Two technologies you are going to hear a lot about this month are CBRS and LAA, sometimes branded as Gigabit LTE. A recent announcement showcased Gigabit speeds purely on CBRS alone. For the medium term, we consider what the potential to combine licenced, CBRS and LAA spectrum are likely to be.
Squeezing the most out of CBRS
As we explained in a recent article on upcoming LTE technologies, CBRS is standard TD-LTE in the 3.5GHz band (Band 48). It’s different because anyone can potentially use these frequencies, not just licenced network operators, yet it is fully standardised LTE over the radio link. The actual frequency and RF power allocation for each small cell is co-ordinated by central servers, such as Federated Wireless.
Qualcomm, Ericsson, Verizon and Federated Wireless announced last week that they have successfully demonstrated aggregating CBRS channels to achieve Gigabit data rates. The demo in Ericsson’s Plano lab in Texas combined 2x20MHz CBRS TD-LTE carriers operating at maximum 256QAM modulation rates to achieve 1Gbps throughput. Note that this is under lab conditions and that TD-LTE means it’s 1Gbps in one direction at a time, so don't be confused into thinking it's just as fast as wired Cat5 Ethernet which is full duplex. Of course real-world outdoor deployments would be slower but usable rates of several hundreds of Mbps would be very impressive.
With CBRS spectrum likely to be in strong demand, it’s worth questioning how likely it is that a single organisation will be given such a generous allocation – 40MHz out of the entire 150MHz available. Looking at the FCC rules, organisations can bid for and be assigned up to four 10MHz three year Priority Access Licences, so this will be permitted by regulators. How much you’d have to pay for the privilege will depend on the bidding in each particular area.
For General Authorised Access users, my expectation would be that 10MHz would be more typical and 20MHz would be rare. Nonetheless, you could install quite a high capacity, high performance in-building solution with 10MHz using a small cell solution.
Combining CBRS and LAA
LAA allows an existing LTE data session to additionally use spectrum in the 5GHz band (normally used by Wi-Fi) to boost downlink speeds. This is a slightly modified version of TD-LTE over the air interface, tweaked to behave nicely and co-operate with Wi-Fi in the same area. At the moment, it can’t boost uplink speeds (you’ll have to wait for eLAA for that) or operate standalone (that’s what MulteFire will do).
Combining CBRS with LAA would enable those headline Gbps peak rates even when only 10MHz CBRS spectrum has been assigned. It will be relatively short range since LAA is at 5GHz, so most likely deployed indoors. Again, this isn’t purely about speed but opens up huge amounts of extra capacity through small cell deployment.
Such a combination will require standards, small cells and handsets to support it. Technically this is quite feasible and will depend on market demand but seems quite a logical medium to long term objective.
CBRS standalone vs speed boost only
I’m hearing that some of the existing US network operators (MNOs) are thinking of using CBRS more as a supplementary “speed boost” capability using Carrier Aggregation rather than standalone. This alleviates concerns if the CBRS channels aren’t working as well as their existing licenced LTE bands for any reason, whether down to the shorter range of the RF or if installed/provided by a third party.
The idea would be that in areas where CBRS was deployed, your network operator would have access to faster speeds and much more capacity. Heavy traffic use could be offloaded to those bands but still anchored and controlled by existing licenced frequencies.
That might work OK outdoors when served from existing cellsites but could backfire if adopted for indoor use in locations which already suffer from poor indoor service. The CBRS signal would be strong while the outdoor anchor channel is weak. The result could be dropping from an excellent multi-megabit service to nothing when moving around the deeper areas of a building. Not good.
Indoor or Out
To my mind, CBRS is ideal for indoor use and will open up many opportunities for Private LTE in-building systems to be deployed. These would be concentrated through Neutral Host organisations that provide core network services, central management and interconnection with the major networks.
In the short to medium term, I think we are likely to see existing operators deploy the technology outdoors, effectively adding extra spectrum and capacity to their existing sites in those most demanding peak urban areas. As more smartphone devices become capable of using this band (typically the high end, higher capacity/more demanding users first), the offloading of traffic will be benefit both those users and others remaining in the now less congested licenced spectrum.
Standalone CBRS offers tremendous capabilities when it launches. Looking ahead, there are several potential spectrum combinations for CBRS with both licenced and unlicenced bands. Those chosen will influence where and how the technology evolves.
Expect to hear a stream of CBRS, LAA and Gigabit LTE announcements in the coming weeks. We’ll be reporting from the MWC Americas event where many of these will be demonstrated and looking to understand the timescales and wider implications.
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