Chapter 1

Introduction to Body Area Communications

The ever-advancing miniaturization and low-power consumption of electronic devices, combined with recent developments in wireless communication, is leading to a rapidly increasing demand for wireless communications in the human body area. In a scenario of human body area communications, various communication devices may locate on, in or near the human body to form a wireless link or a small-scaled network to share data, reduce functional redundancies, and allow for new services. As an emerging communication technique, it is especially expected to be useful in medical, healthcare and consumer electronics applications. It may provide new possibilities in high-quality medical and healthcare services by linking various on/in-body vital sensors to establish a body area network (BAN) of personal health information. It may also allow high convenience and security in consumer electronics and user identification systems.

1.1 Definition

Body area communications is a short range wireless communication technique in the vicinity of, or inside, a human body. Differing from other short range communication systems such as Bluetooth and Zigbee, it focuses on communications just in the human body area, that is, the immediate environment around the human body which only includes the nearest objects that may be one part of the body.

As a most promising scenario for body area communications, BAN is attracting much attention especially for medical and healthcare applications. The concept of BAN was first proposed by Zimmermann (1996), and the definition of BAN is given by the IEEE 802.15.6 task group (IEEE802.15.TG6). BAN operates in the body area with radio frequencies to provide a wireless network of wearable and implanted sensors and/or devices in the human body. It can take a continuous measure and transmit a vital sign or body physiological data to facilitate remote monitoring for the purposes of healthcare services, assistance for people with disabilities, and entertainment or user identification. Since it operates on or in the human body and focuses on personal information, requirements such as support for the quality of service to keep a highly reliable communication link, extremely low consumption power for long term use, and high data rate for real time transmission, should be considered. Moreover, body area communications uses the human body as a transmission medium. The transmitter and receiver are also in close vicinity in the body area. This means human body effects on the transmitting and receiving antennas have to be considered. As a transmission medium, the human body not only creates a completely different channel characteristic but also introduces a safety issue. The safety of the human body in body area communications has a higher priority than for other wireless communications.

In addition, BAN can be divided into wearable BAN and implant BAN according to its location on or in the human body where it operates. Wearable BAN includes all of the communication devices worn on the body, while implant BAN has some in-body devices which communicate with on- or off-body devices. The different operating environments lead to some differences between a wearable BAN and an implant BAN or on- and in-body communications. First, on-body communication may mainly suffer from a shadowing due to the body shape and structure or a multipath fading due to the body movement, while in-body communication mainly undergoes severe signal decay during the transmission through the lossy human tissue (Hall and Hao, 2006). These result in different requirements for the operating frequency bands. Secondly, in-body communication devices are generally more power limited and sometimes require smaller or specific shape due to their locations inside the body. Thirdly, both need to consider the bio-electromagnetic compatibility issue or transmitting power restriction to ensure human safety.

1.2 Promising Applications

There are different categorizations for application and usage models of body area communications. Table 1.1 gives the categorization (Astrin, Li, and Kohno, 2009): (1) medical and healthcare applications; (2) assistance to people with disabilities; and (3) consumer electronics and user identification.

Table 1.1 Categorization of applications of body area communications.

Medical and healthcare applications	Assistance to people with disabilities	Consumer electronics and user identification
Medical check-up	Blind person	Wireless headphone
Medical diagnosis and treatment	Speech disability	Audio/video streaming share
Physical rehabilitation	Artificial hands and legs	User identification
Physiological monitoring	Accident prevention for elderly people	Automatic payment

1.2.1 Medical and Healthcare Applications

1.2.1.1 Healthcare Monitoring in Hospital and at Home

Today's aging population is leading to a wide-scale demand for more advanced and efficient medical and healthcare treatment using wireless communication techniques. For example, the demand for wireless health-state monitoring for both in-hospital and at-home patients is growing dramatically. This is because wireless patient monitoring can effectively reduce the inconvenience of wire links, and save time and resources when people are monitored remotely at home.

