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(@trewmte)
Posts: 1877
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Cell Site Analysis (CSA) has had a good deal of airing recently here on the forum, so I thought you might like to see images from the work that I get involved.


Image 1

Image 1 is one slide from the training course material to introduce students to CSA when starting out discussing radio test measurements. It should be noted that this image represents less than 1% of all data acquired during radio test measurements.


Image 2

I thought it would be useful to include this Terrain and Clutter Map (Image 2) as I use this software to assist me in complex cases. Terrain and Clutter are discussed during training and as it was a topic of the discussion about UK Criminal Evidence Delays I thought it would be helpful to let forum members see that I am not referring to theoretical matters, terrain and clutter analysis actually takes place.

UK Criminal Evidence Delays http//www.forensicfocus.com/index.php?name=Forums&file=viewtopic&t=3961


Image 3

It is essential to understand, when conducting radio test measurements, that just because radio signals can travel some distance from a particular Mast (Image 3) that coverage should not be dismissed or excluded. Operators set threshold limits, hard limits and boundary limits. It does not follow that just because a mobile is in the Green area shown in the Single Cell Prediction Map that the mobile will be excluded from using that coverage.

Do you remember the discussion that I put up here about fringe coverage http//trewmte.blogspot.com/2008/11/mobile-phones-and-fringe-coverage.html


Image 4

Best serving coverage is often posed as the deal-clincher to suggest the mobile phone was most likely or consistent with being at a particular location. There can be numerous points that could (and I say 'could' advisedly) point to best server coverage being used but rarely does it come up in evidence because the radio content in evidence rarely gets disclosed these days.

It is possible with best serving coverage that it can induce a negative outcome that may prevent calls taking place, so it is always important to see the other side of the coin, so to speak

http//trewmte.blogspot.com/2007/02/gsm-radio-test-measurements-non.html

http//trewmte.blogspot.com/2007/01/gsm-radio-test-measurements.html

I hope the above provides a further illustration of how smart and intelligent a science Cell Site Analysis really is and that by not applying it properly and dumbing down this art of this forensic science

- is not only a great loss to the law of evidence
- it reduces the examiner's/expert's knowledge and understanding about the subject with which they are dealing - mobile telephone evidence.

 
Posted : 26/08/2009 1:13 am
chrisdavies
(@chrisdavies)
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i enjoyed reading that, never looked a phone forensic before

 
Posted : 26/08/2009 4:02 pm
jhup
 jhup
(@jhup)
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on the terrain & clutter I presume the terrain and building heights are summed to get the "clutter" level.

Is there a consideration for the "clutter" material in these maps?

I can see where the building material can create a tunnel, extending the coverage, and just as well a block, reducing the coverage…

 
Posted : 26/08/2009 9:38 pm
(@trewmte)
Posts: 1877
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As you do find Cell Site Analysis (CSA) interesting you may like to know that results from terrain and clutter analysis and radio test measurements can be defined in many different ways that can demonstrate particular elements of importance to a case.


Image 5

First we need to model (Image 5) the landscape that represents the geographical area and natural and manmade phenomenon in the surrounding area. In this case the scene of crime is close to a crossroads in the middle of small urban town.

For the sake of comfort, juries rarely understand radio coverage that is verbally discussed but respond much better to discussion revolving around a visual aid presentation.


Image 6

In this particular case I want to show the jury that two microcells* were used and each microcell first needs to be defined (Image 6) to the jury so they have it clearly in their minds the origin and direction of the radio coverage that forms part of the discussion.

In the first posting in this thread coverage maps were shown defining large cell/macrocell coverage. Here, it is possible to refine and finesse coverage to a specific area with microcell coverage. Importantly, it is a really good idea to make sure the first image the jury sees represents the first radio coverage that a particular mobile phone has used that you want to talk about.


Image 7

The second microcell coverage (Image 7) should also be defined and distinguished. It's always best to remember with microcell coverage radio path is shaped in the same way as the High Street. Microcells don't go around corners.


Image 8

Finally the culmination of the presentation defines how the coverage from both microcells blend (Image 8 ) at particular points along the radio path.

*Remember that mobile telephones need to be encouraged to use microcell coverage and the microcell location, coverage boundary, speed at which a mobile phone is moving and cell reselection cause system challenges that required the use of a new criterion that was introduced into the GSM Phase 2 Standards in 1996. Do you know what that criterion is called and how it works?

