Direct Sequence Spread Spectrum Technique Research Articles

Structure of Spread Spectrum Telemetry Radio Link for LEO Small Satellite

The paper considers the design of telemetry radio link for low Earth orbit (LEO) satellites, particularly based on CubeSat format. A significant limitation of such spacecrafts are the available dimensions for antennas and the transmitting power, which leads to low energy level at the ground receiving point of transmitted signal. The article presents the physical level structure for data frame based on direct sequence spread spectrum technique, which allows for additional signal gain to achieve the required level of link performance. Using such principle also make possible to implement adaptive data rate control depending on dynamics in signal-to-noise ratio when the distance from the satellite to the ground point changes. For proposed data frame structure, an analysis of received information size during a communication session was carried out, which is parameterized on the maximum observable elevation angle of the satellite. The issue of datalink layer interaction between devices is also considered.

Performance of the Direct Sequence Spread Spectrum Underwater Acoustic Communication System with Differential Detection in Strong Multipath Propagation Conditions

The underwater acoustic communication (UAC) operating in very shallow-water should ensure reliable transmission in conditions of strong multipath propagation, significantly disturbing the received signal. One of the techniques to achieve this goal is the direct sequence spread spectrum (DSSS) technique, which consists in binary phase shift keying (BPSK) according to a pseudo-random spreading sequence. This paper describes the DSSS data transmission tests in the simulation and experimental environment, using different types of pseudo-noise sequences: m-sequences and Kasami codes of the order 6 and 8. The transmitted signals are of different bandwidth and the detection at the receiver side was performed using two detection methods: non-differential and differential. The performed experiments allowed to draw important conclusions for the designing of a physical layer of the shallow-water UAC system. Both, m-sequences and Kasami codes allow to achieve a similar bit error rate, which at best was less than 10 −3. At the same time, the 6th order sequences are not long enough to achieve an acceptable BER under strong multipath conditions. In the case of transmission of wideband signals the differential detection algorithm allows to achieve a significantly better BER (less than 10 −2) than nondifferential one (BER not less than 10 −1). In the case of narrowband signals the simulation tests have shown that the non-differential algorithm gives a better BER, but experimental tests under conditions of strong multipath propagation did not confirm it. The differential algorithm allowed to achieve a BER less than 10 −2 in experimental tests, while the second algorithm allowed to obtain, at best, a BER less than 10 −1. In addition, two indicators have been proposed for a rough assessment which of the detection algorithms under current propagation conditions in the channel will allow to obtain a better BER.

Implementation of Underwater Electric Field Communication Based on Direct Sequence Spread Spectrum (DSSS) and Binary Phase Shift Keying (BPSK) Modulation.

Stable communication technologies in complex waters are a prerequisite for underwater operations. Underwater acoustic communication is susceptible to multipath interference, while underwater optical communication is susceptible to environmental impact. The underwater electric field communication established based on the weak electric fish perception mechanism is not susceptible to environmental interference, and the communication is stable. It is a new type of underwater communication technology. To address issues like short communication distances and high bit error rates in existing underwater electric field communication systems, this study focuses on underwater electric field communication systems based on direct sequence spread spectrum (DSSS) and binary phase shift keying (BPSK) modulation techniques. To verify the feasibility of the established spread spectrum electric field communication system, static communication experiments were carried out in a swimming pool using the DSSS-based system. The experimental results show that in fresh water with a conductivity of 739 μS/cm, the system can achieve underwater current electric field communication within a 11.2 m range with 10-6 bit errors. This paper validates the feasibility of DSSS BPSK in short-range underwater communication, and compact communication devices are expected to be deployed on underwater robots for underwater operations.

CBTC Security and Reliability Enhancements by a Key-Based Direct Sequence Spread Spectrum Technique

CBTC Security and Reliability Enhancements by a Key-Based Direct Sequence Spread Spectrum Technique

Complementary Coded Identical Code Cyclic Shift Multiple Access Under Asynchronous Frequency-Selective Fading Channels

A complementary coded code-division multiple-access (CC-CDMA) system is built on the direct sequence (DS) spread spectrum technique, which can suppress multipath interferences and multiple-access interferences due to the ideal correlation property of complementary codes (CCs). However, the DS spread spectrum technique will cause poor bandwidth efficiency; the CC-CDMA system suffers from serious interferences due to the ideal correlation of CCs may not be reconstructed at the receiver after passing through asynchronous frequency selective fading channels. In this paper, we propose a complementary coded identical code cyclic shift multiple access (CC-ICCSMA) system under asynchronous frequency selective fading channels, which allows multiple data streams to transmit in parallel by sharing one spreading code for improving the bandwidth efficiency. Considering the impact of interferences, we propose an ICCS matched filterbank to tackle the interferences, which can decode the data under all paths and achieve a high multipath diversity gain. Simulation results show that the proposed CC-ICCSMA system can achieve higher bandwidth efficiency than that of traditional CC-CDMA and can outperform the traditional DS-CDMA schemes in terms of bit-error rates and transmission rates.

