing routing anomaly detection schemes by guaranteeing routing data-plane availability and consistency of control- and data-plane. Toward a new securing BGP scheme, we propose Anti-TIGER to detect and defend against TIGER attacks. Anti-TIGER enables robust TIGER detection by collaborations between ASes. In particular, we leverage Spread Spectrum Communication technique to watermark certain special probing packets, which manifest the existence of TIGER attacks. Anti-TIGER does not require any modifications in routing data-plane, therefore it is easy to deploy and incrementally deployable. We evaluate the effectiveness of TIGER and Anti-TIGER by experiments with real AS topologies of the Internet. Our experiment results show that TIGER attacks can successfully hijack a considerable number of prefixes. In the meanwhile, Anti-TIGER can achieve 100 percent detection ratio of TIGER attacks.

A motion tracking method that applies a spread spectrum communication technique to tagging MR imaging.

We propose a new motion tracking method that encodes an object's position information using tagging magnetic resonance (MR) images as digital codes, and we assess the method's feasibility in stationary and moving phantoms. The encoding and decoding of tag patterns employ principles of spread spectrum communication. We used a segmented fast low angle shot cine sequence (FLASH) with spatial modulation of magnetization (SPAMM) preparation pulses to encode position information as 7-bit code words and used this spread code to decode the position information. To make 7-bit code words using tag images, we adjusted the flip angle and phase of the 4 composite radiofrequency (RF) pulses and the gradient magnetic field strength in the SPAMM pulse to generate 7 types of tag patterns. The proposed method required 7 acquisitions with 7 types of tag patterns. We compared results with images obtained by conventional tagging in stationary and moving phantom experiments. In a stationary phantom, the proposed method showed the same ability to identify pixel position as conventional tagging method using improved SNR images with the average of 7 acquisitions. In a moving phantom, pixel position was successfully decoded by the proposed method on a pixel-by-pixel basis. In this method, the motion of the phantom was detected by the simple calculation of the correlation coefficient of the code words. We introduced a spread spectrum communication technique to tagging MR imaging that regards tag patterns as digital codes, and we demonstrated the method's potential to detect pixel position in sub-pixel resolution.

Robust Segments Detector for De-Synchronization Resilient Audio Watermarking

A robust feature points detector for invariant audio watermarking is proposed in this paper. The audio segments centering at the detected feature points are extracted for both watermark embedding and extraction. These feature points are invariant to various attacks and will not be changed much for maintaining high auditory quality. Besides, high robustness and inaudibility can be achieved by embedding the watermark into the approximation coefficients of Stationary Wavelet Transform (SWT) domain, which is shift invariant. The spread spectrum communication technique is adopted to embed the watermark. Experimental results show that the proposed Robust Audio Segments Extractor (RASE) and the watermarking scheme are not only robust against common audio signal processing, such as low-pass filtering, MP3 compression, echo addition, volume change, and normalization; and distortions introduced in Stir-mark benchmark for Audio; but also robust against synchronization geometric distortions simultaneously, such as resample time-scale modification (TSM) with scaling factors up to ±50%, pitch invariant TSM by ±50%, and tempo invariant pitch shifting by ±50%. In general, the proposed scheme can well resist various attacks by the joint RASE and SWT approach, which performs much better comparing with the existing state-of-the art methods.

A proposal of a vehicle network using intervehicle transmission method

AbstractIn this paper, a mobile vehicle network is proposed to be utilized for intervehicle communication. A network building method is described based on using spread spectrum communication technique and establishing individual links between each vehicle while combining communication and distance measurement between the vehicles within a defined area. In order to more completely utilize network capability, a new concept of zone is introduced and defined. Along with the explanation of the network building method, the evaluation of practical usage of such networks based on computer simulation techniques is also provided. © 2001 Scripta Technica, Electron Comm Jpn Pt 1, 85(3): 40–50, 2002

OCDD/CDMA: a new DS/CDMA with orthonormal code diversity detection

The paper presents a new spread spectrum communication system called orthonormal code diversity detection (OCDD)/CDMA system based on the novel concept of orthonormal-basis diversity which is a generalization of the existing spread spectrum diversity concepts such as path diversity and frequency diversity. The OCDD/CDMA system is similar to the conventional DS/CDMA system in the transmitter structure, but is different in the receiver structure as it employs the extended orthonormal basis-function set which is the union of the Walsh basis-functions multiplied by the PN sequences and, optionally, their delayed replicas. The received signal is matched to the extended basis functions, and the matched signal components are combined together after individual channel compensation. The proposed OCDD/CDMA system exhibits the bit error performance which is much improved over the conventional DS/CDMA system using maximal ratio combing. In addition, it is robust to the chip timing error, which becomes more crucial in the future DS/CDMA systems having a higher data rate and smaller chip interval. From the simulation results, we confirm that the OCDD/CDMA system is a unique spread spectrum communication technique that can effectively increase the diversity utilization in the slowly fading channel, overcoming the inherent problems in the DS/CDMA and OFDM/CDMA systems.

