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1.10 Bluetooth in Context

Bluetooth does not exist in a vacuum. This section summarises some of the issues that affect Bluetooth devices which are not covered by the Bluetooth specification itself: how to implement Bluetooth, related technologies, the market for Bluetooth, health concerns, and the future of the specification.

1.10.1 Implementing the Technology

The key issue faced by implementers is that of partitioning. The hardware/software partition inside the Bluetooth subsystem trades off performance, cost, and power consumption against risk and time to market. The partition between the host system and the Bluetooth subsystem is where (usually in software) the stack is partitioned. This will either add loading to the host's processing resources or require more performance and resources in the highly cost sensitive Bluetooth subsystem. Ultimately, the demand for a full implementation as a self contained, embedded Bluetooth solution will require very careful design and optimisation to avoid creating an uncommercial product.

The quality of the "user experience" is very important for any Bluetooth product and will also require careful design and a good understanding and specification of the target application. Bluetooth is going to be a very high volume system and demand very low cost with high levels of optimisation being crucial.

1.10.2 Related Technologies and Standards

Bluetooth, like most innovations throughout history, does not have the field to itself. There are many other initiatives and standards for wired and wireless data communications, either already deployed or under development. They vary between overlapping with Bluetooth's sphere of operation, while exhibiting clear differentiators, to potential head-on competitors of Bluetooth. The two most active areas of work at the current time are the distribution of data and voice in a personal sphere of influence, the so called Personal Area Network (PAN), which appears to be Bluetooth's home ground, and the emerging demand for high speed wireless multimedia data distribution.

1.10.3 The Bluetooth Market

Most commentators agree that the Bluetooth market is going to be huge, with forecasts putting the installed base at half a billion devices by 2004, with a total market for Bluetooth components worth $2 billion in the same year. It seems that, for once, the technology push provided by Bluetooth is a good match for the market pull in terms of consumer needs and wants at this time.

There are a great many opportunities for Bluetooth-enabled products which exploit the various features of the technology to add value. However, there are many issues which are yet to be resolved. Potentially competing technologies could cause consumer confusion and at worst push Bluetooth into a niche corner. For manufacturers, the cost of the technology is paramount, and for Bluetooth to become ubiquitous, it must be built into all products, not just the high-end models.

For consumers, poor interoperability and/or poor user experience would be a major problem for Bluetooth and cause it to falter. The well-discussed "Out of Box Experience" has to be seamless and simple. The hope is that the strength of the Bluetooth brand will promote the notion of reliability and ease of use.

1.10.4 Health

Bluetooth uses frequency spectrum in the range of 2400 MHz to 2483.5 MHz. This range encompasses the natural frequency of H2O molecular oscillation at 2450 MHz, which is also used by microwave ovens specifically to excite water molecules inside food in order to cook it.

Sharing the same frequency range as microwave ovens has led to some concerns that Bluetooth devices might cook their users. Some microwave radiation will be absorbed in flesh. It will be absorbed by field-induced rotation of polarized water molecules, which is converted to heat through molecular friction. Basically, the microwaves shake the water in flesh, and it heats up as it shakes. But, as the radiated output power of Bluetooth devices is incredibly low and spread in spectrum in time, experts concur that Bluetooth radiation does not pose a risk to health.

A 1 mW Bluetooth radio emits 1/1,000,000 the amount of power in a 1 KW microwave oven. Also, in a microwave oven, all the power is directed inward at the food, whereas in a Bluetooth device, the power is radiated outward, so the user only ever intercepts the smallest fraction of the radio waves which are heading in their direction.

It is interesting to compare Bluetooth devices with other popular communications devices. Bluetooth operates at 2.4 GHz and uses 1 mW (0 dBm) for most applications, with a maximum of 100 mW (20 dBm) for extended range. This means that Bluetooth signals have a penetration depth of only 1.5 cm into flesh. In comparison, cellular handsets have a power of 10 mW to 2 W peak, using 450 MHz to 2200 MHz, and exhibit a penetration depth of 2.5 cm in the middle of their range at 900 MHz. So, mobile cellular handsets give rise to a measurable heating effect of 0.1ºC, compared with no measurable increase for Bluetooth devices. Although studies have shown this small heating effect, it is too low to be noticed by the user. Most of the temperature increases that mobile phone users feel when holding a handset next to their ears is caused by an insulating effect. Since the head radiates a lot of heat, if a handset blocks that radiation, then the head heats up. Getting a hot ear from a mobile phone is not necessarily a sign that you are absorbing radiation!

There has already been some controversy regarding cellular handsets and whether they have a negative impact on health. Although scientific opinion is pretty conclusive that there are no risks, to be safe, various organisations have undertaken studies and research and have laid down guidelines for exposure to radio frequencies.

The WHO, ICNIRP, and IEEE have developed Radio Frequency (RF) exposure recommendations and these guidelines have been adopted by many national authorities. In the usual way of health and safety guidelines, they incorporate large safety margins. The guidelines specify near-field1 restrictions (referred to as SAR) between 10 MHz to 10 GHz, which devices with an output power of less than 1.6 mW are incapable of exceeding. So, all low power Bluetooth devices will fall within these restrictions. Higher power Bluetooth devices may need to be tested for SAR limits, and this will be done as part of radio regulatory testing.

The guidelines also specify a standard for total RF exposure. This is given as a power density of 10 W/m2. This level of spectral density would require an unrealistic number of Bluetooth devices to operate continuously in a very small space, which would actually not be possible due to the limited spectrum in the ISM band.

Several expert panels formed from organisations such as WHO, ICNIRP, EC, and the Royal Society of Canada have debated the topic of health in the context of existing higher power cellular technology in recent years. They have all concluded that there is no credible or convincing evidence that RF exposure from wireless devices operating within accepted exposure limits causes adverse human health effects. They did, however, recommend additional research to clarify some areas and fill gaps in existing knowledge.

In conclusion, experts agree that Bluetooth devices are too low in power to have any negative health consequences. Even the higher power devices are an order of magnitude lower in power than existing cellular devices, which, based on existing research and official guidelines, have already been proven to be safe.

1.10.5 The Future

The Bluetooth SIG has a series of working groups continuing the development of the Bluetooth specification in three key areas: correction and clarification of the version 1.1 specification, development of further profiles, and evolution of the core specification for enhanced performance. The core specification will evolve from version 1.1 to include various improvements affecting different parts of the system; Radio, Baseband, and Protocol software.

The mechanism for adopter companies to propose more profiles will facilitate optimised Bluetooth implementations for specific applications. Future versions of the specification are expected to provide higher data rates for Bluetooth (between 2 and 10 Mb/s) and to provide the multimedia distribution facilities which are becoming a key requirement for the future of information technology. Other work is underway to improve on the overall feature set of the 1.1 specification in areas such as quality of service and link handover between devices in a way that is similar to that which occurs in mobile cellular phone networks.

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