Sunday, July 13, 2014

CSA - Site Survey Method 2

The purpose of these CSA - Site Survey Method discussions invites examiners, technicians and students to consider the wider area analysis involved in cell site analysis (CSA) beyond simply conducting radio test measurements at site and producing test results from particular Masts.

The wider area analysis enables examiners, technicians and students to suggest why coverage is being detected at particular locations. The coverage detected may not be LOS (line of sight) but due to NLOS (non line of sight). With these two radio scenarios there are a wide range of propagation models/components that are commonly referred to and used for mobile (cellular) communications.

Uniformity for CSA surveys is not impossible and has been established by industry and mobile radio network operators and radio architects/designers. It is simply due to lack of consensus in the forensic community that has largely stopped consensus. The latter state has arisen because of the way investigations have been subjected to intervening factors/limitation imposed, caused by constraints: financial constraints; knowledge, skill and experience constraints; timing constraints; combination of constraints. Can you imagine a DNA or Blood specialist giving evidence in court and stating the results I obtained are these but I have no clue as to why those results would be obtained at a particular juncture/point in the examination / survey and there is no consensus in industry as to what I should refer to as a criteria or norm.

CSA can be defined by five practical forensic headings:

1) Call-Billing Records/Cell Details/Operational Records/Network Records;
2) Radio Coverage and Mast-Tower BTS;
3) Radio Coverage and Mobile Station-Smartphone;
4) Radio Coverage and Geo-Clutter;
5) Radio Coverage and Scene of Crime.

It is agreed that each heading will have its own subset headings but for each of the main five headings it is possible to produce primers for each. It is also accepted that another reason for naming convention consensus yet to be achieved in the forensic community is due to the disparate range of definitions by industry. Mobile Forensics must develop a generic title and statement. This would not only assist the prosecution and defence to have firm ground upon which to question/cross examine a witness but aid the court to understand submissions. And this is only right and proper. With medical principals and practices it roughly takes 10-20 years to accept/understand each medical terms, yet we find after 30 years of cellular radio technology the courts and legal profession still struggle to get to grips with mobile cellular terminology and techniques. Thus using headings such as those above with appropriate descriptions attached to them should reduce or remove that problem. The following discussion illustrates established norms that are available that can be used consensually between expert, forensic and legal parties. 

The discussion in CSA - Site Survey Methods form subsets of 2), 3), 4) and 5). By way of illustration in the discussion here [ ] it refers to affects to radio coverage. The examiner, technician and student having obtained all the information at 1) above may wish to then consider 2) and 4) above.


The above photo of a Mast-BTS/NodeB/eNodeB shows an example of identified radio transmssion technology that the examiner, technician and student should identify at first instance to comprehend (a) communications transmissions available and (b) the services to be obtained from this type of multi-basestation.

The examiner, technician and student are ultimately considering scenarios into which radio-coverage will be propagated. These will not just simply be the standard radio coverage frequencies allocated to GSM/W-CDMA/CDMA/LTE etc but also microwave links for backhaul of the sites traffic where no landline backhaul is possible.

It follows therefore background knowledge about propagation, models and survey profiles etc can assist how an examiner, technican and student may plan on-site surveys and radio test measurements or those components that might be involved in the results detected. Some examples are:

Basic algorithm: COST 231 Model (ETR 364, COST 231 Final Report)
Type: Point-to-area (multipoint)
Frequency: about 800 MHz - 2 GHz
Distance: up to 5 km
Basic algorithm: IEEE 802.16
Type: Point-to-area (multipoint)
Frequency: about 2 GHz - 5 GHz
Distance: up to 70 km

Type: Point-to-point
Frequency: 150MHz - 1500 MHz
Distance: 1Km to 20 MHz
Allows for correction factor where mobile is different from baseline height 1.5m

Type: Point-to-multipoint
Frequency: ~ 150 MHz - 2 GHz
Distance: up to 100 km

Line of Sight
Basic algorithm: ITU-R P.452-14
Type: Point-to-point and Point-to-multipoint
Frequency: about 700 MHz - 40 GHz
Distance: up to 100 - 150 km

ITU-R P.1411 provides guidance on outdoor propagation for systems that operate under distances 1 km, and over the frequency range 300 MHz to 100 GHz

ITU-R P.1546 provides guidance on outdoor propagation for systems that operate over distances of 1 km and greater, and over the frequency range 30 MHz to 3 GHz

Effective Antenna Height:

Analysing point to point/area components:

Examiners, technicians and students should note I have used in these examples the ITU (international telecommunications union) recommendations adopted around the world by its members. This means whether the CSA is located in Europe, Middle East, Asia, Africa, North America etc these are useful recommendations to consider and refer to in final reports. Put another way there should be nothing in a final report that should have be made-up (false statement) by the report's author.

Free space path loss: ITU-R P.525-2
Fresnel zone ellipsoids: ITU-R P.526-11
Path clearance: ITU-R P.530-13

Reflection, Diffraction, Scattering and Attenuation:
Specific attenuation: ITU-R P.676-8
Preciptation attenuation: ITU-R P.837-5
Specific Rain attentuation: ITU-R P.838-3
Rain Height Model ITU-R P.839-3
Hydrometeors attenuation: ITU-R P.530-13
Fog attenuation: ITU-R P.840-5
Single knife-edge: ITU-R P.526-11
Deygout: ITU-R P.526-11
Average: ITU-R P.530-15
Spherical Earth: ITU-R P.526-11
Reflection: ITU-R-REC-P.527-3
Multipath: ITU-R-REC-P.1407-5
Scattering due to RET: ITU-R P.833-5
Vegetation: ITU-R-REC-P.833-8
Polar and Desert Dry Temperatures: ITU-R-REC-P.841-4
Buildings: ITU-R-REC-P.1812-3
Building Materials and Structures: ITU-R-REC-P.2040-0 

There are of course other regional specific cellular transmission technology standards for North American, Europe etc e.g. ETR 364: Digital cellular telecommunications system; Radio network planning aspects. These shall be referred to in another discussion.

PLEASE NOTE: The page will be updated with other ITU recommendations from time to time.

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