Spectrum needed to grow capacity
Looking at the United States as an example, we see that the Federal Communications Commission (FCC) has gradually added spectrum allocations to the mobile services as shown in the figure below. From the original 9 MHz of spectrum allocated in 1947 to the 40 MHz added in 1979, the allocations have grown to 614 MHz with the recent H-block auction. Curve fitting this to a constant growth rate we find a best fit of 10.2% annual growth rate.
Yet even so, the traffic has been growing at a much faster rate, exceeding 200% per year for several years, and currently growing at 81% globally (according to 2013 VNI report) and 49% for the US (Data Traffic-Smartphone according to Ericssson Traffic Exploration). (CTIA Reported in May 2013 a growth rate of 69.3%.)
Spectrum is a critical component needed to address the growing demand, but adding just 10.3% more spectrum per year cannot keep up with the extraordinarily demanding growth of traffic. Along with hard-fought for improvements in spectral efficiency, and additional base stations — from small cell deployments, additional spectrum is the most readily utilized means of adding capacity to existing base station sites.
But where will additional spectrum come from?
The Obama administration has spearheaded efforts to make 500 MHz of additional spectrum available to the wireless industry, nearly doubling the spectrum available. This spectrum is being transitioned from other services through improved spectrum sharing technology means including:
- Spectrum sharing through whitespace. By allowing dynamic spectrum use where primary services are not operating, such as in idle broadcast TV channels, whitespace devices may better utilize previously underutilized spectrum.
- Traditional spectrum auctions of frequency bands that have previously been technologically difficult to use. For example, the February 2014 auction of H-block spectrum (1915 to 1920 MHz and 1995 to 2000 MHz).
- Sharing spectrum with federal users through coordination databases that protect primary users from coordinated secondary users based upon geography and time of use. For example, naval radars need to be protected near coastlines but only while the naval operations are active along the coastal areas. Coordination with the NTIA has been proceeding through the Commerce Spectrum Management Advisory Committee (CSMAC) meetings.
- Sharing spectrum among unlicensed and licensed services is also anticipated, particularly in the 5.8GHz NIU and 3.5 GHz bands.
- Incentive Auctions: Transitioning television broadcast licenses from the high frequency end of the UHF frequency band (500 to 700 MHz) to mobile use through an incentive auction in which broadcasters may be encouraged to vacate existing bands to share lower frequency blocks or to go off air entirely.
- Higher frequencies in the microwave and mm-wave regions of the spectrum promise large blocks of spectrum but at new mobile frequencies that are unproven for use in mobile applications. Some proposals such as from Samsung and the IWPC have suggested using spectrum above 6 GHz including bands from 10 GHz to 95 GHz totaling over 62 GHz of available spectrum. However, these high frequencies are as yet unproven for applicability to mobile applications where Doppler, fading penetration and link budgets are challenged by a need for much more signal processing and beam-forming, with it's associated complexities and overheads.
Editor, 5G News . org