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Text Neck is a diagnosed condition denoting overuse of the neck muscles with technology devices such as tablets, smartphones, and video game consoles. The condition is prevalent in all age groups, particularly in those who are heavy users of smartphones , ,. The main contributor to text neck is the frequency of handheld technology device use and the length of time that a user is engaged with their device without physical movement, while their head is in a forward posture. It is said to be a type of repetitive stress injury that can affect the spine, neck, shoulder, upper back, muscles, and associated ligaments. Although studies vary in their findings, adults use their mobile phones on average for 5 hours per day, university students for about 8.5 hours per day, and others on average about 2 hours per day , , ,. Some studies have shown that people have their mobile phones with them for all but 2 hours of the whole day, increasing the ease with which to access online applications, thus continuing to aggravate existing strains. Text Neck, also referred to as iNeck, is now recognized as a global public health problem. [ABSTRACT FROM AUTHOR]

Low-light image enhancement (LLIE) aims at improving the perception or interpretability of an image captured in an environment with poor illumination. Recent advances in this area are dominated by deep learning-based solutions, where many learning strategies, network structures, loss functions, training data, etc. have been employed. In this paper, we provide a comprehensive survey to cover various aspects ranging from algorithm taxonomy to unsolved open issues. To examine the generalization of existing methods, we propose a low-light image and video dataset, in which the images and videos are taken by different mobile phones’ cameras under diverse illumination conditions. Besides, for the first time, we provide a unified online platform that covers many popular LLIE methods, of which the results can be produced through a user-friendly web interface. In addition to qualitative and quantitative evaluation of existing methods on publicly available and our proposed datasets, we also validate their performance in face detection in the dark. This survey together with the proposed dataset and online platform could serve as a reference source for future study and promote the development of this research field. The proposed platform and dataset as well as the collected methods, datasets, and evaluation metrics are publicly available and will be regularly updated. Project page: https://www.mmlab-ntu.com/project/lliv_survey/index.html. [ABSTRACT FROM AUTHOR]

Although the GPS-based positioning is ubiquitous for its high precision, the high power consumption brought by the high sampling frequency and the poor GPS signal penetration limits its availability in locating low-power mobile devices (especially mobile phones). As a promising complement, the cellular-based positioning has attracted great attention since it consumes much less power as well as its higher availability. However, the sparsity of cellular-based data (due to lower sampling rate) and large localization errors make the measurement accuracy becomes the main challenge of the cellular-based positioning. hidden Markov model can well solve the problem of positioning error of GPS data, but it is less accurate when applied to map matching of cellular-base data. Therefore, to improve accuracy, in this article, we propose a novel algorithm called the tailored hidden Markov model (THMM) that is optimized for the cellular-based data. Specifically, the geometric, the topological, and the probabilistic characteristics have been considered and fully exploited in the THMM design. Our proposed schemes are evaluated using real-world motor vehicle movement trajectories collected in Tianjin and the experimental results are encouraging compared with the state-of-the-art algorithms. [ABSTRACT FROM AUTHOR]

The world’s first 5-carrier aggregation (CA) supporting digital-intermediate frequency (IF) receiver (RX) to support 5G sub-6 GHz new radio (NR) and CA/E-UTRA NR dual connectivity (CA/EN-DC) maintaining 2G and 3G in 14-nm FinFET CMOS technology is presented. Three digital-IF RXs with a shared local oscillator-phase-locked loop (LO-PLL) are integrated for supporting inter-/intra-band 5-CA to reduce power consumption and area of the massive number of RX paths. The RX features nine single-ended low-noise amplifiers (LNAs) with low/mid/high band (L/M/HB) characteristics. It achieves noise figure (NF) of 1.5 dB with 18 dB external LNA gain and +7.6-dBm out-of-band (OOB) input intercept point 3 (IIP3), and input intercept point 2 (IIP2) calibration is not required thanks to IF planning. The RX achieves an error vector magnitude (EVM) of 2.5% by intra-4CA for B1 LTE10MHz and LTE20MHz in one single RX path, as well as inter-3CA for B3, B5, and B7 long-term evolution (LTE) 20 MHz with a shared LO-PLL. The estimated power saving by sharing a single LO-PLL is 17% compared to 3-CA RXs with three separate LO-PLLs. [ABSTRACT FROM AUTHOR]

In this article, a millimeter-wave (mmWave) endfire phased array antenna with ±45° linear polarizations is proposed for fifth generation (5G)/B5G mobile communications. The proposed antenna achieves ±45° polarizations by utilizing a modified substrate integrated waveguide (SIW) slot polarizer. The polarizer generates dual orthogonal modes with equal amplitudes and a 0°/180° phase difference, thereby yielding $+ 45^{\circ }/- 45^{\circ }$ -polarization radiated waves in the far field. In a practical metal-framed mobile phone environment, the ±45 polarizations are verified to provide more balanced radiation patterns and, consequently, a higher polarization-multiple input multiple output (MIMO) efficiency. A prototype of the proposed 1 $\times $ 4 array is fabricated and measured, achieving a −10 dB impedance bandwidth of 23.4–30.0 GHz (covers 5G band of n257/n258), with an isolation better than 15.6 dB and a realized gain above 8.9 dBi in the operating bandwidth. A peak gain of 11.4 dBi and a 3 dB scanning range of 87° can be observed at 27.0 GHz. Furthermore, the prototype is characterized on a metal-framed mobile phone platform, experimentally demonstrating its superiority to conventional vertical/horizontal polarized (V-/H-pol) arrays. The validated advantages of the balanced radiation patterns and robust impedance matching make the proposed ±45°-polarization endfire antenna array a promising candidate for mobile terminals in the era of 5G/B5G. [ABSTRACT FROM AUTHOR]

Android malware is an ongoing threat to billions of smart devices’ security, ranging from mobile phones to car infotainment systems. Despite numerous approaches and previous studies to develop solutions for detecting and preventing Android malware, the rapid continuous development of new malware variants requires a careful reconsideration and the development of effective methods to identify malware families given a meager number of malware instances. In this paper, we present DroidMalVet, a novel Android malware family classification and detection approach that does not require to perform complex program analyses or utilize large feature sets. DroidMalVet is the first to use a promising, diverse, and small set of software metrics as features in a supervised learning platform to classify and detect various Android malware families. Our extensive empirical evaluations on two large public malware datasets show that DroidMalVet accurately detects both small and large malware families with F-Score accuracy of 94.4% and 96%, and AUC equal to 99.5% and 99.7% on the malware families in Drebin and AMD datasets, respectively. Moreover, our results demonstrate the superior performance of DroidMalVet in detecting small families (i.e., families with few samples). DroidMalVet complements existing approaches and presents an early warning tool for detecting known and emerging malware families. [ABSTRACT FROM AUTHOR]