 
Posted : 26/08/2009 9:51 pm
(@trewmte)
Posts: 1877
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Topic starter
 

on the terrain & clutter I presume the terrain and building heights are summed to get the "clutter" level.

Is there a consideration for the "clutter" material in these maps?

I can see where the building material can create a tunnel, extending the coverage, and just as well a block, reducing the coverage…

Buildings are clutter - manmade, trees are clutter - natural phenomenon.

The maps can show terrain and clutter for the purpose of illustrating objects likely to cause attentuation etc, they are not defined specifically in the radio overlays of, in effect, ordnance survey data. The maps above are generated post terrain and clutter considerations - so they do not show specifically a defined clutter etc although on the computer screen within the program yes you can define a path and illustrate clutter etc from that point.

Fair questions to ask also would be (a) does the coverage defined represent usable outdoor and/or indoor coverage and (b) is it rooftop coverage down to 2-metres or coverage for blocks of flats etc?

 
Posted : 26/08/2009 10:04 pm
jhup
 jhup
(@jhup)
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My thought would be "are those buildings are all made with aluminum sidings?"… Radio waves bounce… I can imagine a scenario where there is unexpected coverage. I have experienced this before. (Why is it that is never unexpected when it is lack of coverage?)

Do you also consider other environmental impacts? I don't know how much cellular/mobile telephones are impacted, but from my old DX days we looked forward to special sunspots and such…

 
Posted : 27/08/2009 4:14 am
(@trewmte)
Posts: 1877
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My thought would be "are those buildings are all made with aluminum sidings?"… Radio waves bounce… I can imagine a scenario where there is unexpected coverage. I have experienced this before. (Why is it that is never unexpected when it is lack of coverage?)

Do you also consider other environmental impacts? I don't know how much cellular/mobile telephones are impacted, but from my old DX days we looked forward to special sunspots and such…

jhup the reflective surface of buildings or materials is most certainly considered if a) the relecting facet is large enough b) the positioning of the antennas on the Mast c) the antennas are far away enough from the reflecting surface d) the wavelength and e) the radii of the curvature of the surfaces are electrically large.

GSM 900MHz wavelength is approximately 30-32cm and GSM 1800MHz is about half 900MHz. The degradation to the signals requires a maximum acceptable boundary (35Km/21.7 miles), hard limits can be set, thresholds for signal reception at the receiver are based on tolerance of degraded signals

- received at the handset e.g downlink -102dBm (however testing to -120dBm is required in the standards)
- uplink received at the Mast varies (but BTS1 (-105dBm) is common starting point)

In the UK due to clutter and other considerations and the geographical landscape there are over 50,000 Masts (declared). I suspect that figure may not take account of certain Microcell or pico-cells. The impact of the density of Masts (hence why the production of e.g. 'Best Server Plot/Density Map') means the RF footprint in rural areas requires less Masts. I suspect aluminium buildings would be fairly negligible to the propagation overall but important if someone was standing behind it, or worse still, inside. Urban and Dense Urban have Masts closer together so maybe a tall structure of aluminium could have greater impact as the RF footprint from each Mast would be smaller; height of the antennas would also be relevant.

When writing the above a Reflected Field principle that came to mind was Fermat's principle SPO you might find interesting the reflected ray path SPO can be obtained by minimising the length of the path - basically it looks at the incident ray reflected in the specular direction from a surface, known also as Snell's law.

Natural atmospheric conditions can only have impact for GSM based upon intensity. The old analogue system UK TACS could be partial at times to be influenced by matters between the transmitter and receiver such as temperature inversion an atmospheric corridor created where cold descends and the Sun's heat of the earth's surface, heated during the day, rises to meet the cold. However, certain prevailling conditions need to be examined calm maybe light wind -v- full scale blowout, clear skies -v- low cloud etc….

GSM has some issues when temperature rises raidply. You can often hear radio engineers discussing temperature. At court barristers would think ahhh haaa it was a sunny hot day it affects the radio signals in the ether. This is not the temperature being spoken of. The relevant temperature is that of overheating given the energy speed and power delivered along the coaxial cable to and at the feeders; keeping it cool in very hot temperatures can be a nightmare; it can cause interference and so on. Rainfall was discussed in the thread UK Criminal Evidence Delays.

I enjoy this subject very much but I wont go on, so as not to become boring….

 
Posted : 27/08/2009 12:35 pm
Sloman
(@sloman)
Posts: 5
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Most excellent work!

 
Posted : 27/08/2009 10:09 pm
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