With the potentially flawed systems that we end up with after an initially planned cellular network it is usually necessary to do some tuning and optimization. In doing so the provider can keep running a good running network and provide customers with the services they need. We have seen in 3.1 that most networks usually need continuous maintenance due to complexity in the network and we will briefly go through the different benefits that come with cell optimizations.
3.4.1
Initial tuning
After initially constructing a network but before actually rolling it out to the public initial tuning of the original plan has to be performed. Simulations and propagation models will not always predict the reality with good enough precision so it of course important to amend for these imperfections. However important, this initial procedure will not be analyzed further in this thesis since the process itself is so similar to the cell optimizations performed at a later stage.
3.4.2
Continuous optimization
To be able to maintain a good cellular network that probably is expanding it is important to continuously analyze the system. This can be done either by gathering actual network data from the system itself and building a model that estimates the coverage and capacity and so on. But when the problems get to complex it is always better to have a real life overview of the system. By doing field testing and getting readings from actual hot spots one can better see when and where problems arise. This allows engineers to rapidly assess the situation and act upon it. [12, pp 395] describes it as:
The rapid transition from prediction-based performance estimation to measured facts about the network and service performance are the essence of operational efficiency.
With the rapid and extensive change from second to third generation of networks there are quite few new things that have to be considered when it comes to cell optimization as well. The most important of which is the frequent change into packet based data with a lot of different kinds of services. Parameters such as QoS1 for each of the different services are things that the operator wants to focus on to able to optimize the earnings for a specific traffic profile. There are different kinds of situations that the different operators want to be able to handle. For example one operator could be focusing on good coverage whilst another one tries having better quality and faster links in order to compete and gain customers.
The Radio Resource Utilization (RRU) is a theoretical term that describes the utilization of the radio spectrum. The operator’s role is to optimize its network within the RRU in order to get the feature that it wants, for instance better coverage. When the operator adds new base stations or new services it is
3.5. FIELD TESTING 17 of course important to keep the focus on the kind of quality and coverage that it wants to offer. [12]
3.5
Field testing
Today there are a number of different field testing tools from different companies, many of which have been around for a long time. The main purpose of a field testing tool is to gather a lot of real life traffic data from the networks that you operate in order to spot problems and of course to do general cell optimizations as described in section 3.4. Perhaps the easiest way of doing this is to go by car and driving around the area of interest while constantly logging the network and saving it together with a GPS-location stamp and a time stamp.
3.5.1
UE testing tools
A field testing tool can take many shapes, ranging from entire vans to simple handsets. What I will focus on in this thesis is the UE simple handset type of testing tool. Most of the new modern cellular phones released today have a built in field engineer mode or a field test mode, which can aid the manufacturer of the phone to discern if the phone is of good quality or not. This information however is not always sufficient for network operators since they usually need more extensive information and the capabilities of saving the gathered data together with a GPS location stamp. For this purpose there are a handful of developers that specialize in making analyzing tool aimed for operators that want to analyze and optimize their networks.
In order to be able to do the optimizations described in section 3.4 there are a lot of information that has to be gathered. The continuous feedback loops usually only needs rather general information such as the signal quality and signal strength in a given sector, but if a more specific problem in the network occurs it is favorable with detailed information about what happened. Information such as dropped call percentage and event information on lower layers help provide the person doing the analysis to come up with the reason for the problem and hopefully a way of mending it.
Since the cellular network is a rather complex of base stations and controllers it might be insufficient to only rely on field testing data to completely improve the entire network. Irregularities observed at individual base stations can be the result of deeper and more complex problems, such as improper spreading factors etc.
Nonetheless, the extensive deployment of field engineers with field testing tools remains an important part of the overall network maintenance and of course to the cell optimization process.
3.5.2
Scanners
A scanner does exactly what it sounds like, it scans the networks. These kinds of tools are perhaps not as useful in many cases as the normal UE type of scanning devices because pure scanner devices do not interact with the network. This means that phenomena that would occur when using a UE tool will not be able to occur. Because scanners do not have to register on the network like typical
18 CHAPTER 3. CELLULAR NETWORK ARCHITECTURES UE handsets do it can be useful to use a scanner when you want to observe the network as a whole. Although scanners can be useful they are not that frequently in use anymore as most problems that need solving can be analyzed with the help of UE handsets. For this reason scanners will not be handled further in this thesis.
3.5.3
Common principles and practices
Due to the random nature of the users of cellular phones it is important to do field testing that also tests randomly and evenly distributed over the network. By gathering more and more data it is also easier to get a good overview of the network as the utilization generally change over time. By following local traffic and high density commuter lines one can get good readings as it can be assumed that these areas are also more likely to utilize the cellular network.
Chapter 4
Design and implementation
This chapter deals with the overall design problems that were encountered when developing the RAT-UE application and the resulting design ready for implementation. In order to develop such a specialized application as a network data gatherer for GSM/UMTS networks one has to pay respect to the constraints and the possibly limited number of options in the development process. Access to a specific radio chipset is not something that is readily available for normal developers without approved partnership programs with the vendor, so in order to be able to develop anything at all one has to consider the possibilities of gaining access to the radio chipset.