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

This paper considers the multiuser power control problem in a frequency-selective interference channel. The interference channel is modeled as a noncooperative game, and the existence and uniqueness of a Nash equilibrium are established for a two-player version of the game. An iterative water-filling algorithm is proposed to efficiently reach the Nash equilibrium. The iterative water-filling algorithm can be implemented distributively without the need for centralized control. It implicitly takes into account the loop transfer functions and cross couplings, and it reaches a competitively optimal power allocation by offering an opportunity for loops to negotiate the best use of power and frequency with each other. When applied to the upstream power backoff problem in very-high bit-rate digital subscriber lines and the downstream spectral compatibility problem in asymmetric digital subscriber lines, the new power control algorithm is found to give a significant performance improvement when compared with existing methods.

Distributed multiuser power control for digital subscriber lines

From the Publisher:
Multi-carrier modulation, in particular orthogonal frequency division multiplexing (OFDM), has been successfully applied to a wide variety of digital communications applications for several years. Although OFDM has been chosen as the physical layer standard for a diversity of important systems, the theory, algorithms, and implementation techniques remain subjects of current interest. 

This book is intended to be a concise summary of the present state of the art of the theory and practice of OFDM technology. This book offers a unified presentation of OFDM theory and high speed and wireless applications. In particular, ADSL, wireless LAN, and digital broadcasting technologies are explained. 

It is hoped that this book will prove valuable both to developers of such systems, and to researchers and graduate students involved in analysis of digital communications, and will remain a valuable summary of the technology, providing an understanding of new advances as well as the present core technology.

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Multi-Carrier Digital Communications: Theory and Applications of OFDM

The mutual information of independent parallel Gaussian-noise channels is maximized, under an average power constraint, by independent Gaussian inputs whose power is allocated according to the waterfilling policy. In practice, discrete signaling constellations with limited peak-to-average ratios (m-PSK, m-QAM, etc.) are used in lieu of the ideal Gaussian signals. This paper gives the power allocation policy that maximizes the mutual information over parallel channels with arbitrary input distributions. Such policy admits a graphical interpretation, referred to as mercury/waterfilling, which generalizes the waterfilling solution and allows retaining some of its intuition. The relationship between mutual information of Gaussian channels and nonlinear minimum mean-square error (MMSE) proves key to solving the power allocation problem.

/pdf/optimum-power-allocation-for-parallel-gaussian-channels-with-6fj5ovds2s.pdf

Optimum power allocation for parallel Gaussian channels with arbitrary input distributions

Many engineering problems that can be formulated as constrained optimization problems result in solutions given by a waterfilling structure; the classical example is the capacity-achieving solution for a frequency-selective channel. For simple waterfilling solutions with a single waterlevel and a single constraint (typically, a power constraint), some algorithms have been proposed in the literature to compute the solutions numerically. However, some other optimization problems result in significantly more complicated waterfilling solutions that include multiple waterlevels and multiple constraints. For such cases, it may still be possible to obtain practical algorithms to evaluate the solutions numerically but only after a painstaking inspection of the specific waterfilling structure. In addition, a unified view of the different types of waterfilling solutions and the corresponding practical algorithms is missing. The purpose of this paper is twofold. On the one hand, it overviews the waterfilling results existing in the literature from a unified viewpoint. On the other hand, it bridges the gap between a wide family of waterfilling solutions and their efficient implementation in practice; to be more precise, it provides a practical algorithm to evaluate numerically a general waterfilling solution, which includes the currently existing waterfilling solutions and others that may possibly appear in future problems.

Practical algorithms for a family of waterfilling solutions

1. DSL Fundamentals. Alternatives to DSLs: Fiber, Wireless, and Coax. Worldwide Extent. Voice-Band Modems and DSLs. Transmission Modes. DSL Terminology. Rate Versus Reach. Crosstalk. Enabling and Disabling Forces. Applications. Evolution of Digital Transmission. 2. Types of DSLs. DSL Design Margin. DSL Precursors. Basic Rate ISDN. HDSL. ADSL. VDSL. 3. Twisted-Pair Transmission. Twisted-Wire-Pair Origins. Telephone Network and Loop Plant Characteristics. Line Powering. Sealing Current. Transmission Line Characterization. Noises. Spectral Compatibility. More Two-Port Networks. Three-Port Networks for DSLs. References. 4. Comparison with Other Media. Fiber-to-the-Home. Coax and Hybrid Fiber Coax. Wireless Alternatives. Satellite Services. References. 5. Transmission Duplexing Methods. Four-Wire Duplexing. Echo Cancellation. Time-Division Duplexing. Frequency-Division Multiplexing. References. 6. Basic Digital Transmission Methods. Basic Modulation and Demodulation. Baseband Codes. Passband Codes. References. 7. Loop Impairments, Solutions, and DMT. Intersymbol Interference. Multichannel Line Codes. Trellis Coding. Error Control. References. 8. Initialization, Timing and Performance. Initialization Methods. Adaptation of Receiver and Transmitter. Measurement of Performance. Timing Recovery Methods. References. 9. Operations, Administration Maintenance, and Provisioning. OAM&P Features. Loop Qualification. 10. DSL in the Context of the ISO Reference Model. The ISO Model. Theory and Reality. The Internet Protocol Suite. ATM in the Seven-Layer Model. 11. ADSL: The Bit Pump. ADSL System Reference Model. ATU-C Reference Model. ATU-R Reference Model. Specific Configurations to Support ATM. Framing. Operations and Maintenance. Initialization. Reference. 12. ATM Transmission Convergence on ADSL. Functions of ATM Transmission Convergence. Transmission Convergence in an ADSL Environment. Reference. 13. Frame-Based Protocols over ADSL. PPP over a Frame-Based ADSL. FUNI over ADSL. Reference. 14. ADSL in the Context of End-to-End Systems. An Overview of a Generic DSL Architecture. Potential ADSL Services and the Service Requirements. Specific Architectures for Deploying ADSL in Different Business Models. Several ADSL Architectures. References. 15. Network Architecture and Regulation. Private Line. Circuit Switched. Packet Switched. ATM. Remote Terminal. Competitive Data Access Alternatives. Regulation. 16. Standards. ITU. Committee T1. ETSI. ADSL Forum. ATM Forum. DAVIC. IETF. EIA/TIA. IEEE. The Value of Standards and Participation in Their Development. Standards Process. Appendix A: Glossary. Appendix B: Selected Standards and Specifications. Appendix C: Selected T1E1.4 Contributions and ADSL Forum Technical Reports (found on website). Index.

Thomas Starr

Papers

Understanding Digital Subscriber Line Technology