NTT Docomo of Japan and SK Telecom of South Korea are always in the forefront of next generation mobile network developments, and both have announced new breakthroughs on the road to 5G.
Docomo has been talking about its contribution to the 5G waveform debate. While the initial releases of the standards – focused mainly, and conventionally, on sub-6 GHz spectrum and mobile broadband use cases – will continue to use OFDM, other waveforms are expected to be adopted in Release 16 and beyond, to support millimeter wave spectrum more efficiently, and to be better optimized for functions like ultra-low latency.
Some companies, from start-ups like Cohere to majors like Huawei, have been disappointed by the relatively conservative approach in Release 15, though the OFDM will come with new numerology, frame structure and coding. But these companies continue to develop their alternatives and hope for adoption in future standards.
Docomo’s contribution is NOMA (Non-Orthogonal Multiple Access), which it has starting testing on a test chipset from MediaTek, along with Multiuser Interference Cancellation (MUIC).
The companies said that the field test resulted in spectral efficiency improvements of up to 2.3 times, compared with single user MIMO using the same transmit/receiver antenna configuration.
NOMA enables the base station to transmit signals to multiple devices in the area simultaneously on the same frequency, by controlling the transmission power and interference cancellation process to each device. Docomo explained this works by multiplexing signals at the base station to leverage the increased signal processing capacity of user devices, and cancel interference among the multiplexed user signals.
In the trial, three test devices based on the MediaTek chips were situated at different locations, with super-positioned signals transmitted from a small cell base station fitted with four 3.5 GHz antennas. They were transmitted at the same frequency, for different devices, at the same time. The interfered signal was able to be successfully recovered thanks to the interference cancellation technology.
Docomo has also announced a trial with Sony to transmit high definition video in real time via a 5G network, to a 4K digital signage system fitted to the outside of Sony’s experimental vehicle, the New Concept Cart. The test will be conducted at the 5G Trial Site in Tokyo, which the MNO built to evaluate 5G technologies and potential commercial services.
And finally, the operator said it had worked with Huawei to claim the world’s first successful outdoor trial of 5G for ultra-reliable low latency communications (URLLC), using 4.5 GHz spectrum (a target 5G band in China and Japan).
During the trial, which used a stationary mobile terminal, Docomo said it achieved over-the-air latency of less than one millisecond and a packet transmission success rate of more than 99.999% (both 3GPP and ITU requirements for URLLC).
URLLC was also achieved at distances of 0.3 to 0.6 kilometers from the base station, when the mobile terminal was moving at approximately 25km per hour.
A combination of key elements underpinned the test, including technology to retransmit radio signals irrespective of the terminal’s radio conditions, to boost reliability; antenna diversity; and a new radio frame structure incorporating extremely short transmission time slots to reduce over-the-air latency.
Meanwhile, SK Telecom said it had tested new technology which enables 5G to process data traffic 10 times more quickly than LTE, boosting peak data rates as high as 200Gbps, and with the potential to break the Tbps barrier in future by harnessing server virtualization. The operator plans to submit its findings to 3GPP and ETSI as a potential standard.
The new technology enables packet switching equipment to serve as a gateway for voice and data traffic, generated from mobile devices, to access wireless networks. This supports faster, stabilized processing of wireless traffic.
In the LTE network, the maximum speed for packet switching per server stands at 20Gbps, but SK Telecom is targeting 200Gbps, and then 1Tbps, speeds by adding virtual servers. It says its technology also reduces the size of packet switching equipment, so that it can be deployed at base stations to reduce latency.
“Ultra-fast packet processing technology is essential in delivering best quality of 5G services,” said Park Jin-hyo, head of network technology at the operator’s R&D Center. “It is a significant result for SK Telecom as this virtualization-based high performing equipment could enable us to deliver a faster, efficient 5G roll-out.”
The MNO also demonstrated what it believes will be an essential element of 5G – an indoor-only relay to boost speeds and coverage indoors. It used an in-building 5G relay repeater operating in both 28 GHz and 3.5 GHz spectrum in the 5G trial network at its Bundang office. This improves signal quality by transferring wireless signals to radio shadow areas and the company achieved peak speeds of 4Gbps.
The company has worked with SK Telesys to develop the 3.5 GHz relay repeater.