Internet of Things Network Synchronizer
By the end of the decade billions so called Internet-of-Things (IoT) devices will be connected to the Internet. IoT nodes can range from electrical energy meters to tiny positioning nodes connected to a network. While legacy 2G GSM has long been used for cellular IoT applications, recent advancements in the 3GPP standardization organization address the growing need for IoT modems. In particular, the Extended Coverage GSM for IoT (EC-GSM-IoT) standard with 20 dB coverage increase and low-power features is getting finalized during 2016 [1,2]. Current research at the institute includes a first prototype of an EC-GSM-IoT modem by the end of 2016.
A state of the art 2G GSM modem can synchronize to a base station as long as the signal level lies above the noise level (10 dB SNR or higher). Lower SNR ranges are not interesting for normal communication. With the introduction of EC-GSM-IoT, synchronization is all of a sudden necessary far below the noise level (-8 dB SNR and lower). The synchronization procedure for initial time and frequency offset acquisition includes Multi-Frame Detection (MFD), Frequency Offset Estimation (FOE) and EC-SCH decoding. EC-GSM-IoT synchronization requirements can be divided into [3,4,5]:
- Frequency offset: The frequency offset to the base station has to be estimated and corrected such that it is below 0.1 ppm at the receive signal level (or receive signal level to interference level ratio) defined as reference sensitivity point for EC-SCH, which lies at -124.5 dBm for ST channel conditions (AWGN) without interference.
- Timing offset: The timing offset with respect to the receive time of the base station signal has to lie below 1 normal symbol period. Similar to requirement R1a this has to be achieved at the receive signal level (or receive signal level to interference level ratio) defined as reference sensitivity point for EC-SCH.
- Time to synchronize to BCCH carrier: The maximum time to synchronize (successfully decode EC-SCH data) is 2 s. This does not mean that requirements R1a and R1b need to be met after 2 s, it only means that one has at most 2 s for MFD and EC-SCH decoding.
During this project, algorithms to meet the above requirements shall be studied, evaluated, and implemented. In addition, solutions for accurate receive signal level measurements below the noise level as well as frequency and time offset tracking on normal bursts shall be studied. The found algorithms should be adaptable to work with legacy GSM, as well.
 3GPP. Cellular System Support for Ultra Low Complexity and Low Throughput Internet of Things. http://www.3gpp.org/DynaReport/45820.htm, December 2015. TR 45.820 v13.1.0.
 3GPP. Release 13. http://www.3gpp.org/release-13, 2016.
 3GPP. GSM/EDGE Radio transmission and reception. https://portal.3gpp.org/desktopmodules/Specifications/SpecificationDetails.aspx?specificationId=2709, September 2016. TS 45.005 v13.2.1.
 3GPP. GSM/EDGE Radio subsystem link control. https://portal.3gpp.org/desktopmodules/Specifications/SpecificationDetails.aspx?specificationId=2710, September 2016. TS 45.008 v13.3.0.
 3GPP. GSM/EDGE Radio subsystem synchronization. https://portal.3gpp.org/desktopmodules/Specifications/SpecificationDetails.aspx?specificationId=2712, September 2016. TS 45.010 v13.3.0.