An Extended Coverage System on Chip for the Cellular Internet of Things

Abstract

Billions of devices are expected to be connected to the so called Internet of Things (IoT) by 2020. Applications range from smart meters over cargo tracking to more exotic applications such as beehive temperature monitoring in remote areas. Many IoT applications require years of battery life and, needless to say in a billion devices network, low-cost chip-sets. Furthermore, numerous current and anticipated IoT applications are latency agnostic and, therefore, low-data rates are sufficient. However, genuine global coverage is almost always a key requirement as e.g. cargo tracking does not work without coverage. In this context scores of Low Power Wide Area Network (LPWAN) standards targeting low-power and Extended Coverage (EC) IoT applications emerged in the past few years. 3GPP standards form the cellular IoT ecosystem and comprise well established but without EC and without low-power support GPRS and EGPRS. There are also newer EC and low-power enabled 3GPP standards such as Extended Coverage GSM for the IoT (EC-GSM-IoT), Narrow-Band-IoT (NB-IoT), and enhanced Machine-Type Communication (eMTC). The latter three promise up to 20dB of coverage increase by means of blind repetitions and, in addition, up to 10 years of battery life. Truly, GPRS is the most widely used communication standard for the IoT today. In addition, in this well established cellular IoT ecosystem EC enabled extensions will become instantly available by means of software upgrades in the Base Station (BS). However, the Mobile Station (MS) side requires more than just a new firmware. This thesis focuses on EC-GSM-IoT Digital Baseband (DBB) algorithms for the MS and provides solutions for signal processing clearly below the thermal noise floor. The signal processing problems range from repetition combining over frequency acquisition with large frequency offsets enabling the use of a cheap Digitally Controlled Oscillator (DCXO) to time synchronization algorithms. What’s more, the provided signal processing algorithms are trimmed to be implementation friendly and are incorporated in a complete dual-mode EC-GSM-IoT/NB-IoT modem SoC comprising not only DBB but also RF front-end and CPU system. This modem SoC achieves a sensitivity as low as -128.9dBm surpassing requirements by 4.9dB while providing close to 600kbps throughput with EGPRS2A fallback thus enabling a wide range of IoT applications.