Bluetooth and Zigbee: Two New Low Power Radio Standards. Technology and Adaptability.

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.

 

Continua Health Alliance PAN and LAN interfaces.

The Bluetooth wireless technology was chosen after analyzing other outstanding wireless technologies in a process that took almost 10 months of review. According to a recent market study developed by In-Stat during 2013 circa 2 billion of Bluetooth devices will be shipped worldwide , and considering also that today there are more than 40 million Bluetooth enabled healthcare devices, Bluetooth technology has to be considered for half of the ICs delivered worldwide for health devices by 2015; thus, it is not premature to assume that Bluetooth technology is already the de facto wireless standard for health devices. In the updated Version 1.5 Design Guidelines, Continua selected for the Personal Area Network (PAN) interface the Bluetooth Low Energy (BLE) standard and its health device profiles. Considering that the benefits of a healthy lifestyle and the independent monitoring of chronic diseases will increase the market for wireless health devices, the selection of the Bluetooth technology hasn’t come as a random solution, but was decided after thoroughly understanding the benefits of this technology. There are a variety of key factors that lead to the selection of Bluetooth Low Energy: between these factors, indeed the fact that Continua has always supported the selection of Bluetooth Low Energy in health care applications has been a predominant element. So why did Continua selected exactly the Bluetooth technology for wireless connectivity of personal health care devices? After months of research and analysis of a variety of low power technologies such as Sensium, ANT+, BodyLAN and Z-Wave, in late 2009 Continua announces the selection of two new low power radio standards: Bluetooth Low Energy wireless technology for low power mobile devices for monitoring a user’s health or fitness level, and ZigBee was instead selected for low power sensors in a variety of settings to promote independent living.
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.

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.

References:
[1] http://ebinder.blogger.idv.tw/archives/633
[2] http://electronicdesign.com/article/communications/bluetooth-low-energy-set-to-storm-the-wireless-market
[3] http://webpages.uncc.edu/~jmconrad/ECGR6185-2007-01/notes/IEEE_ZigBee.pdf

Guidelines Evolution and Reference Architecture.

By exploiting existing industry standards to have interoperable building blocks, Continua is providing guidelines and certifications that will allow multiple vendors to reduce differentiation and cut market costs. The publication of the Continua Health Alliance Version 1.0 Design Guidelines was announced in 2007, and was modeled primarily on connectivity standards. After the announcement, it took almost two years and the collaboration of more than 175 member companies to release the official Version 1 Design Guidelines in February 2009. The First Version Guideline was a major milestone since it was based on the specifications and standards that Continua selected following on their interoperability vision. In order to achieve the required interoperability, also further requirements and constraints were specified in this version, making possible the reduction of the available choices in the underlying standard: this was done by adding some specifications not mentioned previously. The function of these guidelines is primarily to give a design specification tool for companies than intend to certify their devices with the Continua logo. The Version 1.0 Design Guidelines deals with the interfaces necessary for realizing the entire eHealth process, starting from collecting health data to the accumulation of information on the databases of healthcare structures. Since Continua only focuses on interoperability and does not suggest any specification, the interest for Continua’s guidelines is based on the definition of the interfaces essential for connecting between different components of a personal eHealth system, thus, LAN, PAN, WAN, and the electronic or personal health record network xHRN.
These Interfaces are the principal elements to be considered for interoperability goals, and form the basis of Continua Certification process.
The interfaces considered for the Version 1.0 were the PAN Interface (Personal Area Network) between PAN devices and AHD (Application Hosting Devices), and the xHRN Interface (Health Record Network) between WAN (Wide Area Network) devices and health record devices to export medical personal data. The Continua Reference Architecture including the connections and interfaces to be tested in Version 1.0 are shown in the following figure:

