Mobile communications have been undergoing a generational change every ten years or so. However, the time difference between the so-called “G’s” is also decreasing. While fifth-generation (5G) systems are becoming a commercial reality, there is already significant interest in systems beyond 5G, which we refer to as the sixth generation (6G) of wireless systems. In contrast to the already published papers on the topic, we take a top-down approach to 6G. More precisely, we present a holistic discussion of 6G systems beginning with lifestyle and societal changes driving the need for next-generation networks. This is followed by a discussion into the technical requirements needed to enable 6G applications, based on which we dissect key challenges and possibilities for practically realizable system solutions across all layers of the Open Systems Interconnection stack (i.e., from applications to the physical layer). Since many of the 6G applications will need access to an order-of-magnitude more spectrum, utilization of frequencies between 100 GHz and 1 THz becomes of paramount importance. As such, the 6G ecosystem will feature a diverse range of frequency bands, ranging from below 6 GHz up to 1 THz. We comprehensively characterize the limitations that must be overcome to realize working systems in these bands and provide a unique perspective on the physical and higher layer challenges relating to the design of next-generation core networks, new modulation and coding methods, novel multiple-access techniques, antenna arrays, wave propagation, radio frequency transceiver design, and real-time signal processing. We rigorously discuss the fundamental changes required in the core networks of the future, such as the redesign or significant reduction of the transport architecture that serves as a major source of latency for time-sensitive applications. This is in sharp contrast to the present hierarchical network architectures that are not suitable to realize many of the anticipated 6G services. While evaluating the strengths and weaknesses of key candidate 6G technologies, we differentiate what may be practically achievable over the next decade, relative to what is possible in theory. Keeping this in mind, we present concrete research challenges for each of the discussed system aspects, providing inspiration for what follows.

6G Wireless Systems: Vision, Requirements, Challenges, Insights, and Opportunities

The real-time health monitoring system is a promising body area network application to enhance the safety of firefighters when they are working in harsh and dangerous environments. Other than monitoring the physiological status of the firefighters, on-body monitoring networks can be also regarded as a candidate solution of motion detection and classification. In this paper, we consider motion classification with features obtained from the on-body radio frequency (RF) channel. Various relevant RF features have been identified and a support vector machine (SVM) has been implemented to facilitate human motion classification. In particular, we distinguish the most frequently appearing human motions of firefighters including standing, walking, running, lying, crawling, climbing, and running upstairs with an average true classification rate of 88.69 percent. Classification performance has been analyzed from three different perspectives including typical classification results, effects of candidate human motions, and effects of on-body sensor locations. We prove that even a subset of available RF features provides an acceptable classification rate, which may result in less computational cost and easier implementation by using our proposed scheme.

Enlighten Wearable Physiological Monitoring Systems: On-Body RF Characteristics Based Human Motion Classification Using a Support Vector Machine

Body-centric wireless communications represent a well-established field of research, with many studies and applications developed in a range of frequencies that extend from 400 MHz up to 10 GHz. However, many advantages can be found in operating such systems at millimeter-wave frequencies. For example, compact antennas suitable for body-centric applications can be obtained together with other benefits, such as higher data rates and reduced interference and "observability". Meanwhile, numerical modeling of antennas and propagation at millimeter-wave frequencies represents a major challenge in terms of efficiency and accuracy. The aim of this paper is to provide a review of recent progresses and outstanding challenges in the field of body-centric communication at frequencies of 60 GHz and 94 GHz.

Antennas and Propagation for Body-Centric Wireless Communications at Millimeter-Wave Frequencies: A Review [Wireless Corner]

Body-centric wireless communications represent a well-established field of research, with many studies and applications developed in a range of frequencies that extend from 400 MHz up to 10 GHz. However, many advantages can be found in operating such systems at millimeter-wave frequencies. For example, compact antennas suitable for body-centric applications can be obtained together with other benefits, such as higher data rates and reduced interference and "observability." Meanwhile, numerical modeling of antennas and propagation at millimeter-wave frequencies represents a major challenge in terms of efficiency and accuracy. The aim of this paper is to provide a review of recent progresses and outstanding challenges in the field of body-centric communication at frequencies of 60 GHz and 94 GHz.

Antennas and propagation for body centric wireless communications at millimeter wave frequencies: a review

Wireless Body Area Networks (WBANs) represent one of the most promising approaches for improving the quality of life, allowing remote patient monitoring and other healthcare applications. The deployment of a WBAN is a critical issue that impacts both the network lifetime and the total energy consumed by the network. This work investigates the optimal design of wireless body area networks by studying the joint data routing and relay positioning problem, in order to increase the network lifetime. To this end, we propose a mixed integer linear programming model, the Energy-Aware WBAN Design model, which optimizes the number and location of relays to be deployed and the data routing towards the sink, minimizing both the network installation cost and the energy consumed by wireless sensors and relays. We solve the proposed model in both realistic WBAN scenarios and general topologies, and compare the model performance to the most notable approaches proposed in the literature. Numerical results demonstrate that our model (1) provides a good tradeoff between the energy consumption and the number of installed relays, and (2) designs energy-efficient and cost-effective WBANs in a short computation time, thus representing an interesting framework for the dynamic WBAN design problem.

Optimal design of energy-efficient and cost-effective wireless body area networks

On-body area ultrawideband (UWB) communication is of high importance for promising new biomedical applications. However, there are currently few measurements or models describing on-body area propagation channels which put an emphasis on various body postures. Using the frequency-dependent finite-difference time domain (FDTD) method and a realistic human body model, we simulate various body postures for modeling on-body channels. Based on the FDTD numerical results, we derive an on-body propagation model and determine the model parameters for some representative transmission links on the human body. A good match is obtained between the data derived from FDTD and the statistically implemented models in terms of key communication metrics. In addition, for the chest-to-right-waist transmission link, an experiment is performed in order to verify the results from the FDTD method, and it is found that the model parameters agree well between the two approaches.

An On-Body Channel Model for UWB Body Area Communications for Various Postures

In compliance assessments of radio-frequency exposure from cellular-phone-base station antennas, the root of 6-min time average of the squared electric fields is commonly required. Under the assumption that the time-varying electric fields belong to an ergodic process, a new approach has been proposed to estimate the 6-min time average from the ensemble average of the squared electric fields based on amplitude probability distribution (APD) measurements for a shorter time, much less than 6 min. The usefulness of the approach has been demonstrated at the 800-MHz band and the 1.5-GHz band, and the results have shown that by using a fast sampling rate, 1-min APD measurements could give a good estimate of the 6-min time average with an accuracy of within 10%.

T. Tayamachi

Papers

An On-Body Channel Model for UWB Body Area Communications for Various Postures

Amplitude Probability Distribution Measurement for Electric Field Intensity Assessment of Cellular-Phone-Base Stations