RF Drive Testing
Major issues arise when the automated software analysis of call detail records (CDRs) is not verified by a qualified expert. Worldwide, juries are being presented with CDR and cell phone location information as part of trial evidence. This information can sometimes exonerat or convict an accused. However, today, many verdicts are under review around the globe due to improper analysis of cellular Call Detail Records (CDR)s. But there are certain verification techniques that can help further confirm the accuracy and completeness of a CDR analysis. This practice is called forensic radio frequency surveys, or drive testing.
What is a Forensic Radio Frequency Survey?
Radio Frequency Survey or "Drive Testing" Companies
This practice, commonly referred to as "drive testing," is performed by using particular techniques and specialized hardware and software to collect data on radio frequencies in an area of interest. Forensic experts use this data to determine the actual coverage area of a cell tower and its sectors. From there, they can create what's known as a propagation map, or a coverage map, for a specific tower. With that information, it is easier to pinpoint a determine if cell tower has service for a phone that may be reviewed as part of a criminal investigation.
Many law enforcement agencies and private companies have dedicated resources to analyze and process this data and there is a growing market for software tools that assist and expedite the analysis of call detail records. However, one major flaw of this process is that it allows anyone to import the call detail records and produce a map, that can then be presented to a jury. These software tools exponentially speed up the mapping process and are often used as an “easy button” when analyzing call detail records. But just because someone knows how to use the software, does not mean they also understand, or have been properly trained to, read or provide an analysis of the CDR in question. This failure to understand the underlying data used to produce the maps has been known to create real problems in legal cases.
The Value of RF Drive Testing
When we receive information concerning CDR's, we only know the tower and sector in which a phone was connected at a particular time. Radio frequency engineering data is not provided to an examiner. Through the use of a drive test, the examiner can now see:
- Areas of the tower that are stronger than others
- Areas that have hot spots (or cell tower coverage that bleeds into others creating "spots" of coverage that allow someone to connect to a cell tower farther away than expected)
- Areas that may not have coverage
- Other factors that may have affected signal coverage such as nearby wooded areas, bodies of water, large buildings or topography
In other words, our cell phone examiners can determine in much greater detail the likelihood of a cell phone connecting to a particular cell tower at a location. This data is used to validate claims concerning the location of a person, as well as challenge a claim if radio frequency data collected through drive testing doesn't coincide with the mapping from the original call detail records.