Carrier Aggregation: Making the Whole Greater than the Sum of Its Parts

04 June 2015

Five years after the initial commercial launch of Long Term Evolution, the latest 4th generation cellular technology supporting fully mobile connectivity from devices such as smartphones and tablets, it is clear that consumer demand for faster and lower latency connectivity is far from satiated and in fact has increased. Given a taste of what next generation technologies like LTE can enable, from HD video streaming to ubiquitous and rapid access to cloud based information, consumers are now demanding even more from their cellular devices and networks.

High definition content is a prime example of this increase in demand. What started out as consumers getting used to watching high definition movies, videos and other content, has evolved into a voracious appetite for uploading user generated content not only in HD but also in 4k resolution for sharing and later consumption on larger displays such as 4k capable TVs. The initial demand for HD content consumption was hard enough to address with exponential increases in the downlink, but the resulting increase in user generated content has put a further strain on the uplink as well.

Compounding this general increase in traffic in both directions, HD and 4K content also come with larger file sizes which require higher bandwidths and lower latencies to ensure that the consumer is not waiting for an inordinate amount of time for their photos or video to finish uploading or downloading. Given LTE’s initial ability to deliver these larger file sizes, not only consumers but designers of websites also have started to increase the resolution of embedded images and videos in their websites further adding fuel to the fire.

This is only one such example in a world where consumers now live their digital lives in high definition. expecting to share and consume information and content instantaneously or as close to it as the industry can deliver. Such use case dynamics are creating demand that is rapidly outpacing basic LTE capabilities and pulling the industry to continue to provide enabling technologies that meet the requirements of the consumer’s high definition life.

This is where carrier aggregation comes in and to help shed some light on this next stage of LTE evolution, IHS is delivering a series of Carrier Aggregation Insights to further explore this latest evolution, what it means to mobile network operators (MNOs), device OEMs and ultimately the consumer. This article is the first of this series.

Critical Areas of Exploration

Over the course of the series, IHS will explore the following:

  • What is carrier aggregation, how does it help MNOs and OEMs and how can it best be communicated to consumers who might not necessarily understand the technical complexities of why they need it?
  • Where is carrier aggregation currently in the adoption cycle? Is it real or still a theoretical concept?
  • What’s next for carrier aggregation and its role in enabling a high definition life?

Carrier Aggregation: What Is It?

The primary benefits of LTE when compared to 3rd generation networks are increased bandwidth, decreased latency and improved spectrum efficiency. However, these benefits, when compared to HSPA+ are not fully realized until channel bandwidths of greater than 10MHz are used. At 10MHz channel widths, LTE performance, while still better than HSPA+, are arguably, only marginally so. As such, in order to optimize consumer experience as well as the operator’s return on investment for building out an LTE network, there is a demand for finding ways of using 15, 20, 40 and even 60 MHz and above channels.

Unfortunately, due to existing usage of licensed spectrum, most countries’ spectrum plans do not allow for contiguous 20MHz channels. Additionally, even if they did, the technology itself has a maximum single channel bandwidth of 20MHz. Consequently, to get to 40 or 60 MHz that certain applications or network designs require, carrier aggregation is a must. This is where carrier aggregation, introduced in Release 10 of the LTE standard, comes in.

In its simplest form, carrier aggregation allows an enabled device to combine two, smaller, non-contiguous channels into a larger channel yielding the same benefits as a contiguous channel of the same larger size would provide. However, as in most things about LTE, implementing carrier aggregation will not be limited to this most basic form. Designs enabling carrier aggregation will need to take into account many different types of channel combinations including but not limited to:

  • Up to five aggregated channels of the same or varying bandwidths
  • Non-contiguous channels in the same frequency band (i.e. all within the 700 MHz band)
  • Contiguous channels in the same frequency band – usually required when attempting to reach the larger 40 and 60 MHz combinations but could be utilized with smaller bandwidths as well.
  • Channels from two different frequency bands but both being on the high end of the spectrum (i.e. one channel from the 1.9GHz band and another from the 2.1GHz band)

The latter two cases are both a type of interband carrier aggregation, but it is worth noting them separately as the further apart the aggregated channels are, the more complex the modem design will need to be in order to address the different physical characteristics of those RF signals.

The number of channels aggregated and their individual bandwidths result in different theoretical maximum speeds which then dictate which LTE user equipment (UE) category is supported. The table below provides some examples of carrier aggregation combinations and which LTE UE category they enable.

Once combined, the aggregated channels typically yield performance that is greater than having the same number of channels acting individually especially for bursty traffic data. Among other reasons, this is due to the aggregated channels being able to share signaling and control overhead as well as signal gains associated with the different RF characteristics, environment and propagation paths of the aggregated channels.

