Chip Rate Research Articles

Spreading Code Selection for Multiple Chip Rate DS-CDMA Systems

In this paper, we analyze the interuser interference (IUI) in multiple chip rate (MCR) direct-sequence code-division multiple-access (DS-CDMA) systems employing realistic chip waveforms. In MCR DS-CDMA systems, different users may have different chip rates, which makes IUI unavoidable even if the employed spreading codes are orthogonal. Here, we consider orthogonal variable spreading factor (OVSF) codes and random spreading codes. We find that the spreading code of the low chip rate user does not affect the IUI at all. The IUI depends only on the bit patterns of the high chip rate user corresponding to one chip duration of the low chip rate user and on the carrier frequency separation of the users. We provide a closed-form equation for the IUI power of random codes, and we show that a judicious choice of the spreading codes can reduce the IUI significantly for OVSF codes.

Next generation of GUIDAR technology

The next generation of guided radar (GUIDAR) is based on ultra wide band (UWB) radar signal processing. Just as spread spectrum technology has revolutionized the communications industry UWB is dramatically changing radar signal processing. These advanced signal processing techniques are adapted to leaky coaxial cable technology in the next generation GUIDAR to provide new features and enhanced performance. At the core of the new technology is an ultra high-speed digital correlator implemented in a field programmable gate array (FPGA). Complementary orthogonal codes based on Golay codes are used to produce thumbtack correlation functions simultaneously in multiple range bins. The net result is near continuous wave (CW) performance (97% duty cycle) in forty to eighty 11.6-meter long-range bins with targets located within one meter along the length of cable. This is a dramatic improvement over the 3% duty cycle of the original GUIDAR and the typical 100 to 200 meter long zones of current CW leaky cable sensors. Orthogonal complementary codes are transmitted on each of two leaky coaxial cables. The responses from the parallel receive cables are fed to a direct digital receiver. The orthogonal nature of the code allows the composite coded pulse response to be de-multiplexed into the independent response for each of the two cables. This ultra-high speed correlation process involves the addition and subtraction of the sampled in-phase and quadrature-phase responses to the multiple range bin accumulators at 10 million samples per second. Synchronous sampling at twice the chip rate ensures that each target is observed in three adjacent sample bins. The phase and amplitude response in the three adjacent samples are combined to precisely pinpoint (within 1 meter) the locations of targets along the length of each of the two cables. The ability to precisely locate and track multiple simultaneous targets on each of two cables leads to numerous new features and performance benefits relative to existing leaky cable sensors. With a separate calibrated threshold for every meter of cable the sensor sensitivity is much more uniform and installation restrictions on burial depth, cable spacing, and medium homogeneity can be relaxed. Potential sources of nuisance alarms can easily be located and overcome. The pinpoint location can be used to provide better CCTV assessment, target capture for video motion sensors and more effective response to intrusions. Through the use of parallel cables the sensor can be used to detect the direction of crossing and to classify targets such as small animals, people, and vehicles. This patented next generation of GUIDAR technology represents a dramatic step forward from that which was introduced at the 1976 Carnahan Conference in Lexington, Kentucky, and the numerous CW leaky coaxial cable sensors that evolved from that work. This technology effectively addresses residential, commercial, industrial, and governmental requirements including those relating to homeland security, military operations, and prisons.

A low-power and compact CDMA matched filter based on switched-current technology

A low-power and compact code-division multiple-access (CDMA) matched filter has been developed using the switched-current technology. On-chip V-I and I-V converters featuring moderate linear characteristics have been developed for the chip. The low-power operation has been achieved by the sub-block architecture, which reduced the current flowing in current-memory cells. A low-power clock-on-demand shift register has also been developed. The 256-chip matched filter fabricated in a 0.35-/spl mu/m technology demonstrated the power dissipation of 1.95 mW at the chip rate of 8 Mchip/s under 2-V power supply. The chip occupies the area of 0.54 mm/sup 2/.

