Long Term Evolution System Research Articles

LTE Human Exposure Evaluation: Maximum RF Field Strength Extrapolation Technique Repeatability Analysis

The measurement of human exposure to electromagnetic fields (EMFs) is an important topic in today's scenarios where a pervasive diffusion of cellular networks, as well as short-range and personal wireless devices, negatively affects the human exposure issues. Focusing the attention on cellular systems, despite regulators and normative committees are conveying specific guidelines for the measurements of EMFs generated by cellular networks, there are several issues still to be addressed regarding the most reliable measurement procedures and the evaluation of their measurement uncertainty. In this framework, this article focuses on long-term evolution (LTE) systems by providing a large experimental analysis aimed at evaluating the repeatability of the measurement results, achieved by means of one widely recognized human exposure assessment methods, i.e., maximum RF field strength extrapolation technique, which is recommended to give worst case and time-independent estimations of the maximum electric field. To this aim, a huge amount of signal acquisitions (about 112 000 traces) is collected for several weeks, by considering two mobile network operators and two frequency bands. Results have shown how some factors, as instrument settings and the time interval in which the measurements are taken, can significantly affect the measurement results and their repeatability. Furthermore, in some cases, such effects become comparable to or even larger than typical uncertainty components of the measurement chain. To mitigate these issues, the authors also suggest some possible solutions to improve the measurement procedure's overall repeatability.

Unitary Matrix Method for PAPR Reduction of IDFT-VFDM Signals

To enable the frequency reuse between the new radio (NR) and the long-term evolution (LTE) systems, inverse discrete Fourier transform-based Vandermonde-subspace frequency division multiplexing (IDFT-VFDM) has been proposed to exploit the guard intervals of the conventional orthogonal frequency division multiplexing (OFDM) system. One important issue of the IDFT-VFDM system is the high peak-to-average power ratio (PAPR), which distorts the transmitted signal and causes severe performance degradation. Compared to OFDM, the method to reduce the PAPR in IDFT-VFDM requires unique design to guarantee zero interference to the legacy LTE system. To deal with this problem, a unitary matrix based method is proposed to design the precoder at the NR users to reduce the PAPR, which can also guarantee the minimum residual interference to the LTE system. Simulation results are demonstrated to verify the effectiveness of the proposed scheme.

Reinforcement Learning for Efficient and Fair Coexistence Between LTE-LAA and Wi-Fi

Long-Term Evolution (LTE) over unlicensed spectrum extends LTE technology to the spacious unlicensed spectrum with readily available bandwidth. The provided capacity surge makes it one of the most high-profile technologies to meet the explosive growth of mobile traffic demand. Among its different variants, Licensed Assisted Access (LAA) is considered as a promising global solution attributed to its mandatory listen-before-talk (LBT) procedure. Nevertheless, although LBT effectively maintains transmission fairness between LTE and other unlicensed systems (e.g., Wi-Fi), the current LAA protocol specified in 3GPP Release 13 is far from perfect to achieve harmony coexistence. To this end, in this paper, we first develop an analytical model to evaluate the throughput performance of Category 4 (Cat 4) algorithm agreed in 3GPP release 13. Subject to the system fairness constraint, the aggregate throughput of LTE-LAA and Wi-Fi networks is maximized based on a semi branch and bound algorithm. To make the complex optimization tractable, reinforcement learning techniques are introduced to intelligently tune the contention window size for both LTE-LAA and Wi-Fi nodes. Specifically, a cooperative learning algorithm is developed assuming that the information between different systems is exchangeable. A non-cooperative version is subsequently developed to remove the previous assumption for better practicability. Extensive simulations are conducted to demonstrate the performance of the proposed learning algorithms in contrast to the analytical upper bound under various conditions. It is shown that both proposed learning algorithms can significantly improve the total throughput performance while satisfying the fairness constraints. Particularly, the proposed cooperative learning algorithm can closely approach the analytical bound.

Integrated LTE and Millimeter-Wave 5G MIMO Antenna System for 4G/5G Wireless Terminals.