Orthogonal frequency-division multiplexing (OFDM) has been selected as a baseline waveform for long-term evolution (LTE) and fifth-generation new radio (5G NR). Fast-convolution (FC)-based frequency-domain signal processing has been recently considered as an effective tool for transmitter and receiver side subband filtering of OFDM-based waveforms. However, for the original continuous FC-based model, the filtering can, in general, be configured in time-direction only with the granularity of half subframe, corresponding to 7, 14, or 28 symbols with 15kHz, 30kHz, or 60kHz subcarrier spacing, respectively. In this paper, we present a symbol-synchronous FC-processing scheme flexibly allowing filter re-configuration with the time resolution equal to one OFDM symbol while supporting tight carrier-wise filtering for 5G NR in mixed-numerology scenarios with adjustable subcarrier spacings, center frequencies, and subband bandwidths, as well as providing co-existence with LTE. Proposed approach segments each stream of time-domain OFDM symbols into overlapping processing blocks of fixed size. Symbol synchronous processing is achieved by dynamically adjusting the overlap between the processing blocks while aligning the payload part of the processing blocks with the boundaries of the OFDM symbols. The proposed scheme is demonstrated to support the envisioned use cases of 5G NR and provide a flexible starting point for sixth generation (6G) development. [ABSTRACT FROM AUTHOR]

Severe contrast degradation in an image result in a substantial loss of crucial visible information. A novel unsupervised image enhancement algorithm is proposed in this paper to unravel hidden visual details in perceptually invisible images. In this paper, new algorithms are designed to solve the range localization problem. The proposed algorithm intends to expand the image range to maximize its intensity level utilization. Outliers present in an image intensity range are truncated based on their power distribution. Based on the type of input image, maxima-minima, or frequency-based expansion of truncated levels, is exercised to avoid over-enhancement. Two novel parameters, namely the transmission map and zero-frequency spread, are coined. The visually enhanced result successfully exhibits the camouflaged information and avoids over-enhancement. Consumer gadgets, such as cameras, have difficulty taking pictures in very dark and cloudy settings. The suggested algorithm can improve low-contrast photos that are both very dark and severely attenuated. The unsupervised nature of the proposed algorithm makes it suitable for application in the field of consumer electronics like mobile phones and digital cameras. A consumer-focused, platform-independent app is created and made available to the general public for additional study. [ABSTRACT FROM AUTHOR]

Our world is full of cameras, whether they are installed in the environment or integrated into mobile devices such as mobile phones or head-mounted displays. Displaying external camera views in our egocentric view with a picture-in-picture approach allows us to understand their view; however, it would not allow us to correlate their viewpoint with our perceived reality. We introduce Projective Bisector Mirrors for visualizing a camera view comprehensibly in the egocentric view of an observer with the metaphor of a virtual mirror. Our concept projects the image of a capturing camera onto the bisecting plane between the capture and the observer camera. We present extensive mathematical descriptions of this novel paradigm for multi-view visualization, discuss the effects of tracking errors and provide concrete implementation for multiple exemplary use-cases. [ABSTRACT FROM AUTHOR]

Disasters and the resulting emergencies are increasingly presenting situations where tele-communications infrastructure (e.g., functioning base stations) is often compromised, leading to diminished network capacity. In these situations, providing trapped populations in isolated areas with network access to be able to communicate with rescue and recovery personnel or volunteer teams is critical. Further, when network capacity is diminished, it is essential that mobile network users be alerted to “comply” and not overload the network with non-essential bandwidth-intensive traffic unrelated to the emergency unfolding. While the current evolution of the Integrated Public Alert and Warning System (IPAWS) is able to generate and disseminate such emergency alerts, there has been no analysis or evaluation of the effectiveness of such alerts as well as the design of mechanisms that can ensure such compliance to prevent network outage. In this work, we present a framework for Cognitive Public Alerts to Wireless Subscribers (CPAWS) that is able to predict and prevent mobile network overload/outage during emergencies using a mix of behavioral studies and machine learning tools that consider real-time monitoring information of the environmental status, network situation, and user compliance. Specifically, we study the efficacy of wireless emergency alerts (WEAs) in terms of saving network bandwidth by using surveys on Amazon MTurk to test the effectiveness of seven designed WEAs on reducing users' non-essential traffic across 12 designated cell phone applications. Additionally, we design complementary access and alert control strategies to ensure that the network load remains below the diminished available capacity during emergencies. CPAWS is also backward-compatible since it extends IPAWS by adding a feedback loop for real-time monitoring and control. [ABSTRACT FROM AUTHOR]

Natural disasters affect millions of people every year. Finding missing persons in the shortest possible time is of crucial importance to reduce the death toll. This task is especially challenging when victims are sparsely distributed in large and/or difficult-to-reach areas and cellular networks are down. In this paper we present SARDO, a drone-based search and rescue solution that leverages the high penetration rate of mobile phones in the society to localize missing people. SARDO is an autonomous, all-in-one drone-based mobile network solution that does not require infrastructure support or mobile phones modifications. It builds on novel concepts such as pseudo-trilateration combined with machine-learning techniques to efficiently locate mobile phones in a given area. Our results, with a prototype implementation in a field-[1], show that SARDO rapidly determines the location of mobile phones ($\sim \!3$ ∼ 3 min/UE) in a given area with an accuracy of few tens of meters and at a low battery consumption cost ($\sim \!5\%$ ∼ 5 % ). State-of-the-art localization solutions for disaster scenarios rely either on mobile infrastructure support or exploit onboard cameras for human/computer vision, IR, thermal-based localization. To the best of our knowledge, SARDO is the first drone-based cellular search-and-rescue solution able to accurately localize missing victims through mobile phones. [ABSTRACT FROM AUTHOR]

