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Checking and plotting cell use
SRC can prepare coverage maps using bespoke software
Cell site analysis - What are the limitations?
Cell site analysis may provide useful evidence to enabling an expert to state that a telephone was traveling 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 requiring more in-depth considerations.
When cases involve a telephone being located in a fairly small geographical 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 an alleged crime scene and/or where the defendant states they were located. In such a situations detailed analysis will generally be required.
Some terms were (wrongly) used in cell site analysis in the past by other experts which still still cause confusion about what is and is not possible and what is relevant to consider. This may include concepts such as assessing the likelihood of use of a cell and which cell would be most likely used etc. Although these may seem reasonable propositions to consider, they are not scientifically valid. It is only possible to state that a cell (or cells) could be used at a specific location or not. Cell site analysis usually cannot state the phone was at the location since it cannot pin-point a phone. Sam discusses this further within
Best Serving/Most Likely Cell and Evaluating Use.
In general the limitations in cases are specific to the location and cell use, hence, there are no generic answers meaning that Sam will need to carefully explain these for each of the relevant cell usage in your case.
Cell site analysis - Co-Location and Attribution Assessments
Cell site analysis may be conducted to allege a certain phone is in use by a particular party based on its location behaviour or its usage compared with other attributed/known use. SRC can assess this use checking any software generated (or expert) assessments made by others and consider if at any times the phones are inconsistent with the alleged use or otherwise. This can also be combined with full attribution assessments of the available digital evidence including handset examinations, contact analysis and general cell (top) usage etc.
Cell Coverage and Network (RF) Readings/Surveys
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 type of cell (2G, 3G, 4G or 5G), 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 mobile signal from a particular cell in a given location is also variable. Hence, when a phone uses cells, it must be carefully considered by an expert where it can be stated the phone may have/have not resided.
It is particularly important to note that when cell site analysis is conducted,
all cells use by a phone
must be considered including before and after the time of interest, and to correctly interpret any data session use.
Cell use should never be considered simplying in isolation
since it will provide misleading and incorrect results.
Sam realises cell site analysis cases are complex and can be expensive. The main objective in all Sam's work is to provide a report which provides the answers in cases (and not more questions) in the most cost effective way. Hence, it is important when instructing/advising in cell site analysis that the objectives of the analysis are clear so that SRC can recommend the best approach. This will generally reduce the costs and ensure that any work supplied will address the answers to the questions required. In some cases, SRC has completed work in less than 15% of the time quoted by others or determined (for no fee) there was no benefit to pursuing the case point. Details of what information SRC will require in order to assess and provide an estimate for an instruction are provided at the end of this page.
Particularly, SRC is often initially instructed in requirements for radio frequency (RF) readings/surveys - these are also sometimes called network readings. However, RF surveys/readings are very expensive to properly conduct and consider - it is also Sam's experience that in the majority of cases they are not actually required. Hence, it is may be possible to save considerable time/costs by performing a 'paper study' analysis first to determine if surveys will be useful in the case or otherwise. This type of analysis is also likely to narrow the scope in the event radio frequency readings are required, hence, reducing overall costs.
SRC can examine (and capture) RF readings where this is necessary. Sam is familiar with readings captured via CSurv, Nemo, TEMS and ICS-500 devices. She uses her own computer programs to process such data and plot cell use to independently test such data and also obtain further potential coverage from analysis of neighbouring cells and other information.
Best serving/Most Likely Cell Use and Establishing Use
It should also be noted that which cell is ‘most likely’ or ‘best serving’ cell in a location of interest are not a scientifically valid concepts in cell site analysis unless large amounts of data are gathered at the time of interest. It is only possible to state if a cell(s) of interest could be used at a location or not.
In a simple scenario where a Cell A can provide coverage (meaning that it can be used within a telephone call, text or data use) at location X and not Y, then in such a situation it can be concluded that the phone may have been at X and not at Y. In the event Cell A provides coverage to both X and Y it can only be stated the phone could have been at location X or Y (and any other location where Cell A can serve). It cannot state if X or Y is the most probable location nor pin-point a phone to X or Y.