This work demonstrates an integrated multiple-input multiple-output (MIMO) antenna solution for Long Term Evolution (LTE) and Millimeter-Wave (mm-wave) 5G wireless communication services. The proposed structure is comprised of a two-element LTE MIMO antenna, and a four-element 5G MIMO configuration with rectangular and circular defects in the ground plane. For experimental validation, the proposed structure is fabricated on a Rogers RO4350B substrate with 0.76 mm thickness. The overall substrate dimensions are 75 mm × 110 mm. The proposed structure is capable of operating at 5.29–6.12 GHz (LTE 46 and 47 bands) and 26–29.5 GHz (5G mm-wave) frequency bands. Additionally, the measured peak gain of 5.13 and 9.53 dB is attained respectively for the microwave and mm-wave antennas. Furthermore, the analysis of the MIMO performance metrics demonstrates good characteristics, and excellent field correlation performance across the operating bands. Furthermore, the analysis of the Specific Absorption Rate (SAR) and Power Density (PD) at the lower frequency band (5.9 GHz) and PD only at mm-Wave frequency band (28 GHz) verifies that the proposed antenna system satisfies the international human safety standards. Therefore, the proposed integrated MIMO antenna configuration ascertains to be a potential contender for the forthcoming communication applications.

Observed time difference of arrival based position estimation for LTE systems: simulation framework and performance evaluation

Precise user equipment (UE) location is paramount for the reliable operation of location-based services provided by mobile network operators and other emerging applications. In this paper, the Long Term Evolution (LTE) network positioning performance based on mobile assist Observed Time Difference of Arrival (OTDoA) method is considered. The received signal time difference (RSTD) measurements are estimated by the UE using dedicated position reference signal (PRS) transmitted in the downlink frame where the reported time measurements are used by the network for location calculation. A simulation framework for the position estimation in LTE networks is presented where the LTE downlink communication link is implemented. The correlation-based method for the time of arrival measurement is used for the implementation of OTDoA. The simulation framework provides different configurations and adjustments for the system and network parameters for evaluating the performance of LTE positioning using OTDoA over multipath fading channels. Different simulation scenarios are conducted to identify the influence of various parameters of LTE system and positioning procedure setup on the positioning accuracy. Simulation results demonstrated that the positioning accuracy is highly affected by the channel fading condition where the accuracy of time of arrival measurements is deteriorated in severe fading environments; however, the positioning accuracy can be significantly improved by increasing the positioning sequences involved in the estimation process either in the frequency domain or in the time domain.

Effective Time, Frequency, and Sidelink Synchronization for Cellular Device-to-Device Communications

This article proposes an efficient time, frequency, and sidelink synchronization algorithm for device-to-device communication in a long-term evolution system. To end this, the proposed synchronization scheme uses both the structure of cyclic prefix and sidelink synchronization signals. By performing cyclic prefix mode and primary sidelink synchronization signal detection in the time domain, the performance of the frequency-domain synchronization receiver, including carrier frequency offset and sidelink identity detection, is improved. To assess the usefulness of the proposed synchronization method, the mean square error and the detection probability are theoretically derived. Simulation results show that the proposed synchronization scheme achieves robust detection of carrier frequency offset, symbol timing offset, cyclic prefix mode, and sidelink synchronization signal in a time-frequency doubly selective fading channel.

Rendimiento de la técnica de acceso múltiple no ortogonal (NOMA) en un sistema de comunicación móvil Long-Term Evolution (LTE)

La creciente demanda de datos a través de las redes móviles y la búsqueda de servicios más eficientes por parte de los usuarios han inducido a la generación de nuevas técnicas que incrementen la eficiencia espectral. El acceso múltiple no-ortogonal (NOMA) es una de las técnicas que están siendo evaluadas dentro del 3GPP (Third Generation Partnership Project), esta proporciona servicios a múltiples usuarios mediante multiplexación en potencia. Esta investigación evalúa el rendimiento de NOMA en sistemas LTE (Long Term Evolution) mediante simulaciones de capa física, en relación con las tecnologías de acceso múltiple ortogonales convencionales TDM (Time Division Multiplexing) y FDM (Frequency Division Multiplexing). Se compararán, además, las ganancias obtenidas, con las publicadas en la bibliografía de Advanced Television Systems Committee(ATSC) 3.0. Los resultados demuestran que NOMA es mejor que TDM en los casos que se utilice una tasa baja en el receptor móvil y una tasa media en el receptor fijo, demostrando ganancias de 3.35 y 0.25 respectivamente.

