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NB-IoT and band 70 \u2013 What is your view?<\/h1>\n\n\n\n

RF engineers already know that signal propagation characteristics vary according to frequency. In simple terms, signals carried at lower frequencies travel further.<\/p>\n\n\n\n

\"wavelength
Radio wave and wavelength – image credit Harald Naumann<\/strong><\/figcaption><\/figure>\n\n\n\n

Since wavelength equals the speed of light divided by the period of the carrier signal, we can see that low frequency signals have a long wavelength. Long wavelength, low frequency radio waves are able to diffract over obstacles such as hills and valleys where a line of sight is not possible. They also follow the curvature of the earth leading to extended range. We will see on another blog how the earth\u2019s curvature is related to antenna height and maximum range.<\/p>\n\n\n\n

This type of signal propagation is called \u201cground wave\u201d. Attenuation of signal strength over distance by absorption into the ground is lower for long wavelength radio waves than it is for high frequency, short wave transmissions. This is why the LPWAN industry is fortunate to have access to sub-1 GHz frequency spectrum \u2013 so called ISM (Industrial, Scientific and Medical) bands. In the EU these are usually centred around 868 MHz \u2013 around 915 MHz in the US. However, intelligent protocols such as Weightless-P are also able to use 169 MHz and 470MHz with a 12.5 kHz channel bandwidth.<\/p>\n\n\n\n

Every developer wants the best coverage and range so you\u2019d imagine that the 3GPP community would not be looking to use higher<\/em> frequencies when we have already seen how this compromises signal propagation. Band 70 uses spectrum in the 1695 \u2013 1710 MHz range for uplink and 1995 \u2013 2020 MHz for downlink. The higher frequency compromises range and the large range of frequencies from 1695 \u2013 2020 MHz makes antenna design significantly more complex. In short, why use band 70 in NB-IoT if band 8 and 20 offer so much more range?<\/p>\n\n\n\n

Read more: 3GPP Approves NB-IoT Support for Band 70:<\/a><\/em><\/p>\n\n\n\n

The Egli model is a terrain-based radio propagation model. Based on real world measurements in the first part of the 20th<\/sup> century It tells us that the Egli free space loss in point to point free space (including a consideration to the curvature of the earth) is given by the formula 10log10 (4 x Pi x distance x 7 \/ c)2<\/sup><\/strong>.<\/p>\n\n\n\n

We can use the Egli model to look at the differences between the nBioT frequency bands under discussion.  We need to set parameters in the Egli model and we have used the following:<\/p>\n\n\n\n