Direct Sequence Spread Spectrum Code Research Articles

Millimeter-Precision Ultrasonic DSSS Positioning Technique With Geometric Triangle Constraint

In this paper, we present a 3-D ultrasonic measurement technique that uses direct sequence spread spectrum (DSSS) with simultaneous multiple code-division multiple access (CDMA) signals. This technique can be applied in precise indoor locating systems. By placing three microphones close to one another separated by distances on the order of the ultrasound wavelength and imposing the constraint that one transducer and two from the three microphones form three triangles in the space (i.e., the triangle constraint) for 3-D ultrasonic DSSS trilateration measurement, millimeter 3-D positioning precision is achieved. The experimental results for a positioning system comprising a set of three microphones and four ultrasound transducers, each of them transmitting its respective 256-bit DSSS code, demonstrate that the proposed system can measure the spatial 3-D location of the receiver with a standard deviation of less than 1.21 mm. The proposed technique is suitable for potential future indoor positioning system (IPS) applications that require sub-centimeter 3-D positioning.

Algorithms for distributing DSSS codes in industrial WSNs with real transmitters and narrow-band interference

The versatility of simple electronic nodes and debugging of communication protocols in unlicensed frequency bands constitute the main reasons for the adoption of industrial wireless sensor networks (IWSNs). However, the industrial environments, in which IWSNs function, are characterized by a harsh impact of physical and electromagnetic factors that destabilize the operation of equipment and worsen the noise immunity of channels. To consider the effect of these two groups of factors on communication quality, we develop a novel model of an IWSN channel as the dependence of bit error probability (BEP) on signal distortions and interference impact. We found that direct sequence spread spectrum (DSSS) codes of a signal have different effects on the compensation of nonlinear signal distortions and external interference. Further, we propose an algorithm for the distribution of DSSS codes among real transmitters by BEP values in channels with known additive and multiplicative interference. Here, the distribution of codes is based on the minimax criterion. Finally, for cases when a signal is characterized by a-priori uncertainties of fading, we suggest an alternative algorithm for selecting a DSSS code based on Pareto bicriteria optimization.

Subcentimeter Precision Ranging System for Moving Targets With a Doppler-Effect- Compensated Ultrasonic Direct Sequence Spread Spectrum

In this article, we present a Doppler-effect-compensated ranging system that can be applied to subcentimeter-precision ultrasonic distance measurement for moving targets using a direct sequence spread spectrum (DSSS). First, the theory of the Doppler compensation technique is explained, and then, the evaluation results obtained using maximum-length-sequence coded ultrasonic signals are discussed. In this study, we employ a 128-b DSSS code with three wavelengths per bit. The experimental results demonstrate that the proposed system can measure a target accelerating at 9.8 m/s2 with a speed of up to 2 m/s in the range of 0.1–1.6 m, with a standard deviation of less than 5 mm. We also confirmed by simulation that the system can track a target accelerating at 30 m/s2 with a speed of up to 5.5 m/s in the range of 4–6 m.

Chirp-rate quasi-orthogonality based DSSS-CDMA system for underwater acoustic channel

Underwater network node positioning is a key supporting technology for underwater networks. Generally, nodes at known locations (anchor nodes) are used to transmit location information to the node to be located, and the node to be located performs location calculation according to the arrival time of the received information, which requires multiple access communication between the anchor nodes and the node to be located. In order to reduce the multiple access interference (MAI) and distinguish the information of different anchor nodes, it is necessary to study the underwater multiple access method. The GPS positioning system uses direct sequence spread spectrum code division multiple access(DSSS-CDMA) technology, and the positioning satellite transmits a signal formed by the BPSK modulation by transmitting a pseudo-random sequence (PN sequence) to the binary code sequence corresponding to the navigation message to the user equipment to be located. The underwater acoustic (UWA) channel has a complex multipath structure and Doppler effect, which causes a large interference to the communication system. Compared with narrowband communication, spread spectrum communication has a strong anti-interference ability, and can maintain the reliability of the communication system in the UWA channel. Based on this, this paper proposes a quasi-orthogonal Chirp-rate based DSSS-CDMA method under UWA channel, and carries out simulation analysis and experimental verification.

Spread Spectrum-Coded OFDM Chirp Waveform Diversity Design

This paper proposes an approach to design multiple-input multiple-output radar waveforms that are orthogonal on both the transmitter and receiver. The proposed method jointly utilizes the direct sequence spread spectrum coding and orthogonal frequency division multiplexing (OFDM) chirp signaling techniques. We name it spread spectrum-coded OFDM chirp waveform diversity design. The performance of the designed waveforms is analyzed by examining the ambiguity function and correlation function. The influences of the spread spectrum code choice and the OFDM chirp parameters are also investigated. It is verified that the proposed design scheme can ensure these waveforms stay orthogonal on the receiver and have large time-bandwidth product which is beneficial to separate closely spaced targets.

