# A Survey on Wireless Body Area Networks for eHealthcare Systems in Residential Environments
## 2 Candidate Wireless Technologies
### Alternative Low-Power Wireless Technologies
#### 2.2.13 Emerging Intra-Body Communication Technologies  
Intra-Body Communication (IBC) technology is one of the emerging possible solutions for providing an ultra-low power communication over very short range links that specifically target WBAN applications. This technology is a non-RF wireless communication that utilizes human body as the medium for data transmission. IBC has recently been outlined in the newly ratified IEEE 802.15.6 standard and has shown to have advantages in terms of energy efficiency over many existing low-power RF protocols as it is able to transmit data with ultra-low transmission power below 1 mW [88; 89]. The IBC technology utilizes three main approaches to wirelessly interconnect in-body implanted devices: ultrasonic communication, capacitive coupling and galvanic coupling techniques. Ultrasonic communication has recently been proposed in [90] to address the limitations of RF propagation in the human body. In water-based environments such as the human body where 65 percent is composed of water, radio waves are not perfectly suited. This is mainly due to the fact that water typically absorbs some portion of the radio waves. Thus, more amount of energy is required to successfully transfer the RF signal in the human body. Hence, acoustic waves are considered one of the possible transmission technologies of choice for in-body communications as they are recognized to enhance the data throughput in media mostly composed of water comparing to RF signals [91]. Furthermore, Federal Communication Commission (FCC) regulations has limited the maximum allowable bandwidth that can be used for RF electromagnetic wave propagation available to Implanted Medical Devices (IMD) [91]. This therefore has greatly limited the data throughput of such devices [91]. As an example, for frequency range of 401-406 MHz, the maximum allowable bandwidth that can be used is around 300 kHz which greatly limits the communication rates of such devices to a maximum of 50 kb/s [91]. Alternatively, [PERSON] _et al._, showed in [92] that digital acoustic intra-body systems can provide up to 0.5-1.0 Mbit/s data rate at BER = 0.001 with real acoustic transducers in frequency range of about 1-2 MHz [92]. In the capacitive coupling technique, human body is capacitively coupled to the surrounding environment [88]. In this technique, a current loop through the external ground creates the signal between the body channel transceiver. Alternatively, galvanic coupling method is performed by coupling Alternating Current (AC) in to the human body. In this technique, AC current is flowed through the body and human body is considered as a waveguide [88; 89]. The energy efficiency advantage of these two coupling techniques over wireless protocols is mainly due to two reasons. One is due to the existence of lower path loss which does not include the otherwise detrimental effects of body shadowing in RF communications. The other reason is due to the utilization of wearable electrodes that are used as communication interface rather than low-impedance antennas. Moreover, in terms of security, IBC technology was shown itself to be more secure and less susceptible to interference compared to RF communication which makes it a possible low-power communication solution for Body Area Network (BAN) applications. Nevertheless, IBC technology cannot solely be used in BAN systems. The data gathered by IBC-based sensors are required to be transmitted to a base station for further processing. For this reason, IBC technology must be combined with one of the existing energy efficient communication protocols such as ZigBee or Bluetooth Low Energy (BLE) [93]. Figure 2 shows a typical architecture of a possible energy efficient BAN system. In this scenario, IBC technology is employed for intra-body communications. IBC based sensor devices transfer the health-relevant information through the body to a central node which acts as a coordinator. This central coordinator is in charge of establishing a communication link between on-body devices and a base station.