With the rapid development of wireless communication, the requirements of high-integration and low-cost radio frequency (RF) front-end modules in mobile phones result in more usage of silicon-on-insulator field effect transistors (SOIFETs) for the manufacturing of RF switches. However, the nonlinear behavior of SOIFET switches in off-state always produces unwanted harmonics distortion interference when they are excited by a large signal. In this article, we simplify the well-known physics-based surface potential model to an interelectrode nonlinear capacitance (INC) model since it adequately describes the harmonic effects produced by the transistor. The INC model, referred to as the coarse model, cannot match the behavior of the real switch, since many parameters of the switch cannot be accurately determined. This article proposes a novel dynamic neuro-space mapping network model, referred to as the fine model, to optimize the INC model. The proposed model takes advantage of the high accuracy of the fine model and the fast speed of the coarse model. Ultimately, the proposed method can accurately predict the harmonics interference for SOIFET switches in the complex RF front-end environment and provides an intuitive guideline under the design stage to prevent EMI problems. [ABSTRACT FROM AUTHOR]

In this article, an effective method using reverberation chambers (RCs) to measure the total radiated power (TRP) from mobile phones (MPs) is shown. The method exploits a novel measurement setup that links the MP under test inside the working volume of the RC to a real external wireless communication system. Therefore, no radio base station emulator (BSE) is necessary in the proposed method. For the aim of the method, we have found that the connection of the MP under test with the real wireless network system is held stable by the measurement setup in both line of sight and non-line-of-sight configurations. Hence, TRPs from MPs are measured in different conditions of connection even though the received and transmitted signals are not completely controllable. Measured TRPs are shown up to maximum values, which are useful for both electromagnetic interference evaluation and human exposure assessment in a world where wireless devices are spreading more and more. By maximum TRP values, which meaningfully allow result comparisons regardless of the use or not of a BSE, we also show a novel method to estimate the part of TRP absorbed into user body during a call. [ABSTRACT FROM AUTHOR]

The recent advance in motion tracking (e.g., Visual Inertial Odometry) allows the use of a mobile phone as a 3D pen, thus significantly benefiting various mobile Augmented Reality (AR) applications based on 3D curve creation. However, when creating 3D curves on and around physical objects with mobile AR, tracking might be less robust or even lost due to camera occlusion or textureless scenes. This motivates us to study how to achieve natural interaction with minimum tracking errors during close interaction between a mobile phone and physical objects. To this end, we contribute an elicitation study on input point and phone grip, and a quantitative study on tracking errors. Based on the results, we present a system for direct 3D drawing with an AR-enabled mobile phone as a 3D pen, and interactive correction of 3D curves with tracking errors in mobile AR. We demonstrate the usefulness and effectiveness of our system for two applications: in-situ 3D drawing, and direct 3D measurement. [ABSTRACT FROM AUTHOR]

Trajectory prediction for mobile phone users is a cornerstone component to support many higher-level applications in LBSs (Location-Based Services). Most existing methods are designed based on the assumption that the explicit location information of the trajectories is available (e.g., GPS trajectories). However, collecting such kind of trajectories lays a heavy burden on the mobile phones and incurs privacy concerns. In this paper, we study the problem of trajectory prediction based on cell-id trajectories without explicit location information and propose a deep learning framework (called DeepCTP) to solve this problem. Specifically, we use a multi-graph embedding method to learn the latent spatial correlations between cell towers by exploiting handoff patterns. Then, we design a novel spatial-aware loss function for the encoder-decoder network to generate cell-id trajectory predictions. We conducted extensive experiments on real datasets. The experiment results show that DeepCTP outperforms the state-of-the-art cell-id trajectory prediction methods in terms of prediction error. [ABSTRACT FROM AUTHOR]

Codecs using spectral-spatial transforms efficiently compress raw camera images captured with a color filter array (CFA-sampled raw images) by changing their RGB color space into a decorrelated color space. This study describes two types of spectral-spatial transform, called extended Star-Tetrix transforms (XSTTs), and their edge-aware versions, called edge-aware XSTTs (EXSTTs), with no extra bits (side information) and little extra complexity. They are obtained by (i) extending the Star-Tetrix transform (STT), which is one of the latest spectral-spatial transforms, to a new version of our previously proposed wavelet-based spectral-spatial transform and a simpler version; (ii) considering that each 2D predict step of the wavelet transform is a combination of two 1D diagonal or horizontal-vertical transforms; (iii) weighting the transforms along the edge directions in the images. Compared with XSTTs, the EXSTTs can decorrelate CFA-sampled raw images well: they reduce the difference in energy between the two green components by about 3.38–30.08 % for high-quality camera images and 8.97–14.47 % for mobile phone images. The experiments on JPEG 2000-based lossless and lossy compression of CFA-sampled raw images show better performance than conventional methods. For high-quality camera images, the XSTTs/EXSTTs produce results equal to or better than the conventional methods: especially for images with many edges, the type-I EXSTT improves them by about 0.03–0.19 bpp in average lossless bitrate and the XSTTs improve them by about 0.16–0.96 dB in average Bjøntegaard delta peak signal-to-noise ratio. For mobile phone images, our previous work perform the best, whereas the XSTTs/EXSTTs show similar trends to the case of high-quality camera images. [ABSTRACT FROM AUTHOR]

Traditional steganography methods are usually designed on a lossless channel; thus, messages are often not extracted correctly from an image transmitted over a lossy channel that includes attacks such as scaling. To address this issue, in recent years, the field of robust steganography has emerged. In this paper, the process of image scaling by interpolation is first observed and serves as the basis for proposing the idea of inverse interpolation. Subsequently, the idea of constructing an inverse interpolation equation set is proposed to solve the problem of intersectional blocks during the inverse interpolation process. Then, the scaling factor’s valid range of inverse interpolation is analyzed. Next, the inverse interpolation is successfully applied in robust image steganography. A method that combines antiscaling and antidetection is proposed. Afterward, actual tests on the top 9 mobile phone brands with 28 models and 2 social communication apps that are currently popular in China are done. The scaling factor’s valid range of the proposed method is verified to match the actual lossy channel. The experimental results show that the proposed method achieves a reliable extraction of embedded messages for common interpolation scaling attacks while maintaining high statistical detection resistance. [ABSTRACT FROM AUTHOR]