Vehicle to Vehicle Communication Using DS-CDMA Radar

Abstract Tremendous amount of research is going on in the area of Intelligent Transport System. The automotive companies like General Motors, Toyota, Mercedes etc have announced launch of high end vehicles with inbuilt V2X(Vehicle to infrastructure/Vehicle) systems. In this paper we have proposed a scheme to implement vehicle to vehicle communication using Direct Sequence Spread Spectrum Code Division Multiple Access radar (DS-CDMA). The system is capable of performing ranging as well as communication with multiple targets.

System study on direct sequence spectrum of radio-frequency identification

This paper considers points of secure and anti-collision of the Radio-frequency identification (RFID) technology. Source symbols are represented by a special coding, termed Minimum Energy (ME) coding, which exploits redundant bits for saving power when transmitted via RF links with On-Off Keying (OOK). This ME coding is applied to Direct Sequence Spread Spectrum (DSSS) RFID tag in order to enhance security as well as to reduce collision. This synchronized DSSS RFID system is designed and simulation is conducted to verify the advantage of DSSS RFID and present the power efficiency enhance 4 dB, quantities are taken at Bit Error Rate (BER) of 10e-4. When the channel uses the ME coding combined with a DSSS code and OOK without FM0 encoding as is disclosed in the EPC-C1G2/ISO 18000-6 Type C standard. Finally, the maximum number of users in this Direct-Sequence Code Division Multiple Access (DS-CDMA) RFID system is calculated under the condition of successfully acquired.

A Blind Adaptive Kalman-PIC MUD Algorithm for the Multiple Access Communication Network

In the parallel signal processing, the multi-user detection precision of parallel interference cancellation (PIC) detector is always easily affected by the decision error diffusion. Based on the fast convergence and low complexity of blind adaptive Kalman algorithm, a new blind adaptive Kalman-PIC (KPIC) multi-user detection (MUD) algorithm is proposed for the direct sequence spread spectrum code division multiple access (DS-CDMA) system network with strong multiple access interference (MAI). Compared with traditional standard Kalman filter and PIC algorithm, the proposed combined program can totally track the time-varying channel, effectively estimate unknown noise statistics characteristics on-line while conducting state filtering, possibly minimize the detection error diffusion in the interference cancellation processing of single PIC algorithm, thus effectively suppress MAI. Simulation results show that the KPIC algorithm is of better convergence, dynamic tracking ability and precision

Long-Range Double-Differentially Coded Spread-Spectrum Acoustic Communications With a Towed Array

This paper presents a novel double-differentially coded spread-spectrum (DD-SS) system design for long-range acoustic communications (LRAC) between a moving source and a towed horizontal line array (HLA). The proposed design relies on two techniques that have been historically developed for radio-frequency terrestrial wireless communications, namely, direct sequence spread spectrum and double-differential coding. In DD-SS, direct sequence spread spectrum is employed to: 1) increase the signal-to-noise ratio; 2) suppress multipath interference; and 3) support data multiplexing, while double-differential coding makes reliable symbol recovery possible without explicit phase and Doppler tracking/correction. Thanks to the two techniques together with traditional beamforming, the DD-SS system is shown capable of effectively dealing with many challenging issues posed by LRAC with a towed HLA, without using complicated receiver processing. During the 2010 Long-Range Acoustic Communication Experiment (LRAC10) in deep waters, the DD-SS system was tested by using a moving source at a speed of 2-3 kn at 75-m depth and a 64-element HLA towed at 3.5 kn at a depth of 200 m. Excellent uncoded error performance (less than 4% bit error rate) is demonstrated at a data rate of 6.4 b/s for a bandwidth of 200 Hz and at a range of 550 km.

A Blind Adaptive SOR/JGS Iterative Kalman MUD Algorithm for Multiple Access Communication System

Based on the fast stable convergence characteristics of successive over relaxation (SOR) iterative and Jacobi Gauss- Seidel (JGS) iterative, a blind adaptive SOR/JGS iterative Kalman multi-user detection (MUD) algorithm (SJK) is proposed for multiple access communication system as direct sequence spread spectrum code division multiple access (DS- CDMA) system with multi-path fading channel. The proposed combination of blind adaptive Kalman filtering theory, SOR and JGS iterative method can adaptively control the selection of relaxation parameters and damping parameter, and then effectively deal the problem as time-varying noise statistics estimation. Compared with traditional standard Kalman filter (SKF), fading Kalman filter (FKF) and robust adaptive Kalman filter (RAKF) algorithm, the proposed algorithm can effectively estimate unknown noise statistics characteristics on-line while conducting state filtering, totally track the time-varying channel, minimize the detection error diffusion, and thus effectively reduce multiple access interference (MAI). Simulation results show that the SJK algorithm is of better detection accuracy, convergence ability, dynamic tracking capability, and lower bit error rate (BER) performance.  Index Terms communication system is asynchronous or synchronous. When the distance between interference user and base station is closer than expected user, the received power of interference user would be much larger than expected user, then the correlation between spreading sequence and interference user would surely be much larger than that between spreading sequence and expected user. This would always cause a significant increase of MAI component in the traditional Multi-User Detection (MUD) receiver, and it may easily cause that the expected user signal is submerged by interference user signal. Namely, the Bit Error Rate (BER) of MUD receiver is very sensitive to the difference between expected user and interference user. Based on the above situation, the traditional MUD algorithm for DS-CDMA system such as Matched Filter (MF) and decorrelation detection receiver cannot effectively eliminate the impact of MAI and FNP. This makes SKF, Fading Kalman Filter (FKF) and Robust Adaptive Kalman Filter (RAKF) the focus of research.