One of the challenges with carrier aggregation is that in order to implement it correctly, a strong foundation in basic LTE functionality and subsequent expertise as each level of higher category is implemented, building on the previous categories is required. This type of capability, building on previous categories, can only be developed through many years of iterative engineering and design. Fortunately, consumers are now starting to see commercially available solutions from a select few suppliers of chipsets, devices and infrastructure equipment as LTE continues to mature and deliver on its promise of Long Term Evolution.

Carrier Aggregation: The Ultimate Win-Win for MNOs and Consumers

As a result of the rapid growth of consumer demand both in the uplink and the downlink, the scarcity of spectrum resources as well as competitive price pressures limiting revenue growth, mobile network operators or MNOs are desperate to find more efficient use of the spectrum that they already own to deliver higher data rates and lower latencies without a similar increase in their cost basis—or at the very least if they do need to invest in new spectrum to implement carrier aggregation, that the return on investment of such a capital expenditure would be more than recouped in terms of network capacity and performance gains, competitiveness, and user experience.

Due to inherent technical improvements ranging from modulation schemes to error correction and signaling and coding efficiencies, LTE and each subsequent higher category of carrier aggregation delivers increased spectral efficiency both in the uplink and the downlink. Consequently, the higher the level of carrier aggregation that an MNO implements, the lower their cost per bit becomes for delivering the same or even higher performance to the end consumer.

For consumers, the higher throughputs and lower latencies enabled by each higher level of carrier aggregation not only makes certain real time applications possible, but it makes it usable as well. For example, 4k video streaming might be possible with earlier generations. However, if the consumer has to sit and wait multiple minutes for enough content to allow for local storage to buffer enough data to start playing the video and then after five or 10 minutes have to wait again for more buffering the occur, the consumer experience degrades to a point such that the service becomes unusable. Additionally, given that mobile device power is most used during transmission and reception of data, the increased on cycle duty time of the modem to enable even this poor user experience greatly diminishes battery life further degrading overall experience. In contrast, carrier aggregation reduces both buffering time as well as the amount of time the modem in the phone is actually transmitting and receiving.

This example of improved user experience on multiple fronts consequently leads to lower churn (measure of how many subscribers an MNO loses to the competition) for MNOs and ultimately increases the amount of data a consumer uses and, consequently, driving them to higher data tariff levels.

It must be noted that this is just one example of such gains by both the MNOs and the end consumers. With consumers’ increasing use of other services and applications that require real time or near real time communications such as cloud-based services, carrier aggregation becomes even more imperative turning it from a nice to have into a need.

OEMs: Ignore CA at Your Peril

Due to increased component content, especially on the radio side of the modem design, as well as the fact that not many chipset suppliers have carrier aggregation commercially available, it is commonly believed that carrier aggregation is a feature only available on high end devices and some handful of mid-tier handsets that have traded off functionality in other areas. However, over the last 12-18 months, solutions have been introduced in the market from chipset suppliers enabling carrier aggregation in various category capabilities designed specifically for all tiers of handsets from high all the way to low tier and everything in between.

As such, not only is it now possible for even small regional OEMs to start planning and implementing carrier aggregation in their roadmaps, but IHS expects that, without such a roadmap, OEMs across the board from those targeting high innovation segments to low cost, short life cycle devices will find themselves at a competitive disadvantage in the next design cycle if they are not already feeling the pressure. OEMs who market their devices through MNOs are already seeing this through requests for proposals (RFPs) coming from MNOs due to the efficiencies and improved performance mentioned above. As these MNOs start to market the improved performance to their subscribers through non-technical marketing of new services which require carrier aggregation, even those OEMs which primarily use direct to consumer channels will also start to feel the pressure. Given the highly competitive and short time to market requirements of those latter channels, getting an early start in including carrier aggregation in current roadmaps will yield dividends in the next couple of design cycles.

Additionally, as those same OEMs upgrade other features of their offering in order to compete such as more sensors, higher resolution cameras, larger displays, etc., it is imperative that the wide area networking connectivity enabled by LTE also keeps pace in order to ensure that user experience does not degrade when generating and consuming content or utilizing applications that require real time connectivity to the cloud—a trend that continues to grow with the latest generation of applications and services being offered today and in the future.

Theory vs Reality

It is clear that carrier aggregation is a critical evolutionary step in the world of high-definition lifestyles required by today’s consumer. But how real is it? In the reality of cellular devices, there is often a chicken or egg dynamic that exists when it comes to advanced capabilities. Even if the devices can support the capability, will the network be able to do so? On the other hand, if the MNOs invest time and money in building out the infrastructure to support the capability, will there be devices that will be able to take advantage of the capability and ultimately allow the MNOs to monetize their investment?

In the next issue of LTE Carrier Aggregation Insights, IHS will explore where we are as an industry in terms of CAs commercial availability and perhaps answer the question, is your strategy in on the ground floor or are you already well behind the curve?

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