Among all the road accidents, speeding is the most deadly factor. To reduce speeding, it is essential to devise efficient schemes for ubiquitous speed monitoring. Traditional approaches either suffers from using special equipment(e.g., radar speed gun) or special deployment(e.g., position-fixed cameras). In this article, we propose SpeedTalker, a mobile phone-based approach to perform speed detection on automobiles. By leveraging the built-in microphones and camera from the mobile phone, SpeedTalker estimates the automobile speed by passively sensing the acoustic and image signals. We propose an integrated solution to effectively estimate the automobile’s speed based on COTS devices, and provide a platform for every pedestrian to help report the speeding event of automobiles. Specifically, we use the time difference of arrivals (TDOA) model based on acoustic signals to figure out the candidate trajectories of automobile, and use the pin-hole model based on image frames to figure out the vertical distance between the user’s position and the automobile’s trajectory, thus to estimate the unique trajectory. Combined with the time stamp of the trajectory, the automobile speed can be estimated. Besides, we propose a method to effectively mitigate the influence of the movement jitters of mobile phone. We implemented a system prototype for SpeedTalker and estimated the automobile speed with high accuracy. Experiment results show that in the scenario of single automobile, SpeedTalker can achieve an average estimation error of 6.1 percent compared to radar speed guns. In the scenario of multiple automobiles, SpeedTalker can achieve an average estimation error of 9.8 percent, which is acceptable for usage. [ABSTRACT FROM AUTHOR]

A low specific absorption rate (SAR) multiple-input and multiple-output (MIMO) antenna array is designed for 5G mobile phones based on the theory of characteristic modes (TCMs). First, a geometrically symmetric dipole antenna is analyzed using TCM. The modal currents with symmetrical and reverse distributions are selected and excited to obtain the low-SAR antenna element. Then the antenna element is further optimized, and eight antenna elements constitute an MIMO array. The −6 dB impedance bandwidth of the proposed MIMO array is from 3.4 to 3.6 GHz. The isolations between different antenna elements are higher than 16 dB. Their total efficiencies range from 48% to 67%. Its envelope correlation coefficient (ECC) is lower than 0.08. The 1 g spatial-average head SAR and 10 g spatial-average body SAR of the proposed antenna are simulated and measured. [ABSTRACT FROM AUTHOR]

In this article, we propose a novel metasurface-basedmagnetic coupling resonant wireless power transfer (MCR-WPT) system to realize planar omnidirectional WPT at a mid-range distance. The resonator devices—dielectric-constant disks or planar helixes—are located on both sides of the metasurface, which comprises conducting wires placed in a planar sunburst pattern. Transmission efficiency of >40% is achieved on a circular plane with a diameter of ∼40 cm. In addition, the transfer efficiency is insensitive to the placement of a human hand near the proposed MCR-WPT system. The maximum permissible input powers for the coil and dielectric resonator versions of the proposed MCR-WPT system are 0.83 and 2.56 W, respectively, in compliance with the limit prescribed in the International Commission of Non-Ionizing Radiation Protection guidelines. The proposed design may help realize many potential WPT applications, especially for the desktop wireless charging of household devices, such as mobile phones, tablets, and LED desk lamps. [ABSTRACT FROM AUTHOR]

A low-specific absorption rate (SAR) four-antenna multiple-input–multiple-output (MIMO) antenna array is designed for fifth-generation (5G) mobile phones based on the theory of characteristic modes (TCM) of the composite perfect electric conductor (PEC) and lossy dielectric structures. First, the TCM of composite PEC-lossy dielectric structures is reviewed briefly. Then, the application of the theory for low-SAR antenna design is demonstrated through a four-antenna MIMO antenna array. Finally, the proposed MIMO array is fabricated, and its performance is measured. Its −10 dB impedance bandwidth can cover the desired frequency band from 3.4 to 3.6 GHz. The isolations between different antenna elements are higher than 15.4 dB. Their total efficiencies range from 81.3% to 89.9%. The envelope correlation coefficient (ECC) is lower than 0.07. The 10 g spatial-average body SAR corresponding to the situation that four antennas simultaneously radiate is 0.47 W/kg. Compared with the state-of-the-art 5G MIMO antenna arrays, the proposed MIMO antenna array has the lowest peak SAR value, satisfactory efficiency, isolation, and ECC. This article provides a general methodology for the design of low-SAR mobile phone antennas. [ABSTRACT FROM AUTHOR]

This article describes a compact dual-polarized endfire antenna array for fifth-generation (5G) millimeter-Wave (mm-Wave) mobile application. The dual-polarized endfire antenna element is constructed by a compact open-ended cavity with cavity mode for vertical polarization (VP) radiation and open-slot mode for horizontal polarization (HP) radiation. With the integrated design of VP and HP elements, the proposed antenna shows a much more compact size compared to existing schemes. To enhance the bandwidth of low-profile VP radiation, a slot is etched on the cavity to create a new mode for dual-resonance response, realizing a wide bandwidth of 24.5–29.5 GHz for both polarizations. In addition, radiation pattern modification techniques are employed to achieve good endfire beams with a high front-to-back ratio for both polarizations, thus enabling a high peak gain of 10.3 and 11.3 dBi for VP and HP, respectively. A wide beam scanning range of ±50° with realized gain above 7 dBi is realized at 27 GHz for both polarizations. In virtue of compact size, wide bandwidth, high gain, and good spatial coverage, the proposed design strategy is promising for future 5G mm-Wave mobile phones. [ABSTRACT FROM AUTHOR]

Most mobile phones today have capacitive micro-electro-mechanical systems (MEMSs) microphones that use either single or dual diaphragms. Methods to detect failures easily and non-invasively have become of critical importance for microphones mobile phone manufacturers as a basis for built-in self-test (BIST) and self-repair (BISR) strategies. In that regard, a four-layer framework is presented that includes lumped element modeling (LEM), failure mode simulation, failure mode discrimination, and recovery. The frequency response of the microphone is taken as the main output to analyze. To experimentally validate this framework, this article provides a failure mode induction method based on bias voltage sweeping and four new techniques, based solely on acoustic measurements to discriminate the states of electrostatic capture for single diaphragm capacitive MEMS microphones. These include 1) analysis of an acoustic signature that is unique to electrostatic capture based on cosine similarity analysis; 2) −3 dB point measurement; 3) +3 dB point measurement; and 4) cluster analysis. Measurement of pull-in voltage and snapback voltage ranges is further demonstrated based on sensitivity measurements in laboratory conditions and response magnitude and noise power measurements in non-laboratory conditions. Up to 100% success rate in detecting electrostatic capture of diaphragm is reported for this type of device. [ABSTRACT FROM AUTHOR]

