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

Abstract

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 many 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 the lifestyle and societal changes driving the need for next generation networks, to the technical requirements needed to enable 6G applications, through to the challenges, as well as possibilities for practically realizable system solutions across all layers of the Open Systems Interconnection stack (i.e., from application to the physical layer). Since many of the 6G applications will need access to an orderof-magnitude more spectrum, utilization of frequencies between 100 GHz and 1 THz becomes of paramount importance. As such, the 6G eco-system will feature a diverse range of frequencies, 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, as well as 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, as well as 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 timesensitive applications. This is in sharp contrast to the present hierarchical network architectures, which 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.

FBMC Receiver Design and Analysis for Medium and Large Scale Antenna Systems

“…The authors in [6] have shown that even with an infinite number of antennas, a residual interference remains at the output of any of the above combiners. It has been also noted that for a large number of antennas, all the above combiners converge to 1 N H m , [34]. Accordingly, the equivalent channel impulse response between the transmitted symbols at subcarrier m ′ of terminal k ′ and the received and combined signal at subcarrier m of BS output corresponding to terminal k may be expressed as…”

“…To summarize, the main contributions of this paper are the following; (1) We propose a joint multiuser and spectrally efficient channel estimation technique for the uplink of FBMCbased networks that is applicable to massive MIMO with both co-located and distributed antennas. We also derive the required statistics of the channel estimation errors to be used for their compensation at the equalization stage; (2) We investigate the channel equalization problem in FBMC-based massive MIMO and propose a practical two-stage equalization tech-nique that is highly effective in both co-located and distributed antenna architectures; (3) We take into account the equalizer length in the design procedure to achieve an equalizer with a practical length; (4) We integrate the PDP estimates of the channel into our equalizer design framework and propose a practical PDP-based equalizer with a practical/short length; (5) We formulate FBMC-based cell-free massive MIMO for the first time and investigate channel estimation and equalization in this setup; (6) We derive the statistical characteristics of the estimation errors of our proposed channel estimator and incorporate them into our proposed equalizers to tackle the imperfect CSI effects.…”

Seven Defining Features of Terahertz (THz) Wireless Systems: A Fellowship of Communication and Sensing

“…Fourth, ubiquitous access through these systems necessitates the use of edge computing and storage. Nonetheless, computing problems will arise due to the onboard limitations of small satellites [88]. Thus, it necessary to develop novel networking frameworks that overcome the computing limitations and provide low latency THz communications for NTNs.…”

Deep Reinforcement Learning for Radio Resource Allocation and Management in Next Generation Heterogeneous Wireless Networks: A Survey

“…Existing wireless networks, such as the sub 6 GHz, suffers from a severe bandwidth shortage which is even exacerbated with the explosive increase in the user devices [6]. Fortunately, the mmWave and the emerging THz bands can considerably overcome this shortcoming by providing an extra 3.25 GHz and 10-100 GHz bandwidth, respectively [38]. It is also expected that modern wireless user devices will be equipped with advanced capabilities that enable them to aggregate all these three frequency bands, i.e., the sub 6GHz, mmWave, and THz, to support future disruptive technologies and services [39].…”