Deploying dense and scalable indoor small cell systems is not straightforward. SpiderCloud’s experience shows the indoor RF environment gets increasingly complex and challenging as the density of the deployment increases. This is particularly true in multi-story buildings where mobile devices experience a three-dimensional (3D) RF environment. A single handset is able to see a very large number of small cells, some on its own floor and others from floors above and below it. The radio signal inside buildings experiences flat fading, which means that even a stationary handset sees signal from small cells fluctuate by 6-8 dB. Despite such variation in signal quality, a small cell RAN should remain stable and not drop calls, or experience throughput degradation.
Figure 1: Indoor radio environment is more challenging in dense small cell deployments than macro networks.
In the coming years, wireless operators will have to use all their spectrum assets to deliver capacity. Dedicating spectrum for indoor small cells will not be a luxury that any operator will be able to afford. Not only must all small cells inside a building operate on the same channel, they must share this channel with the macro-cellular network. 3GPP standards define a number of techniques in which interference is managed between cells (3G soft handover, ICIC using FFR, eICIC for HetNets). However, all of them require some form of coordination between cells. To implement them, the indoor RAN system should have an entity that can coordinate interference between its cells and with the macro-cellular network.
Minimize Load on Core Network
The 3D RF environment, combined with flat fading, increases the number of handover events experienced by mobile devices. In some of SpiderCloud’s dense small cell deployments, mobile devices experience as many as two handover events per minute. If inter-small cell handover events are allowed to reach the core network, handling them can become a big expense for the operator. Ideally, all handover (mobility) events should be handled within the indoor RAN.
Deploying indoor RANs can be expensive if it requires extensive radio (RF) planning, dedicated cabling and manual configuration. The need for specialised technicians to do these operations can further slow down the pace of deployments. This is the case with today’s distributed antenna systems. Deploying such systems in a 12-16 story building can take 6-9 months and cost $1-$2 per ft2, where more than half the cost is in the installation.
For indoor RANs to be widely deployed, they should be able to use the building’s existing Ethernet infrastructure for both network connectivity and power, as much as possible. A small team of technicians, without specialized cellular wireless knowledge, should be able to install the system. And after that, the system should just work, without the need for manual configuration or optimization.
The number of 3G subscribers will continue to grow in many networks, even after LTE is launched, because 3G handsets will be less expensive than LTE handsets. Even subscribers with LTE devices will continue to use 3G for voice services, till Voice-over-LTE is launched. As a result, it is essential that operators deploy indoor RANs that support both 3G and LTE.