Body area communications provides a wide range of possibilities in supporting such medical and healthcare services (Li, Yazdandoost, and Zhen, 2010). It may cover three areas: medical check-up; physical rehabilitation; and physiological monitoring. As a typical usage model, the body area communication device is a transceiver together with a health information sensor or a set of health information sensors. For medical check-up, such devices can collect electroencephalogram (EEG) data for monitoring brain electrical activity, electrocardiogram (ECG) data for monitoring heart activity, breathing data for monitoring respiration, as well as blood pressure, heart rate and body temperature. For physical rehabilitation, tilt sensors for monitoring accidental falls, foot sensors for monitoring steps, movement sensors for monitoring activities, breathing sensors for monitoring respiration, as well as blood pressure sensors, heart rate sensors and body temperature sensors are all possible candidates. For physiological monitoring, acceleration sensors for monitoring instant behavior, foot sensors for monitoring steps, breathing sensors for monitoring respiration, as well as blood pressure sensors, heart rate sensors and body temperature sensors may be required.

A typical application of these sensor data is the real time monitoring of patient state in a hospital. Another typical application is the real time monitoring of the health state of elderly people at home. By attaching such devices to patients or elderly people, vital healthcare data are automatically collected, and then forwarded to medical staff in a hospital or medical center for medical and healthcare administration (Bonato, 2010). Figure 1.1 shows the concept of the two applications. The sensor data are collected at an on-body server as shown by the circle in the center of the body, and then sent to a hospital or medical center. The wireless link to the on-body server needs a body area communication technique, while the data transmission to a hospital or medical center can employ cellular systems or local area networks (LANs). This usage mode reduces the work load of the medical staff and results in increased efficiency of patient or at-home elderly people management. Moreover, as a simple extension, the patient monitoring system in a hospital can be also used in a sports center to monitor physiological information. The data from the physiological sensors are collected by using the on-body communication technique and are then sent to trainers for analysis and administration.

1.2.1.2 Healthcare Monitoring in a Car

The application of body area communications to healthcare monitoring has broad possibilities. A promising use is to monitor a driver's health as a means of in-car communication. In this scenario, as shown in Figure 1.2, some vital sensors are placed on the driver's body to collect healthcare data such as ECG, blood pressure and pulse rate. The vital sensors may be embedded in the driver's seat, seat belt, or the steering wheel so that the driver unconsciously wears the sensors. These parts of the car are chosen as they are always in contact with the driver's body when driving. Such a system makes it easy to collect the driver's healthcare data and send them to a control unit with the body area communication technique. The control unit can then analyze the driver's health and generate warning signs or take automatic control of the car, if necessary, for driving safety.

1.2.1.3 Medical Diagnoses and Treatment

Body area communications can also be used in medical diagnoses and treatment. In this scenario, an in-body device should consist of a sensor, a transceiver and an operation unit. The sensor data are sent to an on- or off-body control unit by the wireless transceiver. The control unit makes a medical measurement and sends the corresponding command for medical treatment to the operation unit. The operation unit then carries out medical treatment based on the received command. One example of this scenario is an automatically controlled cardiac pacemaker (Bradley, 2007). A cardiac pacemaker is an electronic device which helps people with irregular heart beat problems. As shown in Figure 1.3, first, the pacemaker collects sympathetic nerve signals using sensors and sends them to a control unit. Then, the control unit calculates the correct heart beat rate and instructs the pacemaker. Finally, the pacemaker helps to adjust the heart beat to the correct beating rhythm.

Another example of body area communications for medical diagnosis is the capsule endoscope. The ingestible capsule consists of a camera and a transceiver. It takes pictures during its course through the digestive tract after being swallowed, and transmits the pictures or video data in real time from the in-body transceiver to off-body medical instruments. Figure 1.4 shows the concept of this scenario, which can effectively promote the noninvasive diagnosis.

In addition, automatic insulin injection for diabetes patients is also a possible application of body area communications. Using the data from a glucose sensor under the skin, an injection control unit linked by the body area communication technique can decide the correct amount of insulin to be injected. Then, an insulin pump carries out the injection according to the instruction from the control unit.

The required data rate for various medical and healthcare data can be calculated with the number of used channels N_C, the sampling rate f_s and the number of quantization bits N_b by f_b = N_C f_s N_b. On-body sensor data are usually sampled with a sampling rate f_s between 0.2 and 256 Hz and quantized with a 12- or 16-bit analog to digital converter. On the other hand, the raw data for the capsule endoscope may need a data rate of 76 Mbps for real time transmission. Even if an image compression technique is employed, a data rate as high as 10 Mbps may be still necessary for a high-quality picture or video transmission. Table 1.2 summarizes some estimated data rates required for body area transmission of medical and healthcare information data (Misic and Misic, 2010). A data rate ranging from several bps to 10 Mbps should be supported by body area communications.

