CDMA Signals Research Articles

Cognitive Detection of Unknown Beacons of Terrestrial Signals of Opportunity for Localization

A cognitive approach is proposed to detect unknown beacons of terrestrial signals of opportunity (SOPs). Two scenarios are considered in the paper: (i) detection of unknown beacons with integer constraints (IC) and (ii) detection of unknown beacons with no integer constraint (NIC). An example of beacons with IC is the pseudo-noise (PN) sequences in cellular code division multiple access (CDMA) signals. On the other hand, the reference signals (RSs) in orthogonal frequency-division multiplexing (OFDM)-based systems can be considered as beacons signals with NIC. Matched subspace detectors are proposed for both scenarios, and it is shown experimentally that the proposed matched subspace detectors are capable of detecting cellular third-generation (3G) cdma2000 signals and fifth-generation (5G) OFDM signals. A low complexity method is derived to simplify the matched subspace detector with IC for <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> -ary phase shift keying ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> PSK) modulation. The effect of symbol errors in the estimated beacon signal on the carrier to noise ratio (CNR) is characterized analytically. Closed-form expressions for the asymptotic probability of detection and false alarm are derived. Experimental results are presented showing an application of the proposed cognitive approach by enabling an unmanned aerial vehicle (UAV) to detect and exploit terrestrial cellular signals for navigation purposes. In one experiment, the UAV achieved submeter-level accurate navigation over a trajectory of 1.72 km, by exploiting signals from four 3G cdma2000 transmitters. In another experiment, the UAV achieves a position root mean-squared error (RMSE) of 4.63 m over a trajectory of 416 m, by exploiting signals from two 5G transmitters.

Understanding the characteristic of GLONASS inter-frequency clock bias using both FDMA and CDMA signals

Understanding the characteristic of GLONASS inter-frequency clock bias using both FDMA and CDMA signals

GLONASS\u2013only FDMA+CDMA RTK: Performance and outlook

An assessment of standalone GLONASS RTK performance is provided using its FDMA and CDMA signals. The new integer-estimable GLONASS FDMA model (Teunissen 2019), which guarantees the integer-estimability of its ambiguities, is employed. We introduce the combined integer-estimable GLONASS FDMA+CDMA model and compare its strength against the FDMA model for instantaneous integer ambiguity resolution and positioning. Various combinations of GLONASS signals are considered including FDMA L1, FDMA+CDMA L1+L3, FDMA L1+L2 and FDMA+CDMA L1+L2+L3. To provide insight into the current RTK performance of GLONASS, we used observations of a short baseline to analyze the integer ambiguity resolution success rate and positioning precision, formally and empirically. To provide insight into the future RTK performance of GLONASS, we present a formal analysis of the integer ambiguity resolution success rate and ADOP, assuming that all the GLONASS satellites transmit FDMA L1, L2 and CDMA L3 signals. A formal analysis of standalone GLONASS ambiguity resolution based on current and future GLONASS constellation is then presented for different locations around the world.

Применение теории решетчатых упаковок в задаче определения временных корректирующих поправок для высокоточного абсолютного местоопределения по ионосферосвободным измерениям в ГНСС с кодовы м разделением

Using of lattice packing theory for computation of precise satellite clock corrections based on measurements from a ground network of GNSS CDMA signals (network solution) is considered. Advantage of lattice packing theory for this task solution in comparison with algebraic graph theory is described. Network solution based on of algebraic graph theory was considered in previous paper of the authors [3]. The precise satellite clock corrections are transmitted into the user receiver and applied to get the user coordinates with the errors usually not exceeding 1–3 cm. Ambiguity resolution of carrier phase measurements is used to get such precise satellite clock corrections; it leads to a considerable increase in positioning accuracy and a significant reduction of convergence time for user solution.