Efficient and fair Wi-Fi and LTE-U coexistence via communications over content centric networking

With the increasingly huge mobile traffic, numerous mobile operators try to seek some ways to alleviate the situation, such as expanding the LTE (Long Term Evolution) system into unlicensed spectrums. However, LTE-U (LTE in unlicensed spectrums) may interfere with Wi-Fi system that originally communicates in unlicensed spectrums and lead to marked decline of both Wi-Fi and LTE-U service qualities. To enable the fair coexistence of Wi-Fi and LTE-U systems in unlicensed spectrums, a novel mechanism over CCN (Content Centric Networking) containing two modes of communication (direct and indirect) between LTE-U and Wi-Fi systems is proposed in this paper. Moreover, the fair coexistence of LTE-U and Wi-Fi systems in unlicensed spectrums can be regarded as a resource allocation problem and formulated as a constrained optimization problem whose goal is to maximize the amount of data transmitted by different systems in a communication cycle, two approaches are also proposed to solve the optimization problem by adjusting the transmission time of different systems. The performance of the proposed mechanism and approaches is evaluated by simulations via NS-3 and theoretical calculations, the results demonstrate that the proposed mechanism and approaches can effectively ensure the fair coexistence of LTE-U and Wi-Fi in unlicensed spectrums and improve the overall channel utilization of unlicensed spectrums.

Effective Joint Detection of Synchronization Signal, Duplex Mode, and Frequency Offset for LTE Machine-Type Communications

In this article, a complexity effective and robust cell search method is proposed for machine-type communication in a long-term evolution system. The correlation between the primary synchronization signal (PSS) and secondary synchronization signal (SSS) in the frequency domain is exploited to remove the effect of channel fading distortion and symbol timing offset. This design facilitates robust synchronization of the carrier frequency offset, sector ID, and duplex mode without performing hypothesis testing on SSS candidates, followed by the detection of group ID. Both theoretical and experimental results are presented to justify the effectiveness of the proposed cell search scheme. The simulation results show that the proposed method achieves robust and reduced-complexity cell search when there are nonnegligible residual symbol timing error and frequency-selective fading distortion, compared to existing methods.

IDFT-VFDM for Supplementary Uplink and LTE-NR Co-Existence

During the first phase of the deployment of new radio (NR) networks, base station (BS) and user equipment (UE) are expected to operate alongside the pre-existing long-term evolution (LTE) networks. This paper proposes a solution to be adopted by NR UE to perform an uplink transmission towards NR BS over the same time and frequency resources as the legacy LTE system, which would extend the uplink coverage when operating at the supplementary uplink band. In order to guarantee the absence of interference towards LTE BS, we design a new waveform termed as inverse discrete Fourier transform-based Vandermonde-subspace frequency division multiplexing (IDFT-VFDM) with the following important features. On one hand, an NR UE communicating with an NR BS through IDFT-VFDM would not generate any interference at the legacy LTE BS, regardless of the number of antennas present at both ends of the interference channel. On the other hand, an IDFT-VFDM signal can always be designed to occupy the same signal bandwidth as a legacy single-carrier frequency division multiple access signal for LTE uplink transmission. Numerical results demonstrate the merit of IDFT-VFDM and confirm its potential as a candidate solution to achieve LTE-NR co-existence in multi-antenna multi-user scenarios.

LTE Quality of Service Enhancement Under OFDM Modulation Techniques

Recently, to satisfy the ever-growing data needs, Long Term Evolution (LTE) has been deployed by many operators. LTE enables better spectrum management and avoids the adjacent channel interference by using the Orthogonal Frequency Division Multiple Access (OFDMA) for downlink and Single Carrier Frequency Division Multiple Access (SC-FDMA) for uplink connection. Even though the spectrum is limited, the number of active devices is increasing which requires the need for extra spectrum. OFDM is capable of better Quality of Service (QoS) as it avoids the multipath fading using equalization and immune to inter-symbol interference, in addition to its attractive spectral efficiency. However, the LTE system is suffered from Peak to Average Power Ratio (PAPR) which reduces the QoS of the communication. Therefore, in this paper, we have proposed a QoS enhancement using a hybridized clipping-selective mapping (Clip-SLM) technique. Different QoS enhancement methods are evaluated for different modulation techniques, phase sequences, and number of sub-carriers. From the simulation results, we have shown that the proposed hybridized technique results in significant PAPR reduction which results in substantial Bit Error Rate (BER) reduction and hence QoS enhancement.

