Wideband Code Division Multiple Access Research Articles

A Highly Extended High-Efficiency Range Class-F–C Doherty Power Amplifier

This paper presents a new extended high-efficiency-range Doherty power amplifier (DPA) with a main and only a single auxiliary amplifier. In order to extend the output high-efficiency range with a high-efficiency level, asymmetrical cells are employed as the main and auxiliary amplifiers in class-F and class-C complex combining load (CCL) methodology, respectively. To verify the proposed methodology, a DPA with 12-dB output back-off (OBO) is designed and fabricated for wideband code division multiple access (WCDMA) applications. Large-signal continuous-wave measurement results show the power gain of about 11[Formula: see text]dB with a drain efficiency of 59.9% at 12[Formula: see text]dB of OBO. A two-tone test exhibits a third-order intermodulation distortion (IMD) of lower than [Formula: see text][Formula: see text]dBc. Modulated wave measurements show over 55% of average drain efficiency and an adjacent channel leakage power ratio (ACLR) of lower than [Formula: see text][Formula: see text]dBc at an output power level of 31.5[Formula: see text]dBm.

Evolution of random access process: From Legacy networks to 5G and beyond

AbstractIn this paper, we discuss the random access procedures in legacy networks, long‐term evolution, LTE‐Advanced, and 5G networks. Random access is the first and incumbent step for connection establishment between base station/eNodeB/gNodeB and user equipment. Keeping in view its importance, there has been a regular thrive to improve the procedures of random access in communication networks. With the advent of new concepts such as machine‐type communication and Internet of Things, random access becomes extremely critical because huge number of devices try to connect to the network simultaneously. We present the evolution of random access process from legacy networks such as global system for mobile or wideband code division multiple access to 5G networks and beyond and their analysis. Simulations are performed in MATLAB to show various performance metrics such as access delay, total service time, and collision probability to demonstrate the pros and cons of one technique over another.

Embedded 3D multi‐band antenna with ETS process technology covering LTE/WCDMA/ISM band operations in a smart wrist wearable wireless mobile communication device design

An internal etching for three-dimensional structures (ETS) antenna capable of operating in the 810-960, 1370-1450 and 1710-2630 MHz bands, respectively, for long-term evolution (LTE)/wideband code division multiple access (WCDMA)/2.4 GHz industrial, scientific and medical (ISM) band operations suitable for being embedded within a smart wrist wearable wireless mobile communication device is proposed. The proposed antenna radiation efficiency can achieve 37.8-55.3% from 810-960 MHz, 53.1-92.63% from 1370-1450 MHz and 52.9-93.1% from 1710-1630 MHz for LTE/WCDMA bands and 87.4% for ISM band without the hand phantom in the free space condition. The antenna radiation efficiency of the LTE/WCDMA and ISM bands is reduced by half because of the hand phantom with lossy material properties. Furthermore, the health risk related to exposure to electromagnetic radiation, the specific absorption rates of the device are evaluated and the results were far below the limits required by the Federal Communications Commission (FCC) organisation. The embedded three-dimensional (3D) multi-band antenna can be adapted for the smart wrist wearable wireless mobile communication device. This study breaks the pattern that wearable devices must work with mobile phones. The wearable device proposed herein can directly communicate with the carrier base station independently.

Space-time diversity signal processing employed by W-CDMA systems

Transmit diversity under transmission of signals from the base station to mobile station using the code-division multiple-access (CDMA) system allows us obtaining the performance gains close to the mobile station receiver diversity without complexity of the mobile station receiver antenna array. The multipath diversity can be achieved using the pre-RAKE precoding at the transmitter that could be employed and there is no need to install the RAKE receiver at the mobile station. We investigate several transmitter diversity techniques employed by wideband CDMA (W-CDMA) systems. We also study a possibility to combine transmitter diversity and precoding that achieves the gain of maximum ratio combining of all space and frequency diversity branches jointly with long-term prediction algorithm. It was demonstrated that the performance of the space-time pre-RAKE method approaches the performance of the maximum ratio combining for all space and frequency diversity branches. It is shown that all closed loop methods depend on the long range prediction to approximate the ideal performance in the fast fading environment.

