Small Cell Design (Indoor) – Soft RF Considerations
Once the physical considerations of a small cell design are accounted for, there is the soft side of it that also needs to be looked at to ensure if fits into the overall network and provides the desired impact. There are many soft considerations on specific parameters that are unique to each vendors in terms of load balancing, offsets and such, but we will consider some of the major soft considerations that impact the design. These include:
- Understand Macro Layer Coverage
- Small Cell Bleed Out Impacts
- PCI/PSC Availability
- Neighbor Considerations
Macro Layer Coverage: RF Survey is the initial phase of indoor small cell design and it gives an idea how you will do the design. We have to make sure macro coverage is not strong inside so small cell design is eligible for the floor or building. In some cases, there is macro dominance near edge of the floor/windows or part of the building. We always try to avoid partial floor designs because it brings lots of problems after the site is on-air in performance point of view. Since you don’t know exactly where macro and small cell network interact in partial floor design, it is hard to monitor where handovers happening and achieve desired KPIs. It is preferred to assign clear frequency/ channel for small cells. If the channel is overlapping with existing macro network carriers, design will be challenging. +6 dB dominance over the rastered macro carrier gives best small cell Ec/Io inside the building and good isolation between macro & leaked small cell outside the building. If clear channel is used for small cells, RSSI values should be measured in survey stage and small cell design will be done to overcome RSSI values inside the building.
Bleed Out: Bleed out is one of the main concerns in indoor small cell design. While you put small cells inside the venue to provide coverage, the aim is to keep signal inside and not bleeding outside. If the signal bleeds outside from grid small cells (not interacting with macro) and if people camps on them and then when they walk away from the building they cannot hand in to macro network. Also for high-rise type of venues, if small cell signal bleeds outs it can interfere people in another building or people in adjacent floors. It is always preferred to give service and quality from closest small cells inside. Bleed out plots of building and between floors should be checked in design and make sure concerns will be addressed.
PSC/PCI Planning: Like every design, model tuning will give more benefits in small cell design too. It is better to take measurements before and after design so you can calibrate your existing model. If you calibrate your model for different types of environments such as office spaces, warehouses, stores you can use same model for same type of venue in the future. Every small cell is acting like a macro cell in the network. So they need systematic PSC planning like macro cells. If you have a large venue with high number of small cells, it is always good to assign same PSCs for the ones not interacting each other so you can able to use PSCs more efficiently. For gateway small cells, which are interacting with macro network, unique PSCs should be used. Another important thing is, if you have different venues with small cells in the same macro RNC border, gateways small cells PSCs should be also unique. In design stage, PSC planning need more attention and using same PSCs for small cells need to be avoided.
Neighbor Considerations: In small cell design, defining small cells as gateway or grid is important. Grids are the ones do not interact with macro network. Gateways are interacting with macro network and they are the ones serving ingress/egress points of the floor or building. Gateways need to be defined in macro cell neighbor lists to enable mobility between small cells and macro network. But macro cells have limited number of neighbors allowed, so more attention is required to provide space for them. For some vendors, not only providing space for small cells is enough, but also giving correct priority is necessary.