# A Survey on Wireless Body Area Networks for eHealthcare Systems in Residential Environments
## 3 Discussion
### Energy Efficiency  
Without a proper, in-depth analysis of these protocols, very little can be derived in terms of their energy efficiency. However, comparing the characteristics of these protocols can provide an approximate estimation of their energy expenditures during data transmission. Multiple access schemes are one of the important features that need to be considered more carefully as these can affect the energy efficiency of protocols. BLE uses Frequency Division Multiple Access (FDMA) along with Time Division Multiple Access (TDMA) schemes, whereas ZigBee employs CSMA/CA scheme. FDMA/TDMA schemes are more suitable to be used on high-load networks as they share the communication channel more efficiently and fairly, but are inefficient at low-load networks as there is usually delay in channel access. While the CSMA/CA scheme is more appropriate to be employed at low-load networks as there is no delay in channel access, is inefficient at high-load networks as packet collisions may happen. For more comprehensive comparison of ZigBee and BLE, see Tables 2-5. Due to the limited range requirements of a residential environment eHealthcare system, full meshing capability of any wireless communication platform may not be necessary, however if no meshing is supported, the infrastructure must be extended so that the premises is fully covered. Alternatively, multi-hop based routing of wireless communication packets may provide the required range of the application, but this solution requires multiple nodes with adequate power budget. Alternative low-power wireless technologies include ANT, but also include recently developed proprietary technologies. These technologies usually are very constrained solutions that provide extremely low power requirements at the expense of much reduced data rate or range of communication. Some of them offer the flexibility of variable data rate and hence power consumption, and can operate at a number of radio frequencies. A few of these protocols such as RuBee, Zarlink and Dash7 are only able to operate on lower frequency bands. Lower frequency bands are less crowded with radio services and they are less exposed to external interference, hence they have lower likelihood of packet collisions which results in lower power consumption. In addition, operating on lower frequency bands come with an advantage of good signal penetration through a variety of materials including the human body, however, the required antenna size is larger than those used at higher frequencies. Among the low-power protocols, only ZigBee uses DSSS whereas BLE, Bluetooth and Wavenis employ FHSS. Spread spectrum techniques are employed for a range of reasons including increasing resistance to unwanted interference and noise. DSSS radios are believed to operate better for large data packets in low to medium interference environments, while FHSS radios operate better for small data packets in high interference environments. Moreover, FHSS radios perform better indoors and in harsh multipath environments because frequency hopping techniques are able to manage multipath fading environments by hopping to new frequency channels [94]. In terms of robustness, ANT, RuBee and Z-Wave only use error detection schemes such as CRC or Longitudinal Redundancy Check (LRC) whereas the rest of the protocols take advantage of an additional Forward Error Correction (FEC) technique along with error detection schemes. Error detection schemes are used in two-way communication systems in which packet retransmission will be requested by the receivers if errors are detected in the received data. This error control technique offers high transmission reliability and very low system complexity and is able to protect the information against most possible error occurrences over a comparatively quiet channel. However, applying a simple error-detection-only technique can also have a severe disadvantage.