# Towards Efficient Wireless Body Area Network Using Two-Way Relay Cooperation
## 1 Introduction
Furthermore, equations are derived for incremental three-stage relay scenario [18] and the simulation results [19] showed an improved PER at the cost of EE. The energy consumption based on various modulation schemes is discussed in [20] for simple and coded WBAN links. Network coding is being used in non-invasive WBANs for improving the reliability of transmission in healthcare units [21]. The paper discusses the signal strength versus bit error rate (BER), but the effect of distance and in-body transmissions is neglected. WBAN is a ubiquitous technology that is evolving at a swift pace. The novel advances and rapid growth in WBAN come with the challenges of robustness, reliability, and efficiency, which needs to be addressed. The aim of this paper is to analyze various WBAN links for direct and cooperative communication in order to achieve an efficient system. The WBAN systems are not as dense as the conventional wireless sensor networks; therefore, single relay cooperation scenarios are considered. The two-way relay cooperation scenario is introduced, which provides improved results compared to both a direct link and a one-way relay link. The one-way relay scenario is used to provide a diversity path in the case of heavy shadowing or deep fades. The two-way relay scenario is useful when two different parameters are needed for decision-making in a single situation. For example, the cardiological issues are closely related to blood pressure and, in the case of monitoring both electrocardiogram (ECG) and blood pressure, the values are measured by two sensors and coordinated using two-way relay cooperation. A similar case is the coordination between glucometer and insulin pump. Specifically, in this paper, the following contributions are made:  
1. The analytical expressions of PER and EE are derived for a two-way relay cooperation scenario. Using realistic transceiver specifications, the optimal packet sizes that provide maximum EE are investigated. Based on this investigation, a hybrid scheme is proposed that allows switching between the three communication modes, namely, direct link, one-way relay cooperation and two-way relay cooperation in terms of EE and optimal packet size. The performance in the case of a quasi-static channel resulting from body posture changes is also shown over the hybrid scheme. 2. A joint network-channel (JNC) coding scheme is applied for various WBAN transmission scenarios using convolutional and BCH codes. The hop length extensions in terms of EE for each of the three communication modes are studied while considering packet overhead. The existing literature spans EE calculations over direct link [22], incremental relaying with single and two-stage relays [17], and a similar incremental relaying scenario extended to three-stage relay [18; 19]. In our work, a two-way relaying scenario is presented particularly for WBAN to reduce the number of transmissions and the number of sensor nodes, which provide better results compared to previously used techniques. A hybrid system, based on these observations, is introduced, which allows switching between the proposed two-way relay and previously defined multi-stage one-way relay and direct link to maximize EE, and also demonstrated over quasi-static channel. To the best of our knowledge, a hybrid scheme and JNC coding have not been proposed before in prior WBAN literature. The rest of the paper is arranged in the following manner. The system model and channel specifications are described in Section 2. The analysis of system spanning PER and EE expressions is presented in Section 3. The simulation results for PER and EE are shown in Section 4. It also covers the performance of asymmetrical links and optimal packet size for given communication links over specified hop-length. The proposed system that includes all three transmission schemes and can adapt to enhance the energy efficiency of overall system is depicted in Section 5 along with quasi-static channel behavior. Hop-length extension and diversity are achieved by JNC coding in Section 6.