New technology from Semtech enables 10 x greater range than competing systems and the capacity to connect tens of thousands of nodes to a single gateway in a star architecture while maintain low power for multi-year battery operation. This will enable the next wave of applications for internet of things (IoT), smart cities, smart environments, and machine-to-machine (M2M) applications. With everyadvancement in technologythat extended wirelessrange, new applications have been enabled and the total available market sizefor wireless connected devices has dramatically increased. For example, the range extension provided by the development of mesh networks has led to the adoption and roll-out of smart-meters in North America and Europe over the last few years.
Gartner predicts that there will be 26-million IoT installed devices by 2020 compared to 7,3-billion smartphones, tablets, and PC devices, with a global population of 7,7-billion. Many corporations predict that IoTconnected devices will exceed 50billion by 2020. Cellular M2M modules are predicted to contribute less than 10% of IoT connected devices due to cost and battery life constraints. Systems today based on mesh networking have a limited capacity and are typically constrained to a single application which restricts the return on investment (ROI) thereby limiting deployments of smart city, smart environments, agriculture, and sensor network applications. The range of existing systems forces the use of multiple repeaters which increase the deployment and maintenance costs. The ROI for smart parking systems is viable but installing a repeater on every third light pole for a mesh network smart parking system is a limiting factor for many city governments. Other applications such as smart street lighting don’t provide a viable ROI when a separate network is required for just this application. A long range network with minimal infrastructure and a high capacity to connect numerous applications to the same network is the only way to enable the predicted IoT volumes.
Fig. 1 : LoRa network architecture.
Frequency shift keying (FSK) modulation has been used as the modulation of choice over the past 15 years for sub-GHz and 2,4 GHz applications due to its low power and low cost implementation. While great for low power, FSK modulation suffers in the total link budget and associated range. Semtech’s LoRa modulation which is integrated along with traditional FSK in its SX127x family utilises the same low power RF architecture as FSK but delivers significantly longer range and better interference immunity than FSK. LoRa is a spread spectrum based technology that has been used for years in different applications, but Semtech is the first to make a low cost implementation that is suitable for battery operated sensor networks. When using a low cost bill of materials without an expensive temperature controlled oscillator (TCXO) LoRa increases the link budget by more than 25 dB compared to conventional FSK systems. LoRa is capable of demodulating 20dB below the noise floor and when combined with integrated forward error correction (FEC) it significantly increases the immunity to interference.
With the increased link budget and range capability of LoRa there is no need for a meshnetwork architecture. A mesh network extends the range of the network but comes at the cost of reduced network capacity, synchronisation overhead, and reduced battery lifetime due to synchronisation and hops. To take full advantage of LoRa properties Semtech designed the gateway chip set and MAC to permit a long range star architecture with capacity to handle tens of thousands of nodes per gateway chip (SX1301). Multiple SX1301 chips can be placed in parallel to create a network with capacity to handle hundreds of thousands of nodes communicating to a single gateway over a 15 km radius. To take advantage of the spread spectrum orthogonally of different spreading factors, adaptive link rate is designed into the MAC to increase the network capacity, optimise battery life, and create a fully scalable system. Like CDMA technology, using different spreading factors permits simultaneous use of a single channel by multiple different data rates at the same time.
Nodes which are close to the gateway and don’t require maximum link budget will use a high data rate to minimise their time on air. Only nodes which are at the limit of the range will use the lowest LoRa data rate and highest output power. The other critical advantage of adaptive link rate is that it creates a scalable system.As the network starts to reach its capacity limits, more gateways can be deployed and the adaptive link will automatically scale the end-node devices to a higher data rate communicating with the nearest gateways and therefore increasing the network capacity. In current systems based on FSK modulation with a single data rate, when the network hits its capacity limit there is nothing that can be done except tear it down and deploy a new architecture.
A LoRa network architecture is demonstrated in Fig.1. The gateway acts as a pass through or packet forwarded and the network is managed by the network server. Eliminating duplicate packets, scheduling acknowledgement, and adapting data rates is managed in the cloud by the network server making it very easy to deploy and manage a LoRa network.
The LoRa long range start network architecture has a link budget 5-10 dB more than cellular systems and mimics existing cellular architecture. This permits use of existing elevated cellular base stations to be equipped with LoRa gateways. With the additional link budget of LoRa, the same coverage can be achieved with the added benefit of in-building and basement coverage. With LoRa’s lower cost and significantly lower power nodes which could previously not be connected with cellular are now feasible to connect.
Whether you are a public or private network operator the LoRa system provides a cost effective, low power, and high capacity solution with ability to connect hundreds of thousands of nodes over many different applications. Whether you are a large or small volume customer, Semtech has established an infrastructure of partner solutions including modules, gateways, and full system solutions based on the LoRa technology.
Contact Willem Hijbeek, Tempe Technologies, Tel 011 455-5587, willem.hijbeek@tempetech.co.za
