CBRS Opportunities and Challenges
The demand for bandwidth and coverage of wireless communications is growing at an amazing speed. To meet this demand service providers are investing significant resources in the enhancement of their network capacity and in the introduction of new technologies, often to find that they have a new bottleneck – the radio spectrum in the air interface. The licensed spectrum is becoming more and more occupied, and this is expected to become even worse with the adoption of Internet-of-Things (IoT), which will require many new devices to be connected. The spectrum has thus become one of the most valuable resources in wireless communications, and one that can easily become a bottleneck in a service provider's ability to expand his network capacity.
Telecom regulators are looking for creative ideas to release the spectrum bottleneck, and in the U.S. the FCC has addressed this by allocating the unlicensed 3.5 GHz band for use by telecom service providers. With its new allocation the FCC named this band Citizens Broadband Radio Service (CBRS).
The CBRS band has traditionally been used for military applications, such as for U.S. Navy radars and fixed satellite earth stations, which occasionally still have a need to continue using it; but when they don't, it can be released for other users.
To ensure that its incumbent military users can continue to make use of the CBRS band whenever they need it, a 3-tier spectrum allocation model has been developed, in which every tier has priority over the lower tiers. The incumbent users of this band are Tier 1, and they are protected from attempts of Tier 2 and Tier 3 to use it. This bandwidth allocation system is managed by an entity called the Spectrum Access System (SAS).
Due to this allocation model, from the service provider's point of view the CBRS band is a shared resource, which may very often be available for use, while sometimes it may not. When it's available the service provider can benefit from the additional spectrum resource, but when it's not he may have to reduce the performance available to his subscribers or use alternative licensed bands. Switching between those two modes of operation, in which CBRS is available and is not available, must happen smoothly and reliably.
To ensure this, the service provider must perform extensive testing on the CBRS-based LTE, which among others should cover the following areas:
- Performance monitoring, with focus on the difference in performance when the CBRS band is available and when it's not.
- Handover between the CBRS band and other bands.
This comes on top of the challenges of testing any standard LTE network, which are applicable for CBRS as well.
CBRS testing is one of the areas that we at TraceSpan are addressing with our LTE-Advanced Xpert analyzer. It has a variety of capabilities for testing of CBRS, including the following:
- Monitoring performance and throughput.
- Validating carrier aggregation functionality and performance, where the primary carrier is the licensed band and at least one the secondary carriers is CBRS.
- Analysis of the handover process between CBRS and a licensed band.