GLOBAL NAVIGATION SATELLITE SYSTEMS AND THEIR ROLE IN PRECISION AGRICULTURE TECHNOLOGIES

Today, global navigation satellite systems are being implemented in many structural units of the Ukrainian economic complex, many spheres of human activity, and every year they continue to develop. One of the main feature of these satellite systems is the requirements for high accuracy and speed of received data. They provide the opportunity to reduce operating costs and increase the efficiency of use of equipment and other resources. Therefore, the use of navigation satellite systems for controlling machine units, establishing their location, monitoring soil condition and yield mapping is becoming increasingly relevant today. The subject of study in this article were global navigation satellite systems NAVSTARGPS (USA), GLONASS (RF), GALILEO (EU), BEIDOU (China) and regional navigation systems NavIC (India) and QUASI-ZENITH (Japan). The purpose of the work was to clarify and establish the main characteristics of global navigation satellite systems and their role in the implementation of precision agriculture technologies. The task of the work was: to analyze the functional characteristics of global positioning satellite systems and their main elements; to find out principles of operation of systems: navigation, coordinates, time; to establish the accuracy of navigation systems; to substantiate the role of global positioning satellite systems in the effective implementation of precision agriculture technologies in agriculture. The research methodology was based on the method of materialistic dialectics, methods of analysis and synthesis of both information from official sources and information from the works of other researchers. Two major operators of satellite navigation systems the NAVSTAR GPS and GLONASS, which are similar in many respects, have been identified in the scientific work. Among the distinctive features there are the nature of the location, the motion of satellites in orbits and their total number, methods of encoding the CDMA and FDMA signals, the use of different coordinate systems WGS-84 and PZ90.11. As for the other two satellite navigation systems GALILEO and BEIDOU, they are developing rapidly with great ambition and potential. It is established that at the present time the accuracy of determining the coordinates of the GLONASS system is inferior to the performance of the American satellite navigation system GPS. GLONASS provides more accurate positioning in the northern latitudes and GPS in the middle. It is noted that the positioning accuracy of machine units for the implementation of precision farming technologies can be improved (from 2 to 20 cm) due to differential signal correction with the help of free and commercial wideband satellite navigation subsystems. These services will allow to implement the tasks of precision driving, and therefore, to ensure the accurate implementation of sowing material, fertilizers and herbicides to spare them, accurate inter-row cultivation of industrial crops, accurate harvesting, etc., when performing agro-technological operations using ground vehicles and landless vehicles.

Определение временных корректирующих поправок для высокоточного абсолютного местоопределения по сигналам ГНСС с кодовым разделением каналов

Определение временных корректирующих поправок для высокоточного абсолютного местоопределения по сигналам ГНСС с кодовым разделением каналов

High Drain Efficiency and High Linear Two Inverted Way Doherty Amplifier with High Power for CDMA Signal

A novel high drain efficiency two inverted Doherty amplifier is presented, A carrier amplifier and a peak amplifier are set to asymmetrical drain voltages to extend the power range where a high efficiency of the amplifier is maintained, matching circuits of the carrier amplifier and peak amplifier in the two inverted Doherty amplifier are designed for each drain voltage so that the efficiency and signal linearity of the amplifier at a 6.8dB back-off point from its’ saturated output power (Psat) become higher than those of a conventional amplifier. A Doherty amplifier containing laterally-diffused metal-oxide semiconductor (LDMOS) field-effect transistors (FETs) achieves an adjacent channel leakage power ratio (ACLR) of -30.8dBc and a drain efficiency of 50% at an output power of 49.3dBm.This is the highest drain efficiency of a Doherty amplifier use LDMOS for a WCDMA signal to the best of the authors’ knowledge.

Hiding Stealth Optical CDMA Signals in Public BPSK Channels for Optical Wireless Communication

A new optical steganography scheme is proposed that transmits a stealth optical code-division multiple-access (OCDMA) signal through a public binary phase-shift keying (BPSK) channel. Polarization beam splitters and arrayed waveguide gratings are used to implement a spectral-polarization coding (SPC) system with an incoherent optical source. We employ a Walsh–Hadamard code as the signature code of the user who wants to transmit stealth information using the system. A free space optical link applied to this system maintains the polarization states of light during propagation. The secret data are extracted using correlation detection and balanced subtraction in the OCDMA decoder of the intended receiver, and the other signal from the public channel is reduced by the OCDMA decoder. At the demodulator of the public channel, BPSK demodulation eliminates the stealth signal so that the public channel is not affected by the stealth signal. The two signals cannot interfere with each other. The results of this study show that our proposed optical steganography system is highly secure. The stealth signal can be favorably hidden in the public channel when the average source power of the stealth signal, public noise, and public signal are −5, −3, and 0 dBm, respectively.