Robust Rate-Maximization Precoder Design for VFDM System

The new radio (NR) system is recently proposed to deploy alongside the long term evolution (LTE) system to improve the wireless communication capacity. The Vandermonde-subspace frequency division multiplexing (VFDM) is an efficient technique for such a two tier network, whereby the NR transmitter can reuse the frequency spectrum of LTE system meanwhile guaranteeing interference free to LTE. In this paper, we first investigate the robust rate-maximization problem in the VFDM system. In the condition of imperfect channel state information (CSI), the precoder is optimized to satisfy both non-interference to LTE system and rate-maximization in the NR system. To tackle the challenge in solving such a non-convex problem, an iterative algorithm is proposed based on the block coordinate descent (BCD) and penalty dual decomposition (PDD) methods. Finally, simulation results demonstrate the superiority of the proposed algorithm in terms of robustness and achievable rate over the conventional SVD-based VFDM technique.

Blind Signal Detection in Cellular Bands

In this article, we propose a blind wideband signal detection algorithm to detect and locate occupied channels in cellular bands without a priori knowledge of the band channelization. This is formulated as a change-point detection problem. The proposed algorithm is validated using over-the-air measurements taken at different cellular bands and shown to work in a global system for mobile communication, long-term evolution (LTE), and universal mobile telecommunications system bands.

Demonstration of a hybrid optical fiber–wireless 5G fronthaul coexisting with end-to-end 4G networks

The plethora of services envisaged to support 5G use-cases requires the development of a radio access network (RAN) infrastructure with the capability to integrate a variety of user-demanded mobile traffic characteristics. It is therefore interesting to study a 5G deployment scenario showcasing heterogeneous transmission. In order to address this challenge, in this paper, we propose and experimentally assess a coarse-wavelength-division-multiplexing-compatible optical access network for joint provisioning of 4G/5G RAN services, supporting the coexistence of both digital and analog radio-over-fiber (ARoF) fronthauling. Resorting to an integrated testbed, we demonstrate the transport of 100 MHz 5G downlink using low-latency and bandwidth-efficient ARoF over 8 km fiber, seamlessly coexisting on the same fronthaul infrastructure with a legacy full-fledged 4G long-term evolution (LTE) network supported by Ethernet-based digital RoF with different functional splits. In addition, we experimentally demonstrate the successful operation of the 4G/5G system in a hybrid fiber–wireless scenario including a free-space optics fronthaul extension with 55 m. The proposed heterogeneous RAN architecture is demonstrated to provide a flexible and robust integration path for novel 5G technologies, enabling their coexistence with currently deployed 4G LTE systems over a shared fronthaul infrastructure.

Indoor propagation models for emulated LTE networks

The growth in mobile network data traffic is even more noticeable in networks compatible with the Long-Term Evolution (LTE) standard. As such, both academia and industry seek mechanisms aimed at improving new communications systems, therefore, new test benches are required. The emulators are candidates to validate the proposals without affecting the real central systems. However, many papers that seek to address LTE emulation ignore the not-so-insignificant effect of wireless media propagation features. In this work, a characterization of the main propagation models used by typical emulation systems has been carried out. The network simulator three tool using indoor propagation models, has compared the outcomes achieved compared with the results obtained in a real test bench. Since most mobile data in the coming years is forecast to be mobile video traffic, this study focuses on a live video streaming service, considering both real-time message protocol and real-time streaming protocol transmission protocols. From the results, we demonstrate that only one of the propagation models under study is able to equate with a real LTE system performance. Thereby, the emulation system under this specific setup is well suited to conducting performance tests of LTE networks supporting video streaming services in indoor scenarios.

