| An introduction into Cell Site Analysis | | | | cover of each transmitter and receiver. |
| Technical Background of Cell Site Analysis by Simon | | | | Even when mobile phones are not executing a call, |
| Steggles – Mobile Phone Forensics | | | | they are still logged on the network providers systems, |
| Cell phones, (or Mobile phones) used today are | | | | ready for their next call/message. This information is |
| transceivers which use little power. They combine both | | | | not stored historically, however when a call is made or |
| a transmitter and a receiver. Although most cell | | | | received, it is. When a phone is ‘live’ i.e. |
| phones, (or Mobile phones), are used to provide a | | | | switched on and connected to the network providers, |
| telephone service for the public, they are still radio | | | | it is possible to track it by the non recorded records |
| transmitters and receivers. Because of this, mobile | | | | which get switched on manually. |
| phones, (or mobile phones), behave in the same way | | | | Geographical locations can be specified for a mobile |
| that traditional radio equipment does. Mobile phones | | | | phone by referring to the call detail records, |
| operate through networks, (which in the UK are run by | | | | (CDR’s). This can give you information of which cell |
| O2, Vodafone, Orange and T-Mobile). These networks | | | | site was being used. From checking the records about |
| are GSM, (Global Systems for Mobile communications), | | | | the specific site in question, it is then possible to find out |
| and are built around an array of transmitters, receiving | | | | about if the aerial was a full 360 degrees, or an |
| stations which cover nearly all of the United Kingdom. | | | | azimuth of 120 degrees, (these can vary). If the call |
| Many other countries follow this similar rule; however, | | | | was coming from aerial 3 on a cell site, then it is right |
| they may have different networks run by different | | | | to assume that the specific geographic location of that |
| companies, (Verizon, AT&T etc). | | | | cell phone is now only a third or the original area it was |
| These transmit and receive stations (or beacons), are | | | | thought to be in, (e.g. If a call was made from the south |
| also known as ‘Cell Sites’. Each cell site | | | | of a cell site, then it is likely that the mobile phone was |
| consists of multiple receivers and transmitters and of | | | | within a reasonable, (varies) distance from the south of |
| course the relevant aerials associated with each one. | | | | that cell site). |
| These sites are often on masts, can be sited above | | | | Things to take into consideration: |
| police stations, schools or other tall buildings, (giving | | | | 1. Cell Site Analysis is not a proven science. Even if a |
| clearer transmissions, therefore clearer line of site | | | | mobile phone was used in position A, to the south of a |
| transmission). | | | | cell site, it doesn’t necessarily mean that the phone |
| Each cell site has a reference number and name. | | | | was actually there. It could well be anywhere up to a |
| Using this information, one can state exactly the area | | | | theoretical 35Kms away if all the cell sites between |
| of the cell site. From this we can pin point to a very | | | | the phone and the used cell site had achieved |
| small area if the suspect phone has been used in this | | | | maximum usage, (cell sites can only accommodate a |
| area. | | | | finite amount of traffic at one time) or are not in |
| Whenever a mobile phone is ‘on’, it scans the | | | | service. |
| radio frequencies assigned to it by its designated | | | | 2. The cell site chosen is not necessarily chosen by the |
| network provider, and then links up the cell that gives it | | | | phone, it may be the network ‘re-directing’ the |
| the best coverage. This process is called registration, | | | | phone to a ‘not so busy’ cell site. |
| and is of course necessary for the networks so that | | | | 3. Geographical locations may also prevent the usage |
| they can direct incoming or outgoing calls to the | | | | of a cell site, (large building in the way, dense woodland |
| correct phone. When travelling, (for example), a phone | | | | etc). |
| may move from one cell site to another. This is | | | | The latest system for mobile phones is 3G, (third |
| achieved by the phone evaluating the signal at all times, | | | | generation). This relies on UMTS, (Universal Mobile |
| and switching over to the appropriate best one. This is | | | | Telecommunications System), a faster data transfer |
| also logged by the networks and is known as a | | | | system using Duplexing technologies. In the UK 5 |
| ‘handover’. The handover also ensures a | | | | licenses were won for the ability to provide these |
| continuation of the call, rather than the requirement to | | | | services. These network providers are 3G |
| redial every time a new better cell site is found. | | | | Technologies, Hutchinson 3G, Orange, Vodafone, O2 |
| Network providers positioned their cell sites after | | | | and T-Mobile. Although a different style/type of |
| carrying out extensive testings on the frequency, | | | | service, UMTS is recorded in the same way as |
| geographical position, and potential transmission | | | | traditional GSM. Handover occurs in the same way |
| reception hazards. Extensive maps of these tests are | | | | between UMTS and GSM as GSM to GSM. |
| kept by the network providers, showing the specific | | | | |