A Triple-Band CMOS Power Amplifier Using Multi-Band and Switchable Matching Network for Wireless Mobile

A triple-band CMOS power amplifier (PA) is presented. We propose a design methodology using an input matching network to support triple-band operation at 0.9, 1.8, and 2.4 GHz. We also propose an output matching network for the triple-band operation. Given that 1.8 and 2.4 GHz are the harmonic components when the PA is operating at 0.9 GHz, we design the output matching network to be switchable to suppress the harmonic components at the operating frequency. Using this switchable network, we obtain an optimum power matching point for each of the three operating frequencies. To verify the feasibility of the proposed structure, we designed a PA using a 180-nm RFCMOS process. It was measured using a wideband code division multiple access (WCDMA), Long-Term Evolution (LTE) at a 10/20-MHz bandwidth and wireless local area network (WLAN) 802.11n applications. The measured output power was 27.2/26.6 dBm, and the power-added efficiency (PAE) was 22.9%/30.6% under an adjacent channel leakage ratio (ACLR) of -33 dBc at 0.95/1.8 GHz, respectively, with a WCDMA modulation signal. In the case of an LTE modulation signal, the measured output power was 25.1/23.5 dBm, and the PAE was 27.7%/23.6% under an ACLR of −30 dBc for a 10/20-MHz bandwidth, respectively, at 1.8 GHz. The measured output power was 21 dBm, and the PAE was 20% under an error vector magnitude (EVM) of 3.98% at 2.4 GHz for a WLAN modulation signal. Based on the measured results, we successfully verified the feasibility of the proposed PA.

IMPROVISATION OF MESH NETWORK WITH WIDEBAND CODE DIVISION MULTIPLE ACCESS

Mesh Networks are employed in various applications despite issues relevant to interference and network capacity. These networks also impose delay in routing and reconfiguration. Traditionally, TDMA and FDMA techniques have been used in these networks. This paper proposes wideband code division multiple access (WCDMA) technique for enabling maximum power transfer, low energy consumption, interference free and plug-and-play feature enabling easy implementation of the technology. The spatial configuration and node count bounds are stated ensuring continuous satisfaction of quality of service by the communication link. Additionally, dynamic parallel orthogonal transmission and turbo coding schemes are used in combination to improve the efficiency of the network even for large hop counts.

A Miniaturized Dual-Band Dual-Polarized Band-Notched Slot Antenna Array With High Isolation for Base Station Applications

In this article, a miniaturized dual-band dual-polarized slot antenna array is proposed for base station applications. It consists of two closely located $1 \times 4$ subarrays for the digital cellular system (DCS) and wideband code division multiple access (WCDMA) operations. The band-notched slot antenna (BNSA) is designed and adopted as the subarray element with radiation-suppression characteristic at notch frequencies. The notch frequency for one subarray is designed at the center operating frequency of the other subarray. As a result, the radiation from DCS subarray could be effectively suppressed within the WCDMA band and vice versa, resulting in high isolation between two subarrays with a small separation distance. By using the artificial magnetic conductor (AMC) reflector, the array height could be reduced by half, as compared with the perfect electric conductor (PEC) counterpart. In addition, a four-way unequal power divider is designed for the array's beam-pattern synthesis. For the demonstration, the proposed array is fabricated and measured. The measurement results show that the dual-band array achieves the impedance bandwidths of 1.65-1.88 and 1.89-2.22 GHz, the isolations over 25 dB, the realized boresight gains of 12.2-12.8 and 12.3-13.2 dBi, and the sidelobe levels below -18 dB. The results indicate that the proposed array is a promising candidate for base-station applications.

Comparative Analysis of Greedy Pursuits for the Order Reduction of Wideband Digital Predistorters

This paper provides a review of greedy pursuits for optimizing Volterra-based behavioral models structure and estimating its parameters. An experimental comparison of the digital predistortion (DPD) linearization performance achieved by these approaches for model-order reduction, such as compressive sampling matching pursuit (CoSaMP), subspace pursuit (SP), orthogonal matching pursuit (OMP), and the novel doubly OMP (DOMP), is presented. A benchmark of the techniques in the DPD of a commercial class AB power amplifier (PA) and a class J PA operating over a 15-MHz Long-Term Evolution (LTE) signal is presented, giving a clear overview of their pruning characteristics in terms of linearization indicators and regressor selection capabilities. In addition, the benchmark is run in a cross-validation scheme by identifying the DPD with a 30-MHz 5G-new radio (NR) signal and validating with the same signal and a 20-MHz multicarrier wideband code division multiple access (WCDMA) signal. The DOMP is shown to be a promising technique since it achieves an enhanced model-order reduction for a similar linearization performance and precision.