Table 1.2 Required data rates for medical and healthcare information.

Health information	Data rate
On-body
ECG	36 kbps
EEG	98 kbps
Pulse rate	2.4 kbps
Respiratory rate	1.0 kbps
Blood pressure	1.92 kbps
Heart rate	1.92 kbps
Body temperature	2.4 bps
In-body
Capsule endoscope	10 Mbps

1.2.2 Assistance to People with Disabilities

In the second category of applications, there are also plenty of possible scenarios (Li, Takizawa, and Kohno, 2008). One of the typical scenarios is the application for assisting people with visual disabilities. In this application, a wireless body area link is formed among the sensors attached to the belongings of a person and a transceiver worn by the person. A reasonable range between these sensors and the transceiver is set in advance. When the person forgets his or her belongings and leaves them over the pre-set range, a warning signal will be generated automatically from the transceiver. Moreover, in advanced applications, a camera with on-body communication function can be attached to a person with visual disability. Pictures taken by the camera are sent to an on-body control unit, where they are converted to audio signal to provide guidance to the person. A similar principle can also be used for assisting people with speech disability. Here, sensors to catch finger and hand movements are used, and the obtained information is converted into speech.

Accident prevention or rescue for elderly people is also a promising application of body area communications. For example, an elderly person can wear a foot sensor for monitoring steps and some tilt sensors for monitoring accidental falls. The sensor data are continuously sent to an on-body receiver by means of the body area communication technique. If these sensors detect anything unusual, the receiver can give a warning signal to the elderly person or emit a warning sound.

1.2.3 Consumer Electronics and User Identification

The third category of applications is for consumer electronic connectivity. A typical example is to connect a headphone to a music player without wires. By using body area communications, we can not only increase convenience by removing wires but also provide a method of source sharing in audio or video streaming. In these applications, for example, two or more people can share the same music player by using wireless headphones. People can also exchange their business card information by handshake.

On the other hand, body area communications also provides a paradigm shift toward intuitive applications on user identification and user–machine interface (Baldus et al., 2009). By wearing an on-body transceiver, we can communicate with a machine by touching it to establish a body area link. For example, we can embed a user identification function in the on-body transceiver and an entrance door. Then, when we touch the door knob, an on-body communication link is established and the door will be unlocked. A similar system is to embed the user identification function in the mouse of a personal computer. Instead of entering a password, we only need to touch the mouse and the user identification will be automatically made. In a more advanced application, we may embed an automatic payment function in the on-body transceiver. Such a system can be used for passing through an automatic ticket gate. As long as the person touches the ticket gate, the gate will open and a charge is paid.

1.3 Available Frequency Bands

Based on these promising application scenarios, it is found that body area communications may utilize a broad data rate range. Very low consumption power is also a remarkable feature. Figure 1.5 makes a comparison of the requirements between body area communications and other short range communications as well as wireless LANs. To meet such a broad range of data rates, different frequency bands may be required to best fit theses requirements.

1.3.1 UWB Band

The ultra wideband (UWB) technique generally employs very narrow or short duration pulses as modulation signal, which results in a very large frequency bandwidth coverage. The UWB signal is defined as the fractional bandwidth (FBW) being greater than 0.20–0.25 or the whole occupied bandwidth being greater than 500 MHz. Within the defined fractional bandwidth the UWB signal is restricted by the power spectrum density (PSD). The PSD is the ratio of the transmitting power P_T to the frequency bandwidth B, that is,

(1.1)

In 2002, the US Federal Communications Commission (FCC) approved the first rules regarding the UWB transmission system (FCC, 2002). The formula proposed for calculating the fractional bandwidth is

(1.2)

where f_H is the upper frequency of the −10 dB PSD point and f_L is the lower frequency of the −10 dB PSD point. The center frequency of the UWB transmission is defined as the average of the upper and lower −10 dB points, that is, (f_H + f_L)/2. Figure 1.6 shows the FCC-regulated PSD mask for UWB transmission. The equivalent isotropic radiated power (EIRP) of a UWB transmitter is required to meet this PSD mask. The EIRP is the amount of power that a theoretically isotropic antenna would emit to produce the peak power density observed in the direction of maximum antenna gain. With P_T as the transmitting power and G_T as the antenna gain, we have

(1.3)

From 3.1 to 10.6 GHz, the measured EIRP is not allowed to exceed −41.3 dBm/MHz or 74.13 nW/MHz. This yields an maximum allowable power of 0.556 mW in the full UWB band.