In this article, a CMOS tunable channel-selection (CH-SEL) low-noise amplifier (LNA) with a feedforward (FF) $N$ -path filter and a gain- and phase-calibrated interference- cancellation technique is proposed for advanced front-end module (FEM)-less cellular transceivers. The proposed LNA exhibits a high- $Q$ RF bandpass/band-rejection filter characteristic based on a four-path filter, an active blocker cancellation with an FF translational loop, and an LC tank at the input, internal node, and output, respectively. The proposed gain- and phase-calibration block and tunable high-pass filter in the FF filtering path adjust the notch frequency corresponding to the transmitter leakage signal and help realize sharp notch filtering. The proposed CH-SEL LNA with CMOS duplexers compensates for the limited filtering performance of the CMOS duplexer and improves the blocker-tolerance and linearity of the receiver, and thus, can replace surface acoustic wave duplexers in the FEM. Fabricated in the 65-nm CMOS process, the CH-SEL LNA achieves a maximum voltage gain of 19.3 dB, minimum NF of 5.1 dB, and notch rejection ratio of more than 27.8 dB. It can also cover mid-band frequencies in the range of 1.35–2.7 GHz for 5G new radio cellular applications, exhibits an average current of 20 mA from a supply voltage of 1 V, and has an active die area of 1.16 mm2. [ABSTRACT FROM AUTHOR]

In this article, a blocker-tolerant receiver (RX) front end employing a dual-band $N$ -path balun low-noise amplifier (balun-LNA) is presented for advanced cellular applications. The proposed RX front end can achieve a superior input-referred second-order intercept point (IIP2) performance without any IIP2 calibration, as the $N$ -path balun-LNA performs RF bandpass filtering and enhances blocker tolerance as well as the overall linearity of the RX. The proposed band-switchable differential inductor with a center tap enables the LC tank of the balun-LNA to support the operation of both low-band (LB) and mid-band (MB) frequencies for 5G new radio (NR) sub-6-GHz cellular applications. The RX front end is comprised of the dual-band $N$ -path balun-LNA, a $G_{m}$ -stage, current-mode passive mixers with a 25% duty-cycle local oscillator signal, current-mode passive RC low-pass filters, and transimpedance amplifiers. The RX front end was fabricated through a 65-nm CMOS process, and it was characterized primarily in the 5G NR LB and MB frequencies. The active die area was 2.24 mm2, and the RX front end drew a bias current of 15.1 mA from a nominal supply voltage of 1 V. It achieved a noise figure of 4.5 dB, a conversion gain of 43.5 dB, an out-of-band input-referred third-order intercept point of 7.89 dBm, and an IIP2 of more than 55 dBm. [ABSTRACT FROM AUTHOR]

A wideband low-profile eight-element microstrip multiple-input–multiple-output (MIMO) antenna for fifth-generation (5G) mobile phones is proposed. The antenna is designed to be integrated on the back-cover of a mobile phone without occupying its inner space or ground clearance. The elements of the MIMO antenna can simultaneously excite the TM01, TM10, TM02, and TM11 modes, and their broad operating bands come from combining the four modes together. The proposed MIMO antenna which is a simple single-layer plane structure with a thickness of only 0.787 mm is fabricated and tested. The experimental results show that the −6 dB impedance operating band of the MIMO antenna is 4.4–5.04 GHz which can cover the 5G N79 band of 4.4–5 GHz. It achieves a broad relative bandwidth of 13.6% with a low profile of $0.01~\lambda _{0}$ , where $\lambda _{0}$ is the free-space wavelength of the center frequency. It has an efficiency of higher than 42%, the mutual coupling of lower than −18 dB, the envelope correlation coefficients (ECCs) of lower than 0.24, and the ratios of mean effective gains (MEGs) of lower than 1.96 dB in the operating band. [ABSTRACT FROM AUTHOR]

This article proposes a tripolar plane-type (TPT) transmitter enabling three-dimensional (3-D) omnidirectional wireless power transfer (WPT) for consumer electronics, such as mobile phones and tablet computers. The proposed TPT transmitter is a 2-D plan-type structure, but it shows a 3-D omnidirectional power transmitting capability. This structure consists of two crossed bipolar coils and a unipolar circular coil, and the three coils are mutually decoupled naturally. By calculating the magnetic field distribution generated by the TPT transmitter, a 3-D omnidirectional magnetic field can be obtained. Then, a detailed circuit topology based on the inductor-capacitor-capacitor-series compensation networks and full-bridge inverters with phase-shift control is modeled and analyzed. On this base, an excitation current vector modulation strategy based on a targeting magnetic field is designed, which can improve and stabilize the system output power and efficiency. Finally, an experimental prototype is set up to verify the 3-D omnidirectional power transmitting capability of the proposed TPT transmitter and the effectiveness of the designed current vector modulation strategy. Besides, the superiority of the proposed 3-D omnidirectional WPT system is verified by comparison with other methodologies. The experimental results show that the system output power and efficiency are maintained at 61.4–80.6W and 80.7%–85.2% under arbitrary angular misalignment of the receiver. [ABSTRACT FROM AUTHOR]

Owing to the complex stress condition of the on-board devices in a mobile phone under drop impact condition, high test cost, and long validation period are usually spent on product-level drop test for product design. Most of the standardized test protocols including the Joint Electron Device Engineering Council (JEDEC) standard for handheld electronic products are essentially based on board-level tests, not taking into account the interaction between the printed circuit board (PCB) and other internal components, so the accurate experimental validation of product-level drop reliability remains time-consuming. This article established a finite element model of a whole mobile phone for the simulation of its product-level drop tests. By conducting simulation of six-side and four-corner drop postures, it is found that the risk of overstress failure of the critical large chips and solder joints on the PCB are relatively higher in the case of back drop and front drop. The bending of the PCB and the collision between the shielding frame and the front frame of the mobile phone are the decisive factors that bring the overstress failure risk of the chip and solder joint. Finally, a series of product-level drop tests were conducted and compared with the simulations, with a variance of stress value within 20%, which proves that the simulation model could provide useful insights for the reliability design and validation phase during the development of new products. [ABSTRACT FROM AUTHOR]

In this study, wideband Doherty power amplifiers (DPAs) based on converters comprising one transformer and two capacitors are investigated. Moreover, the parallel and series-type Doherty combiners are investigated. The series-type Doherty combiner is shown to have wider characteristics than the parallel-type converter-based Doherty combiner via numerical analysis. An approximate analysis was applied to the series-type combiner, and a quasi-optimum design parameter was derived for wideband matching. A quasi-optimum design parameter was compared with a true optimum solution derived by numerical analysis, and its certainty was verified. A combiner with parameters close to the true optimum solution was designed and evaluated. A DPA fabricated using this combiner was adequately small for a 5G mobile handset and could be operated in the frequency range of 2.2–2.7 GHz with efficiency exceeding 35% and a sufficiently low distortion under an amplifying wideband modulated signal [fractional bandwidth (FBW): 4% = 0.1/2.5 GHz]. The proposed combiner and its design techniques helped in designing a compact and long battery life of 5G mobile phones with high data throughput at a few gigahertz frequency ranges. [ABSTRACT FROM AUTHOR]