Chaotic network synchronization with application to communications

AbstractChaotic signals are widely exploited for the spread spectrum communication technique. Synchronization of a chaotic communication system between a single point and multiple points is recognized as an essential issue. In this paper, a chaotic network synchronization scheme is proposed to tackle the problem of multi‐access synchronization. The proposed synchronization scheme enables the realization of a fast synchronization of multiple chaotic systems. In this paper, the proposed system is validated by application to direct‐sequence (DS) spread spectrum communication (SSC) with code division multiple access (CDMA). Promising results were obtained on the applications of speech, characters and image communications. The obtained results indicate that the proposed SSC is effective and reliable even under the situations of a noisy channel, and multi‐path interference. Copyright © 2001 John Wiley & Sons, Ltd.

A robust echo canceler for acoustic environments

This paper presents a novel acoustic echo canceler for teleconference and speakerphone systems based upon input orthogonalization and spread spectrum communication techniques. The new echo canceler represents a significant departure from traditional methods of removing acoustical echo and solves the open problem of echo cancellation during double-talk transmission. A decorrelation based adaptive filtering algorithm is introduced and its performance studied. A contraction mapping principle is applied to obtain a tight bound on the step size for the convergence of the adaptive algorithm. In conjunction, a direct sequence spread spectrum correlation technique is used to estimate the room impulse response during double-talk. Both components of the echo canceler rely on an innocuous wide-band training signal which is transmitted into the room along with the speech. The new echo canceler was implemented on a TMS320C30 DSP processor and experimental results are presented. The echo canceler was found to give excellent performance for all operating conditions, including during double-talk transmission.

A synchronized spread-spectrum local area network

As the number of nodes connected to a local area network increases, the network throughput decreases owing to channel contention. This is conventionally overcome by either upgrading the network channel bandwidth, and hence increasing the data rate, or introducing a hierarchical network structure. This paper describes an adaptation of spreadspectrum communication techniques, used by the military, to a localized network. The resulting system enables multiple simultaneous communications within a channel rather than the conventional single communication. Such a system is capable of retaining communications facilities in a heavily loaded multi-user environment.

Acoustical sensing by time delay spectrometry

Active acoustical sensing should utilize signal modalities with sufficient degrees of freedom to identify range, range rate, and those higher derivatives necessary to identify object rotation, as well as potential spectral properties which could be used for signature analysis of specific objects in a field. In addition, the specular nature of acoustic relfection from smooth objects demands signal processing which has substantial dynamic range along with good noise immunity. It is also shown that time delay spectrometry (TDS) is a modality which meets these requirements. The principles of TDS are developed as they apply to its use as a phase-coherent spread-spectrum communication technique. A constant amplitude signal with programmable phase structure is used as acoustic stimulus. System response to that stimulus consists of an ensemble of delayed replicas with complex amplitude and phase modulation. This can be interpreted as a signal whose dimensionality is determined by the degrees of freedom in the programmable phase structure. Selective spatial filtering followed by mapping to a lower-dimensional space can bring the property of interest to a usable form. This includes the conventional time domain reponses (range, rate,…) and frequency domain responses (spectrum, cepstrum,…).

The potential application of analogue matched and adaptive filters in spread-spectrum communications

Spread-spectrum communication techniques use a common wideband channel to obtain subscriber accessing in secure, jam resistant links. Phase shift keying (p.s.k.) and frequency hopping (f.h.) under the control of a pseudo-noise (p.n.) code are favoured signal waveforms. The paper reviews the performance of surface acoustic wave and charge-coupled device fixed coded and electronically programmable analogue matched filters for the detection of short (13 to 1023 chip) 1 kHz to 20 MHz chip (clock) rate p.n.-p.s.k. coded signals. The extension of these matched filters to accommodate the longer codes 10000 chips) and integration times (several milliseconds) used in current spread-spectrum systems is reviewed, and their importance in reducing synchronization acquisition is highlighted. Surface acoustic wave device approaches to synthesize and detect the alternative f.h. spread-spectrum waveforms are also discussed. The realizations of digitally-controlled coherent frequency synthesizers using s.a.w. chirp filters and bandpass filterbanks are highlighted. Finally the paper identifies the problem in many spread-spectrum systems, where the input-signal-to-interference ratio is so low that code matched filtering alone is not sufficient to detect the transmitted data, and it investigates the use of adaptive signal processing techniques for further suppression of wide and narrowband interference.

Spread spectrum communications--Myths and realities

Spread spectrum communication techniques date back to the early fifties. Since the earliest applications, system improvements have been more evolutionary than revolutionary. Like most improvements in electronic systems, these are due primarily to the availability of ever higher speed integrated circuit components, which translate in this case to wider spread spectra. In three decades the achievable spreading factor has grown by about three orders of magnitude’ to the point that we are now limited more by bandwidth allocations than by technology limitations. Before we xamine the quantitative effects of spreading, let us catalog briefly the multiple purposes of spread spectrum communications. First, we note that spreading here refers to expansion of the bandwidth well beyond what is required to transmit digital data. Thus, a system transmitting data at a rate ( R ) of 100 Mbits/s using approximately 100 MHz of bandwidth (W) is not spread at all, while a system transmitting at 100 bits/s spread over a spectrum of about 100 MHz has a factor W/R = 106, or 60 dB of so-calledprocessing gain.