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GCT Combines Sigfox With NB-IoT

October 24, 2017

Author: Mike Demler

GCT Semiconductor’s new GDM7243i is the first single-chip modem to enable low-bit-rate IoT devices that operate on both Narrowband-LTE (NB-LTE) systems and the Sigfox low-power wide-area network (LPWAN). Although the chip gives OEMs the option to build one device for both cellular and LPWAN systems, they can at the same BOM cost build both lower-price Sigfox-only models and higher-price models with additional LTE capabilities.

The GDM7243i integrates two RF front ends (RFFEs), a low-band circuit for use with 700–900MHz LTE frequencies, and a high-band circuit for 1.7–2.6GHz, as Figure 1 shows. The modem supports the 3GPP’s Release 13 Cat-M1 and Cat-NB1 standards, along with the sub-1GHz frequencies that Sigfox employs (see MPR 8/31/15, “Low-Rate LTE Delivers IoT WANs”). It targets devices requiring long battery life, such as asset trackers and agricultural IoT, along with security alarms, smart meters, telematics, and other traditional M2M systems. The chip is sampling now and will likely enter production in 1Q18.

The GDM7243i can run the low- and high-band RFFEs in parallel and switch between them “on demand,” but the company withheld details of how that switching occurs. An example application involves using the Sigfox network as a backup in case of lost cellular-network coverage owing to congestion or equipment failure. We thus expect the device can automatically choose the network with the strongest signal. In security systems, the GDM7243i could use the Sigfox channel to circumvent attempts to jam the cellular radio.

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