Potential Spectrum Considerations For Wireless Networks Beyond 5G

According to the Ericsson Mobility Report 2017, monthly data traffic per smartphone continues to increase in all regions, despite large differences in data consumption patterns between networks, markets and subscriber segments. At present Asia Pacific has the traffic usage of about 3GB per month per active smartphone and is expected to reach near to 10 GB per month per active smartphone by 2022. With the substantial growth of demand for mobile data traffic, the trade-off between capacity requirement and spectrum shortage becomes increasingly prominent. Current mobile communication services use carrier frequencies ranging from 700MHz to 2.6GHz for supporting mobile data traffic demand. The several different communication systems however, cover this spectrum with disjoint frequency bands leaving narrow pieces of unused frequencies scattered in the 2GHz range.

"The bottleneck of wireless bandwidth becomes a key problem of the next generation 5G wireless networks."

To support the requirements for wide contiguous bandwidths 5G cellular systems are likely to operate in or around the millimeter wave (mmWave) frequency band of 30-300GHz, where vast spectrum currently exists in light use. Millimeter wave frequencies have much smaller wavelengths, ranging from 1mm to 10mm, almost comparable to the size of a human finger nail, whereas 4G frequencies have wavelengths that are tens of centimeters. Smaller wavelengths at these frequencies have often been thought to result in higher attenuation (due to the precipitation and oxygen absorption) through air, than that observed at today’s cellular bands. With increasing carrier frequency the propagation conditions become more demanding than at the lower frequencies traditionally used for wireless services.

 In particular both the path loss and diffraction loss become more severe, atmospheric effects must be accounted for, and the use of directional antennas becomes necessary. The result will be comparatively short links which to some degree basically rely on line-of-sight paths. In fact, this can be considered an advantage rather than a drawback, as in dense urban areas cell sizes are becoming much smaller anyway (e.g. of the order of hundreds of meters) in order to provide high capacity. Furthermore, advances in technology development such as 3D beam-forming and massive MIMO techniques will realize their full potential when taking advantage of the short wavelengths, which come with high frequency bands. Higher carrier frequencies can provide wide contiguous bandwidth for very high overall system capacity, as the effective user range becomes relatively short, enabling very efficient frequency reuse over a given geography.

"The potential mmWave Spectrum bands of 28GHz and 38GHz are considered feasible for use in 5G Wireless Networks, since the propagation loss is considerably less in 28GHz and 38GHz regime compared to other mmWave frequencies."

References - Ericsson Mobility Report June 2017, 5G Vision Brochure by 5G Infrastructure PPP and 5G mmWave Research Papers published by NYU WIRELESS.