Performance of DSSS Signal Transmission with SCM over Low-Frequency MMF Passbands

The transmission of a high data rate signal over low-frequency passbands of multimode fibers is studied in this paper. The subcarrier multiplexing (SCM) technique is applied to mitigate the frequency-selective nature of the passbands, at which many nulls can degrade the signal transmission. The subcarrier frequencies must be chosen appropriately, especially for some low-frequency passbands; otherwise, poorly received subcarrier signals will be obtained, affecting the entire transmission. Rather than transmitting many subcarrier signals over these passbands, the direct sequence spread spectrum (DSSS) technique can be adopted. In this work, a high data rate signal is transmitted over 1 km of multimode fiber using the 3-dB modal band and six other low-frequency passbands. The signal is separated into four sub-signals transmitted over four different channels: the 3-dB modal band, two low-frequency passbands, and one passband (containing four low-frequency passbands). In the last passband, the sub-signal is transmitted using the DSSS, while the other sub-signals are transmitted through amplitude shift keying (ASK) modulation. The performance of the system is determined using the bit error rate (BER). The findings reveal that by applying the DSSS to some low-frequency passbands, robustness is obtained in the subcarrier frequency for use in the DSSS passband. A BER lower than 10-9 with a total data rate of 600 Mbps is achieved. This data rate is three times higher than the data rate obtained by the 3-dB modal band. This performance is achieved without applying any error-correction code.

High-Reliability Underwater Acoustic Communication Using an M-ary Cyclic Spread Spectrum

Multipath propagation, frequency selective fading, low-propagation velocity, and narrow bandwidth are all characteristics of underwater acoustic channels. Doppler shifts and diffusions can occur as a result of the low transmission speed of an acoustic signal, which can be caused by the movement of ocean currents or the transceiver. Furthermore, frequency selective fading and excessive noise interference can disrupt underwater acoustic communication on a continual basis. Because of its high anti-interference ability and high confidentiality, spread spectrum technology is commonly adopted in underwater acoustic communications. Although the direct sequence spread spectrum method has a low data rate, it is advantageous in a multipath propagation channel environment or an environment with a low signal-to-noise ratio (SNR). This advantage is suitable for long-distance transmission or LPD (Low Probability of Detection) communication, and the direct sequence spread spectrum method is applied. In this paper, we propose a highly reliable M-ary cyclic spread spectrum technique by superimposing the M-ary spread spectrum, an extension of the direct sequence spread spectrum technique, and cyclic shift keying. Furthermore, by estimating the Doppler frequency using M-ary spread spectrum codes and performing synchronization correction of the ensuing symbol based on the estimation results, higher performance can be attained. Simulations and experiments showed that the M-ary cyclic spread spectrum method can reduce Doppler estimation and synchronization error accumulation while maintaining a high data rate. Furthermore, the MCSS method had a lower bit error rate than the standard spread spectrum method.

A New Scheme for Spreading & De-spreading in the Direct Sequence Spread Spectrum Mechanism

Direct Sequence Spread Spectrum (DSSS) and Frequency Hopping Spread Spectrum (FHSS) techniques are widely used to implement code-division multiple access (CDMA) in wireless communication systems. Both DSSS and FHSS systems help reducing the effects of interference on the transmitted information making it robust against channel impairments. DSSS uses a signal bandwidth that is much broader than the information signal bandwidth. Traditionally, the wide band signal is generated by multiplying the narrowband information signal with a binary code, often designated as a spreading code, to generate the wideband signal that is transmitted. The original information signal can be recreated at the receiver by multiplying the received wideband signal by the same binary code (now designated as a de-spreading code) used to generate the wideband transmitted signal. To extract the original information signal, the spreading and de-spreading codes must be in synchronism at the receiver and amplitude match with each other. A new modification for the direct sequence spread spectrum is proposed in this paper. The mechanism introduced in this approach implicates generating the wideband signal by circularly shifting the spreading code (PN) by n places, where n represents the value of the current byte of information signal. The yielded signal is modulated using BPSK modulator before transmitting it. The original information signal is extracted at the receiver by correlating the received signal (which is actually the original spread sequence circularly shifted by n places) with a locally generated replica of the spreading code. The position of the maximum value of the cross-correlation vector represents the value of the information signal byte. The proposed configuration has been implemented using Simulink simulator and the obtained results show that its performance is identical with the conventional DSSS.