On the other hand, in Europe and East Asia, the UWB bands are further divided into low band and high band (EC, 2009). This is mainly for removing the 5 GHz band where wireless LANs are being used. The low band may range from 3.1 to 4.8 GHz, and the high band may range from 6.0 to 10.2 GHz, although there are some minor differences among regions and countries. Moreover, in the UWB low band, low duty cycle or detected-and-avoid (DAA) algorithm is used to avoid possible interference with other systems.

The UWB technique has shown an extensive potential for applications on either high data rates over short ranges or low data rates over largely attenuated channels. The extremely low PSD of the UWB signal can be thought to have less influence on medical equipment than other communication systems such as Bluetooth, wireless LAN and cellular phones. Its wideband nature also permits a fine time resolution which is particularly beneficial for health monitoring, human body probing and real time diagnosis (Staderini, 2002). In addition, the hardware miniaturization and low consumption power can be expected for UWB transceivers because of its simpler modulation and demodulation schemes. All of these features make UWB a promising candidate for wireless body area communications, especially for providing a high data rate.

1.3.2 MICS Band

The medical implant communication service (MICS) band is specified between 402 MHz and 405 MHz for communication with medical implants (ITU-R SA.1346, 1998). It allows bi-directional wireless communication with a pacemaker or other electronic implants. With a MICS band technique, one can establish a wireless link between an in-body medical device and on- or off-body monitoring and control equipment. In order to reduce the risk of interfering with other users of the same band, the permissible maximum transmitting power in the MICS band is very low, with an EIRP = 25 μW or −16 dBm. The maximum bandwidth is also limited to 300 kHz, thus a high data rate is difficult. The main advantage of the MICS band signal is its low attenuation compared with the UWB signal when the signal propagates through the human body. This feature makes it a promising choice, especially for in-body communications.

In Japan, MICS devices are classified as specific low power equipment permitted to have an emission up to 0.01 W. An adequate modification for the permissible maximum transmitting power may significantly increase the usefulness of this frequency band. In addition, the wireless medical telemetry system (WMTS) is assigned to 420–430 and 440–450 MHz. WMTS devices are also classified as specific low power equipment, which exhibit potential for use in body area communications.

1.3.3 ISM Band

The industrial, scientific and medical (ISM) bands are mainly for the use of radio frequency (RF) energy for industrial, scientific and medical purposes other than communications. The ISM band does not need end-user licenses up to 1 W, but may be subjected to authorization of local administrations. Despite the intent of the original allocations, in recent years many short range and low power communication systems have been used in these bands.

Suitable ISM bands for body area communications may include the 430 MHz band and the 2.4 GHz band. The former is currently available in Europe and the maximum effective radiated power may be up to 10 mW. The latter is supporting the fast growth in various short range communication services such as Bluetooth, Zigbee, and wireless LAN. A drawback of the 2.4 GHz band is the lack of any protection against interference from other communication services in the same band. The coexisting issue with current communication services also limits the introduction of body area communications.

1.3.4 HBC Band

Human body communication (HBC) uses the human body as a communication route to transmit data. It usually operates in the range of dozens of kHz to dozens of MHz, since at these frequencies the propagation loss along the human body is smaller than that through air. Based on the consideration in IEEE 802.15.6, we here refer to the frequency band from 10 to 50 MHz as the HBC band. HBC provides a new possibility for low data rate on-body communication. Its low propagation loss may yield superior communication performance compared with UWB and ISM bands, and the low radiation outward the human body also leads to high security.

There is not a common regulation in this frequency band, which actually covers several bands including wireless card and amateur radios. In Japan, a transceiver in this frequency band may be classified as extremely low power radio equipment in which the radiated electric field from the transceiver is asked to not exceed 500 μV/m at a distance of 3 m. When this requirement is met, no license is needed for the transceiver. In view of the low radiation feature of HBC, an HBC-based on-body communication link can be established under extremely low power radio regulation.