Inspired by excellent precision of carrier phase positioning, this paper presents a new carrier phase positioning technique for 5G new radio cellular networks with a focus on clock synchronization and integer ambiguity resolution. A carrier-phase based clock offset estimation method is first proposed to achieve precise clock synchronization among base stations, and proved to achieve the Cramér–Rao Lower Bound (CRLB) asymptotically. A fusion method is developed to fuse the estimated positions of a mobile station (MS) based on time-difference-of-arrival, with the estimated position changes based on the temporal changes of carrier phase measurements. While circumventing the integer ambiguities of the carrier phase measurements, the fusion method provides quality interim estimates of the MS positions, at which the measurements can be linearized to resolve the integer ambiguities. As a result, precise MS positions can be obtained based on the disambiguated carrier phase measurements. Numerical simulations show that the proposed carrier phase positioning can achieve a centimeter-level accuracy in wireless cellular networks. [ABSTRACT FROM AUTHOR]

Mobile networks’ evolution is strictly related to connected cars evolution, making in-car propagation modeling and analysis key enablers in the forthcoming telecommunication competition scenario. The recent availability of mobile device power measurements enriched by GPS position, the so-called 3GPP minimization of drive test (MDT) feature, nowadays, empowers new approaches to propagation studies targeting mobile service and quality improvements. The novelty of the research presented in this article is the use of a huge quantity of MDT geolocated radio measurements in a connected state (more than 370 million during the three-day MDT campaign) along 187 km of Italian A22 Motorway, part of the planned Munich-Bologna EU cross-border corridors for connected and automated mobility (CAM). In particular, MDT measurements of LTE received signal received power (RSRP) are compared between rain and dry road situations, showing how wet environments reshape electromagnetic propagation, even for LTE frequency bands (below 3 GHz) that have line-of-sight propagation marginally influenced by rain. Explanations of measured effects and simulations are presented. The rain effect on cellular propagation should be carefully considered in the perspective of connected car evolution, specifically considering new worldwide available 5G bands, more affected by rain situations, and autonomous driving scenarios. [ABSTRACT FROM AUTHOR]

High-altitude platform station (HAPS) as International Mobile Telecommunications (IMT) base station (HIBS) has been attracting the attention of aerospace and telecommunication companies from many countries in recent years. The HIBS' remarkable differential feature is the possibility of using HAPS to complement the IMT terrestrial coverage, benefiting from the platforms being located in the stratosphere, enabling much wider coverage when compared to conventional terrestrial solutions. In addition, the COVID-19 pandemic has highlighted the technological and social differences among countries, mainly due to the poor quality, or even absence, of Internet connectivity. HIBSs might efficiently support reducing the digital divide, since they provide connectivity to the same mobile devices as the terrestrial networks, which allows this non-terrestrial connectivity solution to increase global coverage and expand mobile connectivity for everyone. This article describes the fundamentals of the HIBS, as well as its deployment scenarios and regulatory aspects. Furthermore, it is reported, for the first time in the literature, a coexistence analysis between HIBS and fixed services point-to-point (FS-PP), as an International Telecommunication Union - Radio-communication Sector preparatory study for the support of decisions to be made at the 2023 World Radiocommunication Conference. The simulations demonstrate the feasibility of coexistence between HIBS and FS-PP active links, sharing the HIBS Band 2 around 2 GHz. [ABSTRACT FROM AUTHOR]

Implementation of an antenna array on a 5G mobile phone chassis is crucial in ensuring the radio link quality, especially at the millimeter-waves. However, we generally lack the ability to design antennas under practical operational conditions involving body effects of a mobile user in a repeatable manner. We developed numerical and physical phantoms of a human body for evaluation of mobile handset antennas at 28 GHz. While the numerical human model retains a realistic and accurate body shape, our physical phantom has a much simpler hexagonal cross section to represent a body. Gains of the phased antenna array configuration on a mobile phone chassis, called colocated array is numerically and experimentally evaluated. The array is formed by placing two sets of 4-element dual-polarized patch antenna arrays, called two modules, at two locations of a mobile phone chassis. Modules are intended to collect the maximum amount of energy to the single transceiver chain. Spherical coverage of the realized gain by the array shows that the experimental statistics of the realized gains across entire solid angles agree with numerical simulations. We thereby demonstrate that our antenna evaluation method reproduces the reality and our phantom serves repeatable tests of antenna array prototypes at 28 GHz. [ABSTRACT FROM AUTHOR]

In a cellular radio access network relying on control- and user-plane separation (RAN-CUPS), control base stations (CBSs) make up the control plane (CP) taking charge of coverage, and traffic base stations (TBSs) in the user plane (UP) are responsible for transmitting high-speed data under the umbrella of CP. In order to increase the coverage probability of CP, non-orthogonal multiple access (NOMA) is introduced into CP while UP adopts orthogonal frequency division multiple access (OFDMA). Then, we develop a tractable analytical model for NOMA-enabled RAN-CUPS based on stochastic geometry. Simulation results show that compared with OFDMA, NOMA could improve coverage probability, spectral efficiency, and energy efficiency of CP, which can further improve the spectral efficiency of UP. [ABSTRACT FROM AUTHOR]

This article proposes a supply modulator (SM) that uses high switching frequency gallium-nitride (GaN) devices to achieve a four-phase fast step-down converter for the fast-tracking ability of the envelope tracking (ET). The ET signal is reshaped to generate an average power tracking (APT)-based signal to control the size of GaN switches to further increase light-load efficiency due to reduced switching loss. Moreover, a high-bandwidth and low-loss linear amplifier (LA) is used to supply the power amplifier (PA) to sufficiently provide fast-tracking speed for 5th generation (5G) NR ET. At a power of 3.5 W for 5G mobile phones, the peak efficiency that is tested with NR −130 MHz in the ET mode is as high as 85.7% over a wide load range. [ABSTRACT FROM AUTHOR]

