Body Area Networks
A Body Area Network (BAN) is a short-range wireless network comprised of devices positioned in, on, and around the body. It provides data communication over short distances, limited to ranges of just a few meters. Figure 1 below illustrates the basic concept.
This new, inherently personal type of network uses wearable and implanted electronic circuits. It implements highly useful functions and capabilities in convenient, unobtrusive configurations that operate at very low power and deliver superlative security.
Relatively few products and applications based on BAN technology exist today. However, that situation isn't likely to last for long. Renesas anticipates enormous growth from innovative implementations and refinements. It is expected that BAN products will rapidly become popular and sales will skyrocket, just as has been the case for many types of personal electronic devices.
Our corporate optimism with regard to Body Area Networks is based on important advantages inherent in BAN technology. Transmission distances are short, so these networks operate at very low power. This, in turn, makes the systems very secure, because their weak signals are undetectable at significant distances. Eavesdropping isn't possible beyond the immediate proximity of the BAN user. And importantly, since the operation of these networks is automated and transparent to users, BAN-based systems are attractive and convenient solutions for many different functions that have digital data gathering and sharing requirements.
Choosing a communication technique
Three different types of data transmission techniques can be used in BAN implementations: electric-field communication, electric-current communication, and electromagnetic (radio-wave) communication. These methods are described below and illustrated in Figure 2.
- Electric-field communication is driven by electric induction. This non-contact approach relies on changes in electric charge on the body's surface.
- Electric-current communication makes use of trace currents that pass through the BAN wearer's body. This method requires the person to make contact with electrodes on external electronics equipment to send or receive data.
- Low-power radio communication is the familiar ubiquitous wireless technology. Data transmissions are generally carried out at high frequencies—either in the UHF band (from 300MHz to 3GHz) or in the ultra-wide band (3.1GHz to 10.6GHz).
Focusing on electric-field communication for BAN applications
Engineers in Renesas' R& D laboratories have carefully studied the design challenges, benefits and limitations of these three network communication methods. Based on their findings, our management has decided to concentrate our R& D efforts on developing new semiconductor solutions for BANs that utilize electric-field communication.
Our experts rejected the use of radio-wave communication for Body Area Networks due to potential signal interference from the growing variety and numbers of other short-range wireless transmissions. Moreover, they decided against pursuing the electric-current approach because requiring BAN wearers to touch an external pad unacceptably compromises their freedom of action.
Electric-field communication avoids these issues, of course. Our researchers believe that it is the best way to handle a vast span of potential Body Area Network applications.
Propagating digital signals between sites on the skin
Many people are at least somewhat familiar with wireless transmissions and electric-current transmissions. Yet that probably isn't the case for electric-field communication. Few applications have used it in the past for various reasons, including the limitations of previous IC technology.
Basically, in an electric-field based BAN the transmitter of a sensing device is positioned in an electronics module close to the skin. It sends sensor data by generating an alternating electric field. Because the human body is approximately two-thirds water, that electric field induces corresponding field changes on the skin surface, thereby propagating the signal, moving it along the body's limbs and trunk. A detector in an electronics module located in another area near the skin, acts as the receiver. Thus, the signal containing sensor data moves from the transmitter to the skin, and then along the skin to the receiver.
Figure 3 illustrates the physics of this communication process sequence in more detail. In Step 1, electronic circuits apply a positive charge to the transmitter electrode. Step 2 shows that electrostatic induction causes a negative charge to collect on the user's body near the area of the transmitter electrode. Step 3 shows that the movement of negative charge toward the area of the body near the transmitter electrode leaves positive charge in other areas of the body. Finally, Step 4 illustrates that the positive charge on that area of the body induces via electrostatic induction a negative charge in the electrode of the receiver, completing the data transmission process.
- A positive charge on the transmitter electrode induces a negative charge on the user's skin near that electrode.
- As a negative charge on the skin collects near the location of the transmitter electrode, it leaves a positive charge in other areas of the body
- At the receiver, that positive charge on the body induces a negative charge in the receive electrode
- This process serially transmits one bit of data in the BAN.
There is an important point to understand here. Although a BAN can use implanted electronics for its data nodes, it is not necessary for a sensor module or receiver to make direct contact with the skin. As Figure 3 shows, the transmitter can be placed in a pocket, for example. In such a case, reception can be achieved simply by bringing one's hand close to the receiving device.
