# A Survey on Wireless Body Area Networks for eHealthcare Systems in Residential Environments
## 3 Discussion
### Energy Efficiency
In erroneous channels, if the level of noise increases such that there is a high possibility that packets have at least one error, then the channel will quickly be occupied with retransmissions. As a consequence, no new information will be transmitted and the system throughput will decrease, and ultimately approach zero (This drawback affects many latency-sensitive applications such as health monitoring systems). Therefore, a combination of CRC and FEC techniques that most of the protocols use in this survey can protect the information in various channel conditions. Many of these protocols such as BLE, Bluetooth, ANT, Z-Wave, Wavenis, BodyLAN and Dash7 use GFSK modulation while a number of other protocols such as Zarlink, Insteon and ONE-NET employ FSK modulation. GFSK modulation is an improved version of the FSK in which the data must be filtered via a Gaussian filter prior to modulating the carrier. This leads to a narrower power spectrum of the modulated signal which results in higher transfer speed of data in the same channel bandwidth [95]. In addition, GFSK modulation has the potential to cover a greater communication range compared to FSK modulation [96]. All these protocols are equipped with at least one type of encryption or level of security. Some of these encryptions are strong while others are very limited and offer little protection. In addition, Bluetooth, RuBee, Dash7 and EnOcean provide alternative security engines within the same chip which may be beneficial in particular applications. Some applications require less stringent security, whilst others may be able to exploit the optional extra encryption methods at different times. It is difficult to mention which security technique is more appropriate as it is so application and regulatory dependent. However, the fact that all radios offer some method of securing the communication channel ensures a level of security. Alternative radios may also provide benefits such as a flexible packet format (length) that may result in more efficient packing of data per transmission. Most of these radios such as ZigBee, Wavenis and Dash7 do not require additional infrastructure in order to fully cover a residential area; however, some of them such as BLE, Bluetooth, Sensium and Zarlink may require more infrastructure to support a greater range. For more comprehensive comparison of alternative low-power wireless technologies, see Tables 6-13. Star symbol in the Tables 6-13 refers to undefined information. Different protocols offer various connection management schemes. It may be considered a disadvantage if a body-worn sensor node has to maintain link with specific infrastructure or other sensor nodes. It may be advantageous if a link can be made and broken at any point without severely affecting latency and power budget. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Characteristic** & **Bluetooth** & **ANT** & **RuBee** & **Sensium** & **Zarlink** & **Insteon** \\ \hline Multiple Access Scheme & TDMA & TDMA & \(\ast\) & TDMA, FDMA & \(\ast\) & TDMA + Simulcast \\ Maximum Packet Size & 358 bytes & 19 bytes & 128 bytes & \(\ast\) & \(\ast\) & Standard: 10 bytes \\ Error Control Method & CRC, FEC & CRC & CRC & CRC, FEC & CRC, FEC & CRC, FEC \\ Checksum Length & 1-byte/2-byte & 2-byte & 1-byte & \(\ast\) & \(\ast\) & 1-byte \\ Identifiers & 48-bit Public Device & \(\ast\) & 32-bit & \(\ast\) & \(\ast\) & 24-bit Module ID \\ \hline \hline \end{tabular}  
* refers to undefined information.  
\end{table} 
Table 6: Physical layer comparison of Bluetooth, Ant, RuBee, Sensium, Zarlink and Insteon.