High performance miniaturized compact diplexer based on optimized integrated passive device fabrication technology

In this study, we proposed a compact miniaturized diplexer using 650 μm polished gallium arsenide (GaAs) substrate via thin film integrated passive device (TF-IPD) fabrication technology. The introduction of the three-order elliptic function diplexer can achieve low insertion loss and high isolation between the two outputs with a dimension of 1.9 mm × 0.8 mm × 0.2 mm (0.0053 λ0 × 0.0023 λ0 × 0.0005 λ0). The optimized IPD techniques for spiral inductor and metal-insulator-metal capacitor (MIMCAP) are discussed to achieve high Q-factor and excellent stability of the fabricated devices. Notably, the compact GaAs-based diplexer exhibits high performance with insertion loss of 0.5 dB and return loss larger than 16 dB. Besides, the isolation level between the two output ports is higher than 30 dB, which ensures the two ports can work independently without interference from each other. This study provides a facile fabrication approach for global system for mobile communications (GSM) and wideband code division multiple access (WCDMA) wireless communication systems.

Impact analysis of mobile phone electromagnetic radiations on human electroencephalogram

The experimental study of electromagnetic interference of mobile phone radiations on brain waves is a contemporary research area and the ever-increasing use of mobile phones make it more imperative to explore the problem area in detail. Electromagnetic signal from mobile phones operating in Global System for Mobile (GSM) and wide band code division multiple access (WCDMA), has been considered in this paper and their interference impacts have been analyzed on the human electroencephalogram (EEG). The impact on brain waves i.e., delta, theta, alpha, beta and gamma waves are analyzed in five modes namely ideal mode i.e., when mobile phone is not in use, transmission mode and the receiving modes of second generation (2G) and third generation (3G) networks. The data has been acquired from 75 young and healthy students of a post graduate institute while the students were making their routine calls. The acquired EEG signal is analyzed using various parameters viz.; Approximate Entropy(ApEn), Largest Lyapunov Exponent (LLE), Hurst Exponent (HE), Correlation dimension (CD) and the power of the brain waves have also been analyzed. It has been found that due to mobile phone usage, there is variation in the nonlinear parameters and increase in the power of the alpha brain waves at T5O1 during 3GRx and decrease in alpha power at the P4O2 channel in all modes. It has been observed that the change at the right temporal region is more, the side to which mobile phone was held. The Statistical analysis has also been done using SPSS software which shows significant variations at some of the channels in different modes.

Performance evaluation of a downlink MIMO wideband code‐division multiple access‐based radio‐over‐fibre system using Alamouti space‐time block code

In this work, the effect of a radio-over-fibre (RoF) subsystem on the bit error rate (BER), total degradation (TD) and system capacity performances of downlink multiple-input multiple-output (MIMO) wideband code division multiple access (WCDMA) are assessed. The research investigates the use of maximal ratio combining (MRC) in single-input multiple-output (SIMO) schemes and Alamouti space-time block coding (STBC) in MIMO systems to compensate for the collective effects of the optical subsystem and the radio channel for different channel conditions and number of users. Results show that the aforementioned techniques are effective methods to compensate for both the non-linearity of the optical subsystem and the time-varying wireless radio frequency (RF) channel. It is also demonstrated that by increasing the number of users for severe non-linearity conditions, the BER performance of the system is significantly affected. Also, an appropriate quiescent point can always be found for the optical subsystem which improves the system performance irrespective of different conditions.

Experimental Study on the Impact of Weather Conditions on Wide Code Division Multiple Access Signals in Nigeria

In cellular network activities, before a site is integrated it is expected that each cell of the site meets the Nigerian Communication Commission (NCC) standard of ≥98% for both service accessibility and call completion rate which in turn depicts a ≤2% in both blocked call rate (BCR) and dropped call rate (DCR). It is suggested that weather conditions have a very strong negative effect on the performance of wideband code division multiple access (WCDMA) network as it could lead to signal attenuation or change the polarization. In this paper, we study the impact of weather conditions on WCDMA network in Nigeria. To achieve this, network samples (log-files) were collected weekly during a driving test in Enugu State Nigeria for a period of five years for both rainy and dry seasons, in which blocked and dropped calls were extracted. Results show that during adverse weather conditions, BCR and DCR rise greater than 8% and 4% respectively. Although with a slight relationship between the weather conditions, the weather condition during the dry season has a better-blocked call rate of 8.76% in comparison with the rainy season with 12.89%. Calls tend to drop more during the dry season. From the outcome of the experiment, a model was developed for predicting an unknown network call statistics variables.

