After the Version1.0 Design Guideline was published in early 2009, Continua simplified any possible decision by selecting for the transport level of the PAN Interface the Bluetooth Health Device Profile for wireless communications and USB Personal Healthcare Devices for wired communication while for enabling data format interoperability the ISO/IEEE 11073 Personal Health Device family of standards was selected. After the first Version of Guidelines other updated versions were published and Continua’s 2012 Design Guidelines is currently undergoing to Interoperability testing since it will be released publicly by the end of 2012. Before analyzing the latest solutions picked in the new version of the Guidelines, I will first try to define the reasons behind the selection of Bluetooth as a predominant technology for eHealth devices, considering the key factors in the decision process.
Bluetooth is the only wireless technology included in Continua’s design guidelines. With the cooperation of Continua Health Alliance and IEEE 11073 Personal Health Devices Group the Bluetooth SIG created the Health Device Profile.
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Continua
Health Alliance PAN and LAN interfaces.
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The differentiation between the selected technologies was made in terms ease of use between a list of devices that we have around us all day and we carry everywhere (PAN), such as a mobile phone or a tablet, and devices that are constrained to stay within a building, either a home or medical structure (LAN); Bluetooth Low Energy was selected for PAN (Personal Area Devices), while ZigBee was selected for LAN (Local Area Network).
The selected standards are relatively similar in terms complexity, but BLE have a longer battery life due to its faster data rate, the use of short packet overhead, excellent resistance to interference, reduced number of packet exchanges for a short connect time and power optimization, while Zigbee by using as a modulation scheme the Direct Sequence Spread Spectrum (DSSS) with orthogonal coding, has a better reliability and benefits from a longer range and a mesh like clustered star networking structure. While for most of the people outside the standardization groups this decision can look quite insignificant, it does have some relevant implications when considering that a medical device manufacturer cannot be able to decide which of these two wireless standards to choose. If we are developing a wireless connected healthcare system, it is important to not have confused manufacturers about which of two incompatible standards to use, because this can clearly lead to a delay in availability and implementation. The differentiation between PAN and WAN devices is going to disappear for consumer medical devices, since everything will be oriented towards mobile devices. For example, the implementation of smaller, mobile and personal medical devices is already happening in the sports and fitness devices sector. And that leads us to eliminate the distinction between PAN and WAN interfaces, because the medical devices simply become the things that we carry with us, without a reference of place or location. This simplification brings us to the dilemma of the device manufacturers that need to select one of the two technologies to go with.
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| Bluetooth Low Energy Devices |
Although both interfaces were selected in the Version 1.5 Design Guidelines, this dual interface vision is a possible barrier to the spread of a wide number of eHealth systems, since the lack of specifications in terms of interoperability can be a real problem for the possible user. In terms of costs, having both BLE and Zigbee on the same device [1] doesn’t mean that the costs will double since both the solutions have many similarities: specifically, BLE has a Gaussian Minimum Shift Keying (GMSK) [2] modulation scheme and Zigbee is based on Offset QPSK (O-QPSK) [3], and this makes possible to support both standards in a device simply using a reconfigurable transceiver with a digital IF sub-sampling architecture on the receiver side. Now, everyone knows that Bluetooth is in their mobile phones and over half of the world's population owns a mobile phone, so it is obvious I think, that the Bluetooth was the dominator in this dilemma. This is connected with technical reasons but mainly is related to an ease of use, because Bluetooth provides the "scale". Bluetooth oriented medical devices can easily be connected with smart phones, without additional device, while Zigbee oriented medical devices have the requirement of an additional adaptor that can plug into a tablet or phone. Bluetooth Low Energy is designed for light and peripheral data exchange and results to be different from the Bluetooth that is used in medical devices, since it has the added value of being able to talk to the next generation of smart phones. It is also true that wireless technologies has to be in a certain way, adapted to the application they are intended for, and the choice is not simply between Bluetooth and Zigbee but is between Bluetooth Low Energy standard and Zigbee, thus the ability that has BLE to be provided in mobile phones and even more to be provided in the new generation of smart phones is the key advantage. The problem of having two alternatives is that the medical device manufacturers have to make a decision of which to add to their products, considering that adding both the standards in not a possible solution since it would be too expensive as an option. Without a regulation, the market will decide what technology to adopt. The situation that Continua Alliance had to face while working on the Version 1.5 Design Guidelines was clearly to have two alternatives in the eHealth system; my idea is that adaptation is a very predominant factor in life and principally in technology and the ability to connect to a cellphone will be the dominant decision. If we consider the features of each of the proposed wireless technologies, it is clear that each standard has good features, mainly Bluetooth Low energy has the mobile phone connection, and Bluetooth has a higher bandwidth but it is difficult to understand what ZigBee really offers in the eHealth market since the prospect of connecting a device with a mobile phone is a powerful tool for health devices. Let’s see now if the progress has followed adaptation.
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