In this paper, we define content-identifier (ContentID) to represent the characteristics of shot. The ContentID carries both positional and temporal color information. Based on the concept of ContentID, we propose a video retrieval method. The method is robust to compression, format conversion, frame dropping and noise such as watermark and so on. Furthermore, based on our retrieval method, we implemented a copyright protection system for digital video using spread-spectrum based watermarking technique.

In CDMA mobile system, network connection is constructed with orthogonal spreading codes assigned to each user in order to distinguish one from the other. The number of distinguishable codes and the process speed are different according to the orthogonal spreading factors which, in another literature, can be described as the tree structure. In this paper, we investigate methods to improve the quality of services (QoS) of communication, by changing the spreading factors of orthogonal spreading codes according to the number of users. We propose the effective method to reconstruct the tree structure of orthogonal spreading codes for supporting various data rates transmission in DS-CDMA mobile system. We compare spreading factors with and without the reconstruction and evaluate the effectiveness of the reconstruction method.

In synchronous CDMA system, the orthogonal spreading sequences are employed to reduce the multiple access interference. However, as the frequency selectivity of the propagation channel strengthens, the orthogonality among different users tends to diminish because of increasing inter-path interference. In this paper, various binary and nonbinary orthogonal sequences are discussed. In order to maintain the orthogonality among different users, a new concept of generalized orthogonality is defined and the corresponding sequences are presented, including binary, quadriphase and nonbinary code sequences. Based on a simplified synchronous CDMA system model, the related system performance is also analyzed and compared for different orthogonal and generalized orthogonal spreading sequences. Our analytical and simulation results show that the generalized orthogonal code sequences are indeed more robust in the multipath propagation channels, compared with the traditional orthogonal code sequences.

In this paper, the authors derived the distributions of the probability of detection and of false alarm in function of the decision threshold. An Optimized Threshold Decision (OTD) algorithm was proposed to decide the optimal threshold for reaching the best system performance in a given known channel noise. By applying this OTD algorithm, the multiple access capacity can thus be maximized.

In this paper, we study macro/micro diversity techniques for code acquisition of a direct-sequence spread-spectrum signal in an indoor packet communication system. In the system discussed, the base station has several radio ports each with a cluster of antennas, and the terminal also has multiple antennas. The performance in the uplink of this system is analyzed under Lognormal shadowing and flat Rayleigh fading. The numerical results show great performance improvements by proposed diversity techniques. In addition, it is clarified that the mean acquisition time, which is often used as the measure of performance, is not suitable for packet radio systems as it underestimates the necessary preamble length for initial code acquisition.

A modified sequential acquisition scheme is proposed in this letter to avoid the significant high error probabilities (false alarm and missing probabilities) occurring with the conventional sequential acquisition scheme in direct-sequence spread-spectrum systems while a high frequency offset is present. A new estimator of Ek/N0 is also designed to effectively solve the problems caused by the channel fading effects. Extensive computer simulation results have indicated that the proposed technique can achieve the desired low error probabilities, and furthermore its performance is very close to that with the perfect channel estimation.

One of the basic GPS features is its inherent anti-jamming (AJ) characteristics based on great processing gain as a result of using direct sequence spread spectrum (DS-SS) technique. For calculated jamming threshold for GPS receivers operating with L1 C/A, L1 P(Y) and L2 P(Y) signals, jamming range has been analyzed with respect to the characteristic jamming signals and under various effective radiated power of jamming signals. The tests of C/A GPS receiver jamming resistance on different jamming strategies, during the tracking and acquisition phase have been performed. The influence of jamming strategy on jamming efficiency has been proved. At the same time AJ characteristics of GPS receiver have been checked.

This paper presents a new technique for the synthesis of orthogonal-base-set sequences suitable for applications requiring sets of uncorrelated pseudo-white-noise sources. The synthesized sequences (vectors) are orthogonal to each other, and each sequence also has a flat power spectrum and low peak factor. In order to construct the orthogonal-base-set sequences, the new application of ta-sequence (trigonometric function aliasing sequence) introduced in this paper uses Latin-squares and Walsh-Hadamard sequences. The ta-sequence itself is a very new concept, and the method presented here provides the means for generating various orthogonal-base-set sequences at sizes required for such applications as system measurement (needing uncorrelated test signals), pseudo noise synthesis for spread spectrum communication, and audio signal processing (needing synthesis of stereo or multichannel signals from mono sources).

