We often hear of customer or quality problems during network upgrades. As most networks are moving to 4G and expanding 3G capacity, maintaining 2G and 3G quality is important, as it will have the greatest impact on the existing subscriber base. Many marketeers will insist that our existing customer is more important than a new one, reflecting their understanding of customer acquisition costs and lifetime customer value. So ensuring the quality of the network and service during network upgrades will be critical to customer retention, satisfaction and references to winning new customers.
Upgrading a mobile radio network to 4G is a complex project involving many technical aspects. Good housekeeping and attention to detail are needed to minimise disruption and maximise return on investment. This is particularly so in the acceptance process from the system integrator, vendor or internal roll-out team.
Before describing potential quality impacts, I think that the concept of the cell-edge is important. A cell usually has more than one cell-edge. The main cell-edge is outdoors, readily understood and relatively smooth. It exists where our cell meets the neighbouring cell, or where coverage runs out, usually in rural areas. While changes to this cell edge have an impact, they are usually mitigated by overlapping coverage, existing terrain limits or low population density. While in theory a 3dB reduction in carrier power should halve the cell area, the fact that the cell edge is already determined by a terrain obstacle or overlaps with a neighbouring cell mitigates this. However, many other cell edges exist as internal holes in the cell. Less than perfect indoor coverage means that, in reality, cells are more like Swiss-cheese having many internal edges. This can be seen in the figure below. A change of a few dB in available carrier power can therefore make a significant difference to a large number of customers. As an analogy, consider Norway and the United States as the real cell and ideal cell respectively. While the square area of the US is thirty times greater than that of Norway, Norway has a 25% longer coastline. A change to the edge of the ‘Norway’ cell will have a much bigger customer impact than the ‘US’ cell.
There are many ways that existing customer quality can be impacted by a 4G overlay or 3G capacity expansion. I will describe just three of them for the moment. The first one is the impact from the introduction of new coupling systems. This is done where a coupler is introduced so that 2G/3G/4G systems can share the same antenna and feeder systems or when two sites are being consolidated as part of a network sharing agreement. This coupler represents an extra insertion loss along with the extra associated connection losses.
The second impact occurs when extra 3G carriers are added to a cell, often at the same time as a 4G upgrade. The addition of this extra 3G capacity reduces the output power available per carrier. For example, consider a cell with two carriers and a 60W power amplifier. Each carrier has 30W of power. Adding a third carrier sharing the same power output reduces the power output for each carrier to 20W, reducing the downlink cell edge by 1.8dB. This increases the size of the numerous coverage holes within the cell creating a significant customer impact.
A third affect to be considered is the impact of a BTS upgrade on the feeder system. Upgrades such as these involve the disconnection and reconnection of numerous cables and connectors. Connector losses from improperly made or hand-tightened connections are very high. This is very basic stuff but in our experience is often neglected due to time and cost pressures. Nothing beats a proper torque wrench for ensuring rigging quality.
These are just three of the ways that a network upgrade can affect our existing customers. Understanding these potential impacts can help the process of mitigating them and inform the acceptance and project management practices put in place. Doing this, we can ensure that our investments in the network lift the quality of experience for all customers and not bring in new capabilities at the expense of existing offerings.