Pseudo-Noise

The Chinese digital television terrestrial broadcasting (DTTB) standard uses pseudo-noise (PN) sequence as guard interval (GI) and the training sequence. This PN sequence is used to do channel estimation and synchronization in the system. The existing channel estimation methods often have to adopt iterative scheme when the length of channel impulse response (CIR) is long, which will increase the receiver complexity dramatically. In this paper, a channel estimation scheme for time domain synchronous OFDM (TDS-OFDM) systems is proposed. Interference free CIR information can be obtained by constructing special correlation windows, rather than removing interference from the time domain sequences through iteration. Moreover, the estimation can be achieved by using correlation process. Comparing to conventional schemes, the proposed algorithm greatly reduces the computational complexity. Simulation results show that the proposed method can meet the requirement of the Chinese DTTB systems. And the scheme is also suitable for other communication OFDM systems with time domain sequence headers.

This paper addresses the problem of initial synchronization of pseudo-noise code. A new code acquisition technique for spread-spectrum communication systems using band-limited chip waveforms is presented. Unlike conventional power detector based on testing the estimated maximum of the ambiguity function, the devised detector exploits a fast parabolic interpolation, running on three estimated ambiguity samples in the neighborhood of the coarse estimate. Performance analysis is carried out in comparison with conventional detector. Mathematical expressions for the probability of false alarm and detection are derived. They are numerically evaluated, under operating settings, by a reduced Tayloriquests expansion up to the second order. The theoretical results, substantiated by computer simulations, have evidenced that the devised method is well suited for asynchronous spread-spectrum communications. In particular, the acquisition performance depends on the actual offset between the received and the reference code waveforms, which are randomly distributed (in chip-asynchronous systems) within one sampling period. In fact, the parabolic interpolation technique outperforms the conventional detector for a wide range of code offsets because it is able to self-synchronize the testing variable around the true offset.

Digital television/terrestrial multimedia broadcasting (DTMB) was announced as the Chinese digital television terrestrial broadcasting (DTTB) standard in August, 2006. It adopts TDS-OFDM (time-domain synchronous-orthogonal frequency division multiplexing) as the baseline modulation technology. There is not pilot information in order to avoid reduction of channel throughput. It uses pseudo-noise (PN) sequence as guard interval (GI) and the training sequence for both multi- and single-carrier block transmissions which makes the synchronization faster than CP-OFDM (cyclic prefix-orthogonal frequency division multiplexing) systems. It can resist the inter-symbol interference (ISI) and can be used for channel estimation and synchronization. In this paper, a full-mode channel estimation scheme for DTMB demodulator is developed. This method utilizes the PN sequence to obtain channel estimation and equalization both in three kinds of frame head (FH) mode as well as in single and multi-carrier modulation transmission mode. To implement on hardware realization, interference cancellation is predigested, then equalization and filter for channel impulse response are optimized. A low cost VLSI architecture for channel estimation and equalization is proposed which works effectually and achieves low complexity as well. Computational simulation results show that the proposed scheme has little BER loss in performance.

Abstract-We discuss present and near-term uses for highpower fiber lasers and amplifiers for NASA-specific applications including planetary topography and atmospheric spectroscopy. Fiber lasers and amplifiers offer numerous advantages for both near-term ...

We propose a watermarking scheme to hide copyright information in an image. The scheme employs visual masking to guarantee that the embedded watermark is invisible and to maximize the robustness of the hidden data. The watermark is constructed for arbitrary image blocks by filtering a pseudo-noise sequence (author id) with a filter that approximates the frequency masking characteristics of the visual system. The noise-like watermark is statistically invisible to deter unauthorized removal. Experimental results show that the watermark is robust to several distortions including white and colored noises, JPEG coding at different qualities, and cropping

Efficient detection of people hidden by walls or rubble is of interest for rescue, surveillance and security operations. A useful method applies an ultra-wideband radar approach for this purpose since electromagnetic waves in the lower GHz-range penetrate most non-metallic materials. The paper gives a short overview of the particular radar conception and shows some experimental results for the tracking of

Abstract-We discuss present and near-term uses for highpower fiber lasers and amplifiers for NASA-specific applications including planetary topography and atmospheric spectroscopy. Fiber lasers and amplifiers offer numerous advantages for both near-term ...

