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in Hold the Key to Optimal 4G LTE Delivery

Smartphone chipset suppliers must assemble the right ingredients in a crowded, lightning-fast game

Fast website downloads, smooth video playback, However, support for basic LTE functionality isn’t compelling social networking, unlimited roaming, enough. To enable a truly compelling user experience, long battery life—these are some of the key elements chipset providers must include modems that can that define the quality of consumers’ experiences handle the advanced aspects of LTE. when using a . Critical to meeting user expectations in the phones of today and tomorrow is “Basic” support for LTE is not that basic the 4G next-generation known Before assessing more advanced capabilities such as as Long Term Evolution (LTE). Because of this, carrier aggregation and coexistence optimization, the it’s essential for the suppliers of the chipsets that challenges that chip suppliers face in supporting LTE at constitute the heart of smartphones to deliver products its most basic functionality must first be evaluated— that support LTE’s capabilities. namely, mobile data connectivity on one contiguous channel.

IHS.com/telecominnovation Standards certification and interoperability testing At their core, these questions really concern two require the to perform specific steps in order to modem design elements: the protocol stack and acquire the base station, authenticate, transmit/receive peripheral algorithms; and the -frequency data, perform handovers from one site to the next, (RF) architecture. Modems in and manage power levels—all done within network parameters. But an optimized modem goes beyond The protocol stack and the peripheral algorithms are these “must-have” capabilities and also addresses essentially the “programs” that run on the baseband important questions such as: of the modem chipset. These programs in turn dictate Smartphones • How quickly can the modem perform how and when the modem should communicate with these steps? the network as defined by the supported air interface • How well does the modem operate in technology—in this case, LTE—to perform functions low--strength environments? like base-station acquisition, authentication, radio- Hold the Key • How efficiently can the modem deliver optimum resource requests and traffic-channel acquisition. performance while maintaining battery life? to Optimal 4G Teardown image of a Samsung Galaxy smartphone, showing modem components for 4G LTE LTE Delivery

IHS.com/telecominnovation When designed properly, the protocol stack allows not can help deliver improved consumer experience at a only for the rapid processing of control elements— fraction of battery life. called Layer 2 and 3 messages—that enable the aforementioned functions, but also mitigates the But to accomplish this, the RF architecture must effects that poor signaling algorithms could impose on minimize any self-inflicted noise and interference the consumer’s experience of the data call. generated by its own components, while also dealing with—or otherwise offsetting—the effects of external Smooth handoff noise and interference inherently present in a lossy For instance, one element that all LTE modems are such as air. System-level design required to support is handing over calls between and the inclusion of capabilities such as antenna tuning the LTE network and a legacy 3G network. A modem and envelope tracking also help in achieving this ideal. might demonstrate it could do this in the lab or in ideal conditions that would allow the device to pass a A brief history of LTE certification test. In the field, however, where the LTE The first commercially available LTE devices that signal in cell-boundary conditions is potentially just as generated production volumes hit the market in 2009, bad as the lower-generation 3G signal, conditions are marked by Telia Sonera’s LTE launch in Europe’s Nordic less than ideal. If the algorithm for this function is not countries. Currently the majority of LTE smartphones optimized, the modem could simply bounce back and available in the market utilize a chipset made by forth between technology modes and never establish Qualcomm, which controlled 97 percent of mobile a traffic channel, causing the consumer experience to handset LTE baseband shipments as of the first half degrade. of 2013.

