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Uplink Carrier Aggregation Arrives with a Splash and User Smiles

by Chris Taylor | Jun 08, 2016

LTE uplink carrier aggregation (UL CA) is the latest global phenomenon in cellular.  Four wireless operators have rolled it out in S. Korea and China, and at least four more operators across Western Europe, the US and Malaysia will soon follow.

UL CA improves the user experience and enables a huge trend, the growth of social video.  UL CA also represents the leading edge of LTE, a challenging but profitable segment to serve.  With smartphone growth down this year, this is an opportunity for component suppliers, phone OEMs and operators alike to out-distance the competition.

  • UL CA combines two or more LTE signals (component carriers), transmitted (uplinked) from a single user device to the wireless base station, dramatically increasing the speed with which a user can upload content and files.
  • With the rapidly growing popularity of video telephony, video messaging and posting user-generated content to social networking sites, consumers can enjoy a big improvement in the user experience with UL CA.

Just to underscore the importance of video, it now makes up more than half of wireless data traffic carried by most LTE operators.  The important 18 to 34 year old demographic watches more video on the Internet than on TVs, and with the ubiquity of video-capable smartphones, social networking web sites have experienced an explosion of user-posted short videos along with video watching.

Some facts touted for social video sites include:

  • Facebook users watch more than 8 billion video clips per day, and more than 75 percent of this is consumed on mobile devices.Video posts per person, mostly generated using phones, is up 75 percent from a year ago, and the total number of videos posted has increased to 3.6 times what is was a year ago.
  • Snapchat too claims more than 8 billion video views per day, three times what it was just six months ago.
  • Instagram, owned by Facebook, has morphed into a popular site for video ads and messaging.In response to demand, Instagram just increased the maximum allowed video duration from 15 to 60 seconds.
  • More than 80 percent of Twitter users watch video content on the site, and 90 percent watch it on mobile devices.
  • Periscope, now owned by Twitter, conservatively has more than 50 million users a little over a year after launch.The Periscope app allows users to stream live content from their phones to watchers around the world, simultaneously sending out links via Twitter.
  • The first Internet video site YouTube now has more than 1 billion users, most of them watching searchable content on specific topics and products.YouTube has responded to the rise of social video with Live and 360.

Largely in support of the demand for uploading videos from phones, all three operators in South Korea have launched UL CA.  Together LG Uplus, SK Telecom and KT have approximately 60 million subscribers, most of them using LTE, and most of them now with access to UL CA.

In South Korea, phones with UL CA transmit on two different bands at the same time, approximately doubling previously available uplink speeds:

  • As deployed in S. Korea, UL CA uses two component carriers (CCs) in separate LTE bands with an aggregate bandwidth of 30 MHz (20 MHz + 10 MHz UL). Operators in S. Korea also support 64-QAM for the uplink instead of the more common 16-QAM.
  • LG Uplus combines 20 MHz in B7 (2600 MHz) with 10 MHz in B5 (850 MHz) to offer peak uplink speeds up to 112.5 Mbps.
  • We have not confirmed how SKT and KT operate UL CA, but SKT has B1, B3 and B5 available, while KT has B1, B3 and B8.We suspect that the two operators both use 20 MHz on B3 plus 10 MHz on B1.This would allow the same phones to operate with UL CA on both networks.SKT supports peak UL CA speeds of 131.25 Mbps.KT supports peak UL CA speeds of 93.75 Mbps.
  • The first phones to support UL CA in S. Korea are variants of the LG G5, which uses Qualcomm’s Snapdragon 820.
  • Huawei provided the wireless base station equipment for UL CA and other LTE Advanced Pro features, among these support for 64-QAM in the UL direction, which improves UL capacity in bursty conditions and in high density areas not too far from a base station.
  • Note that LTE Advanced Pro, frozen by the 3GPP as Release 13 in March 2016, allows up to 40 MHz of aggregate UL bandwidth, providing up to 150 Mbps UL peak data rate when used with 64-QAM.  The 150 Mbps UL data rate is classified as LTE UL Cat. 13.  South Korea uses the eRAN11.1 version of LTE Advanced Pro for UL CA.