A Low-Cost Time-Hopping Impulse Radio System for High Data Rate Transmission

We present an efficient, low-cost implementation of time-hopping impulse radio that fulfills the spectral mask mandated by the FCC and is suitable for high-data-rate, short-range communications. Key features are: (i) all-baseband implementation that obviates the need for passband components, (ii) symbol-rate (not chip rate) sampling, A/D conversion, and digital signal processing, (iii) fast acquisition due to novel search algorithms, (iv) spectral shaping that can be adapted to accommodate different spectrum regulations and interference environments. Computer simulations show that this system can provide 110Mbit/s at 7-10m distance, as well as higher data rates at shorter distances under FCC emissions limits. Due to the spreading concept of time-hopping impulse radio, the system can sustain multiple simultaneous users, and can suppress narrowband interference effectively.

High-performance optical code generation and recognition by use of a 511-chip, 640-Gchip/s phase-shifted superstructured fiber Bragg grating

The generation and recognition of a record-length 511-chip optical code is experimentally demonstrated by use of a superstructured fiber Bragg grating (SSFBG) with a chip rate of 640 Gchips/s. Very high reflectivity (92%) is achieved with high-quality correlation properties. The temperature deviation tolerance is approximately +/- 0.3 degrees C, which is within the package's temperature stability range (+/- 0.1 degrees C). Experimental results show good agreement with the theory. They indicate the SSFBG's potential for processing a long optical code with an ultrahigh chip rate, which could significantly improve the system's performance.

A DSP-Based Reconfigurable SDR Platform for 3G Systems

As the code division multiple access (CDMA) based third generation cellular infrastructure requires high performance signal processing in a baseband modem, an application-specific integrated circuit or a field-programmable gate array has commonly been used for chip rate processing. In this paper, the use of digital signal processors (DSP) is explored for a cdma2000 and a wideband CDMA channel modem with the goal of increasing flexibility. The design concepts of the prototype software-defined radio platform we implemented to estimate the potential and feasibility of commercial SDR platforms are presented. We discuss the hardware and software architecture of the platform, considerations for reconfigurability, and the test results. We also address practical issues for real-time chip rate processing and optimization schemes of DSP software, and provide detailed measurement results of DSP performance.

LINC digital component separator for single and multicarrier W-CDMA signals

An implementation of a digital component separator for a linear amplification using nonlinear components (LINC) system on a field-programmable gate array is presented. It employs a flexible upconversion architecture, which can be easily configured as an image-reject or direct-upconversion architecture for transmission of single or combined multicarrier wireless code-division multiple-access (W-CDMA) signals and uses the phase-modulation method. Four direct digital synthesizers are applied as phase modulators, operating first on a low IF carrier varying from 0 to 1/4 of the sampling frequency. The sampling frequency can be chosen up to 32 times (122.88 MHz) the symbol rate of the W-CDMA chip rate of 3.84 Mbit/s. The system allows a flexible frequency assignment and spacing of one or two independent W-CDMA channels. This paper outlines how the envelope and phase information of two combined W-CDMA channels may be pre-calculated in real time. This information may be used for the generation of two phase-modulated signals, which are then supplied to a single LINC transmitter. The achieved performance is demonstrated for single and multicarrier application utilizing direct and/or image-reject upconversion including simulated and experimental data (adjacent channel power ratio, complementary cumulative distribution function, error vector magnitude).

New theoretical bounds on the aperiodic correlation functions of binary sequences

In order to reduce or eliminate the multiple access interference in code division multiple access (CDMA) systems, we need to design a set of spreading sequences with good autocorrelation functions (ACF) and crosscorrelation functions (CCF). The importance of the spreading codes to CDMA systems cannot be overemphasized, for the type of the code used, its length, and its chip rate set bounds on the capability of the system that can be changed only by changing the code. Several new lower bounds which are stronger than the well-known Sarwate bounds, Welch bounds and Levenshtein bounds for binary sequence set with respect to the spreading sequence length, family size, maximum aperiodic autocorrelation sidelobe and maximum aperiodic crosscorrelation value are established.