Commuting to and from work presents daily stressors for most workers. It is typically demanding in terms of time and cost, and can impact people's mental health, job performance, and, broadly speaking, personal life. We use mobile phones and wearable sensing to capture location-related context, physiology, and behavioral patterns of N=275 information workers while they commute, mainly by driving, between home and work locations spread across the United States for a one-year period. We assess the impact of commuting on participant's workplace performance, showing that we can predict self-reported workplace performance metrics based on passively collected mobile-sensing features captured during commute periods. [ABSTRACT FROM AUTHOR]

The mechanism for the radiation efficiency local minimum in antennas, especially for open-slot antennas and T-shaped antennas, has been investigated. It is found that the local minimum in those antennas always corresponds to an ideal differential mode. Furthermore, the frequency position of the ideal differential mode is decided by the parasitic parts of the antennas. Simple methods for estimating the local minimum position are proposed based on the mechanism we have found. In addition, the duality relation between those two types of antennas is also discussed. Our findings provide a guideline for designing mobile phone antennas with improved efficiency. [ABSTRACT FROM AUTHOR]

The rapid growth of the advanced consumer 5G wireless mobile phones has propelled the demands of fabricating surface acoustic wave (SAW) filters with smaller size and high performance. Three-dimension wafer-level package (3-D WLP) for SAW filter is a promising solution to replace conventional surface mounted technology and chip-scale packaging. In this article, a new WLP for SAW filter with a size of 1.3 mm × 1.1 mm × 0.35 mm is developed using thin dry film capping. The new 3-D WLP significantly reduces the overall thickness which is particularly meaningful for low-profile smartphones and tablets. A number of key processes were developed. To improve the quality, finite element modeling (FEM) is used to simulate the mechanical stress to optimize cavity structure. Reliability tests were performed and the results indicated that there were no significant frequency response changes occurred and low insertion loss (IL) in pass band was less than 0.2 dB after pro-conditional level 3 test, unbiased highly accelerated stress (uHAST) test, and temperature cycling (TC) test on SAW filter packages. It can be concluded that 3-D WLP for SAW filter achieves miniaturization, good electrical performance, and reliability. [ABSTRACT FROM AUTHOR]

Image distortion during multiple-exposure capture is a common scenario, and most of the existing legacy image content is in the low dynamic range (LDR). For both of these problems, pseudo multiple exposure image generation from a single image is a possible solution. Hence, in this article, we propose a novel method for high dynamic range (HDR)-like image generation by fusing pseudo-multi-exposure images that are produced from only one single image. The proposed pseudo-exposure image generation method is based on intensity mapping function (IMF). First, our system learns the relation between different exposure images with the help of genetic algorithm and generates long and short exposure images. In the second step, we fuse images with different exposures to generate the HDR-like image. Our method outperforms several inverse tone mapping operator (ITMO)-based methods. The simplicity and good performance of the proposed method makes it suitable for mobile phones and other consumer electronics. We also develop a demo software to validate the proposed method. [ABSTRACT FROM AUTHOR]

We seek to predict the 6 degree-of-freedom (6DoF) pose of a query photograph with respect to a large indoor 3D map. The contributions of this work are three-fold. First, we develop a new large-scale visual localization method targeted for indoor spaces. The method proceeds along three steps: (i) efficient retrieval of candidate poses that scales to large-scale environments, (ii) pose estimation using dense matching rather than sparse local features to deal with weakly textured indoor scenes, and (iii) pose verification by virtual view synthesis that is robust to significant changes in viewpoint, scene layout, and occlusion. Second, we release a new dataset with reference 6DoF poses for large-scale indoor localization. Query photographs are captured by mobile phones at a different time than the reference 3D map, thus presenting a realistic indoor localization scenario. Third, we demonstrate that our method significantly outperforms current state-of-the-art indoor localization approaches on this new challenging data. Code and data are publicly available. [ABSTRACT FROM AUTHOR]

In this article, we present a client-based multipath TCP (cMPTCP) framework that can cope with path heterogeneity across multiple LTE networks deployed by different operators. cMPTCP is the first work to apply the mobile client's inference based on our observation that an out-of-order queue in an MPTCP receiver (i.e., mobile client) builds up with increasing heterogeneity between different subflows and can significantly degrade throughput performance compared to that achieved by single-path TCP via the best path. For agile and accurate control for the existing MPTCP architecture, we argue that mobile clients are the best network entities to infer the bottleneck state of an end-to-end MPTCP connection. Our proposed cMPTCP consists of two main components: client-initiated multipath selection and subflow-level rate control mechanisms. These mechanisms are compatible with the default MPTCP architecture implemented in the Linux kernel. For performance evaluation, we prototype a complete LTE network testbed consisting of mobile phones, LTE base stations, LTE cores, and application servers. Our experimental results confirm that cMPTCP outperforms existing server-side schedulers in practical dynamic channel conditions. [ABSTRACT FROM AUTHOR]

Major commercial client-side video players employ adaptive bitrate (ABR) algorithms to improve the user quality of experience (QoE). With the evolvement of ABR algorithms, increasingly complex methods such as neural networks have been adopted to pursue better performance. However, these complex methods are too heavyweight to be directly deployed in client devices with limited resources, such as mobile phones. Existing solutions suffer from a trade-off between algorithm performance and deployment overhead. To make the deployment of sophisticated ABR algorithms practical, we propose PiTree, a general, high-performance, and scalable framework that can faithfully convert sophisticated ABR algorithms into decision trees with teacher-student learning. In this way, network operators can train complex models offline and deploy converted lightweight decision trees online. We also present theoretical analysis on the conversion and provide two upper bounds of the prediction error during the conversion and the generalization loss after conversion. Evaluation on three representative ABR algorithms with both trace-driven emulation and real-world experiments demonstrates that PiTree could convert ABR algorithms into decision trees with < 3% average performance degradation. Moreover, compared to original deployment solutions, PiTree could save considerable operating expenses for content providers. [ABSTRACT FROM AUTHOR]

Internet of Mobile Things (IoMTs) refers to the interconnection of mobile devices, for example, mobile phones, vehicles, robots, etc. For mobile data, strong extra processing resources are normally required due to the limited physical resources of the mobile devices in IoMTs. Due to latency or bandwidth limitations, it may be infeasible to transfer a large amounts of mobile data to remote server for processing. Thus, distributed computing is one of the potential solutions to overcome these limitations. We consider the device mobility in IoMTs. Two situations of the movement position of the mobile devices, i.e., unpredictable and predictable, are considered. In addition, three possible relative positions between the two server sets which respectively correspond to the positions of a mobile device for computation tasks offloading and for output results receiving, i.e., within the same server sets, with two different server sets and with two adjacent server sets, are studied. Coded schemes with high flexibility and low complexity are proposed based on Fountain codes to reduce the total processing time and latency of the distributed fog computing process in IoMTs for the above different situations. The latency related performance, i.e., the computation, the communication and the transmission loads, is analyzed. We also compare of the Fountain code-based and the uncoded schemes and numerical results demonstrate that shorter total processing time and lower latency can be achieved by the Fountain code-based schemes. [ABSTRACT FROM AUTHOR]

