Bandwidth Efficient Coding

John B. Anderson

• Publisher: Wiley-IEEE Press
• Year: 2017
• Print ISBN: 9781119345336
• eBook ISBN: 9781119345220
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Mobile & Wireless Communications
• Index: Technology & Engineering

This book addresses coding, a new solution to the major challenge of communicating more bits of information in the same radio spectrum.

• Explores concepts and new transmission methods that have arisen in the last 15 years
• Discusses the method of faster than Nyquist signaling
• Provides self-education resources by including design parameters and short MATLAB routines

Bandwidth Efficient Coding takes a fresh look at classical information theory and introduces a different point of view for research and development engineers and graduate students in communication engineering and wireless communication.

1
Introduction

Prologue

How does one transmit information when bandwidth is expensive? One can explore new wavelengths. One can use multiple antennas to distinguish more pathways. One can design better modulation and coding for each pathway. This book is about the last.

According to the laws of nature, sending bits of information via an electrical medium requires two main resources: energy and bandwidth. Each bit needs energy, and just as in soccer football, a certain energy is needed to hit the ball far enough. Adding bandwidth to football needs new rules. Suppose every player has a ball and all must pass through a narrow passage on the way to the goal. How difficult is it to reach the goal?

Electrical communication is a game too, played according to nature's laws. In the first half of the twentieth century, several of these became clear. First, much less energy is needed per bit if the signal bandwidth is widened. Second, a certain type of energy pulse, called “orthogonal,” is easier to process. These facts were well established in 1949 when Claude Shannon published something different, a formula for the ultimate capacity of a set bandwidth and energy to carry information. The key to approaching that limit is coding, that is, imposing clever patterns on the signals. As much as 90% of signal energy can be saved compared to rudimentary methods, or the information can be sent much further. In principle, whatever configuration of energy and bandwidth was available, it could be coded.

Nonetheless, those who designed codes in the following decades thought of them, consciously or not, as trading more bandwidth for less energy. Even with a simple trade, a signal could travel much further if its bandwidth were scaled up. In this way—and only this way—signals reached Mars and even Pluto. Neither was crowded with players, so that wide bandwidth signals were practical. There will soon be rovers from several nations on Mars, so that allotting wide bandwidth to each is not quite so practical. Here on Earth the situation is more desperate. Such services as cellular wireless and digital video must share a very crowded spectrum; furthermore, governments have discovered they can force providers to pay astonishing prices for bandwidth. Today, bandwidth costs far more than energy. Everyone needs to minimize it.

In the 1970s, methods of signal coding were discovered that did not increase bandwidth; signals could travel farther and easier without scaling up bandwidth. This was clear in Shannon's 1949 formula from the first day, but the concepts took time to sink in. What his formula really says is that coding leads to large savings no matter what the combination of energy and bandwidth. Today, with bandwidth costly, we want to work at narrow bandwidth and higher energy, not the reverse. The problem is: We know little about how to design the coding. The purpose of this book is to take that next step. How should efficient signal coding work when very narrow bandwidths per bit are available?

1.1 Electrical Communication

This chapter introduces important and potentially troublesome concepts in a mostly philosophical way. Among them are bandwidth and time, pulse shapes, modulation, and coding. The needed formal communication background is Chapter 2, and Shannon's theory appears in Chapter 3. Certain concepts need some evolution to fit modern needs. The outcome of the book is that practical coding schemes exist that work well in a very narrowband world.

Communication transmits messages through time and space. In this book, the medium is electrical signals, and we will restrict ourselves to radio. For our purposes, messages are composed of symbols, and we want to transmit these accurately and efficiently through the physical world. In communication engineering, sending a symbol has three basic costs, energy, bandwidth, and implementation complexity. Each trades off against the others. Once the three costs are set the measure of good performance is most often probability of symbol error.

Even a century ago, it was clear enough that error may be reduced by spending more energy. A basic fact of communication, that first became evident with FM broadcasting, is that for the same performance, energy may be traded for bandwidth. Error-correcting codes, as first used, were thought of as a manifestation of this fact: By transmitting extra check bits, energy could be saved overall. But Claude Shannon's 1949 work [7] implied that energy or bandwidth or both could be reduced while maintaining the same error performance. Each combination of energy and bandwidth had a certain capacity to carry symbols but alas, there was no free lunch, and rapidly diverging “coding” complexity is required to approach this capacity. Today, energy, bandwidth, and complexity are a three-way trade-off.

Since 1949 there have been 60 years of progress ...

Table of contents

• Cover
• Series Page
• Title Page
• Copyright
• Preface
• Chapter 1: Introduction
• Chapter 2: Communication Theory Foundation
• Chapter 3: Gaussian Channel Capacity
• Chapter 4: Faster Than Nyquist Signaling
• Chapter 5: Multicarrier FTN
• Chapter 6: Coded Modulation Performance
• Chapter 7: Optimal Modulation Pulses
• Index
• IEEE Press Series on Digital and Mobile Communication
• End User License Agreement