INTEGRATED CIRCUITS FOR COMMUNICATIONS LTE-Advanced Pro RF Front-End Implementations to Meet Emerging Carrier Aggregation and DL MIMO Requirements David R. Pehlke and Kevin Walsh The authors describe best ABSTRACT ated to reach 74 percent growth in 2015 alone. practices for meeting the Smart devices (defined as mobile devices that challenging coexistence, RF front-end (RFFE) architectures and imple- have a minimum of third generation [3G] connec- harmonic management, mentations are developing new ways to optimize tivity and advanced multimedia/computing capa- LTE-Advanced PRO (Rel 13) multi-component bility) accounted for 90 percent of that growth linearity, and efficiency carrier aggregation, advanced features to increase figure. Mobile video traffic accounted for 55 per- performance related to spectral efficiency such as higher order modula- cent of total mobile data traffic, and specifically the functional partitioning, tion and higher order MIMO, and the concurrent for handsets, smartphones (including large screen optimized integration, operation of all of these features together. In this phablets) were responsible for 97 percent of total and technology selection article, we describe best practices for meeting the global handset traffic. There is no end in sight to challenging coexistence, harmonic management, this overwhelming trend toward big mobile data of the RFFE. linearity, and efficiency performance related to enabled by smartphones, and as we look ahead the functional partitioning, optimized integration, to 2020, predictions indicate a 53 percent com- and technology selection of the RFFE. Recent pound annual growth rate (CAGR) in mobile data trends to improve radio performance are driving traffic, attaining a total 30 exabytes/mo globally. specific blocks (e.g., the low noise amplifier) into the RFFE, with associated architecture changes in LTE-ADVANCED PRO: SOLUTIONS FOR THE both primary and diversity paths. Carrier aggrega- CHALLENGE OF BIG MOBILE DATA tion features are supported in a number of differ- ent methods with different insertion loss, isolation, In order to address this explosive demand for data and noise figure trade-offs, and here we examine rates and total mobile data consumption, manu- benefits of a new category of highly integrated facturers are called to increase data throughput of diversity receive modules to enhance receiver consumer UE. A number of enabling features are sensitivity across all use cases. Movement toward being standardized and rolled out in commercial higher order MIMO in the DL is compounding handset products. The highest priority to date has additional RF Rx path support and requirements, been deployment of carrier aggregation (CA), and cost-effective solutions for optimum perfor- which was introduced in the Third Generation mance trade-offs require a holistic and complete Partnership Project’s (3GPP’s) Release 10, and RF system view of both Tx and Rx in order to involves the addition of more and more carrier address these emerging requirements. bandwidth. CA essentially allows mobile opera- INTRODUCTION tors to “widen the pipe” and enable higher data rates simply by the simultaneous use of more As the requirements of future cellular communi- spectrum as a dedicated resource to a single user. cations are being realized, there is an enormous LTE is defined to support flexible channel band- focus on the following top priorities for user widths from 1.4 MHz to a maximum of 20 MHz, equipment (UE) radio and RF front-end (RFFE) but these critical extra channels (each up to 20 development: MHz wide) can be added within a defined band • An incredible demand for higher data rates of operation (intra-band CA) or in additional dif- mandates advanced features into the UE. ferent bands of operation (inter-band CA). The • These features, and especially their simultane- number of combinations of the channel alloca- ous concurrent use, are significantly increas- tions and combinations of bands employed for ing handset complexity and performance CA in the standard has exponentially grown over challenges. the last several years, as indicated in the summary • More robust “always on” connections to the by the 3GPP Release in Fig. 1, and we see the Internet with an acceptable cell edge user continued use of CA as a vital part of increasing experience, even in the most challenging data rates