Digital communication systems are ubiquitous. Examples of digital communication systems include cell phones, Bluetooth, WiFi, and cable modems. This book explores in depth how these communication systems work and the fundamental limits on the performance of digital communication systems. We begin in this chapter with a high-level description of digital communication systems so as to understand the trade-offs in designing a communication system. We also explore the fundamental limits that can be achieved in terms of the data rate possible for a given bandwidth and the energy needed for a given level of noise.

The optimal receiver finds the most likely noise signal corresponding to a transmitted signal.

Stage 6 of the journey addresses various aspects of how information is conveyed and organized in a sentence, beginning with the stubborn problems that led to the development of dynamic semantics (‘donkey sentences’ and cross-sentential anaphora), through properties of expressions that are used to refer (descriptions, proper names, indexical expressions), to the organization of information (presuppositions and projective content, topic, focus, coherence). As such, it is a step to the next stage that concerns utterance meaning.

Noise is an important aspect of what limits the performance of communication systems. As such, it is important to understand the statistical properties of noise. Noise at the input of a receiver will affect the performance of a communication system. The received signal consists of the desired signal plus noise. Because receivers filter the received signal, it is important to be able to characterize the noise out of a linear system (i.e. a filter).

Stage 7 of the journey moves to utterance meaning and to various ways of explaining how speakers communicate more than what the sentence says. It introduces the intention-and-inference-based concept of meaning in Grice’s and post-Gricean pragmatics, travelling though maxims, principles, and heuristics proposed by various scholars of this orientation. It then moves to introducing (i) approaches that advocate the ‘maximalist’, contextualist semantic content and (ii) semantic minimalism that preserves a much clearer boundary between semantics and pragmatics – suggesting ‘food for thought’ at many points in the discussion.

These modulation techniques are widely used in practice. We quantify the trade-off between data rate and energy for these techniques and compare performance with the capacity limits discussed in Chapter 1. We begin by discussing MPSK, where the information determines the phase of a sinusoidal signal. Second, we discuss PAM and QAM, in which the amplitude in one and two dimensions, respectively, are varied depending on the data. Third, we discuss orthogonal modulation in which the bandwidth efficiency is very low, but the required energy is also very low.

This stage of the journey moves to ‘things speakers do with language’ in communication, covering a broad area from the literal-non-literal distinction and approaches to metaphor, through speech acts, ending with the ‘crossroads’ with ethical and social debates, such as those to do with negotiation and joint construction of meaning, questions of accountability and commitment (also in the case of lying and misleading), as well as politeness and appropriateness, including the use of taboo and offensive language. It offers a glimpse of how these topics benefit from an interdisciplinary manner of research and pauses with ample ‘food for thought’ questions on the way.

In this chapter we first discuss the relationship between transmitted signals and received signals. There are three effects of the propagation medium on the transmitted signals: path loss, shadowing, and multipath fading. Path loss refers to the relation between the average received power and the transmitted power as a function of distance. Shadowing refers to the situation where buildings or other objects might block the line of sight between the transmitter and receiver.

In Stage 5, the journey moves to meaning relations within sentences, introducing such topics of quantification (including generalized quantifiers), representing events and states, temporal, aspectual, and modal distinctions in semantics, and propositional attitude reports.