Test solution for narrowband Internet of Things (NB-IOT)

introduction

With the development of society, people's demand for the Internet of Things is getting stronger and stronger; however, the 2G modules that are currently in use are no longer able to meet new application requirements. In order to solve this problem, a very important part of 3GPP Release 13 is to define a new wireless air interface, which is optimized according to the characteristics of machine-to-machine communication, thus defining a new cellular-based interface. The IoT system of communication is called Narrow Band-Internet Of Things (NB-IOT).

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This article will do a brief analysis of NB-IOT technology and give the corresponding factory test solution.

Introduction to NB-IOT

For IoT applications, a large category of requirements is applied to a variety of remote applications such as electricity meters, water meters, gas meters, etc. The typical characteristics of such devices are that their positions are basically stationary and the amount of data to be transmitted. It is small and not sensitive to delay, but the number of such watches is huge and widely distributed. In the Release 13 version of 3GPP, the NB-IOT is defined to address the needs of this type of application scenario. NB-IOT greatly simplifies system complexity and energy consumption of IoT devices while ensuring communication between objects and objects, thereby greatly reducing the cost of IoT devices; it not only eliminates support for Handover, Moreover, the terminal equipment can only work in the half-duplex state. With these simplifications, the new standard allows the cost of NB-IOT to be controlled below $5, while batteries can be used for up to 10 years.    

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At the system level, NB-IOT can work not only at the same time as the LTE network, but also independently to meet the special needs of certain IoT applications. In order to meet the demand for the number of IoT terminals in a specific application, in a NB-IOT network, each cell can support up to 50,000 devices.

NB-IOT system operating mode

NB-IOT can use the following three modes of operation:
1. Independent networking operation:
The NB-IOT can be independently networked and has a bandwidth of 180 kHz. It can be networked only with a very narrow spectrum of resources. Moreover, its bandwidth is less than 200 kHz of GSM, and it can also be deployed in a channel of the GSM network, which is very flexible.

2. In-band networking operation:
NB-IOT is highly compatible with LTE networks and can be deployed in LTE networks. In addition to 1.4MHz LTE networks, LTE networks with other bandwidths can be embedded in NB-IOT networks.

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3. Border network operation:

Guard-Band is available on both sides of the bandwidth of the LTE network. The NB-IOT can be deployed here to meet the NB-IOT requirements and improve spectrum utilization.

Figure 1 NB-IOT network mode

NB-IOT physical layer introduction

NB-IOT is based on cellular communication. Based on the LTE network, the application scenarios for the Internet of Things are improved and simplified on the network and terminal devices.

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In the access mode, the same technology as LTE is adopted, that is, the downlink adopts OFDMA uplink adopts SCDMA technology, and its subcarrier spacing and frame structure are also the same as LTE. For the narrowband system of NB-IOT, the bandwidth is limited to 1 PRB or 180 kHz, and its subcarrier spacing is increased by 3.75 kHz in addition to 15 kHz. The corresponding number of subcarriers is 12 and 48 respectively. In practice, NB-IOT devices can use only a single frequency point or multiple frequency points simultaneously.

In the modulation mode, NB-IOT downlink adopts QPSP modulation mode; while uplink uses PI/2 BPSK or PI/4 QPSK in single frequency, and when using multi-frequency, QPSK modulation is adopted. The maximum rate supported by it is 28Kbit/s downstream and 64Kbit/s.

Considering the simplification of system complexity and the need for low power consumption, NB-IOT only supports half-duplex communication mode, that is, transmission and reception adopts time division multiplexing, which is very similar to GSM system in this point.

NB-IOT RF test
The requirements for NB-IOT testing are also defined in 3GPP's Physical Layer Test Specification 56.521, including emission testing and receiver testing. Transmitter testing mainly includes power, modulation, spectrum and other indicators; receiver testing focuses on sensitivity testing.

Figure 2 NB-IOT transmitter test

Figure 3 NB-IOT adjacent channel leakage ratio test

LitePoint provides a complete IoT test solution, in which IQxstream-M/IQxstream fully supports all test projects of NB-IOT. One instrument is equipped with up to four RF modules, each module is equipped with 8 RF ports, which is especially suitable for massive NB-IOT. Production testing of equipment.

Conclusion

With the advancement of technology, NB-IOT will gradually enter our lives, not only can serve a variety of life watches, but also begin to apply to the increasingly popular shared bicycle industry. I believe that in the near future, NB-IOT technology will serve a very important member of the Internet of Things to serve the work and life of mankind.