Improved subspace-based channel estimation algorithm for DS∕CDMA systems exploiting pulse-shaping information

An improved subspace-based channel estimation algorithm for DS/CDMA system is presented. The proposed algorithm is based on the Torlak/Xu algorithm for asynchronous DS/CDMA systems. The aim is to incorporate knowledge of the pulse-shaping filter into the Torlak/Xu subspace algorithm with the objective of reducing the variance of the channel estimates. The improved algorithm is developed from a system model of a DS/CDMA system where the output is oversampled with respect to the chip rate. By oversampling the received signal, knowledge of the pulse-shaping filter is incorporated into the proposed channel estimation algorithm. It is shown that the variance of the channel estimate for the proposed subspace algorithm is less than the Torlak/Xu algorithm that does not exploit pulse-shaping filter information. A mathematical expression of the mean square error of estimation for the improved algorithm is also derived. It is shown that the analytical expression provides a good approximation of the actual mean square error for high SNR signals.

A Cost-Effective Fast Frequency-Hopped Code-Division Multiple-Access Light Source Using Self-Seeded Fabry–PÉrot Laser With Fiber Bragg Grating Array

We propose a novel light source for the optical fast frequency-hopped code-division multiple-access scheme using a self-seeded gain-switched Fabry-Pe/spl acute/rot laser diode (FP-LD) with the reconfigurable fiber Bragg grating array (FBGA). The embedded FBGA in the external cavity loop encodes the input pulses both temporally and spectrally. Before feeding back into the FP-LD, the encoded optical pulses propagate the FBGA with reverse direction and are again temporally combined. With the corporation of the variable fiber delay line, the limitation of the pulse rate by the fixed external cavity length is removed and makes the scheme more flexible. The output with sidemode suppression ratio of more than 20 dB has been obtained. With three fiber Bragg gratings on the FBGA, we demonstrate the encoded chip rate of 1.425 GHz under the driving radio frequency of 475 MHz. It is proved that a different codeword can be generated by simply reconfiguring the encoder without changing the rest of the experimental setup.

Asymptotic Analysis of Optimum and Suboptimum CDMA Downlink MMSE Receivers

In this paper, we investigate the performance of two linear receivers for code-division multiple-access (CDMA) downlink transmissions over frequency-selective channels, the users having possibly different powers. The optimum minimum mean-square error (MMSE) receiver is first considered. Because this receiver requires the knowledge of the code vectors attributed to all the users within the cell when these vectors are time varying, its use may be unrealistic in the forward link. A classical suboptimum receiver, consisting in a chip rate equalizer followed by a despreading with the code of the user of interest, is therefore studied and compared to the optimum MMSE receiver. Performance of both receivers is assessed through the signal-to-interference-plus-noise ratio (SINR) at their outputs. The analytical expressions of these SINRs depend in a rather nonexplicit way on the codes allocated to the users of the cell, and are therefore not informative. This difficulty is dealt with by modeling the users code matrix by a random matrix. Because the code matrices used in the forward link are usually isometric, the code matrix is assumed to be extracted from a Haar-distributed random unitary matrix. The behavior of the SINRs is studied when the spreading factor and the number of users converge to /spl infin/ at the same rate. Using certain results of the free probability theory, we establish the fact that the SINRs converge almost surely toward quantities that depend only on the complex amplitudes of propagation channel paths. We then use the expressions of these SINR limits to discuss the influence of the various parameters on the performance of the receivers.

Scalable Video Transmission Over Wireless DS-CDMA Channels Using Minimum TSC Spreading Codes

In this letter, we report results on the relative performance of scalable video transmission via a single-rate or a multirate direct sequence code-division multiple-access channel using minimum total squared correlation spreading codes. Our findings demonstrate the superiority of the multirate system on a wide range of chip rates of practical interest.

Wavelet based spectral correlation method for DPSK chip rate estimation

A wavelet-based spectral correlation algorithm to detect and estimate BPSK signal chip rate is proposed. Simulation results show that the proposed method can correctly estimate the BPSK signal chip rate, which may be corrupted by the quadratic characteristics of the spectral correlation function, in a low SNR environment.

Microbial dustiness and particle release of different biofuels.