Hysteresis Current Control for Multilevel Converter in Parallel-Form Switch-Linear Hybrid Envelope Tracking Power Supply

Parallel-form switch-linear hybrid (SLH) envelope tracking (ET) power supply is constituted by a linear amplifier and a switched-mode converter connected in parallel. The switched-mode converter is usually implemented by a buck converter with hysteresis current control. However, the slew rates of the load current and the inductor current of the buck converter cannot match well when the slew rate of the load current has a wide variation range. The unmatched slew rates will lead to a high switching frequency of the buck converter or a large loss of the linear amplifier, which degrades the overall efficiency. In this paper, a multilevel converter is adopted to replace the buck converter in the parallel-form SLH ET power supply, and the hysteresis current control scheme is proposed for the multilevel converter to dynamically adjust its inductor current slew rate to approach that of the load current to improve the overall efficiency. The optimal design for the efficiency-related parameters including the inductor, the current hysteresis, and the number and values of the voltage levels in the multilevel converter is given. A prototype of the parallel-form SLH ET power supply with hysteresis current controlled multilevel converter is fabricated and tested in the lab. The measured overall efficiency is 79.4% when tracking the envelope of wideband code division multiple access signal with 5 MHz bandwidth and outputs 18 W average power, and a 3.8% efficiency improvement is achieved over that with the hysteresis current controlled buck converter.

Multi–Dimensional Wireless Signal Identification Based on Support Vector Machines

Radio air interface identification provides necessary information for dynamically and efficiently exploiting the wireless radio frequency spectrum. In this study, a general machine learning framework is proposed for Global System for Mobile communications (GSM), Wideband Code Division Multiple Access (WCDMA), and Long Term Evolution (LTE) signal identification by utilizing the outputs of the spectral correlation function (SCF), fast Fourier Transform (FFT), auto–correlation function (ACF), and power spectral density (PSD) as the training inputs for the support vector machines (SVMs). In order to show the robustness and practicality of the proposed method, the performance of the classifier is investigated with respect to different fading channels by using simulation data. Various over–the–air real–world measurements are taken to show that wireless signals can be successfully distinguished from each other without any prior information while accounting for a comprehensive set of parameters such as different kernel types, number of in–phase/quadrature (I/Q) samples, training set size, or signal–to–noise ratio (SNR) values. Furthermore, the performance of the proposed classifier is compared to the existing well–known deep learning (DL) networks. The comparative performance of the proposed method is also quantified by classification confusion matrices and Precision/Recall/ $F_{1}$ –scores. It is shown that the investigated system can be also utilized for spectrum sensing and its performance is also compared with that of cyclostationary feature detection spectrum sensing.

A Novel Multi-Band Reduced Sampling Rate and I/Q Compensation Technique for RF Power Amplifiers

In this paper, a novel multi-band reduced sampling rate technique is proposed for power amplifier (PA) linearization system. It is used to enhance performance and reduce hardware costs in spectrum aggregation discontinuous broadband systems and compensate in-phase/quadrature (I/Q) imbalance in the multi-band case. During the feedback loop process of sampling rate, a band-limited filter is introduced, and the frequency band extrapolation is carried out so that the spectrum outside the limited band is compensated effectively. Theoretical analysis is performed to compare the proposed method and the conventional methods. To evaluate the performance of the proposed method, a broadband PA is excited by a tri-band signal composed of a 20 MHz long-term evolution (LTE) signal at 1.31 GHz, a 20 MHz 4-carrier wideband code division multiple access (WCDMA) signal at 2.49 GHz, and a 20 MHz 2-carrier WiMAX signal at 2.58 GHz respectively. The experimental results demonstrate that the normalized mean square error (NMSE) can get high accuracy less than −41 dB, with peak-to-average power ratio (PAPR) equaling 9 dB accompanied by a large reduction in sampling rate. Error vector magnitude (EVM) is 1% better than band-limited memory polynomial (MP) model and 2.3% better than conventional MP model.