A Radio Frequency Radiation Exposure System for Rodents based on Reverberation Chambers.

In this paper we present the novel design features, their technical implementation, and an evaluation of the radio Frequency (RF) exposure systems developed for the National Toxicology Program (NTP) of the National Institute of Environmental Health Sciences (NIEHS) studies on the potential toxicity and carcinogenicity of 2nd and 3rd generation mobile-phone signals. The system requirements for this 2-year NTP cancer bioassay study were the tightly-controlled lifetime exposure of rodents (1568 rats and 1512 mice) to three power levels plus sham simulating typical daily, and higher, exposures of users of GSM and CDMA (IS95) signals. Reverberation chambers and animal housing were designed to allow extended exposure time per day for free-roaming individually-housed animals. The performance of the chamber was characterized in terms of homogeneity, stirred to unstirred energy, efficiency. The achieved homogeneity was 0.59 dB and 0.48 dB at 900 and 1900 MHz respectively. The temporal variation in the electric field strength was optimized to give similar characteristics to that of the power control of a phone in a real network using the two stirrers. Experimental dosimetry was performed to validate the SAR sensitivity and determine the SAR uniformity throughout the exposure volume; SAR uniformities of 0.46 dB and 0.40 dB, respectively, for rats and mice were achieved.

Integrating Correlation Acquisition with Location Optimization for Accurate Indoor Lightwave Robot Positioning

In this paper, we proposed an indoor lightwave positioning system contains correlation operations with genetic algorithms. The implemented CDMA signaling system by spread spectrum (SS) codes can locate the position of the robot receiver as against noise interference. In the allocated LED transmitters, each channel of the transmitted signals is modulated into a series of maximal-length sequence code (M-sequence code) by LED light blinking. In the robot receiver, correlation peaks detection between received summed signal and each local replica signal is based to estimate the distance from each transmitter to the robot. We choose three transmitters among five to closest to the robot for more reliable positioning information. The robot positioning is first estimated by time difference of arrival (TDOA) and then genetic algorithm (GA) optimization is applied for more accurate robot location. We finally simulate out the TDOA result and analyze the accuracy of the robot position.

Toward a More Generalized Doherty Power Amplifier Design for Broadband Operation

The conventional Doherty power amplifier (DPA) theory is limited to single carrier operations, leading to a nongeneric structure. This paper presents a new analysis that generalizes the conventional DPA (CDPA) theory for increased efficiency and bandwidth. We demonstrate that by introducing a theoretical parameter $\alpha$ at the output combiner, we can redefine the relationships among the output combiner elements for a greater level of design flexibility than it was possible in the CDPA. We also show that previously published works in this area can be considered as special cases of the proposed general theory. As a demonstrator, a specific design, named reduced- $\alpha$ DPA, realized using GaN HEMTs is provided to illustrate the robustness of the approach. This design proves effective for further improving the performance of the previously published 2.14-/2.655-GHz dual-band parallel DPA. A maximum drain efficiency of 84% and 67% at an average of 43-dBm peak and 6-dB back-off power levels, respectively, was measured with continuous wave signals. To quantify the linearity performance, the proposed DPA was tested using wideband CDMA and long-term evolution signals where the adjacent channel leakage ratio was recorded at −25 dBc with an average output power of 38.7 and 36.5 dBm at 2.14 and 2.655 GHz, respectively.

