Saturday, December 31, 2011

Mini Course in Cell Site Identification (Pt2)

Mini Course in Cell Site Identification (Pt2)

Further to the introduction to CSI in Part 1 which can be accessed here:

The mini course continues, Part 2, with consideration about further observations as to the information gathering process and evidence issues associated with cell site identification (CSI) and further points about  masts (a.k.a  whether they be BTS, Node B, eNode B and so on).

The concept of cell site identification (CSI) as a procedure within cell site analysis (CSA) should never be under-estimated by adopting a belief e.g. because the operator takes care of the radio network side the radio coverage can assumed. The operator has never claimed to have designed and rolled out a mobile radio network that ticks all the boxes for forensics and/or evidential requirements. The whole point of CSI/CSA is for the examiner, investigator or expert to identify the operating component factors or integers that corroborates identifiers and other evidence of the locale in which the target MS (mobile station) is said to have been used.

Whilst CSI may parallel the work, in part, at least, of an RF test engineer, the outcomes sought for CSA are very different to that of the network operator's test engineer.  It may be helpful to summarise that difference by referring to the fact the person conducting CSI, for instance, conducts a technical fact-finding investigation to establish a "chain of causation" linking the activing of a target MS in a radio coverage area, a particular terrain and/or property where a crime is alleged to have been committed.

To illustrate some points for cell site identification that may be of interest to the reader, there are six images below. The images displayed below also contain a short narrative explaining operating component factors or integers to consider about the coverage itself. Of course those images omit narrative which the viewer needs to comprehend for CSI for him/herself, so some additional observations have been added.

The masts in the images suggests the coverage in each image is being transmitted from a single source BTS. Which one of the images omits to mention (if at all) that the mast may provide coverage to a location because it is a Repeater?

The images show radio coverage and how radio signals can be affected by natural or manmade phenomenon. But for CSI what about mast identities as broadcast in the radio coverage. Is the content in the radio coverage prepared and made by MSC and/or BSC or does the BTS have any part to play in preparing or making content?

The images show radio coverage delivered to the azimuth but not if coverage has been subjected to antenna tilt. Does your radio test equipment decode data broadcast from the BTS which corroborates the degree of tilt per antenna?

The masts in the images are depicted as being permanent building or ground-fixed structures. There are though masts that provide coverage on a temporary basis called 'mobile cell sites' which are not permanent building-fixed or ground-fixed. I believe in the US they have coined the phrase COW (cell (cellular) on wheels).

There are many examples that could be given but I wanted to select a few examples to challenge concepts. Concepts such as merely going to site and taking a photo of a mast, whilst helpful, does not communicate other important factors; particularly where those other factors are not communicated anywhere else.