Cell site analysis (often shortened to CSA) is a technique to determine the general geographical vicinity of a mobile telephone at the time of its past connections. The procedure is very different to a live analysis of a telephone's movements or telephone tracking since the amount of data available when performing cell site analysis is often very limited.
Background Information to Mobile Networks
What is Cell Site Analysis? What are the limitations?
The geographical landscape of the UK and Ireland is scattered with mobile telephone masts. Each mast has one or more cells (shown in figure 1). In simple terms, when a mobile telephone is making/receiving a call or a text message it uses a cell to manage the connection.
Each cell has a unique number assigned to it known as the Cell ID. It is this unique cell number that the network providers store for each connection a telephone makes and receives on their network. The records containing this information are known as the Call Data (Detail) Records (CDRs for short). It is these CDRs that allow cell site analysis to be conducted.
There are two main types of mobile network in the UK: 2G and 3G. On a 2G network, a cell has a theoretical range of 35Km, however, it is theoretically possible, using repeaters (signal boosters) to extend this coverage to a distance of 70Km. For 3G cells, the coverage is determined by multiple factors but usually would not exceed 30Km within the United Kingdom.
However, it is important to appreciate that these ranges are theoretical and would only apply in the event the terrain was complete flat, the network was not receiving many connections and that the conditions for the transfer of radio signals were perfect.
Coverage of Cells
Each cell has a geographical area in which it may be used to make a call or text. However, the coverage of a cell is determined by many factors including its orientation, the physical landscape surrounding it, if the cell and those surrounding are functioning correctly etc. Additionally, just like how your radio signal sometimes can be intermittent, the received mobile signal from a particular cell in a given location is also variable due to physcial changes in the landscape/local area, changes in the positioning and configuration of cells, weather and network usage.
Sam Raincock works as principal scientist and expert witness at SRC and has also found large differences in the signal strength provided by a cell depending on whether a mobile telephone is located inside or outside a building including large difference sometimes being noted between rooms inside a building. Hence, she often conducts her cell site analysis to replicate the scenario including taking readings in all of the rooms of a building, taking the readings at approximately the same time as the past calls and taking the readings for as long as possible to obtain a better indication of the signal strength variability being detected.
Figure 1: A mast containing multiple cells.
Cell site analysis uses the connection records from the network provider to determine which cells were used at particular times of interest in a case. The process of cell site analysis is then determining the possible locations of the telephone using these cells at these times.
Cell site analysis is useful in enabling an expert to state that a telephone was travelling over large distances (for example, a telephone moving from the London area to the Manchester area), however, for short distances or static locations things become more variable and uncertain.
When cases involve a telephone being located in a fairly small georgraphical area (in the order of less than 2-5 miles), usually cell site analysis is conducted to answer questions about a particular scenario. Typically, it will be used to address if a telephone could have been located at the scene of a crime and/or where the defendant states they were located. In such a situation, an expert is likely to conduct network signal testing of the mobile network at both locations.
Instructing SRC in Cell Site Analysis cases
SRC specialises in large and complex cell site analysis cases particularly involving multiple locations, drive testing interpretations (when network readings are obtained via driving around the general area in a vehicle) and cases where the congregation of telephones in certain areas is significant.
In previous cases, Sam's analysis has resulted in experts revising their statements, provision of joint statements of agreement, evidence being withdrawn and disproving a case scenario via the demonstration of contrary information. See recent testimonials for cases in which SRC has previously been instructed.
Sam is also very passionate about the possibilities of miscarriages of justice due to misinterpretations of cell site analysis evidence or inappropriate analysis - she can provide a free initial review of your appeals case to determine if she may be able to assist. In such a case she may be able to provide a reduced rate or an element of Pro-Bono work.
Sam has recently worked on as a cell site analysis expert in a number of high profile cases including:
- DPP v John O’Brien (murder (acquitted)). May 2008
- R v Eusop Milne (murder and attempted murder). June 2008 and retrial July 2009.
- R v Christopher Morrissey (murder of a sub-postmaster's son). December 2009.
- R v Christopher Caunter (murder). November 2008.
- DPP v Joseph O'Rielly (murder). Quality validation for initial trial in June 2007 and review of the case for appeal in March 2009.
- DPP v Gerald Barry (murder of a Swiss national). March 2009.
- DPP v Garrett O'Brien (cell site analysis and connection evaluation - murder). June 2011.
- R v Ishaq Hussain (cell site analysis - Murder (Acquitted)). December 2011.