We are pleased to present this Special Issue on this timely and important topic. The next generation ISO/IEC MPEG and ITU-T VCEG video coding standard called versatile video coding (VVC) was released in July 2020 ,. Gls vvc includes some coding tools enabling an important coding gains estimated to 35% of bit-rate reductions for the same quality in terms of peak signal to noise ration (PSNR) compared with high efficiency video coding (HEVC) in random access (RA) coding configurations. For all intra (AI) configuration the improvement is a bit lower and estimated in a 25%. Moreover, subjective comparison recently conducted between HEVC and the VVC reference software, has shown that this gain is even higher reaching up to 50% of bit-rate reduction for the same perceived quality -. Unfortunately the coding gain is associated to an increase in the algorithm complexity at both encoder and decoder sides. The VVC encoder is estimated to be $8\times $ more complex than HEVC in RA configuration and $25\times $. The complexity of the VVC decoder is doubled compared to HEVC. Therefore, complexity reduction and optimization of VVC is critical to design of software and hardware real time VVC codecs for successful deployment on video consumer devices including among others TVs, mobile phones and tablets. [ABSTRACT FROM AUTHOR]

This article focuses on the design of a low specific absorption rate (SAR) mobile phone antennas. First, the interaction mechanism of the radiation fields of mobile phone antennas with nearby human tissues is analyzed by using boundary conditions of electromagnetics. The relations between SAR and the electric field are constructed. Then, a concept of reverse current is proposed to decrease the electric field radiated by the antenna at the air–tissue interface and, consequently, reduce the SAR of human tissues. Finally, a metal-rimmed mobile phone antenna is designed according to the proposed theory. The ground clearance of the designed antenna is 2 mm. Their measured normalized peak head and body SAR values are lower than 1.0 W/kg, much less than the SAR safety limit of 1.6 W/kg according to the guidelines of IEEE and FCC or 2.0 W/kg according to the guidelines of the International Commission on Non-Ionizing Radiation Protection (ICNIRP). The measured −6 dB impedance bandwidths are 830–1040 and 1670–2730 MHz, respectively. The measured efficiencies are higher than −5 dB at the lower band and −4 dB at the higher band. The measured results prove that the proposed theory can provide guidance for the design of low-SAR mobile phone antennas. [ABSTRACT FROM AUTHOR]

We contribute MobileVisFixer, a new method to make visualizations more mobile-friendly. Although mobile devices have become the primary means of accessing information on the web, many existing visualizations are not optimized for small screens and can lead to a frustrating user experience. Currently, practitioners and researchers have to engage in a tedious and time-consuming process to ensure that their designs scale to screens of different sizes, and existing toolkits and libraries provide little support in diagnosing and repairing issues. To address this challenge, MobileVisFixer automates a mobile-friendly visualization re-design process with a novel reinforcement learning framework. To inform the design of MobileVisFixer, we first collected and analyzed SVG-based visualizations on the web, and identified five common mobile-friendly issues. MobileVisFixer addresses four of these issues on single-view Cartesian visualizations with linear or discrete scales by a Markov Decision Process model that is both generalizable across various visualizations and fully explainable. MobileVisFixer deconstructs charts into declarative formats, and uses a greedy heuristic based on Policy Gradient methods to find solutions to this difficult, multi-criteria optimization problem in reasonable time. In addition, MobileVisFixer can be easily extended with the incorporation of optimization algorithms for data visualizations. Quantitative evaluation on two real-world datasets demonstrates the effectiveness and generalizability of our method. [ABSTRACT FROM AUTHOR]

With the development of applications on end devices, such as cell phones and tablets, more and more passengers would like to have entertainment on these end devices when they are cruising on vehicles. Due to the limited computation ability of the end devices, some of these applications have back-end components on the edge clouds, which are realized by Service Entities (SEs). In this work, we propose a system named DSEP to Dynamically determine the SE Placement, such that the maximum latency experienced by the passengers can be minimized. To this end, we first train two sequential neural networks to predict the position of each individual vehicle, and propose an efficient algorithm based on optimization relaxation and Lagrange decomposition to determine the SE placement. Through extensive real-data driven simulations, we find that with the two sequential neural networks proposed in this paper, there are less than 1 percent errors on estimating where the passengers will access the edge cloud system. When the computation resources in the edge cloud are limited, DSEP can reduce the response latency by up to 43 percent compared with the nearest placement scheme. Even averaging the performance improvement over all simulation settings, DSEP can reduce the response latency by 16 percent. [ABSTRACT FROM AUTHOR]

Mobile location-based services are important context-aware services that are more and more used for enforcing security policies, for supporting indoor room navigation, and for providing personalized assistance. However, a major problem still remains unaddressed—the lack of solutions that work across buildings while not using additional infrastructure and also accounting for privacy and reliability needs. A privacy-preserving, multi-modal, cross-building, collaborative localization platform is proposed based on Wi-Fi Received Signal Strength Indicator (RSSI) (existing infrastructure), Cellular RSSI, sound, light, and geo-magnetic levels, that enables sub-room level localization. The solution is fully based on mobile phones and existing Wi-Fi infrastructure, and has privacy inherently built into it via cryptographically-secured onion routing and perturbation/randomization techniques. It also exploits the idea of weighted collaboration to increase the reliability as well as to limit the effect of noisy devices (due to sensor noise/privacy). The solution has been analyzed in terms of latency overhead due to onion-routing, request load on phones, privacy-accuracy tradeoffs, optimum parameters, granularity, different classification algorithms using real location data collected at multiple indoor and outdoor locations via an Android application. The additional features other than Wi-Fi RSSI values are shown to increase the accuracy to a maximum of 15 percent, while considering Geo-magnetic field is shown to enhance the granularity from $2.5~\mathrm {m}$ 2. 5 m to $\approx 1~\mathrm {m}$ ≈ 1 m , a 60 percent improvement. [ABSTRACT FROM AUTHOR]