China’s largest operator China Mobile (CMCC) has said that it would roll out UL CA in Q4 2016, and it looks as though China will grow into the highest volume market for UL CA-enabled devices at least for the next few years:

  • CMCC conducted a trial of UL CA through its Zhejiang Mobile affiliate in Hangzhou Provence in 2015, and has unofficially allowed the service to continue in one city.  CMCC used equipment from Huawei for the trial.  You can find more information here.
  • UL CA addresses the uplink weakness of TDD-LTE, which normally has a 5:1 to 6:3 speed ratio asymmetry favoring downlink over uplink.  Supported phones get an increase in peak UL rate from 10 Mbps to 31 Mbps.
  • CMCC licenses 2,575 MHz to 2,635 MHz in LTE Band 41.  By using up to the full 60 MHz available to it, CMCC can support up to three 20 MHz CCs in each direction; with 64QAM, the operator can enhance device UL performance without taking additional timeslots from the DL (downlink).
  • In the present implementation, CMCC uses three CCs in the downlink direction (3x DL CA) and two in the uplink (2x UL CA) plus UL 64-QAM.
  • The first phone to use UL CA in China is the LeMax Pro from LeEco (formerly known as LeTV).  CMCC also announced the A2, an RMB 799 (about $122) phone with both UL and DL CA.  The LeMax Pro uses a Qualcomm Snapdragon 820.  The CMCC A2 uses a Snapdragon 617.

Mobile video is exploding in China.  China’s Tencent is promoting its social video platform with the help of the wildly popular WeChat service (Weixin, translating roughly as ‘micro message’), which has 1.1 billion user accounts and more than 690 million users of its smartphone app.  Other video platforms, apps and services in China include Youku-Tudou, supported by Alibaba, iQiyi (Baidu), and CMCC’s “And.”  As social video increases in China, so will demand for phones with UL CA.

At least two European operators are rumored to have UL CA in trial and could soon offer it commercially.  In Singapore, operator M1 recently completed a trial of UL CA.  In the US, it seems likely that Sprint will find the benefits of UL CA quite attractive.  Like CMCC, Sprint uses TDD-LTE in B41.

What does all this mean for cellular radio components and suppliers?

  • Benefits to Qualcomm.  The UL CA-enabled LG G5, LeEco LeMax Pro and CMCC A2 all use Qualcomm’s Snapdragon SoCs and associated radio chipsets.  So far, Qualcomm is the only company shipping radio chips into mobile devices that implement UL CA.  Samsung, HiSilicon and Intel have announced chipsets with UL CA, but these are either not yet in production or at best are not used in any phones with UL CA.
  • More Challenging RF Front Ends.  In an FDD-LTE device, UL CA uses two power amps (PAs) simultaneously.  As long as the PAs are not in the same range of frequencies roughly defined in the industry as LB (low band, typically 700 MHz – 960 MHz, MB (mid band, typically 1700 MHz to 2,200 MHz) or HB (typically 2,300 MHz to 2,700 MHz), UL CA can use the parallel multiband PAs already in the hardware reference design.  In phones for LG Uplus, one PA operates in a low band (B5), and one operates in a high band (B7), probably routed to different antennas.  In cases such as this, the HB receive frequency can be perilously close to the third harmonic of the LB transmit frequency, putting stiff requirements on component isolation, linearity, and filter and duplexer rejection.
  • More PAs.  Assuming that phones for SKT and KT use UL CA on B1 and B3, then these would need a second mid-band PA, probably connected to the diversity antenna and requiring an additional switch throw, a duplexer and some filtering to protect the diversity receive chain.
  • Better PAs.  The phones for CMCC use intra-band UL CA in B41, requiring an aggregate channel bandwidth of up to 40 MHz for two CCs. This is more demanding on PA linearity and efficiency than a single CC.
  • Even Better PAs.  It is our understanding that intra-band UL CA in FDD-LTE devices calls for very low out-of-band harmonics, which can spill into the adjacent receive channel, so specifications for intra-band PAs in future FDD devices will be much harder to meet than in today’s TDD devices.  Future FDD bands that might use UL CA include B1 (1920 MHz – 1980 MHz), B7 (2,500 MHz – 2,570 MHz) and B25 (1,850 MHz – 1,915 MHz).

In summary, UL CA is not just a technology looking for a killer application – it serves the spectacular growth of social video.  LTE with UL CA also represents the leading edge of cellular technology in production today, historically the most challenging but most profitable segment to serve.  As in the past (as the saying goes, more or less), with UL CA your company can either get on the train, get out of the way, or get left behind.

You can read more about the growth of cellular, LTE, and the future demand for radio components for cellular devices here.

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