Some Underlying Physics of 5G Network

[personal notes]

1. Friis Transmission Law
  ${\frac {P_{r}}{P_{t}}}=D_{t}D_{r}\left({\frac {\lambda }{4\pi d}}\right)^{2}$
2. frequency is inversely proportional to wavelength
  $\displaystyle v=f\lambda$
3. in the case of electromagnetic radiation, v is approximate 3×10⁸ m/s

In ITU standards,

Extremely high frequency (EHF) = 30 to 300 GHz in frequency = 10 to 1 mm in wavelength, so called millimeter-wave (mmW)

Ultra high frequency (UHF) = 300 MHz to 3 GHz in frequency = 1 to 0.1 m in wavelength

UHF is where our current mobile networks live on, with 4G mostly on 700 MHz, 1700-2100 MHz, 1900MHz and 2500-2700 MHz across the globe.

Under the Friis Transmission Law, higher frequency has much higher loss (attenuation) in free-space. For mmW, additional transmission losses occur when traveling through the atmosphere are absorbed by molecules of oxygen, water vapor and other gaseous atmospheric constituents.

Important absorption peaks occur at 24 GHz (for water vapor) and 60 GHz (for oxygen).

mmW attenuation | Source: T.S. Rappaport, NYU Wireless

As range of 5G signals are limited, small cells deployment, collaboration and integration will be essential. Current experiments found a 200-meter range doable.

Signal Outage (200 m Cell) in NYC using Adaptive Single Beam Antennas | Source: T.S. Rappaport, NYC Wireless

Appendix – Frequency Allocation