Exposure to organic dust originating from biofuels can cause adverse health effects. In the present study we have assessed the dustiness in terms of microbial components and particles of various biofuels by using a rotating drum as a dust generator. Microbial components from straw, wood chips, wood pellets and wood briquettes were quantified by several methods. Excellent correlations (r >/= 0.85, P < 0.0001) were found: between lipopolysaccharide (LPS) (as determined by 3-hydroxy fatty acid analysis) and endotoxin (as determined by a Limulus test), cultivable bacteria, total number of bacteria and muramic acid; between endotoxin and cultivable bacteria, total number of bacteria and muramic acid; between total number of bacteria and muramic acid; between cultivable fungi and total number of fungi. Straw was dustier than the other biofuels in terms of actinomycetes, bacteria, muramic acid, endotoxin, LPS, particle mass and number of particles. One of the wood chips studied and the straws had comparatively high dustiness in terms of fungi, while both wood pellets and wood briquettes had comparatively low dustiness in terms of all microbial components. An initially high particle generation rate of straw and wood chips decreased over time whereas the particle generation rate of wood briquettes and wood pellets increased during a 5 min rotation period. Particles of non-microbial origin may be the determining factor for the health risk in handling briquettes and pellets. Straw dust contained significantly more microorganisms per particle than did wood chip dust, probably because bacteria were most abundant in straw dust. The concentrations of endotoxin and fungi were high in wood and straw dust; dust from one of the straws contained 3610 EU/mg and dust from one of the chips contained 7.3 x 10(6) fungal spores/mg. An exposure to 3 mg of straw or wood chips dust/m(3) (the Swedish and Danish OEL of unspecific inhalable dust) could cause exposures to endotoxin and fungi higher than levels were health symptoms are seen to develop. The very different levels of dustiness in terms of particles and microbial components of different biofuels shows that dustiness is an important health-relevant factor to consider when choosing among biofuels and when designing worksites for handling of biofuels.

BER Improvement Effect of Optical Delay Insertion in ROF Ubiquitous Antenna for Road-to-Vehicle Wireless Coded CDM System

This paper proposes the application of optical delay insertion and convolutional coding to Radio-on-Fiber ubiquitous antenna for Road-to-Vehicle wireless CDM (Code Division Multiplexing) system. In ubiquitous antenna system, the orthogonality of codes collapse, because a MS (Mobile Station) receives interference signals transmitted from different RBSs (Radio Base Station). So BER performance becomes worse. In order to solve this problem, we propose the application of convolutional coding. In addition, in ubiquitous antenna system, a MS sometimes receives signals transmitted from different RBSs at same chip timing. Therefore these signals become interference each other. In order to solve this problem, we propose the application of optical delay insertion as a MS does’t receive signals transmitted from different RBSs at same chip timing. In the case the distance between RBSs is 20[m] and chip rate is 32[Mcps], we can acquire the BER improvement all over the area by insertion of a 10[m] optical fiber.

Modeling of optical link for OCDMA‐based cascaded optical networks

AbstractIn cascaded optical networks, the BER performance of optical CDMA (OCDMA) signals has been evaluated. In order to simulate the optical link, the optical source, receiver, and fiber channel are modeled as lowpass filters by using Butterworth/Chebyshev approximations. Bipolar codes are used for spreading, and at the chip rate of 8 Gc/s, multi‐user interference (MUI) and distortion introduced by the optical link are found to be insignificant. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 40: 122–124, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11303

Radio-over-Fiber 시스템을 위한 40 GHz 대역에서 직접 광스위칭 CDMA 연구

Radio-over-Fiber(RoF) 시스템에서 직접 광스위칭 CDMA(Direct Optical Switching CDMA : DOS-CDMA) 기법을 이용하여 기존 이동통신에서 연구되어왔던 수 ㎓ 대역보다 주파수가 훨씬 높은 40 ㎓ 대역의 MMW (millimeter wave)를 반송파로 사용한 차세대 이동통신을 위한 MMW DOS-CDMA 시스템 연구를 실험적으로 수행했다. 부호 분할 다중화에 사용된 직교 부호(orthogonal codes)는 단극성(unipolar) 형태의 상호상관이 2이하(crosscorrelation<TEX>$\leq$</TEX>2)인 부호열을 선택했으며, 부호 길이(code length)는 16 chips, 칩율(chip rate)은 2.5 Gchip/sec 였다. 광원은 10 ㎓ 광섬유 링 레이저를 유리고조모드 잠김시켜 진폭 균등화한 40 ㎓ 의 안정된 레이저 펄스를 발생시켜 사용하였다. We have experimentally demonstrated a Direct Optical Switching (DOS) CDMA for future wide-band mobile communication systems at the 40 ㎓ band by using orthogonal (crosscorrelation <TEX>$\leq$</TEX>2) unipolar type codes with code length of 16 and chip rate of 2.5 Gcps for radio-over-fiber (RoF) systems. Pulse-amplitude-equalized 40 ㎓ laser pulses were provided by rational-harmonically mode-locking a 10 ㎓ fiber ring laser.