The Sequential Estimation (SE) technique introduced by Ward was designed for the acquisition of pseudo-noise (PN) signals. It proves to be an effective model in medium SNRs as long as inverted PN sequences are not encountered. Recognizing that negative data bits invert PN sequences in spread spectrum transmissions, Chiu and Lee developed an Improved Sequential Estimator (ISE) that processes both types of sequences. The ISE design, however, erroneously despreads the incoming signal by inverting it during negative bit acquisitions. In some applications, this could be a problem, hence a Dual Correlating Sequential Estimator (DCSE) is proposed in this paper. The DCSE detects modulation errors by gathering correlation measurements from resident SE and ISE subsystems and corrects for them with an inverting mechanism. Key performance parameters such as mean timing and the variance of acquisition for the sequential estimator designs are derived via the generalized signal flow graph method and verified through simulation. In an additive White Gaussian noise (AWGN) environment, the DCSE design is shown to outperform the SE for every tested signal-to-noise ratio (SNR).

The performance of a CDMA based wireless system is largely dependent on the characteristics of pseudorandom spreading codes. The spreading codes should be carefully chosen to ensure highest possible peak value of auto-correlation function and lower correlation peaks (side-lobes) at non-zero time-shifts.
Simultaneously, zero cross-correlation value at all time shifts is required in order to eliminate the effect of multiple access interference at the receiver. But no such code family exists which possess both characteristics simultaneously. That’s why an exhaustive effort has been made in this paper to evaluate
the peak correlation characteristics of various non-orthogonal spreading codes and suggest a suitable solution.

This paper addresses and implements a Direct Sequence Spread Spectrum (DSSS) transceiver for Visible Light Communication (VLC) systems based on FPGA. A transceiver was implemented including a transmitter capable of driving an array of light emitting diodes (LED) and a Pseudo-Noise (PN) matched decorrelator. The receiver architecture uses a discrete FIR correlator for data synchronization and acquisition. In this paper, a novel and simple PN code with a 10 bit sequence length is developed. This code ...

In contrast to the classical cyclic prefix (CP)-OFDM, the time domain synchronous (TDS)-OFDM employs a known pseudo noise (PN) sequence as guard interval (GI). Conventional channel estimation methods for TDS-OFDM are based on the exploitation of the PN sequence and consequently suffer from intersymbol interference (ISI). This paper proposes a novel data-aided channel estimation method which combines the channel estimates

Multiple access techniques which allow a communication medium to be shared between different users represent one of the most challenging topics in digital communications. In terms of the number of users that can be accommodated on a given channel, there are two distinct classes of multiple access techniques. The first class includes the well-known FDMA, TDMA, and OCDMA. On a

We present the architecture and design of a new transponder to support deepspace and near-Earth missions in the post-2010 time frame. This transponder is designed to provide direct-to-Earth command and telemetry service; spacecraftto-spacecraft command and telemetry service; direct-to-Earth navigation in the form of coherent Doppler turnaround, sequential turn-around ranging, pseudo-noise regenerative ranging, and differential one-way ranging; and spacecraft-to-spacecraft navigation in the form of coherent Doppler turnaround and one-way pseudo-noise code ranging.

Constant False Alarm Rate (CFAR) algorithms are used in digital signal processing applications to extract targets from background in noisy environments. Some examples of applications are target detection in radar environments, image processing, medical engineering, power quality analysis, features detection in satellite images, Pseudo-Noise (PN) code detectors, among others. This paper presents a versatile hardware architecture that implements six variants

We introduce a code-division multiple access (CDMA) concept which allows one to accommodate a higher number of users than the spreading factor N. The idea is to assign orthogonal spreading sequences to the first N users and pseudo-noise (PN) spreading sequences to all additional users. The proposed technique can thus accommodate N users without any mutual interference and some additional at the expense of some signal-to-noise ratio (SNR) penalty. This represents a significant capacity increase with respect to presently available multiple access techniques. When the number of users is larger than N, detection is performed in two separate steps, one for the set of users with orthogonal spreading sequences and one for the set of users with PN sequences. Furthermore, the process is iterated two or more times to obtain more reliable receiver decisions

Multiple access techniques which allow a communication medium to be shared between different users represent one of the most challenging topics in digital communications. In terms of the number of users that can be accommodated on a given channel, there are two distinct classes of multiple access techniques. The first class includes the well-known FDMA, TDMA, and OCDMA. On a