## 1 Introduction  
The health Internet of Things (IoT) is one of the most promising approaches in improving the quality of human life. This is through healthcare monitoring and remote telemedicine support systems, which are able to deliver real-time data collection, transmission and visualization via the Internet [1; 2]. In our previous work, we have presented a flexible quality of service (QoS) target-specific smart healthcare system [3]. This consisted of a smart gateway, a collection of sensor nodes and wireless communication links that can continuously acquire, process and transmit human vital signs to a remote medical server. Such a system makes remote patient health status monitoring by doctors and nurses a feasible proposition [1; 3]. Moreover, the large volume of data collected makes it possible for researchers to develop new healthcare products and provide effective health education to people via the internet [1; 4]. A wireless body area network (WBAN) is a networking technology that offers the prospect of the early detection of abnormal health conditions, real-time healthcare monitoring and remote telemedicine support systems. The Institute of Electrical and Electronic Engineers (IEEE) 802.15.6 Task Group has established the first international wireless communication standardisation of WBANs that optimises power consumption and provides safety guidance for medical and non-medical applications operating inside, on, or around the human body [4]. To date, the existing research work has mainly focused on on-body and off-body communication systems rather than in-body or I2O body communication systems [1; 4; 5]. We previously proposed a biological implant WBAN communication channel [5], where the communication link was specific for the human cephalic region and covered a limited communication range. Thus in this paper, the proposed I2O body WBAN systems enable transmission of real-time medical data from the in-body to the on-body area, which can enhance several practical health IoT scenarios [1; 4]. Figure 1 shows the system in total, with the focus of this paper being the I2O tranmission link shown on the frontal thorax of the human outline. WBANs differ from traditional wireless communication systems in terms of propagation medium, transmission power restrictions and human tissue/organ safety requirements [5]. Over 65% of the human intra-body region is composed of water. Moreover, organ-tissue communications and drug transportation is via the blood [6]. This makes radio frequency (RF) signals remarkably attenuated when transmitting data through tissues/organs, even at relatively low frequencies such as the medical implant communication service (MICS) 402-405 MHz band proposed by the IEEE [5]. The 2.45 GHz industrial, scientific and medical (ISM) radio band is investigated in this article, as this brings advantages for WBAN systems. These are primarily that: (a) various compact small-sized antennas are available for implantation; (b) satisfactory performance is obtained with low energy consumption; (c) there is significant bandwidth to support high data transmission rates [4]. Increasing transmission power is one option to account for the energy attenuation but may result in damage to human tissues or organs due to heat absorption [4; 7]. Thus, the transmission power must comply with the Federal Communications Commission (FCC) regulations and the specific absorption rate (SAR) must be lower than that laid down by IEEE and the International Commission on Non-Ionizing Radiation Protection (ICNIRP) [8; 9]. The concept of telemedicine has changed from'medicine practiced at a distance' to 'personalised ubiquitous healthcare on the move' under the health IoT [1]. Concerning hospital or home healthcare monitoring scenarios, wireless implanted healthcare monitoring devices would significantly improve the comfort and mobility for patients when compared with wired connected medical devices.