for consumers [2]. This feature is fur- radio environments, are required. ther illustrated in Fig. 2, where the addition of The demand for higher data rates is clear from component carriers (CCs) that aggregate more the recently published statistics on mobile data bandwidth to the signal can benefit users through- growth [1] indicating that global mobile data traf- out the entire cell (all the way to cell edge). The fic will grow tenfold in five years, having acceler- darker shade of the larger number of aggregated Digital Object Identifier: 10.1109/MCOM.2017.1601221 The authors are with Skyworks Solutions, Inc. 134 0163-6804/17/$25.00 © 2017 IEEE IEEE Communications Magazine • April 2017 Mobile data traffic growth prediction 35 30.6 EB Growth in introduction of 3GPP specified CA 30 53% CAGR 2015 - 2020 combinations by release 546 21.7 EB 25 600 h t 500 Total CA combinations=900 20 14.9 EB ions t 400 es per mon t 15 9.9 EB A combina 300 Exaby C 10 6.2 EB 3.7 EB 200 107 123 5 Number of 100 3 21 0 0 2015 2016 2017 2018 2019 2020 Rel 10 Rel 11 Rel 12 Rel 13 Rel 14 a) b) Band groups 2DL CA combinations Band groups 4DL CA combinations LB/MB 5/2, 5/66, 12/2, 12/66, 13/2, 13/66, 29/2, 29/66 LB/LB/LB/MB 2/5/12/12, 4/5/12/12 LB/HB 5/7, 12/7, 5/30, 12/30, 29/30 LB/LB/MB/MB 2/2/12/12, 2/2/5/5, 2/4/12/12, 2/4/5/5, 2/5/5/66, 4/4/12/12, LB/LAA 5/46, 12/46, 13/46 LB/LB/MB/HB 2/5/5/30, 4/5/5/30 MB/MB 2/4, 2/66, 2/2, 4/4, 25/25, 66/66 LB/MB/MB/MB 13/66/66/66, 2/13/66/66, 2/2/13/66, 2/2/5/66, 2/5/66/66, MB/HB 2/30, 2/7,m 4/30, 66/7 LB/HB/LAA/LAA 5/7/46/46 MB/LAA 2/46, 66/46 LB/LAA/LAA/LAA 13/46/46/46, 28/46/46/46, 5/46/46/46 HB/LAA 7/46, 41/46 MB/MB/MB/MB 2/2/66/66, 2/66/66/66 MB/MB/HB/HB 2/4/7/7 Band groups 3DL CA combinations MB/LAA/LAA/LAA 2/46/46/46, 4/46/46/46, 66/46/46/66 LB/LB/LB 5/12/12 HB/LAA/LAA/LAA 7/46/46/46 LB/LB/MB 2/12/12, 2/5/5, 4/12/12, 4/5/5, 5/5/66 LB/LB/HB 5/5/30 Band groups 5DL CA combinations LB/MB/MB 12/66/66, 13/66/66, 2/12/66, 2/13/66, 2/5/66 LB/LB/MB/MB/HB 2/2/5/5/30, 2/4/5/5/30, 4/4/5/5/30 LB/HB/HB 5/7/7 LB/HB/LAA/LAA/LAA 5/7/46/46/46 LB/LAA/LAA 13/46/46, 5/46/46 LB/LAA/LAA/LAA/LAA 5/46/46/46/46 MB/MB/MB 2/66/66 MB/LAA/LAA/LAA/LAA 2/46/46/46/46, 4/46/46/46/46, 66/46/46/46/46 MB/MB/HB 2/7/66 HB/LAA/LAA/LAA/LAA 7/46/46/46/46 MB/HB/HB 2/7/7, 4/7/7 LB: B12, B13, B29, B5, B26 MB/LAA/LAA 2/46/46, 4/46/46, 46/46/66 MB: B2, B25, B4, B66 HB/LAA/LAA 7/46/46 HB: B7, B30, B41 License assisted access (LAA): B46 c) Figure 1. a) Mobile data traffic per month and traffic growth predictions 2015–2020 (1 exabyte = 1018 bytes) [1]; b) exponential growth in the definition of band combinations employed for carrier aggregation as part of the 3GPP standard [2]; c) North Ameri- ca example of requirements for downlink CA combinations across 2DL, 3DL, 4DL, and 5DL use cases. CCs indicates higher throughput as this feature tively transmits multiple data streams (or layers) linearly increases data rate proportional to the from a number of antennas at the transmitter to total bandwidth employed. multiple antennas on the receiver. This applica- Another technique designed to increase the tion uses the spatial differences of the antenna spectral efficiency of bandwidth is to effectively reception and multi-path through varying radio increase the data rate in bits per Hertz. Termed environments of each data stream in order to “higher order modulation,” defined in 3GPP’s separate out the overlying signals even though Release 12 (spring 2015) to be a maximum of they are transmitted at the same frequency. This 256-quadratuer amplitude modulation (QAM) digital extraction of the signals based on known for the downlink (DL), and 3GPP’s Release 14 unique radio path transfer functions (derived (expected spring 2017) to support a maximum from reference signals within each link) enables of 256-QAM for the uplink (UL). As the standard a further multiplication factor of the data rate has started with modulations of quadrature phase according to the number of transmit/receive shift keying (QPSK) (2 bits/symbol), to 16-QAM antennas that are employed. As an example of (4 bits/symbol), to 64-QAM (6 bits/symbol), and the DL signals, if four data streams are transmit- now to 256-QAM (8 bits/symbol), the spectral ted from the base station (eNodeB) and four efficiency is increased by the factor of bits per separated antennas with low envelope correla- symbol.