Aggregated CDMA Crossbar With Hybrid ARQ for NoCs

Network-on-chips (NoCs) are the dominant interconnection technique in modern system-on-chips (SoCs). The medium access technique used in the physical layer of NoC routers profoundly impacts the performance and footprint of the router. Code division multiple access (CDMA) is a medium access technique widely deployed in various wireless communication systems, and it has recently been proposed as a prominent switching method for NoC routers. In a CDMA crossbar, several processing elements (PEs) can communicate simultaneously over a single communication channel by applying the direct-sequence spread spectrum technique to digital interconnects. However, existing CDMA switches are bit-wise architectures in which a binary data bit is spread and serially communicated on an exclusive digital channel while replicating this configuration to communicate multiple data bits, which increases the crossbar area and wiring density. In this work, we propose aggregated CDMA (ACDMA) to improve the area, throughput, and power consumption of existing CDMA NoC routers. ACDMA exploits the static nature and relative noise immunity of on-chip interconnects to aggregate transmission of multiple data bits into M-ary symbols on a single digital communication channel, which significantly reduces the wiring density and area overhead of the crossbar. Serial and parallel variants of the ACDMA crossbar offering a wide range of area-speed trade-offs are implemented in the ASIC <inline-formula> <tex-math notation="LaTeX">$65~nm$ </tex-math></inline-formula> standard cell technology. The implementation results show that the throughput-per-area (TPA) of the serial and parallel ACDMA crossbars is improved by 96.3&#x0025;, 18.2&#x0025;, and 118.6&#x0025;; and 400&#x0025;, 255.3&#x0025;, and 184.2&#x0025; compared to the serial and parallel counterparts of the Walsh Basis (WB), Standard Basis (SB), and Overloaded CDMA Interconnect (OCI) crossbars, respectively. A 65-node ACDMA NoC router is fully realized and compared to the state-of-the-art CDMA and CONNECT NoC routers under multiple synthetic workloads. Communication reliability of the ACDMA NoC router subject to noise is investigated and a hybrid ARQ approach is proposed to improve the interconnect reliability.

Transformation of AC to DC using Direct Sequence Spread Spectrum (DSSS) Technique for Electromagnetic Inference

Before more functions of the circuit are integrated into several electromagnetic a single die or small integrated die or small integrated interference (EMI) people impacted by ac-dc converter kit, expanding. The dominant electromagnetic emission. In this paper Alternate Current (AC) - Direct Current (DC) converter source is delineated by gauging the ac-dc converter source of the nodes' power spectrum. The activity of the noise scanner is linked to a noise scanner, a crowded ac-dc converter single-chip prototype. The data revealed the converter's superior electromagnetic source of the emission is the switching node, not the output node. The technique of direct sequence spread spectrum to counteract the switching node toxins, the ac- dc converter should be used and its profitability is the temperature distribution and pragmatically validated. The Mathematical statement of the technique of direct sequence spread spectrum is proposed for the study of its pharmacokinetics in the significant decrease of EMI and optimal installation using the technique of direct sequence spread spectrum with 0.18-μm CMOSS, dead-time control is assembled and coding. The plotted reduction in the power spectrum. The optimum direct sequence spread spectrum technique installation and managerial staff of dead-time is the node at the 16 dB switch. The stock of the proposed declines in the EMI reduction. The IC-strip line approach improved the design by 12.6 dB on fundamental frequency switching.

Multipoint intermittent fault detection of electronic interconnections using channel sounding techniques

Intermittent faults (IFs) in electrical interconnection are short duration transients. These faults are random, non-predictable and non-stationary in nature making them hard to troubleshoot using traditional equipment. They can be detected only if the test equipment has test coverage both in time and area at that instant. This paper proposes a novel approach of intermittent fault detection by injecting a wideband signal and using channel-sounding techniques. A novel Direct Sequence Spread Spectrum (DS-SS) technique is presented for multipoint IF detection and health monitoring. Digital communication sounding technology and its methods devised for detection and classification of an IF, and channel characterisation by its transfer function is discussed in detail. A combination of transmitter and receiver provide an effective tool for continuously monitoring of the multi-point interconnect. The proposed method has been tested using a functional prototype having pre-induced IFs. Intermittent signal is generated by applying external vibration on the connector and intermittency is detected by acquiring and processing the propagated signal. The results demonstrate the effectiveness of the method in detection and classification of intermittent interconnections.

