# A Survey on Wireless Body Area Networks for eHealthcare Systems in Residential Environments
## 3 Discussion
### Protocol Efficiency  
Protocol efficiency needs to be considered before selecting a low-power communication protocol. It greatly influences the energy efficiency of the selected protocol. This is because an inefficient communication protocol spends the majority of its time transferring overhead information rather than transmitting the actual payload data. Thus, little data may be transferred over a fixed duration of time and devices transferring the information may quickly run out of power. The efficiency of protocols can be calculated based on the ratio of actual payload information to the total length of the data packets.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Characteristic** & **ZigBee** & **Bluetooth Low Energy** \\ \hline Network Topology & P2P, Star, Cluster Tree, Mesh & P2P, Star \\ Single-hop/Multi-hop & Multi-hop & Single-hop \\ Nodes/Active Slaves & \textgreater{}65,000 & Unlimited \\ Device Types & Coordinator, Router, End Device & Master, Slave \\ Networking Technology & PAN & PAN \\ \hline \hline \end{tabular}
\end{table}
Table 4: Network layer comparison of ZigBee and Ble.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Characteristic** & **ZigBee** & **Bluetooth Low Energy** \\ \hline Frequency Band & 2400, 868, 915 MHz & 2400 MHz \\ \hline Bit Rate & 20 Kb/s (868 MHz), 40 Kb/s (915 & \(1\) Mb/s \\  & MHz), 250 Kb/s (2400 MHz) & \(1\) Mb/s \\ \hline Modulation Type & BPSK, O-QPSK & GFSK \\ \hline Spread Spectrum Technology & DSSS & FHSS \\ \hline Nominal TX Power & \textgreater{}32 dBm to 0 dBm & \textgreater{}20 dBm to 10 dBm \\ \hline Receiver Sensitivity & \textgreater{}85 dBm & \textgreater{}70 dBm \\ \hline \multirow{3}{*}{Number of Physical Channels} & 27 channels: 16 channels in the & 40 channels in FDMA: \\  & 2450 MHz, 10 channels in the & 3 advertising channels, \\  & 915 MHz, 1 channel in the 868 MHz & 37 data channels \\ \hline Channel Bandwidth & 2 MHz (5 MHz wasteful spectrum) & 2 MHz (no wasteful spectrum) \\ \hline \hline \end{tabular}
\end{table}
Table 2: Physical layer comparison of ZigBee and Ble.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Characteristic** & **ZigBee** & **Bluetooth Low Energy** \\ \hline Multiple Access Scheme & CSMA-CA, slotted CSMA-CA & FDMA, TDMA \\ Maximum Packet Size & 133 Bytes & 47 Bytes \\ Protocol Efficiency (ratio of & 102/133 = 0.76 (76 Percent Efficient) & 31/47 = 0.66 (66 Percent Efficient) \\ payload to total packet length) & \multirow{2}{*}{
\begin{tabular}{c} ARQ, FEC \\ 2 Bytes \\ \textless{}16 ms (beacon-centric network) \\ \end{tabular} } & ARQ, FEC \\ CRC Length & 2 Bytes & 2 Bytes \\ Latency & \textless{}3 ms \\ Identifiers & 16-bit short address & 48-bit public device address \\  & 64-bit extended address & 48-bit random device address \\ \hline \hline \end{tabular}
\end{table}
Table 3: Link layer comparison of ZigBee and Ble.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Characteristic** & **ZigBee** & **Bluetooth Low Energy** \\ \hline Network Topology & P2P, Star, Cluster Tree, Mesh & P2P, Star \\ Single-hop/Multi-hop & Multi-hop & Single-hop \\ Nodes/Active Slaves & \textgreater{}65,000 & Unlimited \\ Device Types & Coordinator, Router, End Device & Master, Slave \\ Networking Technology & PAN & PAN \\ \hline \hline \end{tabular}
\end{table}
Table 5: Comparison of other properties of ZigBee and Ble.  
It is therefore very easy to compute the protocol efficiency of ZigBee and BLE by considering their packet formats (see Table 3); BLE has protocol efficiency of 66%, whereas ZigBee has protocol efficiency of 76%. Although, the results show that ZigBee is more protocol efficient than BLE, in many low data-rate low-power health monitoring systems wearable sensor nodes are only required to partially utilize the total available payload space to transfer data, hence, lower protocol efficiency does not necessarily mean that a particular protocol is inappropriate.