Cell Site Analysis Expert Witness

The records containing the cell information including the Cell ID, are known as the Call Data (Detail) Records (or CDRs for short).   They are available from the UK mobile networks usually for a period of 12 months.   However, in criminal cases, they are often obtained by the police.   This data is available for both contract phones and those on a Pay as You Go (PAYG) arrangement.

It is the CDRs that allow cell site analysis (as well as other connection charting and behaviour analysis / attribution assessments) to be conducted.  Sam is an expert in manually examining these records including ensuring that they have been provided to you in the correct and original formats.   She has a wealth of experience of reviewing this data in their raw formats throughout the past 20 years.

Sam can also assist you in obtaining disclosure of these records from the police/CPS or directly from the network providers (where available/necessary). Details of what SRC will require in order to assess an instruction and also for your convenience the wording for requesting the call data records are provided within Instructing SRC in Cell Site Analysis cases at the end of this page.

Sam can provide assessments to specifically determine what the records mean and their limitations as well as identify their 'quirks' and errors.   She also plots the data using computer programs she has written herself to independently test the accuracy of data including identifying omissions and preparing chronologies of use of phones.   

Sam can also use other technical location data including considering WiFi usage, WiFi calling and MAC address/IP address usage as well as location evidence stored on phones or within Cloud accounts (e.g. Google maps).

Cell site analysis in the movies is used to zoom in on a phone.   In practice it is unlikely to be that accurate, unless in exceptional circumstances.  However, cell site analysis is particularly powerful when a telephone has been travelling over large distances (for example, a telephone moving from the London area to the Manchester area), for shorter distances or when static locations/use in specific locations, things become more variable and uncertain requiring more in-depth expert considerations.

When cases involve a telephone being located in a particular area of interest, usually cell site analysis is conducted to answer questions about case-based scenarios. Typically, it will be used to address if a telephone may have been located at the scene of an alleged crime scene and/or where the defendant states they were located (or the scope of where they may have been located).  In such a situation, 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.   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 below within Best Serving/Most Likely Cell and Evaluating Use.

In general, the limitations in cell site analysis cases are specific to the location and cell use, there are no generic answers.  It is essential that this is fully evaluated to examine the data and carefully explain the limitations for each of the relevant time period(s) in your case.

Every cell has a geographical area in which it may be used to make a call or text (or used for data). However, the coverage of a cell is determined by many factors including its: 

• Orientation - its horizontal bearing known as its azimuth and also its vertical tilt. 
• The type of technology of the cell (2G, 3G, 4G or 5G).
• The type of cell - Macro, femto, pico, nano etc.
• Buildings in the area and the general topology of the landscape.
• The type of handset in use and its settings.
• The congestion level of the network.
• The height of a mast/cell.
• The physical landscape surrounding it.
• If the cell and those surrounding are functioning correctly etc. 
• Et al.

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.  This means it must be carefully considered by an expert, where it can be stated the phone may have/have not resided.

It is particularly important that when cell site analysis is conducted, all cells use by a phone (as recorded in the CDRs - see above)  must be considered, including before and after the time of interest, and considerng travel time and use between them, in order to correctly interpret any use.  Cell use should never be considered in isolation, since it may provide misleading and incorrect results.  

Sam realises cell site analysis cases are complex and also that they 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.  Particularly, with respect to this, 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/useful.    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 computer programs coded by her, 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. 

Sam is often asked which cell is ‘most likely’ or ‘best serving’ cell in a location of interest, or which location out of a possiblity of several, is the most likely the phone was located at.   However, neither of these are scientifically valid questions in cell site analysis.   It is only possible to address the question, can a Cell A be used at a location X or not.  It is easier to explain this as examples:

• Let's say Cell A can provide coverage (meaning that it can used to coordinate a call/text/data) at location X and not Y - in such a situation it will be concluded that the phone may have been at X and not at Y.   
• In another scenario where Cell A provides coverage to both X and Y, it can only be stated the phone may have been at location X or Y.   It cannot state if X or Y is the most probable location, nor pin-point a phone to X or Y (since the phone could be at any other location where Cell A can coordinate a connection).

The above can be 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.

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 (external site - opens in new browser window).

The BTS connects to the BSC and that to the MCS...........

Telecoms is full of acronyms. Sam believes using these do not assist the Court's understanding.  In her reports, she attempts to simplify the concepts and write in a more understandable (and still technically accurate) way, allowing for the key concepts and issues to be clearly discussed.

Sam is sometimes asked to conduct radio frequency readings to determine a full list of all cells proving coverage to a particular location.   This data may sound helpful, however, in practice this is very time consuming to properly conduct (so expensive) and often will have very limited (or no) worth to the overall case.   

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.   This means establishing what other cells are available, does not assist addressing the use.

In Sam's view, cell site analysis should now be thought of as the evidence of last resort.  Why?

• It is complex (and expensive) to properly perform.
• Other sources of evidence may allow for a accurate assessment of the location and use (including attribution) of a phone.  

Sam can also provide assessments of tracker/Sat Nav or vehicle telematics and/or location evidence on devices/mobile phones which can be used to determine location information some of which may exceed (and supercede) 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 CDRs if they have been requested correctly, and also may be 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 Sam's previous case list for examples of previous cases work on.