Applying IEEE standards that have already been approved
The '802' series of standards from the IEEE (Institute of Electrical and Electronics Engineers) covers local and metropolitan area networks (LANs and MANs). These widely accepted standards enable interoperability among all kinds of networks used around the globe.
Engineers developing BAN products and systems can maximize the flexibility and applicability of their designs by ensuring that they conform to the specifications of Section 802.15.6, which is highlighted in Figure 4. This section establishes specifications for the physical (PHY) and media access control (MAC) layers of Body Area Networks. The fact that these standards have already been developed and approved is a big plus for the growth of BAN markets.
As Figure 4 shows, three types of PHY layer designs are recognized in that standards section: UWB (ultra-wideband), NB (narrow-band), and HBC (human-body communication, an electric-field mode). Section 802.15.6 also recognizes two MAC modes: secure (for applications where security is an issue) and non-secure. Interestingly, the IEEE standards do not cover electric-current communication techniques.
Exploring some of the many possible BAN applications
Because approved BAN standards are available now and since other standardization efforts are ongoing and making progress, Renesas expects personalized, user-centric networks to become core components of the expanding smart-society infrastructure in countries around the world. Support seems poised to grow with surprising rapidity for a proliferating range of applications.
Some of the most promising uses BANs are highlighted in Figure 5, and specific examples are described in the following paragraphs.
Typical Application #1:
User authentication for notebook computers—To protect property and privacy, a BAN can be used to authenticate the user of a notebook computer. The operator wears a " smart watch" , a small device with a built-in BAN function. When the user touches the computer's touchpad, a controller embedded in the touchpad picks up the ID data and verifies the requisite access-control information, enabling login.
Typical Application #2:
Room entry control—No key or pass code is needed to enter a controlled access area if the person is wearing a BAN communication device. When their hand is placed near the doorknob or touches it, the BAN transmits the individual's ID information to a network bridge connected to the knob. From there that data goes to the access controller and authentication server, where authentication is completed. The system then releases the door lock, allowing the properly authorized individual to enter the room.
Typical Application #3:
Fitness monitoring—Health and safety are increased when a Body Area Network serves as a pulse monitor during exercise workouts. A sensor near the skin tracks the person's pulse and transmits the data to the smart watch worn on a wrist. The user can check the pulse rate in real time by viewing the watch display.
Overcoming signal-weakness and noise-interference issues
System engineers on R& D projects aimed at developing BANs and wireless sensor networks typically face design challenges in two areas that impact the reliability of the network communication: signal weakness and noise interference. Successful design approaches must use semiconductor devices that ensure stable communication. Intermittent connectivity can't be allowed; the data flow should be continuous.
One system-design problem in this regard is that the signal at the receiver in a BAN that applies electric-field communication is particularly weak, because much of the induced charge leaks out through the transmitter and ground. Accordingly, there is a need to develop stronger receiving technology; i.e., chips that can reliably detect very-low-level signals. Our semiconductor engineers are finding innovative ways to minimize signal loss and maximize receiver sensitivity and selectivity, to maximize data-transfer reliability.
Another system-design problem is that the electric field used in a BAN is highly susceptible to interference from external electromagnetic noise. To address this issue, Renesas IC designers are working on ways to improve the network's ability to withstand such noise. One approach they are pursuing is to tune into the signal frequency band with greater precision. Selective filtering can boost the signal-to-noise (S/N) ratio by excluding noise that is outside the band being used for data transmission.
More specifically, Renesas researchers have independently investigated S/N ratios, gain characteristics, scattering parameters (S-parameters), and other characteristics related to signal reliability issues. They have gathered test data using a " phantom" subject, an artificial torso that exhibits electrical characteristics like those of the human body.
Driving our capabilities to higher levels
Going forward, the Renesas technologists working on wireless sensor networks are continually enhancing our semiconductor manufacturing processes and chip designs to improve performance and create new capabilities. They are also striving to better understand market needs so we can facilitate the design and success of new applications for Body Area Networks.
Be sure to watch for announcements of future chips that will enable BANs to implement exciting products that create end-user enthusiasm and confidence. Further, we welcome your comments and questions on our R&D activities and IC breakthroughs. Please feel free to contact us using the Contact control on our website.