Systems coupling embedded computing and sensing have vast potential, particularly when wirelessly networked. However, the focus of much of the literature for wireless sensor network is on idealized systems with potentially millions of members (see for example), with minimal power, weight, and size. This focus on idealized systems can lead to discounting the use of current WLAN technologies such as 802.11, or WiFi, in sensor network applications. In this chapter we discuss the applicability of WiFi, as the preeminent WLAN technology, to wireless sensor network applications. We begin this discussion with an introduction to wireless sensor networks. Then we describe how the adhoc capabilities and communication efficiency of 802.11 radios are suited to certain sensor network applications. Finally, to illustrate a type of sensor network for which 802.11 radio properties are appropriate we provide an overview of a prototype wireless network for sonobuoys developed by Sensoria Corporation and Exponent Corporation, which was demonstrated using 802.11b radios.

Introduction

One application of ubiquitous computing is to create autonomous or semi-autonomous systems that monitor and report changes in the physical environment. When communicating wirelessly, this large range of systems is called wireless sensor networks. These networks are envisioned as large numbers of individual sensing “nodes”, each connected to its neighbors wirelessly, and networked together to enable communication, coordination, and collaboration. This interaction is envisioned between groups of nodes locally as well as across the network to entities potentially on external networks.

Introduction

In 1993 the ITU recommended that in spectrum prices should follow a set of principles [1].

• All spectrum users should pay a charge.

• Non-discrimination – the spectrum charge should be calculated fairly, i.e. if two users are using the same amount of spectrum in the same way, both should pay the same charge.

• The spectrum charge should be proportionate to the amount of bandwidth used.

• The charges should reflect the spectrum's value to society, i.e. if need be, frequencies used for public services should be subject to lower charges.

• The cost of spectrum regulation should not be borne by the state.

• Spectrum users should be consulted about intended adjustments in spectrum charges.

• The pricing structure should be clear, transparent and comprehensive, without unnecessarily lengthening the licensing process.

• The pricing structure should reflect the scarcity of available spectrum and the level of demand for spectrum in different frequency bands.

• The spectrum charge should be calculated so as to recover the costs of spectrum regulation. Spectrum pricing should not seek to maximise revenue for the government.

• The ability to levy spectrum charges should be anchored in law.

As discussed in the previous chapter, the contemporary approach to the setting of incentive based spectrum prices places a greater emphasis on economic factors. While some of the principles above remain relevant to the setting of spectrum prices, the 1993 ITU recommendations contain contradictions. For example, it is generally not possible to set spectrum prices to reflect scarcity while at the same time recover only the administrative costs of regulating spectrum.

Introduction

Much of the discussion in previous chapters has revolved around problems of spectrum management likely to be encountered in developed countries. It is thus pertinent to ask how the situation differs for developing countries.

If anything, their dependence on spectrum-using technologies is even greater. Lacking fixed networks to deliver communications services such as voice telephony and broadcasting, they are heavily reliant on spectrum for commercial and non-commercial services. This is illustrated by recent ITU data, which show the growth of penetration (per 100 inhabitants) of fixed and mobile lines in the least developed countries. It shows that mobile lines were roughly the same in number as fixed lines in 2001 (see Figure 16.1), but by 2004 they outnumbered fixed lines by three to one. Over the 2000–4 period the number of television receivers, mostly relying on terrestrial distribution, also increased by 50%. These data emphasise the importance of getting spectrum policy right.

Consequences for spectrum management

What special aspects of spectrum management are important in developing countries? It is helpful first to identify the differentiating factors between the two environments that are relevant.

• Developing countries are characterised by a lower per capita income, which reduces consumption of all items including spectrum-using services.

• Conversely, a lack of alternative platforms places a high priority on the development of wireless systems; there is also growing evidence that mobile communications can improve business efficiency, widen markets and promote income growth in developing countries.

• At the same time, much spectrum in developing countries is not yet assigned, or assigned wastefully to government departments, especially defence forces.

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Introduction

In earlier chapters we have stated that there is a need for, and a benefit associated with, regulating radio spectrum use. In practice the costs of regulation are typically recovered through licence fees paid by radio spectrum users and hence there is a price associated with the use of licensed radio spectrum. For example, in the USA the FCC applies two types of fees – application fees and regulatory fees which cover the administrative cost of managing the use of spectrum, respectively. They may also serve to discourage the filing of frivolous applications. If set too high, however, fees can result in under-utilisation of the spectrum, while if set too low hoarding and congestion may arise.

The simple recovery of administrative costs via licence fees, while practised by almost every spectrum management agency around the world, fails to make use of one of the most powerful incentive mechanisms available to encourage more efficient use of radio spectrum. By varying licence fees in a suitable way, a spectrum manager can improve the economic and technical efficiency of spectrum management. The setting of incentive based prices is especially attractive in circumstances where spectrum has been assigned and/or allocated via administrative means rather than auctions. Incentive based pricing also works well in the absence of secondary trading, but as we show in this chapter, it can also work alongside spectrum trading.

Licence fees are a potent means of achieving greater efficiency for radio spectrum licensees holding non-auctioned spectrum.