## 2 Survey of Existing HCWSNs
The designations of RPs as the sole nodes with forwarding capabilities allow PMs to duty cycle their radios and reduce their energy consumption. On the other hand, RPs cannot duty cycle because they are actively forwarding packets. However, due to the static nature of the RPs, they can utilize the regular power supply from the hospital or use batteries in scenarios with no infrastructure. Another feature that MEDiSN offers is an over-the-air management interface that remotely controls individual PMs using downstream messaging. _MASN_[20]: the robust Medical _Ad hoc_ Sensor Network (MASN) is a practical hardware and software platform designed to perform real-time collection of health care data. MASN adopts a reliable cluster-based communication scheme as its routing protocol for transmitting data. The protocol groups wireless sensor nodes in clusters to detect signals for the purpose of prolonging the lifetime of MASN, load balancing, and scalability. The clustering scheme reliably relays collected ECG data to the ECG server (sink) in the form of aggregated packets. As a result, it is able to provide fast and accurate event detection and reliability control capabilities to the area where the event is occurring because the overhead, latency, and packet loss are reduced. Figure 3 provides an overview of the MASN architecture and the operation of the different components. As previously mentioned, groups of patients equipped with ECG sensors are organized into clusters. In these clusters, a clusterhead is elected and used as an aggregation point to relay data to the ECG server. After the data is collected, wavelet-based ECG feature extraction and classification techniques are applied to the patient data and characteristic points of interest are extracted. The main benefit of the ECG data mining mechanism is that it provides meaningful information for the diagnosis of possible cardiovascular diseases and also  
Figure 2: Overview of MEDiSN architecture and operation. automates the extended recordings of ECG signals, instead of using human processing that is very time consuming and may lead to human errors. To secure the wireless transmission of vital patient data, MASN also employs a low overhead and low complexity encryption and decryption security scheme. The security scheme periodically issues session keys (SK) to cluster heads for secure transmission of data between clusters. Therefore, the security scheme must secure against possible gateway attacks (SKs are issued by the gateway), SK attacks among cluster heads, patient ECG data corruption, and man-in-the-middle attacks [20]. The security scheme successfully defends against these attacks, but does so by adding up to 20% overhead to data packet transmissions [20]. MASN also features a patient location tracking system that is an enhanced version of the CodeBlue MoteTrack [13] algorithm. Using only radio signal information, MoteTrack can determine the location of a patient with an accuracy of 1 meter. The enhanced version of MoteTrack does not use GPS. Rather, the RF chip on each MASN sensor node broadcasts beacon messages at a range of different transmission power levels that the MoteTrack algorithm uses to perform location estimation of patients' positions. This section is concluded with an assessment of how well the system characteristics of CodeBlue, MEDiSN, and MASN meet the specific needs of HCWsNs as outlined in Section 1. Table 1 provides a summary of the HCWsN characteristics used to meet the specific needs. Clearly, the performance achieved and therein stated is dependent on each system's specific operational environment and its particular configuration. As such, Table 1 just summarizes the capabilities of the reviewed systems under their respective operational environments, as reported by their proponents. In terms of reliability, CodeBlue delivers approximately 83% of data packets when the path length between a sender and the receiver is varied between 1 and 6 hops.