Hacker News Reader

> 5G uses the same old frequencies as 2/3/4G for the bulk of the traffic, it only uses the >1Ghz frequencies for microcells in malls and other dense areas where appropriate.

That's simply not true. 5G cannot achieve its advanced speeds without higher frequencies, which cannot be deployed without greater density of base stations. Higher frequencies beget faster signal falloff and greater susceptibility to obstruction. "5G needs spectrum across low, mid and high spectrum ranges to deliver widespread coverage and support all use cases. All three have important roles to play." [1]

Microcells use high-band, not mid-band, spectrum. High-band may not be useful outside of dense areas because of its reduced range, but it is essential to 5G and the FCC is releasing about 5GHz of spectrum for this purpose. Mid-band (1GHz-6GHz) is the bread and butter of 5G, and the FCC has pushed to open this part of the spectrum as much as possible for 5G to work as intended. This part of the spectrum is the most versatile, but it is in short supply [2].

Part of the challenge of 5G involves more frequent handoffs between base stations versus past generations of mobile phone radio. Similarly, 5G devices use various mitigation techniques to deal with interference from nearby base stations. For both of these reasons, there is a substantial amount of interaction between a single handset and nearby base stations that may not be presently serving it.

[1] https://www.gsma.com/spectrum/wp-content/uploads/2020/03/5G-...

[2] https://docs.fcc.gov/public/attachments/DOC-363622A1.pdf

View on HN

The spectral efficiency of Massive MIMO grows monotonically with the number of antennas [28]. Thus, we can expect a future where hundreds or thousands of antennas are used to serve a set of users. There are, however, practical limits to how many antennas can be deployed at conventional towers and rooftop locations, for example, determined by the array dimensions allowed by the site owner, the weight, and the wind load. [...] Nevertheless, the spatial multiplexing capability of these two dimensional planar arrays in our three-dimensional world is far from what has been demonstrated in the academic literature, where large one-dimensional arrays are often considered in a two-dimensional world. In many practical deployment scenarios, the user channels are mainly separable in the horizontal domain [35] since the variations in elevation angle between different users and scattering objects are relatively small. [...] However, to deploy more than a few hundred antennas per site and to obtain a truly massive spatial resolution in the horizontal domain, we need new antenna deployment strategies. Instead of gathering all the antennas in a single box, which will be visible and heavy, the antennas can be distributed over a substantially larger area and made invisible by integrating them into existing construction elements.