Environmental sustainability has been of increasing interest in designing any system in recent times. Computing systems usually contribute to this drive of sustainability from two different perspectives: (i) the energy perspective and (ii) the equipment-recycling perspective. Sections 6.1 and 6.2 describe these perspectives of sustainability of computing systems in general. All subsequent sections will focus on how to ensure sustainability for BANs from the energy perspective.

The energy perspective

Sustainability from the energy perspective, also referred to as energy-sustainability, has two main objectives: (i) reducing the carbon footprint from the power grid and (ii) reducing the need for battery replacement (for computing equipment running on limited-energy batteries). To ensure that both these objectives are attained, energy-sustainability can be described as the balance between the power required for computation and the power available from renewable or green energy sources (e.g., sources in the environment such as solar power). Ideally, if the power available from external renewable energy sources is more than the power required for computation then a power grid (or battery) might not be needed, and computation can be said to be energy-sustainable. However, in reality, both the available and the required power may vary over time. For example, solar power is available only during the day, but power may be required during the night (depending on the time-varying computing operations performed). In such a case, power may need to be extracted from a power grid (or battery) during the night, thus making computing operations unsustainable.

This book is a guide to the Weightless technology. The definitive documentation for Weightless is the Weightless standard as published by the Weightless SIG and this book in no way is intended as an alternative. However, standards documents are not designed for readability and it is often helpful to start with a more descriptive text. This book is designed to explain the context for Weightless, the key design decisions and to provide a readable overview to the standard. That may be sufficient for some, and for those that will go on to read the standard they will better understand the details that they find there.

This book was written to accompany version 0.6 of the standard. This is referred to throughout the book simply as the standard. Of course, this standard will evolve and it is envisaged that this book will be updated to accompany major revisions to the standard.

Why the name ‘Weightless’? Like many standards such as Zigbee and Bluetooth, the name chosen is often more whimsy than descriptive. In this case, it came indirectly from making the point that this was not a new generation of cellular standard, measured in generations (2G, 3G …). Indeed, it was outside of this generation pattern and so perhaps zero-G. Zero-G is often associated with no gravity leading to weightlessness … At the time it was conceived most thought that a different name would emerge during the early standardisation process, but as is often the case names acquire a momentum all of their own, even those that have no weight.