Optical steganography transmission of optical CDMA signals over a public BPSK channel

Purpose – The purpose of this paper is to propose a new optical steganography framework that can be applied to public optical binary phase-shift keying (BPSK) systems by transmitting a stealth spectrum-amplitude-coded optical code-division multiple-access signal through a BPSK link. Design/methodology/approach – By using high-dispersion elements, the stealth data pulses temporally stretch and the amplitude of the signal decreases after stretching. Thus, the signal can be hidden underneath the public signal and system noise. At the receiver end, a polarizer is used for removing the public BPSK signal and the stealth signal is successfully recovered by a balanced detector. Findings – In a simulation, the bit-error rate (BER) performance improved when the stealth power increased. Research limitations/implications – The BER performance worsens when the noise power become large. Future work will consider increasing the system performance during high-noise power situation. Practical implications – By properly adjusting the power of the amplified spontaneous emission noise, the stealth signal can be hidden well in the public channel while producing minimal influence on the public BPSK signal. Originality/value – In conclusion, the proposed optical steganography framework makes it more difficult for eavesdroppers to detect and intercept the hidden stealth channel under public transmission, even when using a dispersion compensation scheme.

Performance Evaluation of Broad Band CDMA Signal Using Beam Forming Antenna Technology for Next Generation Communications

&lt;p&gt;In order to accommodate various multimedia services, next generation wireless networks are characterized by very high transmission rates. Thus, in such systems and networks, the received signal is not only limited by noise like Additive White Gaussian noise (AWGN) but especially with increasing data transmission rate by the Intersymbol Symbol Interference (ISI) due to time dispersion of channel. A number of techniques such as rake receiver in CDMA systems and equalizers in GSM systems have been proposed to combat the effect of fading so as to improve the performance of wireless communication network. In this paper we evolve the performance of uncoded uplink transmission in broadband CDMA using beam forming technique under multipath conditions. The beam-former has been implemented using Transport Delay Line (TDL) filters. An expression for the optimal weights of a TDL based beam former has been derived. A carrier frequency of 2 Ghz has been used in this work as they are useful for next generation wireless systems. Simulation results show that TDL beamformer can reduce the multipath fading and Multiple Access Interferance (MAI). It has been shown that if SNR (related with Variance of the channel) is maintained at 10 db and if a 3 ray based beamformer having 3 antennas with 3 taps is used, the Error Rate of 0.1was found without using channel coding.&lt;/p&gt;

High frequency CMOS amplifier with improved linearity

In this paper, a novel amplifier linearisation technique based on the negative impedance compensation is presented. As demonstrated by using Volterra model, the proposed technique is suitable for linearising amplifiers with low open-loop gain, which is appropriate for RF/microwave applications. A single-chip CMOS amplifier has been designed using the proposed method, and the simulation results show that high gain accuracy (improved by 38%) and high linearity (IMD3 improved by 14 dB, OIP3 improved by 11 dB and adjacent channel power ratio (ACPR) improved by 44% for CDMA signal) can be achieved.

Improved Multi-Channel Blind De-Convolution Algorithm for Linear Convolved Mixture DS/CDMA Signals

In this paper, an improved multi-channel blind de- convolution algorithm for code division multiple access signals is proposed. Through minimizing the average squared cross- output-channel-correlation, the proposed scheme achieves a better source separation performance for the linear convolved mixture system. Unlike most of the existing linear convolved mixture separation algorithms in the literature, the improved algorithm can obtain the original users' signal even in low signal-to-noise ratio in a non-cooperation scenario. Simulation results show that the proposed optimal scheme not only achieves superior performance on the bit error rate to those of the existing ones, but also provides a convergent solution under different channel conditions.  Index Terms—CDMA signal, non-cooperation, blind de- convolution, gradient algorithms

Peak to Average Power Ratio Reduction in Mc Cdma System by Using Pulse Shaping Technique

One of the drawback of multicarrier code division multiple access (MC CDMA) is the high peak to average power ratio (PAPR). In this paper A novel scheme based on pulse shaping described for PAPR reduction. Here three different pulse shaping filters (Raised cosine, Sinc power pulse and Nyqist pulse) are described for PAPR reduction in MC CDMA system. The method is based on the proper selection of the pulses for shaping the different sub carriers of the MC CDMA modulation scheme. It is shown by computer simulation that the scheme achieves the significant improvement in PAPR reduction in MC CDMA system. Its implementation complexity is much low in comparison to the previous published methods. Thus pulse shaping technique can be used not only to shape the spectrum of the transmitted signal but also to reduce its PAPR. In computer simulation It is observed that by using nyquist pulse near about 6.8 db PAPR is obtained. Which is considerable PAPR reduction than a PAPR value of Original MC CDMA signal