Tuning range extension by active mode-locking of external cavity laser including a linearly chirped fiber bragg grating

We demonstrate electrical wavelength tuning by mode locking of an external cavity laser (ECL) with linearly chirped fiber Bragg grating (LCFBG). The configuration consists of a laser chip providing the gain coupled to an LCFBG with a large chip rate of 10 or 55 nm/cm providing the counter-reaction for laser oscillation. The laser chirp is electrically modulated by a sinusoidal signal in such a way that the ECL is mode locked. By changing the modulation frequency, a wavelength tuning range of 27 nm is achieved with the 10 nm/cm LCFBG, and a partial tuning range over 41 nm is demonstrated with the 55-nm/cm LCFBG. The output pulse stream at a specific mode-locking frequency and a corresponding wavelength is obtained for both positively and negatively chirped grating. A time bandwidth product reduction is measured in the case of negatively chirp grating when compared with positively chirp grating. A simple general law between the laser parameters is given (locking frequency, tuning range, and FBG chirp value). The parameters for a 40-nm tunable source modulated at 10 GHz are given. This simple tuning mechanism is very well adapted for a structure that requires accurate wavelength monitoring.

Experiment Plan of ETS-8 in orbit: Mobile communications and navigation

The experiment of mobile communications and broadcasting by S-band and the satellite navigation by L/S-band are the main objectives of Engineering Test Satellite - 8 (ETS-8), which will be launced in 2004 into geostationary orbit at 146 degree East. In this paper, the current status of ETS-8 is introduced at first and the basic experiment plan is described. For the mobile communications/broadcasting, two deployable reflectors (17 meters × 19 meters, each) and a 400 W class active phased array feeder with 31 SSPAs are installed in ETS-8. Three beams are used simultaneously to cover Japan and neighbor region. Two kinds of onboard processors are also installed, which are dedicated to voice and high-speed packet communication, respectively. The ground terminal for voice communications is as small as conventional cellular phone, and that for packet is similar size of notebook type PC. For satellite navigation, two Cesium clocks are installed. The coverage area is Asia-Pacific hemisphere. The experiment will be conducted by use of ground stations and signals from GPS. The positioning accuracy is evaluated by changing RF frequency, code pattern and chip rate. To determine the precise orbital parameters of satellite, the laser ranging method is adopted. This satellite navigation experiment will be conducted in cooperation with foreign and domestic institutes. After the funtion tests of satellite in orbit, it will be from 2005 year, the opportunity to conduct some experiment used of ETS-8 will provide. The participation of those who have interest in these experiments is welcome.

Measured channel parameters for the disturbed wide‐bandwidth HF channel

The wideband HF (WBHF) channel impulse response measurements presented here were taken over a high‐latitude auroral path using the MITRE experimental WBHF test facility. A nominal instantaneous bandwidth of 1 MHz was used for the majority of the tests. These tests took place from 14 March through 1 April 1992 over a path from Sondrestrom AFB, Greenland, to Bedford, Massachusetts, a distance of approximately 3,100 km. The measurements were made using a direct‐sequence pseudo‐noise (DSPN) channel probe with a (±180°) chip modulation and chip rate of 1024 kchips/second. Complex channel impulse response values at increments of 500 nanoseconds in delay were derived by correlating the received signal with a set of local DSPN references uniformly spaced in delay over a delay range of 2 ms. Each of these channel impulse response values was sampled in time at a rate of up to 62.5 samples per second, resulting in the ability to observe (one‐sided) Doppler spectra and shifts of up to 31.25 Hz. From these measurements, the channel scattering function, rms (2σ) Doppler spread, rms (2σ) Delay spread, Doppler shift, and rms (2σ) spread factor were calculated. In addition, for the first time, the impulse response correlation along the delay axis was calculated. These latter measurements support the use of an uncorrelated scattering hypothesis in modeling the disturbed WBHF channel.