# Slotted ALOHA on LoRaWAN-Design, Analysis, and Deployment
## 2 Related Works  
The number of connected IoT devices is expected to rise at an annual rate of 32% and market forecasts anticipate 21B devices by the end of this decade [2]. Some of the newest applications require coverage of entire cities or huge buildings at very low energy use and cost. These requirements are hard to achieve using traditional methods and infrastructures such as WPAN or cellular [1]. Large-scale IoT installations are becoming a reality, as networks are being deployed for urban monitoring applications [2], smart city [17], intelligent transportation systems [18], and urban monitoring applications [19]. Several radio technologies, such as Sigfox, LoRa(tm), IEEE 802.15.4 NB-IoT, BLE 5.0 and DASH7, are currently competing in the arena of Device-to-Device (D2D) long-distance, low-power communication [20]. Different communication technologies aimed at low power have been proposed and deployed. It is possible, as discussed in [5], to split them in two categories: low power local area networks, such as IEEE 802.15.4, and Bluetooth Low Energy which are typically utilized in short-range personal area networks; low power wide area networks, with a transmission range greater than 1000 m; this category includes LoRaWAN, Sigfox, and DASH7 as major players. Sigfox is a protocol based on a variation of the cellular system which permits remote devices to connect to an access point through Ultra Narrow Band. It is a proprietary technology, developed and distributed by Sigfox. Full specifications are difficult to obtain, so it is difficult to carry out a clear and comprehensive comparison with other protocols. Each end-device can send 140 messages per day, with a payload size of 12 octets, at a data rate up to 100 bps. Each Sigfox access point can handle up to a million end-devices, with a coverage area of 30-50 km in rural areas and 3-10 km in urban areas [21]. The payload and number of packetslimits make Sigfox networks hardly usable in application scenarios where communication is not very sporadic: LoRaWAN is less prescriptive and more flexible. DASH7 [22] is a wireless sensor and actuator full Open Systems Interconnection (OSI) stack protocol that operates in the 433 MHz, 868 MHz, and 915 MHz unlicensed ISM bands. It originates from the ISO 18,000-7 standard [23]. DASH7 can provide communication in the range of 2 km with low latency, mobility support, and multi-year battery life. A secure AES 128-bit shared key encryption is supported with a data rate up to 167 Kbit/s. However, DASH7 needs more power per bit than other protocols like LoRaWAN, and for applications that do not require synchronization or low latency uplink, LoRaWAN would be preferred. Moreover, during fast motion in rural areas, DASH7 connections are not as reliable as other LPWAN solutions. In the LoRaWAN(tm) architecture [24], sensor nodes communicate with the gateway, which serves as a bridge between the nodes and a network server. Three types of functional classes are defined for end-devices: A, B, and C. Currently, several papers analyze LoRa performance [5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23; 24; 25; 26; 27; 28; 29; 30]. In these works, LoRa deployments are compared in terms of network throughput and power consumption. In Ref. [3] the coverage of LoRa is studied and in Ref. [31], the authors analyze the LoRa network capacity and propose LoRa-Blink to support multi-hop communications. In Ref. [32], [PERSON] and [PERSON] presented an analytical model that characterizes the current consumption, lifetime and energy cost in LoRaWAN Class A. The proposed model allows to quantify the impact of physical and MAC layers, as well as bit error rate and collisions, on energy performance. As mentioned in the Class A ISO/IEC ISM regulations [24], the end nodes and gateways can transmit \"at will\" without any carry sensing. This makes the LoRaWAN's MAC similar to ALOHA [33]. The ALOHA mechanism can cause substantial inefficiency in LoRaWAN networks, as highlighted by the simulation study reported in Ref.