Like every wireless service, Wireless Internet Service Providers (WISPs) fight for every bit of unlicensed spectrum they can get, as subscriber rolls increase along with the bandwidth needed to serve them. Fortunately, they have recently gained 250 MHz of additional spectrum, 150 MHz at 3.5 GHz in the U.S. and 100 MHz at 5 GHz Canada, without which WISPs would be less able to increase capacity and data rates. Collectively, it represents more than two-thirds of the spectrum a major carrier uses for all its 3G and 4G networks.
Although millions of people in underserved (or unserved) rural areas rely on WISPs as their means of obtaining broadband and voices services, hardly anyone else even knows they exist. However, WISPs provide the only means for many households to obtain respectable broadband and voice services (Figure 1). There are several thousand in the U.S. alone serving about 4 million people and in addition to their primary market, provide wireless links for other purposes such as SCADA and IoT connectivity. They range from very small companies with a few hundred subscribers to several large ones with several hundred thousand, such as PEAK Internet, King Street Wireless, and Rise Broadband.
WISPs are classified as Fixed Wireless Access (FWA) providers as they use line-of-light point-to-multipoint microwave links between their towers, and millimeter-wave links for transmitting and receiving signals to the customer. WISPs use either Wi-Fii, a proprietary protocol, or most recently LTE in unlicensed spectrum at 900 MHz, along with 2.4 and 5 GHz between the tower and subscriber (Figure 2) and higher millimeter-wave frequencies for the tower-to-tower links. The subscriber typically has a transceiver and directional antenna mounted outdoors bore-sighted on the service provider’s tower, after which an Ethernet cable connects to a modem or router. Download speeds are increasing and today top out at about 30 Mb/s.
Three rulings (two in the U.S. and one in Canada), pave the way for the WISP industry to expand its services. In March 2014, the FCC changed the rules governing the 5150 and 5250 MHz Unlicensed National Information Infrastructure (U-NII-1) band. The ruling focused on improving IEEE 802.11ac Wi-Fi performance in the hope, among other goals, of increasing capacity in more places, and achieving speeds up to 1 Gb/s. As many WISPs use Wi-Fi as their delivery technology to the end-user, the ruling offers some potential benefits.
The most appealing aspect of the rule changes for WISPs is an increase in the maximum Effective Isotropic Radiated Power (EIRP) to 1 W for mobile devices and 4 W for access points. As higher radiated power at these frequencies increases maximum range and provides better coverage, WISPs can increase performance and capacity. The new rules also eliminated the indoor-only restriction and device manufacturers are required to use secure software to prevent modifications that could cause interference.
The second and more recent FCC ruling was finalized in April 2015, and oddly called the Citizen Broadband Radio Service (CBRS), which is one of the most interesting spectrum opportunities in years. Although complex in how it manages operators and their devices, if offers 150 MHz of shared spectrum between 3550 and 3700 MHz with few limitations on what types of services they deploy, as long a digital transmission scheme is used. LTE is sure to be the overwhelming choice.
CBRS accomplishes spectrum sharing with a three-tiered hierarchy (Figure 3). The highest tier includes existing services (incumbents) that are principally Navy coastal radars and some fixed satellite systems that must be interference-protected from the two lower-tier operators. The next level down is the Priority Access License (PAL) that will offer each operator 10-MHz channel in a single, small “tract” defined by the census bureau for statistical purposes. Licenses will be acquired through FCC auction within 100 MHz (3550 to 3650 MHz) of the total available bandwidth. PAL licensees are protected from lowest-tier General Authorized Access (GAA) users, for whom access is free but receive no protection. In practice, a GAA user will be able to access? operators in 80 MHz of the total in each tract.
One of the FCC’s primary goals in establishing CBRS was to make spectrum available to more types of services at lower cost, which it predicts will be achievable because the coverage area for each PAL license is small so the auction price for each one should be low. CBRS has been dubbed the “innovation band” because it is “application agnostic,” allowing new services to be created by organizations without the resources of wireless carriers. Perhaps the most interesting of these applications is the private LTE network, which was previously too expensive for organizations to build and deploy. This has appeal for companies seeking a secure network without carrier participation, for example.
WISPs typically use unlicensed spectrum but often licensed spectrum as well for backhaul and other purposes, so the fact that CBRS offers may be appealing. The propagation characteristics at 3500 MHz are also somewhat better suited for line-of-sight communications than at 5 GHz, so capacity and coverage should be less expensive to achieve. In addition, as the PAL tracts are small, WISPs can choose to acquire licenses in small, specific areas rather than much larger (and far more expenses ones.
The only caveat is that CBRS requires an elaborate system to ensure interference protection for the incumbents and PAL operators called a Spectrum Access System (SAS). This cloud-based, database-type system manages the shared frequencies, their users, and their devices performs a long list of tasks. This includes assigning channels for devices, determining their maximum power at every location and ensuring it is not exceeded, registering, and authenticating them, communicating with them for various purposes, resolving conflicts, and addressing reports of interference and requests for additional interference protection. To ensure the incumbent radar systems are protected, sensors will be installed near each one that sense the presence of interference and alert the SAS, which in turn commands the potential interferer to change channels.
A similar approach has been used before with less-than-spectacular results, and is one of the reasons why the sharing of TV white space in the U. S. has become something of a fiasco. Although the CBRS SAS is a more sophisticated system, how well it works this time remains to be seen. This is also the case with any appeal to WISPs that may find such a complex approach too cumbersome.
New Benefits for Canadian WISPs
The last spectrum opportunity is directly targeted at the WISP industry, as it specifically addresses fixed point-to-multipoint and point-to-point services. The opportunity was created in May when Canada’s Innovation, Science, and Economic Development (ISED) department authorized the use of higher power and outdoor RLAN devices (HPODs) indoors and outdoors between 5150 and 5250 MHz. The ruling provides 100 MHz of additional spectrum for WISPs, doubling their current allocations in the 5 GHz band.
The ISED imposes no complex interference management scheme like the one to be employed in CBRS, instead placing the onus on operators to ensure they cause no interference to any other services. Equipment deployed in the band must incorporate contention-based protocols to manage the interference between HPOD devices and regulators will only intercede when complaints are received. All operators must obtain a 1-year renewable license and must fall into the category of “radio communications service providers” and “radio communication users.”
The overall goals are to alleviate congestion in the 2400 and 5800 MHz bands that are currently saturated and to take a step toward in achieving higher broadband downlink and uplink data rates for all Canadians. Each license is issued on a nationwide basis with no licensing fees. There is no limit on the number of licensees in any area, nor is there any type of tiered priority access for specific types of services.
The allocation will also harmonize with the rules for this band in the U.S. Maximum RF power to the antenna is 1 W for point-to-point systems whose antenna gain must be 23 dBi or less, resulting in an EIRP of 4 W. Indoor and outdoor systems have the same power limit, but their antenna gain can be only 6 dB. Operators must also limit radiation to 125 mW EIRP in the vertical plane to avoid interfering with satellites and provide a 25-km exclusion zone around receiving earth stations.