We examine the detection of coded hybrid direct-sequence frequency-hopped spread-spectrum signals in the presence of narrowband interference. Since blind interference suppression requires a reliable estimate of the data, while at the same time data decoding requires interference suppression, we advocate an iterative ("turbo") detection scheme whereby information is exchanged between the interference suppressor and the soft-input soft-output decoder. Several suppression schemes are examined and compared. Simulation results show that this new scheme is robust, i.e., exhibits good performance under a modicum of assumptions on the interference structure. Turbo codes and convolutional codes are compared, showing that the former perform better.

Path loss and delay profile characteristics of the 3-GHz band are measured and compared for line-of-sight (LOS) and non-line-of-sight (NLOS) paths in a suburban residential area. For the LOS path, the path loss increases as a function of distance squared; and hence the propagation is considered as the free space propagation. For the NLOS paths, it is found that corner losses occur ranging from 28 to 40 dB, and subsequent losses increase as a function of distance squared, but in case of there are open spaces, spaces between the rows of houses or roads intersecting LOS road, the increase was small. The delay spread for the LOS path increased in proportion to power of the distance; and the exponents ranging from 1.9 to 2.9 is found smaller than in urban areas. The delay spreads for the NLOS paths were several times greater than that for the LOS path, and the rate of delay spread increase with distance was found to be several orders of magnitude greater for NLOS paths than the LOS path.

This paper conducts performance evaluation for a code division multiple access (CDMA) system when channel bands of multiple neighboring CDMA/DSSS are overlapped in frequency domain. It is assumed that all systems adopt direct-sequence spread-spectrum (DSSS) technique and are BPSK modulated by the different carrier frequencies. Automatic power control (APC) is also applied in the interfered system such that the receiver gets the same power from all users. Without loss generality, an additive white Gaussian noise (AWGN) channel is also assumed during analysis. In this paper, the analytic solution of the signal to noise ratio (SNR) is first derived in which both CDMA systems are modulated by different carrier frequencies. This analysis is good for general cases; and the result shows an excellent computational performance. In particular, the result is very close to Pursly's result, when the systems have the same code length with no carrier difference.

Reverse link performance analysis in single-code and multi-code CDMA systems is presented. Results show that the single-code system yields better performance than does the multi-code system in terms of link capacity and signal power. This improvement increases as spreading bandwidth is reduced and the number of spreading codes assigned to a user is increased.

For a wireless communication system to work effectively without interference, the electromagnetic environment needs to be controlled. We experimentally and analytically investigated the requirements for controlling the electrical field strength and delay spread so as to achieve the best communication without electromagnetic interference in selected regions for a 2.4-GHz-band wireless LAN system. To control the coverage, partitions were placed around desks in a test environment and covered on the inside with electromagnetic absorbing board from the top of the desks to the top of the partitions; four indoor environments that combined one of two wall-material types and one of two partition heights were used. The transmission loss and delay spread were measured, then calculated using ray tracing to verify the effectiveness of using ray-tracing calculation. The throughput and BER characteristics were measured for the same environments to clarify the requirements for controlling the coverage. We found that covered and uncovered regions could be created by using partitions with absorbing boards and that the delay spread must be less than 15 ns and the received-signal must be stronger than -75 dBm for a region to be covered. We verified that the delay spread can be calculated to within 5 ns and the received-signal level can be calculated to within 5 dB of the measured data by using ray tracing. Therefore, ray tracing can be used to design antenna positions and indoor environments where electromagnetic environments are controlled for 2.4-GHz-band wireless LAN systems.

Relating to the radiated emission sources finding method based on CISPR emission measurement system, which uses only amplitude data without phase data, the applicability to horizontally polarized sources was studied. We experimentally verified by using two spherical dipole antennas as ideal emission sources in the frequency range from 300 MHz to 1GHz. As the results, the position estimation deviation Δd was less than 0.09 m, the amplitude estimation deviation Δj was less than 1.5 dB, in which position estimation accuracy was raised so much compared with that for vertically polarized sources, and additionally the angle of its horizontal current direction could be estimated. Furthermore, it was revealed that this method can be also applied even when several sources exist, consequently the applicability of this method has been greatly expanded.