Similarly, should the algorithm for requesting the Other suppliers that also have solutions are new 3G channel be called upon too late and the signal MediaTek, Samsung, , GCT , with the LTE channel is lost prior to establishing a new Nvidia and Broadcom. However, not all these modem traffic channel, the effect on the consumer experience suppliers have design wins that have ramped up to would be akin to someone disconnecting the production volumes. cable while in the middle of trying to stream the end of a championship football match on a PC—an unpleasant Advanced functionality via carrier aggregation experience, to say the least. As challenging and nuanced as the designs might be for basic modem functionality, building on them The RF front-end architecture, meanwhile, is the to include advanced LTE features adds another few section of the core chipset that handles the conversion layers of complexity. Furthermore, the successful of the information sent or received with mobile devices implementation of the advanced features depends on between digital and analog states, and is responsible how well the basic functionality was implemented to for the physical transmission and reception of the RF begin with. that carry voice or data packets over the air. RF architecture design utilizes components such as RF The primary benefits of LTE are increased , , power amplifiers, switches, duplexes, low- decreased latency and improved spectrum efficiency. noise amplifiers, filters, antenna tuners and envelope But these benefits are not fully realized until channel trackers. bandwidths of greater than 10 megahertz (MHz) are used. To optimize consumer experience as well as the When executed properly, the RF architecture design operator’s return on investment for building out an will have the ideal objective of using the least amount LTE network, there is a demand for finding ways of of power during transmission and reception, while still using 15-, 20- and even 40-MHz and above channels. ensuring the best speed and latency possible for current Unfortunately, due to existing usage of licensed channel conditions. This is because transmitting data spectrum, most countries’ spectrum plans do not allow is the most power-hungry function that a modem for contiguous 20-MHz channels, much less 40. can execute; and by minimizing the amount of time a modem is actively transmitting, the RF architecture

IHS.com/telecominnovation Here is where an advanced functionality like carrier frequency of the main carrier, these spurious signals aggregation comes in. Carrier aggregation, in its could lie in the same frequency as the aggregated simplest form, allows an enabled device to combine two carrier, and if the RF architecture enabling carrier smaller, non-contiguous channels into a larger channel, aggregation is not designed properly, it could cause yielding the same benefits that a contiguous channel interference that materially degrades signal conditions of the same larger size would provide. But designs and, consequently, consumer experience. enabling carrier aggregation will need to take into account many different types of channel combinations A third—but by no means final—complexity is simple including, but not limited to: physical size. Inherent in supporting carrier aggregation • Non-contiguous channels in the same frequency is the need to support multiple bands. Supporting band—i.e., all within the 700-MHz band multiple bands requires more components on the front • Channels from two different frequency bands but end—at least on the receive chain because for now, from the same end of the spectrum and in different carrier aggregation is only supported on the downlink. bands—i.e., one channel from the 1.9GHz band, and Even with the trend toward larger form factors in another from the 2.1-gigahertz (GHz) band mobile devices, the increases in size are not enough to • Channels from two different frequency bands but offset the increase in the number of components that from different ends of the spectrum—i.e., one advanced LTE designs require. channel from the 700-MHz band, and one from the 2.1-GHZ band Therefore, the ability of the LTE modem supplier to integrate while maintaining—or even surpassing— Achieving these different combinations might appear capability delivered by more discrete solutions will as simple as adding one channel with the other. But be critical in enabling advanced LTE capabilities, because of RF propagation characteristics, fundamental such as carrier aggregation, within the limitations of physics and the limits imposed by physical dimensions, contemporary mobile device form factors. attempting such a feat increases design complexity exponentially. Francis Sideco is Senior Director for Consumer & at IHS Technology. For example, in the case of the third type above, aggregating channels from different ends of the spectrum Connect with Francis on LinkedIn: requires that the differing propagation characteristics http://bit.ly/Fsideco of a signal transmitted at 700 MHz, versus that of a signal transmitted at 2.1GHz, be taken into account in For more information visit ihs.com/ the overall system design. Signals transmitted at lower telecominnovation frequencies have longer wavelengths, which in turn allow for the signal to travel further given similar power and channel conditions. So, if a mobile device was aggregating two carriers from each of those bands and they were coming from the same base station, the signal strength and/or the channel quality could be significantly different. This would need to be addressed by not only the receive chain of the device, but also the baseband in how it processes—and ultimately—combines the two channels.

Another consideration when dealing with multiple active channels is the RF phenomenon known as intermodulation, and the harmonics caused by non- linear behavior of the required signal processing. This phenomenon causes spurious, unwanted signals to 6175_0814PB appear in other parts of the spectrum different from the frequency of the main carrier. Depending on the

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