High-Rejection RF Code Domain Receivers for Simultaneous Transmit and Receive Applications

Code-domain signal processing techniques implemented at radio frequencies (RFs) enable simultaneous transmit and receive (STAR) applications. With direct sequence spread spectrum (DSSS) techniques and RF correlators, transmit (TX) self-interference (SI) is separated from the receive (RX) signal at the antenna interface for STAR. The processing gain inherent in the code-domain approach increases the TX SI rejection in the RF domain to relax filtering and linearity requirements of the RX. A code-domain RX demonstrates 52 dB of TX SI rejection with TX code-notch and RX code-pass filters operating at the same center frequency. The RX is tunable from 0.25 to 1.25 GHz and has a gain of 39 dB at 1 GHz while consuming 90 mW of which 40 mW are consumed in the front-end filters. The RX is implemented in a 45-nm CMOS SOI process and full-duplex operation is verified through an over-the-air demonstration.

Analysis of confidentiality of information transfer in DSSS systems in conditions of limited systems of used signal constructions

Information security in telecommunications can be provided at the physical level of telecommunication systems by means of energy and structural secrecy of information transfer. Spread-spectrum telecommunications, in particular the DSSS (Direct Sequence Spread Spectrum) technique, are the most suitable for the implementation of such approach to information security. Ensuring the necessary level of structural secrecy of information transfer using DSSS technique is that this technique uses systems of signal constructions with a sufficiently large number of signals in the system. There are requirements to correlation properties of each such signal construction, because in accordance with the Wiener-Khinchin theorem they determine the spectral characteristics of signals in a telecommunication system and, as a result, the structural spectral and energy secrecy of information transfer. The problem boils down to the fact that the systematic deterministic methods for synthesizing systems of signal constructions with a low peak sidelobe level of the autocorrelation function for the case of an arbitrary length of signal constructions and the number of ones in the system of signals are unknown, and the complexity of this problem is associated with an algorithmic undecidability of arbitrary algebraic Diophantine equations. The confidentiality of information transfer at the physical level of DSSS telecommunication systems while using some known systems of signal constructions with a low peak sidelobe level of the autocorrelation function and in the case of attacks, which are performed by an unauthorized user by means of optimal signal processing methods (optimal detection of biorthogonal signals), is analyzed in the article.

A Background Spread-Spectrum Radio Frequency Nonlinear Parameter Measurement Technique

We report a new correlation-based direct sequence spread-spectrum technique that estimates low-pass-equivalent Volterra coefficients for weakly nonlinear RF systems. The methodology provides robust coefficient estimates at test signal amplitudes well below the operating signal level during normal system operation, demonstrating that the technique can be used for “background” nonlinearity measurement. We demonstrate the methodology by measuring third-order Volterra kernels for a power amplifier chain operated in compression with a 10 MHz bandwidth signal at 1960 MHz.

Interference management using direct sequence spread spectrum (DSSS) technique in LTE-Wi-Fi network

In this paper, an enhance DSSS technique was proposed which considers both serving and its neighbouring base stations in the network. New coefficients, chip rate coefficient ( a ) and radius fraction coefficient ( b ) were applied in DSSS technique in order to improve the SINR value. First, SINR MUE and SINR WUE for the standard DSSS were simulated. Then, by using the obtained analysis, the enhance DSSS technique was proposed. As the results, the SINR at MUE using a -coefficient gives better SINR than standard around 4%~5% improvement. On the other hand, the SINR at WUE using a -coefficient also gives better SINR than standard around 9%~10% improvement. Other than that, by applying both a -coefficient and b -coefficient into the proposed DSSS based on modified interference power, the improvement for SINR MUE increases to 11%~13%. For SINR WUE, the percentage spikes to 74%~84%.

Implementation of Transmitter Zigbee System based on Wireless Sensor Network of IEEE 802.15.4 Standard

Abstract&#x0D; &#x0D; Zigbee is considered to be one of the wireless sensor networks (WSNs) designed for short-range communications applications. It follows IEEE 802.15.4 specifications that aim to design networks with lowest cost and power consuming in addition to the minimum possible data rate. In this paper, a transmitter Zigbee system is designed based on PHY layer specifications of this standard. The modulation technique applied in this design is the offset quadrature phase shift keying (OQPSK) with half sine pulse-shaping for achieving a minimum possible amount of phase transitions. In addition, the applied spreading technique is direct sequence spread spectrum (DSSS) technique, which has the effect in getting better performance for the transmitter system in multipath environments. The system is developed through the use of MATLAB/Simulink to show the performance of the proposed system in response to the appliy modulation technique.&#x0D; &#x0D; Keywords: DSSS technique, IEEE 802.15.4, MSK, OQPSK, Zigbee.

