WIRELESS & SENSING Revision 1 July 2013 2013 Semtech Corporation 1 SX1272/3/6/7/8 LoRa Modem Design Guide SX1272/3/6/7/8: LoRa Modem Designers Guide AN1200.13 TCo WIRELESS & SENSING Revision 1 July 2013 2013 Semtech Corporation 2 SX1272/3/6/7/8 LoRa Modem Design Guide Table of Contents 1. Overview . 3 2 Principles of LoRa Design . 3 2.1 LoRa Modulation . 3 2.2 Receiver Sensitivity . 3 2.3 SNR and Spreading Factor . 3 2.4 BW and Chip Rate. 4 3 Advanced LoRa Design Parameters . 5 3.1 Forward Error Correction . 5 3.2 Hardware Implementation . 6 3.3 Low Data Rate Optimisation Mode & Header Mode . 6 4 The LoRa Packet Format & Time On Air . 7 5 LoRa Calculator . 8 Table of Figures Figure 1. The LoRa Bandwidth Corresponds to the Double Sided Transmit Spectrum Bandwidth . 4 Figure 2. Influence of Coding Rate on Sensitivity (SF = 7, BW = 125 kHz, 13 Byte Payload) . 5 Figure 3. Individual RF transmit and receive paths (left) provides better sensitivity than the single shared TRx path (right). . 6 Figure 4. LoRa Modem Packet formatting. . 7 Figure 5. The LoRa Calculator Interface. . 8 DISCLAIMER The performance figures are for indication only. For definitive product performance data please refer to the datasheet. WIRELESS & SENSING Revision 1 July 2013 2013 Semtech Corporation 3 SX1272/3/6/7/8 LoRa Modem Design Guide 1. Overview This guide provides the basic information necessary for the designer to evaluate the suitability of the LoRa modem for their radio application. The design is split into two sections covering basic and advanced design topics. 2 Principles of LoRa Design 2.1 LoRa Modulation LoRa is a spread spectrum modulation scheme that that uses wideband linear frequency modulated pulses whose frequency increases or decreases over a certain amount of time to encode information. The main advantages of this approach are twofold: a substantial increase in receiver sensitivity due to the processing gain of the spread spectrum technique and a high tolerance to frequency misalignment between receiver and transmitter. To better understand how to implement a radio design using the LoRa modulation format it is necessary to briefly examine the factors influencing radio receiver sensitivity. 2.2 Receiver Sensitivity The sensitivity of a radio receiver at room temperature is given by: Eqn. 1 The first term is due to thermal noise in 1 Hz of bandwidth and can only be influenced by changing the temperature of the receiver. The second term, BW, is the receiver bandwidth. NF Is the receiver noise figure and is fixed for a given hardware implementation. Finally, SNR represents the signal to noise ratio required by the underling modulation scheme. It is the signal to noise ratio and bandwidth that are available as design variables to the LoRa designer. 2.3 SNR and Spreading Factor The basic premise of spread spectrum is that each bit of information is encoded as multiple chips. The relationship between the bit and chip rate for LoRa modulation, and resp