Design of a digital modulator and demodulator for reader-less RFID Tag in 0.18 µm CMOS process

Both the Radio Frequency Identification (RFID) and Wireless Fidelity (WiFi) are popular and ubiquitous technologies. However, RFID is lagging behind due to vendor specific solutions and excessive reader cost. A WiFi compatible IEEE 802.11 RFID tag can eliminate the reader. A digital modulator and demodulator for the reader-less RFID tag in IEEE 802.11 protocol employing Direct Sequence Spread Spectrum (DSSS) and Barker code are proposed in this paper. To generate the 11-bit Barker code, MOD-11 synchronous counter and encoder are designed by utilizing only four D flip-flops instead of preloading the code sequence in multiple registers. For modulation, data are multiplied with this Barker code and for demodulation, the received data are multiplied with the same Barker code. Designed in 0.18 µm CMOS technology, the minimum, average and maximum power consumptions are 3.64 nA, 17.64 µA and 7.61 mA, respectively. The simulation results show the correct functionality of the modulator and demodulator where 1 bit is spread to 11 bits and 11 bits received data are de-spread to 1 bit, respectively. The design would help to implement the modulator and demodulator for the reader-less RFID tag with resistance to multi-path fading and interference and covering the highest distance with lower Bit Error Rate (BER).

A Blind Adaptive Kalman-SIC MUD Algorithm of the Wireless Multiple Access Mobile Communication System

The multi-user detection precision of successive interference cancellation (SIC) detector is always affected by the decision error diffusion. This paper focuses on the SIC algorithm of direct sequence spread spectrum code division multiple access (DS-CDMA) system with strong multiple access interference (MAI) and inter symbol interference (ISI). A blind adaptive Kalman-SIC multi-user detection (MUD) algorithm is proposed in this paper. This algorithm can totally track the time-varying channel, minimize the detection error diffusion, and thus effectively suppress MAI and ISI. Simulation results show that the blind adaptive Kalman-SIC algorithm is of better tracking ability, convergence and detection precision.  Index Terms—Successive interference cancellation, Kalman, DS-CDMA, multiple access interference.

Blind detection of spread spectrum flow watermarks

ABSTRACTRecently, the direct sequence spread spectrum (DSSS)‐based technique has been proposed to trace anonymous network flows. In this technique, homogeneous pseudo‐noise (PN) codes are used to modulate multiple bit signals that are embedded into the target flow as watermarks. This technique could be maliciously used to degrade an anonymous communication network. In this paper, we propose an effective single flow‐based scheme to detect the existence of these watermarks. Our investigation shows that, even if we have no knowledge of the applied PN code, we are still able to detect malicious DSSS watermarks via mean‐square autocorrelation (MSAC) of a single modulated flow's traffic rate time series. MSAC shows periodic peaks because of self‐similarity in the modulated traffic caused by homogeneous PN codes that are used in modulating multiple bit signals. Our scheme has low complexity and does not require any PN code synchronization. We evaluate this detection scheme's effectiveness via simulations. Our results demonstrate a high detection rate with a low false positive rate. Real‐world experiments on Tor also validate the feasibility of the detection scheme. Our scheme is more flexible and accurate than the existing multiflow‐based approach in DSSS watermark detection. We also present a theory for reconstructing the DSSS code once the DSSS code length is known and simulations validate the feasibility. Copyright © 2012 John Wiley & Sons, Ltd.

Two-Dimensional Optical Code-Division Modulation With Quantum-Noise Aided Encryption for Applications in Key Distribution

We propose and demonstrate an advanced optical modulation format that makes use of both spectral and temporal phase encodings (2-D) for applications requiring exceptional security. The method combines modulation techniques used in direct-sequence spread-spectrum coding, spectral-phase encoding, and M-ary phase-shift keying with codes generated using cryptographically secure pseudorandom number generators. The wideband transmission signal is very difficult for an eavesdropper to record or analyze. Signal-to-noise ratio limitations imposed by quantum effects enhance the security further. The properties of the transmitted signal make it especially useful for physics-based key expansion systems. We have successfully used this setup to transmit encrypted 155 Mb/s data over 70 km of fiber with a BER value of 4E-5.

