Nokia’s four step solution towards Small Cells for in-building connectivity

Inbuilding Cellular UserRecognising that over 80% of cellular traffic is consumed indoors, Nokia takes a slightly different approach from other vendors to address the problem. We review a white paper that discusses and expounds their views on how operators can best evolve their networks to meet the indoor challenges.



The four step roadmap towards indoor densification

Nokia’s indoor roadmap comes in the following four stages:

  1. Maximise indoor coverage from existing outdoor macrocell sites
  2. Deploy outdoor small cell sites in congested areas (city centre, shopping streets) for street level outdoor-in
  3. Start deploying small cells in high value congested public indoor spaces
  4. Expand small cell installations to include enterprises and public buildings

Outdoor macrocell sites have limits

It can be difficult, expensive and time consuming to identify and deploy suitable new macrocell rooftop sites in congested urban areas. However there are several technical options available to make the most of existing sites including:

  • sector splitting
  • lighting up additional spectrum
  • refarming spectrum from 2G/3G to LTE
  • using higher order MIMO
  • introducing higher order QAM

Each has their benefits and disadvantages.

  • Additional or larger antennas may incur higher site rental fees
  • Additional spectrum can be costly. Low band (600MHz) may be less useful in highly congested areas whereas high band unlicenced (5GHz LAA) may have very short range
  • Refarming to LTE may be hampered by end user device compatibility
  • Higher order QAM requires a high signal to noise ratio that is unlikely to be achieved when penetrating inside buildings from outdoors.

Ultimately there are capacity and coverage limits for this approach, and each new feature adds cost. Some analysts believe we have crossed the threshold where the TCO (Total Cost of Ownership) for complementary small cell deployment is less than the traditional outside-in macrocell approach. Finally, buildings environmental regulations in many countries makes outdoor-in no longer technically viable.

Outdoor Urban Small Cells have their sweet spot for indoor too

Urban pedestrian street canyons can be one of the most demanding areas to cover effectively and cost efficiently. This is where targeted deployment of urban street level small cells can be a game changer, serving the pedestrian footfall and slow moving traffic in the streets. Costs vary widely depending on the region, depending on many factors from local planning laws to backhaul availability. Wireless mesh backhaul at street level can simplify deployment logistics.

Street level urban small cells can also serve users in the lower floors of adjacent buildings, such as those in retail outlets. They won’t reach those on the higher floors or deep inside.

Inbuilding Cellular User Large

Lighting up from the inside

Nokia argue that there is already a strong business case to provide service for high footfall public areas using in-building systems.

DAS (Distributed Antenna Systems) have been a common choice up to now, partly because they are can support multiple operators and are technology agnostic. Upfront costs for DAS are typically quite high, offset by the ability to split the cost between operators. They are more suitable for large and very large buildings where the high costs can be amortised across many users. Complexity can make it expensive to upgrade or expand in the future.

Service should be very reliable and consistent, although long term under-investment results in customer dissatisfaction with both the operator and the venue.

One option to enhance existing DAS is by using lower cost, lower power small cells to drive them rather than full size macrocells. These add capacity through additional sectors, rather than additional spectrum, within each building.

Another option to enhance the capacity of an existing legacy DAS deployment is with an overlay of LTE indoor small cells. A few strategically placed units covering the highest footfall areas may give the older 2G/3G equipment a new lease of life and help differentiate higher quality of service for that one operator. Backhaul connection using standard Cat5 Ethernet cabling simplifies installation.

Public Wi-Fi

Many venues and public areas have invested in their own Wi-Fi networks with variable success. Those which are well engineered can provide a good user experience, while those that are poorly constructed or have outgrown their original capacity design can be very disappointing.

The advent of more seamless authentication, either using Hotspot 2.0 or proprietary methods, can improve the user experience. Excessive advertising, poor service quality or spam has the opposite result.

One option for operators with their own Wi-Fi networks is to augment LTE service with a mix of indoor Wi-Fi and LTE small cells.

Indoor Small Cells are the most efficient

There is an inherent technical superiority of LTE, which uses a co-ordinated and tightly scheduled radio interface compared to that of best-effort, un-coordinated Wi-Fi. Fewer LTE small cells can provide higher capacity, data speeds and full mobility compared to a similar Wi-Fi installation.

Trade-offs between these options are illustrated in the chart below for a 60 floor skyscraper with the highest total capacity per floor coming from a larger number of low power small cells.

Five Small Cell Scenarios

Planning ahead for 2020

Rather than just playing catch-up, its best to be able to plan ahead for the number of cells required to meet future demand. The chart below indicates the number of small cells for a dense indoor deployment per 10,000 m2 (approx. 100,000 sq feet) in 2020.

The four figures shown are for 20 vs 25dBm and for shared vs dedicated spectrum respectively. As you can see, dedicated indoor spectrum would require far fewer small cells than if spectrum is shared with outdoors.

Indoor Spectrum Efficiency

Further reading

Nokia’s clear four-stage approach to network densification takes cellular service indoors where consumption is highest. It seems to me to be an inevitable transition for all operators to make at some point, and will be an essential element in everybody’s strategic roadmap.

Nokia have published a 10 page White Paper expanding on the topic above, well worth reading and available to download here.

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