1.4 Standardization (IEEE Std 802.15.6-2012)

The IEEE 802 Standards Committee is an international organization which develops international standards on wireless communications. As one of the working groups under IEEE 802, IEEE 802.15 focuses on wireless personal area networks. A task group referred to as IEEE 802.15.6 was set up in December 2007 for defining new physical (PHY) and media access control (MAC) layers for wireless BANs. Its scope is to cover not only medical healthcare applications but also consumer electronics applications. The large scope of applications and wide range of technical requirements, however, mean the standard allows multiple PHY layers. In order to provide a common platform for the multiple PHY layers, a common MAC layer, both a beacon mode and a nonbeacon mode, is then defined. The typical number of devices is assumed to be 6 nodes but should be scalable up to 256 nodes.

The IEEE Standard for local and metropolitan area networks – Part 15.6: Wireless Body Area Networks (IEEE Std 802.15.6-2012) was approved in February 2012. In the introduction it is stated that:

IEEE Std 802.15.6-2012 is a standard for short-range, wireless communications in the vicinity of, or inside, a human body (but not limited to humans). It uses ISM and other bands as well as frequency bands in compliance with applicable medical and communication regulatory authorities. It allows devices to operate on very low transmit power for safety to minimize the specific absorption rate (SAR) into the body and increase the battery life. It supports quality of service (QoS), for example, to provide for emergency messaging. Since some communications can carry sensitive information, it also provides for strong security.

In IEEE Std 802.15.6-2012, the main PHY proposals include narrowband PHY in MICS band, WMTS band and ISM band, UWB PHY as well as HBC band PHY. First, the basic modulation schemes for narrowband PHY are π/2-shifted differential binary phase shift keying (DBPSK), π/4-shifted differential quadrature phase shift keying (DQPSK) and Gaussian minimum shift keying (GMSK) at a data rate of 50 kbps to 1 Mbps. The use of Bose–Chaudhuri–Hocquenghem (BCH) error correction code, which belongs to a class of cyclic codes with efficient multiple-error-correcting features, is further recommended to improve communication performance. Secondly, the basic modulation/demodulation schemes for UWB are impulse radio UWB (IR-UWB) and wideband frequency modulation UWB (FM-UWB) with noncoherent detection or differentially coherent detection at a data rate of 0.2–12 Mbps. An automatic repeat request (ARQ) algorithm is suggested for maintaining a high quality of service. Finally, the HBC band PHY employs 21 MHz to implement a baseband transmission of digital signals over the human body at a data rate of 164 kbps to 1.3 Mbps.

Since this book focuses on the PHY layer of body area communications, we here only summarize the basic PHY specifications in IEEE Std 802.15.6-2012.

1.4.1 Narrow Band PHY Specification

In order to transmit a PHY service data unit (PSDU), one first needs to transform it into a PHY protocol data unit (PPDU). As shown in Figure 1.7, the PPDU is composed of a PHY layer convergence protocol (PLCP) preamble, a PLCP header and a PSDU. The PLCP preamble is used to aid the receiver in packet detection, timing synchronization and carrier recovery, and the PLCP header is used to convey the necessary PHY parameter information to aid the decoding of the PSDU. The PLCP head also includes BCH parity bits for improving its robustness.

Based on this definition, a packet is transmitted in the order of the PLCP preamble, the PLCP header and the PSDU. The available operating frequency bands and modulation parameters are summarized in Table 1.3.

Table 1.3 Modulation parameters in narrow band PHY layer. Reproduced with permission from IEEE Std 802.15.6-2012 (2012): IEEE Standard for Local and metropolitan area networks – Part 15.6: Wireless Body Area Networks.

According to Table 1.3, the binary bit stream b(n) in the PPDU will be mapped onto either a rotated and differentially encoded constellation referred to as DPSK or a corresponding frequency deviation referred to as GMSK. In GMSK, the frequency deviation is equal to the product of the symbol rate and a modulation index of 0.5 divided by two. The Gaussian pulse shape is used to filter the symbol and shape the spectrum. In DPSK, the encoded information is carried in the phase transitions between symbols. Denoting the mapped sequence by a complex value expression

(1.4)

the phase change will be determined in terms of the bit stream b(n) as given in Table 1.4.

Table 1.4 Relationship between the bit stream and phase change.