Space-Time-Frequency Machine Learning for Improved 4G/5G Energy Detection

In this paper, the future Fifth Generation (5G New Radio) radio communication system has been considered, coexisting and sharing the spectrum with the incumbent Fourth Generation (4G) Long-Term Evolution (LTE) system. The 4G signal presence is detected in order to allow for opportunistic and dynamic spectrum access of 5G users. This detection is based on known sensing methods, such as energy detection, however, it uses machine learning in the domains of space, time and frequency for sensing quality improvement. Simulation results for the considered methods: k-Nearest Neighbors and Random Forest show that these method significantly improves the detection probability.

A Robust Joint Cell Identification and Frequency Recovery Scheme for LTE Machine-Type Communications

The main features for future machine-type communication (MTC) cellular networks are to support low-power consumption, low-bandwidth, and long-range communication. One of the most challenging issues to meet these goals in the MTC cellular network is a low-complexity and reliable initial synchronization. To address this issue, in this article an efficient joint detection of integer carrier frequency offset (IFO) and cell identity (CID) is proposed for MTC in a long-term evolution (LTE) system. Unlike the conventional approach, the primary synchronization signal (PSS) and secondary synchronization signal (SSS) transmitted in the LTE-MTC system are used together to remove the effect of channel fading and symbol timing offset (STO). This design facilitates robust detection of the IFO and CID in the presence of residual STO without priori information on the SSS. The grouping of PSS subcarriers is integrated for joint detection, which plays an important role on reducing computational load. Both analytical and simulation results are provided to corroborate the feasibility of the proposed method. It has been demonstrated that the unique characteristics of the PSS and SSS sequences are effectively used for robust cell search in the presence of residual STO, compared to existing methods.

Performance evaluation of different signal shaping techniques for the advancing cellular networks

Recently, to satisfy the ever-growing data needs, long term evolution (LTE) has been deployed by many operators. LTE enables better spectrum management and avoids the adjacent channel interference by using the orthogonal frequency division multiple access (OFDMA) for downlink and single carrier frequency division multiple access (SC-FDMA) for uplink connection. Even though the spectrum is limited, the number of active devices is increasing which requires the need for extra spectrum. Orthogonal frequency division multiplexing (OFDM) is capable of better quality of service (QoS) as it avoids the multipath fading using equalisation and immune to inter-symbol interference, in addition to its attractive spectral efficiency. However, the LTE system is suffered from peak to average power ratio (PAPR) which reduces the QoS of the communication. Therefore, in this paper, we have proposed a QoS enhancement using a hybridised clipping - selective mapping (Clip-SLM) technique. Different QoS enhancement methods are evaluated for different modulation techniques, phase sequences and number of sub-carriers. From the simulation results, we have shown that the proposed hybridised technique results into significant PAPR reduction which brings substantial bit error rate (BER) reduction and hence QoS enhancement.

Is Centimeter Accuracy Achievable for LTE-CSI Fingerprint-Based Indoor Positioning?

Channel state information (CSI) fingerprint based indoor positioning has been extensively studied. While centimeter-level positioning accuracy has been demonstrated for Wi-Fi systems, only meter-level accuracy was reported for Long-term Evolution (LTE) systems. To investigate whether the centimeter accuracy is achievable or not for LTE systems, we examine the factors that affect the positioning accuracy to guide the implementation of a LTE-CSI fingerprinting system, where a novel phase compensation method is proposed to improve the CSI quality. We demonstrate for the first time that the centimeter-level positioning accuracy is achievable for LTE systems through extensive experiments.

Non-orthogonal filter bank multi carrier systems with higher overlap factor filters for 5G communications and beyond

The current 4G long-term evolution (LTE) system has few limitations such as lower spectral efficiency, no support for asynchronous data transfer, high out-of-band emissions. Filter bank multi carrier (FBMC) technique is getting used as one of the 5G waveform modulations to overcome the above mentioned limitations. The objective of this work is to design, simulate and verify the FBMC-based 5G communication system with prototype filters of higher order spreading factors 4, 6 and 8 along with LTE to study the performance in terms of spectral efficiency, out of band emissions, peak to average power ratio (PAPR) and bit error rate (BER) under AWGN and outdoor line of sight (LOS) fading conditions using the Keysight test-bed and tools. The results show that the FBMC with higher order spreading factors resulting in to good spectral efficiency, very minimal out-of-band emissions, comparable BER performance and slightly better PAPR than that of LTE systems.