# Opportunities and Challenges for Error Correction Scheme for Wireless Body Area Network--A Survey
## 5 Review on ECS Methods on WBAN
### Modulation  
Researchers used the modulation technique of different orders as the error correction procedure. In this technique, the adaption of different order of modulation according to channel condition is used as an ECS. In [58; 59], the authors introduced the link adaption technique in WBAN while considering the IEEE 802.15.4 standard to reduce packet loss where CSMA/CA in MAC and different modulation schemes in physical layer are combined. The link adaptation technique does not use any ECC and the WBAN considered in these papers is one-hop star topology. The link adaptation technique requires channel estimation at each node in the WBAN. The channel estimation in terms of SNR is performed while using received beacon power and signal to interference ratio (SIR) is evaluated while using failure probability during packet transmission. The link adaptation i.e., selection of modulation scheme (from node to coordinator) is performed using SNR only in [60] and using SNR and SIR both in [58]. The data rate adapted according to SNR only in [60] and SNR and SIR both in [58]. The important concern is the issue of channel estimation in terms of SNR and SIR in WBAN nodes. The papers discussed how to perform channel estimation at the node, but the cost that is associated with channel estimation at the computationally and energy-constrained node is not considered during the study.  
We present a summary of FECs that are based on modulation in Table 8. From the literature review, we found that modulation order update is happening according to link conditions. The estimation of link condition and SIR requires a good channel estimation technique that is an energetically and computationally complex process. However, there is a lack of research on how much cost is associated with estimation and how it affects the overall cost.  
We observed from the literature review that the researchers utilize standard techniques of error corrections to enhance reliability without considering the constraints that are faced in WBAN. Some researchers used ECS with complex decoder instead of ECS with a simple decoder. However, the decoding cost that is introduced by the complex decoder is not taken into consideration during the result. Another case to consider is that the researcher uses lower rate ECC, Which enhanced the reliability when compared with higher rate ECC, but it does not consider the code rate during the result and discussion.  
In WBAN, the communications scenarios are different significantly from other communications systems in many factors. Firstly, there are different types of nodes (implant node, body surface node, and external node) and computational and energy constraints that are faced by these nodes are different, but those constraints are not exploited on the proposed ECS in the literature. In addition, there are a variety of channels types and scenarios (refer to Table 3) that exist in WBAN. In the following section, we discuss the research challenges and opportunities on ECS design for WBAN. The ECS for  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Ref. (Yr)** & **Proposed Technique** & **WBAN/Standard/Layer/Data/Channel** & **Results** \\ \hline \multirow{3}{*}{[58] (010)} & Modulation order & One hop star network (considering SNR & \\  & (O-QPSK, 2,4,8-DPSK) & and SIR)/IEEE 802.15.4/PHY/no & PER \\  & according to link & discussion/AWGN & \\ \hline \multirow{3}{*}{[60] (012)} & Modulation order & One hop star network (considering SNR)/IEEE 802.15.4/PHY/no & PER \\  & according to link & discussion/AWGN & \\ \hline \hline \end{tabular}
\end{table}
Table 8: A review of modulation based ECS.  
WBAN should consider computational complexity and energy constraints of nodes, different types of possible channels of WBAN, and different types of QoS requirements.