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vor 7 Jahren

7-2016

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Fachzeitschrift für Hochfrequenz- und Mikrowellentechnik

RF & Wireless Figure 3:

RF & Wireless Figure 3: When mobile users connect with more data-intensive devices, as in the U.S. LTE market, the decline in revenue-per- connection is muted and operators generate higher ARPU. Source of image is GSMA Wireless Intelligence.www.gsma.com/ (MIMO) spatial multiplexing, and AAS with embedded RF, present new design challenges in next-generation eNodeB radios. A disruptive bits-to-RF solution is introduced that can help engineers shape alternative radio transmitter architectures. The discussion focuses on novel RF digital-to-analog converter (RF- DAC) technology that yields a single-chip, wideband RF transmitter solution. Readers will learn about system-level applications of the RF-DAC and the integration benefits that it delivers to eNodeB radio design. Overview Long-Term Evolution (LTE) is recognized as the fastest growing mobile broadband technology, and becoming the most widely adopted cellular standard worldwide. LTE‘s global rate of adoption by wireless service providers has exceeded prior second- generation (2G) and third-generation (3G) deployments. The popularity of LTE is mainly due to its high spectral efficiency and high peak data rates, low-latency IP-based network, and evolutionary roadmap. For consumers, this translates to reliable high- speed mobile access and anywhere-anytime connectivity. For wireless service providers, LTE offers efficient spectrum utilization, network capacity gains and significant improvements in total cost of ownership (TCO). But LTE is not „true 4G“ service and is technically still considered 3.9G. The true fourth-generation (4G) radio communication standard, known as International Mobile Telecommunications-Advanced (IMT-Advanced), must meet the requirements set forth by the International Telecommunication Union Radio Sector (ITU-R). IMT-Advanced defines 4G as a service that delivers 100Mbps peak data rates to high-mobility users, and 1Gbps peak data rates for low-mobility clients. To comply with the IMT-Advanced vision, the 3GPP has developed many enhancements since the initial LTE Rel-8 standard published in 2008. In Rel-10 the 3GPP introduced LTE-Advanced as „true 4G“ service to meet or exceed the IMT- Advanced requirements. LTE-A Rel-10 was the next step in the mobile broadband evolution and further expanded on LTE‘s basic feature set. Presently, Rel- 12 is close to introduction with a functional freeze date planned for March 2015. Rel-12 will include evolutionary enhancements across radio access technology. Figure 1 illustrates LTE development timelines where it can be seen that theoretical peak downlink (DL) and uplink (UL) data rates have increased about 10x and 20x, respectively, from DL = 300 Mbps/UL = 75 Mbps in Rel-8 to DL = 3Gbps/UL = 1.5Gbps in Rel-10. The extraordinary increase in peak data rates is due in part to wideband CA, complimented by multilayer spatial multiplexing introduced in Rel-10 and now an important part of Rel-12 enhancements. LTE-A Rel-12 and the Impact on eNodeB Radios Rel-12 enhancements will significantly impact how evolved NodeB (eNodeB) radios are designed. Some of the important Rel-12 items include new combinations of carrier aggregation, spatial multiplexing enhancements with downlink MIMO, and RF requirements needed in AAS. Figure 2 summarizes some of the Rel-12 items with respective features and benefits. A closer look at the Rel-12 features Figure 4: To sustain data growth, the operator CAPEX investment in mobile networks is forecast to exceed .7 trillion (USD) from 2012 to 2020. Source of image is GSMA Wireless Intelligence Figure 5: Four primary market forces are driving evolutionary improvements in radio access technology 62 hf-praxis 7/2016

RF & Wireless Figure 6: Illustration summarizes the different types of carrier aggregation, different CA classes, and transmission bandwidth configurations reveals how the LTE mobile broadband network is evolving to realize improvements in capacity, spectrum utilization, peak data rates, and coverage. Carrier aggregation allows operators to deliver higher peak data rates (bits/sec) and better manage fragmented radio spectrum spanning 700MHz to 3.5GHz. Adopting spatial multiplexing with 8x8 MIMO increases spectral efficiency (bits/sec/ Hz) to serve users with higher peak data rates while maximizing limited and valuable spectrum resources. Migration to AAS enables macro-cell base stations to implement beamforming techniques that will improve celledge and sector capacity while reducing power consumption. The Rel-12 feature enhancements bring many benefits to the LTE ecosystem, along with new radio design and radio architecture challenges. Downlink carrier aggregation (DL-CA) means that base-station radio transmitters must support ultra-wide bandwidths with carrier frequency agility, and 8x8 MIMO requires more RF transmitter channels. AAS with embedded RF dedicates a radio transceiver for each antenna element with up to 16 antenna elements. This significantly increases radio channel density. In macro cell base- station applications the DL-CA, MIMO, and AAS features drive Figure 7: The evolution of base stations from the first-generation BTS through contemporary Generation IV a need for compact, low-power, high-dynamic-performance radio solutions. Bound by a triad constraint of form-factor size, power consumption, and system cost, the effect of Rel- 12 enhancements is profound. RF engineer‘s face new eNodeB design challenges: integrate more radio channels in a smaller footprint and operate at lower power with better dynamic performance, all without increasing system cost. To help engineers overcome these challenges, RF analog integration and disruptive radio architectures offer a solution that can reshape eNodeB transmitter design. Before addressing the details of Rel-12 features, it is important to understand the market drivers and why LTE-A Rel-12 is being drafted. Simply put, is there market demand for more capacity, better coverage, and higher quality of experience? And is there a business case to justify capital expenditure (CAPEX) investment in deploying LTE- Advanced? Market Forces Driving LTE-A Mobile traffic is transitioning from voice to „data centric“ as mobile users embrace video streaming, web browsing, and social networking on their smartphones, tablets, and mobile PCs. Over the next five years the mobile industry forecasts exponential growth in mobile data traffic and mobile broadband subscribers on the order of 60% data traffic growth and 27% subscriber growth. The anticipated result will be 16 exabytes per month traffic and six billion worldwide subscribers in 2018. experts acknowledge that to sustain the surge in mobile broadband demand and ensure high quality-of-experience services with ubiquitous connectivity, the wireless service providers must improve network coverage, increase capacity, and maximize spectrum utilization. Meeting these objectives requires that the service provider invest in network modernization hf-praxis 7/2016 63

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