# Opportunities and Challenges for Error Correction Scheme for Wireless Body Area Network--A Survey
## 5 Review on ECS Methods on WBAN
### Harq
#### 5.2.1 Harq-I  
In [46], the authors proposed adaptive HARQ-I for the wireless control of medical equipment to get high reliability communications between controller and sensors node. In the proposed technique, HARQ-I combines convolutional code with ARQ. The paper assumed that the wireless control system works as a rotated inverted pendulum. In the proposed system, the code rate adaption (three possible rates) of the convolutional code is performed using puncturing according to the importance of quantity of state of the control system according. The control quality is improved by the method of limitation of retransmission. The paper presented the comparison result of MAE and the rate of increase of  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Ref. (Yr)** & **Proposed FEC** & **WBAN/Standard/Layer/Data/Channel** & **Results** \\ \hline
[33] (010) & LT & One hop star network and single WBAN/IEEE & Packet erasure ratio, retransmission \\  & & 802.15.6 Task Group/PHY/no discussion/erasure & probability \\ \hline
[34] (012) & LT & One hop star network and single WBAN/IEEE & PER, retransmission \\  & & 802.15.6 Task Group/PHY/no discussion/erasure & probability and throughput LT and RS codes \\ \hline
[35] (016) & RS, convolutional code & One hop star network and single WBAN/IEEE & \\  & and Concatenated code & 802.15.6/PHY/medical and non-medical/AWGN, & BER and coding gain \\  & & Rayleigh and Rician fading & \\ \hline
[36] (015) & LT & One hop star network and single WBAN/IEEE & BER, coding gain and \\  & & 802.15.6/PHY/no discussion/channel & packet acceptance rate \\  & & adapted from [41, 44, 45] & \\ \hline
[37] (013) & RS & One hop star network and single WBAN/IEEE & BER \\  & & 802.15.6/MAC/no discussion/AWGN and fading & \\ \hline
[39, 40] (017, 018) & Raptor code & One hop star network and single WBAN/IEEE & \\  & & 802.15.6/PHY/no discussion/Nakagami, Rayleigh & Energy consumption \\  & & and Rician & \\ \hline
[41] (016) & Linear block code & Two hop star network and single WBAN/no & \\  & & discussion/PHY/no discussion/Rayleigh and & BER \\ \hline
[42] & LDPC with modified & One hop star network and single WBAN/IEEE & \\  & WBF & 802.15.6/PHY/no discussion/Implant to implant & BER, and no of iterations \\ \hline
[43] (018) & Adaptive & One hop star network and single WBAN/IEEE & \\  & convolutional code & 802.15.6/PHY/medical and non-medical/AWGN & Theoretical bit \\  & & and Rayleigh & error probability \\ \hline \hline \end{tabular}
\end{table}
Table 5: A review of forward error correction (FEC) based ECS.  
frequency band versus SNR over AWGN channel for HARQ-I and showed the proposed adaptive HARQ-I. The proposed system performs slightly better than HARQ-I. The presented results of the proposed method are standalone performance without considering the WBAN setting. Table 6 shows the summary of HARQ-I based ECS.  
In [47], the authors introduced the error control strategy for WBAN, while ultrasonic waves were used as a communication medium. The paper considers three types of strategies: ARQ only, HARQ-I (called A&F that combines ARQ with fixed maximum retransmission and BCH), and adaptive HARQ-I (called UECS that combines ARQ with adaptive retransmission and BCH). This work presented the energy consumption and delivery ratio of ARQ only, A&F, and UECS against SNR. Consequently, the results do not take the code rate of the adaptive coding into consideration i.e., do not consider the overhead that is caused by ECS. Therefore, the comparison that is made in [47] is not fair and reasonable. Additionally, the authors did not consider energy consumption due to encoding and decoding that is the key drawbacks of this paper. Furthermore, the adaption is performed using SNR estimation and the cost that is associated with channel estimation is not considered during energy consumption estimation. The presented results are standalone results without considering the practical WBAN setting.