# Opportunities and Challenges for Error Correction Scheme for Wireless Body Area Network--A Survey
## 5 Review on ECS Methods on WBAN
### Forward Error Correction (FEC)  
As per the WBAN standard, error correction on WBAN communication is performed at bottom two layers of OSI. From the literature review, we also observed that FEC could be applied to the bottom \begin{table}
\begin{tabular}{c c c} \hline \hline
**OSI Layer** & **ECS Methods** \\ \hline PHY & FEC and modulation & Cross layer: ARQ, HARQ, FEC/ARQ/HARQ \\ \hline MAC & FEC applied to MAC & combined with access control mechanism \\ \hline \hline \end{tabular}
\end{table} 
Table 4: ECS classification based on Open Systems Interconnection (OSI) layers. Figure 5: One hop star WBAN topology. Figure 6: Two-hop extended star network WBAN topology. two layers: PHY or MAC. In [33; 34; 35; 36], FEC is applied on PHY layer only, whereas in [37] the same is applied at the MAC layer only. In [38], the authors presented the experimental result of measured RSS around a human body, keeping two antennas attached to the body at 444.5 MHz and 2.45 GHz in an anechoic chamber i.e., with very limited interference. Subsequently, the measured RSS value is used to calculate BER and PER using Agilent' Advanced Design System (ADS) Ptolemy solution. In [33; 34], the authors extended their work of [38] and presented the measured RSS result around a human body keeping two antennas attached to the body at 444.5 MHz [33] and 2.45 GHz [33; 34]. Next, the measured RSS value in the office room used for fading duration, and consequently the packer erasure ratio corresponding to various data rate for both frequency bands when considering various receiver's sensitivity threshold values [33]. Following, the paper introduced the Luby Transform (LT) code as rateless code as an erasure correction code and presented a theoretical analysis of retransmission probability for various data rates and packet sizes under an erasure channel. The packer erasure ration that was calculated from the measured RSS measurement value around human body and the design criteria that were developed for the rateless code are isolated work. The result presented is a standalone performance of the rateless code without considering real WBAN setting. In [34], the measured RSS values used to calculate PER versus various data rate. Subsequently, the authors proposed LT codes as an error mitigation technique to achieve high reliability in WBAN during the shadowing effect. The paper also presented theoretical throughput of LT and RS codes versus the number of transmitting packets. The authors claim that LT code outperforms the RS code in WBAN when the probability error rate of the channel is high due to the shadowing effect. However, RS codes perform better than LT codes in other conditions. The PER calculation from the measured RSS measurement value around the human body and the throughput performance result of the two codes are isolated work. The presented throughput results of those codes is a standalone performance of these codes without considering the real WBAN setting. In [35], the authors proposed an adaptive ECC to select ECC according to channel conditions and different type of transmission data, including medical and non-medical data. The requirement of different QoS for the different types of transmission data is considered. The authors proposed convolutional code (2, 1) for AWGN channel and concatenated RS (63, 51)-convolutional code (2, 1) codes for Rician and Rayleigh channels for medical data to meet the desired QoS, respectively. Whereas, the RS (63, 51) code for the AWGN channel and concatenated convolutional code (2, 1) codes for Rician and Rayleigh channels are proposed for non-medical data to meet the desired QoS. For medical data, the paper recommended using the convolutional code (2,1) against RS (63,51) code in the AWGN channel, despite that both codes are achieving the required QoS and RS (63,51) having a higher coding rate, but the same reason is given for code selection in other scenarios. Hence, their method of code selection is not consistent.