This paper proposes a new protocol for ad hoc based CDMA wireless local area networks, Hierarchy Schedule Sensing (HSS) protocol. It adopts hierarchical sensing to schedule transmission requests to avoid collisions. Multi-level group spreading codes are used to reduce scheduling delay. The network performance under the HSS protocol is evaluated using a two-dimensional Markov chain model in consideration of collided packets capture effect at receivers. The paper also focuses on the impacts of multiple packet collisions on the performance. A closed formula of the average collision rate is derived explicitly. The results show that the HSS protocol offers a robust performance with low hardware requirement.

This paper presents a 7th-order channel-select filter for a spread-spectrum wireless receiver operating with a minimum power supply of 2.5 V. The channel-select filter implements a sharp transition from 2 MHz to 4 MHz and a stopband attenuation of 50 dB. The 7th-order filter is realized by a cascade of a passive RC integrator, a 3rd-order leapfrog filter, an operational amplifier based differentiator, a 2nd-order notch filter, and a 1st-order allpass filter. It is designed in a 0.35 µm single-poly BiCMOS process. Simulation results show feasibility of the proposed filter.

Watermarking methods that employ orthogonal transformations are very robust against non-geometrical modifications such as lossy compression, but attaining robustness against image translation or cropping is difficult. This report describes a watermarking method that increases robustness against geometrical modifications such as image translation and cropping by embedding watermark data in the frequency component of an image and detecting that data by considering the phase difference of the coefficients that results from translation of the image. Experimental results demonstrate the robustness of this method against both non-geometrical image changes and image translation and cropping.

We have two goals in this paper. One is the comparison of Spread Spectrum (SS) CDMA and Spread Time (ST) CDMA. The other is to propose a new SS-ST CDMA system, which is an adaptive CDMA with both merits of SS and ST CDMA. SS and ST CDMA are compared from the view point of two dimensional space "frequency (B Hz)-time (T Sec)" together with their communication capacity. A primary modulation is assumed to be PPM in ST CDMA, and FSK in SS CDMA which is regarded as PPM in frequency axis. Both SS and ST CDMA are combined to give the proposed SS-ST CDMA, where transmitted signals are spread both in time and frequency domain. In order to realize the proposed system, a transmitter model is presented, and two receiver structures are discussed. The discrete Fourier transform (DFT) is employed for the system flexibility. Although SS, ST and SS-ST CDMA are shown to have the same capacity of 0.7213, the combined SS-ST CDMA has a merit of adaptability to adjust spreading gain of ST and SS according to property of channels, an impulsive noise dominated or a CW interference dominated channel. Numerical results of DFT are also shown to illustrate the waveform and spectrum of the proposed SS-ST CDMA system. Finally the symbol error probability performance of ST PPM, SS FSK and combined SS-ST systems in CW and impulsive environment is presented.

Measurements of delay spread were performed at microwave frequencies of 3.35, 8.45 and 15.75 GHz along quasi line-of-sight streets in metropolitan Tokyo. It is found that the delay spreads increase with the measurement distance and reach around 600 ns up to 1 km. It is also confirmed that a cumulative probability of the delay spreads follows a log-normal distribution. The gradients of delay spreads against the distance are greater for a lower mobile antenna height hm = 1.6 m than for hm = 2.7 m in these measurements because of blocking effect by the traffic of vehicles and pedestrians on the road. When the mobile antenna height is 2.7 m, the delay spreads within the range before the break points are observed relatively small: 90 ns (3.35 GHz), 140 ns (8.45 GHz) and 150 ns (15.75 GHz) at the cumulative probability of 90%. The gradients of delay spreads against the distance are greater for wider streets in our measurements.

In inter-vehicle communication (IVC) expectation for spread spectrum techniques is high. However, in a decentralized network environment, power control is difficult and until now perfect power control has been assumed. In this paper the use of sector antennas are proposed as a solution to the problems of power control in inter-vehicle communication. Results are shown for an IVC protocol in both no power control and imperfect power control environments in a realistic fading channel. Omni-directional, uniform sector antennas and non-uniform sector antennas are examined by computer simulation. Non-uniform sector antennas are shown to be the best solution and to have high packet reception rates even for no power control environments.