A Full Picture of 5G Indoor Coverage Solutions

In the 4G era, 80% of mobile services take place indoors. In the 5G era, the rich MBB services represented by AR/VR and 4K/8K video will further promote the development of indoor data traffic. It is estimated that more than 85% of 5G services will occur indoors. Therefore, the importance of 5G indoor coverage will be more significant.

In order to have bigger bandwidth, indoor 5G introduces higher frequency bands including C-Band and mmWave. Higher frequency means greater transmission and penetration loss. This article introduces the major 5G indoor coverage solutions.


1. Indoor coverage by outdoor macro cell


While deploying 5G networks, the outdoor macro cell should be fully utilized to achieve 5G indoor shallow coverage of some buildings. For example, 3.5GHz macro cells (mostly Massvie MIMO cells) can achieve outdoor 5G coverage while simultaneously realizing shallow indoor coverage of small and medium-sized buildings that are within 100 meters away from the base station. For buildings within about 100 meters from a 3.5GHz base station, the shallow indoor area could have a theoretical data throughput of more than 3Mbit/s, with penetration loss of 25dB in consideration.



Figure 1 Indoor 5G coverage by outdoor macro cell


2. Integrated picocell


The integrated picocell is a small low-power base station that connects to mobile core network through fixed broadband (PON, Ethernet, PTN, etc.) to provide users with 5G & LTE services. The picocell serves to provide network coverage in breadth and depth. It could not only be used to provide or enhance signal for blind or weak areas of macro cells’ coverage, but also be adopted to offload the heavy traffic from macro cells. It can be widely used in crowded areas such as urban hot spots, supermarkets, stadiums, etc.


Figure 2 Architecture of integrated picocell


3. Indoor distribution system


The mainstream indoor distribution systems mainly include passive DAS (Passive Distributed Antenna System), integrated picocell plus passive DAS systems, and active DAS (Active Distributed Antenna System).


3.1 Passive DAS


The passive DAS is an indoor distribution solution that has been used since the 2G era. The radio source is split by a series of passive components such as power splitters and couplers, and the signal is distributed to each low-power antenna installed in different areas of the building through the feeder. In this way, the signal is transmitted without amplification. For multi-system signal coverage, the combiner or POI could be used to combine the various radio sources and distributed through shared DAS system.


Figure 3 Passive DAS architecture


3.2 Integrated picocell + passive DAS


A solution combining integrated picocells and passive DAS is commonly used for multi-floor indoor coverage. An integrated picocell is deployed on each floor of the building, and the passive DAS system is connected to external antenna ports of the picocell to cover the floor. With this solution, the total cost could be significantly reduced.

To upgrade an existing system to support 5G, the picocell should be replaced by a dual-mode model. At the same time, it is necessary to evaluate whether the deployed passive DAS system meets the requirements of 5G. If not, related passive components should be replaced.


Figure 4 Integrated picocell + passive DAS


3.3 Active DAS


The active DAS is also known as optical fiber distribution system.

The active DAS consists of a main unit (MAU), an extension unit (MEU) and a remote unit (MRU). MAU can access radio signals from different sources, combine them through A/D conversion and digital processing, and transmit them after photoelectric conversion; The signals are then distributed to different MRUs through MEU and optical fiber network; Finally, the MRUs separate the signals of different sources, convert them back to radio signals through D/A conversion and modulation, and transmit them through antennas.

Compared with passive DAS, the active DAS does not require a precise calculation of link budget. Therefore, the cable layout is simple, and the construction is fast. Since it adopts a distributed architecture, the expansion is quite easy.


Figure 5 Active DAS


4. Digital indoor system


The new digital indoor system is a solution that has emerged in recent years and has received widespread attention from major equipment manufacturers who have proposed their own solutions, such as Huawei’s Lampsite, Nokia’s ASIR, ZTE’s QCell, and Ericsson’s RDS. The basic architecture of the digital indoor system consists of a baseband processing unit (BBU), a remote CPRI data aggregation unit, and a remote radio unit (picoRRU). The BBU can be shared with that of macro cells. The remote CPRI data aggregation unit is responsible for branching and aggregation of the CPRI data of the pRRU. And the pRRU processes the radio signal. The BBU and the remote CPRI data aggregation unit are connected by optical fiber, and the aggregation unit is connected with the pRRU through ethernet cable or optical fiber.


Figure 6 Digital indoor system


Compared with the traditional indoor distribution system, the new digital indoor system has the following advantages:

(1) The network architecture is simple and no link budget calculation is required.

(2) Sharing the same network O&S with the macro cells to have easy management.

(3) Compared with the active DAS, it solves the problem of uplink ground noise lift.

(4) Flexible cell merging and splitting, and easy capacity control.

(5) One net indoors and outdoors to facilitate macro-micro coordination.

(6) Support multi-stream transmission.


5. 5G Cellular signal booster


Cellular signal booster is also known as cell signal amplifier and cell phone signal booster.

5G cellular signal boosters collect 5G/4G signals from cell towers outdoor, amplify them, and redistribute the amplified signals indoors for seamless connectivity and uninterrupted communication. Cellular signal boosters provide a simple, rapidly-deployed and low-cost solution to solve the 5G&4G signal coverage issue of closed blind areas or weak coverage areas. Considering that the penetration capability of 5G signals from outdoor BTS to indoor areas is very weak because of the much higher frequency adopted by 5G technology, cellular signal boosters are commonly used at underground or semi-underground spaces, homes, shops and markets, elevators, small offices, etc.

The major advantage of this solution is that it’s plug and play, and users can install it by themselves according to the manual. Besides, the cost is low. And of course, as you can imagine, there is limitation. Firstly, it is only applicable to indoor areas from 100 to around 1000 square meters; Secondly, the user density couldn’t be high.


Figure 7  5G Cellular signal booster


6. Conclusion


Both performance and cost should be taken into account when choosing a suitable 5G indoor distribution solution. Generally, residential areas will still be covered by outdoor macro cells. The integrated picocell is suitable for large venues without partitions, but the cost is high. The traditional passive DAS has the advantage of low cost. However, the construction is difficult, and the multi-stream transmission feature of 5G cells could hardly be utilized. When upgrading from existing passive DAS, it’s mandatory to evaluate whether 5G frequency (>2.6 GHz) is supported. Generally, passive DAS is applicable to scenarios with low capacity and user experience requirements. The combined solution of integrated picocell and passive DAS harnesses the construction convenience of the picocell and the low-cost of passive DAS, while avoiding some disadvantages of passive DAS. The digital indoor system is the trend of the future indoor coverage solution. It might be applied to various scenarios, but the cost is relatively high. It is generally deployed in large traffic hubs, large shopping malls, high-end office buildings and other places with high traffic and demanding user experience. The cell signal booster is an ideal solution to very quickly solve 5G signal coverage issues with low cost for areas of typically hundreds of square meters, such as villas, houses, underground rooms, shops, etc.


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