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Triband aggregation pushes TD-LTE limits

Three-carrier aggregation, TDD and 256QAM – a mounting number of trials points to a dream team for 4G

As operators push for ever-greater 4G speeds, carrier aggregation is becoming more essential, and more complicated. Combining three, four or even five bands will push LTE to new limits, and the trials are piling up. The latest results come from SK Telecom in Korea and Nokia Networks, which showed peak download speeds of 428Mbps using triband TD-LTE carrier aggregation (CA), together with 256QAM modulation.

This demonstration is a vital proof point for the TD-LTE community, said the partners, which worked with Qualcomm Snapdragon on the device modem side. Unpaired TDD spectrum is often more plentiful and affordable than FDD bands, and may provide opportunities for new or disruptive entrants. The Chinese carriers, and some others such as Sprint and Softbank, will make heavy use of FDD/TDD combinations to drive up their capacity and improve their economics.

The test used Nokia’s Flexi Multiradio 10 base station with software to aggregate three 20 MHz carriers in Band 41 spectrum (2496-2690 MHz). Load balancing capabilities were important to optimize spectrum efficiency and user experience across the carriers. The next step will be to establish a TD-LTE testbed and conduct wider trials of specific services and applications.

Tests like these are, then, important to prove the capabilities of TD-LTE to deliver the highest performance. This was the first example of TD-LTE 3xCA with 256QAM, and “lays the foundation for the introduction of TD-LTE in Korea”, according to SK Telecom. The head of its network technology R&D center, Jin-hyo Park, said: “We have showcased our readiness to prepare for the introduction of TD-LTE in Korea – which will provide an altogether unmatched service experience to our users across the country.”

Nokia added in a statement: “The trial verifies the clear benefits of 3xCA combined with 256QAM-capable devices that can boost the peak throughput from 110Mbps to 428Mbps. Nokia’s SingleRAN Advanced platform provides a strong foundation for SK Telecom to build the most advanced TD-LTE network capable of effectively addressing the demand for bandwidth-intensive services.”

Recently, Telstra of Australia became the first operator to boast a successful trial of five-carrier aggregation, working with Ericsson to get close to 1Gbps. The firms aggregated 100 MHz of Telstra’s spectrum holdings across five separate 4G channels integrated on the carrier’s LTE network.

Its group managing director for networks, Mike Wright, wrote in a blog post that end-to-end tests achieved download speeds of over 950Mbps using a specialized field test application, as well as speeds of around 843Mbps over the internet to speedtest.net.

Telstra’s commercial LTE-A network currently delivers 600Mbps peak speeds, using triband CA, in selected areas. It is also working with Ericsson on pre-5G RAN and core network projects.

And Singapore’s StarHub has been showing off some of the gains that are available from combining FDD and TDD spectrum, together with VoLTE for voice. It recently achieved the first TDD-FDD VoLTE handover using its 4G HetNet, which includes a dense roll-out of outdoor small cells, in the island state’s busy Marina Bay.

Its supplier Nokia said the deployment uses LTE-Advanced carrier aggregation technology to improve data rates, and small cells at strategic locations to handle peak-hour data demand. It also provided load balancing and project management capabilities for the trial.

“With HetNet and through our close collaboration with Nokia Networks, we are proud to deliver the world’s fastest, future-ready 4G network that can address the ever-growing data traffic demands of our customers without compromising on the quality of service, paving the way for Singapore to build the world’s first Smart Nation,” StarHub CTO Mock Pak Lum commented.

In Greece, Ericsson has worked with Cosmote on Europe’s first trial of 3xCA with 256QAM, this time with FDD spectrum. The companies demonstrated download speeds of 500Mbps in a live LTE network in November using Ericsson base stations and Networks Software 16A. The Swedish vendor said its 256QAM downlink encoding technology provides up to 33% higher downlink throughput in good radio conditions, boosting spectral efficiency.

Ericsson also recently demonstrated three-carrier aggregation and 256QAM with China Mobile in Beijing, once again using its RBS 6000 base stations in a live LTE network. This reached downlink peaks of 426Mbps in TDD mode.

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