A Memory Term Reduction Approach for Digital Pre-Distortion Using the Attention Mechanism

Over recent years, the memory effect compensated digital pre-distortion (DPD) has been widely used for linearizing wideband radio frequency power amplifiers (RF-PAs). However, with the increase of memory depth, the DPD model becomes more accurate, but the computational complexity of the DPD is significantly increased. In this paper, an approach using the attention mechanism is proposed, which can be used for locating and eliminating the memory terms with a small contribution to the performance of the DPD model so that the complexity of the DPD model is significantly reduced. The attention mechanism is employed to obtain the weighted correlation coefficient matrix of the memory effect. And the memory terms in the DPD model will be retained only if the contributions are high, which are evaluated by ensemble averaging over each diagonal of the weighted correlation coefficient matrix. To verify the applicability of the approach, a three-carrier wideband code-division multiple access signals with a bandwidth of 15 MHz and a single carrier long-term evaluation signal with a bandwidth of 20 MHz are employed for testing two Doherty RF-PAs with an operating frequency of 460 and 1900 MHz. Moreover, the generalized memory polynomial model is used to verify the effectiveness of the proposed approach. The simulation and experimental results show that the modeling accuracy and the DPD linearization performance of the DPD model with and without the memory term reduction are all almost the same, which indicates the effectiveness of the proposed approach.

Compact wideband transparent antenna for 5G communication systems

AbstractA compact wideband transparent antenna designed on plexiglass substrate (10 × 12 × 1.48 mm3) is presented. The optically transparent antenna consists of a radiation patch and a ground plane fabricated using AgHT‐8. The antenna design comprises of rectangular shaped branches optimized to attain the wideband characteristics. The proposed antenna design has impedance bandwidth of 58.71% covering the frequency range of 23.92‐43.8 GHz. The radiation pattern of the proposed antenna shows directional radiation pattern with electrical tilt. All calculated and measured results show that proposed compact transparent antenna is an excellent candidate for 5G communication systems and wideband code division multiple access applications.

A common gate LNA with negative resistance for noise reduction

This paper presents a common-gate (CG) low-noise amplifier (LNA) using a novel negative resistance to improve its noise figure (NF). The new negative-resistance CG-LNA (NR CG-LNA) shows superior performance over the conventional CG-LNAs in terms of power consumption, gain and NF. A prototype designed in 180 nm CMOS technology, occupied a silicon area of 0.57 mm2. The post layout simulations show a maximum gain of 20.2 dB, and a minimum NF of 2.3 dB with 8.5-mW of power consumption operating in 1.95 GHz–2.3 GHz bandwidth, which could be used in Wideband Code- Division Multiple Access (WCDMA) applications.

On the Reduction of Transmission Complexity in MIMO-WCDMA Frequency-Selective Fading Orientations via Eigenvalue Analysis

In this paper, a novel transmission strategy for Mutliple Input Multiple Output Wideband Code Division Multiple Access (MIMO-WCDMA) orientations operating in frequency-selective fading environments is investigated, in terms of overall algorithmic complexity reduction. To this end, Principal Component Analysis (PCA) is employed on the received data matrix, in order to define the significant terms that are taken into account during transmission matrix formulation. According to the presented results, feedback information of only the primary eigenvector of the corresponding covariance matrix of the received data matrix is required, in order to maintain the mean Bit Error Rate (BER) at acceptable levels. In particular, a complexity reduction of up to 10% can be achieved, when comparing BER values derived by the selection of all components of the received covariance matrix during transmission matrix formulation, and the corresponding BER when selecting half of the components. This reduction is maintained to 10%, when considering a realistic four-element antenna design; however, in this case mean BER inaccuracy is further reduced to 1%.

A Frequency Selective Feedback Receiver for Multi‐Bands Operation

AbstractFor a frequency‐division duplex (FDD) wide‐band code‐division multiple‐access (WCDMA) system, transmit (TX) signal leakage at the receiver input degrades the receiver performance. To cancel this TX leakage, a frequency selective feedback was previously proposed, but it had an unpredictable feedback loop characteristic due to the uncertainty of the duplexer impedance. This paper presents a new method to achieve TX leakage cancellation regardless of the duplexer impedance. In addition, a local oscillator (LO) phase shift technique is proposed to apply this method for multi‐band. A receiver adopting these proposed techniques is implemented using a 0.18‐μm CMOS process to prove the concept. The measured TX attenuations of the high‐ and low‐band are 17‐dB and 20‐dB, respectively, and the measured noise Figure (NF) degradations of the high‐ and low‐band are 0.6‐dB and 0.5‐dB, respectively. The measurement results demonstrate effectiveness of the proposed techniques.