PARTNER FEATURE: As worldwide LTE deployments have expanded to nearly 500 total networks in about 160 countries, and LTE connections passed the 1.5-billion mark in the third quarter, the technology certainly has not remained static as the industry looks ahead to 5G. Operators in many regions have moved quickly to dual- and tri-band carrier aggregation to expand capacity and boost theoretical peak downlink speeds to 300Mb/s and higher.
But for many operators, with limited spectrum resources, multiple carrier aggregation is not always an option. The rapid advance of multiple antenna technology, specifically massive multiple-input multiple-output (MIMO), is giving TDD operators the ability to boost data throughput by improving spectral efficiency.
The industry has seen a raft of promising MIMO trials around the world over the past year, with the pace of innovation picking up since September 2015.
From concept to reality
A year ago, China Mobile Shanghai, together with the Research Institute of China Mobile and Huawei, completed the world’s first Massive MIMO deployment on a 4G commercial network. The tests were conducted using commercial smartphones, and the results indicated a downlink throughput per single cell exceeding 650Mb/s with a single 20MHz carrier – breaking the record for air-interface throughput in commercial LTE TDD networks. That’s roughly six times the speed usually achieved with a 20MHz block of TDD spectrum.
Shanghai, with more than 400 skyscrapers over 100 metres tall and the highest population density in China, is one of the most challenging environments in the world to deploy wireless infrastructure.
China Mobile Shanghai, to simulate the various coverage difficulties faced in the city, used Massive MIMO technology from Huawei to verify different coverage scenarios. By using 3D beam-forming technology, a single Massive MIMO eNodeB installed at a height of 25 metres was capable of providing 3D coverage to a building 75 metres tall, which was just 73 metres away.
China Mobile deployed Massive MIMO on its Shanghai commercial network and the results have been “very promising”, increasing spectrum efficiency by up to eight times, according to Liu Guangyi, CTO of China Mobile Research Institute’s wireless department.
Massive MIMO has made even greater progress this year. In September SoftBank announced it was the first operator in the world to commercially deploy Massive MIMO technology in base stations. It is working on the co-called “5G Project”, with the first step to deploy Massive MIMO technology in 100 base stations in Tokyo. According to SoftBank, Massive MIMO can boost 4G network speeds 6.7 times.
Vodafone had also worked with Huawei in the UK to test 4×4 MIMO and eight-way transmit and receive technology since the first half of 2016. Furthermore, in September Vodafone trialed Massive MIMO in the UK, which is the first 4.5G Massive MIMO network in Europe.
In November China Mobile Hong Kong finished a Massive MIMO trial on its 2.3GHz network. Band 40 is very popular in many regions, especially in Southeast Asia. The peak rate achieved was 650Mb/s, and the commercial launch is expected in 2017.
Also in November, China Mobile Shanghai launched the world’s first commercial wideband Massive MIMO, which supports use of 3x20MHz, which greatly reduces the cost per bit.
In addition, Mobily just finished its Massive MIMO trial, which was the first Massive MIMO trial in Middle East. Many other operators in Asia and Europe are expected to quickly follow.
The TDD opportunity
These trials clearly demonstrate that 4.5G (TDD+) is able to boost the potential value of TDD spectrum for mobile operators. China Mobile’s Liu said it expects TDD-LTE to be an important part of 5G because of its future-oriented architecture. New 5G spectrum is expected to be mostly in TDD bands.
As a fundamental 5G technology, Massive MIMO can provide mobile services simultaneously for multiple end-users by deploying a large number of antennas at base stations.
At its core, Massive MIMO is an ultra large-scale multi-antenna system, based on Space Division Multiple Access (SDMA) technology. It uses many antenna elements and coordinated beam forming to focus beams on specific users. Beam forming and multi-receiving diversity combine signals from multiple angles and co-located antennas to reduce interference and improve cell throughput, making the technology well suited to boost performance in urban areas.
Massive MIMO supports all mainstream TDD-LTE frequency bands and is compatible with all existing 4G terminals. Many smartphones already support TDD-LTE, such as all iPhones (after the iPhone 5s) and Galaxy series models (after the Galaxy Note 2). Massive MIMO is based on BBU-AAU distributed architecture and can easily expand the capacity without changing the antenna. BBU can smoothly evolve to 5G by changing to a new 5G capable baseband card. Another key point is a Massive MIMO base station is as small as 0.5m by 1m, so operators don’t have to worry about having no space for a Massive MIMO base station.
Keeping up with demand
Long before 5G is even standardised, much less deployed commercially, mobile operators continue their search for cost-effective ways to keep up with skyrocketing data demand. According to Cisco’s Virtual Network Index, mobile data traffic in Asia Pacific will jump nine-fold between 2015 and 2020, while in Europe and the US data usage will expand six-fold during that timeframe.
The improvements Massive MIMO deliver in terms of higher throughput and better cell coverage mean more operators are looking to TDD as they expand their network capacity as well as prepare to evolve towards 5G. The lower cost per bit will allow them to stay competitive as data tariffs face continued downwards pressure in many markets.
“The huge capacity gains may fundamentally change network capacity design principles and business logic,” said Veni Shone, President of Huawei TDD Product Line. He added that the use of Massive MIMO not only can enhance capacity and coverage in challenging urban conditions, it also can significantly decrease an operator’s network costs, maximising their current investment in existing sites and spectrum without having to add new frequency bands.