Statistical tuning of walfisch-bertoni pathloss prediction model based on building and street geometry sensitivity parameters in built−up terrains

One of the underlying difficulties with the application of a prediction pathloss model for any environment is that no two areas are identical in the composition of the buildings and terrain. A pathloss model developed by Walfisch-Bertoni considers the impact of rooftops and building heights by using diffraction to predict average signal strength loss at street level. However, the error between the average path loss predicted by the model and that observed in practice will be smallest when the propagation environment conforms closely with the models assumptions (i.e. those urban environments exhibiting minimal variation in the height and separation of buildings). In particular, any building height variations can be expected to cause a significant error in the model predictions. Firstly, in this paper, we demonstrate the sensitivity impact of varying certain parameters on the performance W/B model in the study environments. The goal is to give the user an idea of the value associated with altering parameters that are in fact adjustable and showing the significance of the unchangeable parameters in the loss calculations. Secondly, a new statistical tuning method is proposed by extending the technique of Walfisch- Bertoni model which is now valid for generalized conditions in the CDMA2000 signal propagation environments. The results showed that tuned pathloss data agree strongly with measured data in the different study locations.

Performance Analysis of Independent Component Analysis Algorithms for Multi-user Detection of DS-CDMA

conventional detection process of direct sequence code division multiple access (DS-CDMA) is limited by multiple access interference (MAI) due to loss of orthogonality between spreading waveforms in multipath propagation channel environment.. In this paper RADICAL Independent Component Analysis (ICA) algorithm is proposed for detection of DS-CDMA signals and compared with FastICA, JADE ICA algorithm. Independent component analysis (ICA) is statistical technique based on higher order statistics, represent set random variables as linear transformation of statistically independent components and these conditions are satisfied in multi-user CDMA environment. Conventional methods mitigate sources of interference by taking into account all available information and at times seeking additional information channel characteristics, direction of arrival, etc. Combining an ICA element to conventional signal detection reduces multiple access interference (MAI) and enables a robust, computationally efficient structure. The proposed algorithm takes advantage of differential entropy estimation and converges quickly. Bit error rate simulations of these algorithms have been given and compared for different number of users, SNR. The simulation results show that RADICAL ICA algorithm performs best on detecting the source signals from the mixed CDMA signals.

A Clock-Harvesting Receiver Using 3G CDMA Signals in the 1900-MHz Band

A clock-harvesting receiver is presented, which extracts a 1.2-kHz clock embedded within the third-generation code-division multiple-access standard for the wake-up of a wireless sensor network. The energy-detection-based receiver was fabricated in 0.13-μm CMOS and designed for low-power heavily duty-cycled operation. In active mode, the receiver has a measured sensitivity of -73 dBm while consuming only 298 μW. The harvested-clock output has 7 μs of root-mean-square jitter at the sensitivity level, which improves with higher received power. In sleep mode, the receiver consumes only 44 pW with a start-up time of 80 μs.

Reduction Techniques of Peak-to-Average Power Ratio in MC-CDMA Systems

The high peak-to-average power ratio (PAPR) is one of the main disadvantages of multicarrier code division multiple access (MC-CDMA) system. To reduce the PAPR of multicarrier CDMA signals, a lot of studies have been focused on the power characteristics of spreading sequences. This paper presents the main techniques to reduce the PAPR in MC-CDMA like Amplitude Clipping and Filtering, Coding, Selective Mapping, The adaptive predistortion technique and DFT Spreading. Then a comparison of all these techniques is done in order to clarify the main advantages and disadvantages of each technique. DOI: http://dx.doi.org/10.11591/ij-ict.v1i2.558