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CommSolid IP Simplifies NB-IoT

September 5, 2017

Author: Linley Gwennap

NB-IoT promises to provide a low-cost cellular connection for remote IoT devices. Several chip vendors have already released NB-IoT modems to add this capability in existing IoT devices. But to truly minimize cost, the modem must move into the SoC. To enable this integration, German startup CommSolid has created the first complete NB-IoT baseband intellectual property (IP). The tiny CSN130 core, based on a proven Tensilica architecture with custom extensions, implements the complete digital baseband function; designers need add only the RF front end. The company is currently licensing production RTL for this core.

Unlike other LTE standards, NB-IoT operates at just 126kbps on the downlink and 156kbps on the uplink. Thus, the hardware required to implement the technology is much simpler than for high-speed LTE. Whereas a 450Mbps (Category 10) LTE modem requires tens of millions of gates, the CSN130 comprises less than a million. NB-IoT data rates are similar to those of 2G standards such as GSM/GPRS, a technology that SoCs easily integrated several years ago.

The CSN130 starts with a Fusion F1 DSP from Cadence. The DSP implements the base Xtensa ISA, which includes standard CPU instructions as well as DSP extensions. Thus, it can execute both the modem control code and the baseband processing, eliminating the need for separate CPU and DSP cores. Taking advantage of Xtensa’s instruction-extension technology (TIE), CommSolid created more than 25 custom extensions to efficiently execute Gold-sequence, Viterbi, FFT, complex-arithmetic, and other NB-IoT baseband functions. Using these extensions, the DSP can execute the entire NB-IoT stack at the full data rate while running at just 64MHz. Its low speed and small area minimize power consumption.

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