As of today, orthogonal frequency division multiplexing (OFDM) has been the dominant technology for broadband multicarrier communications. However, in certain applications such as cognitive radios and uplink of multiuser multicarrier systems, where a subset of subcarriers is allocated to each user, OFDM may be an undesirable solution. In this article, we address the shortcomings of OFDM in these and other applications and show that filter bank multicarrier (FBMC) could be a more effective solution. Although FBMC methods have been studied by a number of researchers, and some even before the invention of OFDM, only recently has FBMC been seriously considered by a few standard committees.

OFDM Versus Filter Bank Multicarrier

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

In the past two decades, the synthetic development of magnetic nanoparticles (NPs) has been intensively explored for both fundamental scientific research and technological applications. Different from the bulk magnet, magnetic NPs exhibit unique magnetism, which enables the tuning of their magnetism by systematic nanoscale engineering. In this review, we first briefly discuss the fundamental features of magnetic NPs. We then summarize the synthesis of various magnetic NPs, including magnetic metal, metallic alloy, metal oxide, and multifunctional NPs. We focus on the organic phase syntheses of magnetic NPs with precise control over their sizes, shapes, compositions, and structures. Finally we discuss the applications of various magnetic NPs in sensitive diagnostics and therapeutics, high-density magnetic data recording and energy storage, as well as in highly efficient catalysis.

Organic Phase Syntheses of Magnetic Nanoparticles and Their Applications.

The realization of a digital recording system using partial-response class-IV signaling with maximum-likelihood sequence detection (MLSD) is described. To perform MLSD at the high data rates encountered in recording systems, a simple implementation of the Viterbi detector based on a difference-metric algorithm is developed. Decision-directed schemes for gain control and timing recovery, for tracking variations of the gain and timing phase during data readback, and for fast initial adjustment from a known preamble are presented. The dynamic behavior of the control algorithms was studied by computer simulations. Coding was used to facilitate timing recovery and gain control, to limit the path memory length of the Viterbi detector, and to allow fast and reliable startup of the receiver. The design and properties of rate 8/9 constrained codes are examined. The problem of equalization is addressed, and analog and combined analog/digital filter implementations are developed. A simple adaptive equalizer capable of compensating variations of the recording channel characteristics with track radius and/or head-to-medium distance is described. >

A PRML system for digital magnetic recording

Communication Networks--The center of the information revolution High performance networks are revolutionizing our lives in ways we cannot yet fully perceive. Meet your evolving needs with this in-depth presentation of emerging technologies used to build high speed, high performance communication networks. Authoritatively written, it explains how the converging telephone, data, and CATV technologies are combined into high performance networks, and how to plan, manage, and control these networks. An essential guide for networking professionals This book is well suited for a variety of networking needs. It enables network specialists and system administrators to make informed decisions for implementing and maintaining their companies' networks. It supplies network hardware and software developers with the tools to develop networking solutions, and it provides students in electrical engineering, computer science, operations research, and industry courses with a substantial introduction to networking principles. Features Explains the principles of network design and operation, and their implementation in state-of-the-art technologies such as Internet, high speed LANs and WANs, ISDN, ATM, BISDN, and SONET. Combines the perspectives of the communications engineer, the computer scientist and the economist to provide a system-level understanding of the core networking principles and technologies. Presents essential tools for analyzing, designing, and managing high performance networks. Provides unique coverage of economic issues including cost recovery and pricing schemes. Includes up-to-date coverage of delays, losses, admission control, routing, flow control, switching, networkplanning, pricing, and billing.

High-Performance Communication Networks

A filter-bank modulation technique called filtered multitone (FMT) and its application to data transmission for very high-speed digital subscriber line technology are described. The proposed scheme leads to significantly lower spectral overlapping between adjacent subchannels than for known multicarrier techniques such as discrete multitone (DMT) or discrete wavelet multitone. FMT modulation mitigates interference due to echo and near-end crosstalk signals, and increases the system throughput and reach. Signal equalization in an FMT receiver is accomplished in the form of per-subchannel symbol-spaced or fractionally spaced linear or decision-feedback equalization. The problem of channel coding for this type of modulation is also addressed, and an approach that allows combined removal of intersymbol-interference via precoding and trellis coding is described. Furthermore, practical design aspects regarding filter-bank realization, initial transceiver training, adaptive equalization, and timing recovery are discussed. Finally, simulation results of the performance achieved by FMT modulation for very high-speed digital subscriber line systems, where upstream and downstream signals are separated by frequency-division duplexing, are presented and compared with DMT modulation.

