# LoRaWAN Base Station Improvement for Better Coverage and Capacity
## 2 Overview of LoRaWAN  
Overview of LoRaWAN technology is given in this section for completeness. LoRaWAN is the most utilized LPWAN technology that operates in unlicensed spectrum with 151 network operators in 167 countries in 2021 according to [22]. The modulation technology used in the physical layer of LoRaWAN is patented [23] by Semtech Corporation, but to reach wider community, it is licensed to other commercial companies which produce radio modules.  
To keep the network complexity and power consumption low, LoRaWAN uses star topology where end devices communicate directly with base stations using LoRaWAN protocol on different channels and with variable data rates. End devices do not connect to a specific base station but send their data to all nearby base stations that forward it via TCP/IP protocol to a network server. Network server is the main part of LoRaWAN network as it manages join requests and device addressing, data delivery to and from a user application, duplicate frame filtering, adapting data rate and security functions. The last component of the architecture is an application server that communicates with the network server over TCP/IP, decodes the received data and initiates messages towards end devices.  
Before sending any data, the end device has to be activated using either Over-The-Air Activation (OTAA) or Activation By Personalization (ABP) method. The main difference between the two options is in generating the device identifier (DevAddr) and the session keys in the network: in ABP activation they are hardcoded in the device while in OTAA they are assigned at the start of the connection (in Join Request/Join Response phase). Session keys are used in Advanced Encryption Standard (AES) [24] to provide secure end-to-end communication. More detailed research regarding security in LoRaWAN can be found in [25; 26].  
In order to retain low power consumption while providing bi-directional communication, LoRaWAN is based on a simple ALOHA protocol with three defined end device classes: A, B and C. Class A is the basic one and is designed for ultra low power end devices enabling only two short receive windows for downlink transmission (from base station to end device) after a packet is sent. In class B, on top of class A, there is one more receive window open in the scheduled interval while class C devices are able to receive all the time when they are not transmitting providing lowest downlink latency [27]. On the other hand, as shown in [28], class A devices require lowest, while class C devices require highest power consumption.  
Compared to LPWAN technologies that operate in licensed spectrums, LoraWAN has lower data rate and payload size. Specifically, LoRaWAN can send a maximum of 256 B of payload with data rate of 27 kbps [27] while in NB-IoT maximum payload size is 1600B which can be transmitted with data rate of 250 kbps [29]. However, this is balanced by the fact that LoRaWAN devices are more energy efficient [30] and affordable [31]. In LoRaWAN, bandwidth (\(BW\)) can be 125, 250 or 500 kHz, where higher bandwidth corresponds with higher data rate, but also with lower sensitivity. Generally, all mentioned LPWAN technologies provide 2-5 km range in urban and over 10 km in rural areas and, with transmission power limited to around 25 mW, low energy consumption with device's battery life of 10 years [32].