## 6 Design Considerations for LPWAN Networks
### Energy-Efficient Operations and Low Power Sources  
Energy-efficient operations involve decreasing complexity and enabling efficient utilization of resources. The following are some key design considerations for extending the lifetime of devices to 10+ years of operation.  
For energy-efficient designs, the use of multiple energy-saving low power modes, for example, sleep mode, is a desirable approach. A significant number of LPWAN applications involve sending of frame sizes of the order of tens of Bytes transmitted a few times per day at ultra-low speeds [11]. For such applications, the intent is to operate the nodes with an extremely low duty cycle so that the nodes will be in sleep mode most of the time. Selected high power consuming elements like data transceivers may be turned off when not required. This reduces the amount of consumed energy. Only when data are to be transmitted or received, the transceiver is to be turned on. In the case where data are to be transmitted by the access station, the access station may wait until the time of sleep has expired, or it may send explicit wake-up signals.  
Media access control (MAC) is particularly influential in improving resource utilization efficiency and extending battery life. Efficient resource utilization can be done via scheduling optimization. Efficient scheduling involves the assignment of transmission resources to selected devices with higher levels of channel quality. Another approach for extending battery life is by harvesting energy from other sources. Natural sources, for example, wind or solar power, can be used. However, these sourcesmay be unpredictable and unreliable. Capacitors may be utilized to store energy from these types of alternate sources. For consistent availability of energy, power may be derived from radio frequency signals that transfer control and data information. There is a tradeoff between the lifecycle of a battery without these enhancements versus the resulting availability of additional power from the alternate sources after you take into account the overhead of these enhancements.  
Lightweight MAC protocols and techniques to offload complexity from end devices are some typical techniques that may be considered for energy efficiency. Use of simple media access techniques is an example of such an approach. In order to match the range and data rate requirements, flexible and inexpensive hardware designs are needed for implementing multiple physical layers [11]. Each of these layers can offer complementary solutions to corresponding applications.  
Generally, from an energy consumption perspective, communication operations consume more energy than processing operations in end devices. Power utilization in the devices can be reduced by using less complex or less frequent communication mechanisms as long as the corresponding additional processing power is still manageable. As an example, to reduce communication overhead, sending a large number of unformatted data can be replaced by consolidating them into one formatted package prior to their transmission.  
With the increasing number of connected LPWAN devices, additional design considerations that can be explored include the use of channel diversity, opportunistic efficient spectrum utilization, and adaptive transmission. The use of MIMO at the LPWANs access stations can also significantly increase the diversity gain or the data rates. Using space division multiplexing, the access station can boost the number of LPWAN devices that it can support.  
Efficient spectrum utilization pertains to optimized usage of the overall spectrum resources in time, frequency, bandwidth, and spatial dimensions. In many instances, the spectrum is not fully utilized. The access station or the device can sense and identify the gaps in spectrum usage and improve the efficiency of spectrum utilization [12]. Such an approach can also reduce cross-interference.