A direct sequence spread spectrum code acquisition circuit for wireless sensor networks

Narrow band (NB), spread spectrum (SS), and ultra wide band (UWB) are three physical layer bandwidth types used in wireless sensor networks (WSN). SS and UWB technologies have many advantages over NB, which make them preferable for WSN. Synchronisation of different nodes in a WSN is an important task that is necessary to improve cooperation and lifetime of nodes. Code acquisition is the main step of a node’s time synchronisation. In this article, a pseudo noise code generator and a code acquisition circuit are proposed, designed and tested using direct sequence SS technique. To investigate the properties of the designed circuits, simulations are carried out via Xilinx Foundation Series software in the real mode. The results demonstrate excellent performance of the proposed algorithms and circuits in all realistic conditions. The code acquisition circuit proposed an adaptive testing window for single dwell serial search method. The code acquisition circuit is a clock phase free approach, thus the clock coherency step is cancelled. Moreover, clock phase difference between transmitter and receiver nodes does not mostly affect the acquisition and thus synchronisation time.

A Variable-Rate Spread-Spectrum System for Underwater Acoustic Communications

A key research area in underwater acoustic (UWA) communication is the development of advanced modulation and detection schemes for improved performance and range-rate product. In this communication, we propose a variable-rate underwater data transmission system based on direct sequence spread spectrum (DSSS) and complementary code keying (CCK), particularly for shallow-water acoustic channels with severe multipath propagation. We provide a suboptimum receiver that consists of a bidirectional decision feedback equalizer (BiDFE) to cancel both postcursor and precursor intersymbol interference (ISI). We also develop iterative signal processing and time-reversal (TR) diversity processing to mitigate the effect of error propagation in BiDFE. We present performance analysis on bit error rate (BER) for different data rates. Our works show that this new variable-data-rate DSSS-CCK is a suitable candidate for UWA communications over varying channel conditions and distance.

Direct sequence code acquisition in multiplicative and non-Gaussian noises

A new detector for direct sequence spread spectrum code acquisition in multiplicative and non-Gaussian noises is proposed in this article. Modelling the acquisition problem as a hypothesis-testing problem, a detector is derived for multiplicative and non-Gaussian noises, based on the locally optimum detection technique. Numerical results show that the proposed detector can offer substantial performance improvement over the conventional schemes in multiplicative and non-Gaussian noises.

Indoor Geolocation Using FCDMA Pseudolites: Signal Structure and Performance Analysis

: The signal structure performance of a direct sequence spread spectrum (DSSS) code division multiple access (CDMA) frequency division multiple access (FDMA) pseudolite indoor communication and localization (geolocation) system is presented and discussed in this paper. The signal structure of a DSSS-FCDMA (or C-CDMA) pseudolite indoor geolocation system appears to elegantly solve the near-far problem when subject to a slowly varying frequency-selective Rayleigh fading channel with additive white Gaussian noise and Doppler shift, which is the main obstacle of a DSSS-CDMA pseudolite indoor geolocation system at roughly equal transmitter and post radio frequency (RF) receiver complexity. Based on our theoretical analysis and simulation results, it appears that FCDMA (or C-CDMA) signal structure may be a suitable candidate for indoor geolocation to achieve 3D centimeter level position accuracy and 3D centimeter-per-second level velocity accuracy 99.9% of the time.

A Simple Expression for the Optimization of Spread-Spectrum Code Acquisition Detectors Operating in the Presence of Carrier-Frequency Offset

In this letter, we present a simple expression for the optimization of the threshold detection performance for direct-sequence spread-spectrum code acquisition in the presence of carrier-frequency offset. The proposed scheme divides the total integration time into subintervals, and the results of the coherent integrations performed over these subintervals are noncoherently combined prior to detection. The proposed expression allows obtaining the optimum number of coherent-integration subintervals for a given total integration time.

Role of contemporary communications systems in the process of planning, organizing and realization of military operations

Fast progress in commercial communications systems development has made possibilities to fulfill communications needs in military organizations especially during the periods of peace. A reconnaissance system, based on specific military technology such as passive radar systems and acoustic sensors, available in commercial market, represents a possible realization of a simple and highly efficient system. Necessary communication with a higher command, also as actions that are made based on gathered information, could de supported through use of commercial communications systems employing adaptive modulation processes, direct sequence and freqyency hopping spread spectrum communications and code division multiple access. In this way organized systems completely fulfill communication needs of the Army of Serbia and Montenegro during peacetime, but the applicability of such systems expends partially or fully on cases of limited military interventions antiterrorist actions and nature disasters.