Filtered multitone modulation for very high-speed digital subscriber lines

The paper investigates the application of low-density parity-check (LDPC) codes to digital subscriber-line (DSL) transmission systems that employ discrete multitone modulation. A family of linear-time encodable binary LDPC codes that are well-suited for DSL transmission is introduced. Encoding and symbol mapping for multilevel modulation are described. Simulation results show that even under tight latency constraints good net coding gains can be achieved. Implementation complexity is analyzed and compared with that of trellis-coded modulation as employed in current asymmetric DSL transceivers. The incorporation of powerful LDPC coding techniques into next-generation DSL modems appears to be possible with reasonable increase in transceiver complexity.

/pdf/low-density-parity-check-codes-for-digital-subscriber-lines-36a60knduo.pdf

Low-density parity-check codes for digital subscriber lines

The recording performance of a new magnetic tape based on perpendicularly oriented barium ferrite particles was investigated using a 90-nm-wide giant-magnetoresistive reader and a prototype enhanced-field write head. A linear density of 600 kb/in with a postdetection byte-error rate $ was demonstrated based on measured recording data and a software read channel that used a noise-predictive maximum likelihood detection scheme. Using a new iterative decoding architecture, a user bit-error rate of $ can be achieved at this operating point. To facilitate aggressive scaling of the track density, we made several advances in the area of the track-following servo. First, we developed an experimental low-noise tape transport. Second, we implemented an optimized servo channel that together with an experimental timing-based servo pattern enables the generation of position estimates with nanoscale resolution at a high update rate. Third, we developed a field-programmable gate array-based prototyping platform in which we have implemented the servo channel and an $H_{\infty }$ -based track-following controller, enabling real-time closed-loop track-following experiments. Combining these technologies, we achieved a position-error signal (PES) with a standard deviation of 10.3 nm. This magnitude of PES in combination with a 90-nm-wide reader allows the writing and reading of 177-nm-wide tracks at 600 kb/in, for an equivalent areal density of 85.9 Gb/in $^{2}$ . This paper clearly demonstrates the continued scaling potential of tape technologies based on low-cost particulate media.

29.5- $\hbox{Gb/in}^{2}$ Recording Areal Density on Barium Ferrite Tape

We present a filter-bank modulation technique called filtered multitone (FMT) and describe its application to data transmission for very-high-speed digital subscriber line (VDSL) technology. The proposed scheme leads to significantly lower spectral overlapping between adjacent subchannels than for known multicarrier techniques such as discrete multitone (DMT) or discrete wavelet multitone. This allows mitigating interference due to echo and near-end crosstalk signals, increasing system throughput and reach, and simplifying system operations for VDSL transmission. In the receiver of an FMT system, signal equalization is accomplished in the form of per-subchannel symbol-spaced or fractionally-spaced linear or decision-feedback equalization. We study by simulation the performance that can be achieved by FMT modulation for VDSL systems where upstream and downstream signals are separated by frequency-division duplexing. We also provide comparisons with DMT modulation for a typical transmission scenario.

Filtered multitone modulation for VDSL

We describe a decoder architecture intended for decoding array-code-based low-density parity-check (LDPC) codes using the sum-product algorithm (SPA). The advantages of the proposed architecture, as compared to the fully parallel implementation of the SPA, are: reduced memory size, avoidance of complex signal interconnect patterns, and ease of programmability to accommodate various code parameters. These advantages are derived from exploiting the well-defined structure of the parity-check matrix of array-code based LDPC codes. Sum-product decoding with modified message-passing schedules are proposed to simplify the decoder implementation further.

S. Olcer

Papers

Filtered multitone modulation for very high-speed digital subscriber lines

Low-density parity-check codes for digital subscriber lines

29.5- $\hbox{Gb/in}^{2}$ Recording Areal Density on Barium Ferrite Tape

Filtered multitone modulation for VDSL

Decoder architecture for array-code-based LDPC codes