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TO BE DELETED-LTE-M and NB-IoT Basics

Transition from Standard LTE to LTE-M and NB-IoT

One of the most prominent steps into transitioning from standard LTE to a version of LTE more fitted for IoT was in the 3GPP Release 13 in 2016 which introduced the LTE Category M1, known as LTE-M. Changes made to standard LTE to transition into LTE-M were envisioned to cover 3 key aspects of LTE:

  • Device Complexity and Power Consumption
  • Coverage
  • Number of Supported Devices

Device Complexity and Power Consumption

To offer LTE-M as an enabler for IoT, the modem complexity, power consumption, and price had to be reduced. This was achieved by modifying a number of LTE specifications.

  • Peak Data Rate: Standard LTE used 10 Mbps for DL and 5 Mbps for UL. In LTE-M, both were reduced to 1 Mbps or less
  • Antenna Diversity: Standard LTE used more than 1 receive antenna, to achieve receive-antenna diversity and mitigate the effects of multipath propagation. This was reduced to only 1 receive antenna in LTE-M
  • Duplex mode: Standard LTE used full duplex operation. LTE-M limited it to half duplex
  • Bandwidth: Standard LTE used up to 20 MHz as channel bandwidth. In LTE-M, this was reduced to 1.4 MHz only
  • Output power: Standard LTE devices can transmit with up to 23 dBm. In LTE-M, this was reduced to only 20 dBm
  • Power Saving Techniques: To be introduced in subsequent topics

Coverage

One of the key methods to achieve longer range is to repeat the messages being sent multiple times. The more times a message is sent, the more likely it will be correctly received by the recipient. Therefore, allowing for more latency can give the sending device the time needed for repeated transmission. In addition, decreasing the data rate increases the allowed transmission distance, assuming the same output power and channel bandwidth.

Number of Supported Devices

Improvements to the the LTE-M system capacity are non-stop. Techniques increasing the system’s capacity usually revolve around improving resource management techniques and reducing overhead signalling involved with establishing and maintaining links.

NB-IoT

NB-IoT was designed to target IoT applications which need ultra-low power consumption, massive number of connected devices, and longer range. As 2G technologies started being outdated and overshadowed by LTE, service providers started re-farming their 2G technologies and making them available for LTE use. Therefore, the fact that NB-IoT is actually narrowband, with a system bandwidth of 180 KHz, was useful as it allowed much spectrum flexibility.

Compared to LTE, NB-IoT achieves its reduced device complexity, power consumption, and cost through getting rid of some of the complex LTE features and replacing them with features requiring less processing power. Such changes towards less power-hungry procedures include giving up antenna diversity, MIMO, full-duplex transmissions, and using simpler channel coding schemes.