In practice, the radio applications often require high ranges in both outdoor and indoor space. In Europe, such applications are often implemented in the license-free sub-GHz frequency ranges at 433MHz or 868MHz. Since the low attenuation characteristics prevail in these frequency bands due to the low frequencies, larger ranges can be achieved with comparable transmission levels than in the 2.4 GHz frequency band.
However, this advantage is offset by two disadvantages of these frequency bands:
● Legally allowed duty cycle. For example, the transmission duration is limited to 1 percent (that is 36s per hour).
● The fact that the sub-GHz frequency bands are not harmonized worldwide.
Especially the latter can lead to enormous costs for the necessary radio approval outside of Europe.
Especially home automation applications such as lighting, heating, locking systems, air conditioners, and utility meters are often developed because of the requirement for longer range, in the sub-GHz frequency range. The limitation by the duty cycle is accepted because the application by nature rarely transmits data or the transmission frequency of the most battery-powered devices is limited by the battery capacity itself.
The 20mm × 25mm radio module iM282A needs to be in pure transmission mode - if the microcontroller is in power saving mode - with 8dBm output power only 25mA, in case of reception 9mA and in power saving mode well below 1μA.
The disadvantage of the costs for the approval of a radio product thus still remains. The sub-GHz frequency range is more of a patchwork worldwide, with frequency ranges and legal requirements differing from region to region. The 2.4 GHz band, vice versa, is harmonized worldwide and offers a more favourable alternative with regard to approval. In addition, an application in the 2.4 GHz frequency range is not subject to duty cycle restrictions
Popular wireless technologies that work in this frequency band are Wi-Fi, Bluetooth or Zigbee. But without additional increase, you can achieve only ranges of a few tens of meters. Higher range requirements require complex and therefore expensive wireless networks with multiple base stations, relay nodes or power amplifiers. A simple and cost-effective wireless system with a long-range in the 2.4 GHz frequency band has not been available so far.
10 km range at 2.4 GHz
With the iM282A radio transceiver module (Fig. 1), IMST GmbH is opening up the 2.4 GHz band for long ranges. Up to 10km (line of sight) is possible with the LoRa modulation (frequency spread) without additional power amplifiers.
The iM282A radio module is based on Semtech's new SX1280 radio transceiver IC and has a Cortex M3 microcontroller. The transceiver IC contains three wireless modems. In addition to LoRa modulation, it can also use the modulation types (G) FSK (Gaussian Frequency Shift Keying) and (G) MSK (Gaussian Minimum Shift Keying) and FLRC (Fast Long Range Communication). FLRC is based on coherent demodulation of GMSK combined with forwarding error correction and interleaving techniques and enables data rates up to 1.3Mbps with 8 to 10dB higher receiver sensitivity (Figure 2). Depending on the range to be achieved, raw data rates of 476bit/s up to 2.3Mbit/s can be achieved with the SX1280 transceiver.
Picture 2a. Semtech´s SX1280 transceiver has three basic modes of operation: LoRa, Fast Long Range Communication (FLRC), and Frequency Shift Keying (FSK).
Picture 2b. Each operating mode allows many operating points so that the most favourable operating point can be selected on the basis of the raw data transmission rate and the achievable receiver sensitivity.
Picture 3. In the LoRa operating mode, the eight spreading factors (SF5 to SF12) with the four selectable bandwidths allow a total of 32 working points for the SX1280 radio transceiver IC in the iM282A radio module, which also results in different sensitivity values.
Test results of a 2.4 GHz radio link, realized with the starter kit SK-iM282A.
The iM282A radio module is the part of our product range available directly from our warehouse. The SK-iM282A starter kit can be ordered upon request on favourable terms.
If you are interested in any of IMST or you need more information, we are ready to help you at sales@soselectronic.com
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