LTE modem

The long term evolution (LTE) modem consists of baseband processing and RF parts, which together implement a complete 3GPP LTE release 13 (Rel-13) Cat-M1 and Cat-NB1 and LTE release 14 (Rel-14) Cat-NB1 and Cat-NB2 capable product.

As shown in the following figure, the parts of the LTE modem are:

• RF transceiver
• Modem baseband (BB)
• Embedded flash/RAM
• Modem host processor and peripherals

The modem baseband and host processor provide functions for the LTE L1, L2, and L3 (layers 1, 2, and 3 respectively) as well as IP communication layers. Modem peripherals provide hardware services for the modem operating system and the modem secure execution environment.

Figure 1. LTE modem within the nRF91

Application and modem domains interact through the interprocessor communication (IPC) mechanism. The LTE modem is accessible to users through the modem API.

The application processor is the system master and is responsible for starting and stopping the modem. The LTE modem enables the clocks and power required for its own operation. The platform handles shared resources, such as clocks, and does not need user participation. In cases where a hard fault is detected in the modem, the application domain will perform a hard reset for the modem.

The key features of the LTE modem are:

• Complete modem with baseband and RF transceiver
• 3GPP release 13 compliant LTE categories:
  • Cat-M1 (eMTC - enhanced machine type communication)
  • Cat-NB1 (NB-IoT - narrowband internet of things (IoT))
• 3GPP release 14 compliant LTE categories:
  • Cat-NB1 (NB-IoT)
  • Cat-NB2 (NB-IoT)
• Power saving modes
• Supports LTE bands from 700 MHz to 2.2 GHz through a single typical 50 Ω antenna pin
  • ANT antenna pin is DC grounded
• RX sensitivity: -108 dBm for Cat-M1 and -114 dBm for Cat-NB1 and Cat-NB2
  • As defined in 3GPP conformance test specification TS 36.521-1
• 1.8 V MIPI RFFE (RF front-end) digital control interface and MAGPIO control interface for external RF applications.
• LTE modem internal ADC that is also used for some AT command interface services, for example, for battery monitoring
• 1.8 V UICC (universal integrated circuit card) interface, based on ISO/IEC 7816-3 and compliant with:
  • ICC (ETSI TS 102 221)
  • eUICC (ETSI TS 103 383)