1.4.2 UWB PHY Specification

The UWB PHY specification includes two types of techniques: one is IR-UWB and the other is FM-UWB.

A UWB PPDU is composed of a synchronization header (SHR), a PHY header (PHR) and a PSDU, as shown in Figure 1.8. The SHR is further divided into two parts. The first part is the preamble used for timing synchronization, packet detection and carrier recovery, and the second part is the start-of-frame delimiter for frame synchronization. The PHR contains information about the data rate, pulse shape, burst mode, and so on.

To transmit the bits of the PPDU as a RF signal, there are three possible modulation schemes: on-off keying (OOK), DBPSK/DQPSK or a combination of continuous-phase BFSK and wideband frequency modulation, FM-UWB. The operating frequency bands are listed in Table 1.5. A UWB device must operate in either channel 1 or channel 6. The other channels are optional.

Table 1.5 UWB operating frequency bands.

The shape of pulses to be transmitted is not mandatorily defined, but it must fulfill the transmit power spectral mask given as follows:

(1.5)

where T = 1/499.2 MHz.

The date rates depend on the PSDU symbol duration T_s and modulation schemes. For uncoded transmission, the data rates are 1/T_s for OOK and DBPSK, and 2/T_s for DQPSK, respectively. When the channel coding is made, a channel coding rate, defined as the number of information bits divided by the number of coded bits, will be introduced. Then the coded data rates are given by the channel coding rate/T_s for OOK and DBPSK, and twice the channel coding rate/T_s for DQPSK, respectively. Table 1.6 summarizes the data rates for IR-UWB with OOK and Table 1.7 summarizes that for IR-UWB with DPSK. R0, R1 and R2 are defined in the PHR frame for specifying a data rate.

Table 1.7 Data rates for IR-UWB with DPSK modulation. Reproduced with permission from IEEE Std 802.15.6-2012 (2012): IEEE Standard for Local and metropolitan area networks – Part 15.6: Wireless Body Area Networks.

Table 1.6 Data rates for IR-UWB with OOK modulation. Reproduced with permission from IEEE Std 802.15.6-2012 (2012): IEEE Standard for Local and metropolitan area networks – Part 15.6: Wireless Body Area Networks.

1.4.3 HBC PHY Specification

A HBC packet is composed of a PLCP preamble, a start frame delimiter (SFD), a PLCP header, and a PSDU, as shown in Figure 1.9. During packet reception, the receiver achieves the packet synchronization by detecting the PLCP preamble, and then finds the starting point of each frame by detecting the SFD. The PLCP header records the transmission parameters such as data rate, burst mode, PSDU length and so on. Such a packet is transmitted based on a frequency selective digital transmission scheme, in which the data are spread in the frequency domain using frequency selective spread codes.

Referring to Figure 1.10, the data to be transmitted are created by mapping 4 bits (a symbol) from serial-to-parallel converter to a 16-bit chip. The 16-bit chip is then spread by applying a frequency shift code. This modulation scheme is referred to as a frequency selective spreader. It is composed of orthogonal coding and frequency shift coding. The frequency shift code may be a repeated [0,1] code. The number of repeated times is defined as the spreading factor. For a spreading factor of 8, for example, the frequency shift code will be [0,1, 0, 1, 0, 1, 0, 1], that is, 8 bits. In Figure 1.10, the final chip rate at the output of the frequency selective spreader is thus the same regardless of the input data rate. Since the HBC frequency band is centered at 21 MHz, the operating clock frequency is fixed at 42 MHz. Table 1.8 shows the main modulation parameters at 21 MHz in the HBC PHY layer.

Table 1.8 Modulation parameters for the PLCP header and PSDU in the HBC PHY layer.

In addition, the transmit power spectrum is required to be under the mask in order to avoid possible interference with other bands, especially in the 400 MHz band. The transmit power spectral mask is defined in Figure 1.11 within the channel bandwidth of 5.25 MHz at the central frequency of 21 MHz. The vertical axis is the PSD (in units of dB) relative to the maximum spectral density of the signal. The maximum transmit power in a HBC transmitter is limited by local regulations which usually define a radiated electric field level at a specified distance from the transmitter in free space.

IEEE Std 802.15.6-2012 is a new international standard for body area communications, especially for wireless BANs. In this book, although we treat many parts of it, we will go beyond it using more fundamental and broader viewpoints of body area communications.

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