Time-Hopping Sequence Design for Virtual Full Duplex via Rapid On-Off-Division Duplex

To achieve virtual full-duplex(VFD)communication using half-duplex radios,the rapid on-off-division(RODD)technique has been proposed in recent years.The time-hopping(TH)sequence is critical to controlling self-interference introduced in the paradigm.By constructing the collision model with a symbol level time scale,the periodic collision correlation function properties are introduced as the performance metric for the TH sequence in the RODD system.To achieve the best VFD performance,an optimization-based method for TH sequence design is proposed.In addition,the conventional TH frame structure design for RODD system is improved.Numerical simulations are presented to demonstrate that the proposed approach can significantly increase system performance.Results indicate that the TH sequence design is very effective for the RODD system.

Narrow-band interference excision in spread-spectrum systems using new N-sigma algorithm based on fuzzy threshold

The key to narrow-band interference excision in frequency domain is to determine the excision thresh- old in direct-sequence spread-spectrum （DS-SS） systems. The excision threshold is a non-linear function related to the number and the power of interference, and attempting to get the exact relation of threshold related to the number and the power of interference is almost impossible. The N-sigma algorithm determines the excision threshold using subsection function; however, the excision threshold determined by this method is not exact. A new method to determine the threshold of N-sigma algorithm is proposed. The new method modifies the scale factor N by use of the membership function. The threshold determined by this method is consecutive and smooth, and it is closer to the fact than that of the initial N-sigma algorithm. The GPS signal and single-tone （CW） interference （that is, typical narrow-band interference） are implemented in the simulation, and the results are presented to demonstrate the validity of the new algorithm.

An improved method of generating the self-balanced chaotic spread-spectrum code

An improved method of generating the self-balanced chaotic spread-spectrum code is presented. The chaotic-map pseudorandom sequence is used as the generated source. After a series of processing two-valued quantization, inversion, all upside down, radix-S block upside down and shift combination, the proposed code is achieved. Theory analysis and simulation performance of the improved code are illustrated. And the results indicate that the suggested method gains a better performance than the traditional one by reasonable choices of the initial value and the S parameter in the im- proved method. Meanwhile the chaotic sequence＇ s characteristic of large addresses is inherited when the chaotic-map is used as the source. This advantage makes this improved code very suitable for the multiple access application in communication system.

Secure Spread-Spectrum Watermarking for Telemedicine Applications

This paper presents a secure spread-spectrum watermarking algorithm for digital images in discrete wavelet transform (DWT) domain. The algorithm is applied for embedding watermarks like patient identification /source identification or doctors signature in binary image format into host digital radiological image for potential telemedicine applications. Performance of the algorithm is analysed by varying the gain factor, subband decomposition levels, size of watermark, wavelet filters and medical image modalities. Simulation results show that the proposed method achieves higher security and robustness against various attacks.

Blind Estimation of Long Code DSSS Signal Based On Subspace Tracking

Aiming at solving the blind estimation problem of dispreading spectrum sequence under low SNR, a spread-spectrum estimation algorithm based subspace tracking is studied in this paper. This method avoids the direct eigen decomposition, using the sliding window technique to obtain the code synchronization, then use segmentation subspace tracking method estimate spreading sequence and splice in a certain order to achieve pseudo-code blind estimation. The results show that the algorithm can complete the accurate estimation of PN code sequence in low SNR conditions, reduce the amount of data storage and be easy hardware implementation

On Two-Tier Femtocell over Fading Environments

In this paper the system performance of an MC-CDMA (multi-carrier coded-division multiple-access) system operating over single-cell with two-tier femtocell environment is analyzed. Consider two-tier scenario is deployed with a macrocell site in which is being surrounded several femtocells, which are designed to serve a group of subscribers locate in a small coverage area such as small office, home office or a house. The coverage area is typically up to 100 meters in radius. Mostly, the femtocell is applied to serve indoor subscribers, thus, the Rayleigh fading is adopted to characterize the propagation channel. The technique of TH-MC- CDMA (time-hopped multi-carrier coded-division multiple-access) technique is supposed to transmit each symbol alternatively with fair time (slotting)/frequency (coding) for each user in the hotspots (the area around 0th femtocell). The intensity of signals estimated at a mobile unit located in the second tie, i.e., the femtocell coverage area, is an important issue. The contribution of the paper is mainly to evaluate the system performance with both the BER (bit error rate) and OP (outage probability) according to the most important parameters, for example, the activating user number, the hopping number provided by TH-MC-CDMA system and the subcarrier number. Furthermore, the discussion of interference avoidance is also discussed with non-analytically.

Modeling and Simulation of CDMA Codes in Scilab

Prior to hardware implementation, simulation is an important step in the study of systems such as Direct Sequence Code Division Multiple Access (DS-CDMA). A useful technique is presented, allowing to model and simulate Linear Feedback Shift Register (LFSR) for CDMA. It uses the Scilab package and its modeling tool for dynamical systems Xcos. PN-Generators are designed for the quadrature-phase modulation and the Gold Code Generator for Global Positioning System (GPS). This study gives a great flexibility in the conception of LFSR and the analysis of Maximum Length Sequences (MLS) used by spread spectrum systems. Interesting results have been obtained, which allow the verification of generated sequences and their exploitation by signal processing tools.

An advanced monolithic digitalized random carrier frequency spread-spectrum clock generator for EMI suppression

A novel monolithic digitalized random carrier frequency modulation spread-spectrum clock generator （RCF-SSCG） is proposed.In this design,the output frequency of the proposed RCF-SSCG changes with the intensity of the capacitive charge and discharge current.Its analytical model is induced and the effect of the modulation parameters on the spread spectrum is numerically simulated and discussed.Compared with other works,this design has the advantages of small size,low power consumption and good robustness.The circuit has been fabricated in a 0.5μm CMOS process and applied to a class D amplifier in which the proposed RCF-SSCG occupies an area of 0.112 mm^2 and consumes 9 mW.The experimental results confirm the theoretical analyses.

Spatiotemporal Chaotic Synchronization and Spread-Spectrum Communication

A method of Direct Sequence Spread-Spectrum(DS/SS)corn,nunication based on synchronizedspatiotemporal chootic sequences is proposed.We use Coupled Logistic Maps(CLM)to generate the chaotictimes sequences.This coupled mop lattices has long chaotic transient and can be recovered easily.Therobustness and the error probability is discussed and the advantage of the method in Spectral spreading andsecure communication is demonstrated.

A 3-5 GHz TH-UWB transmitter in 0.18-μm RF CMOS technology

An RF transmitter is proposed for 3-5 GHz time-hopping ultra wideband（TH-UWB） wireless applications.The transmitter consists of a 4-GHz oscillator, a switch with a controllable attenuator and an output matching circuit.Through controlling the low frequency signals with time-hopping pulse position modulation（TH-PPM）, the circuit supplies TH-UWB signals and can directly drive an antenna by a transmission line.The transmitter was implemented in a 0.18-μm CMOS technology;the output amplitude is about 65 mV at a 50 ？ load from a 1.8-V supply, the return loss（S 11） at the output port is less than-10 dB, and the chip size is 0.7 × 0.8 mm2, with a power consumption of 12.3 mW.