Continua Reference Architecture and V1 interfaces to be tested

The Continua End-to-End (E2E) Architecture gives a clear overview of the general distributed-systems structure, highlighting possible topology constraints. The structure is based on five device classes and four network interfaces that are the the principal elements to investigate for interoperability. The network interfaces are subject of certification and testing processes and are responsible of connecting the devices to a reference topology. In order to have a better understanding of  the possible selected standards and interfaces, it is necessary to analyze first the Continua Reference Architecture.
The Peripheral Area Network Interface (PAN) describes the connection between PAN devices such as sensors (for example a heart-rate monitor) or actuators( for example an output text) and an application hosting device (AHD) , such as a mobile phones, tablets , PC. Continua has developed standards for the two layers of the PAN interface; for the lower layers or transport level component comprising the open-systems interconnection layers 1-4, Continua has selected the Bluetooth Health Device Profile for a Wireless communication and USB for wired communications. In the above level is the data level or upper-layer component comprising the classic OSI layers 5-7, for which Continua has selected to use the ISO/IEEE 11073-20601 Optimized Exchange Protocol to enable data exchange and interoperability.
The Local Area Network (LAN) is the Interface between a LAN device and an application hosting device. This device has a proxy function, thus collects and shares the PAN devices information. If we consider a Lan device it is important to underline that it can be seen both as a sensor or as and actuator; this has the direct consequence that the LAN interface upper layers and the PAN interface upper layers can maintain the same data model, the ISO/IEEE 11073-20601 model. The fact to have the same data model in the upper layers of the both PAN and Lan Interfaces is very important for assuring the required interoperability feature.
The Wide Area Networ (WAN) is the Interface between a variety of WAN devices and an application-hosting device. The function of a WAN device is to collect the information, thus acting as a managed-network-based service. The upper layers have a device data model compatible with the LAN Interface data model, thus to make sure an interoperable and exchangeable data model.
Untill this point we have analyzed Interfaces where the data exchange is made possible between an application hosting device and a Continua’s device. The Electronic and Personal Health Records Network (xHRN) is the connection between WAN devices and electronic or personal health records. Typically a xHRN interface is necessary for creating the connection between different companies offering a sevice such as weight loss or chronic disease management for example, and the electronic health records which traditionally come from the healthcare provider domain, such as a hospital where the doctor has all the available electronic data for keeping track of their patients. The Personal Health Records platforms (PHR) such as Google Health and Microsoft HealthValut, allow a patient to access and store their own health data and have control of their data. The merit of the xHRN Interface is to allow data exchange between electronic health records and personal health records promoting in this way data sharing between different parts of the process. For making possible a communication between WAN devices and xHR systems Continua selected the Integrating the Healthcare (IHE) and Cross-Enterprise Document Reliable Interchange (XDR) profile. For having a reliable data encoding the Health Level 7 (HL7) and the Personal Monitoring (PHM) document formats were adopted.

In its Version1.0 Guidelines, Continua selected to focus in two specific interfaces, namely the Personal Area Network (PAN) interface and Electronic or Personal Health Record Network (xHRN) interface. The decision to focus on the PAN and xHRN interfaces was taken by Continua, considering which were the highest priority interfaces to work on, and also considering the necessity to show visible results in a limited amount of time. Based on the interoperability goal, for its Version 1.0 several standards in the PAN interface have been selected and then constrained to meet Continua Guidelines for certification. In addition, the PAN interface for devices was focused on wireless protocols that need to be energy or battery efficient. In the seek of interoperability in the Version 1.0 several standards in the PAN and device data exchange have been developed. In this version of particular note is the expansion of IEEE 11073 which is supposed to have a prescriptive approach which ensures that devices from different manufacturers can be used by the same application. Precisely Continua prescribes in the Version1 eight PAN devices  as it is shown in the following figure:

Overview of Continua Interface Standards
Source: Continua Health Alliance

In addition to the currently released Design Guidelines are even more oriented towards interoperability and data sharing since they also incorporate Wide Area Network (WAN) interface to link a hub device or health appliance with servers. Continua selected ZigBee and Bluetooth Low Energy (BLE) for the updated Design Guidelines. The choice to select ZigBee wireless technology as a Continua’s low power local area network (LAN) standard was due to the fact that this wireless protocol works efficiently for multiple sensing and controlling in a variety of settings both professional and familiar offering secure wireless connectivity and it coexists with other wireless technologies.
The recent Version 2011 of Design Guidelines “Adrenaline” were made freely available to the public just recently during April 2012, in order to promote creativity and integration among systems developers. In the 2010 and 2011 Design Guidelines, the standards used for transporting data were Zigbee, Bluetooth, Bluetooth Low Energy and USB : let’s see now the reasons that led to the selection of some standards and if in the newest Version the standardization process has evolved by selecting new technology.