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The Next Breakthrough in Indoor Wireless: Distributed Massive MIMO

Importance of In-Building Wireless in the 5G Era

5G is entering the mass market in late-2020 and early adopters, as well as large-scale deployments, are illustrating best practices for the rest of the world. An important conclusion from many advanced Asian markets, including South Korea and China, is that outdoor 5G deployments need to take place in parallel with indoor deployments, especially when enterprise applications are considered. For example, many mobile operators in Asia, the Middle East, and Europe have started deploying 5G in outdoor macro sites, as well as busy indoor areas, such as airports, railways, stadiums, and subways.

South Korea has been the first country to aggressively roll out 5G networks and its Ministry of Science and ICT (MIST) expanded its outdoor test scenarios to include indoor environments, including airports, malls, offices, hospitals, campuses, and train stations. South Korean operators can practically only use an indoor wireless infrastructure known as Digital Indoor Systems (DISs), rather than the traditional Distributed Antenna Systems (DASs). The adoption of DIS wireless infrastructure enables operators to reduce deployment costs and operate both 4G and 5G technologies in one system, while maintaining future compatibility.

All of these aspects will be vital to meet future enterprise requirements, especially when several applications require low-latency, high-throughput capabilities to enable mission-critical or even life-critical applications. For example, a smart electronics factory may need a very high uplink capacity that traditional DASs cannot support, in the order of >1 Gigabits per Second (Gbps)/1000 Square Meter (m2) or a train station may need to connect hundreds of thousands of subscribers per day; the Shanghai railway station is used by 330,000 subscribers daily, who generate more than 17 Terabytes (TB) per day.

Huawei LampSite Introduces 5G Distributed Massive MIMO for Indoor Deployments

The Huawei LampSite solution is an integrated in-building wireless solution that includes the following components:

  • Baseband Unit (BBU): Performs processing capabilities, including resource allocation, and coordinates the distributed radios
  • Remote Radio Unit (RRU) Hub: A concentrator that connects the radios to the BBU
  • Pico Radio Remote Units (pRRU): The distributed active radios that are deployed throughout a venue

The Huawei LampSite solution has been deployed in several large-scale indoor networks worldwide and allows the introduction of major new features through software upgrades. One of these features is called 5G distributed massive MIMO. This new technology has been developed to address the demanding requirements of several in-building enterprise wireless environments, which often require low-latency and Gbps-level connectivity. Current in-building wireless systems only offer 4T4R capabilities and are largely unable to satisfy these requirements. The upgraded solution allows massive MIMO technology to be introduced into indoor LampSite deployments, while keeping the radio heads as 4T4R, but the system is 64T64R with distributed pRRUs connected to a single baseband processing unit. In this way, LampSite deployments can achieve the beamforming gain and spatial multiplexing gains. 5G distributed massive MIMO introduces significant innovation that has, so far, only been applied to the outdoor domain and is a breakthrough as to what can be deployed in an indoor environment.

The tight coordination between the different distributed radio units allows for what is referred to as distributed massive MIMO, where multiple logical antennas act as a large system with the ability to track users. This advanced feature mitigates interference that is typically a debilitating factor when cell splitting is used for in-building wireless systems as a technique to increase capacity. 5G distributed massive MIMO can deliver a gigabit experience anywhere and anytime, which satisfies the key requirement in hotspot and enterprise production systems.

Distributed massive MIMO does introduce significant improvements compared to traditional capacity upgrade processes:

  • Compared to traditional cell splitting, which will cause significant interference in an overlapping area, the distributed massive MIMO converts interference signals from neighboring pRRUs into enhanced signals by multiple pRRU scheduling. Commercial deployments have illustrated that the user’s perceived speed can improve by 300%.
  • At the system level, distributed massive MIMO can enable a function of Multi User-MIMO (MU-MIMO), which allows different devices to share the same radio resources, thus achieving 3X to 4X the cell capacity in both uplink and downlink.

These features can be introduced through a software upgrade and present massive improvements over previous indoor wireless deployments and traditional systems.

Global Commercial Rollout of Distributed Massive MIMO

Huawei held its most recent Global Mobile Broadband Forum in mid-November, along with several leading global operators and industry partners, during which enterprises discussed the requirements of both outdoor and indoor 5G deployments, particularly in the context of enterprise use cases. Notable examples of distributed massive MIMO deployments were:

  • China Unicom launched its 5G capital project, aiming to deliver a high-quality experience for its subscribers, both outdoors and indoors. The operator deployed distributed massive MIMO in several VIP buildings, including factories and shopping malls. The operator, in partnership with Huawei, also deployed the new technology in the National Centre of Performing Arts of China. In this deployment, the distributed massive MIMO system achieved 4.7 Gbps peak throughput and a walk test of the venue resulted in an average speed of 1.2 Gbps throughout the venue.
  • LG U+ faced a different challenge, competing against major operators in a saturated market and operating with the disadvantage of owning limited spectrum assets compared to SK Telecom and KT. Nevertheless, the LG U+ strategy has been to offer the best possible experience in South Korea and has deployed distributed massive MIMO in shopping malls, subway stations, and other indoor environments. This has allowed the operator to offer continuous Gbps-level user experiences. Many recent road and network tests by third-party vendors have illustrated that LG U+ is leading in terms of performance in South Korea. It is important to note that LG U+ and Huawei collaborated to create the distributed massive MIMO technology and LGU+ has achieved 1Gbps speed in its indoor wireless deployments and boasts a 3X overall capacity increase.

There are also several other deployments where distributed massive MIMO has been deployed in existing LampSite systems, providing >1 Gbps consistent throughputs. Two such examples are in the Wuhan subway and Chengdu railway stations, where distributed massive MIMO has resulted in up to 368% performance improvement with traditional DISs.

Conclusions and Recommendations

Huawei’s experience in existing in-building wireless LampSite deployments, combined with the operator requirements highlighted above, indicate that large-scale 5G deployments need to be positioned toward both consumer and enterprise applications, often considering both downlink and uplink requirements. Moreover, a future-proof indoor wireless network will allow advanced technologies, such as indoor positioning to a Centimeter (cm)-level that The 3rd Generation Partnership Project (3GPP) Release 17 and future releases will allow.

Huawei’s initial distributed massive MIMO deployments show the rest of the world that a software upgrade can result in significant capacity improvements, a better user experience, and the potential use of the LampSite solution for both consumer and enterprise applications. The distributed massive MIMO breakthrough is truly the next step in enhancing in-building wireless deployments and is the first appearance of massive MIMO indoors. This offers significant benefits and an easier deployment for mobile operators; no more careful indoor planning is necessary to minimize interference from adjacent cells, while the level of service, in terms of both capacity and latency, will propel indoor wireless systems to a new era. This will transform both consumer domains, where the indoor user experience will match the outdoor one, and the enterprise domain, where cellular will be able to fulfill the stringent requirements of many enterprise verticals.

Content in this article is based on original research by ABI Research and is sponsored by Huawei.