Page 42

EETE OCT 2014

RF & MICROWAVE DESIGN Next generation RF switching solutions for 4G/5G By Igor Lalicevic and Karim Segueni History of wireles technology development can be summarized as a history of data speed improvements. Cellular standards have gone a long way from the analog, voice only 1G standard introduced in the 1980s which originally modulated a single band at 150MHz frequency. Moving to 2G, first digital cellular standard introduced quad-band system solutions and the trend of increasing frequency bands allocations has continued with 3G typically supporting up to 8 frequency bands in order to support global roaming and higher data speed and capacity needs. Today, with 4G Long Term Evolution Advanced (LTE-A), we are witnessing an explosion of allocated frequency bands. LTE development has become dominated by the need for global roaming and wider frequency bandwidth. Currently we have over 40 bands allocated to LTE FDD and LTE TDD applications. Together with frequency bands expansion, we have experienced significant data speed and capacity increases. Coming from 2G 14.4kps for both Down Link (DL) and Up Link (UL), nowadays LTE cat6 will provide up to 300 Mbps DL and 50Mbps UL data rate. Still, customers and market requirements are ever increasing. Peak data rate targets for LTE-A are up to 1Gbps for UL connection. Even this is just a first step and targets will have to be improved rapidly and constantly. Combined with this challenge, increasing mobile broadband capacity is a must. According to Ericsson research, mobile data traffic is expected to grow 12 times between 2012 and 2018 and, by the end of 2018, there will be over 3 billion smartphone subscriptions. The need for significant data rate and data capacity increase Fig. 1: Future handset linearity requirements. is referred to in the wireless industry as “Enabling 1000x Mobile Data Challenge”. Solutions that will help us to achieve this 1000x mobile data challenge will require more frequency spectrum. We already see that 3.5GHz (LTE TDD bands 42 & 43) will be introduced in Japan in 2015, with others to follow. Another step will be the introduction of 100MHz DL CA (Carrier Aggregation). Just for comparison, LTE cat6 is using 40MHz (20MHz+20MHz) CA in a 2x1 MIMO mobile handset configuration. For 100MHz CA bandwidth it will be necessary combine TDD and FDD LTE bands. While DL data rate speed going from LTE cat1 to LTE cat6 has increased 30 times going from 10Mbps to 300Mbps, UL data rate speed has increased only 10 times, from 5Mbps for LTE cat1 to 50Mbps for LTE cat6. But, for the first time, during recent major public events like Super Ball World Cup, Olympic Games etc. carriers have experienced UL data exceeding DL data capacity. This of course raised concerns among operators about DL/UL development discrepancy, they are become increasingly eager to find a ways to reduce DL/UL data rate speed ratio. The first steps in this direction will be TX Diversity Path introduction (or 2x2 MIMO) in handsets configurations and introduction of UL (or Tx) Carrier Aggregation. In “Enabling 1000x mobile data challenge” targets are going even further, and, in moving closer towards a 5G standard, mobile handset or User Equipment (UE) RF performance is becoming a really key bottleneck in the market. RF Front End (RF-FE) architecture in high-end smartphones has become exceptionally complex, having to support large numbers of bands due to global roaming needs and a minimized numbers of phone model variants approach. Hence, the list of needed RF-FE components is becoming increasingly long. This complex RF environment introduces many challenges for components; Insertion Loss (IL), Isolation and Linearity performances. Inter-band CA requires the use of multiple active Rx/ Tx paths within the single RF-FE, with the resulting impact on Fig. 2: SOI can no longer cope. cost, performance and power bringing supplementary complexities resulting in the need to reduce intermodulation and cross-modulation from the two or more active Rx and Tx paths. In this environment RF Antenna Switch linearity performance is becoming a crucial specification – see figure 1. The 3GPP standard is used by the industry to determine the degree of linearity Igor Lalicevic is Director of Radiofrequency platforms at DelfMEMS - www.delfmems.com Karim Segueni is DelfMEMS’ CTO. 30 Electronic Engineering Times Europe October 2014 www.electronics-eetimes.com


EETE OCT 2014
To see the actual publication please follow the link above