Data transmission in the hydroacoustic channel – experimental researches

ABSTRACTThe paper presents the results of experimental researches of data transmission in water using Direct Sequence Spread Spectrum technique and the RAKE receiver. The signal with the QPSK modulation was spread by factor of 4, 8 or 16 chips. Researches were made to verify that spread spectrum technique can be used to underwater voice communications. Static studies were conducted in a small laboratory water tank and in a harbour. Propagation properties were evaluated based on the estimated impulse response of the hydroacoustic channel.

High accuracy displacement measuring system using strain gauge based displacement sensor and direct sequence spread spectrum techniques in data acquisition system

The present article portrays a design and implementation of microcontroller based system for displacement measurement using strain gauge based displacement sensor. A displacement transducer may be capacitive or resistive, is an uncontrollable device. Improvement in filtering increases the speed of measurement and enhances the measurement accuracy. In this paper a new algorithm and architecture is proposed as filter for the displacement measuring system with strain gauge based displacement sensor. We verify and implement the novel algorithm with this displacement transducer in the measuring of displacement successfully.

Chaotic direct-sequence spread-spectrum with variable symbol period: A technique for enhancing physical layer security

In chaotic direct-sequence spread-spectrum (DSSS) technique, chaotic sequences with typical properties such as aperiodic variation, wideband spectrum, good correlation, and initial condition sensitivity have been used as spreading codes in order to improve the security at physical layer. However, a number of recent studies have proved that an intruder can recover chaotic sequences by blind estimation methods and use the sequences to detect symbol period, which will result in the original data being exposed. To overcome this security weakness, this paper proposes a novel chaotic DSSS technique, where the symbol period is varied according to behavior of the chaotic spreading sequence in the communication process. The data with variable symbol period is multiplied with the chaotic sequence to perform the spread-spectrum process. Discrete-time models for the spreading scheme with variable symbol period and the despreading scheme with sequence synchronization are presented and analyzed. Multiple-access performance of the proposed technique in the presence of the additional white Gaussian noise (AWGN) is calculated by means of both theoretical derivation and numerical computation. Computer simulations are carried out and simulated performances are shown to verify the estimated ones. Obtained results point out that our proposed technique can protect the DSSS systems against the detection of symbol period from the intruder, even if he has full information on the used chaotic sequence.

Use of Matched Filter in Direct Sequence Spread Spectrum Techniques

Objectives: The protection of signal against jamming is accomplished using Spread Spectrum (SS) techniques. In this research paper, noise rejecting property of the matched filter and Binary Phase Shift Keying (BPSK) modulation is used in Direct Sequence Spread Spectrum (DSSS) system for secure communication. Methods/Statistical Analysis: Here, DSSS system has been developed and simulated using C-programming language on windows platform. In order to perform the simulation, different parameters are initialized and message bits are generated by random function. With the help of binary message signal and PN sequence, a SS signal is generated which is modulated using BPSK modulation technique at the transmitter side. In the channel, noise/jamming signal is added to the transmitted signal. Then the received signal is demodulated using coherent BPSK receiver (i.e., correlation receiver) and matched filtering is followed by despreading the demodulated signal at the receiver side. Finally, the received binary message bits are detected by threshold detector and various parameters such as input SNR, output SNR, probability of error are calculated. Findings: It has been found that matched filter is a linear filter which has a noise rejection property (means jamming signals can be treated just like other random noise) and hence provides signal security. This particular property of matched filter is used in DSSS communication. As far as matched filter is concerned, it cannot remove the total effect of interference but still the waveforms can be detected in the presence of noise/jamming signal. So, a matched filter receiver is supposed to be an ideal receiver for a signal which is corrupted by AWGN/jamming signal. Here, an average probability of symbol error decreases because it maximizes the output signal to noise ratio. These parameters are supposed to be the most important factors that determine the efficiency of performance of the system. Applications: DSSS systems using matched filter are strong contender for mobile and personnel communications, due to their very large user handling capacity. They also have better transmission quality and capability by incorporating wireless services such as data, short transaction messages, and multimedia etc.