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Examining LTE-A Release 12 transmitter (Part 1)

17 Mar 2015  | Damian Anzaldo

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A closer look at the Rel-12 features reveals how the LTE mobile broadband network is evolving to realise improvements in capacity, spectrum utilisation, peak data rates, and coverage. Carrier aggregation allows operators to deliver higher peak data rates (bit/sec) and better manage fragmented radio spectrum spanning 700MHz to 3.5GHz. Adopting spatial multiplexing with 8x8 MIMO increases spectral efficiency (bit/sec/Hz) to serve users with higher peak data rates, while maximising limited and valuable spectrum resources. Migration to AAS enables macro cell base stations to implement beamforming techniques that will improve cell-edge 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 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 engineers 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 analogue integration and disruptive radio architectures offer solutions 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 [1],[2]. Industry experts acknowledge that to sustain the surge in mobile broadband demand and ensure high quality-of-experience services with ubiquitous connectivity, wireless service providers must improve network coverage, increase capacity, and maximise spectrum utilisation. Meeting these objectives requires that the service provider invest in network modernisation with upgrades to infrastructure that transition from 3G to 4G radio access technology and core network equipment.

Upgrading from 3G to 4G requires new network equipment. Therefore, LTE networks are more costly to deploy and require higher initial CAPEX investment. This makes CAPEX investment an important market driver. Consequently, justifying the CAPEX investment on 4G wireless infrastructure equipment demands a compelling business case that demonstrates profitability and adequate return on investment (ROI). The 4G-LTE networks are about 4x faster than 3G on average [3], allowing service providers to capitalise on the growing mobile data demand. Also, the flat all-IP LTE network is less expensive to operate than 3G, making 4G ideal for lowering the cost-per-bit service and improving profitability.

LTE-A plays a critical role in bringing differentiated service to mobile networks and acts as a conduit for monetizing mobile data growth. Early LTE adopters who invested in LTE infrastructure (like South Korea, Japan, and the United States, the world's most advanced mobile markets), have seen successful revenue growth and increasing data average-revenue-per-user (ARPU). Furthermore, because LTE provides lower cost-per-bit service, the early adopters achieved better control over operational expenses which, in turn, helped improve TCO. The early adopters quickly realised the importance of "first to market" and "best to market,"or phrased another way, "build it and they will come."

Verizon Wireless [4], SK Telecom [5], and NTT DoCoMo are good examples where the major wireless service providers invested early in migrating to LTE. Each has reported data ARPU growth with stable profitability. Conversely in Europe, where wireless providers delayed LTE and tried to recoup expensive 3G investments, those providers are experiencing sharp declines in ARPU. Figure 3 illustrates the contrast between the average revenue per connection (ARPC) and ARPU in the U.S. versus Europe [6], where consumers in both markets are seeing the benefit of lower cost per connection. However, because U.S. consumers connect with more data-intensive devices, the revenue per subscription is increasing. The ARPU-ARPC gap coincides with LTE network deployments and mobile ecosystem expansion in the U.S. In fact, in 2013 the two largest U.S. operators spent $21B in CAPEX, more than all 20 operators serving the five largest EU countries. Consequently, to achieve revenue growth and profitability like that seen in the early LTE adopter markets, today the global investment in 4G infrastructure is a major reason why service provider CAPEX will reach $250B in 2017.

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.

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