What is NB-IoT(Narrowband IoT), its operation mode and features

In order to meet the requirements of IoT world, the 3GPP has designed the narrow band internet of things (NB-IoT) standard in its recent Release 13. The NB-IoT operates on the principal of LPWA(Low power consumption and wide coverage).

Uses of NB-IoT:- The potential uses of NB-IoT is communication(Machine 2 Machine) for IoT applications. Some of are as below:

1.Smart Metering(Electricity, Gas, Water)

2. Smart City

3. Security systems

4. Asset Tracking

5. Agriculture

Operating Mode for NB-IoT: NB-IoT is working on 180Khz Bandwidth(1 PRB in LTE).There are 3 operating modes which are explained below:

1. In-Band Operation:- Utilizing Resource blocks within an LTE carrier.( No Extra cost for Hardware upgradation but chances of increasing interference is high as we are using 1 PRB within the same band).

2. Guard-Band Operation:- Utilizing the unused resource blocks within an LTE carrier guard bands.(No Extra cost for hardware as well as chances of Interference is very less)

3. Standalone Operation:- Utilizing of currently used GSM frq.( Hardware upgradation required and chances of Interference is more, we have to do spectral refarming to overcome this).

Features of IoT:- There are 2 important features of NB-IoT which are listed below.

1. Wide Coverage Area:- NB-IoT offers 20dB of MCL(Maximum coupling loss) higher than LTE(up to 164dB). In order to meet this several modification have been deployed and one of the major is number of retransmissions(128 for Uplink and 2048 for Downlink). These repetitions are combined at receiver side to improve the SINR.

                                 There are 3 Coverage Enhancement(CE) mode in NB-IoT.

CE mode0:- Normal coverage with MCL~144dB and sub carrier spacing of 15khz.

CE mode1:- Robust coverage with MCL~154dB and  sub carrier spacing of 15Khz.

CE mode2:- Extreme coverage with MCL~164dB and sub carrier spacing of 3.75Khz.

The choice of the mode dependent upon channel conditions. Each mode determines the transmission parameters including the number of repetitions. Depending upon the coverage level the serving cell indicates the UE to repeat the transmission(in UL and UE informs to eNodeB in DL) using the same transmission power on each transmission. Combining the different retransmissions results in coverage enhancements.

2. Low Power consumption:- there are mainly 2 techniques used in NB-IoT to achieve this.

       Idle mode extended discontinuous reception (I-eDRX): this mode allows a discontinuous reception for maximum of 3 hours, which saves UE battery but still allows it to be reachable by the network through paging messages or downlink control channels.
Power saving mode (PSM): this power saving mode allows unconnected state for up to 13 days, where UE enters to a deep sleep. Unlike in I-eDRX, UE is unreachable while remains registered in the network.

The configurations and implementation of NB-IoT will discuss in next blogs..