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Written by Gregor Tomic | November 21, 2018

NB-IoT: How to find NB-IoT carriers in the spectrum (part 6)

Identifying NB-IoT carriers with a pure RF power scan is very difficult and sometimes impossible. After describing the benefits of NB-IoT MIB/SIB demodulation in the previous NB-IoT post, this post discusses the challenges in identifying NB-IoT carriers in the spectrum and offers solutions. The extended Automatic Channel Detection (ACD) feature finds and identifies NB-IoT carriers automatically and display the findings in R&S®ROMES4.

NB IoT find carriers in the spectrum

NB-IoT is a very flexible technology in terms of spectrum implementation. It only requires a narrowband carrier (180 kHz only), preferably implemented for 700/800/900 MHz spectrum to boost sufficient indoor signal penetration.

NB-IoT implementation modes

The spectrum is heavily occupied by mobile broadband services, and NB-IoT requires different operation modes. To overcome this problem, NB-IoT is flexible in terms of implementation and supports three different operation modes: in-band, guard-band and stand-alone. This offers spectrum refarming possibilities and the “seamless implementation” in available LTE carriers.

The in-band operation uses one physical resource block in an existing LTE carrier, requiring no dedicated NB-IoT spectrum outside the LTE carrier. Another alternative is placing the NB-IoT carrier in the guard-band of an existing LTE carrier.

An example of spectrum refarming is exchanging GSM carriers with NB-IoT carriers, using the same bandwidth as one GSM channel. Like GSM carriers, the NB-IoT carriers are implemented in the spectrum as stand-alone carriers (stand-alone mode).

NB-IoT operation modes
Figure 1: NB-IoT operation modes
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The idea of IoT is to connect the world. This entails its massive presence, and the ability to connect all sorts of devices and to create new use cases, from improved efficiency in energy management and smart cities to automated production facilities.

NB-IoT carriers: testing challenges

In a hyperconnected world, operators are facing new challenges to maintain the needed service KPIs. It is extremely important to ensure NB-IoT network quality through constant measurements. Since spectrum is a very scarce and expensive resource, operators often decide to implement NB-IoT in-band followed by guard-band approaches.

In the in-band mode, the NB-IoT carrier is buried somewhere in the LTE carrier. Although its power is sometimes boosted to achieve an extended coverage (usually by 6 or 9 dB), the identification of an in-band NB-IoT carrier is a tough task due to the mutual impact on SINR (LTE to NB-IoT and vice versa). The possibility of placing such a narrowband signal in an LTE carrier is much higher compared to guard-band.

LTE carrier spectrum view
Figure 2: LTE carrier spectrum view with NB-IoT carrier in in-band operation
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In a guard-band implementation, it is less complex to find the carrier: the LTE carrier’s edge frequency ranges restrict the possible positions for placing an NB-IoT carrier. The stand-alone operation is trickier since there is no orientation, in terms of LTE carrier, for an initial scanner search. The possibilities of placing the NB-IoT carrier in stand-alone mode are much wider.

IoT devices are also used to test the network and service performance, as discussed in the post “NB-IoT: How to test quality of service in NB-IoT networks”. Due to the nature of IoT devices being cheap and having long battery standby times, they require low energy consumption. This means that the implemented algorithms should consume minimal power. Consequently, it takes time for IoT devices to find the proper NB-IoT channel and attach to the network.

Wouldn’t it be more convenient to find NB-IoT carriers automatically with a scanner?

For years, solutions from Rohde & Schwarz mobile network testing (MNT) have supported the automatic identification of signals from all mobile communications technologies in all used frequency bands. The Automatic Channel Detection (ACD) feature quickly generates an overview of all radio signals that are transmitting at a certain position in all relevant frequency bands.

As of the latest software release in October 2018, the R&S®ROMES4 drive test software, in combination with measurements and the unique algorithms of the R&S®TSMx scanner family, supports the automatic identification of NB-IoT channels. The ACD setup for NB-IoT scans the selected (configurable) bands and searches for unique primary and secondary synchronization signals of NB-IoT; these are different from LTE.

ACD automatically displays:

  • the technology being transmitted
  • channel bandwidth
  • EARFCN
  • the operator’s name and logo

Due to the ability to decode MIB/SIB messages transmitted in the air interface, the ACD setup for NB-IoT decodes the channels’ mobile country (MCC) and mobile network codes (MNC) and identifies the NB-IoT operator.

ACD view in R&S®ROMES4 with detected channels
Figure 3: ACD view in R&S®ROMES4 with detected channels, including the in-band NB-IoT channel
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Why is this beneficial? Including NB-IoT carriers in ACD improves the efficiency across various tasks:

  • Easily find NB-IoT carriers in the spectrum; their exact position is often unknown, even to an operator
  • Fast scanner setup: don´t waste time setting up the exact channel to be measured – let the measurement setup find the channels
  • Easily identify what is being transmitted and never miss an on-air channel in any frequency band used (your own or other)
  • Interference evaluation: easily identify potential interferers (e.g. cross-border interference evaluation or in any other area)
  • Competitor network analysis: ACD identifies all air signals and is able to decode the MCC and MNC of each detected channel

Figure 3 represents the ACD view in R&S®ROMES4 with an NB-IoT carrier. The view is separated by different bands; the spectrum is visible on the background layer while the decoded carrier, including additionally decoded information, is visible on the layer above.

R&S®ROMES4, combined with R&S®TSMx scanner measurements, provides all the information about the spectrum and on-air transmitted channels, whether in your spectrum or your competitor´s. The addition of NB-IoT to the ACD feature enables the fast and automatic identification of NB-IoT channels in all three modes while boosting your operating efficiency.

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