The above can be a lot more complex in practice since there may be multiple cells in use and the surrounding use will need to be considered. In other more involved considerations it may also be required to evaluate more complex scenarios, for example, "did the journey of a phone occurred via Y route or Z or potentially both being valid/neither?" etc.
Additionally, radio frequency readings to determine a full list of all cells which may provide coverage to a particular location may sound helpful, however, in practice this is very time consuming to properly conduct and often will have very limited (or no) worth to the overall case. Since cell site analysis primarily is used to deal with the question "Can Cell A provided coverage to location X?". It cannot state which cell is most likely to provide coverage to X nor the probability of such usage, it can only answer the question as yes or no.
These concepts of most likely/best serving cell have been used in the past by mobile network engineers, however, it is SRC's view that they do not apply to cell site analysis and can be misleading. For further details in relation to this, see the Forensic Regulator's Code of Practice for Cell Site Analysis.
Other Location Evidence
Cell site analysis should be thought of as the evidence of last resort since it is complex to perform and other sources of evidence may provided much more accurate assessments of where a phone has resided or also who is using a phone. Sam can also provide assessments of tracker or other location evidence on devices/satellite navigation units and mobile phones which can be used to determine additional location information some of which may exceed the ability of cell site analysis for the same device. It can also be used to compare use - for example, comparing the cell use of a phone with a car tracker as part of attribution assessments or otherwise.
It is also possible for mobile telephones to use WiFi to coordinate calls/texts in a process known as WiFi calling. Information about the use of this may be available within the connection records and also present within evidence stored on the handset. SRC can combine these two sources of evidence in order to incorporate WiFi usage with cell site analysis.
Sam can provide provide a free overview and advice for your case evidence to determine the best way to progress given your case scenario and assist you how to obtain the required records from the CPS/police or directly from the network providers. Contact SRC for provision of this service. See SRC's previous case list for examples of previous cases work on.
Instructing SRC in Cell Site Analysis cases
SRC specialises in large and complex cell site analysis cases particularly involving multiple dates, phones and usage as well as considering co-location and other usage assessments. Sam also specialises in cases where there is the potential for congregation of telephones in certain areas.
SRC only undertakes instructions to an expert level, hence SRC does not routinely supply tables/mappings since Sam is of the view that without an expert level assessment they are open to potential misinterpretation by the Court or at times can even be misleading.
In all cases, SRC will need the call data records for the phones of interest in their non-redacted form and can provide checks on these records to ensure they are provided to a satisfactory standard. If you do not have the call data records in your case you will need to ask for them as soon as possible since cell site analysis cannot be commenced without these fundamental records. You should request the following:
“The original, complete and unredacted PDF and spreadsheet call data records including full cell information for standard use, data use and DDR information (where available) for <insert telephones>”.
If you are unsure regarding what has been provided to you,
contact SRC for a free review.
In most cell site analysis cases, SRC will also require case information to accurately provide an initial opinion/guidance and to establish the type of analysis required to accurately estimate the time and costs. In general it will be useful to address the following:
It will also be useful to supply the following in the event these are available:
In complex cases Sam can also provide initial evaluations of the case to assist you with how to start/ways forward in the case and to obtain the disclosure of data required. SRC can supply initial estimates for this process and then supply a full estimate when in possession of all required information/instructions.
As part of the analysis in cell site analysis cases, SRC can also review any reports prepared by analysts, experts or otherwise and comment on the potential issues of presenting the Court with tables/maps of use or other representations. Sam is also experienced in conducting conferences/discussions and formal expert meetings which she finds are now frequently requested by the Court. In previous cases, this has involved other experts revising their statements, provision of joint statements of agreement/disagreement, and disproving a case scenario via the demonstration of contrary information.
See SRC's previous case list for examples of previous cell site analysis cases.
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